0001564590-21-010726 | 10-K | XBRL Viewer

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2020	Feb. 26, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Registrant Name	Dyne Therapeutics, Inc.
Entity Central Index Key	0001818794
Entity File Number	001-39509
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-4883909
Entity Address, Address Line One	830 Winter Street
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	786-8230
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 Common Stock, Shares Outstanding		51,457,555
Entity Shell Company	false
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	DYN
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Entity Public Float			$ 0
Documents Incorporated by Reference	The Registrant intends to file a definitive proxy statement pursuant to Regulation 14A relating to the 2021 Annual Meeting of Stockholders within 120 days of the end of the Registrant’s fiscal year ended December 31, 2020. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.

Consolidated Balance Sheets - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 300,852,000	$ 14,632,000
Marketable securities	44,462,000	0
Prepaid expenses and other current assets	3,773,000	127,000
Total current assets	349,087,000	14,759,000
Property and equipment, net	1,946,000	1,486,000
Restricted cash and other assets	2,301,000	191,000
Total assets	353,334,000	16,436,000
Current liabilities:
Accounts payable	3,440,000	1,256,000
Accrued expenses and other current liabilities	7,527,000	1,102,000
Total current liabilities	10,967,000	2,358,000
Deferred rent		42,000
Total liabilities	10,967,000	2,400,000
Commitments and contingencies (Note 12)
Stockholders’ equity
Preferred stock
Common stock, $0.0001 par value; 200,000,000 and 68,000,000 shares authorized at December 31, 2020 and 2019, respectively; 45,446,903 and 3,239,017 shares issued and 45,076,574 and 2,586,535 shares outstanding at December 31, 2020 and 2019, respectively	5,000	1,000
Additional paid-in capital	421,572,000	6,352,000
Accumulated other comprehensive loss	(27,000)
Accumulated deficit	(79,183,000)	(19,746,000)
Total stockholders’ equity	342,367,000	14,036,000
Total liabilities and stockholders’ equity	$ 353,334,000	16,436,000
Convertible Preferred Stock
Stockholders’ equity
Preferred stock		$ 27,429,000

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001
Preferred stock, shares authorized	10,000,000
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	68,000,000
Common stock, shares issued	45,446,903	3,239,017
Common stock, shares outstanding	45,076,574	2,586,535

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 45,200	$ 11,040
General and administrative	13,447	2,786
Total operating expenses	58,647	13,826
Loss from operations	(58,647)	(13,826)
Other (expense) income:
Interest income	56	290
Interest expense	(396)
Change in fair value of preferred stock tranche obligations		(1,323)
Change in success fee obligation	(450)
Total other (expense) income, net	(790)	(1,033)
Net loss	$ (59,437)	$ (14,859)
Net loss per share, basic and diluted	$ (4.13)	$ (6.08)
Weighted average common shares outstanding, basic and diluted	14,395,955	2,442,872
Comprehensive loss:
Net loss	$ (59,437)	$ (14,859)
Other comprehensive loss:
Unrealized losses on marketable securities	(27)
Comprehensive loss	$ (59,464)	$ (14,859)

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Convertible Preferred Stock	Convertible Preferred Stock Series A Convertible Preferred Stock	Convertible Preferred Stock Series B Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2018	$ (4,879)							$ 1	$ 7		$ (4,887)
Beginning Balance, Shares at Dec. 31, 2018								2,110,404
Beginning Balance at Dec. 31, 2018		$ 9,061
Beginning Balance, Shares at Dec. 31, 2018		12,500,000
Issuance of Series A redeemable convertible preferred stock, net of issuance costs of $0.1 million		$ 19,989
Issuance of Series A redeemable convertible preferred stock, net of issuance costs of $0.1 million, Shares		20,000,000
Settlement of Tranche Right I		$ (1,621)
Reclassification of redeemable convertible preferred stock and preferred stock tranche obligations	33,748	$ (27,429)			$ 27,429				6,319
Reclassification of redeemable convertible preferred stock and preferred stock tranche obligations, Shares		(32,500,000)			32,500,000
Stock-based compensation	26								26
Vesting of restricted shares								476,131
Net loss	(14,859)										(14,859)
Ending Balance at Dec. 31, 2019	14,036				$ 27,429			$ 1	6,352		(19,746)
Ending Balance, Shares at Dec. 31, 2019					32,500,000			2,586,535
Issuance of stock, net of issuance costs	246,388		$ 19,467	$ 115,319		$ 19,467	$ 115,319	$ 1	246,387
Issuance of stock, net of issuance costs, Shares						19,500,000	41,159,724	14,089,314
Conversion of convertible preferred stock into common stock upon initial public offering					$ (162,215)			$ 3	162,212
Conversion of convertible preferred stock into common stock upon initial public offering, Shares					(93,159,724)			28,086,375
Exercise of stock options	$ 30								30
Exercise of stock options, Shares	32,197							32,197
Stock-based compensation	$ 6,591								6,591
Vesting of restricted shares								282,153
Unrealized gains on marketable securities	(27)									$ (27)
Net loss	(59,437)										(59,437)
Ending Balance at Dec. 31, 2020	$ 342,367							$ 5	$ 421,572	$ (27)	$ (79,183)
Ending Balance, Shares at Dec. 31, 2020								45,076,574

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Common Stock
Stock issuance costs	$ 2.6
Series A Redeemable Convertible Preferred Stock
Stock issuance costs		$ 0.1
Series A Convertible Preferred Stock
Stock issuance costs	0.1
Series B Convertible Preferred Stock
Stock issuance costs	$ 0.4

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (59,437)	$ (14,859)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,591	26
Depreciation and amortization expense	700	271
Amortization of debt discount	64
Amortization (accretion) of premium (discount) on marketable securities	12
Changes in fair value of preferred stock tranche obligations		1,323
Changes in success fee obligation	450
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(3,455)	(284)
Accounts payable and other liabilities	8,567	1,689
Net cash used in operating activities	(46,508)	(11,834)
Cash flows from investing activities:
Purchases of property and equipment	(1,161)	(1,647)
Purchases of marketable securities	(44,500)
Net cash used in investing activities	(45,661)	(1,647)
Cash flows from financing activities:
Proceeds from initial public offering of common stock, net of issuance costs	246,388
Settlement of success fee obligation	(450)
Proceeds from issuance of convertible preferred stock, net of issuance costs	134,786	19,989
Proceeds from issuance of debt, net of issuance costs	9,936
Repayment of debt	(10,000)
Proceeds from exercise of stock options	30
Net cash provided by financing activities	380,690	19,989
Net increase in cash, cash equivalents and restricted cash	288,521	6,508
Cash, cash equivalents and restricted cash, beginning of year	14,632	8,124
Cash, cash equivalents and restricted cash, end of year	303,153	14,632
Supplemental cash flow information:
Cash paid for interest and taxes	328
Supplemental disclosure of non-cash investing and financing information:
Reclassification of preferred stock tranche obligation liability to permanent equity		6,319
Conversion of convertible preferred stock to common stock	$ 162,215
Settlement of Tranche Right I		$ 1,621

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Nature of Business and Basis of Presentation

1. Nature of business and basis of presentation

Dyne Therapeutics, Inc. (the “Company”) is building a leading muscle disease company focused on advancing innovative life-transforming therapeutics for people living with genetically driven diseases that was incorporated in Delaware on December 1, 2017 and has a principal place of business in Waltham, Massachusetts.

The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, fluctuations in operating results, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes, the impact of the COVID-19 pandemic and the ability to secure additional capital to fund operations. Programs currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization of a product. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

On September 21, 2020, the Company completed its initial public offering (“IPO”) pursuant to which it issued and sold 14,089,314 shares of its common stock, including 1,837,736 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $19.00 per share, resulting in net proceeds of $246.4 million, after deducting underwriting discounts and commissions and offering expenses. Upon the closing of the IPO, all of the Company’s then outstanding convertible preferred stock automatically converted into shares of common stock.

On January 25, 2021, the Company completed a follow-on public offering of common stock pursuant to which it issued and sold 6,000,000 shares of its common stock at a public offering price of $28.00 per share, resulting in net proceeds of $157.3 million, after deducting underwriting discounts and commissions and offering expenses.

