Adicet Bio (ACET) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 09, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Entity Registrant Name	Adicet Bio, Inc.
Entity Central Index Key	0001720580
Trading Symbol	ACET
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity File Number	001-38359
Entity Tax Identification Number	81-3305277
Entity Address, Address Line One	200 Clarendon Street
Entity Address, Address Line Two	Floor 6
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02116
City Area Code	650
Local Phone Number	503-9095
Entity Common Stock, Shares Outstanding		31,955,450
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE

Consolidated Balance Sheets (un

Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 192,226	$ 84,330
Short-term marketable debt securities	0	10,284
Prepaid expenses and other current assets	6,799	5,722
Total current assets	199,025	100,336
Property and equipment, net	11,395	2,790
Operating lease right-of-use asset	20,865	23,066
Goodwill	19,462	20,089
In-process research and development		1,190
Restricted cash	4,527	4,527
Other non-current assets	1,921	1,837
Total assets	257,195	153,835
Current liabilities:
Accounts payable	4,631	1,552
Contract liabilities — related party, current	10,088	13,980
Accrued and other current liabilities	4,601	5,732
Operating lease liability	712	1,215
Total current liabilities	20,032	22,479
Operating lease liability, net of current portion	19,823	20,424
Contingent consideration liability		980
Deferred tax liability		125
Other Liabilities, Noncurrent	116
Total liabilities	39,971	44,008
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2021 and December 31, 2020, respectively; none issued and outstanding as of September 30, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value, 150,000,000 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 31,955,050 and 19,677,249 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	3	2
Additional paid-in capital	369,732	216,126
Accumulated deficit	(152,511)	(106,325)
Accumulated other comprehensive income		24
Total stockholders’ equity	217,224	109,827
Total liabilities and stockholders’ equity	$ 257,195	$ 153,835

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) (unaudited) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	31,955,050	19,677,249
Common stock, shares outstanding	31,955,050	19,677,249
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

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue—related party	$ 3,429	$ 3,028	$ 4,262	$ 12,493
Operating expenses:
Research and development	11,926	8,942	34,285	24,651
General and administrative	5,213	7,741	15,868	17,684
Total operating expenses	17,139	16,683	50,153	42,335
Loss from operations	(13,710)	(13,655)	(45,891)	(29,842)
Interest income	4	153	54	704
Interest expense	(50)	(50)	(151)	(84)
Other income (expense), net	(246)	(1,224)	(312)	(1,174)
Loss before income tax expense (benefit)	(14,002)	(14,776)	(46,300)	(30,396)
Income tax expense (benefit)	11	3	(114)	(2,676)
Net loss	$ (14,013)	$ (14,779)	$ (46,186)	$ (27,720)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.44)	$ (2.84)	$ (1.54)	$ (8.69)
Weighted-average common shares used in computing net loss per share attributable to common stockholders, basic and diluted	31,876,016	5,208,887	29,954,616	3,190,557
Other comprehensive income (loss):
Unrealized (loss) gain on marketable debt securities, net of tax	$ 0	$ (114)	$ (24)	$ 60
Total other comprehensive (loss) income	0	(114)	(24)	60
Comprehensive loss	$ (14,013)	$ (14,893)	$ (46,210)	$ (27,660)

Consolidated Statement of Redee

Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Pain In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2019	$ (60,366,000)			$ 9,258,000	$ (69,647,000)	$ 23,000
Balance, shares at Dec. 31, 2019			2,155,578
Balance, temporary equity at Dec. 31, 2019		$ 114,083,000
Balance, temporary equity, shares at Dec. 31, 2019		12,048,698
Issuance of common stock upon exercise of stock options	42,000			42,000
Issuance of common stock upon exercise of stock options, shares			19,947
Stock-based compensation expense	299,000			299,000
Net loss	(4,486,000)				(4,486,000)
Other comprehensive income (loss)	(15,000)					(15,000)
Balance at Mar. 31, 2020	(64,526,000)			9,599,000	(74,133,000)	8,000
Balance, shares at Mar. 31, 2020			2,175,525
Balance, temporary equity at Mar. 31, 2020		$ 114,083,000
Balance, temporary equity, shares at Mar. 31, 2020		12,048,698
Balance at Dec. 31, 2019	(60,366,000)			9,258,000	(69,647,000)	23,000
Balance, shares at Dec. 31, 2019			2,155,578
Balance, temporary equity at Dec. 31, 2019		$ 114,083,000
Balance, temporary equity, shares at Dec. 31, 2019		12,048,698
Net loss	(27,720,000)
Conversion of redeemable convertible preferred stock warrants to common stock warrants	2,922,000
Balance at Sep. 30, 2020	116,930,000		$ 1,000	214,213,000	(97,367,000)	83,000
Balance, shares at Sep. 30, 2020			19,589,637
Balance, temporary equity at Sep. 30, 2020		$ 0
Balance, temporary equity, shares at Sep. 30, 2020		0
Balance at Mar. 31, 2020	(64,526,000)			9,599,000	(74,133,000)	8,000
Balance, shares at Mar. 31, 2020			2,175,525
Balance, temporary equity at Mar. 31, 2020		$ 114,083,000
Balance, temporary equity, shares at Mar. 31, 2020		12,048,698
Issuance of common stock upon exercise of stock options	7,000			7,000
Issuance of common stock upon exercise of stock options, shares			3,101
Stock-based compensation expense	351,000			351,000
Net loss	(8,455,000)				(8,455,000)
Other comprehensive income (loss)	189,000					189,000
Balance at Jun. 30, 2020	(72,434,000)			9,957,000	(82,588,000)	197,000
Balance, shares at Jun. 30, 2020			2,178,626
Balance, temporary equity at Jun. 30, 2020		$ 114,083,000
Balance, temporary equity, shares at Jun. 30, 2020		12,048,698
Issuance of common stock upon exercise of stock options	144,000			144,000
Issuance of common stock upon exercise of stock options, shares			100,092
Stock-based compensation expense	2,966,000			2,966,000
Net loss	(14,779,000)				(14,779,000)
Other comprehensive income (loss)	(114,000)					(114,000)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger		$ (114,083,000)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger, shares		(12,048,698)
Conversion of shares of redeemable convertible preferred stock to shares of common stock in connection with the Merger	114,083,000		$ 1,000	114,082,000
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	84,142,000			84,142,000
Exchange of common stock in connection with the Merger, shares			5,262,248
Conversion of redeemable convertible preferred stock warrants to common stock warrants	2,922,000			2,922,000
Balance at Sep. 30, 2020	116,930,000		$ 1,000	214,213,000	(97,367,000)	83,000
Balance, shares at Sep. 30, 2020			19,589,637
Balance, temporary equity at Sep. 30, 2020		$ 0
Balance, temporary equity, shares at Sep. 30, 2020		0
Balance at Dec. 31, 2020	109,827,000		$ 2,000	216,126,000	(106,325,000)	24,000
Balance, shares at Dec. 31, 2020			19,677,249
Issuance of common stock upon exercise of stock options	976,000			976,000
Issuance of common stock upon exercise of stock options, shares			393,991
Issuance of common stock related to financing	143,754,000		$ 1,000	143,753,000
Issuance of common stock related to financing, shares			11,729,353
Exercise of warrant, shares			1,806
Stock-based compensation expense	3,043,000			3,043,000
Net loss	(21,319,000)				(21,319,000)
Other comprehensive income (loss)	(22)					(22)
Balance at Mar. 31, 2021	236,259,000		$ 3,000	363,898,000	(127,644,000)	2,000
Balance, shares at Mar. 31, 2021			31,802,399
Balance at Dec. 31, 2020	$ 109,827,000		$ 2,000	216,126,000	(106,325,000)	24,000
Balance, shares at Dec. 31, 2020			19,677,249
Issuance of common stock upon exercise of stock options, shares	546,642
Net loss	$ (46,186,000)
Conversion of redeemable convertible preferred stock warrants to common stock warrants
Balance at Sep. 30, 2021	217,224,000		$ 3,000	369,732,000	(152,511,000)
Balance, shares at Sep. 30, 2021			31,955,050
Balance at Mar. 31, 2021	236,259,000		$ 3,000	363,898,000	(127,644,000)	2,000
Balance, shares at Mar. 31, 2021			31,802,399
Issuance of common stock upon exercise of stock options	279,000			279,000
Issuance of common stock upon exercise of stock options, shares			39,603
Stock-based compensation expense	2,659,000			2,659,000
Net loss	(10,854,000)				(10,854,000)
Other comprehensive income (loss)	(2,000)					$ (2,000)
Balance at Jun. 30, 2021	228,341,000		$ 3,000	366,836,000	(138,498,000)
Balance, shares at Jun. 30, 2021			31,842,002
Issuance of common stock upon exercise of stock options	367,000			367,000
Issuance of common stock upon exercise of stock options, shares			113,048
Stock-based compensation expense	2,529,000			2,529,000
Net loss	(14,013,000)				(14,013,000)
Balance at Sep. 30, 2021	$ 217,224,000		$ 3,000	$ 369,732,000	$ (152,511,000)
Balance, shares at Sep. 30, 2021			31,955,050

