0001564590-20-050870 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2020	Oct. 31, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
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	No
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		45,445,115
Entity Shell Company	false
Document Quarterly 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

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 379,606	$ 14,632
Prepaid expenses and other current assets	234	127
Total current assets	379,840	14,759
Property and equipment, net	1,441	1,486
Other assets	191	191
Total assets	381,472	16,436
Current liabilities:
Accounts payable	1,488	1,256
Accrued expenses and other current liabilities	3,190	1,102
Total current liabilities	4,678	2,358
Long-term debt—net of unamortized debt discount	9,936
Deferred rent	13	42
Total liabilities	14,627	2,400
Commitments and contingencies (Note 11)
Stockholders’ equity
Common stock, $0.0001 par value; 200,000,000 and 68,000,000 shares authorized at September 30, 2020 and December 31, 2019, respectively; 45,445,115 and 3,239,017 shares issued and 45,004,247 and 2,586,535 shares outstanding at September 30, 2020 and December 31, 2019, respectively	5	1
Additional paid-in capital	417,374	6,352
Accumulated deficit	(50,534)	(19,746)
Total stockholders’ equity	366,845	14,036
Total liabilities and stockholders’ equity	$ 381,472	16,436
Convertible Preferred Stock
Stockholders’ equity
Convertible preferred stock (Note 7)		$ 27,429

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	68,000,000
Common stock, shares issued	45,445,115	3,239,017
Common stock, shares outstanding	45,004,247	2,586,535

Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 9,679	$ 2,982	$ 23,102	$ 6,781
General and administrative	3,841	647	6,945	1,575
Total operating expenses	13,520	3,629	30,047	8,356
Loss from operations	(13,520)	(3,629)	(30,047)	(8,356)
Other (expense) income:
Interest income		110	24	223
Interest expense	(130)		(315)
Change in fair value of preferred stock tranche obligations		(2,352)		(1,323)
Change in success fee obligation	(270)		(450)
Total other (expense) income, net	(400)	(2,242)	(741)	(1,100)
Net loss	$ (13,920)	$ (5,871)	$ (30,788)	$ (9,456)
Net loss per share—basic and diluted	$ (2.01)	$ (2.36)	$ (7.51)	$ (3.94)
Weighted-average common shares outstanding used in net loss per share—basic and diluted	6,920,008	2,491,487	4,100,504	2,401,039

