0001453687-25-000060 | 10-K | XBRL Viewer | Cartesian Therapeutics INC

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Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Payroll and employee related expenses	$ 3,534	$ 4,390
Accrued patent fees	813	472
Accrued external research and development costs	2,987	4,896
Accrued professional and consulting services	3,674	4,331
Property and equipment	782	128
Other	286	516
Accrued expenses	$ 12,076	$ 14,733

Leases - Moscow, Russia Lease (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating Leased Assets [Line Items]
Lessee-paid construction costs	$ 4,394	$ 2,629
Moscow Russia Lease
Operating Leased Assets [Line Items]
Lessee-paid construction costs	$ 5,500	$ 3,800

Merger - Schedule of Intangible Assets Acquired (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Nov. 13, 2023
Business Acquisition [Line Items]
Impairment	$ 0
Carrying value	$ 150,600,000	$ 150,600,000
Old Cartesian
Business Acquisition [Line Items]
Acquisition Date Fair Value			$ 150,600,000
Old Cartesian \| Descartes-08 for MG
Business Acquisition [Line Items]
Acquisition Date Fair Value			93,900,000
Old Cartesian \| Descartes-08 for SLE
Business Acquisition [Line Items]
Acquisition Date Fair Value			$ 56,700,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Revenue:
Collaboration and license revenue	$ 38,275	$ 26,004
Grant revenue	638	0
Total revenue	38,913	26,004
Operating expenses:
Research and development	45,105	71,260
General and administrative	30,126	40,450
Impairment of long-lived assets	7,579	710
Total operating expenses	82,810	112,420
Operating loss	(43,897)	(86,416)
Interest income	7,386	4,964
Foreign currency transaction, net	0	38
Interest expense	0	(2,833)
Change in fair value of warrant liabilities	2,558	12,746
Change in fair value of contingent value right liability	(36,900)	(18,300)
Change in fair value of forward contract liabilities	(6,890)	(149,600)
Other income, net	606	691
Loss before income taxes	(77,137)	(238,710)
Income tax (expense) benefit	(287)	19,000
Net loss	(77,424)	(219,710)
Other comprehensive loss:
Foreign currency translation adjustment	(21)	(53)
Unrealized gain on marketable securities	0	11
Total comprehensive loss	$ (77,445)	$ (219,752)
Net loss per share allocable to common stockholders:
Basic (in dollars per share)	$ (4.48)	$ (49.76)
Diluted (in dollars per share)	$ (4.49)	$ (49.76)
Weighted-average common shares outstanding:
Basic (in shares)	17,276,822	5,170,319
Diluted (in shares)	17,357,943	5,170,319

Related-Party Transactions

12 Months Ended

Dec. 31, 2024

Related-Party Transactions

2024 Securities Purchase Agreement

On July 2, 2024, the Company entered into the 2024 Securities Purchase Agreement with the Purchasers. The Purchasers included (i) Dr. Timothy A. Springer, a member of the Company’s Board of Directors; (ii) TAS Partners LLC, an affiliate of Dr. Springer, and (iii) Dr. Chafen Lu, Dr. Springer’s wife (see Note 11). The below issuances and sales to related parties of the Company were made during the year ended December 31, 2024.


Name	Shares of Series B Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	1,636,832	$	32,737
TAS Partners LLC, affiliate of Timothy A. Springer, Ph.D.	721,361	$	14,427
Chafen Lu, Ph.D., wife of Timothy A. Springer, Ph.D.	1,307	$	26

2023 Securities Purchase Agreement

On November 13, 2023, the Company entered into the 2023 Securities Purchase Agreement with (i) Dr. Timothy A. Springer, (ii) TAS Partners LLC, and (iii) Seven One Eight Three Four Irrevocable Trust, a trust associated with Dr. Murat Kalayoglu, in which the Company agreed to issue and sell an aggregate of 149,330.115 shares of Series A Preferred Stock for an aggregate purchase price of $60.25 million (see Note 11). The 2023 Private Placement included a delayed settlement mechanism, and as a result, the below issuances and sales to related parties of the Company were made during the year ended December 31, 2024.


Name	Shares of Series A Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	99,140.326	$	40,000

The below issuances and sales to related parties of the Company were made subject to the 2023 Private Placement during the year ended December 31, 2023.


Name	Shares of Series A Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	24,785.081	$	10,000
TAS Partners LLC (affiliate of Timothy A. Springer, Ph.D.)	24,785.081	$	10,000
Seven One Eight Three Four Irrevocable Trust (affiliate of Murat Kalayoglu, MD, Ph.D.)	619.627	$	250

Exercise of Amended 2019 Warrants

On March 26, 2024, TAS Partners LLC exercised 65,681 Amended 2019 Warrants, paid the per-share exercise price of $43.80 in cash for an aggregate exercise price of $2.9 million, and received 65,681 shares of common stock and 1,970,443 CVRs.

- 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.

