TScan Therapeutics (TCRX) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 05, 2021	Nov. 01, 2021
Document Information [Line Items]
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	TCRX
Entity Registrant Name	TSCAN THERAPEUTICS, INC.
Entity Central Index Key	0001783328
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	001-40603
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-5282075
Entity Address, Address Line One	830 Winter Street
Entity Address, State or Province	MA
Entity Address, City or Town	Waltham
Entity Address, Postal Zip Code	02451
City Area Code	857
Local Phone Number	399-9500
Title of 12(b) Security	Voting Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Voting Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		18,624,902
Non-voting Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding			5,143,134

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 182,312,000	$ 34,791,000
Prepaid expenses and other current assets	4,691,000	1,654,000
Total current assets	187,003,000	36,445,000
Property and equipment, net	11,295,000	5,659,000
Right-of-use assets	5,830,000	6,873,000
Restricted cash	595,000	595,000
Long-term deposit	166,000	166,000
Total assets	204,889,000	49,738,000
Current liabilities:
Accounts payable	5,072,000	2,910,000
Accrued expenses and other current liabilities	4,285,000	2,494,000
Operating lease liability, current portion	1,620,000	1,415,000
Deferred revenue, current portion	11,967,000	10,627,000
Total current liabilities	22,944,000	17,446,000
Deferred revenue, net of current portion	2,844,000	8,816,000
Operating lease liability, net of current portion	4,791,000	6,019,000
Other long term liabilities	236,000	238,000
Total liabilities	30,815,000	32,519,000
Commitments and contingencies (Note 8)
Convertible preferred stock (Note 5)		59,681,000
Stockholders' deficit:
Additional paid-in capital	252,029,000	1,070,000
Accumulated deficit	(77,958,000)	(43,533,000)
Total stockholders' deficit	174,074,000	(42,462,000)
Total liabilities, convertible preferred stock and stockholders' deficit	204,889,000	49,738,000
Voting Common Stock
Stockholders' deficit:
Common stock	2,000	$ 1,000
Non-voting Common Stock
Stockholders' deficit:
Common stock	$ 1,000

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Voting Common Stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	165,210,543
Common stock, shares issued	18,822,600	1,574,138
Common stock, shares outstanding	18,618,087	1,135,858
Non-voting Common Stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	10,000,000	0
Common stock, shares issued	5,143,134	0
Common stock, shares outstanding	5,143,134	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue
Collaboration and license revenue	$ 2,412	$ 290	$ 7,287	$ 290
Revenue from Contract with Customer, Products and Services [Extensible List]	http://www.tscan.com/#CollaborationAndLicenseRevenueMember	http://www.tscan.com/#CollaborationAndLicenseRevenueMember	http://www.tscan.com/#CollaborationAndLicenseRevenueMember	http://www.tscan.com/#CollaborationAndLicenseRevenueMember
Operating expenses:
Research and development	$ 14,206	$ 5,813	$ 32,346	$ 14,613
General and administrative	4,048	1,648	9,380	4,100
Total operating expenses	18,254	7,461	41,726	18,713
Loss from operations	(15,842)	(7,171)	(34,439)	(18,423)
Other income:
Interest and other income (loss), net	3	1	14	103
Net loss	$ (15,839)	$ (7,170)	$ (34,425)	$ (18,320)
Net loss per share, basic and diluted	$ (0.80)	$ (7.16)	$ (4.55)	$ (20.44)
Weighted average common shares outstanding—basic and diluted	19,875,428	1,001,853	7,562,436	896,100