The accompanying consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Since inception, the Company has funded its operations with proceeds from the sales of preferred stock and common stock, including the IPO completed in September 2020 and the follow-on offering completed in January 2021. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance of these consolidated financial statements.

To continue its development efforts, the Company will need to obtain substantial additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements in order to fund its research and development and ongoing operating expenses. The Company may not be able to obtain financing on acceptable terms, when needed or at all, and the Company may not be able to enter into collaborations, strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Any collaborations, strategic alliances or licensing arrangements may require the Company to relinquish rights to certain of its technologies, future revenue streams, research programs or product candidates or grant licenses on terms that may not be favorable to the Company. If the Company is unable to obtain funding, the Company could be forced to delay, limit, reduce or eliminate some or all of its research and development programs, pipeline expansion or future commercialization efforts or grant rights to develop and market product candidates, which could adversely affect its business prospects. Although management will continue 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 when needed or at all.

To date, the Company has not experienced material business disruptions, including with its vendors, as a result of the COVID-19 pandemic. In March 2020, the Company implemented a remote working policy for many of its employees and began restricting non-essential travel, and on May 18, 2020, when Massachusetts began its staged reopening plan, the Company began implementing a return-to-work plan, in accordance with the guidance and requirements of federal and state authorities. The Company expects to continue to take actions as may be required or recommended by government authorities or as it determines are in the best interests of its employees and other business partners. The Company is continuing to monitor the potential impact of the pandemic, but cannot be certain what the overall impact will be on its business, financial condition, results of operations and prospects.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of significant accounting policies

The accompanying consolidated financial statements reflect the operations of the Company and the Company’s wholly owned subsidiary, Dyne Therapeutics Securities Corporation. Intercompany balances and transactions have been eliminated in consolidation. The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Use of estimates

The preparation of 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 financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. 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, as there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results may differ from those estimates or assumptions.

Concentrations of credit risk and of significant suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company believes the depository institutions in which the cash and cash equivalents are held are of high-credit quality. The Company maintains its cash equivalents in money market funds that invest in U.S. treasury securities. The Company’s marketable securities as of December 31, 2020 consisted of commercial paper and corporate debt securities. The Company has adopted an investment policy that limits the amounts the Company may invest in the securities of any single issuer with the exclusion of the U.S. government. The Company has not experienced any credit losses.

The Company is dependent on a small number of third-party suppliers for its drug substance and drug product. In particular, the Company relies, and expects to continue to rely, on third-party suppliers for certain materials and components required for the development of its programs and future production of any product candidates it may develop for its programs. These programs could be adversely affected by a significant interruption in the supply process.

Cash and cash equivalents

Cash includes cash in readily available checking accounts and cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase.

Restricted cash

Amounts included in restricted cash represent amounts pledged as collateral for letters of credit required for security deposits on the Company’s leased facilities. Restricted cash totaled $2.3 million and $0.0 million at December 31, 2020 and 2019, respectively. These amounts are classified as restricted cash on the Company’s consolidated balance sheets.

Marketable securities

The Company’s marketable securities as of December 31, 2020 consisted of commercial paper, certificates of deposit and corporate debt securities and are classified as available-for-sale and are reported at fair value. Unrealized losses on available-for-sale debt securities are reported as a component of accumulated other comprehensive loss in stockholders’ equity. Realized gains and losses are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss.

The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Deferred rent

Payment escalations, rent holidays and other lease incentives that may be included in lease agreements are accrued or deferred as appropriate such that rent expense for each lease is recognized on a straight-line basis over the respective lease term. Adjustments for such items are recorded as deferred rent and amortized over the respective lease terms.

Property and equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:

		Estimated Useful Life
Laboratory equipment		3 years
Furnitures and fixtures		5 years
Computer equipment		3 years
Leasehold improvements		Shorter of life of lease or 10 years

Costs for capital assets not yet placed into service are capitalized as construction-in-progress and depreciated once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance which do not improve or extend the life of the respective assets are charged to expense as incurred.

Impairment of long-lived assets

Long-lived assets consist of property and equipment. The Company evaluates the recoverability of its long-lived assets when circumstances indicate that an event of impairment may have occurred. The Company recognizes an impairment loss only if the carrying amount of a long-lived asset is not recoverable based on its undiscounted future cash flows. Impairment is measured based on the difference between the carrying value of the related assets and the fair value of such assets. The Company has not recorded any impairment charges in the periods presented in these financial statements.

Segment information

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s chief operating decision maker is the chief executive officer (“CEO”). The CEO views the Company’s operations and manages the business as one operating segment.

Research and development costs

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and bonuses, stock-based compensation, employee benefits, facilities costs, laboratory supplies, depreciation and amortization, manufacturing expenses and external costs of vendors engaged to conduct preclinical development activities as well as the cost of licensing technology.

Upfront payments and milestone payments made for the licensing of technology are expensed as research and development expenses in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are consumed or the services are performed.

Research and manufacturing contract costs and accruals

The Company has entered into various research and development and manufacturing contracts. These agreements are generally cancelable, and related payments are recorded as the corresponding expenses are incurred. The Company records accruals for estimated ongoing costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the research studies and manufacturing activities, 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 from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

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.

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 financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years 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 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 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.

Fair value measurements

Certain assets and liabilities are carried at fair value. 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. 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—Unadjusted quoted prices in active markets that are accessible to the reporting entity at the measurement date for identical assets and liabilities.

•	Level 2—Inputs other than quoted prices in active markets for identical assets and liabilities that are observable either directly or indirectly for substantially the full term of the asset or liability. Level 2 inputs include the following:

•

quoted prices for similar assets and liabilities in active markets;

•

quoted prices for identical or similar assets or liabilities in markets that are not active;

•

observable inputs other than quoted prices that are used in the valuation of the asset or liabilities (e.g., interest rate and yield curve quotes at commonly quoted intervals); and

•

inputs that are derived principally from or corroborated by observable market data by correlation or other means.

•	Level 3—Unobservable inputs for the assets or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).

Net loss per share

The Company follows the two-class method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. During periods of loss, the Company does not allocate loss to participating securities because they have no contractual obligation to share in the losses of the Company.

Basic net loss per share is computed by dividing the net income loss by the weighted average number of shares of common stock outstanding for the period. Diluted net loss is computed by adjusting net loss to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share is computed by dividing the diluted net loss by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares assuming the dilutive effect of common stock equivalents.

Redeemable convertible preferred stock

The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any issuance costs. The Company classified stock that was redeemable in circumstances outside of the Company’s control outside of permanent equity. No accretion was recognized as the contingent events that could give rise to redemption were not deemed probable.

Stock-based compensation

The Company accounts for stock-based awards at fair value, and measures fair value using the Black-Scholes option-pricing model. Stock-based compensation costs are recognized as expense over the requisite service period, which is generally the vesting period, on a straight-line basis for all time-vested awards. Forfeitures are recognized as they occur.

Success fee obligation

The Company’s loan and security agreement (the “Loan Agreement”) entered into in 2020 required the Company to pay a success fee of $0.5 million upon the occurrence of a specified liquidity event, as described in the Loan Agreement, which included the Company’s IPO. The liability was initially deemed immaterial upon entering into the Loan Agreement and was subsequently remeasured to fair value at each reporting date. Following the completion of the IPO, the success fee of $0.5 million was paid in September 2020.

Comprehensive loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the year ended December 31, 2020, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities.

Accounting pronouncements issued and not adopted

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). The new standard requires that all lessees recognize the assets and liabilities that arise from leases on the balance sheet and disclose qualitative and quantitative information about its leasing arrangements. The Company plans to adopt ASU 2016-02 on January 1, 2021 using the modified retrospective approach transition method as of the date of adoption such that prior periods will not be restated. The Company will also elect a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. The adoption of the new standard is expected to result in the recognition of material liabilities and right-of-use assets, however, the Company has not completed the assessment.

