0001564590-21-012664 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2020	Mar. 10, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Entity Registrant Name	Adicet Bio, Inc.
Entity Central Index Key	0001720580
Entity File Number	001-38359
Trading Symbol	ACET
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 40.0
Entity Common Stock, Shares Outstanding		31,780,347
Document Annual Report	true
Document Transition Report	false
Entity Tax Identification Number	81-3305277
Entity Incorporation, State or Country Code	DE
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Entity Address, Address Line One	500 Boylston Street
Entity Address, Address Line Two	13th Floor
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
City Area Code	857
Local Phone Number	315-5528
Entity Address, Postal Zip Code	02116
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference	Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2021 annual meeting of shareholders, scheduled to be held on April 27, 2021 which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2020. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 84,330	$ 10,607
Short-term marketable debt securities	10,284	51,793
Prepaid expenses and other current assets	5,722	1,786
Total current assets	100,336	64,186
Property and equipment, net	2,790	2,121
Operating lease right-of-use asset	23,066
Goodwill	20,089
In-process research and development	1,190
Restricted cash	4,527	4,282
Long-term marketable debt securities		10,588
Other non-current assets	1,837	410
Total assets	153,835	81,587
Current liabilities:
Accounts payable	1,552	1,052
Contract liabilities—related party, current	13,980	10,993
Accrued and other current liabilities	5,732	2,820
Operating lease liability	1,215
Total current liabilities	22,479	14,865
Contract liabilities—related party, net of current portion		10,890
Deferred rent, net of current portion		234
Operating lease liability, net of current portion	20,424
Redeemable convertible preferred stock warrant liability		1,881
Contingent consideration liability	980
Deferred tax liability	125
Total liabilities	44,008	27,870
Commitments and contingencies (Note 12)
Stockholders’ equity (deficit):
Preferred stock, value
Common stock, $0.0001 par value; 150,000,000 and 140,200,938 shares authorized as of December 31, 2020 and 2019, respectively; 19,677,249 and 2,155,578 shares issued and outstanding as of December 31, 2020 and 2019, respectively	2
Additional paid-in capital	216,126	9,258
Accumulated deficit	(106,325)	(69,647)
Accumulated other comprehensive income	24	23
Total stockholders’ equity (deficit)	109,827	(60,366)
Total liabilities, redeemable convertible preferred stock, and stockholders’ equity (deficit)	$ 153,835	81,587
Redeemable Convertible Preferred Stock
Stockholders’ equity (deficit):
Preferred stock, value		$ 114,083

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	140,200,938
Common stock, shares issued	19,677,249	2,155,578
Common stock, shares outstanding	19,677,249	2,155,578
Preferred Stock, par value	$ 0.0001	$ 0.0001
Preferred stock shares authorized	10,000,000	10,000,000
Preferred stock shares issued	0	0
Preferred stock shares outstanding	0	0
Redeemable Convertible Preferred Stock
Preferred Stock, par value	$ 0.0001	$ 0.0001
Preferred stock shares authorized	0	99,363,444
Preferred stock shares issued	0	97,166,921
Preferred stock shares outstanding	0	97,166,921
Preferred stock, liquidation preference, value	$ 0	$ 128,195

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenue—related party	$ 17,903	$ 995	$ 8,181
Operating expenses:
Research and development	34,334	23,691	14,717
General and administrative	22,760	8,692	8,428
Total operating expenses	57,094	32,383	23,145
Loss from operations	(39,191)	(31,388)	(14,964)
Interest income	785	938	543
Interest expense	(134)
Other income (expense), net	(953)	2,331	4,533
Loss before income tax benefit	(39,493)	(28,119)	(9,888)
Income tax expense (benefit)	(2,815)	19	(589)
Net loss	$ (36,678)	$ (28,138)	$ (9,299)
Net loss per share attributable to common stockholders, basic and diluted	$ (5.01)	$ (13.15)	$ (4.78)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted	7,319,977	2,138,973	1,946,976
Other comprehensive income (loss):
Unrealized gain (loss) on marketable debt securities, net of tax	$ 1	$ 36	$ (13)
Total other comprehensive income (loss)	1	36	(13)
Comprehensive loss	$ (36,677)	$ (28,102)	$ (9,312)

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2017	$ (26,948)			$ 5,262	$ (32,210)
Balance, temporary equity, shares at Dec. 31, 2017		31,074,017
Balance, temporary equity at Dec. 31, 2017		$ 26,341
Balance, shares at Dec. 31, 2017			2,016,838
Issuance of Series A redeemable convertible preferred stock		$ 10,825
Issuance of Series A redeemable convertible preferred stock, shares		9,020,833
Exercise of the redeemable convertible preferred stock tranche liability		$ 902
Issuance of common stock upon exercise of stock options	$ 221			221
Issuance of common stock upon exercise of stock options, shares	123,949		123,949
Vesting of early exercised stock options	$ 44			44
Stock-based compensation expense	2,479			2,479
Net loss	(9,299)				(9,299)
Unrealized gain (loss) on marketable debt securities, net of tax	(13)					$ (13)
Balance at Dec. 31, 2018	(33,516)			8,006	(41,509)	(13)
Balance, temporary equity, shares at Dec. 31, 2018		40,094,850
Balance, temporary equity at Dec. 31, 2018		$ 38,068
Balance, shares at Dec. 31, 2018			2,140,787
Issuance of Series A redeemable convertible preferred stock		$ 88
Issuance of Series A redeemable convertible preferred stock, shares		67,656
Issuance of Series B redeemable convertible preferred stock, net of issuance cost of $5,216		$ 74,784
Issuance of Series B redeemable convertible preferred stock, shares		57,004,415
Termination of redeemable convertible preferred stock tranche liability		$ 1,143
Issuance of common stock upon exercise of stock options	$ 30			30
Issuance of common stock upon exercise of stock options, shares	14,791		14,791
Vesting of early exercised stock options	$ 47			47
Stock-based compensation expense	1,175			1,175
Net loss	(28,138)				(28,138)
Unrealized gain (loss) on marketable debt securities, net of tax	36					36
Balance at Dec. 31, 2019	(60,366)			9,258	(69,647)	23
Balance, temporary equity, shares at Dec. 31, 2019		97,166,921
Balance, temporary equity at Dec. 31, 2019	114,083	$ 114,083
Balance, shares at Dec. 31, 2019			2,155,578
Issuance of common stock upon exercise of stock options	$ 460		$ 1	459
Issuance of common stock upon exercise of stock options, shares	210,752		210,752
Stock-based compensation expense	$ 5,263			5,263
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger	114,083		$ 1	114,082
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger, shares		(97,166,921)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger		$ (114,083)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger, shares			12,048,671
Exchange of common stock in connection with the Merger	83,516			83,516
Exchange of common stock in connection with the Merger, shares			5,207,695
Issuance of common stock upon accelerated vesting ofrestricted stock units in connection with the Merger	626			626
Issuance of common stock upon accelerated vesting of restricted stock units in connection with the Merger (Shares)			54,553
Conversion of redeemable convertible preferred stock warrants to common stock warrants	2,922			2,922
Net loss	(36,678)				(36,678)
Unrealized gain (loss) on marketable debt securities, net of tax	1					1
Balance at Dec. 31, 2020	$ 109,827		$ 2	$ 216,126	$ (106,325)	$ 24
Balance, temporary equity, shares at Dec. 31, 2020		0
Balance, shares at Dec. 31, 2020			19,677,249

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Series B Redeemable Convertible Preferred Stock
Stock issuance cost	$ 5,216

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (36,678)	$ (28,138)	$ (9,299)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	1,226	1,238	1,222
Noncash lease expense	725
Stock-based compensation expense	5,263	1,175	2,479
Gain on disposal of property and equipment		(27)
Net amortization of premiums and accretion of discounts on investments	5	(197)
Change in fair value of redeemable convertible preferred stock tranche liability and TRDF liability		(2,024)	(4,536)
Change in fair value of redeemable convertible preferred stock warrant liability	897	(250)
Impairment of in-process research and development	2,300
Remeasurement of contingent consideration liability	(1,900)
Amortization of deferred debt issuance costs	134
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,233)	1,405	(2,825)
Other non-current assets	(1,260)	(88)	(302)
Accounts payable	(814)	527	(282)
Contract liabilities—related party	(7,903)	(995)	(3,181)
Deferred rent	400	(148)	(132)
Operating lease liabilities	(859)
Accrued and other current liabilities	787	(360)	(1,324)
Deferred tax liability	(242)
Net cash used in operating activities	(41,552)	(27,882)	(18,180)
Cash flows from investing activities
Cash and restricted cash acquired in connection with the Merger	64,114
Purchases of marketable debt securities	(5,700)	(76,078)	(15,182)
Proceeds from maturities of marketable debt securities	57,793	29,099
Proceeds from sale of property and equipment		118
Purchase of property and equipment	(990)	(1,070)	(876)
Net cash provided by (used in) investing activities	115,217	(47,931)	(16,058)
Cash flows from financing activities
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		76,915	10,825
Proceeds from exercise of stock options	460	30	221
Payment of debt issuance costs	(157)
Net cash provided by financing activities	303	76,945	11,046
Net change in cash, cash equivalents and restricted cash	73,968	1,132	(23,192)
Cash, cash equivalents and restricted cash, at the beginning of the period	14,889	13,757	36,949
Cash, cash equivalents and restricted cash, at the end of the period	88,857	14,889	13,757
Reconciliation of cash, cash equivalents and restricted cash to consolidated balance sheets:
Cash and cash equivalents	84,330	10,607	9,475
Restricted cash	4,527	4,282	4,282
Cash, cash equivalents and restricted cash, at the end of the period	88,857	14,889	13,757
Supplemental cash flow information
Cash paid for income taxes	3	1	5,109
Cash received for income tax refunds	664
Supplemental disclosures of noncash investing and financing activities
Purchase of property and equipment included in accounts payable	115	48	61
Operating lease right-of-use asset obtained in exchange for operating lease liability	22,367
Issuance of redeemable convertible preferred stock warrants in connection with the Loan Agreement	144
Conversion of redeemable convertible preferred stock into common stock	114,083
Conversion of redeemable convertible preferred stock warrants to common stock warrants	2,922
Fair value of net assets acquired in Merger	84,142
Measurement period adjustment to goodwill	650
Vesting of early exercised stock options		47	44
Exercise of redeemable convertible preferred stock tranche liability			$ 902
Termination of redeemable convertible preferred stock tranche liability		1,143
Settlement of TRDF liability		88
Series B Redeemable Convertible Preferred Stock
Supplemental disclosures of noncash investing and financing activities
Redeemable convertible preferred stock warrants issued in connection with issuance of Series B redeemable convertible preferred stock, net of issuance costs		$ 2,131
Topic 842
Supplemental disclosures of noncash investing and financing activities
Right-of-use assets recognized upon adoption of ASC 842	$ 1,424

Organization and Nature of Business

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Nature of Business

1. Organization and Nature of the Business

Adicet Bio, Inc. (formerly resTORbio, Inc. (resTORbio)), together with its subsidiaries, (the Company) is a biotechnology company discovering and developing allogeneic gamma delta T cell therapies for cancer and other diseases. The Company is advancing a pipeline of off-the-shelf gamma delta T cells, engineered with chimeric antigen receptors (CARs) and T cell receptor-like antibodies to enhance selective tumor targeting, facilitate innate and adaptive anti-tumor immune response, and improve persistence for durable activity in patients. The Company believes its approach has potentially significant advantages over alpha beta T cells, which are the basis of standard CAR-T cell therapies. The Company was incorporated in November 2014 in Delaware. The principal executive offices are located in Boston, Massachusetts. The Company also has another office in Menlo Park, California.

Adicet Bio, Inc. (when referred to prior to the Merger (as defined below), (Former Adicet)) was incorporated in November 2014 in Delaware and was headquartered in Menlo Park, CA. Adicet Bio Israel Ltd. (formerly Applied Immune Technologies Ltd.) (Adicet Israel) is a wholly owned subsidiary of Former Adicet and is located in Haifa, Israel. Adicet Israel was founded in 2006. During 2019, Former Adicet consolidated its operations, including research and development activities, in the U.S. and as a result substantially reduced its operations in Israel.

Merger with resTORbio

Prior to September 15, 2020, the Company was a clinical-stage biopharmaceutical company known as resTORbio that had historically focused on developing innovative medicines that target the biology of aging, to prevent or treat age-related diseases with the potential to extend healthy lifespans. On April 28, 2020, resTORbio entered into a definitive Merger Agreement with Former Adicet. Under the terms of the Merger Agreement, Former Adicet agreed to merge with a wholly owned subsidiary of resTORbio in an all-stock transaction with Former Adicet surviving as a wholly owned subsidiary of resTORbio and changing its name to “Adicet Therapeutics, Inc.” (such transactions, the Merger). Under the exchange ratio formula in the Merger Agreement, immediately following the Effective Time of the Merger, the securityholders of Former Adicet as of immediately prior to the Effective Time of the Merger owned approximately 75% of the outstanding shares of the Company’s common stock on a fully-diluted basis and securityholders of resTORbio as of immediately prior to the Effective Time of the Merger owned approximately 25% of the outstanding shares of the Company’s common stock on a fully-diluted basis (in each case excluding equity incentives available for grant).

The Company concluded that the transaction represented a business combination pursuant to Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) Topic 805, Business Combinations. Further, Former Adicet was determined to be the accounting acquirer based upon the terms of the Merger and other factors including: (i) Former Adicet’s securityholders own approximately 75% of the voting rights of the combined company (on a fully-diluted basis excluding equity incentives available for grant); (ii) Former Adicet designated a majority (five of seven) of the initial members of the Board of Directors of the combined company; and (iii) the terms of the exchange of equity interests based on the exchange ratio at the announcement of the Merger factored in an implied premium to resTORbio’s stockholders. The composition of senior management of the combined company was determined to be a neutral factor in the accounting acquirer determination, as the combined company will leverage the expertise of the senior management of both companies. Accordingly, the reported operating results prior to the business combination are those of Former Adicet.

On September 15, 2020, the Company completed the Merger pursuant to the Merger Agreement (the Effective Time). In connection with the Merger, and immediately prior to the Effective Time, resTORbio effected a reverse stock split of its common stock at a ratio of 1-for-7 (the Reverse Stock Split). Also, in connection with the Merger, the Company changed its name from “resTORbio, Inc.” to “Adicet Bio, Inc.” (the Name Change), Former Adicet changed its name from “Adicet Bio, Inc.” to “Adicet Therapeutics, Inc.” and the business conducted by the Company became primarily the business, which was previously conducted by Former Adicet, which is a biotechnology company discovering and developing allogeneic gamma delta T cell therapies for cancer and other diseases.

At the Effective Time, each outstanding share of Former Adicet capital stock was converted into the right to receive 0.1240 (the Exchange Ratio) shares of Company’s common stock, as set forth in the Merger Agreement. The Exchange Ratio was determined based on the total number of outstanding shares of Company’s common stock and Former Adicet capital stock, each on a fully diluted basis, and the respective valuations of Former Adicet and resTORbio at the time of execution of the Merger Agreement. In connection with the Merger, the Company also assumed certain outstanding Former Adicet warrants and Former Adicet stock options under Former Adicet’s 2015 Stock Incentive Plan (the 2015 Adicet Stock Incentive Plan) and Former Adicet’s 2014 Share Option Plan (the 2014 Share Option Plan and, together with the 2015 Adicet Stock Incentive Plan, the Former Adicet Plans), with such stock options and warrants henceforth representing the right to purchase a number of shares of Company’s common stock equal to the Exchange Ratio multiplied by the number of shares of Former Adicet’s capital stock previously represented by such stock options and warrants, as applicable, with a proportionate adjustment in exercise price.

Immediately following the Effective Time, there were approximately 19,589,828 shares of the Company’s common stock outstanding (post Reverse Stock Split), with the former equity holders of Former Adicet holding approximately 75% of the outstanding shares of Company’s common stock on a fully-diluted basis and the former equity holders of resTORbio holding approximately 25% of the outstanding shares of Company’s common stock on a fully-diluted basis (in each case excluding equity incentives available for grant).

Please refer to Note 3 “Business Combinations” for further discussions of the Merger.

Liquidity and Going Concern

The Company has incurred significant net operating losses and negative cash flows from operations since inception and had an accumulated deficit of $106.5 million as of December 31, 2020. The Company has historically financed its operations primarily through a collaboration and licensing arrangement, the private placement of equity securities and debt, and cash received in the Merger. To date, none of the Company’s product candidates have been approved for sale and therefore the Company has not generated any revenue from product sales. Management expects operating losses and negative cash flows to continue for the foreseeable future, until such time, if ever, that it can generate significant sales of its product candidates currently in development.

As of June 23, 2020, the issuance date of the Company’s consolidated financial statements for the year ended December 31, 2019, the Company had concluded that there was substantial doubt about its ability to continue as a going concern. As of December 31, 2020, the Company had $94.6 million in cash, cash equivalents, and marketable debt securities. In February 2021, the Company completed an underwritten public offering of 10,575,513 shares of its common stock, including the exercise in full by the underwriters of their option to purchase up to an additional 1,344,743 shares of common stock at a public offering price of $13.00 per share. The company received aggregate gross proceeds from the offering, before deducting underwriting discounts and commissions and offering expenses of approximately $137.5 million. In connection with the offering, the Company also entered into a stock purchase agreement with certain existing investors for $15.0 million of shares of the Company’s common stock at a price per share equal to the public offering price, with an initial closing for certain investors held simultaneously with the closing of the offering and a subsequent closing for certain additional investors. These two recent events have alleviated the substantial doubt about the Company’s ability to continue as a going concern. The Company expects that its cash, cash equivalents and marketable debt securities, including the gross proceeds it received in February 2021 from its underwritten public offering and the proceeds received from a stock purchase agreement with certain existing investors, will be sufficient to fund its forecasted operating expenses, capital expenditure requirements and debt service payments for at least the next twelve months from the issuance of these annual consolidated financial statements.

All of the Company’s revenue to date is generated from the Regeneron Agreement, which is a collaboration and license agreement with Regeneron Pharmaceuticals, Inc. (Regeneron). The Company does not expect to generate any significant product revenue until it obtains regulatory approval of and commercialize any of the Company’s product candidates or enter into additional collaborative agreements with third parties, and it does not know when, or if, either will occur. The Company expects to continue to incur significant losses for the foreseeable future, and it expects the losses to increase as the Company continues the development of, and seek regulatory approvals for, its product candidates and begin to commercialize any approved products. The Company is subject to all of the risks typically related to the development of new product candidates, including, but not limited to, raising additional capital, development by its competitors of new technological innovations, risk of failure in preclinical and clinical studies, safety and efficacy of its product candidates in clinical trials, the risk of relying on external parties such as contract research organizations (CROs) and contract manufacturing organizations (CMOs), the regulatory approval process, market acceptance of the Company’s products once approved, lack of marketing and sales history, dependence on key personnel and protection of proprietary technology and it may encounter unforeseen expenses, difficulties, complications, delays, and other unknown factors that may adversely affect its business.

Until such time as the Company can generate significant revenue from product sales, if ever, the Company expects to finance its operations through the sale of equity, debt financings, collaborative or other arrangements with corporate or other sources of financing. Adequate funding may not be available to the Company on acceptable terms or at all. The Company’s failure to raise capital as and when needed could have a negative impact on its financial condition and the Company’s ability to pursue its business strategies. Although the Company continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements and related disclosures have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP or GAAP).

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The U.S. dollar is the functional and reporting currency of the Company and its subsidiaries.

Exchange Ratio

At the Effective Time, each outstanding share of Former Adicet capital stock was converted into the right to receive 0.1240 (the Exchange Ratio) shares of Company’s common stock, as set forth in the merger agreement. Accordingly, all shares and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect the Exchange Ratio.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent liabilities at the date of the consolidated financial statements as well as the reported amounts of revenues and expenses during the reporting period. Such estimates include the valuation of the intangible assets acquired in business combinations, redeemable convertible preferred stock warrant liability, redeemable convertible preferred stock tranche liability, the Technion Research and Development Foundation liability (TRDF Liability), contingent consideration liability for contingent value right (CVR), deferred tax assets, useful lives of property and equipment, accruals for research and development activities, revenue recognition and stock-based compensation and the Company’s incremental borrowing rate. Actual results could differ from those estimates.

Business Combination

Business combinations are accounted for under the acquisition method. The Company recognizes the assets acquired and liabilities assumed in business combinations on the basis of their fair values at the date of acquisition. The Company assesses the fair value of assets acquired, including intangible assets, and liabilities assumed using a variety of methods. Each asset acquired and liability assumed is measured at fair value from the perspective of a market participant. The method used to estimate the fair values of intangible assets incorporates significant estimates and assumptions regarding the estimates a market participant would make in order to evaluate an asset, including a market participant’s use of the asset, future cash inflows and outflows, probabilities of success, asset lives, and the appropriate discount rates. Acquired in-process research and development (IPR&D) is recognized at fair value and initially characterized as an indefinite-lived intangible asset, irrespective of whether the acquired IPR&D has an alternative future use. Any excess purchase price over the fair value of the net tangible and intangible assets acquired is allocated to goodwill. Transaction costs and restructuring costs associated with a business combination are expensed as incurred.

During the measurement period, which extends no later than one year from the acquisition date, the Company may record certain adjustments to the carrying value of the assets acquired and liabilities assumed with the corresponding offset to goodwill. After the measurement period, all adjustments are recorded in the consolidated statements of operations as operating expenses or income.

Contingent Consideration Liability (CVR)

The estimated fair value of the CVR, initially measured and recorded on the acquisition date, is considered to be a Level 3 instrument. The contingent consideration liability is recorded at fair value at the end of each reporting period with changes in estimated fair values recorded in research and development expenses in the consolidated statements of operations and comprehensive loss. The Company performed a remeasurement of the fair value of the CVR as of December 31, 2020 and recognized a gain of $1.9 million in research and development expense in the statements of operations and comprehensive loss for the year ended December 31, 2020.

Goodwill

Goodwill represents the excess of the purchase price over the fair value of net tangible and identified intangible assets acquired in a business combination. Goodwill is not amortized but is evaluated at least annually for impairment or when a change in facts and circumstances indicate that the fair value of the goodwill may be below the carrying value.

