Acumen Pharmaceuticals (ABOS) 10-Q 14 May 24 2024 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2024	May 08, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-40551
Entity Registrant Name	Acumen Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-4108129
Entity Address, Address Line One	427 Park St.
Entity Address, City or Town	Charlottesville
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22902
City Area Code	434
Local Phone Number	297-1000
Title of 12(b) Security	Common stock, par value $0.0001 per share
Trading Symbol	ABOS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		60,079,778
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Central Index Key	0001576885
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets
Cash and cash equivalents	$ 46,930	$ 66,886
Marketable securities, short-term	205,582	176,636
Prepaid expenses and other current assets	3,319	3,093
Total current assets	255,831	246,615
Marketable securities, long-term	44,108	62,553
Right-of-use asset	353	381
Restricted cash	234	233
Property and equipment, net	117	122
Other assets	324	221
Total assets	300,967	310,125
Current liabilities
Accounts payable	3,079	1,379
Accrued clinical trial expenses	2,367	4,387
Accrued expenses and other current liabilities	2,905	6,339
Finance lease liability, short-term	0	756
Operating lease liability, short-term	121	110
Total current liabilities	8,472	12,971
Operating lease liability, long-term	252	284
Debt, long-term	30,209	29,897
Total liabilities	38,933	43,152
Commitments and contingencies (Note 10)
Stockholders’ equity
Preferred stock, $0.0001 par value; 10,000,000 shares authorized and no shares issued and outstanding as of March 31, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value; 300,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 60,079,778 and 57,910,461 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively	6	6
Additional paid-in capital	499,843	489,453
Accumulated deficit	(237,671)	(222,798)
Accumulated other comprehensive income (loss)	(144)	312
Total stockholders’ equity	262,034	266,973
Total liabilities and stockholders’ equity	$ 300,967	$ 310,125

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	60,079,778	57,910,461
Common stock, shares outstanding (in shares)	60,079,778	57,910,461

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses
Research and development	$ 12,449	$ 8,713
General and administrative	5,325	4,422
Total operating expenses	17,774	13,135
Loss from operations	(17,774)	(13,135)
Other income (expense)
Interest income	4,005	1,832
Interest expense	(1,000)	0
Change in fair value of embedded derivatives	(50)	0
Other expense, net	(54)	(4)
Total other income	2,901	1,828
Net loss	(14,873)	(11,307)
Other comprehensive gain (loss)
Unrealized loss on marketable securities	(456)	227
Comprehensive loss	$ (15,329)	$ (11,080)
Net loss per common share, basic (in dollars per share)	$ (0.25)	$ (0.28)
Net loss per common share, diluted (in dollars per share)	$ (0.25)	$ (0.28)
Weighted-average shares outstanding, basic (in shares)	59,812,000	41,025,062
Weighted-average shares outstanding diluted (in shares)	59,812,000	41,025,062

Condensed Statements of Changes

Condensed Statements of Changes in Stockholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2022		41,025,062
Beginning balance at Dec. 31, 2022	$ 188,775	$ 4	$ 359,949	$ (170,427)	$ (751)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain (loss) on marketable securities	227				227
Stock-based compensation	1,390		1,390
Net loss	(11,307)			(11,307)
Ending balance (in shares) at Mar. 31, 2023		41,025,062
Ending balance at Mar. 31, 2023	$ 179,085	$ 4	361,339	(181,734)	(524)
Beginning balance (in shares) at Dec. 31, 2023	57,910,461	57,910,461
Beginning balance at Dec. 31, 2023	$ 266,973	$ 6	489,453	(222,798)	312
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash, net of issuance costs of $87 (in shares)		2,068,246
Issuance of common stock for cash, net of issuance costs of $87	7,938		7,938
Issuance of common stock for restricted stock units, net of shares withheld for taxes (in shares)		101,071
Issuance of common stock for restricted stock units, net of shares withheld for taxes	(32)		(32)
Unrealized gain (loss) on marketable securities	(456)				(456)
Stock-based compensation	2,484		2,484
Net loss	$ (14,873)			(14,873)
Ending balance (in shares) at Mar. 31, 2024	60,079,778	60,079,778
Ending balance at Mar. 31, 2024	$ 262,034	$ 6	$ 499,843	$ (237,671)	$ (144)

Condensed Statements of Chang_2

Condensed Statements of Changes in Stockholders’ Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Common Stock
Payments of stock issuance costs	$ 87

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities
Net loss	$ (14,873)	$ (11,307)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	16	14
Stock-based compensation expense	2,484	1,390
Amortization of premiums and accretion of discounts on marketable securities, net	(1,763)	(334)
Change in fair value of embedded derivatives	50	0
Amortization of right-of-use asset	28	38
Realized gain on marketable securities	(2)	0
Non-cash interest expense	268	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(226)	(899)
Other assets	35	(44)
Accounts payable	1,700	(878)
Accrued clinical trial expenses	(2,020)	2,486
Accrued expenses and other current liabilities	(3,512)	(603)
Finance lease liability	(23)	0
Operating lease liability	(21)	(38)
Net cash used in operating activities	(17,859)	(10,175)
Cash flows from investing activities
Purchases of marketable securities	(45,292)	(52,131)
Proceeds from maturities and sales of marketable securities	36,100	10,204
Purchases of property and equipment	(11)	0
Net cash used in investing activities	(9,203)	(41,927)
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	7,938	0
Payment for financing lease	(739)	0
Payments for deferred offering costs	(60)	0
Repurchase of common shares to pay employee withholding taxes	(32)	0
Net cash provided by financing activities	7,107	0
Net change in cash and cash equivalents and restricted cash	(19,955)	(52,102)
Cash and cash equivalents and restricted cash at the beginning of the period	67,119	130,101
Cash and cash equivalents and restricted cash at the end of the period	47,164	77,999
Supplemental disclosure of cash flow information
Cash paid for income taxes	0	0
Cash paid for interest	756	0
Supplemental disclosure of noncash investing and financing activities
Deferred offering costs in accrued expenses and other current liabilities	$ 78	$ 0

DESCRIPTION OF ORGANIZATION AND

DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS	DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS Acumen Pharmaceuticals, Inc. (“Acumen” or the “Company”) was incorporated in 1996 in the state of Delaware. Acumen is a clinical-stage biopharmaceutical company developing a novel disease-modifying approach to target what the Company believes to be a key underlying cause of Alzheimer’s disease (“AD”). Alzheimer’s disease is a progressive neurodegenerative disease of the brain that leads to loss of memory and cognitive functions and ultimately results in death. The Company’s scientific founders pioneered research on soluble amyloid-beta oligomers (“AßOs”), which are globular assemblies of the amyloid-beta (“Aß”) peptide that are distinct from Aß monomers and amyloid plaques. Based on decades of research and supporting evidence, AßOs have gained increasing scientific acceptance as a primary toxin involved in the initiation and propagation of AD pathology. The Company is currently focused on advancing a targeted immunotherapy drug candidate, sabirnetug, in the Phase 2 portion of a Phase 2/3 clinical trial called “ALTITUDE-AD” following Phase 1 results in “early AD” patients (patients with mild cognitive impairment or mild dementia due to Alzheimer’s pathology) that were first reported in July 2023. Sabirnetug is a recombinant humanized immunoglobulin gamma 2 (“IgG2”) monoclonal antibody (“mAb”) that was designed to selectively target AßOs, has demonstrated functional and protective effects in in vitro assays, and has previously demonstrated in vivo safety and pharmacologic activity in multiple animal species, including transgenic mouse models for AD. The Company intends to amend the ALTITUDE-AD clinical protocol in 2024 to change the current Phase 2/3 study to a Phase 2 standalone study. The Company is subject to the uncertainty of whether its intellectual property will develop into successful commercial products. Liquidity and Capital Resources The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of March 31, 2024 and December 31, 2023, the Company had an accumulated deficit of $237.7 million and $222.8 million, respectively, and working capital of $247.4 million and $233.6 million, respectively. Management believes that the Company has sufficient cash to continue operating activities for beyond 12 months from issuance of these condensed financial statements. Future capital requirements will depend upon many factors, including the timing and extent of spending on research and development and market acceptance of the Company’s products, if approved for commercial sale. The Company expects that it will need to obtain additional financing to complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. Until such time, if ever, as the Company can generate revenue sufficient to achieve profitability, the Company expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. There can be no assurance that any such financing will be available on terms acceptable to the Company, or at all. To the extent that the Company raises additional capital through the sale of equity or convertible debt securities, the ownership interest of its stockholders will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect the rights of common stockholders. Debt financing and preferred equity financing, if available, may involve agreements that include covenants limiting or restricting the Company’s ability to take specific actions, such as incurring additional debt, making acquisitions or capital expenditures or declaring dividends. If the Company is unable to maintain sufficient financial resources, its business, financial condition and results of operations will be materially and adversely affected. The Company may be required to delay, limit, reduce or terminate its product discovery and development activities or future commercialization efforts. The Company completed a Phase 1 clinical trial of sabirnetug in the second quarter of 2023, which the Company named “INTERCEPT-AD.” This trial enrolled 65 patients with “early AD” and 62 participants received at least one dose of study drug. INTERCEPT-AD was a U.S.-based, multi-center, randomized, double-blind, placebo-controlled clinical trial with overlapping single ascending dose and multiple ascending dose cohorts evaluating patients with early AD. In July 2023, the Company announced topline results from INTERCEPT-AD, which demonstrated that sabirnetug met the primary and secondary objectives of this study in 62 participants with early AD. The Company announced the dosing of the first patient in the ALTITUDE-AD study in May 2024.

