Tcr2 Therapeutics (TCRR) 10-K22 Mar 222021 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
Document and Entity Information - USD ($) $ in Thousands	Dec. 31, 2021	Mar. 18, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	TCRR
Entity Registrant Name	TCR2 Therapeutics Inc.
Entity Central Index Key	0001750019
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		38,546,345
Entity Public Float			$ 492,524,243
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.0001 Par Value
Entity File Number	001-38811
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4152751
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Entity Address, Address Line One	100 Binney
Entity Address, Address Line Two	Street, Suite 710
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	949-5200
ICFR Auditor Attestation Flag	false
Document Annual Report	true
Document Transition Report	false
Auditor Name	KPMG LLP
Auditor Location	Boston, MA
Auditor Firm ID	185

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 222,564	$ 94,155
Investments	43,029	133,831
Prepaid expenses and other current assets	10,534	7,552
Total current assets	276,127	235,538
Property and equipment, net	17,075	10,013
Right-of-use assets, operating leases	28,283	0
Restricted cash	1,156	583
Other assets, non-current	730	61
Total assets	323,371	246,195
Liabilities and stockholders’ equity
Accounts payable	2,144	2,448
Accrued expenses and other current liabilities	13,094	6,392
Operating lease liabilities	3,367	0
Total current liabilities	18,605	8,840
Operating lease liabilities, non-current	22,996	0
Other liabilities	293	807
Total liabilities	41,894	9,647
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock, $0.0001 par value; 10,000,000 shares authorized, no shares issued or outstanding as of December 31, 2021 and December 31, 2020, respectively.	0	0
Common stock, $0.0001 par value; 150,000,000 shares authorized; 38,496,484 and 33,516,795 shares issued and outstanding as of December 31, 2021 and December 31, 2020, respectively.	4	3
Additional paid-in capital	631,008	486,197
Accumulated other comprehensive income	(13)	63
Accumulated deficit	(349,522)	(249,715)
Total stockholders’ equity	281,477	236,548
Total liabilities and stockholders’ equity	$ 323,371	$ 246,195

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	10,000,000	10,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (shares)	150,000,000	150,000,000
Common stock, shares issued (shares)	38,496,484	33,516,795
Common stock, shares outstanding (shares)	38,496,484	33,516,795

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses
Research and development	$ 77,239	$ 51,980
General and administrative	22,503	16,720
Total operating expenses	99,742	68,700
Loss from operations	(99,742)	(68,700)
Interest income, net	224	1,737
Loss before income tax expense	(99,518)	(66,963)
Income tax expense	289	161
Net loss	$ (99,807)	$ (67,124)
Per share information
Net loss per share of common stock, basic and diluted	$ (2.63)	$ (2.40)
Weighted average shares outstanding, basic and diluted	37,935,554	27,990,564

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (99,807)	$ (67,124)
Unrealized gain (loss) on investments, net	(76)	(79)
Comprehensive loss	$ (99,883)	$ (67,203)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (shares) at Dec. 31, 2019		23,981,109
Beginning balance at Dec. 31, 2019	$ 160,449	$ 2	$ 342,896	$ (182,591)	$ 142
Issuance of common stock, net of issuance costs (shares)		9,200,000
Issuance of common stock, net of issuance costs	133,571	$ 1	133,570
Reclassification of shares issued and previously subject to repurchase (shares)		69,826
Reclassification of shares issued and previously subject to repurchase	51		51
Exercise of stock options including ESPP shares issued	$ 1,188		1,188
Exercise of stock options including ESPP shares issued (shares)	241,995	265,860
Stock-based compensation expense	$ 8,492		8,492
Unrealized gain (loss) on investments	(79)				(79)
Net loss	(67,124)			(67,124)
Ending balance at Dec. 31, 2020	$ 236,548	$ 3	486,197	(249,715)	63
Ending balance (shares) at Dec. 31, 2020	33,516,795	33,516,795
Issuance of common stock, net of issuance costs (shares)		4,590,164
Issuance of common stock, net of issuance costs	$ 131,330	$ 1	131,329
Exercise of stock options including ESPP shares issued	$ 1,217		1,217
Exercise of stock options including ESPP shares issued (shares)	371,636	389,525
Stock-based compensation expense	$ 12,265		12,265
Unrealized gain (loss) on investments	(76)				(76)
Net loss	(99,807)			(99,807)
Ending balance at Dec. 31, 2021	$ 281,477	$ 4	$ 631,008	$ (349,522)	$ (13)
Ending balance (shares) at Dec. 31, 2021	38,496,484	38,496,484

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating activities
Net loss	$ (99,807)	$ (67,124)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	2,827	1,592
Asset impairment due to restructuring	559
Stock-based compensation expense	12,265	8,492
Amortization (accretion) on investments	837	(702)
Deferred tax liabilities	99	131
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,496)	(1,101)
Operating leases, net	(2,416)	0
Accounts payable	(771)	451
Accrued expenses and other liabilities	7,300	1,522
Cash used in operating activities	(81,603)	(56,739)
Investing activities
Purchases of equipment	(11,098)	(7,164)
Software development costs	(351)	0
Purchases of investments	(50,726)	(152,812)
Proceeds from sale or maturity of investments	140,622	111,041
Cash provided by (used in) investing activities	78,447	(48,935)
Financing activities
Proceeds from public offering of common stock, net of issuance costs	131,330	133,571
Proceeds from the exercise of stock options	1,217	1,189
Payment of deferred offering costs	(409)	(61)
Cash provided by financing activities	132,138	134,699
Net change in cash, cash equivalents, and restricted cash	128,982	29,025
Cash, cash equivalents, and restricted cash at beginning of year	94,738
Cash, cash equivalents, and restricted cash at end of period	223,720	94,738
Supplemental disclosure of noncash activities
Property and equipment additions in accounts payable	517	611
Right-of-use assets obtained in exchange for operating lease liabilities	21,315	0
Operating cash flows used in operating leases	$ 11,291	$ 0

Organization and Description of

Organization and Description of Business	12 Months Ended
Organization and Description of Business	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organiza tion and Description of Business TCR 2 Therapeutics Inc. (the Company) is a clinical-stage immunotherapy company developing the next generation of novel T cell therapies for patients suffering from cancer. The Company was incorporated under the laws of the State of Delaware on May 29, 2015 under the name TCR 2 , Inc. In November 2016, the Company changed its name to TCR 2 Therapeutics Inc. The Company’s principal operations are located in Cambridge, Massachusetts. The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. Shelf registration statement On March 16, 2021, the Company filed an automatic shelf registration statement on Form S-3 (the Shelf), with the Securities and Exchange Commission (SEC), which covers the offering, issuance and sale of an indeterminate amount of the Company’s common stock, preferred stock, debt securities, warrants and/or units of any combination thereof. The Shelf was automatically effective when filed. As of December 31, 2021, no sales have been made under the Shelf. Equity offerings On July 31, 2020, the Company closed a public offering of its common stock pursuant to which it issued and sold 9,200,000 shares of its common stock at a price to the public of $ 15.50 per share. The aggregate net proceeds received by the Company from the offering were approximately $ 133.6 million after deducting $ 9.0 million relating to underwriting discounts and commissions and offering expenses. On January 22, 2021, the Company closed a public offering of its common stock pursuant to which it issued and sold 4,590,164 shares of its common stock at a price to the public of $ 30.50 per share. The aggregate net proceeds received by the Company from the offering were approximately $ 131.3 million after deducting $ 8.7 million relating to underwriting discounts and commissions and offering expenses.

