0001558370-21-003043 | 10-K | XBRL Viewer

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2020	Mar. 10, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Entity Registrant Name	Akero Therapeutics, Inc.
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	AKRO
Security Exchange Name	NASDAQ
Entity Well Known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		34,770,319
Entity Public Float			$ 477,922,638
Entity Central Index Key	0001744659
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 187,242	$ 64,788
Short-term marketable securities	81,145	71,612
Prepaid expenses and other current assets	2,958	1,649
Total current assets	271,345	138,049
Property and equipment, net	131
Right of use asset	1,662
Other assets, noncurrent	201	69
Total assets	273,339	138,118
Current liabilities:
Accounts payable	3,428	947
Accrued expenses and other current liabilities	9,683	8,422
Total current liabilities	13,111	9,369
Operating lease liability, noncurrent	1,516
Other liabilities, noncurrent		23
Total liabilities	14,627	9,392
Commitments and contingencies (Note 11)
Stockholders’ equity:
Common stock, $0.0001 par value, 150,000,000 shares authorized as of December 31, 2020 and December 31, 2019; 34,741,649 and 28,567,837 shares issued and outstanding as of December 31, 2020 and December 31, 2019, respectively	4	3
Additional paid-in capital	468,238	259,049
Accumulated other comprehensive loss	(3)	(6)
Accumulated deficit	(209,527)	(130,320)
Total stockholders’ equity	258,712	128,726
Total liabilities and stockholders’ equity	$ 273,339	$ 138,118

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Consolidated Balance Sheets
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	34,741,649	28,567,837
Common stock, shares outstanding	34,741,649	28,567,837

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 64,916	$ 37,046
General and administrative	15,238	8,605
Total operating expenses	80,154	45,651
Loss from operations	(80,154)	(45,651)
Other income:
Other income	947	1,896
Net loss	(79,207)	(43,755)
Net unrealized gain (loss) on short-term marketable securities	3	(6)
Comprehensive loss	$ (79,204)	$ (43,761)
Net loss per common share, basic and diluted	$ (2.52)	$ (2.90)
Weighted-average number of shares used in computing net loss per common share, basic and diluted	31,463,248	15,070,728

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Redeemable convertible preferred stock	Common Stock	Additional Paid-In-Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Total
Balance at beginning at Dec. 31, 2018	$ 124,728		$ 36,646		$ (86,565)	$ (49,919)
Balance at beginning (in shares) at Dec. 31, 2018	64,730,410	238,986
Conversion of convertible preferred stock into common stock upon closing of public offering	$ (124,728)					(124,728)
Conversion of convertible preferred stock into common stock upon closing of public offering (in shares)	(64,730,410)
Conversion of convertible preferred stock into common stock upon closing of public offering		$ 2	124,726			124,728
Conversion of convertible preferred stock into common stock upon closing of public offering (in shares)		21,056,136
Issuance of stock		$ 1	95,452			95,453
Issuance of stock (in shares)		6,612,500
Issuance of restricted common stock upon early exercise of stock options (in shares)		491,207
Exercise of stock options			130			$ 130
Exercise of stock options (in shares)		164,503				655,710
Vesting of restricted stock			240			$ 240
Issuance of common stock pursuant to ESPP purchases			85			85
Issuance of common stock pursuant to ESPP purchases (in shares)		4,505
Stock-based compensation expense			1,770			1,770
Net unrealized gain (loss) on short-term marketable securities				$ (6)		(6)
Net loss					(43,755)	(43,755)
Balance at ending at Dec. 31, 2019		$ 3	259,049	(6)	(130,320)	128,726
Balance at ending (in shares) at Dec. 31, 2019		28,567,837
Issuance of stock		$ 1	202,553			202,554
Issuance of stock (in shares)		6,012,390
Exercise of stock options			303			$ 303
Exercise of stock options (in shares)		150,343				150,343
Vesting of restricted stock			61			$ 61
Issuance of common stock pursuant to ESPP purchases			198			198
Issuance of common stock pursuant to ESPP purchases (in shares)		11,079
Stock-based compensation expense			6,022			6,022
Disgorgement of stockholders' short-swing profits, net			52			52
Net unrealized gain (loss) on short-term marketable securities				3		3
Net loss					(79,207)	(79,207)
Balance at ending at Dec. 31, 2020		$ 4	$ 468,238	$ (3)	$ (209,527)	$ 258,712
Balance at ending (in shares) at Dec. 31, 2020		34,741,649

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit)
Net issuance costs and underwriting fees	$ 906	$ 10,348

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (79,207)	$ (43,755)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,022	1,770
Depreciation	17
Non-cash lease expense	196
Net amortization of premiums and discounts on short-term investments	83	(104)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,378)	(507)
Accounts payable	2,481	(426)
Accrued expenses and other current liabilities	1,122	7,395
Other liabilities	(2)
Operating lease liability	(138)
Net cash used in operating activities	(70,804)	(35,627)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of short-term marketable securities	(115,037)	(71,513)
Proceeds from sales of short-term marketable securities	9,864
Proceeds from maturities of short-term marketable securities	95,560
Purchase of property and equipment	(148)
Net cash used in investing activities	(9,761)	(71,513)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the issuance of common stock in follow-on public offering, net of issuance costs and underwriting fees	202,554
Proceeds from the issuance of common stock in initial public offering, net of issuance costs and underwriting fees		95,452
Proceeds from the exercise of stock options	303	130
Proceeds from the issuance of common stock pursuant to employee stock purchase plan purchases	198	85
Proceeds from the disgorgement of stockholders' short-swing profits, net	52
Proceeds from the early exercise of stock options in exchange for restricted common stock		321
Net cash provided by financing activities	203,107	95,988
Net increase in cash, cash equivalents and restricted cash	122,542	(11,152)
Cash, cash equivalents and restricted cash at the beginning of the year	64,848	76,000
Cash, cash equivalents and restricted cash at the end of the year	187,390	64,848
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Right of use asset obtained in exchange for operating lease liability	1,751
Net unrealizable gain (loss) on marketable securities	3	(6)
Remeasurement of right-of-use asset ($173) and operating lease liability (-$173)	$ 173
Conversion of convertible preferred stock into common stock		$ 124,728

Nature of the business and basis of presentation	12 Months Ended
Nature of the business and basis of presentation	Dec. 31, 2020
Nature of the business and basis of presentation
Nature of the business and basis of presentation	1. Nature of the business and basis of presentation Akero Therapeutics, Inc., together with its wholly owned subsidiary Akero Securities Corporation, (“Akero” or the “Company”) is a cardio-metabolic nonalcoholic steatohepatitis, or NASH, company dedicated to developing pioneering medicines designed to restore metabolic balance and improve overall health. NASH is a severe form of nonalcoholic fatty liver disease, or NAFLD, characterized by inflammation and fibrosis in the liver that can progress to cirrhosis, liver failure, cancer and death. The Company’s lead product candidate, EFX, is an analog of fibroblast growth factor 21, or FGF21, which is an endogenously expressed hormone that protects against cellular stress and regulates metabolism of lipids, carbohydrates and proteins throughout the body. The Company conducted a Phase 2a clinical trial, the BALANCED study, to evaluate EFX in the treatment of biopsy-confirmed NASH patients. The main portion of this study in NASH patients with F1-F3 fibrosis showed EFX’s potential to reduce liver fat, improve liver health, reverse fibrosis, improve glycemic control and reduce risks of cardiovascular disease. In February 2021 the Company began screening for a Phase 2b clinical trial, the HARMONY study, to evaluate EFX in the treatment of NASH patients with F2/F3 fibrosis. Based on clinical data to date, the Company believes EFX has the potential to be a foundational NASH monotherapy. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, completion and success of clinical testing, development by competitors of new technological innovations, compliance with governmental regulations, dependence on key personnel and protection of proprietary technology and the ability to secure additional capital to fund operations. EFX will require extensive clinical testing prior to regulatory approval and commercialization. These efforts require significant amounts of additional capital, adequate personnel, and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Basis of presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company after elimination of all intercompany accounts and transactions. All adjustments necessary for the fair presentation of the Company’s consolidated financial statements for the periods have been reflected. Initial public offering On June 24, 2019, Akero completed its initial public offering or IPO at which time the Company issued 6,612,500 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 862,500 additional shares of common stock, at a public offering price of $16.00 per share. The Company received $98,394, net of underwriting discounts and commissions, but before deducting offering costs payable by the Company, which were $2,942. Upon the closing of the IPO, all outstanding shares of redeemable convertible preferred stock converted into 21,056,136 shares of common stock (see Note 6). In connection with the completion of its IPO in June 2019, the Company amended its certificate of incorporation to authorize the issuance of up to 150,000,000 shares of $0.0001 par value common stock and 10,000,000 shares of $0.0001 par value preferred stock designated as undesignated preferred stock. Reverse stock split On June 6, 2019, the Company effected a one-for-3.07418 reverse stock split of the Company’s common stock. All common stock, stock options and per share information presented have been adjusted to reflect the reverse stock split on a retroactive basis for all periods presented. There was no change in the par value of the Company’s common stock. The ratio by which shares of preferred stock are convertible into shares of common stock was adjusted to reflect the effects of the reverse stock split. Liquidity In accordance with Accounting Standards Update (“ASU”) No. 2014‑15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205‑40), the Company has evaluated whether there are certain conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. Since its inception, the Company has funded its operations primarily with proceeds from sales of redeemable convertible preferred stock and most recently with proceeds from its IPO in June 2019 and a follow-on public offering of its common stock in July 2020. The Company has incurred recurring losses since its inception, including a net loss of $79,207 and $43,755 for the years ended December 31, 2020 and 2019, respectively. In addition, as of December 31, 2020, the Company had an accumulated deficit of $209,527. The Company expects to continue to generate operating losses for the foreseeable future. As of March 16, 2021, the issuance date of these consolidated financial statements, the Company expects that its existing cash, cash equivalents and short-term marketable securities of $268,387 as of December 31, 2020, will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of these consolidated financial statements. The Company expects that it will require additional funding beyond this time to complete the clinical development of EFX, commercialize EFX, if it receives regulatory approval, and pursue in-licenses or acquisitions of other product candidates. If the Company is unable to obtain funding, the Company will be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Summary of significant accounting policies

12 Months Ended

Dec. 31, 2020

Summary of significant accounting policies

Summary of significant accounting policies

2. Summary of significant accounting policies

Use of estimates

The preparation of the Company's consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuations of common stock and the valuation allowance for deferred tax assets. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Cash and cash equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the time of purchase to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts.