Marketable Securities and Fair Value Measurements

12 Months Ended

Dec. 31, 2020

Marketable Securities And Fair Value Measurements [Abstract]

Marketable Securities and Fair Value Measurements

3. Marketable securities and fair value measurements

Marketable securities by security type at December 31, 2020 consisted of the following:

(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Total
Commercial paper		6,412		—		—			6,412
Certificates of deposit		1,504		—		—			1,504
Corporate debt securities		36,572		—		(27	)		36,545
Total	$	44,489	$	—	$	(27	)	$	44,462

The Company did not have marketable securities as of December 31, 2019.

The following tables set forth by level, within the fair value hierarchy (see Note 2), the assets carried at fair value on a recurring basis for the periods presented:

	Fair Value Measurements as of December 31, 2020
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents
Money market funds		155,017		—		—		155,017
Commercial paper		2,999		—		—		2,999
Certificates of deposit		—		5,309		—		5,309
Marketable securities
Commercial paper		6,412				—		6,412
Certificates of deposit		—		1,504		—		1,504
Corporate debt securities		—		36,545		—		36,545
Total	$	164,428	$	43,359	$	—	$	207,787

	Fair Value Measurements as of December 31, 2019
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents
Money market funds	$	14,420		—		—	$	14,420
Total	$	14,420	$	—	$	—	$	14,420

The fair value of U.S. government money market funds and commercial paper were determined by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. Certificates of deposit 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. During the years ended December 31, 2020 and 2019, there were no transfers between Level 1, Level 2 and Level 3.

The following table summarizes the scheduled maturity for the Company’s marketable securities at December 31, 2020:

(in thousands)	December 31, 2020
Maturing in one year or less	$	28,623
Maturing after one year through two years		24,147
Maturing after two years		—
Total	$	52,770

There were no sales of marketable securities during the year ending December 31, 2020.

The fair value of the preferred stock tranche obligations in connection with the unfunded tranches associated with the Series A Preferred Stock Purchase Agreement (see Note 7) was determined based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the preferred stock tranche obligations was determined by considering as inputs the future value of the Series A Preferred Stock, the difference between the future value of the Series A Preferred Stock and the contract price, the number of shares underlying the contract, the probability of achieving the funding of the tranches, expected timing of the tranche closing and the discount rate. The future value of Series A Preferred Stock was estimated by calibrating, or backsolving, to the price of the Series A Preferred Stock as set forth in the Series A Preferred Stock Purchase Agreement. The contractual price of the shares to be issued in addition to the number of shares underlying the contract are both provided for by the Series A Preferred Stock Purchase Agreement. The probability of achieving the funding of the tranches and the expected timing of those closings were estimates made by the Company. The discount rate was equal to the risk-free rate for the estimated timing of each tranche closing.

The fair value of the liability recognized in connection with the contingent success fee associated with the Loan Agreement (see Note 6) was determined based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the liability was determined using the probability-weighted expected return method (“PWERM”), which considered as inputs the probability of occurrence of a specified liquidity event, the expected timing of a liquidity event, the amount of the success fee and a risk-adjusted discount rate. The initial fair value of the liability was de minimis due to the low probability of the events probable of triggering payment. As of September 21, 2020, the closing date of the IPO, the event occurred and the probability increased to 100% and the discount rate was assessed to be 0%. Based on these inputs, the Company determined that the fair value of the derivative liability was $0.5 million as of September 21, 2020. Following the completion of the IPO, the success fee of $0.5 million was paid in September 2020.

The following table presents a roll-forward of the aggregate fair values of the Company’s liabilities for which fair value is determined by Level 3 inputs:

(in thousands)	Preferred Stock Tranche Obligations			Success Fee Obligation
Balance—January 1, 2019	$	3,375		$	—
Settlement of Tranche Right I		1,621			—
Change in fair value		1,323			—
Reclassification of Tranche Right II to equity		(6,319	)		—
Balance—December 31, 2019		—			—
Initial fair value of success fee obligation		—			—
Change in fair value		—			450
Settlement of derivative instrument		—			(450	)
Balance—December 31, 2020	$	—		$	—

Financial instruments not recorded at fair value

The carrying values of cash, cash equivalents, accounts payable and accrued expenses that are reported on the balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

Property and Equipment

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and equipment

Property and equipment consisted of the following:

	December 31,
(in thousands)	2020			2019
Laboratory equipment	$	2,744		$	1,705
Office and computer equipment		78			62
Leasehold improvements		14			14
Construction in process		105			—
Property and equipment—at cost		2,941			1,781
Less accumulated depreciation and amortization		(995	)		(295	)
Property and equipment—net	$	1,946		$	1,486

Depreciation expense totaled $0.7 million and $0.3 million for the years ended December 31, 2020 and 2019, respectively.

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

5. Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:

	December 31,
(in thousands)	2020		2019
Payroll and benefits	$	2,105	$	540
Consulting services		263		60
Legal services		325		—
Research and development		4,782		484
Facility costs		52		18
Total	$	7,527	$	1,102

Debt Financing

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Debt Financing

6. Debt financing

On February 20, 2020, the Company entered into a Loan Agreement pursuant to which the lender made term loans to the Company in an aggregate principal amount of $10.0 million. Borrowings under the Loan Agreement were collateralized by substantially all of the Company’s assets, excluding intellectual property.

Interest on the outstanding loan balance accrued at a variable annual rate equal to the greater of (i) the lender’s prime rate plus 0.25% and (ii) 5.00%, and the Company was required to make interest-only payments on the loans on a monthly basis through August 2021. The outstanding borrowings were repaid in October 2020.

As part of the Loan Agreement, a success fee of $0.5 million was required in the event of a liquidation event, including an IPO. The success fee represented an embedded derivative which the Company bifurcated from the debt arrangement and carried at fair value. In September 2020, the Company completed its IPO and paid the success fee of $0.5 million.

Convertible Preferred Stock

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Convertible Preferred Stock

7. Convertible preferred stock

Since inception, the Company issued Series A convertible preferred stock (the “Series A Preferred Stock”) and Series B convertible preferred stock (the “Series B Preferred Stock”). Collectively the Series A Preferred Stock and the Series B Preferred Stock are referred to as the Preferred Stock.

Upon the closing of the IPO in September 2020, the Company’s Preferred Stock automatically converted into 28,086,375 shares of common stock.

Series A Preferred Stock

On November 29, 2018, the Company entered into the Series A Preferred Stock Purchase Agreement with its initial investors committing to purchase an aggregate of $50.0 million in shares of Series A Preferred Stock. At the initial closing, 12,500,000 shares of Series A Preferred Stock were issued by the Company at a purchase price of $1.00 per share, for gross cash proceeds of $7.5 million. Of the 12,500,000 shares issued, 5,000,000 shares were issued upon conversion of the then outstanding SAFEs, which had a fair value of $5.0 million. In April 2019, the Company issued an additional 20,000,000 shares of Series A Preferred Stock under the terms of the Series A Preferred Stock Purchase Agreement at a purchase price of $1.00 per share for total gross proceeds of $20.0 million. Issuance costs associated with each closing of the Series A Preferred Stock financing were $0.1 million. On March 18, 2020, the Company entered into a separate Series A Preferred Stock Purchase Agreement with an additional investor and issued 2,000,000 shares of Series A Preferred Stock at a purchase price $1.00 per share for gross cash proceeds of $2.0 million. In July 2020, the Company issued and sold 17,500,000 shares of Series A Preferred Stock at a price of $1.00 per share, for gross proceeds of $17.5 million.

Series B Preferred Stock

In August 2020, the Company issued and sold 41,159,724 shares of Series B Preferred Stock at a price of $2.81 per share for gross proceeds of $115.7 million.

Tranche Rights

Included in the terms of the November 2018 Series A Preferred Stock Purchase Agreement were certain rights (“Tranche Rights”) granted to the investors who purchased the Series A Preferred Stock purchased in November 2018. The Tranche Rights contingently obligated the investors to purchase, and the Company to sell, up to an aggregate of 37,500,000 shares of Series A Preferred Stock at $1.00 per share upon the satisfaction of specified research and development milestones by the Company. The Tranche Rights are also exercisable at the option of the holders of the Series A Preferred Stock. The Tranche Rights were divided into separate rights and obligations to purchase 20,000,000 shares (“Tranche Right I”) and 17,500,000 shares (“Tranche Right II”) based on the achievement of specified milestones for each tranche.