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+ Details

Insider Trading Policies and Procedures	12 Months Ended
Insider Trading Policies and Procedures	Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Equity - December 2019 Financing (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Dec. 20, 2022	Dec. 18, 2019	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Class of warrant or right, outstanding (in shares)			692,523	1,040,813	1,040,932
Exercise price (in dollars per share)			$ 46.96	$ 45.98	$ 46.03
Issuance costs			$ 66	$ 0
2019 Warrants
Class of Stock [Line Items]
Warrant issued	$ 800
December 2019 Financing
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		1,254,496
Share price (in dollars per share)		$ 43.80
Class of warrant or right, outstanding (in shares)		766,275
Warrant issued		$ 40,700
Total aggregate purchase price		65,600
Issuance costs		$ 4,400
Warrant liabilities, net of current portion			3,800
Warrant, increase (decrease) in equity, amount			$ 2,600	$ 12,700
December 2019 Financing \| Common Warrant
Class of Stock [Line Items]
Share price (in dollars per share)		$ 3.75
Exercise price (in dollars per share)		$ 43.80
Warrants and rights outstanding, term		5 years
December 2019 Financing \| Pre-Funded Warrant
Class of Stock [Line Items]
Class of warrant or right, number of warrants exercised (in shares)		278,070
Exercise price (in dollars per share)		$ 0.003

Leases - Schedule of Additional Information Related to Operating Leases (Details)	Dec. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Weighted-average remaining lease term	4 years 6 months	4 years 3 months 18 days
Weighted-average discount rate	11.70%	9.90%

Equity - “At-the-Market” Offerings (Narrative) (Details) - At-The-Market Offering - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 13, 2024	Oct. 25, 2021
Class of Stock [Line Items]
Aggregate maximum gross sales proceeds			$ 100.0	$ 51.0
Sale of stock, number of shares issued in transaction (in shares)	0	0

- 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

Net Loss Per Share Allocable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2024

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net Loss Per Share Allocable to Common Stockholders

The following table sets forth the computation of basic and diluted net loss per share allocable to common stockholders (in thousands, except share and per-share data):


	Year Ended December 31,
		2024		2023
Numerator:
Net loss		$	(77,424)	$	(219,710)
Less: CVR distribution to participating securities		—		(37,550)
Net loss allocable to shares of common stock - basic		(77,424)		(257,260)
Less: Change in fair value of forward contract liability settled in February 2024		(446)		—
Net loss allocable to shares of common stock - diluted		$	(77,870)	$	(257,260)
Denominator:
Weighted-average common shares outstanding - basic		17,276,822		5,170,319
Plus: Dilutive effect of forward contract liability settled in February 2024		81,121		—
Weighted-average common shares outstanding - diluted		17,357,943		5,170,319
Net loss per share:
Basic		$	(4.48)	$	(49.76)
Diluted		$	(4.49)	$	(49.76)

Schedule of Potential Dilutive Shares of Common Stock Excluded from the Computation of the Diluted Net Loss Per Share Allocable to Common Stockholders

The following table represents the potential dilutive shares of common stock excluded from the computation of the diluted net loss per share allocable to common stockholders for all periods presented, as the effect would have been anti-dilutive:


	Year Ended December 31,
	2024	2023
Common stock options and RSUs	2,150,273	776,865
Warrants to purchase common stock	692,523	1,040,813
Series A Preferred Stock	4,026,346	14,503,993
Series B Preferred Stock	437,927	—
Forward contract to issue Series A Preferred Stock	—	3,304,677
Series A Preferred Stock options	—	470,403
Total	7,307,069	20,096,751

Equity - Schedule of Warrant Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Number of Warrants
Beginning balance (in shares)	1,040,813	1,040,932
Expired (in shares)	(282,609)	(119)
Exercises (in shares)	(65,681)
Ending balance (in shares)	692,523	1,040,813
Weighted average exercise price
Beginning balance (in dollars per share)	$ 45.98	$ 46.03
Expired (in dollars per share)	44.09	503.10
Exercises (in dollars per share)	43.80
Ending balance (in dollars per share)	$ 46.96	$ 45.98
Warrant
Number of Warrants
Beginning balance (in shares)	966,393	966,393
Expired (in shares)	(280,681)	0
Exercises (in shares)	0
Ending balance (in shares)	685,712	966,393
Warrant
Number of Warrants
Beginning balance (in shares)	74,420	74,539
Expired (in shares)	(1,928)	(119)
Exercises (in shares)	(65,681)
Ending balance (in shares)	6,811	74,420

Convertible Preferred Stock - Redemption (Narrative) (Details)	12 Months Ended
	Dec. 31, 2024 day
Temporary Equity Disclosure [Abstract]
Preferred stock, redemption term	18 months
Preferred stock, convertible, threshold consecutive trading days	10

Equity (Tables)

12 Months Ended

Dec. 31, 2024

Equity [Abstract]

Schedule of Warrant Activity

The following is a summary of warrant activity for the years ended December 31, 2024 and 2023:


	Number of Warrants
	Equity classified	Liability classified	Total	Weighted average exercise price
Outstanding at December 31, 2022	74,539	966,393	1,040,932	$	46.03


Expired	(119)	—	(119)	$	503.10

Outstanding at December 31, 2023	74,420	966,393	1,040,813	$	45.98
Exercises	(65,681)	—	(65,681)	43.80

Expired	(1,928)	(280,681)	(282,609)	44.09

Outstanding at December 31, 2024	6,811	685,712	692,523	$	46.96

Schedule of Authorized Shares of Common Stock for Future Issuance

The Company has authorized shares of common stock for future issuance as follows:


			As of
			December 31, 2024
Exercise of warrants			692,523
Shares available for future stock incentive awards			4,205,199

Unvested restricted stock units			444,238
Outstanding common stock options			1,706,035
Series A Preferred Stock			4,026,346
Series B Preferred Stock			437,927
Total			11,512,268

