0001558370-21-006942 | 10-Q | XBRL Viewer

Print Document View Excel Document

Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Interactive Data Current	Yes
Entity Central Index Key	0001733294
Current Fiscal Year End Date	--12-31
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2021
Entity Registrant Name	GENERATION BIO CO.
Trading Symbol	GBIO
Entity File Number	001-39319
Entity Incorporation, State or Country Code	DE
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Address, Address Line One	301 Binney Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	655-7500
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.0001 Par Value
Entity Common Stock, Shares Outstanding		56,633,563
Entity Ex Transition Period	false

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 366,304	$ 62,889
Marketable securities	84,779	199,438
Prepaid expenses and other current assets	4,702	5,408
Total current assets	455,785	267,735
Property and equipment, net	23,202	23,781
Operating lease right-of-use assets	32,706
Restricted cash, noncurrent	2,051	2,051
Deferred offering costs		336
Other long-term assets	337	252
Total assets	514,081	294,155
Current liabilities:
Accounts payable	296	267
Accrued expenses and other current liabilities	6,281	10,953
Operating lease liability	4,217
Total current liabilities	10,794	11,220
Operating lease liability, net of current portion	44,551
Deferred rent, net of current portion		14,922
Total liabilities	55,345	26,142
Commitments and contingencies (Note 9)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 5,000,000 shares authorized and no shares issued or outstanding at March 31, 2021 and December 31, 2020
Common stock, $0.0001 par value; 150,000,000 shares authorized at March 31, 2021 and December 31, 2020; 56,559,217 and 46,970,012 shares issued at March 31, 2021 and December 31, 2020, respectively; 56,094,529 and 46,291,877 shares outstanding at March 31, 2021 and December 31, 2020, respectively	6	5
Additional paid-in capital	673,257	456,974
Accumulated other comprehensive income	10	9
Accumulated deficit	(214,537)	(188,975)
Total stockholders' equity (deficit)	458,736	268,013
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 514,081	$ 294,155

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000
Common stock, shares issued	56,559,217	46,970,012
Common stock, shares outstanding	56,094,529	46,291,877

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 18,753	$ 13,394
General and administrative	6,902	4,642
Total operating expenses	25,655	18,036
Loss from operations	(25,655)	(18,036)
Other income (expense):
Interest income and other income (expense), net	93	319
Net loss and net loss attributable to common stockholders	$ (25,562)	$ (17,717)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.46)	$ (3.22)
Weighted average common shares outstanding, basic and diluted	55,366,238	5,495,013
Comprehensive loss:
Net loss	$ (25,562)	$ (17,717)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	1
Comprehensive loss	$ (25,561)	$ (17,717)

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Preferred Stock [Member] Series C Convertible Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]	Total
Beginning balance, convertible preferred stock at Dec. 31, 2019		$ 115,593
Beginning balance, convertible preferred stock, shares at Dec. 31, 2019		26,425,664
Beginning balance at Dec. 31, 2019			$ 1	$ 9,859		$ (108,452)	$ (98,592)
Beginning balance, shares at Dec. 31, 2019			5,270,889
Issuance of common stock upon exercise of stock options				154			154
Issuance of common stock upon exercise of stock options, shares			34,829
Vesting of restricted common stock, shares			264,934
Issuance of Series C convertible preferred stock, net of issuance costs of $2,640, shares	19,936,296
Issuance of Series C convertible preferred stock, net of issuance costs of $2,640	$ 108,832
Stock-based compensation expense				1,504			1,504
Net loss						(17,717)	(17,717)
Ending balance, convertible preferred stock at Mar. 31, 2020		$ 224,425
Ending balance, convertible preferred stock, shares at Mar. 31, 2020		46,361,960
Ending balance at Mar. 31, 2020			$ 1	11,517		(126,169)	(114,651)
Ending balance, shares at Mar. 31, 2020			5,570,652
Beginning balance at Dec. 31, 2020			$ 5	456,974	$ 9	(188,975)	268,013
Beginning balance, shares at Dec. 31, 2020			46,291,877
Issuance of common stock upon exercise of stock options				1,519			1,519
Issuance of common stock upon exercise of stock options, shares			387,578
Vesting of restricted common stock, shares			215,074
Issuance of common stock upon initial public offering, net of issuance costs of $590			$ 1	211,285			211,286
Issuance of common stock upon initial public offering, net of issuance costs of $590, shares			9,200,000
Stock-based compensation expense				3,479			3,479
Unrealized gains (losses) on marketable securities					1		1
Net loss						(25,562)	(25,562)
Ending balance at Mar. 31, 2021			$ 6	$ 673,257	$ 10	$ (214,537)	$ 458,736
Ending balance, shares at Mar. 31, 2021			56,094,529

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands		3 Months Ended
	Jan. 09, 2020	Mar. 31, 2021	Mar. 31, 2020
Common Stock [Member]
Stock issuance of costs		$ 590
Series C Convertible Preferred Stock [Member]
Stock issuance of costs	$ 2,600		$ 2,640