The Company concluded that the Tranche Rights met the definition of a freestanding financial instrument, as the Tranche Rights were legally detachable and separately exercisable from the Series A Preferred Stock. Therefore, the Company allocated the proceeds from the November 2018 issuance between the Tranche Rights and the Series A Preferred Stock. As the Series A Preferred Stock was redeemable upon a deemed liquidation event at the election of the holder-controlled Board, and therefore outside of the control of the Company, the Tranche Rights were initially classified as a liability and were initially recorded at their fair value of $3.4 million. The Tranche Rights were then remeasured at fair value at each reporting period, with changes in fair value recorded in the statement of operations. The estimated fair value of the Tranche Rights was determined at each reporting date using a probability-weighted present value model that considers the probability of closing a tranche, the estimated future value of the Series A Preferred Stock to be issued at each closing, and the investment required at each closing. Future values were converted to present value using a discount rate appropriate for probability-adjusted cash flows.

In April 2019, Tranche Right I was settled when the Company closed on the issuance of 20,000,000 shares Series A Preferred Stock. The fair value of the Tranche Right I as of the closing date was reclassified from a liability to Series A Preferred Stock within equity.

In September 2019, the size of the Board was increased from five to six members, including three independent members, which allowed the Company to conclude that the redemption rights of the holders of the Series A Preferred Stock was within the control of the Company. As a result, the Company concluded that Tranche Right II qualified for equity classification as of that date. The preferred stock tranche obligation liability, with a fair value of $6.3 million, was reclassified into permanent equity and was no longer remeasured at fair value. In July 2020, Tranche Right II was settled when the Company closed on the issuance of 17,500,000 shares Series A Preferred Stock.

The Preferred Stock had the followings rights and privileges:

Dividends

Holders of the Preferred Stock were entitled to receive non-cumulative dividends when, as and if declared by the Board. The Company did not declare dividends on any class of preferred or common stock.

Liquidation

In the event of any liquidation, dissolution, or winding-up of the Company, which would include the sale of the Company, the Preferred Stock was senior to common stock.

Voting

The holders of the Preferred Stock were entitled to the number of votes equal to the number of shares of common stock into which the shares of Preferred Stock held by each holder were then convertible.

Conversion

The holders of the Preferred Stock were able to convert, at any time, each share of Preferred Stock into shares of common stock at the stated conversion price.

Equity

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Equity

8. Equity

As of December 31, 2020, the Company’s restated certificate of incorporation authorized the Company to issue 200,000,000 shares of common stock, par value $0.0001 per share, and 10,000,000 shares of preferred stock, par value $0.0001 per share.

As of December 31, 2019, the Company had authorized 68,000,000 shares of common stock. The voting, dividend and liquidation rights of the holders of the Company’s common stock was subject to and qualified by the rights, powers and preferences of the holders of the Preferred Stock as set forth above.

Stock-based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

9. Stock-based compensation

2018 Stock incentive plan

The Company’s 2018 Stock Incentive Plan (the “2018 Plan”) provided for the Company to sell or issue incentive stock options or nonqualified stock options, restricted stock, and other equity 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.

The total number of shares of common stock authorized under the 2018 Plan was 8,267,252 shares. Upon the effectiveness of the 2020 Plan, the Company ceased granting awards under the 2018 Plan, and the 1,928,487 shares of common stock remaining under the 2018 Plan became available for future issuance under the 2020 Plan.

2020 Stock incentive plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Plan (together with the 2018 Plan the “Plans”), which became effective on September 16, 2020. The 2020 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards to employees, directors, consultants and advisors of the Company. The 2020 Plan is administered by the Company’s board of directors or by a committee appointed by the board of directors. Upon the effectiveness of the 2020 Plan, the Company ceased granting awards under the 2018 Plan. The number of shares initially reserved for issuance under the 2020 Plan was 4,884,233. The number of shares of common stock reserved for issuance under the 2020 Plan automatically increases on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lower of (1) 5% of the shares of common stock outstanding on such date and (2) an amount determined by the Company’s board of directors. On January 1, 2021, 2,272,345 shares were added to the shares reserved for issuance under the 2020 Plan in the first of these annual increases.

As of December 31, 2020, 3,237,244 shares remained available for future issuance under the 2020 Plan.

2020 Employee Stock Purchase Plan

In August 2020 the Company’s board of directors adopted and the Company’s stockholders approved the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective September 16, 2020. The 2020 ESPP is administered by the Company’s board of directors or by a committee appointed by the board of directors. The 2020 ESPP initially provides participating employees with the opportunity to purchase up to an aggregate of 488,414 shares of common stock. The number of shares of common stock reserved for issuance under the 2020 ESPP will automatically increase on the first day of each fiscal year, beginning with the fiscal year commencing on January 1, 2021 and continuing for each fiscal year until, and including the fiscal year commencing on, January 1, 2030, in an amount equal to the lowest of (1) 1,953,656 shares of common stock, (2) 1% of the shares of common stock outstanding on such date, and (3) an amount determined by the board of directors. As of December 31, 2020, no offering periods have commenced under the 2020 ESPP and 488,414 shares remained available for issuance.

Stock option valuation

The Company typically grants stock options at exercise prices deemed by the Board to be equal to the fair value of the common stock at the time of grant. In the periods prior to the IPO, the fair value of the common stock was determined by the Board at each measurement date based on a variety of different factors, including the results obtained from independent third-party appraisals, the Company’s financial position and historical financial performance, the status of development of the Company’s programs, the current climate in the marketplace, the illiquid nature of the common stock, the effect of the rights and preferences of the preferred stockholders, and the prospects of a liquidity event, among others. In the periods following the IPO, the fair value is determined based upon the quoted price of the Company’s common stock.

The fair value of stock option grants is estimated using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of 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 stock price. For options with service-based vesting conditions, 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 and does not expect to pay any cash dividends in the foreseeable future.

The assumptions that the Company used to determine the grant-date fair value of options granted were as follows:

	Year Ended December 31, 2020		Year Ended December 31, 2019
Expected volatility	75%		74%
Risk-free interest rate	0.31% — 1.67%		1.46% — 2.50%
Expected term (in years)	6			6
Expected dividend yield		—		—

Stock option activity

The following table summarizes the option activity:

(in thousands, except share and per share data)	Options			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
Outstanding January 1, 2020		311,303		$	0.93		9.5	$	30
Granted		6,252,967			7.13
Exercised		(32,197	)		0.93
Canceled		(110,484	)		1.04
Outstanding December 31, 2020		6,421,589		$	6.97		9.5	$	90,112
Options exercisable— December 31, 2020		447,925		$	4.74		9.2	$	7,282
Options vested or expected to vest— December 31, 2020		6,421,589		$	6.97		9.5	$	90,112

The weighted-average grant date fair value of the options granted during the years ended December 31, 2020 and 2019 was $4.50 per share and $0.62 per share, respectively. As of December 31, 2020 there was $20.3 million of unrecognized compensation expense, which the Company expects to recognize over a weighted-average period of 2.71 years. Additionally, as of December 31, 2020, the Company has unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance has not been deemed probable of $2.6 million.

Restricted stock units

A restricted stock unit (“RSU”) represents the right to receive one share of common stock upon vesting of the RSU. The Company grants RSUs with service conditions that vest in four equal annual installments provided that the employee remains employed with the Company. The Company also grants RSUs with performance conditions that vest upon the achievement of specified milestones. The fair value of each RSU is based on the closing price of the Company’s common stock on the date of grant. A summary of the Company’s RSU activity and related information for the 2020 Plan for the year ended December 31, 2020 is as follows:

	Number of Shares Underlying RSUs		Weighted Average Grant Date Fair Value
Issued and unvested as of January 1, 2020		—		—
Granted		403,355	$	23.60
Vested		—		—
Forfeited		—		—
Issued and unvested as of December 31, 2020		403,355	$	23.60

As of December 31, 2020, there was $7.7 million of unrecognized compensation costs related to unvested RSUs, which are expected to be recognized over a weighted-average period of 2.75 years. Additionally, as of December 31, 2020, the Company has unrecognized compensation cost of $0.6 million related to unvested stock-based awards with performance-based vesting conditions for which performance has not been deemed probable.

