Vor Biopharma (VOR) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Registrant Name	VOR BIOPHARMA INC.
Entity Central Index Key	0001817229
Entity File Number	001-39979
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-1591163
Entity Address, Address Line One	100 Cambridgepark Drive
Entity Address, Address Line Two	Suite 400
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02140
City Area Code	617
Local Phone Number	655-6580
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		37,289,504
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	VOR
Security Exchange Name	NASDAQ

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 143,034	$ 48,539
Investments	82,934
Prepaid expenses	5,355	467
Other current assets	749	100
Total current assets	232,072	49,106
Restricted cash equivalents	2,413	1,559
Property and equipment, net	5,990	4,728
Operating lease right-of-use assets	16,016	17,117
Other assets	2,141	3,398
Total assets	258,632	75,908
Current liabilities:
Accounts payable	1,957	2,361
Accrued expenses	5,676	6,260
Operating lease liability	1,147	863
Other current liabilities	430	723
Total current liabilities	9,210	10,207
Long-term liabilities:
Operating lease liabilities—non-current	16,465	17,430
Total liabilities	25,675	27,637
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value; 10,000,000 and 0 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 0 shares issued and outstanding as of September 30, 2021 and December 31, 2020
Common stock, $0.0001 par value; 400,000,000 and 420,000,000 shares authorized as of September 30, 2021 and December 31, 2020 respectively; 37,247,414 and 893,231 shares issued and 37,018,282 and 505,074 outstanding as of September 30, 2021 and December 31, 2020, respectively	4	1
Additional paid-in capital	344,824	2,158
Accumulated deficit	(111,871)	(61,224)
Total stockholders’ equity (deficit)	232,957	(59,065)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	$ 258,632	75,908
Series A-1 Redeemable Convertible Preferred Stock
Long-term liabilities:
Redeemable convertible preferred stock		2
Series A-2 Redeemable Convertible Preferred Stock
Long-term liabilities:
Redeemable convertible preferred stock		42,786
Series B Redeemable Convertible Preferred Stock
Long-term liabilities:
Redeemable convertible preferred stock		$ 64,548

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	420,000,000
Common stock, shares issued	37,247,414	893,231
Common stock, shares outstanding	37,018,282	505,074
Series A-1 Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	20,000,000
Redeemable convertible preferred stock, shares issued	0	20,000,000
Redeemable convertible preferred stock, shares outstanding	0	20,000,000
Redeemable convertible preferred stock, liquidation preference		$ 4,000
Series A-2 Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	107,194,866
Redeemable convertible preferred stock, shares issued	0	107,194,866
Redeemable convertible preferred stock, shares outstanding	0	107,194,866
Redeemable convertible preferred stock, liquidation preference		$ 42,878
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	211,778,825
Redeemable convertible preferred stock, shares issued	0	124,519,220
Redeemable convertible preferred stock, shares outstanding	0	124,519,220
Redeemable convertible preferred stock, liquidation preference		$ 64,750

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 12,925	$ 8,142	$ 34,836	$ 20,288
General and administrative	5,677	3,643	15,876	7,415
Total operating expenses	18,602	11,785	50,712	27,703
Loss from operations	(18,602)	(11,785)	(50,712)	(27,703)
Other income:
Interest income	48		65	29
Total other income	48		65	29
Net loss and comprehensive loss	(18,554)	(11,785)	(50,647)	(27,674)
Cumulative dividends on redeemable convertible preferred stock		(2,185)	(1,228)	(3,755)
Net loss attributable to common stockholders	$ (18,554)	$ (13,970)	$ (51,875)	$ (31,429)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.50)	$ (61.23)	$ (1.62)	$ (177.84)
Weighted-average common shares outstanding, basic and diluted	36,934,311	228,144	32,067,535	176,726

