Tcr2 Therapeutics (TCRR) 10-Q 12 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 03, 2020
Cover [Abstract]
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.0001 Par Value
City Area Code	617
Entity Address, Address Line One	100 Binney Street
Entity Incorporation, State or Country Code	DE
Entity File Number	001-38811
Document Transition Report	false
Document Quarterly Report	true
Entity Registrant Name	TCR2 Therapeutics Inc.
Entity Central Index Key	0001750019
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		33,422,129
Entity Tax Identification Number	47-4152751
Entity Address, Address Line Two	Suite 710
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
Local Phone Number	949-5200
Trading Symbol	TCRR
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes

Unaudited Consolidated Balance

Unaudited Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 101,614	$ 65,296
Investments	145,109	92,828
Prepaid expenses and other current assets	7,509	5,061
Total current assets	254,232	163,185
Property and equipment, net	6,201	4,926
Restricted cash	417	417
Total assets	260,850	168,528
Liabilities and stockholders’ equity
Accounts payable	2,948	2,483
Accrued expenses and other current liabilities	4,904	5,050
Total current liabilities	7,852	7,533
Other liabilities	635	546
Total liabilities	8,487	8,079
Commitments and contingencies (Note 7)
Stockholders’ equity
Preferred stock, $0.0001 par value. 10,000,000 shares authorized, no shares issued or outstanding at September 30, 2020 and December 31, 2019, respectively.
Common stock, $0.0001 par value; 150,000,000 shares authorized; 33,397,669 and 24,050,936 shares issued; 33,380,211 and 23,981,109 shares outstanding at September 30, 2020 and December 31, 2019, respectively.	3	2
Additional paid-in capital	483,433	342,896
Accumulated other comprehensive income	191	142
Accumulated deficit	(231,264)	(182,591)
Total stockholders’ equity	252,363	160,449
Total liabilities and stockholders’ equity	$ 260,850	$ 168,528

Unaudited Consolidated Balanc_2

Unaudited Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
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)	33,397,669	24,050,936
Common stock, shares outstanding (shares)	33,380,211	23,981,109

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses
Research and development	$ 12,820	$ 11,374	$ 37,682	$ 28,096
General and administrative	4,371	3,522	12,451	9,715
Total operating expenses	17,191	14,896	50,133	37,811
Loss from operations	(17,191)	(14,896)	(50,133)	(37,811)
Interest income, net	300	1,090	1,546	3,039
Loss before income taxes	(16,891)	(13,806)	(48,587)	(34,772)
Income taxes	31		86
Net loss	(16,922)	(13,806)	(48,673)	(34,772)
Accretion of redeemable convertible preferred stock to redemption value				(49,900)
Net loss attributable to common stockholders	$ (16,922)	$ (13,806)	$ (48,673)	$ (84,672)
Per share information
Net loss per share of common stock, basic and diluted	$ (0.56)	$ (0.58)	$ (1.86)	$ (4.21)
Weighted average shares outstanding, basic and diluted	30,340,355	23,874,593	26,158,040	20,125,955

Unaudited Consolidated Statem_2

Unaudited Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,922)	$ (13,806)	$ (48,673)	$ (34,772)
Unrealized gain (loss) on investments, net	(211)	18	49	336
Comprehensive loss	$ (17,133)	$ (13,788)	$ (48,624)	$ (34,436)

Unaudited Consolidated Statem_3

Unaudited Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Initial Public Offering (IPO)	Series A redeemable convertible preferred stock	Series B redeemable convertible preferred stock	Common Stock	Common StockInitial Public Offering (IPO)	Additional Paid-in Capital	Additional Paid-in CapitalInitial Public Offering (IPO)	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Redeemable convertible preferred stock beginning balance at Dec. 31, 2018			$ 72,980	$ 136,250
Redeemable convertible preferred stock, beginning balance (shares) at Dec. 31, 2018			44,500,001	62,500,000
Beginning balance at Dec. 31, 2018	$ (85,696)								$ (85,590)	$ (106)
Beginning balance (shares) at Dec. 31, 2018					726,990
Reclassification of shares issued and previously subject to repurchase	13						$ 13
Reclassification of shares issued and previously subject to repurchase (shares)					39,779
Exercise of stock options (shares)					124
Stock-based compensation expense	1,141						1,141
Unrealized gain (loss) on investments	107									107
Accretion of redeemable preferred stock to redemption value			$ 34,789	$ 15,111
Accretion of redeemable preferred stock to redemption value	(49,900)						(498)		(49,402)
Conversion of shares upon IPO			$ (107,769)	$ (151,361)
Conversion of shares upon IPO (in shares)			(44,500,001)	(62,500,000)	17,275,299
Conversion of shares upon IPO	259,130				$ 2		259,128
Issuance of common stock, net of issuance costs		$ 77,155						$ 77,155
Issuance of common stock, net of issuance costs (shares)						5,750,000
Net loss	(9,903)								(9,903)
Ending balance at Mar. 31, 2019	192,047				$ 2		336,939		(144,895)	1
Ending balance (shares) at Mar. 31, 2019					23,792,192
Redeemable convertible preferred stock beginning balance at Dec. 31, 2018			$ 72,980	$ 136,250
Redeemable convertible preferred stock, beginning balance (shares) at Dec. 31, 2018			44,500,001	62,500,000
Beginning balance at Dec. 31, 2018	$ (85,696)								(85,590)	(106)
Beginning balance (shares) at Dec. 31, 2018					726,990
Exercise of stock options (shares)	82,509
Unrealized gain (loss) on investments	$ 336
Accretion of redeemable preferred stock to redemption value	49,900
Net loss	(34,772)
Ending balance at Sep. 30, 2019	171,154				$ 2		340,686		(169,764)	230
Ending balance (shares) at Sep. 30, 2019					23,944,083
Beginning balance at Mar. 31, 2019	192,047				$ 2		336,939		(144,895)	1
Beginning balance (shares) at Mar. 31, 2019					23,792,192
Reclassification of shares issued and previously subject to repurchase	13						13
Reclassification of shares issued and previously subject to repurchase (shares)					39,777
Exercise of stock options	18						18
Exercise of stock options (shares)					24,721
Stock-based compensation expense	1,444						1,444
Unrealized gain (loss) on investments	211									211
Issuance of common stock, net of issuance costs		$ (34)						$ (34)
Net loss	(11,063)								(11,063)
Ending balance at Jun. 30, 2019	182,636				$ 2		338,380		(155,958)	212
Ending balance (shares) at Jun. 30, 2019					23,856,690
Reclassification of shares issued and previously subject to repurchase	13						13
Reclassification of shares issued and previously subject to repurchase (shares)					19,115
Exercise of stock options	281						281
Exercise of stock options (shares)					68,278
Stock-based compensation expense	2,012						2,012
Unrealized gain (loss) on investments	18									18
Net loss	(13,806)								(13,806)
Ending balance at Sep. 30, 2019	171,154				$ 2		340,686		(169,764)	230
Ending balance (shares) at Sep. 30, 2019					23,944,083
Beginning balance at Dec. 31, 2019	$ 160,449				$ 2		342,896		(182,591)	142
Beginning balance (shares) at Dec. 31, 2019	23,981,109				23,981,109
Reclassification of shares issued and previously subject to repurchase	$ 13						13
Reclassification of shares issued and previously subject to repurchase (shares)					17,456
Exercise of stock options	185						185
Exercise of stock options (shares)					57,904
Stock-based compensation expense	2,055						2,055
Unrealized gain (loss) on investments	(604)									(604)
Net loss	(15,506)								(15,506)
Ending balance at Mar. 31, 2020	146,592				$ 2		345,149		(198,097)	(462)
Ending balance (shares) at Mar. 31, 2020					24,056,469
Beginning balance at Dec. 31, 2019	$ 160,449				$ 2		342,896		(182,591)	142
Beginning balance (shares) at Dec. 31, 2019	23,981,109				23,981,109
Exercise of stock options (shares)	122,869
Unrealized gain (loss) on investments	$ 49
Accretion of redeemable preferred stock to redemption value	0
Net loss	(48,673)
Ending balance at Sep. 30, 2020	$ 252,363				$ 3		483,433		(231,264)	191
Ending balance (shares) at Sep. 30, 2020	33,380,211				33,380,211
Beginning balance at Mar. 31, 2020	$ 146,592				$ 2		345,149		(198,097)	(462)
Beginning balance (shares) at Mar. 31, 2020					24,056,469
Reclassification of shares issued and previously subject to repurchase	13						13
Reclassification of shares issued and previously subject to repurchase (shares)					17,456
Exercise of stock options	125						125
Exercise of stock options (shares)					30,670
Stock-based compensation expense	2,064						2,064
Unrealized gain (loss) on investments	864									864
Net loss	(16,245)								(16,245)
Ending balance at Jun. 30, 2020	133,413				$ 2		347,351		(214,342)	402
Ending balance (shares) at Jun. 30, 2020					24,104,595
Reclassification of shares issued and previously subject to repurchase	13						13
Reclassification of shares issued and previously subject to repurchase (shares)					17,457
Exercise of stock options	432						432
Exercise of stock options (shares)					58,159
Stock-based compensation expense	2,067						2,067
Unrealized gain (loss) on investments	(211)									(211)
Issuance of common stock, net of issuance costs	133,571				$ 1		133,570
Issuance of common stock, net of issuance costs (shares)					9,200,000
Net loss	(16,922)								(16,922)
Ending balance at Sep. 30, 2020	$ 252,363				$ 3		$ 483,433		$ (231,264)	$ 191
Ending balance (shares) at Sep. 30, 2020	33,380,211				33,380,211

