0001485003-24-000005 | 10-K | XBRL Viewer

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Related-Party Transactions	12 Months Ended
Related-Party Transactions	Dec. 31, 2023
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party TransactionsThe Company has a collaboration and license agreement with Moderna, a significant shareholder (Note 12).

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Background (Details)	Mar. 07, 2023
CARISMA Therapeutics Inc, Legacy, Stockholders \| Carisma Therapeutics Inc.
Background
Exchange ratio of shares of Sesen Bio for each share of Legacy Carisma	0.742
CARISMA Therapeutics Inc, Legacy, Stockholders \| Sesen Bio, Inc. \| Carisma Therapeutics Inc.
Background
Common stock at an exchange ratio	1.8994
Sesen Bio Stockholders \| Sesen Bio, Inc.
Background
Ownership interest held after the merge	25.80%

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Audit Information [Abstract]
Auditor Firm ID	185
Auditor Name	KPMG LLP
Auditor Location	Philadelphia, Pennsylvania

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Noncontrolling interests
Beginning balance (in shares) at Dec. 31, 2021	8,700,885
Beginning balance at Dec. 31, 2021	$ 107,808
Ending balance (in shares) at Dec. 31, 2022	8,700,885
Ending balance at Dec. 31, 2022	$ 107,808
Beginning balance (in shares) at Dec. 31, 2021		2,059,072
Beginning balance at Dec. 31, 2021	(81,784)	$ 2	$ 816	$ 0	$ (96,997)	$ 14,395
Stockholders' Equity (Deficit)
Exercise of stock options (in shares)		158,665
Exercise of stock options (in shares)	106		106
Stock-based compensation	275		275
Unrealized gain (loss) on marketable securities	(41)			(41)
Reclassification to net loss of previous unrealized gain on marketable securities	0
Net loss	(61,226)				(61,226)
Ending balance (in shares) at Dec. 31, 2022		2,217,737
Ending balance at Dec. 31, 2022	$ (142,670)	$ 2	1,197	(41)	(158,223)	14,395
Convertible preferred stock
Conversion of convertible preferred stock and non-controlling interests to common stock (in shares)	(8,700,885)
Conversion of convertible preferred stock and non-controlling interests to common stock	$ (107,808)
Ending balance (in shares) at Dec. 31, 2023	0
Ending balance at Dec. 31, 2023	$ 0
Stockholders' Equity (Deficit)
Exercise of stock options (in shares)	128,716	128,716
Exercise of stock options (in shares)	$ 187		187
Stock-based compensation	2,316		2,316
Unrealized gain (loss) on marketable securities	440			440
Reclassification to net loss of previous unrealized gain on marketable securities	(399)			(399)
Issuance of common stock for cash in pre-closing financing (in shares)		3,730,608
Issuance of common stock for cash in pre-closing financing	30,640	$ 4	30,636
Issuance of common stock upon settlement of convertible promissory note, accrued interest, and related derivative liability (in shares)		5,059,338
Issuance of common stock upon settlement of convertible promissory note, accrued interest, and related derivative liability	42,447	$ 5	42,442
Issuance of common stock to Sesen Bio shareholders in reverse capitalization (in shares)		10,374,272
Issuance of common stock to Sesen Bio shareholders in reverse capitalization	72,044	$ 10	72,034
Conversion of convertible preferred stock and non-controlling interests to common stock (in shares)		18,872,711
Conversion of convertible preferred stock and non-controlling interests to common stock	107,809	$ 19	122,185			(14,395)
Sale of common stock, net of issuance costs (in shares)		226,533
Sale of common stock under Open Market Sales Agreement, net of issuance costs	597		597
Net loss	(86,879)				(86,879)
Ending balance (in shares) at Dec. 31, 2023		40,609,915
Ending balance at Dec. 31, 2023	$ 26,532	$ 40	$ 271,594	$ 0	$ (245,102)	$ 0

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Mar. 07, 2023	Mar. 31, 2024	Dec. 31, 2023	Jun. 06, 2023	Jun. 05, 2023	Apr. 17, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Shares issued in a pre-closing funding (in shares)	3,730,608
Issue price per share (in USD per share)	$ 8.21
Sale of common stock under Open Market Sales Agreement, net of issuance costs	$ 30,600		$ 597
Issuance of common stock upon settlement of convertible promissory note, accrued interest, and related derivative liability (in shares)	5,059,338
Issuance of common stock upon settlement of convertible promissory note, accrued interest, and related derivative liability	$ 35,000		$ 42,447
Shares issued upon conversion of convertible preferred stock and exchangeable shares previously presented as noncontrolling interests (in shares)	18,872,711
Issuance of common stock to Sesen Bio shareholders in reverse capitalization (in shares)	10,374,272
Stock offering, amount						$ 300,000
Common stock, par value (in USD per share)			$ 0.001				$ 0.001
Common stock, shares authorized (in shares)			350,000,000	350,000,000	100,000,000		350,000,000
Preferred stock, shares authorized (in shares)			5,000,000	5,000,000			5,000,000
Preferred stock, par value (in USD per share)			$ 0.001	$ 0.001			$ 0.001
At-The-Market Offering \| Jefferies LLC
Class of Stock [Line Items]
Stock offering, amount						$ 100,000
Sale of stock (in shares)			226,533
Gross proceeds			$ 600
At-The-Market Offering \| Jefferies LLC \| Subsequent Event
Class of Stock [Line Items]
Sale of stock (in shares)		931,250
Gross proceeds		$ 2,400

Moderna Collaboration and License Agreement

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Moderna Collaboration and License Agreement

In January 2022, the Company entered into the Moderna License Agreement, which provides for a broad strategic collaboration to discover, develop and commercialize in vivo engineered CAR-M therapeutics for up to twelve oncology programs. Under the Moderna License Agreement, the Company and Moderna initiate research programs during a research term, focused on the discovery and research of products directed to biological targets. Moderna’s mRNA platform builds on continuous advances in basic and applied mRNA science, delivery technology and manufacturing, and has allowed the development of therapeutics and vaccines for infectious diseases, immuno-oncology, rare diseases, cardiovascular diseases and auto-immune diseases. Moderna has the right to designate up to twelve research targets as development targets. The first five research targets have been designated and all programs are currently in the discovery phase. Moderna funds the cost of the Company's activities in accordance with an agreed research budget. The Company is responsible for discovering and optimizing development candidates, and Moderna is responsible for the clinical development thereafter. Pursuant to the Moderna License Agreement, the Company and Moderna formed a joint steering committee (JSC) that is responsible for the coordination and oversight of all research activities to which the Company is responsible for providing. The JSC is comprised of representatives from the Company and Moderna and with Moderna having final decision-making authority, subject to specified limitations.

During the term of the Moderna License Agreement, the Company and its affiliates are subject to various exclusivity obligations under which the Company is not permitted to research, develop or commercialize particular products outside of the collaboration, including products for use as in vivo therapies in the field of oncology, products directed to any target included in the collaboration, or products containing a polypeptide provided by the Company to Moderna in connection with a research program that are directed to any development target. Additionally, the Company has granted Moderna an exclusive worldwide royalty free license to the Company’s intellectual property associated with the product candidates that permits Moderna to conduct its research and development activities. Upon Moderna’s election of a development target (and payment of a related development target designation milestone) for commencement of pre-clinical development of a product candidate, the Company will grant Moderna an exclusive worldwide, sublicensable royalty bearing license to develop, manufacture and commercialize the product candidate.

Under the terms of the Moderna License Agreement, Moderna made an upfront non-refundable payment of $45.0 million to the Company. Assuming Moderna develops and commercializes 12 products, each directed to a different development target, the Company is eligible to receive up to between $247.0 million and $253.0 million per product in development target designation, development, regulatory and commercial milestone payments. Moderna also will reimburse the Company for all costs incurred by the Company in connection with its research and development activities under the Moderna License Agreement plus a reasonable margin for the respective services performed (with a minimum commitment to reimburse $10.0 million in research and development costs over the first three years from execution of the Moderna License Agreement). The Company is also eligible to receive tiered mid-to-high single digit royalties of net sales of any products that are commercialized under the agreement, which may be, subject to reductions. In addition, Moderna has agreed to cover the cost the Company incurs for certain milestone payments royalties the Company owes as a licensor under one of its intellectual property in-license agreements with Penn that the Company is sublicensing to Moderna under the Moderna License Agreement, which royalties Moderna may deduct in part from any royalties owed to the Company. The Moderna License Agreement terminates on a product-by-product basis upon the latest of expiration of the applicable product patents, expiration of regulatory exclusivity and the tenth anniversary of first commercial sale, unless terminated earlier by the Company or Moderna.

At commencement, the Company identified several potential performance obligations within the Moderna License Agreement, including research and development services on research targets, option rights held by Moderna, a non-exclusive royalty-free license to use the Company’s intellectual property to conduct research and development activities and participation on the JSC. The Company determined that there were 2 performance obligations comprised of (i) research and development services and (ii) option rights.

For the research and development services, the stand-alone selling price was determined considering the expected passthrough costs and cost of the research and development services and a reasonable margin for the respective services. The material rights from the option rights were valued based on the estimated discount at which the option is priced and the Company’s estimated probability of the options’ exercise as of the time of the agreement. The transaction price allocated to research and development services is recognized as collaboration revenues as the research and development services are provided to satisfy the underlying obligation related to the research and development target. The transfer of control occurs over this period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation.

The transaction price of $45.0 million allocated to the options rights, which are considered material rights, will be recognized in the period that Moderna elects to exercise or elects to not exercise its option right to license and commercialize the underlying research and development target.

The Company included the $45.0 million up-front and nonrefundable payment and $73.9 million of variable consideration for expected research and development services to be performed during the five-year contract term, inclusive of passthrough costs, in the transaction price as of the outset of the arrangement. During the year ended December 31, 2023 and 2022, the Company recognized $14.9 million and $9.8 million, respectively, of research and development services as collaboration revenues as the Company is the principal in providing such services. The Company recognized $24.7 million of collaboration revenues since inception of the Moderna License Agreement through December 31, 2023. The following table includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied as of December 31, 2023 (in thousands):


	Transaction price unsatisfied
Performance obligations:
Research and development	$	49,183
Option rights	45,000
Total performance obligations	$	94,183

Amounts due to the Company for satisfying the revenue recognition criteria or that are contractually due based upon the terms of the collaboration agreements are recorded as accounts receivable in the Company’s consolidated balance sheets. Contract liabilities consist of amounts received prior to satisfying the revenue recognition criteria, which are recorded as deferred revenue in the Company’s consolidated balance sheets.