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (25,562)	$ (17,717)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	3,479	1,504
Depreciation and amortization expense	1,064	677
Amortization (accretion) of premium (discount) on marketable securities	260
Changes in operating assets and liabilities:
Tenant receivable		416
Prepaid expenses and other current assets	704	(210)
Other noncurrent assets	(334)	(17)
Accounts payable	(145)	(1,304)
Accrued expenses and other current liabilities	(2,493)	(917)
Deferred rent		(212)
Net cash used in operating activities	(23,027)	(17,780)
Cash flows from investing activities:
Purchases of property and equipment	(915)	(2,011)
Sales and maturities of marketable securities	114,400
Net cash provided by (used in) investing activities	113,485	(2,011)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs incurred and paid in current period		109,044
Proceeds from initial public offering of common stock, net of underwriting discounts and commissions	211,876
Payment of offering costs	(438)	(65)
Proceeds from exercise of stock options	1,519	154
Net cash provided by financing activities	212,957	109,133
Net increase in cash, cash equivalents and restricted cash	303,415	89,342
Cash, cash equivalents and restricted cash at beginning of period	64,940	17,183
Cash, cash equivalents and restricted cash at end of period	368,355	106,525
Supplemental disclosure of noncash investing and financing information:
Purchases of property and equipment included in accounts payable and accrued expenses	64	82
Offering costs included in accounts payable and accrued expenses	$ 111	658
Issuance costs included in accrued expenses		$ 125

Nature of the Business and Basis of Presentation	3 Months Ended
Nature of the Business and Basis of Presentation	Mar. 31, 2021
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Generation Bio Co., or Generation Bio, was incorporated on October 21, 2016 as Torus Therapeutics, Inc. and subsequently changed its name to Generation Bio Co. Generation Bio and its consolidated subsidiary, or the company, we, our or us, are an innovative genetic medicines company creating a new class of gene therapy utilizing our proprietary non-viral gene therapy platform to provide durable, redosable treatments for millions of patients living with rare and prevalent diseases. Our non-viral gene therapy platform incorporates our high-capacity DNA construct called closed-ended DNA, or ceDNA, our cell-targeted lipid nanoparticle delivery system, or ctLNP, and our established, scalable capsid-free manufacturing process. Using our approach, we are developing novel gene therapies to provide targeted delivery of genetic payloads that include large and multiple genes to a range of tissues across a broad array of diseases. We are also engineering our gene therapies to be redosable, which may enable individualized patient titration to reach the desired therapeutic expression and to maintain efficacy throughout a patient’s life. We are headquartered in Cambridge, Massachusetts. We are 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, compliance with government regulations, the ability to establish clinical- and commercial-scale manufacturing processes 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 our development efforts are successful, it is uncertain when, if ever, we will realize significant revenue from product sales. In June 2020, we completed our initial public offering, or IPO, pursuant to which we issued and sold 12,105,263 shares of our common stock, including 1,578,947 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares resulting in net proceeds of $210.7 million, after deducting underwriting discounts and commissions and other offering expenses. Upon the closing of the IPO, all of our outstanding convertible preferred stock automatically converted into shares of common stock. In January 2021, we issued and sold 9,200,000 shares of our common stock, including 1,200,000 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, in a follow-on public offering, resulting in net proceeds of $211.3 million after deducting underwriting discounts and commissions and other offering expenses. The accompanying condensed 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, we have funded our operations with proceeds from the sales of instruments convertible into convertible preferred stock (which converted into convertible preferred stock in 2017), the sale of convertible preferred stock, and most recently, with proceeds from the sale of common stock in underwritten public offerings. We have incurred recurring losses, including net losses of $25.6 million for the three months ended March 31, 2021 and $17.7 million for the three months ended March 31, 2020. As of March 31, 2021, we had an accumulated deficit of $214.5 million. We expect to continue to generate operating losses in the foreseeable future. As of May 12, 2021, the issuance date of these condensed consolidated financial statements, we expect that our cash, cash equivalents and marketable securities will be sufficient to fund our operating expenses and capital expenditure requirements for at least 12 months. We will need to obtain additional funding through public or private equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. We may not be able to obtain financing on acceptable terms, or at all, and we may not be able to enter into collaborative or strategic alliances or licensing arrangements. The terms of any financing may adversely affect the holdings or the rights of our stockholders. Arrangements with collaborators or others may require us to relinquish rights to certain of our technologies or programs. If we are unable to obtain funding, we could be forced to delay, reduce or eliminate some or all of our research and development programs, pipeline expansion or commercialization efforts, which could adversely affect our business prospects. Although management will continue to pursue these plans, there is no assurance that we will be successful in obtaining sufficient funding on terms acceptable to us to fund continuing operations when needed or at all. The accompanying condensed consolidated financial statements reflect the operations of Generation Bio and our wholly owned subsidiary, Generation Bio Securities Corporation. Intercompany balances and transactions have been eliminated in consolidation. The accompanying condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America, or GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB.