Unaudited Consolidated Statem_4

Unaudited Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (48,673)	$ (34,772)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,114	558
Stock-based compensation expense	6,186	4,597
Deferred tax liabilities	86	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,449)	(3,615)
Accounts payable	610	489
Accrued expenses and other liabilities	(114)	1,697
Cash used in operating activities	(43,240)	(31,046)
Investing activities
Purchases of equipment	(2,523)	(3,060)
Purchases of investments	(162,147)	(126,534)
Proceeds from sale or maturity of investments	109,916	82,990
Cash used in investing activities	(54,754)	(46,604)
Financing activities
Proceeds from public offering of common stock, net of issuance costs	133,570	79,121
Proceeds from the exercise of stock options	742	299
Cash provided by financing activities	134,312	79,420
Net change in cash, cash equivalents, and restricted cash	36,318	1,770
Cash, cash equivalents, and restricted cash at beginning of year	65,713	47,964
Cash, cash equivalents, and restricted cash at end of period	102,031	49,734
Supplemental disclosure of noncash activities
Conversion of redeemable convertible preferred stock to common stock	0	259,130
Accretion of redeemable preferred stock to redemption value	0	49,900
Property and equipment additions in accounts payable	$ 125	$ 323

Organization and Description of

Organization and Description of Business	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business TCR 2 2 2 Initial public offering In February 2019, the Company completed the initial public offering of its common stock (the IPO) pursuant to which it issued and sold 5,750,000 shares of its common stock at a price to the public of $15.00 per share. The shares began trading on The Nasdaq Global Select Market on February 14, 2019. The aggregate net proceeds received by the Company from the offering were approximately $77.1 million. Upon the closing of the IPO, all outstanding shares of redeemable convertible preferred stock converted into 17,275,299 shares of common stock. Additionally, as of the closing of the IPO, the Company is authorized to issue 150,000,000 shares of common stock and 10,000,000 shares of preferred stock. Reverse stock split On February 1, 2019, the Company effected a 1-for-6.1938 Shelf registration statement On March 6, 2020, the Company filed a shelf registration statement on Form S-3 (the Shelf), with the Securities and Exchange Commission (SEC), which covers the offering, issuance and sale of up to an aggregate of $300.0 million of the Company’s common stock, preferred stock, debt securities, warrants and/or units of any combination thereof. The Company simultaneously entered into a sales agreement with Jefferies LLC, as sales agent, to provide for the issuance and sale by the Company of up to $75.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf, which the Company refers to as the ATM Program. The Shelf was declared effective by the SEC on April 28, 2020. As of September 30, 2020, no sales have been made pursuant to the ATM Program. Equity offering 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.