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Series A-1 Redeemable Convertible Preferred Stock	Series A-2 Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock
Beginning Balance at Dec. 31, 2019	$ (17,429)		$ 458	$ (17,887)
Beginning Balance, Shares at Dec. 31, 2019		119,936
Beginning Balance at Dec. 31, 2019					$ 2	$ 25,067
Beginning Balance, Shares at Dec. 31, 2019					20,000,000	62,819,866
Issuance of redeemable convertible preferred stock						$ 17,719
Issuance of redeemable convertible preferred stock, Shares						44,375,000
Issuance of common stock upon exercise of stock options	43		43
Issuance of common stock upon exercise of stock options, Shares		31,384
Stock-based compensation expense	112		112
Net loss	(7,849)			(7,849)
Ending Balance at Mar. 31, 2020	(25,123)		613	(25,736)
Ending Balance, Shares at Mar. 31, 2020		151,320
Ending Balance at Mar. 31, 2020					$ 2	$ 42,786
Ending Balance, Shares at Mar. 31, 2020					20,000,000	107,194,866
Beginning Balance at Dec. 31, 2019	(17,429)		458	(17,887)
Beginning Balance, Shares at Dec. 31, 2019		119,936
Beginning Balance at Dec. 31, 2019					$ 2	$ 25,067
Beginning Balance, Shares at Dec. 31, 2019					20,000,000	62,819,866
Net loss	(27,674)
Ending Balance at Sep. 30, 2020	(44,142)		1,419	(45,561)
Ending Balance, Shares at Sep. 30, 2020		277,724
Ending Balance at Sep. 30, 2020					$ 2	$ 42,786	$ 64,548
Ending Balance, Shares at Sep. 30, 2020					20,000,000	107,194,866	124,519,220
Beginning Balance at Mar. 31, 2020	(25,123)		613	(25,736)
Beginning Balance, Shares at Mar. 31, 2020		151,320
Beginning Balance at Mar. 31, 2020					$ 2	$ 42,786
Beginning Balance, Shares at Mar. 31, 2020					20,000,000	107,194,866
Issuance of redeemable convertible preferred stock							$ 64,548
Issuance of redeemable convertible preferred stock, Shares							124,519,220
Issuance of common stock upon exercise of stock options	17		17
Issuance of common stock upon exercise of stock options, Shares		13,990
Stock-based compensation expense	153		153
Net loss	(8,040)			(8,040)
Ending Balance at Jun. 30, 2020	(32,993)		783	(33,776)
Ending Balance, Shares at Jun. 30, 2020		165,310
Ending Balance at Jun. 30, 2020					$ 2	$ 42,786	$ 64,548
Ending Balance, Shares at Jun. 30, 2020					20,000,000	107,194,866	124,519,220
Issuance of common stock upon exercise of stock options	153		153
Issuance of common stock upon exercise of stock options, Shares		112,414
Stock-based compensation expense	483		483
Net loss	(11,785)			(11,785)
Ending Balance at Sep. 30, 2020	(44,142)		1,419	(45,561)
Ending Balance, Shares at Sep. 30, 2020		277,724
Ending Balance at Sep. 30, 2020					$ 2	$ 42,786	$ 64,548
Ending Balance, Shares at Sep. 30, 2020					20,000,000	107,194,866	124,519,220
Beginning Balance at Dec. 31, 2020	$ (59,065)	$ 1	2,158	(61,224)
Beginning Balance, Shares at Dec. 31, 2020	505,074	505,074
Beginning Balance at Dec. 31, 2020					$ 2	$ 42,786	$ 64,548
Beginning Balance, Shares at Dec. 31, 2020					20,000,000	107,194,866	124,519,220
Issuance of redeemable convertible preferred stock							$ 45,375
Issuance of redeemable convertible preferred stock, Shares							87,259,605
Conversion of redeemable convertible preferred stock into common stock upon closing of initial public offering					$ (2)	$ (42,786)	$ (109,923)
Conversion of redeemable convertible preferred stock into common stock upon closing of initial public offering, Shares					(20,000,000)	(107,194,866)	(211,778,825)
Conversion of redeemable convertible preferred stock into common stock upon closing of initial public offering	$ 152,711	$ 2	152,709
Conversion of redeemable convertible preferred stock into common stock upon closing of initial public offering, Shares		24,924,501
Issuance of common shares upon closing of initial public offering, net of offering costs and underwriter fees of $17,132	186,308	$ 1	186,307
Issuance of common shares upon closing of initial public offering, net of offering costs and underwriter fees, Shares		11,302,219
Issuance of common stock upon vesting and exercise of stock options	65		65
Issuance of common stock upon vesting and exercise of stock options, Shares		38,216
Stock-based compensation expense	891		891
Net loss	(13,723)			(13,723)
Ending Balance at Mar. 31, 2021	267,187	$ 4	342,130	(74,947)
Ending Balance, Shares at Mar. 31, 2021		36,770,010
Beginning Balance at Dec. 31, 2020	$ (59,065)	$ 1	2,158	(61,224)
Beginning Balance, Shares at Dec. 31, 2020	505,074	505,074
Beginning Balance at Dec. 31, 2020					$ 2	$ 42,786	$ 64,548
Beginning Balance, Shares at Dec. 31, 2020					20,000,000	107,194,866	124,519,220
Net loss	$ (50,647)
Ending Balance at Sep. 30, 2021	$ 232,957	$ 4	344,824	(111,871)
Ending Balance, Shares at Sep. 30, 2021	37,018,282	37,018,282
Ending Balance, Shares at Sep. 30, 2021					0	0	0
Beginning Balance at Mar. 31, 2021	$ 267,187	$ 4	342,130	(74,947)
Beginning Balance, Shares at Mar. 31, 2021		36,770,010
Issuance of common stock upon vesting and exercise of stock options	224		224
Issuance of common stock upon vesting and exercise of stock options, Shares		115,362
Stock-based compensation expense	1,067		1,067
Net loss	(18,370)			(18,370)
Ending Balance at Jun. 30, 2021	250,108	$ 4	343,421	(93,317)
Ending Balance, Shares at Jun. 30, 2021		36,885,372
Issuance of common stock upon vesting and exercise of stock options	249		249
Issuance of common stock upon vesting and exercise of stock options, Shares		132,910
Stock-based compensation expense	1,154		1,154
Net loss	(18,554)			(18,554)
Ending Balance at Sep. 30, 2021	$ 232,957	$ 4	$ 344,824	$ (111,871)
Ending Balance, Shares at Sep. 30, 2021	37,018,282	37,018,282
Ending Balance, Shares at Sep. 30, 2021					0	0	0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Statement of Stockholders' Equity [Abstract]
Issuance of common shares upon closing of initial public offering, offering costs and underwriter fees	$ 17,132

