Molecular Templates (MTEM) 10-Q 15 May 24 2024 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2024	May 06, 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	001-32979
Entity Registrant Name	Molecular Templates, Inc.
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	9301 Amberglen Blvd
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Austin
Entity Address, State or Province	TX
Entity Tax Identification Number	94-3409596
Entity Address, Postal Zip Code	78729
City Area Code	512
Local Phone Number	869-1555
Title of 12(b) Security	Common Stock, $0.001 Par Value Per Share
Trading Symbol	MTEM
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	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		6,583,880
Entity Central Index Key	0001183765
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 6,779	$ 11,523
Prepaid expenses	1,200	2,195
Grants revenue receivable	412	250
Other current assets	2,299	2,804
Total current assets	10,690	16,772
Operating lease right-of-use assets	8,647	9,161
Property and equipment, net	6,284	7,393
Other assets	1,498	2,057
Total assets	27,119	35,383
Current liabilities:
Accounts payable	2,681	1,523
Accrued liabilities	2,748	4,279
Deferred revenue, current		9,031
Other current liabilities	3,152	2,488
Total current liabilities	8,581	17,321
Operating lease liabilities, long term portion	9,075	9,742
Contingent value right liability	2,158	2,702
Other liabilities	1,435	1,406
Total liabilities	21,249	31,171
Commitments and contingencies (Note 9)
Stockholders' equity
Preferred stock, $0.001 par value per share: Authorized: 2,000,000 shares as of March 31, 2024 and December 31, 2023; Issued and outstanding: 250 shares as of March 31, 2024 and December 31, 2023
Common stock, $0.001 par value per share: Authorized: 150,000,000 shares as of March 31, 2024 and December 31, 2023; Issued and outstanding: 5,374,268 shares as of March 31, 2024 and December 31, 2023	5	5
Additional paid-in capital	458,185	457,099
Accumulated deficit	(452,320)	(452,892)
Total stockholders' equity	5,870	4,212
Total liabilities and stockholders' equity	$ 27,119	$ 35,383

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
CONDENSED CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	250	250
Preferred stock, shares outstanding	250	250
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	5,374,268	5,374,268
Common stock, shares outstanding	5,374,268	5,374,268

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Total revenue	$ 11,086	$ 36,629
Operating expenses:
Research and development	7,405	19,042
General and administrative	3,731	5,802
Total operating expenses	11,136	24,844
Income/(loss) from operations	(50)	11,785
Interest and other income, net	109	455
Interest and other expense, net	(31)	(1,395)
Change in valuation of contingent value right (Note 4)	544
Net income attributable to common stockholders	$ 572	$ 10,845
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.11	$ 2.89
Diluted (in dollars per share)	$ 0.08	$ 2.89
Weighted average number of shares used in net income/(loss) per share calculations:
Basic (in shares)	5,374,268	3,756,711
Diluted (in shares)	7,015,864	3,756,711
Research and development revenue
Total revenue	$ 10,924	$ 33,627
Grant revenue
Total revenue	$ 162	$ 3,002

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income	$ 572	$ 10,845
Other comprehensive income:
Unrealized gain on available-for-sale securities		67
Comprehensive income	$ (572)	$ (10,912)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands		Common Stock		Additional Paid-In Capital		Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2022		$ 4	[1]	$ 429,698	[1]	$ (66)	$ (444,768)	$ (15,132)
Beginning balance (shares) at Dec. 31, 2022	[1]	3,756,711
Stock-based compensation	[1]			2,310
Other comprehensive income/(loss)						67
Net Income (Loss)							10,845
Ending balance at Mar. 31, 2023		$ 4	[1]	432,008	[1]	1	(433,923)	(1,910)
Ending balance (shares) at Mar. 31, 2023	[1]	3,756,711
Beginning balance at Dec. 31, 2023		$ 5	[1]	457,099	[1]		(452,892)	$ 4,212
Beginning balance (shares) at Dec. 31, 2023		5,374,268	[1]					5,374,268
Stock-based compensation	[1]			1,086
Other comprehensive income/(loss)						$ 0
Net Income (Loss)							572
Ending balance at Mar. 31, 2024		$ 5	[1]	$ 458,185	[1]		$ (452,320)	$ 5,870
Ending balance (shares) at Mar. 31, 2024		5,374,268	[1]					5,374,268
[1] Prior period a mounts have been retrospectively adjusted for the 1-for-15 reverse stock split that was effective August 11, 2023 (see Note 1).

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical)	Aug. 11, 2023
CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT)
Reverse stock split ratio	0.066

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net income	$ 572	$ 10,845
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation, amortization and other	1,122	1,928
Stock-based compensation expense	1,086	2,310
Amortization of debt discount and accretion related to debt		234
Accretion of asset retirement obligations	29	27
Change in valuation of contingent value right	(544)
Changes in operating assets and liabilities:
Prepaid expenses	995	1,450
Grants revenue receivable	(162)	(2,838)
Other assets	551	(1,258)
Operating lease right-of-use assets and liabilities	(79)	(12)
Accounts payable	1,158	2,201
Accrued liabilities	(1,531)	(3,281)
Other liabilities	590
Deferred revenue	(9,031)	(30,967)
Net cash used in operating activities	(5,244)	(19,361)
Cash flows from investing activities:
Purchases of property and equipment		(183)
Purchase of marketable securities		(2,364)
Sales of marketable securities		28,500
Net cash provided by investing activities		25,953
Net (decrease)/increase in cash, cash equivalents, and restricted cash	(5,244)	6,592
Cash, cash equivalents and restricted cash, beginning of period	12,838	34,679
Cash, cash equivalents and restricted cash, end of period	7,594	41,271
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	6,779	38,782
Restricted cash included in other assets	$ 815	$ 2,489
Restricted Cash and Cash Equivalents, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Total cash, cash equivalents and restricted cash	$ 7,594	$ 41,271
Supplemental Cash Flow Information
Cash paid for interest		1,111
Non-Cash Investing Activities
Fixed asset additions in accounts payable and accrued expenses	$ 0	$ 13

ORGANIZATION AND SUMMARY OF SIG

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2023
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 1 — ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of the Business Molecular Templates, Inc. (the “Company”) is a clinical stage biopharmaceutical company formed in 2001, with a biologic therapeutic platform for the development of novel targeted therapeutics for cancer, headquartered in Austin, Texas. The Company’s focus is on the research and development of therapeutic compounds for a variety of cancers. The Company operates its business as a single segment, as defined by U.S. generally accepted accounting principles (“U.S. GAAP”). Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. GAAP and include the accounts of the Company and its wholly owned subsidiary and reflect the elimination of intercompany accounts and transactions. The preparation of condensed consolidated financial statements requires management to make estimates and assumptions that affect the recorded amounts reported therein. A change in facts or circumstances surrounding the estimates could result in a change to estimates and impact future operating results. Certain accounts in the prior financial statements have been reclassified for comparative purposes to conform to the presentation in the current financial statements. These reclassifications have no material effect on previously reported financials. In the opinion of management of the Company, all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation have been included. The unaudited condensed consolidated financial statements and related disclosures have been prepared with the presumption that users of the interim unaudited condensed consolidated financial statements have read or have access to the audited consolidated financial statements for the preceding fiscal year. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2023 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 29, 2024. On August 11, 2023, the Company filed with the Secretary of State of the State of Delaware a Certificate of Amendment to its Amended and Restated Certificate of Incorporation to effect a one-time reverse stock split of the Company’s common stock, at a ratio of 1-for-15 (the “Reverse Stock Split”). The Reverse Stock Split was effective at 5 p.m. Eastern Time, after the close of trading on the Nasdaq Capital Market, on August 11, 2023 (the “Effective Time”). At the Effective Time, every 15 shares of the Company’s issued and outstanding common stock were automatically converted into one share of common stock, without any change in the par value per share. Any stockholder who was entitled to a fractional share of common stock created as a result of the Reverse Stock Split received a cash payment in lieu thereof equal to the fractional share to which the stockholder was entitled multiplied by the closing sales price of a share of common stock on August 11, 2023, as adjusted for the Reverse Stock Split. All common stock, per share and related information presented in the condensed consolidated financial statements and notes prior to the Reverse Stock Split have been retroactively adjusted to reflect the Reverse Stock Split for all periods presented, to the extent applicable. Going Concern The Company has adopted as required the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 205-40, Presentation of Financial Statements - Going Concern, which requires that management contemplate the realization of assets and liquidation of liabilities in the normal course of business, and evaluate whether there are relevant conditions and events that in the aggregate raise substantial doubt about the entity’s ability to continue as a going concern and to meet its obligations as they become due within one year after the date that the financial statements are issued. Under this standard, management’s assessment shall not take into consideration the potential mitigating effects of management’s plans that have not been fully implemented as of the date the financial statements are issued. As of March 31, 2024, the Company had an accumulated deficit of $452.3 million and had unrestricted cash and cash equivalents of $6.8 million. Based on the Company’s unrestricted cash and cash equivalents as of March 31, 2024 and subsequent to the closing of the amended and restated second tranche of the July 2023 Private Placement (as defined below), management anticipates that the Company will be able to fund its planned operating expenses and capital expenditure requirements into the fourth quarter of 2024. The Company has not yet established an ongoing source of revenues sufficient to cover its operating and cash expenditure requirements or to cover any potential payments that may become due and payable pursuant to the CVR Agreement as described in Note 7 “Borrowing Arrangements and Debt Extinguishment” to provide sufficient certainty that it will continue as a going concern. For these reasons, there is substantial doubt about the Company’s ability to continue as a going concern as of the issuance of these financial statements. Historically, the Company financed its operations to date primarily through partnerships, funds received from public offerings of common and preferred stock, private placements of equity securities, a reverse merger, upfront and milestone payments received from its prior and current collaboration agreements, a debt financing facility, as well as funding from governmental bodies and bank and bridge loans. The Company plans to address this condition through the sale of common stock in public offerings and/or private placements, debt financings, or through other capital sources, including collaborations with other companies or other strategic transactions, but there is no assurance these plans will be completed successfully or at all. If the Company is unable to obtain additional capital when and as needed to continue as a going concern, it might have to further reduce or scale back its operations, cease operations entirely, and/or liquidate its assets, and the values it receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in its financial statements. These financial statements do not give effect to any adjustments which will be necessary should the Company be unable to continue as a going concern and therefore be required to realize its assets and discharge its liabilities in other than the normal course of business and at amounts different from those reflected in the accompanying financial statements. Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2024, as compared to the significant accounting policies disclosed in Note 1 “Organization and Summary of Significant Accounting Policies,” to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. Cash and Cash Equivalents The Company considers temporary investments having original maturities of three months or less from date of purchase to be cash equivalents. Restricted cash is recorded in other assets, based on when the restrictions expire. Other assets include $0.8 million and $1.3 million of restricted cash as of March 31, 2024 and December 31, 2023, respectively, related to letters of credit in lieu of a cash deposit for the Company’s leases. Fair Value Measurement The Company accounts for its marketable securities in accordance with ASC 820 “Fair Value Measurements and Disclosures.” hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value: Level 1 Level 2 Level 3 The Company utilizes the market approach or probability approach to measure fair value for its financial assets and liabilities. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities. For Level 2 securities that have market prices from multiples sources, a “consensus price” or a weighted average price for each of these securities can be derived from a distribution-curve-based algorithm which includes market prices obtained from a variety of industrial standard data providers (e.g. Bloomberg), security master files from large financial institutions, and other third-party sources. Level 2 securities with short maturities and infrequent secondary market trades are typically priced using mathematical calculations adjusted for observable inputs when available. Level 3 securities utilize a probability weighted expected return method or Black-Scholes option-pricing model. Significant estimates and assumptions required for these valuations include, but are not limited to, probabilities related to the timing and outcome of future financing and/or liquidity events. These unobservable inputs represent a Level 3 measurement because they are supported by little or no market activity and reflect our own assumptions in measuring fair value. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash and cash equivalents are with two major financial institutions in the United States. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. As of March 31, 2024, the Company’s exposure to credit risk associated with non-payment will be affected principally by conditions or occurrences within Bristol-Myers Squibb Company (“Bristol-Myers Squibb”). Bristol-Myers Squibb accounted for approximately 99% and 92% of total revenues for the three months ended March 31, 2024 and 2023, respectively. Biologic candidates developed by the Company require approvals or clearances from the U.S. Food and Drug Administration (the “FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s biologic candidates will receive any of the required approvals or clearances. If the Company were to be denied approval or clearance or any such approval or clearance were to be delayed, it would have a material adverse impact on the Company. Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (Subtopic 470-20: Debt with Conversion and Other Options and Subtopic 815-40: Derivatives and Hedging - Contracts in Entity’s Own Equity). The new guidance simplifies accounting for convertible instruments by removing major separation models, removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, and it also simplifies the diluted earnings per share calculation in certain areas. The amendment is effective for the Company for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years, using a modified retrospective approach. The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In December 2023, the FASB issued ASU No. 2023-09, “Improvements to Income Tax Disclosures” (Topic 740: Income Taxes). The new guidance requires that public entities disclose more consistent categories and greater disaggregation of information in the income tax rate reconciliations and further disaggregate income taxes paid by jurisdiction. The amendment is effective for the Company for fiscal years beginning after December 15, 2024. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements. ​