BASIS OF PRESENTATION AND SUMMA

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. In the opinion of management, the unaudited condensed financial statements reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position and results of its operations and its cash flows for the periods presented. Certain information and note disclosures normally included in the Company’s annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. These unaudited condensed financial statement results are not necessarily indicative of results to be expected for the full fiscal year or any future period. A description of the Company’s significant accounting policies is included in the Company’s Annual Report. Other than as described below, there have been no material changes in the Company’s significant accounting policies to those previously disclosed in the Company’s Annual Report. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the unaudited condensed financial statements, as well as the reported amounts of expenses during the reporting periods. These estimates and assumptions are based on the Company’s historical experience, and on various other factors that management believes are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected. The more significant estimates and assumptions by management include, among others: the valuation allowance of deferred tax assets resulting from net operating losses, the valuation of stock options and the valuation of embedded derivatives within the Company’s long-term debt. Cash and Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. All of the Company’s cash equivalents have liquid markets and high credit ratings. The Company had $46.4 million and $66.2 million in cash equivalents as of March 31, 2024 and December 31, 2023, respectively. Restricted cash primarily consists of deposited cash collateral for the Company’s credit card program. The following table provides a reconciliation of cash, cash equivalents and restricted cash from the balance sheets to the statements of cash flows (in thousands): March 31, 2024 December 31, 2023 Cash and cash equivalents $ 46,930 $ 66,886 Restricted cash 234 233 Total cash, cash equivalents and restricted cash $ 47,164 $ 67,119

MARKETABLE SECURITIES

MARKETABLE SECURITIES	3 Months Ended
	Mar. 31, 2024
Marketable Securities [Abstract]
MARKETABLE SECURITIES	MARKETABLE SECURITIES The Company’s marketable securities consisted of the following (in thousands): March 31, 2024 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale securities, short-term Corporate debt securities $ 172,005 $ 19 $ (271) $ 171,753 Government and agency - U.S. 33,820 12 (3) 33,829 Total available-for-sale securities, short-term 205,825 31 (274) 205,582 Available-for-sale securities, long-term Corporate debt securities 39,065 88 — 39,153 Government and agency - U.S. 4,945 10 — 4,955 Total available-for-sale securities, long-term 44,010 98 — 44,108 Total available-for-sale securities $ 249,835 $ 129 $ (274) $ 249,690 December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale securities, short-term Corporate debt securities $ 144,184 $ 97 $ (191) $ 144,090 Government and agency - U.S. 32,470 82 (6) 32,546 Total available-for-sale securities, short-term 176,654 179 (197) 176,636 Available-for-sale securities, long-term Corporate debt securities 57,240 320 (15) 57,545 Government and agency - U.S. 4,985 23 — 5,008 Total available-for-sale securities, long-term 62,225 343 (15) 62,553 Total available-for-sale securities $ 238,879 $ 522 $ (212) $ 239,189 The following tables summarize the amount of unrealized losses, defined as the amount by which the amortized cost exceeds fair value, and the related fair value of available-for-sale marketable securities with unrealized losses, which have been segregated into two categories: those that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for 12 or more months (in thousands): March 31, 2024 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 121,622 $ (177) $ 27,670 $ (94) $ 149,292 $ (271) Government and agency - U.S. 11,756 (3) — — 11,756 (3) Total $ 133,378 $ (180) $ 27,670 $ (94) $ 161,048 $ (274) December 31, 2023 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 78,995 $ (152) $ 12,074 $ (54) $ 91,069 $ (206) Government and agency - U.S. 5,585 (6) — — 5,585 (6) Total $ 84,580 $ (158) $ 12,074 $ (54) $ 96,654 $ (212) As of March 31, 2024, the Company’s available-for-sale securities classified as short-term mature in one year or less and the Company’s available-for-sale securities classified as long-term mature within less than two years . As noted in the table above, although some of the Company’s available-for-sale marketable securities as of March 31, 2024 have been in an unrealized loss position for more than 12 months, the Company does not intend to sell these securities and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be at maturity. No credit losses were recognized on the Company’s available-for-sale securities during the three months ended March 31, 2024 and 2023. The Company recorded an immaterial realized gain during the three months ended March 31, 2024 and no realized gains or losses during the three months ended March 31, 2023 .

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company’s financial assets and liabilities subject to fair value measurement on a recurring basis and the level of inputs used for such measurements were as follows (in thousands): Fair value measurements at reporting date using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value at March 31, 2024 Assets included in: Cash and cash equivalents Money market securities $ 46,395 $ — $ — $ 46,395 Marketable securities Corporate debt securities — 210,906 — 210,906 Government and agency - U.S. — 38,784 — 38,784 Total fair value $ 46,395 $ 249,690 $ — $ 296,085 Liabilities included in: Debt, long-term Embedded derivatives liabilities $ — $ — $ 2,610 $ 2,610 Total fair value $ — $ — $ 2,610 $ 2,610 Fair value measurements at reporting date using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value at December 31, 2023 Assets included in: Cash and cash equivalents Money market securities $ 66,207 $ — $ — $ 66,207 Marketable securities Corporate debt securities — 201,635 — 201,635 Government and agency - U.S. — 37,554 — 37,554 Total fair value $ 66,207 $ 239,189 $ — $ 305,396 Liabilities included in: Debt, long-term Embedded derivatives liabilities $ — $ — $ 2,560 $ 2,560 Total fair value $ — $ — $ 2,560 $ 2,560 The carrying values reported in the Company’s condensed balance sheets for cash (excluding cash equivalents, which are recorded at fair value on a recurring basis), restricted cash, accounts payable, accrued clinical trial expenses and accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items. The carrying amount of the Company’s long-term debt approximates fair value due to its variable market interest rate and management’s opinion that current rates and terms that would be available to the Company with the same maturity and security structure would be essentially equivalent to that of the Company’s long-term debt. Certain features of the Company’s term loan facility (the “Term Loan”) were determined to be an embedded derivative requiring separate measurement from the loan host instrument. For additional information regarding the Term Loan, see Note 6. Debt . The fair value of the Company’s money market funds is determined using quoted market prices in active markets for identical assets. The fair value for the available-for-sale marketable securities is determined based on valuation models using inputs that are observable either directly or indirectly (Level 2 inputs), such as quoted prices for similar assets or liabilities, yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures. The following table presents changes in Level 3 liabilities measured at fair value for the three months ended March 31, 2024 (in thousands): Balance, December 31, 2023 $ 2,560 Change in fair value of embedded derivatives 50 Balance, March 31, 2024 $ 2,610 As of March 31, 2024 and December 31, 2023, the fair value of the embedded derivatives in the Term Loan has been estimated using the Monte Carlo model. A summary of the weighted-average significant unobservable inputs (Level 3 inputs) used in measuring the embedded derivatives in the Term Loan as of March 31, 2024 and December 31, 2023 is as follows: March 31, 2024 December 31, 2023 Conversion price $2.53 $2.53 Expected term (in years) 4.5 4.7 Expected equity volatility 102.9% 106.7% Risk-free interest rate 4.3% 3.9% Discount for lack of marketability 15.0% 11.5% Expected dividend yield 0% 0%