Condensed Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Redeemable Convertible Preferred Stock	Convertible Preferred Stock	Convertible Preferred Stock Series A Redeemable 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 Deficit
Beginning Balance at Dec. 31, 2018					$ 9,061
Beginning Balance, Shares at Dec. 31, 2018					12,500,000
Beginning Balance at Dec. 31, 2018	$ (4,879)									$ 1	$ 7	$ (4,887)
Beginning Balance, Shares at Dec. 31, 2018										2,110,404
Vesting of restricted shares										239,503
Stock-based compensation	2										2
Net loss	(2,087)											(2,087)
Ending Balance at Mar. 31, 2019	(6,964)									$ 1	9	(6,974)
Ending Balance, Shares at Mar. 31, 2019										2,349,907
Ending Balance at Mar. 31, 2019					$ 9,061
Ending Balance, Shares at Mar. 31, 2019					12,500,000
Beginning Balance at Dec. 31, 2018					$ 9,061
Beginning Balance, Shares at Dec. 31, 2018					12,500,000
Beginning Balance at Dec. 31, 2018	(4,879)									$ 1	7	(4,887)
Beginning Balance, Shares at Dec. 31, 2018										2,110,404
Settlement of Tranche Right I	(1,621)
Net loss	(9,456)
Ending Balance at Sep. 30, 2019	19,427					$ 27,429				$ 1	6,339	(14,342)
Ending Balance, Shares at Sep. 30, 2019						32,500,000				2,508,614
Beginning Balance at Dec. 31, 2018					$ 9,061
Beginning Balance, Shares at Dec. 31, 2018					12,500,000
Beginning Balance at Dec. 31, 2018	(4,879)									$ 1	7	(4,887)
Beginning Balance, Shares at Dec. 31, 2018										2,110,404
Net loss	(14,900)
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
Beginning Balance at Mar. 31, 2019					$ 9,061
Beginning Balance, Shares at Mar. 31, 2019					12,500,000
Beginning Balance at Mar. 31, 2019	(6,964)									$ 1	9	(6,974)
Beginning Balance, Shares at Mar. 31, 2019										2,349,907
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)
Vesting of restricted shares										84,478
Stock-based compensation	4										4
Net loss	(1,497)											(1,497)
Ending Balance at Jun. 30, 2019	(8,457)									$ 1	13	(8,471)
Ending Balance, Shares at Jun. 30, 2019										2,434,385
Ending Balance at Jun. 30, 2019					$ 27,429
Ending Balance, Shares at Jun. 30, 2019					32,500,000
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
Vesting of restricted shares										74,229
Stock-based compensation	7										7
Net loss	(5,871)											(5,871)
Ending Balance at Sep. 30, 2019	19,427					$ 27,429				$ 1	6,339	(14,342)
Ending Balance, Shares at Sep. 30, 2019						32,500,000				2,508,614
Beginning Balance at Dec. 31, 2019	14,036					$ 27,429				$ 1	6,352	(19,746)
Beginning Balance, Shares at Dec. 31, 2019						32,500,000				2,586,535
Issuance of stock, net of issuance costs		$ 1,972					$ 1,972
Issuance of stock, net of issuance costs, Shares							2,000,000
Vesting of restricted shares										70,538
Stock-based compensation	66										66
Net loss	(7,886)											(7,886)
Ending Balance at Mar. 31, 2020	8,188					$ 29,401				$ 1	6,418	(27,632)
Ending Balance, Shares at Mar. 31, 2020						34,500,000				2,657,073
Beginning Balance at Dec. 31, 2019	$ 14,036					$ 27,429				$ 1	6,352	(19,746)
Beginning Balance, Shares at Dec. 31, 2019						32,500,000				2,586,535
Exercise of stock options, Shares	30,409
Net loss	$ (30,788)
Ending Balance at Sep. 30, 2020	366,845									$ 5	417,374	(50,534)
Ending Balance, Shares at Sep. 30, 2020										45,004,247
Beginning Balance at Mar. 31, 2020	8,188					$ 29,401				$ 1	6,418	(27,632)
Beginning Balance, Shares at Mar. 31, 2020						34,500,000				2,657,073
Exercise of stock options, Shares										753
Vesting of restricted shares										70,539
Stock-based compensation	75										75
Net loss	(8,982)											(8,982)
Ending Balance at Jun. 30, 2020	(719)					$ 29,401				$ 1	6,493	(36,614)
Ending Balance, Shares at Jun. 30, 2020						34,500,000				2,728,365
Issuance of stock, net of issuance costs	246,411		$ 17,495	$ 115,319				$ 17,495	$ 115,319	$ 1	246,410
Issuance of stock, net of issuance costs, Shares								17,500,000	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	24										24
Exercise of stock options, Shares										29,656
Vesting of restricted shares										70,537
Stock-based compensation	2,235										2,235
Net loss	(13,920)											(13,920)
Ending Balance at Sep. 30, 2020	$ 366,845									$ 5	$ 417,374	$ (50,534)
Ending Balance, Shares at Sep. 30, 2020										45,004,247

Condensed Statements of Stockholders' Equity (Deficit) (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Jun. 30, 2019
Common Stock
Stock issuance costs	$ 2.6
Series A Redeemable Convertible Preferred Stock
Stock issuance costs		$ 0.1	$ 0.1
Series A Convertible Preferred Stock
Stock issuance costs	0.1
Series B Convertible Preferred Stock
Stock issuance costs	$ 0.4

