Molecular Templates (MTEM) 10-Q 13 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Trading Symbol	MTEM
Entity Registrant Name	Molecular Templates, Inc.
Entity Central Index Key	0001183765
Current Fiscal Year End Date	--12-31
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 File Number	001-32979
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3409596
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 Address, Postal Zip Code	78729
City Area Code	512
Local Phone Number	869-1555
Entity Common Stock, Shares Outstanding		5,374,268
Title of 12(b) Security	Common Stock, $0.001 Par Value Per Share
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands		Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents		$ 15,811	$ 32,190
Marketable securities, current			28,859
Prepaid expenses		2,999	3,459
Other current assets		3,890	3,790
Total current assets		22,700	68,298
Operating lease right-of-use assets		9,667	11,132
Property and equipment, net		8,578	14,632
Other assets		3,116	3,486
Total assets		44,061	97,548
Current liabilities:
Accounts payable		2,583	504
Accrued liabilities		3,303	8,823
Deferred revenue, current		13,210	45,573
Other current liabilities		2,416	2,182
Total current liabilities		21,512	57,082
Deferred revenue, long-term			5,904
Long-term debt, net of current portion			36,168
Operating lease liabilities, long term portion		10,396	12,231
Contingent value right liability		3,975
Other liabilities		1,377	1,295
Total liabilities		37,260	112,680
Commitments and contingencies (Note 10)
Stockholders' equity/(deficit)
Preferred stock, $0.001 par value: Authorized: 2,000,000 shares as of September 30, 2023 and December 31, 2022; Issued and outstanding: 250 shares at September 30, 2023 and December 31, 2022
Common stock, $0.001 par value: Authorized: 150,000,000 shares as of September 30, 2023 and December 31, 2022; Issued and outstanding: 5,374,268 shares at September 30, 2023 and 3,756,711 shares at December 31, 2022 respectively	[1]	5	4
Additional paid-in capital	[1]	455,739	429,698
Accumulated other comprehensive income/(loss)		1	(66)
Accumulated deficit		(448,944)	(444,768)
Total stockholders' equity/(deficit)		6,801	(15,132)
Total liabilities and stockholders' equity/(deficit)		$ 44,061	$ 97,548
[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 Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical)	Sep. 30, 2023 $ / shares shares	Dec. 31, 2022 $ / shares shares
Statement Of Financial Position [Abstract]
Preferred stock, par value | $ / shares	$ 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 | $ / shares	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	5,374,268	3,756,776
Common stock, shares outstanding	5,374,268	3,756,711

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Total revenue		$ 6,796	$ 4,240	$ 50,290	$ 17,143
Operating expenses:
Research and development		7,624	21,973	40,079	64,835
General and administrative		4,309	5,934	15,306	20,120
Total operating expenses		11,933	27,907	55,385	84,955
Loss from operations		5,137	23,667	5,095	67,812
Interest and other income, net		210	307	1,030	563
Interest and other expense, net	[1]	(31)	(1,224)	(2,615)	(3,365)
Gain on extinguishment of debt				1,795
Change in valuation of contingent value right (Note 5)		881		1,184
Loss on disposal of property and equipment	[1]	(76)	(28)	(475)	(29)
Loss before provision for income taxes		4,153	24,612	4,176	70,643
Provision for income taxes			26		26
Net loss attributable to common shareholders		$ 4,153	$ 24,638	$ 4,176	$ 70,669
Net loss per share attributable to common stockholders:
Basic		$ 0.82	$ 6.56	$ 0.99	$ 18.82
Diluted		$ 0.82	$ 6.56	$ 0.99	$ 18.82
Weighted average number of shares used in net income per share calculations:
Basic		5,092,859	3,756,658	4,206,986	3,755,178
Diluted		5,092,859	3,756,658	4,206,986	3,755,178
Research and development revenue
Total revenue		$ 5,732	$ 4,240	$ 45,986	$ 17,143
Grant revenue
Total revenue		$ 1,064	$ 0	$ 4,304	$ 0
[1] Loss on disposal of property and equipment was included in interest and other expense, net in the prior year presentation.

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ 4,153	$ 24,638	$ 4,176	$ 70,669
Other comprehensive income/(loss):
Unrealized gain/(loss) on available-for-sale securities		103	67	(179)
Comprehensive loss	$ 4,153	$ 24,535	$ 4,109	$ 70,848

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, 2021		$ 4	[1]	$ 417,756	[1]	$ (48)	$ (352,050)	$ 65,662
Beginning balance (shares) at Dec. 31, 2021	[1]	3,753,606
Issuance of common stock pursuant to stock plans	[1]			33
Issuance of common stock pursuant to stock plans (shares)	[1]	3,105
Stock-based compensation	[1]			9,305
Other comprehensive income/(loss)						(179)
Net loss							(70,669)	(70,643)
Ending balance at Sep. 30, 2022		$ 4	[1]	427,094	[1]	(227)	(422,719)	4,152
Ending balance (shares) at Sep. 30, 2022	[1]	3,756,711
Beginning balance at Jun. 30, 2022		$ 4	[1]	424,444	[1]	(330)	(398,081)	26,037
Beginning balance (shares) at Jun. 30, 2022	[1]	3,755,906
Issuance of common stock pursuant to stock plans	[1]			9
Issuance of common stock pursuant to stock plans (shares)	[1]	805
Stock-based compensation	[1]			2,641
Other comprehensive income/(loss)						103
Net loss							(24,638)	(24,612)
Ending balance at Sep. 30, 2022		$ 4	[1]	427,094	[1]	(227)	(422,719)	4,152
Ending balance (shares) at Sep. 30, 2022	[1]	3,756,711
Beginning balance at Dec. 31, 2022		$ 4	[1]	429,698	[1]	(66)	(444,768)	$ (15,132)
Beginning balance (shares) at Dec. 31, 2022		3,756,711	[1]					3,756,711
Issuance of common stock and prefunded warrants pursuant to private placement, net of issuance costs	[1]	$ 1		18,382
Issuance of common stock pursuant to private placement (shares)	[1]	1,617,365
Issuance of common stock pursuant to stock plans	[1]			1
Issuance of common stock pursuant to stock plans (shares)	[1]	192
Stock-based compensation	[1]			5,342
Issuance of warrants	[1]			2,316
Other comprehensive income/(loss)						67
Net loss							(4,176)	$ (4,176)
Ending balance at Sep. 30, 2023		$ 5	[1]	455,739	[1]	1	(448,944)	$ 6,801
Ending balance (shares) at Sep. 30, 2023		5,374,268	[1]					5,374,268
Beginning balance at Jun. 30, 2023		$ 4	[1]	436,108	[1]	1	(444,791)	$ (8,678)
Beginning balance (shares) at Jun. 30, 2023	[1]	3,756,711
Issuance of common stock and prefunded warrants pursuant to private placement, net of issuance costs	[1]	$ 1		18,382
Issuance of common stock pursuant to private placement (shares)	[1]	1,617,365
Issuance of common stock pursuant to stock plans	[1]			1
Issuance of common stock pursuant to stock plans (shares)	[1]	192
Stock-based compensation	[1]			1,248
Other comprehensive income/(loss)						0
Net loss							(4,153)	(4,153)
Ending balance at Sep. 30, 2023		$ 5	[1]	$ 455,739	[1]	$ 1	$ (448,944)	$ 6,801
Ending balance (shares) at Sep. 30, 2023		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
Statement Of Stockholders Equity [Abstract]
Reverse stock split ratio	0.66