SUPPLEMENTAL FINANCIAL INFORMAT

SUPPLEMENTAL FINANCIAL INFORMATION	3 Months Ended
	Mar. 31, 2024
Supplemental Financial Information [Abstract]
SUPPLEMENTAL FINANCIAL INFORMATION	SUPPLEMENTAL FINANCIAL INFORMATION Prepaid expenses and other current assets consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development service agreements $ 2,200 $ 1,680 Prepaid insurance 411 807 Interest receivable 189 225 Prepaid raw materials 124 98 Other 395 283 Total prepaid expenses and other current assets $ 3,319 $ 3,093 Other assets consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development service agreements $ 186 $ 221 Deferred offering costs 138 — Total other assets $ 324 $ 221 Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development $ 1,140 $ 2,186 Compensation and other employee liabilities 1,035 3,692 Interest 249 249 Other 481 212 Total accrued expenses and other current liabilities $ 2,905 $ 6,339

DEBT

DEBT	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
DEBT	DEBT On November 10, 2023, the Company entered into a Loan and Security Agreement with K2 HealthVentures LLC (the “Loan Agreement”). The Loan Agreement provided the Company with a term loan facility (the “Term Loan”), in the aggregate principal amount of $50 million, of which the Company borrowed $30 million in the first tranche upon closing. The remaining $20 million is available for borrowing upon the Company’s request based on review of certain information and discretionary approval from the lenders. The Loan Agreement bears interest per annum at the greater of (i) 9.65% or (ii) the sum of the prime rate last quoted in The Wall Street Journal plus 1.15% for such interest period and the principal amount of the Term Loan outstanding under the Loan Agreement. The Term Loan matures on November 1, 2027, and can be extended to November 1, 2028, if the Company achieves certain financing milestones. The Loan Agreement provides for a final payment fee of an additional $1.6 million (the “Final Payment”) due upon repayment of the Term Loan. The principal and interest of the Term Loan are to be repaid in equal monthly installments beginning on July 1, 2026 through the maturity of the Loan Agreement. The Loan Agreement allows prepayment of the entire Term Loan or a portion of the Term Loan of more than $5 million, provided that any partial prepayment will leave outstanding borrowings of at least $15 million. The lenders can elect to convert up to $2.5 million of the Term Loan (the “Conversion Amount”) into the Company’s common stock at a conversion price of $2.53 (the “Conversion Option”). If the lenders elect to convert the Conversion Amount upon the Next Qualified Financing, as defined in the Loan Agreement whereby the Company receives aggregate gross proceeds of at least $20 million, the conversion price will equal the lowest effective cash price per share of securities issued in such Qualified Financing (the “Share-Settled Redemption”). The Conversion Option and Share-Settled Redemption within the Loan Agreement are required to be bifurcated as a single compound embedded derivative (the “Embedded Derivatives”) at fair value, with subsequent changes in fair value recognized in the statements of operations and comprehensive loss. In accordance with the Loan Agreement, the Company issued an equity-classified warrant to purchase 730,769 shares of common stock (the “Loan Warrant”), with an initial allocated fair value of $1.1 million. See additional discussion in Note 8. Stockholders’ Equity. The initial recognition of the direct fees of $0.5 million, the Final Payment of $1.6 million, the initial fair value of the Embedded Derivatives of $1.2 million and the fair value of the Loan Warrant of $1.1 million for the Loan Agreement resulted in a discount of $4.4 million, which is being amortized to interest expense over the term of the Loan Agreement using the effective interest method. Outstanding debt consisted of the following (in thousands): March 31, 2024 December 31, 2023 Principal value of Term Loan, including Final Payment of $1,635 $ 31,635 $ 31,635 Fair value of bifurcated embedded derivatives 2,610 2,560 Unamortized debt discount (4,036) (4,298) Total debt, long-term $ 30,209 $ 29,897 The following table provides the components of interest expense (in thousands): Three Months Ended Interest expense based on the coupon interest rate of the outstanding debt $ 732 Accretion of debt discount 262 Total interest expense related to debt $ 994 For the three months ended March 31, 2024, the effective interest rate for the Term Loan was 13.4%. As of March 31, 2024, the aggregate principal payments due for the Term Loan by year are as follows (in thousands): Year ended December 31, 2026 $ 10,104 Year ended December 31, 2027 21,531 Total principal payments due for Term Loan $ 31,635 The obligations of the Company under the Loan Agreement are secured by substantially all of the assets of the Company, excluding the Company’s intellectual property.

LEASES

LEASES	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
LEASES	LEASES Office Lease On September 11, 2023, the Company entered into a lease for office space in Newton, Massachusetts, with a lease term of approximately 38 months beginning October 20, 2023, and which expires on December 31, 2026. During 2022, the Company entered into two leases for office space in the same building in Charlottesville, Virginia that both expired in December 2023. Upon the lease expiration, in accordance with the lease terms, the Company began leasing the office space on a month-to-month basis and included these costs in short-term lease rent expense for the three months ended March 31, 2024. Computer Equipment Lease The Company has a finance lease, which was effective in October 2023, for certain computer equipment for its ALTITUDE-AD clinical trial. The equipment will be returned to the vendor at the completion of the vendor’s services under the agreement. Upon lease commencement, the Company recorded non-cash expense in research and development expense in the statement of operations and comprehensive loss for the right-of-use assets related to the computer equipment lease as the equipment is being used for research and development and does not have an alternative future use to the Company. In January 2024, the Company paid $0.8 million for the leased equipment and related interest, and has no further payments due for the computer equipment under the finance lease. The following table summarizes quantitative information about the Company’s leases (in thousands): Three Months Ended March 31, 2024 2023 Finance lease Interest lease cost $ 6 $ — Finance lease expense 6 — Operating leases Operating lease cost 37 40 Variable lease cost 1 — Less: sublease income — (3) Operating lease expense 38 37 Short-term lease rent expense 18 1 Total rent expense $ 62 $ 38 Supplemental information related to leases was as follows (dollar amounts in thousands): Three Months Ended March 31, 2024 2023 Finance cash flows from finance leases $ 739 $ — Operating cash flows from finance lease $ 23 $ — Operating cash flows from operating leases $ 30 $ 40 Weighted-average remaining lease term – finance leases (in years) 3.5 — Weighted-average remaining lease term – operating leases (in years) 2.8 0.4 Weighted-average discount rate – operating leases 9.7 % 10.0 % As of March 31, 2024, the present value of maturities of the Company’s operating lease liabilities were as follows (in thousands): Nine months ended December 31, 2024 $ 113 Year ended December 31, 2025 155 Year ended December 31, 2026 158 Total 426 Less: present value discount (53) Operating lease liability $ 373
LEASES	LEASES Office Lease On September 11, 2023, the Company entered into a lease for office space in Newton, Massachusetts, with a lease term of approximately 38 months beginning October 20, 2023, and which expires on December 31, 2026. During 2022, the Company entered into two leases for office space in the same building in Charlottesville, Virginia that both expired in December 2023. Upon the lease expiration, in accordance with the lease terms, the Company began leasing the office space on a month-to-month basis and included these costs in short-term lease rent expense for the three months ended March 31, 2024. Computer Equipment Lease The Company has a finance lease, which was effective in October 2023, for certain computer equipment for its ALTITUDE-AD clinical trial. The equipment will be returned to the vendor at the completion of the vendor’s services under the agreement. Upon lease commencement, the Company recorded non-cash expense in research and development expense in the statement of operations and comprehensive loss for the right-of-use assets related to the computer equipment lease as the equipment is being used for research and development and does not have an alternative future use to the Company. In January 2024, the Company paid $0.8 million for the leased equipment and related interest, and has no further payments due for the computer equipment under the finance lease. The following table summarizes quantitative information about the Company’s leases (in thousands): Three Months Ended March 31, 2024 2023 Finance lease Interest lease cost $ 6 $ — Finance lease expense 6 — Operating leases Operating lease cost 37 40 Variable lease cost 1 — Less: sublease income — (3) Operating lease expense 38 37 Short-term lease rent expense 18 1 Total rent expense $ 62 $ 38 Supplemental information related to leases was as follows (dollar amounts in thousands): Three Months Ended March 31, 2024 2023 Finance cash flows from finance leases $ 739 $ — Operating cash flows from finance lease $ 23 $ — Operating cash flows from operating leases $ 30 $ 40 Weighted-average remaining lease term – finance leases (in years) 3.5 — Weighted-average remaining lease term – operating leases (in years) 2.8 0.4 Weighted-average discount rate – operating leases 9.7 % 10.0 % As of March 31, 2024, the present value of maturities of the Company’s operating lease liabilities were as follows (in thousands): Nine months ended December 31, 2024 $ 113 Year ended December 31, 2025 155 Year ended December 31, 2026 158 Total 426 Less: present value discount (53) Operating lease liability $ 373