Goodwill is tested for impairment at the reporting unit level annually in the fourth quarter, or more frequently when events or changes in circumstances indicate that the asset might be impaired. Examples of such events or circumstances include, but are not limited to, a significant adverse change in legal or business climate, an adverse regulatory action or unanticipated competition. The Company has determined that it operates in a single operating segment and has a single reporting unit.

Prior to performing the impairment test, the Company assesses qualitative factors to determine whether the existence of events or circumstances would indicate that it is more likely than not that the fair value of the reporting unit was less than the carrying amount. If after assessing the totality of events or circumstances, the Company were to determine that it is more likely than not that the fair value of the reporting unit is less than the carrying amount, then the Company would perform a quantitative impairment test.

The quantitative impairment test involves comparing the fair value of the reporting unit to the carrying value. If the fair value of the reporting unit exceeds the carrying value of the net assets, goodwill is not impaired, and no further testing is required. If the fair value of the reporting unit is less than the carrying value, the Company measures the amount of impairment loss, if any, as the excess of the carrying value over the fair value of the reporting unit. The Company performed an annual test for goodwill impairment in the fourth quarter of the fiscal year ended December 31, 2020 and determined that goodwill was not impaired.

Intangible Assets

In connection with the Merger, the Company acquired certain IPR&D assets, which were classified as indefinite-lived intangible assets. Acquired IPR&D represents the fair value assigned to research and development assets that the Company acquires and have not been completed at the acquisition date. The fair value of IPR&D acquired in a business combination is recorded on the Company’s consolidated balance sheets at the acquisition-date fair value and is determined by estimating the costs to develop the technology into commercially viable products, estimating the resulting revenue from the products, and discounting the projected net cash flows to present value. IPR&D is not amortized, but rather is reviewed for impairment on an annual basis or more frequently if indicators of impairment are present, until the project is completed, abandoned, or transferred to a third party. The Company performed an annual review for impairment of IPR&D in the fourth quarter of the year ended December 31, 2020 and recognized an impairment charge of $2.3 million as of December 31, 2020, which was recorded as research and development expenses in the consolidated statement of operations and comprehensive loss.

Segments

The Company operates and manages its business as one reportable and operating segment, which is the business of research and development of allogeneic immunotherapies for cancer and other diseases. The Company’s Chief Executive Officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance.

Concentration of Credit Risk

Financial instruments, which potentially subject the Company to concentrations of credit risk, consist principally of cash and cash equivalents, and marketable debt securities. The Company’s cash and cash equivalents are held at two financial institutions in the U.S. and one financial institution in Israel and such amounts may, at times, exceed insured limits. The Company invests its cash equivalents and marketable debt securities in money market funds, U.S. government securities, commercial paper, corporate bonds, and asset-backed securities. The Company limits its credit risk associated with cash equivalents and marketable debt securities by placing them with banks and institutions it believes are highly creditworthy and in highly rated investments. The Company has not experienced any losses on its deposits of cash and cash equivalents and marketable debt securities to date.

The Company has one customer, Regeneron Pharmaceuticals, Inc. (Regeneron), which represents 100% of the Company’s total revenue during the years ended December 31, 2020, 2019 and 2018 (see Note 10).

Risks and Uncertainties

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical studies, clinical trials, and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance and reporting.

The Company’s product candidates are still in development and, to date, none of the Company’s product candidates have been approved for sale and, therefore, the Company has not generated any revenue from product sales.

There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from other pharmaceutical and biotechnology companies.

The current COVID-19 (coronavirus) pandemic, which is impacting worldwide economic activity, poses risk that the Company or its employees, contractors, suppliers, and other partners may be prevented from conducting business activities for an indefinite period of time, including due to shutdowns that may be requested or mandated by governmental authorities. The extent to which the coronavirus impacts the Company’s operations will depend on future developments, which are highly uncertain and cannot be predicted with confidence, including the duration of the outbreak, new information that will emerge concerning the severity of the coronavirus and the actions to contain the coronavirus or treat its impact, among others. COVID-19 may impact the timing of regulatory approval of the INDs for clinical trials, the enrollment of any clinical trials that are approved, the availability of clinical trial materials and regulatory approval and commercialization of our products. COVID-19 may also impact the Company’s ability to access capital, which could negatively impact short-term and long-term liquidity.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with maturities of three months or less from the purchase date to be cash equivalents. As of December 31, 2020 and 2019, cash and cash equivalents consist of cash deposited with banks and investments in money market funds with maturities of three months or less from the date of purchase.

Marketable Debt Securities

Marketable debt securities are investments in marketable debt securities with maturities greater than three months at the time of purchase. The Company determines the appropriate classification of its investments in marketable debt securities at the time of purchase and reevaluates such designation at each balance sheet date. The Company has classified and accounted for its marketable debt securities as available-for-sale. The Company classifies highly liquid securities with maturities beyond 12 months as long-term marketable debt securities in the consolidated balance sheet. These securities are carried at fair value as determined based upon quoted market prices or pricing models for similar securities. Unrealized gains and losses, if any, are excluded from earnings and are reported as a component of accumulated other comprehensive income (loss). The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest income on the consolidated statements of operations and comprehensive loss. Realized gains and losses, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. The Company did not identify any of its marketable debt securities as other-than-temporarily impaired as of December 31, 2020 and 2019.

Restricted Cash

Restricted cash is comprised of cash that is restricted as to withdrawal or use under the terms of certain contractual agreements. Restricted cash for years ended December 31, 2020 and 2019 consists of collateral for letters of credit issued in connection with the real estate leases (see Note 12).

Fair Value of Financial Instruments

The carrying amounts of certain financial instruments of the Company, including cash equivalents, restricted cash, accounts payable and accrued and other current liabilities approximate fair value due to their relatively short maturities. The Company’s marketable debt securities, CVR, redeemable convertible preferred stock warrant liability, redeemable convertible preferred stock tranche liability and TRDF Liability are carried at fair value (see Notes 4 and 5).

Redeemable Convertible Preferred Stock

The Company recorded all shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs, if applicable. The redeemable convertible preferred stock was recorded outside of permanent equity because while it was not mandatorily redeemable, in certain events considered not solely within the Company’s control,

such as a merger, acquisition or sale of all or substantially all of the Company’s assets (each, a deemed liquidation event), the redeemable convertible preferred stock became redeemable at the option of the holders of at least a majority of the then outstanding shares. The Company has not adjusted the carrying values of the redeemable convertible preferred stock to its liquidation preference because a deemed liquidation event obligating the Company to pay the liquidation preferences to holders of shares of redeemable convertible preferred stock was not probable of occurring. All outstanding shares of redeemable convertible preferred stock converted into common stock upon Effective Time of the Merger.

Redeemable Convertible Preferred Stock Tranche Liability

The Company determined that its obligations to issue additional shares of redeemable convertible preferred stock upon the achievement of certain milestones or at the option of the respective holders of such shares represent freestanding financial instruments. These instruments were initially measured at fair value and were subject to remeasurement with changes in fair value recognized in other income (expense), net in the consolidated statements of operations and comprehensive loss until they were exercised, terminated, or settled (see Note 14).

Redeemable Convertible Preferred Stock Warrants

The Company’s redeemable convertible preferred stock warrants required liability classification and accounting as the underlying redeemable convertible preferred stock was considered contingently redeemable and could have obligated the Company to transfer assets to the holders at a future date upon occurrence of a deemed liquidation event. The warrants were initially recorded at fair value upon issuance and were subject to remeasurement to fair value at each balance sheet date, with any changes in fair value recognized in other income (expense), net in the consolidated statements of operations and comprehensive loss. Upon the closing of the Merger, pursuant to the Merger Agreement, all of the outstanding redeemable convertible preferred stock was converted to shares of the Company’s common stock and the redeemable convertible preferred stock warrants converted to warrants for the purchase of the shares of the Company’s common stock. Upon the closing of the Merger, the warrant liability was reclassified to additional paid-in capital (see Note 1).

Property and Equipment, Net

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed on a straight-line basis over the estimated useful lives of the related assets, generally three years. Leasehold improvements are amortized using the straight-line method over the shorter of the assets’ estimated useful lives or the remaining term of the lease. Maintenance and repairs are charged to operations as incurred. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the consolidated balance sheet and any resulting gain or loss is reflected in the consolidated statements of operations and comprehensive loss in the period realized.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group may not be recoverable. Recoverability is measured by comparison of the carrying amount of the asset or asset group to the future net cash flows which the asset or asset group is expected to generate. If such asset or asset group is considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset or asset group exceeds the fair value of the asset or asset group. There has been no such impairment of long-lived assets during the years ended December 31, 2020 and 2019.

Revenue Recognition

Under ASC 606, Revenue from Contracts with Customers (ASC 606), the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps as prescribed by ASC 606:

(i)

identify the contract(s) with a customer;

(ii)

identify the performance obligations in the contract;

(iii)

determine the transaction price;

(iv)

allocate the transaction price to the performance obligations in the contract; and

(v)

recognize revenue when (or as) the Company satisfies a performance obligation.

A contract with a customer exists when (i) the Company enters into a legally enforceable contract with a customer that defines each party’s rights regarding the products or services to be transferred and identifies the payment terms related to these products or services, (ii) the contract has commercial substance and (iii) the Company determines that collection of substantially all consideration for products or services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration.

At contract inception, once the contract is determined to be within the scope of ASC 606, the Company identifies the goods or services promised and determines the performance obligations by assessing whether each promised good or service is distinct. Goods or services that are not distinct are bundled with other goods or services in the contract until a bundle of goods or services that is distinct is created. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

All of the Company’s revenues are derived through a license and collaboration agreement (see Note 10).

For revenue recognition purposes, the Company determines the term of its license or collaboration agreements by evaluating the period during which present and enforceable rights and obligations exist. This determination is impacted by the existence of substantive termination penalties, among other factors.

The Company recognizes revenue under the Company’s license or collaboration agreements that are within the scope of ASC 606. These agreements include promises related to licenses to intellectual property and research and development services. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgement to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. Accordingly, the transaction price is generally comprised of a fixed fee due at contract inception and at specified future dates, variable consideration in the form of milestone payments due upon the achievement of specified events and tiered royalties earned when customers recognize net sales of licensed products. The Company measures the transaction price based on the amount of consideration to which it expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes the “most likely amount” method to estimate the amount of variable consideration to which it will be entitled for the contract. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. At the inception of each arrangement that includes development and regulatory milestone payments, the Company evaluates whether the associated event is considered most likely to be achieved and estimates the amount to be included in the transaction price.

Payments or reimbursements for the Company’s research and development efforts where such efforts are considered part of or a single performance obligation are recognized over time using a measure of progress that best reflects the Company’s performance in satisfying the obligation.

Upfront payments are recorded as contract liabilities upon receipt or when due and may require deferral of revenue recognition to a future period until the Company performs its obligation under these arrangements. Amounts payable to the Company are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from its collaboration arrangement.

Research and Development Expenses

Research and development expenses include costs directly attributable to the conduct of research and development programs, including payroll and related expenses, costs for CMOs, costs for CROs, materials, supplies, depreciation on and maintenance of research equipment, consulting costs, and the allocated portions of facility costs, such as rent, utilities,

insurance, repairs and maintenance, depreciation, information technology costs and general support services. All costs associated with research and development are expensed within the consolidated statements of operations and comprehensive loss as incurred.

Costs incurred in obtaining technology licenses are charged to research and development expense as acquired in-process research and development if the technology licensed has not reached technological feasibility and has no alternative future use.

Accrued CRO, CMO, and Research and Development Expenses

The Company has entered into various agreements with CMOs and CROs. The Company’s research and development accruals are estimated based on the level of services performed, progress of the studies, including the phase or completion of events, and contracted costs. The estimated costs of research and development provided, but not yet invoiced are included in accrued and other current liabilities on the consolidated balance sheets. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments made to CMOs and CROs under these arrangements in advance of the performance of the related services are recorded as prepaid expenses and other current assets on the consolidated balance sheets until the services are rendered. Through December 31, 2020 there had been no material adjustments to the Company’s prior period estimates of accrued research and development expenses.

Leases

Effective January 1, 2020, the Company adopted ASC Topic 842, “Leases” (ASC 842), using the modified retrospective approach and utilizing the effective date as its date of initial application, for which prior periods are presented in accordance with the previous guidance in ASC Topic 840, “Leases” (ASC 840).

Prior to January 1, 2020, the Company met the requirements to account for these leases as operating leases under ASC 840. The Company recognized rent expense on a straight-line basis over the non-cancelable lease term. Where leases contained escalation clauses, rent abatements or concessions, such as rent holidays and landlord or tenant incentives or allowances, the Company applied them in the determination of straight-line rent expense over the lease term. As of December 31, 2019, the Company recorded the difference between the rent paid and the straight-line rent as a deferred rent liability. The leasehold improvements funded by landlord incentives or allowances were recorded as leasehold improvement assets and a corresponding deferred rent liability. The leasehold improvement asset was amortized over the lesser of the term of the lease or life of the asset. The deferred rent liability was amortized on a straight-line basis as a reduction to rent expense over the term of the lease agreement.

Upon adoption of ASC 842, as described below under Recently Adopted Accounting Pronouncements, the Company determined if an arrangement is a lease, or contains a lease, at inception. Leases with a term greater than 12 months are recognized on the balance sheet as Right-of-Use (ROU) assets and current and long-term operating lease liabilities, as applicable. The Company has elected not to recognize on the balance sheet leases with terms of 12 months or less. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. The Company monitors its plan to renew its leases no less than on a quarterly basis. In addition, the Company’s lease agreements generally do not contain any residual value guarantees or restrictive covenants.

In accordance with ASC 842, the ROU assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate (IBR), which is the estimated rate the Company would be required to pay for a fully collateralized borrowing equal to the total lease payments over the term of the lease, to determine the present value of future minimum lease payments. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. For lease agreements entered into or reassessed after the adoption of ASC 842, the Company does not combine lease and non-lease components. Variable lease payments are expenses as incurred.

Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease.

Upon the adoption of ASC 842, the Company recognized an ROU asset of $1.4 million and lease liabilities of $1.8 million as of January 1, 2020, primarily related to office leases based on the present value of future lease payments. As of December 31, 2020, the Company has recorded an ROU asset of $23.1 million and lease liabilities of $21.6 million on its consolidated

balance sheets. There was no impact to retained earnings upon the adoption of ASC 842. As of December 31, 2020, the Company had no finance leases.

Fair Value of Common Stock

Prior to the Merger the fair value of the Company’s common stock was determined by its Board of Directors with input from management and third-party valuation specialists. The Company’s approach to estimate the fair value of the Company’s common stock is consistent with the methods outlined in the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. Determining the best estimated fair value of the Company’s common stock requires significant judgement and management considers several factors, including the Company’s stage of development, equity market conditions affecting comparable public companies, significant milestones and progress of research and development efforts. Subsequent to the Merger, the fair value of the Company’s common stock is determined based on its closing market price.

Stock-Based Compensation

The Company accounts for stock-based compensation arrangements with employees and non-employees using a fair value method which requires the recognition of compensation expense for costs related to all stock-based payments including stock options. The fair value method requires the Company to estimate the fair value of stock-based payment awards on the date of grant using an option-pricing model. The Company uses the Black-Scholes option-pricing model to estimate the fair value of options granted that are expensed on a straight-line basis over the requisite service period, which is generally the vesting period. The Company accounts for forfeitures as they occur. Option valuation models, including the Black-Scholes option-pricing model, require the input of several assumptions. Changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility and the expected life of the award.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences attributable to differences between carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax reporting purposes and for operating loss and tax credit carryforwards. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes.

The Company’s deferred tax assets and liabilities are measured using enacted tax rates expected to apply in the years in which these temporary differences are expected to be recovered or settled. A valuation allowance is recorded to reduce deferred tax assets if it is determined that it is more likely than not that all or a portion of the deferred tax asset will not be realized. The Company considers many factors when assessing the likelihood of future realization of deferred tax assets, including recent earnings results, expectations of future taxable income, carryforward periods available and other relevant factors. The Company records changes in the required valuation allowance in the period that the determination is made.

The Company assesses its income tax positions and records tax benefits for all years subject to examination based upon management’s evaluation of the facts, circumstances and information available as of the reporting date. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, the Company does not recognize a tax benefit in the consolidated financial statements. The Company records interest and penalties related to uncertain tax positions, if applicable, as a component of income tax expense (benefit).

Comprehensive Income (Loss)

Comprehensive income (loss) is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The other comprehensive loss disclosed in the Company’s consolidated statements of operations and comprehensive loss for the years ended December 31, 2020, 2019 and 2018 consists of changes in unrealized gains and losses on marketable debt securities.

Net Loss per Share Attributable to Common Stockholders

Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-

average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, the redeemable convertible preferred stock, redeemable convertible preferred stock warrants, redeemable convertible preferred stock tranche liability, common stock subject to repurchase and stock options are considered to be potentially dilutive securities. Basic and diluted net loss per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities as the redeemable convertible preferred stock and early exercised stock options are considered to be participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in undistributed earnings as if all income (loss) for the period had been distributed. The Company’s participating securities do not have a contractual obligation to share in the Company’s losses. As such, the net loss is attributed entirely to common stockholders. Since the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB under its ASC or other standard setting bodies and adopted by the Company as of the specified effective date, unless otherwise discussed below.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (ASC 842), which sets out the principles for the recognition, measurement, presentation, and disclosure of leases for both parties to a contract (i.e. lessees and lessors). In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases, which provides clarification to ASU 2016-02. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. These ASUs (collectively the new leasing standard) requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease, respectively. A lessee is also required to record a ROU and a lease liability for all leases with a term of greater than 12 months regardless of their classification. ASC 842 provides a lessee with an option to not account for leases with a term of 12 month or less as leases in the scope of ASC 842. ASC 842 supersedes the previous leases standard, ASC 840 Leases. The new leasing standard is effective for public business entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, and should be applied through a modified retrospective transition approach for leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Early adoption is permitted. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements, which allows entities to elect an optional transition method where entities may continue to apply the existing lease guidance during the comparative periods and apply the new lease requirements through a cumulative effect adjustment in the period of adoptions rather than in the earliest period presented. In June 2020, the FASB issued ASU 2020-05, which delays the adoption dates for ASU 2016-02 for non-public entities to fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early application continues to be allowed.

The Company adopted ASC 842 effective January 1, 2020, using the modified retrospective approach to recognize a cumulative-effect adjustment as of the adoption date. Results for reporting periods beginning after January 1, 2020 are presented under ASC 842, while prior period amounts are not adjusted and continue to be reported in accordance with the Company’s historical accounting under ASC 840. The Company elected the package of practical expedients permitted under the transition guidance within ASC 842, which allowed the Company to carry forward the historical lease classification, retain the initial direct costs for any leases that existed prior to the adoption of the standard and not reassess whether any contracts entered into prior to the adoption are leases. The Company also elected to account for lease and non-lease components in the Company’s lease agreements as a single lease component in determining lease assets and liabilities. In addition, the Company elected not to recognize the ROU assets and liabilities for leases with lease terms of 12 months or less. Upon the adoption of ASC 842, the Company recognized an ROU asset of $1.4 million and lease liabilities of $1.8 million as of January 1, 2020, primarily related to office leases based on the present value of future lease payments. The adoption of the new leasing standard during 2020 resulted in the recognition of ROU asset of $23.1 million and operating lease liability of $21.6 million and derecognition of deferred rent of $0.4 million related to the operating leases on the consolidated balance sheets as of December 31, 2020 with no material impact to the consolidated statements of operations and comprehensive loss, consolidated statements of redeemable convertible preferred stock and stockholder’s deficit or consolidated statements of cash flows. The additional disclosures required by the new standard have been included in Note 12, Commitments and Contingencies.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies the disclosure requirements on fair value measurements. The new disclosure requirements include disclosure related to changes in unrealized gains or losses

included in other comprehensive income (loss) for recurring Level 3 fair value measurements held at the end of each reporting period and the explicit requirement to disclose the range and weighted-average of significant unobservable inputs used for Level 3 fair value measurements. This ASU removes the requirement to disclose: the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; the policy for timing of transfers between levels; and the valuation processes for Level 3 fair value measurements. For all entities, this ASU is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted. The Company adopted this ASU effective January 1, 2020. The adoption of this ASU did not have a material effect on the Company’s consolidated financial statements and related disclosures.

Accounting Pronouncements Not Yet Adopted

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. This ASU replaces the existing incurred loss impairment model with an expected loss model. It also eliminates the concept of other-than-temporary impairment and requires credit losses related to available-for-sale debt securities to be recorded through an allowance for credit losses rather than as a reduction in the amortized cost basis of the securities. These changes will result in earlier recognition of credit losses. For public business entities that meet the definition of a Securities and Exchange Commission (SEC) filer, excluding entities eligible to be smaller reporting companies as defined by the SEC, adoption is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. For SEC filers that are eligible to be smaller reporting companies and for all other entities, this ASU is effective for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact the adoption of this ASU will have on its consolidated financial statements and related disclosures.

In November 2018, FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606, which is intended to clarify the circumstances under which certain transactions in collaborative arrangements should be accounted for under the revenue recognition standard. Certain transactions between collaboration arrangement participants should be accounted for as revenue under ASC Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. For public business entities, this ASU is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. For all other entities, this ASU is effective for fiscal years and interim periods within those years beginning after December 15, 2020. Early adoption is permitted. The Company is currently evaluating the impact the adoption of this ASU will have on its consolidated financial statements and related disclosures.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740)—Simplifying the Accounting for Income Taxes, which simplify various aspects related to the accounting for income taxes. This ASU removes exceptions to the general principles in Topic 740 related to the approach for intra-period tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. For public companies, this ASU is effective for interim and annual reporting periods beginning after December 15, 2020. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early adoption is permitted. The Company is currently evaluating the impact the adoption of this ASU will have on its consolidated financial statements and related disclosures.

In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848) (ASU 2020-04). The amendments in ASU 2020-04 provide optional expedients and exceptions for applying generally accepted accounting principles to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments in ASU 2020-04 are effective for all entities as of March 12, 2020 through December 31, 2022. An entity may elect to apply the amendments for contract modifications by Topic or Industry Subtopic as of any date from the beginning an interim period that includes or is subsequent to March 12, 2020, or prospectively from the date that the financial statements are available to be issued. Once elected for a Topic or an Industry Subtopic, the amendments must be applied prospectively for all eligible contract modifications for that Topic or Industry Subtopic. The Company may elect to apply ASU 2020-04 as its contracts referenced in London Interbank Offered Rate (LIBOR) are impacted by reference rate reform. The Company is currently evaluating the impact of the adoption of this ASU on the Company’s consolidated financial statements.