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies 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 expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. We base our estimates on historical experience, known trends and other market-specific or other relevant factors that we believe 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. Unaudited interim financial information The condensed consolidated balance sheet as of December 31, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of March 31, 2021 and for the three months ended March 31, 2021 and 2020 have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission, or SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with our audited financial statements included in our Annual Report on Form 10-K that was filed with the SEC on March 18, 2021. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation of our financial position as of March 31, 2021, the results of operations for the three months ended March 31, 2021 and 2020, and cash flows for the three months ended March 31, 2021 and 2020 have been made. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021 or any other period. Concentrations of credit risk and of significant suppliers Financial instruments that potentially expose us to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. We believe that we are not exposed to significant credit risk due to the financial strength of the depository institutions in which our cash and cash equivalents are held. We maintain our cash equivalents in money market funds that invest in U.S. treasury securities. Our marketable securities as of March 31, 2021 consisted of U.S. government treasury securities, commercial paper and corporate debt securities. We have adopted an investment policy that limits the amounts that we may invest in the securities of single issuer with the exclusion of the U.S. government. We have not experienced any credit losses. We are dependent on a small number of third-party suppliers for our drug substance and drug product. In particular, we rely, and expect to continue to rely, on third-party suppliers for certain materials and components required for the production of any product candidates we may develop for our programs. These programs could be adversely affected by a significant interruption in the supply process. Marketable securities Our marketable securities that consist of debt securities as of March 31, 2021 are classified as available-for-sale and are reported at fair value. Unrealized gains and losses on available-for-sale debt securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Effective January 1, 2021, we adopted ASU 2016‑13, Financial Instruments – Credit Losses (Topic 326), using the effective date method. As we have never recorded any other-than-temporary-impairment adjustments to our available-for-sale debt securities prior to January 1, 2021, no transition provisions are applicable to our condensed consolidated financial statements and related disclosures. We assess our available-for-sale debt securities under the available-for-sale debt security impairment model in Topic 326 as of each reporting date in order to determine if a portion of any decline in fair value below carrying value recognized on our available-for-sale debt securities is the result of a credit loss. We record credit losses in the condensed consolidated statements of operations and comprehensive loss as credit loss expense, which is limited to the difference between the fair value and the amortized cost of the security. To date, we have not recorded any credit losses on our available-for-sale debt securities. Leases We determine whether a contract is, or contains, a lease at inception. We classify each of our leases as operating or financing considering factors such as the length of the lease term, the present value of the lease payments, the nature of the asset being leased, and the potential for ownership of the asset to transfer during the lease term. Leases with terms greater than one-year are recognized on the condensed consolidated balance sheets as right-of-use assets and lease liabilities and are measured at the present value of the fixed payments due over the expected lease term less the present value of any incentives, rebates or abatements we expect to receive from the lessor. Options to extend a lease are included in the expected lease term if exercise of the option is deemed reasonably certain. Costs determined to be variable and not based on an index or rate are not included in the measurement of the lease liability and are expensed as incurred. The interest rate implicit in lease contracts is typically not readily determinable. As such, we utilize the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis an amount equal to the lease payments over a similar term and in a similar economic environment. To estimate our incremental borrowing rate, a credit rating applicable to our company is estimated using a synthetic credit rating analysis since we do not currently have a rating agency-based credit rating. We record expense to recognize fixed lease payments on a straight-line basis over the expected lease term. We have elected the practical expedient not to separate lease and non-lease components for real estate leases. Recently adopted accounting pronouncements In February 2016, the FASB issued ASU 2016‑02, Leases (Topic 842). The 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. In July 2018, the FASB issued ASU 2018‑11, which provided entities with an additional transition method to adopt Topic 842. Under the new transition method, an entity initially applies the new lease requirements at the adoption date, not the earliest period presented, and recognizes a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2019. Early adoption was permitted for all entities. In November 2019, the FASB issued ASU 2019‑10, which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. In June 2020, the FASB issued ASU 2020‑05, which granted a one-year effective-date delay for nonpublic entities to annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption continues to be allowed. We early adopted 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. We elected 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. Please read Note 5 for additional disclosures related to accounting for leases under this new standard. The adoption of the new standard has had a material impact on our condensed consolidated balance sheet as the standard requires us to measure and recognize a right-of-use asset and lease liability. As most leases do not provide an implicit rate, our incremental borrowing rate was determined based on the information available at the date of adoption to measure our lease liability. Costs determined to be variable and not based on an index or rate were not included in the measurement of the lease liability. We recognized a lease liability and related right-of-use asset on our condensed consolidated balance sheet of approximately $49.7 million and $33.4 million, net of deferred rent, respectively, as of January 1, 2021, which are presented as separate line items on the condensed consolidated balance sheet as of March 31, 2021. The adoption of the standard did not have a material impact on our condensed consolidated statement of operations and comprehensive loss and did not require a cumulative adjustment to accumulated deficit on our condensed consolidated statement of stockholders’ equity as of March 31, 2021. In June 2016, the FASB issued ASU 2016‑13, Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as available-for-sale. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2020. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU 2019‑10, which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2022, including interim periods within those fiscal years. We adopted ASU 2016-13 on January 1, 2021 and the adoption did not have a material impact on our condensed consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes – Simplifying the Accounting for Income Taxes (Topic 740). The amendments in this update simplify the accounting for income taxes by removing certain exceptions to the general principles as well as clarifying and amending existing guidance to improve consistent application. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2020 and for interim periods within those fiscal years. For nonpublic entities, the guidance is effective for annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption is permitted for all entities. Depending on the amendment, adoption may be applied on the retrospective, modified retrospective or prospective basis. We early adopted the amendments as of January 1, 2021 on a prospective basis. The amendments did not have a significant impact on our condensed consolidated financial statements and related disclosures. Recently issued accounting pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. We qualify as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and we elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, we can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that we either (i) irrevocably elect to “opt out” of such extended transition period or (ii) no longer qualify as an emerging growth company.

Marketable Securities and Fair Value Measurements

3 Months Ended

Mar. 31, 2021

Marketable Securities and Fair Value Measurements [Abstract]

Marketable Securities and Fair Value Measurements

3. Marketable Securities and Fair Value Measurements

The following tables present our marketable securities by security type:


	As of March 31, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value
U.S. treasury securities	$	57,265	$	12	$	—	$	57,277
Commercial paper		22,481		—		—		22,481
Corporate debt securities		5,023		—		(2)		5,021
Totals	$	84,769	$	12	$	(2)	$	84,779


	As of December 31, 2020
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value
U.S. treasury securities	$	129,446	$	9	$	(4)	$	129,451
Commercial paper		52,441		—		—		52,441
Corporate debt securities		17,542		4		—		17,546
Totals	$	199,429	$	13	$	(4)	$	199,438

As of March 31, 2021 and December 31, 2020, marketable securities consisted of investments that mature within one year.