Restricted common stock

During the year ended December 31, 2018, the Company granted restricted common stock with service-based vesting conditions. Shares of unvested restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award. The grant date fair value of these shares was immaterial. The following table summarizes the Company’s restricted common stock award activity for the year ended December 31, 2020:

	Number of Restricted Shares
Issued and unvested as of January 1, 2020		652,482
Vested		(282,153	)
Issued and unvested as of December 31, 2020		370,329

The Company recorded stock-based compensation expense in the following expense categories of its statements of operations:

	Year Ended December 31,
(in thousands)	2020		2019
Research and development	$	2,699	$	13
General and administrative		3,892		13
Total	$	6,591	$	26

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

10. Income taxes

There is no provision for income taxes because the Company has historically incurred net operating losses and maintains a full valuation allowance against its deferred tax assets. The reported amount of income tax expense/benefit for the years ended December 31, 2020 and 2019 differs from the amount that would result from applying domestic federal statutory rates to pretax losses primarily because of changes in the valuation allowance.

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 income tax expense at statutory rate		21	%		21	%
State taxes—net of federal benefit	5				6
Change in fair value of preferred stock tranche obligations		—			(2	)
Other permanent differences		—			(1	)
Federal & state R&D credits	1				4
Increase in valuation allowance		(27	)		(28	)
Effective income tax rate		0	%		0	%

Significant components of the Company’s net deferred tax assets at December 31, 2020 and 2019 are as follows:

	Year Ended December 31,
(in thousands)	2020			2019
Deferred tax assets:
Stock-based compensation	$	1,349		$	1
Net operating loss carryforwards		18,858			4,848
Credit carryforwards		1,155			612
Intangible assets		—			12
Accrued expenses		580			161
Total deferred tax assets		21,942			5,634
Valuation allowance		(21,899	)		(5,607	)
Total net deferred tax assets		43			27
Deferred tax liabilities:
Fixed assets		(43	)		(27	)
Total deferred tax liability		(43	)		(27	)
Total deferred tax assets (liabilities)	$	—		$	—

As of December 31, 2020, the Company had federal and state net operating loss carryforwards of $69.1 million and $68.9 million, respectively. The federal net operating loss carryforwards are indefinite lived and the state net operating loss carryforwards begin to expire in 2038. As of December 31, 2020, the Company also had federal and state research and development tax credit carryforwards $0.8 million and $0.4 million, respectively, which begin to expire in 2039 and 2033, respectively.

Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 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. 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 Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards and research and development tax credit carryforwards. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products or generation of any revenue from product sales since inception and concluded that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2020 and 2019. The increase in the valuation allowance for deferred tax assets during the years ended December 31, 2020 and 2019 totaled $16.3 million and $4.2 million, respectively, and related primarily to the increase in net operating loss carryforwards.

The Company’s policy is to record estimated interest and penalties related to uncertain tax positions in income tax expense. The Company has no amounts recorded for any unrecognized tax positions, accrued interest or penalties as of December 31, 2020 and 2019.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates, including the United States and the Commonwealth of Massachusetts. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company’s tax returns are open under statute from 2018 to the present.

- 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

Earnings Per Share [Abstract]

Net Loss per Share

11. Net loss per share

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

	Year Ended December 31,
(in thousands, except share and per share data)	2020			2019
Numerator:
Net loss	$	(59,437	)	$	(14,859	)
Denominator:
Weighted-average common shares outstanding—basic and diluted		14,395,955			2,442,872
Net loss per share—basic and diluted	$	(4.13	)	$	(6.08	)

The following potentially dilutive common stock equivalents, presented based on amounts outstanding at each period end, were excluded 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		6,421,589		311,303
Unvested restricted common stock		370,329		652,482
Unvested restricted stock units		403,355		—
Convertible preferred stock (as converted to common stock)		—		9,798,298
Total		7,195,273		10,762,083

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and contingencies

Operating leases

In May 2019, the Company entered into a sublease agreement for laboratory and office space in Waltham, Massachusetts. The term of the sublease commenced on July 1, 2019 and expires on December 31, 2021.

In December 2020, the Company entered into a lease agreement (the “Lease”), pursuant to which the Company will lease approximately 68,187 square feet of additional office and laboratory space located in Waltham, Massachusetts (the “Premises”). The Lease will have a term of eight years and six months that will commence when the Premises are ready for occupancy. The Company’s obligation for the payment of base rent for the Premises begins six months after the commencement date and will be $0.4 million per month, increasing up to $0.5 million during the term of the Lease. The Company has two options to extend the term of the Lease, each for a period of an additional five years. The Company expects the Premises to be ready for occupancy in the second half of 2021.

Rent expense for the years ended December 31, 2020 and 2019 totaled $0.8 million and $0.7 million, respectively.

Future minimum lease payments under the non-cancelable operating leases consisted of the following as of December 31, 2020:

Year Ending December 31,	(in thousands)
2021	$	800
2022		4,603
2023		4,741
2024		4,883
2025		5,029
Thereafter		21,672
Total	$	41,728

Legal proceedings

The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to any such legal proceedings.

Other contractual obligations

The Company enters into contracts in the normal course of business with third parties for preclinical research studies, clinical trials and testing and manufacturing services. These contracts typically do not contain minimum purchase commitments and are generally cancelable by the Company upon written notice. Payments due upon cancellation consist of payments for services provided or expenses incurred, including noncancelable obligations of the service providers, up to the date of cancellation and in the case of certain arrangements may include non-cancelable fees.

The Company has also entered into a license agreement (the “UMONS Agreement”) with the University of Mons (“UMONS”) in April 2020, pursuant to which UMONS granted to the Company an exclusive, worldwide license to certain patents and patent applications and a non-exclusive, worldwide license to existing, related know-how. Each of the issued patents licensed to the Company under the UMONS Agreement is scheduled to expire in 2031. The licenses under the UMONS Agreement confer on the Company the right to research, develop and commercialize products (“licensed products”), and to practice processes, in each case, covered by the licensed patents and existing, related know-how.

Under the UMONS Agreement, the Company is obligated to use commercially reasonable efforts to develop at least one licensed product and, to the extent regulatory approval is obtained in such jurisdictions, to commercialize at least one licensed product in the United States and the United Kingdom or a member country of the European Union. Unless terminated earlier, the UMONS Agreement will remain in effect until the last to expire of the licensed patent rights on a licensed product-by-licensed product and country-by-country basis. UMONS may terminate the UMONS Agreement in the event of a material breach by the Company and the Company’s failure to cure such breach within a specified time period. The Company may voluntarily terminate the UMONS Agreement with prior notice to UMONS.

In connection with the Company’s entry into the UMONS Agreement, the Company paid UMONS an upfront payment of €0.1 million. The Company also agreed to make milestone payments to UMONS upon the achievement of specified development and regulatory milestones up to a maximum aggregate total of €0.4 million for the first licensed product to achieve such milestones and up to a maximum aggregate total of €0.2 million for each subsequent licensed product to achieve each such milestones, as well as a low single-digit percentage royalty on net sales of licensed products by the Company, its affiliates and sublicensees. These royalty obligations continue on a licensed product-by-licensed product and country-by-country basis until the expiration of the last licensed patent rights covering such licensed product in such country. In addition, if the Company sublicenses rights under the UMONS Agreement, the Company is required to pay a low double-digit percentage of the sublicense revenue to UMONS. Additionally, if the Company chooses to file, prosecute or maintain any patents included in the licensed patent rights under the UMONS Agreement, it will be required to bear the full cost and expenses of preparing, filing, prosecuting and maintaining any such patents.

No amounts have been accrued under this arrangement with respect to potential milestone payment obligations or royalty obligations given the uncertainty of achieving the specified milestones and commercial sales of any licensed products.