NET INCOME PER COMMON SHARE

NET INCOME PER COMMON SHARE	3 Months Ended
	Mar. 31, 2024
NET INCOME PER COMMON SHARE
NET INCOME PER COMMON SHARE	NOTE 2 — NET INCOME PER COMMON SHARE Basic net income per common share is computed by dividing net income by the weighted-average number of common shares outstanding during the period utilizing the two-class method. Preferred stockholders participate equally with common stockholders in earnings, but do not participate in losses, and are excluded from the basic net income calculation. Diluted net income per share is computed by giving effect to all potential dilutive common shares, including outstanding options, warrants, convertible common shares related to the Conversion Right, as defined in the CVR Agreement and described in Note 4 “Fair Value Measurements,” and convertible preferred stock. ​ The shares excluded from the diluted net income per share calculation were 881,000 and 579,000 for the three months ended March 31, 2024 and 2023, respectively. The effect of those shares was antidilutive under the treasury stock method, as the assumed proceeds of the options and the common warrants per unit were above the Company’s average share price during those periods. ​ The following table provides the calculation of diluted weighted-average shares outstanding: ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ ​ 2024 ​ 2023 Basic weighted-average shares outstanding ​ 5,374,268 ​ 3,756,711 Prefunded Warrants ​ 1,216,663 ​ — Shares issuable under Conversion Right of CVR Agreement ​ 408,267 ​ — Preferred shares ​ 16,666 ​ — Diluted weighted-average shares outstanding ​ 7,015,864 ​ 3,756,711 ​

RESEARCH AND DEVELOPMENT AGREEM

RESEARCH AND DEVELOPMENT AGREEMENTS	3 Months Ended
	Mar. 31, 2024
RESEARCH AND DEVELOPMENT AGREEMENTS
RESEARCH AND DEVELOPMENT AGREEMENTS	NOTE 3 — RESEARCH AND DEVELOPMENT AGREEMENTS Bristol-Myers Squibb Collaboration Agreement In February 2021, the Company entered into a Collaboration Agreement, as amended (the “BMS Collaboration Agreement”), with Bristol-Myers Squibb to perform strategic research collaboration leveraging the Company’s engineered toxin body (“ETB”) technology platform to discover and develop novel products containing ETBs directed to multiple targets. On March 13, 2024, Bristol-Myers Squibb notified the Company that it does not intend to continue the research collaboration it entered into with the Company pursuant to the BMS Collaboration Agreement and would be terminating the BMS Collaboration Agreement in its entirety. The termination will be effective on June 13, 2024, or 90 days following the Company’s receipt of Bristol-Myers Squibb’s written notice of termination. Pursuant to the terms of the BMS Collaboration Agreement, the Company granted Bristol-Myers Squibb a series of exclusive options to obtain one or more exclusive licenses under the Company’s intellectual property to exploit products containing ETBs directed against certain targets designated by Bristol-Myers Squibb. Bristol-Myers Squibb paid the Company an upfront payment of $70.0 million. In addition to the upfront payment, the Company would have been eligible to receive near term and development and regulatory milestone payments of up to $874.5 million. The Company would also have been eligible to receive up to an additional $450.0 million in payments upon the achievement of certain sales milestones, and subject to certain reductions, tiered royalties ranging from mid-single digits up to mid-teens as percentages of calendar year net sales, if any, on any licensed product. The Company would have been responsible for conducting the research activities through the designation, if any, of one or more development candidates. Upon the exercise of its option for a development candidate, Bristol-Myers Squibb would have been responsible for all development, manufacturing, regulatory and commercialization activities with respect to that development candidate, subject to the terms of the BMS Collaboration Agreement. Unless earlier terminated, the BMS Collaboration Agreement would have expired (i) on a country-by-country basis and licensed product-by-licensed product basis, on the date of expiration of the royalty payment obligations under the BMS Collaboration Agreement with respect to such licensed product in such country and (ii) in its entirety upon the earlier of (a) the expiration of the royalty payment obligations under the BMS Collaboration Agreement with respect to all licensed products in all countries or (b) upon Bristol-Myers Squibb’s decision not to exercise any option on or prior to the applicable option deadlines. Bristol-Myers Squibb had the right to terminate the BMS Collaboration Agreement for convenience upon prior written notice to the Company. Either party had the right to terminate the BMS Collaboration Agreement (a) for the insolvency of the other party or (b) subject to specified cure periods, in the event of the other party’s uncured material breach. The Company had the right upon prior written notice to terminate the BMS Collaboration Agreement in the event that Bristol-Myers Squibb or any of its affiliates asserts a challenge against the Company’s patents. The Company identified multiple performance obligations at the inception of the BMS Collaboration Agreement consisting of research and development services and material rights related to additional developmental targets. The transaction price of $70.0 million was allocated to the performance obligations based upon their relative stand-alone selling price and was recognized over time as the underlying research and development services are performed. The Company recognized revenue for research and development services under the BMS Collaboration Agreement using a cost-based input measure. In applying the cost-based input method of revenue recognition, the Company would use actual costs incurred relative to budgeted costs expected to be incurred. These costs consisted primarily of internal employee efforts and third-party contract costs. Revenue was recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completed its performance obligation over the estimated service period. For the three months ended March 31, 2024 and 2023, the Company recognized $10.9 million and $33.6 million, respectively, of research and development revenue related to the BMS Collaboration Agreement, which was primarily related to the completion of the research program for one of the collaboration’s targets and the completion of the related performance obligation by the Company under the BMS Collaboration Agreement, resulting in recognition of $25.8 million of research and development revenue in the quarter ended March 31, 2023, offset by the termination of the BMS Collaboration Agreement and the completion of the remaining research programs and related performance obligations, resulting in recognition of $10.9 million of research and development revenue in the quarter ended March 31, 2024. The Company had zero and $9.0 million of deferred revenue, current, as of March 31, 2024 and December 31, 2023, respectively, related to the BMS Collaboration Agreement. The Company had no deferred revenue, non-current, as of March 31, 2024 and December 31, 2023, related to the BMS Collaboration Agreement. Grant Agreements In September 2018, the Company entered into a Cancer Research Agreement (the “CD38 CPRIT Agreement”) with the Cancer Prevention and Research Institute of Texas (“CPRIT”) which was extended in September 2023, under which CPRIT awarded a $15.2 million product development grant to fund research of a cancer therapy involving a CD38 targeting ETB. As of March 31, 2024, the Company has cumulatively recognized $14.3 million of grant revenue related to the CD38 CPRIT Agreement. Pursuant to the CD38 CPRIT Agreement, the Company may also use such funds to develop a replacement CD38 targeting ETB, with or without a partner. For the three months ended March 31, 2024 and 2023, the Company recognized grant revenue under this award of $0.2 million and $3.0 million, respectively. Qualified expenditures submitted for reimbursement in excess of amounts received are recorded as receivables in grant revenue receivable. As of March 31, 2024 and December 31, 2023, the Company recorded grant revenue receivable of $0.4 million and $0.3 million, respectively. As of both March 31, 2024 and December 31, 2023, the Company recorded no deferred revenue related to CD38 CPRIT Agreement.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2024
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	NOTE 4 — FAIR VALUE MEASUREMENTS The following table sets forth the Company’s financial assets (cash equivalents) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ March 31, 2024 Level 1 Level 2 Level 3 Money market funds ​ $ 5,896 ​ $ 5,896 ​ $ — ​ $ — Total ​ $ 5,896 ​ $ 5,896 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2023 Level 1 Level 2 Level 3 Money market funds ​ $ 11,395 ​ $ 11,395 ​ $ — ​ $ — Total ​ $ 11,395 ​ $ 11,395 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 11,395 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 11,395 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The Company invests in highly-liquid, investment-grade securities. The following is a summary of the Company’s available-for-sale securities (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2024 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 5,896 ​ $ — ​ $ — ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2023 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 11,395 ​ $ — ​ $ — ​ $ 11,395 ​ As of both March 31, 2024 and December 31, 2023, all of the Company’s available-for-sale investments were due in one year or less. The Company received no proceeds from the sale of available-for-sale securities for the three months ended March 31, 2024 and 2023, and no ​ Contingent Value Right and Common Stock Warrant Valuation ​ scenario, the stock price at each event was forecasted to determine if K2VH would convert $3.0 million of the Remaining Value into shares of the Company’s common stock. If K2HV elected to convert any amount up to $3.0 million into shares of the Company’s common stock, then the value of the Conversion Right was the expected stock price times the number of conversion shares; otherwise, the value was determined to be zero. The Contingent Value Right liability component was calculated as the Remaining Value less $3.0 million conversion amount if converted at the time of the event, discounted back to present value. As of June 16, 2023, the value of the Conversion Right and Contingent Value Right liability were calculated within each scenario and probability weighted to derive the total fair value of the Conversion Right and the Contingent Value Right liability was $3.3 million and $1.9 million, respectively. As of March 31, 2024, the fair value of the Conversion Right and the Contingent Value Right liability was $0.9 million and $1.2 million, respectively. As of December 31, 2023, the fair value of the Conversion Right and the Contingent Value Right liability was $1.5 million and $1.2 million, respectively. For the three months ended March 31, 2024, the total change in fair value of the Contingent Value Right liability was $0.5 million. The following table sets forth the Company’s financial liabilities (convertible secured contingent value right) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ March 31, 2024 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 2,158 ​ $ — ​ $ — ​ $ 2,158 Total ​ $ 2,158 ​ $ — ​ $ — ​ $ 2,158 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2023 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 2,702 ​ $ — ​ $ — ​ $ 2,702 Total ​ $ 2,702 ​ $ — ​ $ — ​ $ 2,702 ​ The following table is a reconciliation of the change in fair value of the Conversion Right and Contingent Value Right liability for the three months ended March 31, 2024 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements Using Significant Unobservable Inputs (Level 3) ​ ​ Conversion right and contingent value right liability ​ Total Balance as of December 31, 2023 ​ $ 2,702 ​ $ 2,702 Change in valuation included in net income ​ ​ (544) ​ ​ (544) Balance as of March 31, 2024 ​ $ 2,158 ​ $ 2,158 ​ In satisfaction of its obligations to issue the warrant to K2HV’s affiliated holder pursuant to the CVR Agreement, the Company issued a warrant to purchase up to 340,222 shares of the Company’s common stock at an exercise price of $5.8785 per share. The warrant has a term of 10 years. The Company accounted for its common stock warrants under the guidance in ASC 480, “ Distinguishing Liabilities from Equity “Derivatives and Hedging,” ​ ​ ​ ​ ​ ​ ​ ​ ​ June 16, 2023 ​ Risk-free interest rate ​ ​ 3.77 % Expected term (in years) ​ ​ 10.0 ​ Dividend yield ​ ​ — ​ Volatility ​ ​ 80.00 % Stock price ​ $ 0.53 ​ ​ On June 16, 2023, the Company determined the fair value of the warrants to be $2.3 million and classified that amount to additional paid in capital.

