Tcr2 Therapeutics (TCRR) 10-K 30 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 21, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	TCRR
Entity Registrant Name	TCR2 Therapeutics Inc.
Entity Central Index Key	0001750019
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		24,075,906
Entity Public Float			$ 216,090,573
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.0001 Par Value
Entity File Number	001-38811
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4152751
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Entity Address, Address Line One	100 Binney Street
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
City Area Code	617
Local Phone Number	949-5200
Document Annual Report	true
Document Transition Report	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 65,296	$ 47,674
Investments	92,828	75,493
Prepaid expenses and other current assets	5,061	2,326
Total current assets	163,185	125,493
Property and equipment, net	4,926	1,638
Restricted cash	417	290
Deferred offering costs	0	2,012
Total assets	168,528	129,433
Liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)
Accounts payable	2,483	2,663
Accrued expenses and other current liabilities	5,050	2,802
Total current liabilities	7,533	5,465
Other liabilities	546	434
Total liabilities	8,079	5,899
Commitments and contingencies (Note 7)
Redeemable convertible preferred stock	0	209,230
Stockholders’ equity (deficit)
Preferred stock, $0.0001 par value. 10,000,000 shares and no shares authorized, no shares issued or outstanding at December 31, 2019 and 2018, respectively.	0	0
Common stock, $0.0001 par value; 150,000,000 and 20,988,730 shares authorized; 24,050,936 and 914,602 shares issued; 23,981,109 and 726,990 shares outstanding at December 31, 2019 and 2018, respectively.	2
Additional paid-in capital	342,896	0
Accumulated other comprehensive income (loss)	142	(106)
Accumulated deficit	(182,591)	(85,590)
Total stockholders’ equity (deficit)	160,449	(85,696)
Total liabilities, redeemable convertible preferred stock, and stockholders’ equity (deficit)	168,528	129,433
Series A redeemable convertible preferred stock
Liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)
Redeemable convertible preferred stock		72,980
Series B redeemable convertible preferred stock
Liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)
Redeemable convertible preferred stock	$ 0	$ 136,250

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	10,000,000	0
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	20,988,730
Common stock, shares issued (shares)	24,050,936	914,602
Common stock, shares outstanding (shares)	23,981,109	726,990
Series A redeemable convertible preferred stock
Redeemable convertible preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized (shares)	0	45,000,000
Redeemable convertible preferred stock, shares issued (shares)	0	44,500,001
Redeemable convertible preferred stock, shares outstanding (shares)	0	44,500,001
Series B redeemable convertible preferred stock
Redeemable convertible preferred stock, par value (USD per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized (shares)	0	62,500,000
Redeemable convertible preferred stock, shares issued (shares)	0	62,500,000
Redeemable convertible preferred stock, shares outstanding (shares)	0	62,500,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Operating expenses
Research and development	$ 9,392	$ 11,374	$ 8,833	$ 7,889	$ 6,219	$ 5,386	$ 5,175	$ 2,893	$ 37,488	$ 19,673
General and administrative	4,179	3,522	3,307	2,886	2,222	1,704	1,634	1,220	13,894	6,780
Total operating expenses	13,571	14,896	12,140	10,775	8,441	7,090	6,809	4,113	51,382	26,453
Loss from operations	(13,571)	(14,896)	(12,140)	(10,775)	(8,441)	(7,090)	(6,809)	(4,113)	(51,382)	(26,453)
Interest income, net	846	1,090	1,077	872	751	702	622	127	3,885	2,202
Loss before income taxes	(12,725)	(13,806)	(11,063)	(9,903)	(7,690)	(6,388)	(6,187)	(3,986)	(47,497)	(24,251)
Income taxes	102								102
Net loss	(12,827)	(13,806)	(11,063)	(9,903)	(7,690)	(6,388)	(6,187)	(3,986)	(47,599)	(24,251)
Accretion of redeemable convertible preferred stock to redemption value				(49,900)	(3,730)	(11,590)	(11,145)	(10,833)	(49,900)	(37,298)
Net loss attributable to common stockholders	$ (12,827)	$ (13,806)	$ (11,063)	$ (59,803)	$ (11,420)	$ (17,978)	$ (17,332)	$ (14,819)	$ (97,499)	$ (61,549)
Per share information
Net loss per share of common stock, basic and diluted	$ (0.54)	$ (0.58)	$ (0.46)	$ (4.85)	$ (16.22)	$ (27.25)	$ (27.97)	$ (28.90)	$ (4.62)	$ (98.53)
Weighted average shares outstanding, basic and diluted	23,961,960	23,874,593	23,818,003	12,328,805	703,874	659,840	619,749	512,685	21,104,195	624,659

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (47,599)	$ (24,251)
Unrealized gain (loss) on investments, net	248	(106)
Comprehensive loss	$ (47,351)	$ (24,357)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A redeemable convertible preferred stock	Series B redeemable convertible preferred stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Redeemable convertible preferred stock beginning balance at Dec. 31, 2017		$ 47,102
Redeemable convertible preferred stock, beginning balance (shares) at Dec. 31, 2017		44,500,001
Beginning balance at Dec. 31, 2017	$ (26,324)					$ (26,324)
Beginning balance (shares) at Dec. 31, 2017				435,626
Sake of Series B preferred stock, net of issuance costs			$ 124,830
Sake of Series B preferred stock, net of issuance costs (shares)			62,500,000
Reclassification of shares issued and previously subject to repurchase	50				$ 50
Reclassification of shares issued and previously subject to repurchase (shares)				89,284
Exercise of stock options and warrants	100				100
Exercise of stock options and warrants (shares)				202,080
Stock-based compensation expense	2,133				2,133
Unrealized gain (loss) on investments	(106)						$ (106)
Accretion of redeemable preferred stock to redemption value	37,298	$ 25,878	$ 11,420
Accretion of redeemable preferred stock to redemption value	(37,298)				(2,283)	(35,015)
Net loss	(24,251)					(24,251)
Redeemable convertible preferred stock ending balance at Dec. 31, 2018	209,230	$ 72,980	$ 136,250
Redeemable convertible preferred stock, ending balance (shares) at Dec. 31, 2018		44,500,001	62,500,000
Ending balance at Dec. 31, 2018	$ (85,696)					(85,590)	(106)
Ending balance (shares) at Dec. 31, 2018	726,990			726,990
Reclassification of shares issued and previously subject to repurchase	$ 52				52
Reclassification of shares issued and previously subject to repurchase (shares)				117,785
Exercise of stock options and warrants	391				391
Exercise of stock options and warrants (shares)				111,035
Stock-based compensation expense	6,702				6,702
Unrealized gain (loss) on investments	248						248
Accretion of redeemable preferred stock to redemption value	49,900	$ 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
Initial public offering, net of issuance costs	77,121				77,121
Initial public offering, net of issuance costs (in shares)				5,750,000
Net loss	(47,599)					(47,599)
Redeemable convertible preferred stock ending balance at Dec. 31, 2019	0		$ 0
Redeemable convertible preferred stock, ending balance (shares) at Dec. 31, 2019		0	0
Ending balance at Dec. 31, 2019	$ 160,449			$ 2	$ 342,896	$ (182,591)	$ 142
Ending balance (shares) at Dec. 31, 2019	23,981,109			23,981,109

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Redeemable Convertible Preferred Stock | Series B redeemable convertible preferred stock
Redeemable convertible preferred stock issuance costs	$ 170