STOCKHOLDERS_ EQUITY

STOCKHOLDERS’ EQUITY	3 Months Ended
	Mar. 31, 2024
Stockholders' Equity Note [Abstract]
STOCKHOLDERS’ EQUITY	STOCKHOLDERS’ EQUITY Authorized Shares As of March 31, 2024, the total number of shares of capital stock authorized to be issued per the Company’s Amended and Restated Certificate of Incorporation is 310,000,000, with 10,000,000 shares designated as preferred stock with a par value of $0.0001, and 300,000,000 shares designated as common stock with a par value of $0.0001. Each share of common stock is entitled to one vote. Shelf Registration and Equity Offerings On July 1, 2022, the Company filed a shelf registration statement on Form S-3 (the “2022 Registration Statement”). Pursuant to the 2022 Registration Statement, the Company may offer and sell securities having an aggregate public offering price of up to $200 million. On July 21, 2023, the Company issued 16,774,193 shares of common stock at a price of $7.75 per share (the “Offering”). The net proceeds from the Offering, after underwriting discounts and commissions and other offering expenses, were $121.9 million. In connection with the filing of the 2022 Registration Statement, the Company also entered into a sales agreement (the “Sales Agreement”) with BofA Securities, Inc. (“BofA”) and Stifel, Nicolaus & Company, Incorporated (“Stifel”), as sales agents, pursuant to which the Company may issue and sell shares of its common stock for an aggregate offering price of up to $50 million under an at-the-market offering program (the “ATM”), which is included in the $200 million of securities that may be offered pursuant to the 2022 Registration Statement. On April 23, 2023, the Company entered into an amendment to the Sales Agreement (as amended, the “Amended Sales Agreement”) to add BTIG, LLC (“BTIG”) as a sales agent under the Amended Sales Agreement (BTIG, together with BofA and Stifel, the “Sales Agents”). Pursuant to the Amended Sales Agreement, the Company will pay the Sales Agents a commission rate of up to 3.0% of the gross proceeds from the sale of any shares of common stock. The Company is not obligated to make any sales of shares of its common stock under the ATM. During the three months ended March 31, 2024, the Company issued and sold 2,068,246 shares of common stock under the ATM for net proceeds of $7.9 million, or $3.84 per share. The Company has issued shares of common stock for aggregate gross proceeds of $12.2 million under the ATM since the program’s inception. On March 27, 2024, the Company filed a shelf registration statement on Form S-3 (the “2024 Registration Statement”). Pursuant to the 2024 Registration Statement, the Company may offer and sell securities having an aggregate public offering price of up to $200 million. Common Stock Warrant

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION 2021 Equity Incentive Plan The 2021 Equity Incentive Plan (the “2021 Plan”), which provides for the grant of incentive stock options to employees, and the grant of nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of stock awards to employees, directors and consultants, became effective on June 30, 2021. The 2021 Plan is a successor to the Company’s Amended and Restated Stock Performance Plan that was adopted by the Company’s Board of Directors (the “Board”) and stockholders on April 8, 2013 (as amended from time to time, most recently on November 20, 2020, the “2013 Plan”). The maximum number of shares of common stock that may be issued upon the exercise of incentive stock options under the 2021 Plan is 12,000,000. Following the effectiveness of the 2021 Plan, no further grants may be made under the 2013 Plan; however, any outstanding equity awards granted under the 2013 Plan continue to be governed by the terms of the 2013 Plan. As of March 31, 2024, there were 3,231,274 options outstanding under the 2013 Plan. The number of shares of common stock reserved for issuance under the 2021 Plan automatically increases on January 1 of each calendar year through January 1, 2031, in an amount equal to 5% of the total number of shares of common stock outstanding on December 31 of the fiscal year before the date of each automatic increase, or a lesser number of shares determined by the Board prior to the applicable January 1. On January 1, 2024, the number of shares of common stock reserved for issuance under the 2021 Plan automatically increased by 2,895,523 shares. As of March 31, 2024, a total of 14,668,721 shares were authorized for issuance under the 2021 Plan and 2,882,485 shares remained available for issuance under the 2021 Plan. The Company recorded stock-based compensation expense in the following expense categories of its condensed statements of operations for the periods shown (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 1,646 $ 958 Research and development 838 432 Total stock-based compensation $ 2,484 $ 1,390 Stock Options The Black-Scholes option-pricing model was used to estimate the fair value of stock options granted during the three months ended March 31, 2024 and 2023 with the following weighted average assumptions: Three Months Ended March 31, 2024 2023 Risk-free interest rate 3.82% - 4.33% 3.58% - 4.13% Expected term (in years) 5.3 - 6.1 5.8 - 6.1 Expected volatility 101% - 104% 90% Expected dividend yield 0% 0% The weighted average grant date fair value of options granted during the three months ended March 31, 2024 and 2023, was $3.18 per share and $4.52 per share, respectively. Stock options granted after December 31, 2017 generally vest monthly over a range of 12 to 48 months or vest monthly over a total of 48 months following a one-year cliff and all have a 10-year contractual term. Beginning in 2022, the Company has also issued annual option awards to its Board that vest in full on the first anniversary of the grant date. Stock options granted prior to December 31, 2017 were either fully vested upon grant or generally vested monthly over a range of three its own historical volatility. Due to the lack of historical exercise history, the expected term of the Company’s stock options has been determined using the “simplified” method for awards. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The following table reflects summarized stock option activity: Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2023 7,523,947 $ 4.01 Granted 2,491,550 $ 3.87 Outstanding as of March 31, 2024 10,015,497 $ 3.98 8.0 $ 10,392 Vested and exercisable as of March 31, 2024 4,516,852 $ 3.30 7.0 $ 8,062 As of March 31, 2024, total unrecognized compensation costs related to unvested stock option awards was approximately $18.3 million, which the Company expects to recognize over a weighted-average period of approximately 2.7 years. Restricted Stock Units In January 2024 and 2023, the Company granted a restricted stock unit (“RSU”) award to each of its then-current employees. These RSU awards vest in equal annual installments on the first three anniversaries of the grant date. Number of Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2023 328,500 $ 6.11 Granted 1,204,640 $ 4.15 Vested (109,493) $ 6.11 Unvested as of March 31, 2024 1,423,647 $ 4.45 As of March 31, 2024, total unrecognized compensation costs related to unvested RSUs was approximately $5.8 million, which the Company expects to recognize over a weighted-average period of approximately 2.6 years. Employee Stock Purchase Plan