Short-term marketable securities

The Company invests in short-term marketable securities, primarily money market funds, commercial paper, U.S. treasury securities and corporate debt securities. The Company classifies its short-term marketable securities as available-for-sale securities and reports them at fair value in short-term marketable securities on the consolidated balance sheets with related unrealized gains and losses included within accumulated other comprehensive gain (loss) on the consolidated balance sheets. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in other income on the consolidated statements of operations and comprehensive loss. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in other income.

The Company regularly reviews all its investments for other-than-temporary declines in estimated fair value. This review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. When the Company determines that the decline in estimated fair value of an investment is below the amortized cost basis and the decline is other-than-temporary, the carrying value of the security will be reduced and a loss will be recorded for the amount of such decline.

Restricted cash

As of December 31, 2020 the Company was required to maintain a separate cash balance of $108 for the benefit of the landlord in connection with the Company’s Gateway office space lease in South San Francisco, California (the “Gateway Lease”), which is classified within other assets (non-current) on the 2020 consolidated balance sheet (see Note 12). As of December 31, 2019 the Company was required to maintain a separate cash balance of $20 for the benefit of the landlord in connection with the Company’s Harbor office space lease in South San Francisco, California (the “Harbor Lease”), which is classified within other assets (non-current) on the 2019 consolidated balance sheet (see Note 12).

As of December 31, 2020 and 2019, the Company was required to maintain a separate cash balance of $40 to collateralize corporate credit cards with a bank, which are classified within other assets (non-current) on the consolidated balance sheets.

Concentrations of credit risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents and short-term marketable securities. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash investments in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. At December 31, 2020 and 2019, all of the Company's cash, cash equivalents and short-term investments were held at one accredited financial institution.

Property and equipment

Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is provided using the straight-line method over the estimated useful lives of the assets, which is three years for furniture and equipment. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the improvements. Depreciation and amortization begin at the time the asset is placed in service.

Leases

Leases (Topic 842) Effective January 1, 2020

The Company determines whether an arrangement is or contains a lease at inception by assessing whether the arrangement contains an identified asset and whether the Company has the right to control the identified asset. Right-of-use, or ROU, assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Lease liabilities are recognized at the lease commencement date based on the present value of future lease payments over the lease term. ROU assets are based on the measurement of the lease liability and are further adjusted by any lease payments made prior to or on lease commencement, lease incentives received and initial direct costs incurred, as applicable. The Company elected, as allowed under Topic 842 (or “ASC 842”), to not recognize leases with a lease term of one year or less on its balance sheet. Operating lease costs included in the measurement of the lease are recognized on a straight-line basis over the lease term. Variable lease costs are expensed as incurred as an operating expense.

In accordance with ASC 842, components of a lease should be split into three categories: lease components, non-lease components, and non-components. The fixed and in-substance fixed contract consideration (including any consideration related to non-components) must be allocated, based on the respective relative fair values, to the lease components and non-lease components.

Entities may elect not to separate lease and non-lease components. Accordingly, entities making this election would account for each lease component and related non-lease component together as a single lease component. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and allocate all of the contract consideration to the lease component only.

ASC 842 allows for the use of judgment in determining whether the assumed lease term is for a major part of the remaining economic life of the underlying asset and whether the present value of lease payments represents substantially all of the fair value of the underlying asset. The Company applies the bright line thresholds referenced in ASC 842 to assist in evaluating leases for appropriate classification. The aforementioned bright lines are applied consistently to the Company’s leases.

The Company determines the lease classification and the present value of future lease payments at the time of the lease commencement using an incremental borrowing rate that it estimates based upon the Company’s credit risk and term of the lease. The interest rate implicit in lease contracts has not historically been readily determinable and the Company must therefore use the appropriate incremental borrowing rate to measure its leases. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating.

Leases (Topic 840) Prior to the Adoption of Topic 842

The Company entered into lease agreements for office facilities which were classified as operating leases. Rent expense was recognized on a straight-line basis over the noncancelable term of the lease and, accordingly, the Company recorded the difference between cash rent payments and the recognition of rent expense as a deferred rent liability, which was included within accrued expenses and other current liabilities (short-term portion) and other liabilities (long-term portion) on the condensed consolidated balance sheet.

Deferred offering costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process common equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction of additional paid-in capital generated as a result of such offering. Should an 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 and comprehensive loss. As of December 31, 2020, the Company recorded deferred offering costs of $46, which are classified within other assets, noncurrent, on the 2020 consolidated balance sheet. As of December 31, 2019, the Company did not have any deferred offering costs.

Segment information

The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. The Company's singular focus is developing and commercializing transformative treatments for serious metabolic diseases, with an initial focus on NASH.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, third-party license fees and external costs including fees paid to consultants, contract manufacturing organizations, or CMOs, and clinical research organizations, or CROs, in connection with drug product manufacturing, nonclinical studies and clinical trials, and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered.

Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses.

Research contract costs and accruals

The Company has entered into various research and development and other agreements with commercial firms, researchers and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company's estimates.

Patent costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Stock-based compensation

The Company measures all stock-based awards granted to employees and nonemployees based on the fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award, on a straight-line basis. The Company accounts for forfeitures as they occur. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model. Prior to the Company’s initial public offering, the exercise price for all stock options granted was at the estimated fair value of the underlying common stock as determined on the date of grant by the Company’s board of directors.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the option, the risk-free interest rate for a period that approximates the expected term of the option, and the Company's expected dividend yield. The Company went public in June 2019 and accordingly, lacks sufficient company-specific historical and implied volatility information for its shares traded in the public markets. Therefore, it estimates its expected share price volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. The expected term of the Company's stock options has been determined utilizing the "simplified" method for awards that qualify as "plain-vanilla" options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. The fair value of each common stock award is estimated on the date of grant based on the fair value of the Company's common stock on that same date.

Compensation expense for purchases under the Employee Stock Purchase Plan is recognized based on the fair value of the common stock estimated based on the closing price of our common stock as reported on the date of offering, less the purchase discount percentage provided for in the plan.

The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss 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.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders' equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s comprehensive loss is comprised of net loss and changes in unrealized gains and losses on its short-term marketable securities.

Income taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company's tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Net loss per share

Basic net loss per share is calculated by dividing the net loss by the weighted average number of shares of common stock outstanding during the period, without consideration of common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the Company’s net loss.

Emerging growth company

The Company is an emerging growth company as defined in the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”). Under the JOBS Act, companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected this exemption to delay adopting new or revised accounting standards until such time as those standards apply.

Recently adopted accounting pronouncements

In February 2016 the FASB issued ASU 2016-02, Leases (Topic 842, ASC 842 or ASU 2016-02). ASU 2016-02 amends several aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a ROU asset and corresponding liability, measured at the present value of the lease payments. On January 1, 2020, the Company adopted Topic 842 using the modified retrospective approach and the adoption date as the initial date of application. Results prior to the adoption effective date are presented under Topic 840. No prior period amounts were adjusted and continue to be reported in accordance with previous lease guidance, Accounting Standards Codification Topic 840, Leases, or Topic 840.

Topic 842 provides a number of optional practical expedients in transition. The Company elected the short-term lease expedient for leases with a term of one year or less, which permits a lessee to not recognize lease assets and lease liabilities for those leases. The Company elected the practical expedients to not reassess its prior conclusions about lease identification under the new standard, to not reassess lease classification, and to not reassess initial direct costs for its existing leases at adoption.

Operating lease liabilities and their corresponding ROU assets are recorded based on the present value of future lease payments over the expected remaining lease term at lease commencement. In transition to ASC 842, the Company utilized the remaining lease term of its leases, as of the effective date, in determining the appropriate incremental borrowing rate. Lease cost for operating leases is recognized on a straight-line basis over the lease term as an operating expense.

The impact of the Company’s adoption of Topic 842 as of January 1, 2020 was as follows:


			Adjustments
			Due to the
	December 31,		Adoption of		January 1,
	2019		Topic 842		2020
Assets:
Operating lease ROU asset	$	—	$	280	$	280
Liabilities:
Operating lease liabilities, current (included in accrued expenses and other current liabilities)		—		224		224
Deferred rent, current (included in accrued expenses and other current liabilities)		2		(2)		—
Operating lease liabilities, noncurrent (included in other liabilities)		—		60		60
Deferred rent, noncurrent (included in other liabilities)		2		(2)		—

In August 2018, the FASB issued No. ASU 2018 13, Fair Value Measurement (Topic 820)—Disclosure Framework (“ASU 2018 13”), which improves the disclosure requirements for fair value measurements. The Company adopted ASU 2018 13 on January 1, 2020, which did not have a material impact on its consolidated financial statements.

Recently issued accounting pronouncements not yet adopted

In June 2016, the FASB issued No. ASU 2016-13, Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 requires measurement and recognition of expected credit losses for financial assets. In November 2019, the FASB issued No. ASU 2019-10 to modify the effective date for ASU 2016-13 for other public business entities includes smaller reporting companies, as defined by the SEC. This guidance will become effective for us beginning in the first quarter of 2023. Early adoption is permitted. The Company is currently evaluating the impact that the adoption of ASU 2016-13 will have on its consolidated financial statements.