Liquidity

Liquidity	12 Months Ended
Liquidity	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Liquidity	2. Liq uidity The Company’s operations to date have focused on organization and staffing, business planning, raising capital, acquiring technology and assets, manufacturing and conducting clinical and preclinical studies. The Company does not have any product candidates approved for sale and has not generated any revenue from product sales. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding for the ongoing and planned clinical development of its product candidates. Because of the numerous risks and uncertainties associated with pharmaceutical products and development, the Company is unable to accurately predict the timing or amount of funds required to complete development of its product candidates, and costs could exceed the Company’s expectations for a number of reasons, including reasons beyond the Company’s control. The Company is also subject to a number of other risks including possible failure of preclinical studies or clinical trials, the need to obtain marketing approval for its product candidates, the development of new technological innovations by competitors, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and uncertainty around intellectual property matters. If the Company does not successfully commercialize any of its products, it will be unable to generate product revenue or achieve profitability. The Company has incurred net losses from operations since inception. The Company expects to continue to generate losses for the foreseeable future. The Company expects that its cash, cash equivalents and investments as of December 31, 2021 of $ 265.6 million will be sufficient to fund its operating expenses and capital expenditure requirements through at least twelve months from the date of issuance of these consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. Sum mary of Significant Accounting Policies Principles of consolidation and basis of presentation The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB ). Use of estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, and the fair value of stock-based compensation awards granted under the Company’s equity-based compensation plans. Due to the uncertainty of factors surrounding the estimates or judgments used in the preparation of the consolidated financial statements, actual results may materially vary from these estimates. Estimates and assumptions are periodically reviewed, and the effects of revisions are reflected in the consolidated financial statements in the period they are determined to be necessary. Concentrations of credit risk and of manufacturing risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held by financial institutions in the United States. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions. As of December 31, 2021 , the Company had manufacturing arrangements with vendors for the supply of materials for use in preclinical and clinical studies. If the Company were to experience any disruptions in the vendors' ability or willingness to continue to provide manufacturing services, the Company may experience significant delays in its product development timelines and may incur substantial costs to secure alternative sources of manufacturing. Cash equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2021 and 2020 , cash equivalents consisted of U.S treasuries, corporate bonds and government-backed money market funds. Investments As of December 31, 2021, all investments were classified as available-for-sale and were carried at their estimated fair value. Unrealized gains and losses are recorded as a component of accumulated other comprehensive income (loss) until realized. The Company determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company periodically reviews its investments in debt securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. If losses on these securities are considered to be other than temporary, the loss is recognized in the statement of operations. The Company classifies its available-for-sale marketable securities as current or non-current based on each instrument’s underlying effective maturity date and for which the Company has the intent and ability to hold the investment for a period of greater than 12 months. Marketable securities with maturities of less than 12 months are classified as current and are included in investments in the consolidated balance sheets. Marketable securities with maturities greater than 12 months for which the Company has the intent and ability to hold the investment for greater than 12 months are classified as non-current and are included in investments, non-current in the consolidated balance sheets. Fair value of financial instruments As of December 31, 2021 and 2020 , the Company’s financial instruments consist of money market funds, commercial paper, agency and corporate bonds, and asset-backed securities are included in investments. The carrying value of investments is the estimated fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Property and equipment Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life. Assets not placed in service Assets not placed in service includes direct costs related to the acquisition of property including leasehold improvements, primarily from the Rockville manufacturing facility. Such costs are not depreciated until the asset is completed and placed into service. Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. During the year ended December 31, 2021, the Company recognized impairment of long-lived assets in association with the wind down of the UK manufacturing operations. See Note 13, Restructuring. No impairments of long-lived assets for the year ended December 31, 2020 were recognized. Restricted cash Cash accounts that are restricted as to withdrawal or usage are presented as restricted cash in the Company's balance sheets. Restricted cash includes amounts held as a security deposit in the form of a letter of credit for the Company’s leased facilities. Deferred offering costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations. Stock-based compensation The Company measures employee stock-based awards at grant-date fair value and records compensation expense on a straight-line basis over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions. The Company accounts for forfeitures as they occur. The Company measures the fair value of stock-based awards granted to non-employees on the date at which the related service is complete. Compensation expense is recognized over the period during which services are rendered by such non-employee consultants until completed. Estimating the fair value of stock options and warrants requires the input of subjective assumptions, including the expected life of the instrument and stock price volatility. The Company uses the value of its stock price as quoted on the Nasdaq Global Select Market to determine fair value of the Company’s common stock. The Company uses the Black-Scholes option pricing model to value its stock option awards and warrants. The assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, stock-based compensation expense could be materially different for future awards. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases are classified at their commencement date, which is defined as the date on which the lessor makes the underlying asset available for use by the lessee, as either operating or finance leases based on the economic substance of the agreement. The Company recognizes lease right-of-use assets and related liabilities in its consolidated balance sheets for both operating and finance leases. Lease liabilities are measured at the lease commencement date as the present value of the future lease payments using the interest rate implicit in the lease, or the incremental borrowing rate if the rate implicit in the lease is not readily determinable. Lease right-of-use assets are measured as the lease liability plus initial direct costs and prepaid lease payments less lease incentives. The lease term is the non-cancelable period of the lease and includes options to extend or terminate the lease when it is reasonably certain that an option will be exercised. The Company recognizes operating lease costs in operating expenses in its consolidated statements of operations, inclusive of rent escalation provisions and rent holidays, on a straight-line basis over the respective lease term. Research and development expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Upfront milestone payments made to third parties who perform research and development services on the Company’s behalf are expensed as services are rendered. Income taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A reduction in the carrying value of the deferred tax assets is required when it is not more likely than not that such deferred tax assets are not realizable. Net loss per share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. Dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted loss per share are the same. The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2021 and 2020, as they would be antidilutive: As of December 31, 2021 2020 Stock options outstanding 6,181,335 5,011,349 Common stock warrants 203,676 203,676 Restricted stock units 66,000 - Employee stock purchase plan 24,513 5,141 Total 6,475,524 5,220,166 Comprehensive loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources (which excludes investments from owners). The Company’s only element of other comprehensive loss is unrealized gains and losses on investments. Common stock Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Preferred stock The Board of Directors or any authorized committee thereof is expressly authorized, to the fullest extent permitted by law, to provide by resolution or resolutions for, out of the unissued shares of Undesignated Preferred Stock, the issuance of the shares of Undesignated Preferred Stock in one or more series of such stock, and by filing a certificate of designations pursuant to applicable law of the State of Delaware, to establish or change from time to time the number of shares of each such series, and to fix the designations, powers, including voting powers, full or limited, or no voting powers, preferences and the relative, participating, optional or other special rights of the shares of each series and any qualifications, limitations and restrictions thereof. As of December 31, 2021, there are no preferred shares issued. Reconciliation of cash, cash equivalents and restricted cash as presented in the statements of cash flows The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2021 and 2020. As of December 31, 2021 2020 Cash and cash equivalents $ 222,564 $ 94,155 Restricted cash 1,156 583 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 223,720 $ 94,738 Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one consolidated operating segment. JOBS Act accounting election The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. Recently adopted accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASC 842”), which amended a number of aspects of lease accounting and required entities to recognize right-of-use assets and liabilities on the balance sheet. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”), which provided a transition option to entities adopting ASC 842. The Company adopted ASC 842, Leases, including ASU 2018-11, effective January 1, 2021 on a modified-retrospective basis under which required the recognition of lease liabilities and right-of use assets at the adoption date but did not require retrospective adjustments of prior periods. The amended guidance resulted in the recognition of additional assets and corresponding liabilities on the Company's balance sheets. The Company elected the optional transition approach of not adjusting its comparative period financial statements for the impacts of adoption. The Company elected the package of transition practical expedients for leases that commenced prior to January 1, 2021, allowing it not to reassess (i) whether any expired or existing contracts contain leases, (ii) the lease classification for any expired or existing leases and (iii) the initial indirect costs for any existing leases. The Company recorded, upon adoption of ASC 842 effective January 1, 2021, operating lease assets and liabilities of $ 11.3 million and $ 11.8 million, respectively, related to its real estate leases under ASC 842. The cumulative effect of applying ASC 842 on the Company’s consolidated balance sheet as of January 1, 2021 was as follows: Assets Balance as of Adjustments Balance as of Prepaid expenses and other current assets $ 7,552 $ ( 154 ) $ 7,398 Right-of-use assets, operating leases - 11,300 11,300 Total assets $ 11,146 Liabilities and Shareholders' Equity Accrued expenses and other current liabilities $ 6,392 $ ( 168 ) $ 6,224 Operating lease liabilities - 2,630 2,630 Other liabilities 807 ( 482 ) 325 Operating lease liabilities, non-current - 9,166 9,166 Total liabilities and shareholders' equity $ 11,146 Adopting ASC 842 did not result in a material impact to the Company's statements of operations or cash flows.

Investments and Fair Value Meas

Investments and Fair Value Measurements	12 Months Ended
Investments and Fair Value Measurements	Dec. 31, 2021
Fair Value And Debt Securities Available For Sale [Abstract]
Investments and Fair Value Measurements	4. Invest ments and Fair Value Measurements As of December 31, 2021, investments were comprised of the following: Amortized Unrealized Unrealized Fair Corporate bonds $ 33,048 $ - $ ( 11 ) $ 33,037 U.S. Treasury securities 9,994 - ( 2 ) 9,992 Total $ 43,042 $ - $ ( 13 ) $ 43,029 As of December 31, 2020, investments were comprised of the following: Amortized Unrealized Unrealized Fair Corporate bonds $ 34,801 $ 60 $ - $ 34,861 U.S. Treasury securities 98,967 3 - 98,970 Total $ 133,768 $ 63 $ - $ 133,831 The Company follows FASB’s accounting guidance on fair value measurements for financial assets and liabilities measured on a recurring basis. Fair value is defined as the price at which an asset could be exchanged in a current transaction between knowledgeable, willing parties. Where available, fair value is based on observable market prices, or parameters derived from such prices. Where observable prices or inputs are not available, valuation models are applied. This hierarchy requires the use of observable market data when available and to minimize the use of unobservable inputs when determining fair value. These valuation techniques involve some level of management estimation and judgment. The degree of management estimation and judgment is dependent on the price transparency for the instruments, or market, and the instruments’ complexity. The guidance requires fair value measurements to be classified and disclosed in one of the following three categories: Level 1 — Quoted prices (unadjusted in active markets for identical assets or liabilities) Level 2 — Inputs other than quoted prices in active markets that are observable either directly or indirectly Level 3 — Unobservable inputs in which there is little or no market data, which require the Company to develop its own assumptions The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2021: Fair Value Measurement Based on Amortized Quoted Significant Significant Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 219,162 $ 219,162 $ 219,162 $ - $ - Corporate bonds 33,048 33,037 - 33,037 - U.S. Treasury securities 9,994 9,992 - 9,992 - Total $ 262,204 $ 262,191 $ 219,162 $ 43,029 $ - (1) Includes cash sweep accounts, U.S. Treasury money market mutual fund, bank certificates of deposit, U.S. Treasury bills and corporate bonds that have a maturity of three months or less from the original acquisition date. The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2020: Fair Value Measurement Based on Amortized Quoted Significant Significant Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 89,319 $ 89,319 $ 89,319 $ - $ - Corporate bonds 34,801 34,861 - 34,861 - U.S. Treasury securities 98,967 98,970 - 98,970 - Total $ 223,087 $ 223,150 $ 89,319 $ 133,831 $ - (1) Includes cash sweep accounts, U.S. Treasury money market mutual fund, bank certificates of deposit, U.S. Treasury bills and corporate bonds that have a maturity of three months or less from the original acquisition date. During the years ended December 31, 2021 and 2020 , there were no transfers among the Level 1, Level 2 and Level 3 categories.