BALANCE SHEET COMPONENTS

BALANCE SHEET COMPONENTS	3 Months Ended
	Mar. 31, 2024
BALANCE SHEET COMPONENTS
BALANCE SHEET COMPONENTS	NOTE 5 — BALANCE SHEET COMPONENTS Accrued liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2024 December 31, 2023 Accrued liabilities: ​ ​ ​ ​ ​ General and administrative $ 291 ​ $ 225 Clinical trial related costs ​ ​ 2,105 ​ ​ 3,574 Non-clinical research and manufacturing operations ​ 301 ​ ​ 404 Payroll related ​ 43 ​ ​ 60 Other accrued expenses ​ 8 ​ ​ 16 Total Accrued liabilities $ 2,748 ​ $ 4,279 ​

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	3 Months Ended
	Mar. 31, 2024
PROPERTY AND EQUIPMENT
PROPERTY AND EQUIPMENT	NOTE 6—PROPERTY AND EQUIPMENT Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ 2024 2023 Laboratory equipment ​ $ 20,695 ​ $ 20,695 Leasehold improvements ​ ​ 12,974 ​ ​ 12,974 Furniture and fixtures ​ ​ 518 ​ ​ 518 Computer and equipment ​ ​ 254 ​ ​ 254 ​ ​ ​ 34,441 ​ ​ 34,441 Less: Accumulated depreciation ​ ​ (28,157) ​ ​ (27,048) Total property and equipment, net ​ $ 6,284 ​ $ 7,393 ​ Depreciation expense was $1.1 million and $2.0 million for the three months ended March 31, 2024 and 2023, respectively. As of March 31, 2024 and December 31, 2023, the Company had net Asset Retirement Obligation (“ARO”) assets totaling $0.2 million and $0.2 million, respectively. The ARO assets are included in leasehold improvements.

BORROWING ARRANGEMENTS AND DEBT

BORROWING ARRANGEMENTS AND DEBT EXTINGUISHMENT	3 Months Ended
	Mar. 31, 2024
BORROWING ARRANGEMENTS AND DEBT EXTINGUISHMENT
BORROWING ARRANGEMENTS AND DEBT EXTINGUISHMENT	NOTE 7 — BORROWING ARRANGEMENTS AND DEBT EXTINGUISHMENT K2 HealthVentures Loan and Security Agreement In May 2020, the Company entered into a Loan and Security Agreement with K2HV (the “K2 Loan and Security Agreement”) in the amount of $45.0 million. The K2 Loan and Security Agreement was drawable in three tranches and the Company had drawn down $35.0 million with the remaining tranche of $10.0 million having lapsed as of December 31, 2021. Pursuant to the terms of the K2 Loan and Security Agreement, the principal accrued interest at an annual rate equal to the greater of 8.45% or the sum of the Prime Rate plus 5.2%. In April 2022, the K2 Loan and Security Agreement was amended in exchange for a $0.3 million amendment fee so that (i) payments would be interest only until the loan’s maturity date of June 1, 2024, and (ii) the Financial Covenant would apply for the entire term of the K2 Loan and Security Agreement. This amendment resulted in a debt modification with the $0.3 million amendment fee recorded as a debt discount. On June 16, 2023, the Company entered into the CVR Agreement with K2HV to fully discharge and satisfy the Company’s outstanding loan obligations under the K2 Loan and Security Agreement, and to terminate the K2 Loan and Security Agreement, in exchange for an aggregate repayment in cash of $27.5 million, the granting of a contingent value right to K2HV, and the issuance of a warrant to purchase shares of common stock to K2HV’s affiliated holder. These contingent value rights require payments to K2HV if certain Contingent Payment Events, as defined in the CVR Agreement, occur, or if there is an Acceleration Event, as defined in the CVR Agreement. The payment due upon any Contingent Payment Event or an Acceleration Event is capped at an amount (the “Remaining Value”) which is initially $10,303,646, which amount, to the extent not repaid is subject to escalating multipliers which increases from the closing date by multiplying the Remaining Value by a multiplier ranging between 1.0 at closing to 2.5x for any Remaining Value not yet paid as of September 16, 2024, resulting in a potential maximum payment obligation of $25,759,115. In addition, upon a Change in Control, as defined in the CVR Agreement, the Company is required to pay an additional payment of $2,500,000. For Contingent Payment Events, the Company must pay K2HV either a specified percentage of the proceeds received, up to an amount equaling the applicable Remaining Value, 50% of such Remaining Value, or 100% of the Remaining Value, depending on the Contingent Payment Event which occurred. Upon the occurrence and continuation of any Acceleration Event, the applicable Remaining Value shall, at the election of K2HV, be due and payable in full. The Company may at any time elect to repay some or all of the Remaining Value without penalty. In lieu of a portion of these contingent value rights, K2HV may convert up to $3,000,000 of the Remaining Value into an aggregate of 408,267 shares of common stock, subject to adjustment for any stock splits and similar events so long as the number of shares of common stock underlying such conversion right, together with the shares of common stock underlying the warrants described below, do not exceed 19.99% of the number of shares of common stock outstanding immediate prior to the execution of the CVR Agreement. In satisfaction of its obligations to issue the warrant to K2HV’s affiliated holder pursuant to the CVR Agreement, the Company issued a warrant to purchase up to 340,222 shares of the Company’s common stock at an exercise price of $5.8785 per share. The warrant has a term of 10 years. To protect its interest in any potential payment of the Remaining Value, K2HV has a security interest in, subject to certain limited exceptions, all assets (including intellectual property) of the Company. Further, the Company may not (i) incur any indebtedness for borrowed money that is structured as senior or pari passu to K2HV’s outstanding contingent payments without K2HV’s consent or (ii) permit any other liens (other than customary permitted liens) on this collateral without K2HV’s consent. In accordance with ASC Topic 740-50 “ Debt – Modifications and Extinguishments, ​

