Tourmaline Bio (TRML) 10-Q 12 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 01, 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
Trading Symbol	TALS
Entity Registrant Name	TALARIS THERAPEUTICS, INC.
Entity Central Index Key	0001827506
Current Fiscal Year End Date	--12-31
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		41,354,643
Entity Current Reporting Status	Yes
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Entity File Number	001-40384
Entity Tax Identification Number	83-2377352
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	570 S. Preston St
Entity Address, City or Town	Louisville
Entity Address, State or Province	KY
Entity Address, Postal Zip Code	40202
City Area Code	502
Local Phone Number	398-9250

Balance Sheets (Unaudited)

Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 27,311	$ 17,589
Marketable securities	227,423	131,899
Prepaid and other current assets	3,493	1,263
Total current assets	258,227	150,751
Property and equipment, net	2,994	2,013
Other assets	104	14
Total assets	261,325	152,778
Current liabilities:
Accounts payable	1,182	767
Accrued expenses	3,800	2,637
Total current liabilities	4,982	3,404
Share repurchase liability	694	996
Contingent stock liability		373
Total liabilities	5,676	4,774
Commitments and contingencies (Note 8)
Convertible preferred stock
Total convertible preferred stock		186,151
Stockholders’ deficit
Common stock, $0.0001 par value, 140,000,000 voting shares authorized and 39,562,723 shares issued and outstanding and 10,000,000 non-voting shares authorized and 1,150,000 issued and outstanding as of September 30, 2021 and 36,366,101 shares authorized and 7,087,130 issued and outstanding as of December 31, 2020	4	1
Additional paid-in-capital	332,222	4,879
Accumulated deficit	(76,606)	(43,014)
Accumulated other comprehensive income (loss)	29	(13)
Total stockholders’ equity (deficit)	255,649	(38,147)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 261,325	152,778
Series A Convertible Preferred Stock
Convertible preferred stock
Total convertible preferred stock		37,383
Series A-1 Convertible Preferred Stock
Convertible preferred stock
Total convertible preferred stock		34,272
Series B Convertible Preferred Stock
Convertible preferred stock
Total convertible preferred stock		$ 114,496

Balance Sheets (Unaudited) (Par

Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized		36,366,101
Common stock, shares issued		7,087,130
Common stock, shares outstanding		7,087,130
Series A Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	40,000,000
Preferred stock, shares issued	0	40,000,000
Preferred stock, shares outstanding	0	40,000,000
Preferred stock. liquidation preference		$ 40,000
Series A-1 Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	28,000,000
Preferred stock, shares issued	0	28,000,000
Preferred stock, shares outstanding	0	28,000,000
Preferred stock. liquidation preference		$ 35,000
Series B Convertible Preferred Stock
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	0	62,499,993
Preferred stock, shares issued	0	62,499,993
Preferred stock, shares outstanding	0	62,499,993
Preferred stock. liquidation preference		$ 114,994
Voting Shares
Common stock, shares authorized	140,000,000
Common stock, shares issued	39,562,723
Common stock, shares outstanding	39,562,723
Non-voting Shares
Common stock, shares authorized	10,000,000
Common stock, shares issued	1,150,000
Common stock, shares outstanding	1,150,000

Statements of Operations and Co

Statements of Operations and Comprehensive Loss (Unaudited) - 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	$ 9,183	$ 3,956	$ 23,655	$ 10,896
General and administrative	3,874	2,182	9,464	4,953
Total operating expenses	13,057	6,138	33,119	15,849
Loss from operations	(13,057)	(6,138)	(33,119)	(15,849)
Interest and other income (expense), net	116	(279)	(473)	(79)
Net loss	(12,941)	(6,417)	(33,592)	(15,928)
Unrealized (loss) gain on marketable securities	(5)	(12)	42	8
Total other comprehensive loss	(12,946)	(6,429)	(33,550)	(15,920)
Total comprehensive loss	(12,946)	(6,429)	(33,550)	(15,920)
Net loss attributable to common stockholders	$ (12,941)	$ (6,417)	$ (33,592)	$ (15,928)
Net loss per common share, basic and diluted	$ (0.32)	$ (0.94)	$ (1.33)	$ (2.44)
Weighted average number of common shares outstanding used in computation of net loss per common share, basic and diluted	40,669,412	6,823,163	25,190,479	6,537,820

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series A-1 Convertible Preferred Stock	Series B Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2019	$ (17,102)				$ 1	$ 3,204	$ (20,307)
Beginning balance, shares at Dec. 31, 2019		40,000,000	16,000,000
Beginning balance at Dec. 31, 2019		$ 37,383	$ 19,307
Beginning balance, shares at Dec. 31, 2019					6,390,137
Stock-based compensation expense	123					123
Net loss	(4,848)						(4,848)
Unrealized loss on marketable securities	13							$ 13
Ending balance at Mar. 31, 2020	(21,814)				$ 1	3,327	(25,155)	13
Ending balance, shares at Mar. 31, 2020		40,000,000	16,000,000
Ending balance at Mar. 31, 2020		$ 37,383	$ 19,307
Ending balance, shares at Mar. 31, 2020					6,390,137
Beginning balance at Dec. 31, 2019	(17,102)				$ 1	3,204	(20,307)
Beginning balance, shares at Dec. 31, 2019		40,000,000	16,000,000
Beginning balance at Dec. 31, 2019		$ 37,383	$ 19,307
Beginning balance, shares at Dec. 31, 2019					6,390,137
Net loss	(15,928)
Unrealized loss on marketable securities	8
Ending balance at Sep. 30, 2020	(32,042)				$ 1	4,184	(36,235)	8
Ending balance, shares at Sep. 30, 2020		40,000,000	28,000,000	62,499,993
Ending balance at Sep. 30, 2020		$ 37,383	$ 34,276	$ 114,496
Ending balance, shares at Sep. 30, 2020					6,985,928
Beginning balance at Dec. 31, 2019	(17,102)				$ 1	3,204	(20,307)
Beginning balance, shares at Dec. 31, 2019		40,000,000	16,000,000
Beginning balance at Dec. 31, 2019		$ 37,383	$ 19,307
Beginning balance, shares at Dec. 31, 2019					6,390,137
Net loss	(22,700)
Ending balance at Dec. 31, 2020	(38,147)				$ 1	4,879	(43,014)	(13)
Ending balance, shares at Dec. 31, 2020		40,000,000	28,000,000	62,499,993
Ending balance at Dec. 31, 2020	$ 186,151	$ 37,383	$ 34,272	$ 114,496
Ending balance, shares at Dec. 31, 2020	7,087,130				7,087,130
Beginning balance at Mar. 31, 2020	$ (21,814)				$ 1	3,327	(25,155)	13
Beginning balance, shares at Mar. 31, 2020		40,000,000	16,000,000
Beginning balance at Mar. 31, 2020		$ 37,383	$ 19,307
Beginning balance, shares at Mar. 31, 2020					6,390,137
Issuance of common stock upon exercise of stock options	25					25
Issuance of common stock upon exercise of stock options, shares					26,530
Stock-based compensation expense	119					119
Net loss	(4,663)						(4,663)
Unrealized loss on marketable securities	7							7
Ending balance at Jun. 30, 2020	(26,326)				$ 1	3,471	(29,818)	20
Ending balance, shares at Jun. 30, 2020		40,000,000	16,000,000
Ending balance at Jun. 30, 2020		$ 37,383	$ 19,307
Ending balance, shares at Jun. 30, 2020					6,416,667
Issuance of common stock upon exercise of stock options	526					526
Issuance of common stock upon exercise of stock options, shares					569,261
Issuance of Preferred Stock upon exercise of stock options, net of issuance costs			$ 14,969	$ 114,496
Issuance of Preferred Stock upon exercise of stock options, net of issuance costs, shares			12,000,000
Stock-based compensation expense	187					187
Net loss	(6,417)						(6,417)
Unrealized loss on marketable securities	(12)							(12)
Ending balance at Sep. 30, 2020	(32,042)				$ 1	4,184	(36,235)	8
Ending balance, shares at Sep. 30, 2020		40,000,000	28,000,000	62,499,993
Ending balance at Sep. 30, 2020		$ 37,383	$ 34,276	$ 114,496
Ending balance, shares at Sep. 30, 2020					6,985,928
Issuance of Preferred Stock upon exercise of stock options, net of issuance costs, shares				62,499,993
Issuance of Preferred Stock upon exercise of stock options, net of issuance costs, shares		40,000,000	28,000,000	62,499,993
Beginning balance at Dec. 31, 2020	(38,147)				$ 1	4,879	(43,014)	(13)
Beginning balance, shares at Dec. 31, 2020		40,000,000	28,000,000	62,499,993
Beginning balance at Dec. 31, 2020	$ 186,151	$ 37,383	$ 34,272	$ 114,496
Beginning balance, shares at Dec. 31, 2020	7,087,130				7,087,130
Issuance of common stock upon exercise of stock options	$ 123					123
Issuance of common stock upon exercise of stock options, shares					117,181
Stock-based compensation expense	835					835
Net loss	(9,299)						(9,299)
Unrealized loss on marketable securities	22							22
Ending balance at Mar. 31, 2021	(46,466)				$ 1	5,837	(52,313)	9
Ending balance, shares at Mar. 31, 2021		40,000,000	28,000,000	62,499,993
Ending balance at Mar. 31, 2021		$ 37,383	$ 34,272	$ 114,496
Ending balance, shares at Mar. 31, 2021					7,204,311
Beginning balance at Dec. 31, 2020	(38,147)				$ 1	4,879	(43,014)	(13)
Beginning balance, shares at Dec. 31, 2020		40,000,000	28,000,000	62,499,993
Beginning balance at Dec. 31, 2020	$ 186,151	$ 37,383	$ 34,272	$ 114,496
Beginning balance, shares at Dec. 31, 2020	7,087,130				7,087,130
Issuance of common stock upon exercise of stock options, shares	65,600
Net loss	$ (33,592)
Unrealized loss on marketable securities	42
Ending balance at Sep. 30, 2021	255,649				$ 4	332,222	(76,606)	29
Ending balance, shares at Sep. 30, 2021		0	0	0
Ending balance, shares at Sep. 30, 2021					40,712,723
Beginning balance at Mar. 31, 2021	(46,466)				$ 1	5,837	(52,313)	9
Beginning balance, shares at Mar. 31, 2021		40,000,000	28,000,000	62,499,993
Beginning balance at Mar. 31, 2021		$ 37,383	$ 34,272	$ 114,496
Beginning balance, shares at Mar. 31, 2021					7,204,311
Issuance of common stock, net of underwriting discounts and issuance costs	137,166				$ 1	137,165
Issuance of common stock, net of underwriting discounts and issuance costs, shares					8,825,000
Conversion of convertible preferred stock to common stock, value		$ (37,383)	$ (34,272)	$ (114,496)
Conversion of convertible preferred stock to common stock, shares		(40,000,000)	(28,000,000)	(62,499,993)
Conversion of convertible preferred stock to common stock, value	186,151				$ 2	186,149
Conversion of convertible preferred stock to common stock, shares					24,392,498
Issuance of contingent common stock, value	831					831
Issuance of contingent common stock, shares					48,889
Issuance of common stock upon exercise of stock options	102					102
Issuance of common stock upon exercise of stock options, shares					100,436
Stock-based compensation expense	896					896
Net loss	(11,352)						(11,352)
Unrealized loss on marketable securities	25							25
Ending balance at Jun. 30, 2021	267,353				$ 4	330,980	(63,665)	34
Ending balance, shares at Jun. 30, 2021					40,571,134
Issuance of common stock upon exercise of stock options	188					188
Issuance of common stock upon exercise of stock options, shares					141,589
Stock-based compensation expense	1,054					1,054
Net loss	(12,941)						(12,941)
Unrealized loss on marketable securities	(5)							(5)
Ending balance at Sep. 30, 2021	$ 255,649				$ 4	$ 332,222	$ (76,606)	$ 29
Ending balance, shares at Sep. 30, 2021		0	0	0
Ending balance, shares at Sep. 30, 2021					40,712,723
Issuance of Preferred Stock upon exercise of stock options, net of issuance costs, shares		0	0	0