The following table summarizes the changes in deferred revenue (in thousands):


	Year Ended December 31,
	2023		2022
Balance at the beginning of the period	$	47,459	$	—
Deferral of revenue	13,873		57,293
Recognition of unearned revenue	(14,919)		(9,834)
Balance at the end of the period	$	46,413	$	47,459

The current portion of deferred revenue represents advanced payments received from Moderna for costs expected to be incurred by the Company within the next twelve months. The noncurrent portion of deferred revenue represents the $45.0 million upfront, non-refundable and non-creditable payment allocated to customer option right which is not expected to be recognized within the next 12 months.

- Definition

The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Development-Stage Risks and Liquidity	12 Months Ended
Development-Stage Risks and Liquidity	Dec. 31, 2023
Development-Stage Risks and Liquidity
Development-Stage Risks and Liquidity	Development-Stage Risks and Liquidity The accompanying consolidated financial statements have been prepared on a going-concern basis, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. The Company has incurred losses and negative cash flows from operations since inception and has an accumulated deficit of $245.1 million as of December 31, 2023. The Company anticipates incurring additional losses until such time, if ever, that it can generate significant sales from its product candidates currently in development. As of December 31, 2023, the Company had $77.6 million of cash and cash equivalents. Absent any other action, the Company would have required additional liquidity to continue its operations over the next 12 months, which would have raised substantial doubt about its ability to continue as a going concern. As discussed in Note 1, Background, in March 2024, the Company and its board of directors approved a revised operating plan that suspends certain development programs, reduces its workforce and decreases other non-essential activities to extend the Company’s cash runway. The Company projects this revised operating plan will alleviate the substantial doubt that has been raised by significantly decreasing expenses, thereby reducing ongoing liquidity needs to enable the continuation of operations for at least 12 months from the issuance date of these consolidated financial statements. The Company is subject to those risks associated with any specialty biotechnology company that has substantial expenditures for research and development. There can be no assurance that the Company’s research and development projects will be successful, that products developed will obtain necessary regulatory approval, or that any approved product will be commercially viable. In addition, the Company operates in an environment of rapid technological change and is largely dependent on the services of its employees and consultants.

Stock-based Compensation - Schedule of Estimated Using The Black-Scholes Option-Pricing Model (Details) - Stock options	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Stock-based Compensation
Expected term	6 years	6 years
Expected dividend yield	0.00%	0.00%
Minimum
Stock-based Compensation
Risk-free interest rate	2.92%	2.40%
Expected volatility	57.77%	54.54%
Maximum
Stock-based Compensation
Risk-free interest rate	4.76%	3.05%
Expected volatility	103.00%	56.50%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Income Taxes - Narratives (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes - Narratives (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 84.5	$ 13.7
Research and Development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, amount	9.9
Federal
Operating Loss Carryforwards [Line Items]
NOL carryforwards	317.6
State
Operating Loss Carryforwards [Line Items]
NOL carryforwards	229.4
Local
Operating Loss Carryforwards [Line Items]
NOL carryforwards	40.8
Pre-2018 \| Federal
Operating Loss Carryforwards [Line Items]
NOL carryforwards	120.0
Post-2017 \| Federal
Operating Loss Carryforwards [Line Items]
NOL carryforwards	197.6
Expiring in 2023 \| Local
Operating Loss Carryforwards [Line Items]
NOL carryforwards	$ 29.7

Summary of Significant Accounting Policies - Schedule of The Changes in Fair Value of Derivative Liability Associated With The Redemption Feature of Convertible Promissory Note (Details) - Derivative liability - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Changes in fair value of derivative liabilities
Balance at the beginning of the period	$ 5,739	$ 0
Balance at issuance	0	3,820
Change in fair value	84	1,919
Derecognition upon conversion of convertible promissory note	(5,823)	0
Balance at the end of the period	$ 0	$ 5,739

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	December 31,
	2023		2022
Research and development	$	3,131	$	4,326
Professional fees	1,366		2,100
Compensation and related expenses	3,100		2,809
Interest	—		1,126
Other	65		—
	$	7,662	$	10,361

Commitments and Contingencies - Narratives (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies
Financing liability		$ 872
Accrued settlement		200
Lab equipment
Commitments and Contingencies
Proceeds from sale and leaseback transactions		1,200	$ 1,600
Financing liability		1,900
Penn License Agreement \| Penn
Commitments and Contingencies
Annual payments to be made		25,000
Additional milestone payments for first CAR-M product		1,700
Penn License Agreement \| Penn \| Maximum
Commitments and Contingencies
Milestone payments		10,900
Additional milestone payments		$ 30,000
Novartis Agreement
Commitments and Contingencies
Agreement term	5 years
Renewal term	1 year
Amount payable per calendar year for reserved capacity	$ 1,000
Termination fee payable	$ 4,000

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Schedule of Fair Value Hierarchy of Assets and Liabilities Measured on Recurring Basis

The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis:


(in thousands)	Fair value measurement at reporting date using
	(Level 1)		(Level 2)		(Level 3)
December 31, 2023
Assets:
Cash equivalents – money markets accounts	$	62,999	$	—	$	—
December 31, 2022
Assets:
Cash equivalents – money markets accounts	$	7,794	$	—	$	—
Marketable securities – U.S. Treasuries	$	27,802	$	—	$	—
Liability:
Derivative liability – redemption feature on convertible promissory note	$	—	$	—	$	5,739

Schedule of Marketable Securities

The following is a summary of the Company’s available-for-sale marketable securities as of December 31, 2022:


	Amortized cost		Gross unrealized loss		Fair value
U.S. Treasury securities	$	27,843	$	(41)	$	27,802

Schedule of The Changes in Fair Value of Derivative Liability Associated With The Redemption Feature of Convertible Promissory Note

The table presented below is a summary of the changes in fair value of the Company’s derivative liability associated with the redemption feature of the Company’s convertible promissory note (Level 3 measurement):


(in thousands)	Year Ended December 31,
	2023		2022
Balance at the beginning of the period	$	5,739	$	—
Balance at issuance	—		3,820
Change in fair value	84		1,919
Derecognition upon conversion of convertible promissory note	(5,823)		—
Balance at the end of the period	$	—	$	5,739

Schedule of Anti-Dilutive Securities

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares of common stock outstanding, as they would be anti-dilutive:


	December 31,
	2023	2022
Convertible preferred stock and exchangeable shares	—	9,936,148
Stock options	6,023,370	3,356,937
Conversion of convertible promissory note	—	3,258,151
	6,023,370	16,551,236

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP). Any references in these notes to applicable guidance is meant to refer to GAAP as found in Accounting Standards Codification (ASC) and Accounting Standards Update (ASU) promulgated by the Financial Accounting Standards Board (FASB).

The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from such estimates. Estimates and assumptions are periodically reviewed, and the effects of revisions are reflected in the consolidated financial statements in the period they are determined to be necessary.

Significant areas that require management’s estimates include the fair value of the Company’s common stock and the derivative liability prior to the Merger, stock-based compensation assumptions, the estimated useful lives of property and equipment, and accrued research and development expenses.

Fair Value of Financial Instruments

Management believes that the carrying amounts of the Company’s financial instruments, including cash equivalents and accounts payable, approximate fair value due to the short-term nature of those instruments. The Company considered the carrying value of its convertible promissory note (Note 8) as of December 31, 2022 to approximate fair value due to its short-term nature. The derivative liability was recorded at its estimated fair value prior to its derecognition in March 2023 upon conversion of the associated convertible promissory notes.

Fair Value Measurements

The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines fair value based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels:

•Level 1 Inputs: Unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date.

•Level 2 Inputs: Other than quoted prices included in Level 1 inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability.

•Level 3 Inputs: Unobservable inputs for the asset or liability used to measure fair value to the extent that observable inputs are not available, thereby allowing for situations in which there is little, if any, market activity for the asset or liability at the measurement date.

The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis:


(in thousands)	Fair value measurement at reporting date using
	(Level 1)		(Level 2)		(Level 3)
December 31, 2023
Assets:
Cash equivalents – money markets accounts	$	62,999	$	—	$	—
December 31, 2022
Assets:
Cash equivalents – money markets accounts	$	7,794	$	—	$	—
Marketable securities – U.S. Treasuries	$	27,802	$	—	$	—
Liability:
Derivative liability – redemption feature on convertible promissory note	$	—	$	—	$	5,739

As of December 31, 2023, the Company had no marketable securities. The following is a summary of the Company’s available-for-sale marketable securities as of December 31, 2022:


	Amortized cost		Gross unrealized loss		Fair value
U.S. Treasury securities	$	27,843	$	(41)	$	27,802

The Company evaluated a redemption feature within the convertible promissory note issued in January 2022 and determined bifurcation of the redemption feature was required. The redemption feature is classified as a liability on the accompanying consolidated balance sheet and is marked-to-market each reporting period with the changes in fair value

recorded in the accompanying statements of operations until it is triggered, terminated, reclassified or otherwise settled. The fair value of the derivative was determined based on an income approach that identified the cash flows using a with-and-without valuation methodology. The inputs used to determine the estimated fair value of the derivative instrument were based primarily on the probability of an underlying event triggering the embedded derivative occurring and the timing of such event.

During the year ended December 31, 2022, the discount factor used was 12% and a 90% to 100% probability of completing a qualified financing prior to the maturity date of the convertible promissory note was assumed. The estimated time of conversion ranged from three to twelve months.


(in thousands)	Year Ended December 31,
	2023		2022
Balance at the beginning of the period	$	5,739	$	—
Balance at issuance	—		3,820
Change in fair value	84		1,919
Derecognition upon conversion of convertible promissory note	(5,823)		—
Balance at the end of the period	$	—	$	5,739

During the year ended December 31, 2023 and 2022, there were no transfers between Level 1, Level 2 and Level 3.

Revenue Recognition

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers (ASC 606). This standard applies to all contracts with customers, except for contracts that are within the scope of other standards. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services.

The Company enters into collaboration and licensing agreements with strategic partners, which are within the scope of ASC 606, under which it may exclusively license rights to research, develop, manufacture, and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: (1) non-refundable, upfront license fees (2) reimbursement of certain costs; (3) customer option fees for additional goods or services; (4) development milestone payments, (5) regulatory and commercial milestone payments; and (6) royalties on net sales of licensed products.