Business Combination

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

Business Combination

3. Business Combination

On September 15, 2020, Former Adicet completed its merger with resTORbio. Based on the Exchange Ratio of 0.1240, immediately following the Merger, resTORbio stockholders and holders of resTORbio restricted stock units and options to acquire resTORbio common stock owned approximately 25.0% of the outstanding capital stock of the combined company on a fully diluted basis, and Former Adicet stockholders, holders of options or warrants to acquire Former Adicet capital stock owned approximately 75.0% of the outstanding capital stock of the combined company on a fully diluted basis.

resTORbio’s stockholders continued to own and hold their existing shares of the Company’s common stock (after giving effect to the 1-for-7 reverse stock split). Pursuant to the terms of the Merger, the vesting of all outstanding resTORbio stock options was accelerated in full as of immediately prior to the Effective Time. All out-of-the-money resTORbio stock options were cancelled for no consideration. All in-the-money resTORbio stock options remained outstanding after the completion of the Merger in accordance with their terms. For accounting purposes, the Company assumed 81,370 in-the-money resTORbio stock options after giving effect to reverse stock split. In addition, 91,309 unvested resTORbio restricted stock units outstanding and unsettled, after giving effect to reverse stock split, as of immediately prior to the Effective Time of the Merger, were accelerated in full and the holders of such restricted stock units received 54,553 shares of the Company’s common stock (after reduction by the number of shares of resTORbio common stock necessary to satisfy applicable tax withholding obligations at the maximum statutory rate). The fair value of these modified stock options and restricted stock units attributable to pre-combination services was recorded as a component of consideration transferred and the fair value of these modified stock options and restricted stock units attributable to post-combination services was recognized as stock compensation expense in the Company’s consolidated statements of operations and comprehensive loss.

At the closing of the Merger, all shares of Former Adicet common stock and Former Adicet redeemable convertible preferred stock then outstanding were converted to Former Adicet’s common stock under their original terms and were then exchanged for the Company’s common stock.

In connection with the Merger, the Company entered into a Contingent Value Rights Agreement (the CVR Agreement) with Computershare Inc. and Computershare Trust Company, N.A. as joint rights agent. Per the terms of the Merger, each holder of resTORbio common stock as of immediately prior to the completion of the Merger is entitled to one contractual contingent value right, subject to and in accordance with the terms and conditions of the CVR Agreement, for each share of resTORbio common stock held by such holder as of immediately prior to the Effective Time. The CVR holders are entitled to receive net proceeds from the commercialization, if any, from a third-party commercial partner of RTB101, resTORbio’s small molecule product candidate that is a potent inhibitor of target of rapamycin complex 1 (TORC1), for a COVID-19 related indication.

The total purchase price was allocated to the tangible and intangible assets acquired and liabilities assumed of resTORbio based on their fair values as of the completion of the Merger, with the excess allocated to goodwill. The purchase price is calculated based on the fair value of resTORbio common stock that the resTORbio stockholders owned as of the closing date of the Merger because, with no active trading market for shares of Former Adicet, the fair value of the resTORbio’s common stock represented a more reliable measure of the fair value of consideration transferred in the Merger. The following summarizes the purchase price in the Merger (in thousands, except share and per share amounts):

Fair value of common stock shares of the combined company

owned by resTORbio stockholders (1)

84,142

Fair value of contingent consideration liability with respect to CVR (2)

2,880

Purchase price

87,022

(1)	Represents the share consideration of the combined company that the resTORbio stockholders own as of the closing of the Merger calculated as follows:

Number of shares of the combined company owned by resTORbio stockholders (a)		5,207,695
Multiplied by the fair value per share of resTORbio common stock (b)	$	16.59
Acquisition date fair value of resTORbio common shares		86,396
Acceleration of 54,553 shares of restricted stock units upon merger (3)		626
Less: portion of the fair value to be distributed as CVR (c)		(2,880	)
Fair value of shares of the combined company owned by resTORbio stockholders	$	84,142

Represents the number of shares of common stock of the combined company that the resTORbio stockholders owned as of the closing of the Merger. This amount is calculated as 5,207,695 shares (post-reverse stock split) of resTORbio common stock outstanding as of September 15, 2020.

The fair value of shares of the combined company owned by resTORbio stockholders is based on the closing price of resTORbio common stock on September 14, 2020.

The fair value of resTORbio common stock was further adjusted to remove the estimated fair value of the CVR embedded within the closing price, as each holder of resTORbio stock received one contractual CVR immediately prior to the Merger.

(2)

Each holder of resTORbio common stock as of immediately prior to the completion of the Merger was entitled to one CVR issued by resTORbio, subject to and in accordance with the terms and conditions of the CVR Agreement, for each share of resTORbio common stock held by such holder as of immediately prior to the Effective Time of the Merger.

(3)

Based on the capitalization of resTORbio as of September 15, 2020, 91,309 outstanding unvested resTORbio restricted stock units were accelerated in connection with the Merger and holders of the restricted stock units were issued approximately 54,553 shares of resTORbio common stock on a net settlement basis. Similarly, in connection with the Merger, vesting of outstanding resTORbio stock options was accelerated in full and the stock options that were not in the in-the-money on the close of the Merger were canceled, resulting in approximately 81,370 surviving stock options. The acquisition date fair value of these modified resTORbio restricted stock units and resTORbio stock options attributable to the pre-combination services is included in the estimated purchase price.

The Merger was accounted for as a business combination which requires that assets acquired, and liabilities assumed be recognized at their fair value as of the acquisition date. While the Company uses its best estimates and assumptions as part of the purchase price allocation process to value the assets acquired and liabilities assumed on the acquisition date, its estimates and assumptions are subject to refinement. Fair value estimates are based on a complex series of judgments about future events and uncertainties and rely heavily on estimates and assumptions. The judgments used to determine the estimated fair value assigned to each class of assets acquired and liabilities assumed, as well as asset lives, can materially impact the Company’s results of operations.

During the fourth quarter of 2020, the Company identified and recorded measurement period adjustments of $0.7 million to its preliminary purchase price allocation that was disclosed in prior periods based on the facts and circumstances existing as of the acquisition date.

The following summarizes the allocation of the purchase price to the net tangible and intangible assets acquired at the date of acquisition both as disclosed in the Company’s quarterly report on Form 10-Q as of September 30, 2020 and as adjusted for measurement period adjustments identified during the fourth quarter of 2020 (in thousands):

	As of September 15, 2020 (preliminary)			Measurement Period Adjustments			As of December 31, 2020 (as adjusted)
Net assets acquired:
Cash and cash equivalents	$	63,869		$	—		$	63,869
Prepaid expenses and other current assets		2,505			554			3,059
Property and equipment		318			—			318
IPR&D		3,490			—			3,490
Restricted cash		245			—			245
Accounts payable		(1,316	)		—			(1,316	)
Accrued and other current liabilities		(2,421	)		56			(2,365	)
Other liabilities		(40	)		40			—
Deferred tax liability		(367	)		—			(367	)
Goodwill		20,739			(650	)		20,089
Purchase price	$	87,022		$	—		$	87,022

The goodwill of $20.1 million is not tax deductible and represents the excess of the consideration paid over the fair value of assets acquired and liabilities assumed. Goodwill is mainly attributable to the enhanced value of the combined company, as reflected in the increase in market value of the resTORbio common shares following the announcement of the Merger with Former Adicet.

The fair value of acquired IPR&D related to the research and development of RTB101 for a COVID-19 related indication. The RTB101 compound IPR&D project was valued using an income approach, specifically a projected discounted cash flow method, adjusted for the probability of technical success (PTS). The projected discounted cash flow models used to estimate

the Company’s IPR&D reflect significant assumptions regarding the estimates a market participant would make in order to evaluate a drug development asset, including the following:

•

Estimates of potential cash flows to be generated by the project and resulting asset, which was developed utilizing estimates of total patient population, market penetration rates, demand risk adjustment factors, and product pricing;

•

Estimates regarding the timing of and the expected costs of goods sold, research and development expenses, selling, general and administrative expenses to advance the clinical programs to commercialization, cash flow adjustments and partner profit split;

•

The projected cash flows were then adjusted using PTS factors that were selected considering both the current state of clinical development and the nature of the proposed indication, (i.e., respiratory therapeutics); and

•

Finally, the resulting probability adjusted cash flows were discounted to a present value using a risk-adjusted discount rate, developed considering the market risk present in the forecast and the size of the asset.

This IPR&D intangible asset is not amortized, but rather are reviewed for impairment on an annual basis or more frequently if indicators of impairment are present, until the project is completed, abandoned, or transferred to a third party.

The contingent consideration for the CVR was valued using an income approach, leveraging the probability adjusted discounted cash flow used in the valuation of the IPR&D and then deducting the administrative fee to be retained by the combined company and other permitted deductions in order to arrive at the net cash expected to be paid out to the CVR holders. The probability adjusted cash flow includes significant estimates and assumptions pertaining to commercialization events and cash consideration received by the Company for the grant of rights to commercialize RTB101 during the term of the CVR Agreement (as discussed above). These cash flows were then discounted to present value using the same discount rate applied in the valuation of the IPR&D.

Transaction costs for the Merger were $7.1 million for the year ended December 31, 2020 and were expensed as incurred in general and administrative expenses in the consolidated statements of operations and comprehensive loss.

The following supplemental unaudited pro forma information represents the Company’s financial results as if the acquisition of resTORbio had occurred on January 1, 2019 (in thousands).

	For the Year Ended December 31,
	2020			2019
Revenue - related party	$	17,903		$	995
Net loss	$	(35,757	)	$	(113,151	)

The above unaudited pro forma information was determined based on the historical GAAP results of the Company and resTORbio. The unaudited pro forma consolidated results are not necessarily indicative of what the Company’s consolidated results of operations would have been if the acquisition was completed on January 1, 2019. The unaudited pro forma consolidated net loss includes pro forma adjustments of $15.6 million primarily relating to the reclassification of transaction costs, severance payments and stock-based compensation expense directly related to the closing of the Merger from the year ended December 31, 2020 to the year ended December 31, 2019. The unaudited proforma information include proforma adjustments to eliminate the impact of the change in the fair value of the TRDF liability during the year ended December 31, 2019, and the redeemable convertible preferred stock tranche liability and redeemable convertible warrant liability during the years ended December 31, 2020 as the redeemable convertible preferred stock tranche liability, TRDF liability, and redeemable convertible warrant liability did not exist once the redeemable convertible preferred stock were converted to common stock in the Merger. The unaudited proforma information also includes proforma adjustments to reclassify stock compensation expense related to the conversion of resTORbio stock options and restricted stock units and the modification of stock option awards to Former Adicet CEO in connection with the Merger to January 1, 2019. Further, stock compensation expense related to resTORbio stock options and restricted stock units recognized in the books of resTORbio prior to the Merger in 2019 and 2020 was reversed in the proforma information.

Former Chief Executive Officer’s Transition Agreement

On April 28, 2020, in connection with the Merger the Company entered into a transition agreement with Anil Singhal, Former Adicet’s Chief Executive Officer and President, pursuant to which Dr. Singhal transitioned from his role as Chief Executive Officer and President to an advisory role immediately after the closing of the Merger. In accordance with such agreement, Dr. Singhal was entitled to the following compensation: (1) cash payments of (i) $470,000 within 60 days

following the closing of the Merger, (ii) an amount equal to his pro-rated bonus of $212,000 for the 2020 calendar year payable within 60 days following the closing of the Merger, (iii) $250,000 payable in one lump sum on January 1, 2021 and (iv) $24,000 payable within 60 days following the closing of the Merger, (2) 12 months’ of accelerated vesting of his unvested options to purchase the Company’s common stock upon completion of the Merger, and (3) a 12-month post-termination exercise period following termination of his independent contractor services agreement, dated April 28, 2020 (the ICSA), subject to any earlier expiration of the options to purchase the Company’s common stock by their terms. In addition, Dr. Singhal is entitled to reimbursement of up to $15,000 of his reasonable and documented legal expenses incurred in connection with such transition agreement. Pursuant to such agreement, subject to Dr. Singhal’s continued service through the completion of the Merger and contingent on completion of the Merger, Dr. Singhal’s continued service for purposes of vesting of his options to purchase the Company’s common stock will continue until the earlier of (i) May 7, 2021 or (ii) termination of the ICSA, provided, however, if the ICSA is terminated early without cause, Dr. Singhal is entitled to accelerated vesting of unvested options that would have vested from the date of such termination through May 7, 2021. In addition, Dr. Singhal’s existing options acceleration provisions will terminate. Pursuant to the ICSA, Dr. Singhal will provide certain advisory services to the Company for a term of 12 months following the closing of the Merger and is entitled to payments of $12,500 per month for such services. The ICSA was terminated without cause in February 2021.

Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

The Company determines the fair value of financial and non-financial assets and liabilities using the fair value hierarchy which establishes three level of inputs that may be used to measure fair value, as follows:

Level 1 — Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2 — Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 — Unobservable inputs which reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.

In determining fair value, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as considers counterparty credit risk in its assessment of fair value.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability.

The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands):

	December 31, 2020
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds⁽¹⁾	$	63,817	$	—	$	—	$	63,817
Marketable debt securities
Asset-backed securities		—		7,522		—		7,522
Corporate debt securities		—		1,762		—		1,762
Commercial paper		—		1,000		—		1,000
Marketable debt securities		—		10,284		—		10,284
Total fair value of assets	$	63,817	$	10,284	$	—	$	74,101
Liabilities:
Contingent consideration	$	—	$	—	$	980	$	980
Total fair value of liabilities	$	—	$	—	$	980	$	980

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds⁽¹⁾	$	7,232	$	—	$	—	$	7,232
Marketable debt securities
Asset-backed securities		—		19,598		—		19,598
Corporate debt securities		—		19,394		—		19,394
Commercial paper		—		17,892		—		17,892
U.S. Government agency bonds		—		5,497		—		5,497
Marketable debt securities		—		62,381		—		62,381
Total fair value of assets	$	7,232	$	62,381	$	—	$	69,613
Liabilities:
Redeemable convertible preferred stock warrant liability	$	—	$	—	$	1,881	$	1,881
Total fair value of liabilities	$	—	$	—	$	1,881	$	1,881

(1)	Included in cash and cash equivalents in the consolidated balance sheets

Money market funds are included within Level 1 of the fair value hierarchy because they are valued using quoted market prices. Corporate debt securities, U.S. government agency bonds, commercial paper and asset-backed securities are classified within Level 2 of the fair value hierarchy as they take into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income-based and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate the fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities, prepayment/default projections based on historical data and other observable inputs.

The following table presents a summary of the changes in the fair value of the Company’s Level 3 financial instrument (in thousands):

	Redeemable Convertible Preferred Stock Tranche Liability			TRDF Liability			Redeemable Convertible Preferred Stock Warrant Liability			Contingent Consideration Liability
Fair value as of January 1, 2018	$	8,557		$	136		$	—		$	—
Change in the fair value included in other income (expense), net		(4,542	)		6			—			—
Exercise		(902	)		—			—			—
Fair value as of December 31, 2018		3,113			142			—			—
Recognition of preferred stock warrant liabilities		—			—			2,131			—
Settlement		—			(88	)		—			—
Change in the fair value included in other income (expense), net		(1,970	)		(54	)		(250	)		—
Termination		(1,143	)		—			—			—
Fair value as of December 31, 2019		—			—			1,881			—
Recognition of preferred stock warrant liability		—			—			144			—
Recognition of contingent consideration liability		—			—			—			2,880
Change in the fair value included in other income (expense), net		—			—			897			—
Change in the fair value included in research and development expense		—			—			—			(1,900	)
Conversion of convertible preferred stock warrant into common stock warrant in connection with Merger		—			—			(2,922	)		—
Fair value as of December 31, 2020	$	—		$	—		$	—		$	980

The fair value of the redeemable convertible preferred stock tranche liability, TRDF Liability, the redeemable convertible preferred stock warrant liability is based on significant unobservable inputs, which represent Level 3 measurements within the fair value hierarchy.

The Company determined that the obligations to issue additional shares of Series A redeemable convertible preferred stock at the Milestone Closing and Additional Closing were freestanding instruments that are required to be accounted as a liability initially recorded and subsequently remeasured at fair value until such instruments are exercised or expire. The Milestone Closing liability and Additional Closing liability were initially recorded at $6.2 million and $5.0 million, respectively.

The Milestone Closing liability was settled in November 2018 upon the Milestone Closing and the related TRDF liability was settled in March 2019. In July 2019, as part of the Series B redeemable convertible preferred stock purchase agreement the Additional Closing liability and the related TRDF liability were terminated. The Company recorded $2.0 million gain from the remeasurement of the redeemable convertible preferred stock tranche liability associated with the Additional Closing and termination in other income (expense), net in its consolidated statements of operations and comprehensive loss during the year ended December 31, 2019.

There were no warrants outstanding for the purchase of redeemable convertible preferred stock as of December 31, 2020, as all such warrants were converted to warrants for the purchase of shares of common stock upon the Merger.

The fair value of the TDRF Liability was determined based on the fair value of the Company’s Series A redeemable Preferred stock.

As part of the acquisition of resTORbio, the Company entered into a CVR Agreement and recorded the fair value of the CVR as part of consideration transferred. The Company considers the contingent consideration liability a Level 3 instrument (one with significant unobservable inputs) in the fair value hierarchy. In November 2020, management terminated the nursing home study due to poor enrollment and consequently lowered the probability of finding a partner due to the delay in time to commercialization of RTB101. As a result, the fair value of the CVR liability decreased by $1.9 million to $1.0 million.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Debt Securities

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Marketable Debt Securities

5. Marketable Debt Securities

The following tables summarize the Company’s marketable debt securities (in thousands):

	December 31, 2020
	Amortized Cost		Unrealized Losses		Unrealized Gains		Fair Value
Asset-backed securities	$	7,507	$	—	$	15	$	7,522
Corporate debt securities		1,754		—		8		1,762
Commercial paper		999		—		1		1,000
Total	$	10,260	$	—	$	24	$	10,284

	December 31, 2019
	Amortized Cost		Unrealized Losses			Unrealized Gains		Fair Value
Asset-backed securities	$	19,589	$	(1	)	$	10	$	19,598
Corporate debt securities		19,387		(3	)		9		19,393
Commercial paper		17,882		—			11		17,893
U.S. Government agency bonds		5,500		(3	)		—		5,497
Total	$	62,358	$	(7	)	$	30	$	62,381

The following table summarizes the Company’s marketable debt securities by contractual maturity (in thousands):

	December 31, 2020
	Amortized Cost		Fair Value
Within one year	$	10,260	$	10,284
After one year through five years		—		—
After five years		—		—
Total	$	10,260	$	10,284

The following table summarizes the classification of the Company’s marketable debt securities in the consolidated balance sheets (in thousands):

	December 31
	2020		2019
Short-term marketable debt securities	$	10,284	$	51,793
Long-term marketable debt securities		—		10,588
Total	$	10,284	$	62,381

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2020

Prepaid Expense And Other Assets Current [Abstract]

Prepaid Expenses and Other Current Assets

6. Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):

	December 31
	2020		2019
Prepaid maintenance and other	$	1,185	$	615
Prepaid insurance		1,443		57
Tax receivable		2,711		722
Interest receivable		20		213
Other current assets		363		179
Total	$	5,722	$	1,786

Property and Equipment, Net

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, Net

7. Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):

			As of December 31,
	Useful life (years)		2020			2019
Laboratory equipment	3		$	4,350		$	3,872
Leasehold improvements	Lesser of useful life or lease term			1,427			1,327
Furniture and fixtures	3			524			68
Construction in progress		—		1,090			300
Computer equipment	3			93			42
Software	3			170			150
				7,654			5,759
Less: Accumulated depreciation and amortization				(4,864	)		(3,638	)
Property and equipment, net			$	2,790		$	2,121

Depreciation and amortization expense for each of the years ended December 31, 2020, 2019 and 2018 was $1.2 million. All of the Company’s property and equipment as of December 31, 2020 and 2019 is located in the U.S.

Accrued and Other Current Liabilities

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Accrued and Other Current Liabilities

8. Accrued and Other Current Liabilities

Accrued and other current liabilities consisted of the following (in thousands):

	December 31
	2020		2019
Accrued compensation	$	3,833	$	1,359
Accrued research and development expenses		1,187		450
Accrued professional services		386		301
Accrued other liabilities		326		710
Total	$	5,732	$	2,820

Term Loan

12 Months Ended

Dec. 31, 2020

Term Loan [Abstract]

Term Loan

9. Term Loan

On April 28, 2020, the Company entered into a Loan and Security Agreement with Pacific Western Bank for a term loan not exceeding $12.0 million (the Loan Agreement) to finance leasehold improvements for the facilities in Redwood City, CA and other purposes permitted under the Loan Agreement, with an interest rate equal to the greater of 0.25% above the Prime Rate (as defined in the Loan Agreement) or 5.00%. The Loan Agreement granted to Pacific Western Bank a security interest on substantially all of the Company’s assets other than intellectual property to secure the performance of the Company’s obligations under the Loan Agreement, and contains a variety of affirmative and negative covenants, including required financial reporting, limitations on certain dispositions of assets or distributions, limitations on the incurrence of additional debt or liens and other customary requirements. As of December 31, 2020, the Company was in compliance with such covenants and had no indebtedness outstanding under the Loan Agreement.

In connection with the entrance into the Loan Agreement, the Company issued Pacific Western Bank a warrant to purchase shares of its Series B redeemable convertible preferred stock at an exercise price of $1.4034 per share (the Existing PacWest Warrant). The Existing PacWest Warrant was initially exercisable for 42,753 shares of the Company’s Series B redeemable convertible preferred stock (not adjusted for the Exchange Ratio). Pursuant to the terms of the Existing PacWest Warrant and the Merger agreement (see Note 3), at the Effective Time of the Merger, the Company issued a new common stock warrant to Pacific Western Bank (the New PacWest Warrant) which replaced the Existing PacWest Warrant. The New PacWest Warrant is initially exercisable solely for 5,301 shares of the Company’s common stock and will be exercisable for an additional number of shares of the Company’s common stock equal to 1.00% of the aggregate original principal amount of all term loans made pursuant to the Loan Agreement (up to an aggregate maximum of 15,903 shares of the Company’s common stock). Any restriction on the exercise set forth in the Existing PacWest Warrant are in full force and effect in the New PacWest Warrant and the term, exercisability, vesting schedule and other provisions of the Existing PacWest warrant otherwise remain unchanged in the New PacWest Warrant. Further, the New PacWest Warrant to purchase 5,301 shares of the Company’s common stock is immediately exercisable. See Note 15 for further discussion regarding terms of warrants. The New PacWest Warrant was exercised in February 2021.