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (47,599)	$ (24,251)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	862	419
Stock-based compensation expense	6,702	2,133
Accretion on investments	(225)	(280)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,057)	(1,433)
Accounts payable	(179)	2,224
Accrued expenses and other liabilities	2,137	2,450
Cash used in operating activities	(41,359)	(18,738)
Investing activities
Purchase of investments	(126,261)	(97,810)
Proceeds from sale or maturity of investments	109,725	22,490
Purchases of equipment	(3,879)	(1,019)
Cash used in investing activities	(20,415)	(76,339)
Financing activities
Proceeds from the sale of Series B preferred stock, net of issuance costs	0	124,830
Proceeds from initial public offering, net of issuance costs	79,132	0
Proceeds from the exercise of stock options	391	100
Deferred offering costs	0	(1,990)
Cash provided by financing activities	79,523	122,940
Net increase in cash, cash equivalents, and restricted cash	17,749	27,863
Cash, cash equivalents, and restricted cash at beginning of year	47,964	20,101
Cash, cash equivalents, and restricted cash at end of period	65,713	47,964
Supplemental disclosure of noncash financing activities
Conversion of redeemable convertible preferred stock to common stock	259,130	0
Accretion of redeemable preferred stock to redemption value	49,900	37,298
Deferred offering costs included in accounts payable	0	558
Property and equipment additions in accounts payable	$ 270	$ 14

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business TCR 2 2 2 The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated. 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 $77,121, after deducting underwriting discounts and commissions and other offering expenses payable by the Company of $9,129. 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 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s redeemable convertible preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the redeemable convertible preferred stock conversion ratios.

Liquidity

Liquidity	12 Months Ended
	Dec. 31, 2019
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 and conducting clinical and preclinical studies. The Company does not have any product candidates approved for sale and has not generated any revenue from product sales. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding for the ongoing and planned clinical development of its product candidates. Because of the numerous risks and uncertainties associated with pharmaceutical products and development, the Company is unable to accurately predict the timing or amount of funds required to complete development of its product candidates, and costs could exceed the Company’s expectations for a number of reasons, including reasons beyond the Company’s control. The Company is also subject to a number of other risks including possible failure of preclinical studies or clinical trials, the need to obtain marketing approval for its product candidates, the development of new technological innovations by competitors, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and uncertainty around intellectual property matters. If the Company does not successfully commercialize any of its products, it will be unable to generate product revenue or achieve profitability. The Company has incurred net losses from operations since inception. The Company expects to continue to generate losses for the foreseeable future. The Company expects that its cash, cash equivalents and investments as of December 31, 2019 of $158,124 will be sufficient to fund its operating expenses and capital expenditure requirements through at least twelve months from the date of issuance of these consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Principles of consolidation and basis of presentation The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). Use of estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, the valuation of 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 consolidated financial statements, actual results may materially vary from these estimates. Estimates and assumptions are periodically reviewed, and the effects of revisions are reflected in the consolidated financial statements in the period they are determined to be necessary. Concentrations of credit risk and of manufacturing risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held by financial institutions in the United States. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions. As of December 31, 2019, the Company had manufacturing arrangements with vendors for the supply of materials for use in preclinical and clinical studies. If the Company were to experience any disruptions in either 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 December 31, 2019 and 2018, the Company’s financial instruments consist of money market funds, commercial paper, agency and corporate bonds, and asset-backed securities are included in investments. The carrying value of investments is the estimated fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Cash equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2019 and 2018, cash equivalents consisted of U.S treasuries, corporate bonds and government-backed money market funds. Investments As of December 31, 2019, all investments were classified as available-for-sale and were carried at their estimated fair value. Unrealized gains and losses are recorded as a component of accumulated other comprehensive income (loss) until realized. The Company determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company periodically reviews its investments in debt securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. If losses on these securities are considered to be other than temporary, the loss is recognized in the statement of operations. The Company classifies its available-for-sale marketable securities as current or non-current based on each instrument’s underlying effective maturity date and for which the Company has the intent and ability to hold the investment for a period of greater than 12 months. Marketable securities with maturities of less than 12 months are classified as current and are included in investments in the consolidated balance sheets. Marketable securities with maturities greater than 12 months for which the Company has the intent and ability to hold the investment for greater than 12 months are classified as non-current and are included in investments, non-current in the consolidated balance sheets. Property and equipment Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life. Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. The Company has not recognized any impairment of long-lived assets for the years ended December 31, 2019 and 2018. Deferred offering costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations. Restricted cash 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 contain certain redemption features that are 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. 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. Prior to the IPO, 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 options and stock price volatility. Since the IPO, the Company uses the value of its stock price as quoted on the Nasdaq Global Select Market to determine fair value of the Company’s common stock. The Company uses the Black-Scholes option pricing model to value its stock option awards and warrants. The assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, stock-based compensation expense could be materially different for future awards. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Research and development expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Upfront milestone payments made to third parties who perform research and development services on the Company’s behalf are expensed as services are rendered. Income taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A reduction in the carrying value of the deferred tax assets is required when it is not more likely than not that such deferred tax assets are not realizable. Net loss per share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company’s outstanding redeemable convertible preferred stock contractually entitles the holders of such shares to participate in distributions but contractually does not require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards granted by the Company entitle the holder of such awards to dividends declared or paid by the Board of Directors, regardless of whether such awards are unvested, as if such shares were outstanding shares of common stock at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted loss per share are the same. The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2019 and 2018, as they would be antidilutive: As of December 31, 2019 2018 Series A redeemable convertible preferred stock - 7,184,588 Series B redeemable convertible preferred stock - 10,090,711 Stock options outstanding 4,189,292 2,121,551 Employee stock purchase plan 7,092 - Unvested shares of restricted stock - 47,960 Common stock warrants 203,676 203,676 Total 4,400,060 19,648,486 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 consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2019 and 2018. As of December 31, 2019 2018 Cash and cash equivalents $ 65,296 $ 47,674 Restricted cash 417 290 Cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 65,713 $ 47,964 Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one consolidated operating segment. JOBS Act accounting election The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. Recently 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, the amendments are effective for fiscal years beginning after December 15, 2020. The Company will adopt the new standard beginning January 1, 2021. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. The standard includes a number of practical expedients that the Company is evaluating and may elect to apply. 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. Recently adopted accounting pronouncements Beginning January 1, 2019, the Company adopted ASU 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash, which requires entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. The standard requires retrospective application in the consolidated statements of cash flows. In June 2018, the FASB issued ASU 2018-07, Compensation — Stock Compensation (Topic 718) Improvements to Non-employee Share-Based Payment Accounting. The amendments in this update expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. Under this ASU, an entity should apply the requirements of Topic 718 to non-employee awards except for specific guidance on inputs to an option pricing model and the attribution of costs (that is, the period of time over which share-based payment awards vest and the pattern of cost recognition over that period). The guidance is applicable to public business entities for fiscal years beginning after December 15, 2018 including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. In June 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. As a result of the adoption of ASU 2018-07, there was no material impact to the financial statements.

