Keros Therapeutics (KROS) 10-Q 6 Nov 23 2023 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-39264
Entity Registrant Name	KEROS THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-1173868
Entity Address, Address Line One	1050 Waltham Street,
Entity Address, Address Line Two	Suite 302
Entity Address, City or Town	Lexington,
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02421
City Area Code	617
Local Phone Number	314-6297
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	KROS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		29,959,378
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001664710

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
CURRENT ASSETS:
Cash and cash equivalents	$ 287,893	$ 279,048
Prepaid expenses and other current assets	16,542	6,719
Total current assets	304,435	285,767
Operating lease right-of-use assets	15,669	15,548
Property and equipment, net	3,357	2,021
Restricted cash	1,212	1,327
Other long-term assets	1,574	2,118
TOTAL ASSETS	326,247	306,781
CURRENT LIABILITIES:
Accounts payable	3,867	3,339
Current portion of operating lease liabilities	611	455
Accrued expenses and other current liabilities	12,223	12,753
Total current liabilities	16,701	16,547
Operating lease liabilities, net of current portion	13,704	12,811
Total liabilities	30,405	29,358
STOCKHOLDERS' EQUITY:
Common stock, par value of $0.0001 per share; 200,000,000 shares authorized as of September 30, 2023 and December 31, 2022; 29,679,143 and 27,543,453 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	3	2
Additional paid-in capital	637,022	505,855
Accumulated deficit	(341,183)	(228,434)
Total stockholders' equity	295,842	277,423
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 326,247	$ 306,781

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	29,679,143	27,543,453
Common stock, shares outstanding (in shares)	29,679,143	27,543,453

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Total revenue	$ 8,000	$ 0	$ 8,000	$ 0
OPERATING EXPENSES:
Research and development	(34,140,000)	(21,039,000)	(97,765,000)	(62,398,000)
General and administrative	(9,148,000)	(6,937,000)	(25,729,000)	(20,432,000)
Total operating expenses	(43,288,000)	(27,976,000)	(123,494,000)	(82,830,000)
LOSS FROM OPERATIONS	(43,280,000)	(27,976,000)	(123,486,000)	(82,830,000)
OTHER INCOME (EXPENSE), NET
Interest expense, net	0	0	0	(1,000)
Research and development incentive income	0	3,705,000	0	7,081,000
Other income, net	3,840,000	762,000	10,737,000	789,000
Total other income, net	3,840,000	4,467,000	10,737,000	7,869,000
Net loss	(39,440,000)	(23,509,000)	(112,749,000)	(74,961,000)
Net loss attributable to common stockholders—basic	(39,440,000)	(23,509,000)	(112,749,000)	(74,961,000)
Net loss attributable to common stockholders— diluted	$ (39,440,000)	$ (23,509,000)	$ (112,749,000)	$ (74,961,000)
Net loss per share attributable to common stockholders - basic (in USD per share)	$ (1.33)	$ (0.92)	$ (3.86)	$ (3.05)
Net loss per share attributable to common stockholders - diluted (in USD per share)	$ (1.33)	$ (0.92)	$ (3.86)	$ (3.05)
Weighted-average common stock outstanding - basic (in shares)	29,668,247	25,549,701	29,218,143	24,538,159
Weighted-average common stock outstanding - diluted (in shares)	29,668,247	25,549,701	29,218,143	24,538,159
Revenue, Product and Service [Extensible Enumeration]	License	License	License	License