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Unaudited) - USD ($)	Total	Initial Public Offering	Convertible Preferred Stock	Convertible Preferred StockInitial Public Offering	Common Stock	Common StockInitial Public Offering	Additional Paid-In Capital	Additional Paid-In CapitalInitial Public Offering	Accumulated Deficit
Balances at Dec. 31, 2019	$ (17,138,000)						$ 268,000		$ (17,406,000)
Balances, shares at Dec. 31, 2019			7,063,104
Balances at Dec. 31, 2019			$ 59,681,000
Balances, shares at Dec. 31, 2019					642,903
Exercise of stock options	248,000				$ 1,000		247,000
Exercise of stock options, shares					125,298
Vesting of restricted common stock, shares					264,226
Stock-based compensation expense	365,000						365,000
Net loss	(18,320,000)								(18,320,000)
Balances at Sep. 30, 2020	(34,845,000)				$ 1,000		880,000		(35,726,000)
Balances, shares at Sep. 30, 2020			7,063,104
Balances at Sep. 30, 2020			$ 59,681,000
Balances, shares at Sep. 30, 2020					1,032,427
Balances at Jun. 30, 2020	(27,804,000)				$ 1,000		751,000		(28,556,000)
Balances, shares at Jun. 30, 2020			7,063,104
Balances at Jun. 30, 2020			$ 59,681,000
Balances, shares at Jun. 30, 2020					944,305
Exercise of stock options	1,000						1,000
Exercise of stock options, shares					470,000
Vesting of restricted common stock, shares					87,652
Stock-based compensation expense	128,000						128,000
Net loss	(7,170,000)								(7,170,000)
Balances at Sep. 30, 2020	(34,845,000)				$ 1,000		880,000		(35,726,000)
Balances, shares at Sep. 30, 2020			7,063,104
Balances at Sep. 30, 2020			$ 59,681,000
Balances, shares at Sep. 30, 2020					1,032,427
Balances at Dec. 31, 2020	(42,462,000)				$ 1,000		1,070,000		(43,533,000)
Balances, shares at Dec. 31, 2020			7,063,104
Balances at Dec. 31, 2020	59,681,000		$ 59,681,000
Balances, shares at Dec. 31, 2020					1,135,858
Issuance of Series C convertible preferred stock (net of issuance costs of $270)			$ 99,730,000
Issuance of Series C convertible preferred stock (net of issuance costs of $270), shares			8,553,168
Issuance of common stock, net of issuance costs	89,647,000				$ 1,000		89,646,000
Issuance of common stock, net of issuance costs, shares					6,666,667
Conversion of convertible preferred stock to common stock upon closing of initial public offering				$ 159,411,000
Conversion of convertible preferred stock to common stock upon closing of initial public offering, shares				15,616,272
Conversion of convertible preferred stock to common stock upon closing of initial public offering		$ 159,411,000				$ 1,000		$ 159,410,000
Conversion of convertible preferred stock to common stock upon closing of initial public offering, shares						15,616,272
Exercise of stock options	171,000						171,000
Exercise of stock options, shares					108,657
Vesting of restricted common stock, shares					233,767
Stock-based compensation expense	1,732,000						1,732,000
Net loss	(34,425,000)								(34,425,000)
Balances at Sep. 30, 2021	174,074,000				$ 3,000		252,029,000		(77,958,000)
Balances, shares at Sep. 30, 2021					23,761,221
Balances at Jun. 30, 2021	(60,030,000)				$ 1,000		2,088,000		(62,119,000)
Balances, shares at Jun. 30, 2021			15,616,272
Balances at Jun. 30, 2021			$ 159,411,000
Balances, shares at Jun. 30, 2021					1,419,819
Issuance of common stock, net of issuance costs	89,647,000				$ 1,000		89,646,000
Issuance of common stock, net of issuance costs, shares					6,666,667
Conversion of convertible preferred stock to common stock upon closing of initial public offering				$ 159,411,000
Conversion of convertible preferred stock to common stock upon closing of initial public offering, shares				15,616,272
Conversion of convertible preferred stock to common stock upon closing of initial public offering		$ 159,411,000				$ 1,000		$ 159,410,000
Conversion of convertible preferred stock to common stock upon closing of initial public offering, shares						15,616,272
Vesting of restricted common stock, shares					58,463
Stock-based compensation expense	885,000						885,000
Net loss	(15,839,000)								(15,839,000)
Balances at Sep. 30, 2021	$ 174,074,000				$ 3,000		$ 252,029,000		$ (77,958,000)
Balances, shares at Sep. 30, 2021					23,761,221

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Unaudited) (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Convertible Preferred Stock
Net issuance costs	$ 270
Common Stock
Net issuance costs	$ 10,400

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (34,425)	$ (18,320)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	2,186	834
Stock-based compensation	1,732	365
Changes in current assets and liabilities:
Prepaid expenses and other assets	(3,037)	(189)
Right-of-use assets and lease liabilities, net	20	386
Accounts payable	2,472	1,071
Accrued expense and other liabilities	1,387	373
Deferred revenue	(4,632)	19,807
Net cash used in operating activities	(34,297)	4,327
Cash flows from investing activities:
Purchases of property and equipment	(7,730)	(2,853)
Net cash used in investing activities	(7,730)	(2,853)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	99,730
Proceeds from exercise of stock options	171	248
Proceeds from initial public offering, net of issuance costs	89,647
Net cash provided by financing activities	189,548	248
Net increase (decrease) in cash, cash equivalents and restricted cash	147,521	1,722
Cash, cash equivalents, and restricted cash - beginning of period	35,386	42,359
Cash, cash equivalents, and restricted cash - end of period	182,907	44,081
Supplemental cash flow information:
Purchase of property and equipment in accounts payable and accrued liabilities	1,427	$ 458
Conversion of convertible preferred stock to common stock upon closing of initial public offering	$ 159,411