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (50,647)	$ (27,674)
Adjustments to reconcile net loss to net cash used in operations:
Depreciation expense	1,039	363
Non-cash lease expense	2,260	461
Stock-based compensation	3,112	748
Other	38
Changes in operating assets and liabilities:
Operating lease liability	(1,840)	545
Prepaid expenses and other current assets	(5,537)	(847)
Accounts payable and accrued expenses	333	3,746
Other assets	(315)
Net cash used in operating activities	(51,557)	(22,658)
Cash flow from investing activities
Purchases of investments	(82,972)
Purchases of property and equipment	(2,726)	(2,684)
Net cash used in investing activities	(85,698)	(2,684)
Cash flow from financing activities
Proceeds from issuance of redeemable convertible preferred stock	45,375	82,267
Proceeds from the issuance of common stock upon closing of initial public offering, net of underwriter fees	189,199
Payment of initial public offering costs	(2,215)
Proceeds from stock option exercises	245	213
Net cash provided by financing activities	232,604	82,480
Net increase in cash, cash equivalents and restricted cash equivalents	95,349	57,138
Cash, cash equivalents and restricted cash equivalents, beginning of period	50,098	8,025
Cash, cash equivalents and restricted cash equivalents, end of period	145,447	65,163
Supplemental disclosure of non-cash activities
Lease incentive paid by the landlord on behalf of the Company		151
Operating right-of-use assets and operating lease liability recorded upon lease commencement	35	17,899
Purchases of property and equipment in accounts payable	18	599
Conversion of redeemable convertible preferred stock to common stock upon closing of the initial public offering	$ 152,711
Deferred offering costs in accounts payable and accrued expenses		$ 355

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 143,034	$ 48,539	$ 63,604
Restricted cash equivalents	2,413	1,559	1,559
Total cash, cash equivalents and restricted cash equivalents as shown on the statements of cash flows	$ 145,447	$ 50,098	$ 65,163	$ 8,025

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Nature of the Business	1. Nature of the Business Vor Biopharma Inc. (the “Company”) is a clinical-stage cell and genome engineering company that combines a novel patient engineering approach with targeted therapies to provide a single company solution for patients suffering from hematological malignancies. The Company’s proprietary platform leverages its expertise in hematopoietic stem cell (“HSC”) biology, genome engineering and targeted therapy development to genetically modify HSCs to remove surface targets expressed by cancer cells. The Company is headquartered in Cambridge, Massachusetts. The Company was incorporated on December 30, 2015 . Initial Public Offering On February 9, 2021, the Company completed an initial public offering (“IPO”) of its common stock. At the closing of the IPO, the Company sold 11,302,219 shares of its common stock, at a public offering price of $ 18.00 per share. The Company received net proceeds of $ 186.3 million from the IPO, after deducting underwriters’ discounts and commissions and other offering expenses paid by the Company. Upon closing of the IPO, all shares of the Company’s Series A-1, A-2 and B redeemable convertible preferred stock then outstanding automatically converted into an aggregate of 24,924,501 shares of common stock. Upon conversion of the redeemable convertible preferred stock, the Company reclassified the carrying value of the redeemable convertible preferred stock to common stock and additional paid-in capital. In connection with the IPO, the Company filed an amended and restated certificate of incorporation that amended and restated the Company’s certificate of incorporation in its entirety to, among other things, authorize the Company to issue up to 400,000,000 shares of common stock, $ 0.0001 par value per share, and 10,000,000 shares of preferred stock, $ 0.0001 par value per share, all of which shares of preferred stock are undesignated and the rights and preferences of such preferred stock may be established by the Company’s board of directors from time to time. Reverse Stock Split On January 29, 2021, the Company effected a 13.6-for-1 reverse stock split of the Company’s common stock. All shares, stock options, and per share information in the condensed consolidated financial statements were previously adjusted to reflect the reverse stock split. There was no change in the par value and authorized number of shares of the Company’s common stock. Risks and Uncertainties The Company is subject to a number of risks common to development stage companies in the biotechnology industry, including, but not limited to, risks of failure of preclinical studies and clinical trials, dependence on key personnel, protection of proprietary technology, reliance on third party organizations, risks of obtaining regulatory approval for any product candidate that it may develop, development by competitors of technological innovations, compliance with government regulations, the impact of the COVID-19 pandemic, including impacts related to the variants of the virus, and the need to obtain additional financing. The Company anticipates that it will continue to incur significant operating losses for the next several years as it continues to develop its product candidates. The Company believes that its existing cash, cash equivalents and investments at September 30, 2021 will be sufficient to allow the Company to fund its current operations through at least a period of one year after the date the financial statements are issued.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Use of Estimates The preparation of the condensed consolidated financial statements in conformity with GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the condensed consolidated financial statements and the reported amount of expenses during the reporting period. Actual results could differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies in developing the estimates and assumptions that are used in the preparation of the condensed consolidated financial statements. Management must apply significant judgment in this process. Management’s estimation process often may yield a range of potentially reasonable estimates and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: estimating the fair value of the Company’s common stock (prior to the IPO); accrued expenses and research and development expenses. Investments Investments represent excess cash balances held in marketable debt securities and are classified as available-for-sale. Investments with maturities beyond one year may be classified as short-term based on their highly liquid nature and because such securities represent an investment of cash that is available for current operations. Available-for-sale investments are reported at fair value at each balance sheet date. Changes in the market value of available-for-sale investments, excluding other-than-temporary impairments, are reflected as other comprehensive income, a component of stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income in our condensed consolidated statements of operations and comprehensive loss. Investments are evaluated for other-than-temporary impairment at the end of each reporting period. Impairment is evaluated considering numerous factors, and their relative significance varies depending on the situation. Factors considered include whether a decline in fair value below the amortized cost basis is due to credit-related factors or non-credit-related factors, the financial condition and near-term prospects of the issuer, and our intent and ability to hold the investment to allow for an anticipated recovery in fair value. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded to other income (expense) and a new cost basis in the investment is established. Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents, restricted cash equivalents and investments. The Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company’s investments consist of money market funds and marketable debt securities, including corporate bonds and U.S. Treasury securities. The Company’s investments may include commercial paper and other debt securities of U.S. government agencies, corporate entities, and banks. The Company’s investment policy limits instruments to investment grade securities with high credit quality issuers with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations. Unaudited Interim Financial Information The condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation. 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 presentation of the results for the reported interim periods. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. The accompanying condensed consolidated balance sheet as of December 31, 2020 has been derived from the Company’s audited consolidated financial statements for the year ended December 31, 2020. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited interim condensed consolidated financial statements should be read in conjunction with the audited annual consolidated financial statements and notes in the Company's Annual Report on Form 10-K for the year ended December 31, 2020 (the “2020 Annual Report”). During the nine months ended September 30, 2021 , other than the addition of the investments accounting policy and disclosure of related credit risks, there have been no changes to the Company’s significant accounting policies as described in the 2020 Annual Report. Recent Accounting Pronouncements In 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740) : Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which introduces a number of amendments that are designed to simplify the application of accounting for income taxes. Such amendments include removing certain exceptions for intraperiod tax allocation, interim reporting when a year-to-date loss exceeds the anticipated loss, reflecting the effect of an enacted change in tax laws or rates in the annual effective tax rate and recognition of deferred taxes related to outside basis differences for ownership changes in investments. ASU 2019-12 also provides clarification related to when a step up in the tax basis of goodwill should be considered part of the business combination in which the book goodwill was originally recognized and when it should be considered a separate transaction. In addition, ASU 2019-12 provides guidance on the recognition of a franchise tax (or similar tax) that is partially based on income as an income-based tax and accounting for any incremental amount incurred as a non-income-based tax. The Company adopted ASU 2019-12 effective January 1, 2021 , and the adoption did not have a material impact on its interim condensed consolidated financial statements.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	3. Investments The amortized cost and estimated fair value of investments, by contractual maturity are as follows: September 30, 2021 (in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value Maturing in one year or less Corporate debt $ 1,406 $ — $ — $ 1,406 U.S. Treasuries 10,173 — — 10,173 Maturing after one year through five years Corporate debt 6,439 — — 6,439 U.S. Treasuries 64,916 — — 64,916 Total $ 82,934 $ — $ — $ 82,934