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

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+ Details

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2024
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Selecta (RUS), LLC, or Selecta (RUS), a Russian limited liability corporation, Selecta Biosciences Security Corporation, a Massachusetts securities corporation which the Company dissolved in December 2024, and Cartesian Bio, LLC, a Delaware limited liability company, which is a variable interest entity for which the Company is the primary beneficiary. All significant intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company’s management considers many factors in selecting appropriate financial accounting policies and controls, and bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. In preparing these consolidated financial statements, management used significant estimates in the following areas, among others: estimated fair value of the intangible assets acquired in connection with the Merger, estimated fair value of the CVRs, deferred income taxes, revenue recognition, estimated accrued research and development expenses, stock-based compensation expense, estimated fair value of the liability-classified warrants, and impairment of long-lived assets. The Company assesses the above estimates on an ongoing basis; however, actual results could materially differ from those estimates.
Segment Information	Segment Information Operating segments are defined as components of an enterprise for which separate and discrete information is available for evaluation by the chief operating decision maker, or the CODM, for the purposes of assessing performance and allocating resources. The Company views its operations and manages its business in one operating segment, which prior to the Merger related to the research and development of nanoparticle immunomodulatory drugs for the treatment and prevention of human diseases and subsequent to the Merger relates to the research and development of cell therapy product candidates. The Company’s CODM function is fulfilled by its Chief Executive Officer. The CODM function assesses performance for the segment and decides how to allocate resources based on consolidated net loss that is also reported on the consolidated statements of operations and comprehensive loss. The CODM function uses net loss to monitor budget versus actual results to assess performance of the segment. Segment assets are the same as total assets on the Company’s consolidated balance sheets. All long-lived assets are located in the United States. Long-lived assets consist of property and equipment, net, and operating lease right-of-use assets.
Cash Equivalents, Marketable Securities and Investments	Cash Equivalents, Marketable Securities and Investments Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Marketable securities consist of securities with remaining maturities greater than 90 days when purchased. The Company classifies these marketable securities as available-for-sale and records them at fair value in the accompanying consolidated balance sheets. Marketable securities with less than one year until maturity are classified as short term, while marketable securities with maturities greater than one year are classified as long term. Unrealized gains or losses are included in accumulated other comprehensive loss. Premiums or discounts from par value are amortized to interest income over the life of the underlying investment. Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined based on the specific identification method for purposes of recording realized gains and losses. The Company has also in the past invested in equity securities of a company whose securities are not publicly traded and where fair value is not readily available. This investment is recorded using cost minus impairment adjusted for changes in observable prices, depending on our ownership percentage and other factors that suggest we have significant influence. The Company monitors this investment to evaluate whether any increase or decline in its value has occurred, based on the implied value of recent company financings, public market prices of comparable companies and general market conditions. This investment is included in investments in the consolidated balance sheets.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash, cash equivalents, short-term deposits, investments, accounts receivable, and unbilled receivables. Cash and cash equivalents are deposited with federally insured financial institutions in the United States and may, at times, exceed federally insured limits. Management believes that the financial institutions that hold the Company’s deposits are financially creditworthy and, accordingly, minimal risk exists with respect to those balances.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments consist mainly of cash equivalents, restricted cash, accounts receivable, accounts payable, accrued expenses and other current liabilities, investments, warrants to purchase common stock, forward contract liabilities, and contingent value rights. The carrying amounts of cash equivalents, restricted cash, accounts receivable, accounts payable, and accrued expenses and other current liabilities approximate their estimated fair value due to their short-term maturities. Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three-level hierarchy is used to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements), and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy are described below: Level 1—Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2—Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. If the asset or liability has a specified (contractual) term, a Level 2 input must be observable for substantially the full term of the asset or liability. Level 3—Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair value of warrant liabilities and contingent value rights are determined using Level 3 inputs. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may change for many instruments. This condition could cause an instrument to be reclassified within levels in the fair value hierarchy. The carrying amounts reflected in the consolidated balance sheet for investments approximate fair value and are assessed for impairment quarterly.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, generally seven years for furniture and fixtures, five years for laboratory equipment, software and office equipment and three years for computer equipment. Leasehold improvements are amortized over their useful life or the life of the lease, whichever is shorter. Major additions and betterments are capitalized. Maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to operations as incurred. Costs incurred for construction in progress are recorded as assets and are not amortized until the construction is substantially complete and the assets are ready for their intended use.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. In order to determine if assets have been impaired, assets are tested at the lowest level for which identifiable independent cash flows are available. An impairment loss is recognized when the sum of projected undiscounted cash flows is less than the carrying value of the asset group. The measurement of the impairment loss to be recognized is based on the difference between the fair value and the carrying value of the asset group. The Company recognized an impairment charge on its right of use assets and related furniture and fixtures during the year ended December 31, 2024 and on a right-of-use asset during the year ended December 31, 2023.
Debt Issuance Costs	Debt Issuance Costs Debt issuance costs and fees paid to lenders are recorded as a direct deduction from the face amount of the related debt. Debt issuance costs are amortized over the term of the related debt using the effective interest method and recorded as interest expense.
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Comprehensive loss is defined as the change in the equity of a business entity during a period from transactions and other events and circumstances from non-owner sources. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners. Comprehensive loss consists of: (i) all components of net loss and (ii) all components of comprehensive loss other than net loss, referred to as other comprehensive loss. Other comprehensive loss is comprised of unrealized gains and losses on debt securities and foreign currency translation adjustments.
Collaboration and License Revenue Recognition	Collaboration and License Revenue Recognition Revenue is recognized when a 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. Pursuant to ASC Topic 606, Revenue from Contracts with Customers (ASC 606), a customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract, including whether they are distinct in the context of the contract; (iii) determine the transaction price, including the constraint on variable consideration; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. If a promised good or service is not distinct, it is combined with other promised goods or services into a performance obligation. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaboration and License Revenue: The Company currently generates its revenue through collaboration and license agreements with strategic collaborators for the development and commercialization of product candidates. Collaboration and license agreements with customers are generally accounted for in accordance with ASC 606. The Company analyzes collaboration arrangements by first assessing whether they are within the scope of ASC Topic 808, Collaborative Arrangements (ASC 808), and evaluates whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. Collaboration agreements with customers that are not within the scope of ASC 808 are accounted for in accordance with ASC 606. To the extent the collaboration agreement is within the scope of ASC 808, the Company also assesses whether any aspects of the agreement are within the scope of other accounting literature (specifically ASC 606). If the Company concludes that some or all aspects of the agreement are distinct and represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606. The Company recognizes the shared costs incurred that are not within the scope of other accounting literature as a component of the related expense in the period incurred by analogy to ASC Topic 730, Research and Development (ASC 730), and records reimbursements from counterparties as an offset to the related research and development costs. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements in accordance with ASC 606, the Company performs the five steps above. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. The terms of the Company’s arrangements typically include one or more of the following: (i) upfront fees; (ii) milestone payments related to the achievement of development, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) reimbursements or cost-sharing of research and development expenses; and (v) profit/loss sharing arising from co-promotion arrangements. Licenses of Intellectual Property: If the license to the Company’s intellectual property is determined to be distinct from the other promised goods and services identified in the arrangement, the Company recognizes revenues 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. If not distinct, the license is combined with other promised goods and services in the contract. For licenses that are combined with other promised goods and services, the Company assesses 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. Optional licenses are evaluated to determine if they are issued at a discount, and therefore, represent material rights and accounted for as separate performance obligations. Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. The Company also evaluates the milestone to determine whether they are considered probable of being reached 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 to be allocated, otherwise, such amounts are constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are evaluated to determine if they are distinct and optional. For optional services that are distinct, the Company assesses if they are priced at a discount, and therefore, provide a material right to the licensee to be accounted for as separate performance obligations. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint.
Grant Revenue	Grant Revenue The Company has contracts with government-sponsored organizations for research and development related activities that provide for payments for reimbursable costs. The Company recognizes grant revenue from these contracts as it performs services under these arrangements when the funding is committed. Expenses associated with these contracts are recognized when incurred as research and development expense. Grant revenue and related expenses are presented gross in the consolidated statements of operations and comprehensive loss as the Company has determined it is the primary obligor under the arrangements relative to the research and development services it performs as lead technical expert. Amounts incurred that are subject to reimbursement from the sponsor are recorded as accounts receivable on the consolidated balance sheets.
Research and Development Costs	Research and Development Costs Costs incurred in the research and development of the Company’s products are expensed as incurred. Research and development expenses include costs incurred in performing research and development activities, including salaries and benefits, stock-based compensation expenses, facilities cost, overhead costs, contract services, supplies and other outside costs. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.
Clinical Trial Costs	Clinical Trial Costs Clinical trial expenses are a significant component of research and development expenses, and the Company outsources a significant portion of these costs to third-parties. Third-party clinical trial expenses include patient costs, clinical research organization costs and costs for data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through costs. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as a prepaid asset or accrued clinical trial cost. These third-party agreements are generally cancellable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future research and development activities are recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. The Company also records accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical clinical accrual estimates made by the Company have not been materially different from the actual costs.
Income Taxes	Income Taxes The Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax assets to the amount that will more-likely-than-not be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more-likely-than-not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. To date, the Company has not incurred interest and penalties related to uncertain tax positions.
Warrants	Warrants The Company determines the accounting classification of warrants that are issued, as either liability or equity, by first assessing whether the warrants meet liability classification in accordance with ASC 480-10, Accounting for Certain Financial Instruments with Characteristics of both Liabilities and Equity, and then in accordance with ASC 815-40, Accounting for Derivative Financial Instruments Indexed to, and Potentially Settled in, a Company’s Own Stock. Under ASC 480, warrants are considered liability classified if the warrants are mandatorily redeemable, obligate the issuer to settle the warrants or the underlying shares by paying cash or other assets, or must or may require settlement by issuing variable number of shares. If warrants do not meet liability classification under ASC 480-10, the Company assesses the requirements under ASC 815-40, which states that contracts that require or may require the issuer to settle the contract for cash are liabilities recorded at fair value, irrespective of the likelihood of the transaction occurring that triggers the net cash settlement feature. If the warrants do not require liability classification under ASC 815-40, in order to conclude equity classification, the Company assesses whether the warrants are indexed to its common stock and whether the warrants are classified as equity under ASC 815-40 or other applicable U.S. GAAP. After all relevant assessments are made, the Company concludes whether the warrants are classified as liability or equity. Liability classified warrants are required to be accounted for at fair value both on the date of issuance and on subsequent accounting period ending dates, with all changes in fair value after the issuance date recorded in the statements of operations as a gain or loss. Equity classified warrants are accounted for at fair value on the issuance date with no changes in fair value recognized after the issuance date.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value and is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis, net of estimated forfeitures. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were adjusted. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that ultimately vest.
Net Loss Per Share	Net Loss Per Share The Company applies the two-class method to compute basic and diluted net income (loss) per share attributable to common stockholders when it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. The Company’s Series A Preferred Stock, Series B Preferred Stock and 2022 Warrants participate in any dividends declared by the Company and are therefore considered to be participating securities. The participating securities are not required to participate in the losses of the Company, and therefore during periods of loss there is no allocation required under the two-class method. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potentially dilutive common shares. For purposes of this calculation, outstanding options to purchase common stock and Series A Preferred Stock, forward contracts to issue Series A Preferred Stock, restricted stock units, warrants to purchase common stock, employee stock purchase plan stock, contingently issuable shares, Series A Preferred Stock, and Series B Preferred Stock are considered potential dilutive common shares.
Contingent Liabilities	Contingent Liabilities The Company accounts for its contingent liabilities in accordance with ASC Topic 450, Contingencies (ASC 450). A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter.
Leases	Leases The Company accounts for its leases in accordance with ASC Topic 842, Leases (ASC 842), and determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Most leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company elected not to recognize leases with an original term less than one year on its balance sheet. Operating lease right-of-use assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow, on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, the fixed and in-substance fixed contract consideration must be allocated to lease and non-lease components based on their relative fair values. Non-components of a contract (e.g., administrative tasks that do not transfer a good or service to the Company, reimbursement or payment of a lessor’s cost, etc.) do not receive an allocation of the consideration in the contract. Although allocation of consideration of lease and non-lease components is required, the Company elected the practical expedient to not separate lease components (e.g. land, building, etc.) and non-lease components (e.g., common area maintenance, consumables, etc.). The lease component results in an operating right-of-use asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense. Right-of-use assets and operating lease liabilities are remeasured upon certain modifications to leases using the present value of remaining lease payments and the estimated incremental borrowing rate upon lease modification. The Company enters into lease agreements with terms generally ranging from two to eight years. Some of the Company’s lease agreements include Company options to either extend and/or early terminate the lease, the costs of which are included in its operating lease liabilities to the extent that such options are reasonably certain of being exercised. Leases with renewal options allow the Company to extend the lease term typically between one and five years. When determining the lease term, renewal options reasonably certain of being exercised are included in the lease term. When determining if a renewal option is reasonably certain of being exercised, the Company considers several economic factors, including but not limited to, the significance of leasehold improvements incurred on the property, whether the asset is difficult to replace, underlying contractual obligations, or specific characteristics unique to that particular lease that would make it reasonably certain that the Company would exercise such option. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases. Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Company recognizes lease expense for these leases on a straight-line basis over the lease term.