In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use its judgment to determine: (a) the number of performance obligations based on the determination under step (i) above; (b) the transaction price under step (iii) above; (c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above; and (d) the contract term and pattern of satisfaction of the performance obligations under step (v) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied.

Upfront license fees

If the license to the Company's intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, manufacturing, and commercialization capabilities of the customer; the retention of any key rights by the Company; and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the customer can benefit from a promise for its intended purpose without the receipt of the remaining promises, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company exercises judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

Customer options

The Company evaluates the customer options for material rights or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. If an option is not exercised and the research and development target is terminated, the Company will accelerate and recognize all remaining revenue related to the material right performance obligation.

Research and development services

The promises under the Company's collaboration agreements may include research and development services to be performed by the Company for or on behalf of the customer. Payments or reimbursements resulting from the Company's research and development efforts are recognized as the services are performed and presented on a gross basis because the Company is the principal for such efforts. Reimbursements from and payments to the customer that are the result of a collaborative relationship with the customer, instead of a customer relationship, such as co-development activities, are recorded as a reduction to research and development expense.

Milestone payments

At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

Concentration of credit risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash and cash equivalents.

Segment information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one segment.

Cash and Cash Equivalents

The Company considers all highly-liquid investments that have maturities of three months or less when acquired to be cash equivalents. As of December 31, 2023 and 2022, cash equivalents consisted of investments in a money market account. The Company maintained $30,000 as collateral for the Company’s credit card program at September 30, 2023, which was previously reported as restricted cash on its consolidated balance sheet. There were no amounts restricted as of December 31, 2023 and 2022, as the collateral was released to the Company in the fourth quarter of 2023.

Marketable Securities

The Company's marketable securities consisted of investments in U.S. Treasuries that were classified as available-for-sale. The securities were carried at fair value with the unrealized gains and losses included in accumulated other comprehensive loss, a component of stockholders' equity (deficit). Realized gains and losses and declines in value determined to be other than temporary were included in the Company's consolidated statements of operations.

Property and Equipment

Property and equipment are carried at cost less accumulated depreciation and amortization. Depreciation and amortization are calculated using the straight-line method over the estimated useful lives of the assets ranging from two to five years. Leasehold improvements are amortized over the shorter of the life of the lease or the estimated useful life of the assets. Lab equipment that are classified as finance leases are amortized over the lease term.

Long-lived Assets

Long-lived assets, such as property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. When events indicate a triggering event occurred, the recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, then an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. Considerable management judgment is necessary to estimate discounted future cash flows. Accordingly, actual results could vary significantly from such estimates.

The Company did not recognize any impairment of long-lived assets during the years ended December 31, 2023 or 2022.

Deferred Financing Costs

The Company capitalizes costs that are directly associated with in-process equity financings until such financings are consummated, at which time such costs are recorded against the gross proceeds from the applicable financing. If a financing is abandoned, deferred financing costs are expensed immediately. The Company incurred $4.2 million and $4.1 million in deferred financing costs associated with the Merger during the years ended December 31, 2023 and 2022, respectively. Upon completion of the Merger, the $8.3 million of deferred financing costs were recorded against the gross proceeds received as a result of the Merger.

Leases

The Company determines whether an arrangement is or contains a lease, its classification, and its term at the lease commencement date. Leases with a term greater than one year will be recognized on the balance sheet as right-of-use (ROU) assets, current lease liabilities, and if applicable, long-term lease liabilities. The Company includes renewal options to extend the lease term where it is reasonably certain that it will exercise these options. Lease liabilities and the corresponding ROU assets are recorded based on the present values of lease payments over the lease term. The interest rate

implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rates, which are the rates that would be incurred to borrow on a collateralized basis, over similar terms, amounts equal to the lease payments in a similar economic environment. Payments for non-lease components or that are variable in nature that do not depend on a rate or index are not included in the lease liability and are typically expensed as incurred. If significant events, changes in circumstances, or other events indicate that the lease term or other inputs have changed, the Company would reassess lease classification, remeasure the lease liability using revised inputs as of the reassessment date, and adjust the ROU assets. Lease expense is recognized on a straight-line basis over the expected lease term for operating classified leases.

Noncontrolling Interest

To the extent that ownership interests in the Company’s subsidiary are held by entities other than the Company, management reports these as noncontrolling interests on the consolidated balance sheet. Prior to the Merger, an investor had outstanding Class B and Class B-1 shares in the Company’s Luxembourg subsidiary related to the sale of the Company’s Series A convertible preferred stock (Series A) and Series B convertible preferred stock (Series B). The shares were nonvoting shares at the subsidiary entity level and were presented as noncontrolling interests in the accompanying consolidated balance sheet at December 31, 2022. In connection with the Merger, the Company's noncontrolling interests exchangeable shares converted into shares of common stock (Note 8).

Research and Development Costs

Research and development costs are charged to expense as incurred. Up-front and milestone payments made to third parties who perform research and development services on the Company's behalf are expensed as services are rendered.

Stock-Based Compensation

The Company measures stock-based awards, including stock options, at their grant-date fair value and records compensation expense over the requisite service period, which is the vesting period of the awards. The Company accounts for forfeitures as they occur.

Estimating the fair value of stock options requires the use of subjective assumptions, including the fair value of the Company's common stock prior to the Merger, and, for stock options, the expected term of the option and expected stock price volatility. The Company uses the Black-Scholes option-pricing model to value its stock option awards. The assumptions used in calculating the fair value of stock options represent management's best estimates and involve inherent uncertainties and the application of management's judgment. As a result, if factors change and management uses different assumptions, stock-based compensation expense could be materially different for future awards.

Prior to the Merger, the fair value of the Company's common stock was estimated by the Company's board of directors, with input by management considering the Company's most recently available third-party valuation of the Company's common stock. The expected term of stock options for employees is estimated using the simplified method, as the Company has limited historical information to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. The simplified method is the midpoint between the vesting date and the contractual term of the option. The contractual term is used as the expected term for stock options granted to nonemployees. For stock price volatility, the Company uses comparable public companies as a basis for the expected volatility to calculate the fair value of option grants. The risk-free rate is based on the U.S. Treasury yield curve commensurate with the expected term of the option. The expected dividend yield is zero given the Company does not expect to pay dividends for the foreseeable future.

Income taxes

Income taxes are accounted for under the asset and liability method. The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of the Company's assets and liabilities, and the expected benefits of net operating loss and income tax credit carryforwards. The impact of changes in tax rates and laws on deferred taxes, if any, applied during the period in which temporary differences are expected to be settled, is reflected in the Company's consolidated financial statements in the period of enactment. The measurement of deferred tax assets is reduced, if necessary, if, based on weight of the evidence, it is more likely than not that some, or all,

of the deferred tax assets will not be realized. As of December 31, 2023 and 2022, the Company has concluded that a full valuation allowance is necessary for all of its net deferred tax assets. The Company had no amounts recorded for uncertain tax positions, interest, or penalties in the accompanying consolidated financial statements. Although there are no unrecognized income tax benefits, when applicable, the Company’s policy is to report interest and penalties related to unrecognized income tax benefits as a component of income tax expense.

Net loss per share

Basic net loss per share of common stock is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during each period. Diluted net loss per share of common stock includes the effect, if any, from the potential exercise or conversion of securities, such as convertible preferred stock and stock options, which would result in the issuance of incremental shares of common stock. For diluted net loss per share, the weighted-average number of shares of common stock is the same for basic net loss per share due to the fact that when a net loss exists, potentially dilutive securities are not included in the calculation as their impact is anti-dilutive.

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares of common stock outstanding, as they would be anti-dilutive:


	December 31,
	2023	2022
Convertible preferred stock and exchangeable shares	—	9,936,148
Stock options	6,023,370	3,356,937
Conversion of convertible promissory note	—	3,258,151
	6,023,370	16,551,236

Recently adopted accounting pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), which requires financial assets measured at amortized cost basis to be presented at the net amount expected to be collected. This standard is effective for fiscal years beginning after December 15, 2022. The Company adopted the guidance using a modified retrospective approach as of January 1, 2023 which resulted in no cumulative-effect adjustment to accumulated deficit and did not have a material impact on the Company’s consolidated financial statements.

Recently issued but not yet adopted accounting pronouncements

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07), which requires disclosure of incremental segment information on an annual and interim basis. This ASU is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024 on a retrospective basis. The Company is currently evaluating the effect of this pronouncement on its disclosures.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09), which expands the disclosures required for income taxes. This ASU is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. The amendment should be applied on a prospective basis while retrospective application is permitted. The Company is currently evaluating the effect of this pronouncement on its disclosures.

Property and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 12,915	$ 11,942
Less: accumulated depreciation and amortization	(6,151)	(3,314)
Property and equipment, net	6,764	8,628
Finance lease, accumulated amortization	1,700	600
Computer software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	903	1,062
Lab equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,392	10,260
Sale lease-back asset	3,400	2,600
Finance lease, ROU assets	2,900	2,900
Sale leaseback transaction, accumulated depreciation	900	300
Office furniture
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	267	267
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	340	340
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 13	$ 13

Income Taxes- Schedule of Deferred Tax Assets for Federal Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Net operating losses	$ 72,689	$ 27,021
Capitalized research and development costs, net of amortization	33,778	11,907
Research and development credits	9,746	5,643
Start-up costs	4,407	4,744
Deferred revenue	13,353	0
Lease liability	668	1,451
Amortizable assets and other	21	59
Equity compensation	87	74
Gross deferred tax assets	134,749	50,899
Valuation allowance	(133,580)	(49,105)
Deferred tax assets, net of valuation allowance	1,169	1,794
Deferred tax liabilities
Right of use asset	(645)	(1,430)
Depreciation	(524)	(364)
Deferred tax liabilities	(1,169)	(1,794)
Net deferred tax assets and liabilities	$ 0	$ 0

Commitments and Contingencies - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	$ 5,764	$ 4,750
Operating cash used in finance leases	139	98
Financing cash used in finance leases	$ 1,301	$ 865

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal tax benefit at statutory rate	(21.00%)	(21.00%)
State and local tax, net of federal benefit	(8.50%)	(7.80%)
State and local tax rate change	1.60%	6.20%
Permanent differences	0.40%	2.00%
Research and development	(0.90%)	(2.90%)
Change in valuation allowance	28.40%	22.40%
Return to provision	0.00%	1.10%
Total provision	0.00%	0.00%

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation and Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

Fair Value of Financial Instruments

Fair Value Measurements

•Level 1 Inputs: Unadjusted quoted prices in active markets for identical assets or liabilities accessible to the reporting entity at the measurement date.