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	1. Nature of Business and Basis of Presentation Nature of Business TScan Therapeutics, Inc. and its wholly owned subsidiary, TScan Securities Corporation, (the Company) is a biotechnology company that was incorporated in Delaware on April 17, 2018 and has a principal place of business in Waltham, Massachusetts. The Company is a biopharmaceutical company focused on developing a pipeline of T cell receptor-engineered T cell (TCR-T) therapies for the treatment of patients with cancer. Initial Public Offering In July 2021, the Company completed the initial public offering (IPO) in which the Company issued and sold 6,666,667 shares of its voting common stock at a public offering price of $ 15.00 per share, for aggregate gross proceeds of $ 100 million and its shares started trading on the Nasdaq Global Market under the ticker symbol “TCRX.” The Company received $ 89.6 million in net proceeds after deducting $ 7.0 million in underwriting discounts and commissions, and $ 3.4 million in offering costs borne by us. Upon closing of the IPO, all of the Company's outstanding shares of convertible preferred stock automatically converted into 15,616,272 shares of common stock (of which 5,143,134 shares are non-voting common stock). In connection with the closing of IPO, the Company amended and restated its in its entirety certificate of incorporation to, among other things: (i) authorize 300,000,000 shares of voting common stock; (ii) authorize 10,000,000 shares of non-voting common stock; (iii) eliminate all references to the previously existing series of preferred stock; and (iv) authorize 10,000,000 shares of preferred stock that may be issued from time to time by the Board in one or more series. Risks, Uncertainties and Going Concern The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, successful development of technology, obtaining additional funding, protection of proprietary technology, compliance with government regulations, risks of failure of preclinical studies, clinical studies and clinical trials, the need to obtain marketing approval for its product candidates and the ability to successfully market its therapies any products that receive approval, fluctuations in operating results, economic pressure impacting therapeutic pricing, dependence on key personnel, risks associated with changes in technologies, development by competitors of technological innovations and the ability to scale manufacturing to large scale production. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from therapy sales. The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. The Company has primarily funded its operations with proceeds from sales of convertible preferred stock and with payments received under its license and collaboration agreements. Since its inception, the Company has incurred recurring losses, including net losses of $ 34.4 million and $ 18.3 million for the nine months ended September 30, 2021 and 2020, respectively. As of September 30, 2021, the Company had an accumulated deficit of $ 78.0 million. The Company expects to continue to generate operating losses in the foreseeable future. The Company expects that its cash and cash equivalents as of September 30, 2021 will be sufficient to fund the Company’s operations for at least the next twelve months from the date of the issuance of the financial statements. Reverse Stock Split The Company’s board of directors (the Board) and stockholders approved a 1-for- 8.2 reverse stock split of the Company’s issued and outstanding common and preferred stock, which became effective on May 13, 2021. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been retroactively adjusted to reflect the reverse stock split. Impact of COVID-19 In December 2019, a novel strain of coronavirus, which causes the disease known as COVID-19, was reported to have surfaced in Wuhan, China. Since then, COVID-19 coronavirus has spread globally. In March 2020, the World Health Organization declared the COVID-19 outbreak a pandemic. The ongoing COVID-19 global and national health emergency has caused significant disruption in the international and United States economies and financial markets. The spread of COVID-19 has caused illness, quarantines, cancellation of events and travel, business and school shutdowns, reduction in business activity and financial transactions, labor shortages, supply chain interruptions and overall economic and financial market instability and business disruptions for the Company and many of the Company’s vendors. In response to public health directives and orders and to help minimize the risk of the virus to employees, the Company has taken a series of actions aimed at safeguarding the Company’s employees and business associates, including implementing a flexible work-at-home policy. These disruptions could result in increased costs of execution of development plans or may negatively impact the quality, quantity, timing and regulatory usability of data that the Company would otherwise be able to collect. While these disruptions are currently expected to be temporary, there is considerable uncertainty around the duration of these disruptions. Therefore, the related financial impact and duration cannot be reasonably estimated at this time. To date, the Company has not experienced material business disruptions, including with its vendors, as a result of the COVID-19 pandemic. Emerging Growth Company Status The Company qualifies as “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected to “opt in” to the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (US GAAP) and applicable rules and regulations of the Securities and Exchange Commission (the SEC) regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by US GAAP for complete financial statements. Management believes that the interim financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company’s financial position, results of its operations and cash flows. The condensed consolidated financial statements include the accounts of TScan Therapeutics, Inc. and its subsidiary TScan Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 , any other interim periods, or any future year or period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and unaudited condensed consolidated statements included in the Company’s final prospectus related to the Company’s IPO dated July 15, 2021 and filed with the Securities Exchange Commission on July 16, 2021, pursuant to Rule 424(b) under the Securities Act of 1933, as amended (the Prospectus).

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables set forth by level, within the fair value hierarchy, the assets (liabilities) carried at fair value (in thousands): Fair value measurements at September 30, 2021 using: Level 1 Level 2 Level 3 Total Assets Cash equivalents – money market funds $ 181,300 $ - $ - $ 181,300 Total financial assets $ 181,300 $ - $ - $ 181,300 Fair value measurements at December 31, 2020 using: Level 1 Level 2 Level 3 Total Assets Cash equivalents – money market funds $ 33,748 $ - $ - $ 33,748 Total financial assets $ 33,748 $ - $ - $ 33,748 The cash equivalents are comprised of funds held in an exchange traded money market fund and the fair value of the cash equivalents is determined based upon quoted market price for that fund. There were no transfers among Level 1, Level 2, or Level 3 categories in the periods presented. The carrying value of accounts payable and accrued expenses that are reported on the condensed consolidated balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	4. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued employee compensation and benefits $ 1,747 $ 1,535 Accrued research and development 1,398 60 Accrued consulting and professional services 445 189 Accrued legal services and license fee 27 578 Other 668 132 Total accrued expenses and other current liabilities $ 4,285 $ 2,494

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	5. Convertible Preferred Stock Series A Preferred Stock In 2018, the Company entered into the Series A Preferred Stock Purchase Agreement with its founding investors providing $ 25 million in Series A Preferred Stock equity financing and issued 3,209,240 shares of Series A Preferred Stock. Issuance costs associated with the transaction were $ 0.1 million. Series B Preferred Stock In 2019, the Company entered into the Series B Preferred Stock Purchase Agreements providing $ 35 million in Series B Preferred Stock equity financing and issued 3,853,864 shares of Series B Preferred Stock. Issuance costs associated with the transaction were $ 0.2 million. Series C Preferred Stock In 2021, the Company entered into the Series C Preferred Stock Purchase Agreements providing $ 100 million in Series C Preferred Stock equity financing and issued 8,553,168 shares of Series C Preferred Stock. Issuance costs associated with the transaction were $ 0.3 million. As of December 31, 2020, the preferred stock consisted of the following (in thousands, except for share data): December 31, 2020 Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Liquidation Common Stock Series A Preferred Stock 26,315,790 3,209,240 $ 24,874 $ 29,838 3,209,240 Series B Preferred Stock 31,601,732 3,853,864 34,807 39,037 3,853,864 Total 57,917,522 7,063,104 $ 59,681 $ 68,875 7,063,104 Upon the completion of the Company’s IPO in July 2021, all outstanding shares of the Company’s preferred stock were converted into 15,616,272 shares of common stock (of which 5,143,134 shares are non-voting common stock). As a result, as of September 30, 2021 , no shares of preferred stock are presently outstanding.