LEASES

LEASES	3 Months Ended
	Mar. 31, 2024
LEASES
LEASES	NOTE 8 — LEASES The Company has operating leases for administrative offices and research and development facilities, and certain finance leases for equipment. The operating leases have remaining terms of less than two years to less than six years. Leases with an initial term of 12 months or less will not be recorded on the condensed consolidated balance sheets as operating leases or finance leases, and the Company will recognize lease expense for these leases on a straight-line basis over the lease term. Certain leases include options to renew, with renewal terms that can extend The following table summarizes the components of lease expense for the three months ended March 31, 2024 and 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 2023 Operating leases ​ ​ ​ ​ ​ ​ Operating lease expense ​ $ 725 ​ $ 727 Variable lease expense ​ ​ 145 ​ ​ 104 Total operating lease expense ​ $ 870 ​ $ 831 ​ The following table summarizes the balance sheet classification of leases as of March 31, 2024 (in thousands): ​ ​ ​ ​ ​ ​ March 31, ​ 2024 Operating leases ​ ​ ​ Operating lease right-of-use assets ​ $ 8,647 ​ ​ ​ ​ Operating lease liabilities, current 1 ​ $ 2,561 Operating lease liabilities, non-current ​ ​ 9,075 Total operating lease liabilities ​ $ 11,636 1. Included in other current liabilities. ​ The following table presents other information on leases as of March 31, 2024 and December 31, 2023: ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2024 2023 Weighted average remaining lease term, operating leases ​ 4.44 years 4.65 years Weighted average discount rate, operating leases ​ 8.21 % 8.21 % ​ Maturities of lease liabilities were as follows as of March 31, 2024 (in thousands): ​ ​ ​ ​ ​ Operating Leases 2024 (remaining) ​ $ 2,535 2025 ​ ​ 3,299 2026 ​ ​ 2,564 2027 ​ ​ 2,636 2028 ​ ​ 2,148 Thereafter ​ ​ 724 Total lease payments ​ $ 13,906 Less: ​ ​ ​ Imputed interest ​ ​ (2,270) Total lease liabilities ​ $ 11,636 ​ Supplemental cash flow information related to the Company’s leases were as follows (in thousands): ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows operating leases ​ $ 834 ​

CONTRACTUAL COMMITMENTS

CONTRACTUAL COMMITMENTS	3 Months Ended
	Mar. 31, 2024
CONTRACTUAL COMMITMENTS
CONTRACTUAL COMMITMENTS	NOTE 9 — CONTRACTUAL COMMITMENTS The Company has entered into project work orders for each of its clinical trials with clinical research organizations (each, a “CRO”) and related laboratory vendors. Under the terms of these agreements, the Company is required to pay certain upfront fees for direct services costs. Based on the particular agreement some of the fees may be for services yet to be rendered and are reflected as a current prepaid asset and have an unamortized balance of approximately zero as of March 31, 2024. The Company has entered into agreements with CROs and other external service providers for services, primarily in connection with the clinical trials and development of the Company’s biologic candidates. The Company was contractually obligated for up to approximately $35.1 million of future services under these agreements as of March 31, 2024, for which amounts have not been accrued as services have not been performed. The Company’s actual contractual obligations will vary depending upon several factors, including the progress and results of the underlying services. The Company has entered into estimated purchase obligations. These estimated purchase obligations total in range from $3.8 million to $4.1 million.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2024
STOCK-BASED COMPENSATION
STOCK-BASED COMPENSATION	NOTE 10 — STOCK-BASED COMPENSATION Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, 2024 2023 Research and development ​ $ 376 ​ $ 1,233 General and administrative ​ ​ 710 ​ ​ 1,077 Total stock-based compensation ​ $ 1,086 ​ $ 2,310 ​ As of March 31, 2024, the total unrecognized compensation cost related to unvested stock-based awards granted to employees under the Company’s equity incentive plans was approximately $3.7 million. This cost will be recorded as compensation expense on a ratable basis over the remaining weighted average requisite service period of approximately 2.8 years. Valuation Assumptions The Company estimated the fair value of stock options granted using the Black-Scholes option-pricing formula and a single option award approach. This fair value is being amortized ratably over the requisite service periods of the awards, which is generally the vesting period. The fair value of employee stock options was estimated using the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 2023 Employee Stock Options: ​ ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ ​ 3.92 % ​ 3.94 % Expected term (in years) ​ ​ 6.08 ​ ​ 6.08 ​ Dividend yield ​ ​ — ​ ​ — ​ Volatility ​ ​ 77.14 % ​ 77.17 % Weighted-average fair value of stock options granted ​ $ 2.50 ​ $ 5.10 ​ ​ Equity Incentive Plans These plans consist of the 2018 Equity Incentive Plan; the 2014 Equity Incentive Plan, as amended; the 2004 Amended and Restated Equity Incentive Plan; and the Amended and Restated 2004 Employee Stock Purchase Plan. As of May 31, 2018, the 2014 Equity Incentive Plan and the 2004 Amended and Restated Equity Incentive Plan were terminated, and no further shares will be granted from those plans. The following table summarizes stock option activity under the Company’s equity incentive plans: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding Options Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in millions): Balances, December 31, 2022 ​ 562,878 ​ $ 115.50 ​ 7.09 ​ $ — Granted ​ 236,651 ​ $ 7.25 ​ ​ ​ ​ ​ Exercised ​ (192) ​ $ 7.20 ​ ​ ​ ​ ​ Cancelled ​ (285,273) ​ $ 88.62 ​ ​ ​ ​ ​ Balances, December 31, 2023 ​ 514,064 ​ $ 80.62 ​ 7.03 ​ $ — Granted ​ 100,298 ​ $ 3.59 ​ ​ ​ ​ ​ Exercised ​ — ​ $ — ​ ​ ​ ​ ​ Cancelled ​ (6,739) ​ $ 27.35 ​ ​ ​ ​ ​ Balances, March 31, 2024 ​ 607,623 ​ $ 68.50 ​ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest, March 31, 2024 ​ 607,623 ​ $ 68.50 ​ 7.20 ​ $ — Exercisable at March 31, 2024 ​ 330,945 ​ $ 110.50 ​ 5.54 ​ $ — ​ The total intrinsic value of stock options exercised during the three months ended both March 31, 2024 and 2023, was zero, as determined at the date of the option exercise. Cash received from stock option exercises was zero, for both the three months ended March 31, 2024 and 2023. The Company issues new shares of common stock upon exercise of options.

RESTRUCTURING RELATED EXPENSES

RESTRUCTURING RELATED EXPENSES	3 Months Ended
	Mar. 31, 2024
RESTRUCTURING RELATED EXPENSES
RESTRUCTURING RELATED EXPENSES	NOTE 11 – RESTRUCTURING RELATED EXPENSES On March 29, 2023 and June 16, 2023, the Company implemented a strategic reprioritization and corresponding reduction in workforce, by approximately 68%, designed to focus on the clinical development programs for MT-6402, MT-8421 and MT-0169, and preclinical activities related to the Company’s collaboration with Bristol-Myers Squibb (the “Restructuring”). The Restructuring reduced the Company’s workforce, ceased further development of the Company’s MT-5111 clinical development program, and refocused the majority of the Company’s pre-clinical efforts around activities related to the Bristol-Myers Squibb collaboration. On April 11, 2024, the Company approved a reduction in force, (the “Reduction in Force”) in order to extend its resources to better position the organization and to allow the Company to continue to support its clinical studies for MT-6402, MT-8421 and MT-0169, as further described in Note 13 “Subsequent Events.” For the three months ended March 31, 2024 and 2023, the Company incurred zero and $0.3 million, respectively, in expenses related to the Restructuring, which is included in research and development and general and administrative expenses in the condensed consolidated statement of operations. The expenses related to the Restructuring related to severance pay and other related termination benefits. The following table summarizes the activity for expenses related to the Restructuring accruals, which are included in Accrued liabilities in the Company’s condensed consolidated balance sheets (in thousands): ​ ​ ​ ​ Balance, December 31, 2022 $ — Expenses related to the Restructuring ​ ​ 276 Cash payments ​ ​ (276) Balance, December 31, 2023 $ — Expenses related to the Restructuring ​ ​ — Cash payments ​ ​ — Balance, March 31, 2024 ​ $ — ​

STOCKHOLDERS' EQUITY (DEFICIT)