Acquisitions	Acquisitions The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If the screen is met, the transaction is accounted for as an asset acquisition. If the screen is not met, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the requirements of a business. If determined to be a business combination, the Company accounts for the transaction under the acquisition method of accounting which requires the acquiring entity in a business combination to recognize the fair value of all assets acquired, liabilities assumed, and any non-controlling interest in the acquiree and establishes the acquisition date as the fair value measurement point. Accordingly, the Company recognizes assets acquired and liabilities assumed in business combinations based on the fair value estimates as of the date of acquisition. In accordance with ASC Topic 805, Business Combinations (ASC 805) the Company recognizes and measures goodwill as of the acquisition date, as the excess of the fair value of the consideration paid over the fair value of the identified net assets acquired.
Goodwill	Goodwill Goodwill represents the amount of consideration paid in excess of the fair value of the identified net assets acquired as a result of the Company’s business acquisitions accounted for using the acquisition method of accounting. Goodwill is not amortized and is subject to impairment testing at a reporting unit level on an annual basis or when a triggering event occurs that may indicate the carrying value of the goodwill is impaired. An entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Such qualitative factors include macroeconomic conditions, industry and market considerations, cost factors, overall financial performance and other relevant events. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. The Company evaluates goodwill for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable.
Indefinite-Lived Intangible Assets	Indefinite-Lived Intangible Assets Indefinite-lived intangible assets consist of in-process research and development, or IPR&D. The fair values of IPR&D assets acquired in business combinations are capitalized. These assets are treated as indefinite-lived intangible assets until completion or abandonment of the projects, at which time the assets are amortized over the remaining useful life or written off, as appropriate. Intangible assets with indefinite lives, including IPR&D, are tested for impairment if impairment indicators arise and, at a minimum, annually. However, an entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more likely than not that an indefinite-lived intangible asset’s fair value is less than its carrying amount. Otherwise, no further impairment testing is required. The indefinite-lived intangible asset impairment test consists of a one-step analysis that compares the fair value of the intangible asset with its carrying amount. If the carrying amount of an intangible asset exceeds its fair value, an impairment loss is recognized in an amount equal to that excess. The Company considers many factors in evaluating whether the value of its intangible assets with indefinite lives may not be recoverable, including, but not limited to, expected growth rates, the cost of equity and debt capital, general economic conditions, the Company’s outlook and market performance of the Company’s industry and recent and forecasted financial performance. The Company evaluates indefinite-lived intangible assets for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable.
Convertible Preferred Stock and Series A Preferred Stock Options	Convertible Preferred Stock The Company records its convertible preferred stock upon issuance at its fair value. The fair value includes the original issuance price, the settlement of any related forward contract, and is less issuance costs. The Company classifies its convertible preferred stock outside of stockholders’ deficit if the redemption of such shares is outside the Company’s control. For shares classified outside of stockholders’ deficit, the Company does not adjust the carrying value of its convertible preferred stock to redemption value until it is probable of becoming redeemable. As of December 31, 2024, there were no conditions that could have required cash redemption of the convertible preferred stock and therefore, all convertible preferred stock were classified within stockholders’ deficit. Series A Preferred Stock Options The Company classifies a portion of the fair value of the vested stock options for Series A Preferred Stock equal to the estimated redemption value on the measurement date outside of stockholders’ deficit, if the redemption of the shares underlying the options are outside the Company’s control. Any fair value in excess of the estimated redemption value is recognized as additional paid-in capital. The estimated redemption value is based on the intrinsic value of the option. The Company does not adjust the carrying value of the stock options for Series A Preferred Stock until the underlying Series A Preferred Stock is probable of becoming redeemable. The Company records the stock options for Series A Preferred Stock based on the intrinsic value of the vested options.
Variable Interest Entities	Variable Interest Entities The Company evaluates its variable interests in variable interest entities, or VIEs, and consolidates VIEs when the Company is the primary beneficiary. The Company determines whether it is the primary beneficiary of a VIE based on its assessment of whether the Company possesses both (i) the power to direct the activities that most significantly affect the VIE’s economic performance and (ii) the obligation to absorb losses that could be significant to the VIE or the right to receive benefits that could be significant to the VIE. The Company reevaluates the accounting for its VIEs upon the occurrence of events that could change the primary beneficiary conclusion.
Contingent Value Right Liability	Contingent Value Right Liability The CVRs distributed by the Company pursuant to the terms of the CVR Agreement (as defined below) represent financial instruments that are accounted for under the fair value option election in ASC Topic 825, Financial Instruments (ASC 825). Under the fair value option election, the CVRs are initially measured at the aggregate estimated fair value of the CVRs and will be subsequently remeasured at estimated fair value on a recurring basis at each reporting period date. The estimated fair value of the CVR liability was determined using a discounted cash flow methodology as of December 31, 2023 and a Monte Carlo simulation method as of December 31, 2024 to estimate future cash flows associated with the legacy assets, including the expected milestone and royalty payments under the Sobi License, net of deductions. Changes in fair value of the liability are presented in the consolidated statements of operations and comprehensive loss. The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of success, expected volatilities of revenues (Monte Carlo simulation) and risk-adjustment discount rate (discounted cash flow methodology), which represent a Level 3 measurement within the fair value hierarchy.
Forward Contract Liabilities	Forward Contract Liabilities The Company accounts for contracts related to the future issuance of its convertible preferred stock as a liability if the underlying shares include a redemption feature that may require the Company to settle the instrument by transferring an asset. The forward contract liability is carried at fair value through the date the underlying shares are issued. The fair value of the Series A Preferred Stock forward contract liability was initially measured based on the fair value of the Series A Preferred Stock issued in the 2023 Private Placement (see Note 11), less the purchase price, if any. Subsequent measurement of the fair value of the Series A Preferred Stock forward contract liability was based on the market price of the Company’s common stock, which represented the redemption and conversion value of the Series A Preferred Stock, less the purchase price, if any, on an as-converted basis. The remeasurement of the forward contract liability is based on Level 2 inputs within the fair value hierarchy as it’s based on observable market data. Changes in fair value of the liability are presented within change in fair value of forward contract liabilities in the consolidated statements of operations and comprehensive loss.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07), which requires an enhanced disclosure of significant segment expenses on an annual and interim basis. This guidance is effective for the annual period beginning the year ended December 31, 2024, and for interim periods beginning January 1, 2025, with early adoption permitted. The Company adopted the new standard during the year ended December 31, 2024 and the amendments have be applied retrospectively to all prior periods presented in the consolidated financial statements. See Note 21 for additional information. Not Yet Adopted In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09), which improves the transparency of income tax disclosures by requiring consistent categories and greater disaggregation of information in the effective tax rate reconciliation and income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. This guidance will be effective for the annual period beginning the year ended December 31, 2025. Early adoption is permitted. Upon adoption, the guidance can be applied prospectively or retrospectively. The Company is currently in the process of evaluating the impact of the standard’s adoption on its consolidated financial statements and related disclosures In November 2024, the FASB issued ASU 2024-03, Income Statement Reporting- Comprehensive Income- Expense Disaggregation Disclosures (ASU 2024-03), which requires public companies to disclose, in interim and annual reporting periods, additional information about certain expenses in notes to financial statements, including purchases of inventory, employee compensation, depreciation, amortization of intangible assets, and selling expenses. This guidance will be effective for the annual period beginning the year ended December 31, 2027 and for interim periods beginning January 1, 2028, with early adoption permitted. The Company is currently in the process of evaluating the impact of the standard’s adoption on its consolidated financial statements and related disclosures.