The Company may request to draw upon the term loan at any time through the date eighteen months after the date of the Loan Agreement (Availability End Date), which is October 28, 2021. As of December 31, 2020, no amounts have been drawn under the Loan Agreement.

At issuance, the Company accounted for the fair value of the Existing PacWest Warrant, determined to be $0.1 million, as a liability and as a corresponding deferred debt issuance cost which was amortized on a straight-line basis until the Availability End Date in interest expenses. The liability was adjusted to fair value each reporting period through earnings. Upon issuance of the New PacWest Warrant, the liability was reclassified to additional paid-in capital and is no longer subject to remeasurement at fair value. The fair value of the New PacWest Warrant was equal to the fair value of the Existing PacWest Warrant on the Merger date. Accordingly, no incremental expense was recognized at the Merger date.

Upon each draw of the term loan, the Company will derecognize the proportionate unamortized amount of the deferred asset and account for it as a debt discount to the drawn term loan. The debt discount will be presented in the consolidated balance sheet as a direct adjustment to the carrying value of the term loan. The debt discount will be amortized using the effective interest rate method over the term of the debt and recorded as an interest expense.

As of December 31, 2020, the deferred debt issuance costs were $0.2 million and are included in other non-current assets on the Company’s consolidated balance sheets.

Regeneron License and Collaboration Arrangement

12 Months Ended

Dec. 31, 2020

Revenue Recognition And Deferred Revenue [Abstract]

Regeneron License and Collaboration Arrangement

10. Regeneron License and Collaboration Arrangement

Agreement Terms

On July 29, 2016, the Company entered into a license and collaboration agreement with Regeneron Pharmaceuticals, Inc. (Regeneron), which was amended in April 2019, with such amendment becoming effective in connection with Regeneron’s investment in the Company’s Series B redeemable convertible preferred stock private placement transaction in July 2019 (as amended, the Regeneron Agreement).

Agreement Structure. The Regeneron Agreement has two principal components: (a) a research collaboration component under which the parties will research, develop, and commercialize next-generation engineered gamma delta immune cell therapeutics (ICPs), namely engineered gamma delta immune cells with CARs and TCRs directed to disease-specific cell surface antigens, which includes the grant of certain licenses to intellectual property between the two parties, and (b) for a certain period following the effective date, a license to the Company to use certain of Regeneron’s proprietary mice to develop and commercialize ICPs generated by the Company, with certain limitations relating to targets under the Regeneron Agreement.

Research Collaboration. Research activities under the collaboration are governed by research plans, which include the strategy, goals, activities, and responsibilities of the parties with respect to a target. The Company is primarily responsible for generating, validating, and optimizing ICPs, developing processes for manufacture of ICPs, and certain preclinical and clinical manufacturing activities for ICPs; Regeneron’s key responsibility is generating, validating, and optimizing CARs and TCRs that bind to the applicable target. The parties have formed a joint research committee to monitor and govern the research and development efforts during the research program term.

Rights to Research Targets. Under the terms of the five-year research collaboration, the parties will conduct research on mutually agreed upon targets. Regeneron may obtain exclusive rights for the targets that it chooses in accordance with the target selection mechanism set forth in the Regeneron Agreement, and the Company similarly may obtain exclusive rights for targets it chooses in accordance with such target selection mechanism. The Company has the right to develop and commercialize ICPs to the first collaboration target to come out of the research program. In connection with an IND submission, Regeneron has an option to exercise exclusive rights for ADI-002 and potentially for additional targets to be mutually agreed upon. For those targets it does not have an option to license, Regeneron has a right of first negotiation for up to two targets. Regeneron has the right to terminate the research program in its entirety (a) for convenience on six months prior written notice given at any time after December 31, 2019, or (b) following a change of control (as defined in the Regeneron Agreement) of the Company. The parties mutually agreed to their first product declaration criteria for collaboration ICP, CD20, in 2018.

Rights to Company-Developed Targets. Regeneron has an exclusive license to use targeting moieties generated by the Company by its use of Regeneron’s proprietary mice to develop and commercialize non-ICPs.

Exclusivity. During the five-year target selection period, the Company may not directly or indirectly research, develop, manufacture or commercialize an ICP, or grant a license to do the foregoing, except pursuant to the agreement. For so long as either party is researching or developing an ICP to a target under the research program, neither party may research, develop, manufacture or commercialize any other ICP to such target, or grant a license to do the foregoing. And for so long as a party is researching, developing or commercializing an ICP to target that is licensed to it (and royalty bearing) under the agreement, neither party may research, develop, manufacture or commercialize any other ICP to such target, or grant a license to permit another party to do the foregoing. These exclusivity obligations are limited to engineered gamma delta immune cells to targets reasonably considered to have therapeutic relevance in oncology. The Regeneron Agreement includes certain exceptions to the exclusivity obligations of the parties, including with respect to targets that are rejected by one party in the target selection process, as well as protections in the event of a change of control of a party where the acquirer has a competing program.

Co-Funding and Profit Sharing. The Company has an option to co-fund specified portions of the future development costs for, and to co-promote, ICPs to a target for which Regeneron has exercised an option, and to participate in the profits for such target. The Company has the right to exercise this right in various geographic regions, including on a worldwide basis. In the event the Company exercises such right, the parties will share further development costs and revenues proportionally to their co-funding percentages.

Financial Terms. The Company received a non-refundable upfront payment of $25.0 million from Regeneron upon execution of the Regeneron Agreement, has received an aggregate of $20.0 million of additional payments for research funding from Regeneron as of December 31, 2020. In addition, Regeneron may have to pay the Company additional amounts in the future consisting of up to an aggregate of $100.0 million of option exercise fees, as specified in the Regeneron Agreement. Regeneron must also pay the Company high single digit royalties as a percentage of net sales for ICPs to targets for which it has exclusive rights, and low single digit royalties as a percentage of net sales on any non-ICP product comprising a targeting moiety generated by the Company through the use of Regeneron’s proprietary mice. The Company must pay Regeneron mid-single to low double digit, but less than teens, of royalties as a percentage of net sales of ICPs to targets for which the Company has exercised exclusive rights, and low to mid-single digit of royalties as a percentage of net sales of targeting moieties generated from the Company’s license to use Regeneron’s proprietary mice. Royalties are payable until the longer of the expiration or invalidity of the licensed patent rights or twelve (12) years from first commercial sale.

Other Terms. The Regeneron Agreement contains customary representations, warranties and covenants by the Company and Regeneron and includes (i) an obligation of the Company to use commercially reasonable efforts to develop and commercialize at least one product based on a collaboration ICP that is not an optioned collaboration ICP for each collaboration target and (ii) an obligation of Regeneron to use commercially reasonable efforts to develop and commercialize at least one product based on an optioned collaboration ICP for each collaboration target. The Company and Regeneron are required to indemnify the other party against all losses and expenses related to breaches of its representations, warranties and covenants under the Regeneron Agreement.

Term and Termination. The term of the Regeneron Agreement expires, on a product-by-product basis, on the expiration of the obligation to pay royalties for such product. The Regeneron Agreement is subject to early termination by either party upon uncured material breach by the other party. The licenses to develop and commercialize an ICP to a target that one party has exclusively licensed may be terminated by such party for convenience.

Equity Investments. In connection with its collaboration, Regeneron and the Company entered into a side letter pursuant to which, among other matters, Regeneron was granted certain stockholder rights and investment rights in connection with the Company’s next equity financing that met certain criteria and in connection with an initial public offering by the Company. Regeneron exercised its investment right and purchased approximately $10.0 million of the Company’s Series B redeemable convertible preferred stock in a private placement transaction in July 2019. The remaining obligations under the side letter agreement terminated immediately prior to the Effective Time of the Merger.

Revenue Recognition

The Company identified the following material promises under the Regeneron Agreement: (1) a research license, (2) a collaboration invention license, (3) a trademark license, (4) research and development services during the research term, (5) manufacturing services to manufacture collaboration ICPs for the research programs, (6) participation in the joint research committee, and (7) information sharing during the research term. The Company considered that the licenses granted under the Regeneron Agreement are not capable of being distinct and are not distinct from the research and development and manufacturing services within the context of the Regeneron Agreement, because 1) such licenses are for the research and development effort during the research term, unless Regeneron exercises its option under the Regeneron Agreement, 2) the research and development services significantly increase the utility of such licenses, and 3) research and development services require collaboration ICPs being manufactured. Specifically, the Company’s granted licenses can only provide benefit to Regeneron in combination with the Company’s research and development and manufacturing services to discover the collaboration ICPs. Similarly, the participation in the joint research committee and information sharing are not capable of being distinct and are not distinct from the research and development and manufacturing services within the context of the agreement, because the participation in the joint research committee is for monitoring and governing of the research and development efforts and the information sharing is for sharing results of such research and development efforts. Therefore, all of the promises above are combined into a single performance obligation.

The Company also evaluated whether the option provided to Regeneron represents a material right that would require separate deferral and recognition. The option exercise will provide Regeneron with a development and commercial license to develop and commercialize the optioned collaboration ICPs. The Company concluded that the $25.0 million upfront payment to the Company was not negotiated to provide incremental discount for the future option fees payable upon Regeneron’s exercise of the option.

Regeneron could decide not to exercise the option at its own discretion. The exercise of the option by Regeneron is not certain and is dependent on many factors, such as progress made on the specific option-eligible collaboration ICP, Regeneron’s overall assessment of commercial feasibility of the further research, development and commercialization of the Option products, availability and cost of alternative programs and products. The option provides Regeneron with a license for intellectual property that will be improved from the inception of the Regeneron Agreement. In addition, the option fee is significant compared to the sum total of the upfront payment and research funding fees in the original Regeneron Agreement. Therefore, the Company determined that the option provided to Regeneron does not represent a material right and that any potential exercise of the option should be accounted as a separate contract. Hence, upon the option exercise by Regeneron the option fee would be allocated to the development and commercial license which would be the only performance obligation in that separate contract and recognized as revenue when control of the license rights is transferred to Regeneron.

For revenue recognition purposes, the Company determined that the duration of the contract is the same as the research term of five years beginning on the execution of the Regeneron Agreement on July 29, 2016. The contract duration is defined as the period during which parties to the contract have present and enforceable rights and obligations. The Company determined that Regeneron faces significant in-substance penalties were it to terminate the Regeneron Agreement prior to the end of the research term.

At contract inception, the Company determined a transaction price of the Regeneron Agreement consisting of the $25.0 million upfront payment and the aggregate research funding fees payable over the research term. In order to determine the transaction price, the Company evaluated all the payments to be received during the duration of the contract. Per the terms of the original Regeneron Agreement prior to the amendment effective from July 2019, the research funding fees were payable merely due to the passage of time and therefore did not represent a variable consideration. After the amendment became effective in July 2019, certain of these fees became contingent upon meeting certain development and regulatory milestones. Therefore, the Company concluded that after the amendment such potential payments became variable consideration. The receipt of the variable consideration was subject to substantial uncertainty and was therefore excluded from the transaction price upon the effective date of the amendment. As a result, during the three months ended September 30, 2019, the Company recorded $6.6 million as a reduction to cumulative revenue recognized prior to the amendment effective date. The Company will re-evaluate the transaction price if there is a significant change in facts and circumstances at least at the end of each reporting period. The Company increased the transaction price by $10.0 million in June 2020 when it achieved the milestone for the selection of a clinical candidate to the second collaboration target under the Regeneron Agreement, resulting in the recognition of an additional $5.0 million in revenue during the three months ended June 30, 2020.

The Company also considered the existence of any significant financing component within the Regeneron Agreement given its upfront payment structure. Based upon this assessment, the Company concluded that the up-front payment was provided for valid business reasons and not for the purpose of providing financing. The reason for the initial advance payment at the beginning of the contract is not to provide financing to the Company, but to ensure Regeneron’s commitment to the contract and to provide assurance that the customer will perform its obligations under the contract. Accordingly, the Company has concluded that the upfront payment structure of the Regeneron Agreement does not result in the existence of a significant financing component.

The royalty payments will be recognized when the related sales occur as they were determined to relate predominantly to the intellectual property licenses granted to Regeneron and therefore have also been excluded from the transaction price.

The Company has determined that the combined performance obligation is satisfied over time. ASC 606 requires the Company to select a single revenue recognition method for the performance obligation that depicts the Company’s performance in transferring control of the services. Accordingly, the Company utilizes a cost-based input method to measure proportional performance and to calculate the corresponding amount of revenue to recognize. The Company believes this is the best measure of progress because it reflects how the Company transfers its performance obligation to Regeneron. In applying the cost-based input method of revenue recognition, the Company uses actual costs incurred relative to budgeted costs to fulfill the combined performance obligation. These costs consist primarily of internal full-time equivalent effort and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligations over the research term of five years. A cost-based input method of revenue recognition requires management to make estimates of costs to complete the Company’s performance obligations. In making such estimates, significant judgment is required to evaluate assumptions related to cost estimates. The cumulative effect of revisions to estimated costs to complete the Company’s performance obligations will be recorded in the period in which changes are identified and amounts can be reasonably estimated. A significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods.

The following table presents changes in the Company’s contract liabilities (in thousands):

Year ended December 31, 2020	Balance at beginning of period		Additions		Additions (Deductions) ⁽¹⁾			Balance at end of period
Contract asset	$	—	$	10,000	$	(10,000	)	$	—
Contract liability	$	21,883	$	10,000	$	(17,903	)	$	13,980

Year ended December 31, 2019	Balance at beginning of period		Additions		Additions (Deductions) ⁽¹⁾			Balance at end of period
Contract liability	$	22,878	$	—	$	(995	)	$	21,883

(1)	Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

Contract assets are reflected as accounts receivable—related party on the consolidated balance sheet. The Company achieved the milestone for the selection of a clinical candidate to the second collaboration target under the Regeneron Agreement in June 2020 and was entitled to receive a payment of $10.0 million from Regeneron. The Company received the payment from Regeneron in July 2020.

Contract liabilities related to the Regeneron Agreement of $14.0 million and $21.9 million as of December 31, 2020 and 2019, respectively, which was comprised of the $25.0 million upfront payment and additional $5.0 million research funding fees in each of 2017 and 2018, and $10.0 million for achievement of the milestone for the selection of a clinical candidate to the second collaboration target in June 2020, less $31.0 million and $13.1 million of license and collaboration revenue recognized from the inception of the Regeneron Agreement as of December 31, 2020 and 2019, respectively, will be recognized as the combined performance obligation is satisfied.

During the years ended December 31, 2020, 2019 and 2018, the Company recognized $17.9 million, $1.0 million and $8.2 million of license and collaboration revenue, respectively, from amounts included in the contract liability balances at the beginning of the period. There were no costs to obtain or fulfill the contract that meet the criteria to be capitalized.

License Funding and Other Agreements Related to the CVR

12 Months Ended

Dec. 31, 2020

License Funding And Other Agreements [Abstract]

License, Funding and Other Agreements Related to the CVR

11. License, Funding and Other Agreements Related to the CVR

Contingent Value Rights Agreement

As discussed in Note 3, in connection with the Merger, the Company entered into the CVR Agreement with Computershare Inc. and Computershare Trust Company, N.A. as joint rights agent. The CVR holders are entitled to receive net proceeds from the commercialization, if any, received from a third-party commercial partner of RTB101 for a COVID-19 related indication. The total fees and expenses of the Company’s clinical trials for a COVID-19 related indication of RTB101 is limited to $3.0 million under the CVR Agreement. Through October 31, 2020, the Company’s total accumulated spend was $1.1 million of expenses. In November 2020, management terminated the nursing home study due to poor enrollment and as a consequence lowered the probability of finding a partner due to the delay in time to commercialization of RTB101. As a result, the fair value of the CVR liability was decreased by $1.9 million to $1.0 million.

Novartis License Agreement

On March 23, 2017, resTORbio entered into an exclusive license agreement with Novartis International Pharmaceutical Ltd. (Novartis). Under the agreement, Novartis granted resTORbio an exclusive, field-restricted, worldwide license, to certain intellectual property rights owned or controlled by Novartis, to develop, commercialize and sell one or more therapeutic products comprising RTB101 or RTB101 in combination with everolimus in a fixed dose combination. The exclusive field under the license agreement is for the treatment, prevention and diagnosis of disease and other conditions in all indications in humans and animals.

The agreement may be terminated by either party upon a material breach of obligation by the other party that is not cured with 60 days after written notice. resTORbio may terminate the agreement in its entirety or on a product-by-product or country-by-country basis with or without cause with 60 days’ prior written notice.

As consideration for the license, resTORbio is required to pay up to an aggregate of $4.3 million upon the satisfaction of clinical milestones, up to an aggregate of $24 million upon the satisfaction of regulatory milestones for the first indication approved, and up to an aggregate of $18 million upon the satisfaction of regulatory milestones for the second indication approved. In addition, resTORbio is required to pay up to an aggregate of $125 million upon the satisfaction of commercial milestones, based on the amount of annual net sales. resTORbio is also required to pay tiered royalties ranging from a mid-single digit percentage to a low-teen digit percentage on annual net sales of products. These royalty obligations last on a product-by-product and country-by-country basis until the latest of (i) the expiration of the last valid claim of a Novartis patent covering a subject product, (ii) the expiration of any regulatory exclusivity for the subject product in a country, or (iii) the 10^th anniversary of the first commercial sale in the country, and are subject to a reduction after the expiration of the last valid claim of a Novartis patent or the introduction of a generic equivalent of a product in a country. As of December 31, 2020, none of the remaining clinical milestones, regulatory milestones, sales milestones, or royalties had been reached or were probable of achievement.

National Institute of Health

In May 2019, resTORbio was awarded a 5-year grant for up to $1.5 million from the National Institutes of Health (the NIH) to study RTB101 and the regulation of antiviral immunity in the elderly. resTORbio is entitled to use the award solely to conduct the research and is solely responsible for commencing and conducting the research and will furnish periodic progress

updates to the NIH throughout the term of the award. After completing the research, resTORbio must provide the NIH with a formal report describing the work performed and the results of the research.

For funds received under the NIH funding agreement, resTORbio recognizes a reduction in research and development expenses in an amount equal to the qualifying expenses incurred in each period up to the amount funded by the NIH. Qualifying expenses incurred by resTORbio in advance of funding by the NIH are recorded in the consolidated balance sheets as other current assets. For the year ended December 31, 2020, $0.7 million qualifying expenses have been incurred and $0.6 million have been funded by the NIH.

Commitments and Contingences

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingences

12. Commitments and Contingencies

Operating Leases

On September 30, 2015, the Company entered into a lease agreement (the Menlo Park Lease) to lease approximately 17,352 square feet of office and laboratory space located in Menlo Park, CA. The total base lease payments over the life of the lease are $3.4 million, offset by $0.8 million in tenant improvement allowances. The lease expires on March 31, 2022. The landlord maintains responsibility for maintenance and risk of loss throughout the term of the lease agreement. The lease is recorded as an operating lease.

On September 30, 2019 and October 19, 2020, the Company entered into amendments to the Menlo Park lease agreement for the office and laboratory space in Menlo Park to lease from the same landlord additional nearby buildings with approximately 7,973 and 4,862 square feet of office and laboratory space, respectively. The leases commenced on October 1, 2019 and October 1, 2020, respectively, and both amendment leases expire on March 31, 2022. The total base lease payments over the life of the lease amendments are $0.4 million and $0.3 million, respectively.

On October 28, 2018, the Company entered into a new lease agreement to lease approximately 50,305 square feet of office and laboratory space located in Redwood City, CA. The total base lease payments over the life of the lease are $29.5 million, offset by $3.0 million in tenant improvement allowances. On December 30, 2020, the Company entered an amendment to the Redwood City lease to change the manner in which tenant improvements will be constructed at the premises. The lease has not commenced as the office and laboratory space is not available for use by the Company. The lease expires on February 28, 2030.

In April 2019, the Company amended its multi-year lease agreement to relocate its office space in Boston, MA under an operating lease agreement. The amended lease term is for a period of seven years from the date of relocation on August 1, 2019. The total base lease payments over the remaining lease term are $3.5 million.

The Company recognized rent expense of $0.9 million, $0.7 million and $0.5 million for the years ended December 31, 2020, 2019 and 2018, respectively.

As a result of adopting ASC 842 in 2020, the Company recorded lease right-of-use, (ROU) asset of $1.4 million and lease liabilities of $1.8 million as of January 1, 2020, primarily related to office leases based on the present value of future lease payments. There was no impact to retained earnings upon the adoption of ASC 842. As of December 31, 2020, the Company had no finance lease.

The adoption of ASC 842 resulted in the recognition of an operating lease ROU asset and corresponding liability in 2020 based on the present value of remaining lease payments discounted at the Company’s estimated IBR. The IBR and the remaining lease terms of our facilities and their weighted average IBR and remaining terms are as follows as of December 31, 2020:

Lease Locations	IBR	Remaining Terms (in years)
Redwood City, CA	6.90%	9.2
Boston, MA	9.30%	5.6
Menlo Park, CA	6.80%	1.3
Weighted Average	7.20%	8.4

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2020:

	For the Year Ended December 31, 2020
Lease Cost	(in thousands)
Operating lease cost	$	894
Short-term lease cost		56
Variable lease cost		—
Total lease cost	$	950
Other Information
Operating cash flows used for lease payments	$	3,168
Operating cash flows used for lease liabilities	$	859
Operating lease right of use asset obtained in exchange of operating lease liability	$	22,367

As of December 31, 2020, operating lease assets were $23.1 million and operating lease liabilities were $21.6 million. The Company has no finance leases. The maturities of the operating lease liabilities as of December 31, 2020 were as follows (in thousands):

2021	$	2,505
2022		2,818
2023		3,429
2024		3,525
2025		3,624
2026 and thereafter		13,747
Total undiscounted lease payments		29,648
Less: imputed interest		8,009
Total operating lease liability		21,639
Less: current portion		1,215
Operating lease liability, net of current maturities	$	20,424

The future minimum lease payments under all non-cancelable operating lease obligations as of December 31, 2019 under ASC 840 were as follows (in thousands):

2020	$	2,721
2021		3,518
2022		2,942
2023		2,798
2024		2,882
2025 and thereafter		16,328
Total	$	31,189

In conjunction with the Menlo Park lease agreement, the Company issued a cash-collateralized letter of credit in lieu of security deposit of $0.2 million. In addition, the Company issued a cash-collateralized letter of credit for $4.1 million in 2018 for the new office lease in Redwood City, CA. The Company also maintains a letter of credit of $0.2 million for the benefit of the landlord in connection with the Company’s office lease in Boston, MA. All cash amounts are recorded as restricted cash on the consolidated balance sheet as of December 31, 2020 and 2019.