Property and Equipment

Property and Equipment	12 Months Ended
Property and Equipment	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Property and Equipment	5. Prop erty and Equipment Property and equipment, net, consisted of: As of December 31, 2021 December 31, 2020 Laboratory equipment $ 13,115 $ 8,566 Computer hardware and equipment 54 109 Furniture and fixtures 376 432 Leasehold improvements 551 320 Assets not placed in service 7,592 3,320 21,688 12,747 Less: accumulated depreciation ( 4,613 ) ( 2,734 ) $ 17,075 $ 10,013 Depreciation expense was $ 2,827 and $ 1,592 for the years ended December 31, 2021 and 2020 , respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
Accrued Expenses and Other Current Liabilities	Dec. 31, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Ac crued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of: As of December 31, 2021 December 31, 2020 Employee compensation and related benefits $ 4,631 $ 3,808 Professional fees 413 224 Contract manufacturing organization fees 1,261 582 Contract research organization fees 2,810 487 Property received not yet invoiced 748 385 Accrued restructuring charges 2,401 - Other 830 906 $ 13,094 $ 6,392

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitm ents and Contingencies Litigation The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings. Royalty transfer agreement In connection with the sale of Series A redeemable convertible preferred stock prior to the Company's IPO, certain investors are entitled to receive, in the aggregate, a royalty from the Company equal to one percent of (i) all global net sales of any Company products and (ii) any license income on intellectual property that was in existence at the time of the Series A preferred stock financing. The Company has elected to account for this liability at fair value with changes recognized in the statement of operations. Given the early-stage nature of the underlying technology and inherent risks associated with obtaining regulatory approval and achieving commercialization, the Company ascribed no value to the royalty agreement at inception and for the years ended December 31, 2021 and 2020 . The Company currently does no t have any net sales or license income and as a result has paid no royalties under this obligation as of December 31, 2021 and 2020 no r has the Company accrued any liability as of December 31, 2021 and 2020 .

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2021
Leases [Abstract]
Leases	8. Lea ses The Company leases all of its offices and facilities, including its corporate headquarters, under operating leases. The Company has entered into various non-cancellable lease arrangements for facilities expiring at various times through 2036. Certain of these arrangements have free rent periods or escalating rent payment provisions. None of the Company's leases include residual value guarantees. Fixed fees for use of property or equipment and other services are included in the right-of-use assets and lease liabilities. Rent expense is recognized on a straight-line basis for total rent over the lease period. Variable service costs are included in the lease expense as incurred. The Company is generally obligated for the cost of property taxes, insurance, common area maintenance, and other administrative fees relating to its leases, which are considered variable lease costs and are expensed as incurred. In addition, the Company enters into contracts that have different service obligations. These contracts are considered multiple-element service contracts. When leases are embedded in multiple-element service contracts, all contract services are accounted for as a single lease component since the Company elected the practical expedient to not separate lease components and non-lease components. Operating Leases Office space and lab facility, Cambridge, Massachusetts In March 2018, the Company entered into a lease for office and laboratory facilities that expires in July 2025 . Under the terms of the lease, the Company placed a $ 290 letter of credit into a restricted cash account as security for the facility. Manufacturing facility, Stevenage, United Kingdom In December 2018, the Company signed a collaboration agreement (the Collaboration Agreement) with Cell Therapy Catapult Limited (Catapult) to establish the Company's manufacturing process in Catapult’s good manufacturing practice (GMP) manufacturing facility in the United Kingdom. The Collaboration Agreement provides for Catapult to provide identified space, called a module. The Company has concluded that the Collaboration Agreement contained an embedded lease as the Company has the right to operate the module in a manner it determines. The initial term of the Collaboration Agreement is three years which began March 1, 2019. The Company can terminate the Collaboration Agreement earlier with 12 months ’ notice and continued payment for contributions during the 12-month termination period. In December 2021, the Company elected to cease manufacturing operations at its Catapult facility by the end of 2021. As a result, the Company recognized a $ 1.5 million variable lease cost as of December 31, 2021 reflecting its estimated obligation for the 12-month termination period. Office space, Cambridge, Massachusetts In September 2019, the Company entered into a lease for office facilities that expires in September 2024 .Under the terms of the lease, the Company placed a $ 127 letter of credit into a restricted cash account as security for the facility. Lab facility, Cambridge Massachusetts In November 2020, the Company entered into a lease for office and laboratory facilities that expires in January 2024 . Under the terms of the lease, the Company placed $ 166 letter of credit into a restricted cash account as security for the facility. Manufacturing facility, Waltham, Massachusetts In November 2020, the Company entered into a manufacturing agreement with ElevateBio LLC (ElevateBio) which includes identified space dedicated to the Company. The Company has determined the agreement contains an embedded lease. The lease began in February 2021 when the Company obtained control of the dedicated manufacturing space and ends July 2022. In addition, in February 2022 we executed an agreement that expanded our partnership with ElevateBio by partnering for a second GMP manufacturing suite at ElevateBio BaseCamp in Waltham, Massachusetts through December 2023. Manufacturing facility, Rockville, Maryland In March 2021, the Company entered into a lease for a new manufacturing facility for an initial term of 15 years through June 2036 . The Company also has an option to extend the term of the lease for two consecutive terms of five years each. The Company placed a $ 557 letter of credit into a restricted cash account as security for the facility. Right-of-use assets and lease liabilities as of December 31, 2021 and January 1, 2021, the date of adoption of ASC 842, were as follows: December 31, January 1, Assets: Right-of-use assets, operating leases $ 28,283 $ 11,300 Liabilities Operating lease liabilities $ 3,367 $ 2,630 Operating lease liabilities, non-current 22,996 9,166 Total lease liabilities $ 26,363 $ 11,796 The components of the lease costs for the year ended December 31, 2021 were as follows: December 31, Operating lease costs $ 8,031 Short-term lease costs 548 Variable lease costs 5,937 Total lease costs $ 14,516 Total lease costs above are recognized in the consolidated statements of operation for the year ended December 31, 2021. Variable lease costs include the $ 1,501 cost associated with the Company’s decision to cease manufacturing operations at the Catapult facility during 2021. Weighted average remaining lease term and discount rate as of December 31, 2021 were as follows: December 31, Weighted-average remaining lease term (in years) Operating leases 11.5 Weighted-average discount rate: Operating leases 12.7 % The following table presents future minimum lease payments under for operating leases as of December 31, 2021: December 31, 2021 2022 $ 7,710 2023 7,144 2024 6,351 2025 5,255 2026 4,327 Thereafter 36,347 Total minimum payments required 67,134 Less amounts representing imputed interest ( 40,771 ) Present value of lease liabilities $ 26,363 Prior to adoption of ASC 842, future minimum lease payments under non-cancelable operating lease agreements as of December 31, 2020, were as follows: December 31, 2020 Minimum Lease Payments 2021 $ 4,966 2022 3,985 2023 3,690 2024 2,537 2025 1,054 Thereafter - Total $ 16,232 Rent expense for the year ended December 31, 2020 was $ 3.6 million.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2021
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	9. 401( k) Savings Plan The Company maintains a defined contribution 401(k) plan in which employees may contribute a portion of their compensation, subject to statutory maximum contribution amounts. For the years ended December 31, 2021 and 2020 , the matching contribution expense was $ 376 and $ 369 , respectively.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
Stock-based Compensation	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	10. St ock-Based Compensation In February 2019, the Company’s Board of Directors and stockholders approved the 2018 Stock Option and Incentive Plan (the 2018 Plan), which replaced the 2015 Plan. The shares under the 2015 Plan which were not issued, were rolled into the 2018 Plan. The number of shares of our common stock reserved for issuance under the 2018 Plan shall be cumulatively increased on January 1, 2020 and each January 1 thereafter by 4 % of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year or a lesser number of shares determined by our Board of Directors. The 2018 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s officers, employees, directors and other key persons (including consultants) are eligible to receive awards under the 2018 Plan. The amount, terms of grants, and exercisability provisions are determined and set by the Company’s Board of Directors. The maximum number of authorized shares to be issued under the Plan was 7,394,606 . As of December 31, 2021 , there were 433,343 shares of common stock available for future issuance. The term of the options may be up to 10 years, and options are exercisable in cash or as otherwise determined by the Board of Directors. Generally, options and restricted stock awards vest over a four-year period. The Company recorded stock-based compensation expense in the following expense categories of its accompanying consolidated statements of operations: For the Years Ended December 31, 2021 2020 Research and development $ 5,592 $ 3,351 General and administrative 6,673 5,141 $ 12,265 $ 8,492 Stock options The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2021 and 2020: Shares Weighted Weighted Balance as of January 1, 2020 4,189,292 $ 10.31 8.9 Granted 1,252,365 28.12 Exercised ( 241,995 ) 3.91 Forfeited ( 188,313 ) 12.31 Balance as of December 31, 2020 5,011,349 $ 14.99 8.4 Granted 2,094,554 9.32 Exercised ( 371,636 ) 2.55 Forfeited ( 552,932 ) 21.63 Balance as of December 31, 2021 6,181,335 $ 13.32 6.1 Exercisable as of December 31, 2021 2,482,070 $ 10.52 2.6 Vested and expected to vest as of December 31, 2021 6,181,335 - As of December 31, 2021 , there was $ 30,797 in unrecognized compensation cost that is expected to be recognized over an estimated weighted-average amortization period of 2.6 years. The aggregate intrinsic value of options outstanding and options exercisable as of December 31, 2021 was $ 1,368 . The aggregate intrinsic values of options exercised during the year ended December 31, 2021 was $ 2,608 . The fair value of options is estimated using the Black-Scholes option pricing model, which takes into account inputs such as the exercise price, the value of the underlying common stock at the grant date, expected term, expected volatility, risk-free interest rate and dividend yield. The fair value of each grant of options during the years ended December 31, 2021 and 2020 was determined using the methods and assumptions discussed below: ▪ The expected term of employee options is determined using the “simplified” method, as prescribed in the SEC Staff Accounting Bulletin (SAB) No. 107, whereby the expected life equals the arithmetic average of the vesting term and the original contractual term of the option due to the Company’s lack of sufficient historical data. The expected term of non-employee options is equal to the contractual term. ▪ The expected volatility is based on historical volatilities of similar entities within the Company’s industry which were commensurate with the expected term assumption as described in SAB No. 107. ▪ The estimated annual dividend yield is 0 % because the Company has not historically paid, and does not expect for the foreseeable future to pay, a dividend on its common stock. ▪ The Company is traded on the Nasdaq Select Market. Fair value is determined by the stock price quoted on the Nasdaq. For the years ended December 31, 2021 and 2020, the grant date fair value of all option grants was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: For the Years Ended December 31, 2021 2020 Risk-free interest rate 1.2 % 0.5 % Expected term (in years) 6.1 6.1 Expected volatility 70.2 % 75.0 % Annual dividend yield 0 % 0 % Fair value of common stock $ 9.42 $ 18.51 Restricted stock units During the year ended 2021, the Company granted 66,000 restricted stock units to employees. The restricted stock units (RSUs) vest over two years . The weighted-average grant date fair value of RSUs granted during the year ended December 31, 2021 was $ 4.80 . As of December 31, 2021, there was $ 317 of unrecognized compensation cost related to unvested employee RSUs. This amount is expected to be recognized over a weighted-average period of 1.7 years. Warrants Warrants issued to non-employees in connection with providing consulting services are issued outside of the Plan and are accounted for as stock-based compensation. The warrants have an exercise price of $ 0.74 per share and will expire at the earlier of ten years from the date of issuance or a change in control event as defined in the warrant agreements. As of December 31, 2021 and 2020, there were 203,676 warrants outstanding. During the years ending December 31, 2021 and 2020, the Company granted no warrants and there were no forfeitures. Employee stock purchase plan (ESPP) In February 2019, the Company’s Board of Directors adopted and the Company’s stockholders approved the 2018 Employee Stock Purchase Plan (2018 ESPP). The 2018 ESPP enables eligible employees to purchase shares of the Company's common stock at the end of each six-month offering period at a price equal to 85 % of the fair market value of the shares on the first business day or the last business day of the offering period, whichever is lower. Eligible employees generally included all employees. Offering periods began on the first trading day September 1 and March 1 of each year and ended on the last trading day in February and August of each year. Share purchases are funded through payroll deductions of up to 15 % of an employee’s eligible compensation for each payroll period, or $ 25 each calendar year. During the years ended December 31, 2021 and 2020, there were 17,889 and 23,864 shares issued under the 2018 ESPP, respectively