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (30,788)	$ (9,456)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,376	12
Depreciation and amortization expense	483	125
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 current assets	(107)	(329)
Accounts payable and other liabilities	1,114	505
Net cash used in operating activities	(26,472)	(7,820)
Cash flows from investing activities:
Purchases of property and equipment	(438)	(910)
Net cash used in investing activities	(438)	(910)
Cash flows from financing activities:
Proceeds from initial public offering of common stock, net of issuance costs	247,454
Proceeds from issuance of debt, net of issuance costs	9,936
Settlement of success fee obligation	(450)
Proceeds from issuance of convertible preferred stock, net of issuance costs	134,920	19,989
Proceeds from exercise of stock options	24
Net cash provided by financing activities	391,884	19,989
Net increase in cash and cash equivalents	364,974	11,259
Cash and cash equivalents at beginning of period	14,632	6,508
Cash and cash equivalents at end of period	379,606	17,767
Supplemental cash flow information:
Cash paid for interest and taxes	311
Supplemental disclosure of non-cash investing and financing information:
Reclassification of preferred stock tranche obligation liability to permanent equity		6,319
Settlement of Tranche Right I		1,621
Conversion of convertible preferred stock to common stock	162,215
Purchase of property and equipment in accounts payable		$ 370
Issuance costs from convertible preferred stock included in accounts payable or accrued expenses	134
Public offering costs included in accounts payable or accrued expenses	$ 1,043

Nature of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the 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.

The accompanying 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 instruments convertible into convertible preferred stock (which converted into convertible preferred stock in 2018), the sale of convertible preferred stock, borrowings under a loan and security agreement (the “Loan Agreement”) and most recently, the sale of common stock in the IPO completed in September 2020. The Company has incurred recurring losses, including net losses of $30.8 million for the nine months ended September 30, 2020 and $14.9 million for the year ended December 31, 2019. As of September 30, 2020, the Company had an accumulated deficit of $50.5 million. The Company expects to continue to generate operating losses for the foreseeable future. As of November 5, 2020, the issuance date of these interim condensed financial statements, the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance of these interim condensed 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

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

The accompanying 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”).

Unaudited interim financial information

The financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited interim financial statements have been prepared on the same basis as audited annual financial statements, except certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair representation of the results for the reported periods. Accordingly, these financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Prospectus that forms a part of the Company’s Registration Statement on Form S-1 (File No. 333-248414), which was filed with the SEC pursuant to Rule 424(b)(4) on September 17, 2020 (the “Prospectus”). The results for the nine months ended September 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020, any other interim periods, or any future year or period.

Use of estimates

The preparation of the financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.

Summary of significant accounting policies

The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies,” to the Company’s financial statements included in the Prospectus. There have been no material changes to the significant accounting policies during the three months ended September 30, 2020.

Accounting pronouncements issued and not adopted

In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases and will require lessees to record most leases on the balance sheet but recognize expense in a manner similar to the previous standard. The Company will use a modified retrospective approach of adoption for its leases. The Company plans to adopt this standard on January 1, 2022 and is currently evaluating the impact that the adoption will have on its financial statements. The Company expects to recognize a lease obligation and right to use asset upon adoption of ASU 2016-02.

Fair Value Measurements

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The following tables set forth by level, within the fair value hierarchy, the assets and liabilities carried at fair value on a recurring basis for the periods presented:

	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

Money market funds were valued by the Company based on quoted market prices. There were no transfers among Level 1, Level 2, or Level 3 categories during the periods presented.

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 value of the success fee obligation for which fair value is determined by Level 3 inputs:

(in thousands)	Success Fee Obligation
Balance—January 1, 2020	$	—
Initial fair value of success fee obligation		—
Change in fair value		450
Settlement of derivative instrument		(450	)
Balance—September 30, 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. The carrying value of the long-term debt at September 30, 2020 approximates fair value given that the debt was issued in February 2020 and settled in October 2020 at amounts that approximate the carrying value.