Statements of Convertible Pre_2

Statements of Convertible Preferred Stock and Stockholders' Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2020
Net of underwriting discounts and issuance costs		$ 12,858,764
Series A-1 Convertible Preferred Stock
Net of underwriting discounts and issuance costs			$ 31
Series B Convertible Preferred Stock
Net of underwriting discounts and issuance costs	$ 500		$ 476

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (12,941)		$ (6,417)	$ (33,592)	$ (15,928)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization				435	322
Accretion and amortization of marketable securities, net				378	(131)
Stock-based compensation expense				2,784	429
Fair value adjustment of contingent stock liability		$ 360	310	735	311
Other					(4)
Changes in operating assets and liabilities:
Prepaid and other current assets				(2,229)	905
Other assets				(92)	6
Accounts payable				210	94
Accrued expenses				1,213	434
Net cash used in operating activities				(30,158)	(13,562)	$ (19,200)
Cash flows from investing activities:
Purchases of property and equipment				(1,248)	(1,037)
Purchases of marketable securities				(210,789)	(51,124)
Maturities of marketable securities				114,929	23,224
Net cash used in investing activities				(97,108)	(28,937)
Cash flows from financing activities:
Proceeds from issuance of common stock				139,523
Payment of partial settlement of contingent stock liability				(277)
Proceeds from exercise of stock options				111	1,647
Net cash provided by financing activities				136,988	131,647
Net increase (decrease) in cash and cash equivalents				9,722	89,148
Cash and cash equivalents at beginning of period		$ 17,589		17,589	38,978	38,978
Cash and cash equivalents at end of period	$ 27,311		$ 128,126	27,311	128,126	$ 17,589
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment additions included in accounts payable and accrued expenses				252	78
Preferred stock issuance costs included in accounts payable and accrued expenses					508
Issuance of shares of common stock in partial settlement of contingent stock liability				831
Preferred Stock A
Cash flows from financing activities:
Proceeds from issuance of Preferred Stock					15,000
Preferred Stock B
Cash flows from financing activities:
Proceeds from issuance of Preferred Stock					$ 115,000
Common Stock
Cash flows from financing activities:
Stock issuance costs				$ (2,369)

Nature of Business and Liquidit

Nature of Business and Liquidity	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business and Liquidity	1. Nature of Business and Liquidity Talaris Therapeutics, Inc. (“Talaris” or the “Company”) is a late-clinical stage, cell therapy company developing an innovative method of allogeneic hematopoietic stem cell transplantation (“allo-HSCT”), called Facilitated Allo-HSCT Therapy, that the Company believes has the potential to transform the standard of care in solid organ transplantation, certain severe autoimmune diseases and certain severe non-malignant blood, immune and metabolic disorders. The Company believes that these indications, individually and collectively, represent a significant unmet need and commercial opportunity. The Company maintains corporate offices in Boston, Massachusetts, a laboratory in Houston, Texas and its cell processing facility in Louisville, Kentucky. Initial Public Offering The Company completed an initial public offering (“IPO”) on May 11, 2021 in which the Company issued and sold 8,825,000 shares of its common stock at a public offering price of $17.00 per share. The Company’s aggregate gross proceeds from the sale of shares in the IPO was $150.0 million before underwriting discounts and commissions and other expenses of approximately $12.9 million. Upon completion of the offering, the Company’s outstanding convertible preferred stock was automatically converted into shares of common stock and non-voting common stock. Following the IPO, there were no shares of preferred stock outstanding. Prior to the IPO, on April 30, 2021, the Company’s board of directors and shareholders approved a one-for-5.35 Liquidity The accompanying financial statements have been prepared assuming that the Company will continue as a going concern. Management has evaluated whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. Since its inception, the Company has incurred net losses and negative cash flows from operations. During the nine months ended September 30, 2021 and the year ended December 31, 2020, the Company incurred a net loss of $33.6 million and $22.7 million, respectively, and used $30.2 million and $19.2 million in cash for operations, respectively. In addition, as of September 30, 2021, the Company had an accumulated deficit of $76.6 million. The Company expects to continue to generate operating losses and negative cash flows for the foreseeable future. The Company currently expects the cash and cash equivalents of $27.3 million and marketable securities of $227.4 million as of September 30, 2021, will be sufficient to fund its operating expenses and capital requirements for more than 12 months from the date the financial statements are available to be issued. Additional funding will be needed to finance future clinical, pre-clinical, manufacturing and commercial activities. There is no assurance the Company will be successful in obtaining such additional financing on terms acceptable to it, if at all, and it may not be able to enter into other arrangements. If the Company is unable to obtain funding, it could be forced to delay, reduce or eliminate our research and development programs, portfolio expansion or commercialization efforts, which could adversely affect its business prospects and ability to continue operations. The Company is subject to risks common to companies in the biopharmaceutical industry. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for its intellectual property will be maintained, that any products developed will obtain required regulatory approval, or that any approved products will be commercially viable. Even if the development efforts are successful, it is uncertain when, if ever, the Company will generate significant product sales and ultimately net income. Coronavirus Pandemic In March 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. The worldwide COVID-19 pandemic has affected and may affect in the future the Company’s ability to initiate and complete preclinical studies, delay the initiation and completion of its current and planned clinical trials, disrupt regulatory activities or have other adverse effects on its business, results of operations, financial condition and prospects. In addition, the pandemic has caused substantial disruption in the financial markets and may adversely impact economies worldwide, both of which could adversely affect the Company’s business, operations and ability to raise funds to support its operations. The Company cannot be certain what the overall impact of the COVID-19 pandemic will be on its business, and it has the potential to adversely affect its business, financial condition, results of operations and prospects.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Summary Of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions, and estimates that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of financial statements, and the reported amounts of income and expense during the reporting period. The most significant estimates relate to the determination of the fair value of stock option grants and estimates related to the amount of prepaid and accrued research and development expenses as of the balance sheet date. For periods presented prior to the Company’s IPO, significant estimates were used in the determination of the fair value of the Company’s common stock. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, and makes adjustments when the facts and circumstances dictate. These estimates are based on information available as of the date of the financial statements; therefore, actual results could differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of September 30, 2021 and December 31, 2020, cash and cash equivalents consisted primarily of checking and savings deposits, money market fund holdings, and commercial paper. Marketable Securities The Company classifies its marketable securities as available-for-sale securities, which are carried at their fair value based on the quoted market prices of the securities. Unrealized gains and losses are reported as accumulated other comprehensive loss, a separate component of stockholders’ deficit. Realized gains and losses on available-for-sale securities are included in net loss in the period earned or incurred. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Equipment and furniture and fixtures are depreciated over five or seven year lives. Leasehold improvements are amortized over the shorter of the lease term or the five-year Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist primarily of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset exceeds the fair value of the asset. No impairments have been identified as of September 30, 2021 and December 31, 2020. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. The Company’s investment policy includes guidelines regarding the quality of the financial institutions and financial instruments and defines allowable investments that it believes minimizes the exposure to concentration of credit risk. The Company may invest in money market funds (minimum of $1 billion in assets), U.S. Treasury securities, corporate debt, bank debt, U.S. government-related agency securities, other sovereign debt, municipal debt and commercial paper. These deposits may exceed federally insured limits. The Company has not experienced any losses historically in these accounts and believes that it is not exposed to significant credit risk as its deposits are held at financial institutions that management believes to be of high credit quality. Fair Value of Financial Instruments Fair value is defined as the price that the Company would receive to sell an investment in a timely transaction or pay to transfer a liability in a timely transaction with an independent buyer in the principal market, or in the absence of a principal market, the most advantageous market for the investment or liability. A framework is used for measuring fair value utilizing a three-tier hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 investments) and the lowest priority to unobservable inputs (Level 3 investments). The three levels of the fair value hierarchy are as follows: • Level 1 inputs: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; • Level 2 inputs: Quoted prices in markets that are not considered to be active or financial instrument valuations for which all significant inputs are observable, either directly or indirectly; and, • Level 3 inputs: Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. Financial instruments are categorized in their entirety based on the lowest level of input that is significant to the fair value measurement. The assessment of the significance of a particular input to the fair value measurement requires judgment and considers factors specific to the investment. The Company’s money market funds and marketable securities are carried at fair value determined according to the fair value hierarchy described above (Level 1 and Level 2, respectively). The Company’s contingent stock liability as of Research and Development Expenses Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organization agreements, investigational sites, and consultants; (iii) the cost of acquiring, developing, and manufacturing clinical study materials; (iv) costs associated with preclinical and clinical activities and regulatory operations; (v) costs incurred in development of intellectual property; and (vi) an allocated portion of facilities and other infrastructure costs associated with our research and development activities. Costs incurred in connection with research and development activities are expensed as incurred. The Company enters into consulting, research, and other agreements with commercial entities, researchers, universities, and others for the provision of goods and services. Such arrangements are generally cancelable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the respective vendors, including the Company’s clinical sites. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved, and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly. Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees, nonemployees, and directors based on the fair value on the date of the grant and recognizes stock-based compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock option awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company’s policy is to account for forfeitures when they occur. The Company classifies stock-based compensation expense in its statement of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recently completed its IPO and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the US Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero because the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. Prior to the Company’s IPO, the Company considered the estimated fair value of the common stock as of the measurement date in determining the exercise price for options granted. The estimated fair value of the common stock was determined at each grant date based upon a variety of factors, including the illiquid nature of the common stock, arm’s-length sales of the Company’s capital stock (including convertible preferred stock), the effect of the rights and preferences of the preferred shareholders, and the prospects of a liquidity event. Among other factors are the Company’s financial position and historical financial performance, forecasted future operations of the Company, an evaluation or benchmark of the Company’s competition, and the current business climate in the marketplace. Significant changes to the key assumptions underlying the factors used could result in different fair values of common stock at each valuation date. The fair value for options granted since the Company’s IPO are based on the closing stock price on grant date. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. These reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. The Company had no significant uncertain tax positions as of September 30, 2021 and December 31, 2020. Basic and Diluted Net Loss Per Share The Company calculates basic and diluted net loss per share using the two-class method. The two-class method requires income available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s Series A convertible preferred stock, Series A-1 convertible preferred stock and Series B convertible preferred stock are participating securities. These participating securities do not contractually require the holders of such shares to participate in the Company’s losses. As such, net losses for the years presented were not allocated to the Company’s participating securities. Accordingly, basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the dilutive effects of potentially dilutive securities outstanding during the period. Potentially dilutive securities include vested and unexercised stock options, restricted stock issued upon early exercise of stock options, convertible preferred shares and contingent stock liabilities. The dilutive effect of stock options and contingent stock liabilities are computed using the treasury stock method and the dilutive effect of convertible preferred shares is calculated using the if-converted method. The Company has generated a net loss for all periods presented, therefore diluted net loss per share is the same as basic net loss per share since the inclusion of potentially dilutive securities would be anti-dilutive. Segments Operating segments are defined as components of an entity for which separate financial information is made available and is regularly evaluated by the chief operating decision maker (“CODM”) in making decisions regarding resource allocation and assessing performance. The Company’s CODM is the chief executive officer and operations are managed as a single segment for the purposes of assessing performance and making operating decisions. Comprehensive Loss Comprehensive loss represents net loss for the period plus the results of certain other changes in stockholders’ equity (deficit). The Company’s comprehensive loss included unrealized gains related to marketable securities for the three and nine months ended September 30, 2021 and 2020. Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments—Credit Losses In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (ASC 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis and indicates the fair value hierarchy of the inputs the Company utilized to determine such fair value (in thousands) September 30, 2021 Total Level 1 Level 2 Level 3 Financial assets: Money market funds (cash equivalents) $ 23,385 $ 23,385 $ — $ — Marketable securities 227,423 15,173 212,250 — Total financial assets measured at fair value $ 250,808 $ 38,558 $ 212,250 $ — December 31, 2020 Total Level 1 Level 2 Level 3 Financial assets: Money market funds (cash equivalents) $ 13,943 $ 13,943 $ — $ — Marketable securities 131,899 11,169 120,730 — Total financial assets measured at fair value $ 145,842 $ 25,112 $ 120,730 $ — Financial liabilities: Contingent stock liability $ 373 $ — $ — $ 373 Total financial liabilities measured at fair value $ 373 $ — $ — $ 373 The contingent stock liability in the table above represents the fair value of contingent equity consideration equal to 65,186 shares of common stock contingently issuable to the University of Louisville Research Foundation Inc. (“ULRF”) in connection with its amended and restated exclusive license agreement with the Company. In conjunction with the Company’s IPO, the Company issued 48,889 shares of common stock and paid the cash equivalent fair value of 16,297 shares, or $0.3 million, to ULRF in May 2021 (see Note 8). A rollforward of the contingent common stock liability, which is measured at fair value for the three and nine months ended September 30, 2021 and 2020, is represented as follows (in thousands) Fair value as of January 1, 2020 $ 63 Change in fair value — Fair value as of March 31, 2020 63 Change in fair value — Fair value as of June 30, 2020 63 Change in fair value 310 Fair value as of September 30, 2020 $ 373 Fair value as of January 1, 2021 $ 373 Change in fair value 360 Fair value as of March 31, 2021 733 Change in fair value 375 Share issuance in partial settlement of contingent stock (831 ) Cash payment in partial settlement of contingent stock (277 ) Fair value as of June 30, 2021 — Change in fair value — Fair value as of September 30, 2021 $ — Valuation techniques used to measure fair value maximize the use of relevant observable inputs and minimize the use of unobservable inputs. Prior to the Company’s IPO, the Company’s contingent stock liability was classified within Level 3 of the fair value hierarchy because its fair value measurement is based, in part, on significant inputs not observed in the market, which incorporates assumptions and estimates to value the Company’s common stock. As there was no public market for the Company’s common stock prior to May 2021, the estimated fair value was determined by the Company’s board of directors with input from management, considering the most recently available third-party valuations of common stock, and the board of directors’ assessment of additional objective and subjective factors that it believed were relevant and which may have changed from the date of each valuation. Historically, these third-party valuations of the Company’s common stock were performed contemporaneously when events occurred which management believed would have an impact on the valuation of the Company. The Company’s common stock valuation was prepared using the option-pricing method, (“OPM”), which uses a market approach to estimate enterprise value. The fair value of the Company’s common stock used to value the contingent stock liability as of September 30, 2020 and December 31, 2020 was $5.72