STOCKHOLDERS' EQUITY (DEFICIT)	3 Months Ended
	Mar. 31, 2024
STOCKHOLDERS' EQUITY (DEFICIT)
STOCKHOLDERS' EQUITY (DEFICIT)	NOTE 12 — STOCKHOLDERS’ EQUITY (DEFICIT) K2HV CVR Agreement and Related Warrants On June 16, 2023, in satisfaction of its obligations to issue the warrant to K2HV’s affiliated holder pursuant to the CVR Agreement, as further described in Note 7 “Borrowing Arrangements and Debt Extinguishment,” the Company issued a warrant to purchase up to 340,222 shares of the Company’s common stock at an exercise price of $5.8785 per share. The warrant is exercisable upon issuance and have a term of ten years. The Company determines whether the warrant should be classified as a liability or equity according to ASC 480, “ Distinguishing Liabilities from Equity Derivatives and Hedging July 2023 Private Placement and Related Warrants On July 12, 2023, the Company entered into a securities purchase agreement (the “July 2023 Purchase Agreement”) with certain institutional and accredited investors (the “July 2023 Purchasers”) which provided for the private placement (the “July 2023 Private Placement”) of shares of the Company’s common stock and warrants to purchase shares of the Company’s common stock in two tranches, as described below. ​ The closing of the initial tranche occurred on July 17, 2023 and consisted of the issuance of (i) 1,617,365 shares of the Company’s common stock and at a price of $7.05 per share and (ii) pre-funded warrants exercisable for up to 1,222,100 shares of the Company’s common stock (the “July 2023 Pre-Funded Warrants”). The price of the July 2023 Pre-Funded Warrants was $7.035 per underlying share of the Company’s common stock, and the exercise price for the Pre-Funded Warrants was $0.015 per underlying share. The Company received approximately $20.0 million in gross proceeds in connection with the closing of the initial tranche and net proceeds, following the payment of related offering expenses, of approximately $18.4 million. The Company has assessed the July 2023 Pre-Funded Warrants for appropriate equity or liability classification. The July 2023 Pre-Funded Warrants are equity classified because they (i) are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, (ii) are immediately exercisable, (iii) do not embody an obligation for the Company to repurchase its shares, (iv) permit the holders to receive a fixed number of shares of common stock upon exercise, (v) are indexed to the Company's common stock and (vi) meet the equity classification criteria. In addition, the July 2023 Pre-Funded Warrants do not provide any guarantee of value or return and do not provide the warrant holders with the option to settle any unexercised warrants for cash outside of the Company's control. The July 2023 Pre-Funded Warrants also include a separate provision whereby the exercisability of the warrants may be limited if, upon exercise, the warrant holder or any of its affiliates would beneficially own more than 19.99% of the Company’s common stock. The Company valued the pre-funded common stock warrants at issuance, concluding that their sale price approximated their fair value. Accordingly, the July 2023 Pre-Funded Warrants are accounted for as a component of additional paid-in capital at the time of issuance. Pursuant to the July 2023 Purchase Agreement, the Company granted to the July 2023 Purchasers certain registration rights, pursuant to which, among other things, the Company agreed to (i) file with the SEC a registration statement on Form S-3 after each of the initial tranche and the second tranche to register for resale the shares of common stock issued (and the shares issuable upon exercise of any pre-funded warrants or Second Closing July 2023 Second Closing of July 2023 Private Placement On March 28, 2024, the Company and certain institutional and accredited investors (the “March 2024 Purchasers”) entered into an Amended and Restated July 2023 Purchase Agreement, pursuant to which the Company issued, at closing, common stock, prefunded warrants, and common warrants with an aggregate purchase price of $9.5 million on amended and restated second tranche terms. The closing of the second tranche occurred on April 2, 2024. The second tranche, as amended and restated, consisted of the sale and issuance of (i) 1,209,612 shares of the Company’s common stock (and, in lieu thereof, prefunded warrants to purchase 2,460,559 shares of the Company’s common stock (the “March 2024 Prefunded Warrants”) for a purchase price of $2.35 per share of the Company’s common stock (the closing price of our common stock on March 27, 2024 as reported by the Nasdaq Capital Market) and $2.349 per March 2024 Prefunded Warrant, and (ii) common stock warrants (the “March 2024 Common Warrants”) to purchase up to 7,340,342 shares of the Company’s common stock (or March 2024 Prefunded Warrants in lieu thereof) at an exercise price of $2.35 per share of the Company’s common stock underlying the March 2024 Common Warrants. The March 2024 Common Warrants were sold at a price of $0.125 per underlying share of common stock and have a term of five years. The March 2024 Prefunded Warrants will expire when fully exercised in accordance with their terms. The March 2024 Prefunded Warrants and March 2024 Common Warrants may not be exercised if the aggregate number of shares of our common stock beneficially owned by the holder thereof immediately following such exercise would exceed a specified beneficial ownership limitation (4.99%/9.99%/19.99%); provided, however, that a holder may increase or decrease the beneficial ownership limitation by giving 61 days’ notice to the Company, but not to any percentage in excess of 19.99%. The Amended and Restated July 2023 Purchase Agreement contains customary representations and warranties and agreements of the Company and the March 2024 Purchasers and customary indemnification rights and obligations of the parties. The second tranche included gross proceeds of approximately $9.5 million and net proceeds, following the payment of related offering expenses, of approximately $8.8 million. The Company has assessed the March 2024 Prefunded Warrants and March 2024 Common Warrants for appropriate equity or liability classification. The March 2024 Prefunded Warrants and March 2024 Common Warrants are equity classified because they (i) are freestanding financial instruments that are legally detachable and separately exercisable from the equity instruments, (ii) are immediately exercisable, (iii) do not embody an obligation for the Company to repurchase its shares, (iv) permit the holders to receive a fixed number of shares of common stock upon exercise, (v) are indexed to the Company's common stock, and (vi) meet the equity classification criteria. In addition, the March 2024 Prefunded Warrants and March 2024 Common Warrants do not provide any guarantee of value or return and do not provide the warrant holders with the option to settle any unexercised warrants for cash outside of the Company's control. The March 2024 Prefunded Warrants and March 2024 Common Warrants also include a separate provision whereby the exercisability of the warrants may be limited if, upon exercise, the warrant holder or any of its affiliates would beneficially own more than a specified percentage limitation (4.99%/9.99%/19.99%) of the Company’s common stock. The Company valued the prefunded stock warrants and common stock warrants at issuance, concluding that their sale price approximated their fair value. Accordingly, the March 2024 Prefunded Warrants and March 2024 Common Warrants are accounted for as a component of additional paid-in capital at the time of issuance on April 2, 2024. Pursuant to the Amended and Restated July 2023 Purchase Agreement, the Company granted to the March 2024 Purchasers certain registration rights, pursuant to which, among other things, the Company agreed to (i) file with the SEC a registration statement on Form S-3 after the second tranche of the July 2023 Private Placement to register for resale the shares of common stock (and the shares of common stock issuable upon exercise of the prefunded warrants and common warrants) issued in the second tranche of the July 2023 Private Placement, within 30 calendar days following the second tranche closing (the “Second Closing”), and (ii) use its commercially reasonable efforts to have the registration statement declared effective as soon as practicable, and in any event no later than 90 days following the Second Closing date (or 120 days following the Second Closing date if the registration statement is reviewed by the SEC). The registration rights covenants are subject to customary terms and conditions for a transaction of this type, including certain customary cash penalties on the Company for its failure to satisfy specified filing and effectiveness time periods. On April 25, 2024, the Company filed with the SEC a registration statement on Form S-3 (File No. 333-278932), which was declared effective by the SEC on May 3, 2024, registering for resale up to 11,010,513 shares of the Company’s common stock, which consist of 1,209,612 shares of the Company’s common stock, 2,460,559 shares of the Company’s common stock issuable upon the exercise of the March 2024 Prefunded Warrants, and 7,340,342 shares of the Company’s common stock issuable upon the exercise of the March 2024 Warrants. Additionally, the Amended and Restated July 2023 Purchase Agreement contains customary representations and warranties and agreements of the Company and the March 2024 Purchasers and customary indemnification rights and obligations of the parties. ​

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2024
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	NOTE 13 — SUBSEQUENT EVENTS Reduction in Force On April 11, 2024, the Company and Board of Directors approved the Reduction in Force in order to extend its resources to better position the organization and to allow the Company to continue to support its clinical studies for MT-6402, MT-8421 and MT-0169. The Reduction in Force reduced the Company’s current workforce by approximately 30%. The Company estimates that it will incur aggregate pre-tax charges of approximately $0.1 million in connection with the Reduction in Force, primarily consisting of legal fees and other related termination costs. The Reduction in Force was completed by the end of April 2024 and the Company expects that the one-time charges will be incurred in the second quarter of 2024. Second Closing of the July 2023 Private Placement As described in Note 12 “Stockholders’ Equity (Deficit) - Second Closing of the July 2023 Private Placement,” the closing of the second tranche of the July 2023 Private Placement occurred on April 2, 2024. ​

ORGANIZATION AND SUMMARY OF S_2

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2024
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. GAAP and include the accounts of the Company and its wholly owned subsidiary and reflect the elimination of intercompany accounts and transactions. The preparation of condensed consolidated financial statements requires management to make estimates and assumptions that affect the recorded amounts reported therein. A change in facts or circumstances surrounding the estimates could result in a change to estimates and impact future operating results. Certain accounts in the prior financial statements have been reclassified for comparative purposes to conform to the presentation in the current financial statements. These reclassifications have no material effect on previously reported financials. In the opinion of management of the Company, all adjustments, consisting of normal recurring adjustments, considered necessary for a fair presentation have been included. The unaudited condensed consolidated financial statements and related disclosures have been prepared with the presumption that users of the interim unaudited condensed consolidated financial statements have read or have access to the audited consolidated financial statements for the preceding fiscal year. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2023 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 29, 2024. On August 11, 2023, the Company filed with the Secretary of State of the State of Delaware a Certificate of Amendment to its Amended and Restated Certificate of Incorporation to effect a one-time reverse stock split of the Company’s common stock, at a ratio of 1-for-15 (the “Reverse Stock Split”). The Reverse Stock Split was effective at 5 p.m. Eastern Time, after the close of trading on the Nasdaq Capital Market, on August 11, 2023 (the “Effective Time”). At the Effective Time, every 15 shares of the Company’s issued and outstanding common stock were automatically converted into one share of common stock, without any change in the par value per share. Any stockholder who was entitled to a fractional share of common stock created as a result of the Reverse Stock Split received a cash payment in lieu thereof equal to the fractional share to which the stockholder was entitled multiplied by the closing sales price of a share of common stock on August 11, 2023, as adjusted for the Reverse Stock Split. All common stock, per share and related information presented in the condensed consolidated financial statements and notes prior to the Reverse Stock Split have been retroactively adjusted to reflect the Reverse Stock Split for all periods presented, to the extent applicable.
Going Concern	Going Concern The Company has adopted as required the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 205-40, Presentation of Financial Statements - Going Concern, which requires that management contemplate the realization of assets and liquidation of liabilities in the normal course of business, and evaluate whether there are relevant conditions and events that in the aggregate raise substantial doubt about the entity’s ability to continue as a going concern and to meet its obligations as they become due within one year after the date that the financial statements are issued. Under this standard, management’s assessment shall not take into consideration the potential mitigating effects of management’s plans that have not been fully implemented as of the date the financial statements are issued. As of March 31, 2024, the Company had an accumulated deficit of $452.3 million and had unrestricted cash and cash equivalents of $6.8 million. Based on the Company’s unrestricted cash and cash equivalents as of March 31, 2024 and subsequent to the closing of the amended and restated second tranche of the July 2023 Private Placement (as defined below), management anticipates that the Company will be able to fund its planned operating expenses and capital expenditure requirements into the fourth quarter of 2024. The Company has not yet established an ongoing source of revenues sufficient to cover its operating and cash expenditure requirements or to cover any potential payments that may become due and payable pursuant to the CVR Agreement as described in Note 7 “Borrowing Arrangements and Debt Extinguishment” to provide sufficient certainty that it will continue as a going concern. For these reasons, there is substantial doubt about the Company’s ability to continue as a going concern as of the issuance of these financial statements. Historically, the Company financed its operations to date primarily through partnerships, funds received from public offerings of common and preferred stock, private placements of equity securities, a reverse merger, upfront and milestone payments received from its prior and current collaboration agreements, a debt financing facility, as well as funding from governmental bodies and bank and bridge loans. The Company plans to address this condition through the sale of common stock in public offerings and/or private placements, debt financings, or through other capital sources, including collaborations with other companies or other strategic transactions, but there is no assurance these plans will be completed successfully or at all. If the Company is unable to obtain additional capital when and as needed to continue as a going concern, it might have to further reduce or scale back its operations, cease operations entirely, and/or liquidate its assets, and the values it receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in its financial statements. These financial statements do not give effect to any adjustments which will be necessary should the Company be unable to continue as a going concern and therefore be required to realize its assets and discharge its liabilities in other than the normal course of business and at amounts different from those reflected in the accompanying financial statements.
Significant Accounting Policies	Significant Accounting Policies There have been no material changes to the Company’s significant accounting policies during the three months ended March 31, 2024, as compared to the significant accounting policies disclosed in Note 1 “Organization and Summary of Significant Accounting Policies,” to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers temporary investments having original maturities of three months or less from date of purchase to be cash equivalents. Restricted cash is recorded in other assets, based on when the restrictions expire. Other assets include $0.8 million and $1.3 million of restricted cash as of March 31, 2024 and December 31, 2023, respectively, related to letters of credit in lieu of a cash deposit for the Company’s leases.
Fair Value Measurement	Fair Value Measurement The Company accounts for its marketable securities in accordance with ASC 820 “Fair Value Measurements and Disclosures.” hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value: Level 1 Level 2 Level 3 The Company utilizes the market approach or probability approach to measure fair value for its financial assets and liabilities. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities. For Level 2 securities that have market prices from multiples sources, a “consensus price” or a weighted average price for each of these securities can be derived from a distribution-curve-based algorithm which includes market prices obtained from a variety of industrial standard data providers (e.g. Bloomberg), security master files from large financial institutions, and other third-party sources. Level 2 securities with short maturities and infrequent secondary market trades are typically priced using mathematical calculations adjusted for observable inputs when available. Level 3 securities utilize a probability weighted expected return method or Black-Scholes option-pricing model. Significant estimates and assumptions required for these valuations include, but are not limited to, probabilities related to the timing and outcome of future financing and/or liquidity events. These unobservable inputs represent a Level 3 measurement because they are supported by little or no market activity and reflect our own assumptions in measuring fair value.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to concentrations of risk consist principally of cash and cash equivalents, investments, long term debt and accounts receivable. The Company’s cash and cash equivalents are with two major financial institutions in the United States. The Company performs an ongoing credit evaluation of its strategic partners’ financial conditions and generally does not require collateral to secure accounts receivable from its strategic partners. As of March 31, 2024, the Company’s exposure to credit risk associated with non-payment will be affected principally by conditions or occurrences within Bristol-Myers Squibb Company (“Bristol-Myers Squibb”). Bristol-Myers Squibb accounted for approximately 99% and 92% of total revenues for the three months ended March 31, 2024 and 2023, respectively. Biologic candidates developed by the Company require approvals or clearances from the U.S. Food and Drug Administration (the “FDA”) or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s biologic candidates will receive any of the required approvals or clearances. If the Company were to be denied approval or clearance or any such approval or clearance were to be delayed, it would have a material adverse impact on the Company.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (Subtopic 470-20: Debt with Conversion and Other Options and Subtopic 815-40: Derivatives and Hedging - Contracts in Entity’s Own Equity). The new guidance simplifies accounting for convertible instruments by removing major separation models, removes certain settlement conditions that are required for equity contracts to qualify for the derivative scope exception, and it also simplifies the diluted earnings per share calculation in certain areas. The amendment is effective for the Company for fiscal years beginning after December 15, 2023, including interim periods within those fiscal years, using a modified retrospective approach. The impact of the adoption of this standard did not have a material impact on the Company’s consolidated financial statements. ​ In December 2023, the FASB issued ASU No. 2023-09, “Improvements to Income Tax Disclosures” (Topic 740: Income Taxes). The new guidance requires that public entities disclose more consistent categories and greater disaggregation of information in the income tax rate reconciliations and further disaggregate income taxes paid by jurisdiction. The amendment is effective for the Company for fiscal years beginning after December 15, 2024. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