Indemnification Agreements

In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never

incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ liability insurance.

Legal Proceedings

In connection with the Merger, seven lawsuits were filed against the Company, its directors, Former Adicet, and/or Merger Sub. which were either dismissed or settled for of $0.2 million in the fourth quarter of 2020.

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

13. Redeemable Convertible Preferred Stock

As of December 31, 2019, redeemable convertible preferred stock consists of the following (in thousands, except per share and share amounts):

	Shares Authorized		Original Issue Price		Shares Issued and Outstanding		Carrying Value		Liquidation Preference		Common Stock Issued Upon Conversion ⁽¹⁾
Series A		37,104,185	$	1.20		37,104,185	$	35,960	$	44,525		4,600,920
Series A-1		629,633		1.20		629,633		447		756		78,074
Series A-2		2,428,688		1.20		2,428,688		1,749		2,914		301,157
Series B		59,200,938		1.40		57,004,415		75,927		80,000		7,068,520
		99,363,444				97,166,921	$	114,083	$	128,195		12,048,671

⁽¹⁾ Adjusted to reflect the Exchange Ratio.

Following the closing of the Merger, all outstanding shares of the redeemable convertible preferred stock converted into 12,048,671 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of redeemable convertible preferred stock outstanding as of December 31, 2020.

Redeemable Convertible Preferred Stock Tranche Liability

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock Tranche Liability

14. Redeemable Convertible Preferred Stock Tranche Liability

The Milestone Closing liability was settled in November 2018 upon the Milestone Closing and the related TRDF liability was settled in March 2019. In July 2019, as part of the Series B redeemable convertible preferred stock purchase agreement the Additional Closing liability and the related TRDF liability were terminated. The Company recorded $2.0 million gain from the remeasurement of the redeemable convertible preferred stock tranche liability in other income (expense), net in its consolidated statements of operations and comprehensive loss during the years ended December 31, 2019.

The Additional Closing liability was valued using the following assumptions under the option-pricing method:

Fair Value of Series A

Preferred Stock

Term

Interest rate

Volatility

December 31, 2018

10.48

1.88 years

2.50

69.80

July 25, 2019

7.18

1.31 years

1.95

69.10

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants

12 Months Ended

Dec. 31, 2020

Liabilities And Stockholders Equity [Abstract]

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants

15. Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants

In connection with Series B redeemable convertible preferred stock financing transactions, the Company issued to its financial advisor warrants to purchase 1,781,387 shares of our Series B redeemable convertible preferred stock at an exercise price of at $1.4034 per share. These warrants will terminate at the earlier of seven-year anniversary from the issuance date and a liquidation of the company. Additionally, in connection with the entrance into the Loan Agreement, the Company issued

Pacific Western Bank a warrant to purchase shares of its Series B redeemable convertible preferred stock (see Note 9). These warrants together are referred to as Series B Warrants.

Prior to the Merger, the Company classified the Series B Warrants as a liability on its consolidated balance sheet because the warrants are freestanding financial instruments that may have required the Company to transfer assets upon exercise. The liability associated with each of these warrants was initially recorded at fair value upon the issuance date of each warrant and was subsequently remeasured to fair value as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss. Upon the closing of the Merger (see Note 3), pursuant to the Merger Agreement, all of the Series B Warrants converted to warrants for the purchase of the shares of the Company’s common stock. The Company assessed the features of the warrants and determined that they qualify for classification as permanent equity upon the closing of the Merger. Accordingly, the Company remeasured the warrants to fair value upon the closing of the Merger, which was $2.9 million on September 15, 2020. Upon the closing of the Merger, the warrant liability was reclassified to additional paid-in capital. The fair value of the warrants to purchase shares of the Company’s common stock was equal to the fair value of the Series B Warrants on the Merger date. Accordingly, no incremental expense was recognized at the Merger date.

The Series B Warrants had a fair value of $1.9 million as of December 31, 2019. The change in fair value of $0.8 and $0.2 million during the years ended December 31, 2020 and 2019, respectively, was recorded as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss.

The redeemable convertible preferred stock warrant liability was valued using the following assumptions under the Black-Scholes option-pricing model:

	September 14, 2020 (Conversion Date)			April 28, 2020 (Issuance Date of PacWest Warrants)			December 31, 2019
Stock price	$	16.59		$	11.61		$	11.32
Expected term (years)	5.86 - 6.62				7.00		6.57 - 6.74
Expected volatility	81.1% - 82.1%				91.17	%	82.1% - 93.3%
Risk-free interest rate	0.35% - 0.42%				0.52	%	1.53% - 1.93%
Dividend yield		0	%		0	%		0	%

The following table provides a roll forward of outstanding warrants:

	Number of Warrants			Weighted Average Exercise Price		Weighted Average Contractual Term (Years)
Outstanding and exercisable warrants to purchase preferred shares as of December 31, 2019		1,781,387		$	1.4034
Issued		128,260
Impact of converting to warrants for the purchase of common stock and adjusted for the Exchange Ratio and Reverse Stock Split		(1,683,456	)
Outstanding and exercisable warrants to purchase common stock as of December 31, 2020		226,191		$	11.3177		5.66

As of December 31, 2020, the Company’s outstanding warrants to purchase shares of common stock, including the New PacWest Warrant, consisted of the following:

Issuance Date	Number of Shares of Common Stock Issuable		Exercise Price		Classification	Expiration Date
September 15, 2020		101,610	$	11.3177	Equity	July 25, 2026
September 15, 2020		30,924	$	11.3177	Equity	August 21, 2026
September 15, 2020		77,312	$	11.3177	Equity	September 19, 2026
September 15, 2020		11,044	$	11.3177	Equity	September 26, 2026
September 15, 2020		5,301	$	11.3177	Equity	April 28, 2027
		226,191

As of December 31, 2019, the Company’s outstanding warrants to purchase shares of redeemable convertible preferred stock (which converted into warrants to purchase common stock upon close of the Merger) consisted of the following (not adjusted for the Exchange Ratio):

Warrant Name

Issuance Date

Number of

Shares of

Preferred

Stock Issuable

Exercise

Price

Exercisable

for

Classification

Expiration Date

Series B warrants

July 25, 2019

819,438

1.4034

Series B

Liability

July 25, 2026

Series B warrants

August 21, 2019

249,394

1.4034

Series B

Liability

August 21, 2026

Series B warrants

September 19, 2019

623,486

1.4034

Series B

Liability

September 19, 2026

Series B warrants

September 26, 2019

89,069

1.4034

Series B

Liability

September 26, 2026

1,781,387

Common Stock

12 Months Ended

Dec. 31, 2020

Stockholders Equity Note [Abstract]

Common Stock

16. Common Stock

The Company’s Certificate of Incorporation, as amended, authorized the Company to issue 150,000,000 shares of $0.0001 par value common stock as of December 31, 2020.

Common stockholders are entitled to dividends if and when declared by the Board of Directors subject to the prior rights of the preferred stockholders. As of December 31, 2020 and 2019, no dividends on common stock had been declared by the Board of Directors.

The Company has the following shares of common stock reserved for future issuance:

	December 31
	2020		2019
Conversion of redeemable convertible preferred stock (as converted to common stock)		—		12,048,671
Conversion of additional authorized and unissued redeemable convertible preferred stock		—		51,506
Stock options available for future grant		1,739,621		653,136
Stock options issued and outstanding		3,706,945		1,860,646
Redeemable convertible preferred stock warrants issued and outstanding		—		220,890
Common stock warrants issued and outstanding		226,191		—
Total common stock reserved		5,672,757		14,834,849

At-the-Market (ATM) Offering

12 Months Ended

Dec. 31, 2020

Stockholders Equity Note [Abstract]

At-the-Market (ATM) Offering

17. At-the-Market (ATM) Offering

On December 1, 2020, the Company entered into a Sales Agreement (the 2020 Sales Agreement) with Evercore Group L.L.C. and H.C. Wainwright & Co., LLC (collectively, the Agents), pursuant to which the Company may sell, from time to time, at its option, up to an aggregate of $50.0 million of shares of the Company’s common stock, through the Agents, as its sales agents. No sales of Shares have been made under the 2020 Sales Agreement. The ATM offering was terminated in February 2021.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

18. Stock-Based Compensation

Summary of Plans

Upon completion of the Merger with resTORbio on September 15, 2020, Former Adicet’s 2014 Share Option Plan (the 2014 Plan), Former Adicet’s 2015 Stock Incentive Plan (the 2015 Plan), resTORbio’s 2017 Stock Incentive Plan (the 2017 Plan), resTORbio’s 2018 Stock Incentive Plan (the 2018 Plan) and resTORbio’s 2018 Employee Stock Purchase Plan (the 2018 ESPP, and, collectively with the 2014 Plan, the 2015 Plan, the 2017 Plan and the 2018 Plan, the Plans) were assumed by the Company. The Plans are administered by the Board of Directors or, at the discretion of the Board of Directors, by a committee of the Board of Directors. No further shares will be issued from the 2014 Plan or 2017 Plan. The exercise prices, vesting and other restrictions are determined at the discretion of the Board of Directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of the stock option may not be greater than ten years. Incentive stock options granted to employees and restricted stock awards granted to employees, officers, members of the Board of Directors, advisors, and consultants of the Company typically vest over four years. Non-statutory options granted to employees, officers, members of the Board of Directors, advisors, and consultants of the Company typically vest over three or four years. Shares that are expired, terminated, surrendered or canceled under the Plans without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

The 2017 Plan and 2018 Plan

In 2017, resTORbio adopted the 2017 Plan. In connection with resTORbio’s initial public offering completed in January 2018, the resTORbio Board adopted and resTORbio’s stockholders approved the 2018 Plan. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of resTORbio’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board. On January 1, 2021, the number of shares reserved and available for issuance under the 2018 Plan automatically increased by 787,089 shares of Common Stock equal to 4% of the number of shares of Common Stock issued and outstanding on December 31, 2020.

Since the date of effectiveness of the 2018 Plan, resTORbio has not and the Company will not grant any further awards under the 2017 Plan. However, any shares of common stock subject to awards under the 2017 Plan that expire, terminate, or otherwise are surrendered, canceled, forfeited or repurchased without having been fully exercised or resulting in any common stock being issued will become available for issuance under the 2018 Plan.

As of December 31, 2020, the number of shares of common stock available for grant under the 2017 and 2018 Plan is 1,456,492. As of December 31, 2020, an aggregate of 1,317,892 shares of common stock were issuable upon the exercise of outstanding stock options under the 2017 Plan and 2018 Plans at a weighted average exercise price of $15.62 per share.

The 2014 Plan and 2015 Plan

At the Effective Time of the Merger, each outstanding and unexercised option to purchase Former Adicet’s common stock, whether vested or unvested, pursuant to the 2015 Plan and a subset of options issued pursuant to the 2014 Plan were converted into options to purchase a number of shares of the Company’s common stock based on the Exchange Ratio.

As of December 31, 2020, the number of shares of common stock available for grant under the 2014 and 2015 Plan is 283,129. As of December 31, 2020, an aggregate of 1,957,536 shares of common stock were issuable upon the exercise of outstanding stock options under the 2015 plan at a weighted average exercise price of $7.43 per share and an aggregate of 69,014 shares of common stock were issuable upon the exercise of outstanding stock options under the 2014 Plan at a weighted average exercise price of $1.27 per share.

Since the date of effectiveness of the Merger, the Company has not and will not grant any further awards under the 2014 Plan.

2018 Employee Stock Purchase Plan

The resTORbio Board adopted and resTORbio’s stockholders approved the 2018 ESPP, which became effective on the date immediately preceding the date on which resTORbio’s registration statement on Form S-1 became effective. As a result of the Merger, the 2018 ESPP enables eligible employees to purchase shares of the Company’s common stock at a discount. Prior to the Merger, the number of shares of common stock originally reserved for issuance under the 2018 ESPP were 39,290 shares. The 2018 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and increasing each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of

the Company’s common stock on the immediately preceding December 31; (ii) 77,703 shares or (iii) such number of shares as determined by the ESPP administrator. On January 1, 2019, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 39,290 to 79,369 shares. On January 1, 2020, as a result of the foregoing evergreen provision, the number of shares of common stock available for issuance under the 2018 ESPP automatically increased from 79,369 to 131,432 shares. No shares have been issued under the 2018 ESPP during the year ended December 31, 2020.

Inducement Grants

As of December 31, 2020, an aggregate of 362,503 shares were issuable upon the exercise of inducement grants of stock options approved by the Company in accordance with Nasdaq listing Rule 5635(c)(4) at a weighted average exercise price of $14.33 per share.

Former CEO’s Stock Option Modification

In connection with the Merger, the stock options granted to Dr. Singhal were modified (see Note 3), which resulted in acceleration and recognition of the stock compensation expense of $0.6 million during the quarter ended September 30, 2020. The modification also resulted in incremental stock compensation expense of $0.1 million that will be recognized through May 7, 2021 as the Company determined that Dr. Singhal will be providing substantial services under the ICSA through that date. The ICSA was terminated in February 2021.

Former CEO’s Performance Option

On July 14, 2020, the Company’s Board of Directors confirmed that the conditions for Dr. Singhal’s Second Target Milestone Option (as defined in Dr. Singhal’s amendment to his employment agreement with the Company, dated October 15, 2019) had been fulfilled as the Company achieved the milestone for the selection of a clinical candidate to the second collaboration target under the Regeneron Agreement. According to Dr. Singhal’s employment agreement, Dr. Singhal would be granted an option to purchase 22,574 shares of the Company’s common stock related to the achievement of this milestone option. However, as this milestone option was earned during his transition from Chief Executive Officer to an advisory role, only 75% of this option vested. As a result, following the Merger, on September 17, 2020, the Company’s Board of Directors granted this option to Dr. Singhal to purchase 16,931 shares of the Company’s common stock at an exercise price of $16.11 per share, (i) one-third of the shares vesting on the first anniversary of May 6, 2019, (ii) one-third of the shares vesting in 12 equal monthly installments following such first anniversary, and (iii) one-third of the shares vesting in accordance with the terms of his Transition Agreement which consisted of 12 months’ of accelerated vesting of his unvested options to purchase the Company’s common stock upon completion of the Merger. The Company recognized $0.1 million in stock compensation expense associated with this reward during the year ended December 31, 2020.

Options

A summary of stock option activity is set forth below (in thousands, except share and per share data):

				Outstanding Awards
	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options			Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, January 1, 2018		38,055			963,435		$	2.02			9.27	$	4,977
Options authorized		837,000
Options granted		(210,452	)		210,452		$	2.26
Options exercised		—			(123,949	)	$	1.92
Options forfeited or cancelled		153,399			(153,399	)	$	2.25
Outstanding, December 31, 2018		818,002			896,539		$	2.04			8.57	$	2,436
Options authorized		814,184
Options granted		(1,124,430	)		1,124,430		$	5.39
Options exercised		—			(14,791	)	$	(2.12	)
Options forfeited or cancelled		145,380			(145,532	)	$	2.17
Outstanding, December 31, 2019		653,136			1,860,646		$	4.05			8.53	$	5,812
Assumed as part of the Merger		2,707,144			81,370		$	8.39
Options granted		(1,914,142	)		2,276,645		$	15.14
Options exercised					(210,752	)	$	2.18
Options forfeited or cancelled		293,483			(300,964	)	$	6.04
Outstanding, December 31, 2020		1,739,621			3,706,945		$	10.90			7.98	$	15,126
Shares exercisable December 31, 2020					1,219,904		$	4.64			5.11	$	11,563
Vested and expected to vest, December 31, 2020					3,706,945		$	10.90			7.98	$	15,126

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the fair value of the Company’s common stock for stock options that were in-the-money at December 31, 2020, 2019 and 2018.

The aggregate intrinsic value of stock options exercised during the years ended on December 31, 2020, 2019 and 2018 was $2.5 million, $0.1 million and $0.4 million, respectively.

The total fair value of options that vested during the years ended December 31, 2020, 2019 and 2018 was $2.4 million, $0.9 million and $1.8 million, respectively. The options granted during the years ended December 31, 2020, 2019 and 2018 had a weighted-average per share grant-date fair value of $9.96 per share, $2.98 per share and $3.95 per share, respectively. As of December 31, 2020, the total unrecognized stock-based compensation expense related to unvested stock options was $21.6 million, which is expected to be recognized over the remaining weighted-average vesting period of 3.6 years.

Restricted Stock

Activity with respect to restricted stock was as follows:

	Number of Shares Underlying Outstanding Restricted Stock			Weighted Average Grant Date Fair Value
Unvested, January 1, 2018		165,699		$	4.19
Vested		(134,516	)	$	4.19
Unvested, December 31, 2018		31,183		$	4.19
Vested		(31,183	)	$	4.19
Unvested, December 31, 2019		—		$	—

As of December 31, 2020, there was no unrecognized compensation cost related to restricted stock.

The fair value of restricted stock vested during the years ended December 31, 2020, 2019 and 2018 was $0, $0.1 million and $0.6 million, respectively.

Stock-Based Compensation Associated with Awards to Employees and Non-Employees

Total stock-based compensation expense recognized was as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	1,674	$	274	$	285
General and administrative		3,589		901		2,194
Total stock-based compensation	$	5,263	$	1,175	$	2,479

The Company estimated the fair value of stock options using the Black Scholes option-pricing model. The fair value of stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2020	2019	2018
Expected volatility	72.6%-96.3%	71.5%-86.5%	73.3%-74%
Risk-free interest rate	0.1%-1.7%	1.6%-2.5%	2.7%-2.8%
Dividend yield	0%	0%	0%
Expected term	1.00-6.08 years	5.15-6.08 years	6.02-6.08 years

The assumptions are as follows:

•

Expected volatility. The expected volatility was determined by examining the historical volatilities for comparable publicly traded companies within the biotechnology and pharmaceutical industry using an average of historical volatilities of the Company’s industry peers.

•

Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury yield with a maturity equal to the expected term of the option in effect at the time of grant.

•

Dividend yield. The expected dividend is assumed to be zero as dividends have never been paid and there are no current plans to pay dividends on common stock.

•

Expected term. The expected term represents the period that the stock-based awards are expected to be outstanding. The expected term is calculated using the simplified method which is used when there is insufficient historical data about exercise patterns and post-vesting employment termination behavior. The simplified method is based on the vesting period and the contractual term for each grant, or for each vesting-tranche for awards with graded vesting. The mid-point between the vesting date and the maximum contractual expiration date is used as the expected term under

this method. For awards with multiple vesting-tranches, the times from grant until the mid-points for each of the tranches may be averaged to provide an overall expected term.

In addition to the assumptions used in the Black-Scholes option-pricing model, the Company recognizes the actual forfeitures by reducing the employee stock-based compensation expense in the same period the forfeiture occurs.

The Company will continue to use judgment in evaluating the expected volatility, risk-free interest rates, dividend yield and expected term, utilized for stock-based compensation on a prospective basis.

Net Loss Per Share

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss per Share

19. Net Loss Per Share

The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders, which excludes unvested restricted shares and shares which are legally outstanding, but subject to repurchase by the Company (in thousands, except share and per share data):

	Year Ended December 31,
	2020			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(36,678	)	$	(28,138	)	$	(9,299	)
Denominator:
Weighted-average shares outstanding		7,319,977			2,148,317			2,049,680
Less: weighted-average unvested restricted shares and shares subject to repurchase		—			(9,344	)		(102,704	)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted		7,319,977			2,138,973			1,946,976
Net loss per share attributable to common stockholders, basic and diluted	$	(5.01	)	$	(13.15	)	$	(4.78	)

The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive:

	December 31,
	2020		2019		2018
Redeemable convertible preferred stock (as converted to common stock)		—		12,048,671		4,971,762
Options to purchase common stock		3,706,945		1,860,646		896,539
Redeemable convertible preferred stock warrants		—		220,890		—
Common stock warrants		226,191		—		—
Unvested early exercised common stock options		—		—		27,709
Unvested restricted stock awards		—		—		31,183
Redeemable convertible preferred stock tranche liability and TRDF obligation		—		—		743,317
Total		3,933,136		14,130,207		6,670,510

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

20. Income Taxes

The components of the provision for (benefit from) income taxes are as follows (in thousands):

	Year Ended December 31,
	2020			2019		2018
Current:
Federal	$	(2,678	)	$	—	$	—
State		105			1		(589	)
Foreign		—			18		—
Total current		(2,573	)		19		(589	)
Deferred:
Federal		(242	)		—		—
State		—			—		—
Foreign		—			—		—
Total deferred		(242	)		—		—
Provision for (benefit from) income taxes	$	(2,815	)	$	19	$	(589	)

On March 27, 2020, the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”) was enacted in response to the COVID-19 Pandemic. The tax relief measures under the CARES Act for businesses include a five-year net operating loss carryback, suspension of annual deduction limitation of 80% of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief, and a technical correction to allow accelerated deductions for qualified improvement property.

The Company recognized income tax benefit of $2.8 million for the year ended December 31, 2020 due to the net operating loss carryback under the CARES Act which generated a refund of income taxes paid in 2017 and revaluation of IPR&D at year-end. The state tax expense for the year ended December 31, 2020 is due to state minimum and franchise taxes, and true-up of state tax refund.