Income Tax Expense

Income Tax Expense	12 Months Ended
Income Tax Expense	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax expense	11. Inc ome Tax Expense Loss before income tax expense for the years ended December 31, 2021 and 2020 consisted of the following: For the Years Ended December 31, 2021 2020 United States $ ( 100,607 ) $ ( 67,625 ) Foreign 1,089 662 Loss before income taxes $ ( 99,518 ) $ ( 66,963 ) The income tax expense for the years ended December 31, 2021 and 2020 consisted of the following components: For the Years Ended December 31, 2021 2020 Current tax State $ 17 $ 30 Foreign 181 - Total current tax 198 30 Deferred tax Foreign 91 131 Total deferred tax 91 131 Income tax expense $ 289 $ 161 Subject to the limitations described below, at December 31, 2021, we have cumulative federal and state net operating loss carryforwards of approximately $ 4.1 million and $ 217.6 million available to reduce federal and state taxable income, respectively, which begin to expire in 2035 . Additionally, we have $ 214.8 million of federal net operating loss carryforwards which carryforward indefinitely. We have cumulative federal and state tax credit carry forwards of $8.1 million and $ 3.1 million, respectively, available to reduce federal and state income taxes which begin to expire in 2035 and 2031 , respectively. Section 382 of the Internal Revenue Code of 1986, as amended (the Code) provides for limitation on the use of net operating loss and research and development tax credit carryforwards following certain ownership changes (as defined in Code) that could limit the Company’s ability to utilize these carryforwards. Pursuant to Section 382 of the Code, an ownership change occurs when the stock ownership of a 5% stockholder increases by more than 50% over a three-year testing period. The Company may have experienced various ownership changes, as defined by the Code, as a result of past financings and may in the future experience an ownership change. Accordingly, the Company’s ability to utilize the aforementioned carryforwards may be limited. Additionally, U.S. tax laws limit the time during which these carryforwards may be applied against future taxes. The Company has not performed an Internal Revenue Code Section 382 study in connection with changes in control. The components of net deferred income tax assets (liabilities) as of December 31, 2021 and 2020 are as follows: As of December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 59,771 $ 34,749 Research and development credits 10,574 7,584 Equity-based compensation 1,810 2,874 Capitalized costs 5,029 5,646 Operating lease liabilities 7,124 - Accrued expenses and other temporary differences 921 1,020 Total deferred tax assets 85,229 51,873 Deferred tax liabilities: Depreciation ( 489 ) ( 392 ) Right-of-use assets, operating leases ( 7,643 ) - Total deferred tax liabilities ( 8,132 ) ( 392 ) Less: valuation allowance ( 77,391 ) ( 51,683 ) Total net deferred tax assets (liabilities) $ ( 294 ) $ ( 202 ) In assessing the realizability of the net deferred tax assets, the Company considers all relevant positive and negative evidence in determining whether it is more likely than not that some portion or all of the deferred income tax assets will not be realized. The realization of the gross deferred tax assets is dependent on several factors, including the generation of sufficient taxable income prior to the expiration of the net operating loss carryforwards. Management believes that it is more likely than not that the Company’s U.S. deferred income tax assets will not be realized. As such, there is a full valuation allowance against the net U.S. deferred tax assets as of December 31, 2021 and 2020. The Company is in a net deferred tax liability position in the United Kingdom and believes it is more likely than not that the foreign deferred income tax assets will be realized. As such, there is no valuation allowance against the U.K. deferred tax assets. The valuation allowance in the U.S. increased by approximately $ 25.7 million during the year ended December 31, 2021 primarily as a result of the increase in net operating loss carryforwards. The valuation allowance increased by approximately $ 21.4 million during the year ended December 31, 2020 primarily as a result of the increase in net operating loss carryforwards. The Company did no t have unrecognized tax benefits as of December 31, 2021 or 2020. The Company recognizes interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. A reconciliation of income tax expense at the statutory federal income tax rate and income taxes as reflected in the financial statements is as follows: As of December 31, 2021 2020 Statutory Federal income tax rate 21.0 % 21.0 % State income tax, net of federal benefit 5.1 % 6.4 % Stock compensation - 3.1 % 0.0 % Permanent differences - 0.2 % 0.1 % Research and development credit benefit 2.7 % 4.1 % Change in valuation allowance - 25.8 % - 32.0 % Effective income tax rate - 0.3 % - 0.4 % The Company’s remains subject to examination by U.S. Federal, state, local, and foreign tax authorities for tax years 2018 through 2021. With a few exceptions, we are no longer subject to U.S. Federal, state, local, and foreign examinations by tax authorities for the tax year 2017 and prior. However, net operating losses from the tax year 2017 and prior would be subject to examination if and when used in a future tax return to offset taxable income. Management believes that the Company does not have any uncertain tax positions that would result in a material impact on the Company’s financial statements. The Company files income tax returns in the above jurisdictions as well as the applicable state jurisdictions in the United States. There are currently no income tax examinations ongoing. If and when applicable, the Company will recognize interest and penalties on uncertain tax positions as income tax expense.

Related Party Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	12. Rela ted Party Transactions Manufacturing agreement During November 2020, we entered into a manufacturing partnership with ElevateBio, LLC. Dr. Ansbert Gadicke is a member of the board of directors at the Company and ElevateBio, LLC. The agreement is to establish a manufacturing partnership with ElevateBio, LLC for production of the Company’s clinical trial products. During the year ended December 31, 2021, we incurred $ 1,786 in expenses and have incurred additional costs of $ 252 for equipment owned by us for use by ElevateBio, LLC. Consulting arrangements On October 1, 2015, the Company entered into a consulting agreement with Dr. Patrick Baeuerle. Pursuant to the consulting agreement, Dr. Baeuerle agreed to perform such consulting, advisory and related services to and for the Company as may be reasonably requested. In exchange, the Company agreed to pay Dr. Baeuerle a consulting fee of € 15 per month. On November 1, 2016, the Company amended the consulting agreement to revise Dr. Baeuerle’s consulting fee to be € 3 per month. Dr. Baeuerle is also eligible for an annual bonus equal to 33 % of the annual fees paid under the consulting agreement, subject to the discretion of the Company's Board of Directors based on Dr. Baeuerle’s performance and the Company's performance. The term of the agreement is one year , and automatically extends for additional one-year periods unless terminated. Dr. Baeuerle was a member of the Company's Board of Directors and is a managing director at MPM Capital, the beneficial owner of more than 5 % of the Company's voting securities. As of August 24, 2021, Dr. Baeuerle resigned from the Board of Directors and is no longer considered a related party. During the year ended December 31, 2020, we incurred fees and travel related expenses to Dr. Baeuerle in the amount of $ 74 under the consulting agreement. During 2021, and prior to his departure from the board, we incurred fees and travel related expenses of $ 39 under the consulting agreement.