NET INCOME PER COMMON SHARE (Ta

NET INCOME PER COMMON SHARE (Tables)	3 Months Ended
	Mar. 31, 2024
NET INCOME PER COMMON SHARE
Schedule of Weighted Average Number of Shares	The following table provides the calculation of diluted weighted-average shares outstanding: ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ ​ 2024 ​ 2023 Basic weighted-average shares outstanding ​ 5,374,268 ​ 3,756,711 Prefunded Warrants ​ 1,216,663 ​ — Shares issuable under Conversion Right of CVR Agreement ​ 408,267 ​ — Preferred shares ​ 16,666 ​ — Diluted weighted-average shares outstanding ​ 7,015,864 ​ 3,756,711 ​

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2024
FAIR VALUE MEASUREMENTS
Financial Assets at Fair Value on Recurring Basis	The following table sets forth the Company’s financial assets (cash equivalents) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ March 31, 2024 Level 1 Level 2 Level 3 Money market funds ​ $ 5,896 ​ $ 5,896 ​ $ — ​ $ — Total ​ $ 5,896 ​ $ 5,896 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2023 Level 1 Level 2 Level 3 Money market funds ​ $ 11,395 ​ $ 11,395 ​ $ — ​ $ — Total ​ $ 11,395 ​ $ 11,395 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 11,395 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 11,395 ​ ​ ​ ​ ​ ​ ​ ​ ​
Summary of Company's Available-for-Sale Securities	The following is a summary of the Company’s available-for-sale securities (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2024 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 5,896 ​ $ — ​ $ — ​ $ 5,896 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2023 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 11,395 ​ $ — ​ $ — ​ $ 11,395
Financial Liabilities at Fair Value on Recurring Basis	The following table sets forth the Company’s financial liabilities (convertible secured contingent value right) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ March 31, 2024 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 2,158 ​ $ — ​ $ — ​ $ 2,158 Total ​ $ 2,158 ​ $ — ​ $ — ​ $ 2,158 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2023 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 2,702 ​ $ — ​ $ — ​ $ 2,702 Total ​ $ 2,702 ​ $ — ​ $ — ​ $ 2,702
Schedule of Reconciliation of the Change in Fair Value of the Conversion Right and Contingent Value Right Liability	The following table is a reconciliation of the change in fair value of the Conversion Right and Contingent Value Right liability for the three months ended March 31, 2024 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value Measurements Using Significant Unobservable Inputs (Level 3) ​ ​ Conversion right and contingent value right liability ​ Total Balance as of December 31, 2023 ​ $ 2,702 ​ $ 2,702 Change in valuation included in net income ​ ​ (544) ​ ​ (544) Balance as of March 31, 2024 ​ $ 2,158 ​ $ 2,158
Schedule of Fair Value of Warrants Key Inputs	The fair value of these warrants was determined using a Black-Scholes option-pricing model with the following key inputs: ​ ​ ​ ​ ​ ​ ​ ​ ​ June 16, 2023 ​ Risk-free interest rate ​ ​ 3.77 % Expected term (in years) ​ ​ 10.0 ​ Dividend yield ​ ​ — ​ Volatility ​ ​ 80.00 % Stock price ​ $ 0.53 ​

BALANCE SHEET COMPONENTS (Table

BALANCE SHEET COMPONENTS (Tables)	3 Months Ended
	Mar. 31, 2024
BALANCE SHEET COMPONENTS
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ March 31, 2024 December 31, 2023 Accrued liabilities: ​ ​ ​ ​ ​ General and administrative $ 291 ​ $ 225 Clinical trial related costs ​ ​ 2,105 ​ ​ 3,574 Non-clinical research and manufacturing operations ​ 301 ​ ​ 404 Payroll related ​ 43 ​ ​ 60 Other accrued expenses ​ 8 ​ ​ 16 Total Accrued liabilities $ 2,748 ​ $ 4,279 ​

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2024
PROPERTY AND EQUIPMENT
Schedule of Property and Equipment	Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ 2024 2023 Laboratory equipment ​ $ 20,695 ​ $ 20,695 Leasehold improvements ​ ​ 12,974 ​ ​ 12,974 Furniture and fixtures ​ ​ 518 ​ ​ 518 Computer and equipment ​ ​ 254 ​ ​ 254 ​ ​ ​ 34,441 ​ ​ 34,441 Less: Accumulated depreciation ​ ​ (28,157) ​ ​ (27,048) Total property and equipment, net ​ $ 6,284 ​ $ 7,393

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2024
LEASES
Components of Lease Expense	The following table summarizes the components of lease expense for the three months ended March 31, 2024 and 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 2023 Operating leases ​ ​ ​ ​ ​ ​ Operating lease expense ​ $ 725 ​ $ 727 Variable lease expense ​ ​ 145 ​ ​ 104 Total operating lease expense ​ $ 870 ​ $ 831
Schedule of Balance Sheets Classification of Leases	The following table summarizes the balance sheet classification of leases as of March 31, 2024 (in thousands): ​ ​ ​ ​ ​ ​ March 31, ​ 2024 Operating leases ​ ​ ​ Operating lease right-of-use assets ​ $ 8,647 ​ ​ ​ ​ Operating lease liabilities, current 1 ​ $ 2,561 Operating lease liabilities, non-current ​ ​ 9,075 Total operating lease liabilities ​ $ 11,636 1. Included in other current liabilities.
Schedule of Leases Information	The following table presents other information on leases as of March 31, 2024 and December 31, 2023: ​ ​ ​ ​ ​ ​ ​ ​ March 31, ​ December 31, ​ ​ 2024 2023 Weighted average remaining lease term, operating leases ​ 4.44 years 4.65 years Weighted average discount rate, operating leases ​ 8.21 % 8.21 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities were as follows as of March 31, 2024 (in thousands): ​ ​ ​ ​ ​ Operating Leases 2024 (remaining) ​ $ 2,535 2025 ​ ​ 3,299 2026 ​ ​ 2,564 2027 ​ ​ 2,636 2028 ​ ​ 2,148 Thereafter ​ ​ 724 Total lease payments ​ $ 13,906 Less: ​ ​ ​ Imputed interest ​ ​ (2,270) Total lease liabilities ​ $ 11,636
Supplemental Cash Flow Information	Supplemental cash flow information related to the Company’s leases were as follows (in thousands): ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows operating leases ​ $ 834 ​