The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis:


(in thousands)	Fair value measurement at reporting date using
	(Level 1)		(Level 2)		(Level 3)
December 31, 2023
Assets:
Cash equivalents – money markets accounts	$	62,999	$	—	$	—
December 31, 2022
Assets:
Cash equivalents – money markets accounts	$	7,794	$	—	$	—
Marketable securities – U.S. Treasuries	$	27,802	$	—	$	—
Liability:
Derivative liability – redemption feature on convertible promissory note	$	—	$	—	$	5,739

As of December 31, 2023, the Company had no marketable securities. The following is a summary of the Company’s available-for-sale marketable securities as of December 31, 2022:


	Amortized cost		Gross unrealized loss		Fair value
U.S. Treasury securities	$	27,843	$	(41)	$	27,802


(in thousands)	Year Ended December 31,
	2023		2022
Balance at the beginning of the period	$	5,739	$	—
Balance at issuance	—		3,820
Change in fair value	84		1,919
Derecognition upon conversion of convertible promissory note	(5,823)		—
Balance at the end of the period	$	—	$	5,739

During the year ended December 31, 2023 and 2022, there were no transfers between Level 1, Level 2 and Level 3.

Revenue Recognition

Upfront license fees

Customer options

Research and development services

Milestone payments

Concentration of credit risk

Segment information

Cash and Cash Equivalents

Marketable Securities

Property and Equipment

Long-lived Assets

The Company did not recognize any impairment of long-lived assets during the years ended December 31, 2023 or 2022.

Deferred Financing Costs

Leases

Noncontrolling Interest

Research and Development Costs

Stock-Based Compensation

Income taxes

Net loss per share

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares of common stock outstanding, as they would be anti-dilutive:


	December 31,
	2023	2022
Convertible preferred stock and exchangeable shares	—	9,936,148
Stock options	6,023,370	3,356,937
Conversion of convertible promissory note	—	3,258,151
	6,023,370	16,551,236

Recently adopted accounting pronouncements and Recently issued but not yet adopted accounting pronouncements

Recently adopted accounting pronouncements

Recently issued but not yet adopted accounting pronouncements

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (86,879)	$ (61,226)
Adjustment to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization expense	2,837	1,893
Loss on disposal of property and equipment	159	0
Stock-based compensation expense	2,316	275
Reduction in the operating right of use assets	5,428	4,197
Amortization of debt discount	1,283	2,537
Change in fair value of derivative liability	84	1,919
Accretion on marketable securities	(709)	0
Realized gain on marketable securities	(399)	0
Non-cash interest expense	139	93
Changes in operating assets and liabilities:
Prepaid expenses and other assets	1,046	(1,361)
Accounts payable	2,191	(473)
Accrued expenses	(2,899)	4,230
Deferred revenue	(1,046)	47,459
Operating lease liabilities	(4,941)	(4,659)
Other long term liabilities	213	0
Net cash used in operating activities	(81,177)	(5,116)
Cash flows from investing activities:
Purchase of marketable securities	(34,460)	(90,900)
Proceeds from the sale of marketable securities	108,000	63,000
Purchases of property and equipment	(1,132)	(4,660)
Net cash provided by (used in) investing activities	72,408	(32,560)
Cash flows from financing activities:
Cash, cash equivalents and restricted cash acquired in connection with the reverse recapitalization	37,903	0
Payment of reverse recapitalization finance costs	(5,814)	0
Proceeds from the issuance of common stock in pre-closing financing	30,640	0
Payment of principal related to finance lease liabilities	(1,301)	(865)
Proceeds from failed sale-leaseback arrangement	1,183	1,626
Payment of finance liability from failed sale-leaseback arrangements	(1,069)	(98)
Payment of deferred financing costs	(146)	(2,450)
Proceeds from issuance of convertible promissory note	0	35,000
Proceeds from the exercise of stock options	187	106
Sale of common stock under Open Market Sales Agreement, net of issuance costs	597	0
Net cash provided by financing activities	62,180	33,319
Net increase (decrease) in cash and cash equivalents	53,411	(4,357)
Cash and cash equivalents at beginning of the year	24,194	28,551
Cash and cash equivalents at end of the year	77,605	24,194
Supplemental disclosures of cash flow information:
Cash paid for interest	352	98
Supplemental disclosure of non-cash financing and investing activities:
Conversion of convertible preferred stock and non-controlling interests upon Merger	122,204	0
Conversion of convertible promissory note, accrued interest and derivative liability upon Merger	42,447	0
Unrealized gain (loss) on marketable securities	41	(41)
Deferred financing costs in accrued expenses	0	1,661
Right-of-use assets obtained in exchange for new operating lease liabilities	2,779	6,440
Right-of-use assets obtained in exchange for new financing lease liabilities	0	2,898
Allocation of debt proceeds to derivative liability	$ 0	$ 3,820

Commitments and Contingencies - Schedule of Lease Term and Discount Rate Information (Details)	Dec. 31, 2023	Dec. 31, 2022
Weighted-average remaining lease term (in years)
Operating leases	2 years 7 months 6 days	2 years 2 months 12 days
Finance leases	1 year 6 months	2 years 2 months 12 days
Weighted-average discount rate
Operating leases	9.80%	9.40%
Finance leases	9.00%	9.00%

Moderna Collaboration and License Agreement - Schedule of Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Movement in Deferred Revenue [Roll Forward]
Balance at the beginning of the period	$ 47,459	$ 0
Deferral of revenue	13,873	57,293
Recognition of unearned revenue	(14,919)	(9,834)
Balance at the ending of the period	$ 46,413	$ 47,459

Moderna Collaboration and License Agreement - Narratives (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2022 USD ($) target product	Dec. 31, 2023 USD ($) obligation	Dec. 31, 2022 USD ($)
Moderna Collaboration and License Agreement
Research and development services as collaboration revenues		$ 14,900	$ 9,800
Collaboration revenues		$ 14,919	$ 9,834
Collaboration and License Agreement \| Research and Development Services
Moderna Collaboration and License Agreement
Upfront non-refundable payment received	$ 45,000
Variable consideration	$ 73,900
Term of contract	5 years
Noncurrent portion of deferred revenue	$ 45,000
Collaboration and License Agreement \| Moderna
Moderna Collaboration and License Agreement
Maximum of research targets \| target	12
Number of research targets, designate as development targets \| target	12
Number of research targets designated \| target	5
Collaboration and License Agreement \| Moderna \| Research and Development Services
Moderna Collaboration and License Agreement
Upfront non-refundable payment received	$ 45,000
Number of products developed and commercialized \| product	12
Minimum commitment to reimburse research and development costs	$ 10,000
Period of reimbursement of research and development costs	3 years
Number of performance obligations \| obligation		2
Collaboration and License Agreement \| Moderna \| Minimum \| Research and Development Services
Moderna Collaboration and License Agreement
Amount receivable per product	$ 247,000
Collaboration and License Agreement \| Moderna \| Maximum \| Research and Development Services
Moderna Collaboration and License Agreement
Amount receivable per product	$ 253,000
Moderna License Agreement
Moderna Collaboration and License Agreement
Collaboration revenues		$ 24,700

Merger with Sesen Bio

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Merger with Sesen Bio

On March 7, 2023, Legacy Carisma completed the Merger with Sesen Bio as discussed in Note 1. The Merger was accounted for as a reverse recapitalization under GAAP because the primary assets of Sesen Bio were cash, cash equivalents and marketable securities. For financial reporting purposes Legacy Carisma was determined to be the accounting acquirer based upon the terms of the Merger and other factors, including: (i) Legacy Carisma stockholders own approximately 74.2% of the Combined Company, (ii) Legacy Carisma holds the majority (six of seven) of board seats of

the Combined Company and (iii) Legacy Carisma management holds all key positions of management. Accordingly, the Merger was treated as the equivalent of Legacy Carisma issuing stock to acquire the net assets of Sesen Bio. As a result of the Merger, the net assets of Sesen Bio were recorded at their acquisition-date fair value in the consolidated financial statements and the reported operating results prior to the Merger are those of Legacy Carisma. Immediately after the Merger, there were 40,254,666 shares of the Company’s common stock outstanding.

The following table shows the net assets acquired in the Merger (in thousands):


	March 7, 2023
Cash and cash equivalents	$	37,873
Marketable securities	44,588
Prepaid expenses and other assets	1,316
Restricted cash	30
Accounts payable and accrued expenses	(3,499)
Total net assets acquired	80,308
Less: Transaction costs	(8,264)
Total net assets acquired less transaction costs	$	72,044

Subsequent to March 7, 2023, the Company paid $4.6 million of severance and personnel costs related to Sesen Bio.

Summary of Significant Accounting Policies - Schedule of Fair Value Hierarchy of Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023
Liability:
Derivative Liability Statement Of Financial Position Extensible Enumeration Not Disclosed Flag	Derivative liability – redemption feature on convertible promissory note
Recurring \| Level 1
Assets:
Cash equivalents – money markets accounts	$ 7,794	$ 62,999
Marketable securities – U.S. Treasuries	27,802
Liability:
Derivative liability – redemption feature on convertible promissory note	0
Recurring \| Level 2
Assets:
Cash equivalents – money markets accounts	0	0
Marketable securities – U.S. Treasuries	0
Liability:
Derivative liability – redemption feature on convertible promissory note	0
Recurring \| Level 3
Assets:
Cash equivalents – money markets accounts	0	$ 0
Marketable securities – U.S. Treasuries	0
Liability:
Derivative liability – redemption feature on convertible promissory note	$ 5,739

Moderna Collaboration and License Agreement (Tables)

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Schedule of Estimated Revenue Expected to be Recognized in The Future Related to Performance Obligations

The following table includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied as of December 31, 2023 (in thousands):


	Transaction price unsatisfied
Performance obligations:
Research and development	$	49,183
Option rights	45,000
Total performance obligations	$	94,183

Schedule of Changes in Deferred Revenue

The following table summarizes the changes in deferred revenue (in thousands):


	Year Ended December 31,
	2023		2022
Balance at the beginning of the period	$	47,459	$	—
Deferral of revenue	13,873		57,293
Recognition of unearned revenue	(14,919)		(9,834)
Balance at the end of the period	$	46,413	$	47,459

Commitments and Contingencies - Schedule of Future Maturities of Lease Liabilities (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Operating Leases
2024	$ 1,510
2025	219
2026	226
2027	233
2028	240
Thereafter	184
Total future minimum payments	2,612
Less imputed interest	(361)
Present value of lease liabilities	2,251
Finance Leases
2024	600
2025	339
2026	0
2027	0
2028	0
Thereafter	0
Total future minimum payments	939
Less imputed interest	(67)
Present value of lease liabilities	$ 872

Development-Stage Risks and Liquidity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Development-Stage Risks and Liquidity
Accumulated deficit	$ 245,102	$ 158,223
Cash, cash equivalents and marketable securities	$ 77,600

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

A reconciliation of income tax benefit at the statutory federal income tax rate and income taxes as reflected in the consolidated financial statements is as follows:


	Year Ended December 31,
	2023		2022
Federal tax benefit at statutory rate	(21.0)	%	(21.0)	%
State and local tax, net of federal benefit	(8.5)		(7.8)
State and local tax rate change	1.6		6.2
Permanent differences	0.4		2.0
Research and development	(0.9)		(2.9)
Change in valuation allowance	28.4		22.4
Return to provision	—		1.1
Total provision	—	%	—	%

Deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates in effect for years in which differences are expected to reverse.