Liquidity

Liquidity	9 Months Ended
	Sep. 30, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Liquidity	2. Liquidity The Company’s operations to date have focused on organization and staffing, business planning, raising capital, acquiring technology and assets, manufacturing, conducting preclinical studies and clinical activities. 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 expects to continue to generate losses for the foreseeable future. The Company expects that its cash, cash equivalents and investments as of September 30, 2020 of $246,723 will be sufficient to fund its operating expenses and capital expenditure requirements through at least 12 months from the date of issuance of these unaudited consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Principles of consolidation and basis of presentation The unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and in accordance with Article 10 of Regulation S-X of the SEC, and reflect the financial position, results of operations and cash flows of the Company's business. Accordingly, they do not include all of the disclosures required by U.S. GAAP for a complete set of annual audited financial statements. All significant intercompany accounts and transactions are eliminated in consolidation. The unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. The accompanying financial information should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company's Annual Report on Form 10-K filed with the SEC on March 30, 2020 for the year ended December 31, 2019 (the 2019 Form 10-K). In the opinion of the Company's management, all adjustments (consisting of normal and recurring adjustments) considered necessary for a fair statement of the results for the interim periods presented have been included. Use of estimates The preparation of the accompanying unaudited consolidated financial statements in conformity with U.S. 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 unaudited consolidated financial statements and reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these unaudited consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, the valuation of redeemable convertible preferred and common stock prior to the IPO 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 unaudited 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 September 30, 2020, the Company has 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 party’s 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 At September 30, 2020 and December 31, 2019, the Company’s financial instruments consist of money market funds, U.S. Treasury securities, and corporate bonds and 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 The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of September 30, 2020 and December 31, 2019, cash equivalents consisted of U.S treasuries, corporate bonds, and government-backed money market funds. Investments As of September 30, 2020, 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 earnings. 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. Restricted cash Cash accounts that are restricted as to withdrawal or usage are presented as restricted cash. Restricted cash includes amounts held as a security deposit in the form of a letter of credit for the Company’s leased facilities. Classification and accretion of redeemable convertible preferred stock Through the date of the IPO, the Company had classified redeemable convertible preferred stock outstanding and classified outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company. The carrying value of the redeemable convertible preferred stock was accreted to redemption value at the end of each reporting period, up to the date of the IPO, as if the end of the reporting period were the redemption date. Increases to the carrying value of redeemable convertible preferred stock were charged to additional paid-in capital or, in the absence of additional paid-in capital, charged to accumulated deficit. Upon completion of the IPO during February 2019, all redeemable convertible preferred stock was converted to common stock. 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. For stock-based awards granted to non-employees, compensation expense is recognized over the period during which services are rendered by such non-employees until completed. Compensation expense is recognized over the period during which services are rendered by such non-employee consultants until completed. In the second quarter of 2019, the Company adopted ASU 2018-07 on a retrospective basis effective January 1, 2019, the beginning of the fiscal year of adoption. Prior to the adoption of ASU 2018-07, share-based payments awards granted to non-employees were measured at fair value on their grant date, subject to periodic remeasurement at each reporting period, and share-based compensation expense was recognized over their vesting terms. After the adoption of ASU 2018-07, the fair value of all outstanding and unvested previously granted non-employee awards was established on January 1, 2019, the effective date of adoption, and share-based compensation expense will continue to be recorded on a straight-line basis over their remaining vesting period, consistent with share-based payment awards granted to employees. Common shares issued and stock-options exercised prior to vesting are subject to repurchase by the Company until vested at the lesser of the initial exercise price and the fair market value of the Company’s common stock at the time of repurchase. The proceeds from the shares subject to repurchase are classified as a liability and reclassified to equity as the shares vest. Estimating the fair value of stock-based awards requires the input of subjective assumptions, including the fair value of the Company’s common stock, and, for stock options and warrants, the expected life of the instrument and stock price volatility. 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 costs are expensed as incurred and consist primarily of funds paid 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. 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 September 30, 2020 and 2019, as they would be antidilutive: As of September 30, 2020 2019 Stock options outstanding 4,131,932 3,433,743 Common stock warrants 203,676 203,676 Employee stock purchase plan 1,557 1,910 Unvested shares of restricted stock - 1,660 Total 4,337,165 3,640,989 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. 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 unaudited consolidated balance sheets to the total of the same such amounts shown in the unaudited consolidated statements of cash flows for the nine months ended September 30, 2020 and 2019. As of September 30, 2020 2019 Cash and cash equivalents $ 101,614 $ 49,317 Restricted cash 417 417 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 102,031 $ 49,734 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 opt 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 accounting pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) which will require lessees to record most operating leases on their balance sheets but recognize the expenses in the statements of operations in a manner similar to current practice. Under the new standard, lessees will be required to recognize a lease liability for the obligation to make lease payments, and an asset for the right to use the underlying asset for the lease term, for all leases with terms longer than 12 months. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the statements of operations. Expenses related to operating leases will be recognized on a straight-line basis, while those determined to be financing leases will be recognized following a front-loaded expense profile, in which interest and amortization are presented separately in the statements of operations. The principal effect on the Company’s financial statements will be an increase in assets and liabilities. The standard will be effective for public business entities for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. For all other entities and emerging growth companies, the amendments are effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company will adopt the new standard beginning January 1, 2022. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. An entity may choose to apply the standard either (1) on the January 1, 2022 effective date, or (2) the beginning of the earliest comparative period presented in its financial statements. The standard includes a number of practical expedients that the Company is evaluating and may elect to apply. Early adoption is permitted. The Company expects that the adoption of the new leasing standards will result in the recognition of material right-of-use assets and lease liabilities on the consolidated balance sheets but does not expect it to have a material impact on its results of operations or cash flows.

Investments and Fair Value Meas

Investments and Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value And Debt Securities Available For Sale [Abstract]
Investments and Fair Value Measurements	4. Investments and Fair Value Measurements As of September 30, 2020, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 45,973 $ 205 $ - $ 46,178 U.S. Treasury securities 98,945 - (14 ) 98,931 Total $ 144,918 $ 205 $ (14 ) $ 145,109 As of December 31, 2019, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 92,686 $ 145 $ (3 ) $ 92,828 The amortized cost and estimated fair value of marketable securities, by contractual maturity: September 30, 2020 Amortized Cost Fair Value Due within one year or less $ 144,918 $ 145,109 December 31, 2019 Amortized Cost Fair Value Due within one year or less $ 92,686 $ 92,828 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 As of September 30, 2020, the Company has classified assets measured at fair value on a recurring basis as follows: Fair Value Measurement Based on Amortized Quoted Prices in Active Market Significant Other Observable Inputs Significant Unobservable Inputs Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 100,070 $ 100,070 $ 100,070 $ - $ - Corporate bonds 45,973 46,178 - 46,178 - U.S. Treasury securities 98,945 98,931 - 98,931 - Total $ 244,988 $ 245,179 $ 100,070 $ 145,109 $ - As of December 31, 2019 , the Company has classified assets measured at fair value on a recurring basis as follows: Fair Value Measurement Based on Amortized Quoted Prices in Active Market Significant Other Observable Inputs Significant Unobservable Inputs Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 61,237 $ 61,237 $ 61,237 $ - $ - Corporate bonds 92,686 92,828 - 92,828 - Total $ 153,923 $ 154,065 $ 61,237 $ 92,828 $ - (1)

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment, net, consisted of: As of September 30, 2020 December 31, 2019 Laboratory equipment $ 7,805 $ 5,717 Computer hardware and equipment 201 105 Furniture and fixtures 432 396 Leasehold improvements 320 312 Construction in process 352 203 9,110 6,733 Less: accumulated depreciation (2,909 ) (1,807 ) $ 6,201 $ 4,926 Depreciation expense was $430 and $258 for the three months ended September 30, 2020 and 2019, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of: As of September 30, 2020 December 31, 2019 Employee compensation and related benefits $ 2,812 $ 2,816 Professional fees 488 300 Contract manufacturing organization fees 766 500 Contract research organization fees 248 182 University partnerships 187 448 Property received not yet invoiced 198 260 Other 205 544 $ 4,904 $ 5,050