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss		$ 4,153	$ 24,638	$ 4,176	$ 70,669
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and other				5,447	5,564
Stock-based compensation expense				5,342	9,305
Interest accrued (paid) on long-term debt				(376)	64
Amortization of debt discount and accretion related to debt				393	747
Gain on extinguishment of debt				(1,795)
Accretion of asset retirement obligations				82	98
Loss on disposal of property and equipment	[1]	76	28	475	29
Change in valuation of contingent value right		(881)		(1,184)
Changes in operating assets and liabilities:
Prepaid expenses				460	188
Other assets				58	(724)
Operating lease right-of-use assets and liabilities				(136)	(572)
Accounts payable				2,079	(572)
Accrued liabilities				(4,935)	(694)
Deferred revenue				(38,267)	(13,356)
Net cash used in operating activities				(36,533)	(70,592)
Cash flows from investing activities:
Purchases of property and equipment				(200)	(2,886)
Proceeds from sale of equipment				260
Purchase of marketable securities				(2,364)	(52,132)
Sales of marketable securities				31,400	121,990
Net cash provided by investing activities				29,096	66,972
Cash flows from financing activities:
Proceeds from issuance of common stock and prefunded warrants, net offering expenses				18,383
Proceeds from stock option exercises				1	33
Repayment of long-term debt				(27,500)
Fees paid on loan modification				0	(298)
Net cash used in financing activities				(9,116)	(265)
Net decrease in cash, cash equivalents, and restricted cash				(16,553)	(3,885)
Cash, cash equivalents and restricted cash, beginning of period				34,679	28,651
Cash, cash equivalents and restricted cash, end of period		18,126	24,766	18,126	24,766
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents		15,811	22,277	15,811	22,277
Restricted cash included in other assets		$ 2,315	$ 2,489	$ 2,315	$ 2,489
Restricted Cash and Cash Equivalents, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Other assets	Other assets	Other assets	Other assets
Total cash, cash equivalents and restricted cash		$ 18,126	$ 24,766	$ 18,126	$ 24,766
Supplemental Cash Flow Information
Cash paid for interest				2,293	2,471
Non-Cash Investing Activities
Fixed asset additions in accounts payable and accrued expenses				$ 0	$ 50
[1] Loss on disposal of property and equipment was included in interest and other expense, net in the prior year presentation.

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
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, 2022 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 30, 2023. 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 September 30, 2023, the Company had an accumulated deficit of $448.9 million. There is substantial doubt about the Company’s ability to continue as a going concern as of the date of issuance of these financial statements as 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 8 “Borrowing Arrangements and Debt Extinguishment” to provide sufficient certainty that it will continue as a going concern. 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. As of September 30, 2023, the Company had unrestricted cash and cash equivalents of $15.8 million. Based on the Company’s cash and cash equivalents as of September 30, 2023, the proceeds from the first tranche of the private placement described in Note 13 “Stockholders’ Equity/(Deficit)” and the anticipated cost-savings from the restructuring described in Note 12 “Restructuring Related Expenses,” and other assumptions, management anticipates that the Company will be able to fund its planned operating expenses and capital expenditure requirements to the end of the second quarter of 2024. 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 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 nine months ended September 30, 2023, 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, 2022. 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 $2.3 million and $2.5 million of restricted cash as of September 30, 2023 and December 31, 2022, 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 September 30, 2023, 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”). In past years, the Company’s exposure to credit risk associated with non-payment were also affected principally by conditions or occurrences within Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda Pharmaceutical Company Ltd. (“Takeda”). Takeda accounted for approximately 0% of total revenues for both the three months ended September 30, 2023 and 2022, and approximately 0% and 15% of total revenues for the nine months ended September 30, 2023 and 2022, respectively. Bristol-Myers Squibb accounted for approximately 84% and 100% of total revenues for the three months ended September 30, 2023 and 2022, respectively, and approximately 91% and 85% of total revenues for the nine months ended September 30, 2023 and 2022, respectively. Drug or biologic candidates developed by the Company require approvals or clearances from the U.S. Food and Drug Administration or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug or 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. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Common Share	NOTE 2 — NET LOSS PER COMMON SHARE Basic net loss per common share is computed by dividing net loss 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 loss calculation. Diluted net loss per share is computed by giving effect to all potential dilutive common shares, including outstanding options, warrants and convertible preferred stock. More specifically, as of September 30, 2023 and 2022, stock options, warrants, convertible common shares related to the Conversion Right, as defined in the CVR Agreement and described in Note 5 “Fair Value Measurements,” and, if converted, preferred stock totaling approximately 2,544,000 and 799,000 shares of the Company’s common stock, respectively, were excluded from the computation of diluted net loss per share as their effect would have been anti-dilutive.