Significant components of the Company's deferred tax assets for federal income taxes consisted of the following (in thousands):


	December 31,
	2023		2022
Deferred tax assets
Net operating losses	$	72,689	$	27,021
Capitalized research and development costs, net of amortization	33,778		11,907
Research and development credits	9,746		5,643
Start-up costs	4,407		4,744
Deferred revenue	13,353		—
Lease liability	668		1,451
Amortizable assets and other	21		59
Equity compensation	87		74
Gross deferred tax assets	134,749		50,899
Valuation allowance	(133,580)		(49,105)
Deferred tax assets, net of valuation allowance	1,169		1,794

Deferred tax liabilities
Right of use asset	(645)		(1,430)
Depreciation	(524)		(364)
Deferred tax liabilities	(1,169)		(1,794)
Net deferred tax assets and liabilities	$	—	$	—

As of December 31, 2023, the Company has net operating loss carryforwards (NOLs) for federal income tax purposes of $317.6 million, which are available to offset future federal taxable income. The pre-2018 federal NOLs of $120.0 million will begin to expire in 2037, if not utilized. The post-2017 federal NOLs of $197.6 million carry forward indefinitely. The Company also has NOLs for state and local income tax purposes of $229.4 million and $40.8 million, respectively that are available to offset future taxable income. The state NOLs will begin to expire in 2038 while the city of Philadelphia NOLs expire after three years with $29.7 million expiring in 2023. As of December 31, 2023, the Company also had federal and state research and development tax credit carryforwards of $9.9 million that will begin to expire in 2029, unless previously utilized.

In assessing the need for a valuation allowance, management must determine that there will be sufficient taxable income to allow for the realization of deferred tax assets. Based upon the historical and anticipated future losses, management has determined that the deferred tax assets do not meet the more-likely-than-not threshold for realizability. Accordingly, a full valuation allowance has been recorded against the Company's net deferred tax assets as of December 31, 2023. The valuation allowance increased by $84.5 million and $13.7 million during the years ended December 31, 2023 and 2022, respectively.

The NOLs and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOLs and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50 percent, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has not done an analysis to determine whether or not ownership changes have occurred since inception. Certain state NOLs may also be limited, including Pennsylvania, which limits net operating loss utilization as a percentage of apportioned taxable income.

The Company will recognize interest and penalties related to uncertain tax positions as a component of income tax expense/(benefit). As of December 31, 2023, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company's financial statements. Tax years from 2019 and after remain subject to examination by all of the taxing jurisdictions. The NOLs and research credit carryforwards remain subject to review until utilized.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Collaboration revenues	$ 14,919	$ 9,834
Operating expenses:
Research and development	74,125	56,618
General and administrative	29,525	9,378
Total operating expenses	103,650	65,996
Operating loss	(88,731)	(56,162)
Change in fair value of derivative liability	(84)	(1,919)
Interest income (expense), net	1,936	(3,145)
Net loss	$ (86,879)	$ (61,226)
Share information:
Net loss per share of common stock, basic (in USD per share)	$ (2.59)	$ (28.77)
Net loss per share of common stock, diluted (in USD per share)	$ (2.59)	$ (28.77)
Weighted-average shares of common stock outstanding, basic (in shares)	33,524,197	2,128,069
Weighted-average shares of common stock outstanding, diluted (in shares)	33,524,197	2,128,069
Comprehensive loss
Net loss	$ (86,879)	$ (61,226)
Unrealized gain (loss) on marketable securities	440	(41)
Less: reclassification to net loss of previous unrealized gain on marketable securities	(399)	0
Comprehensive loss	$ (86,838)	$ (61,267)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Research and development	$ 3,131	$ 4,326
Professional fees	1,366	2,100
Compensation and related expenses	3,100	2,809
Interest	0	1,126
Other	65	0
Total accrued expenses	$ 7,662	$ 10,361

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

A reconciliation of income tax benefit at the statutory federal income tax rate and income taxes as reflected in the consolidated financial statements is as follows:


	Year Ended December 31,
	2023		2022
Federal tax benefit at statutory rate	(21.0)	%	(21.0)	%
State and local tax, net of federal benefit	(8.5)		(7.8)
State and local tax rate change	1.6		6.2
Permanent differences	0.4		2.0
Research and development	(0.9)		(2.9)
Change in valuation allowance	28.4		22.4
Return to provision	—		1.1
Total provision	—	%	—	%

Schedule of Deferred Tax Assets for Federal Income Taxes

Significant components of the Company's deferred tax assets for federal income taxes consisted of the following (in thousands):


	December 31,
	2023		2022
Deferred tax assets
Net operating losses	$	72,689	$	27,021
Capitalized research and development costs, net of amortization	33,778		11,907
Research and development credits	9,746		5,643
Start-up costs	4,407		4,744
Deferred revenue	13,353		—
Lease liability	668		1,451
Amortizable assets and other	21		59
Equity compensation	87		74
Gross deferred tax assets	134,749		50,899
Valuation allowance	(133,580)		(49,105)
Deferred tax assets, net of valuation allowance	1,169		1,794

Deferred tax liabilities
Right of use asset	(645)		(1,430)
Depreciation	(524)		(364)
Deferred tax liabilities	(1,169)		(1,794)
Net deferred tax assets and liabilities	$	—	$	—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Schedule of Lease Costs

The elements of the lease costs were as follows (in thousands):


	Year Ended December 31,
	2023		2022
Operating lease cost	$	5,774	$	4,764
Finance lease cost:
Amortization of lease assets	1,187		560
Interest on lease liabilities	139		98
Total finance lease cost	1,326		658
Variable lease cost	1,733		920
Total lease cost	$	8,833	$	6,342

Schedule of Lease Term and Discount Rate Information

Lease term and discount rate information related to leases was as follows:


	December 31,
	2023		2022
Weighted-average remaining lease term (in years)
Operating leases	2.6		2.2
Finance leases	1.5		2.2

Weighted-average discount rate
Operating leases	9.8	%	9.4	%
Finance leases	9.0	%	9.0	%

Schedule of Supplemental Cash Flow Information

Supplemental cash flow information was as follows (in thousands):


	Year Ended December 31,
	2023		2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	$	5,764	$	4,750
Operating cash used in finance leases	$	139	$	98
Financing cash used in finance leases	$	1,301	$	865

Schedule of Future Maturities, Operating Leases

Future maturities of lease liabilities were as follows as of December 31, 2023 (in thousands):


	Operating Leases		Finance Leases
Fiscal year ending:
2024	$	1,510	$	600
2025	219		339
2026	226		—
2027	233		—
2028	240		—
Thereafter	184		—
Total future minimum payments	2,612		939
Less imputed interest	(361)		(67)
Present value of lease liabilities	$	2,251	$	872

Schedule of Future Maturities, Financing Leases

Future maturities of lease liabilities were as follows as of December 31, 2023 (in thousands):


	Operating Leases		Finance Leases
Fiscal year ending:
2024	$	1,510	$	600
2025	219		339
2026	226		—
2027	233		—
2028	240		—
Thereafter	184		—
Total future minimum payments	2,612		939
Less imputed interest	(361)		(67)
Present value of lease liabilities	$	2,251	$	872