Subsequent Events

12 Months Ended

Dec. 31, 2020

Subsequent Events [Abstract]

Subsequent Events

13. Subsequent events

For the year ended December 31, 2020, subsequent events were evaluated through March 4, 2021, the date on which the audited consolidated financial statements were issued.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Use of Estimates

Use of estimates

Concentrations of Credit Risk and of Significant Suppliers

Concentrations of credit risk and of significant suppliers

Cash and Cash Equivalents

Cash and cash equivalents

Cash includes cash in readily available checking accounts and cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase.

Restricted Cash

Restricted cash

Marketable Securities

Marketable securities

Deferred Rent

Deferred rent

Property and Equipment

Property and equipment

		Estimated Useful Life
Laboratory equipment		3 years
Furnitures and fixtures		5 years
Computer equipment		3 years
Leasehold improvements		Shorter of life of lease or 10 years

Impairment of Long-Lived Assets

Impairment of long-lived assets

Segment Information

Segment information

Research and Development Costs

Research and development costs

Research and Manufacturing Contract Costs and Accruals

Research and manufacturing contract costs and accruals

Patent Costs

Patent costs

Income Taxes

Income taxes

Fair Value Measurements

Fair value measurements

•	Level 1—Unadjusted quoted prices in active markets that are accessible to the reporting entity at the measurement date for identical assets and liabilities.

•	Level 2—Inputs other than quoted prices in active markets for identical assets and liabilities that are observable either directly or indirectly for substantially the full term of the asset or liability. Level 2 inputs include the following:

•

quoted prices for similar assets and liabilities in active markets;

•

quoted prices for identical or similar assets or liabilities in markets that are not active;

•

observable inputs other than quoted prices that are used in the valuation of the asset or liabilities (e.g., interest rate and yield curve quotes at commonly quoted intervals); and

•

inputs that are derived principally from or corroborated by observable market data by correlation or other means.

•	Level 3—Unobservable inputs for the assets or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).

Net Loss Per Share

Net loss per share

Redeemable Convertible Preferred Stock

Redeemable convertible preferred stock

Stock-Based Compensation

Stock-based compensation

Success Fee Obligation

Success fee obligation

Comprehensive Loss

Comprehensive loss

Accounting Pronouncements Issued and Not Adopted

Accounting pronouncements issued and not adopted

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule Of Property Plant And Equipment Estimated Useful Lives

Depreciation and amortization expense is recognized using the straight-line method over the estimated useful life of each asset as follows:

		Estimated Useful Life
Laboratory equipment		3 years
Furnitures and fixtures		5 years
Computer equipment		3 years
Leasehold improvements		Shorter of life of lease or 10 years

Marketable Securities and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Marketable Securities And Fair Value Measurements [Abstract]

Summary of Marketable Securities by Security Type

Marketable securities by security type at December 31, 2020 consisted of the following:

(in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Total
Commercial paper		6,412		—		—			6,412
Certificates of deposit		1,504		—		—			1,504
Corporate debt securities		36,572		—		(27	)		36,545
Total	$	44,489	$	—	$	(27	)	$	44,462

Summary of Assets Carried at Fair Value on Recurring Basis

The following tables set forth by level, within the fair value hierarchy (see Note 2), the assets carried at fair value on a recurring basis for the periods presented:

	Fair Value Measurements as of December 31, 2020
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents
Money market funds		155,017		—		—		155,017
Commercial paper		2,999		—		—		2,999
Certificates of deposit		—		5,309		—		5,309
Marketable securities
Commercial paper		6,412				—		6,412
Certificates of deposit		—		1,504		—		1,504
Corporate debt securities		—		36,545		—		36,545
Total	$	164,428	$	43,359	$	—	$	207,787

	Fair Value Measurements as of December 31, 2019
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents
Money market funds	$	14,420		—		—	$	14,420
Total	$	14,420	$	—	$	—	$	14,420

Summary of Scheduled Maturity for Marketable Securities

The following table summarizes the scheduled maturity for the Company’s marketable securities at December 31, 2020:

(in thousands)	December 31, 2020
Maturing in one year or less	$	28,623
Maturing after one year through two years		24,147
Maturing after two years		—
Total	$	52,770

Roll-forward of Aggregate Fair Values of Liabilities Determined by Level 3 Inputs

The following table presents a roll-forward of the aggregate fair values of the Company’s liabilities for which fair value is determined by Level 3 inputs:

(in thousands)	Preferred Stock Tranche Obligations			Success Fee Obligation
Balance—January 1, 2019	$	3,375		$	—
Settlement of Tranche Right I		1,621			—
Change in fair value		1,323			—
Reclassification of Tranche Right II to equity		(6,319	)		—
Balance—December 31, 2019		—			—
Initial fair value of success fee obligation		—			—
Change in fair value		—			450
Settlement of derivative instrument		—			(450	)
Balance—December 31, 2020	$	—		$	—

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following:

	December 31,
(in thousands)	2020			2019
Laboratory equipment	$	2,744		$	1,705
Office and computer equipment		78			62
Leasehold improvements		14			14
Construction in process		105			—
Property and equipment—at cost		2,941			1,781
Less accumulated depreciation and amortization		(995	)		(295	)
Property and equipment—net	$	1,946		$	1,486

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	December 31,
(in thousands)	2020		2019
Payroll and benefits	$	2,105	$	540
Consulting services		263		60
Legal services		325		—
Research and development		4,782		484
Facility costs		52		18
Total	$	7,527	$	1,102

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Assumptions Used to Determine Grant-Date Fair Value of Options Granted

The assumptions that the Company used to determine the grant-date fair value of options granted were as follows:

	Year Ended December 31, 2020		Year Ended December 31, 2019
Expected volatility	75%		74%
Risk-free interest rate	0.31% — 1.67%		1.46% — 2.50%
Expected term (in years)	6			6
Expected dividend yield		—		—

Summary of Stock Option Activity and Related Information

The following table summarizes the option activity:

(in thousands, except share and per share data)	Options			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
Outstanding January 1, 2020		311,303		$	0.93		9.5	$	30
Granted		6,252,967			7.13
Exercised		(32,197	)		0.93
Canceled		(110,484	)		1.04
Outstanding December 31, 2020		6,421,589		$	6.97		9.5	$	90,112
Options exercisable— December 31, 2020		447,925		$	4.74		9.2	$	7,282
Options vested or expected to vest— December 31, 2020		6,421,589		$	6.97		9.5	$	90,112

Summary of RSU Activity

A summary of the Company’s RSU activity and related information for the 2020 Plan for the year ended December 31, 2020 is as follows:

	Number of Shares Underlying RSUs		Weighted Average Grant Date Fair Value
Issued and unvested as of January 1, 2020		—		—
Granted		403,355	$	23.60
Vested		—		—
Forfeited		—		—
Issued and unvested as of December 31, 2020		403,355	$	23.60

Summary of Restricted Common Stock Award Activity

The following table summarizes the Company’s restricted common stock award activity for the year ended December 31, 2020:

	Number of Restricted Shares
Issued and unvested as of January 1, 2020		652,482
Vested		(282,153	)
Issued and unvested as of December 31, 2020		370,329

Summary of Stock-based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its statements of operations:

	Year Ended December 31,
(in thousands)	2020		2019
Research and development	$	2,699	$	13
General and administrative		3,892		13
Total	$	6,591	$	26

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

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 income tax expense at statutory rate		21	%		21	%
State taxes—net of federal benefit	5				6
Change in fair value of preferred stock tranche obligations		—			(2	)
Other permanent differences		—			(1	)
Federal & state R&D credits	1				4
Increase in valuation allowance		(27	)		(28	)
Effective income tax rate		0	%		0	%

Schedule of Deferred Tax Assets and Liabilities

Significant components of the Company’s net deferred tax assets at December 31, 2020 and 2019 are as follows:

	Year Ended December 31,
(in thousands)	2020			2019
Deferred tax assets:
Stock-based compensation	$	1,349		$	1
Net operating loss carryforwards		18,858			4,848
Credit carryforwards		1,155			612
Intangible assets		—			12
Accrued expenses		580			161
Total deferred tax assets		21,942			5,634
Valuation allowance		(21,899	)		(5,607	)
Total net deferred tax assets		43			27
Deferred tax liabilities:
Fixed assets		(43	)		(27	)
Total deferred tax liability		(43	)		(27	)
Total deferred tax assets (liabilities)	$	—		$	—