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2021
Marketable Securities [Abstract]
Marketable Securities	4. Marketable Securities The fair value of the Company’s marketable securities as of September 30, 2021 and December 31, 2020 is based on level 1 and level 2 inputs. The Company’s investments consist mainly of U.S. government and agency securities, government-sponsored bond obligations and certain other corporate debt securities. Fair value is determined by taking into consideration valuations obtained from third-party pricing services. The third-party pricing services utilize industry standard valuation models, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities; issuer credit spreads; benchmark securities; and other observable inputs. There were no transfers between levels within the hierarchy during the nine months ended September 30, 2021 and the year ended December 31, 2020. The Company has assessed U.S. government treasuries as level 1 and all other marketable securities as level 2 within the fair value hierarchy of ASC 820. The Company classifies its entire investment portfolio as available-for-sale as defined in ASC 320, Debt Securities . Securities are carried at fair value with the unrealized gains (losses) reported in other comprehensive loss. As of September 30, 2021 and December 31, 2020, none of the Company’s investments were determined to be other than temporarily impaired. The following table summarizes the Company’s investments (in thousands) September 30, 2021 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial paper $ 191,184 $ 29 $ (1 ) $ 191,212 Government and agency securities 25,189 5 (1 ) 25,193 Corporate debt securities 11,021 — (3 ) 11,018 Total $ 227,394 $ 34 $ (5 ) $ 227,423 December 31, 2020 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial paper $ 73,331 $ 3 $ (10 ) $ 73,324 Corporate debt securities 33,319 1 (11 ) 33,309 Government and agency securities 25,262 4 — 25,266 Total $ 131,912 $ 8 $ (21 ) $ 131,899

Prepaid and Other Current Asset

Prepaid and Other Current Assets	9 Months Ended
	Sep. 30, 2021
Prepaid Expense And Other Assets Current [Abstract]
Prepaid and Other Current Assets	5. Prepaid and Other Current Assets Prepaid and other current assets consisted of the following (in thousands) September 30, December 31, 2021 2020 Prepaid insurance $ 1,891 $ 102 Prepaid research and development expenses 748 702 Other current assets 854 459 Total prepaid and other current assets $ 3,493 $ 1,263

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands) September 30, December 31, 2021 2020 Equipment $ 3,404 $ 2,666 Computer equipment 800 264 Leasehold improvements 643 580 Construction in progress 479 491 Furniture and fixtures 346 255 Total property and equipment 5,672 4,256 Less accumulated depreciation (2,678 ) (2,243 ) Property and equipment, net $ 2,994 $ 2,013 Depreciation expense was $0.4 million and $0.4 million for the nine months ended September 30, 2021 and the year ended December 31, 2020, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities Current [Abstract]
Accrued Expenses	7. Accrued Expenses Accrued expenses consisted of the following (in thousands) September 30, December 31, 2021 2020 Compensation and benefit costs $ 2,211 $ 1,400 Research and development expenses 912 788 Professional fees, consulting and other 677 449 Total accrued expenses $ 3,800 $ 2,637