Investments and Fair Value Meas

Investments and Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value And Debt Securities Available For Sale [Abstract]
Investments and Fair Value Measurements	4. Investments and Fair Value Measurements 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 As of December 31, 2018, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 58,029 $ 1 $ (94 ) $ 57,936 Agency bonds 9,966 - (9 ) 9,957 Commercial paper 7,214 - (4 ) 7,210 Asset-backed securities 390 - - 390 Total $ 75,599 $ 1 $ (107 ) $ 75,493 The Company follows FASB’s accounting guidance on fair value measurements for financial assets and liabilities measured on a recurring basis. Fair value is defined as the price at which an asset could be exchanged in a current transaction between knowledgeable, willing parties. Where available, fair value is based on observable market prices, or parameters derived from such prices. Where observable prices or inputs are not available, valuation models are applied. This hierarchy requires the use of observable market data when available and to minimize the use of unobservable inputs when determining fair value. These valuation techniques involve some level of management estimation and judgment. The degree of management estimation and judgment is dependent on the price transparency for the instruments, or market, and the instruments’ complexity. The guidance requires fair value measurements to be classified and disclosed in one of the following three categories: Level 1 — Quoted prices (unadjusted in active markets for identical assets or liabilities) Level 2 — Inputs other than quoted prices in active markets that are observable either directly or indirectly Level 3 — Unobservable inputs in which there is little or no market data, which require the Company to develop its own assumptions The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2019: 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) Includes cash sweep accounts, U.S. Treasury money market mutual fund, bank certificates of deposit, U.S. Treasury bills and corporate bonds that have a maturity of three months or less from the original acquisition date. The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2018: 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) $ 45,974 $ 45,974 $ 45,108 $ 866 $ - Corporate bonds 58,029 57,936 - 57,936 - Agency bonds 9,966 9,957 - 9,957 - Commercial paper 7,214 7,210 - 7,210 - Asset-backed securities 390 390 - 390 - Total $ 121,573 $ 121,467 $ 45,108 $ 76,359 $ - (1) During the years ended December 31, 2019 and 2018, there were no transfers among the Level 1, Level 2 and Level 3 categories.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment, net, consisted of: As of December 31, 2019 2018 Laboratory equipment $ 5,717 $ 2,118 Computer hardware and equipment 105 105 Furniture and fixtures 396 326 Leasehold improvements 312 34 Construction in process 203 - 6,733 2,583 Less: accumulated depreciation (1,807 ) (945 ) $ 4,926 $ 1,638 Depreciation expense was $862 and $419 for the years ended December 31, 2019 and 2018, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2019
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 December 31, 2019 2018 Employee compensation and related benefits $ 2,816 $ 1,676 Professional fees 300 342 Contract manufacturing organization fees 500 173 Contract research organization fees 182 232 University partnerships 448 162 Property received not yet invoiced 260 103 Other 544 114 $ 5,050 $ 2,802

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
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 $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 twelve months’ notice and continued payment for contributions during the twelve-month 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 $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 December 31, 2019: As of December 31, 2020 $ 3,421 2021 3,110 2022 2,553 2023 2,561 2024 2,490 Thereafter 1,054 Total minimum payments required $ 15,189 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 9), certain investors are entitled to receive, in the aggregate, a royalty from the Company equal to one percent

Employee benefit plan

Employee benefit plan	12 Months Ended
	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Employee benefit plan	8. Employee benefit plan The Company maintains a defined contribution 401(k) plan (the 401(k) Plan) in which employees may contribute a portion of their compensation, subject to statutory maximum contribution amounts. The Company assumes all administrative costs of the 401(k) Plan. For the years ended December 31, 2019 and 2018, the expense relating to the matching contribution was $276 and $121, respectively.