The following tables present our assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques that we utilized to determine such fair value:


	Fair Value Measurements at March 31, 2021 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	174,468	$	—	$	—	$	174,468
Marketable securities:
U.S. treasury securities		—		57,277		—		57,277
Commercial paper		—		22,481		—		22,481
Corporate debt securities		—		5,021		—		5,021
Totals	$	174,468	$	84,779	$	—	$	259,247



	Fair Value Measurements at December 31, 2020 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	63,827	$	—	$	—	$	63,827
Marketable securities:
U.S. treasury securities		—		129,451		—		129,451
Commercial paper		—		52,441		—		52,441
Corporate debt securities		—		17,546		—		17,546
Totals	$	63,827	$	199,438	$	—	$	263,265

Money market funds were valued based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. Our marketable securities, which consisted of U.S. treasury securities, commercial paper and corporate debt securities were valued using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy.

- 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

Accrued Expenses

3 Months Ended

Mar. 31, 2021

Accrued Expenses [Abstract]

Accrued Expenses

4. Accrued Expenses

Accrued expenses and other current liabilities consisted of the following:



	March 31, 2021		December 31, 2020
(in thousands)
Accrued employee compensation and benefits	$	2,750	$	6,150
Accrued external research and development expenses		2,034		1,772
Accrued professional fees		858		940
Deferred rent		—		1,389
Other		639		702
	$	6,281	$	10,953

Leases

3 Months Ended

Mar. 31, 2021

Leases [Abstract]

Leases

5. Leases

We lease our office and laboratory space under a noncancelable operating lease that was entered into in August 2018, as amended in July 2019 and June 2020, which expires in 2029. We have an option to extend the lease term for one additional term of five years at the greater of the then-current base rent or the then-current fair market value. Exercise of this option was not determined to be reasonably certain and thus was not considered in determining the operating lease liability on the condensed consolidated balance sheet as of March 31, 2021. We posted a customary letter of credit in the amount of approximately $2.1 million as a security deposit. The letter of credit is subject to increase if we were to sublease any portion of the leased premises. This lease does not include any restrictions or covenants that had to be accounted for under the lease guidance.

The following table presents our costs included in operating expenses related to the operating lease:


		For the Three Months Ended March 31, 2021
Lease Cost		(in thousands)
Operating lease costs	$	1,505
Variable lease cost		446
Total	$	1,951

Net cash paid for the amounts included in the measurement of the operating lease liability on the condensed consolidated balance sheet and operating activities in our condensed consolidated statement of cash flow was $1.8 million for the period ending March 31, 2021. The weighted-average remaining lease term and weighted-average incremental borrowing rate for all leases as of March 31, 2021 was 8.1 years and 6.5%, respectively.

Future lease payments for our noncancelable operating lease as of March 31, 2021 and a reconciliation to the carrying amount of the operating lease liability presented in the condensed consolidated balance sheet as of March 31, 2021 is as follows:


Year Ending December 31,	(in thousands)
2021 (remaining 9 months)	$	5,489
2022		7,267
2023		7,441
2024		7,679
2025		7,881
Thereafter		27,570
Total undiscounted payments due under operating leases		63,327
Less imputed interest		(14,559)
Total	$	48,768

Current operating lease liability	$	4,217
Non-current operating lease liability		44,551
Total	$	48,768

Convertible Preferred Stock	3 Months Ended
Convertible Preferred Stock	Mar. 31, 2021
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	6. Convertible Preferred Stock Prior to the IPO, we had issued Series A convertible preferred stock, or Series A, Series B convertible preferred stock, or Series B, and Series C convertible preferred stock, or Series C. Collectively the Series A, Series B and Series C are referred to as the Preferred Stock. On January 9, 2020, we issued and sold 19,936,296 shares of Series C at a price of $5.5914 per share for gross proceeds of $111.5 million. We incurred issuance costs in connection with this transaction of $2.6 million. Upon issuance of each class of Preferred Stock, we assessed the embedded conversion and liquidation features of the shares and determined that such features did not require us to separately account for these features. We also concluded that no beneficial conversion feature existed on the issuance date of each class of Preferred Stock. Upon the closing of the IPO in June 2020, our Preferred Stock automatically converted into 27,094,085 shares of common stock.

Equity	3 Months Ended
Equity	Mar. 31, 2021
Equity [Abstract]
Equity	7. Equity As of March 31, 2021, our amended and restated certificate of incorporation authorizes us to issue 150,000,000 shares of common stock, par value $0.0001 per share, and 5,000,000 shares of preferred stock, par value $0.0001 per share, all of which preferred stock is undesignated. In January 2021, we issued and sold 9,200,000 shares of our common stock, including 1,200,000 shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, in a follow-on public offering, resulting in net proceeds of $211.3 million after deducting underwriting discounts and commissions and other offering expenses. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of our stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

Stock-Based Awards

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-Based Awards

8. Stock-Based Compensation

Stock incentive plans

Our 2017 Stock Incentive Plan, or the 2017 Plan, provided for us to grant incentive stock options or nonstatutory stock options, restricted stock, restricted stock units and other equity awards to employees, non-employees, and directors. In January 2020, the number of shares of common stock authorized for issuance under the 2017 Plan was increased from 8,407,405 shares to 10,275,717 shares.