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Total	At the Market Offering	COMMON STOCK	COMMON STOCK At the Market Offering	ADDITIONAL PAID-IN CAPITAL	ADDITIONAL PAID-IN CAPITAL At the Market Offering	ACCUMULATED DEFICIT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending balance (in shares)			23,974,834
Ending balance	$ 243,174		$ 2		$ 366,927		$ (123,755)
Beginning balance (in shares) at Dec. 31, 2021			23,974,834
Beginning balance at Dec. 31, 2021	243,174		$ 2		366,927		(123,755)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)			28,269
Exercise of common stock options	118				118
Stock-based compensation	4,388				4,388
Net loss	(24,186)						(24,186)
Beginning balance (in shares) at Dec. 31, 2021			23,974,834
Beginning balance at Dec. 31, 2021	243,174		$ 2		366,927		(123,755)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(74,961)
Ending balance (in shares)			24,003,103
Ending balance	223,494		$ 2		371,433		(147,941)
Beginning balance (in shares) at Mar. 31, 2022			24,003,103
Beginning balance at Mar. 31, 2022	223,494		$ 2		371,433		(147,941)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under the ATM agreement, net of commissions and offering cost (in shares)				355,425
Issuance of common stock under the ATM agreement, net of commissions and offering cost		$ 9,684				$ 9,684
Exercise of common stock options (in shares)			70,854
Exercise of common stock options	502				502
Stock-based compensation	4,794				4,794
Net loss	(27,266)						(27,266)
Ending balance (in shares)			24,429,382
Ending balance	211,208		$ 2		386,413		(175,207)
Beginning balance (in shares) at Jun. 30, 2022			24,429,382
Beginning balance at Jun. 30, 2022	211,208		$ 2		386,413		(175,207)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under the ATM agreement, net of commissions and offering cost (in shares)				1,592,322
Issuance of common stock under the ATM agreement, net of commissions and offering cost		48,476				48,476
Exercise of common stock options (in shares)			55,500
Exercise of common stock options	96				96
Stock-based compensation	4,754				4,754
Net loss	(23,509)						(23,509)
Ending balance (in shares)			26,077,204
Ending balance	241,025		$ 2		439,739		(198,716)
Ending balance (in shares)			27,543,453
Ending balance	277,423		$ 2		505,855		(228,434)
Beginning balance (in shares) at Dec. 31, 2022			27,543,453
Beginning balance at Dec. 31, 2022	277,423		$ 2		505,855		(228,434)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under the ATM agreement, net of commissions and offering cost (in shares)				1,990,927
Issuance of common stock under the ATM agreement, net of commissions and offering cost		$ 107,308		$ 1		$ 107,307
Exercise of common stock options (in shares)			14,269
Exercise of common stock options	370				370
Stock-based compensation	5,687				5,687
Net loss	(35,804)						(35,804)
Beginning balance (in shares) at Dec. 31, 2022			27,543,453
Beginning balance at Dec. 31, 2022	$ 277,423		$ 2		505,855		(228,434)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	144,763
Net loss	$ (112,749)
Ending balance (in shares)			29,548,649
Ending balance	354,984		$ 3		619,219		(264,238)
Beginning balance (in shares) at Mar. 31, 2023			29,548,649
Beginning balance at Mar. 31, 2023	354,984		$ 3		619,219		(264,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)			112,356
Exercise of common stock options	1,740				1,740
Stock-based compensation	7,041				7,041
Net loss	(37,505)						(37,505)
Ending balance (in shares)			29,661,005
Ending balance	326,260		$ 3		628,000		(301,743)
Beginning balance (in shares) at Jun. 30, 2023			29,661,005
Beginning balance at Jun. 30, 2023	326,260		$ 3		628,000		(301,743)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)			18,138
Exercise of common stock options	311				311
Stock-based compensation	8,711				8,711
Net loss	(39,440)						(39,440)
Ending balance (in shares)			29,679,143
Ending balance	$ 295,842		$ 3		$ 637,022		$ (341,183)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders’ Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) shares	Sep. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) shares
Common stock, par value (in USD per share) | $ / shares		$ 0.0001
Exercise of common stock options	$ 370	$ 96	$ 502
Stock-based compensation	5,687	4,754	4,794
Net loss	$ (35,804)	$ (23,509)	$ (27,266)
Common stock
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | shares	14,269	55,500	70,854
ADDITIONAL PAID-IN CAPITAL
Exercise of common stock options	$ 370	$ 96	$ 502
Stock-based compensation	5,687	4,754	4,794
ACCUMULATED DEFICIT
Net loss	(35,804)	(23,509)	(27,266)
At the Market Offering
Issuance costs	$ 1,665	$ 796	$ 153

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (39,440)	$ (35,804)	$ (23,509)	$ (24,186)	$ (112,749)	$ (74,961)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense					568	547
Loss on disposal of fixed asset					4	11
Stock-based compensation expense					21,439	13,936
Non-cash lease expense					1,217	620
Changes in operating assets and liabilities:
Accounts receivable					0	18,000
Prepaid expenses and other current assets					(9,823)	(3,051)
Other assets					0	(1,574)
Accounts payable					570	(1,003)
Right-to-use assets and operating lease liabilities					255	(2,203)
Accrued expenses and other current liabilities					(530)	1,059
Net cash used in operating activities					(99,049)	(48,619)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment					(1,923)	(890)
Net cash used in investing activities					(1,923)	(890)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of offering cost					107,308	58,177
Payment of issuance costs					(27)	0
Proceeds from exercise of stock options					2,421	716
Net cash provided by financing activities					109,702	58,893
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH					8,730	9,384
Cash, cash equivalents and restricted cash at beginning of period		$ 280,375		$ 231,369	280,375	231,369	$ 231,369
Cash, cash equivalents and restricted cash at end of period	289,105		240,753		289,105	240,753	280,375
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Right-of-use assets obtained in exchange for operating lease obligation					1,338	0
Property and equipment purchases in accounts payable					60	13
Issuance cost in accrued expenses					0	17
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	287,893		239,426		287,893	239,426	279,048
Restricted cash	1,212		1,327		1,212	1,327
Total cash, cash equivalents and restricted cash	$ 289,105		$ 240,753		$ 289,105	$ 240,753	$ 280,375