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

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

	Year Ended December 31,
(in thousands, except share and per share data)	2020			2019
Numerator:
Net loss	$	(59,437	)	$	(14,859	)
Denominator:
Weighted-average common shares outstanding—basic and diluted		14,395,955			2,442,872
Net loss per share—basic and diluted	$	(4.13	)	$	(6.08	)

Potential Dilutive Securities Excluded From Calculation Of Net Loss Per Share

	Year Ended December 31,
	2020		2019
Options to purchase common stock		6,421,589		311,303
Unvested restricted common stock		370,329		652,482
Unvested restricted stock units		403,355		—
Convertible preferred stock (as converted to common stock)		—		9,798,298
Total		7,195,273		10,762,083

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments under Non-Cancelable Operating Leases

Future minimum lease payments under the non-cancelable operating leases consisted of the following as of December 31, 2020:

Year Ending December 31,	(in thousands)
2021	$	800
2022		4,603
2023		4,741
2024		4,883
2025		5,029
Thereafter		21,672
Total	$	41,728

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Jan. 25, 2021	Sep. 21, 2020	Dec. 31, 2020
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation date			Dec. 01, 2017
Initial Public Offering \| Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold		14,089,314
Underwriters option to purchase additional shares		1,837,736
Public offering price		$ 19.00
Net proceeds from issuance of common stock		$ 246.4
Follow-on Public Offering \| Common Stock \| Subsequent Event
Nature Of Business And Basis Of Presentation [Line Items]
Number of shares issued and sold	6,000,000
Public offering price	$ 28.00
Net proceeds from issuance of common stock	$ 157.3

Summary of Significant Accounting Policies - Additional Information (Details)		1 Months Ended	12 Months Ended
	Sep. 21, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalent maturity period			90 days
Restricted cash			$ 2,300,000	$ 0
Impairment charges			$ 0
Number of operating segment \| Segment			1
Success fee paid	$ 500,000	$ 500,000
Loan Agreement \| Pacific Western Bank
Summary Of Significant Accounting Policies [Line Items]
Success fee paid			$ 500,000

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Furnitures and Fixtures
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Computer Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	Shorter of life of lease or 10 years

Marketable Securities and Fair Value Measurements - Summary of Marketable Securities by Security Type (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 44,489,000
Unrealized Losses	(27,000)
Total	44,462,000	$ 0
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,412,000
Total	6,412,000
Certificates of Deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,504,000
Total	1,504,000
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	36,572,000
Unrealized Losses	(27,000)
Total	$ 36,545,000

Marketable Securities and Fair Value Measurements - Additional Information (Details)		1 Months Ended	12 Months Ended
	Sep. 21, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities			$ 44,462,000	$ 0
Fair value assets, transfers among level 1, level 2 or level 3			0	$ 0
Sales of marketable securities			$ 0
Fair value liability, payment percentage	100.00%
Fair value of derivative liability	$ 500,000
Success fee paid	$ 500,000	$ 500,000
Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Measurement input	0.00

Marketable Securities and Fair Value Measurements - Summary of Assets Carried at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Total	$ 207,787
Level 1
Assets:
Total	164,428
Level 2
Assets:
Total	43,359
Cash Equivalents
Assets:
Total		$ 14,420
Cash Equivalents \| Money Market Funds
Assets:
Total	155,017	14,420
Cash Equivalents \| Commercial Paper
Assets:
Total	2,999
Cash Equivalents \| Certificates of Deposit
Assets:
Total	5,309
Cash Equivalents \| Level 1
Assets:
Total		14,420
Cash Equivalents \| Level 1 \| Money Market Funds
Assets:
Total	155,017	$ 14,420
Cash Equivalents \| Level 1 \| Commercial Paper
Assets:
Total	2,999
Cash Equivalents \| Level 2 \| Certificates of Deposit
Assets:
Total	5,309
Marketable Securities \| Corporate Debt Securities
Assets:
Total	36,545
Marketable Securities \| Commercial Paper
Assets:
Total	6,412
Marketable Securities \| Certificates of Deposit
Assets:
Total	1,504
Marketable Securities \| Level 1 \| Commercial Paper
Assets:
Total	6,412
Marketable Securities \| Level 2 \| Corporate Debt Securities
Assets:
Total	36,545
Marketable Securities \| Level 2 \| Certificates of Deposit
Assets:
Total	$ 1,504

Marketable Securities and Fair Value Measurements - Summary of Scheduled Maturity for Marketable Securities (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Marketable Securities And Fair Value Measurements [Abstract]
Maturing in one year or less	$ 28,623
Maturing after one year through two years	24,147
Total	$ 52,770

Marketable Securities and Fair Value Measurements - Roll-forward of Aggregate Fair Values of Liabilities Determined by Level 3 Inputs (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Preferred Stock Tranche Obligations
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance—January 1, 2019		$ 3,375
Change in fair value		1,323
Reclassification of Tranche Right II to equity		(6,319)
Preferred Stock Tranche Obligations \| Tranche Right I
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Settlement		$ 1,621
Success Fee Obligation
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Change in fair value	$ 450
Success Fee Obligation \| Derivative Instrument
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Settlement	$ (450)

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment—at cost	$ 2,941	$ 1,781
Less accumulated depreciation and amortization	(995)	(295)
Property and equipment—net	1,946	1,486
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment—at cost	2,744	1,705
Office and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment—at cost	78	62
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment—at cost	14	$ 14
Construction in Process
Property Plant And Equipment [Line Items]
Property and equipment—at cost	$ 105

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 700	$ 271

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Payroll and benefits	$ 2,105	$ 540
Consulting services	263	60
Legal services	325
Research and development	4,782	484
Facility costs	52	18
Total	$ 7,527	$ 1,102

Debt Financing - Additional Information (Details) - Term Loan - USD ($)		1 Months Ended	12 Months Ended
	Feb. 20, 2020	Sep. 30, 2020	Dec. 31, 2020
Line Of Credit Facility [Line Items]
Credit facility, maximum borrowing capacity under loan agreement	$ 10,000,000
Credit facility, interest rate description			Interest on the outstanding loan balance accrued at a variable annual rate equal to the greater of (i) the lender’s prime rate plus 0.25% and (ii) 5.00%, and the Company was required to make interest-only payments on the loans on a monthly basis through August 2021
Debt instrument, frequency of periodic payment of interest			interest-only payments on the loans on a monthly basis
Credit facility, variable interest rate spread	0.25%
Credit facility, interest rate during period	5.00%
Success fee required to pay in the event of liquidation, including IPO	$ 500,000
Success fee paid after IPO		$ 500,000

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended			12 Months Ended
	Mar. 18, 2020	Nov. 29, 2018	Aug. 31, 2020	Jul. 31, 2020	Apr. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Temporary Equity [Line Items]
Proceeds from issuance of convertible preferred stock, net of issuance costs						$ 134,786	$ 19,989
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued upon conversion		5,000,000
Purchase of share		$ 50,000
Shares issued	2,000,000	12,500,000		17,500,000	20,000,000
Convertible preferred stock, price per share	$ 1.00	$ 1.00		$ 1.00	$ 1.00
Proceeds from issuance of convertible preferred stock, net of issuance costs	$ 2,000	$ 7,500		$ 17,500	$ 20,000
Fair value		5,000							$ 6,300
Issuance costs					$ 100
Series A Convertible Preferred Stock \| Tranche Right
Temporary Equity [Line Items]
Fair value		$ 3,400
Series A Convertible Preferred Stock \| Tranche Right \| Maximum
Temporary Equity [Line Items]
Sale of stock		37,500,000
Series A Convertible Preferred Stock \| Tranche Right I
Temporary Equity [Line Items]
Shares issued					20,000,000
Sale of stock		20,000,000
Series A Convertible Preferred Stock \| Tranche Right II
Temporary Equity [Line Items]
Sale of stock		17,500,000
Series B Convertible Preferred Stock
Temporary Equity [Line Items]
Shares issued			41,159,724
Convertible preferred stock, price per share			$ 2.81
Proceeds from issuance of convertible preferred stock, net of issuance costs			$ 115,700
Common Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares issued upon conversion								28,086,375
Shares issued						14,089,314