Stock Based Compensation

Stock Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Based Compensation	6. Stock Based Compensation 2018 Equity Incentive Plan On April 20, 2018, the Company adopted the 2018 Stock Plan (the 2018 Plan). The 2018 Plan, as amended, provided for the issuance of up to 2,902,738 shares of common stock to employees, officers, directors, consultants, and advisors in the form of nonqualified and incentive stock options, unvested stock awards, and other stock-based awards. 2021 Equity Incentive Plan The 2021 Equity Incentive Plan (the 2021 Plan) was approved by the Company’s Board on April 22, 2021 and became effective immediately, although no awards were permitted to be granted under the 2021 Plan until July 15, 2021. The 2021 Plan replaced the 2018 Plan. However, awards outstanding under the 2018 Plan continue to be governed by their existing terms. There were 3,278,048 shares of common stock initially reserved for issuance under the 2021 Plan, plus up to 167,887 shares reserved for issuance under, or issued pursuant to or subject to awards granted under, the 2018 Plan. As of September 30, 2021, there were 2,836,264 shares of common stock available for issuance under the 2021 Plan. The number of shares reserved for issuance under the 2021 Plan will be increased automatically on the first business day of each fiscal year, commencing in 2022 and ending in 2031. The aggregate number of common shares that may be issued under the 2021 Plan shall automatically increase by a number equal to the lesser of (a) 4 % of the total number of shares of common stock actually issued and outstanding on the last day of the preceding fiscal year or (b) a number of shares common stock determined by the Company’s Board. 2021 Employee Stock Purchase Plan The 2021 Employee Stock Purchase Plan (the 2021 ESPP) was approved by the Company’s Board on April 22, 2021 and became effective immediately, although no awards were permitted to be granted under the 2021 Plan until July 15, 2021. A total of 254,390 shares of common stock were initially reserved for issuance under the 2021 ESPP. As of September 30, 2021 , there were 254,390 shares of common stock available for issuance under the 2021 ESPP. The number of shares reserved for issuance will automatically be increased on the first business day of each fiscal year, commencing on January 1, 2022 and ending on January 1, 2041. The aggregate number of shares of common stock that may be issued under the 2021 ESPP shall automatically increase by a number equal to the least of (i) one percent ( 1 %) of the total number of shares of common stock actually issued and outstanding on the last day of the preceding fiscal year, or (ii) a number of shares of common stock determined by the Company’s Board. Shares issued under the 2021 ESPP will be compensatory. Stock Options In general, stock options typically vest over four years and have a maximum term of 10 years. Also, the Company typically grants stock options to employees and non-employees at exercise prices deemed by the Board to be equal to the fair value of the common stock at the time of grant. The fair value of the common stock has been determined by the Board at each measurement date based on a variety of different factors, including the results obtained from third party appraisals, the Company’s financial position and historical financial performance, the status of development of the Company’s services, the current climate in the marketplace, the illiquid nature of the common stock, the effect of the rights and preferences of the preferred stockholders, and the prospects of a liquidity event, among others. The Company utilized the Black-Scholes option-pricing model to estimate the fair value of stock options awarded to employees. The Black-Scholes option-pricing model requires several key assumptions. The key assumptions used to apply this pricing model during the nine months ended September 30, 2021 and 2020, were as follows: Nine Months Ended September 30, 2021 2020 Risk free interest rate 0.76 % 0.91 % Expected term (in years) 6.05 6.06 Expected dividend yield 0 % 0 % Expected volatility of underlying common stock 75 % 71 % The risk-free interest rate was based on rates associated with U.S. Treasury issues approximating the expected life of the stock options. The expected term of stock options granted to employees was determined using the simplified method, which represents the midpoint of the contractual term of the stock option and the weighted-average vesting period of the option. The Company uses the simplified method because it does not have sufficient historical stock option exercise data to provide a reasonable basis upon which to estimate the expected term. The expected dividend-yield assumption was based on the Company’s expectation of no future dividend payments. The expected volatility of the underlying stock was based on the average historical volatility of comparable publicly traded companies based on weekly price returns as reported by a pricing service, as the Company does not have a trading history for its common stock. The following table summarizes the stock option activity under the 2018 Plan and 2021 Plan: Stock Weighted Weighted Intrinsic Outstanding January 1, 2021 1,445,426 $ 2.62 8.74 $ 3,799 Granted 1,882,441 8.80 Exercised ( 108,657 ) 2.18 Canceled ( 128,361 ) 4.82 Outstanding September 30, 2021 3,090,849 $ 6.40 8.91 $ 9,452 Options vested or expected to vest as of September 30, 2021 3,090,849 $ 6.40 8.91 $ 9,452 Stock options exercisable as of September 30, 2021 558,385 $ 2.44 7.76 $ 3,302 The weighted average grant date fair value of stock options granted for the nine months ended September 30, 2021 was $ 5.79 per share. Restricted Common Stock The Company has granted restricted common stock with service based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder, except for transfers for estate planning purposes in which the transferee agrees to remain bound by all restrictions set forth in the original common stock purchase agreement. They are legally issued and outstanding but only accounted for as outstanding when vested. These restrictions lapse over the four year vesting term of each award. The purchase price of each share of restricted common stock was $ 0.001 per share. A summary of the activity for the nine months ended September 30, 2021 is as follows: Number of Weighted Unvested restricted stock as of January 1, 2021 438,280 - Vested ( 233,767 ) - Unvested restricted stock as of September 30, 2021 204,513 - The aggregate fair value of restricted stock awards that vested during the nine months ended September 30, 2021 was nominal. Stock-Based Compensation Expense Stock-based compensation expense was as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 270 $ 61 $ 626 $ 173 General and administrative 615 67 1,106 192 Total stock-based compensation expense $ 885 $ 128 $ 1,732 $ 365 As of September 30, 2021, there was $ 10.6 million of unrecognized stock-based compensation expense related to unvested stock options and restricted common stock, which is estimated to be recognized over a period of 3.09 years.