Condensed Consolidated Statemen

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (46,186)	$ (27,720)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,173	911
Loss on disposal of property and equipment	190
Noncash lease expense	2,201
Stock-based compensation expense	8,231	3,616
Net amortization of premiums and accretion discounts on investments	10	(4)
Change in fair value of redeemable convertible preferred stock warrant liability		897
Amortization of deferred debt issuance costs	151	84
Impairment of in-process research and development	1,190
Remeasurement of contingent consideration liability	(980)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(462)	(5,000)
Other non-current assets	(81)	(1,560)
Accounts payable	3,079	1,442
Contract liabilities — related party	(3,892)	(2,493)
Deferred rent		(119)
Operating lease liabilities	(1,104)	0
Accrued and other current liabilities	(1,244)	1,738
Other non-current liabilities	116	1
Net cash used in operating activities	(37,608)	(28,207)
Cash flows from investing activities
Cash and restricted cash acquired in connection with the Merger		64,114
Proceeds from sales of marketable debt securities	7,500
Purchases of marketable debt securities		(5,700)
Proceeds from maturities of marketable debt securities	2,750	44,985
Purchases of property and equipment	(9,968)	(630)
Net cash provided by investing activities	282	102,769
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	143,754
Proceeds from exercise of stock options	1,622	193
Deferred issuance costs	(154)	(157)
Net cash provided by (used in) financing activities	145,222	36
Net change in cash, cash equivalents and restricted cash	107,896	74,598
Cash, cash equivalents and restricted cash, at the beginning of period	88,857	14,889
Cash, cash equivalents and restricted cash, at the end of period	196,753	89,487
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	192,226	84,960
Restricted cash	4,527	4,527
Cash, cash equivalents and restricted cash, at the end of period	196,753	89,487
Supplemental cash flow information
Cash received from tax refund	214	3
Supplemental disclosures of noncash investing and financing activities
Purchases of property and equipment included in accounts payable	2,585	76
Conversion of redeemable convertible preferred stock into common stock		144,083
Conversion of redeemable convertible preferred stock warrants to common stock warrants		2,922
Fair value of net assets acquired in Merger		84,142
Issuance of redeemable convertible preferred stock warrants in connection with the Loan Agreement		144
Adjustment to goodwill	$ 413

Organization and Nature of Busi

Organization and Nature of Business	9 Months Ended
	Sep. 30, 2021
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 and also natural killer cell-based 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 (the Merger Agreement). 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 (as defined below) 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, the Company effected a reverse stock split of the Company’s 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 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) and the former equity holders of Former Adicet held approximately 75 % of the outstanding shares of Company’s common stock on a fully-diluted basis and the former equity holders of resTORbio held 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 details of the Merger. Liquidity The Company has incurred significant net operating losses and negative cash flows from operations and has an accumulated deficit of $ 152.5 million as of September 30, 2021. The Company has historically financed its operations primarily through a collaboration and licensing arrangement, through 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. In February 2021, the Company completed an underwritten public offering of 10,575,513 shares of its 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. 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 interim 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 Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The unaudited interim 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). Significant Accounting Policies The Company’s significant accounting policies are described in Note 2, Summary of Significant Accounting Policies, to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. There have been no material changes to the significant accounting policies during the nine months ended September 30, 2021. Unaudited Interim Financial Information The consolidated balance sheet as of December 31, 2020 was derived from the Company’s audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020, have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (SEC), for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2020. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2021 and consolidated results of operations for the three and nine months ended September 30, 2021 and 2020 and consolidated cash flows for the nine months ended September 30, 2021 and 2020 have been made. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021. 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, which represents 100 % of the Company’s total revenue for the three and nine months ended September 30, 2021 and 2020 (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 investigational new drug (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. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB 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 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 adopted ASU 2019-12 beginning January 1, 2021 on a prospective basis. The adoption of this standard did not have a material impact on its financial statements and related disclosures. In November 2018, the FASB issued Accounting Standards Update (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 adopted ASU 2018-18 beginning January 1, 2021 on a prospective basis. The adoption of this standard did not have a material impact on its 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 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 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

Business Combination	9 Months Ended
	Sep. 30, 2021
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. 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. resTORbio’s stockholders will continue 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 close of the Merger. 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. RTB101 relates to an exclusive license agreement resTORbio entered with Novartis International Pharmaceutical Ltd. (Novartis) (see Note 11). 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 5,207,695 Multiplied by the fair value per share of resTORbio common stock (b) $ 16.59 Acquisition date fair value of resTORbio 86,396 Estimated fair value of modified stock options and restricted stock units attributable to pre-combination services (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 a. 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 of resTORbio common stock outstanding as of September 15, 2020. b. The purchase price is based on the closing price of resTORbio common stock on September 14, 2020. c. 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 will receive 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. The following summarizes the allocation of the purchase price to the net tangible and intangible assets acquired (in thousands): As of Measurement Final Purchase Net assets acquired: Cash and cash equivalents $ 63,869 $ — $ 63,869 Prepaid expenses and other current assets 3,059 615 3,674 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 ( 2,365 ) 12 ( 2,353 ) Other liabilities — — — Deferred tax liability ( 367 ) — ( 367 ) Goodwill 20,089 ( 627 ) 19,462 Purchase price $ 87,022 $ — $ 87,022 The goodwill of $ 19.5 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 in-process research and development (IPR&D) is 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 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. On July 27, 2021, the Company sent Novartis a termination notice. Termination will automatically take effect as of 60 days from the date of delivery of the termination notice to Novartis, but in no event later than October 1, 2021 without any further notice or action required of either Novartis or the Company. Upon the review of impairment of IPR&D during the second quarter of 2021, the Company concluded that the IPR&D was fully impaired and recorded an impairment charge within research and development expenses in the consolidated statement of operations and comprehensive loss for the remaining balance of the IPR&D intangible asset as of June 30, 2021. The Company recognized IPR&D impairment charges of $ 2.3 million, $ 0.5 million, and $ 0.7 million for the quarters ended as of December 31, 2020, March 31, 2021, and June 30, 2021. 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. The following tables present changes in the Company’s IPR&D and CVR since the Merger (in thousands): Acquisition Date Change in As of Change in As of In-process research and development $ 3,490 $ ( 2,300 ) $ 1,190 $ ( 1,190 ) $ — Contingent Value Rights $ 2,880 $ ( 1,900 ) $ 980 $ ( 980 ) $ —

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
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): September 30, 2021 Level 1 Level 2 Level 3 Total Assets: Money market funds (1) $ 174,945 $ — $ — $ 174,945 Total fair value of assets $ 174,945 $ — $ — $ 174,945 December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds (1) $ 63,817 $ — $ — $ 63,817 Marketable debt securities (2) 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 (1) Included in cash and cash equivalents in the consolidated balance sheets. (2) Included in short-term marketable debt securities 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. 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 June 2021, the Company determined the possibility of any commercialization events for RTB101 was close to zero (see Note 3). As a result, the fair value of the CVR liability was adjusted to zero . On October 27, 2021, the Company provided a Termination Notice under the CVR Agreement to the joint rights agents to terminate its obligations under the CVR Agreement, effective immediately.