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 2024
STOCK-BASED COMPENSATION
Stock-Based Compensation Expense	Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, 2024 2023 Research and development ​ $ 376 ​ $ 1,233 General and administrative ​ ​ 710 ​ ​ 1,077 Total stock-based compensation ​ $ 1,086 ​ $ 2,310
Weighted-Average Fair Value Valuation Assumptions	The fair value of employee stock options was estimated using the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended March 31, ​ 2024 2023 Employee Stock Options: ​ ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ ​ 3.92 % ​ 3.94 % Expected term (in years) ​ ​ 6.08 ​ ​ 6.08 ​ Dividend yield ​ ​ — ​ ​ — ​ Volatility ​ ​ 77.14 % ​ 77.17 % Weighted-average fair value of stock options granted ​ $ 2.50 ​ $ 5.10 ​
Summary of Stock Option Activity Under Equity Incentive Plan	The following table summarizes stock option activity under the Company’s equity incentive plans: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding Options Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in millions): Balances, December 31, 2022 ​ 562,878 ​ $ 115.50 ​ 7.09 ​ $ — Granted ​ 236,651 ​ $ 7.25 ​ ​ ​ ​ ​ Exercised ​ (192) ​ $ 7.20 ​ ​ ​ ​ ​ Cancelled ​ (285,273) ​ $ 88.62 ​ ​ ​ ​ ​ Balances, December 31, 2023 ​ 514,064 ​ $ 80.62 ​ 7.03 ​ $ — Granted ​ 100,298 ​ $ 3.59 ​ ​ ​ ​ ​ Exercised ​ — ​ $ — ​ ​ ​ ​ ​ Cancelled ​ (6,739) ​ $ 27.35 ​ ​ ​ ​ ​ Balances, March 31, 2024 ​ 607,623 ​ $ 68.50 ​ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest, March 31, 2024 ​ 607,623 ​ $ 68.50 ​ 7.20 ​ $ — Exercisable at March 31, 2024 ​ 330,945 ​ $ 110.50 ​ 5.54 ​ $ —

RESTRUCTURING RELATED EXPENSES

RESTRUCTURING RELATED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2024
RESTRUCTURING RELATED EXPENSES
Summary of Activity for Expenses Related to Restructuring Accruals	The following table summarizes the activity for expenses related to the Restructuring accruals, which are included in Accrued liabilities in the Company’s condensed consolidated balance sheets (in thousands): ​ ​ ​ ​ Balance, December 31, 2022 $ — Expenses related to the Restructuring ​ ​ 276 Cash payments ​ ​ (276) Balance, December 31, 2023 $ — Expenses related to the Restructuring ​ ​ — Cash payments ​ ​ — Balance, March 31, 2024 ​ $ — ​

ORGANIZATION AND SUMMARY OF S_3

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Detail) $ in Thousands		3 Months Ended
	Aug. 11, 2023	Mar. 31, 2024 USD ($) Institution	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split ratio	0.066
Accumulated deficit		$ (452,320)		$ (452,892)
Unrestricted cash and cash equivalents		6,779	$ 38,782	11,523
Restricted cash included in other assets		$ 815	$ 2,489	$ 1,300
Restricted Cash and Cash Equivalents, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Other assets	Other assets	Other assets
Number Of Financial Institutions | Institution		2
Revenue | Concentration of Credit Risk and Other Risks and Uncertainties | Bristol Myers Squibb
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenues		99%	92%

NET INCOME PER COMMON SHARE (De

NET INCOME PER COMMON SHARE (Detail) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
NET INCOME PER COMMON SHARE
Common shares excluded from the computation of diluted net income/(loss) per share on effect of anti-dilutive	881,000	579,000

NET INCOME PER COMMON SHARE - C

NET INCOME PER COMMON SHARE - Calculation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
NET INCOME PER COMMON SHARE
Basic weighted-average shares outstanding	5,374,268	3,756,711
Prefunded Warrants	1,216,663
Shares issuable under Conversion Right of CVR	408,267
Preferred shares	16,666
Basic weighted-average shares outstanding	7,015,864	3,756,711

RESEARCH AND DEVELOPMENT AGRE_2

RESEARCH AND DEVELOPMENT AGREEMENTS (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Feb. 28, 2021	Sep. 30, 2018	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			$ 11,086,000	$ 36,629,000
Deferred revenue, current					$ 9,031,000
Grants revenue receivable			412,000		250,000
Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,924,000	33,627,000
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms [Member] | Bristol Myers Squibb
Research And Development Collaboration Agreements [Line Items]
Upfront payment	$ 70,000,000
Transaction price allocated to performance obligations	70,000,000
Deferred revenue, current			0		9,000,000
Deferred revenue, non-current			0		0
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms [Member] | Bristol Myers Squibb | Maximum
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised	874,500,000
Additional milestone payments receivable if option is exercised	$ 450,000,000
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms [Member] | Bristol Myers Squibb | Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,900,000	33,600,000
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms, Target Completion | Bristol Myers Squibb | Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,900,000	25,800,000
CPRIT Agreement | Additional Funding Agreement Terms | Cancer Prevention and Research Institute of Texas | Grant
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			14,300,000
Deferred revenue			0		0
Product development grant awarded		$ 15,200,000
Reimbursement amounts submitted in excess of amounts received are recorded as receivables			200,000	$ 3,000,000
Grants revenue receivable			$ 400,000		$ 300,000

FAIR VALUE MEASUREMENTS - Finan

FAIR VALUE MEASUREMENTS - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 6,779	$ 11,523	$ 38,782
Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	5,896	11,395
Cash and cash equivalents	5,896	11,395
Fair Value, Recurring | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	5,896	11,395
Fair Value, Recurring | Basis of Fair Value Measurements, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	5,896	11,395
Fair Value, Recurring | Basis of Fair Value Measurements, Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	5,896	$ 11,395
Fair Value, Recurring | Basis of Fair Value Measurements, Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0
Fair Value, Recurring | Basis of Fair Value Measurements, Level 2 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0
Fair Value, Recurring | Basis of Fair Value Measurements, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0
Fair Value, Recurring | Basis of Fair Value Measurements, Level 3 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 0

FAIR VALUE MEASUREMENTS - Summa

FAIR VALUE MEASUREMENTS - Summary of Company's Available-for-Sale Securities (Detail) - Money Market Funds - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cost Basis	$ 5,896	$ 11,395
Fair Value	$ 5,896	$ 11,395

FAIR VALUE MEASUREMENTS - Addit

FAIR VALUE MEASUREMENTS - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Investments Debt And Equity Securities [Abstract]
Proceeds from sale of available-for-sale securities	$ 0	$ 0
Available-for-sale securities, realized gain	$ 0	$ 0

FAIR VALUE MEASUREMENTS - Conve

FAIR VALUE MEASUREMENTS - Convertible secured contingent value right (Detail) - Fair Value, Recurring - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	$ 2,158	$ 2,702
Conversion Right and Contingent Value Right
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	2,158	2,702
Basis of Fair Value Measurements, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	2,158	2,702
Basis of Fair Value Measurements, Level 3 | Conversion Right and Contingent Value Right
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	$ 2,158	$ 2,702

FAIR VALUE MEASUREMENTS - Recon

FAIR VALUE MEASUREMENTS - Reconciliation of the Change in Fair Value of the Conversion Right and Contingent Value Right liability (Detail) - Basis of Fair Value Measurements, Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 2,702
Change in valuation included in net income	(544)
Ending Balance	2,158
Conversion Right and Contingent Value Right liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,702
Change in valuation included in net income	(544)
Ending Balance	$ 2,158

FAIR VALUE MEASUREMENTS - Conti

FAIR VALUE MEASUREMENTS - Contingent Value Right and Common Stock Warrant Valuation (Detail)		3 Months Ended
	Jun. 16, 2023 USD ($) item $ / shares shares	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in valuation of contingent value right		$ (544,000)
CVR Agreement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of components | item	2
Remaining value convertible	$ 3,000,000
Expected value of conversion right if rights are not converted into shares	0
Fair value of conversion right	3,300,000	900,000	$ 1,500,000
Fair value of contingent value liability	$ 1,900,000	1,200,000	$ 1,200,000
Change in valuation of contingent value right		$ 500,000
Warrants to purchase shares of common stock | shares	340,222
Exercise price of warrant | $ / shares	$ 5.8785
Warrants term	10 years
Issuance of warrants	$ 2,300,000

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value of Warrants (Detail)	Jun. 16, 2023 Y $ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants measurement input	0.0377
Expected term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants measurement input | Y	10
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants measurement input	0
Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants measurement input	0.8000
Stock price
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants measurement input | $ / shares	0.53

BALANCE SHEET COMPONENTS - Sche

BALANCE SHEET COMPONENTS - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued liabilities:
General and administrative	$ 291	$ 225
Clinical trial related costs	2,105	3,574
Non-clinical research and manufacturing operations	301	404
Payroll related	43	60
Other accrued expenses	8	16
Total Accrued liabilities	$ 2,748	$ 4,279

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 34,441	$ 34,441
Less: Accumulated depreciation	(28,157)	(27,048)
Total property and equipment, net	6,284	7,393
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	20,695	20,695
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, Gross	12,974	12,974
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, Gross	518	518
Computer and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 254	$ 254

PROPERTY AND EQUIPMENT - Additi

PROPERTY AND EQUIPMENT - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Depreciation expense	$ 1.1	$ 2
Leasehold Improvements
Property Plant And Equipment [Line Items]
Asset retirement obligation, asset	$ 0.2		$ 0.2

BORROWING ARRANGEMENTS AND DE_2

BORROWING ARRANGEMENTS AND DEBT EXTINGUISHMENT (Detail)		1 Months Ended		12 Months Ended
	Jun. 16, 2023 USD ($) $ / shares shares	Apr. 30, 2022 USD ($)	May 31, 2020 USD ($)	Dec. 31, 2023 USD ($)	Mar. 31, 2024	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Gain on extinguishment of debt				$ 1,800,000
CVR Agreement
Debt Instrument [Line Items]
Remaining value convertible	$ 3,000,000
Warrants to purchase shares of common stock | shares	340,222
Exercise price of warrant | $ / shares	$ 5.8785
Warrants term	10 years
K2 Loan and Security Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity under loan			$ 45,000,000
Loan and security agreement			$ 35,000,000
Loan and security agreement, lapsed amount						$ 10,000,000
Interest rate					8.45%
Amendment fee		$ 300,000
K2 Loan and Security Agreement | CVR Agreement
Debt Instrument [Line Items]
Aggregate repayment in cash	$ 27,500,000
Maximum remaining value	10,303,646
Maximum payment obligation	25,759,115
Additional payment upon change in control	$ 2,500,000
Number of shares issued upon conversion of remaining value | shares	408,267
Exercise price of warrant | $ / shares	$ 5.8785
Warrants term	10 years
K2 Loan and Security Agreement | CVR Agreement | Contingent payment event one
Debt Instrument [Line Items]
Payments to be made based on percentage of remaining value	50%
K2 Loan and Security Agreement | CVR Agreement | Contingent payment event two
Debt Instrument [Line Items]
Payments to be made based on percentage of remaining value	100%
K2 Loan and Security Agreement | CVR Agreement | Minimum
Debt Instrument [Line Items]
Escalation multiplier	1
K2 Loan and Security Agreement | CVR Agreement | Maximum
Debt Instrument [Line Items]
Escalation multiplier	2.5
Remaining value convertible	$ 3,000,000
Threshold percentage of outstanding common stock that can be issued	19.99%
Warrants to purchase shares of common stock | shares	340,222
K2 Loan and Security Agreement | Prime Rate
Debt Instrument [Line Items]
Interest rate					5.20%