Equity - Additional Information (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock, shares authorized	200,000,000	68,000,000
Common stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000
Preferred stock, par value	$ 0.0001

Stock-Based Compensation - Additional Information (Details) $ / shares in Units, $ in Millions		12 Months Ended
	Sep. 16, 2020 shares	Dec. 31, 2020 USD ($) Installment $ / shares shares	Dec. 31, 2019 $ / shares	Jan. 01, 2021 shares	Sep. 15, 2020 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant date fair value of options granted \| $ / shares		$ 4.50	$ 0.62
Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense \| $		$ 20.3
Unrecognized share based compensation expense, recognition period		2 years 8 months 15 days
Unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance conditions not deemed probable \| $		$ 2.6
Restricted Stock Units ("RSUs")
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense \| $		$ 7.7
Unrecognized share based compensation expense, recognition period		2 years 9 months
Unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance conditions not deemed probable \| $		$ 0.6
Number of share of common stock receivable upon vesting		1
2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total number of shares of common stock authorized	488,414
Number of shares available for future issuance		488,414
Percentage of outstanding shares increased annually under the plan	1.00%
Increase in common stock reserved for future issuance	1,953,656
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total number of shares of common stock authorized					8,267,252
Number of shares available for future issuance					1,928,487
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future issuance		3,237,244
Number of shares initially reserved for issuance	4,884,233
Percentage of outstanding shares increased annually under the plan	5.00%
2020 Plan \| Restricted Stock Units ("RSUs")
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement By Share-based Payment Award Grant Service Conditions to Vest Number of Annual Installments \| Installment		4
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights		The Company grants RSUs with service conditions that vest in four equal annual installments provided that the employee remains employed with the Company. The Company also grants RSUs with performance conditions that vest upon the achievement of specified milestones
2020 Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares initially reserved for issuance				2,272,345

Stock-Based Compensation - Summary of Assumptions Used to Determine Grant-Date Fair Value of Options Granted (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected volatility	75.00%	74.00%
Risk-free interest rate, minimum	0.31%	1.46%
Risk-free interest rate, maximum	1.67%	2.50%
Expected term (in years)	6 years	6 years

Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options
Outstanding, beginning of period	311,303
Granted	6,252,967
Exercised	(32,197)
Canceled	(110,484)
Outstanding, end of period	6,421,589	311,303
Options exercisable— December 31, 2020	447,925
Options vested or expected to vest— December 31, 2020	6,421,589
Weighted Average Exercise Price
Outstanding, beginning of period	$ 0.93
Granted	7.13
Exercised	0.93
Canceled	1.04
Outstanding, end of period	6.97	$ 0.93
Options exercisable— December 31, 2020	4.74
Options vested or expected to vest— December 31, 2020	$ 6.97
Weighted Average Remaining Life (in years)
Outstanding	9 years 6 months	9 years 6 months
Options exercisable— December 31, 2020	9 years 2 months 12 days
Options vested or expected to vest— December 31, 2020	9 years 6 months
Aggregate Intrinsic Value
Outstanding	$ 90,112	$ 30
Options exercisable— December 31, 2020	7,282
Options vested or expected to vest— December 31, 2020	$ 90,112

Stock-Based Compensation - Summary of RSU Activity (Details) - Restricted Stock Units ("RSUs") - 2020 Plan	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Number of Shares Underlying RSUs
Granted \| shares	403,355
Issued and unvested as of December 31, 2020 \| shares	403,355
Weighted Average Grant Date Fair Value
Granted \| $ / shares	$ 23.60
Issued and unvested as of December 31, 2020 \| $ / shares	$ 23.60

Stock-Based Compensation - Summary of Restricted Common Stock Award Activity (Details) - Restricted Common Stock	12 Months Ended
	Dec. 31, 2020 shares
Number of Restricted Shares
Issued and unvested as of January 1, 2020	652,482
Vested	(282,153)
Issued and unvested as of December 31, 2020	370,329

Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 6,591	$ 26
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,699	13
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,892	$ 13

Income Taxes - Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Effective income tax rate reconciliation
Federal income tax expense at statutory rate	21.00%	21.00%
State taxes—net of federal benefit	5.00%	6.00%
Change in fair value of preferred stock tranche obligations		(2.00%)
Other permanent differences		(1.00%)
Federal & state R&D credits	1.00%	4.00%
Increase in valuation allowance	(27.00%)	(28.00%)
Effective income tax rate	0.00%	0.00%

Income Taxes - Significant Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Stock-based compensation	$ 1,349	$ 1
Net operating loss carryforwards	18,858	4,848
Credit carryforwards	1,155	612
Intangible assets		12
Accrued expenses	580	161
Total deferred tax assets	21,942	5,634
Valuation allowance	(21,899)	(5,607)
Total net deferred tax assets	43	27
Deferred tax liabilities:
Fixed assets	(43)	(27)
Total deferred tax liability	(43)	(27)
Total deferred tax assets (liabilities)	$ 0	$ 0

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Increase in valuation allowance for deferred tax assets	$ 16,300,000	$ 4,200,000
Unrecognized tax positions, accrued interest or penalties	$ 0	$ 0
Tax returns open year	2018
U.S. Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 69,100,000
U.S. Federal \| Research and Developments Tax Credit Carryforwards
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 800,000
Research and development tax credit carryforwards expiration year	2039
State and Local Jurisdiction
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 68,900,000
Net operating loss carryforwards expiration year	2038
State and Local Jurisdiction \| Research and Developments Tax Credit Carryforwards
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 400,000
Research and development tax credit carryforwards expiration year	2033

Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (59,437)	$ (14,859)
Denominator:
Weighted-average common shares outstanding—basic and diluted	14,395,955	2,442,872
Net loss per share—basic and diluted	$ (4.13)	$ (6.08)

- 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)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22595-107794

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
-Section 50
-Paragraph 22
-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
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-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
-Section 45
-Paragraph 28
-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
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-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 - Potential Dilutive Securities Excluded From Calculation Of Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	7,195,273	10,762,083
Convertible Preferred Stock (As Converted to Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		9,798,298
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	6,421,589	311,303
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	370,329	652,482
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	403,355

Commitments and Contingencies - Additional Information (Details) € in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) ft²	Dec. 31, 2020 USD ($) ft²	Dec. 31, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 EUR (€) ft²
Leases [Abstract]
Lease executed date		Jul. 01, 2019	Jul. 01, 2019
Lease expiration date		Dec. 31, 2021	Dec. 31, 2021
Additional leased office space \| ft²	68,187	68,187			68,187
Lease term	8 years 6 months	8 years 6 months			8 years 6 months
Lease, description		The Company’s obligation for the payment of base rent for the Premises begins six months after the commencement date and will be $0.4 million per month, increasing up to $0.5 million during the term of the Lease. The Company has two options to extend the term of the Lease, each for a period of an additional five years. The Company expects the Premises to be ready for occupancy in the second half of 2021.	The Company’s obligation for the payment of base rent for the Premises begins six months after the commencement date and will be $0.4 million per month, increasing up to $0.5 million during the term of the Lease. The Company has two options to extend the term of the Lease, each for a period of an additional five years. The Company expects the Premises to be ready for occupancy in the second half of 2021.
Monthly rent expense	$ 400,000
Increase in monthly rent expense	$ 500,000
Existence of option to extend lease	true
Option to extend lease		The Company has two options to extend the term of the Lease, each for a period of an additional five years.	The Company has two options to extend the term of the Lease, each for a period of an additional five years.
Additional period of lease	5 years
Rent expense		$ 800,000		$ 700,000
Upfront payment \| €			€ 0.1
Development and regulatory milestones payment \| €					€ 0.4
Development and regulatory possible second milestones payment \| €					€ 0.2
Accrued milestone payment obligation	$ 0	0
Accrued royalty obligation	$ 0	$ 0

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Non-Cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2021	$ 800
2022	4,603
2023	4,741
2024	4,883
2025	5,029
Thereafter	21,672
Total	$ 41,728