In May 2020, our board of directors adopted, and in June 2020, our stockholders approved, the 2020 Stock Incentive Plan, or the 2020 Plan and, together with the 2017 Plan, the Plans, which became effective on June 11, 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. The number of shares of common stock reserved for issuance under the 2020 Plan is the sum of (1) 2,547,698 shares; plus (2) the number of shares (up to a maximum of 7,173,014 shares) as was equal to the sum of (x) the number of shares of common stock reserved for issuance under the 2017 Plan that remained available for grant under the 2017 Plan on June 11, 2020 and (y) the number of shares of common stock subject to outstanding awards granted under the 2017 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right; plus (3) an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2021 and continuing until, and including, the fiscal year ending December 31, 2030, equal to the lesser of (i) 4% of the number of shares of common stock outstanding on such date, and (ii) an amount determined by the board of directors. In January 2021, the number of shares of common stock authorized for issuance under the 2020 Plan was increased from 10,275,717 shares to 12,154,517 shares. Upon the effectiveness of the 2020 Plan, we ceased granting additional awards under the 2017 Plan.

The Plans are 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 on any award under the Plans are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the Plans with service-based vesting conditions generally vest over four years and expire after ten years. The exercise price for stock options granted is not less than the fair value of common stock as of the date of grant. Prior to our IPO, fair value of common stock was determined by the board of directors. Subsequent to the IPO, fair value of common stock is based on quoted market prices.

As of March 31, 2021, 3,432,597 shares remained available for future issuance under the 2020 Plan. Shares subject to outstanding awards granted under the Plans that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right will be available for future awards under the 2020 Plan.

Grant of stock options

During the three months ended March 31, 2021, we granted service-based options to certain employees, non-employees, and directors for the purchase of 1,227,900 shares of common stock with a weighted average grant date fair value of $19.87 per share that vest over a weighted average period of approximately four years.

Employee stock purchase plan

In May 2020, our board of directors adopted, and in June 2020, our stockholders approved, the 2020 Employee Stock Purchase Plan, or the 2020 ESPP, which became effective June 11, 2020. The 2020 ESPP is administered by our board of directors or by a committee appointed by the board of directors. 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) 1,302,157 shares of common stock, (2) 1% of the number of shares of common stock outstanding on such date, and (3) an amount determined by the board of directors. In January 2021, the number of shares of common stock authorized for issuance under the 2020 ESPP was increased from 481,231 shares to 950,931 shares. The first offering period under the 2020 ESPP commenced on January 1, 2021 and 950,931 shares remain available for issuance as of March 31, 2021.

Stock-based compensation

Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended March 31,
(in thousands)	2021		2020
Research and development expenses	$	1,898	$	827
General and administrative expenses		1,581		677
	$	3,479	$	1,504

As of March 31, 2021, total unrecognized compensation cost related to unvested stock-based awards was $47.3 million, which is expected to be recognized over a weighted average period of 2.9 years. Additionally, as of March 31, 2021, we had unrecognized compensation cost related to unvested stock-based awards with performance-based vesting conditions for which performance has not been deemed probable of $1.9 million.

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies 401(k) Plan We have a defined-contribution plan under Section 401(k) of the Internal Revenue Code of 1986, as amended, or the 401(k) Plan. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. In September 2020, we adopted a match program, beginning on January 1, 2021, for employee contributions to the 401(k) Plan up to a maximum of four percent of the employee’s salary, subject to the maximums established under U.S. Internal Revenue Code of 1986, as amended. Indemnification agreements In the ordinary course of business, we may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, we have entered into indemnification agreements with members of our board of directors and our executive officers that will require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments we could be required to make under these indemnification agreements is, in many cases, unlimited. We have not incurred any material costs as a result of such indemnifications and are not currently aware of any indemnification claims. Legal proceedings We, from time to time, may be party to litigation arising in the ordinary course of business. We were not subject to any material legal proceedings during the three months ended March 31, 2021.

Net Loss per Share

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Net Loss per Share

10. Net Loss per Share

We have generated a net loss in all periods presented, therefore the basic and diluted net loss per share attributable to common stockholders are the same as the inclusion of the potentially dilutive securities would be anti-dilutive. We excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated:


	March 31,
	2021	2020
Convertible preferred stock (as converted to common stock)	—	27,094,085
Unvested restricted common stock	482,728	1,440,254
Unvested restricted common stock units	18,040	—
Stock options to purchase common stock	5,801,170	5,034,210
	6,301,938	33,568,549