Restructuring

Restructuring	12 Months Ended
Restructuring	Dec. 31, 2021
Restructuring and Related Activities [Abstract]
Restructuring	13. Restru cturing During December 2021, the Company decided to wind down its operations in the United Kingdom and consolidated manufacturing operations in the United States. The Company expects the restructuring to be completed during the first quarter of 2022. During 2021, the Company incurred the following expenses which are included in research and development expenses on the statements of operations. Amounts included in lease costs below relate to our estimated obligation for the 12-month termination period for the Catapult facility, which was set to expire in April 2022 , and also a payment for additional space at a separate facility which was committed to during 2021 but never executed. For the Year Ended December 31, 2021 Severance and Related Costs Lease and Other costs Asset Impairment Costs Total Expense $ 885 $ 2,217 $ 559 $ 3,661 Accrued Restructuring Expenses Balances related to this restructuring included in accrued expenses on the balance sheet are as follows: As of December 31, 2021 Severance and Related Costs Lease and Other costs Total Expense $ 885 $ 2,217 $ 3,102 Cash payments ( 701 ) - ( 701 ) Accrued expense $ 184 $ 2,217 $ 2,401

Subsequent Event

Subsequent Event	12 Months Ended
Subsequent Event	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	14. Subs equent Event As previously described in our Form 8-K filing dated November 1, 2021 and as part of consolidating manufacturing in the United States, we have executed a new agreement with ElevateBio LLC for a second clean room to manufacture gavo-cel and future products. On February 11, 2022, our Board of Directors approved the TCR2 Therapeutics Inc. 2022 Inducement Plan (Inducement Plan) pursuant to Listing Rule 5635(c)(4) of the corporate governance rules of the NASDAQ Stock Market, and reserved 1,400,000 shares of our Common Stock for issuance employees of the Company under the Inducement Plan.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2021
Accounting Policies [Abstract]
Principles of consolidation and basis of presentation	Principles of consolidation and basis of presentation The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB
Use of estimates	Use of estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, and the fair value of stock-based compensation awards granted under the Company’s equity-based compensation plans. Due to the uncertainty of factors surrounding the estimates or judgments used in the preparation of the consolidated financial statements, actual results may materially vary from these estimates. Estimates and assumptions are periodically reviewed, and the effects of revisions are reflected in the consolidated financial statements in the period they are determined to be necessary.
Concentrations of credit risk and of manufacturing risk	Concentrations of credit risk and of manufacturing risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held by financial institutions in the United States. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions. As of December 31, 2021 , the Company had manufacturing arrangements with vendors for the supply of materials for use in preclinical and clinical studies. If the Company were to experience any disruptions in the vendors' ability or willingness to continue to provide manufacturing services, the Company may experience significant delays in its product development timelines and may incur substantial costs to secure alternative sources of manufacturing.
Fair value of financial instruments	Fair value of financial instruments As of December 31, 2021 and 2020 , the Company’s financial instruments consist of money market funds, commercial paper, agency and corporate bonds, and asset-backed securities are included in investments. The carrying value of investments is the estimated fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.
Cash equivalents	Cash equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2021 and 2020 , cash equivalents consisted of U.S treasuries, corporate bonds and government-backed money market funds.
Investments	Investments As of December 31, 2021, all investments were classified as available-for-sale and were carried at their estimated fair value. Unrealized gains and losses are recorded as a component of accumulated other comprehensive income (loss) until realized. The Company determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company periodically reviews its investments in debt securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. If losses on these securities are considered to be other than temporary, the loss is recognized in the statement of operations. The Company classifies its available-for-sale marketable securities as current or non-current based on each instrument’s underlying effective maturity date and for which the Company has the intent and ability to hold the investment for a period of greater than 12 months. Marketable securities with maturities of less than 12 months are classified as current and are included in investments in the consolidated balance sheets. Marketable securities with maturities greater than 12 months for which the Company has the intent and ability to hold the investment for greater than 12 months are classified as non-current and are included in investments, non-current in the consolidated balance sheets.
Property and equipment	Property and equipment Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life.
Assets not placed in service	Assets not placed in service Assets not placed in service includes direct costs related to the acquisition of property including leasehold improvements, primarily from the Rockville manufacturing facility. Such costs are not depreciated until the asset is completed and placed into service.
Impairment of long-lived assets	Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. During the year ended December 31, 2021, the Company recognized impairment of long-lived assets in association with the wind down of the UK manufacturing operations. See Note 13, Restructuring. No impairments of long-lived assets for the year ended December 31, 2020 were recognized.
Deferred offering costs	Deferred offering costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations.
Restricted cash	Restricted cash Cash accounts that are restricted as to withdrawal or usage are presented as restricted cash in the Company's balance sheets. Restricted cash includes amounts held as a security deposit in the form of a letter of credit for the Company’s leased facilities.
Leases	Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases are classified at their commencement date, which is defined as the date on which the lessor makes the underlying asset available for use by the lessee, as either operating or finance leases based on the economic substance of the agreement. The Company recognizes lease right-of-use assets and related liabilities in its consolidated balance sheets for both operating and finance leases. Lease liabilities are measured at the lease commencement date as the present value of the future lease payments using the interest rate implicit in the lease, or the incremental borrowing rate if the rate implicit in the lease is not readily determinable. Lease right-of-use assets are measured as the lease liability plus initial direct costs and prepaid lease payments less lease incentives. The lease term is the non-cancelable period of the lease and includes options to extend or terminate the lease when it is reasonably certain that an option will be exercised. The Company recognizes operating lease costs in operating expenses in its consolidated statements of operations, inclusive of rent escalation provisions and rent holidays, on a straight-line basis over the respective lease term.
Stock-based compensation	Stock-based compensation The Company measures employee stock-based awards at grant-date fair value and records compensation expense on a straight-line basis over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues awards with only service-based vesting conditions. The Company accounts for forfeitures as they occur. The Company measures the fair value of stock-based awards granted to non-employees on the date at which the related service is complete. Compensation expense is recognized over the period during which services are rendered by such non-employee consultants until completed. Estimating the fair value of stock options and warrants requires the input of subjective assumptions, including the expected life of the instrument and stock price volatility. The Company uses the value of its stock price as quoted on the Nasdaq Global Select Market to determine fair value of the Company’s common stock. The Company uses the Black-Scholes option pricing model to value its stock option awards and warrants. The assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, stock-based compensation expense could be materially different for future awards. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Research and development expenses	Research and development expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Upfront milestone payments made to third parties who perform research and development services on the Company’s behalf are expensed as services are rendered.
Income taxes	Income taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A reduction in the carrying value of the deferred tax assets is required when it is not more likely than not that such deferred tax assets are not realizable.
Net loss per share	Net loss per share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. Dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted loss per share are the same. The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2021 and 2020, as they would be antidilutive: As of December 31, 2021 2020 Stock options outstanding 6,181,335 5,011,349 Common stock warrants 203,676 203,676 Restricted stock units 66,000 - Employee stock purchase plan 24,513 5,141 Total 6,475,524 5,220,166
Comprehensive loss	Comprehensive loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources (which excludes investments from owners). The Company’s only element of other comprehensive loss is unrealized gains and losses on investments.
Common stock	Common stock Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Preferred stock	Preferred stock The Board of Directors or any authorized committee thereof is expressly authorized, to the fullest extent permitted by law, to provide by resolution or resolutions for, out of the unissued shares of Undesignated Preferred Stock, the issuance of the shares of Undesignated Preferred Stock in one or more series of such stock, and by filing a certificate of designations pursuant to applicable law of the State of Delaware, to establish or change from time to time the number of shares of each such series, and to fix the designations, powers, including voting powers, full or limited, or no voting powers, preferences and the relative, participating, optional or other special rights of the shares of each series and any qualifications, limitations and restrictions thereof. As of December 31, 2021, there are no preferred shares issued.
Reconciliation of cash, cash equivalents and restricted cash as presented in the statements of cash flows	Reconciliation of cash, cash equivalents and restricted cash as presented in the statements of cash flows The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2021 and 2020. As of December 31, 2021 2020 Cash and cash equivalents $ 222,564 $ 94,155 Restricted cash 1,156 583 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 223,720 $ 94,738
Segment information	Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one consolidated operating segment.
JOBS Act accounting election	JOBS Act accounting election The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
Recently issued and adopted accounting pronouncements	Recently adopted accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASC 842”), which amended a number of aspects of lease accounting and required entities to recognize right-of-use assets and liabilities on the balance sheet. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”), which provided a transition option to entities adopting ASC 842. The Company adopted ASC 842, Leases, including ASU 2018-11, effective January 1, 2021 on a modified-retrospective basis under which required the recognition of lease liabilities and right-of use assets at the adoption date but did not require retrospective adjustments of prior periods. The amended guidance resulted in the recognition of additional assets and corresponding liabilities on the Company's balance sheets. The Company elected the optional transition approach of not adjusting its comparative period financial statements for the impacts of adoption. The Company elected the package of transition practical expedients for leases that commenced prior to January 1, 2021, allowing it not to reassess (i) whether any expired or existing contracts contain leases, (ii) the lease classification for any expired or existing leases and (iii) the initial indirect costs for any existing leases. The Company recorded, upon adoption of ASC 842 effective January 1, 2021, operating lease assets and liabilities of $ 11.3 million and $ 11.8 million, respectively, related to its real estate leases under ASC 842. The cumulative effect of applying ASC 842 on the Company’s consolidated balance sheet as of January 1, 2021 was as follows: Assets Balance as of Adjustments Balance as of Prepaid expenses and other current assets $ 7,552 $ ( 154 ) $ 7,398 Right-of-use assets, operating leases - 11,300 11,300 Total assets $ 11,146 Liabilities and Shareholders' Equity Accrued expenses and other current liabilities $ 6,392 $ ( 168 ) $ 6,224 Operating lease liabilities - 2,630 2,630 Other liabilities 807 ( 482 ) 325 Operating lease liabilities, non-current - 9,166 9,166 Total liabilities and shareholders' equity $ 11,146 Adopting ASC 842 did not result in a material impact to the Company's statements of operations or cash flows.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2021
Schedule of Estimated Useful Lives of Property and Equipment	Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life.
Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations	The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2021 and 2020, as they would be antidilutive: As of December 31, 2021 2020 Stock options outstanding 6,181,335 5,011,349 Common stock warrants 203,676 203,676 Restricted stock units 66,000 - Employee stock purchase plan 24,513 5,141 Total 6,475,524 5,220,166
Schedule of Restricted Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2021 and 2020. As of December 31, 2021 2020 Cash and cash equivalents $ 222,564 $ 94,155 Restricted cash 1,156 583 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 223,720 $ 94,738
Effect of ASC 842 \| Adjustment [Member]
Schedule of cumulative effect on condensed balance sheet	The cumulative effect of applying ASC 842 on the Company’s consolidated balance sheet as of January 1, 2021 was as follows: Assets Balance as of Adjustments Balance as of Prepaid expenses and other current assets $ 7,552 $ ( 154 ) $ 7,398 Right-of-use assets, operating leases - 11,300 11,300 Total assets $ 11,146 Liabilities and Shareholders' Equity Accrued expenses and other current liabilities $ 6,392 $ ( 168 ) $ 6,224 Operating lease liabilities - 2,630 2,630 Other liabilities 807 ( 482 ) 325 Operating lease liabilities, non-current - 9,166 9,166 Total liabilities and shareholders' equity $ 11,146