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Leases The Company recognizes rent expense on a straight-line basis over the lease period and has accrued for rent expense incurred but not yet paid. Landlord allowances for tenant improvements are deferred and recognized as a reduction to rent expense on a straight-line basis and over the remaining lease term. 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. 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 GMP manufacturing facility in the United Kingdom. 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. The Collaboration Agreement provides for Catapult to provide identified space, called a module. The agreement calls for the Company to pay certain amounts for use of the module, operating and overhead expenses. The Company has concluded that the Collaboration Agreement contains an embedded lease as the Company has the right to operate the module in a manner it determines. The Company also concluded that it is not the deemed owner during modification of the module nor does the agreement represent a capital lease under ASC 840, “Leases”. As a result, the embedded lease portion of the Collaboration Agreement will be accounted for as an operating lease. The Company determined the amounts to be representative of rent to be £300 per year based on the relative selling prices of the services being provided. This amount will be amortized annually on a straight-line basis as rent expense over the term of the embedded lease, commencing March 1, 2019. In September 2019, the Company entered into a lease for office facilities that expires in August 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. The following table presents future minimum rent payments under non-cancellable operating leases with initial terms in excess of one year at September 30, 2020: As of September 30, 2020 2020 $ 855 2021 3,094 2022 2,550 2023 2,559 2024 2,491 Thereafter 1,054 Total minimum payments required $ 12,603 Rent expense was $866 and $718 for the three months ended September 30, 2020 and 2019, respectively. Rent expense was $2,603 and $2,043 for the nine months ended September 30, 2020 and 2019, respectively. 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 (see Note 8), certain investors are entitled to receive, in the aggregate, a royalty from the Company equal to one percent

Common Stock and Redeemable Con

Common Stock and Redeemable Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2020
Temporary Equity And Stockholders Equity Note [Abstract]
Common Stock and Redeemable Convertible Preferred Stock	8. Common Stock and Redeemable Convertible Preferred 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. Subject to the rights of holders of redeemable convertible preferred stock, common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any. No dividends had been declared through September 30, 2020. 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 September 30, 2020, there are no preferred shares issued. Redeemable convertible preferred stock Upon completion of the IPO during February 2019, all redeemable convertible preferred stock was converted to common stock. Prior to the IPO, the Company elected to accrete the carrying value of the Series A and B preferred stock to redemption value at the end of each reporting period as if the end of the reporting period were the redemption date, increases to the carrying value of redeemable convertible preferred stock are charged to additional paid-in capital or, in the absence of additional paid-in capital, charged to accumulated deficit. Series A redeemable convertible preferred stock Prior to the IPO, there were 44,500,001 Series A preferred shares issued and outstanding. Included in the Series A preferred stock purchase agreement, the investor is required to purchase additional shares upon the achievement of certain Company milestones. The Company evaluated the future commitment obligations at original issuance and determined they were not freestanding instruments as they were not legally detachable. The future commitment obligations were also evaluated as embedded derivatives and determined they did not meet the definition of a derivative instrument for which bifurcation would be required. Upon completion of the IPO in February 2019, all Series A preferred stock was converted to 7,184,588 shares of common stock. Conversion Prior to the IPO, each share of Series A preferred stock was convertible, at the option of the holder, into shares of common stock. Prior to the common stock reverse stock split in February 2019, the shares were convertible on a one-to-one basis. Post-split the Series A stock were convertible at 1-to-0.1615 basis. The Series A conversion rights were subject to adjustment for certain dilutive events. The conversion price could have been adjusted to prevent dilution of the Series A preferred stock. The preferred stock was also mandatorily convertible upon the closing of an initial public offering resulting in gross proceeds to the Company exceeding $50.0 million or by a written election by the majority of the Series A stockholders. Redemption Prior to the IPO, at the election of a majority of the Series A stockholders, the Series A preferred stock was redeemable at any time on or after October 16, 2020. The Series A preferred stock could have been redeemable at a price equal to the greater of (a) the original issuance price, plus any cumulative dividends accrued but unpaid thereon, whether or not declared, or (b) the fair market value as of the date of the redemption. Dividends Prior to the IPO, the holders of shares of Series A preferred stock were entitled to receive cumulative dividends of 6% from the date of issuance. Accumulated dividends were payable only when and if declared by the Board of Directors, in preference to dividends paid to holders of common stock. The dividend preference for Series A preferred stock was $0.06 per share, as adjusted for recapitalizations. No dividends have been declared through September 30, 2020. Liquidation Prior to the IPO, in the event of a liquidation, dissolution or winding up of the Company, either voluntary or involuntary, or in the event of a deemed liquidation event, which included a sale of the Company as defined in the Company’s certificate of incorporation, holders of Series A preferred stock were entitled to receive, subject to the preference of the Series B holders but in preference to common stockholders, an amount equal to their original investment amount plus any declared and unpaid dividends. If upon the occurrence of such event, the assets and funds available for distribution were insufficient to pay such holders the full amount to which they are entitled, then the entire assets and funds legally available for distribution would have been distributed ratably among the holders of the Series A preferred stock in proportion to the full amounts to which they would otherwise be entitled. After payment of the liquidation preference on shares of Series A preferred stock had been made, any remaining assets would have been distributed ratably to common, Series B stockholders and Series A stockholders, on an as-converted basis. Series B redeemable convertible preferred