Research and Development Agreem

Research and Development Agreements	9 Months Ended
	Sep. 30, 2023
Research And Development [Abstract]
Research and Development Agreements	NOTE 3 — RESEARCH AND DEVELOPMENT AGREEMENTS Disaggregated Research and Development Revenue Research and development revenue is attributable to regions based on the location of each of the Company’s collaboration partner’s parent company headquarters. Research and development revenues disaggregated by location were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 United States ​ $ 5,732 ​ $ 4,240 ​ $ 45,986 ​ $ 14,557 Japan ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,586 Total research and development revenue ​ $ 5,732 ​ $ 4,240 ​ $ 45,986 ​ $ 17,143 ​ Collaboration 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. 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 may receive near term and development and regulatory milestone payments of up to $874.5 million. The Company will also be 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 is 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 will be 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 will expire (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 has the right to terminate the BMS Collaboration Agreement for convenience upon prior written notice to the Company. Either party has 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 has 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 will be recognized over time as the underlying research and development services are performed. The Company recognizes 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 will use actual costs incurred relative to budgeted costs expected to be incurred. These costs consist primarily of internal employee efforts and third-party contract costs. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation over the estimated service period. For the three months ended September 30, 2023 and 2022, the Company recognized $5.7 million and $4.2 million, respectively, of research and development revenue related to the BMS Collaboration Agreement. For the nine months ended September 30, 2023 and 2022, the Company recognized $46.0 million and $14.6 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. The Company had $13.1 million and $45.3 million of deferred revenue, current, as of September 30, 2023 and December 31, 2022, respectively, related to the BMS Collaboration Agreement. The Company had zero and $5.9 million of deferred revenue, non-current as of September 30, 2023 and December 31, 2022, respectively, related to the BMS Collaboration Agreement. Takeda Multi-Target Agreement In June 2017, the Company entered into a Multi-Target Collaboration and License Agreement with Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda (the “Takeda Multi-Target Agreement”), in which the Company agreed to collaborate with Takeda to identify and generate ETBs, against two targets designated by Takeda. In March 2022, following the Company’s request to bring the agreement to an end, the Company and Takeda mutually agreed to terminate the Takeda Multi-Target Agreement. As a result of the termination, the Company regained full rights to pursue the targets worked on under the Takeda Multi-Target Agreement. There are no ongoing activities or economic obligations in connection with the Takeda Multi-Target Agreement. For the three months ended September 30, 2023 and 2022, the Company did not recognize research and development revenue related to the Takeda Multi-Target Agreement. For the nine months ended September 30, 2023 and 2022, the Company recognized zero and $2.6 million, respectively, as research and development revenue, related to the Takeda Multi-Target Agreement. As of September 30, 2023 and December 31, 2022, there was no deferred revenue related to the Takeda Multi-Target 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 2022, 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 September 30, 2023, the Company has cumulatively recognized $13.7 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 September 30, 2023 and 2022, the Company recognized grant revenue under this award of $1.1 million and zero, respectively. For the nine months ended September 30, 2023 and 2022, the Company recognized grant revenue under this award of $4.3 million and zero, respectively. Qualified expenditures submitted for reimbursement in excess of amounts received are recorded as receivables in grant revenue receivable. As of both September 30, 2023 and December 31, 2022, the Company recorded grant revenue receivable of zero. As of September 30, 2023 and December 31, 2022, the Company recorded deferred revenue of $0.1 million and $0.2 million, respectively.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2023
Related Party Transactions [Abstract]
Related Party Transactions	NOTE 4 — RELATED PARTY TRANSACTIONS Takeda In connection with the Takeda Multi-Target Agreement described in Note 3 “Research and Development Agreements,” Takeda became a related party, following the Takeda Stock Purchase Agreement described in Note 11 “Stockholders’ Equity,” of the Company’s previously filed Annual Report on Form 10-K for the year ended December 31, 2022, filed with the SEC on March 30, 2023. In August 2021, Takeda ceased to be a related party after a sale of the above-mentioned shares.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	NOTE 5 — FAIR VALUE MEASUREMENTS The following table sets forth the Company’s financial assets (cash equivalents and marketable securities) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ September 30, 2023 Level 1 Level 2 Level 3 Money market funds ​ $ 15,178 ​ $ 15,178 ​ $ — ​ $ — Total ​ $ 15,178 ​ $ 15,178 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2022 Level 1 Level 2 Level 3 Money market funds ​ $ 24,546 ​ $ 24,546 ​ $ — ​ $ — Commercial paper ​ ​ 21,134 ​ ​ — ​ ​ 21,134 ​ ​ — United States Treasury Bills ​ ​ 10,702 ​ ​ — ​ ​ 10,702 ​ ​ — Cash ​ ​ 2,500 ​ ​ 2,500 ​ ​ — ​ ​ — Total ​ $ 58,882 ​ $ 27,046 ​ $ 31,836 ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 30,023 ​ ​ ​ ​ ​ ​ ​ ​ ​ Marketable securities, current ​ ​ 28,859 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents and marketable securities ​ $ 58,882 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The Company invests in highly-liquid, investment-grade securities. The following is a summary of the Company’s available-for-sale securities (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2023 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 15,178 ​ $ — ​ $ — ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper ​ $ 30,022 ​ $ 1 ​ $ — ​ $ 30,023 Marketable securities, current - commercial paper, Treasury bills ​ $ 28,926 ​ $ — ​ $ (67) ​ $ 28,859 ​ As of both September 30, 2023 and December 31, 2022, 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 and nine months ended September 30, 2023 and 2022, and no ​ Contingent Value Right and Common Stock Warrant Valuation ​ months ended September 30, 2023, the change in fair value related to the Conversion Right and Contingent Value Right liability was $0.9 million and $1.2 million, respectively. 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 ​ September 30, 2023 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 3,975 ​ $ — ​ $ — ​ $ 3,975 Total ​ $ 3,975 ​ $ — ​ $ — ​ $ 3,975 ​ 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	9 Months Ended
	Sep. 30, 2023
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	NOTE 6 — BALANCE SHEET COMPONENTS Accrued liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2023 December 31, 2022 Accrued liabilities: ​ ​ ​ ​ ​ General and administrative $ 717 ​ $ 855 Clinical trial related costs ​ ​ 2,126 ​ ​ 1,327 Non-clinical research and manufacturing operations ​ 411 ​ ​ 1,779 Payroll related ​ 38 ​ ​ 4,828 Other accrued expenses ​ 11 ​ ​ 34 Total Accrued liabilities $ 3,303 ​ $ 8,823 ​

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2023
Property Plant And Equipment [Abstract]
Property and Equipment	NOTE 7—PROPERTY AND EQUIPMENT Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ 2023 2022 Laboratory equipment ​ $ 20,695 ​ $ 21,831 Leasehold improvements ​ ​ 12,974 ​ ​ 12,971 Furniture and fixtures ​ ​ 518 ​ ​ 518 Computer and equipment ​ ​ 254 ​ ​ 658 ​ ​ ​ 34,441 ​ ​ 35,978 Less: Accumulated depreciation ​ ​ (25,863) ​ ​ (21,346) Total property and equipment, net ​ $ 8,578 ​ $ 14,632 ​ Depreciation expense was $1.5 million and $2.0 million for the three months ended September 30, 2023 and 2022, respectively. Depreciation expense was $5.5 million and $5.7 million for the nine months ended September 30, 2023 and 2022, respectively. As of September 30, 2023 and December 31, 2022, the Company had net Asset Retirement Obligation (“ARO”) assets totaling $0.2 million and $0.3 million, respectively. The ARO assets are included in leasehold improvements.