- Definition

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

+ References + Details

Property and Equipment

9 Months Ended

Sep. 30, 2020

Property Plant And Equipment [Abstract]

Property and Equipment

4. Property and Equipment

Property and equipment consisted of the following:

	September 30,			December 31,
(in thousands)	2020			2019
Laboratory equipment	$	1,993		$	1,705
Office and computer equipment		79			62
Leasehold improvements		14			14
Construction in process		133			—
Property and equipment—at cost		2,219			1,781
Less accumulated depreciation and amortization		(778	)		(295	)
Property and equipment—net	$	1,441		$	1,486

Depreciation and amortization expense for the three and nine months ended September 30, 2020 was $0.2 million and $0.5 million, respectively. Depreciation and amortization expense for the three and nine months ended September 30, 2019 was $0.1 million and $0.1 million, respectively.

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 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:

	September 30,		December 31,
(in thousands)	2020		2019
Payroll and benefits	$	1,318	$	540
Consulting services	23			60
Legal services	458			—
Research and development	818			484
Facility costs	36			18
Other	537			—
Total	$	3,190	$	1,102

Debt Financing

9 Months Ended

Sep. 30, 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 interest rate was 5.00% at September 30, 2020. 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

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Convertible Preferred Stock

7. Convertible Preferred Stock

The Company had 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.

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.

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.

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

Equity

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Equity

8. Equity

As of September 30, 2020, the Company’s amended and 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, all of which preferred stock is undesignated.

Stock-Based Awards

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

9. Stock-Based Awards

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, or its committee if so delegated.

The total number of shares of common stock authorized under the 2018 Plan was 8,267,252 shares, of which 1,928,487 shares remained available for future issuance prior to the effectiveness of the Company’s 2020 Stock Option and Incentive Plan (the “2020 Plan”). 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 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 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.

As of September 30, 2020, 3,061,794 shares remained available for future issuance under the 2020 Plan. Shares that are expired, terminated, surrendered or canceled without having been fully exercised under the 2018 Plan and the 2020 Plan will be available for future awards 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 September 30, 2020, no offering periods have commenced under the 2020 ESPP and 488,414 shares remain 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 on Nasdaq.

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:

	Nine Months Ended September 30,
	2020		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

A summary of the Company’s stock option activity and related information for the nine months ended September 30, 2020 is as follows:

(in thousands, except share and per share data)	Options			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
Outstanding as of January 1, 2020		311,303		$	0.93		9.5	$	30
Granted		6,167,369			6.94
Exercised		(30,409	)		0.82			589
Canceled		(110,484	)		1.04
Outstanding as of September 30, 2020		6,337,779		$	6.78		9.7	$	84,984
Options exercisable as of September 30, 2020		82,768		$	0.97		8.9	$	1,591
Options vested or expected to vest as of September 30, 2020		6,337,779		$	6.78		9.7	$	84,984

The weighted-average grant date fair value of the options granted during the nine months ended September 30, 2020 was $4.27 per share. As of September 30, 2020 there was $25.0 million of unrecognized compensation expense, which the Company expects to recognize over a weighted-average period of 3.67 years.

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 nine months ended September 30, 2020 is as follows:

	Number of Shares Underlying RSUs		Weighted Average Grant Date Fair Value
Unvested as of January 1, 2020		—	$	—
Granted		375,137		23.90
Vested		—		—
Forfeited		—		—
Unvested as of September 30, 2020		375,137	$	23.90

As of September 30, 2020, there was $8.7 million of unrecognized compensation costs related to unvested RSUs, which are expected to be recognized over a weighted-average period of 3.96 years.