Investments and Fair Value Me_2

Investments and Fair Value Measurements (Tables)	12 Months Ended
Investments and Fair Value Measurements (Tables)	Dec. 31, 2021
Fair Value And Debt Securities Available For Sale [Abstract]
Summary of Amortized Cost and Fair Values of Investment Securities Available-for-sale	As of December 31, 2021, investments were comprised of the following: Amortized Unrealized Unrealized Fair Corporate bonds $ 33,048 $ - $ ( 11 ) $ 33,037 U.S. Treasury securities 9,994 - ( 2 ) 9,992 Total $ 43,042 $ - $ ( 13 ) $ 43,029 As of December 31, 2020, investments were comprised of the following: Amortized Unrealized Unrealized Fair Corporate bonds $ 34,801 $ 60 $ - $ 34,861 U.S. Treasury securities 98,967 3 - 98,970 Total $ 133,768 $ 63 $ - $ 133,831
Summary of Classified Assets Measured at Fair Value on a Recurred Basis	The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2021: Fair Value Measurement Based on Amortized Quoted Significant Significant Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 219,162 $ 219,162 $ 219,162 $ - $ - Corporate bonds 33,048 33,037 - 33,037 - U.S. Treasury securities 9,994 9,992 - 9,992 - Total $ 262,204 $ 262,191 $ 219,162 $ 43,029 $ - (1) Includes cash sweep accounts, U.S. Treasury money market mutual fund, bank certificates of deposit, U.S. Treasury bills and corporate bonds that have a maturity of three months or less from the original acquisition date. The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2020: Fair Value Measurement Based on Amortized Quoted Significant Significant Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 89,319 $ 89,319 $ 89,319 $ - $ - Corporate bonds 34,801 34,861 - 34,861 - U.S. Treasury securities 98,967 98,970 - 98,970 - Total $ 223,087 $ 223,150 $ 89,319 $ 133,831 $ -

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
Property and Equipment (Tables)	Dec. 31, 2021
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment, net, consisted of: As of December 31, 2021 December 31, 2020 Laboratory equipment $ 13,115 $ 8,566 Computer hardware and equipment 54 109 Furniture and fixtures 376 432 Leasehold improvements 551 320 Assets not placed in service 7,592 3,320 21,688 12,747 Less: accumulated depreciation ( 4,613 ) ( 2,734 ) $ 17,075 $ 10,013

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Dec. 31, 2021
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of: As of December 31, 2021 December 31, 2020 Employee compensation and related benefits $ 4,631 $ 3,808 Professional fees 413 224 Contract manufacturing organization fees 1,261 582 Contract research organization fees 2,810 487 Property received not yet invoiced 748 385 Accrued restructuring charges 2,401 - Other 830 906 $ 13,094 $ 6,392

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Rental Payments under Non-cancellable Operating Leases	Prior to adoption of ASC 842, future minimum lease payments under non-cancelable operating lease agreements as of December 31, 2020, were as follows: December 31, 2020 Minimum Lease Payments 2021 $ 4,966 2022 3,985 2023 3,690 2024 2,537 2025 1,054 Thereafter - Total $ 16,232

Leases (Tables)

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2021
Leases [Abstract]
Schedule of Lease Related Right of Use Assets and Lease Liabilities	Right-of-use assets and lease liabilities as of December 31, 2021 and January 1, 2021, the date of adoption of ASC 842, were as follows: December 31, January 1, Assets: Right-of-use assets, operating leases $ 28,283 $ 11,300 Liabilities Operating lease liabilities $ 3,367 $ 2,630 Operating lease liabilities, non-current 22,996 9,166 Total lease liabilities $ 26,363 $ 11,796
Schedule of Components of Lease Costs	The components of the lease costs for the year ended December 31, 2021 were as follows: December 31, Operating lease costs $ 8,031 Short-term lease costs 548 Variable lease costs 5,937 Total lease costs $ 14,516
Schedule of Weighted Average Remaining Lease Term and Discount Rate	Weighted average remaining lease term and discount rate as of December 31, 2021 were as follows: December 31, Weighted-average remaining lease term (in years) Operating leases 11.5 Weighted-average discount rate: Operating leases 12.7 %
Schedule of Future Minimum Lease Payments Under for Operating Leases	The following table presents future minimum lease payments under for operating leases as of December 31, 2021: December 31, 2021 2022 $ 7,710 2023 7,144 2024 6,351 2025 5,255 2026 4,327 Thereafter 36,347 Total minimum payments required 67,134 Less amounts representing imputed interest ( 40,771 ) Present value of lease liabilities $ 26,363
Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases	Prior to adoption of ASC 842, future minimum lease payments under non-cancelable operating lease agreements as of December 31, 2020, were as follows: December 31, 2020 Minimum Lease Payments 2021 $ 4,966 2022 3,985 2023 3,690 2024 2,537 2025 1,054 Thereafter - Total $ 16,232

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
Stock-based Compensation (Tables)	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-based Compensation Expense	The Company recorded stock-based compensation expense in the following expense categories of its accompanying consolidated statements of operations: For the Years Ended December 31, 2021 2020 Research and development $ 5,592 $ 3,351 General and administrative 6,673 5,141 $ 12,265 $ 8,492
Schedule of Stock Option Activity	The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2021 and 2020: Shares Weighted Weighted Balance as of January 1, 2020 4,189,292 $ 10.31 8.9 Granted 1,252,365 28.12 Exercised ( 241,995 ) 3.91 Forfeited ( 188,313 ) 12.31 Balance as of December 31, 2020 5,011,349 $ 14.99 8.4 Granted 2,094,554 9.32 Exercised ( 371,636 ) 2.55 Forfeited ( 552,932 ) 21.63 Balance as of December 31, 2021 6,181,335 $ 13.32 6.1 Exercisable as of December 31, 2021 2,482,070 $ 10.52 2.6 Vested and expected to vest as of December 31, 2021 6,181,335 -
Schedule of Weighted-Average Assumptions	For the years ended December 31, 2021 and 2020, the grant date fair value of all option grants was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: For the Years Ended December 31, 2021 2020 Risk-free interest rate 1.2 % 0.5 % Expected term (in years) 6.1 6.1 Expected volatility 70.2 % 75.0 % Annual dividend yield 0 % 0 % Fair value of common stock $ 9.42 $ 18.51

Income Tax Expense (Tables)

Income Tax Expense (Tables)	12 Months Ended
Income Tax Expense (Tables)	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Components of Loss Before Income Tax Expense	Loss before income tax expense for the years ended December 31, 2021 and 2020 consisted of the following: For the Years Ended December 31, 2021 2020 United States $ ( 100,607 ) $ ( 67,625 ) Foreign 1,089 662 Loss before income taxes $ ( 99,518 ) $ ( 66,963 )
Components of Income Tax Expense	The income tax expense for the years ended December 31, 2021 and 2020 consisted of the following components: For the Years Ended December 31, 2021 2020 Current tax State $ 17 $ 30 Foreign 181 - Total current tax 198 30 Deferred tax Foreign 91 131 Total deferred tax 91 131 Income tax expense $ 289 $ 161
Components of Net Deferred Income Tax Assets (Liabilities)	The components of net deferred income tax assets (liabilities) as of December 31, 2021 and 2020 are as follows: As of December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 59,771 $ 34,749 Research and development credits 10,574 7,584 Equity-based compensation 1,810 2,874 Capitalized costs 5,029 5,646 Operating lease liabilities 7,124 - Accrued expenses and other temporary differences 921 1,020 Total deferred tax assets 85,229 51,873 Deferred tax liabilities: Depreciation ( 489 ) ( 392 ) Right-of-use assets, operating leases ( 7,643 ) - Total deferred tax liabilities ( 8,132 ) ( 392 ) Less: valuation allowance ( 77,391 ) ( 51,683 ) Total net deferred tax assets (liabilities) $ ( 294 ) $ ( 202 )
Reconciliation of Income Tax Expense at Statutory Federal Income Tax Rate and Income Taxes	A reconciliation of income tax expense at the statutory federal income tax rate and income taxes as reflected in the financial statements is as follows: As of December 31, 2021 2020 Statutory Federal income tax rate 21.0 % 21.0 % State income tax, net of federal benefit 5.1 % 6.4 % Stock compensation - 3.1 % 0.0 % Permanent differences - 0.2 % 0.1 % Research and development credit benefit 2.7 % 4.1 % Change in valuation allowance - 25.8 % - 32.0 % Effective income tax rate - 0.3 % - 0.4 %