Common Stock and Redeemable Con

Common Stock and Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2019
Temporary Equity And Stockholders Equity Note [Abstract]
Common Stock and Redeemable Convertible Preferred Stock	9. 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 December 31, 2019. 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. The Series A 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 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 $50,000 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 may be redeemed 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 is $0.06 per share, as adjusted for recapitalizations. No dividends were declared prior to the IPO. 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 $50,000 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 prior to the IPO. 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	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	10. 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 Plan. The shares under the 2015 Plan which were not issued, were rolled into the 2018 Plan. The number of shares of our common stock reserved for issuance under the 2018 Plan shall be cumulatively increased on January 1, 2020 and each January 1 thereafter by 4% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year or a lesser number of shares determined by our Board of Directors. The 2018 Plan provides for the grant of incentive stock options, 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 amount, terms of grants, and exercisability provisions are determined and set by the Company’s Board of Directors. The maximum number of authorized shares to be issued under the Plan was 5,094,691. As of December 31, 2019, there were 805,102 shares of common stock available for future issuance. The term of the options may be up to 10 years, and options are exercisable in cash or as otherwise determined by the Board of Directors. Generally, options and restricted stock awards vest over a four -year The Company recorded stock-based compensation expense in the following expense categories of its accompanying consolidated statements of operations: For the Years Ended December 31, 2019 2018 Research and development $ 2,547 $ 559 General and administrative 4,155 1,574 $ 6,702 $ 2,133 Stock options The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2019 and 2018: SHARES WEIGHTED AVERAGE EXERCISE PRICE PER SHARE WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (IN YEARS) Balance at January 1, 2018 1,215,727 $ 0.74 9.5 Granted 1,185,119 6.14 Exercised (145,618 ) 0.74 Forfeited (133,667 ) 0.74 Balance at December 31, 2018 2,121,561 $ 3.78 9.1 Granted 2,287,889 15.78 Exercised (100,421 ) 2.55 Forfeited (119,737 ) 5.60 Balance at December 31, 2019 4,189,292 $ 10.31 8.9 Exercisable at December 31, 2019 858,316 3.16 7.9 Vested and expected to vest at December 31, 2019 4,189,292 The table above excludes 13,363 shares of common stock subject to repurchase by the Company, which were issued in 2017 upon the early exercise of unvested stock options. In addition, the above table excludes 8,017 options that were granted outside of the Plan. As of December 31, 2019, there was $23,448 in unrecognized compensation cost that is expected to be recognized over an estimated weighted-average amortization period of 3.2 years. The aggregate intrinsic value of options outstanding and options exercisable as of December 31, 2019 was $20,279. The aggregate intrinsic values of options exercised during the year ended December 31, 2019 was $1,411. The fair value of options is estimated using the Black-Scholes option pricing model, which takes into account inputs such as the exercise price, the value of the underlying common stock at the grant date, expected term, expected volatility, risk-free interest rate and dividend yield. The fair value of each grant of options during the years ended December 31, 2019 and 2018 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. ▪ Post IPO, the company is traded on the Nasdaq Select Market. Fair value is determined by the stock price quoted on the 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. For the years ended December 31, 2019 and 2018, the grant date fair value of all option grants was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: For the Years Ended December 31, 2019 2018 Risk free interest rate 2.08 % 2.90 % Expected term (in years) 6.0 6.1 Expected volatility 70.4 % 66.8 % Annual dividend yield —% —% Fair value of common stock $ 10.06 $ 7.62 Restricted stock For restricted stock awards granted, the fair value of the award is the current fair value of the Company’s common stock on the grant date. All restricted stock grants were outside of the Plan. In the event of a termination of employment or consulting services arrangement, the unvested restricted stock awards are subject to repurchase by the Company at the lower of the purchase price paid by the holder and the then current fair value. The following table summarizes the activity related to unvested restricted stock grants to employees and non-employees for the years ended December 31, 2019 and 2018: SHARES Balance at January 1, 2018 137,244 Granted - Vested (89,284 ) Forfeited - Balance at December 31, 2018 47,960 Granted - Vested (47,960 ) Forfeited - Balance at December 31, 2019 - As of December 31, 2019, there was no unrecognized compensation cost. Warrants Warrants issued to non-employees in connection with providing consulting services are issued outside of the Plan and are accounted for as stock-based compensation. The warrants have an initial exercise price of $0.74 per share and will expire at the earlier of ten years from the date of issuance or a change in control event as defined in the warrant agreements. The following table summarizes the activity related to warrant grants to non-employees for the years ended December 31, 2019 and 2018: Warrants Balance at January 1, 2018 373,061 Granted - Exercised (169,385 ) Forfeited - Balance at December 31, 2018 203,676 Granted - Exercised - Forfeited - Balance at December 31, 2019 203,676 The table above includes 56,462 shares of common stock subject to repurchase by the Company, which were issued in 2018 upon the early exercise of unvested warrants. As of December 31, 2019, there was $531 in unrecognized compensation cost that is expected to be recognized over an estimated weighted-average amortization period of 1.0 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 year ended December 31, 2019, there were 10,614 shares issued under the 2018 ESPP.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income taxes	11. Income taxes Loss before income tax expense for the years ended December 31, 2018 and 2019 consist of the following: For the Years Ended December 31, 2019 2018 United States $ (47,960 ) $ (24,251 ) Foreign 463 — Loss before income taxes $ (47,497 ) $ (24,251 ) The income tax expense for the years ended December 31, 2019 and 2018 consisted of the following components: For the Years Ended December 31, 2019 2018 Current Tax State $ 40 $ — Total current tax 40 — Deferred tax Foreign 62 — Total deferred tax 62 — Income tax expense $ 102 $ — Subject to the limitations described below, at December 31, 2019, we have cumulative federal and state net operating loss carryforwards of approximately $4.1 million and $63.9 million available to reduce federal and state taxable income, respectively, which expire through 2037 and 2039, respectively. Additionally, we have $58.1 million of federal net operating loss carryforwards which carryforward indefinitely. We have cumulative federal and state tax credit carryforwards of $3.5 million and $1.7 million, respectively, available to reduce federal and state income taxes which expire through 2039 and 2034, respectively. Section 382 of the Internal Revenue Code of 1986, as amended (the Code) provides for limitation on the use of net operating loss and research and development tax credit carryforwards following certain ownership changes (as defined in Code) that could limit the Company’s ability to utilize these carryforwards. Pursuant to Section 382 of the Code, an ownership change occurs when the stock ownership of a 5% stockholder increases by more than 50% over a three-year testing period. The Company may have experienced various ownership changes, as defined by the Code, as a result of past financings and may in the future experience an ownership change. Accordingly, the Company’s ability to utilize the aforementioned carryforwards may be limited. Additionally, U.S. tax laws limit the time during which these carryforwards may be applied against future taxes. The Company has not performed an Internal Revenue Code Section 382 study in connection with changes in control. The components of net deferred income tax assets (liabilities) as of December 31, 2019 and 2018 are as follows: As of December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 17,120 $ 5,193 Research and development credits 4,814 1,893 Capitalized costs 6,234 6,770 Accrued expenses and other 907 514 Stock compensation 1,311 172 Total deferred tax assets 30,386 14,542 Deferred tax liabilities: Depreciation (171 ) (32 ) Total deferred tax liabilities (171 ) (32 ) Less: valuation allowance (30,277 ) (14,510 ) Total net deferred tax assets (liabilities) $ (62 ) $ - In assessing the realizability of the net deferred tax assets, the Company considers all relevant positive and negative evidence in determining whether it is more likely than not that some portion or all of the deferred income tax assets will not be realized. The realization of the gross deferred tax assets is dependent on several factors, including the generation of sufficient taxable income prior to the expiration of the net operating loss carryforwards. Management believes that it is more likely than not that the Company’s U.S. deferred income tax assets will not be realized. As such, there is a full valuation allowance against the net U.S. deferred tax assets as of December 31, 2019 and 2018. The Company is in a net deferred tax liability position in the United Kingdom and believes it is more likely than not that the foreign deferred income tax assets will be realized. As such, there is no valuation allowance against the U.K. deferred tax assets. The valuation allowance in the U.S. increased by approximately $ 15.8 million during the year ended December 31, 2019 primarily as a result of the increase in net operating loss carryforward s . The valuation allowance increased by approximately $ 7.3 million during the year ended December 31, 2018 primarily as a result of the increase in net operating loss carryforward s . The Company did not have unrecognized tax benefits as of December 31, 2019 or 2018. The Company recognizes interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. A reconciliation of income tax expense at the statutory federal income tax rate and income taxes as reflected in the financial statements is as follows: As of December 31, 2019 2018 Statutory Federal income tax rate 21.0 % 21.0 % State income tax, net of federal benefit 6.4 % 7.3 % Permanent differences -0.4 % -1.3 % Research and development credit benefit 5.9 % 3.3 % Change in valuation allowance -33.1 % -30.3 % Effective income tax rate -0.2 % 0.0 % The Company’s income tax returns remain open and subject to examination for all tax years after 2015. Management believes that the Company does not have any uncertain tax positions that would result in a material impact on the Company’s financial statements. The Company files income tax returns in the above jurisdictions as well as the applicable state jurisdictions in the United States. There are currently no income tax examinations ongoing. If and when applicable, the Company will recognize interest and penalties on uncertain tax positions as income tax expense.

Related party transactions

Related party transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related party transactions	12. Related party transactions Consulting arrangements On October 1, 2015, we 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 us as may be reasonably requested. In exchange, we agreed to pay Dr. Baeuerle a consulting fee of €15 per month. On November 1, 2016, we 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 our Board of Directors based on Dr. Baeuerle’s performance and our performance. The term of the agreement is one year, and automatically extends for additional one-year On March 2, 2016, we 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 us as may be reasonably requested, including making Dr. Finer available to serve as Chairman of our Scientific Advisory Board. Pursuant to the amended and restated consulting agreement, we agreed (i) to pay Pattern Recognition Ventures a consulting fee of $19 per quarter for services provided under the agreement. During the years ended December 31, 2019 and 2018, we incurred fees and travel-related expenses to Pattern Recognition Ventures in the amount of $77 and $76, respectively. Dr. Finer has a financial interest in Pattern Recognition Ventures and is its managing member. Dr. Finer is also a member of our Board of Directors and is an executive partner at MPM Capital, the beneficial owner of more than 5% of our voting securities. On October 1, 2017, we 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. During the years ended December 31, 2019 and 2018, pursuant to the consulting agreement, Globeways Holdings Limited provided consulting, advisory and related services in exchange for consulting fees of $52 and $127, respectively. Dr. Jovan was a member of our Board of Directors until May 2019 and Globeways Holdings Limited is the appointed manager of certain affiliates of F2 Capital that collectively beneficially own more than 5% of our voting securities.

Quarterly Financial Information

Quarterly Financial Information (unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (unaudited)	13. Quarterly Financial Information (unaudited) Three Months Ended December 31, 2019 September 30, 2019 June 30, 2019 March 31, 2019 Operating expenses Research and development $ 9,392 $ 11,374 $ 8,833 $ 7,889 General and administrative 4,179 3,522 3,307 2,886 Total operating expenses 13,571 14,896 12,140 10,775 Loss from operations (13,571 ) (14,896 ) (12,140 ) (10,775 ) Interest income, net 846 1,090 1,077 872 Loss before income taxes (12,725 ) (13,806 ) (11,063 ) (9,903 ) Income taxes 102 - - - Net Loss (12,827 ) (13,806 ) (11,063 ) (9,903 ) Accretion of redeemable convertible preferred stock to redemption value - - - (49,900 ) Net loss attributable to common stockholders $ (12,827 ) $ (13,806 ) $ (11,063 ) $ (59,803 ) Per share information Net loss per share of common stock, basic and diluted $ (0.54 ) $ (0.58 ) $ (0.46 ) $ (4.85 ) Weighted average shares outstanding, basic and diluted 23,961,960 23,874,593 23,818,003 12,328,805 Three Months Ended December 31, 2018 September 30, 2018 June 30, 2018 March 31, 2018 Operating expenses Research and development $ 6,219 $ 5,386 $ 5,175 $ 2,893 General and administrative 2,222 1,704 1,634 1,220 Total operating expenses 8,441 7,090 6,809 4,113 Loss from operations (8,441 ) (7,090 ) (6,809 ) (4,113 ) Interest income, net 751 702 622 127 Loss before income taxes (7,690 ) (6,388 ) (6,187 ) (3,986 ) Income taxes - - - - Net Loss (7,690 ) (6,388 ) (6,187 ) (3,986 ) Accretion of redeemable convertible preferred stock to redemption value (3,730 ) (11,590 ) (11,145 ) (10,833 ) Net loss attributable to common stockholders $ (11,420 ) $ (17,978 ) $ (17,332 ) $ (14,819 ) Per share information Net loss per share of common stock, basic and diluted $ (16.22 ) $ (27.25 ) $ (27.97 ) $ (28.90 ) Weighted average shares outstanding, basic and diluted 703,874 659,840 619,749 512,685