Marketable Debt Securities

Marketable Debt Securities	9 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Debt Securities	5. Marketable Debt Securities The Company had no marketable debt securities as of September 30, 2021 . The following table summarizes the Company’s marketable debt securities as of December 31, 2020 (in thousands): December 31, 2020 Amortized Unrealized Unrealized Fair 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 The following table summarizes the classification of the Company’s marketable debt securities in the consolidated balance sheets (in thousands): September 30, December 31, 2021 2020 Short-term marketable debt securities $ — $ 10,284 Long-term marketable debt securities — — Total $ — $ 10,284

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2021
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): September 30, December 31, Prepaid maintenance and other $ 655 $ 761 Prepayments to CRO's 1,643 420 Prepayments to CMO's 1,340 135 Prepaid insurance 449 1,443 Tax receivable 2,711 2,711 Interest receivable — 23 Other current assets 1 229 Total prepaid expenses and other current assets $ 6,799 $ 5,722

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	. Property and Equipment, net Property and equipment, net consisted of the following (in thousands): Useful life September 30, December 31, Laboratory equipment 3 $ 5,502 $ 4,350 Leasehold improvements Lesser of useful life or lease term 1,614 1,427 Furniture and fixtures 3 303 524 Construction in progress — 9,402 1,090 Computer equipment 3 217 93 Software 3 320 170 17,358 7,654 Less: Accumulated depreciation and amortization ( 5,963 ) ( 4,864 ) Property and equipment, net $ 11,395 $ 2,790 Depreciation and amortization expense was $ 0.4 million and $ 0.3 million for the three months ended September 30, 2021 and 2020, respectively. Depreciation and amortization expense was $ 1.2 million and $ 0.9 million for the nine months ended September 30, 2021 and 2020 , respectively. Construction in progress has increased by $ 6.8 million and $ 9.4 million in the three and nine months ended September 30, 2021, due to building construction related to the Company's leased space in Redwood City. Construction in process will continue to increase through the first half of 2022, upon completion of the construction.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
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): September 30, December 31, Accrued compensation $ 3,316 $ 3,833 Accrued CRO costs 490 955 Accrued CMO costs 165 244 Accrued research and development expenses 294 65 Accrued professional services 301 363 Accrued other liabilities 35 272 Total accrued and other liabilities $ 4,601 $ 5,732

Term Loan

Term Loan	9 Months Ended
	Sep. 30, 2021
Term Loan [Abstract]
Term Loan	9. Term Loan The Company has a Loan and Security Agreement dated as of April 28, 2020 with Pacific Western Bank (PacWest or the Bank) for an initial term loan limit 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 %. As of September 30, 2021 , no amounts had been drawn under the Loan Agreement and the deferred debt issuance costs were $ 0.1 million and are included in other noncurrent assets on the Company’s consolidated balance sheets. On October 21, 2021, the Company entered into a Fourth Amendment of the Loan Agreement (the Loan Amendment) under which the Bank will provide one or more term loans (the Term Loans), as well as certain non-formula ancillary services, which shall not exceed $ 5.5 million in the aggregate. The aggregate sum of the outstanding Term Loans and non-formula ancillary services shall at no time exceed $ 15.0 million, with each term loan to be in an amount of not less than $1.0 million. Pursuant to the Loan Amendment, the interest rate for the Term Loans shall be set at an annual rate equal to the greater of (i) 0.25% above the Prime Rate then in effect and (ii) 4.25% . Other than as disclosed in this Quarterly Report on Form 10-Q, there have been no material changes in the Loan Agreement from those disclosed in Note 9 to consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2020.

Regeneron License and Collabora

Regeneron License and Collaboration Arrangement	9 Months Ended
	Sep. 30, 2021
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, 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). Financial Terms . The Company received a non-refundable upfront payment of $ 25.0 million from Regeneron upon execution of the Regeneron Agreement and an aggregate of $ 20.0 million of additional payments for research funding from Regeneron as of September 30, 2021 . 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. 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 recorded a $ 4.0 million revenue reduction in the first quarter of 2021 as a result of an adjustment to cumulative revenue recognized due to a change in overall estimated costs primarily due to an extension of time to fulfill the combined performance obligation. During the three and nine months ended September 30, 2021 , the Company recorded $ 3.4 million and $ 4.3 million in revenue, respectively. 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. For revenue recognition purposes, the five-year term has been extended to the first quarter of 2022 due to additional time required to complete the performance obligations under the Regeneron Agreement. 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 tables present changes in the Company’s contract liabilities for the nine months ended September 30, 2021 and 2020 (in thousands): Nine Months Ended September 30, 2021 Balance at Additions Additions (Deductions) Balance at Contract liability $ 13,980 $ 370 $ ( 4,262 ) $ 10,088 Nine Months Ended September 30, 2020 Balance at Additions Additions (Deductions) Balance at Contract asset $ — $ 10,000 $ ( 10,000 ) $ — Contract liability $ 21,883 $ 10,000 $ ( 12,493 ) $ 19,390 (1) Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period. As of September 30, 2021 , contract liabilities related to the Regeneron Agreement of $ 10.1 million 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 $ 35.3 million of cumulative license and collaboration revenue recognized from the inception of the Regeneron Agreement as of September 30, 2021 and will be recognized as the combined performance obligation is satisfied. As of September 30, 2020, contract liabilities related to the Regeneron Agreement of $ 19.4 million 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 $ 25.6 million of cumulative license and collaboration revenue recognized from the inception of the Regeneron Agreement as of September 30, 2020. As of September 30, 2020, there were no contract assets which would be 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.

License Funding and Other Agree

License Funding and Other Agreements Related to the CVR	9 Months Ended
	Sep. 30, 2021
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 slow enrollment and as a consequence lowered the probability of finding a partner due to the delay in time to commercialization of RTB101. In February 2021, management terminated the National Institute on Aging study of RTB101 for COVID-19 post-exposure prophylaxis in adults age 65 years and older due to poor enrollment . In March 2021, management estimated that the probability of finding a partner should be further reduced. As a result, the fair value of the CVR liability was decreased by $ 0.4 million to $ 0.6 million. In June 2021, the Company determined the possibility of any commercialization events for RTB101 was close to zero (see Note 3). As a result, the fair value of the CVR liability was adjusted to zero . On October 27, 2021, the Company provided a Termination Notice under the CVR Agreement to the joint rights agent to terminate its obligations under the CVR Agreement, effective immediately. Novartis License Agreement On March 23, 2017, resTORbio entered into an exclusive license agreement with 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. Novartis may terminate the portion of the agreement related to everolimus if resTORbio fails to use commercially reasonable efforts to research, develop and commercialize a product utilizing everolimus for a period of three years. Novartis may terminate the license agreement upon resTORbio’s bankruptcy, insolvency, dissolution or winding up. 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. On July 27, 2021, the Company sent Novartis a termination notice. Termination automatically took effect on September 25, 2021, 60 days from the date of delivery of the termination notice to Novartis, without any further notice or action required of either Novartis or the Company. National Institute of Health In May 2019, the Company 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. The Company is entitled to use the award solely to conduct the research. The Company 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, the Company 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, the Company 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 the Company in advance of funding by the NIH are recorded in the consolidated balance sheets as other current assets. For the three months ended September 30, 2021 , no qualifying expenses have been incurred and $ 36,000 have been funded by the NIH. For the nine months ended September 30, 2021 , $ 0.3 million qualifying expenses have been incurred and $ 0.5 million have been funded by the NIH. The difference in the amount incurred by the Company and funded by the NIH was due to timing of requesting reimbursements from the NIH. On a cumulative basis as of September 30, 2021 , $ 1.3 million has been incurred and $ 1.3 million has been funded by the NIH.