Borrowing Arrangements and Debt

Borrowing Arrangements and Debt Extinguishment	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Borrowing Arrangements and Debt Extinguishment	NOTE 8 — 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 Amount 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	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
Leases	NOTE 9 — 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 three 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 In July 2022, the Company exercised its option to extend the term for its lease of its principal executive office at 9301 Amberglen Blvd, Building J, Austin TX 78729 (the “Property”) for an additional five-year term beginning August 31, 2023 and ending August 31, 2028 pursuant to the terms and conditions of that certain Lease, dated October 1, 2016, by and between the Company and NW Austin Office Partners LLC as previously amended (the “Lease Agreement”). In October 2022, the Company entered into that certain Fourth Amendment to the Lease Agreement, by and between the Company and NW Austin Office Partners LLC (the “Lease Amendment”) which amended the Lease Agreement to document the exercise of the Company’s option to extend the term of its lease of the Property for an additional six-year term beginning September 1, 2023 and ending August 31, 2029 (the “Extension Term”). Pursuant to the terms of the Lease Amendment, the aggregate commitments will be $6.7 million over the six-year Extension Term and the parties agreed that so long as the Company is not in default, an aggregate amount of $0.2 million shall be abated in installments from the monthly lease commitments until exhausted. The Lease Amendment also provides that prior to the expiration of the Extension Term, the Company has the option to extend the Extension Term for an additional period of seven years. The following table summarizes the components of lease expense for the three and nine months ended September 30, 2023 and 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 Operating leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease expense ​ $ 727 ​ $ 684 ​ $ 2,181 ​ $ 1,885 Variable lease expense ​ ​ 153 ​ ​ 156 ​ ​ 399 ​ ​ 367 Total operating lease expense ​ $ 880 ​ $ 840 ​ $ 2,580 ​ $ 2,252 ​ The following table summarizes the balance sheet classification of leases as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ September 30, ​ 2023 Operating leases ​ ​ ​ Operating lease right-of-use assets ​ $ 9,667 ​ ​ ​ ​ Operating lease liabilities, current 1 ​ $ 2,416 Operating lease liabilities, non-current ​ ​ 10,396 Total operating lease liabilities ​ $ 12,812 1. Included in other current liabilities. ​ The following table presents other information on leases as of September 30, 2023 and December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2023 2022 Weighted average remaining lease term, operating leases ​ 4.87 years 5.54 years Weighted average discount rate, operating leases ​ 8.21 % 8.21 % ​ Maturities of lease liabilities were as follows as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ Operating Leases 2023 (remaining) ​ $ 833 2024 ​ ​ 3,369 2025 ​ ​ 3,299 2026 ​ ​ 2,564 2027 ​ ​ 2,636 Thereafter ​ ​ 2,872 Total lease payments ​ $ 15,573 Less: ​ ​ ​ Imputed interest ​ ​ (2,761) Total lease liabilities ​ $ 12,812 ​ Supplemental cash flow information related to the Company’s leases were as follows (in thousands): ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, ​ 2023 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows operating leases ​ $ 2,178 ​

Contractual Commitments

Contractual Commitments	9 Months Ended
	Sep. 30, 2023
Commitments And Contingencies Disclosure [Abstract]
Contractual Commitments	NOTE 10 — 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 September 30, 2023. 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 drug or biologic candidates. The Company was contractually obligated for up to approximately $33.4 million of future services under these agreements as of September 30, 2023, 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, which include signed orders for capital equipment. These estimated purchase obligations total in range from $3.8 million to $4.1 million.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	NOTE 11 — 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 September 30, ​ Nine Months Ended September 30, 2023 2022 2023 2022 Research and development ​ $ 353 ​ $ 1,381 ​ $ 2,411 ​ $ 4,753 General and administrative ​ ​ 895 ​ ​ 1,260 ​ ​ 2,931 ​ ​ 4,552 Total stock-based compensation ​ $ 1,248 ​ $ 2,641 ​ $ 5,342 ​ $ 9,305 ​ As of September 30, 2023, the total unrecognized compensation cost related to unvested stock-based awards granted to employees under the Company’s equity incentive plans was approximately $6.0 million. This cost will be recorded as compensation expense on a ratable basis over the remaining weighted average requisite service period of approximately 2.5 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 September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 ​ Employee Stock Options: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ ​ 4.29 % ​ 3.25 % ​ 4.03 % ​ 2.33 % Expected term (in years) ​ ​ 6.08 ​ ​ 6.08 ​ ​ 6.08 ​ ​ 6.08 ​ Dividend yield ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ Volatility ​ ​ 78.85 % ​ 83.32 % ​ 77.65 % ​ 88.70 % Weighted-average fair value of stock options granted ​ $ 5.82 ​ $ 7.95 ​ $ 5.23 ​ $ 24.90 ​ ​ 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, 2021 ​ 523,411 ​ $ 153.11 ​ 6.72 ​ $ 14.25 Granted ​ 194,679 ​ $ 33.09 ​ ​ ​ ​ ​ Exercised ​ (3,106) ​ $ 10.65 ​ ​ ​ ​ ​ Cancelled ​ (152,106) ​ $ 141.63 ​ ​ ​ ​ ​ Balances, December 31, 2022 ​ 562,878 ​ $ 115.50 ​ 7.09 ​ $ — Granted ​ 213,168 ​ $ 7.46 ​ ​ ​ ​ ​ Exercised ​ (192) ​ $ 7.20 ​ ​ ​ ​ ​ Cancelled ​ (241,027) ​ $ 82.61 ​ ​ ​ ​ ​ Balances, September 30, 2023 ​ 534,827 ​ $ 87.30 ​ 6.61 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest, September 30, 2023 ​ 534,827 ​ $ 87.30 ​ 6.61 ​ $ — Exercisable at September 30, 2023 ​ 327,184 ​ $ 118.84 ​ 5.05 ​ $ — ​ The total intrinsic value of stock options exercised during the nine months ended both September 30, 2023 and 2022, was zero, as determined at the date of the option exercise. Cash received from stock option exercises was zero, for both the nine months ended September 30, 2023 and 2022. The Company issues new shares of common stock upon exercise of options.