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
Restructuring (Tables)	Dec. 31, 2021
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Costs	During 2021, the Company incurred the following expenses which are included in research and development expenses on the statements of operations. Amounts included in lease costs below relate to our estimated obligation for the 12-month termination period for the Catapult facility, which was set to expire in April 2022 , and also a payment for additional space at a separate facility which was committed to during 2021 but never executed. For the Year Ended December 31, 2021 Severance and Related Costs Lease and Other costs Asset Impairment Costs Total Expense $ 885 $ 2,217 $ 559 $ 3,661 Accrued Restructuring Expenses Balances related to this restructuring included in accrued expenses on the balance sheet are as follows: As of December 31, 2021 Severance and Related Costs Lease and Other costs Total Expense $ 885 $ 2,217 $ 3,102 Cash payments ( 701 ) - ( 701 ) Accrued expense $ 184 $ 2,217 $ 2,401

Organization and Description _2

Organization and Description of Business - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 22, 2021	Jul. 31, 2020	Dec. 31, 2021
ATM Program [Member]
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, net of issuance costs (shares)			0
Equity Offering
Subsidiary Sale Of Stock [Line Items]
Shares sold during initial public offering (shares)	4,590,164	9,200,000
Share price (USD per share)	$ 30.50	$ 15.50
Proceeds from issuance of common stock after underwriting discounts and commissions and estimated offering expenses	$ 131.3	$ 133.6
Underwriting discounts, commissions and estimated offering expenses	$ 8.7	$ 9

Liquidity - Narrative (Details)

Liquidity - Narrative (Details) $ in Millions	Dec. 31, 2021USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 265.6

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2021
Laboratory Equipment
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Estimated Useful Lives	5 years
Computer Hardware and Equipment
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Estimated Useful Lives	3 years
Furniture and Fixtures \| Minimum
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Estimated Useful Lives	5 years
Furniture and Fixtures \| Maximum
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Estimated Useful Lives	7 years
Leasehold Improvements
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Estimated Useful Lives	Lesser of lease term or estimated useful life.

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	Dec. 31, 2021USD ($)Voteshares	Jan. 01, 2021USD ($)	Dec. 31, 2020shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Votes per each common stock share \| Vote	1
Preferred stock, shares issued (shares) \| shares	0		0
Operating Lease, Assets		$ 11,300
Operating Lease, Liability	$ 26,363	$ 11,796

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	6,475,524	5,220,166
Stock options outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	6,181,335	5,011,349
Common stock warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	203,676	203,676
Employee stock purchase plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	24,513	5,141
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	66,000

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Reconciliation of Cash and Cash Equivalents and Restricted Cash as presented in the Statements of Cash Flows (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Jan. 01, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 222,564		$ 94,155
Restricted cash	1,156		583
Cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 223,720	$ 94,738	$ 94,738	$ 65,713

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of cumulative effect on consolidated balance sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Assets [Abstract]
Prepaid expenses and other current assets	$ 10,534		$ 7,552
Right-of-use assets, operating leases	28,283	$ 11,300	0
Total assets	323,371		246,195
Liabilities and Equity [Abstract]
Accrued expenses and other current liabilities	13,094		6,392
Operating lease liabilities	3,367	2,630	0
Other liabilities			807
Operating lease liabilities, non-current	22,996	9,166	0
Total liabilities and stockholders’ equity	$ 323,371		$ 246,195
Adjustment [Member]
Assets [Abstract]
Prepaid expenses and other current assets		7,398
Right-of-use assets, operating leases		11,300
Liabilities and Equity [Abstract]
Accrued expenses and other current liabilities		6,224
Operating lease liabilities		2,630
Other liabilities		325
Operating lease liabilities, non-current		9,166
Adjustment [Member] \| Effect of ASC 842 \| Adjustment [Member]
Assets [Abstract]
Prepaid expenses and other current assets		(154)
Right-of-use assets, operating leases		11,300
Total assets		11,146
Liabilities and Equity [Abstract]
Accrued expenses and other current liabilities		(168)
Operating lease liabilities		2,630
Other liabilities		(482)
Operating lease liabilities, non-current		9,166
Total liabilities and stockholders’ equity		$ 11,146

Investments and Fair Value Me_3

Investments and Fair Value Measurements - Summary of Amortized Cost and Fair Values of Investment Securities Available-for-sale (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 43,042	$ 133,768
Unrealized Gains	0	63
Unrealized Losses	(13)	0
Fair Value	43,029	133,831
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	33,048	34,801
Unrealized Gains	0	60
Unrealized Losses	(11)	0
Fair Value	33,037	34,861
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,994	98,967
Unrealized Gains	0	3
Unrealized Losses	(2)	0
Fair Value	$ 9,992	$ 98,970

Investments and Fair Value Me_4

Investments and Fair Value Measurements - Summary of Classified Assets Measured at Fair Value on a Recurred Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 222,564	$ 94,155
Available-for-sale securities, amortized cost	43,042	133,768
Fair Value	43,029	133,831
Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	219,162	89,319
Cash equivalents, fair value	219,162	89,319
Available-for-sale securities, amortized cost	262,204	223,087
Available-for-sale securities, fair value	262,191	223,150
Fair Value, Recurring \| Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	219,162	89,319
Available-for-sale securities, fair value	219,162	89,319
Fair Value, Recurring \| Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	0
Available-for-sale securities, fair value	43,029	133,831
Fair Value, Recurring \| Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	0
Available-for-sale securities, fair value	0
Fair Value, Recurring \| Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost	33,048	34,801
Fair Value	33,037	34,861
Fair Value, Recurring \| Corporate bonds \| Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	0
Fair Value, Recurring \| Corporate bonds \| Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	33,037	34,861
Fair Value, Recurring \| Corporate bonds \| Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	0
Fair Value, Recurring \| U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost	9,994	98,967
Fair Value	9,992	98,970
Fair Value, Recurring \| U.S. Treasury securities \| Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	0
Fair Value, Recurring \| U.S. Treasury securities \| Fair Value, Inputs, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	9,992	98,970
Fair Value, Recurring \| U.S. Treasury securities \| Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value	$ 0

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 21,688	$ 12,747
Less: accumulated depreciation	(4,613)	(2,734)
Property and equipment, net	17,075	10,013
Laboratory equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	13,115	8,566
Computer hardware and equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	54	109
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	376	432
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	551	320
Assets Not Placed In Service
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 7,592	$ 3,320

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 2,827	$ 1,592

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Employee compensation and related benefits	$ 4,631	$ 3,808
Professional fees	413	224
Contract manufacturing organization fees	1,261	582
Contract research organization fees	2,810	487
Property received not yet invoiced	748	385
Accrued restructuring charges	2,401
Other	830	906
Accrued expenses and other current liabilities	$ 13,094	$ 6,392

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Royalty payments, percentage of net sales	1.00%
Royalty payments, percentage of license income	1.00%
Royalty agreement value	$ 0	$ 0
Royalties paid	0	0
Accrued liabilities	0	0
Global Net Sales
Other Commitments [Line Items]
Revenue	0	0
Intellectual License Income
Other Commitments [Line Items]
Revenue	$ 0	$ 0

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended					12 Months Ended
Leases - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Nov. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Lease facility expiration date		2024-01	2024-09		2025-07
Initial term				3 years
Termination period notice requirement				12 months
Termination period				12 months
Restricted Cash	$ 557	$ 166	$ 127		$ 290
Variable lease costs						$ 5,937
Rent expense							$ 3,600
Rockville Maryland [Member]
Lessee, Lease, Description [Line Items]
Lease facility expiration date	2036-06
Initial term	15 years
Variable lease costs						$ 1,501
Lessee, Operating Lease, Existence of Option to Extend [true false]						true
Lessee, Operating Lease, Option to Extend	The Company also has an option to extend the term of the lease for two consecutive terms of five years each.
Stevenage United Kingdom [Member]
Lessee, Lease, Description [Line Items]
Variable lease costs						$ 1,500

Leases - Schedule of Leases Rel

Leases - Schedule of Leases Related Right of Use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Assets [Abstract]
Right-of-use assets, operating leases	$ 28,283	$ 11,300	$ 0
Liabilities [Abstract]
Operating lease liabilities	3,367	2,630	0
Operating lease liabilities, non-current	22,996	9,166	$ 0
Total lease liabilities	$ 26,363	$ 11,796

Leases - Schedule of Components

Leases - Schedule of Components of Lease Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Leases [Abstract]
Operating lease costs	$ 8,031
Short-term lease costs	548
Variable lease costs	5,937
Lease, Cost, Total	$ 14,516