Commitments and Contingences

Commitments and Contingences	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingences	12. Commitments and Contingencies Operating Leases The Company leases office and laboratory space in Menlo Park, CA, Redwood City, CA, and Boston, MA. As of September 30, 2021 , except as described below, there have been no material changes in lease obligation from those disclosed in Note 12 to consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. On June 25, 2021, the Company entered into an amendment to the Menlo Park lease to extend the term of the lease from March 31, 2022 to June 30, 2022 and replace the previously leased premises (known as 173 and 175-177 Jefferson Drive) with another nearby premises (known as 235 Constitution Drive). The lease commenced on July 15, 2021 and expires on June 30, 2022 . In connection with these changes, the Company will incur monthly rent payments ranging from $ 87,286 to $ 89,904 , increasing over the remaining term of the lease. Given the lease is short-term in nature, the Company is using the practical expedient for the lease and has not recorded a right of use asset or lease liability. Therefore, the Company will recognize rent expense on a straight-line basis over the lease term. On July 19, 2021, the Company entered into a Sublease (the Sublease Agreement) with RFS OPCO LLC (Sublessee), whereby the Company agreed to sublease to Sublessee all of the 9,501 rentable square feet of office space in Boston, MA, currently leased by the Company pursuant to the Company’s lease with 500 Boylston & 222 Berkeley Owner (DE) LLC, dated January 8, 2018, as amended (the Master Lease). The term of the sublease started on September 1, 2021 and ends on July 30, 2026. The aggregate base rent due to the Company under the Sublease is approximately $ 3.5 million starting October 1, 2021. Upon execution of the Sublease Agreement, the Company received a cash security deposit of $ 0.1 million from the Subleasee which is recorded as other non-current liabilities in the consolidated balance sheets. The expected sublease income as of September 30, 2021 is as follows (in thousands): 2021 (remaining three months) $ 174 2022 697 2023 711 2024 725 2025 740 2026 and thereafter 439 Total $ 3,486 Further, the Company remains liable for the remaining lease payments under the Master Lease, totaling $ 3.1 million, which is included in future minimum lease payments table below. On July 30, 2021, the Company entered a short-term lease agreement with Boston Properties, Inc. for office space located at 200 Clarendon Street, Boston, MA. The initial lease term commenced on July 30, 2021 and expires on November 30, 2021. In October 2021, the Company extended the lease term to March 31, 2022. The base rent is approximately $ 9,000 per month. Due to the lease being short-term in nature, the Company elected the practical expedient for the lease and has recognized rent expenses as incurred. T he future minimum lease payments under all non-cancelable operating lease obligations as of September 30, 2021 were as follows (in thousands): 2021 $ 503 2022 2,933 2023 3,428 2024 3,525 2025 3,625 2026 and thereafter 13,747 Total undiscounted lease payments 27,761 Less: imputed interest 7,226 Total operating lease liability 20,535 Less: current portion 712 Operating lease liability, net of current maturities $ 19,823

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Common Stock	13. 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 September 30, 2021 and December 31, 2020, no dividends on common stock had been declared by the Board of Directors. As of September 30, 2021, the Company’s outstanding warrants to purchase shares of common stock, 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 220,890 The Company has the following shares of common stock reserved for future issuance: September 30, December 31, Stock options available for future grant 2,693,496 1,739,621 Stock options issued and outstanding 4,276,356 3,706,945 Unvested restricted stock units 217,160 — Common stock warrants issued and outstanding 220,890 226,191 Total 7,407,902 5,672,757

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	14. Stock-based Compensation Stock-based Compensation Expense Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 796 $ 951 $ 3,209 $ 1,125 General and administrative 1,733 2,015 5,022 2,491 Total stock-based compensation $ 2,529 $ 2,966 $ 8,231 $ 3,616 Stock Options A summary of stock option activity for the nine months ended September 30, 2021 is set forth below: Number of Number of Weighted- Weighted- Aggregate Outstanding, December 31, 2020 1,739,621 3,706,945 $ 10.90 7.98 $ 15,126 Options authorized 2,287,089 — Options granted ( 2,171,632 ) 1,954,472 $ 14.89 Options exercised — ( 546,642 ) $ 2.98 Options forfeited or cancelled 838,419 ( 838,419 ) $ 14.15 Outstanding, September 30, 2021 2,693,497 4,276,356 $ 13.10 7.96 $ 2,101 Options exercisable, September 30, 2021 1,329,752 $ 9.77 5.33 $ 1,907 Vested and expected to vest, September 30, 2021 4,276,356 $ 13.10 7.96 $ 2,101 The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair value of common stock $ 7.84 - $ 8.35 $ 5.96 - $ 10.66 $ 7.84 - $ 16.82 $ 4.85 - $ 10.66 Expected term (years) 5.6 - 6.1 1.0 - 6.1 0.9 - 6.1 1.0 - 6.1 Volatility 78.0 % - 78.2 % 77.1 % - 96.4 % 77.9 % - 79.8 % 72.6 % - 96.3 % Risk free rates 0.9 % - 1.2 % 0.1 % - 0.4 % 0.1 % - 1.2 % 0.1 % - 1.7 % Dividend rate 0.0 % 0.0 % 0.0 % 0.0 % Restricted Stock Units In May 2021, the Company granted 6,410 performance stock units (PSUs) to an employee with a grant date fair value of $ 15.60 per share. The PSUs provide immediate acceleration of vesting in the event of a certain performance milestone to be achieved by March 31, 2022. The probability of achieving this milestone is expected to be 100 % as of September 30, 2021 . In addition, the Company granted 210,750 restricted stock units (RSUs) to employees in August 2021 with a weighted-average grant date fair value of $ 7.12 per share. The summary of RSU activity and related information follows: Number of Units Outstanding Weighted- Outstanding, December 31, 2020 — RSUs granted 217,160 $ 7.37 RSUs Vested — RSUs forfeited — Outstanding, September 30, 2021 217,160 $ 7.37 Summary of Plans The Company has 2014 Share Option Plan (the 2014 Plan), 2015 Stock Incentive Plan (the 2015 Plan), 2017 Stock Incentive Plan (the 2017 Plan), 2018 Stock Incentive Plan (the 2018 Plan), and 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). There have been no material changes in the Plans from those disclosed in Note 18 to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020. The 2017 Plan and 2018 Plan As of September 30, 2021 , the number of shares of common stock available for grant under the 2017 and 2018 Plan is 2,349,535 shares. As of September 30, 2021 , an aggregate of 2,686,287 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 $ 15.41 per share. Included in this amount was a grant of 6,410 PSUs and 210,750 shares of RSUs the Company granted in May 2021 and August 2021, respectively. The 2014 Plan and 2015 Plan As of September 30, 2021 , the number of shares of common stock available for grant under the 2014 and 2015 Plans is 343,961 . As of September 30, 2021 , an aggregate of 1,421,746 shares of Former Adicet common stock were issuable upon the exercise of outstanding stock options under the 2015 plan at a weighted average exercise price of $ 8.96 per share and an aggregate of 22,989 shares of Former Adicet common stock were issuable upon the exercise of outstanding stock options under the 2014 Plan at a weighted average exercise price of $ 1.61 per share. 2018 Employee Stock Purchase Plan On January 1, 2021, 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 131,432 to 209,135 shares. During the 2021 Annual Meeting of the stockholders held on April 27, 2021, the stockholders approved an amendment and restatement of the Company's 2018 ESPP. As a result, the Company increased the shares available for issuance under the 2018 ESPP to 524,775 shares. No shares have been issued under the 2018 ESPP during the three and nine months ended September 30, 2021. Inducement Grant As of September 30, 2021 , an aggregate of 362,503 shares of 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.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss per Share	15. 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): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net loss attributable to common stockholders $ ( 14,013 ) $ ( 14,779 ) $ ( 46,186 ) $ ( 27,720 ) Weighted-average shares used in computing net loss per share attributable to common shareholders, basic and diluted 31,876,016 5,208,887 29,954,616 3,190,557 Net loss per share attributable to common stockholders, basic and diluted $ ( 0.44 ) $ ( 2.84 ) $ ( 1.54 ) $ ( 8.69 ) 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: As of September 30, 2021 2020 Redeemable convertible preferred stock — 12,048,671 Options to purchase common stock 4,276,356 1,847,518 Redeemable convertible preferred stock warrants — 220,890 Common stock warrants 220,890 — Total 4,497,246 14,117,079