Collaboration and License Agree

Collaboration and License Agreements	9 Months Ended
	Sep. 30, 2021
Collaboration And License Agreements [Abstract]
Collaboration and License Agreements	7. Collaboration and License Agreements Novartis In March 2020 , the Company entered into a Collaboration and License Agreement (the Novartis Agreement) with Novartis Institutes For Biomedical Research, Inc. (Novartis) to collaborate on their research efforts to discover and develop novel TCR-T therapies. Under the Novartis Agreement, the Company will identify and characterize TCRs in accordance with a research plan, transfer data arising from the research plan. Novartis will have the option to license and develop TCRs for up to three novel targets identified in performance of the collaboration during the collaboration period of the Novartis Agreement. Novartis will also have rights of first negotiation for certain additional targets and TCRs identified in performance of the collaboration during a defined collaboration period of the Novartis Agreement and for 180 days after such collaboration period ends (which collaboration period will end no later than March 2023). If during such 180-day right of first negotiation period, the Company notifies Novartis of the Company’s intent to grant a third party a license to a target or TCR identified in the collaboration, then Novartis may obtain the exclusive right to negotiate a license to such target or TCR for an additional 270 days by providing the Company with a term sheet to license such target or TCR within 90 days of the Company’s notice of such intent. The Novartis Agreement provides for payments of an upfront fee of $ 20.0 million, research funding totaling $ 10.0 million and potential milestone payments contingent on clinical, regulatory and sales success. In addition to payments upon achievement of certain clinical and regulatory milestones, Novartis will pay the Company mid-single to low double-digit royalties on net sales for each product directed to a target licensed by Novartis. After the end of the collaboration period and the expiration of Novartis’ first right of negotiation, the Company is free to develop TCRs against targets not licensed by Novartis. The Company concluded that Novartis meets the definition of a customer, as the Company is delivering research and development activities and know-how rights. The Company identified performance obligations for research and development activities, data reporting and participation in joint steering and research committees. The Company determined there is a single performance obligation due to the services being highly interrelated and are therefore not distinct in the context of the contract. The Company combined the pre-option research services and data reporting into a single performance obligation Novartis has an exclusive option to obtain a commercial license for up to three Targets (as defined in the Novartis Agreement) to pursue further development and commercialization of the respective Target. Pursuant to the Novartis Agreement, the option for Novartis to license, develop, and commercialize Targets is not a performance obligation at the outset of the Novartis Agreement as it is a customer option that does not represent a material right. The Company looked to the promises in the arrangement to determine the method of recognition that best coincides with the pattern of delivery. The Company concluded that the performance of the research services over the expected research term was the predominant promise within the performance obligation. The Company is recognizing the revenue associated with the performance obligation using the input method, according to the actual costs incurred as a percentage of total expected costs to complete the research services. As costs are incurred, the Company will recognize revenue over time. Any change in the estimated percentage complete due to a revised cost forecast will be adjusted in the period in which the change in estimate occurs and the revenue recognition will be updated accordingly. The Company expects the research term to last approximately three years , which is inclusive of the option to extend the arrangement. The Company determined that the $ 20.0 million upfront payment, together with the $ 10.0 million of estimated research costs to be reimbursed by Novartis to be the entirety of the consideration to be included in the transaction price as of the outset of the arrangement. The potential milestone payments that the Company is eligible to receive were excluded from the transaction price, as all milestone amounts were fully constrained based on the assessed probability of achievement. The Company will re-evaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust the estimate of the transaction price. During the nine months ended September 30, 2021, the Company recognized $ 7.0 million of revenue associated with the Novartis Agreement based on performance completed during that period. Additionally, during the nine months ended September 30, 2021, the Company incurred $ 2.4 million of costs associated with the Novartis Agreement that were recorded within research and development expenses in the statements of operations. Additionally, as of September 30, 2021, the Company had current and long-term deferred revenue of $ 12.0 million and $ 2.8 million, respectively due to Novartis Agreement.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Brigham and Women’s License Agreement The Company obtained the worldwide exclusive license to its foundational technology from The Brigham and Women’s Hospital, Inc. (or BWH). The license, as amended, grants worldwide exclusive use to the patent underlying the TargetScan technology in exchange for fees including development milestones and various royalties on product sales should they occur in the future. Royalty Agreement In June 2018, the Company amended and restated an existing royalty agreement with one of its founders. Under the amended and restated royalty agreement, the Company agreed to pay the founder an aggregate royalty of 1 % of net sales of any product sold by the Company or by any of its direct or indirect licensees for use in the treatment of any disease or disorder covered by a pending patent application or issued patent held or controlled by the Company as of the last date that the founder was providing services to the Company as a director or consultant under a written agreement in perpetuity. Royalties are payable with respect to each applicable product for a defined period of time set forth in the royalty agreement. The founder assigned his rights and obligations under the royalty agreement to one of his affiliated entities in January 2021.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Net Loss Per Share Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share data): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Numerator: Net loss $ ( 15,839 ) $ ( 7,170 ) $ ( 34,425 ) $ ( 18,320 ) Denominator: Weighted-average common shares outstanding, basic and diluted 19,875,428 1,001,853 7,562,436 896,100 Net loss per share, basic and diluted $ ( 0.80 ) $ ( 7.16 ) $ ( 4.55 ) $ ( 20.44 ) We have two classes of common stock, each with identical participation rights to earnings and liquidation preferences, and therefore the calculation of net loss per share as described above is identical to the calculation under the two-class method. The Company excluded the following potential common shares from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: September 30, 2021 2020 Series A Preferred Stock (as converted to common stock) - 3,209,240 Series B Preferred Stock (as converted to common stock) - 3,853,864 Unvested restricted common stock 204,513 524,660 Options to purchase common stock 3,090,849 1,410,038 Total 3,295,362 8,997,802