Fair value of financial assets and liabilities

12 Months Ended

Dec. 31, 2020

Fair value of financial assets and liabilities

Fair value of financial assets and liabilities

3. Fair value of financial assets and liabilities

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Observable inputs are inputs that market participants would use in pricing a financial asset or liability based on market data obtained from sources independent of the Company. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

Level 1—Quoted prices in active markets for identical assets or liabilities.

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

Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The following table summarizes our financial assets measured at fair value on a recurring basis as of December 31, 2020 and 2019:


	December 31, 2020
	Total		Level 1		Level 2		Level 3
Money market funds	$	158,023	$	158,023	$	—	$	—
Commercial paper		47,955		—		47,955		—
Corporate debt securities		33,190		—		33,190		—
	$	239,168	$	158,023	$	81,145	$	—

	December 31, 2019
	Total		Level 1		Level 2		Level 3
Money market funds	$	49,948	$	49,948	$	—	$	—
Commercial paper		49,114		—		49,114		—
U.S. treasury securities		6,048		6,048		—		—
Corporate debt securities		20,143		—		20,143		—
	$	125,253	$	55,996	$	69,257	$	—

Commercial paper and corporate debt securities were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities. During the years ended December 31, 2020 and December 31, 2019, there were no transfers between Level 1, Level 2 and Level 3.

- Definition

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

+ References + Details

Short-term marketable securities

12 Months Ended

Dec. 31, 2020

Short-term marketable securities

Short-term marketable securities

4. Short-term marketable securities

The following is a summary of short-term marketable securities presented on the Company’s consolidated balance sheet as of December 31, 2020 and 2019:


	December 31, 2020
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Money market funds	$	158,023	$	—	$	—	$	158,023
Commercial paper		47,955		—		—		47,955
Corporate debt securities		33,193		—		(3)		33,190
	$	239,171	$	—	$	(3)	$	239,168

Cash equivalents							$	158,023
Short-term marketable securities								81,145
							$	239,168

	December 31, 2019
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Money market funds	$	49,948	$	—	$	—	$	49,948
Commercial paper		49,114		—		—		49,114
U.S. treasury securities		6,048		—		—		6,048
Corporate debt securities		20,149		—		(6)		20,143
	$	125,259	$	—	$	(6)	$	125,253

Cash equivalents							$	53,641
Short-term marketable securities								71,612
							$	125,253

As of December 31, 2020 and 2019, all of the Company’s short-term marketable securities had contractual maturities of less than one year.

Accrued expenses and other current liabilities

12 Months Ended

Dec. 31, 2020

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities

5. Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	Year Ended December 31,
	2020		2019
Accrued external research and development expenses	$	8,740	$	6,361
Accrued employee compensation and benefits		495		1,606
Accrued legal and professional fees		154		370
Short-term lease liability and other		294		85
	$	9,683	$	8,422

Redeemable convertible preferred stock	12 Months Ended
Redeemable convertible preferred stock	Dec. 31, 2020
Redeemable convertible preferred stock
Redeemable convertible preferred stock	6. Redeemable convertible preferred stock Upon completion of the Company’s IPO on June 24, 2019, 50,858,462 of the Company’s Series A redeemable convertible preferred stock and 13,871,948 shares of the Company’s Series B redeemable convertible preferred were converted into 21,056,136 shares of common stock and the related carrying value of $124,728 was reclassified to common stock in the amount of $2 and additional paid-in capital in the amount of $124,726. Accordingly, there were no shares of redeemable convertible preferred stock outstanding as of December 31, 2020 or 2019.

Stockholder's equity (deficit)

12 Months Ended

Dec. 31, 2020

Stockholder’s equity (deficit)

Stockholder’s equity (deficit)

7. Stockholders’ equity (deficit)

Common stock

As of December 31, 2020 and 2019, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 150,000,000 shares of $0.0001 par value 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. The holders of common stock, voting exclusively and as a separate class, have the exclusive right to vote for the election of directors of the Company. Common stockholders are entitled to receive dividends, which may be declared by the board of directors. Through December 31, 2020, no cash dividends had been declared or paid.

On June 24, 2019, the Company completed its IPO at which time the Company issued 6,612,500 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 862,500 additional shares of common stock, at a public offering price of $16.00 per share. The Company received $98,394, net of underwriting discounts and commissions, but before deducting offering costs payable by the Company, which were $2,942. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 21,056,136 shares of common stock (see Note 6).

On July 10, 2020, the Company completed a follow-on public offering at which time the Company issued 6,012,390 shares of common stock, including the exercise in full by the underwriters of their option to purchase up to 784,224 additional shares of common stock, at a public offering price of $36.00 per share. The Company received $203,460 net of underwriting discounts and commissions, but before deducting offering costs paid by the Company, which were $906.

As of December 31, 2020 and December 31, 2019, there were 34,741,649 and 28,567,837 shares of common stock issued and outstanding, respectively.

The following shares of common stock were reserved for issuance as follows:


	Year Ended December 31,
	2020	2019
Options outstanding under the 2018 Stock Option and Grant Plan	2,148,019	2,296,029
Options outstanding under the 2019 Stock Option and Incentive Plan	1,585,293	800,526
Options available for future grant	2,127,544	1,771,931
2019 Employee Stock Purchase Plan	543,963	269,364
	6,404,819	5,137,850

Undesignated preferred stock

The Company’s fourth amended and restated certificate of incorporation authorizes the Company to issue up to 10,000,000 shares of undesignated preferred stock, par value $0.0001 per share. There were no undesignated preferred shares issued or outstanding as of December 31, 2020 or 2019.

Restricted common stock

In March 2017, the Company issued an aggregate of 226,400 shares of restricted common stock under restricted stock agreements with the founders. Pursuant to the terms of the agreements, the restricted common stock was initially subject to a vesting schedule over a four-year period commencing in January 2017 and culminating in January 2021. In March 2018, the Company amended the restricted stock agreements such that the restricted common stock became subject to a vesting schedule over a two-year period commencing in May 2018 and culminating in June 2020. As of December 31, 2020, all restricted stock issued to the founders is fully vested.

In April, June and July 2019, the Company amended certain option grant agreements granted under the Company’s 2018 Stock Option and Grant Plan to allow the holders the right to early exercise unvested options, subject to a repurchase right held by the Company equal to the lesser of the original exercise price per share or the fair value of the shares on the repurchase date. The unvested shares issued as a result of the early exercise are deemed restricted stock pursuant to a restricted stock agreement and a vesting schedule identical to the vesting schedule of the original grant agreement. The proceeds related to unvested restricted common stock are recorded as liabilities until the stock vests, at which point they are reclassified to additional paid-in capital. Common shares issued for the early exercise of options are included in issued and outstanding shares.

The following table summarizes restricted stock activity since December 31, 2018:


		Grant-Date Fair
	Number of Shares	Value
Unvested restricted common stock as of December 31, 2018	80,190	$	—
Early exercise of unvested stock options	491,207		0.65
Shares vesting	(416,248)		0.65
Unvested restricted common stock as of December 31, 2019	155,149		0.52
Shares vesting	(121,535)		0.50
Unvested restricted common stock as of December 31, 2020	33,614	$	0.62

As of December 31, 2020, there were 33,614 shares of unvested restricted common stock from the early exercise of stock options which were subject to repurchase by the Company.

Stock-based awards

12 Months Ended

Dec. 31, 2020

Stock-based awards

Stock-based awards

8. Stock-based awards

2018 Stock option and grant plan

The Company’s 2018 Stock Option and Grant Plan (the “2018 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards and other stock-based awards to employees, directors and consultants of the Company. The 2018 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated.

The total number of shares of common stock that could have been issued under the 2018 Plan was 3,071,960 shares, of which 107,635 shares remained available for grant on June 18, 2019, the date that the Company’s 2019 Stock Option and Incentive Plan (the “2019 Plan”) became effective. Upon the effectiveness of the 2019 Plan, the 107,635 remaining shares available under the 2018 Plan were transferred and became available for issuance under the 2019 Plan. Shares of common stock underlying outstanding awards under the 2018 Plan that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) will be added to the shares of common stock available for issuance under the 2019 Plan.

2019 Stock option and incentive plan

The 2019 Plan was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 Plan became effective on June 18, 2019 and replaced the Company’s 2018 Plan on that date. The 2019 Plan allows the board of directors or the compensation committee of the board of directors to make equity-based incentive awards to the Company’s officers, employees, directors or other key persons (including consultants). The number of shares initially reserved for issuance under the 2019 Plan is 2,572,457, which includes the 107,635 shares transferred from the 2018 Plan, and shall be cumulatively increased on January 1, 2020 and each January 1 thereafter by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors. The 2019 Plan was increased by 1,142,713 shares on January 1, 2020 and 1,389,665 shares on January 1, 2021.

The 2019 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. All incentive options granted to any person possessing more than 10% of the total combined voting power of all classes of shares may not have an exercise price of less than 110% of the fair market value of the common stock on the grant date. Stock options granted to employees, officers, members of the board of directors and consultants will typically vest over a four-year period.

Shares that are expired, terminated, surrendered or canceled under the 2019 Plan without having been fully exercised will be available for future awards.

2019 Employee stock purchase plan

The 2019 Employee Stock Purchase Plan (the “2019 ESPP”) was adopted and approved by the Company’s board of directors in May 2019 and by the Company’s stockholders in June 2019. The 2019 ESPP became effective on June 18, 2019, at which time 273,869 shares were reserved for issuance. The 2019 ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2020 and each January 1 thereafter through January 1, 2029, by the least of (i) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31, (ii) 410,803 shares or (iii) such number of shares as determined by the compensation committee. The 2019 ESPP was increased by 285,678 shares on January 1, 2020 and 347,416 shares on January 1, 2021.