NATURE OF BUSINESS AND BASIS OF

NATURE OF BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS AND BASIS OF PRESENTATION	NATURE OF BUSINESS AND BASIS OF PRESENTATION Keros Therapeutics, Inc. (“Keros” or the “Company”) was incorporated in 2015 as a Delaware corporation. Its principal offices are in Lexington, Massachusetts. The Company is a clinical-stage biopharmaceutical company focused on developing and commercializing novel therapeutics to treat a wide range of patients with disorders that are linked to dysfunctional signaling of the transforming growth factor-beta (“TGF-ß”) family of proteins. The Company’s lead protein therapeutic product candidate, KER-050 (elritercept), is an engineered ligand trap comprised of a modified ligand-binding domain of the TGF-ß receptor known as activin receptor type IIA that is fused to the portion of the human antibody known as the Fc domain. KER-050 is being developed for the treatment of low blood cell counts (“cytopenias”), including anemia and thrombocytopenia, in patients with myelodysplastic syndromes (“MDS”) and in patients with myelofibrosis. The Company’s second product candidate, KER-012, is designed to bind to and inhibit the signaling of TGF-ß ligands that stimulate smooth muscle hypertrophy and fibrosis, including activin A, activin B and myostatin (GDF8). KER-012 is being developed for the treatment of pulmonary arterial hypertension (“PAH”) and for the treatment of cardiovascular disorders. The Company's third product candidate, KER-065, is designed to bind to and inhibit TGF-ß ligands, including myostatin (GDF8) and activin A, which are negative regulators of muscle and bone mass and strength. KER-065 is being developed for the treatment of neuromuscular diseases, with an initial focus on Duchenne muscular dystrophy. Since its inception in 2015, the Company has devoted the majority of its resources to business planning, research and development of its product candidates, including conducting clinical trials and preclinical studies, raising capital and recruiting management and technical staff to support these operations. To date, the Company has not generated any revenue from product sales as none of its product candidates have been approved for commercialization. In May 2021, the Company filed a registration statement on Form S-3, which was automatically effective upon filing (the "Shelf Registration Statement"). Pursuant to the Shelf Registration Statement, the Company could issue up to $150.0 million in common stock in sales deemed to be an “at the market offering,” as defined by the Securities Act of 1933, as amended (“Securities Act”), and, so long as the Company qualifies as a “well-known seasoned issuer” as defined in Rule 405 of the Securities Act, an unspecified amount of shares of the Company common stock, preferred stock, debt securities and warrants. In December 2022, the Company filed a prospectus supplement to the Shelf Registration Statement for the issuance and sale, if any, of up to an additional $250.0 million in common stock in sales deemed to be an “at the market offering,” as defined by the Securities Act. Liquidity and Capital Resources The Company’s condensed consolidated financial statements have been prepared on the basis of the Company continuing as a going concern for the next 12 months. Management believes that the Company’s existing $287.9 million in cash and cash equivalents will allow the Company to continue its operations for at least the next 12 months. In the absence of a significant source of recurring revenue, the continued viability of the Company beyond that point is dependent on its ability to continue to raise additional capital to finance its operations. If the Company is unable to obtain additional funding, the Company may be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. The accompanying unaudited interim condensed consolidated financial statements as of September 30, 2023 and for the three and nine months ended September 30, 2023 and 2022 have been prepared by the Company in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and, pursuant to the rules and regulations of Article 10 of Regulation S-X of the Securities Act published by the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes the disclosures are adequate. These unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies The significant accounting policies and estimates used in preparation of the unaudited interim condensed consolidated financial statements are described in the Company’s audited consolidated financial statements as of and for the year ended December 31, 2022, and the notes thereto, which are included in the Annual Report. Except as detailed below, there have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2023. Risks and Uncertainties There have been significant disruptions to global financial markets that have contributed to a general global economic slowdown. While recent trends towards rising inflation have eased prices continue to rise, which may materially affect the Company's business and corresponding financial position and cash flows. Inflationary factors, such as increases in the cost of materials and supplies relating to the Company's clinical trials, interest rates and overhead costs may adversely affect its operating results. Rising interest rates present a recent challenge impacting the U.S. economy and could make it more difficult for the Company to obtain traditional financing on acceptable terms, if at all, in the future. Additionally, the general consensus among economists suggests that the Company should expect a higher recession risk to continue over the next year, which, together with the foregoing, could result in further economic uncertainty and volatility in the capital markets in the near term, and could negatively affect the Company's operations. Furthermore, such economic conditions have produced downward pressure on share prices. Although the Company does not believe that inflation or higher interest rates have had a material impact on its financial position or results of operations to date, the Company may experience increases in the near future (especially if inflation rates rise more quickly) on its operating costs, including its labor costs and research and development costs, due to supply chain constraints, consequences associated with public health crises and global geopolitical tensions as a result of the ongoing war between Russia and Ukraine and the war in Israel, worsening global macroeconomic conditions and employee availability and wage increases, which may result in additional stress on the Company's working capital resources.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): DESCRIPTION SEPTEMBER 30, 2023 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS SIGNIFICANT OTHER OBSERVABLE INPUTS SIGNIFICANT OTHER OBSERVABLE INPUTS Assets Money market funds $ 285,964 $ 285,964 $ — $ — Total financial assets $ 285,964 $ 285,964 $ — $ — DESCRIPTION DECEMBER 31, 2022 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3) Assets Money market funds $ 271,734 $ 271,734 $ — $ — Total financial assets $ 271,734 $ 271,734 $ — $ —