Related-Party Transactions

Related-Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related-Party Transactions	10. Related-Party Transactions Novartis and its affiliates hold shares of voting and non-voting common stock and is the customer in the Novartis Agreement discussed in Note 7.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (US GAAP) and applicable rules and regulations of the Securities and Exchange Commission (the SEC) regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by US GAAP for complete financial statements. Management believes that the interim financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company’s financial position, results of its operations and cash flows. The condensed consolidated financial statements include the accounts of TScan Therapeutics, Inc. and its subsidiary TScan Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 , any other interim periods, or any future year or period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and unaudited condensed consolidated statements included in the Company’s final prospectus related to the Company’s IPO dated July 15, 2021 and filed with the Securities Exchange Commission on July 16, 2021, pursuant to Rule 424(b) under the Securities Act of 1933, as amended (the Prospectus).

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Carried at Fair Value on a Heirarchy Basis	The following tables set forth by level, within the fair value hierarchy, the assets (liabilities) carried at fair value (in thousands): Fair value measurements at September 30, 2021 using: Level 1 Level 2 Level 3 Total Assets Cash equivalents – money market funds $ 181,300 $ - $ - $ 181,300 Total financial assets $ 181,300 $ - $ - $ 181,300 Fair value measurements at December 31, 2020 using: Level 1 Level 2 Level 3 Total Assets Cash equivalents – money market funds $ 33,748 $ - $ - $ 33,748 Total financial assets $ 33,748 $ - $ - $ 33,748

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, 2021 2020 Accrued employee compensation and benefits $ 1,747 $ 1,535 Accrued research and development 1,398 60 Accrued consulting and professional services 445 189 Accrued legal services and license fee 27 578 Other 668 132 Total accrued expenses and other current liabilities $ 4,285 $ 2,494

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Schedule of Preferred Stock	As of December 31, 2020, the preferred stock consisted of the following (in thousands, except for share data): December 31, 2020 Preferred Stock Authorized Preferred Stock Issued and Outstanding Carrying Value Liquidation Common Stock Series A Preferred Stock 26,315,790 3,209,240 $ 24,874 $ 29,838 3,209,240 Series B Preferred Stock 31,601,732 3,853,864 34,807 39,037 3,853,864 Total 57,917,522 7,063,104 $ 59,681 $ 68,875 7,063,104

Stock Based Compensation (Table

Stock Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Key Assumptions Used for Black-Scholes Option-pricing Model to Estimate the Fair Value of Stock Options	The key assumptions used to apply this pricing model during the nine months ended September 30, 2021 and 2020, were as follows: Nine Months Ended September 30, 2021 2020 Risk free interest rate 0.76 % 0.91 % Expected term (in years) 6.05 6.06 Expected dividend yield 0 % 0 % Expected volatility of underlying common stock 75 % 71 %
Summary of Stock Option Activity	The following table summarizes the stock option activity under the 2018 Plan and 2021 Plan: Stock Weighted Weighted Intrinsic Outstanding January 1, 2021 1,445,426 $ 2.62 8.74 $ 3,799 Granted 1,882,441 8.80 Exercised ( 108,657 ) 2.18 Canceled ( 128,361 ) 4.82 Outstanding September 30, 2021 3,090,849 $ 6.40 8.91 $ 9,452 Options vested or expected to vest as of September 30, 2021 3,090,849 $ 6.40 8.91 $ 9,452 Stock options exercisable as of September 30, 2021 558,385 $ 2.44 7.76 $ 3,302
Summary of Restricted Common Stock Activity	A summary of the activity for the nine months ended September 30, 2021 is as follows: Number of Weighted Unvested restricted stock as of January 1, 2021 438,280 - Vested ( 233,767 ) - Unvested restricted stock as of September 30, 2021 204,513 -
Summary of Stock-based Compensation Expense	Stock-based compensation expense was as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 270 $ 61 $ 626 $ 173 General and administrative 615 67 1,106 192 Total stock-based compensation expense $ 885 $ 128 $ 1,732 $ 365