Stock option valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees, directors and consultants were as follows, presented on a weighted average basis:



	Year Ended December 31,
	2020		2019
Expected term (in years)	6.00		6.00
Expected volatility	73.38	%	73.75	%
Weighted average risk-free interest rate	0.65	%	2.12	%
Expected dividend yield	0.00	%	0.00	%

Stock options

The following table summarizes the Company’s stock option activity since December 31, 2018:


		Weighted-		Weighted-
		Average		Average	Aggregate
		Exercise		remaining	Intrinsic
	Number	Price per		contractual	Value
	of Options	Share		term (years)	(000's)
Balance outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,912,352	$	12.42
Options exercised	(655,710)	$	0.69
Balance outstanding, December 31, 2019	3,096,555	$	7.89	9.19		44,323
Options granted	788,320	$	26.94
Options exercised	(150,343)	$	2.01
Options cancelled	(1,220)	$	0.62
Balance outstanding, December 31, 2020	3,733,312	$	12.15	8.53	$	52,498
Exercisable, December 31, 2020	1,069,363	$	8.12	8.21	$	18,933
Vested and expected to vest, December 31, 2020	3,733,312	$	12.15	8.53	$	52,498

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

The weighted average grant-date fair value per share of stock options granted during the year ended December 31, 2020 was $17.07.

Stock-based compensation

The following table summarizes the Company’s stock-based compensation expense for the years ended December 31, 2020 and 2019:


	Year Ended December 31,
	2020		2019
Classified within research and development expense	$	1,633	$	485
Classified within general and administrative expense		4,389		1,285
Total stock-based compensation expense	$	6,022	$	1,770

As of December 31, 2020, total unrecognized compensation cost related to the unvested stock-based awards was $23,156, which is expected to be recognized over a weighted average period of 2.5 years.

In April, June and July 2019, certain option holders early exercised options to purchase 491,207 shares of common stock, at an average exercise price of $0.65 per share, for cash proceeds of $321 (See Note 7). Stock-based compensation expense related to these options will continue to be recognized over the requisite service period of the awards based on the grant-date fair value which was determined using the Black-Scholes option-pricing model.

Amgen license agreement	12 Months Ended
Amgen license agreement	Dec. 31, 2020
Amgen license agreement
Amgen license agreement	9. Amgen license agreement In June 2018, the Company entered into a license agreement (the “Amgen Agreement”) with Amgen pursuant to which the Company was granted an exclusive license to certain patents and intellectual property related to a long-acting FGF21 analog in order to commercially develop, manufacture, use and distribute FGF21 as a treatment for NASH and other serious metabolic diseases. The Amgen Agreement provides the Company with exclusive global rights to the licensed products and the right to grant sublicenses that cover EFX to third parties. In exchange for these rights, the Company made an upfront payment of $5,000 and issued 2,653,333 shares of Series A Preferred Stock with a fair value of $1,353 to Amgen. Amgen was also entitled to maintain a 10% ownership interest of the outstanding shares of the Company’s common stock, on a fully diluted and converted basis, through the second closing of the Company’s Series A Preferred Stock financing. In November 2018, in connection with the second closing of the Company’s Series A Preferred Stock financing, the Company issued 3,205,128 shares of Series A Preferred Stock to Amgen for a total value of $7,404, satisfying its anti-dilution obligation under the Amgen Agreement. Under the Amgen Agreement, the Company made a milestone payment in August 2019 of $2,500 in connection with dosing the first patient in the BALANCED study and is obligated to pay Amgen $7,500 in connection with dosing the first patient in a Phase 3 clinical trial, up to $30,000 in connection with marketing approvals, and aggregate milestone payments of up to $75,000 upon the achievement of specified commercial milestones for all products licensed under the Amgen Agreement. Under the Amgen Agreement, the Company is obligated to pay Amgen tiered royalties ranging from a low to high single-digit percentages on annual net sales of the licensed products, beginning on the first commercial sale of such licensed products in each country and expiring on a country-by-country basis on the latest of (i) the expiration of the last valid patent claim covering such licensed products in such country, (ii) the loss of regulatory exclusivity in such country, and (iii) ten years after the first commercial sale of such licensed product in such country. The royalty payments are subject to reduction under specified conditions set forth in the Amgen Agreement. The Company is solely responsible for all development, manufacturing, and commercial activities and costs of the licensed products, including clinical studies or other tests necessary to support the use of a licensed product. The Company is also responsible for costs related to the filing, prosecution and maintenance of the licensed patent rights. The Amgen Agreement will remain in effect until the expiration of the royalty term in all countries for all licensed products. The Amgen Agreement may be terminated by either party with at least 90 days' notice in the event of material breach by the other party that remains uncured for 90 days, by either party for insolvency or bankruptcy of the other party and immediately by Amgen if the Company challenges the licensed patents. The Company may also terminate the Amgen Agreement with 90 days' written notice for discretionary reasons such as scientific, technical, regulatory or commercial issues, as defined in the Amgen Agreement. During the year ended December 31, 2020, the Company did not record any research and development expense in connection with the Amgen Agreement. During the year ended December 31, 2019, the Company recorded research and development expense of $2,500 related to the achievement of a clinical milestone, as specified in the agreement.

Income taxes

12 Months Ended

Dec. 31, 2020

Income taxes

Income taxes

10. Income taxes

During the years ended December 31, 2020 and 2019, the Company recorded no income tax benefits for the net operating losses incurred or for the research and development tax credits generated in each period due to its uncertainty of realizing a benefit from those items. All of the Company’s operating losses since inception have been generated in the United States.

A summary of the Company’s current and deferred tax provision is as follows:


	Year Ended December 31,
	2020		2019
Current income tax provision:
Federal	$	—	$	—
State		—		24
Total current income tax provision		—		24
Deferred income tax benefit:
Federal		(17,580)		(9,400)
State		(3,135)		688
Total deferred income tax benefit		(20,715)		(8,712)
Change in deferred tax asset valuation allowance		20,715		8,712
Total provision for income taxes	$	—	$	24

The $24 provision for income taxes for the year ended December 31, 2019 was classified within general and administrative expense on the Consolidated Statements of Operations and Comprehensive Loss.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2020		2019
Federal statutory income tax rate	21.0	%	21.0	%
State income taxes, net of federal benefit	4.0		(1.6)
Research and development tax credits	1.3		1.9
Other permanent differences	(0.1)		0.1
Change in deferred tax asset valuation allowance	(26.2)		(19.9)
Effect of Section 382 limitation	-		(1.5)
Effective income tax rate	-	%	-	%

Net deferred tax assets as of December 31, 2020 and 2019 consisted of the following:


	December 31,
	2020		2019
Deferred tax assets
Net operating loss carry forwards	$	29,951	$	11,380
Research and development tax credit carry forwards		2,096		969
License fees		3,364		3,232
Stock based compensation		1,402		196
Accruals, reserves and other		63		44
Total deferred tax assets		36,876		15,821
Deferred tax liabilities
Prepaid expenses		(649)		(309)
Total deferred tax liabilities		(649)		(309)
Net deferred tax assets		36,227		15,512
Valuation allowance		(36,227)		(15,512)
Total net deferred tax assets	$	—	$	—

As of December 31, 2020, the Company had U.S. federal and state net operating loss carryforwards of $127,416 and $47,200, respectively, which may be available to offset future taxable income and begin to expire in 2037. The federal net operating loss carryforwards include $124,973, which may be carried forward indefinitely. As of December 31, 2020, the Company also had U.S. federal and state research and development tax credit carryforwards of $2,441 and $378, respectively, which may be available to offset future tax liabilities and begin to expire in 2032. During the year ended December 31, 2020, gross deferred tax assets, before valuation allowance, increased by $20,715, due to the operating loss incurred by the Company during that period.

Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income or tax liabilities. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three‑year period. The annual limitation is determined by multiplying the value of the Company's stock at the time of such ownership change by the applicable long-term tax-exempt rate. Such limitations may result in expiration of a portion of the NOL carryforwards before utilization. As of December 31, 2020, the Company determined that ownership changes occurred on March 24, 2017, June 7, 2018 and July 8, 2020. As a result of the ownership changes, approximately $2,118 and $3,632 of the NOLs will expire unutilized for federal and state purposes, respectively. The ability of the Company to use its remaining NOL carryforwards may be further limited if the Company experiences a Section 382 ownership change as a result of future changes in its stock ownership.

The Company’s research and development credits are subject to IRC section 383 and are limited due to the ownership changes that the Company has experienced. As of December 31, 2020, the Company has derecognized approximately $87 and $43 of gross federal and state research and development credits, respectively. The Company has not derecognized any of the California research and development credit-related deferred tax assets because the credits do not expire.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets at each reporting period. In doing so, the Company has considered its history of cumulative net losses incurred and its lack of commercialization of any products or generation of any revenue from product sales and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been recorded against the net deferred tax assets as of December 31, 2020 and 2019. Management reevaluates the positive and negative evidence at each reporting period.

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2020 and 2019 are as follows:


	2020		2019
Valuation allowance as of January 1,	$	(15,512)	$	(6,800)
Increases recorded to income tax provision		—		—
Decreases recorded as a benefit to income tax provision		(20,715)		(8,712)
Valuation allowance as of December 31,	$	(36,227)	$	(15,512)

As of December 31, 2020, the Company had gross unrecognized tax benefits of $644, none of which if recognized, would reduce the effective tax rate in a future period, due to the Company's full valuation allowance on U.S. net deferred tax assets. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2020, the Company had not accrued interest or penalties related to uncertain tax positions and no amounts had been recognized in the Company’s consolidated statements of operations and comprehensive loss. For the year ended December 31, 2020, the Company will file income tax returns in the U.S., California, Connecticut, Illinois, Massachusetts, Maryland, New York, and Pennsylvania, as prescribed by the tax laws of the jurisdictions in which it operates. The Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company is open to future tax examination under statute from 2017 to the present.