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 aggregate grant date fair value of these awards was immaterial. The following table summarizes the Company’s restricted common stock award activity for the nine months ended September 30, 2020:

	Number of Restricted Shares
Issued and unvested as of January 1, 2020		652,482
Vested		(211,614	)
Issued and unvested as of September 30, 2020		440,868

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

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	929	$	3	$	984	$	4
General and administrative		1,306		4		1,392		8
Total	$	2,235	$	7	$	2,376	$	12

Net Loss Per Share

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Net Loss per Share

10. Net Loss per Share

The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:

	September 30,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		9,798,298
Unvested restricted common stock		440,868		730,403
Unvested restricted stock units		375,137		—
Stock options to purchase common stock		6,337,779		311,303
Total		7,153,784		10,840,004

Commitments and Contingencies

9 Months Ended

Sep. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

11. Commitments and Contingencies

Operating leases

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

Rent expense for the three months ended September 30, 2020 and 2019 totaled $0.2 million and $0.4 million, respectively. Rent expense for the nine months ended September 30, 2020 and 2019 totaled $0.2 million and $0.4 million, respectively.

Future minimum lease payments under the non-cancelable operating leases consisted of the following as of September 30, 2020:

Year Ending December 31,	(in thousands)
2020 (remaining 3 months)	$	197
2021		800
Total	$	997

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.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2020
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited interim financial information The financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited interim financial statements have been prepared on the same basis as audited annual financial statements, except certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair representation of the results for the reported periods. Accordingly, these financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Prospectus that forms a part of the Company’s Registration Statement on Form S-1 (File No. 333-248414), which was filed with the SEC pursuant to Rule 424(b)(4) on September 17, 2020 (the “Prospectus”). The results for the nine months ended September 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020, any other interim periods, or any future year or period.
Use of Estimates	Use of estimates The preparation of the financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates.
Summary of Significant Accounting Policies	Summary of significant accounting policies The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies,” to the Company’s financial statements included in the Prospectus. There have been no material changes to the significant accounting policies during the three months ended September 30, 2020.
Accounting Pronouncements Issued and Not Adopted	Accounting pronouncements issued and not adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases and will require lessees to record most leases on the balance sheet but recognize expense in a manner similar to the previous standard. The Company will use a modified retrospective approach of adoption for its leases. The Company plans to adopt this standard on January 1, 2022 and is currently evaluating the impact that the adoption will have on its financial statements. The Company expects to recognize a lease obligation and right to use asset upon adoption of ASU 2016-02.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Carried at Fair Value on Recurring Basis

The following tables set forth by level, within the fair value hierarchy, the assets and liabilities carried at fair value on a recurring basis for the periods presented:

	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

Roll-forward of Aggregate Fair Values of Success Fee Obligation Determined by Level 3 Inputs

The following table presents a roll-forward of the aggregate fair value of the success fee obligation for which fair value is determined by Level 3 inputs:

(in thousands)	Success Fee Obligation
Balance—January 1, 2020	$	—
Initial fair value of success fee obligation		—
Change in fair value		450
Settlement of derivative instrument		(450	)
Balance—September 30, 2020	$	—

Property and Equipment (Tables)

9 Months Ended

Sep. 30, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following:

	September 30,			December 31,
(in thousands)	2020			2019
Laboratory equipment	$	1,993		$	1,705
Office and computer equipment		79			62
Leasehold improvements		14			14
Construction in process		133			—
Property and equipment—at cost		2,219			1,781
Less accumulated depreciation and amortization		(778	)		(295	)
Property and equipment—net	$	1,441		$	1,486

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2020

Payables And Accruals [Abstract]

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	September 30,		December 31,
(in thousands)	2020		2019
Payroll and benefits	$	1,318	$	540
Consulting services	23			60
Legal services	458			—
Research and development	818			484
Facility costs	36			18
Other	537			—
Total	$	3,190	$	1,102

Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 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:

	Nine Months Ended September 30,
	2020		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

A summary of the Company’s stock option activity and related information for the nine months ended September 30, 2020 is as follows:

(in thousands, except share and per share data)	Options			Weighted Average Exercise Price		Weighted Average Remaining Life (in years)		Aggregate Intrinsic Value
Outstanding as of January 1, 2020		311,303		$	0.93		9.5	$	30
Granted		6,167,369			6.94
Exercised		(30,409	)		0.82			589
Canceled		(110,484	)		1.04
Outstanding as of September 30, 2020		6,337,779		$	6.78		9.7	$	84,984
Options exercisable as of September 30, 2020		82,768		$	0.97		8.9	$	1,591
Options vested or expected to vest as of September 30, 2020		6,337,779		$	6.78		9.7	$	84,984