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company is not a party to any material legal proceedings and is not aware of any pending or threatened claims. From time to time, the Company may be subject to various legal proceedings and claims that arise in the ordinary course of its business activities. In November 2023, the Company entered into a Non-exclusive Collaboration and License Agreement (the “Halozyme License Agreement”) with Halozyme, Inc. (“Halozyme”). Under the terms of the Halozyme License Agreement, Halozyme granted the Company a non-exclusive license to Halozyme’s drug delivery technology for the development of a subcutaneous formulation of sabirnetug (such combination, the “Halozyme Product”). In January 2024, the Company paid a seven-figure upfront license payment for the Halozyme Product, which was included in accrued expenses and other current liabilities as of December 31, 2023. Additionally, the Company will make milestone payments tied to achievement of certain development and commercialization milestone events with respect to the Halozyme Product, as well as milestone payments based on achievement of certain net sales levels of the Halozyme Product. The Company will also make single-digit royalty payments based on worldwide net sales of the Halozyme Product. In November 2022, the Company entered into a License Agreement (“Lonza License Agreement”) with Lonza Sales AG (“Lonza”). Under the terms of the Lonza License Agreement, Lonza granted the Company a worldwide non-exclusive license to use Lonza’s glutamine synthetase gene expression system to manufacture and commercialize sabirnetug (the “Lonza Product”). Under the terms of the Lonza License Agreement, in consideration of the licenses and consents granted to the Company, the Company paid an upfront fee of 1.0 million Swiss Francs. The Company is also required to pay certain royalties upon commercialization and annual payments on a country-by-country basis in respect of the manufacturing and sale of the Lonza Product, which include (i) a royalty of less than 1% on net sales where Lonza manufactures the Lonza Product, (ii) an annual royalty payment in Swiss Francs in the low six-digits and a royalty of less than 1% on net sales where the Company manufactures the Lonza Product and (iii) an annual payment in Swiss Francs in the mid six-digits per sublicense and a royalty on net sales in the low single digits where a third party manufactures the Lonza Product. These payment obligations expire 10 years from the first commercial sales of the Lonza Product in such country of sale.

NET LOSS PER SHARE

NET LOSS PER SHARE	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Basic and diluted net loss per share was the same for each period presented as the inclusion of all potential common stock outstanding would have been anti-dilutive. Potentially dilutive securities not included in the calculation of diluted net loss per common share, because to do so would be anti-dilutive, were as follows for the periods presented: March 31, 2024 2023 Shares issuable upon exercise of stock options 10,015,497 7,238,893 Shares issuable upon conversion election for Term Loan 988,142 — Shares issuable upon exercise of warrant 730,769 — Unvested RSUs 1,423,647 328,500 Total 13,158,055 7,567,393

BASIS OF PRESENTATION AND SUM_2

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial information, the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. In the opinion of management, the unaudited condensed financial statements reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position and results of its operations and its cash flows for the periods presented. Certain information and note disclosures normally included in the Company’s annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. These unaudited condensed financial statement results are not necessarily indicative of results to be expected for the full fiscal year or any future period.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the unaudited condensed financial statements, as well as the reported amounts of expenses during the reporting periods. These estimates and assumptions are based on the Company’s historical experience, and on various other factors that management believes are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected. The more significant estimates and assumptions by management include, among others: the valuation allowance of deferred tax assets resulting from net operating losses, the valuation of stock options and the valuation of embedded derivatives within the Company’s long-term debt.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash Restricted cash primarily consists of deposited cash collateral for the Company’s credit card program.

BASIS OF PRESENTATION AND SUM_3

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash from the balance sheets to the statements of cash flows (in thousands): March 31, 2024 December 31, 2023 Cash and cash equivalents $ 46,930 $ 66,886 Restricted cash 234 233 Total cash, cash equivalents and restricted cash $ 47,164 $ 67,119

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	3 Months Ended
	Mar. 31, 2024
Marketable Securities [Abstract]
Summary of Marketable Securities	The Company’s marketable securities consisted of the following (in thousands): March 31, 2024 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale securities, short-term Corporate debt securities $ 172,005 $ 19 $ (271) $ 171,753 Government and agency - U.S. 33,820 12 (3) 33,829 Total available-for-sale securities, short-term 205,825 31 (274) 205,582 Available-for-sale securities, long-term Corporate debt securities 39,065 88 — 39,153 Government and agency - U.S. 4,945 10 — 4,955 Total available-for-sale securities, long-term 44,010 98 — 44,108 Total available-for-sale securities $ 249,835 $ 129 $ (274) $ 249,690 December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale securities, short-term Corporate debt securities $ 144,184 $ 97 $ (191) $ 144,090 Government and agency - U.S. 32,470 82 (6) 32,546 Total available-for-sale securities, short-term 176,654 179 (197) 176,636 Available-for-sale securities, long-term Corporate debt securities 57,240 320 (15) 57,545 Government and agency - U.S. 4,985 23 — 5,008 Total available-for-sale securities, long-term 62,225 343 (15) 62,553 Total available-for-sale securities $ 238,879 $ 522 $ (212) $ 239,189
Summary of Unrealized Losses	The following tables summarize the amount of unrealized losses, defined as the amount by which the amortized cost exceeds fair value, and the related fair value of available-for-sale marketable securities with unrealized losses, which have been segregated into two categories: those that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for 12 or more months (in thousands): March 31, 2024 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 121,622 $ (177) $ 27,670 $ (94) $ 149,292 $ (271) Government and agency - U.S. 11,756 (3) — — 11,756 (3) Total $ 133,378 $ (180) $ 27,670 $ (94) $ 161,048 $ (274) December 31, 2023 Less than 12 Months Greater than 12 Months Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 78,995 $ (152) $ 12,074 $ (54) $ 91,069 $ (206) Government and agency - U.S. 5,585 (6) — — 5,585 (6) Total $ 84,580 $ (158) $ 12,074 $ (54) $ 96,654 $ (212)

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Summary of Fair Value, Assets and Liabilities Measured on Recurring Basis	The Company’s financial assets and liabilities subject to fair value measurement on a recurring basis and the level of inputs used for such measurements were as follows (in thousands): Fair value measurements at reporting date using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value at March 31, 2024 Assets included in: Cash and cash equivalents Money market securities $ 46,395 $ — $ — $ 46,395 Marketable securities Corporate debt securities — 210,906 — 210,906 Government and agency - U.S. — 38,784 — 38,784 Total fair value $ 46,395 $ 249,690 $ — $ 296,085 Liabilities included in: Debt, long-term Embedded derivatives liabilities $ — $ — $ 2,610 $ 2,610 Total fair value $ — $ — $ 2,610 $ 2,610 Fair value measurements at reporting date using Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Fair Value at December 31, 2023 Assets included in: Cash and cash equivalents Money market securities $ 66,207 $ — $ — $ 66,207 Marketable securities Corporate debt securities — 201,635 — 201,635 Government and agency - U.S. — 37,554 — 37,554 Total fair value $ 66,207 $ 239,189 $ — $ 305,396 Liabilities included in: Debt, long-term Embedded derivatives liabilities $ — $ — $ 2,560 $ 2,560 Total fair value $ — $ — $ 2,560 $ 2,560
Schedule of the Fair Value using Level 3 Significant Unobservable Inputs	The following table presents changes in Level 3 liabilities measured at fair value for the three months ended March 31, 2024 (in thousands): Balance, December 31, 2023 $ 2,560 Change in fair value of embedded derivatives 50 Balance, March 31, 2024 $ 2,610
Schedule of Estimate of Fair Value in Embedded Derivatives in Term Loan	As of March 31, 2024 and December 31, 2023, the fair value of the embedded derivatives in the Term Loan has been estimated using the Monte Carlo model. A summary of the weighted-average significant unobservable inputs (Level 3 inputs) used in measuring the embedded derivatives in the Term Loan as of March 31, 2024 and December 31, 2023 is as follows: March 31, 2024 December 31, 2023 Conversion price $2.53 $2.53 Expected term (in years) 4.5 4.7 Expected equity volatility 102.9% 106.7% Risk-free interest rate 4.3% 3.9% Discount for lack of marketability 15.0% 11.5% Expected dividend yield 0% 0%