PREPAID EXPENSES AND OTHER CURR

PREPAID EXPENSES AND OTHER CURRENT ASSETS	9 Months Ended
	Sep. 30, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID EXPENSES AND OTHER CURRENT ASSETS	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid service contracts $ 12,805 $ 3,319 Prepaid sales tax 441 872 Prepaid rent — 96 Prepaid subscription 921 470 Prepaid insurance 1,158 941 Interest and dividend receivable 898 841 Other 319 180 Total prepaid expenses and other current assets $ 16,542 $ 6,719

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued external R&D costs $ 1,745 $ 2,429 Accrued external manufacturing costs 3,385 4,240 Accrued compensation and benefits 6,111 4,811 Accrued tax 30 50 Accrued professional fees 549 523 Other 403 700 Total accrued expenses and other current liabilities $ 12,223 $ 12,753

COMMON STOCK

COMMON STOCK	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
COMMON STOCK	COMMON STOCK As of September 30, 2023, the Company’s amended and restated certificate of incorporation authorized the Company to issue 200,000,000 shares of common stock at a par value of $0.0001 per share. On May 3, 2021, the Company entered into a Sales Agreement (the “ATM Sales Agreement”) with SVB Securities LLC (doing business as Leerink Partners LLC) (“Leerink”), as agent, pursuant to which the Company may offer and sell, from time to time, shares of its common stock through Leerink (the "ATM Offering"). On May 3, 2021, the Company filed the Shelf Registration Statement, including a base prospectus and sales agreement prospectus, with the SEC, which became effective immediately upon filing, for the issuance and sale of up to $150.0 million of shares of the Company’s common stock under the ATM Sales Agreement. On December 12, 2022, the Company filed a prospectus supplement to the Shelf Registration Statement for the issuance and sale, if any, of up to an additional $250.0 million of shares of its common stock under the ATM Sales Agreement. For the year ended December 31, 2022 , the Company raised gross proceeds of $121.4 million pursuant to the ATM Offering through the sale of 3,410,384 shares of common stock at a weighted average price of $35.60 per share. The net proceeds from the ATM Offering for the year ended December 31, 2022 were approximately $119.4 million after deducting sales agent commissions of $1.8 million and offering expenses of $0.2 million.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION 2017 Stock Incentive Plan The Board adopted the 2017 Stock Incentive Plan (the "2017 Plan") in February 2017, and the stockholders approved the 2017 Plan in March 2017. The 2017 Plan was most recently amended in March 2020. As of September 30, 2023, there was an aggregate of 555,735 shares of common stock issuable upon the exercise of outstanding options under the 2017 Plan. Any options or awards outstanding under the 2017 Plan remain outstanding and effective. 2020 Equity Incentive Plan In April 2020, the 2020 Equity Incentive Plan (the "2020 Plan") became effective, and, as a result, no further awards will be made under the 2017 Plan. The 2020 Plan provides for the grant of stock options qualifying as incentive stock options ("ISOs"), to employees and for the grant of nonstatutory stock options ("NSOs"), restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of stock compensation to employees, consultants and directors. The 2020 Plan also provides for the grant of performance cash awards to employees, consultants and directors. Any previously granted awards under the 2017 Plan will remain outstanding in accordance with their respective terms. Under the 2020 Plan, there is an annual increase on January 1 of each year from January 1, 2021 continuing through January 1, 2030, by 4.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Board. On January 1, 2023, the Company increased the number of shares available for future grant under the 2020 Plan by 1,101,738 shares. As of September 30, 2023, there was an aggregate of 3,868,372 shares of common stock issuable upon the exercise of outstanding options under the 2020 Plan. Additionally, there were an aggregate of 1,038,414 shares reserved for future issuance under the 2020 Plan, including shares forfeited from the 2017 Plan. Stock Options A summary of option activity during the nine months ended September 30, 2023 is as follows (in thousands except share and per share data): NUMBER OF OPTIONS WEIGHTED-AVERAGE EXERCISE PRICE Outstanding as of December 31, 2022 3,533,169 $ 30.26 Granted 1,292,895 50.27 Exercised (144,763) 16.73 Cancelled or Forfeited (233,398) 45.19 Expired (23,796) $ 57.28 Outstanding as of September 30, 2023 4,424,107 $ 35.61 Options exercisable as of September 30, 2023 2,298,161 $ 24.84 The weighted-average grant date fair value price per share of options granted during the nine months ended September 30, 2023 and 2022 was $36.05 and $31.42, respectively. As of September 30, 2023, there was $63.6 million of unrecognized stock-based compensation expense related to unvested stock options. The unrecognized stock-based compensation expense is estimated to be recognized over a period of 2.7 years. The aggregate intrinsic value of the stock options outstanding and stock options exercisable was $33.6 million and $31.7 million as of September 30, 2023, respectively. The aggregate intrinsic value of stock options exercised was $4.1 million and $5.6 million during the nine months ended September 30, 2023 and 2022, respectively. Stock-Based Compensation Expense Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2023 and 2022 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Research and development $ 4,745 $ 2,132 $ 10,766 $ 6,095 General and administrative 3,966 2,622 10,673 7,841 Total stock-based compensation expense $ 8,711 $ 4,754 $ 21,439 $ 13,936