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Leases The Company currently has six active lease agreements for office and laboratory space and related equipment. The primary lease is located on the University of Louisville campus in Louisville, Kentucky (the “Louisville Lease”). This lease has a termination date in November 2023 December 2021 The Company maintains a lease for office space in Wellesley, Massachusetts, that had an original termination date in March 2021 April 2021 In July 2021, the Company entered into a lease agreement for laboratory space in Houston, Texas. The agreement has a term of five months with the option to extend on a month-to-month basis at the end of the original term. The Company plans to utilize the space under this lease on a temporary basis while construction of a permanent lease is completed. In July 2021, the Company entered into a second lease agreement for laboratory space in Houston, Texas (the “Houston Lease”). The Houston Lease commencement date will be the later of September 2021 or the date the landlord substantially completes agreed-upon renovations. The term of the lease will be 36 months from the commencement date. The Houston lease had not commenced as of September 30, 2021. The future minimum rent payments relating to all six of the Company’s facility operating leases under the terms and conditions existing as of September 30, 2021, as well as amendments the Company has entered into between the date of these financial statements and the date they were available to be issued (as described in Note 13), are summarized as follows (in thousands) Years Ending December 31, 2021 $ 188 2022 $ 909 2023 $ 1,066 2024 $ 931 2025 and beyond $ 1,130 Total $ 4,224 The Company incurred rent expense of $0.5 million and $0.4 million for the nine months ended September 30, 2021 and 2020, respectively. License Agreement In October 2018, the Company entered an amended and restated exclusive license agreement with ULRF related to certain licensed patent rights and know-how related to human facilitating cells for its Facilitated Allo-HSCT Therapy approach. Pursuant to the ULRF License Agreement, ULRF granted the Company an exclusive, worldwide license under such patents and a nonexclusive royalty-bearing, worldwide license for such know-how to research, develop, commercialize and manufacture FCR001 and products containing FCR001 in all fields, without limitation. ULRF also granted the Company the right to grant sublicenses in accordance with the ULRF License Agreement. Under the terms of the agreement, the Company is obligated to compensate ULRF three percent of net sales of all licensed products sold, one third of any non-royalty sublicensing income, and up to $1.625 million in regulatory and sales milestones on each licensed product upon the occurrence of specific events as outlined in the license agreement; and annual license maintenance fees. In addition, upon execution of the ULRF License Agreement, the Company granted contingent equity consideration equal to 65,186 shares of common stock to ULRF. Pursuant to the ULRF License Agreement, on or prior to the Company’s first underwritten public offering or any transaction that is treated as a deemed liquidation event, the Company is required to either issue to ULRF the 65,186 shares in common stock or make a cash payment equal to the 65,186 shares of common stock multiplied by either the price per share of common stock in the underwritten public offering or by the price per share of common stock received in connection with such deemed liquidation event. Coincident with the completion of the Company’s IPO, the Company issued 48,889 shares of common stock to ULRF and provided a cash payment of approximately $0.3 million in lieu of issuing the remaining 16,297 shares of common stock. As of September 30, 2021, the contingent stock liability was fully satisfied. As of December 31, 2020, the Company measured the fair value of the contingent equity consideration and recorded a contingent stock liability of $0.4 million in other liabilities (see Note 3). The Company incurred $0.1 million in expense in February 2021 related to an annual maintenance fee pursuant to the license agreement for the year ended December 31, 2021. The Company incurred a $0.1 million milestone payment to ULRF in June 2020 which was recorded as research and development expense. The Company also incurred $0.1 million in expense in February 2020 related to the annual maintenance fee for the year ended December 31, 2020. Legal Proceedings The Company is not currently a party to any material legal proceedings. At each reporting date, the Company evaluates whether a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to its legal proceedings.

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2021
Convertible Preferred Stock [Abstract]
Convertible Preferred Stock	9. Convertible Preferred Stock Issuances of Convertible Preferred Stock In November 2018, the Company issued 22,500,000 shares of Series A Convertible Preferred Stock at $1.00 per share for gross cash proceeds of $22.5 million. The Company incurred issuance costs of $2.0 million, which have been recorded as a reduction to the value of Series A Convertible Preferred Stock in mezzanine equity in the accompanying balance sheets. In connection with the initial issuance of the Series A Convertible Preferred Stock, the purchasers received the right to purchase, and the Company had the obligation to sell, additional shares of Series A Convertible Preferred Stock at $1.00 per share and a unit, comprised of one share of Series A-1 Convertible Preferred Stock and one product interest right (each a “Unit”), at $1.25 per Unit (together, the “Tranche Rights”) upon achieving certain milestones related to the Company’s research and clinical developments in a series of tranches (the “Tranche 2,” “Tranche 3,” and “Tranche 4”) milestones. In December 2019, the Tranche 2 milestone was met and the Company issued an additional 17,500,000 shares of Series A Convertible Preferred Stock at $1.00 per share for gross cash proceeds of $17,500,000 and 16,000,000 Units (consisting of 16,000,000 shares of Series A-1 Convertible Preferred Stock and 16,000,000 shares of product interest rights) at $1.25 per Unit for gross cash proceeds of $20.0 million. The Company incurred issuance costs of $1.3 million in relation to Tranche 2, which have been recorded as a reduction to the value of Series A-1 Convertible Preferred Stock in mezzanine equity in the accompanying balance sheets. In August 2020, the holders of Series A-1 Convertible Preferred Stock voted to amend the Preferred Stock and Unit Purchase Agreement (“SPA”) and waive the requirements of the Tranche 3 milestone. The Company issued an additional 12,000,000 Units (consisting of 12,000,000 shares of Series A-1 Convertible Preferred stock and 12,000,000 shares of product interest rights) at $1.25 per Unit for gross cash proceeds of $15.0 million. In September 2020, the Company issued 62,499,993 shares of Series B Convertible Preferred Stock at $1.84 per share for gross cash proceeds of $115.0 million. The Company incurred issuance costs of $0.5 million in relation to the issuance of Series B Convertible Preferred Stock, which have been recorded as a reduction to the value of Series B Convertible Preferred Stock in mezzanine equity in the accompanying balance sheets. In conjunction with the Series B Convertible Preferred Stock financing in September 2020, all holders of the Company’s preferred stock entered into an amendment to the SPA to terminate all rights, liabilities and obligations in respect to the Tranche 4 milestone. Tranche Rights The Company determined that the Tranche Rights did not meet the definition of a freestanding financial instrument because the Tranche Rights are not legally detachable from the initial Series A Convertible Preferred Stock issued. The Company made this determination due to the express prohibition of the transfer of the Tranche Rights. Further, the Company determined that the Tranche Rights do not meet the definition of an embedded derivative that would require bifurcation from the initial Series A Preferred Stock issued. Therefore, at the initial issuance of the Series A Convertible Preferred Stock in November 2018, there was no separate recognition of the Tranche Rights. Product Interest Rights After the first commercial sale of product, the product interest right entitles the holders to a product interest payment for each product interest right held equal to 1/48,000,000 multiplied by 9% of net product sales on a territory-by-territory basis. If the Company enters into a license of rights to develop and/or commercialize a product, the holder is entitled to a product interest payment for each product interest right equal to 1/48,000,000 multiplied by 30% of licensing income. If the holder does not participate or events occur in which the holder transfers its ownership, it must determine to transfer either its shares or the unit purchase right. If the holder elects to receive a product interest payment, then a corresponding total number of Series A-1 Convertible Preferred Stock initially underlying a Unit (the “Unit Share”), will be canceled and forfeited. The total number of Unit Shares canceled and forfeited will be determined by dividing the product interest payment received by the fair value of the Unit Share at such time. The product interest right payment term shall commence upon the first commercial sale of product, on a territory-by-territory basis, and continue until the fifteenth anniversary thereafter, or any earlier date that there are no remaining product interest rights outstanding. If at any time, the Unit is transferred, the holder must elect to transfer either (i) the Unit Share underlying the Unit or (ii) the product interest right underlying the Unit. If the holder elects to transfer the Unit Share, the corresponding product interest right underlying the Unit shall be automatically canceled, forfeited, and extinguished for no consideration. If the holder elects to transfer the product interest right, the corresponding Unit Share unit shall be automatically canceled and forfeited for no consideration. The Company determined the product interest rights did not meet the definition of a freestanding financial instrument because the product interest rights are not legally detachable or separately exercisable from the Unit Shares. Further, the Company determined that the product interest rights do not meet the definition of an embedded derivative that would require bifurcation from the Unit Share. Therefore, upon issuance of Units in December 2019, there was no separate recognition of the product interest rights. In March 2021, the Company entered into a termination agreement with the holders of Series A and Series A-1 Convertible Preferred Stock to terminate the Product Interest Rights Agreement between the parties effective immediately prior to, but subject to the closing of the Company’s initial public offering. The termination agreement cancelled all product interest rights associated with the Series A-1 Convertible Preferred Stock. There was no value offered in exchange for the cancellation. Rights and Privileges of Convertible Preferred Stock The rights and privileges of the Series A, Series A-1 and Series B Convertible Preferred Stock (together, “Convertible Preferred Stock”) are as follows: Voting Rights —The holders of each series of Convertible Preferred Stock are entitled to vote on all matters and shall have the number of votes equal to the number of shares of common stock into which the preferred stock is convertible. Dividends —The Company shall not declare, pay, or set aside any dividends on shares of any other class or series of capital stock (other than dividends on shares of common stock payable in shares of common stock), unless the holders of the Convertible Preferred Stock receive a dividend on each outstanding share of Convertible Preferred Stock in an amount at least equal to (i) in the case of a dividend on common stock or any class or series that is convertible into common stock, that dividend per share of Convertible Preferred Stock as would equal the product of (A) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common stock and (B) the number of shares of common stock issuable upon conversion of a share of the applicable series of Convertible Preferred Stock or (ii) in the case of a dividend on any class or series that is not convertible into common stock, at a rate per share of the applicable series of Convertible Preferred Stock determined by (A) dividing the amount of the dividend payable on each share of such class or series of capital stock by the original issuance price of such class or series of capital stock and (B) multiplying such fraction by an amount equal to the original issue price of the applicable series of Convertible Preferred Stock. No dividends were declared or paid during the nine months ended September 30, 2021 and the year ended December 31, 2020. Liquidation Preference —In the event of any voluntary or involuntary liquidation, dissolution, or winding-up of the Company, the holders of shares of Convertible Preferred Stock will receive, in preference to any distribution to the holders of common stock an amount per share equal to the greater of ( i ) the applicable original issue price of such series of Convertible Preferred Stock, plus any dividends declared but unpaid thereon, or (ii) such amount per share as would have been payable had all shares of Convertible Preferred Stock been converted into common stock immediately prior to such liquidation, dissolution, winding-up, or deemed liquidation event. If upon any such liquidation, dissolution, or winding-up of the Company or deemed liquidation event, the assets available for distribution to the Company’s stockholders are not sufficient to pay the holders of Convertible Preferred Stock the full amount to which they shall be entitled, the holders of Convertible Preferred Stock shall share ratably in any distribution of the assets available for distribution in proportion to the respective amounts, which would otherwise be payable in respect of the shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full. In the event of a deemed liquidation event, if the Company does not effect a dissolution within 90 days after such deemed liquidation event, each holder of Convertible Preferred Stock has the right to require the redemption of such shares, and if voting together as a majority, has the right to require redemption of all outstanding Convertible Preferred Stock in accordance with the liquidation preferences afforded to holders of the Convertible Preferred Stock. Any shares of Convertible Preferred Stock that are redeemed or otherwise acquired by the Company or any of its subsidiaries be automatically and immediately canceled and retired and shall not be reissued, sold, or transferred. Neither the Company nor any of its subsidiaries may exercise any voting or other rights granted to the holders of Convertible Preferred Stock following redemption. A Deemed Liquidation Event shall include a merger or consolidation (other than one in which the capital stock of the Company outstanding immediately prior to such merger or consolidation continue to represent a majority by voting power of the capital stock of the surviving corporation) or a sale, lease, transfer, exclusive license, or other disposition of all or substantially all of the assets of the Company. Conversion Conversion Ratio —Each share of Convertible Preferred Stock shall be convertible, at the option of the holder thereof, at any time into such number of fully paid and nonassessable shares of common stock as is determined by dividing the applicable original issue price by the applicable conversion price (Series A original issue price is $1.00 per share and applicable conversion price is $5.35 per share; Series A-1 original issue price is $1.25 and applicable conversion price is $6.69 per share; Series B original issue price is $1.84 per share and applicable conversion price is $9.84 per share), subject to adjustment in the case of termination or fractional shares. Mandatory Conversion —All outstanding shares of Convertible Preferred Stock are automatically convertible based upon either (a) the closing of a firm-commitment underwritten public offering in which the aggregate gross proceeds to the Company of at least $60,000,000 of gross proceeds to the Company and have an offering price to the public of at least $9.84 per share or (b) the vote or written consent of holders of at least a majority of the Convertible Preferred Stock outstanding at that time with respect to the conversion of the Convertible Preferred Stock then all outstanding shares of Convertible Preferred Stock shall automatically be converted into shares of common stock at the then effective conversion rate and such shares may not be reissued