A reconciliation of the beginning and ending unrecognized tax benefits for the years ended December 31, 2020 and 2019 is as follows



Balance at December 31, 2018	$	—
Increases related to prior year tax positions		—
Decreases related to prior year tax positions		—
Increases related to current year tax positions		237
Settlements		—
Lapse of statute of limitations		—
Balance at December 31, 2019	$	237
Increases related to prior year tax positions		—
Decreases related to prior year tax positions		—
Increases related to current year tax positions		407
Settlements		—
Lapse of statute of limitations		—
Balance at December 31, 2020	$	644

On March 27, 2020, the “Coronavirus Aid, Relief and Economic Security (CARES) Act” (the “Act”) was signed into law. The Act includes provisions relating to refundable payroll tax credits, deferment of the employer portion of certain payroll taxes, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The Company analyzed the provisions of the Act and determined there was no significant impact to its income taxes for the year ended December 31, 2020.

On June 29, 2020, the Governor of California signed Assembly Bill 85 (“A.B. 85”), which includes several tax measures, provides for a three-year suspension of the use of net operating losses for medium and large businesses and a three-year cap on the use of business incentive tax credits to offset no more than $5,000 of tax per year. Generally, A.B. 85 suspends the use of net operating losses for taxable years 2020, 2021, and 2022 for taxpayers with taxable income of $1,000 or more. Since the Company is not expected to generate California source taxable income of more than $1,000, no material impact is anticipated at this time.

On December 27, 2020, the “Consolidated Appropriations Act, 2021” (the “CAA”) was signed into law. The CAA includes provisions meant to clarify and modify certain items put forth in the CARES Act, while providing aid to businesses affected by the COVID-19 pandemic. The CAA allows deductions for expenses paid for by Paycheck Protection Program (“PPP”) and Economic Injury Disaster Loan (“EIDL”) Program, clarifies forgiveness of EIDL advances, and other business provisions. The Company analyzed the provisions of the CAA and determined there was no significant impact to its 2020 tax provision.

- Definition

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

+ References + Details

Net loss per share

12 Months Ended

Dec. 31, 2020

Net loss per share

Net loss per share

11. Net loss per share

Basic and diluted net loss per share was calculated as follows:


	Year Ended December 31,
	2020		2019
Numerator:
Net loss	$	(79,207)	$	(43,755)
Denominator:
Weighted average common shares outstanding, basic and diluted		31,463,248		15,070,728
Net loss per share, basic and diluted	$	(2.52)	$	(2.90)

The Company excluded 31,215 shares and 49,568 shares of restricted common stock, presented on a weighted average basis, from the calculations of basic net loss per share for the years ended December 31, 2020 and 2019, respectively, because those shares had not vested.

The Company’s potentially dilutive securities, which include stock options and unvested restricted common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect:


	Year Ended December 31,
	2020	2019
Options to purchase common stock	3,733,312	3,096,555
Unvested restricted common stock	33,614	155,149
	3,766,926	3,251,704

Commitments and contingencies

12 Months Ended

Dec. 31, 2020

Commitments and contingencies

Commitments and contingencies

12. Commitments and contingencies

COVID-19 Pandemic

In December 2019, a novel strain of coronavirus (“COVID-19”) was reported to have surfaced in Wuhan, China. As of March 2021, COVID-19 has spread to other countries, including Europe and the United States, and has been declared a pandemic by the World Health Organization. Efforts to contain the spread of COVID-19 have intensified and the United States, Europe and Asia have implemented severe travel restrictions, social distancing requirements, stay-at-home orders and have delayed the commencement of non-COVID-19-related clinical trials, among other restrictions. The Company’s financial results for the years ended December 31, 2020 and 2019 were not significantly impacted by COVID-19, however, the Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 pandemic will have on its financial condition, operations, and business plans for 2021, including the timing and enrollment of patients in its planned clinical trials and other expected milestones of its product candidate.

Operating leases

In October 2018, the Company entered into a lease agreement for office space in South San Francisco, California. In March 2019, the Company amended this lease agreement (the “First Amendment”) to extend the term of the lease and expand the square footage of the existing leased office space. On May 7, 2020, the Company entered into an agreement to effectuate an early termination of the 2018 office lease agreement in South San Francisco, California, without penalty, resulting in a non-cash reduction to the ROU asset and corresponding lease liability of $173 at that time. This early termination was effective on June 30, 2020 and reduced the Company’s future minimum lease payments by approximately $180.

In September 2019, the Company entered into an agreement to use office space in Cambridge, Massachusetts. The agreement was for an initial six-month term, which was extended until September 2020, and provided for rolling six-month extensions. The Company determined this lease to be short term, as the Company is not obligated at any time for more than a six-month term. The Company made monthly payments of $4 under the agreement until the agreement was terminated on September 30, 2020.

In February 2020, the Company entered into a seven-year agreement to occupy 6,647 square feet of office space in South San Francisco, California. The lease commenced on July 10, 2020 when the Company took occupancy of the leased space and determined that the lease should be classified as an operating lease. Under the agreement, the Company is required to make approximately $2,300 in total minimum payments during the term. The Company is also required to pay its proportionate share of building operating and tax costs after the first year under lease which are not included in the measurement of the lease and treated as variable lease cost and expense when incurred.

As of December 31, 2020, maturities of the Company’s operating lease liabilities were as follows:


2021	$	303
2022		312
2023		321
2024		331
2025		341
2026 and thereafter		559
Total future minimum lease payments		2,167
Less imputed interest		(469)
Present value of operating lease liabilities	$	1,698

As of December 31, 2020, the total lease liability was $1,698, of which $1,516 was noncurrent and $182 was current and classified within “Accrued expenses and other current liabilities” on the balance sheet.

For the year ended December 31, 2020, the components of operating lease cost were as follows:


		Year Ended
		December 31, 2020
Lease cost:	Statement of Operations Classification:
Operating lease cost	General and administrative expense	$	267
Variable operating lease cost	General and administrative expense		43
Short-term lease cost	Research and development expense		32
Total operating lease cost		$	342

Other information:
Cash paid for amounts included in the measurement of operating lease liability		$	210
Weighted average remaining lease term			6.6
Weighted average discount rate			7.6%

Prior to the Company’s adoption of ASC 842 on January 1, 2020, the Company recognized rent expense on a straight-line basis over the respective lease periods and recorded rent expense of $305 for the year ended December 31, 2019. As of December 31, 2019, future minimum commitments due under the Company’s leases totaled $401, of which $321 was due in 2020 and $80 was due in 2021.

Research and manufacturing commitments

The Company has entered into agreements with CROs and CMOs to provide services in connection with its nonclinical studies and clinical trials and to manufacture clinical development materials. As of December 31, 2020, the Company had non-cancelable purchase commitments under these agreements totaling $5,513.

Indemnification agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not currently aware of any indemnification claims and has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2020 or 2019.

Legal proceedings

The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities. 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 intends to expense as incurred the costs related to such legal proceedings if they should arise.

Related parties	12 Months Ended
Related parties	Dec. 31, 2020
Related parties
Related parties	13. Related parties Apple Tree Life Sciences, Inc. The principal and founding member of Apple Tree Life Sciences, Inc. ("Apple Tree"), one of the Company’s significant investors, is a member of the Company’s board of directors. The Company's founders, including the current Executive Vice President and Chief Operating Officer and Chief Scientific Officer, were formerly employees of Apple Tree. During the years ended December 31, 2020 and 2019, the Company incurred fees for certain general and administrative services from Apple Tree totaling $0 and $20, respectively. As of December 31, 2020 and 2019, the Company did not owe any amounts to Apple Tree. Atlas Venture Life Science Advisors, LLC A partner of Atlas Venture Life Science Advisors (“Atlas”), one of the Company’s significant investors, is a member of the Company’s board of directors. In August 2018, the Company entered into a use and occupancy agreement for office space in Cambridge, Massachusetts with Atlas. The parties terminated the agreement in September of 2019. During the year ended December 31, 2019 the Company incurred fees under the use and occupancy agreement with Atlas totaling $22. As of December 31, 2020 and 2019, the Company did not owe any amounts to Atlas.

Benefit plans	12 Months Ended
Benefit plans	Dec. 31, 2020
Benefit plans
Benefit plans	14. Benefit plans The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre‑tax basis. Matching contributions to the plan may be made at the discretion of the Company’s board of directors. The Company did not make any matching contributions to the plan during the years ended December 31, 2020 and 2019.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/topic&trid=2235017

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 3
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-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Subsequent events	12 Months Ended
Subsequent events	Dec. 31, 2020
Subsequent events
Subsequent events	15. Subsequent events The Company evaluated subsequent events through March 16, 2021, the date on which these financial statements were issued. Based on this evaluation, it was determined that no subsequent events occurred that require recognition or disclosure in its financial statements for the year ended December 31, 2020.