LOSS PER SHARE

LOSS PER SHARE	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
LOSS PER SHARE	LOSS PER SHARE The Company’s potentially dilutive securities, which includes stock options, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders at September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: SEPTEMBER 30, SEPTEMBER 30, Options to purchase common stock 4,424,107 3,483,918

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Operating Leases Operating lease liabilities are measured based on the present value of future lease payments over the expected remaining lease term. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term and are initially equal to their corresponding lease liabilities, subject to certain adjustments such as prepaid lease payments, initial direct costs and lease incentives. When the rate implicit in the lease is not readily determinable, the Company uses an incremental borrowing rate based on information available at the commencement date in determining the present value of lease payments. The incremental borrowing rate represents the rate of interest that the Company would have to pay to borrow on a collateralized basis over a similar term at an amount equal to the lease payments in a similar economic environment. The Company estimates this rate based on prevailing market conditions, comparable company and credit analyses, the impact of collateralization, and the term of each of the Company’s lease agreements. On September 7, 2021, the Company entered into an indenture of lease (as amended, the “1050 Waltham Lease”) with Revolution Labs Owner LLC (the “Landlord”), pursuant to which the Company is leasing approximately 35,662 square feet of office, laboratory and vivarium space located at 1050 Waltham Street, Lexington, Massachusetts (the “Premises”) for its new principal executive office. In December 2022, the Company received access to approximately 31,991 square feet of the Premises (the “Phase A Premises”) pertaining to the office and laboratory space in order to prepare for use. Accordingly, the 1050 Waltham Lease for the Phase A Premises, which is considered a distinct lease component, was determined to be classified as an operating lease and the Company recorded an ROU asset of $15.4 million, inclusive of lease payments made prior to commencement of the 1050 Waltham Lease, and a lease liability of $12.9 million on the consolidated balance sheets as of December 31, 2022. In January 2023, the Company entered into a first amendment to the 1050 Waltham Lease (the “Lease Amendment”). Under the terms of the Lease Amendment, a phased delivery of the Premises by the Landlord was established as follows: (i) the delivery of the Phase A Premises in January 2023 and (ii) the delivery of the additional approximately 3,671 rentable square feet of vivarium space (the “Phase B Premises”) in March 2023. As a result of the Lease Amendment, the lease liability for the Phase A Premises was remeasured, resulting in a non-cash decrease to the Company’s operating lease liabilities and ROU assets of $0.5 million in the quarter ended March 31, 2023. Upon delivery of the Phase B Premises in March 2023, the Phase B Premises was determined to be classified as an operating lease and the Company recorded an ROU asset of $1.9 million, inclusive of lease payments made prior to commencement, and a lease liability of $1.4 million on the consolidated balance sheets. Upon delivery of the Phase B Premises, the rent commencement date of the Premises was determined to begin in November 2023, with base rent initially fixed at $0.2 million per month in total for the Premises. Under the 1050 Waltham Lease, base rent will increase by approximately 3% per annum until the 1050 Waltham Lease expires on November 30, 2031. The Company is obligated to reimburse the Landlord for certain variable costs, including its proportional share of taxes and operating expenses which are not included in the measurement of the 1050 Waltham Lease liability. In connection with its entry into the 1050 Waltham Lease, the Company has provided the Landlord a letter of credit in the amount of approximately $1.2 million, which is recognized as restricted cash on the consolidated balance sheets. The Company has the option to extend the term of the 1050 Waltham Lease for a period of an additional 5 years. As of September 30, 2023, the Company has no reasonable certainty that this option to extend will be exercised. Operating lease costs were $2.2 million and $0.7 million for the nine months ended September 30, 2023 and 2022, respectively. Variable lease costs were $0.9 million and $0.5 million for the nine months ended September 30, 2023 and 2022, respectively. Cash paid for operating leases was $0.9 million and $0.7 million for the nine months ended September 30, 2023 and 2022, respectively. The weighted average remaining lease term is 8.2 years at September 30, 2023. The weighted average discount rate is 10.34% at September 30, 2023. Maturities of operating lease liabilities at September 30, 2023 are as follows (in thousands): 2023 (remaining three months) 243 2024 2,431 2025 2,504 2026 2,578 2027 2,657 2028 2,736 2029 2,818 2030 2,903 2031 2,734 Total lease payments 21,604 Less: imputed interest (7,289) Total operating lease liabilities $ 14,315 Included in the consolidated balance sheet: Current portion of operating lease liabilities 611 Operating lease liabilities, net of current portion 13,704 Total operating lease liabilities $ 14,315