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Loss Per Share	Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share data): Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Numerator: Net loss $ ( 15,839 ) $ ( 7,170 ) $ ( 34,425 ) $ ( 18,320 ) Denominator: Weighted-average common shares outstanding, basic and diluted 19,875,428 1,001,853 7,562,436 896,100 Net loss per share, basic and diluted $ ( 0.80 ) $ ( 7.16 ) $ ( 4.55 ) $ ( 20.44 )
Summary of Potential Common Shares Excluded from Computation of Diluted Net Loss per Share	The Company excluded the following potential common shares from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: September 30, 2021 2020 Series A Preferred Stock (as converted to common stock) - 3,209,240 Series B Preferred Stock (as converted to common stock) - 3,853,864 Unvested restricted common stock 204,513 524,660 Options to purchase common stock 3,090,849 1,410,038 Total 3,295,362 8,997,802

Nature of Business and Basis _2

Nature of Business and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	May 13, 2021	Jul. 31, 2021USD ($)$ / sharesshares	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Date of incorporation					Apr. 17, 2018
Net proceeds from issuance of shares | $					$ 89,647
Common stock issuable upon conversion							7,063,104
Net losses | $			$ 15,839	$ 7,170	34,425	$ 18,320
Accumulated deficit | $			$ 77,958		$ 77,958		$ 43,533
Reverse stock split					1-for-8.2
Reverse stock split conversion ratio	8.2
Voting Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock, shares authorized			300,000,000		300,000,000		165,210,543
Non-voting Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock, shares authorized			10,000,000		10,000,000		0
Initial Public Offering | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock issuable upon conversion		15,616,272
Initial Public Offering | Preferred Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Preferred stock, shares authorized		10,000,000
Initial Public Offering | Voting Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued and sold		6,666,667
Sale of stock price per share | $ / shares		$ 15
Gross proceeds from issuance initial public offering | $		$ 100,000
Net proceeds from issuance of shares | $		89,600
Underwriting discounts and commissions | $		7,000
Deferred offering cost | $		$ 3,400
Common stock, shares authorized		300,000,000
Initial Public Offering | Non-voting Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock issuable upon conversion		5,143,134
Common stock, shares authorized		10,000,000

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Carried at Fair Value on a Hierarchy Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]
Total financial assets	$ 181,300	$ 33,748
Cash Equivalents - Money Market Funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents fair value disclosure	181,300	33,748
Level 1
Assets, Fair Value Disclosure [Abstract]
Total financial assets	181,300	33,748
Level 1 | Cash Equivalents - Money Market Funds
Assets, Fair Value Disclosure [Abstract]
Cash and cash equivalents fair value disclosure	$ 181,300	$ 33,748

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair value, assets, level 1 to level 2 transfers	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers	0	0
Fair value, assets, transfers into level 3	0	0
Fair value, assets, transfers out of level 3	$ 0	$ 0

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued employee compensation and benefits	$ 1,747	$ 1,535
Accrued research and development	1,398	60
Accrued consulting and professional services	445	189
Accrued legal services and license fee	27	578
Other	668	132
Total accrued expenses and other current liabilities	$ 4,285	$ 2,494

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2021	Dec. 31, 2020
Temporary Equity [Line Items]
Common stock issuable upon conversion						7,063,104
Preferred stock, Shares outstanding	0	0
Common Stock
Temporary Equity [Line Items]
Stock issuance costs	$ 10.4	$ 10.4
Initial Public Offering | Common Stock
Temporary Equity [Line Items]
Common stock issuable upon conversion					15,616,272
Series A Preferred Stock
Temporary Equity [Line Items]
Preferred stock, value				$ 25
Preferred stock issued, shares				3,209,240
Stock issuance costs				$ 0.1
Common stock issuable upon conversion						3,209,240
Series B Preferred Stock
Temporary Equity [Line Items]
Preferred stock, value			$ 35
Preferred stock issued, shares			3,853,864
Stock issuance costs			$ 0.2
Common stock issuable upon conversion						3,853,864
Series C Preferred Stock
Temporary Equity [Line Items]
Preferred stock, value		$ 100
Preferred stock issued, shares	8,553,168	8,553,168
Stock issuance costs		$ 0.3
Non-voting Common Stock | Initial Public Offering
Temporary Equity [Line Items]
Common stock issuable upon conversion					5,143,134

Convertible Preferred Stock - S

Convertible Preferred Stock - Schedule of Preferred Stock (Details)	Dec. 31, 2020USD ($)shares
Temporary Equity [Line Items]
Preferred Stock Authorized	57,917,522
Preferred Stock Issued and Outstanding	7,063,104
Carrying Value | $	$ 59,681,000
Liquidation Preference | $	$ 68,875,000
Common Stock Issuable Upon Conversion	7,063,104
Series A Preferred Stock
Temporary Equity [Line Items]
Preferred Stock Authorized	26,315,790
Preferred Stock Issued and Outstanding	3,209,240
Carrying Value | $	$ 24,874,000
Liquidation Preference | $	$ 29,838,000
Common Stock Issuable Upon Conversion	3,209,240
Series B Preferred Stock
Temporary Equity [Line Items]
Preferred Stock Authorized	31,601,732
Preferred Stock Issued and Outstanding	3,853,864
Carrying Value | $	$ 34,807,000
Liquidation Preference | $	$ 39,037,000
Common Stock Issuable Upon Conversion	3,853,864