Restructuring Related Expenses

Restructuring Related Expenses	9 Months Ended
	Sep. 30, 2023
Restructuring And Related Activities [Abstract]
Restructuring Related Expenses	NOTE 12 – RESTRUCTURING RELATED EXPENSES On March 29, 2023, the Company implemented a strategic reprioritization and corresponding reduction in workforce, 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 June 16, 2023, the Company implemented an additional reduction in workforce, reducing the Company’s workforce by approximately 44%. For the three and nine months ended September 30, 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 Company estimates that it will not incur any additional Restructuring related costs as of the time of issuance of these financial statements. The following table summarizes the activity for the nine months ended September 30, 2023 for expenses related to the Restructuring accruals, which are included in Accrued liabilities in the Company’s condensed consolidated balance sheets as of September 30, 2023 (in thousands): ​ ​ ​ ​ Balance, December 31, 2022 $ — Expenses related to the Restructuring ​ ​ 276 Cash payments ​ ​ (276) Balance, September 30, 2023 ​ $ — ​

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2023
Stockholders' Equity Note [Abstract]
Stockholders' Equity (Deficit)	NOTE 13 — 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 8 “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 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 provides 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 (the “July 2023 Pre-Funded Warrants”) exercisable for up to 1,222,100 shares of the Company’s common stock. 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 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, 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, July 2023 Pre-Funded Warrants are accounted for as a component of additional paid-in capital at the time of issuance. The second tranche would consist of the sale of an additional 2.8 million shares of the Company’s common stock (or additional pre-funded warrants in lieu thereof) on the same pricing terms as the initial tranche, which would represent further gross proceeds of approximately $20.0 million, and would close if the following conditions were met: within a 12 month measurement period (or such longer period as approved by July 2023 Purchasers who purchased a majority of the securities purchased in the initial tranche), shares of the Company’s common stock trade at a 10-day volume weighted average price of at least $21.15 per share with aggregate trading volume during the same 10-day period of at least 666,666 shares, and certain other customary closing conditions, including the absence of a material adverse event as described in the July 2023 Purchase Agreement, are satisfied. This second tranche is a mandatory funding commitment of the July 2023 Purchasers subject to the foregoing conditions. The 12 month measurement period commences on the later of the filing of an amendment to the Company’s certificate of incorporation to implement a reverse stock split of shares of its common stock currently outstanding, without making a reduction in the number of shares of common stock authorized, following stockholder approval, and the effectiveness of a resale registration statement filed in connection with the first tranche closing. In addition, upon the second tranche closing, the Company would be required to issue to the July 2023 Purchasers common stock warrants representing the right to purchase an additional 5.7 million shares of the Company’s common stock at an exercise price of $7.05 per share (the “Second Closing Warrants”), in exchange for the payment of $1.875 per share of common stock underlying the Second Closing Warrants. In the aggregate, these Second Closing Warrants would represent warrant coverage of the number of shares of common stock (or pre-funded warrants) sold in the initial tranche and to be sold in the second tranche closing. These Second Closing Warrants would have a term of 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

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
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, 2022 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 30, 2023. 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 September 30, 2023, the Company had an accumulated deficit of $448.9 million. There is substantial doubt about the Company’s ability to continue as a going concern as of the date of issuance of these financial statements as 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 8 “Borrowing Arrangements and Debt Extinguishment” to provide sufficient certainty that it will continue as a going concern. 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. As of September 30, 2023, the Company had unrestricted cash and cash equivalents of $15.8 million. Based on the Company’s cash and cash equivalents as of September 30, 2023, the proceeds from the first tranche of the private placement described in Note 13 “Stockholders’ Equity/(Deficit)” and the anticipated cost-savings from the restructuring described in Note 12 “Restructuring Related Expenses,” and other assumptions, management anticipates that the Company will be able to fund its planned operating expenses and capital expenditure requirements to the end of the second quarter of 2024. 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 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 nine months ended September 30, 2023, 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, 2022.
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 $2.3 million and $2.5 million of restricted cash as of September 30, 2023 and December 31, 2022, 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 September 30, 2023, 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”). In past years, the Company’s exposure to credit risk associated with non-payment were also affected principally by conditions or occurrences within Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda Pharmaceutical Company Ltd. (“Takeda”). Takeda accounted for approximately 0% of total revenues for both the three months ended September 30, 2023 and 2022, and approximately 0% and 15% of total revenues for the nine months ended September 30, 2023 and 2022, respectively. Bristol-Myers Squibb accounted for approximately 84% and 100% of total revenues for the three months ended September 30, 2023 and 2022, respectively, and approximately 91% and 85% of total revenues for the nine months ended September 30, 2023 and 2022, respectively. Drug or biologic candidates developed by the Company require approvals or clearances from the U.S. Food and Drug Administration or international regulatory agencies prior to commercial sales. There can be no assurance that the Company’s drug or 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. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

Research and Development Agre_2

Research and Development Agreements (Tables)	9 Months Ended
	Sep. 30, 2023
Research And Development [Abstract]
Schedule of Research and Development Revenues Disaggregated by Location	Research and development revenue is attributable to regions based on the location of each of the Company’s collaboration partner’s parent company headquarters. Research and development revenues disaggregated by location were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 United States ​ $ 5,732 ​ $ 4,240 ​ $ 45,986 ​ $ 14,557 Japan ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,586 Total research and development revenue ​ $ 5,732 ​ $ 4,240 ​ $ 45,986 ​ $ 17,143

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Financial Assets at Fair Value on Recurring Basis	The following table sets forth the Company’s financial assets (cash equivalents and marketable securities) at fair value on a recurring basis (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ September 30, 2023 Level 1 Level 2 Level 3 Money market funds ​ $ 15,178 ​ $ 15,178 ​ $ — ​ $ — Total ​ $ 15,178 ​ $ 15,178 ​ $ — ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Basis of Fair Value Measurements ​ December 31, 2022 Level 1 Level 2 Level 3 Money market funds ​ $ 24,546 ​ $ 24,546 ​ $ — ​ $ — Commercial paper ​ ​ 21,134 ​ ​ — ​ ​ 21,134 ​ ​ — United States Treasury Bills ​ ​ 10,702 ​ ​ — ​ ​ 10,702 ​ ​ — Cash ​ ​ 2,500 ​ ​ 2,500 ​ ​ — ​ ​ — Total ​ $ 58,882 ​ $ 27,046 ​ $ 31,836 ​ $ — Amounts included in: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ $ 30,023 ​ ​ ​ ​ ​ ​ ​ ​ ​ Marketable securities, current ​ ​ 28,859 ​ ​ ​ ​ ​ ​ ​ ​ ​ Total cash equivalents and marketable securities ​ $ 58,882 ​ ​ ​ ​ ​ ​ ​ ​ ​
Summary of Company's Available-for-Sale Securities	The following is a summary of the Company’s available-for-sale securities (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2023 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds ​ $ 15,178 ​ $ — ​ $ — ​ $ 15,178 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2022 ​ Cost Basis Unrealized Gain Unrealized Loss Fair Value Cash equivalents - money market funds, commercial paper ​ $ 30,022 ​ $ 1 ​ $ — ​ $ 30,023 Marketable securities, current - commercial paper, Treasury bills ​ $ 28,926 ​ $ — ​ $ (67) ​ $ 28,859
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 ​ September 30, 2023 Level 1 Level 2 Level 3 Conversion right and contingent value right ​ $ 3,975 ​ $ — ​ $ — ​ $ 3,975 Total ​ $ 3,975 ​ $ — ​ $ — ​ $ 3,975
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)	9 Months Ended
	Sep. 30, 2023
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Components of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2023 December 31, 2022 Accrued liabilities: ​ ​ ​ ​ ​ General and administrative $ 717 ​ $ 855 Clinical trial related costs ​ ​ 2,126 ​ ​ 1,327 Non-clinical research and manufacturing operations ​ 411 ​ ​ 1,779 Payroll related ​ 38 ​ ​ 4,828 Other accrued expenses ​ 11 ​ ​ 34 Total Accrued liabilities $ 3,303 ​ $ 8,823 ​