REVENUE FROM CONTRACTS WITH CUS

REVENUE FROM CONTRACTS WITH CUSTOMERS	9 Months Ended
	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
REVENUE FROM CONTRACTS WITH CUSTOMERS	REVENUE FROM CONTRACTS WITH CUSTOMERS Hansoh License Agreement On December 12, 2021, the Company entered into a license agreement (the “Hansoh Agreement”) with Hansoh (Shanghai) Healthtech Co., Ltd. ("Hansoh"). Under the Hansoh Agreement, the Company granted to Hansoh the exclusive right to develop, manufacture and commercialize KER-050 and licensed products containing KER-050 within the territories of mainland China, Hong Kong and Macau (the “Territory”). In connection with the Hansoh Agreement, Hansoh will purchase clinical trial supply of KER-050 from the Company, and the parties will also negotiate in good faith to enter into an agreement for commercial supply prior to any anticipated commercialization in the Territory. In addition, Hansoh will use commercially reasonable efforts to develop, obtain regulatory approval for, and commercialize licensed products in any region in the Territory. Pursuant to the Hansoh Agreement, the Company received a one-time, net $18.0 million upfront license payment and will also be eligible to receive up to an aggregate of (i) $26.5 million upon the achievement of specified development milestones and (ii) $144.0 million upon the achievement of specified net sales thresholds for all licensed products in the Territory. If a licensed product is approved for marketing in the Territory, the Company will be entitled to receive royalty payments based on a tiered percentage of annual net sales in each region within the Territory, with such percentage ranging from the low double digit to high teens, subject to specified potential royalty reductions. Hansoh’s obligation to pay royalties for a given licensed product in a given region in the Territory will begin on the date of the first commercial sale for such licensed product in such region and continue until the latest of (i) 10 years from the date of the first commercial sale for such licensed product in such region, (ii) the expiration of the last valid claim of certain licensed patents or joint patents, and (iii) expiration of regulatory exclusivity in such region. During the royalty term, neither party will directly nor indirectly commercialize a competing product in the Territory. The Hansoh Agreement will continue in force on a region-by-region basis until the expiration of the royalty term. Hansoh may terminate the Agreement in its entirety for convenience, with notice. The Company may terminate the Hansoh Agreement in its entirety for a patent challenge brought by Hansoh or its affiliates or their sublicensees. Either party may terminate the Hansoh Agreement in its entirety (i) if the other party materially breaches the Hansoh Agreement and fails to cure such breach or (ii) upon the bankruptcy of the other party. The Company evaluated the Hansoh Agreement and concluded that it was subject to ASC 606, as the Company viewed the Hansoh Agreement as a contract with a customer. As such, the Company assessed the terms of the Hansoh Agreement and identified a single performance obligation for the Company to provide Hansoh an exclusive license to develop, manufacture and commercialize KER-050 and licensed products containing KER-050 in the Territory, including the underlying know-how related to such licenses. All other promised goods/services were deemed immaterial in the context of the Hansoh Agreement. Under the Hansoh Agreement, the Company recognized a one-time, upfront license fee of $20.0 million as revenue and $2.0 million in withholding tax expense during the year ended December 31, 2021. The Company received the net payment of $18.0 million during the nine months ended September 30, 2022. The Company will recognize development milestone payments as revenue at the point in time when it is determined that it is probable such milestones will be achieved as all performance obligations will have been satisfied at the point which a milestone might occur (i.e., Hansoh will have assumed all responsibility for the activities under the Hansoh Agreement). The Company will recognize royalty payments and commercial milestone payments as the associated sales of licensed products are recorded by Hansoh, as they predominantly relate to the license granted with the Hansoh Agreement. No milestones have been achieved as of September 30, 2023. In connection with the Hansoh Agreement, the Company entered into a manufacturing technology transfer agreement (the “Tech Transfer Agreement”) with Hansoh, effective in June 2023. The Tech Transfer Agreement governs the transfer to Hansoh, by the Company of all documents and information required to complete the manufacturing technology transfer. Under the Tech Transfer Agreement, Hansoh is obligated to make certain payments to the Company, at the rates set forth in the Tech Transfer Agreement, as manufacturing technology transfer services are provided over the term of the Tech Transfer Agreement. The Tech Transfer Agreement is set to expire on December 30, 2024, unless extended pursuant to its terms. As of September 30, 2023, work under the Tech Transfer Agreement has begun. The Company recognized $8.0 thousand of service revenue as of September 30, 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net loss	$ (39,440)	$ (37,505)	$ (35,804)	$ (23,509)	$ (27,266)	$ (24,186)	$ (112,749)	$ (74,961)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Significant Accounting Policies	The significant accounting policies and estimates used in preparation of the unaudited interim condensed consolidated financial statements are described in the Company’s audited consolidated financial statements as of and for the year ended December 31, 2022, and the notes thereto, which are included in the Annual Report. Except as detailed below, there have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2023.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): DESCRIPTION SEPTEMBER 30, 2023 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS SIGNIFICANT OTHER OBSERVABLE INPUTS SIGNIFICANT OTHER OBSERVABLE INPUTS Assets Money market funds $ 285,964 $ 285,964 $ — $ — Total financial assets $ 285,964 $ 285,964 $ — $ — DESCRIPTION DECEMBER 31, 2022 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3) Assets Money market funds $ 271,734 $ 271,734 $ — $ — Total financial assets $ 271,734 $ 271,734 $ — $ —