Summary of RSU Activity

A summary of the Company’s RSU activity and related information for the 2020 Plan for the nine months ended September 30, 2020 is as follows:

	Number of Shares Underlying RSUs		Weighted Average Grant Date Fair Value
Unvested as of January 1, 2020		—	$	—
Granted		375,137		23.90
Vested		—		—
Forfeited		—		—
Unvested as of September 30, 2020		375,137	$	23.90

Summary of Restricted Common Stock Award Activity

The following table summarizes the Company’s restricted common stock award activity for the nine months ended September 30, 2020:

	Number of Restricted Shares
Issued and unvested as of January 1, 2020		652,482
Vested		(211,614	)
Issued and unvested as of September 30, 2020		440,868

Summary of Stock-based Compensation Expense

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

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	929	$	3	$	984	$	4
General and administrative		1,306		4		1,392		8
Total	$	2,235	$	7	$	2,376	$	12

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Potential Dilutive Securities Excluded From Calculation Of Net Loss Per Share

	September 30,
	2020		2019
Convertible preferred stock (as converted to common stock)		—		9,798,298
Unvested restricted common stock		440,868		730,403
Unvested restricted stock units		375,137		—
Stock options to purchase common stock		6,337,779		311,303
Total		7,153,784		10,840,004

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 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 September 30, 2020:

Year Ending December 31,	(in thousands)
2020 (remaining 3 months)	$	197
2021		800
Total	$	997

Nature of the Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 21, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Nature Of Business And Basis Of Presentation [Line Items]
Net loss		$ (13,920)	$ (8,982)	$ (7,886)	$ (5,871)	$ (1,497)	$ (2,087)	$ (30,788)	$ (9,456)	$ (14,900)
Accumulated deficit		$ (50,534)						$ (50,534)		$ (19,746)
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	$ 246,400

- Definition

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

+ References

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+ Details

Fair Value Measurements - Summary of Assets and Liabilities Carried at Fair Value on Recurring Basis (Details) - Fair Value, Recurring $ in Thousands	Dec. 31, 2019 USD ($)
Assets:
Total	$ 14,420
Level 1
Assets:
Total	14,420
Cash Equivalents - Money Market Funds
Assets:
Total	14,420
Cash Equivalents - Money Market Funds \| Level 1
Assets:
Total	$ 14,420

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

Fair Value Measurements - Roll-forward of Aggregate Fair Values of Success Fee Obligation Determined by Level 3 Inputs (Details) - Success Fee Obligation - Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Change in fair value	$ 450
Settlement of derivative instrument	$ (450)

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment—at cost	$ 2,219	$ 1,781
Less accumulated depreciation and amortization	(778)	(295)
Property and equipment—net	1,441	1,486
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment—at cost	1,993	1,705
Office and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment—at cost	79	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	$ 133

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 200	$ 100	$ 483	$ 125

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Payroll and benefits	$ 1,318	$ 540
Consulting services	23	60
Legal services	458
Research and development	818	484
Facility costs	36	18
Other	537
Total	$ 3,190	$ 1,102

Debt Financing - Additional Information (Details) - Term Loan - USD ($)		1 Months Ended	9 Months Ended
	Feb. 20, 2020	Sep. 30, 2020	Sep. 30, 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%
Credit facility, interest rate at period end		5.00%	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		3 Months Ended	9 Months Ended
	Aug. 31, 2020	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Class Of Stock [Line Items]
Proceeds from issuance of convertible preferred stock, net of issuance costs				$ 134,920	$ 19,989
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Shares issued and sold		17,500,000
Convertible preferred stock, shares issued and sold, price per share		$ 1.00
Proceeds from issuance of convertible preferred stock, net of issuance costs		$ 17,500
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Shares issued and sold	41,159,724
Convertible preferred stock, shares issued and sold, price per share	$ 2.81
Proceeds from issuance of convertible preferred stock, net of issuance costs	$ 115,700
Common Stock
Class Of Stock [Line Items]
Shares issued and sold			14,089,314
Convertible preferred stock, shares issued upon conversion			28,086,375	28,086,375