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Principles of consolidation and basis of presentation	Principles of consolidation and basis of presentation The accompanying consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB).
Use of estimates	Use of estimates The preparation of the accompanying consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the fair value of the royalty transfer agreement obligations, the valuation of 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 consolidated financial statements, actual results may materially vary from these estimates. Estimates and assumptions are periodically reviewed, and the effects of revisions are reflected in the consolidated financial statements in the period they are determined to be necessary.
Concentrations of credit risk and of manufacturing risk	Concentrations of credit risk and of manufacturing risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held by financial institutions in the United States. Amounts on deposit may at times exceed federally insured limits. Management believes that the financial institutions are financially sound, and accordingly, minimal credit risk exists with respect to the financial institutions. As of December 31, 2019, the Company had manufacturing arrangements with vendors for the supply of materials for use in preclinical and clinical studies. If the Company were to experience any disruptions in either 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 December 31, 2019 and 2018, the Company’s financial instruments consist of money market funds, commercial paper, agency and corporate bonds, and asset-backed securities are included in investments. The carrying value of investments is the estimated fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.
Cash equivalents	Cash equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. As of December 31, 2019 and 2018, cash equivalents consisted of U.S treasuries, corporate bonds and government-backed money market funds.
Investments	Investments As of December 31, 2019, all investments were classified as available-for-sale and were carried at their estimated fair value. Unrealized gains and losses are recorded as a component of accumulated other comprehensive income (loss) until realized. The Company determines the appropriate classification of its investments in debt securities at the time of purchase and re-evaluates such determination at each balance sheet date. The Company periodically reviews its investments in debt securities for impairment and adjusts these investments to their fair value when a decline in market value is deemed to be other than temporary. If losses on these securities are considered to be other than temporary, the loss is recognized in the statement of operations. The Company classifies its available-for-sale marketable securities as current or non-current based on each instrument’s underlying effective maturity date and for which the Company has the intent and ability to hold the investment for a period of greater than 12 months. Marketable securities with maturities of less than 12 months are classified as current and are included in investments in the consolidated balance sheets. Marketable securities with maturities greater than 12 months for which the Company has the intent and ability to hold the investment for greater than 12 months are classified as non-current and are included in investments, non-current in the consolidated balance sheets.
Property and equipment	Property and equipment Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life.
Impairment of long-lived assets	Impairment of long-lived assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future undiscounted net cash flows expected to be generated. Impairment charges are recognized at the amount by which the carrying amount of an asset exceeds the fair value of the asset. Assets to be disposed of are reported at the lower of the carrying amount or the fair value less costs to sell. The Company has not recognized any impairment of long-lived assets for the years ended December 31, 2019 and 2018.
Deferred offering costs	Deferred offering costs The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated at which time such costs are recorded against the gross proceeds of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations.
Restricted cash	Restricted cash Cash accounts that are restricted as to withdrawal or usage are presented as restricted cash. 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 contain certain redemption features that are 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. 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. Prior to the IPO, 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 options and stock price volatility. Since the IPO, the Company uses the value of its stock price as quoted on the Nasdaq Global Select Market to determine fair value of the Company’s common stock. The Company uses the Black-Scholes option pricing model to value its stock option awards and warrants. The assumptions used in calculating the fair value of stock-based awards represent management’s estimates and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, stock-based compensation expense could be materially different for future awards. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Research and development expenses	Research and development expenses Research and development costs are expensed as incurred and consist primarily of funds for employee wages and funds paid to third parties for the provision of services for product candidate development, clinical and preclinical development and related supply and manufacturing costs, and regulatory compliance costs. At the end of the reporting period, the Company compares payments made to third party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Upfront milestone payments made to third parties who perform research and development services on the Company’s behalf are expensed as services are rendered.
Income taxes	Income taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A reduction in the carrying value of the deferred tax assets is required when it is not more likely than not that such deferred tax assets are not realizable.
Net loss per share	Net loss per share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average shares of common stock outstanding during the period. The Company’s outstanding redeemable convertible preferred stock contractually entitles the holders of such shares to participate in distributions but contractually does not require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards granted by the Company entitle the holder of such awards to dividends declared or paid by the Board of Directors, regardless of whether such awards are unvested, as if such shares were outstanding shares of common stock at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive shares of common stock are not assumed to have been issued if their effect is anti-dilutive. Therefore, the weighted-average shares used to calculate both basic and diluted loss per share are the same. The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2019 and 2018, as they would be antidilutive: As of December 31, 2019 2018 Series A redeemable convertible preferred stock - 7,184,588 Series B redeemable convertible preferred stock - 10,090,711 Stock options outstanding 4,189,292 2,121,551 Employee stock purchase plan 7,092 - Unvested shares of restricted stock - 47,960 Common stock warrants 203,676 203,676 Total 4,400,060 19,648,486
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 consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2019 and 2018. As of December 31, 2019 2018 Cash and cash equivalents $ 65,296 $ 47,674 Restricted cash 417 290 Cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 65,713 $ 47,964
Segment information	Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one consolidated operating segment.
JOBS Act accounting election	JOBS Act accounting election The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
Recently issued and adopted accounting pronouncements	Recently 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, the amendments are effective for fiscal years beginning after December 15, 2020. The Company will adopt the new standard beginning January 1, 2021. A modified retrospective transition approach is required, applying the new standard to all leases existing at the date of initial application. The standard includes a number of practical expedients that the Company is evaluating and may elect to apply. 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. Recently adopted accounting pronouncements Beginning January 1, 2019, the Company adopted ASU 2016-18, Statement of Cash Flows (Topic 230) Restricted Cash, which requires entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. Entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. The standard requires retrospective application in the consolidated statements of cash flows. In June 2018, the FASB issued ASU 2018-07, Compensation — Stock Compensation (Topic 718) Improvements to Non-employee Share-Based Payment Accounting. The amendments in this update expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. Under this ASU, an entity should apply the requirements of Topic 718 to non-employee awards except for specific guidance on inputs to an option pricing model and the attribution of costs (that is, the period of time over which share-based payment awards vest and the pattern of cost recognition over that period). The guidance is applicable to public business entities for fiscal years beginning after December 15, 2018 including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. In June 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. As a result of the adoption of ASU 2018-07, there was no material impact to the financial statements.
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)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of Estimated Useful Lives of Property and Equipment	Property and equipment are recorded at cost. Depreciation and amortization are determined using the straight-line method over the estimated useful lives. Expenditures for maintenance and repairs are expensed as incurred while renewals and betterments are capitalized. When property and equipment is sold or otherwise disposed of, the cost and related accumulated depreciation are eliminated from the accounts and any resulting gain or loss is reflected in the consolidated statements of operations. Estimated Useful Lives Laboratory equipment 5 years Computer hardware and equipment 3 years Furniture and fixtures 5 - 7 years Leasehold improvements Lesser of lease term or estimated useful life.
Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations	The following potentially dilutive securities, on an as converted basis have been excluded from the computation of diluted weighted-average shares outstanding as of December 31, 2019 and 2018, as they would be antidilutive: As of December 31, 2019 2018 Series A redeemable convertible preferred stock - 7,184,588 Series B redeemable convertible preferred stock - 10,090,711 Stock options outstanding 4,189,292 2,121,551 Employee stock purchase plan 7,092 - Unvested shares of restricted stock - 47,960 Common stock warrants 203,676 203,676 Total 4,400,060 19,648,486
Schedule of Restricted Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the total of the same such amounts shown in the consolidated statements of cash flows for the years ended December 31, 2019 and 2018. As of December 31, 2019 2018 Cash and cash equivalents $ 65,296 $ 47,674 Restricted cash 417 290 Cash, cash equivalents, and restricted cash shown in the statements of cash flows $ 65,713 $ 47,964