Leases

12 Months Ended

Dec. 31, 2024

Leases [Abstract]

Leases

7495 New Horizon Way Leases

On February 28, 2024, the Company entered into a lease agreement with 7495 RP, LLC, or the Landlord, pursuant to which it agreed to lease from the Landlord the manufacturing space located at 7495 New Horizon Way, Frederick, Maryland, or the Frederick Lease Agreement. The space consists of 19,199 leasable square feet of integrated manufacturing and office space. The lease commenced on May 1, 2024 which was the date the Landlord delivered full possession of the premises to the Company. The Frederick Lease Agreement will terminate approximately 7.2 years following the commencement date. The Company will have one option to extend the term of the Frederick Lease Agreement for a period of five years at a cost of 100% of the then-fair market value, not to exceed 103% of the then-current base rent. Base rent, which was due beginning on July 1, 2024, is $0.9 million annually and is subject to an annual upward adjustment of 3% of the then-current rental rate. In addition, the Company is obligated to pay its share of operating costs and taxes related to the property. The Company paid the first month’s rent of $0.1 million upon execution of the Frederick Lease Agreement.

The Company assessed the classification of the lease at the commencement date and concluded it should be accounted for as an operating lease. The Company recorded a lease liability and right-of-use asset of $3.6 million and $3.7 million, respectively, on the commencement date. The Frederick Lease Agreement includes a tenant improvement allowance of up to $0.7 million which was recognized as a reduction in the right-of-use asset and lease liability at the commencement date as the Company was reasonably certain to incur reimbursable costs related to alterations equal to or exceeding the amount. Additionally, the prepaid rent was included as an adjustment to the right-of-use asset. The discount rate of 14% was determined based on the Company’s incremental borrowing rate adjusted for the lease term, including any reasonably certain renewal periods.

Effective May 7, 2024, the Company and the Landlord entered into the first amendment to the Frederick Lease Agreement, or the First Frederick Lease Agreement Amendment, providing for the expansion of the premises leased pursuant to the Frederick Lease Agreement by approximately 7,842 square feet. In connection with the expansion of the leased premises, the Company is obligated to pay $0.3 million in additional annual base rent for the first year of the term, which is subject to an annual upward adjustment of 3% of the then-current rental rate, as well as its share of operating costs and taxes. The lease commenced on May 7, 2024 which was the date the Landlord delivered full possession of the premises to the Company and will be coterminous with the Frederick Lease Agreement. The rent commencement date was September 1, 2024.