stock Prior to the IPO, there were 62,500,000 Series B preferred shares issued and outstanding. The Series B preferred stock is classified outside of stockholders’ equity (deficit) as the preferred holders may, at their option, elect to have their shares redeemed upon written notice by a majority of the preferred shareholders and at any time after February 2023. Upon completion of the IPO in February 2019, all Series B preferred stock was converted to 10,090,711 shares of common stock. Conversion Prior to the IPO, each share of Series B preferred stock was convertible, at the option of the holder, into shares of common stock. Prior to the common stock reverse stock split in February 2019, the shares were convertible on a one-to-one basis. Post-split the Series B stock were convertible at 1-to-0.1615 basis. The Series B conversion rights were subject to adjustment for certain dilutive events. The conversion price could have been adjusted to prevent dilution of the Series B preferred stock. The Series B preferred stock was also mandatorily convertible upon the closing of an initial public offering resulting in gross proceeds to the Company exceeding $50.0 million or by a written election by the majority of the Series B stockholders. Redemption Prior to the IPO, at the election of a majority of the Series B stockholders, the Series B preferred stock was redeemable at any time on or after February 2023. The Series B preferred stock could have been redeemable at a price equal to the greater of (a) the original issuance price, plus any cumulative dividends accrued but unpaid thereon, whether or not declared, or (b) the fair market value as of the date of the redemption. Dividends Prior to the IPO, the holders of shares of Series B preferred stock were entitled to receive cumulative dividends of 6% from the date of issuance. Accumulated dividends were payable only when and if declared by the Board of Directors, in preference to dividends paid to holders of Series B preferred stock and common stock. The dividend preference for Series B preferred stock was $0.12 per share, as adjusted for recapitalizations. No dividends were declared through September 30, 2020. Liquidation Prior to the IPO, in the event of a liquidation, dissolution or winding up of the Company, either voluntary or involuntary, or in the event of a deemed liquidation event, which includes a sale of the Company as defined in the Company’s articles of incorporation, holders of Series B preferred stock were entitled to receive, in preference to the holders of Series A preferred stock or Common Stock, an amount equal to their original investment amount plus any declared and unpaid dividends. If upon the occurrence of such event, the assets and funds available for distribution were insufficient to pay such holders the full amount to which they are entitled, then the entire assets and funds legally available for distribution would have been distributed ratably among the holders of the Series B preferred stock in proportion to the full amounts to which they would otherwise be entitled. After payment of the liquidation preference on shares of Series B preferred stock has been made, any remaining assets would have been distributed ratably to Series A stockholders in an amount equal to their original investment amount plus any accrued dividends, whether or not declared, together with any other dividends declared but unpaid thereon. After payment of the liquidation preference on shares of Series A preferred stock had been made, any remaining assets would have been distributed ratably to common, Series B stockholders and Series A stockholders, on an as-converted basis.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	9. Stock-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 Stock Option and Grant Plan (the 2015 Plan). The shares under the 2015 Plan which were not issued were rolled into the 2018 Plan. The 2018 Plan provides for the grant of incentive stock options, nonstatutory 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 maximum number of authorized shares to be issued under the 2018 Plan is 6,053,935 shares of common stock. The number of shares of 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 common stock outstanding on December 31 of the preceding calendar year or a lesser number of shares determined by the Company's Board of Directors. The amount, terms of grants, and exercisability provisions are determined and set by the Compensation Committee of the Company’s Board of Directors. 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. As of September 30, 2020, there were 1,698,837 shares of common stock available for future issuance under the 2018 Plan. Generally, options and restricted stock awards vest over a four-year The Company recorded stock-based compensation expense in the following expense categories of its accompanying unaudited consolidated statements of operations for the three and nine months ended September 30, 2020 and 2019: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 798 $ 815 $ 2,414 $ 1,729 General and administrative 1,269 1,197 3,772 2,868 $ 2,067 $ 2,012 $ 6,186 $ 4,597 Stock options During the nine months ended September 30, 2019, there were 1,496,340 grants of stock options, 74,903 options forfeited, and 82,509 options exercised, respectively. The following table summarizes the activity related to stock option grants to employees and non-employees for the nine months ended September 30, 2020: Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Life (in Years) Balance at December 31, 2019 4,189,292 $ 10.31 8.9 Granted 207,148 11.97 Exercised (122,869 ) 4.08 Forfeited (141,639 ) 12.94 Balance at September 30, 2020 4,131,932 8.2 Exercisable at September 30, 2020 1,698,232 Vested and expected to vest at September 30, 2020 4,131,932 As of September 30, 2020, there was $18.3 million 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 for the nine months ended September 30, 2020 and 2019 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. ▪ Subsequent to the IPO, the Company is traded on the Nasdaq Select Market. Fair value is determined by the stock price quoted on Nasdaq. Prior to the IPO, the Company considered numerous objective and subjective factors in estimating the fair value of its common stock, including the estimated fair value of the Company’s Series A and Series B preferred stock. 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: Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.5 % 2.27 % Expected term (in years) 6.1 6.0 Expected volatility 72.9 % 70.8 % Annual dividend yield 0 % 0 % Fair value of common stock $ 7.86 $ 10.13 Warrants As of September 30, 2020 and December 31, 2019, there were 203,676 warrants outstanding. During the nine months ended September 30, 2020 and 2019, the Company granted no warrants and there were no forfeitures. As of September 30, 2020, there was $158 in unrecognized compensation cost that is expected to be recognized over an estimated weighted-average amortization period of 0.3 years. 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 During the nine months ended September 30, 2020 and 2019, there were 23,864 shares and 10,614 shares issued under the 2018 ESPP, respectively.