Investments and Fair Value Me_2

Investments and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value And Debt Securities Available For Sale [Abstract]
Summary of Amortized Cost and Fair Values of Investment Securities Available-for-sale	As of December 31, 2019, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 92,686 $ 145 $ (3 ) $ 92,828 As of December 31, 2018, investments were comprised of the following: Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate bonds $ 58,029 $ 1 $ (94 ) $ 57,936 Agency bonds 9,966 - (9 ) 9,957 Commercial paper 7,214 - (4 ) 7,210 Asset-backed securities 390 - - 390 Total $ 75,599 $ 1 $ (107 ) $ 75,493
Summary of Classified Assets Measured at Fair Value on a Recurred Basis	The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2019: 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) Includes cash sweep accounts, U.S. Treasury money market mutual fund, bank certificates of deposit, U.S. Treasury bills and corporate bonds that have a maturity of three months or less from the original acquisition date. The Company has classified assets measured at fair value on a recurring basis as follows as of December 31, 2018: 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) $ 45,974 $ 45,974 $ 45,108 $ 866 $ - Corporate bonds 58,029 57,936 - 57,936 - Agency bonds 9,966 9,957 - 9,957 - Commercial paper 7,214 7,210 - 7,210 - Asset-backed securities 390 390 - 390 - Total $ 121,573 $ 121,467 $ 45,108 $ 76,359 $ - (1)

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Summary of Property and Equipment	Property and equipment, net, consisted of: As of December 31, 2019 2018 Laboratory equipment $ 5,717 $ 2,118 Computer hardware and equipment 105 105 Furniture and fixtures 396 326 Leasehold improvements 312 34 Construction in process 203 - 6,733 2,583 Less: accumulated depreciation (1,807 ) (945 ) $ 4,926 $ 1,638

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of: As of December 31, 2019 2018 Employee compensation and related benefits $ 2,816 $ 1,676 Professional fees 300 342 Contract manufacturing organization fees 500 173 Contract research organization fees 182 232 University partnerships 448 162 Property received not yet invoiced 260 103 Other 544 114 $ 5,050 $ 2,802

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
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 December 31, 2019: As of December 31, 2020 $ 3,421 2021 3,110 2022 2,553 2023 2,561 2024 2,490 Thereafter 1,054 Total minimum payments required $ 15,189

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of Stock-based Compensation Expense	The Company recorded stock-based compensation expense in the following expense categories of its accompanying consolidated statements of operations: For the Years Ended December 31, 2019 2018 Research and development $ 2,547 $ 559 General and administrative 4,155 1,574 $ 6,702 $ 2,133
Schedule of Stock Option Activity	The following table summarizes the activity related to stock option grants to employees and non-employees for the years ended December 31, 2019 and 2018: SHARES WEIGHTED AVERAGE EXERCISE PRICE PER SHARE WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (IN YEARS) Balance at January 1, 2018 1,215,727 $ 0.74 9.5 Granted 1,185,119 6.14 Exercised (145,618 ) 0.74 Forfeited (133,667 ) 0.74 Balance at December 31, 2018 2,121,561 $ 3.78 9.1 Granted 2,287,889 15.78 Exercised (100,421 ) 2.55 Forfeited (119,737 ) 5.60 Balance at December 31, 2019 4,189,292 $ 10.31 8.9 Exercisable at December 31, 2019 858,316 3.16 7.9 Vested and expected to vest at December 31, 2019 4,189,292
Schedule of Weighted-Average Assumptions	For the years ended December 31, 2019 and 2018, the grant date fair value of all option grants was estimated at the time of grant using the Black-Scholes option-pricing model using the following weighted average assumptions: For the Years Ended December 31, 2019 2018 Risk free interest rate 2.08 % 2.90 % Expected term (in years) 6.0 6.1 Expected volatility 70.4 % 66.8 % Annual dividend yield —% —% Fair value of common stock $ 10.06 $ 7.62
Unvested Restricted Stock Activity	The following table summarizes the activity related to unvested restricted stock grants to employees and non-employees for the years ended December 31, 2019 and 2018: SHARES Balance at January 1, 2018 137,244 Granted - Vested (89,284 ) Forfeited - Balance at December 31, 2018 47,960 Granted - Vested (47,960 ) Forfeited - Balance at December 31, 2019 -
Warrants
Schedule of Stock Option Activity	The following table summarizes the activity related to warrant grants to non-employees for the years ended December 31, 2019 and 2018: Warrants Balance at January 1, 2018 373,061 Granted - Exercised (169,385 ) Forfeited - Balance at December 31, 2018 203,676 Granted - Exercised - Forfeited - Balance at December 31, 2019 203,676

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Components of Loss Before Income Tax Expense	Loss before income tax expense for the years ended December 31, 2018 and 2019 consist of the following: For the Years Ended December 31, 2019 2018 United States $ (47,960 ) $ (24,251 ) Foreign 463 — Loss before income taxes $ (47,497 ) $ (24,251 )
Components of Income Tax Expense	The income tax expense for the years ended December 31, 2019 and 2018 consisted of the following components: For the Years Ended December 31, 2019 2018 Current Tax State $ 40 $ — Total current tax 40 — Deferred tax Foreign 62 — Total deferred tax 62 — Income tax expense $ 102 $ —
Components of Net Deferred Income Tax Assets (Liabilities)	The components of net deferred income tax assets (liabilities) as of December 31, 2019 and 2018 are as follows: As of December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 17,120 $ 5,193 Research and development credits 4,814 1,893 Capitalized costs 6,234 6,770 Accrued expenses and other 907 514 Stock compensation 1,311 172 Total deferred tax assets 30,386 14,542 Deferred tax liabilities: Depreciation (171 ) (32 ) Total deferred tax liabilities (171 ) (32 ) Less: valuation allowance (30,277 ) (14,510 ) Total net deferred tax assets (liabilities) $ (62 ) $ -
Reconciliation of Income Tax Expense at Statutory Federal Income Tax Rate and Income Taxes	A reconciliation of income tax expense at the statutory federal income tax rate and income taxes as reflected in the financial statements is as follows: As of December 31, 2019 2018 Statutory Federal income tax rate 21.0 % 21.0 % State income tax, net of federal benefit 6.4 % 7.3 % Permanent differences -0.4 % -1.3 % Research and development credit benefit 5.9 % 3.3 % Change in valuation allowance -33.1 % -30.3 % Effective income tax rate -0.2 % 0.0 %