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2023
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ 2023 2022 Laboratory equipment ​ $ 20,695 ​ $ 21,831 Leasehold improvements ​ ​ 12,974 ​ ​ 12,971 Furniture and fixtures ​ ​ 518 ​ ​ 518 Computer and equipment ​ ​ 254 ​ ​ 658 ​ ​ ​ 34,441 ​ ​ 35,978 Less: Accumulated depreciation ​ ​ (25,863) ​ ​ (21,346) Total property and equipment, net ​ $ 8,578 ​ $ 14,632

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
Components of Lease Expense	The following table summarizes the components of lease expense for the three and nine months ended September 30, 2023 and 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 Operating leases ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating lease expense ​ $ 727 ​ $ 684 ​ $ 2,181 ​ $ 1,885 Variable lease expense ​ ​ 153 ​ ​ 156 ​ ​ 399 ​ ​ 367 Total operating lease expense ​ $ 880 ​ $ 840 ​ $ 2,580 ​ $ 2,252
Schedule of Balance Sheets Classification of Leases	The following table summarizes the balance sheet classification of leases as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ September 30, ​ 2023 Operating leases ​ ​ ​ Operating lease right-of-use assets ​ $ 9,667 ​ ​ ​ ​ Operating lease liabilities, current 1 ​ $ 2,416 Operating lease liabilities, non-current ​ ​ 10,396 Total operating lease liabilities ​ $ 12,812 1. Included in other current liabilities.
Schedule of Leases Information	The following table presents other information on leases as of September 30, 2023 and December 31, 2022: ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2023 2022 Weighted average remaining lease term, operating leases ​ 4.87 years 5.54 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 September 30, 2023 (in thousands): ​ ​ ​ ​ ​ Operating Leases 2023 (remaining) ​ $ 833 2024 ​ ​ 3,369 2025 ​ ​ 3,299 2026 ​ ​ 2,564 2027 ​ ​ 2,636 Thereafter ​ ​ 2,872 Total lease payments ​ $ 15,573 Less: ​ ​ ​ Imputed interest ​ ​ (2,761) Total lease liabilities ​ $ 12,812
Supplemental Cash Flow Information	Supplemental cash flow information related to the Company’s leases were as follows (in thousands): ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, ​ 2023 Cash paid for amounts included in the measurement of lease liabilities: ​ ​ ​ Operating cash flows operating leases ​ $ 2,178 ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
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 September 30, ​ Nine Months Ended September 30, 2023 2022 2023 2022 Research and development ​ $ 353 ​ $ 1,381 ​ $ 2,411 ​ $ 4,753 General and administrative ​ ​ 895 ​ ​ 1,260 ​ ​ 2,931 ​ ​ 4,552 Total stock-based compensation ​ $ 1,248 ​ $ 2,641 ​ $ 5,342 ​ $ 9,305
Weighted-Average Fair Value Valuation Assumptions	The fair value of employee stock options was estimated using the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2023 2022 2023 2022 ​ Employee Stock Options: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Risk-free interest rate ​ ​ 4.29 % ​ 3.25 % ​ 4.03 % ​ 2.33 % Expected term (in years) ​ ​ 6.08 ​ ​ 6.08 ​ ​ 6.08 ​ ​ 6.08 ​ Dividend yield ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ Volatility ​ ​ 78.85 % ​ 83.32 % ​ 77.65 % ​ 88.70 % Weighted-average fair value of stock options granted ​ $ 5.82 ​ $ 7.95 ​ $ 5.23 ​ $ 24.90 ​
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, 2021 ​ 523,411 ​ $ 153.11 ​ 6.72 ​ $ 14.25 Granted ​ 194,679 ​ $ 33.09 ​ ​ ​ ​ ​ Exercised ​ (3,106) ​ $ 10.65 ​ ​ ​ ​ ​ Cancelled ​ (152,106) ​ $ 141.63 ​ ​ ​ ​ ​ Balances, December 31, 2022 ​ 562,878 ​ $ 115.50 ​ 7.09 ​ $ — Granted ​ 213,168 ​ $ 7.46 ​ ​ ​ ​ ​ Exercised ​ (192) ​ $ 7.20 ​ ​ ​ ​ ​ Cancelled ​ (241,027) ​ $ 82.61 ​ ​ ​ ​ ​ Balances, September 30, 2023 ​ 534,827 ​ $ 87.30 ​ 6.61 ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Vested and expected to vest, September 30, 2023 ​ 534,827 ​ $ 87.30 ​ 6.61 ​ $ — Exercisable at September 30, 2023 ​ 327,184 ​ $ 118.84 ​ 5.05 ​ $ —

Restructuring Related Expenses

Restructuring Related Expenses (Tables)	9 Months Ended
	Sep. 30, 2023
Restructuring And Related Activities [Abstract]
Summary of Activity for Expenses Related to Restructuring Accruals	The following table summarizes the activity for the nine months ended September 30, 2023 for expenses related to the Restructuring accruals, which are included in Accrued liabilities in the Company’s condensed consolidated balance sheets as of September 30, 2023 (in thousands): ​ ​ ​ ​ Balance, December 31, 2022 $ — Expenses related to the Restructuring ​ ​ 276 Cash payments ​ ​ (276) Balance, September 30, 2023 ​ $ — ​

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 11, 2023	Sep. 30, 2023 USD ($) Institution	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Institution	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split ratio	0.66
Accumulated deficit		$ (448,944)		$ (448,944)		$ (444,768)
Cash and cash equivalents		15,811	$ 22,277	15,811	$ 22,277	32,190
Restricted cash included in other assets		$ 2,315	$ 2,489	$ 2,315	$ 2,489	$ 2,500
Restricted Cash and Cash Equivalents, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Other assets	Other assets	Other assets	Other assets	Other assets
Number Of Financial Institutions | Institution		2		2
Revenue | Concentration of Credit Risk and Other Risks and Uncertainties | Takeda Pharmaceuticals Inc
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of total revenues		0%	0%	0%	15%
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		84%	100%	91%	85%