Background	12 Months Ended
Background	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background	Background Overview Carisma Therapeutics Inc., a Delaware corporation (collectively with its subsidiaries, the Company), is a clinical-stage cell therapy company focused on using the Company’s proprietary chimeric antigen receptor macrophage and monocyte (CAR-M) cell therapy platform to develop transformative immunotherapies to treat cancer and other serious diseases. The Company has created a comprehensive cell therapy platform to enable the therapeutic use of engineered macrophages and monocytes, which belong to a subgroup of white blood cells called myeloid cells. The Company’s focus is its proprietary CAR-M cell therapy platform, which redirects macrophages against specific tumor associated antigens and enables targeted anti-tumor immunity by utilizing genetically modified myeloid cells (macrophages and monocytes) to express chimeric antigen receptors (CARs), enabling these potent innate immune cells to recognize specific tumor associated antigens on the surface of tumor cells. In March 2024, the Company and its board of directors approved a revised operating plan to reduce monthly operating expenses and conserve cash. The plan, which will be implemented in the second quarter of 2024, includes several measures such as prioritizing CT-0525 as the Company's anti-human epidermal growth factor receptor 2 (HER2) product candidate going forward, suspending the enrollment of new patients for CT-0508 in line with the clinical judgment of the clinical site principal investigator, pausing further development of CT-1119, reducing the workforce, including employees engaged in research and development and general and administration activities, and decreasing spending on other non-essential activities. The Company expects the reduction in workforce to be substantially complete and to pay the majority of the workforce reduction costs in the second quarter of 2024. The revised operating plan considers expenses pertaining to severance costs and potential termination and exit fees. The Company’s first product candidate to enter clinical development, CT-0508, is the first CAR-Macrophage to be evaluated in a human clinical trial and is intended to treat solid tumors that over-express HER2, a protein that is over-expressed on the surface of a variety of solid tumors, including breast cancer, gastric cancer, esophageal cancer, salivary gland cancer, and numerous others. CT-0508 has been granted “Fast Track” status for the treatment of patients with HER2 over-expressing solid tumors by the United States FDA. CT-0508 is currently being studied in a multi-center open label Phase 1 clinical trial in the United States. This ongoing first-in-human study evaluates the safety, tolerability, and manufacturing feasibility of CT-0508 along with several customary exploratory secondary endpoints. CT-0525 utilizes a novel approach to CAR-M therapy that engineers patients’ monocytes directly, without ex vivo differentiation into macrophages. In November 2023, the Company received FDA clearance of the Company's IND for CT-0525, and expects to treat the first patient in the second quarter of 2024. The Company believes that CT-0525 has favorable attributes compared to its initial clinical stage product candidate, CT-0508, and that the CAR-Monocyte approach has the potential to improve upon the potential anti-tumor effect of a CAR-Macrophage. The Company will also continue to focus on its in vivo mRNA/lipid nanoparticle (LNP) CAR-M programs in partnership with Moderna. Although the Company plans to continue ongoing activities under its open label Phase 1 clinical trial of CT-0508 and its sub-study utilizing CT-0508 in combination with pembrolizumab, enrollment of new patients will be suspended in line with the clinical judgment of the clinical site principal investigator. All patients currently enrolled or in screening will continue participation per protocol through the end of study milestone and will complete all required activities. The Company has also elected to pause further development of CT-1119, a mesothelin-targeted CAR-Monocyte, pending additional financing. The Company’s early research and development of multiple assets for the potential treatment of diseases beyond oncology, including fibrosis and other immunologic and inflammatory diseases, also remains ongoing. Pipeline Using its proprietary macrophage and monocyte cell therapy platform, the Company is developing a pipeline of product candidates with an initial focus on advancing multiple ex vivo autologous and in vivo CAR-M therapies for the treatment of solid tumors. The Company is also pursuing early research and development of multiple assets for the potential treatment of diseases beyond oncology, including fibrosis and other immunologic and inflammatory diseases. The Company's ex vivo oncology, fibrosis, and immunology programs are wholly owned. Additionally, under a collaboration agreement (the Moderna License Agreement), with ModernaTX Inc. (Moderna) (Note 12), the Company is developing in vivo CAR-M therapies utilizing Moderna's mRNA/LNP technology. The Company's follow-on product candidate, CT-0525, a CAR-Monocyte intended to treat solid tumors that over-express HER2, utilizes a novel approach to CAR-M therapy that engineers patients' monocytes directly, without ex vivo differentiation into macrophages, as the Company currently does for CT-0508. The CAR-Monocyte approach utilizes a single day manufacturing process, which enables the manufacture of up to ten billion cells from a single apheresis, and leverages an automated, closed-system manufacturing process. In addition, the CAR-Monocyte approach has the potential to improve upon the potential anti-tumor effect of a CAR-Macrophage. By increasing the cell yield, a CAR-Monocyte enables a larger dose than a CAR-Macrophage. In addition, CAR-Monocyte has the potential for improved persistence and trafficking, which were observed in pre-clinical studies. The Company believes that the increased cell yield, and the improved persistence and trafficking may improve tumor control. In November 2023, the Company received FDA clearance of its IND for CT-0525 and the Company expects to treat the first patient in the second quarter of 2024. In addition to the development of ex vivo CAR-M cell therapies, the Company is developing in vivo CAR-M cell therapies, wherein immune cells are directly engineered within the patient’s body. To advance the Company’s in vivo CAR-M therapeutics, the Company established a strategic collaboration with Moderna (Note 12). In the fourth quarter of 2023, the Company presented pre-clinical data from this collaboration demonstrating that CAR-M can be directly produced in vivo, successfully redirecting endogenous myeloid cells against tumor-associated antigens using mRNA/LNP. Additionally, the pre-clinical data demonstrated feasibility, tolerability, and early efficacy of in vivo CAR-M against metastatic solid tumors. In December 2023, the Company announced the nomination of the collaboration's first lead candidate, which will target an antigen present on a solid tumor with significant unmet medical need. In addition to acting as a first line of defense in the innate immune system, macrophages and monocytes are found in all tissues in the body where they serve key regulatory functions such as wound healing, termination of immune responses and tissue regeneration. Using the Company's macrophage and monocyte engineering platform, the Company is pursuing early research and development of multiple assets for the potential treatment of diseases beyond oncology, including fibrosis and other immunologic and inflammatory diseases. Pre-clinical proof of concept for fibrosis is expected in the first half of 2024. Reverse Merger with Sesen Bio On March 7, 2023, the Company (formerly publicly-held Sesen Bio, Inc.) consummated a merger with CTx Operations, Inc. (formerly privately-held CARISMA Therapeutics Inc.) (Legacy Carisma) pursuant to an Agreement and Plan of Merger and Reorganization, as amended (the Merger Agreement), by and among the Company, Legacy Carisma and Seahawk Merger Sub, Inc. (Merger Sub), a Delaware corporation and wholly-owned subsidiary of the Company. The Merger Agreement provided for the merger of Merger Sub with and into Legacy Carisma, with Legacy Carisma continuing as a wholly-owned subsidiary of the Company and the surviving corporation of the merger (the Merger). Pursuant to the Merger Agreement, the Company changed its name from “Sesen Bio, Inc.” to “Carisma Therapeutics Inc.” At the closing of the Merger, (a) each then outstanding share of Legacy Carisma common stock and convertible preferred stock (including shares of Legacy Carisma common stock issued in connection with the pre-closing financing transaction described below) were converted into shares of Sesen Bio, Inc. (Sesen Bio) common stock at an exchange ratio of 1.8994 shares of Sesen Bio for each share of Legacy Carisma (the Exchange Ratio), and (b) each then outstanding stock option to purchase Legacy Carisma common stock was assumed by Sesen Bio, with necessary adjustments to reflect the Exchange Ratio. Except as otherwise indicated, references herein to “Carisma,” the “Company,” or the “Combined Company,” refer to Carisma Therapeutics Inc. on a post-Merger basis, and references to “Legacy Carisma” refer to the business of privately-held CARISMA Therapeutics Inc. prior to the completion of the Merger. References to “Sesen Bio” refer to Sesen Bio, Inc. prior to the completion of the Merger. Following the Merger, the shareholders of Legacy Carisma held 74.2% of the Combined Company and the shareholders of Sesen Bio held 25.8% of the Combined Company. Exchange Ratio As discussed in Note 4, the Merger was accounted for as reverse capitalization under which the historical financial statements of the Company prior to the Merger are Legacy Carisma. All common stock, per share and related information presented in the consolidated financial statements and notes prior to the Merger has been retroactively adjusted to reflect the Exchange Ratio.

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2023:


	Options	Weighted average exercise price		Weighted average remaining contractual term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	3,356,937	$	1.01
Sesen Bio options assumed in the Merger	765,223	27.94
Exercised	(128,716)	1.29			$	134
Granted	2,984,152	6.93
Forfeited	(114,454)	5.80
Expired	(839,772)	29.48
Outstanding as of December 31, 2023	6,023,370	$	3.94	7.8	$	5,929
Exercisable as of December 31, 2023	2,516,594	$	1.16	6.0	$	4,950
Vested and expected to vest at December 31, 2023	6,023,370	$	3.94	7.8	$	5,929

Schedule of Estimated Using The Black-Scholes Option-Pricing Model

The fair values in the year ended December 31, 2023 and 2022 were estimated using the Black-Scholes option-pricing model based on the following assumptions:


	Year Ended December 31,
	2023	2022
Risk-free interest rate	2.92% - 4.76%	2.40% - 3.05%
Expected term	6 years	6 years
Expected volatility	57.77% - 103.00%	54.54% - 56.50%
Expected dividend yield	—	—

Schedule of Stock-based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories in the accompanying consolidated statements of operations:


	Year Ended December 31,
	2023		2022
Research and development	$	1,242	$	143
General and administrative	1,074		132
	$	2,316	$	275

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net loss	$ (86,879)	$ (61,226)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events from the balance sheet date through April 1, 2024, the issuance date of these consolidated financial statements, and has not identified any additional matters requiring disclosure.

Cover - USD ($)	12 Months Ended
Cover - USD ($)	Dec. 31, 2023	Mar. 15, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-36296
Entity Registrant Name	Carisma Therapeutics Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-2025616
Entity Address, Address Line One	3675 Market Street
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19104
City Area Code	267
Local Phone Number	491-6422
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	CARM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 275,726,423
Entity Common Stock, Shares Outstanding		41,542,534
Documents Incorporated by Reference	The registrant intends to file a definitive proxy statement pursuant to Regulation 14A within 120 days of the end of the fiscal year ended December 31, 2023. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001485003
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY

Merger with Sesen Bio - Schedule of Net Assets Acquired in the Merger (Details) $ in Thousands	10 Months Ended
	Dec. 31, 2023 USD ($) seat shares	Mar. 07, 2023 USD ($) shares	Dec. 31, 2022 shares
Merger with Sesen Bio
Number of board seats \| seat	7
Entity common stock, shares outstanding immediately after merger \| shares	40,609,915		2,217,737
Cash and cash equivalents		$ 37,873
Marketable securities		44,588
Prepaid expenses and other assets		1,316
Restricted cash		30
Accounts payable and accrued expenses		(3,499)
Total net assets acquired		80,308
Less: Transaction costs		(8,264)
Total net assets acquired less transaction costs		$ 72,044
Carisma Therapeutics Inc.
Merger with Sesen Bio
Severance and personnel costs paid	$ 4,600
CARISMA Therapeutics Inc, Legacy, Stockholders \| Carisma Therapeutics Inc.
Merger with Sesen Bio
Business acquisition percentage of voting interests acquired		74.20%
Entity common stock, shares outstanding immediately after merger \| shares		40,254,666