SUPPLEMENTAL FINANCIAL INFORM_2

SUPPLEMENTAL FINANCIAL INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2024
Supplemental Financial Information [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development service agreements $ 2,200 $ 1,680 Prepaid insurance 411 807 Interest receivable 189 225 Prepaid raw materials 124 98 Other 395 283 Total prepaid expenses and other current assets $ 3,319 $ 3,093
Schedule of Other Assets	Other assets consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development service agreements $ 186 $ 221 Deferred offering costs 138 — Total other assets $ 324 $ 221
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): March 31, 2024 December 31, 2023 Research and development $ 1,140 $ 2,186 Compensation and other employee liabilities 1,035 3,692 Interest 249 249 Other 481 212 Total accrued expenses and other current liabilities $ 2,905 $ 6,339

DEBT (Tables)

DEBT (Tables)	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Schedule of Outstanding Debt and Interest Expense	Outstanding debt consisted of the following (in thousands): March 31, 2024 December 31, 2023 Principal value of Term Loan, including Final Payment of $1,635 $ 31,635 $ 31,635 Fair value of bifurcated embedded derivatives 2,610 2,560 Unamortized debt discount (4,036) (4,298) Total debt, long-term $ 30,209 $ 29,897 The following table provides the components of interest expense (in thousands): Three Months Ended Interest expense based on the coupon interest rate of the outstanding debt $ 732 Accretion of debt discount 262 Total interest expense related to debt $ 994
Schedule of Aggregate Principal Payments	As of March 31, 2024, the aggregate principal payments due for the Term Loan by year are as follows (in thousands): Year ended December 31, 2026 $ 10,104 Year ended December 31, 2027 21,531 Total principal payments due for Term Loan $ 31,635

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2024
Leases [Abstract]
Schedule of Lease, Cost	The following table summarizes quantitative information about the Company’s leases (in thousands): Three Months Ended March 31, 2024 2023 Finance lease Interest lease cost $ 6 $ — Finance lease expense 6 — Operating leases Operating lease cost 37 40 Variable lease cost 1 — Less: sublease income — (3) Operating lease expense 38 37 Short-term lease rent expense 18 1 Total rent expense $ 62 $ 38 Supplemental information related to leases was as follows (dollar amounts in thousands): Three Months Ended March 31, 2024 2023 Finance cash flows from finance leases $ 739 $ — Operating cash flows from finance lease $ 23 $ — Operating cash flows from operating leases $ 30 $ 40 Weighted-average remaining lease term – finance leases (in years) 3.5 — Weighted-average remaining lease term – operating leases (in years) 2.8 0.4 Weighted-average discount rate – operating leases 9.7 % 10.0 %
Schedule of Lessee, Operating Lease, Liability, Maturity	As of March 31, 2024, the present value of maturities of the Company’s operating lease liabilities were as follows (in thousands): Nine months ended December 31, 2024 $ 113 Year ended December 31, 2025 155 Year ended December 31, 2026 158 Total 426 Less: present value discount (53) Operating lease liability $ 373

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Summary of Share-Based Compensation Expense Related to Stock Options	The Company recorded stock-based compensation expense in the following expense categories of its condensed statements of operations for the periods shown (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 1,646 $ 958 Research and development 838 432 Total stock-based compensation $ 2,484 $ 1,390
Summary of Assumptions Used for Valuation of Fair Value of Stock Options	The Black-Scholes option-pricing model was used to estimate the fair value of stock options granted during the three months ended March 31, 2024 and 2023 with the following weighted average assumptions: Three Months Ended March 31, 2024 2023 Risk-free interest rate 3.82% - 4.33% 3.58% - 4.13% Expected term (in years) 5.3 - 6.1 5.8 - 6.1 Expected volatility 101% - 104% 90% Expected dividend yield 0% 0%
Summary of Stock Option Activity	The following table reflects summarized stock option activity: Stock Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2023 7,523,947 $ 4.01 Granted 2,491,550 $ 3.87 Outstanding as of March 31, 2024 10,015,497 $ 3.98 8.0 $ 10,392 Vested and exercisable as of March 31, 2024 4,516,852 $ 3.30 7.0 $ 8,062
Summary of Nonvested Restricted Stock Units Activity	Number of Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2023 328,500 $ 6.11 Granted 1,204,640 $ 4.15 Vested (109,493) $ 6.11 Unvested as of March 31, 2024 1,423,647 $ 4.45

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Summary of Antidilutive Securities Excluded from Computation of Loss Per Share	Potentially dilutive securities not included in the calculation of diluted net loss per common share, because to do so would be anti-dilutive, were as follows for the periods presented: March 31, 2024 2023 Shares issuable upon exercise of stock options 10,015,497 7,238,893 Shares issuable upon conversion election for Term Loan 988,142 — Shares issuable upon exercise of warrant 730,769 — Unvested RSUs 1,423,647 328,500 Total 13,158,055 7,567,393

DESCRIPTION OF ORGANIZATION A_2

DESCRIPTION OF ORGANIZATION AND BUSINESS OPERATIONS (Details) $ in Thousands	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jul. 31, 2023 participant	Jun. 30, 2023 patient participant
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit | $	$ 237,671	$ 222,798
Working capital | $	$ 247,400	$ 233,600
Number of patients enrolled in trail | patient				65
Number of patients enrolled in trial with one dose of study drug received | participant				62
Number of participants enrolled in trial with one dose of study drug received with primary and secondary objectives met | participant			62

BASIS OF PRESENTATION AND SUM_4

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Cash equivalents	$ 46.4	$ 66.2

BASIS OF PRESENTATION AND SUM_5

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 46,930	$ 66,886
Restricted cash	234	233
Total cash, cash equivalents and restricted cash	$ 47,164	$ 67,119	$ 77,999	$ 130,101

MARKETABLE SECURITIES - Summary

MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Amortized cost, short term	$ 205,825	$ 176,654
Gross unrealized gains, short term	31	179
Gross unrealized losses, short term	(274)	(197)
Fair value, short term	205,582	176,636
Amortized cost, long term	44,010	62,225
Gross unrealized gains, long term	98	343
Gross unrealized losses, long term	0	(15)
Fair value, long term	44,108	62,553
Amortized cost, total	249,835	238,879
Gross unrealized gains, total	129	522
Gross unrealized losses, total	(274)	(212)
Fair value, total	249,690	239,189
Corporate debt securities
Marketable Securities [Line Items]
Amortized cost, short term	172,005	144,184
Gross unrealized gains, short term	19	97
Gross unrealized losses, short term	(271)	(191)
Fair value, short term	171,753	144,090
Amortized cost, long term	39,065	57,240
Gross unrealized gains, long term	88	320
Gross unrealized losses, long term	0	(15)
Fair value, long term	39,153	57,545
Government and agency - U.S.
Marketable Securities [Line Items]
Amortized cost, short term	33,820	32,470
Gross unrealized gains, short term	12	82
Gross unrealized losses, short term	(3)	(6)
Fair value, short term	33,829	32,546
Amortized cost, long term	4,945	4,985
Gross unrealized gains, long term	10	23
Gross unrealized losses, long term	0	0
Fair value, long term	$ 4,955	$ 5,008