The Company assessed the classification of the lease at the commencement date and concluded it should be accounted for as an operating lease. The Company recorded a lease liability and right-of-use asset each of $1.2 million on the commencement date. The First Frederick Lease Agreement Amendment includes a tenant improvement allowance of up to $0.1 million which was recognized as a reduction in the right-of-use asset and lease liability at the commencement date as the Company was reasonably certain to incur reimbursable costs related to alterations equal to or exceeding the amount. The discount rate of 14% was determined based on the Company’s incremental borrowing rate adjusted for the lease term.

Effective August 30, 2024, the Company and the Landlord entered into the second amendment to the Frederick Lease Agreement, or the Second Frederick Lease Agreement Amendment, providing for the expansion of the premises leased pursuant to the Frederick Lease Agreement and First Frederick Lease Agreement Amendment by approximately 2,009 square feet. In connection with the expansion of the leased premises, the Company is obligated to pay $0.1 million in additional annual base rent for the first year of the term, which is subject to an annual upward adjustment of 3% of the then-current rental rate, as well as its share of operating costs and taxes. The lease commenced on September 1, 2024, which was the date the Landlord delivered full possession of the premises to the Company and will be coterminous with the Frederick Lease Agreement. The rent commencement date was September 1, 2024.

The Company assessed the classification of the lease at the commencement date and concluded it should be accounted for as an operating lease. The Company recorded a lease liability and right-of-use asset each of $0.3 million on the commencement date. The discount rate of 14% was determined based on the Company’s incremental borrowing rate adjusted for the lease term.

The Company secured a letter of credit from Silicon Valley Bank, a division of First-Citizens Bank & Trust Company (successor by purchase to the Federal Deposit Insurance Corporation as Receiver for Silicon Valley Bridge Bank, N.A. (as successor to Silicon Valley Bank)), or SVB, for $0.3 million for the Frederick Lease Agreement, the First Frederick Lease Agreement Amendment and the Second Frederick Lease Agreement Amendment, which is recognized as long-term restricted cash as of December 31, 2024 and renews automatically each year.

65 Grove Street Lease

In July 2019, the Company entered into a lease with BRE-BMR Grove LLC for 25,078 square feet of laboratory and office space located at 65 Grove Street, Watertown, Massachusetts, or the Watertown Lease Agreement. As part of the Watertown Lease Agreement, the Company incurred $0.8 million in non-reimbursable construction costs. The lease began in March 2020, when the Company took control of the office space, and the lease term is 8 years. The discount rate of 8.9% was determined based on the Company’s incremental borrowing rate adjusted for the lease term, including any reasonably certain renewal periods. In connection with the Watertown Lease Agreement, the Company secured a letter of credit from SVB for $1.6 million.

On September 1, 2022, the Company entered into an amendment, or the Watertown Lease Agreement Amendment, to its lease agreement with BRE-BMR Grove LLC, originally entered into on July 23, 2019 to expand the Company’s laboratory and office space located at 65 Grove Street, Watertown, Massachusetts by 7,216 square feet. The lease term began on September 1, 2022, consistent with when the Company took control of the office space and the expected lease term is 5.7 years. The discount rate of 11.3% was determined based on the Company’s incremental borrowing rate adjusted for the lease term including any reasonably certain renewal periods. Rent payments began in November 2022, and the base rent for the first year is $0.1 million per month. The Company recorded the right-of-use asset and operating lease liabilities of $3.2 million during the year ended December 31, 2022 as control of the premises was transferred to the Company.

On October 6, 2022, the Company entered into a sublease agreement to sublease 7,216 square feet of space currently rented by the Company at 65 Grove Street, Watertown, Massachusetts. The sublease commenced on October 24, 2022, when the Company, the sublessee and BRE-BMR Grove LLC, executed a Consent to Sublease. The term of the sublease expired on March 31, 2024 with no option to extend the sublease term. Sublease income is included within other income, net in the consolidated statements of operations and comprehensive loss.

As a result of the sublease agreement and Consent to Sublease, rent payments to BRE-BMR Grove LLC for the lease of the office space increased. The change of consideration in the contract was accounted for as a lease modification and the right-of-use asset and lease liability were remeasured at the modification date of October 24, 2022. The discount rate of 11.9% was determined based on the Company’s incremental borrowing rate adjusted for the lease term including any reasonably certain renewal periods as of October 24, 2022, resulting in a decrease of less than $0.1 million to both the right-of-use asset and lease liabilities.

In May 2023, the Company received notice from BRE-BMR Grove LLC that the requirements to reduce the amount of the letter of credit for the Watertown Lease Agreement had been met. In connection therewith, in June 2023, the Company secured a letter of credit from JPMorgan Chase Bank, N.A. for $1.4 million, which is recognized as long-term restricted cash as of December 31, 2024 and 2023, and renews automatically each year. The $1.6 million letter of credit with SVB was released from restriction and returned to the Company on July 17, 2023, and therefore was reclassified into cash and cash equivalents in the consolidated balance sheets.

On October 31, 2023, in connection with entering into Amendment No. 1 to the License and Development Agreement with Sobi as described in Note 14, the Company entered into a sublease agreement with Sobi to sublease approximately 5,600 square feet of space currently rented by the Company at 65 Grove Street, Watertown, Massachusetts for which Sobi paid $1.0 million upfront rental payment. The sublease commenced on November 6, 2023, when the Company, Sobi, and BRE-BMR Grove LLC, executed a Consent to Sublease. The term of the sublease expired on November 5, 2024 with no option to extend the sublease term. As of December 31, 2023, deferred rent of $0.8 million is included within accrued expenses and other current liabilities in the consolidated balance sheet.