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Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 77,605	$ 24,194
Marketable securities	0	27,802
Prepaid expenses and other assets	2,866	2,596
Total current assets	80,471	54,592
Property and equipment, net	6,764	8,628
Right of use assets – operating leases	2,173	4,822
Deferred financing costs	146	4,111
Total assets	89,554	72,153
Current liabilities:
Accounts payable	3,933	1,728
Accrued expenses	7,662	10,361
Deferred revenue	1,413	2,459
Operating lease liabilities	1,391	3,437
Finance lease liabilities	544	1,162
Other current liabilities	965	523
Total current liabilities	15,908	19,670
Deferred revenue	45,000	45,000
Convertible promissory note	0	33,717
Derivative liability	0	5,739
Operating lease liabilities	860	976
Finance lease liabilities	328	872
Other long-term liabilities	926	1,041
Total liabilities	63,022	107,015
Commitments and contingencies (Note 7)
Convertible preferred stock	0	107,808
Stockholders’ equity (deficit):
Preferred stock $0.001 par value, 5,000,000 shares authorized, none issued or outstanding	0	0
Common stock $0.001 par value, 350,000,000 shares authorized, 40,609,915 and 2,217,737 shares issued and outstanding at December 31, 2023 and 2022, respectively	40	2
Additional paid-in capital	271,594	1,197
Accumulated other comprehensive loss	0	(41)
Accumulated deficit	(245,102)	(158,223)
Total Carisma Therapeutics Inc. stockholders’ equity (deficit)	26,532	(157,065)
Noncontrolling interests	0	14,395
Total stockholders’ equity (deficit)	26,532	(142,670)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 89,554	$ 72,153

Commitments and Contingencies - Schedule of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 5,774	$ 4,764
Finance lease cost:
Amortization of lease assets	1,187	560
Interest on lease liabilities	139	98
Total finance lease cost	1,326	658
Variable lease cost	1,733	920
Total lease cost	$ 8,833	$ 6,342

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, shares issued (in shares)	40,609,915	2,217,737
Common stock, shares outstanding (in shares)	40,609,915	2,217,737

Stock-based Compensation -Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options
Outstanding as of December 31, 2022 (in shares)	3,356,937
Sesen Bio options assumed in the Merger (in shares)	765,223
Exercised (in shares)	(128,716)
Granted (in shares)	2,984,152
Forfeited (in shares)	(114,454)
Expired (in shares)	(839,772)
Outstanding as of September 30, 2023 (in shares)	6,023,370	3,356,937
Exercisable as of September 30, 2023 (in shares)	2,516,594
Vested and expected to vest at September 30, 2023 (in shares)	6,023,370
Weighted average exercise price
Outstanding as of December 31, 2022 (in USD per share)	$ 1.01
Sesen Bio options assumed in the Merger (in USD per share)	27.94
Exercised (in USD per share)	1.29
Granted (in USD per share)	6.93
Forfeited (in USD per share)	5.80
Expired (in USD per share)	29.48
Outstanding as of September 30, 2023 (in USD per share)	3.94	$ 1.01
Exercisable as of September 30, 2023 (in USD per share)	1.16
Vested and expected to vest at September 30, 2023 (in USD per share)	3.94
Share based compensation arrangement by share based payment award options grants in period weighted average grant date fair value (in USD per share)	$ 4.29	$ 1.46
Weighted average remaining contractual term (years)
Outstanding as of September 30, 2023	7 years 9 months 18 days
Exercisable as of September 30, 2023	6 years
Vested and expected to vest at September 30, 2023	7 years 9 months 18 days
Aggregate Intrinsic Value
Exercised	$ 134
Outstanding as of September 30, 2023	5,929
Exercisable as of September 30, 2023	4,950
Vested and expected to vest at September 30, 2023	$ 5,929

Property and Equipment, net

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):


	December 31,
	2023		2022
Computer software	$	903	$	1,062
Lab equipment(1)	11,392		10,260
Office furniture	267		267
Leasehold improvements	340		340
Construction in progress	13		13
	12,915		11,942
Less: accumulated depreciation and amortization(2)	(6,151)		(3,314)
	$	6,764	$	8,628

(1) Lab equipment includes failed sale lease-back assets of $3.4 million and $2.6 million, respectively, as of December 31, 2023 and 2022. Lab equipment includes finance lease ROU assets of $2.9 million as of December 31, 2023 and 2022.

(2) The accumulated amortization balance includes $0.9 million and $0.3 million, respectively, related to failed sale-leaseback assets as of December 31, 2023 and 2022. The accumulated amortization balance includes $1.7 million and $0.6 million, respectively, related to finance lease ROU assets as of December 31, 2023 and 2022.

Depreciation and amortization expense was $2.8 million and $1.9 million for the years ended December 31, 2023, and 2022, respectively.

Stock-based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Stock-based Compensation
Stock-based compensation expense	$ 2,316	$ 275
Future compensation cost for awards not vested	$ 11,200
Weighted-average period compensation cost of unvested awards to be expensed	3 years 3 months 18 days
Sesen Bio, Inc.
Stock-based Compensation
Stock-based compensation expense	$ 200
Research and development
Stock-based Compensation
Stock-based compensation expense	1,242	143
General and administrative
Stock-based Compensation
Stock-based compensation expense	$ 1,074	$ 132

Stock-based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

2017 Stock Incentive Plan

Legacy Carisma adopted the CARISMA Therapeutics Inc. 2017 Stock Incentive Plan, as amended (the Legacy Carisma Plan), that provided for the grant of incentive stock options to employees, directors, and consultants. The maximum term of options granted under the Legacy Carisma Plan was ten years, and stock options typically vested over a four-year period. The Company’s stock options vest based on the terms in the awards agreements and generally vest over four years. Upon completion of the Merger, the Company assumed the Legacy Carisma Plan and the outstanding and unexercised options issued thereunder, and ceased granting awards under the Legacy Carisma Plan.

2014 Stock Incentive Plan

The Sesen Bio, Inc. Amended and Restated 2014 Stock Incentive Plan, as amended (the Sesen Bio 2014 Plan), provides for the grant of incentive and non-qualified stock options, restricted stock awards and restricted stock units, stock appreciation rights and other stock-based awards to the Company’s employees, officers, directors, consultants, and advisors, with amounts and terms of grants determined by the Company’s board of directors at the time of grant.

Stock options outstanding under the Sesen Bio 2014 Plan generally vest over a four-year period at the rate of 25% of the grant vesting on the first anniversary of the date of grant and 6.25% of the grant vesting at the end of each successive three-month period thereafter. Stock options granted under the Sesen Bio 2014 Plan are exercisable for a period of ten years from the date of grant.

On March 7, 2023, the Company amended and restated the Sesen Bio 2014 Plan to (i) change the name of the plan to the Carisma Therapeutics Inc. 2014 Amended and Restated Stock Incentive Plan (the 2014 Plan) and (ii) adopt a new form of stock option agreement and a new form of restricted stock unit agreement for the grant of options and restricted stock units under the 2014 Plan. On June 6, 2023, the Company’s stockholders approved an amendment and restatement of the Company’s 2014 Plan, which amendment and restatement had previously been adopted by the Company’s board of directors, subject to stockholder approval. As of December 31, 2023, approximately 4.9 million shares of common stock remained available for issuance.

2014 Employee Stock Purchase Plan

The Sesen Bio 2014 Employee Stock Purchase Plan (the Sesen Bio 2014 ESPP) provides employees with the opportunity to purchase shares of common stock at a 15% discount to the market price through payroll deductions or lump sum cash investments. The purpose of the Sesen Bio 2014 ESPP is to enhance employee interest in the success and progress of the Company by encouraging employee ownership of common stock. On March 7, 2023, the Company amended and restated the Sesen Bio 2014 ESPP to (i) change the name of the plan to Carisma Therapeutics Inc. 2014 Employee Stock Purchase Plan and (ii) restate and integrate all prior amendments thereto. As of December 31, 2023, 0.2 million shares of common stock remained available for issuance.

The following table summarizes stock option activity for the year ended December 31, 2023:


	Options	Weighted average exercise price		Weighted average remaining contractual term (years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	3,356,937	$	1.01
Sesen Bio options assumed in the Merger	765,223	27.94
Exercised	(128,716)	1.29			$	134
Granted	2,984,152	6.93
Forfeited	(114,454)	5.80
Expired	(839,772)	29.48
Outstanding as of December 31, 2023	6,023,370	$	3.94	7.8	$	5,929
Exercisable as of December 31, 2023	2,516,594	$	1.16	6.0	$	4,950
Vested and expected to vest at December 31, 2023	6,023,370	$	3.94	7.8	$	5,929

The weighted-average grant-date per share fair values of options granted during the year ended December 31, 2023 and 2022 were $4.29 and $1.46, respectively. The fair values in the year ended December 31, 2023 and 2022 were estimated using the Black-Scholes option-pricing model based on the following assumptions:


	Year Ended December 31,
	2023	2022
Risk-free interest rate	2.92% - 4.76%	2.40% - 3.05%
Expected term	6 years	6 years
Expected volatility	57.77% - 103.00%	54.54% - 56.50%
Expected dividend yield	—	—

Stock-Based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories in the accompanying consolidated statements of operations:


	Year Ended December 31,
	2023		2022
Research and development	$	1,242	$	143
General and administrative	1,074		132
	$	2,316	$	275

The Company recognized stock-based compensation expense of $0.2 million related to the modification of Sesen Bio options assumed in connection with the Merger. Compensation cost for awards not vested as of December 31, 2023 was $11.2 million and will be expensed over a weighted-average period of 3.3 years

Moderna Collaboration and License Agreement - Schedule of Estimated Revenue Expected to be Recognized in The Future Related to Performance Obligations (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Performance obligations:
Research and development	$ 49,183
Option rights	45,000
Total performance obligations	$ 94,183

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property and equipment, net consisted of the following (in thousands):


	December 31,
	2023		2022
Computer software	$	903	$	1,062
Lab equipment(1)	11,392		10,260
Office furniture	267		267
Leasehold improvements	340		340
Construction in progress	13		13
	12,915		11,942
Less: accumulated depreciation and amortization(2)	(6,151)		(3,314)
	$	6,764	$	8,628

Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Mar. 07, 2023 USD ($)
Business Acquisition [Line Items]
Discount factor percentage		12.00%
Number of operating segments \| segment	1
Restricted cash and cash equivalents	$ 0
Impairment of long-lived assets	$ 0	$ 0
Collateral, credit card program
Business Acquisition [Line Items]
Restricted cash and cash equivalents			$ 30,000
Minimum
Business Acquisition [Line Items]
Probability of convertible qualified financing (as a percent)		90.00%
Derivative instrument, conversion range, term		3 months
Property and equipment, estimated useful lives	2 years
Maximum
Business Acquisition [Line Items]
Probability of convertible qualified financing (as a percent)		100.00%
Derivative instrument, conversion range, term		12 months
Property and equipment, estimated useful lives	5 years
Sesen Bio, Inc.
Business Acquisition [Line Items]
Deferred financing costs	$ 4,200,000	$ 4,100,000		$ 8,300,000

Accrued Expenses

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	December 31,
	2023		2022
Research and development	$	3,131	$	4,326
Professional fees	1,366		2,100
Compensation and related expenses	3,100		2,809
Interest	—		1,126
Other	65		—
	$	7,662	$	10,361

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Leases

The Company has operating leases for its laboratory and office space in Philadelphia, Pennsylvania. The Company’s operating leases have term end dates ranging from 2024 to 2029. The Company also has obligations under an arrangement for the use of certain laboratory equipment that are classified as finance leases that commenced in 2022 and have end dates ranging from 2024 to 2025.