MARKETABLE SECURITIES - Summa_2

MARKETABLE SECURITIES - Summary of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Marketable Securities [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	$ 133,378	$ 84,580
Debt securities, available-for-sale, Continuous unrealized loss position, less than 12 months, accumulated loss	(180)	(158)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	27,670	12,074
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(94)	(54)
Debt securities, available-for-sale, unrealized loss position	161,048	96,654
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(274)	(212)
Corporate debt securities
Marketable Securities [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	121,622	78,995
Debt securities, available-for-sale, Continuous unrealized loss position, less than 12 months, accumulated loss	(177)	(152)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	27,670	12,074
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(94)	(54)
Debt securities, available-for-sale, unrealized loss position	149,292	91,069
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(271)	(206)
Government and agency - U.S.
Marketable Securities [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months	11,756	5,585
Debt securities, available-for-sale, Continuous unrealized loss position, less than 12 months, accumulated loss	(3)	(6)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer	0	0
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	0	0
Debt securities, available-for-sale, unrealized loss position	11,756	5,585
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ (3)	$ (6)

MARKETABLE SECURITIES - Additio

MARKETABLE SECURITIES - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Marketable Securities [Line Items]
Debt securities, available-for-sale, noncurrent, term (in years)	2 years
Debt securities, available-for-sale, allowance for credit loss	$ 0	$ 0
Maximum
Marketable Securities [Line Items]
Debt securities, available-for-sale, current, term (in years)	1 year
Minimum
Marketable Securities [Line Items]
Debt securities, available-for-sale, unrealized loss position period (in months)	12 months

FAIR VALUE MEASUREMENTS - Summa

FAIR VALUE MEASUREMENTS - Summary of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Marketable securities
Total fair value	$ 296,085	$ 305,396
Debt, long-term
Fair value of bifurcated embedded derivatives	2,610	2,560
Total fair value	2,610	2,560
Quoted Prices in Active Markets for Identical Assets (Level 1)
Marketable securities
Total fair value	46,395	66,207
Debt, long-term
Fair value of bifurcated embedded derivatives	0	0
Total fair value	0	0
Significant Other Observable Inputs (Level 2)
Marketable securities
Total fair value	249,690	239,189
Debt, long-term
Fair value of bifurcated embedded derivatives	0	0
Total fair value	0	0
Significant Unobservable Inputs (Level 3)
Marketable securities
Total fair value	0	0
Debt, long-term
Fair value of bifurcated embedded derivatives	2,610	2,560
Total fair value	2,610	2,560
Corporate debt securities
Marketable securities
Marketable securities	210,906	201,635
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Marketable securities
Marketable securities	0	0
Corporate debt securities | Significant Other Observable Inputs (Level 2)
Marketable securities
Marketable securities	210,906	201,635
Corporate debt securities | Significant Unobservable Inputs (Level 3)
Marketable securities
Marketable securities	0	0
Government and agency - U.S.
Marketable securities
Marketable securities	38,784	37,554
Government and agency - U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1)
Marketable securities
Marketable securities	0	0
Government and agency - U.S. | Significant Other Observable Inputs (Level 2)
Marketable securities
Marketable securities	38,784	37,554
Government and agency - U.S. | Significant Unobservable Inputs (Level 3)
Marketable securities
Marketable securities	0	0
Money market securities
Cash and cash equivalents
Cash and cash equivalents	46,395	66,207
Money market securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Cash and cash equivalents
Cash and cash equivalents	46,395	66,207
Money market securities | Significant Other Observable Inputs (Level 2)
Cash and cash equivalents
Cash and cash equivalents	0	0
Money market securities | Significant Unobservable Inputs (Level 3)
Cash and cash equivalents
Cash and cash equivalents	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Level 3 Liabilities Measured at Fair Value (Details) - Embedded Derivative Financial Instruments $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 2,560
Change in fair value of embedded derivatives	50
Ending balance	$ 2,610

FAIR VALUE MEASUREMENTS - Sch_2

FAIR VALUE MEASUREMENTS - Schedule of Significant Unobservable Inputs (Details)	Mar. 31, 2024 $ / shares	Dec. 31, 2023 $ / shares
Conversion price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	2.53	2.53
Expected term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	4.5	4.7
Expected equity volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.029	1.067
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.043	0.039
Discount for lack of marketability
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.150	0.115
Expected dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0	0

SUPPLEMENTAL FINANCIAL INFORM_3

SUPPLEMENTAL FINANCIAL INFORMATION - Summary of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Supplemental Financial Information [Abstract]
Research and development service agreements	$ 2,200	$ 1,680
Prepaid insurance	411	807
Interest receivable	189	225
Prepaid raw materials	124	98
Other	395	283
Prepaid expenses and other current assets	$ 3,319	$ 3,093

SUPPLEMENTAL FINANCIAL INFORM_4

SUPPLEMENTAL FINANCIAL INFORMATION - Summary of Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Supplemental Financial Information [Abstract]
Research and development service agreements	$ 186	$ 221
Deferred offering costs	138	0
Total other assets	$ 324	$ 221

SUPPLEMENTAL FINANCIAL INFORM_5

SUPPLEMENTAL FINANCIAL INFORMATION - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Supplemental Financial Information [Abstract]
Research and development	$ 1,140	$ 2,186
Compensation and other employee liabilities	1,035	3,692
Interest	249	249
Other	481	212
Accrued expenses and other current liabilities	$ 2,905	$ 6,339

DEBT- Additional Information (D

DEBT- Additional Information (Details) - USD ($)	Nov. 10, 2023	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument, Redemption [Line Items]
Fair value of bifurcated embedded derivatives		$ 2,610,000	$ 2,560,000
Common Stock Warrants | Common Stock
Debt Instrument, Redemption [Line Items]
Warrants (in shares)	730,769
Term Loan | Secured Debt
Debt Instrument, Redemption [Line Items]
Borrowing capacity	$ 50,000,000
Interest rate	9.65%
Final payment fee	$ 1,600,000	1,635,000
Minimum required payment (more than)	5,000,000
Minimum required payment, outstanding debt requirement (at least)	15,000,000
Conversion, if-converted amount	$ 2,500,000
Conversion price (in dollars per share)	$ 2.53
Direct fees	$ 500,000
Fair value of bifurcated embedded derivatives	1,200,000	$ 2,610,000	$ 2,560,000
Discount	4,400,000
Effective interest rate		13.40%
Term Loan | Secured Debt | Common Stock Warrants
Debt Instrument, Redemption [Line Items]
Warrant, fair value	$ 1,100,000
Term Loan | Secured Debt | Common Stock Warrants | Common Stock
Debt Instrument, Redemption [Line Items]
Warrants (in shares)	730,769
Term Loan | Secured Debt | Prime Rate
Debt Instrument, Redemption [Line Items]
Variable interest rate	1.15%
Term Loan, First Tranche | Secured Debt
Debt Instrument, Redemption [Line Items]
Borrowing capacity	$ 30,000,000
Term Loan, Second Tranche | Secured Debt
Debt Instrument, Redemption [Line Items]
Borrowing capacity	20,000,000
Covenant, proceeds from issuance of debt required (at least)	$ 20,000,000

DEBT - Schedule of Outstanding

DEBT - Schedule of Outstanding Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Nov. 10, 2023
Debt Instrument, Redemption [Line Items]
Fair value of bifurcated embedded derivatives	$ 2,610	$ 2,560
Total debt, long-term	30,209	29,897
Term Loan | Secured Debt
Debt Instrument, Redemption [Line Items]
Principal value of Term Loan, including Final Payment of $1,635	31,635	31,635
Fair value of bifurcated embedded derivatives	2,610	2,560	$ 1,200
Unamortized debt discount	(4,036)	(4,298)
Total debt, long-term	30,209	$ 29,897
Final payment fee	$ 1,635		$ 1,600

DEBT - Schedule of Interest Exp

DEBT - Schedule of Interest Expense, Debt (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Line Items]
Total interest expense related to debt	$ 1,000	$ 0
Term Loan | Secured Debt
Debt Instrument [Line Items]
Interest expense based on the coupon interest rate of the outstanding debt	732
Accretion of debt discount	262
Total interest expense related to debt	$ 994