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2021
Accounting Policies [Abstract]
Use of estimates	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 expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and stock-based compensation expense. We base our estimates on historical experience, known trends and other market-specific or other relevant factors that we believe 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.
Unaudited interim financial information	Unaudited interim financial information The condensed consolidated balance sheet as of December 31, 2020 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited financial statements as of March 31, 2021 and for the three months ended March 31, 2021 and 2020 have been prepared by us pursuant to the rules and regulations of the Securities and Exchange Commission, or SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with our audited financial statements included in our Annual Report on Form 10-K that was filed with the SEC on March 18, 2021. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair presentation of our financial position as of March 31, 2021, the results of operations for the three months ended March 31, 2021 and 2020, and cash flows for the three months ended March 31, 2021 and 2020 have been made. The results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2021 or any other period.
Concentrations of credit risk and of significant suppliers	Concentrations of credit risk and of significant suppliers Financial instruments that potentially expose us to concentrations of credit risk consist primarily of cash, cash equivalents, and marketable securities. We believe that we are not exposed to significant credit risk due to the financial strength of the depository institutions in which our cash and cash equivalents are held. We maintain our cash equivalents in money market funds that invest in U.S. treasury securities. Our marketable securities as of March 31, 2021 consisted of U.S. government treasury securities, commercial paper and corporate debt securities. We have adopted an investment policy that limits the amounts that we may invest in the securities of single issuer with the exclusion of the U.S. government. We have not experienced any credit losses. We are dependent on a small number of third-party suppliers for our drug substance and drug product. In particular, we rely, and expect to continue to rely, on third-party suppliers for certain materials and components required for the production of any product candidates we may develop for our programs. These programs could be adversely affected by a significant interruption in the supply process.
Marketable securities	Marketable securities Our marketable securities that consist of debt securities as of March 31, 2021 are classified as available-for-sale and are reported at fair value. Unrealized gains and losses on available-for-sale debt securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Effective January 1, 2021, we adopted ASU 2016‑13, Financial Instruments – Credit Losses (Topic 326), using the effective date method. As we have never recorded any other-than-temporary-impairment adjustments to our available-for-sale debt securities prior to January 1, 2021, no transition provisions are applicable to our condensed consolidated financial statements and related disclosures. We assess our available-for-sale debt securities under the available-for-sale debt security impairment model in Topic 326 as of each reporting date in order to determine if a portion of any decline in fair value below carrying value recognized on our available-for-sale debt securities is the result of a credit loss. We record credit losses in the condensed consolidated statements of operations and comprehensive loss as credit loss expense, which is limited to the difference between the fair value and the amortized cost of the security. To date, we have not recorded any credit losses on our available-for-sale debt securities.
Leases	Leases We determine whether a contract is, or contains, a lease at inception. We classify each of our leases as operating or financing considering factors such as the length of the lease term, the present value of the lease payments, the nature of the asset being leased, and the potential for ownership of the asset to transfer during the lease term. Leases with terms greater than one-year are recognized on the condensed consolidated balance sheets as right-of-use assets and lease liabilities and are measured at the present value of the fixed payments due over the expected lease term less the present value of any incentives, rebates or abatements we expect to receive from the lessor. Options to extend a lease are included in the expected lease term if exercise of the option is deemed reasonably certain. Costs determined to be variable and not based on an index or rate are not included in the measurement of the lease liability and are expensed as incurred. The interest rate implicit in lease contracts is typically not readily determinable. As such, we utilize the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis an amount equal to the lease payments over a similar term and in a similar economic environment. To estimate our incremental borrowing rate, a credit rating applicable to our company is estimated using a synthetic credit rating analysis since we do not currently have a rating agency-based credit rating. We record expense to recognize fixed lease payments on a straight-line basis over the expected lease term. We have elected the practical expedient not to separate lease and non-lease components for real estate leases.
Recently issued accounting pronouncements	Recently adopted accounting pronouncements In February 2016, the FASB issued ASU 2016‑02, Leases (Topic 842). The 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. In July 2018, the FASB issued ASU 2018‑11, which provided entities with an additional transition method to adopt Topic 842. Under the new transition method, an entity initially applies the new lease requirements at the adoption date, not the earliest period presented, and recognizes a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2019. Early adoption was permitted for all entities. In November 2019, the FASB issued ASU 2019‑10, which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. In June 2020, the FASB issued ASU 2020‑05, which granted a one-year effective-date delay for nonpublic entities to annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption continues to be allowed. We early adopted 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. We elected 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. Please read Note 5 for additional disclosures related to accounting for leases under this new standard. The adoption of the new standard has had a material impact on our condensed consolidated balance sheet as the standard requires us to measure and recognize a right-of-use asset and lease liability. As most leases do not provide an implicit rate, our incremental borrowing rate was determined based on the information available at the date of adoption to measure our lease liability. Costs determined to be variable and not based on an index or rate were not included in the measurement of the lease liability. We recognized a lease liability and related right-of-use asset on our condensed consolidated balance sheet of approximately $49.7 million and $33.4 million, net of deferred rent, respectively, as of January 1, 2021, which are presented as separate line items on the condensed consolidated balance sheet as of March 31, 2021. The adoption of the standard did not have a material impact on our condensed consolidated statement of operations and comprehensive loss and did not require a cumulative adjustment to accumulated deficit on our condensed consolidated statement of stockholders’ equity as of March 31, 2021. In June 2016, the FASB issued ASU 2016‑13, Financial Instruments – Credit Losses (Topic 326). The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as available-for-sale. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. For nonpublic entities, the guidance was effective for annual reporting periods beginning after December 15, 2020. Early adoption is permitted for all entities. In November 2019, the FASB issued ASU 2019‑10, which deferred the effective date for nonpublic entities to annual reporting periods beginning after December 15, 2022, including interim periods within those fiscal years. We adopted ASU 2016-13 on January 1, 2021 and the adoption did not have a material impact on our condensed consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes – Simplifying the Accounting for Income Taxes (Topic 740). The amendments in this update simplify the accounting for income taxes by removing certain exceptions to the general principles as well as clarifying and amending existing guidance to improve consistent application. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2020 and for interim periods within those fiscal years. For nonpublic entities, the guidance is effective for annual reporting periods beginning after December 15, 2021 and to interim periods within fiscal years beginning after December 15, 2022. Early adoption is permitted for all entities. Depending on the amendment, adoption may be applied on the retrospective, modified retrospective or prospective basis. We early adopted the amendments as of January 1, 2021 on a prospective basis. The amendments did not have a significant impact on our condensed consolidated financial statements and related disclosures. Recently issued accounting pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that we adopt as of the specified effective date. We qualify as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and we elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, we can adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and can do so until such time that we either (i) irrevocably elect to “opt out” of such extended transition period or (ii) no longer qualify as an emerging growth company.