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Detail) - shares	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Stock Options, Warrants and Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common shares excluded from the computation of diluted net income/(loss) per share on effect of anti-dilutive	2,544,000	799,000

Research and Development Agre_3

Research and Development Agreements - Schedule of Research and Development Revenues Disaggregated by Location (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenue Recognition [Line Items]
Total revenue	$ 6,796	$ 4,240	$ 50,290	$ 17,143
Research and development revenue
Revenue Recognition [Line Items]
Total revenue	5,732	4,240	45,986	17,143
Research and development revenue | JAPAN
Revenue Recognition [Line Items]
Total revenue	0	0	0	2,586
Research and development revenue | UNITED STATES
Revenue Recognition [Line Items]
Total revenue	$ 5,732	$ 4,240	$ 45,986	$ 14,557

Research and Development Agre_4

Research and Development Agreements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended			9 Months Ended
	Feb. 28, 2021	Sep. 30, 2018	Sep. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			$ 6,796		$ 4,240	$ 50,290	$ 17,143
Deferred revenue, current			13,210			13,210		$ 45,573
Deferred revenue, long-term								5,904
Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			5,732		4,240	45,986	17,143
Additional Funding Agreement Terms [Member] | Grant
Research And Development Collaboration Agreements [Line Items]
Deferred revenue, current			100			100		200
Grants revenue receivable			0			0		0
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms [Member] | Bristol Myers Squibb
Research And Development Collaboration Agreements [Line Items]
Upfront payment	$ 70,000
Transaction price allocated to performance obligations	70,000
Deferred revenue, current			13,100			13,100		45,300
Deferred revenue, long-term			0			0		5,900
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms [Member] | Bristol Myers Squibb | Maximum [Member]
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised	874,500
Additional milestone payments receivable if option is exercised	$ 450,000
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			5,700		4,200	46,000	14,600
Bristol Myers Squibb Collaboration Agreement | License Agreement Terms, Target Completion [Member] | Bristol Myers Squibb | Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement				$ 25,800
Takeda Multi Target Agreement | License Agreement Terms [Member] | Takeda Pharmaceuticals Inc
Research And Development Collaboration Agreements [Line Items]
Deferred revenue			0			0		$ 0
Takeda Multi Target Agreement | License Agreement Terms [Member] | Takeda Pharmaceuticals Inc | Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			0		0	0	2,600
CPRIT Agreement | Additional Funding Agreement Terms [Member] | Cancer Prevention and Research Institute of Texas | Grant
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement						13,700
Product development grant awarded		$ 15,200
Reimbursement amounts submitted in excess of amounts received are recorded as receivables			$ 1,100		$ 0	$ 4,300	$ 0

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 15,811	$ 32,190	$ 22,277
Marketable securities, current		28,859
Fair Value, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	15,178	58,882
Marketable securities, current		28,859
Fair Value, Recurring [Member] | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	15,178	24,546
Fair Value, Recurring [Member] | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		21,134
Fair Value, Recurring [Member] | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		10,702
Fair Value, Recurring [Member] | Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		2,500
Fair Value, Recurring [Member] | Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	15,178	30,023
Fair Value, Recurring [Member] | 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	15,178	27,046
Fair Value, Recurring [Member] | 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	15,178	24,546
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 1 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 1 | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 1 | Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		2,500
Fair Value, Recurring [Member] | 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	31,836
Fair Value, Recurring [Member] | 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	0
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		21,134
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 2 | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		10,702
Fair Value, Recurring [Member] | Basis of Fair Value Measurements, Level 2 | Cash
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | United States Treasury Bills
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash
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) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Money Market Funds And Commercial Paper
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cost Basis		$ 30,022
Unrealized Gain		1
Unrealized Loss		0
Fair Value		30,023
Money Market Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cost Basis	$ 15,178
Unrealized Gain	0
Unrealized Loss	0
Fair Value	$ 15,178
Commercial Paper And Treasury Bills
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Cost Basis		28,926
Unrealized Gain		0
Unrealized Loss		(67)
Fair Value		$ 28,859

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investments Debt And Equity Securities [Abstract]
Proceeds from sale of available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Available-for-sale securities, realized gain	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements - Conve

Fair Value Measurements - Convertible secured contingent value right (Detail) - Fair Value, Recurring [Member] $ in Thousands	Sep. 30, 2023 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	$ 3,975
Conversion Right and Contingent Value Right
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of financial liabilities	3,975
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	3,975
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	$ 3,975

Fair Value Measurements - Conti

Fair Value Measurements - Contingent Value Right and Common Stock Warrant Valuation (Detail)		3 Months Ended	9 Months Ended
	Jun. 16, 2023 USD ($) item $ / shares shares	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in valuation of contingent value right		$ (881,000)	$ (1,184,000)
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	2,600,000	2,600,000
Fair value of contingent value liability	$ 1,900,000	1,400,000	1,400,000
Change in valuation of contingent value right		$ 900,000	$ 1,200,000
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 - Comp

Balance Sheet Components - Components of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued liabilities:
General and administrative	$ 717	$ 855
Clinical trial related costs	2,126	1,327
Non-clinical research and manufacturing operations	411	1,779
Payroll related	38	4,828
Other accrued expenses	11	34
Total Accrued liabilities	$ 3,303	$ 8,823

Property and Equipment - Compon

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, Gross	$ 34,441	$ 35,978
Less: Accumulated depreciation	(25,863)	(21,346)
Total property and equipment, net	8,578	14,632
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, Gross	20,695	21,831
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, Gross	12,974	12,971
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	$ 658

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Depreciation expense		$ 1,500	$ 2,000	$ 5,500	$ 5,700
Gains (losses) on the disposals of property and equipment	[1]	(76)	$ (28)	(475)	$ (29)
Leasehold Improvements
Property Plant And Equipment [Line Items]
Asset retirement obligation, asset		$ 200		$ 200		$ 300
[1] Loss on disposal of property and equipment was included in interest and other expense, net in the prior year presentation.