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	16. Income Taxes The Company recorded an income tax expense of $ 11,000 and benefit of $ 114,000 during the three and nine months ended September 30, 2021 , respectively. The Company recorded an income tax benefit of $ 3,000 and $ 2.7 million during the three and nine months ended September 30, 2020, respectively. The income tax benefit during the three and nine months ended September 30, 2021 was due to the tax effect of the reduction in the deferred tax liability associated with the basis differences from IPR&D. In comparison, the income tax benefit during the three and nine months ended September 30, 2020 was as a result of the recognition of net operating loss carryback under the Coronavirus Aid, Relief, and Economic Security Act (CARES Act). The Company maintains a full valuation allowance against its deferred tax assets due to the Company’s history of losses as of September 30, 2021 .

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	17. Related Party As of September 30, 2021 and December 31, 2020, Regeneron owned 883,568 shares of the Company’s common stock, respectively. Regeneron became a related party in July 2019 as a result of Series B redeemable convertible preferred stock financing. For the three and nine months ended September 30, 2021 , the Company recorded revenue from the Regeneron Agreement of $ 3.4 million and $ 4.3 million, respectively. For the three and nine months ended September 30, 2020 , the Company recognized revenue from the Regeneron Agreement of $ 3.0 million and $12.5 million, respectively. As of September 30, 2021 , the Company has deferred revenue of $ 10.1 million related to the Regeneron Agreement. See Note 10 for a discussion of the Regeneron Agreement.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited interim 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).
Unaudited Interim Financial Information	Unaudited Interim Financial Information The consolidated balance sheet as of December 31, 2020 was derived from the Company’s audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020, have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (SEC), for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2020. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2021 and consolidated results of operations for the three and nine months ended September 30, 2021 and 2020 and consolidated cash flows for the nine months ended September 30, 2021 and 2020 have been made. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021.
Concentration of Credit Risk	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, which represents 100 % of the Company’s total revenue for the three and nine months ended September 30, 2021 and 2020 (see Note 10).
Risks and Uncertainties	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 investigational new drug (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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB 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 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 adopted ASU 2019-12 beginning January 1, 2021 on a prospective basis. The adoption of this standard did not have a material impact on its financial statements and related disclosures. In November 2018, the FASB issued Accounting Standards Update (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 adopted ASU 2018-18 beginning January 1, 2021 on a prospective basis. The adoption of this standard did not have a material impact on its 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 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 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 (Tables)

Business Combination (Tables)	9 Months Ended
	Sep. 30, 2021
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):
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 5,207,695 Multiplied by the fair value per share of resTORbio common stock (b) $ 16.59 Acquisition date fair value of resTORbio 86,396 Estimated fair value of modified stock options and restricted stock units attributable to pre-combination services (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	The following summarizes the allocation of the purchase price to the net tangible and intangible assets acquired (in thousands): As of Measurement Final Purchase Net assets acquired: Cash and cash equivalents $ 63,869 $ — $ 63,869 Prepaid expenses and other current assets 3,059 615 3,674 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 ( 2,365 ) 12 ( 2,353 ) Other liabilities — — — Deferred tax liability ( 367 ) — ( 367 ) Goodwill 20,089 ( 627 ) 19,462 Purchase price $ 87,022 $ — $ 87,022
Schedule of changes in the Company’s IPR&D and CVR since the Merger	The following tables present changes in the Company’s IPR&D and CVR since the Merger (in thousands): Acquisition Date Change in As of Change in As of In-process research and development $ 3,490 $ ( 2,300 ) $ 1,190 $ ( 1,190 ) $ — Contingent Value Rights $ 2,880 $ ( 1,900 ) $ 980 $ ( 980 ) $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured on Recurring Basis	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): September 30, 2021 Level 1 Level 2 Level 3 Total Assets: Money market funds (1) $ 174,945 $ — $ — $ 174,945 Total fair value of assets $ 174,945 $ — $ — $ 174,945 December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds (1) $ 63,817 $ — $ — $ 63,817 Marketable debt securities (2) 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 (1) Included in cash and cash equivalents in the consolidated balance sheets. (2) Included in short-term marketable debt securities in the consolidated balance sheets.

Marketable Debt Securities (Tab

Marketable Debt Securities (Tables)	9 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Schedule of Marketable Debt Securities	The following table summarizes the Company’s marketable debt securities as of December 31, 2020 (in thousands): December 31, 2020 Amortized Unrealized Unrealized Fair 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
Summary of Classification of Marketable Debt Securities in Condensed Consolidated Balance Sheets	The following table summarizes the classification of the Company’s marketable debt securities in the consolidated balance sheets (in thousands): September 30, December 31, 2021 2020 Short-term marketable debt securities $ — $ 10,284 Long-term marketable debt securities — — Total $ — $ 10,284

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2021
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): September 30, December 31, Prepaid maintenance and other $ 655 $ 761 Prepayments to CRO's 1,643 420 Prepayments to CMO's 1,340 135 Prepaid insurance 449 1,443 Tax receivable 2,711 2,711 Interest receivable — 23 Other current assets 1 229 Total prepaid expenses and other current assets $ 6,799 $ 5,722

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): Useful life September 30, December 31, Laboratory equipment 3 $ 5,502 $ 4,350 Leasehold improvements Lesser of useful life or lease term 1,614 1,427 Furniture and fixtures 3 303 524 Construction in progress — 9,402 1,090 Computer equipment 3 217 93 Software 3 320 170 17,358 7,654 Less: Accumulated depreciation and amortization ( 5,963 ) ( 4,864 ) Property and equipment, net $ 11,395 $ 2,790

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Summary of Accrued and Other Current Liabilities	Accrued and other current liabilities consisted of the following (in thousands): September 30, December 31, Accrued compensation $ 3,316 $ 3,833 Accrued CRO costs 490 955 Accrued CMO costs 165 244 Accrued research and development expenses 294 65 Accrued professional services 301 363 Accrued other liabilities 35 272 Total accrued and other liabilities $ 4,601 $ 5,732

Regeneron License and Collabo_2

Regeneron License and Collaboration Arrangement (Tables)	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Change in Company's Contract Liabilities	The following tables present changes in the Company’s contract liabilities for the nine months ended September 30, 2021 and 2020 (in thousands): Nine Months Ended September 30, 2021 Balance at Additions Additions (Deductions) Balance at Contract liability $ 13,980 $ 370 $ ( 4,262 ) $ 10,088 Nine Months Ended September 30, 2020 Balance at Additions Additions (Deductions) Balance at Contract asset $ — $ 10,000 $ ( 10,000 ) $ — Contract liability $ 21,883 $ 10,000 $ ( 12,493 ) $ 19,390 (1) Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule Of Sublease Income	The expected sublease income as of September 30, 2021 is as follows (in thousands): 2021 (remaining three months) $ 174 2022 697 2023 711 2024 725 2025 740 2026 and thereafter 439 Total $ 3,486
Schedule of Future Minimum Lease Payments	he future minimum lease payments under all non-cancelable operating lease obligations as of September 30, 2021 were as follows (in thousands): 2021 $ 503 2022 2,933 2023 3,428 2024 3,525 2025 3,625 2026 and thereafter 13,747 Total undiscounted lease payments 27,761 Less: imputed interest 7,226 Total operating lease liability 20,535 Less: current portion 712 Operating lease liability, net of current maturities $ 19,823