Marketable Securities and Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

Marketable Securities and Fair Value Measurements [Abstract]

Summary of marketable securities

The following tables present our marketable securities by security type:


	As of March 31, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value
U.S. treasury securities	$	57,265	$	12	$	—	$	57,277
Commercial paper		22,481		—		—		22,481
Corporate debt securities		5,023		—		(2)		5,021
Totals	$	84,769	$	12	$	(2)	$	84,779


	As of December 31, 2020
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
(in thousands)	Cost		Gains		Losses		Value
U.S. treasury securities	$	129,446	$	9	$	(4)	$	129,451
Commercial paper		52,441		—		—		52,441
Corporate debt securities		17,542		4		—		17,546
Totals	$	199,429	$	13	$	(4)	$	199,438

Summary of assets measured at fair value on a recurring basis


	Fair Value Measurements at March 31, 2021 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	174,468	$	—	$	—	$	174,468
Marketable securities:
U.S. treasury securities		—		57,277		—		57,277
Commercial paper		—		22,481		—		22,481
Corporate debt securities		—		5,021		—		5,021
Totals	$	174,468	$	84,779	$	—	$	259,247



	Fair Value Measurements at December 31, 2020 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	63,827	$	—	$	—	$	63,827
Marketable securities:
U.S. treasury securities		—		129,451		—		129,451
Commercial paper		—		52,441		—		52,441
Corporate debt securities		—		17,546		—		17,546
Totals	$	63,827	$	199,438	$	—	$	263,265

Accrued Expenses (Tables)

3 Months Ended

Mar. 31, 2021

Accrued Expenses [Abstract]

Summary of Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:



	March 31, 2021		December 31, 2020
(in thousands)
Accrued employee compensation and benefits	$	2,750	$	6,150
Accrued external research and development expenses		2,034		1,772
Accrued professional fees		858		940
Deferred rent		—		1,389
Other		639		702
	$	6,281	$	10,953

Leases (Tables)

3 Months Ended

Mar. 31, 2021

Leases [Abstract]

Costs included in operating expenses related to the operating lease

The following table presents our costs included in operating expenses related to the operating lease:


		For the Three Months Ended March 31, 2021
Lease Cost		(in thousands)
Operating lease costs	$	1,505
Variable lease cost		446
Total	$	1,951

Future lease payments for noncancelable operating lease


Year Ending December 31,	(in thousands)
2021 (remaining 9 months)	$	5,489
2022		7,267
2023		7,441
2024		7,679
2025		7,881
Thereafter		27,570
Total undiscounted payments due under operating leases		63,327
Less imputed interest		(14,559)
Total	$	48,768

Current operating lease liability	$	4,217
Non-current operating lease liability		44,551
Total	$	48,768

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary of stock-based compensation expense was classified in the statements of operations and comprehensive loss

Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended March 31,
(in thousands)	2021		2020
Research and development expenses	$	1,898	$	827
General and administrative expenses		1,581		677
	$	3,479	$	1,504

Net Loss per Share (Tables)

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Summary of potential dilutive securities, presented based on amounts outstanding


	March 31,
	2021	2020
Convertible preferred stock (as converted to common stock)	—	27,094,085
Unvested restricted common stock	482,728	1,440,254
Unvested restricted common stock units	18,040	—
Stock options to purchase common stock	5,801,170	5,034,210
	6,301,938	33,568,549

Nature of the Business and Basis of Presentation - Additional information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
	Jun. 16, 2020	Jan. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Date of incorporation			Oct. 21, 2016
Net proceeds from shares issued		$ 211,300
Net loss			$ (25,562)	$ (17,717)
Used in BS			$ (214,537)		$ (188,975)
Common Stock [Member]
Shares issued during the period		9,200,000	9,200,000
Common Stock [Member] \| IPO [Member]
Shares issued during the period	12,105,263
Net proceeds from shares issued	$ 210,700
Common Stock [Member] \| Over-Allotment Option [Member]
Shares issued during the period	1,578,947	1,200,000

- 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

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jan. 01, 2021
Accounting Policies [Abstract]
Lease liability	$ 48,768	$ 49,700
Operating lease right-of-use assets	$ 32,706	$ 33,400

Marketable Securities and Fair Value Measurements - Summary of marketable securities (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized cost	$ 84,769	$ 199,429
Gross unrealized gain	12	13
Gross unrealized losses	(2)	(4)
Estimated fair value	84,779	199,438
U.S. treasury securities
Marketable Securities [Line Items]
Amortized cost	57,265	129,446
Gross unrealized gain	12	9
Gross unrealized losses		(4)
Estimated fair value	57,277	129,451
Commercial paper
Marketable Securities [Line Items]
Amortized cost	22,481	52,441
Estimated fair value	22,481	52,441
Corporate debt securities
Marketable Securities [Line Items]
Amortized cost	5,023	17,542
Gross unrealized gain		4
Gross unrealized losses	(2)
Estimated fair value	$ 5,021	$ 17,546