PREPAID EXPENSES AND OTHER CU_2

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)	9 Months Ended
	Sep. 30, 2023
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid service contracts $ 12,805 $ 3,319 Prepaid sales tax 441 872 Prepaid rent — 96 Prepaid subscription 921 470 Prepaid insurance 1,158 941 Interest and dividend receivable 898 841 Other 319 180 Total prepaid expenses and other current assets $ 16,542 $ 6,719

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Schedule of of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued external R&D costs $ 1,745 $ 2,429 Accrued external manufacturing costs 3,385 4,240 Accrued compensation and benefits 6,111 4,811 Accrued tax 30 50 Accrued professional fees 549 523 Other 403 700 Total accrued expenses and other current liabilities $ 12,223 $ 12,753

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Option Activity	A summary of option activity during the nine months ended September 30, 2023 is as follows (in thousands except share and per share data): NUMBER OF OPTIONS WEIGHTED-AVERAGE EXERCISE PRICE Outstanding as of December 31, 2022 3,533,169 $ 30.26 Granted 1,292,895 50.27 Exercised (144,763) 16.73 Cancelled or Forfeited (233,398) 45.19 Expired (23,796) $ 57.28 Outstanding as of September 30, 2023 4,424,107 $ 35.61 Options exercisable as of September 30, 2023 2,298,161 $ 24.84
Schedule of Stock-based Compensation Expense	Total stock-based compensation expense recorded for employees, directors and non-employees during the three and nine months ended September 30, 2023 and 2022 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Research and development $ 4,745 $ 2,132 $ 10,766 $ 6,095 General and administrative 3,966 2,622 10,673 7,841 Total stock-based compensation expense $ 8,711 $ 4,754 $ 21,439 $ 13,936

LOSS PER SHARE (Tables)

LOSS PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded From Computation of Diluted Net Loss Per Share	The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders at September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: SEPTEMBER 30, SEPTEMBER 30, Options to purchase common stock 4,424,107 3,483,918

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of Maturity of Lease Liability	Maturities of operating lease liabilities at September 30, 2023 are as follows (in thousands): 2023 (remaining three months) 243 2024 2,431 2025 2,504 2026 2,578 2027 2,657 2028 2,736 2029 2,818 2030 2,903 2031 2,734 Total lease payments 21,604 Less: imputed interest (7,289) Total operating lease liabilities $ 14,315 Included in the consolidated balance sheet: Current portion of operating lease liabilities 611 Operating lease liabilities, net of current portion 13,704 Total operating lease liabilities $ 14,315

NATURE OF BUSINESS AND BASIS _2

NATURE OF BUSINESS AND BASIS OF PRESENTATION (Details) - USD ($)		1 Months Ended
	May 03, 2021	Dec. 31, 2022	May 31, 2021	Sep. 30, 2023	Sep. 30, 2022
Class of Stock [Line Items]
Cash and cash equivalents		$ 279,048,000		$ 287,893,000	$ 239,426,000
At the Market Offering
Class of Stock [Line Items]
Stock sales agreement, maximum amount authorized to be issued	$ 150,000,000	$ 250,000,000	$ 150,000,000

FAIR VALUE MEASUREMENTS -Schedu

FAIR VALUE MEASUREMENTS -Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets
Money market funds	$ 285,964	$ 271,734
Total financial assets	285,964	271,734
QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)
Assets
Money market funds	285,964	271,734
Total financial assets	285,964	271,734
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2)
Assets
Money market funds	0	0
Total financial assets	0	0
SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3)
Assets
Money market funds	0	0
Total financial assets	$ 0	$ 0

PREPAID EXPENSES AND OTHER CU_3

PREPAID EXPENSES AND OTHER CURRENT ASSETS - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid service contracts	$ 12,805	$ 3,319
Prepaid sales tax	441	872
Prepaid rent	0	96
Prepaid subscription	921	470
Prepaid insurance	1,158	941
Interest and dividend receivable	898	841
Other	319	180
Total prepaid expenses and other current assets	$ 16,542	$ 6,719

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES - Schedule of of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued external R&D costs	$ 1,745	$ 2,429
Accrued external manufacturing costs	3,385	4,240
Accrued compensation and benefits	6,111	4,811
Accrued tax	30	50
Accrued professional fees	549	523
Other	403	700
Total accrued expenses and other current liabilities	$ 12,223	$ 12,753