Summary of significant accounting policies (Policies)

12 Months Ended

Dec. 31, 2020

Summary of significant accounting policies

Use of estimates

Cash and cash equivalents

Short-term marketable securities

Restricted cash

Concentrations of credit risk

Property and equipment

Leases

Leases (Topic 842) Effective January 1, 2020

Leases (Topic 840) Prior to the Adoption of Topic 842

Deferred offering costs

Segment information

Research and development costs

Research contract costs and accruals

Patent costs

Stock-based compensation

Comprehensive loss

Income taxes

Net loss per share

Emerging growth company

Recently adopted accounting pronouncements

The impact of the Company’s adoption of Topic 842 as of January 1, 2020 was as follows:


			Adjustments
			Due to the
	December 31,		Adoption of		January 1,
	2019		Topic 842		2020
Assets:
Operating lease ROU asset	$	—	$	280	$	280
Liabilities:
Operating lease liabilities, current (included in accrued expenses and other current liabilities)		—		224		224
Deferred rent, current (included in accrued expenses and other current liabilities)		2		(2)		—
Operating lease liabilities, noncurrent (included in other liabilities)		—		60		60
Deferred rent, noncurrent (included in other liabilities)		2		(2)		—

Recently issued accounting pronouncements not yet adopted

Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2020

ASU 2016-02

New Accounting Pronouncements or Change in Accounting Principle [Line Items]

Schedule of impact on the balance sheet upon adoption of lease standard

The impact of the Company’s adoption of Topic 842 as of January 1, 2020 was as follows:


			Adjustments
			Due to the
	December 31,		Adoption of		January 1,
	2019		Topic 842		2020
Assets:
Operating lease ROU asset	$	—	$	280	$	280
Liabilities:
Operating lease liabilities, current (included in accrued expenses and other current liabilities)		—		224		224
Deferred rent, current (included in accrued expenses and other current liabilities)		2		(2)		—
Operating lease liabilities, noncurrent (included in other liabilities)		—		60		60
Deferred rent, noncurrent (included in other liabilities)		2		(2)		—

Fair value of financial assets and liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Fair value of financial assets and liabilities

Summary of assets that are measured at fair value on a recurring basis


	December 31, 2020
	Total		Level 1		Level 2		Level 3
Money market funds	$	158,023	$	158,023	$	—	$	—
Commercial paper		47,955		—		47,955		—
Corporate debt securities		33,190		—		33,190		—
	$	239,168	$	158,023	$	81,145	$	—

	December 31, 2019
	Total		Level 1		Level 2		Level 3
Money market funds	$	49,948	$	49,948	$	—	$	—
Commercial paper		49,114		—		49,114		—
U.S. treasury securities		6,048		6,048		—		—
Corporate debt securities		20,143		—		20,143		—
	$	125,253	$	55,996	$	69,257	$	—

Short-term marketable securities (Tables)

12 Months Ended

Dec. 31, 2020

Short-term marketable securities

Summary of cash, cash equivalents and short-term marketable securities


	December 31, 2020
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Money market funds	$	158,023	$	—	$	—	$	158,023
Commercial paper		47,955		—		—		47,955
Corporate debt securities		33,193		—		(3)		33,190
	$	239,171	$	—	$	(3)	$	239,168

Cash equivalents							$	158,023
Short-term marketable securities								81,145
							$	239,168

	December 31, 2019
	Amortized cost		Gross unrealized gains		Gross unrealized losses		Fair value
Money market funds	$	49,948	$	—	$	—	$	49,948
Commercial paper		49,114		—		—		49,114
U.S. treasury securities		6,048		—		—		6,048
Corporate debt securities		20,149		—		(6)		20,143
	$	125,259	$	—	$	(6)	$	125,253

Cash equivalents							$	53,641
Short-term marketable securities								71,612
							$	125,253

Accrued expenses and other current liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Accrued expenses and other current liabilities

Schedule of accrued expenses and other current liabilities


	Year Ended December 31,
	2020		2019
Accrued external research and development expenses	$	8,740	$	6,361
Accrued employee compensation and benefits		495		1,606
Accrued legal and professional fees		154		370
Short-term lease liability and other		294		85
	$	9,683	$	8,422

Stockholder's equity (deficit) (Tables)

12 Months Ended

Dec. 31, 2020

Stockholder’s equity (deficit)

Schedule of common stock reserved for issuance


	Year Ended December 31,
	2020	2019
Options outstanding under the 2018 Stock Option and Grant Plan	2,148,019	2,296,029
Options outstanding under the 2019 Stock Option and Incentive Plan	1,585,293	800,526
Options available for future grant	2,127,544	1,771,931
2019 Employee Stock Purchase Plan	543,963	269,364
	6,404,819	5,137,850

Summary of restricted stock activity

The following table summarizes restricted stock activity since December 31, 2018:


		Grant-Date Fair
	Number of Shares	Value
Unvested restricted common stock as of December 31, 2018	80,190	$	—
Early exercise of unvested stock options	491,207		0.65
Shares vesting	(416,248)		0.65
Unvested restricted common stock as of December 31, 2019	155,149		0.52
Shares vesting	(121,535)		0.50
Unvested restricted common stock as of December 31, 2020	33,614	$	0.62

Stock-based awards (Tables)

12 Months Ended

Dec. 31, 2020

Stock-based awards

Schedule of assumptions used to determine grant-date fair value of stock options granted



	Year Ended December 31,
	2020		2019
Expected term (in years)	6.00		6.00
Expected volatility	73.38	%	73.75	%
Weighted average risk-free interest rate	0.65	%	2.12	%
Expected dividend yield	0.00	%	0.00	%

Summary of stock option activity


		Weighted-		Weighted-
		Average		Average	Aggregate
		Exercise		remaining	Intrinsic
	Number	Price per		contractual	Value
	of Options	Share		term (years)	(000's)
Balance outstanding, December 31, 2018	1,839,913	$	0.61	9.74	$	10,577
Options granted	1,912,352	$	12.42
Options exercised	(655,710)	$	0.69
Balance outstanding, December 31, 2019	3,096,555	$	7.89	9.19		44,323
Options granted	788,320	$	26.94
Options exercised	(150,343)	$	2.01
Options cancelled	(1,220)	$	0.62
Balance outstanding, December 31, 2020	3,733,312	$	12.15	8.53	$	52,498
Exercisable, December 31, 2020	1,069,363	$	8.12	8.21	$	18,933
Vested and expected to vest, December 31, 2020	3,733,312	$	12.15	8.53	$	52,498

Summary of stock-based compensation expense


	Year Ended December 31,
	2020		2019
Classified within research and development expense	$	1,633	$	485
Classified within general and administrative expense		4,389		1,285
Total stock-based compensation expense	$	6,022	$	1,770

Income taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income taxes

Schedule of current and deferred tax provision


	Year Ended December 31,
	2020		2019
Current income tax provision:
Federal	$	—	$	—
State		—		24
Total current income tax provision		—		24
Deferred income tax benefit:
Federal		(17,580)		(9,400)
State		(3,135)		688
Total deferred income tax benefit		(20,715)		(8,712)
Change in deferred tax asset valuation allowance		20,715		8,712
Total provision for income taxes	$	—	$	24

Schedule of reconciliation of the U.S. federal statutory income tax


	Year Ended December 31,
	2020		2019
Federal statutory income tax rate	21.0	%	21.0	%
State income taxes, net of federal benefit	4.0		(1.6)
Research and development tax credits	1.3		1.9
Other permanent differences	(0.1)		0.1
Change in deferred tax asset valuation allowance	(26.2)		(19.9)
Effect of Section 382 limitation	-		(1.5)
Effective income tax rate	-	%	-	%

Schedule of Net deferred tax assets


	December 31,
	2020		2019
Deferred tax assets
Net operating loss carry forwards	$	29,951	$	11,380
Research and development tax credit carry forwards		2,096		969
License fees		3,364		3,232
Stock based compensation		1,402		196
Accruals, reserves and other		63		44
Total deferred tax assets		36,876		15,821
Deferred tax liabilities
Prepaid expenses		(649)		(309)
Total deferred tax liabilities		(649)		(309)
Net deferred tax assets		36,227		15,512
Valuation allowance		(36,227)		(15,512)
Total net deferred tax assets	$	—	$	—

Schedule of changes in the valuation allowance for deferred tax assets


	2020		2019
Valuation allowance as of January 1,	$	(15,512)	$	(6,800)
Increases recorded to income tax provision		—		—
Decreases recorded as a benefit to income tax provision		(20,715)		(8,712)
Valuation allowance as of December 31,	$	(36,227)	$	(15,512)

Schedule of unrecognized tax benefits roll Forward



Balance at December 31, 2018	$	—
Increases related to prior year tax positions		—
Decreases related to prior year tax positions		—
Increases related to current year tax positions		237
Settlements		—
Lapse of statute of limitations		—
Balance at December 31, 2019	$	237
Increases related to prior year tax positions		—
Decreases related to prior year tax positions		—
Increases related to current year tax positions		407
Settlements		—
Lapse of statute of limitations		—
Balance at December 31, 2020	$	644

Net loss per share (Tables)

12 Months Ended

Dec. 31, 2020

Net loss per share

Schedule of basic and diluted net loss per share attributable to common stockholders


	Year Ended December 31,
	2020		2019
Numerator:
Net loss	$	(79,207)	$	(43,755)
Denominator:
Weighted average common shares outstanding, basic and diluted		31,463,248		15,070,728
Net loss per share, basic and diluted	$	(2.52)	$	(2.90)

Schedule of computation of diluted net loss per share attributable to common stockholders


	Year Ended December 31,
	2020	2019
Options to purchase common stock	3,733,312	3,096,555
Unvested restricted common stock	33,614	155,149
	3,766,926	3,251,704

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and contingencies

Schedule of maturity of the Company’s operating lease liabilities

As of December 31, 2020, maturities of the Company’s operating lease liabilities were as follows:


2021	$	303
2022		312
2023		321
2024		331
2025		341
2026 and thereafter		559
Total future minimum lease payments		2,167
Less imputed interest		(469)
Present value of operating lease liabilities	$	1,698

Schedule of components of operating lease expense

As of December 31, 2020, maturities of the Company’s operating lease liabilities were as follows:


2021	$	303
2022		312
2023		321
2024		331
2025		341
2026 and thereafter		559
Total future minimum lease payments		2,167
Less imputed interest		(469)
Present value of operating lease liabilities	$	1,698