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Schedule Of Outstanding Warrants To Purchase Shares of Common Stock	As of September 30, 2021, the Company’s outstanding warrants to purchase shares of common stock, 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 220,890
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: September 30, December 31, Stock options available for future grant 2,693,496 1,739,621 Stock options issued and outstanding 4,276,356 3,706,945 Unvested restricted stock units 217,160 — Common stock warrants issued and outstanding 220,890 226,191 Total 7,407,902 5,672,757

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense	Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 796 $ 951 $ 3,209 $ 1,125 General and administrative 1,733 2,015 5,022 2,491 Total stock-based compensation $ 2,529 $ 2,966 $ 8,231 $ 3,616
Summary of Stock Option Activity	A summary of stock option activity for the nine months ended September 30, 2021 is set forth below: Number of Number of Weighted- Weighted- Aggregate Outstanding, December 31, 2020 1,739,621 3,706,945 $ 10.90 7.98 $ 15,126 Options authorized 2,287,089 — Options granted ( 2,171,632 ) 1,954,472 $ 14.89 Options exercised — ( 546,642 ) $ 2.98 Options forfeited or cancelled 838,419 ( 838,419 ) $ 14.15 Outstanding, September 30, 2021 2,693,497 4,276,356 $ 13.10 7.96 $ 2,101 Options exercisable, September 30, 2021 1,329,752 $ 9.77 5.33 $ 1,907 Vested and expected to vest, September 30, 2021 4,276,356 $ 13.10 7.96 $ 2,101
Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model	The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair value of common stock $ 7.84 - $ 8.35 $ 5.96 - $ 10.66 $ 7.84 - $ 16.82 $ 4.85 - $ 10.66 Expected term (years) 5.6 - 6.1 1.0 - 6.1 0.9 - 6.1 1.0 - 6.1 Volatility 78.0 % - 78.2 % 77.1 % - 96.4 % 77.9 % - 79.8 % 72.6 % - 96.3 % Risk free rates 0.9 % - 1.2 % 0.1 % - 0.4 % 0.1 % - 1.2 % 0.1 % - 1.7 % Dividend rate 0.0 % 0.0 % 0.0 % 0.0 %
Summary of Restricted Stock Unit Activity	The summary of RSU activity and related information follows: Number of Units Outstanding Weighted- Outstanding, December 31, 2020 — RSUs granted 217,160 $ 7.37 RSUs Vested — RSUs forfeited — Outstanding, September 30, 2021 217,160 $ 7.37

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	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): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net loss attributable to common stockholders $ ( 14,013 ) $ ( 14,779 ) $ ( 46,186 ) $ ( 27,720 ) Weighted-average shares used in computing net loss per share attributable to common shareholders, basic and diluted 31,876,016 5,208,887 29,954,616 3,190,557 Net loss per share attributable to common stockholders, basic and diluted $ ( 0.44 ) $ ( 2.84 ) $ ( 1.54 ) $ ( 8.69 )
Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share	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: As of September 30, 2021 2020 Redeemable convertible preferred stock — 12,048,671 Options to purchase common stock 4,276,356 1,847,518 Redeemable convertible preferred stock warrants — 220,890 Common stock warrants 220,890 — Total 4,497,246 14,117,079

Organization and Nature of the

Organization and Nature of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 15, 2020	Sep. 15, 2020	Feb. 28, 2021USD ($)$ / sharesshares	Sep. 30, 2021USD ($)shares	Dec. 31, 2020USD ($)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				31,955,050	19,677,249
Accumulated deficit				$ (152,511)	$ (106,325)
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
Accumulated deficit				$ 152,500
Initial Public Offering
Schedule Of Equity Method Investments [Line Items]
Number of common stock shares sold | shares			10,575,513
Issuance price per shares | $ / shares			$ 13
Underwriting discounts and commissions and other offering expenses			$ 137,500
Net proceeds received from offering			$ 15,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - Customer	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Number of Customer	1	1
Customers percentage of total revenue	100.00%	100.00%

Business Combination - Addition

Business Combination - Additional Information (Details) $ in Thousands	Jul. 27, 2021	Sep. 15, 2020shares	Sep. 15, 2020shares	Mar. 31, 2021USD ($)	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)ValueRight	Dec. 31, 2020USD ($)
Business Acquisition [Line Items]
Impairment charges | $				$ 500	$ 700		$ 2,300
Reverse stock split		1-for-7	1-for-7
Goodwill | $						$ 19,462	$ 20,089
Expiration period termination notice	60 days
resTORbio
Business Acquisition [Line Items]
Contractual Contingent Value Right | ValueRight						1
Reverse stock split exchange ratio		0.1240
Percentage of outstanding capital stock		75.00%	75.00%
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
Goodwill | $						$ 19,462
resTORbio | Common Stock
Business Acquisition [Line Items]
Percentage of outstanding capital stock		25.00%	25.00%

Business Combination - Schedule

Business Combination - Schedule of Summarizes the Purchase Price in the Merger (Details) - USD ($) $ in Thousands	Sep. 15, 2020	Sep. 30, 2021	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 - Schedu_2

Business Combination - Schedule of Estimated Share Consideration of Combined Company (Details) - resTORbio $ / shares in Units, $ in Thousands	Sep. 15, 2020USD ($)$ / sharesshares
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	$ 86,396
Estimated fair value of modified stock options and restricted stock units attributable to pre-combination services	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 - Schedu_3

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

Business Combination - Schedu_4

Business Combination - Schedule of Summarizes the Purchase Price in the Merger (Parenthetical) (Details) - resTORbio	Sep. 15, 2020shares
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 - Schedu_5

Business Combination - Schedule of Summarizes the Allocation of the Purchase Price to the Net Tangible and Intangible Assets Acquired (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Net assets acquired:
Goodwill	$ 19,462	$ 20,089
resTORbio
Net assets acquired:
Cash and cash equivalents	63,869
Prepaid expenses and other current assets	3,674
Property and equipment	318
IPR&D	3,490
Restricted cash	245
Accounts payable	(1,316)
Accrued and other current liabilities	(2,353)
Other liabilities	0
Deferred tax liability	(367)
Goodwill	19,462
Purchase price	87,022
resTORbio | Preliminary
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)
Other liabilities		0
Deferred tax liability		(367)
Goodwill		20,089
Purchase price		$ 87,022
resTORbio | Measurement Period Adjustments
Net assets acquired:
Cash and cash equivalents	0
Prepaid expenses and other current assets	615
Property and equipment	0
IPR&D	0
Restricted cash	0
Accounts payable	0
Accrued and other current liabilities	(12)
Other liabilities	0
Deferred tax liability	0
Goodwill	627
Purchase price	$ 0

Business Combination - Schedu_6

Business Combination - Schedule of changes in the Company's IPR&D and CVR since the Merger (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 15, 2020
In Process Research and Development
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value	$ 0	$ 1,190	$ 3,490
In Process Research and Development | Change in Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value	(1,190)	(2,300)
Contingent Value Rights Agreement
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value	0	980	$ 2,880
Contingent Value Rights Agreement | Change in Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value	$ (980)	$ (1,900)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets		$ 174,945	$ 74,101
Total fair value of liabilities			980
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		1,762
Contingent Consideration
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities			980
Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		7,522
Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		10,284
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets			63,817
Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets			10,284
Fair Value, Inputs, Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		1,762
Fair Value, Inputs, Level 2 | Asset-backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		7,522
Fair Value, Inputs, Level 2 | Marketable Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		10,284
Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities			980
Fair Value, Inputs, Level 3 | Contingent Consideration
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of liabilities			980
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[2]	174,945	63,817
Money Market Funds | Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[2]	$ 174,945	63,817
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		1,000
Commercial Paper | Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total fair value of assets	[1]		$ 1,000
[1]	Included in short-term marketable debt securities in the consolidated balance sheets.
[2]	Included in cash and cash equivalents in the consolidated balance sheets.