Related party transactions

Related party transactions	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related party transactions	10. Related party transactions 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 $54 On March 2, 2016, the Company entered into a consulting agreement with Dr. Mitchell Finer (the Original Finer Agreement), which was amended and restated on May 9, 2017 to, among other things, add Pattern Recognition Ventures as a party. Pursuant to the amended and restated consulting agreement, Pattern Recognition Ventures agreed to perform scientific consulting, advisory and related services to and for the Company as may be reasonably requested, including making Dr. Finer available to serve as Chairman of the Company's Scientific Advisory Board. Pursuant to the amended and restated consulting agreement, the Company agreed to pay Pattern Recognition Ventures a consulting fee of $19 per quarter for services provided under the agreement, commencing on July 1, 2017. On June 5, 2020, the Company and Pattern Recognition Ventures amended the agreement to provide for consulting fees of $100 per year. Dr. Finer was a member of the Board of Directors from 2015 until his resignation on April 30, 2020. Dr. Finer is not considered a related party after his resignation from the Board of Directors. During the nine months ended September 30, 2020 and 2019, the Company incurred fees and travel-related expenses to Pattern Recognition Ventures in the amount of $19 and $58, respectively. Dr. Finer has a financial interest in Pattern Recognition Ventures and is its managing member. Dr. Finer is an executive partner at MPM Capital, the beneficial owner of more than 5% of the Company's voting securities. On October 1, 2017, the Company entered into a consulting agreement with Globeways Holdings Limited. Dr. Morana Jovan-Embiricos has financial interests in Globeways Holdings Limited and is its founding director. Pursuant to the consulting agreement, Globeways Holdings Limited provided consulting, advisory and related services in exchange for consulting fees of $100 per year. During the nine months ended September 30, 2019, the Company incurred fees and travel-related expenses to Globeways Holdings Limited in the amount of $52. Dr. Jovan was a member of the Company's Board of Directors until her resignation on May 13, 2019. Dr. Jovan is the founding director of Globeways Holdings Limited. Globeways Holdings Limited is the appointed manager of certain affiliates of F2 Capital that collectively beneficially own more than 5% of the Company's voting securities. The consulting agreement with Globeways Holdings Limited was terminated in connection with Dr. Jovan-Embiricos's resignation from the Company's Board of Directors.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Principles of consolidation and basis of presentation	Principles of consolidation and basis of presentation The unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and in accordance with Article 10 of Regulation S-X of the SEC, and reflect the financial position, results of operations and cash flows of the Company's business. Accordingly, they do not include all of the disclosures required by U.S. GAAP for a complete set of annual audited financial statements. All significant intercompany accounts and transactions are eliminated in consolidation. The unaudited consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. The accompanying financial information should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company's Annual Report on Form 10-K filed with the SEC on March 30, 2020 for the year ended December 31, 2019 (the 2019 Form 10-K). In the opinion of the Company's management, all adjustments (consisting of normal and recurring adjustments) considered necessary for a fair statement of the results for the interim periods presented have been included.
Use of estimates	Use of estimates The preparation of the accompanying unaudited consolidated financial statements in conformity with U.S. 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 unaudited consolidated financial statements and reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these unaudited consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, the valuation of redeemable convertible preferred and common stock prior to the IPO 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 unaudited 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 September 30, 2020, the Company has 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 party’s 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 At September 30, 2020 and December 31, 2019, the Company’s financial instruments consist of money market funds, U.S. Treasury securities, and corporate bonds and 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 September 30, 2020 and December 31, 2019, cash equivalents consisted of U.S treasuries, corporate bonds, and government-backed money market funds.
Investments	Investments As of September 30, 2020, 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 earnings. 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.
Restricted cash	Restricted cash Cash accounts that are restricted as to withdrawal or usage are presented as restricted cash. Restricted cash includes amounts held as a security deposit in the form of a letter of credit for the Company’s leased facilities.
Classification and accretion of redeemable convertible preferred stock	Classification and accretion of redeemable convertible preferred stock Through the date of the IPO, the Company had classified redeemable convertible preferred stock outstanding and classified outside of stockholders’ equity (deficit) because the shares contained certain redemption features that were not solely within the control of the Company. The carrying value of the redeemable convertible preferred stock was accreted to redemption value at the end of each reporting period, up to the date of the IPO, as if the end of the reporting period were the redemption date. Increases to the carrying value of redeemable convertible preferred stock were charged to additional paid-in capital or, in the absence of additional paid-in capital, charged to accumulated deficit. Upon completion of the IPO during February 2019, all redeemable convertible preferred stock was converted to common stock.
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. For stock-based awards granted to non-employees, compensation expense is recognized over the period during which services are rendered by such non-employees until completed. Compensation expense is recognized over the period during which services are rendered by such non-employee consultants until completed. In the second quarter of 2019, the Company adopted ASU 2018-07 on a retrospective basis effective January 1, 2019, the beginning of the fiscal year of adoption. Prior to the adoption of ASU 2018-07, share-based payments awards granted to non-employees were measured at fair value on their grant date, subject to periodic remeasurement at each reporting period, and share-based compensation expense was recognized over their vesting terms. After the adoption of ASU 2018-07, the fair value of all outstanding and unvested previously granted non-employee awards was established on January 1, 2019, the effective date of adoption, and share-based compensation expense will continue to be recorded on a straight-line basis over their remaining vesting period, consistent with share-based payment awards granted to employees. Common shares issued and stock-options exercised prior to vesting are subject to repurchase by the Company until vested at the lesser of the initial exercise price and the fair market value of the Company’s common stock at the time of repurchase. The proceeds from the shares subject to repurchase are classified as a liability and reclassified to equity as the shares vest. Estimating the fair value of stock-based awards requires the input of subjective assumptions, including the fair value of the Company’s common stock, and, for stock options and warrants, the expected life of the instrument and stock price volatility. 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 paid 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. 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 September 30, 2020 and 2019, as they would be antidilutive: As of September 30, 2020 2019 Stock options outstanding 4,131,932 3,433,743 Common stock warrants 203,676 203,676 Employee stock purchase plan 1,557 1,910 Unvested shares of restricted stock - 1,660 Total 4,337,165 3,640,989
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.
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 unaudited consolidated balance sheets to the total of the same such amounts shown in the unaudited consolidated statements of cash flows for the nine months ended September 30, 2020 and 2019. As of September 30, 2020 2019 Cash and cash equivalents $ 101,614 $ 49,317 Restricted cash 417 417 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 102,031 $ 49,734
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 opt 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 issued accounting pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) which will require lessees to record most operating leases on their balance sheets but recognize the expenses in the statements of operations in a manner similar to current practice. Under the new standard, lessees will be required to recognize a lease liability for the obligation to make lease payments, and an asset for the right to use the underlying asset for the lease term, for all leases with terms longer than 12 months. Leases will be classified as finance or operating, with classification affecting the pattern and classification of expense recognition in the statements of operations. Expenses related to operating leases will be recognized on a straight-line basis, while those determined to be financing leases will be recognized following a front-loaded expense profile, in which interest and amortization are presented separately in the statements of operations. The principal effect on the Company’s financial statements will be an increase in assets and liabilities. The standard will be effective for public business entities for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. For all other entities and emerging growth companies, the amendments are effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company will adopt the new standard beginning January 1, 2022. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. An entity may choose to apply the standard either (1) on the January 1, 2022 effective date, or (2) the beginning of the earliest comparative period presented in its financial statements. The standard includes a number of practical expedients that the Company is evaluating and may elect to apply. Early adoption is permitted. The Company expects that the adoption of the new leasing standards will result in the recognition of material right-of-use assets and lease liabilities on the consolidated balance sheets but does not expect it to have a material impact on its results of operations or cash flows.
Fair value measurement	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

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
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 September 30, 2020 and 2019, as they would be antidilutive: As of September 30, 2020 2019 Stock options outstanding 4,131,932 3,433,743 Common stock warrants 203,676 203,676 Employee stock purchase plan 1,557 1,910 Unvested shares of restricted stock - 1,660 Total 4,337,165 3,640,989
Schedule of Restricted Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the unaudited consolidated balance sheets to the total of the same such amounts shown in the unaudited consolidated statements of cash flows for the nine months ended September 30, 2020 and 2019. As of September 30, 2020 2019 Cash and cash equivalents $ 101,614 $ 49,317 Restricted cash 417 417 Cash, cash equivalents and restricted cash shown in the statements of cash flows $ 102,031 $ 49,734

Investments and Fair Value Me_2

Investments and Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value And Debt Securities Available For Sale [Abstract]
Summary of Amortized Cost and Fair Values of Investment Securities Available-for-sale	As of September 30, 2020, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 45,973 $ 205 $ - $ 46,178 U.S. Treasury securities 98,945 - (14 ) 98,931 Total $ 144,918 $ 205 $ (14 ) $ 145,109 As of December 31, 2019, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 92,686 $ 145 $ (3 ) $ 92,828
Summary of Maturities	The amortized cost and estimated fair value of marketable securities, by contractual maturity: September 30, 2020 Amortized Cost Fair Value Due within one year or less $ 144,918 $ 145,109 December 31, 2019 Amortized Cost Fair Value Due within one year or less $ 92,686 $ 92,828
Summary of Classified Assets Measured at Fair Value on a Recurred Basis	As of September 30, 2020, the Company has classified assets measured at fair value on a recurring basis as follows: Fair Value Measurement Based on Amortized Quoted Prices in Active Market Significant Other Observable Inputs Significant Unobservable Inputs Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 100,070 $ 100,070 $ 100,070 $ - $ - Corporate bonds 45,973 46,178 - 46,178 - U.S. Treasury securities 98,945 98,931 - 98,931 - Total $ 244,988 $ 245,179 $ 100,070 $ 145,109 $ - As of December 31, 2019 , the Company has classified assets measured at fair value on a recurring basis as follows: Fair Value Measurement Based on Amortized Quoted Prices in Active Market Significant Other Observable Inputs Significant Unobservable Inputs Cost Fair Value (Level 1) (Level 2) (Level 3) Cash equivalents (1) $ 61,237 $ 61,237 $ 61,237 $ - $ - Corporate bonds 92,686 92,828 - 92,828 - Total $ 153,923 $ 154,065 $ 61,237 $ 92,828 $ - (1)

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment, net, consisted of: As of September 30, 2020 December 31, 2019 Laboratory equipment $ 7,805 $ 5,717 Computer hardware and equipment 201 105 Furniture and fixtures 432 396 Leasehold improvements 320 312 Construction in process 352 203 9,110 6,733 Less: accumulated depreciation (2,909 ) (1,807 ) $ 6,201 $ 4,926