The Company’s operating and finance lease right-of-use (ROU) assets and the related lease liabilities are initially measured at the present value of future lease payments over the lease term. The Company is responsible for payment of certain real estate taxes, insurance and other expenses on certain of its leases. These amounts are generally considered to be variable and are not included in the measurement of the ROU assets and lease liability. The Company accounts for non-lease components, such as maintenance, separately from lease components.

During the years ended December 31, 2023 and 2022, the Company entered into purchase and sale agreements under which the Company sold lab equipment for $1.2 million and $1.6 million, respectively. Concurrent with the sale of equipment, the Company entered into various lease agreements, with term end dates ranging from 2025 to 2026, whereby the Company will lease back the equipment. The Company accounts for such transactions as failed sale-leasebacks, due to having continuing involvement with the equipment. The Company carries this laboratory equipment as property and equipment, net on the accompanying consolidated balance sheets and the sale proceeds as a finance liability. The ongoing lease payments are recorded as reductions to the finance liability and interest expense. No gain or loss was recorded on the failed sale-leasebacks. As of December 31, 2023, the Company had a $1.9 million financing liability recorded in other current liabilities and other long-term liabilities on the consolidated balance sheets.

The elements of the lease costs were as follows (in thousands):


	Year Ended December 31,
	2023		2022
Operating lease cost	$	5,774	$	4,764
Finance lease cost:
Amortization of lease assets	1,187		560
Interest on lease liabilities	139		98
Total finance lease cost	1,326		658
Variable lease cost	1,733		920
Total lease cost	$	8,833	$	6,342

Lease term and discount rate information related to leases was as follows:


	December 31,
	2023		2022
Weighted-average remaining lease term (in years)
Operating leases	2.6		2.2
Finance leases	1.5		2.2

Weighted-average discount rate
Operating leases	9.8	%	9.4	%
Finance leases	9.0	%	9.0	%

Supplemental cash flow information was as follows (in thousands):


	Year Ended December 31,
	2023		2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash used in operating leases	$	5,764	$	4,750
Operating cash used in finance leases	$	139	$	98
Financing cash used in finance leases	$	1,301	$	865

Future maturities of lease liabilities were as follows as of December 31, 2023 (in thousands):


	Operating Leases		Finance Leases
Fiscal year ending:
2024	$	1,510	$	600
2025	219		339
2026	226		—
2027	233		—
2028	240		—
Thereafter	184		—
Total future minimum payments	2,612		939
Less imputed interest	(361)		(67)
Present value of lease liabilities	$	2,251	$	872

Licensing and Sponsored Research Agreements

Under a license agreement with The Trustees of the University of Pennsylvania (Penn), entered into in November 2017 (Penn License Agreement), the Company is required to make annual payments of $25,000. Penn is eligible to receive up to $10.9 million per product in development upon the achievement of certain clinical, regulatory and commercial milestone events. There are additional milestone payments required to be paid of up to $30.0 million per product in commercial milestones and up to an additional $1.7 million in development and regulatory milestone payments for the first CAR-M product directed to mesothelin. Additionally, the Company is obligated to pay Penn single-digit royalties based on its net sales.

In March 2023, the Company entered into a manufacturing and supply agreement with Novartis Pharmaceuticals Corporation (Novartis) for the manufacturing of the Company’s CT-0508 product candidate (Novartis Agreement). The Novartis Agreement is for five years and shall renew automatically for additional one-year periods unless and until

terminated by either party. In addition to paying to manufacture the product, the Company will also pay $1.0 million per calendar year, payable in quarterly payments, for reserved capacity starting on the date on which the Novartis site is declared ready to produce CT-0508 as determined by the Company. In the event of termination without cause by the Company, a termination fee equal to $4.0 million will be payable by Carisma to Novartis which, pursuant to the terms of the agreement, can be credited in full against amounts due for a substitute product.

Contingencies

Liabilities for loss contingencies, arising from claims, assessments, litigation, fines, penalties, and other sources are recorded when it is probable that a liability has been incurred and the amount of the assessment and/or remediation can be reasonably estimated.

On February 3, 2023, a purported stockholder filed a complaint in the United States District Court for the District of Delaware against Sesen Bio and its board of directors, captioned Plumley v. Sesen Bio, Inc., et al., Case No. 1:23-cv-00131 (D. Del.) (the Plumley Complaint). The Plumley Complaint asserts claims under Section 14(a) of the Exchange Act and Rule 14a-9 promulgated thereunder for allegedly false and misleading statements in the proxy statement/prospectus filed as part of the Registration Statement in connection with the Merger and under Section 20(a) of the Exchange Act for alleged “control person” liability with respect to such allegedly false and misleading statements and seeks, among other relief, an order enjoining the Merger and an award for plaintiffs’ fees and costs. On February 7, 2023, another purported stockholder filed a complaint in the United States District Court for the Southern District of New York against Sesen Bio and its board of directors, captioned Franchi v. Sesen Bio, Inc., et al., 1:23-cv-01041 (S.D.N.Y.) (the Franchi Complaint). The Franchi Complaint contains substantially similar allegations and claims and seeks substantially similar relief as the Plumley Complaint. Additionally, on February 9, 2023, another purported stockholder filed a complaint in the United States District Court for the Southern District of New York against Sesen Bio and its board of directors, captioned Menzer v. Sesen Bio, Inc., et al., 23-cv-01119 (S.D.N.Y.) (the Menzer Complaint). The Menzer Complaint contains substantially similar allegations and claims and seeks substantially similar relief as the Plumley Complaint and the Franchi Complaint. In April 2023, the Company executed a confidential fee agreement to resolve the stockholders’ claim for attorney’s fees and expenses in connection with the Plumley Complaint, Franchi Complaint, and Menzer Complaint. The Company settled and paid the confidential fee agreement resulting in $0.2 million of claim expenses incurred during the year ended December 31, 2023.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Stock-based Compensation - Narratives (Details) shares in Millions	12 Months Ended
	Dec. 31, 2023 shares
Two Thousand Seventeen Stock Incentive Plan \| Stock options
Stock-based Compensation
Vesting period	4 years
Two Thousand Seventeen Stock Incentive Plan \| Stock options \| Maximum
Stock-based Compensation
Terms	10 years
Two Thousand Fourteen Stock Incentive Plan
Stock-based Compensation
Vesting period	4 years
Vesting on first anniversary (as a percent)	25.00%
Vesting at the end of each three-month period after first anniversary (as a percent)	6.25%
Shares available for issuance	4.9
Two Thousand Fourteen Stock Incentive Plan \| Stock options
Stock-based Compensation
Vesting period	10 years
Two Thousand Fourteen Employee Stock Purchase Plan
Stock-based Compensation
Shares available for issuance	0.2
Discount to the market price (as a percent)	15.00%

Merger with Sesen Bio (Tables)

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Schedule of Net Assets Acquired in the Merger

The following table shows the net assets acquired in the Merger (in thousands):


	March 7, 2023
Cash and cash equivalents	$	37,873
Marketable securities	44,588
Prepaid expenses and other assets	1,316
Restricted cash	30
Accounts payable and accrued expenses	(3,499)
Total net assets acquired	80,308
Less: Transaction costs	(8,264)
Total net assets acquired less transaction costs	$	72,044

Property and Equipment, net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 2,837	$ 1,893

Summary of Significant Accounting Policies - Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Marketable securities
Fair value	$ 0
U.S. Treasury securities
Marketable securities
Amortized cost		$ 27,843
Gross unrealized loss		(41)
Fair value		$ 27,802

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
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-Paragraph 3
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Section 50
-Paragraph 3
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Summary of Significant Accounting Policies - Schedule of Anti-Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Net loss per share
Anti-dilutive securities (in shares)	6,023,370	16,551,236
Convertible preferred stock and exchangeable shares
Net loss per share
Anti-dilutive securities (in shares)	0	9,936,148
Stock options
Net loss per share
Anti-dilutive securities (in shares)	6,023,370	3,356,937
Conversion of convertible promissory note
Net loss per share
Anti-dilutive securities (in shares)	0	3,258,151

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2023
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity On March 7, 2023, in connection with the closing of the Merger, the following is reflected on the consolidated statements of convertible preferred stock and stockholders’ equity (deficit) for the year ended December 31, 2023: (i) the sale of 3,730,608 shares of common stock in a pre-closing funding at $8.21 per share for total proceeds of $30.6 million, (ii) the issuance of 5,059,338 shares of common stock upon the settlement of the Company’s $35.0 million convertible promissory note, accrued interest and related derivative liability, (iii) the conversion of convertible preferred stock and exchangeable shares previously presented as noncontrolling interests into 18,872,711 shares of common stock, (iv) the issuance of 10,374,272 shares of common stock to Sesen Bio stockholders as consideration for the Merger. On April 17, 2023, the Company filed a universal shelf registration statement on Form S-3, which was declared effective on May 2, 2023 (Registration Statement). Under the Registration Statement, the Company may offer and sell up to $300.0 million of a variety of securities, including debt securities, common stock, preferred stock, depositary shares, subscription rights, warrants and units from time to time in one or more offerings at prices and on terms to be determined at the time of the offering. On May 12, 2023, the Company entered into an Amended and Restated Open Market Sale AgreementSM (Sale Agreement) with Jefferies LLC, as sales agent, pursuant to which the Company may offer and sell shares of common stock with an aggregate offering price of up to $100.0 million under an “at-the-market" offering program. Through December 31, 2023, the Company sold 226,533 shares for gross proceeds of $0.6 million. From January through March 2024, the Company sold an additional 931,250 shares for gross proceeds of $2.4 million. On June 6, 2023, the Company's stockholders approved an amendment to the Company's Restated Certificate of Incorporation to increase the number of authorized shares of the Company's common stock, $0.001 par value, from 100,000,000 shares to 350,000,000 shares and authorized 5,000,000 shares of preferred stock, $0.001 par value.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
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