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Common Stock	10. Common Stock Common Stock On April 30, 2021, the Company’s stockholders approved the third amended and restated certificate of incorporation of the Company, which included the authorization of 10,000,000 shares of undesignated preferred stock with a par value of $0.0001, authorization of 140,000,000 shares of voting common stock and 10,000,000 shares of non-voting common stock. As of September 30, 2021, no undesignated preferred stock was outstanding. Common Stock Reserved The number of shares of common stock that have been reserved for the potential conversion of Preferred Stock, outstanding stock options granted and stock options available for grant under the Company’s 2021 Stock Option and Incentive Plan (the “2021 Plan”) and the 2018 Equity Incentive Plan (the “2018 Plan”) and shares reserved for issuance under the Company’s 2021 Employee Stock Purchase Plan (the “2021 ESPP”) are as follows: September 30, December 31, 2021 2020 Conversion of Series A Preferred Stock — 7,476,632 Conversion of Series A-1 Preferred Stock — 5,233,637 Conversion of Series B Preferred Stock — 11,682,229 Restricted stock related to early exercise of common stock options 638,676 932,279 Outstanding common stock options 3,694,768 2,745,185 Shares reserved for issuance under equity incentive plans 2,736,134 1,143,820 Shares reserved for issuance under the 2021 Employee Stock Purchase Plan 852,971 — Contingent stock — 65,186 Total 7,922,549 29,278,968

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. Stock-Based Compensation 2021 Employee Stock Purchase Plan In April 2021, the Company’s board of directors and stockholders approved the 2021 ESPP. The 2021 ESPP became effective immediately prior to the effectiveness of the Company’s registration statement on Form S-1 for its IPO. The 2021 ESPP provides employees the opportunity to purchase shares at a 15% discount at the lower of the share price at the beginning or end of six-month st Equity Incentive Plans In April 2021, the Company’s board of directors and stockholders approved the 2021 Plan and terminated the 2018 Plan with respect to any unissued awards. The 2021 Plan became effective immediately prior to the effectiveness of the Company’s registration statement on Form S-1 for its IPO. The 2021 Plan provides for the issuance of up to 3,015,907 new share-based awards, as well as the 3,381,382 options to purchase common stock then outstanding under the 2018 Plan, for a total of 6,397,289 shares. To the extent outstanding options granted under the 2018 Plan are cancelled, forfeited, or otherwise terminated without being exercised and would otherwise have been returned to the share reserve under the 2018 Plan, the number of shares underlying such awards will be available for future grant under the 2021 Plan. As of September 30, 2021, 2,736,134 shares remained available for future grant under the 2021 Plan. 3,619,997 options were outstanding under the 2021 Plan and 2018 Plan as of September 30, 2021. The Company’s 2021 Plan provides for the Company to sell or issue common stock or restricted common stock or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, nonemployees and members of the board of directors of the Company. The 2021 Plan is administered by the board of directors or at the discretion of the board of directors by the compensation committee of the board. The exercise prices, vesting periods, and other restrictions are determined at the discretion of the compensation committee of the board of directors, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the contractual term of stock option may not be greater than 10 years. Stock options granted to date typically vest over four years. Stock Option Valuation The assumptions used to determine the fair values of stock options granted to employees and directors under the 2021 Plan and 2018 Plan are presented as follows: Nine months ended September 30, 2021 2020 Fair value of common stock $5.72 - $16.80 $0.96 - $3.90 Dividend yield — — Volatility 80.60% - 91.25% 72.80% Risk-free interest rate 0.50% - 1.07% 0.31% - 1.46% Expected term (years) 6.25 5.00 - 6.25 Summary of Option Activity The Company’s stock option activity regarding employees, directors, and nonemployees is summarized as follows ( in thousands excepts share and per share amounts) Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate intrinsic value Options outstanding—December 31, 2020 2,745,185 $ 4.20 9.40 $ 4,183 Granted 1,034,622 8.92 Exercised (65,600 ) 1.69 Cancelled (1,335 ) 1.45 Forfeited (18,104 ) 6.14 Options outstanding—September 30, 2021 3,694,768 $ 5.56 8.91 $ 29,574 Options exercisable—September 30, 2021 770,020 $ 3.38 8.29 Options vested and expected to vest—September 30, 2021 1,830,144 $ 2.00 7.82 Additional information with regard to stock option activity involving employees and directors is as follows ( in thousands except per share amounts) Nine months ended September 30, 2021 2020 Weighted-average grant-date fair value per option of total options granted $ 6.49 $ 1.37 Aggregate intrinsic value of stock options exercised 610 236 As of September 30, 2021, total unrecognized compensation cost related to the unvested awards to employees, directors, and nonemployees is $12.0 million, which is expected to be recognized over a weighted-average period of 3.2 years. Stock-Based Compensation The Company recorded stock-based compensation expense regarding its employees, directors, and nonemployees as follows (in thousands) Three months ended September 30, Nine months ended September 30, 2021 2020 2021 2020 Research and development expense $ 568 $ 61 $ 1,311 $ 142 General and administrative expense 486 126 1,474 287 Total $ 1,054 $ 187 $ 2,785 $ 429

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	12. Net Loss Per Share Attributable to Common Stockholders Net Loss Per Share The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts Three months ended September 30, Nine months ended September 30, 2021 2020 2021 2020 Net loss and net loss attributable to common stockholders $ (12,941 ) $ (6,417 ) $ (33,592 ) $ (15,928 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.32 ) $ (0.94 ) $ (1.33 ) $ (2.44 ) Weighted average number of common shares outstanding used in computation of net loss per common share, basic and diluted 40,669,412 6,823,163 25,190,479 6,537,820 The Company’s potential dilutive securities, which include convertible preferred stock, contingent stock liabilities, restricted stock related to early exercise of common stock options and common stock options, have been excluded from the computation of diluted net loss per share as the effect would be antidilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential dilutive securities, presented on an as converted basis, were excluded from the calculation of net loss per share due to their anti-dilutive effect: Nine months ended September 30, 2021 2020 Convertible preferred shares (as converted to common stock and non-voting common stock) — 24,392,498 Options to purchase common stock 3,694,768 1,083,662 Restricted stock related to early exercise of options to purchase common stock 638,676 1,031,834 Contingent common stock (as converted to common stock) — 65,186 4,333,444 26,573,180