Organization and Description _2

Organization and Description of Business - Narrative (Details) $ / shares in Units, $ in Thousands	Feb. 14, 2019USD ($)$ / sharesshares	Feb. 01, 2019	Dec. 31, 2019USD ($)shares	Dec. 31, 2018shares
Subsidiary Sale Of Stock [Line Items]
Initial public offering, net of issuance costs | $			$ 77,121
Common stock, shares authorized (shares) | shares			150,000,000	20,988,730
Preferred stock, shares authorized (shares) | shares			10,000,000	0
Reverse stock split		0.1615
Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Shares sold during initial public offering (shares) | shares	5,750,000
Share price (USD per share) | $ / shares	$ 15
Underwriting discounts and commissions and other offering expenses | $	$ 9,129
Additional Paid-in Capital
Subsidiary Sale Of Stock [Line Items]
Initial public offering, net of issuance costs | $			$ 77,121
Additional Paid-in Capital | Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Initial public offering, net of issuance costs | $	$ 77,121
Common Stock | Initial Public Offering (IPO)
Subsidiary Sale Of Stock [Line Items]
Conversion of shares upon IPO (shares) | shares	17,275,299

Liquidity - Narrative (Details)

Liquidity - Narrative (Details) $ in Thousands	Dec. 31, 2019USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 158,124

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Laboratory Equipment
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Estimated Useful Lives	5 years
Computer Hardware and Equipment
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Estimated Useful Lives	3 years
Furniture and Fixtures | Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Estimated Useful Lives	5 years
Furniture and Fixtures | Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Estimated Useful Lives	7 years
Leasehold Improvements
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Estimated Useful Lives	Lesser of lease term or estimated useful life.

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Impairment of long-lived assets	$ 0	$ 0
Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Operating and financial leases term of contract	12 months

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	4,400,060	19,648,486
Series A redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)		7,184,588
Series B redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)		10,090,711
Stock options outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	4,189,292	2,121,551
Unvested shares of restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)		47,960
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)	7,092

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Reconciliation of Cash and Cash Equivalents and Restricted Cash as presented in the Statements of Cash Flows (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 65,296	$ 47,674
Restricted cash	417	290
Cash, cash equivalents, and restricted cash shown in the statements of cash flows	$ 65,713	$ 47,964	$ 20,101

Investments and Fair Value Me_3

Investments and Fair Value Measurements - Summary of Amortized Cost and Fair Values of Investment Securities Available-for-sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 75,599
Unrealized Gains		1
Unrealized Losses		(107)
Fair Value		75,493
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 92,686	58,029
Unrealized Gains	145	1
Unrealized Losses	(3)	(94)
Fair Value	$ 92,828	57,936
Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		9,966
Unrealized Gains		0
Unrealized Losses		(9)
Fair Value		9,957
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		7,214
Unrealized Gains		0
Unrealized Losses		(4)
Fair Value		7,210
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		390
Unrealized Gains		0
Unrealized Losses		0
Fair Value		$ 390

Investments and Fair Value Me_4

Investments and Fair Value Measurements - Summary of Classified Assets Measured at Fair Value on a Recurred Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		$ 75,599
Available-for-sale securities, fair value		75,493
Cash and cash equivalents	$ 65,296	47,674
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	61,237	45,974
Cash equivalents, fair value	61,237	45,974
Available-for-sale securities, amortized cost	153,923	121,573
Available-for-sale securities, fair value	154,065	121,467
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	61,237	45,108
Available-for-sale securities, fair value	61,237	45,108
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	0	866
Available-for-sale securities, fair value	92,828	76,359
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	0	0
Available-for-sale securities, fair value	0	0
Corporate bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost	92,686	58,029
Available-for-sale securities, fair value	92,828	57,936
Corporate bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value	0	0
Corporate bonds | Fair Value, Measurements, Recurring | 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	92,828	57,936
Corporate bonds | Fair Value, Measurements, Recurring | 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
Agency bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		9,966
Available-for-sale securities, fair value		9,957
Agency bonds | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		9,966
Available-for-sale securities, fair value		9,957
Agency bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value		0
Agency bonds | Fair Value, Measurements, Recurring | 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		9,957
Agency bonds | Fair Value, Measurements, Recurring | 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
Commercial paper | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		7,214
Available-for-sale securities, fair value		7,210
Commercial paper | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value		0
Commercial paper | Fair Value, Measurements, Recurring | 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		7,210
Commercial paper | Fair Value, Measurements, Recurring | 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
Asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		390
Available-for-sale securities, fair value		390
Asset-backed securities | Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, amortized cost		390
Available-for-sale securities, fair value		390
Asset-backed securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value		0
Asset-backed securities | Fair Value, Measurements, Recurring | 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		390
Asset-backed securities | Fair Value, Measurements, Recurring | 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	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,733	$ 2,583
Less: accumulated depreciation	(1,807)	(945)
Property and equipment, net	4,926	1,638
Laboratory equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,717	2,118
Computer hardware and equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	105	105
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	396	326
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	312	$ 34
Construction in process
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 203

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 862	$ 419

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Employee compensation and related benefits	$ 2,816	$ 1,676
Professional fees	300	342
Contract manufacturing organization fees	500	173
Contract research organization fees	182	232
University partnerships	448	162
Property received not yet invoiced	260	103
Other	544	114
Accrued expenses and other current liabilities	$ 5,050	$ 2,802

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) £ in Thousands	1 Months Ended			12 Months Ended
	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019GBP (£)
Other Commitments [Line Items]
Lease facility expiration date	2024-08		2025-07
Restricted cash	$ 127,000		$ 290,000
Initial term		3 years
Termination period notice requirement		12 months
Termination period		12 months
Operating lease liability per year | £						£ 300
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
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	Dec. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 3,421
2021	3,110
2022	2,553
2023	2,561
2024	2,490
Thereafter	1,054
Total minimum payments required	$ 15,189

Employee benefit plan - Narrati

Employee benefit plan - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
401(k) Plan
Defined Contribution Plan Disclosure [Line Items]
Expense relating to the matching contribution under 401(k) plan	$ 276	$ 121

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	Dec. 31, 2019USD ($)voteshares	Dec. 31, 2018shares	Dec. 31, 2017shares
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		0	44,500,001
Redeemable convertible preferred stock, shares outstanding (shares)			44,500,001		0	44,500,001	44,500,001
Shares issued upon conversion (in shares)				0.1615
Minimum proceeds from initial public offering | $					$ 50,000
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		0	62,500,000
Redeemable convertible preferred stock, shares outstanding (shares)			62,500,000		0	62,500,000
Shares issued upon conversion (in shares)				0.1615
Minimum proceeds from initial public offering | $					$ 50,000
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	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Options granted outside of the Plan		8,017
Unrecognized compensation costs		$ 23,448,000
Unrecognized compensation cost, period of recognition		3 years 2 months 12 days
Aggregate intrinsic value of options outstanding and options exercisable		$ 20,279,000
Aggregate intrinsic values of options exercised		$ 1,411,000
Annual dividend yield		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)		10,614
Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options		10 years
Unrecognized compensation cost, period of recognition		1 year
Unrecognized compensation cost		$ 531,000
Initial exercise price of warrants		$ 0.74
Unvested Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock repurchased		56,462
2017 Unvested Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock repurchased		13,363
Unvested shares of restricted stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost		$ 0
2018 Stock Option and Incentive Plan | Stock options outstanding
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for issuance as a percentage of outstanding shares, maximum		4.00%
Number of shares authorized (in shares)		5,094,691
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)		805,102