Leases - Weighted Average Remai

Leases - Weighted Average Remaining Lease Term and Discount Rate (Details)	Dec. 31, 2021
Leases [Abstract]
Operating leases, Weighted-average remaining lease term (in years)	11 years 6 months
Operating leases, Weighted-average discount rate	12.70%

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payment Under for Operating Lease (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021
Leases [Abstract]
2022	$ 7,710
2023	7,144
2024	6,351
2025	5,255
2026	4,327
Thereafter	36,347
Total minimum payments required	67,134
Less amounts representing imputed interest	(40,771)
Present value of lease liabilities	$ 26,363	$ 11,796

Leases - Schedule of Future M_2

Leases - Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 4,966
2022	3,985
2023	3,690
2024	2,537
2025	1,054
Thereafter	0
Total	$ 16,232

401(k) Savings Plan - Narrative

401(k) Savings Plan - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
401(k) Plan
Defined Contribution Plan Disclosure [Line Items]
Expense relating to the matching contribution under 401(k) plan	$ 376	$ 369

Stock-based Compensation - Narr

Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Unrecognized compensation costs		$ 30,797
Unrecognized compensation cost, period of recognition		2 years 7 months 6 days
Aggregate intrinsic value of options outstanding and options exercisable		$ 1,368
Aggregate intrinsic values of options exercised		$ 2,608
Annual dividend yield		0.00%	0.00%
Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock, percentage of fair market value	85.00%
Stock purchase offering period				6 months
Maximum stock purchase value per employee, percent of eligible compensation	15.00%
Maximum stock purchase value per employee	$ 25
ESPP shares issued (in shares)		17,889	23,864
Common stock warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options		10 years
Initial exercise price of warrants		$ 0.74
Warrants outstanding (in shares)		203,676	203,676
Warrants granted (in shares)		0	0
Warrants forfeited (in shares)		0	0
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs		$ 317
Unrecognized compensation cost, period of recognition		1 year 8 months 12 days
Restricted Stock Units, Granted		66,000
Restricted Stock Units, Vesting Period		2 years
Restricted Stock Units, Weighted Average Grant Date Fair Value, Granted		$ 4.80
2018 Stock Option and Incentive Plan \| Employee stock purchase plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance (in shares)		433,343
2018 Stock Option and Incentive Plan \| Stock options outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for issuance as a percentage of outstanding shares, maximum		4.00%
Number of shares authorized (in shares)		7,394,606
Term of options		10 years

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 12,265	$ 8,492
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	5,592	3,351
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 6,673	$ 5,141

Stock-based Compensation - St_2

Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning balance (in shares)	5,011,349	4,189,292
Options granted (in shares)	2,094,554	1,252,365
Options exercised (in shares)	(371,636)	(241,995)
Options forfeited (in shares)	(552,932)	(188,313)
Options outstanding, ending balance (in shares)	6,181,335	5,011,349	4,189,292
Options exercisable (in shares)	2,482,070
Options vested and expected to vest (in shares)	6,181,335
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding, weighted average exercise price per share, beginning balance (in dollars per share)	$ 14.99	$ 10.31
Options granted, weighted average exercise price per share (in dollars per share)	9.32	28.12
Options exercised, weighted average exercise price per share (in dollars per share)	2.55	3.91
Options forfeited, weighted average exercise price per share (in dollars per share)	21.63	12.31
Options outstanding, weighted average exercise price per share, ending balance (in dollars per share)	13.32	$ 14.99	$ 10.31
Options exercisable, weighted average exercise price per share, ending balance (in dollars per share)	$ 10.52
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, weighted average remaining contractual life (in years)	6 years 1 month 6 days	8 years 4 months 24 days	8 years 10 months 24 days
Options exercisable, weighted average remaining contractual life (in years)	2 years 7 months 6 days

Stock-based Compensation - St_3

Stock-based Compensation - Stock Options Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.20%	0.50%
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	70.20%	75.00%
Annual dividend yield	0.00%	0.00%
Fair value of common stock	$ 9.42	$ 18.51

Income Tax Expense - Components

Income Tax Expense - Components of Loss Before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
United States	$ (100,607)	$ (67,625)
Foreign	1,089	662
Loss before income tax expense	$ (99,518)	$ (66,963)

Income Tax Expense - Componen_2

Income Tax Expense - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Current tax
State	$ 17	$ 30
Foreign	181
Total current tax	198	30
Deferred tax
Foreign	91	131
Total deferred Tax	91	131
Income tax expense	$ 289	$ 161

Income Tax Expense - Narrative

Income Tax Expense - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Line Items]
Valuation allowance	$ 77,391	$ 51,683
Unrecognized tax benefits	$ 0	0
Internal Revenue Service (IRS)
Income Tax Disclosure [Line Items]
Ownership change pursuant to section 382 of IRS, description	an ownership change occurs when the stock ownership of a 5% stockholder increases by more than 50% over a three-year testing period.
Federal
Income Tax Disclosure [Line Items]
Cumulative net operating loss carryforwards	$ 4,100
Federal net operating losses carryforward indefinitely	$ 214,800
Operating loss carry forwards expiration year	2035
Tax credit carryforwards expiration year	2035
Valuation allowance increased	$ 25,700	$ 21,400
State
Income Tax Disclosure [Line Items]
Cumulative net operating loss carryforwards	$ 217,600
Operating loss carry forwards expiration year	2035
Tax credit carryforwards expiration year	2031
Cumulative tax credit forward	$ 3,100
U.K
Income Tax Disclosure [Line Items]
Valuation allowance	$ 0

Income Tax Expense - Componen_3

Income Tax Expense - Components of Net Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 59,771	$ 34,749
Research and development credits	10,574	7,584
Equity-based compensation	1,810	2,874
Capitalized costs	5,029	5,646
Accrued expenses and other	921	1,020
Operating lease liabilities	7,124	0
Total deferred tax assets	85,229	51,873
Depreciation	(489)	(392)
Right-of-use assets, operating leases	(7,643)	0
Total deferred tax liabilities	(8,132)	(392)
Less: valuation allowance	(77,391)	(51,683)
Total net deferred tax assets (liabilities)	$ (294)	$ (202)

Income Tax Expense - Reconcilia

Income Tax Expense - Reconciliation of Income Tax Expense at Statutory Federal Income Tax Rate and Income Taxes (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory Federal income tax rate	21.00%	21.00%
State income tax, net of federal benefit	5.10%	6.40%
Stock compensation	(3.10%)	0.00%
Permanent differences	(0.20%)	0.10%
Research and development credit benefit	2.70%	4.10%
Change in valuation allowance	(25.80%)	(32.00%)
Effective income tax rate	(0.30%)	(0.40%)

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) € in Thousands, $ in Thousands	Nov. 01, 2016EUR (€)	Oct. 01, 2015EUR (€)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)
MPM Capital \| TCR2 Therapeutics Inc.
Related Party Transaction [Line Items]
Shareholder ownership, percentage			5.00%
Dr Ansbert Gadicke \| Elevate Bio \| Director
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions			$ 1,786
Additional cost incurred from equipment usage by related party			252
Dr. Patrick Baeuerle \| Consulting Agreement, Fees \| Director
Related Party Transaction [Line Items]
Related party transaction, amount of transaction \| €	€ 3	€ 15
Dr. Patrick Baeuerle \| Consulting Agreement \| Director
Related Party Transaction [Line Items]
Related party transaction, eligible bonus as percentage of annual fees		33.00%
Related party transaction, term of agreement		1 year
Related party transaction, term of agreement, extension option		1 year
Dr. Patrick Baeuerle \| Consulting Agreement, Fees \| Director
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions			$ 39	$ 74

Restructuring - Narrative (Deta

Restructuring - Narrative (Details)	12 Months Ended
Restructuring - Narrative (Details)	Dec. 31, 2021
Restructuring and Related Activities [Abstract]
Lease Expiration Date	Apr. 30, 2022

Restructuring - Schedule of Res

Restructuring - Schedule of Restructuring Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)
Restructuring Cost and Reserve [Line Items]
Lease and Other costs	$ 14,516
Accrued Restructuring Expenses [Member] \| Expense [Member]
Restructuring Cost and Reserve [Line Items]
Severance and Related Costs	885
Lease and Other costs	2,217
Restructuring charges, total	3,102
Accrued Restructuring Expenses [Member] \| Cash Payments [Member]
Restructuring Cost and Reserve [Line Items]
Severance and Related Costs	(701)
Lease and Other costs
Restructuring charges, total	(701)
Accrued Restructuring Expenses [Member] \| Accrued Expense [Member]
Restructuring Cost and Reserve [Line Items]
Severance and Related Costs	184
Lease and Other costs	2,217
Restructuring charges, total	2,401
Research And Development Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Severance and Related Costs	885
Lease and Other costs	2,217
Asset Impairment Costs	559
Restructuring charges, total	$ 3,661

Subsequent Event - Narrative (D

Subsequent Event - Narrative (Details)	Feb. 11, 2022shares
Subsequent Event [Member]
Subsequent Event [Line Items]
Number of shares available for issuance (in shares)	1,400,000

Quarterly Financial Information

Quarterly Financial Information (unaudited) - Summary of Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating expenses
Research and development	$ 77,239	$ 51,980
General and administrative	22,503	16,720
Total operating expenses	99,742	68,700
Loss from operations	(99,742)	(68,700)
Interest income, net	224	1,737
Loss before income tax expense	(99,518)	(66,963)
Loss from operations	(99,742)	(68,700)
Income tax expense	289	161
Net loss	$ (99,807)	$ (67,124)
Per share information
Net loss per share of common stock, basic and diluted	$ (2.63)	$ (2.40)
Weighted average shares outstanding, basic and diluted	37,935,554	27,990,564