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) $ in Millions	Sep. 30, 2021USD ($)
Fair Value Disclosures [Abstract]
Estimated fair value of the CVR liability	$ 0

Marketable Debt Securities - Sc

Marketable Debt Securities - Schedule of Marketable Debt Securities (Details) $ in Thousands	Dec. 31, 2020USD ($)
Marketable Securities [Line Items]
Amortized Cost	$ 10,260
Unrealized Gains	24
Fair Value	10,284
Corporate Debt Securities
Marketable Securities [Line Items]
Amortized Cost	1,754
Unrealized Gains	8
Fair Value	1,762
Asset Backed Securities
Marketable Securities [Line Items]
Amortized Cost	7,507
Unrealized Gains	15
Fair Value	7,522
Commercial Paper
Marketable Securities [Line Items]
Amortized Cost	999
Unrealized Gains	1
Fair Value	$ 1,000

Marketable Debt Securities - Su

Marketable Debt Securities - Summary of Classification of Marketable Debt Securities in Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Short-term marketable debt securities	$ 0	$ 10,284
Long-term marketable debt securities	0	0
Marketable Securities, Total	$ 0	$ 10,284

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid maintenance and other	$ 655	$ 761
Prepayments to CRO's	1,643	420
Prepayments to CMO's	1,340	135
Prepaid insurance	449	1,443
Tax receivable	2,711	2,711
Interest receivable	0	23
Other current assets	1	229
Total prepaid expenses and other current assets	$ 6,799	$ 5,722

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 17,358		$ 7,654
Less: Accumulated depreciation and amortization	(5,963)		(4,864)
Property and equipment, net	11,395	$ 11,395	2,790
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 5,502		4,350
Useful life (in years)	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,614		1,427
Useful life (in years)	Lesser of useful life or lease term
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	$ 303		524
Useful life (in years)	3 years
Construction In Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 9,402		1,090
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 217		93
Useful life (in years)	3 years
Software
Property Plant And Equipment [Line Items]
Total property and equipment	$ 320		$ 170
Useful life (in years)	3 years

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Increase in construction in progress	$ 6,800		$ 9,400
Depreciation and amortization expense	$ 400	$ 300	$ 1,173	$ 911

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Summary of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued compensation	$ 3,316	$ 3,833
Accrued CRO costs	490	955
Accrued CMO costs	165	244
Accrued research and development expenses	294	65
Accrued professional services	301	363
Accrued other liabilities	35	272
Total accrued and other liabilities	$ 4,601	$ 5,732

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - Pacific western bank [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Oct. 21, 2021	Apr. 28, 2020
Class Of Warrant Or Right [Line Items]
term loan to finance leasehold improvements			$ 12
Deferred debt issuance cost	$ 0.1
Prime Rate
Class Of Warrant Or Right [Line Items]
Interest rate for term loan to finance leasehold improvements			5.00%
Minimum
Class Of Warrant Or Right [Line Items]
Interest rate for term loan to finance leasehold improvements			0.25%
Fourth Amendment
Class Of Warrant Or Right [Line Items]
Long-term Debt, Description	each term loan to be in an amount of not less than $1.0 million. Pursuant to the Loan Amendment, the interest rate for the Term Loans shall be set at an annual rate equal to the greater of (i) 0.25% above the Prime Rate then in effect and (ii) 4.25%
Fourth Amendment | Subsequent Event [Member]
Class Of Warrant Or Right [Line Items]
Term loan and non formula ancillary service		$ 15
Loan amount drawn		$ 5.5

Regeneron License and Collabo_3

Regeneron License and Collaboration Arrangement - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jul. 29, 2016	Sep. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Assets									$ 0
Licence agreement cumulative revenue recognised								$ 35.3
Regeneron Pharmaceuticals, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract Assets							$ 10
Non refundable upfront payment received								25
Additional payment for research funding received								$ 20		$ 5	$ 5
License agreement termination description								twelve years
Contract research term period		5 years
Upfront payment	$ 25	$ 25						$ 25
Licence agreement cumulative revenue recognised			$ 3.4		$ 5		$ 10	4.3
License agreement cumulative revenue reduction recognised						$ 6.6
Increase in estimated transaction price					$ 10
Contract liability								10.1	19.4
Regeneron Pharmaceuticals, Inc. | Change in Accounting Estimate
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License agreement cumulative revenue reduction recognised				$ 4
Regeneron Pharmaceuticals, Inc. | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement additional amount payable of option exercise fees								$ 100
Regeneron Pharmaceuticals, Inc. | Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Licence agreement cumulative revenue recognised									$ 25.6

Regeneron License and Collabo_4

Regeneron License and Collaboration Arrangement - Summary of Change in Company's Contract Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020
Contract Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period			$ 0
Additions			10,000
Additions (Deductions) (1)	[1]		(10,000)
Balance at end of period			0
Contract Liability
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at beginning of period		$ 13,980	21,883
Additions		370	10,000
Additions (Deductions) (1)	[1]	(4,262)	(12,493)
Balance at end of period		$ 10,088	$ 19,390
[1]	Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period.

License Funding and Other Agr_2

License Funding and Other Agreements Related to the CVR - Additional Information (Details) - USD ($)	Oct. 31, 2020	Feb. 28, 2021	Nov. 30, 2020	May 31, 2019	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2021	Mar. 23, 2017
Research And Development Arrangement Contract To Perform For Others [Line Items]
Exercised Investment Right and Purchased							$ 10,000,000
Estimated fair value of the CVR liability					$ 0		0
Funding Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Qualifying expenses							300,000
National Institute of Health
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant term				5 years
Grants receivable				$ 1,500,000
Qualifying expenses					36,000
Qualifying expenses on cumulative basis							1,300,000
National Institute of Health | Funding Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Qualifying expenses						$ 0	500,000
Qualifying expenses on cumulative basis							1,300,000
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	$ 1,100,000						3,000,000
Post Exposure Prophylaxis in adults		In February 2021, management terminated the National Institute on Aging study of RTB101 for COVID-19 post-exposure prophylaxis in adults age 65 years and older due to poor enrollment
Increase decrease in estimated fair value of CVR liability			$ 400,000
Estimated fair value of the CVR liability			$ 600,000		$ 0		$ 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								$ 4,300,000
Aggregate amount payable upon satisfaction of regulatory milestones for first indication approved								24,000,000
Aggregate amount payable upon satisfaction of regulatory milestones for second indication approved								18,000,000
Aggregate amount payable upon satisfaction of commercial milestones								$ 125,000,000

Commitment and Contingencies -

Commitment and Contingencies - Additional Information (Details)	Jul. 30, 2021USD ($)	Jul. 19, 2021USD ($)ft²	Jun. 25, 2021USD ($)	Sep. 30, 2021USD ($)
Long Term Purchase Commitment [Line Items]
Amended lease Agreement Description			the Company entered into an amendment to the Menlo Park lease to extend the term of the lease from March 31, 2022 to June 30, 2022 and replace the previously leased premises (known as 173 and 175-177 Jefferson Drive) with another nearby premises (known as 235 Constitution Drive).
Operating leases commencement date				Jul. 15, 2021
Change in lease Obligation.				$ 0
Option to Extend, Existence, Operating Lease				true
Lease Expiration Date				Jun. 30, 2022
Operating Lease, Liability				$ 20,535,000
Maximum [Member]
Long Term Purchase Commitment [Line Items]
Rent expense recognized			$ 89,904,000
Minimum [Member]
Long Term Purchase Commitment [Line Items]
Rent expense recognized			$ 87,286,000
RFS OPCO LLC [Member]
Long Term Purchase Commitment [Line Items]
Area of Sublease | ft²		9,501
Operating Leases, Rent Expense, Sublease Rentals		$ 3,500,000
Cash security deposit received		$ 100,000
Sublease Agreement Description		The term of the sublease started on September 1, 2021 and ends on July 30, 2026. The aggregate base rent due to the Company under the Sublease is approximately $3.5 million starting October 1, 2021.
Boston Properties, Inc. [Member]
Long Term Purchase Commitment [Line Items]
Operating Lease, Liability				$ 3,100,000
Operating Leases, Rent Expense, Sublease Rentals	$ 9,000
Sublease Agreement Description	The initial lease term commenced on July 30, 2021 and expires on November 30, 2021. In October 2021, the Company extended the lease term to March 31, 2022. The base rent is approximately $9,000 per month.