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Details) - USD ($)	Jul. 15, 2021	Sep. 30, 2021	Jul. 14, 2021	Apr. 20, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense		$ 10,600,000
Weighted average period remaining (in years)		3 years 1 month 2 days
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of stock options		4 years
Expected dividend-yield assumption		$ 0
Weighted average value of stock options, granted		$ 5.79
Restricted Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock, vesting term		4 years
Purchase price of restricted common stock		$ 0.001
Maximum | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of stock options		10 years
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock shares under the plan				2,902,738
2021 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock shares under the plan	3,278,048	2,836,264
Number of awards permitted to grant			0
Percentage of number of common stock issued and outstanding	4.00%
2021 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock shares under the plan	167,887
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock shares under the plan		254,390
Number of awards permitted to grant			0
Percentage of number of common stock issued and outstanding	1.00%
Common stock, Reserved for future issuance	254,390

Stock Based Compensation - Key

Stock Based Compensation - Key Assumptions Used for Black-Scholes Option-pricing Model to Estimate the Fair Value of Stock Options (Details)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk free interest rate	0.76%	0.91%
Expected term (in years)	6 years 18 days	6 years 21 days
Expected dividend yield	0.00%	0.00%
Expected volatility of underlying common stock	75.00%	71.00%

Stock Based Compensation - Summ

Stock Based Compensation - Summary of Stock Option Activity (Details) - Stock Options - 2018 and 2021 Equity Incentive Plans - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Outstanding, Beginning balance	1,445,426
Stock Options Outstanding, Granted	1,882,441
Stock Options Outstanding, Exercised	(108,657)
Stock Options Outstanding, Cancelled	(128,361)
Stock Options Outstanding, Ending balance	3,090,849	1,445,426
Stock Options vested or expected to vest	3,090,849
Stock options exercisable	558,385
Stock Options Outstanding, Weighted Average Exercise Price, Beginning Balance	$ 2.62
Stock Options Granted, Weighted Average Exercise Price	8.80
Stock Options Exercised, Weighted Average Exercise Price	2.18
Stock Options Cancelled, Weighted Average Exercise Price	4.82
Stock Options Outstanding, Weighted Average Exercise Price, Ending balance	6.40	$ 2.62
Stock Options vested or expected to vest, Weighted Average Exercise Price	6.40
Stock options exercisable, Weighted Average Exercise Price	$ 2.44
Stock Options Outstanding, Weighted Average Remaining Contractual Life	8 years 10 months 28 days	8 years 8 months 26 days
Stock Options vested or expected to vest, Weighted Average Remaining Contractual Life	8 years 10 months 28 days
Stock options exercisable, Weighted Average Remaining Contractual Life	7 years 9 months 3 days
Stock Options Outstanding, Intrinsic Value, Beginning	$ 3,799
Stock Options Outstanding, Intrinsic Value, Ending	9,452	$ 3,799
Stock Options vested or expected to vest, Intrinsic Value	9,452
Stock options exercisable, Intrinsic Value	$ 3,302

Stock Based Compensation - Su_2

Stock Based Compensation - Summary of Restricted Common Stock Activity (Details) - Restricted Common Stock	9 Months Ended
	Sep. 30, 2021shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested restricted stock, Beginning balance	438,280
Unvested restricted stock, Vested	(233,767)
Unvested restricted stock, Ending balance	204,513

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
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 885	$ 128	$ 1,732	$ 365
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	270	61	626	173
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 615	$ 67	$ 1,106	$ 192

Collaboration and License Agr_2

Collaboration and License Agreements - Additional Information (Details) $ in Thousands	Mar. 31, 2020USD ($)Target	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Collaboration And License Agreements [Line Items]
Collaboration and license revenue		$ 2,412	$ 290	$ 7,287	$ 290
Incurred costs		18,254	$ 7,461	41,726	$ 18,713
Deferred revenue, current portion		11,967		$ 11,967		$ 10,627
Novartis
Collaboration And License Agreements [Line Items]
License agreement date	Mar. 31, 2020
Upfront payment received	$ 20,000
Negotiation period				180 days
Expects research term	3 years
Collaboration and license revenue				$ 7,000
Incurred costs				2,400
Deferred revenue, current portion		12,000		12,000
Long-term deferred revenue		$ 2,800		$ 2,800
Novartis | Maximum
Collaboration And License Agreements [Line Items]
Number of targets identified | Target	3
Novartis | Research Funding
Collaboration And License Agreements [Line Items]
Upfront payment received	$ 10,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jun. 30, 2018
Royalty Agreement
Commitments And Contingencies Disclosure [Line Items]
Percentage of aggregate royalty of net sales of any product sold	1.00%

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (15,839)	$ (7,170)	$ (34,425)	$ (18,320)
Weighted-average common shares outstanding, basic and diluted	19,875,428	1,001,853	7,562,436	896,100
Net loss per share, basic and diluted	$ (0.80)	$ (7.16)	$ (4.55)	$ (20.44)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Potential Common Shares Excluded from Computation of Diluted Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,295,362	8,997,802
Series A Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		3,209,240
Series B Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		3,853,864
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	204,513	524,660
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	3,090,849	1,410,038