For the rate table below the (provision for) benefit from income taxes differ from the amount expected by applying the federal statutory rate to the loss before taxes as follows:

	Year Ended December 31,
	2020			2019			2018
Federal statutory income tax rate		21.0	%		21.0	%		21.0	%
Other permanent differences		(0.5	)%		(0.1	)%		(0.1	)%
State income taxes		6.1	%		5.1	%		3.8	%
Foreign rate differential		0.0	%		0.0	%		0.2	%
Foreign loss		0.0	%		(0.2	)%		(2.2	)%
Federal benefit from NOL carryback		6.7	%		0.0	%		0.0	%
Change in valuation allowance		(25.8	)%		(27.7	)%		(20.0	)%
Change in fair value of redeemable convertible preferred stock tranche liability and TRDF liability		(0.5	)%		1.7	%		8.7	%
Stock-based compensation		0.1	%		0.1	%		(6.0	)%
Benefit from (provision for) income taxes		7.1	%		(0.1	)%		5.4	%

The tax effects of temporary differences and carryforwards of the deferred tax assets are presented below (in thousands):

	December 31,
	2020			2019			2018
Deferred Tax Assets:
Net operating loss carryforwards	$	51,796		$	12,510		$	5,233
Operating lease right-of-use asset liability		5,686			—			—
Deferred revenue		2,857			5,719			5,125
Stock-based compensation		1,750			509			274
Intangible assets		1,195			609			804
Accruals and reserves		654			446			431
Research and development credit carryforwards		26			26			26
Gross deferred tax assets		63,964			19,819			11,893
Less: Valuation allowance		(57,715	)		(19,815	)		(11,739	)
Deferred tax assets, net of valuation allowance		6,249			4			154
Deferred tax liabilities:
Fixed assets		—			(4	)		(154	)
Basis Difference IPR&D		(313	)		—			—
Operating lease right-of-use asset		(6,061	)		—			—
Net deferred tax liability	$	(125	)	$	—		$	—

On September 15, 2020 Adicet Bio and resTORbio completed the Merger upon which Adicet Bio became the parent company of the consolidated group. The Merger did not create a step up in basis for tax basis of the asset as it was considered a tax-free merger. The above deferred tax table includes deferred related to resTORbio.

The Company has established a valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.

ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s recent history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely to be realized and, accordingly, has provided a valuation allowance.

The valuation allowance increased by $37.9 million during 2020 and $8.1 million during 2019.

As of December 31, 2020, the Company had net operating loss carryforwards of $211.4 million, $82.2 million and $16.7 million to reduce future taxable income, if any, for federal, state and foreign income tax purposes, respectively. Of the federal net operating loss carryforwards, $7.6 million will begin to expire in 2037 if not utilized, and $203.8 million can be carried forward indefinitely. The state carryforwards will begin to expire in 2035.

The Company also had California research and development credit carryforwards of less than $0.1 million as of December 31, 2020. The California research credit can be carried forward indefinitely.

Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to an annual limitation under Section 382 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and

any limitation is known, no liability related to uncertain tax positions is recorded in the consolidated financial statements. The Company does not expect its unrecognized tax benefit balance to change materially over the next 12 months.

The Company files income tax returns in the U.S. federal jurisdiction, California, Massachusetts, New York and Israel. The tax years 2015 to 2020 remains open to U.S. federal and state examination to the extent of the utilization of net operating loss and credit carryovers.

As of December 31, 2020, the Company had unrecognized tax benefits of $0.8 million related to the transfer of certain intellectual property from its Israeli subsidiary.

A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Balance at the beginning of the year	$	797	$	797	$	866
Adjustment based on tax positions related to prior years		—		—		(69	)
Balance at the end of the year	$	797	$	797	$	797

The Company recognizes interest expense and penalties related to the above unrecognized tax benefits within income tax expense (benefit). Management determined that no accrual for interest and penalties was required as of December 31, 2020.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Defined Contribution Plan

12 Months Ended

Dec. 31, 2020

Defined Contribution Plan [Abstract]

Defined Contribution Plan

21. Defined Contribution Plan

The Company maintains a defined contribution plan under Section 401(k) of the Internal Revenue Code covering substantially all full-time U.S. employees. Employee contributions are voluntary and are determined on an individual basis subject to the maximum allowable under federal tax regulations. The Company did not make contributions to the 401(k) plan during 2020.

Related Party Transactions

12 Months Ended

Dec. 31, 2020

Related Party Transactions

22. Related Party Transaction

As of December 31, 2020, Regeneron owned 883,568 shares of the Company’s common stock. As of December 31, 2019, Regeneron owned 7,125,552 shares (not adjusted for the Exchange Ratio) of the Company’s redeemable convertible preferred stock. Regeneron became a related party in July 2019 as a result of Series B redeemable convertible preferred stock financing. Upon closing the Merger 7,125,552 shares of the redeemable convertible preferred stock converted into 883,568 shares of the Company’s common stock. For the years ended December 31, 2020, 2019 and 2018, the Company recorded revenue of $17.9 million, $1.0 million and $8.2 million, respectively. As of December 31, 2020, the Company recorded no accounts receivable and has deferred revenue of $14.0 million related to the Regeneron Agreement (See Note 10).

Subsequent Events

12 Months Ended

Dec. 31, 2020

Subsequent Events [Abstract]

Subsequent Events

23. Subsequent Events

In February 2021, we completed an underwritten public offering of 10,575,513 shares of our common stock, including the exercise in full by the underwriters of their option to purchase up to an additional 1,344,743 shares of common stock at a public offering price of $13.00 per share. The aggregate gross proceeds from the offering, before deducting underwriting discounts and commissions and offering expenses were approximately $137.5 million.

In connection with the offering, we also entered into a stock purchase agreement with certain existing investors for $15.0 million of shares of our common stock at a price per share equal to the public offering price, with an initial closing for certain investors held simultaneously with the closing of the offering and a subsequent closing for certain additional investors.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

The consolidated financial statements and related disclosures have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP or GAAP).

Principles of Consolidation

Reverse Stock Split

Exchange Ratio

At the Effective Time, each outstanding share of Former Adicet capital stock was converted into the right to receive 0.1240 (the Exchange Ratio) shares of Company’s common stock, as set forth in the merger agreement. Accordingly, all shares and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect the Exchange Ratio.

Use of Estimates

Business Combination

Contingent Consideration Liability (CVR)

Goodwill

Intangible Assets

Segments

Concentration of Credit Risk

Risks and Uncertainties

Cash and Cash Equivalents

Marketable Securities

Marketable Debt Securities

Restricted Cash

Fair Value of Financial Instruments

Redeemable Convertible Preferred Stock

Redeemable Convertible Preferred Stock Tranche Liability

Redeemable Convertible Preferred Stock Warrants

Property and Equipment, Net

Impairment of Long-Lived Assets

Revenue Recognition

(i)

identify the contract(s) with a customer;

(ii)

identify the performance obligations in the contract;

(iii)

determine the transaction price;

(iv)

allocate the transaction price to the performance obligations in the contract; and

(v)

recognize revenue when (or as) the Company satisfies a performance obligation.

All of the Company’s revenues are derived through a license and collaboration agreement (see Note 10).

Research and Development Expenses

Accrued CRO, CMO, and Research and Development Expenses

Leases

balance sheets. There was no impact to retained earnings upon the adoption of ASC 842. As of December 31, 2020, the Company had no finance leases.

Fair Value of Common Stock

Stock-Based Compensation

Income Taxes

Comprehensive Income (Loss)

Net Loss per Share Attributable to Common Stockholders

Recent Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Accounting Pronouncements Not Yet Adopted

Business Combination (Tables)

12 Months Ended

Dec. 31, 2020

Business Combinations [Abstract]

Schedule of Summarizes the Purchase Price in the Merger

The following summarizes the purchase price in the Merger (in thousands, except share and per share amounts):

Fair value of common stock shares of the combined company

owned by resTORbio stockholders (1)

84,142

Fair value of contingent consideration liability with respect to CVR (2)

2,880

Purchase price

87,022

Schedule of Estimated Share Consideration of Combined Company

(1)	Represents the share consideration of the combined company that the resTORbio stockholders own as of the closing of the Merger calculated as follows:

Number of shares of the combined company owned by resTORbio stockholders (a)		5,207,695
Multiplied by the fair value per share of resTORbio common stock (b)	$	16.59
Acquisition date fair value of resTORbio common shares		86,396
Acceleration of 54,553 shares of restricted stock units upon merger (3)		626
Less: portion of the fair value to be distributed as CVR (c)		(2,880	)
Fair value of shares of the combined company owned by resTORbio stockholders	$	84,142

Schedule of Summarizes the Allocation of the Purchase Price to the Net Tangible and Intangible Assets Acquired

	As of September 15, 2020 (preliminary)			Measurement Period Adjustments			As of December 31, 2020 (as adjusted)
Net assets acquired:
Cash and cash equivalents	$	63,869		$	—		$	63,869
Prepaid expenses and other current assets		2,505			554			3,059
Property and equipment		318			—			318
IPR&D		3,490			—			3,490
Restricted cash		245			—			245
Accounts payable		(1,316	)		—			(1,316	)
Accrued and other current liabilities		(2,421	)		56			(2,365	)
Other liabilities		(40	)		40			—
Deferred tax liability		(367	)		—			(367	)
Goodwill		20,739			(650	)		20,089
Purchase price	$	87,022		$	—		$	87,022

Schedule of Supplemental Unaudited Pro Forma Information

The following supplemental unaudited pro forma information represents the Company’s financial results as if the acquisition of resTORbio had occurred on January 1, 2019 (in thousands).

	For the Year Ended December 31,
	2020			2019
Revenue - related party	$	17,903		$	995
Net loss	$	(35,757	)	$	(113,151	)

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities Measured on Recurring Basis

	December 31, 2020
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds⁽¹⁾	$	63,817	$	—	$	—	$	63,817
Marketable debt securities
Asset-backed securities		—		7,522		—		7,522
Corporate debt securities		—		1,762		—		1,762
Commercial paper		—		1,000		—		1,000
Marketable debt securities		—		10,284		—		10,284
Total fair value of assets	$	63,817	$	10,284	$	—	$	74,101
Liabilities:
Contingent consideration	$	—	$	—	$	980	$	980
Total fair value of liabilities	$	—	$	—	$	980	$	980

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets:
Money market funds⁽¹⁾	$	7,232	$	—	$	—	$	7,232
Marketable debt securities
Asset-backed securities		—		19,598		—		19,598
Corporate debt securities		—		19,394		—		19,394
Commercial paper		—		17,892		—		17,892
U.S. Government agency bonds		—		5,497		—		5,497
Marketable debt securities		—		62,381		—		62,381
Total fair value of assets	$	7,232	$	62,381	$	—	$	69,613
Liabilities:
Redeemable convertible preferred stock warrant liability	$	—	$	—	$	1,881	$	1,881
Total fair value of liabilities	$	—	$	—	$	1,881	$	1,881

(1)	Included in cash and cash equivalents in the consolidated balance sheets

Schedule of Changes in Fair Value of Level 3 Financial Instruments

The following table presents a summary of the changes in the fair value of the Company’s Level 3 financial instrument (in thousands):

	Redeemable Convertible Preferred Stock Tranche Liability			TRDF Liability			Redeemable Convertible Preferred Stock Warrant Liability			Contingent Consideration Liability
Fair value as of January 1, 2018	$	8,557		$	136		$	—		$	—
Change in the fair value included in other income (expense), net		(4,542	)		6			—			—
Exercise		(902	)		—			—			—
Fair value as of December 31, 2018		3,113			142			—			—
Recognition of preferred stock warrant liabilities		—			—			2,131			—
Settlement		—			(88	)		—			—
Change in the fair value included in other income (expense), net		(1,970	)		(54	)		(250	)		—
Termination		(1,143	)		—			—			—
Fair value as of December 31, 2019		—			—			1,881			—
Recognition of preferred stock warrant liability		—			—			144			—
Recognition of contingent consideration liability		—			—			—			2,880
Change in the fair value included in other income (expense), net		—			—			897			—
Change in the fair value included in research and development expense		—			—			—			(1,900	)
Conversion of convertible preferred stock warrant into common stock warrant in connection with Merger		—			—			(2,922	)		—
Fair value as of December 31, 2020	$	—		$	—		$	—		$	980

Marketable Debt Securities (Tables)

12 Months Ended

Dec. 31, 2020

Investments Debt And Equity Securities [Abstract]

Schedule of Marketable Debt Securities

The following tables summarize the Company’s marketable debt securities (in thousands):

	December 31, 2020
	Amortized Cost		Unrealized Losses		Unrealized Gains		Fair Value
Asset-backed securities	$	7,507	$	—	$	15	$	7,522
Corporate debt securities		1,754		—		8		1,762
Commercial paper		999		—		1		1,000
Total	$	10,260	$	—	$	24	$	10,284

	December 31, 2019
	Amortized Cost		Unrealized Losses			Unrealized Gains		Fair Value
Asset-backed securities	$	19,589	$	(1	)	$	10	$	19,598
Corporate debt securities		19,387		(3	)		9		19,393
Commercial paper		17,882		—			11		17,893
U.S. Government agency bonds		5,500		(3	)		—		5,497
Total	$	62,358	$	(7	)	$	30	$	62,381

Schedule of Company’s Marketable Debt Securities by Contractual Maturity

The following table summarizes the Company’s marketable debt securities by contractual maturity (in thousands):

	December 31, 2020
	Amortized Cost		Fair Value
Within one year	$	10,260	$	10,284
After one year through five years		—		—
After five years		—		—
Total	$	10,260	$	10,284

Summary of Classification of Marketable Debt Securities in Consolidated Balance Sheets

The following table summarizes the classification of the Company’s marketable debt securities in the consolidated balance sheets (in thousands):

	December 31
	2020		2019
Short-term marketable debt securities	$	10,284	$	51,793
Long-term marketable debt securities		—		10,588
Total	$	10,284	$	62,381

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2020

Prepaid Expense And Other Assets Current [Abstract]

Summary of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following (in thousands):

	December 31
	2020		2019
Prepaid maintenance and other	$	1,185	$	615
Prepaid insurance		1,443		57
Tax receivable		2,711		722
Interest receivable		20		213
Other current assets		363		179
Total	$	5,722	$	1,786

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

			As of December 31,
	Useful life (years)		2020			2019
Laboratory equipment	3		$	4,350		$	3,872
Leasehold improvements	Lesser of useful life or lease term			1,427			1,327
Furniture and fixtures	3			524			68
Construction in progress		—		1,090			300
Computer equipment	3			93			42
Software	3			170			150
				7,654			5,759
Less: Accumulated depreciation and amortization				(4,864	)		(3,638	)
Property and equipment, net			$	2,790		$	2,121

Accrued and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Summary of Accrued and Other Current Liabilities

Accrued and other current liabilities consisted of the following (in thousands):

	December 31
	2020		2019
Accrued compensation	$	3,833	$	1,359
Accrued research and development expenses		1,187		450
Accrued professional services		386		301
Accrued other liabilities		326		710
Total	$	5,732	$	2,820

Regeneron License and Collaboration Arrangement (Tables)

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Change in Company's Contract Liabilities

The following table presents changes in the Company’s contract liabilities (in thousands):

Year ended December 31, 2020	Balance at beginning of period		Additions		Additions (Deductions) ⁽¹⁾			Balance at end of period
Contract asset	$	—	$	10,000	$	(10,000	)	$	—
Contract liability	$	21,883	$	10,000	$	(17,903	)	$	13,980

Year ended December 31, 2019	Balance at beginning of period		Additions		Additions (Deductions) ⁽¹⁾			Balance at end of period
Contract liability	$	22,878	$	—	$	(995	)	$	21,883

(1)	Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

Commitments and Contingences (Tables)

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of Weighted Average IBR and Remaining Lease Term

The IBR and the remaining lease terms of our facilities and their weighted average IBR and remaining terms are as follows as of December 31, 2020:

Lease Locations	IBR	Remaining Terms (in years)
Redwood City, CA	6.90%	9.2
Boston, MA	9.30%	5.6
Menlo Park, CA	6.80%	1.3
Weighted Average	7.20%	8.4

Summary of Lease Costs and Other Information

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2020:

	For the Year Ended December 31, 2020
Lease Cost	(in thousands)
Operating lease cost	$	894
Short-term lease cost		56
Variable lease cost		—
Total lease cost	$	950
Other Information
Operating cash flows used for lease payments	$	3,168
Operating cash flows used for lease liabilities	$	859
Operating lease right of use asset obtained in exchange of operating lease liability	$	22,367

Maturities Of Operating Lease Liabilities

The maturities of the operating lease liabilities as of December 31, 2020 were as follows (in thousands):

2021	$	2,505
2022		2,818
2023		3,429
2024		3,525
2025		3,624
2026 and thereafter		13,747
Total undiscounted lease payments		29,648
Less: imputed interest		8,009
Total operating lease liability		21,639
Less: current portion		1,215
Operating lease liability, net of current maturities	$	20,424

Schedule Of Future Minimum Rental Payments For Operating Leases

The future minimum lease payments under all non-cancelable operating lease obligations as of December 31, 2019 under ASC 840 were as follows (in thousands):

2020	$	2,721
2021		3,518
2022		2,942
2023		2,798
2024		2,882
2025 and thereafter		16,328
Total	$	31,189

Redeemable Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Summary of Redeemable Convertible Preferred Stock

As of December 31, 2019, redeemable convertible preferred stock consists of the following (in thousands, except per share and share amounts):

	Shares Authorized		Original Issue Price		Shares Issued and Outstanding		Carrying Value		Liquidation Preference		Common Stock Issued Upon Conversion ⁽¹⁾
Series A		37,104,185	$	1.20		37,104,185	$	35,960	$	44,525		4,600,920
Series A-1		629,633		1.20		629,633		447		756		78,074
Series A-2		2,428,688		1.20		2,428,688		1,749		2,914		301,157
Series B		59,200,938		1.40		57,004,415		75,927		80,000		7,068,520
		99,363,444				97,166,921	$	114,083	$	128,195		12,048,671

⁽¹⁾ Adjusted to reflect the Exchange Ratio.

Redeemable Convertible Preferred Stock Tranche Liability (Tables)

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Schedule of Additional Closing Liability Assuming under The Option-Pricing Method

The Additional Closing liability was valued using the following assumptions under the option-pricing method:

Fair Value of Series A

Preferred Stock

Term

Interest rate

Volatility

December 31, 2018

10.48

1.88 years

2.50

69.80

July 25, 2019

7.18

1.31 years

1.95

69.10

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants (Tables)

12 Months Ended

Dec. 31, 2020

Liabilities And Stockholders Equity [Abstract]

Schedule of Redeemable Convertible Preferred Stock Warrant Liability using Black-Scholes Option-Pricing Model

The redeemable convertible preferred stock warrant liability was valued using the following assumptions under the Black-Scholes option-pricing model:

	September 14, 2020 (Conversion Date)			April 28, 2020 (Issuance Date of PacWest Warrants)			December 31, 2019
Stock price	$	16.59		$	11.61		$	11.32
Expected term (years)	5.86 - 6.62				7.00		6.57 - 6.74
Expected volatility	81.1% - 82.1%				91.17	%	82.1% - 93.3%
Risk-free interest rate	0.35% - 0.42%				0.52	%	1.53% - 1.93%
Dividend yield		0	%		0	%		0	%

Schedule of Outstanding Warrants

The following table provides a roll forward of outstanding warrants:

	Number of Warrants			Weighted Average Exercise Price		Weighted Average Contractual Term (Years)
Outstanding and exercisable warrants to purchase preferred shares as of December 31, 2019		1,781,387		$	1.4034
Issued		128,260
Impact of converting to warrants for the purchase of common stock and adjusted for the Exchange Ratio and Reverse Stock Split		(1,683,456	)
Outstanding and exercisable warrants to purchase common stock as of December 31, 2020		226,191		$	11.3177		5.66

Schedule of Outstanding Warrants to Purchase Shares of Common Stock

As of December 31, 2020, the Company’s outstanding warrants to purchase shares of common stock, including the New PacWest Warrant, consisted of the following:

Issuance Date	Number of Shares of Common Stock Issuable		Exercise Price		Classification	Expiration Date
September 15, 2020		101,610	$	11.3177	Equity	July 25, 2026
September 15, 2020		30,924	$	11.3177	Equity	August 21, 2026
September 15, 2020		77,312	$	11.3177	Equity	September 19, 2026
September 15, 2020		11,044	$	11.3177	Equity	September 26, 2026
September 15, 2020		5,301	$	11.3177	Equity	April 28, 2027
		226,191

Schedule of Outstanding Warrants to Purchase Shares of Redeemable Convertible Preferred Stock

Warrant Name

Issuance Date

Number of

Shares of

Preferred

Stock Issuable

Exercise

Price

Exercisable

for

Classification

Expiration Date

Series B warrants

July 25, 2019

819,438

1.4034

Series B

Liability

July 25, 2026

Series B warrants

August 21, 2019

249,394

1.4034

Series B

Liability

August 21, 2026

Series B warrants

September 19, 2019

623,486

1.4034

Series B

Liability

September 19, 2026

Series B warrants

September 26, 2019

89,069

1.4034

Series B

Liability

September 26, 2026

1,781,387

Common Stock (Tables)

12 Months Ended

Dec. 31, 2020

Stockholders Equity Note [Abstract]

Schedule of Number of Shares of Common Stock Reserved for Future Issuance

The Company has the following shares of common stock reserved for future issuance:

	December 31
	2020		2019
Conversion of redeemable convertible preferred stock (as converted to common stock)		—		12,048,671
Conversion of additional authorized and unissued redeemable convertible preferred stock		—		51,506
Stock options available for future grant		1,739,621		653,136
Stock options issued and outstanding		3,706,945		1,860,646
Redeemable convertible preferred stock warrants issued and outstanding		—		220,890
Common stock warrants issued and outstanding		226,191		—
Total common stock reserved		5,672,757		14,834,849

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

A summary of stock option activity is set forth below (in thousands, except share and per share data):

				Outstanding Awards
	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options			Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, January 1, 2018		38,055			963,435		$	2.02			9.27	$	4,977
Options authorized		837,000
Options granted		(210,452	)		210,452		$	2.26
Options exercised		—			(123,949	)	$	1.92
Options forfeited or cancelled		153,399			(153,399	)	$	2.25
Outstanding, December 31, 2018		818,002			896,539		$	2.04			8.57	$	2,436
Options authorized		814,184
Options granted		(1,124,430	)		1,124,430		$	5.39
Options exercised		—			(14,791	)	$	(2.12	)
Options forfeited or cancelled		145,380			(145,532	)	$	2.17
Outstanding, December 31, 2019		653,136			1,860,646		$	4.05			8.53	$	5,812
Assumed as part of the Merger		2,707,144			81,370		$	8.39
Options granted		(1,914,142	)		2,276,645		$	15.14
Options exercised					(210,752	)	$	2.18
Options forfeited or cancelled		293,483			(300,964	)	$	6.04
Outstanding, December 31, 2020		1,739,621			3,706,945		$	10.90			7.98	$	15,126
Shares exercisable December 31, 2020					1,219,904		$	4.64			5.11	$	11,563
Vested and expected to vest, December 31, 2020					3,706,945		$	10.90			7.98	$	15,126