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of: As of September 30, 2020 December 31, 2019 Employee compensation and related benefits $ 2,812 $ 2,816 Professional fees 488 300 Contract manufacturing organization fees 766 500 Contract research organization fees 248 182 University partnerships 187 448 Property received not yet invoiced 198 260 Other 205 544 $ 4,904 $ 5,050

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Rental Payments under Non-cancellable Operating Leases	The following table presents future minimum rent payments under non-cancellable operating leases with initial terms in excess of one year at September 30, 2020: As of September 30, 2020 2020 $ 855 2021 3,094 2022 2,550 2023 2,559 2024 2,491 Thereafter 1,054 Total minimum payments required $ 12,603

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
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 unaudited consolidated statements of operations for the three and nine months ended September 30, 2020 and 2019: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 798 $ 815 $ 2,414 $ 1,729 General and administrative 1,269 1,197 3,772 2,868 $ 2,067 $ 2,012 $ 6,186 $ 4,597
Schedule of Stock Option Activity	The following table summarizes the activity related to stock option grants to employees and non-employees for the nine months ended September 30, 2020: Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Life (in Years) Balance at December 31, 2019 4,189,292 $ 10.31 8.9 Granted 207,148 11.97 Exercised (122,869 ) 4.08 Forfeited (141,639 ) 12.94 Balance at September 30, 2020 4,131,932 8.2 Exercisable at September 30, 2020 1,698,232 Vested and expected to vest at September 30, 2020 4,131,932
Schedule of Weighted-Average Assumptions	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: Nine Months Ended September 30, 2020 2019 Risk-free interest rate 0.5 % 2.27 % Expected term (in years) 6.1 6.0 Expected volatility 72.9 % 70.8 % Annual dividend yield 0 % 0 % Fair value of common stock $ 7.86 $ 10.13

Organization and Description _2

Organization and Description of Business - Narrative (Details)	Jul. 31, 2020USD ($)$ / sharesshares	Mar. 06, 2020USD ($)	Feb. 14, 2019USD ($)$ / sharesshares	Feb. 01, 2019	Sep. 30, 2020USD ($)shares	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)shares	Sep. 30, 2020shares	Dec. 31, 2019shares
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, net of issuance costs					$ 133,571,000
Common stock, shares authorized (shares) | shares					150,000,000			150,000,000	150,000,000
Preferred stock, shares authorized (shares) | shares					10,000,000			10,000,000	10,000,000
Reverse stock split				0.1615
Shelf registration, maximum amount		$ 300,000,000
Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Shares sold during public offering (shares) | shares			5,750,000
Share price (USD per share) | $ / shares			$ 15
Issuance of common stock, net of issuance costs						$ (34,000)	$ 77,155,000
ATM Program
Subsidiary Sale Of Stock [Line Items]
Common stock, maximum offering amount		$ 75,000,000
Issuance of common stock, net of issuance costs (shares) | shares								0
Equity Offering
Subsidiary Sale Of Stock [Line Items]
Shares sold during public offering (shares) | shares	9,200,000
Share price (USD per share) | $ / shares	$ 15.50
Proceeds from issuance of common stock after underwriting discounts and commissions and estimated offering expenses	$ 133,600,000
Underwriting discounts, commissions and estimated offering expenses	$ 9,000,000
Additional Paid-in Capital
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, net of issuance costs					$ 133,570,000
Additional Paid-in Capital | Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, net of issuance costs			$ 77,100,000			$ (34,000)	$ 77,155,000
Common Stock
Subsidiary Sale Of Stock [Line Items]
Issuance of common stock, net of issuance costs					$ 1,000
Issuance of common stock, net of issuance costs (shares) | shares					9,200,000
Common Stock | Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Conversion of shares upon IPO (shares) | shares			17,275,299
Issuance of common stock, net of issuance costs (shares) | shares							5,750,000

Liquidity - Narrative (Details)

Liquidity - Narrative (Details) $ in Thousands	Sep. 30, 2020USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 246,723

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	4,337,165	3,640,989
Stock options outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	4,131,932	3,433,743
Unvested shares of restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0	1,660
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)	1,557	1,910

Summary of Significant Accoun_5

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	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 101,614	$ 65,296	$ 49,317
Restricted cash	417	417	417
Cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 102,031	$ 65,713	$ 49,734	$ 47,964

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	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 144,918
Unrealized Gains	205
Unrealized Losses	(14)
Fair Value	145,109
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	45,973	$ 92,686
Unrealized Gains	205	145
Unrealized Losses	0	(3)
Fair Value	46,178	$ 92,828
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	98,945
Unrealized Gains	0
Unrealized Losses	(14)
Fair Value	$ 98,931

Investments and Fair Value Me_4

Investments and Fair Value Measurements - Summary of Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Due within one year or less	$ 144,918	$ 92,686
Fair Value
Due within one year or less	$ 145,109	$ 92,828

Investments and Fair Value Me_5

Investments and Fair Value Measurements - Summary of Classified Assets Measured at Fair Value on a Recurred Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 101,614	$ 65,296	$ 49,317
Available-for-sale securities, amortized cost	144,918
Available-for-sale securities, fair value	145,109
Fair Value, Measurement, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	100,070	61,237
Cash and cash equivalents, fair value	100,070	61,237
Available-for-sale securities, amortized cost	244,988	153,923
Available-for-sale securities, fair value	245,179	154,065
Fair Value, Measurement, Recurring | Quoted Prices in Active Market (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	100,070	61,237
Available-for-sale securities, fair value	100,070	61,237
Fair Value, Measurement, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0	0
Available-for-sale securities, fair value	145,109	92,828
Fair Value, Measurement, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, fair value	0	0
Available-for-sale securities, fair value	0	0
Fair Value, Measurement, Recurring | Corporate bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost	45,973	92,686
Available-for-sale securities, fair value	46,178	92,828
Fair Value, Measurement, Recurring | Corporate bonds | Quoted Prices in Active Market (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	0	0
Fair Value, Measurement, Recurring | Corporate bonds | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	46,178	92,828
Fair Value, Measurement, Recurring | Corporate bonds | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	0	$ 0
Fair Value, Measurement, Recurring | U.S. Treasury securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost	98,945
Available-for-sale securities, fair value	98,931
Fair Value, Measurement, Recurring | U.S. Treasury securities | Quoted Prices in Active Market (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	0
Fair Value, Measurement, Recurring | U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	98,931
Fair Value, Measurement, Recurring | U.S. Treasury securities | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	$ 0

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 9,110	$ 6,733
Less: accumulated depreciation	(2,909)	(1,807)
Property and equipment, net	6,201	4,926
Laboratory equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,805	5,717
Computer hardware and equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	201	105
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	432	396
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	320	312
Construction in process
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 352	$ 203

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 430	$ 258	$ 1,114	$ 558

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Employee compensation and related benefits	$ 2,812	$ 2,816
Professional fees	488	300
Contract manufacturing organization fees	766	500
Contract research organization fees	248	182
University partnerships	187	448
Property received not yet invoiced	198	260
Other	205	544
Accrued expenses and other current liabilities	$ 4,904	$ 5,050