DEBT - Schedule of Aggregate Pr

DEBT - Schedule of Aggregate Principal Payments (Details) - Term Loan - Secured Debt - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Year ended December 31, 2026	$ 10,104
Year ended December 31, 2027	21,531
Total principal payments due for Term Loan	$ 31,635	$ 31,635

LEASES - Additional Information

LEASES - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 lease	Jan. 31, 2024 USD ($)	Sep. 11, 2023
Lessee, Lease, Description [Line Items]
Number of lease contracts entered | lease	2
Computer Equipment Lease
Lessee, Lease, Description [Line Items]
Finance lease liability | $		$ 0.8
Newton, Massachusetts
Lessee, Lease, Description [Line Items]
Operating lease term (in months)			38 months

LEASES - Summary of Lease, Cost

LEASES - Summary of Lease, Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Finance lease
Interest lease cost	$ 6	$ 0
Finance lease expense	6	0
Operating leases
Operating lease cost	37	40
Variable lease cost	1	0
Less: sublease income	0	(3)
Operating lease expense	38	37
Short-term lease rent expense	18	1
Total rent expense	$ 62	$ 38

LEASES - Summary of Supplementa

LEASES - Summary of Supplemental Information Related To Lease (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
Finance cash flows from finance leases	$ 739	$ 0
Operating cash flows from finance lease	23	0
Operating cash flows from operating leases	$ 30	$ 40
Weighted-average remaining lease term – finance leases (in years)	3 years 6 months	0 years
Weighted-average remaining lease term – operating leases (in years)	2 years 9 months 18 days	4 months 24 days
Weighted-average discount rate – operating leases	9.70%	10%

LEASES - Summary of Lessee, Ope

LEASES - Summary of Lessee, Operating Lease, Liability, Maturity (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Leases [Abstract]
Nine months ended December 31, 2024	$ 113
Year ended December 31, 2025	155
Year ended December 31, 2026	158
Total	426
Less: present value discount	(53)
Operating lease liability	$ 373

STOCKHOLDERS_ EQUITY (Details)

STOCKHOLDERS’ EQUITY (Details) $ / shares in Units, $ in Millions		3 Months Ended	21 Months Ended
	Jul. 21, 2023 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) votingRight $ / shares shares	Mar. 31, 2024 USD ($) votingRight $ / shares shares	Dec. 31, 2023 $ / shares shares	Nov. 10, 2023 $ / shares shares	Jul. 01, 2022 USD ($)
Class of Stock [Line Items]
Common stock and preferred stock, shares authorized (in shares)		310,000,000	310,000,000
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)		300,000,000	300,000,000	300,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Common stock, number of voting rights | votingRight		1	1
Sale of stock, commission rate to sales agents						3%
Common Stock Warrants
Class of Stock [Line Items]
Exercise price (in dollars per share) | $ / shares					$ 1.95
Class of warrants or rights term (in years)					10 years
Common Stock Warrants | Common Stock
Class of Stock [Line Items]
Warrants (in shares)					730,769
2022 Registration Statement
Class of Stock [Line Items]
Sale of stock, maximum authorized amount | $						$ 200
Offering
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	16,774,193
Sale of stock, price per share (in dollars per share) | $ / shares	$ 7.75
Sale of stock, consideration received on transaction | $	$ 121.9
At The Market Offering
Class of Stock [Line Items]
Sale of stock, maximum authorized amount | $						$ 50
Sale of stock, number of shares issued in transaction (in shares)		2,068,246
Sale of stock, price per share (in dollars per share) | $ / shares		$ 3.84	$ 3.84
Sale of stock, consideration received on transaction | $		$ 7.9	$ 12.2

STOCK-BASED COMPENSATION - Addi

STOCK-BASED COMPENSATION - Additional Information (Details) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) anniversary $ / shares shares	Mar. 31, 2023 $ / shares	Dec. 31, 2023 shares	Jan. 01, 2024 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding (in shares)	10,015,497		7,523,947
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of options granted (in dollars per share) | $ / shares	$ 3.18	$ 4.52
Expected dividend yield	0%	0%
Option, cost not yet recognized, amount | $	$ 18.3
Weighted average period of recognition (in years)	2 years 8 months 12 days
Stock Options | Granted after December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in months)	48 months
Cliff period (in years)	1 year
Contractual term (in years)	10 years
Stock Options | Granted prior to December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (in years)	10 years
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognition (in years)	2 years 7 months 6 days
Number of anniversaries for vesting | anniversary	3
Non option, cost not yet recognized, amount | $	$ 5.8
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock maximum	1%
Common stock, capital shares reserved for future issuance (in shares)				579,105
Number of shares authorized (in shares)	1,769,088
Shares of common stock outstanding maximum (in shares)	800,000
Shares issued in period (in shares)	0
Minimum | Stock Options | Granted after December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in months)	12 months
Minimum | Stock Options | Granted prior to December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in months)	3 months
Maximum | Stock Options | Granted after December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in months)	48 months
Maximum | Stock Options | Granted prior to December 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in months)	24 months
2013 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding (in shares)	3,231,274
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum threshold common stock issuable on exercise of incentive stock options (in shares)	12,000,000
Common stock, capital shares reserved for future issuance (in shares)				2,895,523
2021 Equity Incentive Plan | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock maximum			5%
Number of shares authorized (in shares)	14,668,721
Shares available for future grant (in shares)	2,882,485

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Share-Based Compensation Expense Related to Stock Options (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 2,484	$ 1,390
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	1,646	958
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 838	$ 432

STOCK-BASED COMPENSATION - Su_2

STOCK-BASED COMPENSATION - Summary of Assumptions Used for Valuation of Fair Value of Stock (Details) - Stock Options	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Risk-free interest rate, minimum	3.82%	3.58%
Risk-free interest rate, maximum	4.33%	4.13%
Expected volatility, minimum	101%
Expected volatility, maximum	104%
Expected volatility		90%
Expected dividend yield	0%	0%
Minimum
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Expected term (in years)	5 years 3 months 18 days	5 years 9 months 18 days
Maximum
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days

STOCK-BASED COMPENSATION - Su_3

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) $ / shares shares
Stock Options
Beginning balance (in shares) | shares	7,523,947
Granted (in shares) | shares	2,491,550
Ending balance (in shares) | shares	10,015,497
Vested and exercisable (in shares) | shares	4,516,852
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 4.01
Granted (in dollars per share) | $ / shares	3.87
Ending balance (in dollars per share) | $ / shares	3.98
Vested and exercisable (in dollars per share) | $ / shares	$ 3.30
Weighted Average Remaining Contractual Life (in years)
Outstanding balance (in years)	8 years
Vested and exercisable (in years)	7 years
Ending balance, aggregate intrinsic value | $	$ 10,392
Vested and exercisable, aggregate intrinsic value | $	$ 8,062

STOCK-BASED COMPENSATION - Su_4

STOCK-BASED COMPENSATION - Summary of Restricted Stock Units Activity (Details) - RSUs	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Number of Shares
Unvested beginning balance (in shares) | shares	328,500
Granted (in shares) | shares	1,204,640
Vested (in shares) | shares	(109,493)
Unvested ending balance (in shares) | shares	1,423,647
Weighted Average Grant Date Fair Value
Unvested beginning balance (in dollars per share) | $ / shares	$ 6.11
Granted (in dollars per share) | $ / shares	4.15
Vested (in shares) | $ / shares	6.11
Unvested ending balance (in dollars per share) | $ / shares	$ 4.45

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Additional information (Details) - License Agreements SFr in Millions	1 Months Ended
	Nov. 30, 2022 CHF (SFr)
Other Commitments [Line Items]
Payment of upfront fees	SFr 1
Royalty percentage	1%
Payment obligation, term (in years)	10 years

NET LOSS PER SHARE (Details)

NET LOSS PER SHARE (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	13,158,055	7,567,393
Shares issuable upon exercise of stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	10,015,497	7,238,893
Shares issuable upon conversion election for Term Loan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	988,142	0
Shares issuable upon exercise of warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	730,769	0
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	1,423,647	328,500