Equity - Additional Information (Details) - $ / shares	Sep. 30, 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 Awards - Additional Information (Details) $ / shares in Units, $ in Millions		9 Months Ended
	Sep. 16, 2020 shares	Sep. 30, 2020 USD ($) Installment $ / shares 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		$ 4.27
Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense \| $		$ 25.0
Weighted average period of recognition for unrecognized compensation costs		3 years 8 months 1 day
Restricted Stock Units ("RSUs")
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense \| $		$ 8.7
Weighted average period of recognition for unrecognized compensation costs		3 years 11 months 15 days
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		3,061,794
Number of shares transferred from 2018 plan, available for future issuance	1,928,487
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, 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
Share-based Compensation Arrangement By Share-based Payment Award Grant Service Conditions to Vest Number of Annual Installments \| Installment		4

Stock-Based Awards - Summary of Assumptions Used to Determine Grant-Date Fair Value of Options Granted (Details)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 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 Awards - Summary of Stock Option Activity and Related Information (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Options
Outstanding, beginning of period \| shares	311,303
Granted \| shares	6,167,369
Exercised \| shares	(30,409)
Canceled \| shares	(110,484)
Outstanding, end of period \| shares	6,337,779	311,303
Options exercisable as of September 30, 2020 \| shares	82,768
Options vested or expected to vest as of September 30, 2020 \| shares	6,337,779
Weighted Average Exercise Price
Outstanding, beginning of period \| $ / shares	$ 0.93
Granted \| $ / shares	6.94
Exercised \| $ / shares	0.82
Canceled \| $ / shares	1.04
Outstanding, end of period \| $ / shares	6.78	$ 0.93
Options exercisable as of September 30, 2020 \| $ / shares	0.97
Options vested or expected to vest as of September 30, 2020 \| $ / shares	$ 6.78
Weighted Average Remaining Life (in years)
Outstanding	9 years 8 months 12 days	9 years 6 months
Options exercisable as of September 30, 2020	8 years 10 months 24 days
Options vested or expected to vest as of September 30, 2020	9 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding \| $	$ 84,984	$ 30
Exercised \| $	589
Options exercisable as of September 30, 2020 \| $	1,591
Options vested or expected to vest as of September 30, 2020 \| $	$ 84,984

Stock-Based Awards - Summary of RSU Activity (Details) - Restricted Stock Units ("RSUs") - 2020 Plan	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Number of Shares Underlying RSUs
Granted \| shares	375,137
Unvested end of period \| shares	375,137
Weighted Average Grant Date Fair Value
Granted \| $ / shares	$ 23.90
Unvested end of period \| $ / shares	$ 23.90

Stock-Based Awards - Summary of Restricted Common Stock Award Activity (Details) - Restricted Common Stock	9 Months Ended
	Sep. 30, 2020 shares
Number of Restricted Shares
Unvested beginning of period	652,482
Vested	(211,614)
Unvested end of period	440,868

Stock-Based Awards - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,235	$ 7	$ 2,376	$ 12
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	929	3	984	4
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,306	$ 4	$ 1,392	$ 8

Net Loss Per Share - Potential Dilutive Securities Excluded From Calculation Of Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	7,153,784	10,840,004
Convertible Preferred Stock (As Converted to Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		9,798,298
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	440,868	730,403
Restricted Stock Units ("RSUs")
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	375,137
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	6,337,779	311,303

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Lease executed date			Jul. 01, 2019
Lease expiration date			Dec. 31, 2021
Rent expense	$ 0.2	$ 0.4	$ 0.2	$ 0.4

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Non-Cancelable Operating Leases (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2020 (remaining 3 months)	$ 197
2021	800
Total	$ 997