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Sublease Income (Details) $ in Thousands	Sep. 30, 2021USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021 (remaining three months)	$ 174
2022	697
2023	711
2024	725
2025	740
2026 and thereafter	439
Total	$ 3,486

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021 (remaining six months)	$ 503
2022	2,933
2023	3,428
2024	3,525
2025	3,625
2026 and thereafter	13,747
Total undiscounted lease payments	27,761
Less: imputed interest	7,226
Total operating lease liability	20,535
Less: current portion	712	$ 1,215
Operating lease liability, net of current portion	$ 19,823	$ 20,424

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock, shares authorized	150,000,000	150,000,000
Dividends Payable	$ 0	$ 0
Common stock shares issued, par value	$ 0.0001	$ 0.0001

Common Stock - Schedule of Outs

Common Stock - Schedule of Outstanding Warrants to Purchase Shares of Common Stock (Details)	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Class Of Stock [Line Items]
Number of Shares of Common Stock Issuable	220,890
September 15, 2020 Warrant One
Class Of Stock [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	101,610
Warrant exercise price | $ / shares	$ 11.3177
Expiration Date	Jul. 25, 2026
September 15, 2020 Warrant Two
Class Of Stock [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	30,924
Warrant exercise price | $ / shares	$ 11.3177
Expiration Date	Aug. 21, 2026
September 15, 2020 Warrant Three
Class Of Stock [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	77,312
Warrant exercise price | $ / shares	$ 11.3177
Expiration Date	Sep. 19, 2026
September 15, 2020 Warrant Four
Class Of Stock [Line Items]
Issuance Date	Sep. 15, 2020
Number of Shares of Common Stock Issuable	11,044
Warrant exercise price | $ / shares	$ 11.3177
Expiration Date	Sep. 26, 2026

Common Stock - Schedule of Numb

Common Stock - Schedule of Number of Shares of Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	7,407,902	5,672,757
Unvested Restricted Stock Units
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	217,160	0
Stock Options Available for Future Grant
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	2,693,496	1,739,621
Options Issued and Outstanding
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	4,276,356	3,706,945
Common Stock Warrants
Class Of Stock [Line Items]
Number of shares of common stock reserved for future issuance	220,890	226,191

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,529	$ 2,966	$ 8,231	$ 3,616
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	796	951	3,209	1,125
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,733	$ 2,015	$ 5,022	$ 2,491

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Share Based Compensation [Abstract]
Number of Shares Available for Grant, Begining balance	1,739,621
Number of Shares Available for Grant, Options authorized	2,287,089
Number of Shares Available for Grant, Options granted	(2,171,632)
Number of Shares Available for Grant, Options forfeited or cancelled	838,419
Number of Shares Available for Grant, Ending balance	2,693,497	1,739,621
Number of Shares Underlying Outstanding Options, Beginning balance	3,706,945
Number of Shares Underlying Outstanding Options, Options granted	1,954,472
Number of Shares Underlying Outstanding Options, Options exercised	(546,642)
Number of Shares Underlying Outstanding Options, Options forfeited or cancelled	(838,419)
Number of Shares Underlying Outstanding Options, Ending balance	4,276,356	3,706,945
Number of Shares Underlying Outstanding Options exercisable	1,329,752
Number of Shares Underlying Outstanding Options, Vested and expected to vest	4,276,356
Weighted-Average Exercise Price, Outstanding beginning | $ / shares	$ 10.90
Weighted-Average Exercise Price, Options granted | $ / shares	14.89
Weighted-Average Exercise Price, Options exercised | $ / shares	2.98
Weighted-Average Exercise Price, Options forfeited or cancelled | $ / shares	14.15
Weighted-Average Exercise Price, Outstanding ending | $ / shares	13.10	$ 10.90
Weighted-Average Exercise Price, Options exercisable | $ / shares	9.77
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 13.10
Weighted-Average Remaining Contract Term, Outstanding	7 years 11 months 15 days	7 years 11 months 23 days
Weighted-Average Remaining Contract Term, Options exercisable	5 years 3 months 29 days
Weighted-Average Remaining Contract Term, Vested and expected to vest	7 years 11 months 15 days
Aggregate Intrinsic Value, Outstanding | $	$ 2,101	$ 15,126
Aggregate Intrinsic Value, Options exercisable | $	1,907
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 2,101

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - $ / shares	May 31, 2021	Jan. 01, 2021	Jan. 01, 2020	Aug. 31, 2021	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Available for Grant, Options granted						(2,171,632)
Number of shares of common stock available for grant					2,693,497	2,693,497	1,739,621
Number of shares reserved for issuance					362,503	362,503
Weighted-Average Exercise Price, Options exercised						$ 2.98
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					2,349,535	2,349,535
Number of shares reserved for issuance					2,686,287	2,686,287
Weighted-Average Exercise Price, Options exercised						$ 15.41
2014 Stock Incentive Plan Member
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance					22,989	22,989
Weighted-Average Exercise Price, Options exercised						$ 1.61
2015 Stock Incentive Plan Member
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock available for grant					343,961	343,961
Number of shares reserved for issuance					1,421,746	1,421,746
Weighted-Average Exercise Price, Options exercised						$ 8.96
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares reserved for issuance		209,135	131,432			524,775
Number of shares available for sale under employee stock purchase plan					0	0
Inducement Grant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-Average Exercise Price, Options exercised						$ 14.33
Performance Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock available for grant	6,410
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Probability of Achieving Milestone						100.00%
Grant fair value	$ 15.60
Number of shares of common stock available for grant				210,750
Weighted-Average Exercise Price, Options exercised				$ 7.12
Performance Stock Units (PSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares Available for Grant, Options granted	(6,410)

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	78.00%	77.10%	77.90%	72.60%
Expected volatility, maximum	78.20%	96.40%	79.80%	96.30%
Risk free rates, minimum	0.90%	0.10%	0.10%	0.10%
Risk free rates, maximum	1.20%	0.40%	1.20%	1.70%
Dividend rate	0.00%	0.00%	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 7.84	$ 5.96	$ 7.84	$ 4.85
Expected term	5 years 7 months 6 days	1 year	10 months 24 days	1 year
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 8.35	$ 10.66	$ 16.82	$ 10.66
Expected term	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Restricted Stock Unit Activity (Details) - RSUs [Member]	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, December 31, 2020	0
RSUs granted	217,160
Outstanding, September 30, 2021	217,160
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Fair Value, Granted | $ / shares	$ 7.37
Weighted-Average Grant Date Fair Value, Ending | $ / shares	$ 7.37

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (14,013)	$ (14,779)	$ (46,186)	$ (27,720)
Weighted-average common shares used in computing net loss per share attributable to common stockholders, basic and diluted	31,876,016	5,208,887	29,954,616	3,190,557
Net loss per share attributable to common stockholders, basic and diluted	$ (0.44)	$ (2.84)	$ (1.54)	$ (8.69)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,497,246	14,117,079
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	4,276,356	1,847,518
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	220,890	0
Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	12,048,671
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

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Taxes Disclosure [Line Items]
Income tax expense (benefit)	$ 11,000	$ 3,000	$ (114,000)	$ (2,676,000)
COVID-19
Income Taxes Disclosure [Line Items]
Income tax expense (benefit)	$ 11,000	$ (3,000)	$ (114,000)	$ (2,700,000)

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Redeemable convertible preferred stock	0		0		0
Revenue—related party	$ 3,429	$ 3,028	$ 4,262	$ 12,493
Regeneron Pharmaceuticals, Inc.
Related Party Transaction [Line Items]
Revenue—related party	3,400	$ 3,000	4,300
Deferred revenue	$ 10,100		$ 10,100
Regeneron Pharmaceuticals, Inc. | Series B Convertible Preferred Stock [ Member ]
Related Party Transaction [Line Items]
Redeemable convertible preferred stock	883,568		883,568		883,568