Marketable Securities and Fair Value Measurements - Summary of assets measured at fair value on a recurring basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Cash equivalents:
Totals	$ 259,247	$ 263,265
Marketable securities:
Marketable securities	84,779	199,438
Level 1
Cash equivalents:
Totals	174,468	63,827
Level 2
Cash equivalents:
Totals	84,779	199,438
Money Market Funds
Cash equivalents:
Cash equivalents	174,468	63,827
Money Market Funds \| Level 1
Cash equivalents:
Cash equivalents	174,468	63,827
U.S. treasury securities
Marketable securities:
Marketable securities	57,277	129,451
U.S. treasury securities \| Level 2
Marketable securities:
Marketable securities	57,277	129,451
Commercial paper
Marketable securities:
Marketable securities	22,481	52,441
Commercial paper \| Level 2
Marketable securities:
Marketable securities	22,481	52,441
Corporate debt securities
Marketable securities:
Marketable securities	5,021	17,546
Corporate debt securities \| Level 2
Marketable securities:
Marketable securities	$ 5,021	$ 17,546

Accrued Expenses - Summary of Accrued expenses and other current liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued Expenses [Abstract]
Accrued employee compensation and benefits	$ 2,750	$ 6,150
Accrued external research and development expenses	2,034	1,772
Accrued professional fees	858	940
Deferred rent		1,389
Other	639	702
Total	$ 6,281	$ 10,953

Leases - Narrative (Details) $ in Millions	3 Months Ended
Leases - Narrative (Details) $ in Millions	Mar. 31, 2021 USD ($)
Leases [Abstract]
Lessee operating lease year of expiry	2029
Lease existence of option to extend	true
Operating lease agreement option to renewal term	5 years
Letter of credit for security deposit	$ 2.1
Operating lease payments	$ 1.8
Weighted-average incremental borrowing	6.50%
Weighted-average remaining lease term	8 years 1 month 6 days

Leases - Costs included in operating expenses related to the operating lease (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
Leases [Abstract]
Operating lease costs	$ 1,505
Variable lease cost	446
Total	$ 1,951

Leases - Future lease payments for noncancelable operating lease (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jan. 01, 2021
Leases [Abstract]
2021 (remaining 9 months)	$ 5,489
2022	7,267
2023	7,441
2024	7,679
2025	7,881
Thereafter	27,570
Total undiscounted payments due under operating leases	63,327
Less imputed interest	(14,559)
Current operating lease liability	4,217
Non-current operating lease liability	44,551
Total	$ 48,768	$ 49,700

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Jan. 09, 2020	Mar. 31, 2021	Mar. 31, 2020	Jun. 16, 2020
Common Stock [Member]
Temporary Equity [Line Items]
Stock issuance of costs		$ 590
Shares issued upon conversion				27,094,085
Series C Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Shares issued during the period	19,936,296
Shares issued price	$ 5.5914
Gross proceeds	$ 111,500
Stock issuance of costs	$ 2,600		$ 2,640

Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended
	Jun. 16, 2020	Jan. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Common stock, shares authorized			150,000,000
Common stock, par value per share			$ 0.0001	$ 0.0001
Preferred stock, shares authorized			5,000,000
Preferred stock, par value per share			$ 0.0001	$ 0.0001
Net proceeds from shares issued		$ 211.3
Common Stock [Member]
Shares issued during the period		9,200,000	9,200,000
Common Stock [Member] \| Over-Allotment Option [Member]
Shares issued during the period	1,578,947	1,200,000

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Jun. 11, 2020	Mar. 31, 2021	Jan. 31, 2021	Dec. 31, 2020	Jan. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock compensation on account of unvested options		$ 47.3
Unrecognized stock compensation on account of unvested options remaining period over which the compensation is to be recognized		2 years 10 months 24 days
Unvested Stock Awards for Which Performance is not Probable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock compensation on account of unvested options		$ 1.9
Service Based Options [Member] \| Certain Employees Directors and Consultants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of options granted		1,227,900
Share based compensation by share based payment arrangement number of options granted weighted average exercise price per share		$ 19.87
Period of vesting of employee stock options		4 years
2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	2,547,698
Stock based compensation vesting period service based		4 years
Stock based compensation period of expiry		10 years
Common stock shares available for future issuance		3,432,597
2020 Stock Incentive Plan \| Maximum \| Additional From 2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance	7,173,014
2020 Stock Incentive Plan \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	4.00%
Employee Stock Purchase Plan 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance			950,931	481,231
Common stock shares available for future issuance		950,931
Employee Stock Purchase Plan 2020 \| Maximum \| Annual Increase 2021 To 2030
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock shares additionally reserved for issuance	1.00%
Number of share instruments newly issued under a share-based compensation plan	1,302,157
Common Stock [Member] \| 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorized for issuance					10,275,717	8,407,405
Common Stock [Member] \| 2020 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation by share based payment arrangement number of shares authorized for issuance			12,154,517	10,275,717

Stock-Based Awards - Summary of Stock-Based Compensation Expense was Classified in the Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 3,479	$ 1,504
Research and development expense [Member]
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,898	827
General and administrative expenses
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 1,581	$ 677

Commitments and Contingencies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Defined contribution plan, percentage	4.00%

Net Loss per Share - Summary of Potential Dilutive Securities, Presented Based on Amounts Outstanding (Detail) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	6,301,938	33,568,549
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share		27,094,085
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	482,728	1,440,254
Unvested restricted common stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	18,040
Stock option to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive net loss per share	5,801,170	5,034,210