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events The Company has evaluated subsequent events through November 12, 2021, the date the financial statements were available to be issued. The Company has concluded no subsequent events have occurred that require disclosure, except for those referenced below. Leases In November 2021, the Company entered into an amended lease agreement for office space in Wellesley, Massachusetts on substantially the same terms as reflected in Note 8, but for an alternative office location within the same building. The term of the lease under this amendment shall commence on the later of the date the landlord delivers the leased premises to the Company with improvements completed or April 1, 2022. The term of the lease is 39 months from the commencement date. The future minimum rent payments for the lease noted above have been included in the disclosures in Note 8.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Summary Of Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions, and estimates that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of financial statements, and the reported amounts of income and expense during the reporting period. The most significant estimates relate to the determination of the fair value of stock option grants and estimates related to the amount of prepaid and accrued research and development expenses as of the balance sheet date. For periods presented prior to the Company’s IPO, significant estimates were used in the determination of the fair value of the Company’s common stock. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, and makes adjustments when the facts and circumstances dictate. These estimates are based on information available as of the date of the financial statements; therefore, actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of September 30, 2021 and December 31, 2020, cash and cash equivalents consisted primarily of checking and savings deposits, money market fund holdings, and commercial paper.
Marketable Securities	Marketable Securities The Company classifies its marketable securities as available-for-sale securities, which are carried at their fair value based on the quoted market prices of the securities. Unrealized gains and losses are reported as accumulated other comprehensive loss, a separate component of stockholders’ deficit. Realized gains and losses on available-for-sale securities are included in net loss in the period earned or incurred.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Equipment and furniture and fixtures are depreciated over five or seven year lives. Leasehold improvements are amortized over the shorter of the lease term or the five-year
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist primarily of property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset exceeds the fair value of the asset. No impairments have been identified as of September 30, 2021 and December 31, 2020.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. The Company’s investment policy includes guidelines regarding the quality of the financial institutions and financial instruments and defines allowable investments that it believes minimizes the exposure to concentration of credit risk. The Company may invest in money market funds (minimum of $1 billion in assets), U.S. Treasury securities, corporate debt, bank debt, U.S. government-related agency securities, other sovereign debt, municipal debt and commercial paper. These deposits may exceed federally insured limits. The Company has not experienced any losses historically in these accounts and believes that it is not exposed to significant credit risk as its deposits are held at financial institutions that management believes to be of high credit quality.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as the price that the Company would receive to sell an investment in a timely transaction or pay to transfer a liability in a timely transaction with an independent buyer in the principal market, or in the absence of a principal market, the most advantageous market for the investment or liability. A framework is used for measuring fair value utilizing a three-tier hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 investments) and the lowest priority to unobservable inputs (Level 3 investments). The three levels of the fair value hierarchy are as follows: • Level 1 inputs: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; • Level 2 inputs: Quoted prices in markets that are not considered to be active or financial instrument valuations for which all significant inputs are observable, either directly or indirectly; and, • Level 3 inputs: Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. Financial instruments are categorized in their entirety based on the lowest level of input that is significant to the fair value measurement. The assessment of the significance of a particular input to the fair value measurement requires judgment and considers factors specific to the investment. The Company’s money market funds and marketable securities are carried at fair value determined according to the fair value hierarchy described above (Level 1 and Level 2, respectively). The Company’s contingent stock liability as of
Research and Development Expenses	Research and Development Expenses Research and development expenses include (i) employee-related expenses, including salaries, benefits, travel and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organization agreements, investigational sites, and consultants; (iii) the cost of acquiring, developing, and manufacturing clinical study materials; (iv) costs associated with preclinical and clinical activities and regulatory operations; (v) costs incurred in development of intellectual property; and (vi) an allocated portion of facilities and other infrastructure costs associated with our research and development activities. Costs incurred in connection with research and development activities are expensed as incurred. The Company enters into consulting, research, and other agreements with commercial entities, researchers, universities, and others for the provision of goods and services. Such arrangements are generally cancelable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided by the respective vendors, including the Company’s clinical sites. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved, and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.
Stock-Based Compensation	Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees, nonemployees, and directors based on the fair value on the date of the grant and recognizes stock-based compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock option awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company’s policy is to account for forfeitures when they occur. The Company classifies stock-based compensation expense in its statement of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recently completed its IPO and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the US Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero because the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. Prior to the Company’s IPO, the Company considered the estimated fair value of the common stock as of the measurement date in determining the exercise price for options granted. The estimated fair value of the common stock was determined at each grant date based upon a variety of factors, including the illiquid nature of the common stock, arm’s-length sales of the Company’s capital stock (including convertible preferred stock), the effect of the rights and preferences of the preferred shareholders, and the prospects of a liquidity event. Among other factors are the Company’s financial position and historical financial performance, forecasted future operations of the Company, an evaluation or benchmark of the Company’s competition, and the current business climate in the marketplace. Significant changes to the key assumptions underlying the factors used could result in different fair values of common stock at each valuation date. The fair value for options granted since the Company’s IPO are based on the closing stock price on grant date.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions. These reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as a component of income tax expense. The Company had no significant uncertain tax positions as of September 30, 2021 and December 31, 2020.
Basic and Diluted Net Loss Per Share	Basic and Diluted Net Loss Per Share The Company calculates basic and diluted net loss per share using the two-class method. The two-class method requires income available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s Series A convertible preferred stock, Series A-1 convertible preferred stock and Series B convertible preferred stock are participating securities. These participating securities do not contractually require the holders of such shares to participate in the Company’s losses. As such, net losses for the years presented were not allocated to the Company’s participating securities. Accordingly, basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by dividing the net loss by the sum of the weighted average number of common shares outstanding during the period plus the dilutive effects of potentially dilutive securities outstanding during the period. Potentially dilutive securities include vested and unexercised stock options, restricted stock issued upon early exercise of stock options, convertible preferred shares and contingent stock liabilities. The dilutive effect of stock options and contingent stock liabilities are computed using the treasury stock method and the dilutive effect of convertible preferred shares is calculated using the if-converted method. The Company has generated a net loss for all periods presented, therefore diluted net loss per share is the same as basic net loss per share since the inclusion of potentially dilutive securities would be anti-dilutive.
Segments	Segments Operating segments are defined as components of an entity for which separate financial information is made available and is regularly evaluated by the chief operating decision maker (“CODM”) in making decisions regarding resource allocation and assessing performance. The Company’s CODM is the chief executive officer and operations are managed as a single segment for the purposes of assessing performance and making operating decisions.
Comprehensive Loss	Comprehensive Loss Comprehensive loss represents net loss for the period plus the results of certain other changes in stockholders’ equity (deficit). The Company’s comprehensive loss included unrealized gains related to marketable securities for the three and nine months ended September 30, 2021 and 2020.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments—Credit Losses In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (ASC 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on Recurring Basis	The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis and indicates the fair value hierarchy of the inputs the Company utilized to determine such fair value (in thousands) September 30, 2021 Total Level 1 Level 2 Level 3 Financial assets: Money market funds (cash equivalents) $ 23,385 $ 23,385 $ — $ — Marketable securities 227,423 15,173 212,250 — Total financial assets measured at fair value $ 250,808 $ 38,558 $ 212,250 $ — December 31, 2020 Total Level 1 Level 2 Level 3 Financial assets: Money market funds (cash equivalents) $ 13,943 $ 13,943 $ — $ — Marketable securities 131,899 11,169 120,730 — Total financial assets measured at fair value $ 145,842 $ 25,112 $ 120,730 $ — Financial liabilities: Contingent stock liability $ 373 $ — $ — $ 373 Total financial liabilities measured at fair value $ 373 $ — $ — $ 373
Schedule of Contingent Common Stock Liability Measured at Fair Value	A rollforward of the contingent common stock liability, which is measured at fair value for the three and nine months ended September 30, 2021 and 2020, is represented as follows (in thousands) Fair value as of January 1, 2020 $ 63 Change in fair value — Fair value as of March 31, 2020 63 Change in fair value — Fair value as of June 30, 2020 63 Change in fair value 310 Fair value as of September 30, 2020 $ 373 Fair value as of January 1, 2021 $ 373 Change in fair value 360 Fair value as of March 31, 2021 733 Change in fair value 375 Share issuance in partial settlement of contingent stock (831 ) Cash payment in partial settlement of contingent stock (277 ) Fair value as of June 30, 2021 — Change in fair value — Fair value as of September 30, 2021 $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2021
Marketable Securities [Abstract]
Summary of Company's Investments	The following table summarizes the Company’s investments (in thousands) September 30, 2021 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial paper $ 191,184 $ 29 $ (1 ) $ 191,212 Government and agency securities 25,189 5 (1 ) 25,193 Corporate debt securities 11,021 — (3 ) 11,018 Total $ 227,394 $ 34 $ (5 ) $ 227,423 December 31, 2020 Amortized Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Commercial paper $ 73,331 $ 3 $ (10 ) $ 73,324 Corporate debt securities 33,319 1 (11 ) 33,309 Government and agency securities 25,262 4 — 25,266 Total $ 131,912 $ 8 $ (21 ) $ 131,899

Prepaid and Other Current Ass_2

Prepaid and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Prepaid Expense And Other Assets Current [Abstract]
Summary of Prepaid and Other Current Assets	Prepaid and other current assets consisted of the following (in thousands) September 30, December 31, 2021 2020 Prepaid insurance $ 1,891 $ 102 Prepaid research and development expenses 748 702 Other current assets 854 459 Total prepaid and other current assets $ 3,493 $ 1,263

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 (in thousands) September 30, December 31, 2021 2020 Equipment $ 3,404 $ 2,666 Computer equipment 800 264 Leasehold improvements 643 580 Construction in progress 479 491 Furniture and fixtures 346 255 Total property and equipment 5,672 4,256 Less accumulated depreciation (2,678 ) (2,243 ) Property and equipment, net $ 2,994 $ 2,013

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities Current [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands) September 30, December 31, 2021 2020 Compensation and benefit costs $ 2,211 $ 1,400 Research and development expenses 912 788 Professional fees, consulting and other 677 449 Total accrued expenses $ 3,800 $ 2,637

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rent Payments	The future minimum rent payments relating to all six of the Company’s facility operating leases under the terms and conditions existing as of September 30, 2021, as well as amendments the Company has entered into between the date of these financial statements and the date they were available to be issued (as described in Note 13), are summarized as follows (in thousands) Years Ending December 31, 2021 $ 188 2022 $ 909 2023 $ 1,066 2024 $ 931 2025 and beyond $ 1,130 Total $ 4,224

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Schedule of Common Stock Reserved	The number of shares of common stock that have been reserved for the potential conversion of Preferred Stock, outstanding stock options granted and stock options available for grant under the Company’s 2021 Stock Option and Incentive Plan (the “2021 Plan”) and the 2018 Equity Incentive Plan (the “2018 Plan”) and shares reserved for issuance under the Company’s 2021 Employee Stock Purchase Plan (the “2021 ESPP”) are as follows: September 30, December 31, 2021 2020 Conversion of Series A Preferred Stock — 7,476,632 Conversion of Series A-1 Preferred Stock — 5,233,637 Conversion of Series B Preferred Stock — 11,682,229 Restricted stock related to early exercise of common stock options 638,676 932,279 Outstanding common stock options 3,694,768 2,745,185 Shares reserved for issuance under equity incentive plans 2,736,134 1,143,820 Shares reserved for issuance under the 2021 Employee Stock Purchase Plan 852,971 — Contingent stock — 65,186 Total 7,922,549 29,278,968