Borrowing Arrangements and De_2

Borrowing Arrangements and Debt Extinguishment - Additional Information (Detail)		1 Months Ended		9 Months Ended
	Jun. 16, 2023 USD ($) $ / shares shares	Apr. 30, 2022 USD ($)	May 31, 2020 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Gain on extinguishment of debt				$ 1,795,000
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) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 31, 2022	Sep. 30, 2023	Dec. 31, 2022	Jul. 31, 2022
Lessee Lease Description [Line Items]
Lessee, Operating Lease, Existence of Option to Extend [true false]		true
Lessee, operating leases renewal lease term		7 years
Operating lease liabilities, long term portion		$ 10,396	$ 12,231
Texas | Principal Executive Office [Member] | Scenario, Plan [Member]
Lessee Lease Description [Line Items]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	6 years			5 years
Operating lease liabilities, long term portion	$ 6,700
Lessee, Operating Lease, Lease Not yet Commenced, Extension Renewal Term	7 years
Amount abated in installments from the monthly lease commitments	$ 200
Minimum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term.		3 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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Leases [Abstract]
Operating lease expense	$ 727	$ 684	$ 2,181	$ 1,885
Variable lease expense	153	156	399	367
Total operating lease expense	$ 880	$ 840	$ 2,580	$ 2,252

Leases - Schedule of Balance Sh

Leases - Schedule of Balance Sheets Classification of Leases (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Operating leases
Operating lease right-of-use assets	$ 9,667	$ 11,132
Operating lease liabilities, current	$ 2,416
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities
Operating lease liabilities, non-current	$ 10,396	$ 12,231
Total operating lease liabilities	$ 12,812

Leases - Schedule of Leases Inf

Leases - Schedule of Leases Information (Detail)	Sep. 30, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term, operating leases	4 years 10 months 13 days	5 years 6 months 14 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	Sep. 30, 2023 USD ($)
Lease payments
2023 (remaining)	$ 833
2024	3,369
2025	3,299
2026	2,564
2027	2,636
Thereafter	2,872
Total lease payments	15,573
Less: Imputed interest	(2,761)
Total lease liabilities	$ 12,812

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows operating leases	$ 2,178

Contractual Commitments - Addit

Contractual Commitments - Additional Information (Detail)	Sep. 30, 2023 USD ($)
Other Commitments [Line Items]
Upfront fees unamortized balance included in prepaid asset	$ 0
Contractual obligation	33,400,000
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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,248	$ 2,641	$ 5,342	$ 9,305
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	353	1,381	2,411	4,753
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 895	$ 1,260	$ 2,931	$ 4,552

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
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	$ 6,000
Unrecognized compensation cost related to unvested stock-based awards granted to employees under the equity incentive plans, period for recognition	2 years 6 months
Cash received from stock option exercises	$ 1	$ 33
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

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	4.29%	3.25%	4.03%	2.33%
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days	6 years 29 days
Dividend yield	0%	0%	0%	0%
Volatility	78.85%	83.32%	77.65%	88.70%
Weighted-average fair value of stock options granted	$ 5.82	$ 7.95	$ 5.23	$ 24.90

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity Under Equity Incentive Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding Options Number of Shares, Beginning Balance	562,878	523,411
Number of Shares, Options granted	213,168	194,679
Number of Shares, Options exercised	(192)	(3,106)
Number of shares, Options cancelled	(241,027)	(152,106)
Outstanding Options Number of Shares, Ending Balance	534,827	562,878	523,411
Outstanding Options Number of Shares, Vested and expected to vest, June 30, 2023	534,827
Outstanding Options Number of Shares, Exercisable at June 30, 2023	327,184
Weighted Average Exercise Price, Beginning Balance	$ 115.50	$ 153.11
Weighted Average Exercise Price, Options granted	7.46	33.09
Weighted Average Exercise Price, Options exercised	7.20	10.65
Weighted Average Exercise Price, Options cancelled	82.61	141.63
Weighted Average Exercise Price, Ending Balance	87.30	$ 115.50	$ 153.11
Weighted Average Exercise Price, Vested and expected to vest, June 30, 2023	87.30
Weighted Average Exercise Price, Exercisable at June 30, 2023	$ 118.84
Weighted-Average Remaining Contractual Term, Outstanding	6 years 7 months 9 days	7 years 1 month 2 days	6 years 8 months 19 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest, June 30, 2023	6 years 7 months 9 days
Weighted-Average Remaining Contractual Term, Exercisable at June 30, 2023	5 years 18 days
Aggregate Intrinsic Value, Outstanding	$ 0	$ 0	$ 14,250
Aggregate Intrinsic Value, Vested and expected to vest, June 30, 2023	0
Aggregate Intrinsic Value, Exercisable at June 30, 2023	$ 0

Restructuring Related Expense_2

Restructuring Related Expenses - Additional information (Detail)	Jun. 16, 2023
Restructuring And Related Activities [Abstract]
Restructuring reduced the company workforce	44%

Restructuring Related Expense_3

Restructuring Related Expenses - Summary of Activity for Expenses Related to Restructuring Accruals (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
Restructuring And Related Activities [Abstract]
Restructuring expenses	$ 0	$ 276
Cash payments		$ (276)

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Details) $ / shares in Units, $ in Millions	Jun. 16, 2023 USD ($) Y $ / shares shares	Sep. 30, 2023 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
Class of Warrant or Right, Outstanding		340,222
Issuance of warrants | $	$ 2.3

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - July 2023 Private Placement (Details) $ / shares in Units, $ in Thousands				9 Months Ended
	Aug. 11, 2023	Jul. 17, 2023 USD ($) D $ / shares shares	Jul. 12, 2023 tranche	Sep. 30, 2023 USD ($)	Aug. 10, 2023 shares	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Class of Warrant or Right [Line Items]
Net Proceeds From Issuance Of Private Placement | $				$ 18,383
Warrants, Threshold Percentage of Outstanding Common Stock That can be Issued			19.99%
Reverse stock split ratio	0.66
Stockholders equity | $				$ 6,801		$ (8,678)	$ (15,132)	$ 4,152	$ 26,037	$ 65,662
July 2023 Private Placement
Class of Warrant or Right [Line Items]
Number of Tranches | tranche			2
Number of Calendar Days Following Each Closing | D		30
Maximum common stock shares to be resold					2,839,465
Number of common stock shares to be resold					1,617,365
Number of common stock shares issuable upon exercise of Pre-funded warrants					1,222,100
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 | $		$ 20,000
Net Proceeds From Issuance Of Private Placement | $		$ 18,400
July 2023 Private Placement | Closing of second tranche
Class of Warrant or Right [Line Items]
Shares issued		2,800,000
Gross proceeds form private placement | $		$ 20,000
Measurement Period		12 months
Number of days volume weighted average price of | D		10
July 2023 Private Placement | Closing of second tranche | Minimum
Class of Warrant or Right [Line Items]
Share Price | $ / shares		$ 21.15
Minimum number of shares traded		666,666
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
Exercise price per warrants | $ / shares		$ 7.035
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		1,222,100
July 2023 Private Placement | Second Closing Warrants | Closing of second tranche
Class of Warrant or Right [Line Items]
Share Price | $ / shares		$ 1.875
Exercise price of warrant | $ / shares		$ 7.05
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		5,700,000
Warrant coverage on number of shares of common stock or warrants Sold AND To be Sold		100%
Warrants term		5 years