LEASES - Additional Information

LEASES - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2024
Lessee Lease Description [Line Items]
Lessee, Operating Lease, Existence of Option to Extend [true false]	true
Lessee, operating leases renewal lease term	7 years
Minimum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term	2 years
Maximum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term	6 years

LEASES - Components of Lease Ex

LEASES - Components of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
LEASES
Operating lease expense	$ 725	$ 727
Variable lease expense	145	104
Total operating lease expense	$ 870	$ 831

LEASES - Schedule of Balance Sh

LEASES - Schedule of Balance Sheets Classification of Leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Operating leases
Operating lease right-of-use assets	$ 8,647	$ 9,161
Operating lease liabilities, current	$ 2,561
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities
Operating lease liabilities, non-current	$ 9,075	$ 9,742
Total operating lease liabilities	$ 11,636

LEASES - Schedule of Leases Inf

LEASES - Schedule of Leases Information (Detail)	Mar. 31, 2024	Dec. 31, 2023
LEASES
Weighted average remaining lease term, operating leases	4 years 5 months 8 days	4 years 7 months 24 days
Weighted average discount rate, operating leases	8.21%	8.21%

LEASES - Schedule of Maturities

LEASES - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Mar. 31, 2024 USD ($)
Lease payments
2024 (remaining)	$ 2,535
2025	3,299
2026	2,564
2027	2,636
2028	2,148
Thereafter	724
Total lease payments	13,906
Less: Imputed interest	(2,270)
Total lease liabilities	$ 11,636

LEASES - Supplemental Cash Flow

LEASES - Supplemental Cash Flow Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows operating leases	$ 834

CONTRACTUAL COMMITMENTS (Detail

CONTRACTUAL COMMITMENTS (Detail)	Mar. 31, 2024 USD ($)
Other Commitments [Line Items]
Upfront fees unamortized balance included in prepaid asset	$ 0
Contractual obligation	35,100,000
Minimum
Other Commitments [Line Items]
Estimated purchase obligation	3,800,000
Maximum
Other Commitments [Line Items]
Estimated purchase obligation	$ 4,100,000

STOCK-BASED COMPENSATION - Stoc

STOCK-BASED COMPENSATION - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,086	$ 2,310
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	376	1,233
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 710	$ 1,077

STOCK-BASED COMPENSATION - Weig

STOCK-BASED COMPENSATION - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Option - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	3.92%	3.94%
Expected term (in years)	6 years 29 days	6 years 29 days
Dividend yield	0%	0%
Volatility	77.14%	77.17%
Weighted-average fair value of stock options granted	$ 2.50	$ 5.10

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
STOCK-BASED COMPENSATION
Outstanding Options Number of Shares, Beginning Balance	514,064	562,878
Number of Shares, Options granted	100,298	236,651
Number of Shares, Options exercised	0	(192)
Number of shares, Options cancelled	(6,739)	(285,273)
Outstanding Options Number of Shares, Ending Balance	607,623	514,064	562,878
Outstanding Options Number of Shares, Vested and expected to vest	607,623
Outstanding Options Number of Shares, Exercisable	330,945
Weighted Average Exercise Price, Beginning Balance	$ 80.62	$ 115.50
Weighted Average Exercise Price, Options granted	3.59	7.25
Weighted Average Exercise Price, Options exercised	0	7.20
Weighted Average Exercise Price, Options cancelled	27.35	88.62
Weighted Average Exercise Price, Ending Balance	68.50	$ 80.62	$ 115.50
Weighted Average Exercise Price, Vested and expected to vest	68.50
Weighted Average Exercise Price, Exercisable	$ 110.50
Weighted-Average Remaining Contractual Term, Outstanding		7 years 10 days	7 years 1 month 2 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 2 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 6 months 14 days
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0
Aggregate Intrinsic Value, Vested and expected to vest	0
Aggregate Intrinsic Value, Exercisable	$ 0

STOCK-BASED COMPENSATION - Addi

STOCK-BASED COMPENSATION - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans	$ 3.7
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans, period for recognition	2 years 9 months 18 days
Total intrinsic value of stock options exercised	$ 0	$ 0
Equity Incentive Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cash received from stock option exercises	$ 0	$ 0

RESTRUCTURING RELATED EXPENSE_2

RESTRUCTURING RELATED EXPENSES - Additional information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
RESTRUCTURING RELATED EXPENSES
Restructuring and Related Cost, Number of Positions Eliminated, Period Percent			68%
Expenses related to the Restructuring	$ 0	$ 300	$ 276

RESTRUCTURING RELATED EXPENSE_3

RESTRUCTURING RELATED EXPENSES - Summary of Activity for Expenses Related to Restructuring Accruals (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
RESTRUCTURING RELATED EXPENSES
Expenses related to the Restructuring	$ 0	$ 300	$ 276
Cash payments			$ (276)

STOCKHOLDERS' EQUITY (DEFICIT)

STOCKHOLDERS' EQUITY (DEFICIT) - K2HV CVR Agreement and Related Warrants (Details) $ / shares in Units, $ in Millions	Jun. 16, 2023 USD ($) Y $ / shares shares	Mar. 31, 2024 shares
Risk-free interest rate
Class of Warrant or Right [Line Items]
Warrants measurement input	0.0377
Expected term (in years)
Class of Warrant or Right [Line Items]
Warrants measurement input | Y	10
Dividend yield
Class of Warrant or Right [Line Items]
Warrants measurement input	0
Volatility
Class of Warrant or Right [Line Items]
Warrants measurement input	0.8000
CVR Agreement
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock	340,222
Exercise price of warrant | $ / shares	$ 5.8785
Warrants term	10 years
Warrant outstanding		340,222
Issuance of warrants | $	$ 2.3

STOCKHOLDERS' EQUITY (DEFICIT_2

STOCKHOLDERS' EQUITY (DEFICIT) - July 2023 Private Placement and Related Warrants (Details) $ / shares in Units, $ in Millions	Apr. 25, 2024 shares	Mar. 28, 2024 USD ($) $ / shares shares	Aug. 10, 2023 shares	Jul. 17, 2023 USD ($) D $ / shares shares	Jul. 12, 2023 tranche
July 2023 Private Placement
Class of Warrant or Right [Line Items]
Number of tranches | tranche					2
Shares issued			1,617,365
Number of calendar days following each closing | D				30
Maximum common stock shares to be resold			2,839,465
July 2023 Private Placement | Minimum
Class of Warrant or Right [Line Items]
Number of days following applicable closing | D				90
July 2023 Private Placement | Maximum
Class of Warrant or Right [Line Items]
Number of days following applicable closing | D				120
July 2023 Private Placement | Closing of the initial tranche
Class of Warrant or Right [Line Items]
Shares issued				1,617,365
Share price | $ / shares				$ 7.05
Gross proceeds form private placement | $				$ 20
Proceeds from issuance of common stock and prefunded warrants, net offering expenses | $				$ 18.4
July 2023 Private Placement | Prefunded Warrants
Class of Warrant or Right [Line Items]
Shares issued			1,222,100
Threshold percentage of beneficial ownership					19.99%
July 2023 Private Placement | Prefunded Warrants | Closing of the initial tranche
Class of Warrant or Right [Line Items]
Exercise price of warrant | $ / shares				$ 0.015
Price per warrant | $ / shares				$ 7.035
Warrants to purchase shares of common stock				1,222,100
Amended And Restated July 2023 Private Placement | Closing of second tranche
Class of Warrant or Right [Line Items]
Shares issued		1,209,612
Share price | $ / shares		$ 2.35
Gross proceeds form private placement | $		$ 9.5
Proceeds from issuance of common stock and prefunded warrants, net offering expenses | $		$ 8.8
Threshold percentage of beneficial ownership		19.99%
Amended And Restated July 2023 Private Placement | Closing of second tranche | Subsequent Event
Class of Warrant or Right [Line Items]
Shares issued	1,209,612
Maximum common stock shares to be resold	11,010,513
Amended And Restated July 2023 Private Placement | March 2024, Prefunded Warrant | Closing of second tranche
Class of Warrant or Right [Line Items]
Exercise price of warrant | $ / shares		$ 2.349
Warrants to purchase shares of common stock		2,460,559
Amended And Restated July 2023 Private Placement | March 2024, Prefunded Warrant | Closing of second tranche | Subsequent Event
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock	2,460,559
Amended And Restated July 2023 Private Placement | March 2024 Common Warrants | Closing of second tranche
Class of Warrant or Right [Line Items]
Exercise price of warrant | $ / shares		$ 2.35
Price per warrant | $ / shares		$ 0.125
Warrants term		5 years
Amended And Restated July 2023 Private Placement | March 2024 Common Warrants | Closing of second tranche | Subsequent Event
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock	7,340,342
Amended And Restated July 2023 Private Placement | March 2024 Common Warrants | Closing of second tranche | Maximum
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock		7,340,342

SUBSEQUENT EVENTS (Detail)

SUBSEQUENT EVENTS (Detail) - USD ($) $ in Millions		12 Months Ended
	Apr. 11, 2024	Dec. 31, 2023
Subsequent Event [Line Items]
Restructuring and Related Cost, Number of Positions Eliminated, Period Percent		68%
Subsequent Event
Subsequent Event [Line Items]
Restructuring and Related Cost, Number of Positions Eliminated, Period Percent	30%
Restructuring and Related Cost, Expected Cost	$ 0.1

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
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