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: September 30, 2021 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 100,084 $ — $ — $ 100,084 Investments Corporate bonds — 7,845 — 7,845 U.S. Treasuries — 75,089 — 75,089 Total investments — 82,934 — 82,934 Restricted cash equivalents Money market funds 2,413 — — 2,413 Total $ 102,497 $ 82,934 $ — $ 185,431 December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Total Money market fund $ 41,036 $ — $ — $ 41,036 Total $ 41,036 $ — $ — $ 41,036 The fair value of the Company’s cash equivalents and restricted cash equivalents is based on quoted market prices in active markets with no valuation adjustment. The fair value of investments was determined based on observable market inputs. There were no transfers between levels from the year ended December 31, 2020 .

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following: September 30, December 31, (in thousands) 2021 2020 Furniture and equipment $ 108 $ 40 Laboratory equipment 7,451 5,247 Computer equipment 194 167 Property and equipment, gross 7,753 5,454 Accumulated depreciation ( 1,763 ) ( 726 ) Property and equipment, net $ 5,990 $ 4,728 Depreciation expense for the three and nine months ended September 30, 2021 was $ 0.3 million and $ 1.0 million, respectively, and for the three and nine months ended September 30, 2020 was $ 0.2 million and $ 0.4 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: September 30, December 31, (in thousands) 2021 2020 Employee-related and other expenses $ 3,841 $ 2,727 Research and development expenses 801 1,924 Professional fees 861 1,097 License and milestone fees — 450 Other 173 62 Total accrued expenses $ 5,676 $ 6,260

Equity

Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Equity	7 . Equity Redeemable Convertible Preferred Stock Prior to the IPO, the Company had issued Series A-1 redeemable convertible preferred stock (“Series A-1”), Series A-2 redeemable convertible preferred stock (“Series A-2”) and Series B redeemable convertible preferred stock (“Series B” and collectively with the Series A-1 and Series A-2, “Redeemable Convertible Preferred Stock”). Series A-2 Redeemable Convertible Preferred Stock Closing In February 2019 and 2020, the Company issued and sold 88,750,000 and 44,375,000 shares of Series A-2, respectively, at a purchase price of $ 0.40 per share for total gross cash proceeds of $ 35.6 million. Series B Redeemable Convertible Preferred Stock Closing In June 2020 and January 2021, the Company issued and sold 124,519,220 and 87,259,605 shares of Series B, respectively, at a purchase price of $ 0.52 per share for total gross cash proceeds of $ 110.1 million.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Stock Incentive Plan In December 2015, the Company’s board of directors adopted and approved the 2015 Stock Incentive Plan (as amended to date, the “2015 Plan”). The 2015 Plan provided for the granting of incentive stock options, non-statutory stock options, restricted stock awards and other stock-based awards to eligible employees, officers, directors, consultants and advisors as determined by the Company’s board of directors. In February 2021, the Company’s board of directors adopted and stockholders approved the 2021 Equity Incentive Plan (the “2021 Plan”). The 2021 Plan became effective on February 5, 2021, following which no further grants were or will be made under the 2015 Plan. The 2021 Plan provides for the grant of stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of stock compensation to our employees, consultants and directors. As of September 30, 2021, the Company had 2,480,665 shares of its common stock available for future issuance under the 2021 Plan. Stock Options The Company’s stock options generally vest over 48 months with 25 % vesting after one year followed by ratable monthly vesting over the remaining three years and have a contractual term of 10 years. The weighted-average assumptions used principally in determining the fair value of options granted were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair value of common stock $ 13.12 $ 2.87 $ 20.27 $ 2.73 Expected term (in years) 6.0 6.0 6.0 6.0 Expected volatility 76.0 % 77.2 % 78.8 % 77.0 % Risk-free interest rate 0.9 % 0.4 % 0.8 % 0.4 % Dividend yield — — — — During the nine months ended September 30, 2021 and 2020, the Company granted stock options to purchase 637,884 shares and 3,457,481 shares of its common stock, respectively, with aggregate grant date fair values of $ 8.7 million and $ 6.7 million, respectively. As of September 30, 2021, total unrecognized compensation expense related to stock options was $ 14.0 million, which is expected to be recognized over a weighted-average period of 2.69 years. As of September 30, 2021, options for 229,132 shares of Company common stock with a weighted average exercise price of $ 1.88 were exercised and unvested. The underlying proceeds from the unvested exercises of $ 0.4 million is recorded in other current liabilities on the condensed consolidated balance sheet. Stock-Based Compensation Stock-based compensation expense was allocated as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Research and development $ 630 $ 254 $ 1,621 $ 374 General and administrative 524 229 1,491 374 Total stock-based compensation expense $ 1,154 $ 483 $ 3,112 $ 748