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Assumptions Used to Determine the Fair Values of Stock Options Granted	The assumptions used to determine the fair values of stock options granted to employees and directors under the 2021 Plan and 2018 Plan are presented as follows: Nine months ended September 30, 2021 2020 Fair value of common stock $5.72 - $16.80 $0.96 - $3.90 Dividend yield — — Volatility 80.60% - 91.25% 72.80% Risk-free interest rate 0.50% - 1.07% 0.31% - 1.46% Expected term (years) 6.25 5.00 - 6.25
Summary of Option Activity	The Company’s stock option activity regarding employees, directors, and nonemployees is summarized as follows ( in thousands excepts share and per share amounts) Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in years) Aggregate intrinsic value Options outstanding—December 31, 2020 2,745,185 $ 4.20 9.40 $ 4,183 Granted 1,034,622 8.92 Exercised (65,600 ) 1.69 Cancelled (1,335 ) 1.45 Forfeited (18,104 ) 6.14 Options outstanding—September 30, 2021 3,694,768 $ 5.56 8.91 $ 29,574 Options exercisable—September 30, 2021 770,020 $ 3.38 8.29 Options vested and expected to vest—September 30, 2021 1,830,144 $ 2.00 7.82
Summary of Additional Information to Stock Option Activity Involving Employees and Directors	Additional information with regard to stock option activity involving employees and directors is as follows ( in thousands except per share amounts) Nine months ended September 30, 2021 2020 Weighted-average grant-date fair value per option of total options granted $ 6.49 $ 1.37 Aggregate intrinsic value of stock options exercised 610 236
Summary of Stock-based Compensation Expense	The Company recorded stock-based compensation expense regarding its employees, directors, and nonemployees as follows (in thousands) Three months ended September 30, Nine months ended September 30, 2021 2020 2021 2020 Research and development expense $ 568 $ 61 $ 1,311 $ 142 General and administrative expense 486 126 1,474 287 Total $ 1,054 $ 187 $ 2,785 $ 429

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts Three months ended September 30, Nine months ended September 30, 2021 2020 2021 2020 Net loss and net loss attributable to common stockholders $ (12,941 ) $ (6,417 ) $ (33,592 ) $ (15,928 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.32 ) $ (0.94 ) $ (1.33 ) $ (2.44 ) Weighted average number of common shares outstanding used in computation of net loss per common share, basic and diluted 40,669,412 6,823,163 25,190,479 6,537,820
Summary of Potential Dilutive Securities Excluded From Calculation of Net Loss Per Share Due to Anti-dilutive Effect	The following potential dilutive securities, presented on an as converted basis, were excluded from the calculation of net loss per share due to their anti-dilutive effect: Nine months ended September 30, 2021 2020 Convertible preferred shares (as converted to common stock and non-voting common stock) — 24,392,498 Options to purchase common stock 3,694,768 1,083,662 Restricted stock related to early exercise of options to purchase common stock 638,676 1,031,834 Contingent common stock (as converted to common stock) — 65,186 4,333,444 26,573,180

Nature of Business and Liquid_2

Nature of Business and Liquidity - Additional Information (Details) $ / shares in Units, $ in Thousands	May 11, 2021USD ($)$ / sharesshares	Apr. 30, 2021	Sep. 30, 2021USD ($)shares	Jun. 30, 2021USD ($)shares	Mar. 31, 2021USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Underwriting discounts and commissions and other expenses				$ 12,858,764
Preferred stock outstanding | shares	0		0						0
Reverse stock split ratio		0.1869
Net loss			$ 12,941	$ 11,352	$ 9,299	$ 6,417	$ 4,663	$ 4,848	$ 33,592	$ 15,928	$ 22,700
Cash used for operation									30,158	$ 13,562	19,200
Accumulated deficit			76,606						76,606		43,014
Cash and cash equivalents			27,311						27,311		$ 17,589
Marketable securities			$ 227,400						227,400
Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued and sold | shares				8,825,000
Underwriting discounts and commissions and other expenses									$ 2,369
Common Stock | Initial Public Offering
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued and sold | shares	8,825,000
Offering price | $ / shares	$ 17
Gross proceeds from sale of shares	$ 150,000
Underwriting discounts and commissions and other expenses	$ 12,900

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Impairments of long-lived assets	$ 0	$ 0
Expected dividend yield	0.00%
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	5 years
Property, plant and equipment, useful life	amortized over the shorter of the lease term or the five-year estimated useful life of the asset
Computer Equipment and Computer Software
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Minimum | Money Market Funds
Summary Of Significant Accounting Policies [Line Items]
Investment in assets	$ 1,000,000,000
Minimum | Equipment and Furniture and Fixtures
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	5 years
Maximum | Equipment and Furniture and Fixtures
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	7 years

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Summary of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets:
Total financial assets measured at fair value	$ 250,808	$ 145,842
Financial liabilities:
Total financial liabilities measured at fair value		373
Contingent Stock Liability
Financial liabilities:
Total financial liabilities measured at fair value		373
Level 1
Financial assets:
Total financial assets measured at fair value	38,558	25,112
Level 2
Financial assets:
Total financial assets measured at fair value	212,250	120,730
Level 3
Financial liabilities:
Total financial liabilities measured at fair value		373
Level 3 | Contingent Stock Liability
Financial liabilities:
Total financial liabilities measured at fair value		373
Money Market Funds | Cash Equivalents
Financial assets:
Total financial assets measured at fair value	23,385	13,943
Money Market Funds | Level 1 | Cash Equivalents
Financial assets:
Total financial assets measured at fair value	23,385	13,943
Marketable Securities
Financial assets:
Total financial assets measured at fair value	227,423	131,899
Marketable Securities | Level 1
Financial assets:
Total financial assets measured at fair value	15,173	11,169
Marketable Securities | Level 2
Financial assets:
Total financial assets measured at fair value	$ 212,250	$ 120,730

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Details) $ in Thousands	May 11, 2021USD ($)shares	May 31, 2021USD ($)shares	Jun. 30, 2021USD ($)	Sep. 30, 2021shares	Dec. 31, 2020$ / sharesshares	Sep. 30, 2020$ / shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Number of shares equal to fair value of contingent equity consideration				65,186
Common stock, shares issued					7,087,130
Cash payment for contingent equity settlement | $			$ 277
Measurement Input, Share Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value of common stock used to value contingent stock liability | $ / shares					5.72	5.72
ULRF
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Common stock, shares issued	16,297	16,297
IPO | ULRF
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Common stock, shares issued	48,889	48,889
Cash payment for contingent equity settlement | $	$ 300	$ 300

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Schedule of Contingent Common Stock Liability Measured at Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair value, Beginning balance	$ 733	$ 373	$ 63	$ 373	$ 63
Change in fair value	375	360	310	$ 735	311
Share issuance in partial settlement of contingent stock	(831)
Cash payment in partial settlement of contingent stock	$ (277)
Fair value, Ending balance		$ 733	$ 373		$ 373

Marketable Securities - Summary

Marketable Securities - Summary of Company's Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 227,394	$ 131,912
Unrealized Gain	34	8
Unrealized(Loss)	(5)	(21)
Estimated Fair Value	227,423	131,899
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	191,184	73,331
Unrealized Gain	29	3
Unrealized(Loss)	(1)	(10)
Estimated Fair Value	191,212	73,324
Corporate debt securities
Marketable Securities [Line Items]
Amortized Cost	11,021	33,319
Unrealized Gain		1
Unrealized(Loss)	(3)	(11)
Estimated Fair Value	11,018	33,309
Government and agency securities
Marketable Securities [Line Items]
Amortized Cost	25,189	25,262
Unrealized Gain	5	4
Unrealized(Loss)	(1)
Estimated Fair Value	$ 25,193	$ 25,266

Prepaid and Other Current Ass_3

Prepaid and Other Current Assets - Summary of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid insurance	$ 1,891	$ 102
Prepaid research and development expenses	748	702
Other current assets	854	459
Total prepaid and other current assets	$ 3,493	$ 1,263

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	$ 5,672	$ 4,256
Less accumulated depreciation	(2,678)	(2,243)
Property and equipment, net	2,994	2,013
Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,404	2,666
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	800	264
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	643	580
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	479	491
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 346	$ 255

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 0.4	$ 0.4

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Compensation and benefit costs	$ 2,211	$ 1,400
Research and development expenses	912	788
Professional fees, consulting and other	677	449
Total accrued expenses	$ 3,800	$ 2,637

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)

May 11, 2021USD ($)shares

Jul. 31, 2021

May 31, 2021USD ($)shares

Feb. 28, 2021USD ($)

Jun. 30, 2020USD ($)

May 31, 2020

Feb. 29, 2020USD ($)

Oct. 31, 2018USD ($)shares

Jun. 30, 2021USD ($)

Sep. 30, 2021USD ($)Leaseagreement

Sep. 30, 2020USD ($)

Mar. 31, 2021USD ($)

Dec. 31, 2020USD ($)shares

Mar. 31, 2020USD ($)

Dec. 31, 2019USD ($)

Loss Contingencies [Line Items]

Number of active lease agreements | Leaseagreement

6

Lessee, operating lease, existence of option to extend

true

Lease option to extend

three additional years

Lease termination date

Nov. 30, 2023

Lease term period

39 months

Rent expense

$ 500,000

$ 400,000

Common stock issued | shares

7,087,130

Contingent stock liability

$ 63,000

$ 373,000

$ 733,000

$ 373,000

$ 63,000

$ 63,000

Cash payment for contingent equity settlement

$ 277,000

Annual maintenance fee pursuant to license agreement

$ 100,000

$ 100,000

Other Liabilities

Loss Contingencies [Line Items]

Contingent stock liability

$ 400,000

ULRF

Loss Contingencies [Line Items]

Common stock issued | shares

16,297

16,297

ULRF | Research and Development Expense

Loss Contingencies [Line Items]

Milestone payment

$ 100,000

ULRF | IPO

Loss Contingencies [Line Items]

Common stock issued | shares

48,889

48,889

Cash payment for contingent equity settlement

$ 300,000

$ 300,000

ULRF License Agreement | ULRF

Loss Contingencies [Line Items]

Percentage of compensation on net sales of all licensed products sold

3.00%

Compensation on non-royalty sublicensing income

one third

Common stock issued | shares

65,186

ULRF License Agreement | ULRF | Contingent Equity Consideration

Loss Contingencies [Line Items]

Common stock issued | shares

65,186

ULRF License Agreement | ULRF | Maximum

Loss Contingencies [Line Items]

Compensation on regulatory and sales milestones

$ 1,625,000

Wellesley

Loss Contingencies [Line Items]

Lease commencement date

Apr. 30, 2021

Massachusetts

Loss Contingencies [Line Items]

Lease termination date

Mar. 31, 2021

Kentucky

Loss Contingencies [Line Items]

Lease termination date

Dec. 31, 2021

Houston, Texas

Loss Contingencies [Line Items]

Lessee, operating lease, existence of option to extend

true

Lease option to extend

option to extend on a month-to-month basis at the end of the original term.