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 6,702	$ 2,133
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,547	559
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,155	$ 1,574

Stock-based Compensation - St_2

Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning balance (in shares)	2,121,561	1,215,727
Options granted (in shares)	2,287,889	1,185,119
Options exercised (in shares)	(100,421)	(145,618)
Options forfeited (in shares)	(119,737)	(133,667)
Options outstanding, ending balance (in shares)	4,189,292	2,121,561	1,215,727
Options exercisable (in shares)	858,316
Options vested and expected to vest (in shares)	4,189,292
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)	$ 3.78	$ 0.74
Options granted, weighted average exercise price per share (in dollars per share)	15.78	6.14
Options exercised, weighted average exercise price per share (in dollars per share)	2.55	0.74
Options forfeited, weighted average exercise price per share (in dollars per share)	5.60	0.74
Options outstanding, weighted average exercise price per share, ending balance (in dollars per share)	10.31	$ 3.78	$ 0.74
Options exercisable, weighted average exercise price per share, ending balance (in dollars per share)	$ 3.16
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, weighted average remaining contractual life (in years)	8 years 10 months 24 days	9 years 1 month 6 days	9 years 6 months
Options exercisable, weighted average remaining contractual life (in years)	7 years 10 months 24 days

Stock-based Compensation - St_3

Stock-based Compensation - Stock Options Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk free interest rate	2.08%	2.90%
Expected term (in years)	6 years	6 years 1 month 6 days
Expected volatility	70.40%	66.80%
Annual dividend yield	0.00%
Fair value of common stock	$ 10.06	$ 7.62

Stock-based Compensation - Unve

Stock-based Compensation - Unvested Restricted Stock Activity (Details) - Unvested shares of restricted stock - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested restricted stock beginning balance (in shares)	47,960	137,244
Unvested restricted stock vested (in shares)	(47,960)	(89,284)
Unvested restricted stock ending balance (in shares)		47,960

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Warrant Activity (Details) - Warrants - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants beginning balance (in shares)	203,676	373,061
Warrants exercised (in shares)		(169,385)
Warrants forfeited (in shares)	0
Warrants ending balance (in shares)	203,676	203,676

Income taxes - Components of Lo

Income taxes - Components of Loss Before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States	$ (47,960)	$ (24,251)
Foreign	463
Loss before income taxes	$ (47,497)	$ (24,251)

Income taxes - Components of In

Income taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019
Current Tax
State		$ 40
Total current tax		40
Deferred tax
Foreign		62
Total deferred tax		62
Income tax expense	$ 102	$ 102

Income taxes - Narrative (Detai

Income taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Valuation allowance	$ 30,277,000	$ 14,510,000
Unrecognized tax benefits	$ 0	0
Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
Ownership change pursuant to section 382 of IRS, description	an ownership change occurs when the stock ownership of a 5% stockholder increases by more than 50% over a three-year testing period.
Federal [Member]
Income Tax Disclosure [Line Items]
Cumulative net operating loss carryforwards	$ 4,100,000
Federal net operating losses carryforward indefinitely	$ 58,100,000
Operating loss carry forwards expiration year	2037
Tax credit carryforwards expiration year	2039
Cumulative tax credit forward	$ 3,500,000
Valuation allowance increased	15,800,000	$ 7,300,000
State [Member]
Income Tax Disclosure [Line Items]
Cumulative net operating loss carryforwards	$ 63,900,000
Operating loss carry forwards expiration year	2039
Tax credit carryforwards expiration year	2034
Cumulative tax credit forward	$ 1,700,000
U.K [Member]
Income Tax Disclosure [Line Items]
Valuation allowance	$ 0

Income taxes - Components of Ne

Income taxes - Components of Net Deferred Income Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 17,120	$ 5,193
Research and development credits	4,814	1,893
Capitalized costs	6,234	6,770
Accrued expenses and other	907	514
Stock compensation	1,311	172
Total deferred tax assets	30,386	14,542
Depreciation	(171)	(32)
Total deferred tax liabilities	(171)	(32)
Less: valuation allowance	(30,277)	$ (14,510)
Total net deferred tax assets (liabilities)	$ (62)

Income taxes - Reconciliation o

Income taxes - Reconciliation of Income Tax Expense at Statutory Federal Income Tax Rate and Income Taxes (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Statutory Federal income tax rate	21.00%	21.00%
State income tax, net of federal benefit	6.40%	7.30%
Permanent differences	(0.40%)	(1.30%)
Research and development credit benefit	5.90%	3.30%
Change in valuation allowance	(33.10%)	(30.30%)
Effective income tax rate	(0.20%)	0.00%

Related party transactions - Na

Related party transactions - Narrative (Details) € in Thousands, $ in Thousands	Oct. 01, 2017USD ($)	May 09, 2017USD ($)	Nov. 01, 2016EUR (€)	Oct. 01, 2015EUR (€)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
MPM Capital | TCR2 Therapeutics Inc.
Related Party Transaction [Line Items]
Shareholder ownership, percentage					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					$ 72	$ 76
Dr. Mitchell Finer / Pattern Recognition Ventures | Director | Consulting Agreement, Fees
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions					$ 77	76
Dr. Mitchell Finer / Pattern Recognition Ventures | Director | Consulting Agreement, Quarterly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction		$ 19
Globeways Holdings Limited | Director | Consulting Agreement, Yearly Fee
Related Party Transaction [Line Items]
Related party transaction, amount of transaction	$ 52					$ 127

Quarterly Financial Informati_2

Quarterly Financial Information (unaudited) - Summary of Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Operating expenses
Research and development	$ 9,392	$ 11,374	$ 8,833	$ 7,889	$ 6,219	$ 5,386	$ 5,175	$ 2,893	$ 37,488	$ 19,673
General and administrative	4,179	3,522	3,307	2,886	2,222	1,704	1,634	1,220	13,894	6,780
Total operating expenses	13,571	14,896	12,140	10,775	8,441	7,090	6,809	4,113	51,382	26,453
Loss from operations	(13,571)	(14,896)	(12,140)	(10,775)	(8,441)	(7,090)	(6,809)	(4,113)	(51,382)	(26,453)
Interest income, net	846	1,090	1,077	872	751	702	622	127	3,885	2,202
Loss before income taxes	(12,725)	(13,806)	(11,063)	(9,903)	(7,690)	(6,388)	(6,187)	(3,986)	(47,497)	(24,251)
Income taxes	102								102
Net loss	(12,827)	(13,806)	(11,063)	(9,903)	(7,690)	(6,388)	(6,187)	(3,986)	(47,599)	(24,251)
Accretion of redeemable convertible preferred stock to redemption value				(49,900)	(3,730)	(11,590)	(11,145)	(10,833)	(49,900)	(37,298)
Net loss attributable to common stockholders	$ (12,827)	$ (13,806)	$ (11,063)	$ (59,803)	$ (11,420)	$ (17,978)	$ (17,332)	$ (14,819)	$ (97,499)	$ (61,549)
Per share information
Net loss per share of common stock, basic and diluted	$ (0.54)	$ (0.58)	$ (0.46)	$ (4.85)	$ (16.22)	$ (27.25)	$ (27.97)	$ (28.90)	$ (4.62)	$ (98.53)
Weighted average shares outstanding, basic and diluted	23,961,960	23,874,593	23,818,003	12,328,805	703,874	659,840	619,749	512,685	21,104,195	624,659