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	9. Leases Cambridgepark Lease Amendments On June 15, 2021, the Company entered into the first lease amendment (“First Lease Amendment”) and second lease amendment (“Second Lease Amendment” and, together with the First Lease Amendment, the “Lease Amendments”) with PPF Off 100 Cambridge Park Drive, LLC (the “Landlord”). The Lease Amendments amended the Company’s lease agreement for its corporate office and laboratory facilities with the Landlord in Cambridge, Massachusetts to add additional leased space in the same building (the “Amended Cambridgepark Lease”). The First Lease Amendment expands the amount of space leased by the Company by an additional 10,262 square feet in exchange for aggregate total fixed rent payments of approximately $ 8.3 million with the annual fixed rental payments escalating from $ 0.9 million to $ 1.1 million during the term. The First Lease Amendment is estimated to commence during the first quarter of 2022 . The Second Lease Amendment expands the amount of space leased by the Company by an additional 30,175 square feet in exchange for aggregate total fixed rent payments of approximately $ 22.3 million with the annual fixed rental payments escalating from $ 1.2 million to $ 3.0 million during the term. The Second Lease Amendment’s term is estimated to commence during the first quarter of 2022 . Payments due associated with the Lease Amendments include fixed and variable payments. Variable payments relate to the Company’s share of the Landlord’s operating costs associated with the underlying assets and are recognized when the event on which those payments are assessed. The Amended Cambridgepark Lease does not contain a residual value guarantee. The Lease Amendments term end dates are coterminous with the existing lease agreement. In conjunction with the Lease Amendments, the Company was required to increase its irrevocable standby letter of credit to $ 2.4 million for the benefit of the Landlord, which has been secured by money market investments and is presented as restricted cash equivalents. For further information regarding the Company’s Cambridgepark lease, please see Note 10 to the condensed consolidated financial statements included in the 2020 Annual Report. The elements of lease expense were as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands except weighted-average amounts) 2021 2020 2021 2020 Operating lease cost $ 756 $ 748 $ 2,260 $ 1,033 Short-term lease cost — 67 52 308 Variable lease cost 342 1 776 90 Total lease cost $ 1,098 $ 816 $ 3,088 $ 1,431 The following table represents the weighted-average remaining lease term and discount rate information: (in thousands) September 30, 2021 December 31, 2020 Other Information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 1,840 $ 703 Right-of-use assets obtained in exchange for lease obligations 35 17,899 Weighted-average remaining lease term (years) 8.9 9.6 Weighted-average discount rate 9.4 % 9.4 % Right-of-use lease assets and lease liabilities are reported in the Company’s condensed consolidated balance sheets as follows: (in thousands) September 30, 2021 December 31, 2020 Assets Operating right-of-use assets $ 16,016 $ 17,117 Liabilities Operating lease liabilities, current $ 1,147 $ 863 Operating lease liabilities, non-current $ 16,465 $ 17,430 Total lease liabilities $ 17,612 $ 18,293

Significant Agreements

Significant Agreements	9 Months Ended
	Sep. 30, 2021
Significant Agreements [Abstract]
Significant Agreements	10. Significant Agreements Since December 31, 2020, there have been no material changes to the key terms of the Company’s license agreements. For further information regarding the Company’s existing license agreements, please see Note 11 to the condensed consolidated financial statements included in the 2020 Annual Report.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Loss Per Share The following table sets forth the computation of the Company’s basic and diluted net loss per share for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share amounts) 2021 2020 2021 2020 Numerator: Net loss $ ( 18,554 ) $ ( 11,785 ) $ ( 50,647 ) $ ( 27,674 ) Cumulative dividends on redeemable convertible preferred stock — ( 2,185 ) ( 1,228 ) ( 3,755 ) Net loss attributable to common stockholders $ ( 18,554 ) $ ( 13,970 ) $ ( 51,875 ) $ ( 31,429 ) Denominator: Weighted-average number of common shares outstanding, basic and diluted 36,934,311 228,144 32,067,535 176,726 Net loss per share attributable to common stockholders, basic and diluted $ ( 0.50 ) $ ( 61.23 ) $ ( 1.62 ) $ ( 177.84 ) As of the three and nine months ended September 30, 2021 and 2020, the Company’s potentially dilutive securities were redeemable convertible preferred stock and stock options. The Company excluded the following potential common shares from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect: As of September 30, 2021 2020 Series A-1 redeemable convertible preferred stock — 20,000,000 Series A-2 redeemable convertible preferred stock — 107,194,866 Series B redeemable convertible preferred stock — 124,519,220 Options to purchase common stock 5,405,773 4,638,208