Summary of Restricted Stock Activity

Activity with respect to restricted stock was as follows:

	Number of Shares Underlying Outstanding Restricted Stock			Weighted Average Grant Date Fair Value
Unvested, January 1, 2018		165,699		$	4.19
Vested		(134,516	)	$	4.19
Unvested, December 31, 2018		31,183		$	4.19
Vested		(31,183	)	$	4.19
Unvested, December 31, 2019		—		$	—

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	1,674	$	274	$	285
General and administrative		3,589		901		2,194
Total stock-based compensation	$	5,263	$	1,175	$	2,479

Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model

	Year Ended December 31,
	2020	2019	2018
Expected volatility	72.6%-96.3%	71.5%-86.5%	73.3%-74%
Risk-free interest rate	0.1%-1.7%	1.6%-2.5%	2.7%-2.8%
Dividend yield	0%	0%	0%
Expected term	1.00-6.08 years	5.15-6.08 years	6.02-6.08 years

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders

	Year Ended December 31,
	2020			2019			2018
Numerator:
Net loss attributable to common stockholders	$	(36,678	)	$	(28,138	)	$	(9,299	)
Denominator:
Weighted-average shares outstanding		7,319,977			2,148,317			2,049,680
Less: weighted-average unvested restricted shares and shares subject to repurchase		—			(9,344	)		(102,704	)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted		7,319,977			2,138,973			1,946,976
Net loss per share attributable to common stockholders, basic and diluted	$	(5.01	)	$	(13.15	)	$	(4.78	)

Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	December 31,
	2020		2019		2018
Redeemable convertible preferred stock (as converted to common stock)		—		12,048,671		4,971,762
Options to purchase common stock		3,706,945		1,860,646		896,539
Redeemable convertible preferred stock warrants		—		220,890		—
Common stock warrants		226,191		—		—
Unvested early exercised common stock options		—		—		27,709
Unvested restricted stock awards		—		—		31,183
Redeemable convertible preferred stock tranche liability and TRDF obligation		—		—		743,317
Total		3,933,136		14,130,207		6,670,510

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Components of Provision for (Benefit from) Income Taxes

The components of the provision for (benefit from) income taxes are as follows (in thousands):

	Year Ended December 31,
	2020			2019		2018
Current:
Federal	$	(2,678	)	$	—	$	—
State		105			1		(589	)
Foreign		—			18		—
Total current		(2,573	)		19		(589	)
Deferred:
Federal		(242	)		—		—
State		—			—		—
Foreign		—			—		—
Total deferred		(242	)		—		—
Provision for (benefit from) income taxes	$	(2,815	)	$	19	$	(589	)

Schedule of (Provision for) Benefit from Income Taxes Differs from Federal Statutory Rate to the Loss Before Taxes

For the rate table below the (provision for) benefit from income taxes differ from the amount expected by applying the federal statutory rate to the loss before taxes as follows:

	Year Ended December 31,
	2020			2019			2018
Federal statutory income tax rate		21.0	%		21.0	%		21.0	%
Other permanent differences		(0.5	)%		(0.1	)%		(0.1	)%
State income taxes		6.1	%		5.1	%		3.8	%
Foreign rate differential		0.0	%		0.0	%		0.2	%
Foreign loss		0.0	%		(0.2	)%		(2.2	)%
Federal benefit from NOL carryback		6.7	%		0.0	%		0.0	%
Change in valuation allowance		(25.8	)%		(27.7	)%		(20.0	)%
Change in fair value of redeemable convertible preferred stock tranche liability and TRDF liability		(0.5	)%		1.7	%		8.7	%
Stock-based compensation		0.1	%		0.1	%		(6.0	)%
Benefit from (provision for) income taxes		7.1	%		(0.1	)%		5.4	%

Schedule of Deferred Tax Assets and Liabilities

The tax effects of temporary differences and carryforwards of the deferred tax assets are presented below (in thousands):

	December 31,
	2020			2019			2018
Deferred Tax Assets:
Net operating loss carryforwards	$	51,796		$	12,510		$	5,233
Operating lease right-of-use asset liability		5,686			—			—
Deferred revenue		2,857			5,719			5,125
Stock-based compensation		1,750			509			274
Intangible assets		1,195			609			804
Accruals and reserves		654			446			431
Research and development credit carryforwards		26			26			26
Gross deferred tax assets		63,964			19,819			11,893
Less: Valuation allowance		(57,715	)		(19,815	)		(11,739	)
Deferred tax assets, net of valuation allowance		6,249			4			154
Deferred tax liabilities:
Fixed assets		—			(4	)		(154	)
Basis Difference IPR&D		(313	)		—			—
Operating lease right-of-use asset		(6,061	)		—			—
Net deferred tax liability	$	(125	)	$	—		$	—

Schedule of Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Balance at the beginning of the year	$	797	$	797	$	866
Adjustment based on tax positions related to prior years		—		—		(69	)
Balance at the end of the year	$	797	$	797	$	797

Organization and Nature of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Sep. 15, 2020	Sep. 15, 2020	Feb. 28, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Schedule Of Equity Method Investments [Line Items]
Entity incorporation date				Nov. 30, 2014
Entity date of merger				Apr. 28, 2020
Equity method investment, Ownership percentage				25.00%
Reverse stock split	1-for-7	1-for-7
Exchange ratio	0.1240
Common stock, shares outstanding \| shares				19,677,249	2,155,578
Accumulated deficit				$ 106,325	$ 69,647
Adicet Therapeutics [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, Ownership percentage				75.00%
Common stock, shares outstanding \| shares				19,589,828
Cash, cash equivalents and marketable securities				$ 94,600
Accumulated deficit				$ 106,500
Initial Public Offering \| Subsequent Event
Schedule Of Equity Method Investments [Line Items]
Number of common stock shares sold \| shares			10,575,513
Issuance price per shares \| $ / shares			$ 13.00
Underwriting discounts and commissions and other offering expenses			$ 137,500
Net proceeds received from offering			$ 15,000
Initial Public Offering \| Maximum \| Subsequent Event
Schedule Of Equity Method Investments [Line Items]
Option to purchase of common stock at public offering price \| shares			1,344,743

Summary of Significant Accounting Policies - Additional Information (Details)		12 Months Ended
	Sep. 15, 2020	Dec. 31, 2020 USD ($) Customer	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Exchange ratio	0.1240
Gain (loss) on change in fair value of CVR		$ 1,900,000
Goodwill impairment		$ 0
Number of customer \| Customer		1
Customers percentage of total revenue		100.00%	100.00%	100.00%
Asset impairment charges		$ 0	$ 0
Operating lease right-of-use asset		23,066,000			$ 1,400,000
Operating lease liability		21,639,000			$ 1,800,000
Deferred rent		400,000	$ (148,000)	$ (132,000)
Research And Development Expenses
Summary Of Significant Accounting Policies [Line Items]
Impairment charges		$ 2,300,000

Business Combination - Additional Information (Details) $ in Thousands				3 Months Ended	12 Months Ended
	Sep. 15, 2020 shares	Sep. 15, 2020 shares	Apr. 28, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Percentage of outstanding capital stock	75.00%	75.00%
Reverse stock split	1-for-7	1-for-7
Goodwill				$ 20,089	$ 20,089
Transition Agreement [Member]
Business Acquisition [Line Items]
Amount equal to pro-rated bonus			$ 212,000
Lump sum payable			250,000
Payable upon closing of merger			24,000
Legal fees			15,000
Advisory services annual fee			12,500
resTORbio
Business Acquisition [Line Items]
Reverse stock split exchange ratio		0.1240
Number of shares of surviving stock options \| shares		81,370
Unvested restricted stock units outstanding \| shares	91,309	91,309
Number of common stock shares sold \| shares		54,553
Measurement prior adjustment in tangible and intangible assets				700
Goodwill				$ 20,089	20,089
Transaction cost for merger					7,100
Transaction cost for business acquisition					$ 15,600	$ 15,600
resTORbio \| Transition Agreement [Member]
Business Acquisition [Line Items]
Cash payment			$ 470,000
Expiration period closing of the merger			60 days
resTORbio \| Common Stock
Business Acquisition [Line Items]
Percentage of outstanding capital stock	25.00%	25.00%

Business Combination - Schedule of Summarizes the Purchase Price in the Merger (Details) - USD ($) $ in Thousands	Sep. 15, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Contingent consideration liability		$ 980
resTORbio
Business Acquisition [Line Items]
Fair value of common stock shares of the combined company owned by resTORbio stockholders	$ 84,142
Contingent consideration liability	2,880
Purchase price	$ 87,022

Business Combination - Schedule of Estimated Share Consideration of Combined Company (Details) - resTORbio $ / shares in Units, $ in Thousands	Sep. 15, 2020 USD ($) $ / shares shares
Business Acquisition [Line Items]
Number of shares of the combined company owned by resTORbio stockholders \| shares	5,207,695
Multiplied by the fair value per share of resTORbio common stock \| $ / shares	$ 16.59
Acquisition date fair value of resTORbio common shares	$ 86,396
Acceleration of restricted stock units upon merger	626
Less: portion of the fair value to be distributed as CVR	(2,880)
Fair value of common stock shares of the combined company owned by resTORbio stockholders	$ 84,142

Business Combination - Schedule of Estimated Share Consideration of Combined Company (Parenthetical) (Details) - resTORbio	Sep. 15, 2020 shares
Business Acquisition [Line Items]
Number of shares of the combined company owned by resTORbio stockholders	5,207,695
Number of common stock shares sold	54,553

Business Combination - Schedule of Summarizes the Purchase Price in the Merger (Parenthetical) (Details) - resTORbio	Sep. 15, 2020 shares
Business Acquisition [Line Items]
Unvested restricted stock units outstanding	91,309
Number of common stock shares sold	54,553
Number of shares of surviving stock options	81,370

Business Combination - Schedule of Summarizes the Allocation of the Purchase Price to the Net Tangible and Intangible Assets Acquired (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 15, 2020
Net assets acquired:
Goodwill	$ 20,089
resTORbio
Net assets acquired:
Cash and cash equivalents	63,869
Prepaid expenses and other current assets	3,059
Property and equipment	318
IPR&D	3,490
Restricted cash	245
Accounts payable	(1,316)
Accrued and other current liabilities	(2,365)
Deferred tax liability	(367)
Goodwill	20,089
Purchase price	87,022
resTORbio \| Preliminary
Net assets acquired:
Cash and cash equivalents		$ 63,869
Prepaid expenses and other current assets		2,505
Property and equipment		318
IPR&D		3,490
Restricted cash		245
Accounts payable		(1,316)
Accrued and other current liabilities		(2,421)
Other liabilities		(40)
Deferred tax liability		(367)
Goodwill		20,739
Purchase price		$ 87,022
resTORbio \| Measurement Period Adjustments
Net assets acquired:
Prepaid expenses and other current assets	554
Accrued and other current liabilities	56
Other liabilities	40
Goodwill	$ (650)

Business Combination - Schedule of Supplemental Unaudited Pro Forma Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Combinations [Abstract]
Revenue - related party	$ 17,903	$ 995
Net loss	$ (35,757)	$ (113,151)

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	$ 74,101	$ 69,613
Total fair value of liabilities	980	1,881
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	63,817	7,232
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	1,000	17,892
Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	10,284	62,381
Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	7,522	19,598
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	1,762	19,394
US Government Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets		5,497
Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities	980
Redeemable Convertible Preferred Stock Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities		1,881
Fair Value Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	63,817	7,232
Fair Value Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	63,817	7,232
Fair Value Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	10,284	62,381
Fair Value Level 2 \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	1,000	17,892
Fair Value Level 2 \| Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	10,284	62,381
Fair Value Level 2 \| Asset Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	7,522	19,598
Fair Value Level 2 \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	1,762	19,394
Fair Value Level 2 \| US Government Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets		5,497
Fair Value Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities	980	1,881
Fair Value Level 3 \| Contingent Consideration [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities	$ 980
Fair Value Level 3 \| Redeemable Convertible Preferred Stock Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities		$ 1,881

Fair Value Measurements - Schedule of Changes in Fair Value of Level 3 Financial Instruments (Details) - Fair Value Level 3 - Measure of Changes in Fair Value - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Redeemable Convertible Preferred Stock Tranche Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value, beginning balance		$ 3,113	$ 8,557
Change in the fair value included in other income (expense), net		(1,970)	(4,542)
Exercise			(902)
Termination		(1,143)
Fair value, ending balance			3,113
TRDF Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value, beginning balance		142	136
Settlement		(88)
Change in the fair value included in other income (expense), net		(54)	6
Fair value, ending balance			$ 142
Redeemable Convertible Preferred Stock Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value, beginning balance	$ 1,881
Recognition of preferred stock warrant liabilities	144	2,131
Change in the fair value included in other income (expense), net	897	(250)
Conversion of convertible preferred stock warrant into common stock warrant in connection with Merger	(2,922)
Fair value, ending balance		$ 1,881
Contingent Consideration Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Recognition of contingent consideration liability	2,880
Change in the fair value included in research and development expense	(1,900)
Fair value, ending balance	$ 980

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Milestone closing liability	$ 6.2
Additional closing liability	$ 5.0
Warrants outstanding	226,191
Increase decrease in estimated fair value of CVR liability	$ 1.9
Estimated fair value of the CVR liability	$ 1.0
Redeemable Convertible Preferred Stock Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Warrants outstanding	0
Other Income (Expense) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gain from the remeasurement of the redeemable convertible preferred stock		$ 2.0

Marketable Debt Securities - Schedule of Marketable Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 10,260	$ 62,358
Unrealized Losses		(7)
Unrealized Gains	24	30
Fair Value	10,284	62,381
Asset Backed Securities
Marketable Securities [Line Items]
Amortized Cost	7,507	19,589
Unrealized Losses		(1)
Unrealized Gains	15	10
Fair Value	7,522	19,598
Corporate Debt Securities
Marketable Securities [Line Items]
Amortized Cost	1,754	19,387
Unrealized Losses		(3)
Unrealized Gains	8	9
Fair Value	1,762	19,393
Commercial Paper
Marketable Securities [Line Items]
Amortized Cost	999	17,882
Unrealized Gains	1	11
Fair Value	$ 1,000	17,893
US Government Agency Bonds
Marketable Securities [Line Items]
Amortized Cost		5,500
Unrealized Losses		(3)
Fair Value		$ 5,497

Marketable Securities - Schedule of Companys Marketable Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Within one year, Amortized Cost	$ 10,260
Total, Amortized Cost	10,260
Within one year, Fair Value	10,284
Total, Fair Value	$ 10,284	$ 62,381

Marketable Debt Securities - Summary of Classification of Marketable Debt Securities in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Short-term marketable debt securities	$ 10,284	$ 51,793
Long-term marketable debt securities		10,588
Marketable debt securities	$ 10,284	$ 62,381

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Prepaid maintenance and other	$ 1,185	$ 615
Prepaid insurance	1,443	57
Tax receivable	2,711	722
Interest receivable	20	213
Other current assets	363	179
Total prepaid expenses and other current assets	$ 5,722	$ 1,786

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 7,654	$ 5,759
Less: Accumulated depreciation and amortization	(4,864)	(3,638)
Property and equipment, net	2,790	2,121
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,350	3,872
Useful life (in years)	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,427	1,327
Useful life (in years)	Lesser of useful life or lease term
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	$ 524	68
Useful life (in years)	3 years
Construction In Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,090	300
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 93	42
Useful life (in years)	3 years
Software
Property Plant And Equipment [Line Items]
Total property and equipment	$ 170	$ 150
Useful life (in years)	3 years

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,226	$ 1,238	$ 1,222

Accrued and Other Current Liabilities - Summary of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued compensation	$ 3,833	$ 1,359
Accrued research and development expenses	1,187	450
Accrued professional services	386	301
Accrued other liabilities	326	710
Total	$ 5,732	$ 2,820

Term Loan - Additional Information (Details) - USD ($)	12 Months Ended
Term Loan - Additional Information (Details) - USD ($)	Dec. 31, 2020	Apr. 28, 2020	Dec. 31, 2019
Class Of Warrant Or Right [Line Items]
Interest rate for term loan to finance leasehold improvements		5.00%
Warrant exercise price	$ 11.3177		$ 1.4034
Loan availability end date	Oct. 28, 2021
Loan amount drawn	$ 0
Deferred debt issuance cost	100,000
Incremental expense	0
Debt issuance costs, gross	$ 200,000
Common Stock
Class Of Warrant Or Right [Line Items]
Number of securities called		5,301
Series B Convertible Preferred Stock [ Member ]
Class Of Warrant Or Right [Line Items]
Warrant exercise price		$ 1.4034
Number of securities called		42,753
Maximum
Class Of Warrant Or Right [Line Items]
Term loan to finance leasehold improvements		$ 12,000,000.0
Maximum \| Common Stock
Class Of Warrant Or Right [Line Items]
Number of additional securities called		15,903
Minimum [Member] \| Prime Rate
Class Of Warrant Or Right [Line Items]
Interest rate for term loan to finance leasehold improvements		0.25%

Regeneron License and Collaboration Arrangement - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2020	Jul. 29, 2016	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement cumulative revenue recognised						$ 17.9	$ 1.0	$ 8.2
Regeneron Pharmaceuticals, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non refundable upfront payment received	$ 25.0
Additional payment for research funding received	20.0							$ 5.0	$ 5.0
Contract research term period		5 years
Upfront payment		$ 25.0				25.0
Licence agreement additional revenue recognised			$ 5.0
License agreement cumulative revenue reduction recognised				$ 6.6
Increase in estimated transaction price			$ 10.0
Licence agreement cumulative revenue recognised					$ 10.0	31.0	13.1
Contract liability						$ 14.0	$ 21.9
Regeneron Pharmaceuticals, Inc. \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement additional amount payable of option exercise fees	$ 100.0

Regeneron License and Collaboration Arrangement - Summary of Change in Company's Contract Liabilities (Details) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Contract Asset

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additions

$ 10,000

Additions (Deductions)

^[1]

(10,000)

Contract Liability

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Balance at beginning of period

21,883

$ 22,878

Additions

10,000

Additions (Deductions)

^[1]

(17,903)

(995)

Balance at end of period

$ 13,980

$ 21,883

[1]	Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

License Funding and Other Agreements Related to the CVR - Additional Information (Details) - USD ($) $ in Millions		1 Months Ended		12 Months Ended
	Oct. 31, 2020	Nov. 30, 2020	May 31, 2019	Dec. 31, 2020	Mar. 23, 2017
Research And Development Arrangement Contract To Perform For Others [Line Items]
Increase decrease in estimated fair value of CVR liability				$ 1.9
Estimated fair value of the CVR liability				1.0
National Institute of Health
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant term			5 years
Grants receivable			$ 1.5
Qualifying expenses				0.6
National Institute of Health \| Research Funding Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Qualifying expenses				0.7
Contingent Value Rights Agreement \| C O V I D19
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total fees and expenses related to clinical trials	$ 1.1			$ 3.0
Increase decrease in estimated fair value of CVR liability		$ 1.9
Estimated fair value of the CVR liability		$ 1.0
Novartis License Agreement \| Novartis International Pharmaceutical Ltd.
Research And Development Arrangement Contract To Perform For Others [Line Items]
License agreement termination description				The agreement may be terminated by either party upon a material breach of obligation by the other party that is not cured with 60 days after written notice. resTORbio may terminate the agreement in its entirety or on a product-by-product or country-by-country basis with or without cause with 60 days’ prior written notice.
Novartis License Agreement \| Novartis International Pharmaceutical Ltd. \| Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Aggregate amount payable upon satisfaction of clinical milestones					$ 4.3
Aggregate amount payable upon satisfaction of regulatory milestones for first indication approved					24.0
Aggregate amount payable upon satisfaction of regulatory milestones for second indication approved					18.0
Aggregate amount payable upon satisfaction of commercial milestones					$ 125.0

Commitment and Contingencies - Additional Information (Details)					1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 19, 2020 USD ($) ft²	Sep. 30, 2019 USD ($) ft²	Oct. 28, 2018 USD ($) ft²	Sep. 30, 2015 USD ($) ft²	Apr. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) Lawsuit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2020 USD ($)
Long Term Purchase Commitment [Line Items]
Lease payments					$ 3,500,000		$ 3,168,000	$ 700,000	$ 500,000
Amended lease term from the date of relocation					7 years
Operating lease right-of-use asset						$ 23,066,000	23,066,000			$ 1,400,000
Operating lease liability						21,639,000	21,639,000			1,800,000
Finance lease liability						0	0
Operating lease right-of-use asset						23,066,000	$ 23,066,000			1,400,000
Lawsuits Filed Against Company \| Lawsuit							7
Litigation settlement expense						200,000
Topic 842
Long Term Purchase Commitment [Line Items]
Lease payments							$ 900,000
Operating lease right-of-use asset										1,400,000
Operating lease liability										1,800,000
Finance lease liability						0	0
Operating lease right-of-use asset										$ 1,400,000
Menlo Park Lease Agreement [Member]
Long Term Purchase Commitment [Line Items]
Office lease space \| ft²	4,862	7,973		17,352
Lease payments	$ 300,000	$ 400,000		$ 3,400,000
Tenant improvements				$ 800,000
Lease expiration date	Mar. 31, 2022	Mar. 31, 2022		Mar. 31, 2022
Operating leases commencement date	Oct. 01, 2020	Oct. 01, 2019
Letters of Credit issued amount						200,000	200,000
Redwood City Lease Agreement [Member]
Long Term Purchase Commitment [Line Items]
Office lease space \| ft²			50,305
Lease payments			$ 29,500,000
Tenant improvements			$ 3,000,000.0
Lease expiration date			Feb. 28, 2030
Letters of Credit issued amount									$ 4,100,000
Boston, Massachusetts [Member]
Long Term Purchase Commitment [Line Items]
Letters of Credit issued amount						$ 200,000	$ 200,000