Lease term period

5 months

Term of lease not yet commenced

36 months

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Rent Payments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Operating Lease Liabilities Payments Due Rolling Maturity [Abstract]
2021	$ 188
2022	909
2023	1,066
2024	931
2025 and beyond	1,130
Total	$ 4,224

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($)	1 Months Ended				3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020	Aug. 31, 2020	Dec. 31, 2019	Nov. 30, 2018	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020	May 31, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
Convertible Preferred Stock [Line Items]
Issuance costs, incurred					$ 12,858,764,000
Product interest rights held							After the first commercial sale of product, the product interest right entitles the holders to a product interest payment for each product interest right held equal to 1/48,000,000 multiplied by 9% of net product sales on a territory-by-territory basis. If the Company enters into a license of rights to develop and/or commercialize a product, the holder is entitled to a product interest payment for each product interest right equal to 1/48,000,000 multiplied by 30% of licensing income.
Remaining product interest rights outstanding							0.00%
Common Stock
Convertible Preferred Stock [Line Items]
Issuance costs, incurred							$ 2,369,000
Tranche 2
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued			16,000,000
Tranche 3
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued		12,000,000
Series A Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued				22,500,000			0	40,000,000
Shares issued, price per share				$ 1			$ 1
Proceeds from issuance of convertible preferred stock				$ 22,500,000
Issuance costs, incurred				$ 2,000,000
Preferred stock, shares outstanding	40,000,000		40,000,000			40,000,000	0	40,000,000		40,000,000	40,000,000	40,000,000
Conversion price							$ 5.35
Series A Convertible Preferred Stock | Common Stock
Convertible Preferred Stock [Line Items]
Conversion of preferred stock									7,476,632
Series A Convertible Preferred Stock | Tranche 2
Convertible Preferred Stock [Line Items]
Shares issued, price per share			$ 1
Proceeds from issuance of convertible preferred stock			$ 17,500,000
Preferred stock, additional shares issued			17,500,000
Series A-1 Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued							0	28,000,000
Shares issued, price per share				$ 1.25			$ 1.25
Issuance costs, incurred						$ 31,000
Preferred stock, shares outstanding	28,000,000		16,000,000			28,000,000	0	28,000,000		28,000,000	16,000,000	16,000,000
Conversion price							$ 6.69
Series A-1 Convertible Preferred Stock | Common Stock
Convertible Preferred Stock [Line Items]
Conversion of preferred stock									5,233,637
Series A-1 Convertible Preferred Stock | Tranche 2
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued			16,000,000
Shares issued, price per share			$ 1.25
Proceeds from issuance of convertible preferred stock			$ 20,000,000
Issuance costs, incurred			$ 1,300,000
Preferred stock, shares outstanding			16,000,000
Series A-1 Convertible Preferred Stock | Tranche 3
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued		12,000,000
Shares issued, price per share		$ 1.25
Proceeds from issuance of convertible preferred stock		$ 15,000,000
Preferred stock, shares outstanding		12,000,000
Series B Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Preferred stock, shares issued	62,499,993					62,499,993	0	62,499,993
Shares issued, price per share	$ 1.84					$ 1.84	$ 1.84
Proceeds from issuance of convertible preferred stock	$ 115,000,000
Issuance costs, incurred	$ 500,000					$ 476,000
Preferred stock, shares outstanding	62,499,993					62,499,993	0	62,499,993		62,499,993
Conversion price							$ 9.84
Series B Convertible Preferred Stock | Non-voting Common Stock
Convertible Preferred Stock [Line Items]
Conversion of preferred stock									1,150,000
Series B Convertible Preferred Stock | Common Stock
Convertible Preferred Stock [Line Items]
Conversion of preferred stock									10,532,229
Convertible Preferred Stock
Convertible Preferred Stock [Line Items]
Dividends declared							$ 0	$ 0
Dividends paid							0	$ 0
Convertible Preferred Stock | Minimum
Convertible Preferred Stock [Line Items]
Proceeds from issuance of convertible preferred stock							$ 60,000,000
Offering price per share							$ 9.84

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - $ / shares	Sep. 30, 2021	May 11, 2021	Apr. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Authorization of undesignated preferred stock			10,000,000
Undesignated preferred stock, par value			$ 0.0001
Common stock, shares authorized				36,366,101
Undesignated preferred stock, outstanding	0	0
Voting Shares
Class Of Stock [Line Items]
Common stock, shares authorized	140,000,000		140,000,000
Non-voting Shares
Class Of Stock [Line Items]
Common stock, shares authorized	10,000,000		10,000,000

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Reserved (Details) - shares	Sep. 30, 2021	Apr. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Outstanding common stock options	3,694,768		2,745,185
2021 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares reserved for issuance		852,971
Common Stock
Class Of Stock [Line Items]
Restricted stock related to early exercise of common stock options	638,676		932,279
Outstanding common stock options	3,694,768		2,745,185
Contingent stock			65,186
Total	7,922,549		29,278,968
Common Stock | Series A Preferred Stock
Class Of Stock [Line Items]
Conversion of preferred stock			7,476,632
Common Stock | Series A-1 Preferred Stock
Class Of Stock [Line Items]
Conversion of preferred stock			5,233,637
Common Stock | Series B Preferred Stock
Class Of Stock [Line Items]
Conversion of preferred stock			11,682,229
Common Stock | Equity Incentive Plans
Class Of Stock [Line Items]
Shares reserved for issuance	2,736,134		1,143,820
Common Stock | 2021 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Shares reserved for issuance	852,971

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Millions	Apr. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options outstanding, shares		3,694,768	2,745,185
Contractual term of stock option		8 years 10 months 28 days	9 years 4 months 24 days
Unrecognized compensation cost		$ 12
Unrecognized compensation cost, expected to be recognized period		3 years 2 months 12 days
2021 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares remained available for future grant	6,397,289	2,736,134
Options outstanding, shares		3,619,997
Percentage of fair market value of common stock		100.00%
Stock options vesting period		4 years
2021 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized under the plan	3,015,907
Contractual term of stock option		10 years
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares remained available for future grant	3,381,382
Options outstanding, shares		3,619,997
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Discount percentage to purchase shares	15.00%
Offering periods	6 months
Increment in number of shares authorized possible	3,000,000
Number of shares authorized under the plan	852,971
Percentage of cumulative number of shares of common stock issued and outstanding	1.00%

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions Used to Determine the Fair Values of Stock Options Granted (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%
Stock Option | 2021 and 2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility		72.80%
Volatility, minimum	80.60%
Volatility, maximum	91.25%
Risk-free interest rate, minimum	0.50%	0.31%
Risk-free interest rate, maximum	1.07%	1.46%
Expected term (years)	6 years 3 months
Stock Option | 2021 and 2018 Equity Incentive Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years
Stock Option | 2021 and 2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 3 months
Common Stock | Stock Option | 2021 and 2018 Equity Incentive Plan | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 5.72	$ 0.96
Common Stock | Stock Option | 2021 and 2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 16.80	$ 3.90

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award Additional General Disclosures [Abstract]
Options outstanding, beginning balance, shares | shares	2,745,185
Granted, shares | shares	1,034,622
Exercised, shares | shares	(65,600)
Cancelled, shares | shares	(1,335)
Forfeited, shares | shares	(18,104)
Options outstanding, ending balance, shares | shares	3,694,768	2,745,185
Options exercisable, shares | shares	770,020
Options vested and expected to vest, shares | shares	1,830,144
Options outstanding, weighted- average exercise price | $ / shares	$ 4.20
Granted, weighted- average exercise price | $ / shares	8.92
Exercised, weighted- average exercise price | $ / shares	1.69
Cancelled, weighted-average exercise price | $ / shares	1.45
Forfeited, weighted- average exercise price | $ / shares	6.14
Options outstanding, weighted- average exercise price | $ / shares	5.56	$ 4.20
Options exercisable, weighted- average exercise price | $ / shares	3.38
Options vested and expected to vest, weighted- average exercise price | $ / shares	$ 2
Options outstanding, weighted- average remaining contractual life	8 years 10 months 28 days	9 years 4 months 24 days
Options exercisable, weighted- average remaining contractual life	8 years 3 months 14 days
Options vested and expected to vest, weighted- average remaining contractual life	7 years 9 months 25 days
Options outstanding, aggregate intrinsic value | $	$ 29,574	$ 4,183

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Additional Information to Stock Option Activity Involving Employees and Directors (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award Options Additional Disclosures [Abstract]
Weighted-average grant-date fair value per option of total options granted	$ 6.49	$ 1.37
Aggregate intrinsic value of stock options exercised	$ 610	$ 236

Stock-Based Compensation - Su_3

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]
Stock-based compensation expense	$ 1,054	$ 187	$ 2,785	$ 429
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	568	61	1,311	142
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 486	$ 126	$ 1,474	$ 287

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Summary of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 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	Dec. 31, 2020
Earnings Per Share [Abstract]
Net loss and net loss attributable to common stockholders	$ (12,941)	$ (11,352)	$ (9,299)	$ (6,417)	$ (4,663)	$ (4,848)	$ (33,592)	$ (15,928)	$ (22,700)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.32)			$ (0.94)			$ (1.33)	$ (2.44)
Weighted average number of common shares outstanding used in computation of net loss per common share, basic and diluted	40,669,412			6,823,163			25,190,479	6,537,820

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Summary of Potential Dilutive Securities Excluded From Calculation of Net Loss Per Share Due to Anti-dilutive Effect (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from calculation of net loss per share due to anti-dilutive effect	4,333,444	26,573,180
Convertible Preferred Shares (as Converted to Common Stock and Non-voting Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from calculation of net loss per share due to anti-dilutive effect		24,392,498
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from calculation of net loss per share due to anti-dilutive effect	3,694,768	1,083,662
Restricted Stock Related to Early Exercise of Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from calculation of net loss per share due to anti-dilutive effect	638,676	1,031,834
Contingent Common Stock (as Converted to Common Stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities excluded from calculation of net loss per share due to anti-dilutive effect		65,186

Subsequent Events - Additional

Subsequent Events - Additional Information (Details)	Nov. 30, 2021	Sep. 30, 2021
Subsequent Event [Line Items]
Lease term period		39 months
Subsequent Event
Subsequent Event [Line Items]
Lease term period	39 months