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the condensed consolidated financial statements and the reported amount of expenses during the reporting period. Actual results could differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies in developing the estimates and assumptions that are used in the preparation of the condensed consolidated financial statements. Management must apply significant judgment in this process. Management’s estimation process often may yield a range of potentially reasonable estimates and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: estimating the fair value of the Company’s common stock (prior to the IPO); accrued expenses and research and development expenses.
Investments	Investments Investments represent excess cash balances held in marketable debt securities and are classified as available-for-sale. Investments with maturities beyond one year may be classified as short-term based on their highly liquid nature and because such securities represent an investment of cash that is available for current operations. Available-for-sale investments are reported at fair value at each balance sheet date. Changes in the market value of available-for-sale investments, excluding other-than-temporary impairments, are reflected as other comprehensive income, a component of stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income in our condensed consolidated statements of operations and comprehensive loss. Investments are evaluated for other-than-temporary impairment at the end of each reporting period. Impairment is evaluated considering numerous factors, and their relative significance varies depending on the situation. Factors considered include whether a decline in fair value below the amortized cost basis is due to credit-related factors or non-credit-related factors, the financial condition and near-term prospects of the issuer, and our intent and ability to hold the investment to allow for an anticipated recovery in fair value. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded to other income (expense) and a new cost basis in the investment is established.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents, restricted cash equivalents and investments. The Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company’s investments consist of money market funds and marketable debt securities, including corporate bonds and U.S. Treasury securities. The Company’s investments may include commercial paper and other debt securities of U.S. government agencies, corporate entities, and banks. The Company’s investment policy limits instruments to investment grade securities with high credit quality issuers with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation. 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 presentation of the results for the reported interim periods. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. The accompanying condensed consolidated balance sheet as of December 31, 2020 has been derived from the Company’s audited consolidated financial statements for the year ended December 31, 2020. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited interim condensed consolidated financial statements should be read in conjunction with the audited annual consolidated financial statements and notes in the Company's Annual Report on Form 10-K for the year ended December 31, 2020 (the “2020 Annual Report”). During the nine months ended September 30, 2021 , other than the addition of the investments accounting policy and disclosure of related credit risks, there have been no changes to the Company’s significant accounting policies as described in the 2020 Annual Report.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In 2019, the FASB issued ASU No. 2019-12 , Income Taxes (Topic 740) : Simplifying the Accounting for Income Taxes (“ASU 2019-12”), which introduces a number of amendments that are designed to simplify the application of accounting for income taxes. Such amendments include removing certain exceptions for intraperiod tax allocation, interim reporting when a year-to-date loss exceeds the anticipated loss, reflecting the effect of an enacted change in tax laws or rates in the annual effective tax rate and recognition of deferred taxes related to outside basis differences for ownership changes in investments. ASU 2019-12 also provides clarification related to when a step up in the tax basis of goodwill should be considered part of the business combination in which the book goodwill was originally recognized and when it should be considered a separate transaction. In addition, ASU 2019-12 provides guidance on the recognition of a franchise tax (or similar tax) that is partially based on income as an income-based tax and accounting for any incremental amount incurred as a non-income-based tax. The Company adopted ASU 2019-12 effective January 1, 2021 , and the adoption did not have a material impact on its interim condensed consolidated financial statements.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of Amortized Cost and Estimated Fair Value of Investments by Contractual Maturity	The amortized cost and estimated fair value of investments, by contractual maturity are as follows: September 30, 2021 (in thousands) Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Fair Value Maturing in one year or less Corporate debt $ 1,406 $ — $ — $ 1,406 U.S. Treasuries 10,173 — — 10,173 Maturing after one year through five years Corporate debt 6,439 — — 6,439 U.S. Treasuries 64,916 — — 64,916 Total $ 82,934 $ — $ — $ 82,934

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: September 30, 2021 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents Money market funds $ 100,084 $ — $ — $ 100,084 Investments Corporate bonds — 7,845 — 7,845 U.S. Treasuries — 75,089 — 75,089 Total investments — 82,934 — 82,934 Restricted cash equivalents Money market funds 2,413 — — 2,413 Total $ 102,497 $ 82,934 $ — $ 185,431 December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Total Money market fund $ 41,036 $ — $ — $ 41,036 Total $ 41,036 $ — $ — $ 41,036

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following: September 30, December 31, (in thousands) 2021 2020 Furniture and equipment $ 108 $ 40 Laboratory equipment 7,451 5,247 Computer equipment 194 167 Property and equipment, gross 7,753 5,454 Accumulated depreciation ( 1,763 ) ( 726 ) Property and equipment, net $ 5,990 $ 4,728

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
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) 2021 2020 Employee-related and other expenses $ 3,841 $ 2,727 Research and development expenses 801 1,924 Professional fees 861 1,097 License and milestone fees — 450 Other 173 62 Total accrued expenses $ 5,676 $ 6,260