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) £ in Thousands	Mar. 01, 2019	Sep. 30, 2019USD ($)	Dec. 31, 2018	Mar. 31, 2018USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2020GBP (£)
Other Commitments [Line Items]
Lease facility expiration date		2024-08		2025-07
Restricted cash		$ 127,000		$ 290,000		$ 127,000		$ 127,000
Initial term	3 years
Termination period notice requirement			12 months
Termination period			12 months
Operating lease liability per year | £										£ 300
Rent expense					$ 866,000	718,000	$ 2,603,000	2,043,000
Royalty payments, percentage of net sales							1.00%
Royalty payments, percentage of license income							1.00%
Royalty agreement value					0		$ 0		$ 0
Royalties paid					0	$ 0	0	$ 0
Accrued liabilities					$ 0		0		0
Global Net Sales
Other Commitments [Line Items]
Revenue							0		0
Intellectual License Income
Other Commitments [Line Items]
Revenue							$ 0		$ 0

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Rental Payments under Non-cancellable Operating Leases (Details) $ in Thousands	Sep. 30, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 855
2021	3,094
2022	2,550
2023	2,559
2024	2,491
Thereafter	1,054
Total minimum payments required	$ 12,603

Common Stock and Redeemable C_2

Common Stock and Redeemable Convertible Preferred Stock - Narrative (Details)	Feb. 19, 2019shares	Feb. 14, 2019shares	Feb. 13, 2019$ / sharesshares	Feb. 01, 2019	Sep. 30, 2020USD ($)vote	Dec. 31, 2018shares
Class Of Stock [Line Items]
Votes per each common stock share | vote					1
Initial Public Offering (IPO) | Common Stock
Class Of Stock [Line Items]
Conversion of shares upon IPO (shares)		17,275,299
Series A redeemable convertible preferred stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock, shares issued (shares)			44,500,001
Redeemable convertible preferred stock, shares outstanding (shares)			44,500,001			44,500,001
Shares issued upon conversion (in shares)				0.1615
Minimum proceeds from initial public offering | $					$ 50,000,000
Preferred stock dividend rate			6.00%
Preferred stock dividend rate (in dollars per share) | $ / shares			$ 0.06
Series A redeemable convertible preferred stock | Initial Public Offering (IPO) | Common Stock
Class Of Stock [Line Items]
Conversion of shares upon IPO (shares)	7,184,588
Series B redeemable convertible preferred stock
Class Of Stock [Line Items]
Redeemable convertible preferred stock, shares issued (shares)			62,500,000
Redeemable convertible preferred stock, shares outstanding (shares)			62,500,000			62,500,000
Shares issued upon conversion (in shares)				0.1615
Minimum proceeds from initial public offering | $					$ 50,000,000
Preferred stock dividend rate			6.00%
Preferred stock dividend rate (in dollars per share) | $ / shares			$ 0.12
Series B redeemable convertible preferred stock | Initial Public Offering (IPO) | Common Stock
Class Of Stock [Line Items]
Conversion of shares upon IPO (shares)	10,090,711

Stock-based Compensation - Narr

Stock-based Compensation - Narrative (Details) - USD ($)	1 Months Ended	6 Months Ended	9 Months Ended
	Feb. 28, 2019	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period			4 years
Stock options granted (in shares)			207,148	1,496,340
Stock options forfeited (in shares)			141,639	74,903
Stock options exercised (in shares)			122,869	82,509
Unrecognized compensation costs			$ 18,300,000
Unrecognized compensation cost, period of recognition			2 years 7 months 6 days
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	$ 25,000
ESPP shares issued (in shares)			23,864	10,614
Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost, period of recognition			3 months 18 days
Warrants outstanding (in shares)			203,676		203,676
Warrants granted (in shares)			0	0
Warrants forfeited (in shares)			0	0
Unrecognized compensation cost			$ 158,000
2018 Stock Option and Incentive Plan | Stock options outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized (in shares)			6,053,935
Shares available for issuance as a percentage of outstanding shares, maximum			4.00%
Term of options			10 years
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)			1,698,837

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,067	$ 2,012	$ 6,186	$ 4,597
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	798	815	2,414	1,729
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,269	$ 1,197	$ 3,772	$ 2,868

Stock-based Compensation - St_2

Stock-based Compensation - Stock Option Activity (Details) - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning balance (in shares)	4,189,292
Options granted (in shares)	207,148	1,496,340
Options exercised (in shares)	(122,869)	(82,509)
Options forfeited (in shares)	(141,639)	(74,903)
Options outstanding, ending balance (in shares)	4,131,932		4,189,292
Options exercisable (in shares)	1,698,232
Options vested and expected to vest (in shares)	4,131,932
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)	$ 10.31
Options granted, weighted average exercise price per share (in dollars per share)	11.97
Options exercised, weighted average exercise price per share (in dollars per share)	4.08
Options forfeited, weighted average exercise price per share (in dollars per share)	$ 12.94
Options outstanding, weighted average exercise price per share, ending balance (in dollars per share)			$ 10.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, weighted average remaining contractual life (in years)	8 years 2 months 12 days		8 years 10 months 24 days

Stock-based Compensation - St_3

Stock-based Compensation - Stock Options Valuation Assumptions (Details) - $ / shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	0.50%	2.27%
Expected term (in years)	6 years 1 month 6 days	6 years
Expected volatility	72.90%	70.80%
Annual dividend yield	0.00%	0.00%
Fair value of common stock	$ 7.86	$ 10.13

Related party transactions - Na

Related party transactions - Narrative (Details) € in Thousands, $ in Thousands	Jun. 05, 2020USD ($)	Oct. 01, 2017USD ($)	May 09, 2017USD ($)	Nov. 01, 2016EUR (€)	Oct. 01, 2015EUR (€)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2020
MPM Capital | TCR2 Therapeutics Inc.
Related Party Transaction [Line Items]
Shareholder ownership, percentage						5.00%		5.00%
F2 Capital | TCR2 Therapeutics Inc.
Related Party Transaction [Line Items]
Shareholder ownership, percentage						5.00%
Dr. Patrick Baeuerle | Director | Consulting Agreement, Monthly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction | €				€ 3	€ 15
Dr. Patrick Baeuerle | Director | Consulting Agreement
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 | Director | Consulting Agreement, Fees
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions						$ 54	$ 54
Dr. Mitchell Finer / Pattern Recognition Ventures | Director | Consulting Agreement, Fees
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions						$ 19	58
Dr. Mitchell Finer / Pattern Recognition Ventures | Director | Consulting Agreement, Quarterly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction			$ 19
Dr. Mitchell Finer / Pattern Recognition Ventures | Director | Consulting Agreement, Yearly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	$ 100
Globeways Holdings Limited | Director | Consulting Agreement, Fees
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions							$ 52
Globeways Holdings Limited | Director | Consulting Agreement, Yearly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction		$ 100