COMMON STOCK - Narrative (Detai

COMMON STOCK - Narrative (Details) - USD ($)			1 Months Ended		9 Months Ended		12 Months Ended
	Dec. 12, 2022	May 03, 2021	Dec. 31, 2022	May 31, 2021	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			200,000,000		200,000,000		200,000,000
Common stock, par value (in USD per share)			$ 0.0001		$ 0.0001	$ 0.0001	$ 0.0001
Proceeds from issuance of common stock, net of offering cost					$ 107,308,000	$ 58,177,000
At the Market Offering
Class of Stock [Line Items]
Stock sales agreement, maximum amount authorized to be issued		$ 150,000,000	$ 250,000,000	$ 150,000,000
Stock sales agreement, additional (in shares)	250,000,000
At the Market Offering | Common stock
Class of Stock [Line Items]
Proceeds from initial public offering, net of discounts and offering costs					$ 109,000,000		$ 121,400,000
Sale of stock, number of shares issued in transaction (in shares)					1,990,927		3,410,384
Sale of stock, price per share (in USD per share)			$ 35.60		$ 54.74		$ 35.60
Proceeds from issuance of common stock, net of offering cost					$ 107,300,000		$ 119,400,000
Sales agent commissions					1,600,000		1,800,000
Issuance costs					100,000		$ 200,000
Sale of stock, remaining authorized amount					$ 141,000,000

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
	Jan. 01, 2023	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted in period (in shares)		1,292,895
Weighted-average grant date fair value of options granted during the period (in dollars per share)		$ 36.05	$ 31.42
Unrecognized stock-based compensation expense related to unvested stock options		$ 63.6
Options outstanding, value		33.6
Options exercisable, value		31.7
Aggregate intrinsic value of stock options exercised		$ 4.1	$ 5.6
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested award, period for recognition		2 years 8 months 12 days
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)		555,735
2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual percentage increase in shares authorized		4%
Number of additional shares authorized (in shares)	1,101,738
Options granted in period (in shares)		3,868,372
Number of shares available for future grants (in shares)		1,038,414

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2023
NUMBER OF OPTIONS
Outstanding as of beginning of period (in shares)	3,533,169
Granted (in shares)	1,292,895
Exercised (in shares)	(144,763)
Cancelled or Forfeited (in shares)	(233,398)
Expired (in shares)	(23,796)
Outstanding as of end of period (in shares)	4,424,107
Exercisable (in shares)	2,298,161
WEIGHTED-AVERAGE EXERCISE PRICE
Outstanding as of beginning of period (in USD per share)	$ 30.26
Granted (in USD per share)	50.27
Exercised (in USD per share)	16.73
Cancelled or Forfeited (in USD per share)	45.19
Expired (in USD per share)	57.28
Outstanding as of end of period (in USD per share)	35.61
Exercisable (in USD per share)	$ 24.84

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 8,711	$ 4,754	$ 21,439	$ 13,936
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	4,745	2,132	10,766	6,095
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 3,966	$ 2,622	$ 10,673	$ 7,841

LOSS PER SHARE - Schedule of An

LOSS PER SHARE - Schedule of Antidilutive Securities Excluded From Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	4,424,107	3,483,918

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2023 USD ($) ft²	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) ft²	Sep. 07, 2021 ft²
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 15,669		$ 15,548
Operating lease liability		$ 14,315
Renewal term		5 years
Operating lease cost		$ 2,200	$ 700
Variable lease cost		900	500
Right-to-use assets and operating lease liabilities		$ 900	$ 700
Weighted average remaining lease term		8 years 2 months 12 days
Weighted average discount rate		10.34%
Waltham Lease
Lessee, Lease, Description [Line Items]
Area of rental space (sqft) | ft²	3,671			31,991	35,662
Operating lease right-of-use assets				$ 15,400
Operating lease liability				$ 12,900
Lessee, operating lease, monthly base rent	$ 200
Percentage of annual increase in operating lease	3%
Letters of credit outstanding, amount	$ 1,200
Waltham Lease Phase A
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	500
Operating lease liability	500
Waltham Lease Phase B
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	1,900
Operating lease liability	$ 1,400

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Schedule of Maturity of Lease Liability (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
MATURITY OF LEASE LIABILITY
2023 (remaining three months)	$ 243
2024	2,431
2025	2,504
2026	2,578
2027	2,657
2028	2,736
2029	2,818
2030	2,903
2031	2,734
Total lease payments	21,604
Less: imputed interest	(7,289)
Total operating lease liabilities	14,315
Included in the consolidated balance sheet:
Current portion of operating lease liabilities	611	$ 455
Operating lease liabilities, net of current portion	13,704	$ 12,811
Total operating lease liabilities	$ 14,315

REVENUE FROM CONTRACTS WITH C_2

REVENUE FROM CONTRACTS WITH CUSTOMERS (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021	Dec. 12, 2021
Disaggregation of Revenue [Line Items]
Research collaboration revenue	$ 8,000	$ 0	$ 8,000	$ 0
The General Hospital Corporation | License Agreement
Disaggregation of Revenue [Line Items]
Expiration period			10 years
License | Hansoh Shanghai Healthtech Co Ltd
Disaggregation of Revenue [Line Items]
Research collaboration revenue				$ 18,000,000
Revenue, remaining performance obligation, development milestones, variable consideration						$ 26,500,000
Revenue, remaining performance obligation, sales milestones, variable consideration amount						$ 144,000,000
Upfront license fee					$ 20,000,000
Withholding taxes from upfront fee					$ 2,000,000