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of Weighted-Average Assumptions Used Principally in Determining Fair Value of Options Granted	The weighted-average assumptions used principally in determining the fair value of options granted were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair value of common stock $ 13.12 $ 2.87 $ 20.27 $ 2.73 Expected term (in years) 6.0 6.0 6.0 6.0 Expected volatility 76.0 % 77.2 % 78.8 % 77.0 % Risk-free interest rate 0.9 % 0.4 % 0.8 % 0.4 % Dividend yield — — — —
Summary of Stock-Based Compensation Expense	Stock-based compensation expense was allocated as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Research and development $ 630 $ 254 $ 1,621 $ 374 General and administrative 524 229 1,491 374 Total stock-based compensation expense $ 1,154 $ 483 $ 3,112 $ 748

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Summary of Lease Expense	The elements of lease expense were as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands except weighted-average amounts) 2021 2020 2021 2020 Operating lease cost $ 756 $ 748 $ 2,260 $ 1,033 Short-term lease cost — 67 52 308 Variable lease cost 342 1 776 90 Total lease cost $ 1,098 $ 816 $ 3,088 $ 1,431
Summary of Weighted-Average Remaining Lease Term and Discount Rate	The following table represents the weighted-average remaining lease term and discount rate information: (in thousands) September 30, 2021 December 31, 2020 Other Information Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 1,840 $ 703 Right-of-use assets obtained in exchange for lease obligations 35 17,899 Weighted-average remaining lease term (years) 8.9 9.6 Weighted-average discount rate 9.4 % 9.4 %
Summary of Right-of-Use Assets and Lease Liabilities	Right-of-use lease assets and lease liabilities are reported in the Company’s condensed consolidated balance sheets as follows: (in thousands) September 30, 2021 December 31, 2020 Assets Operating right-of-use assets $ 16,016 $ 17,117 Liabilities Operating lease liabilities, current $ 1,147 $ 863 Operating lease liabilities, non-current $ 16,465 $ 17,430 Total lease liabilities $ 17,612 $ 18,293

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of the Company’s basic and diluted net loss per share for the three and nine months ended September 30, 2021 and 2020: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share amounts) 2021 2020 2021 2020 Numerator: Net loss $ ( 18,554 ) $ ( 11,785 ) $ ( 50,647 ) $ ( 27,674 ) Cumulative dividends on redeemable convertible preferred stock — ( 2,185 ) ( 1,228 ) ( 3,755 ) Net loss attributable to common stockholders $ ( 18,554 ) $ ( 13,970 ) $ ( 51,875 ) $ ( 31,429 ) Denominator: Weighted-average number of common shares outstanding, basic and diluted 36,934,311 228,144 32,067,535 176,726 Net loss per share attributable to common stockholders, basic and diluted $ ( 0.50 ) $ ( 61.23 ) $ ( 1.62 ) $ ( 177.84 )
Potential Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share	As of the three and nine months ended September 30, 2021 and 2020, the Company’s potentially dilutive securities were redeemable convertible preferred stock and stock options. The Company excluded the following potential common shares from the computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect: As of September 30, 2021 2020 Series A-1 redeemable convertible preferred stock — 20,000,000 Series A-2 redeemable convertible preferred stock — 107,194,866 Series B redeemable convertible preferred stock — 124,519,220 Options to purchase common stock 5,405,773 4,638,208

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Feb. 09, 2021USD ($)$ / sharesshares	Jan. 29, 2021	Mar. 31, 2021shares	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020$ / sharesshares
Nature Of Business [Line Items]
Incorporation date				Dec. 30, 2015
Net proceeds from issuance of IPO | $				$ 189,199
Common stock, shares authorized	400,000,000			400,000,000	420,000,000
Common stock, par value | $ / shares	$ 0.0001			$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000			10,000,000	0
Preferred stock, par value | $ / shares	$ 0.0001			$ 0.0001	$ 0.0001
Common Stock
Nature Of Business [Line Items]
Common stock shares sold			11,302,219
Net proceeds from issuance of IPO | $	$ 186,300
Common stock shares issued for conversion of redeemable convertible preferred stock	24,924,501		24,924,501
Stockholders' equity, reverse stock split				13.6-for-1 reverse stock split
Stockholders' equity, stock split, conversion ratio		0.0735
IPO | Common Stock
Nature Of Business [Line Items]
Common stock shares sold	11,302,219
Public offering price per share | $ / shares	$ 18

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Change in accounting principle, accounting standards update, adopted [true false]	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]	true
Accounting standards update [Extensible list]	us-gaap:AccountingStandardsUpdate201912Member

Investments - Summary of Amorti

Investments - Summary of Amortized Cost and Estimated Fair Value of Investments by Contractual Maturity (Details) $ in Thousands	Sep. 30, 2021USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 82,934
Fair Value	82,934
Maturing in One Year or Less | Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,406
Fair Value	1,406
Maturing in One Year or Less | U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	10,173
Fair Value	10,173
Maturing after One Year through Five Years | Corporate Debt
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,439
Fair Value	6,439
Maturing after One Year through Five Years | U.S. Treasuries
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	64,916
Fair Value	$ 64,916

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	$ 185,431	$ 41,036
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total		41,036
Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	82,934
Investments | Corporate Debt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	7,845
Investments | U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	75,089
Cash Equivalents | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	100,084
Restricted Cash Equivalents | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	2,413
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	102,497	41,036
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total		$ 41,036
Level 1 | Cash Equivalents | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	100,084
Level 1 | Restricted Cash Equivalents | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	2,413
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	82,934
Level 2 | Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	82,934
Level 2 | Investments | Corporate Debt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	7,845
Level 2 | Investments | U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	$ 75,089

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021USD ($)
Fair Value Disclosures [Abstract]
Fair value assets, level 1 to level 2 transfers amount	$ 0
Fair value assets, level 2 to level 1 transfers amount	0
Fair value assets, transfers into level 3	0
Fair value assets, transfers out of level 3	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 7,753	$ 5,454
Accumulated depreciation	(1,763)	(726)
Property and equipment, net	5,990	4,728
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	108	40
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,451	5,247
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 194	$ 167