Commitment and Contingencies - Schedule of Weighted Average IBR and Remaining Lease Term (Details)	Dec. 31, 2020
Long Term Purchase Commitment [Line Items]
Weighted Average IBR	7.20%
Remaining Terms (in years)	8 years 4 months 24 days
Redwood City, CA
Long Term Purchase Commitment [Line Items]
Weighted Average IBR	6.90%
Remaining Terms (in years)	9 years 2 months 12 days
Boston, MA
Long Term Purchase Commitment [Line Items]
Weighted Average IBR	9.30%
Remaining Terms (in years)	5 years 7 months 6 days
Menlo Park, CA
Long Term Purchase Commitment [Line Items]
Weighted Average IBR	6.80%
Remaining Terms (in years)	1 year 3 months 18 days

Commitment and Contingencies - Summary of Lease Costs and Other Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease Cost
Operating lease cost		$ 894
Short-term lease cost		56
Total lease cost		950
Other Information
Operating cash flows used for lease payments	$ 3,500	3,168	$ 700	$ 500
Operating cash flows used for lease liabilities		859
Operating lease right of use asset obtained in exchange of operating lease liability		$ 22,367

Commitment and Contingencies - Schedule Of Maturities Of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020
Commitments And Contingencies Disclosure [Abstract]
2021	$ 2,505
2022	2,818
2023	3,429
2024	3,525
2025	3,624
2026 and thereafter	13,747
Total undiscounted lease payments	29,648
Less: imputed interest	8,009
Total operating lease liability	21,639	$ 1,800
Less: current portion	1,215
Operating lease liability, net of current maturities	$ 20,424

Commitment and Contingencies - Schedule Of Future Minimum Rental Payments For Operating Leases (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 2,721
2021	3,518
2022	2,942
2023	2,798
2024	2,882
2025 and thereafter	16,328
Total	$ 31,189

Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Details)
$ / shares in Units, $ in Thousands

Dec. 31, 2019

USD ($)

$ / shares

Temporary Equity [Line Items]

Shares Authorized

99,363,444

^[1]

Shares Issued and Outstanding

97,166,921

^[1]

Carrying Value | $

$ 114,083

Liquidation Preference | $

$ 128,195

Common Stock Issued Upon Conversion (1)

12,048,671

^[1]

Series A Redeemable Convertible Preferred Stock

Temporary Equity [Line Items]

Shares Authorized

37,104,185

^[1]

Original Issue Price | $ / shares

$ 1.20

Shares Issued and Outstanding

37,104,185

^[1]

Carrying Value | $

$ 35,960

Liquidation Preference | $

$ 44,525

Common Stock Issued Upon Conversion (1)

4,600,920

^[1]

Series A-1 Redeemable Convertible Preferred Stock

Temporary Equity [Line Items]

Shares Authorized

629,633

^[1]

Original Issue Price | $ / shares

$ 1.20

Shares Issued and Outstanding

629,633

^[1]

Carrying Value | $

$ 447

Liquidation Preference | $

$ 756

Common Stock Issued Upon Conversion (1)

78,074

^[1]

Series A-2 Redeemable Convertible Preferred Stock

Temporary Equity [Line Items]

Shares Authorized

2,428,688

^[1]

Original Issue Price | $ / shares

$ 1.20

Shares Issued and Outstanding

2,428,688

^[1]

Carrying Value | $

$ 1,749

Liquidation Preference | $

$ 2,914

Common Stock Issued Upon Conversion (1)

301,157

^[1]

Series B Redeemable Convertible Preferred Stock

Temporary Equity [Line Items]

Shares Authorized

59,200,938

^[1]

Original Issue Price | $ / shares

$ 1.40

Shares Issued and Outstanding

57,004,415

^[1]

Carrying Value | $

$ 75,927

Liquidation Preference | $

$ 80,000

Common Stock Issued Upon Conversion (1)

7,068,520

^[1]

[1]	⁽¹⁾ Adjusted to reflect the Exchange Ratio.

Redeemable Convertible Preferred Stock - Additional Information (Details) - shares

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Temporary Equity [Line Items]

Number of common stock shares issued upon conversion

^[1]

12,048,671

Redeemable Convertible Preferred Stock

Temporary Equity [Line Items]

Number of common stock shares issued upon conversion

12,048,671

Number of shares outstanding

97,166,921

40,094,850

31,074,017

[1]	⁽¹⁾ Adjusted to reflect the Exchange Ratio.

Redeemable Convertible Preferred Stock Tranche Liability - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Milestone closing liability	$ 6.2
Additional closing liability	$ 5.0
Change in fair value of redeemable convertible preferred stock tranche liability		$ 2.0

Redeemable Convertible Preferred Stock Tranche Liability - Schedule of Additional Closing Liability Assuming under The Option-Pricing Method (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares
December 31, 2018
Temporary Equity [Line Items]
Fair Value of Series A Preferred Stock	$ 10.48
Term	1 year 10 months 17 days
Interest rate	2.50%
Volatility	69.80%
July 25, 2019
Temporary Equity [Line Items]
Fair Value of Series A Preferred Stock	$ 7.18
Term	1 year 3 months 21 days
Interest rate	1.95%
Volatility	69.10%

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 15, 2020
Class Of Warrant Or Right [Line Items]
Number of warrants, Outstanding and exercisable to purchase preferred shares		1,781,387
Warrants outstanding and exercisable, Weighted average exercise price	$ 11.3177	$ 1.4034
Fair value of warrants outstanding			$ 2,900
Change in fair value of redeemable convertible preferred stock warrant liability	$ 897	$ (250)
Series B Warrants
Class Of Warrant Or Right [Line Items]
Fair value of warrants outstanding	1,900
Series B Warrants \| Maximum
Class Of Warrant Or Right [Line Items]
Change in fair value of redeemable convertible preferred stock warrant liability	$ 800	$ 200
Redeemable Convertible Preferred Stock \| Series B Warrants
Class Of Warrant Or Right [Line Items]
Number of warrants, Outstanding and exercisable to purchase preferred shares	1,781,387
Warrants outstanding and exercisable, Weighted average exercise price	$ 1.4034

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Redeemable Convertible Preferred Stock Warrant Liability Using Black-Scholes Option Pricing Model (Details)	Sep. 14, 2020 $ / shares	Apr. 28, 2020 $ / shares	Dec. 31, 2019 $ / shares
Share Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement price	$ 16.59	$ 11.61	$ 11.32
Term [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement term		7 years
Term [Member] \| Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement term	5 years 10 months 9 days		6 years 6 months 25 days
Term [Member] \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement term	6 years 7 months 13 days		6 years 8 months 26 days
Volatility [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input		91.17
Volatility [Member] \| Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input	81.1		82.1
Volatility [Member] \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input	82.1		93.3
Interest Rate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input		0.52
Interest Rate [Member] \| Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input	0.35		1.53
Interest Rate [Member] \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input	0.42		1.93
Dividend yield
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Measurement input	0	0	0

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Outstanding Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Liabilities And Stockholders Equity [Abstract]
Number of warrants, Outstanding and exercisable to purchase preferred shares as of December 31, 2019	1,781,387
Number of warrants, Issued	128,260
Number of warrants, Impact of converting to warrants for the purchase of common stock and adjusted for the Exchange Ratio and Reverse Stock Split	(1,683,456)
Number of warrants, Outstanding and exercisable to purchase common stock as of December 31, 2020	226,191
Warrant exercise price	$ 11.3177	$ 1.4034
Warrants outstanding and exercisable, Weighted average remaining contractual term	5 years 7 months 28 days	6 years 7 months 20 days

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Outstanding Warrants to Purchase Shares of Common Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Class Of Warrant Or Right [Line Items]
Number of Shares of Common Stock Issuable	226,191
Warrant exercise price	$ 11.3177	$ 1.4034
September 15, 2020 Warrant One
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	101,610
Warrant exercise price	$ 11.3177
Expiration Date	Jul. 25, 2026
September 15, 2020 Warrant Two
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	30,924
Warrant exercise price	$ 11.3177
Expiration Date	Aug. 21, 2026
September 15, 2020 Warrant Three
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	77,312
Warrant exercise price	$ 11.3177
Expiration Date	Sep. 19, 2026
September 15, 2020 Warrant Four
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	11,044
Warrant exercise price	$ 11.3177
Expiration Date	Sep. 26, 2026
September 15, 2020 Warrant Five
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	5,301
Warrant exercise price	$ 11.3177
Expiration Date	Apr. 28, 2027

Redeemable Convertible Preferred Stock Warrants and Common Stock Warrants - Schedule of Outstanding Warrants to Purchase Shares of Redeemable Convertible Preferred Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020
Class Of Warrant Or Right [Line Items]
Number of Shares of Common Stock Issuable		226,191
Warrant exercise price	$ 1.4034	$ 11.3177
Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Number of Shares of Common Stock Issuable	1,781,387
Series B Warrants \| Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Warrant exercise price		$ 1.4034
Series B Warrants \| July 25, 2019 Warrant \| Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Issuance Date	Jul. 25, 2019
Number of Shares of Common Stock Issuable	819,438
Warrant exercise price	$ 1.4034
Expiration Date	Jul. 25, 2026
Series B Warrants \| August 21, 2019 Warrant \| Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Issuance Date	Aug. 21, 2019
Number of Shares of Common Stock Issuable	249,394
Warrant exercise price	$ 1.4034
Expiration Date	Aug. 21, 2026
Series B Warrants \| September 19, 2019 Warrant \| Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 19, 2019
Number of Shares of Common Stock Issuable	623,486
Warrant exercise price	$ 1.4034
Expiration Date	Sep. 19, 2026
Series B Warrants \| September 26, 2019 Warrant \| Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Issuance Date	Sep. 26, 2019
Number of Shares of Common Stock Issuable	89,069
Warrant exercise price	$ 1.4034
Expiration Date	Sep. 26, 2026

Common Stock - Additional Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stockholders Equity Note [Abstract]
Common stock, shares authorized	150,000,000	140,200,938
Common stock shares issued, par value	$ 0.0001	$ 0.0001
Common stock dividends declared \| $ / shares	$ 0	$ 0

Common Stock - Schedule of Number of Shares of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	5,672,757	14,834,849
Options Issued and Outstanding
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	3,706,945	1,860,646
Stock Options Available for Future Grant
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	1,739,621	653,136
Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance		12,048,671
Conversion of Additional Authorized and Unissued Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance		51,506
Redeemable Convertible Preferred Stock Warrant Liability
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance		220,890
Common Stock Warrants
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	226,191

At-The-Market (ATM) Offering - Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 01, 2020	Dec. 31, 2020
Class Of Stock [Line Items]
Agreement terminated		2021-02
At The Market Offering [Member]
Class Of Stock [Line Items]
Agreement terminated	2021-02
At The Market Offering [Member] \| Sales Agreement [Member] \| Maximum
Class Of Stock [Line Items]
Maximum aggregate value of common stock available for offering at-the-market price	$ 50.0

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands						1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2021	Sep. 17, 2020	Jul. 14, 2020	Jan. 01, 2020	Jan. 01, 2019	May 07, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock available for grant								1,739,621	653,136	818,002	38,055
Weighted average exercise price								$ 2.18	$ 2.12	$ 1.92
Expense related to options granted							$ 600	$ 5,263	$ 1,175	$ 2,479
Agreement terminated								2021-02
Option granted			22,574
Option vested percentage			75.00%
Weighted average exercise price								$ 15.14	$ 5.39	$ 2.26
Aggregate intrinsic value of options exercised								$ 2,500	$ 100	$ 400
Unrecognized stock-based compensation expense								0
Options Issued and Outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of options vested								$ 2,400	$ 900	$ 1,800
Weighted-average grant date fair value of options granted								$ 9.96	$ 2.98	$ 3.95
Unrecognized compensation expense								$ 21,600
Unrecognized compensation expense, estimated weighted-average period for recognition								3 years 7 months 6 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of options vested								$ 0	$ 100	$ 600
Forecast
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to options granted						$ 100
2018 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of additional shares added on outstanding shares	4.00%							4.00%
2018 Stock Incentive Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares reserved for issuance	787,089
2017 and 2018 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock available for grant								1,456,492
Number of shares reserved for issuance								1,317,892
Weighted average exercise price								$ 15.62
2014 Stock Incentive Plan Member
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance								69,014
Weighted average exercise price								$ 1.27
2015 Stock Incentive Plan Member
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance								1,957,536
Weighted average exercise price								$ 7.43
2014 and 2015 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock available for grant								283,129
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of additional shares added on outstanding shares										1.00%
Number of additional shares reserved for issuance				131,432	79,369
Number of shares reserved for issuance								39,290
Number of shares available for sale under employee stock purchase plan								0
2018 Employee Stock Purchase Plan \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares reserved for issuance								77,703
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance								362,503
Weighted average exercise price								$ 14.33
Merger
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to options granted								$ 100
Option granted		16,931
Weighted average exercise price		$ 16.11
Merger \| Share-based Payment Arrangement, Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights								one-third of the shares vesting on the first anniversary
Merger \| Share-based Payment Arrangement, Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights								one-third of the shares vesting in 12 equal monthly installments following such first anniversary
Merger \| Share-based Payment Arrangement, Tranche Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights								one-third of the shares vesting in accordance with the terms of his Transition Agreement which consisted of 12 months’ of accelerated vesting of his unvested options to purchase the Company’s common stock upon completion of the Merger.

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation [Abstract]
Number of Shares Available for Grant, Beginning balance	653,136	818,002	38,055
Number of Shares Available for Grant, Options authorized		814,184	837,000
Number of Shares Available for Grant, Assumed as part of the Merger	2,707,144
Number of Shares Available for Grant, Options granted	(1,914,142)	(1,124,430)	(210,452)
Number of Shares Available for Grant, Options forfeited or cancelled	293,483	145,380	153,399
Number of Shares Available for Grant, Ending balance	1,739,621	653,136	818,002	38,055
Number of Shares Underlying Outstanding Options, Beginning balance	1,860,646	896,539	963,435
Number of Shares Underlying Outstanding Options, Assumed as part of the Merger	81,370
Number of Shares Underlying Outstanding Options, Options granted	2,276,645	1,124,430	210,452
Number of Shares Underlying Outstanding Options, Options exercised	(210,752)	(14,791)	(123,949)
Number of Shares Underlying Outstanding Options, Options forfeited or cancelled	(300,964)	(145,532)	(153,399)
Number of Shares Underlying Outstanding Options, Ending balance	3,706,945	1,860,646	896,539	963,435
Number of Shares Underlying Outstanding Options, Shares exercisable	1,219,904
Number of Shares Underlying Outstanding Options, Vested and expected to vest	3,706,945
Weighted-Average Exercise Price, Outstanding beginning	$ 4.05	$ 2.04	$ 2.02
Weighted-Average Exercise Price, Assumed as part the Merger	8.39
Weighted-Average Exercise Price, Options granted	15.14	5.39	2.26
Weighted-Average Exercise Price, Options exercised	2.18	2.12	1.92
Weighted-Average Exercise Price, Options forfeited or cancelled	6.04	2.17	2.25
Weighted-Average Exercise Price, Outstanding ending	10.90	$ 4.05	$ 2.04	$ 2.02
Weighted-Average Exercise Price, Shares exercisable	4.64
Weighted-Average Exercise Price, Vested and expected to vest	$ 10.90
Weighted-Average Remaining Contract Term, Outstanding	7 years 11 months 23 days	8 years 6 months 10 days	8 years 6 months 25 days	9 years 3 months 7 days
Weighted-Average Remaining Contract Term, Shares exercisable	5 years 1 month 9 days
Weighted-Average Remaining Contract Term, Vested and expected to vest	7 years 11 months 23 days
Aggregate Intrinsic Value, Outstanding	$ 15,126	$ 5,812	$ 2,436	$ 4,977
Aggregate Intrinsic Value, Shares exercisable	11,563
Aggregate Intrinsic Value, Vested and expected to vest	$ 15,126

Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Stock - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Outstanding, Beginning, Unvested shares	31,183	165,699
Number of Shares Outstanding, Vested	(31,183)	(134,516)
Number of Shares Outstanding, Ending, Unvested shares		31,183
Weighted Average Grant Date Fair Value, Beginning, Unvested	$ 4.19	$ 4.19
Weighted Average Grant Date Fair Value, Vested	$ 4.19	4.19
Weighted Average Grant Date Fair Value, Ending, Unvested		$ 4.19

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 600	$ 5,263	$ 1,175	$ 2,479
Research And Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense		1,674	274	285
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense		$ 3,589	$ 901	$ 2,194

Stock-Based Compensation - Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model (Details) - Options Issued and Outstanding	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	72.60%	71.50%	73.30%
Expected volatility, maximum	96.30%	86.50%	74.00%
Risk-free interest rate, minimum	0.10%	1.60%	2.70%
Risk-free interest rate, maximum	1.70%	2.50%	2.80%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	1 year	5 years 1 month 24 days	6 years 7 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days

Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (36,678)	$ (28,138)	$ (9,299)
Weighted-average shares outstanding	7,319,977	2,148,317	2,049,680
Less: weighted-average unvested restricted shares and shares subject to repurchase		(9,344)	(102,704)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted	7,319,977	2,138,973	1,946,976
Net loss per share attributable to common stockholders, basic and diluted	$ (5.01)	$ (13.15)	$ (4.78)

- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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+ Details

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,933,136	14,130,207	6,670,510
Options To Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,706,945	1,860,646	896,539
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	226,191
Unvested Early Exercised Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			27,709
Unvested Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			31,183
Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		12,048,671	4,971,762
Redeemable Convertible Preferred Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		220,890
Redeemable Convertible Preferred Stock Tranche Liability And TRDF Obligation
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share			743,317

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes Disclosure [Line Items]
Federal statutory income tax rate, percent	21.00%	21.00%	21.00%
Income tax expense (benefit)	$ (2,815,000)	$ 19,000	$ (589,000)
Increase in valuation allowance	37,900	8,100
Net operating loss carryforwards	$ 51,796,000	12,510,000	5,233,000
Ownership change plan description	In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period
Unrecognized tax benefits	$ 797,000	$ 797,000	$ 797,000	$ 866,000
Intellectual Property
Income Taxes Disclosure [Line Items]
Unrecognized tax benefits	800,000
Maximum \| California Research And Development
Income Taxes Disclosure [Line Items]
Tax credit carryforward, amount	100,000
Domestic Tax Authority
Income Taxes Disclosure [Line Items]
Operating loss carryforwards	$ 211,400
Operating loss carryforwards, expiration date	Dec. 31, 2037
Net operating loss carryforwards	$ 7,600,000
Operating Loss Carryforwards Indefinitely	203,800,000
State
Income Taxes Disclosure [Line Items]
Operating loss carryforwards	$ 82,200
Operating loss carryforwards, expiration date	Dec. 31, 2035
Foreign Tax Authority
Income Taxes Disclosure [Line Items]
Operating loss carryforwards	$ 16,700
C O V I D19
Income Taxes Disclosure [Line Items]
Operating loss carryback duration under CARES Act	5 years
Percentage of net operating loss carryforwards	80.00%
Income tax expense (benefit)	$ (2,800,000)

Income Taxes - Schedule of Components of Provision for (benefit from) Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ (2,678)
State	105	$ 1	$ (589)
Foreign		18
Total current	(2,573)	19	(589)
Deferred:
Federal	(242)
Total deferred	(242)
Provision for (benefit from) income taxes	$ (2,815)	$ 19	$ (589)

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Schedule of (Provision for) Benefit from Income Taxes Differs from Federal Statutory Rate to the Loss Before Taxes (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory income tax rate, percent	21.00%	21.00%	21.00%
Other permanent differences	(0.50%)	(0.10%)	(0.10%)
State income taxes	6.10%	5.10%	3.80%
Foreign rate differential	0.00%	0.00%	0.20%
Foreign loss	0.00%	(0.20%)	(2.20%)
Federal benefit from NOL carryback	6.70%	0.00%	0.00%
Change in valuation allowance	(25.80%)	(27.70%)	(20.00%)
Change in fair value of redeemable convertible preferred stock tranche liability and TRDF liability	(0.50%)	1.70%	8.70%
Stock-based compensation	0.10%	0.10%	(6.00%)
Benefit from (provision for) income taxes	7.10%	(0.10%)	5.40%

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets:
Net operating loss carryforwards	$ 51,796	$ 12,510	$ 5,233
Operating lease right-of-use asset liability	5,686
Deferred revenue	2,857	5,719	5,125
Stock-based compensation	1,750	509	274
Intangible assets	1,195	609	804
Accruals and reserves	654	446	431
Research and development credit carryforwards	26	26	26
Gross deferred tax assets	63,964	19,819	11,893
Less: Valuation allowance	(57,715)	(19,815)	(11,739)
Deferred tax assets, net of valuation allowance	6,249	4	154
Deferred tax liabilities:
Fixed assets		$ (4)	$ (154)
Basis Difference IPR&D	(313)
Operating lease right-of-use asset	(6,061)
Net deferred tax liabilities	$ (125)

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Income Tax Disclosure [Abstract]
Balance at the beginning of the year	$ 866
Adjustment based on tax positions related to prior years	(69)
Balance at the end of the year	$ 797

Defined Contribution Plan - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Defined Contribution Plan [Abstract]
Defined contribution plan for employees	$ 0

Related Party Transactions - Additional Information (Details) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Common stock, shares issued

19,677,249

2,155,578

Redeemable convertible preferred stock

Convertible Preferred Stock converted into common stock upon merger

^[1]

12,048,671

Revenue—related party

$ 17,903

$ 995

$ 8,181

Regeneron Pharmaceuticals, Inc.

Common stock, shares issued

883,568

Convertible Preferred Stock converted into common stock upon merger

883,568

Revenue—related party

$ 17,900

$ 1,000

$ 8,200

Accounts receivable

Deferred Revenue

$ 14,000

Regeneron Pharmaceuticals, Inc. | Series B Convertible Preferred Stock [ Member ]

Redeemable convertible preferred stock

7,125,552

[1]	⁽¹⁾ Adjusted to reflect the Exchange Ratio.

Subsequent Events - Additional Information (Details) - Subsequent Event - Initial Public Offering $ / shares in Units, $ in Millions	1 Months Ended
	Feb. 28, 2021 USD ($) $ / shares shares
Subsequent Event [Line Items]
Number of common stock shares sold \| shares	10,575,513
Issuance price per shares \| $ / shares	$ 13.00
Underwriting discounts and commissions and other offering expenses \| $	$ 137.5
Net proceeds received from offering \| $	$ 15.0
Maximum
Subsequent Event [Line Items]
Option to purchase of common stock at public offering price \| shares	1,344,743