Nature of the business and basis of presentation (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 06, 2019	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Subsidiary, Sale of Stock
Common stock issued (in shares)			34,741,649	28,567,837
Proceeds received, net of underwriting discounts and commissions \| $			$ 202,554
Authorized common stock (in shares)			150,000,000	150,000,000
Par value common stock (in dollars per share) \| $ / shares			$ 0.0001	$ 0.0001
Reverse stock split of the common stock		3.07418
Net loss \| $			$ 79,207	$ 43,755
Accumulated deficit \| $			209,527	$ 130,320
Cash, cash equivalents and short-term marketable securities \| $			$ 268,387
IPO
Subsidiary, Sale of Stock
Common stock issued (in shares)	6,612,500
Public offering price (in dollars per share) \| $ / shares	$ 16.00
Proceeds received, net of underwriting discounts and commissions \| $	$ 98,394
Offering costs \| $	$ 2,942
Authorized common stock (in shares)	150,000,000
Par value common stock (in dollars per share) \| $ / shares	$ 0.0001
Authorized Preferred stock (in shares)	10,000,000
Par value preferred stock (in dollars per share) \| $ / shares	$ 0.0001
Conversion of convertible preferred stock into common stock	21,056,136
Over allotment \| Maximum
Subsidiary, Sale of Stock
Common stock issued (in shares)	862,500

Summary of significant accounting policies - Restricted cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Summary of significant accounting policies
Separate cash balance for the landlord	$ 108	$ 20
Separate cash balance to collateralize corporate credit cards with a bank	$ 40	$ 40

Summary of significant accounting policies - Property and equipment (Details)	12 Months Ended
	Dec. 31, 2020
Furniture and equipment
Property and equipment
Estimated useful lives	3 years

Summary of significant accounting policies - Deferred offering costs (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Summary of significant accounting policies
Accrued deferred offering costs	$ 46	$ 0

Summary of significant accounting policies - Recently issue accounting Pronouncement (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset	$ 1,662	$ 280
Operating lease liabilities, current (included in accrued expenses and other current liabilities)	182	224
Deferred rent, current (included in accrued expenses and other current liabilities)			$ 2
Operating lease liabilities, noncurrent (included in other liabilities)	$ 1,516	60
Deferred rent, noncurrent (included in other liabilities			$ 2
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset		280
Operating lease liabilities, current (included in accrued expenses and other current liabilities)		224
Deferred rent, current (included in accrued expenses and other current liabilities)		(2)
Operating lease liabilities, noncurrent (included in other liabilities)		60
Deferred rent, noncurrent (included in other liabilities		$ (2)

Fair value of financial assets and liabilities - Recurring (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 239,168	$ 125,253
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	158,023	49,948
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	47,955	49,114
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		6,048
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	33,190	20,143
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	158,023	55,996
Level 1 \| Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	158,023	49,948
Level 1 \| U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		6,048
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	81,145	69,257
Level 2 \| Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	47,955	49,114
Level 2 \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 33,190	$ 20,143

Fair value of financial assets and liabilities - Textual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair value of financial assets and liabilities
Transfers from level 1 to level 2, Assets	$ 0	$ 0
Transfers from level 2 to level 1, Assets	0	0
Transfers from level 1 to level 2, Liabilities	0	0
Transfers from level 2 to level 1, Liabilities	0	0
Transfers into level 3 Assets	0	0
Transfers out of level 3 Assets	0	0
Transfers into level 3 liabilities	0	0
Transfers out of level 3 liabilities	$ 0	$ 0

Short-term marketable securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 239,171	$ 125,259
Gross unrealized losses	(3)	(6)
Fair value	239,168	125,253
Cash equivalents	158,023	53,641
Short-term marketable securities	81,145	71,612
Total	239,168	125,253
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized cost	158,023	49,948
Fair value	158,023	49,948
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized cost	47,955	49,114
Fair value	47,955	49,114
U.S. treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost		6,048
Fair value		6,048
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	33,193	20,149
Gross unrealized losses	(3)	(6)
Fair value	$ 33,190	$ 20,143

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued expenses and other current liabilities
Accrued external research and development expenses	$ 8,740	$ 6,361
Accrued employee compensation and benefits	495	1,606
Accrued legal and professional fees	154	370
Short-term lease liability and other	294	85
Total accrued expenses and other current liabilities	$ 9,683	$ 8,422

Redeemable convertible preferred stock - Textual (Details) - USD ($) $ in Thousands		12 Months Ended
	Jun. 24, 2019	Dec. 31, 2019	Dec. 31, 2020
Temporary Equity
Preferred Stock , shares outstanding		0	0
Related carrying value of convertible preferred stock converted into common stock	$ 124,728	$ 124,728
IPO
Temporary Equity
Number of shares converted	21,056,136
Common Stock
Temporary Equity
Related carrying value of convertible preferred stock converted into common stock	$ 2	2
Additional Paid-In-Capital
Temporary Equity
Related carrying value of convertible preferred stock converted into common stock	$ 124,726	$ 124,726
Redeemable convertible preferred stock
Temporary Equity
Number of shares converted		64,730,410
Series A Preferred Stock \| IPO
Temporary Equity
Preferred Stock , shares outstanding	50,858,462
Series B Preferred Stock \| IPO
Temporary Equity
Preferred Stock , shares outstanding	13,871,948

Stockholder's equity (deficit) - Common stock (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 10, 2020 USD ($) $ / shares shares	Jun. 24, 2019 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) Vote $ / shares shares	Dec. 31, 2019 $ / shares shares	Jun. 18, 2019 shares
Class of Stock
Common stock, shares authorized			150,000,000	150,000,000
Common stock, par value (in dollars per share) \| $ / shares			$ 0.0001	$ 0.0001
Number of votes per share \| Vote			1
Cash dividend declared \| $ / shares			$ 0
Cash dividend paid \| $ / shares			$ 0
Common stock, shares issued			34,741,649	28,567,837
Proceeds received, net of underwriting discounts and commissions \| $			$ 202,554
Common stock, shares outstanding			34,741,649	28,567,837
Common stock were reserved for issuance
Options available for future grant			6,404,819	5,137,850
Options to purchase common stock
Common stock were reserved for issuance
Options available for future grant			2,127,544	1,771,931
2018 Stock option and grant plan
Common stock were reserved for issuance
Options available for future grant			2,148,019	2,296,029	107,635
2019 Stock Option and Incentive plan
Common stock were reserved for issuance
Options available for future grant			1,585,293	800,526
2019 Employee Stock Purchase Plan
Common stock were reserved for issuance
Options available for future grant			543,963	269,364
Redeemable convertible preferred stock
Class of Stock
Number of shares converted				64,730,410
IPO
Class of Stock
Common stock, shares authorized		150,000,000
Common stock, par value (in dollars per share) \| $ / shares		$ 0.0001
Common stock, shares issued		6,612,500
Public offering price \| $ / shares		$ 16.00
Proceeds received, net of underwriting discounts and commissions \| $		$ 98,394
Offering costs \| $		$ 2,942
Number of shares converted		21,056,136
Follow Up Public Offering
Class of Stock
Number of shares issued	6,012,390
Public offering price \| $ / shares	$ 36.00
Proceeds received, net of underwriting discounts and commissions \| $	$ 203,460
Offering costs \| $	$ 906
Over allotment \| Maximum
Class of Stock
Number of shares issued	784,224
Common stock, shares issued		862,500

Stockholder's equity (deficit) - Undesignated preferred stock and Restricted common stock (Details) - $ / shares	1 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2020	Dec. 31, 2019
Restricted stock
Class of Stock
Shares issued (in shares)		226,400
Stock options vesting period	2 years	4 years
Undesignated Preferred Stock
Class of Stock
Preferred stock, par value (in dollars per share)			$ 0.0001
Preferred stock, shares issued			0	0
Preferred stock, shares outstanding			0	0
Undesignated Preferred Stock \| Maximum
Class of Stock
Preferred stock, shares authorized			10,000,000

Stockholder's equity (deficit) - Restricted stock activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Beginning balance of unvested restricted common stock	155,149	80,190
Early exercise of unvested stock options		491,207
Shares vesting	(121,535)	(416,248)
Ending balance of unvested restricted common stock	33,614	155,149
Grant-Date Fair Value
Beginning balance of unvested restricted common stock	$ 0.52
Early exercise of unvested stock options		$ 0.65
Shares vesting	0.50	0.65
Ending balance of unvested restricted common stock	$ 0.62	$ 0.52

Stockholder's equity (deficit) - Restricted stock activity narrative (Details) - shares	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Unvested restricted common stock	33,614	155,149	80,190

Stock-based awards - Textual (Details) - shares		1 Months Ended
Stock-based awards - Textual (Details) - shares	Jun. 18, 2019	Jun. 30, 2019	Jan. 01, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Share-based awards
Number of shares remained available for grant				6,404,819		5,137,850
2018 Stock option and grant plan
Share-based awards
Number of shares of common stock issued	3,071,960
Number of shares remained available for grant	107,635			2,148,019		2,296,029
2019 Stock option and incentive plan
Share-based awards
Number of shares remained available for grant	107,635
Number of shares initially reserved for issuance		2,572,457
Number of additional shares reserved for issuance			1,389,665		1,142,713
Percent of shares reserved and available for issuance automatically increase annually on January 1		4.00%
Percentage of exercise price per share of stock options		100.00%
Percentage of minimum exercise price, holding more than 10% of voting power		110.00%
Stock options vesting period		4 years
2019 Employee stock purchase plan
Share-based awards
Number of shares initially reserved for issuance	273,869
Number of additional shares reserved for issuance			347,416		285,678
Percent of shares reserved and available for issuance automatically increase annually on January 1		1.00%
Number of shares reserved and available for issuance automatically increase annually on January 1 (in shares)		410,803
Maximum \| 2019 Stock option and incentive plan
Share-based awards
Term of stock option		10 years

Stock-based awards - Stock option valuation (Details)	12 Months Ended
Stock-based awards - Stock option valuation (Details)	Dec. 31, 2020	Dec. 31, 2019
Assumptions to determine grant-date fair value of stock options granted
Expected term (in years)	6 years	6 years
Expected volatility	73.38%	73.75%
Weighted average risk-free interest rate	0.65%	2.12%
Expected dividend yield	0.00%	0.00%