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 300	$ 200	$ 1,039	$ 363

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee-related and other expenses	$ 3,841	$ 2,727
Research and development expenses	801	1,924
Professional fees	861	1,097
License and milestone fees		450
Other	173	62
Total accrued expenses	$ 5,676	$ 6,260

Equity - Additional Information

Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended			8 Months Ended	9 Months Ended		13 Months Ended
	Jan. 31, 2021	Jun. 30, 2020	Feb. 29, 2020	Feb. 28, 2019	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jan. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Feb. 29, 2020
Class Of Stock [Line Items]
Gross proceeds from stock issued									$ 45,375	$ 82,267
Series A-2
Class Of Stock [Line Items]
Redeemable convertible preferred stock, issued and sold			44,375,000	88,750,000			44,375,000
Redeemable convertible preferred stock, price per share											$ 0.40
Gross proceeds from stock issued											$ 35,600
Series B
Class Of Stock [Line Items]
Redeemable convertible preferred stock, issued and sold	87,259,605	124,519,220			87,259,605	124,519,220
Redeemable convertible preferred stock, price per share								$ 0.52
Gross proceeds from stock issued								$ 110,100

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Feb. 05, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	637,884	3,457,481
Aggregate grant date fair value of options granted	$ 8.7	$ 6.7
Unrecognized compensation expense related to stock options	$ 14
Unrecognized share based compensation expense, recognition period	2 years 8 months 8 days
Number unvested options	229,132
Weighted average exercise price of options exercised and unvested	$ 1.88
Proceeds from unvested options exercises	$ 0.4
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights description	vest over 48 months with 25% vesting after one year followed by ratable monthly vesting over the remaining three years
Vesting period	48 months
Contractual term	10 years
Tranche One | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	1 year
Vesting percentage	25.00%
Tranche Two | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
2021 Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future issuance	2,480,665
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future issuance			0

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used Principally in Determining Fair Value of Options Granted (Details) - Stock Options - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 13.12	$ 2.87	$ 20.27	$ 2.73
Expected term (in years)	6 years	6 years	6 years	6 years
Expected volatility	76.00%	77.20%	78.80%	77.00%
Risk-free interest rate	0.90%	0.40%	0.80%	0.40%
Dividend yield	0.00%	0.00%	0.00%	0.00%

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,154	$ 483	$ 3,112	$ 748
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	630	254	1,621	374
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 524	$ 229	$ 1,491	$ 374

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	Jun. 15, 2021USD ($)ft²
Standby Letters of Credit
Lessee Lease Description [Line Items]
Increase in irrevocable line of credit facility	$ 2.4
First Lease Amendment
Lessee Lease Description [Line Items]
Additional space leased | ft²	10,262
Aggregate total fixed rent payments	$ 8.3
Operating lease estimated to commence period	first quarter of 2022
Second Lease Amendment
Lessee Lease Description [Line Items]
Additional space leased | ft²	30,175
Aggregate total fixed rent payments	$ 22.3
Operating lease estimated to commence period	first quarter of 2022
Minimum | First Lease Amendment
Lessee Lease Description [Line Items]
Increase in annual fixed rental payments	$ 0.9
Minimum | Second Lease Amendment
Lessee Lease Description [Line Items]
Increase in annual fixed rental payments	1.2
Maximum | First Lease Amendment
Lessee Lease Description [Line Items]
Increase in annual fixed rental payments	1.1
Maximum | Second Lease Amendment
Lessee Lease Description [Line Items]
Increase in annual fixed rental payments	$ 3

Leases - Summary of Lease Expen

Leases - Summary of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 756	$ 748	$ 2,260	$ 1,033
Short-term lease cost		67	52	308
Variable lease cost	342	1	776	90
Total lease cost	$ 1,098	$ 816	$ 3,088	$ 1,431

Leases - Summary of Weighted-Av

Leases - Summary of Weighted-Average Remaining Lease Term and Discount Rate (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 1,840	$ 703
Right-of-use assets obtained in exchange for lease obligations	$ 35	$ 17,899
Weighted-average remaining lease term (years)	8 years 10 months 24 days	9 years 7 months 6 days
Weighted-average discount rate	9.40%	9.40%

Leases - Summary of Right-of-Us

Leases - Summary of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets
Operating right-of-use assets	$ 16,016	$ 17,117
Liabilities
Operating lease liabilities, current	1,147	863
Operating lease liabilities, non-current	16,465	17,430
Total lease liabilities	$ 17,612	$ 18,293

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (18,554)	$ (18,370)	$ (13,723)	$ (11,785)	$ (8,040)	$ (7,849)	$ (50,647)	$ (27,674)
Cumulative dividends on redeemable convertible preferred stock				(2,185)			(1,228)	(3,755)
Net loss attributable to common stockholders	$ (18,554)			$ (13,970)			$ (51,875)	$ (31,429)
Denominator:
Weighted-average number of common shares outstanding, basic and diluted	36,934,311			228,144			32,067,535	176,726
Net loss per share attributable to common stockholders, basic and diluted	$ (0.50)			$ (61.23)			$ (1.62)	$ (177.84)

Net Loss Per Share - Potential

Net Loss Per Share - Potential Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Series A-1 Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per share		20,000,000
Series A-2 Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per share		107,194,866
Series B Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per share		124,519,220
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from computation of diluted net loss per share	5,405,773	4,638,208