Stock based awards - Stock option activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options
Balance Outstanding, Beginning of the period (in shares)	3,096,555	1,839,913
Options granted ( in shares)	788,320	1,912,352
Options exercised ( in shares)	(150,343)	(655,710)
Options cancelled (in shares)	(1,220)
Balance Outstanding, End of the period (in shares)	3,733,312	3,096,555	1,839,913
Exercisable ( in shares)	1,069,363
Vested and expected to vest ( in shares)	3,733,312
Weighted-Average Exercise Price per Share
Weighted-average exercise price, Beginning of the period (in dollars per share)	$ 7.89	$ 0.61
Weighted-average exercise price, Granted (in dollars per share)	26.94	12.42
Weighted-average exercise price, Exercised (in dollars per share)	2.01	0.69
Weighted-Average Exercise, cancelled (in dollars per share)	0.62
Weighted-average exercise price, End of the period (in dollars per share)	12.15	$ 7.89	$ 0.61
Weighted-average exercise price, Exercisable ( in dollars per share )	8.12
Weighted-average exercise price, Vested and expected to vest at end of the period (in dollars per share)	$ 12.15
Weighted-Average remaining contractual term (years) and Aggregate Intrinsic Value
Weighted-average remaining contractual term outstanding (in years)	8 years 6 months 11 days	9 years 2 months 9 days	9 years 8 months 27 days
Weighted-average remaining contractual term , Options Exercisable(in years)	8 years 2 months 16 days
Weighted-average remaining contractual term vested and expected to vest (in years)	8 years 6 months 11 days
Aggregate Intrinsic Value Balance outstanding	$ 52,498	$ 44,323	$ 10,577
Aggregate Intrinsic Value Exercisable	18,933
Aggregate Intrinsic Value Vested and Expected to vest	$ 52,498
Weighted average grant-date fair value per share of stock options granted	$ 17.07

Stock based awards - Stock-based compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Jul. 31, 2019	Jun. 30, 2019	Apr. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation
Total stock-based compensation expense				$ 6,022	$ 1,770
Total unrecognized compensation cost related to unvested stock-based awards				$ 23,156
Weighted average period of recognition for unrecognized compensation cost				2 years 6 months
Proceeds from the early exercise of stock options in exchange for restricted common stock					$ 321
Common Stock
Stock-based compensation
Issuance of restricted common stock upon early exercise of stock options (in shares)	491,207	491,207	491,207		491,207
Exercise price of common stock purchase	$ 0.65	$ 0.65	$ 0.65
Proceeds from the early exercise of stock options in exchange for restricted common stock	$ 321	$ 321	$ 321
Research and development expense
Stock-based compensation
Total stock-based compensation expense				$ 1,633	$ 485
General and administrative expense
Stock-based compensation
Total stock-based compensation expense				$ 4,389	$ 1,285

Amgen license agreement (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
Amgen license agreement (Details) - USD ($) $ in Thousands	Aug. 31, 2019	Nov. 30, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued value under agreement				$ 202,554	$ 95,453
Research and development expense				64,916	37,046
Amgen Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Initial fair value of the anti-dilution right liability		$ 7,404
Payment for clinical trail	$ 2,500
Obligation for payment in connection with dosing of the first patient	7,500
Amgen Agreement \| Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Aggregate milestone payments upon the achievement of specified commercial milestones	75,000
Payment in connection with dosing of the first patient	$ 30,000
Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Ownership interest of the outstanding shares (as a percent)			10.00%
Amgen Agreement \| Research and development expense
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense				$ 0
Research and development expense upon achievement of clinical milestone					$ 2,500
Amgen Agreement \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront payment			$ 5,000
Amgen Agreement \| Series A Preferred Stock
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued under agreement		3,205,128
Amgen Agreement \| Series A Preferred Stock \| Amgen
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Share Issued under agreement			2,653,333
Share Issued value under agreement			$ 1,353

Income taxes - Current income tax provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current income tax provision:
Income tax benefit related to operating losses and research and development tax credits	$ 0	$ 0
State		24
Total current income tax provision		24
Deferred income tax benefit:
Federal	(17,580)	(9,400)
State	(3,135)	688
Total deferred income tax benefit	(20,715)	(8,712)
Change in deferred tax asset valuation allowance	$ 20,715	8,712
Total provision for income taxes		$ 24

Income taxes - Income tax rate (Details)	12 Months Ended
Income taxes - Income tax rate (Details)	Dec. 31, 2020	Dec. 31, 2019
Income taxes
Federal statutory income tax rate	21.00%	21.00%
State income taxes, net of federal benefit	4.00%	(1.60%)
Research and development tax credits	1.30%	1.90%
Other permanent differences	(0.10%)	0.10%
Change in preferred stock tranche obligation	(26.20%)	(19.90%)
Effect of Section 382 limitation		(1.50%)

Income taxes - Deferred tax (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax assets
Net operating loss carry forwards	$ 29,951	$ 11,380
Research and development tax credit carry forwards	2,096	969
License fees	3,364	3,232
Stock based compensation	1,402	196
Accruals, reserves and other	63	44
Total deferred tax assets	36,876	15,821
Deferred Tax liabilities
Prepaid expenses	(649)	(309)
Total deferred tax liabilities	(649)	(309)
Net deferred tax assets	36,227	15,512
Valuation allowance	$ (36,227)	$ (15,512)	$ (6,800)

Income taxes - Valuation allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income taxes
Valuation allowance as of January 1,	$ (15,512)	$ (6,800)
Decreases recorded as a benefit to income tax provision	(20,715)	(8,712)
Valuation allowance as of December 31,	$ (36,227)	$ (15,512)

Income taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning	$ 237
Increases related to current year tax positions	407	$ 237
Balance at the ending	$ 644	$ 237

Income taxes - Textual (Details) - USD ($) $ in Thousands		12 Months Ended
Income taxes - Textual (Details) - USD ($) $ in Thousands	Jun. 29, 2020	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Income tax benefits			$ 24
Net operating loss carry forwards		$ 29,951	11,380
Deferred Tax Assets, Tax Credit Carryforwards, Research		2,096	969
Increase (Decrease) in Valuation Allowance		20,715	8,712
Accrued interest or penalties related to uncertain tax positions		0
Gross unrecognized tax benefit		644	$ 237
Amount of state tax that can be offset by NOLs and credits for a three year period	$ 5,000
State taxable income amout that can be reduced by NOLs for a three year period.	$ 1,000
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards		127,416
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration		124,973
Deferred Tax Assets, Tax Credit Carryforwards, Research		2,441
NOL carryforwards that expire		2,118
Research and development tax credit derecognized		87
State
Operating Loss Carryforwards [Line Items]
Net operating loss carry forwards		47,200
Deferred Tax Assets, Tax Credit Carryforwards, Research		378
NOL carryforwards that expire		3,632
Research and development tax credit derecognized		43
General and administrative expense
Operating Loss Carryforwards [Line Items]
Income tax benefits		$ 24

Net loss per share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (79,207)	$ (43,755)
Denominator:
Weighted average common shares outstanding, basic and diluted	31,463,248	15,070,728
Net loss per share, basic and diluted	$ (2.52)	$ (2.90)
Number of weighted average restricted common stock	31,215	49,568

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 11: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-03(20))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 13: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121326447&loc=SL5780133-109256

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22658-107794

+ Details

Net loss per share - Anti-Diluted (Details) - shares	12 Months Ended
Net loss per share - Anti-Diluted (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	3,766,926	3,251,704
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	3,733,312	3,096,555
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares excluded from the calculation of diluted earnings per share, total	33,614	155,149

Commitments and contingencies (Details) $ in Thousands		1 Months Ended	12 Months Ended
Commitments and contingencies (Details) $ in Thousands	May 07, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Jul. 10, 2020 ft²	Feb. 29, 2020 USD ($)	Jan. 01, 2020 USD ($)
Commitments and contingencies
Initial lease term under the agreement		6 months
Extension lease term under the agreement		6 months
Operating lease ROU asset	$ 173
Operating liability	173		$ 138
Reduction in future minimum lease payments due to early termination	$ 180
Monthly lease payments under the agreement		$ 4
Lease agreement term					7 years
Square feet of office \| ft²				6,647
Minimum payments during the term					$ 2,300
Non-cancelable purchase commitments with contract research organizations and contract manufacturing organizations			5,513
Total lease liability			$ 1,698
Operating Lease, Liability, Statement of Financial Position [Extensible List]			us-gaap:PrepaidExpenseAndOtherAssetsCurrent us-gaap:OperatingLeaseLiabilityNoncurrent
Operating lease liability, noncurrent			$ 1,516			$ 60
Short-term Liabilities			$ 182			$ 224
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]			Prepaid Expense and Other Assets, Current			Prepaid Expense and Other Assets, Current

Commitments and contingencies - Maturities Of Operating Leases (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	$ 303
2022	312
2023	321
2024	331
2025	341
2026 and thereafter	559
Total future minimum lease payments	2,167
Less imputed interest	(469)
Present value of operating lease liabilities	$ 1,698

Commitments and contingencies - Components of operating lease expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Operating lease expense:
Total operating lease cost	$ 342
Other information:
Cash paid for amounts included in the measurement of operating lease liability	$ 210
Weighted average remaining lease term	6 years 7 months 6 days
Weighted average discount rate	7.60%
General and administrative expense
Operating lease expense:
Operating lease cost	$ 267
Variable operating lease cost	43
Research and development expense
Operating lease expense:
Short-term lease cost	$ 32

Commitments and contingencies - Prior to the Company's adoption of ASC 842 (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Commitments and contingencies
Rent expense	$ 305
Future minimum commitments, 2020	321
Future minimum commitments, 2021	80
Total	$ 401

Related parties (Details) - USD ($) $ in Thousands	12 Months Ended
Related parties (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Apple Tree
Related parties
Expenses for services received from related party	$ 0	$ 20
Due to related party	0	0
Atlas Venture Life Science Advisors, LLC
Related parties
Expenses for services received from related party		22
Due to related party	$ 0	$ 0