During the year ended December 31, 2023, the Company determined that the right-of-use asset related to the operating lease for approximately 7,216 square feet at 65 Grove Street was partially impaired as of November 30, 2023. As a result, the Company recognized a $0.7 million right-of-use asset impairment charge in impairment of long-lived assets on its consolidated statements of operations and comprehensive loss during the year ended December 31, 2023.

As a result of the expiration of the sublease to Sobi in November 2024 and the Company’s decision to cease use of its office and laboratory space at 65 Grove Street, Watertown, Massachusetts, the Company assessed the right-of-use assets and related furniture and fixtures associated with the Watertown Lease Agreement and Watertown Lease Agreement Amendment

for impairment. The carrying value of each asset group was compared against the future net undiscounted cash flows projected to be generated over the remaining lease terms. These projections included management's estimates of cash inflows from potential sublease income. The carrying amount of the asset groups was found to be unrecoverable, thus the Company assessed the fair value of each asset group. The fair value was determined using the income approach, whereby the Company discounted the estimated net cash flows using a rate commensurate with the Company’s estimated incremental borrowing rate. As a result of this assessment, which included unrecoverable operating and maintenance costs, the Company determined that each asset group was fully impaired. As such, an impairment charge of $7.6 million was recognized during the year ended December 31, 2024, $7.4 million of which related to the right-of-use assets and $0.2 million related to property and equipment.

704 Quince Orchard Road Leases

In connection with the Merger, the Company acquired two operating leases for office and laboratory space in Gaithersburg, Maryland. The leases expire in January 2027 and do not contain any renewal rights. The discount rate of 11.5% was determined based on the Company’s incremental borrowing rate adjusted for the lease term.

Rent expense for the years ended December 31, 2024 and 2023 was $5.5 million, $3.8 million, respectively.

For the years ended December 31, 2024 and 2023, the components of lease costs were as follows (in thousands):


	Year Ended December 31,
	2024		2023
Operating lease cost	$	3,856	$	2,828
Variable lease cost	1,609		965
Short-term lease cost	28		8
Less sublease income	(1,099)		(1,172)
Total lease cost	$	4,394	$	2,629

The maturity of the Company’s operating lease liabilities as of December 31, 2024 were as follows (in thousands):


	December 31,
	2024
2025	$	3,645
2026	4,538
2027	4,345
2028	2,314
2029	1,409
Thereafter	2,188
Total future minimum lease payments	18,439
Less: Imputed interest	4,455
Total operating lease liabilities	$	13,984

The supplemental disclosure for the statement of cash flows related to operating leases were as follows (in thousands):


	December 31,
	2024		2023
Cash paid for amounts included in the measurement of lease liabilities:	$	3,559	$	2,696

Other than the initial recording of the right-of-use assets and lease liabilities for the Frederick Lease Agreement, First Frederick Lease Agreement Amendment, and Second Frederick Lease Agreement Amendment during the year ended December 31, 2024, the impairments on the right-of-use assets for the Watertown Lease Agreement and Watertown Lease Agreement Amendment during the years ended December 31, 2024 and 2023, as applicable, and the assumption of the right-of-use assets and lease liabilities in connection with the Merger during the year ended December 31, 2023, which were non-cash, the changes in the Company’s right-of-use assets and lease liabilities for the years ended December 31, 2024 and 2023 are reflected in the non-cash lease expense and accrued expenses and other liabilities, respectively, in the consolidated statements of cash flows.

The following summarizes additional information related to the Company’s operating leases:


	December 31,
	2024		2023
Weighted-average remaining lease term	4.5 years		4.3 years
Weighted-average discount rate	11.7	%	9.9	%

Fair Value Measurements - Schedule of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Cash and cash equivalents	$ 212,610	$ 76,911
Long-term restricted cash	1,669	1,377
Total cash, cash equivalents, and restricted cash	$ 214,279	$ 78,288	$ 108,038

Stock Incentive Plans - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 6,582	$ 25,778
Ginkgo Bioworks Holdings, Inc
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense		1,500
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	3,217	12,985
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 3,365	$ 12,793

Collaboration and License Agreements - Genovis AB (publ.) (Narrative) (Details) $ in Millions	1 Months Ended
	Feb. 28, 2023 USD ($)
Genovis AB
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment	$ 4.0

Merger (Tables)

12 Months Ended

Dec. 31, 2024

Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]

Schedule of Fair Value of Consideration

The total fair value of the consideration of $168.5 million as of the Closing Date is summarized as follows (in thousands):


Forward contract to issue common stock	$	2,713
Forward contract to issue Series A Preferred Stock	155,308
Stock options allocated to consideration paid	10,444
Total consideration	$	168,465

Schedule of Allocation of the Purchase Price to the Estimated Fair Values of the Assets Acquired and Liabilities Assumed

The following table presents the allocation of the purchase price to the estimated fair values of the assets acquired and liabilities assumed as of the Closing Date (in thousands):


Assets acquired:	As of November 13, 2023
Cash and cash equivalents	$	6,561
Prepaid expenses and other current assets	309
Property and equipment, net	215
Right-of-use asset, net	915
In-process research and development assets	150,600
Goodwill	48,163
	$	206,763
Liabilities assumed
Accrued expenses and other current liabilities	$	2,530
Lease liability	292
Lease liability, net of current portion	623
Deferred tax liability	34,853
	$	38,298

Net assets acquired	$	168,465

Schedule of Intangible Assets Acquired

The following summarizes the Company’s intangible assets acquired in the Merger (in thousands):


	Acquisition Date Fair Value
Descartes-08 for MG	$	93,900
Descartes-08 for SLE	56,700
Total in-process research and development assets	$	150,600

Schedule of Pro Forma Financial Information

The following unaudited pro forma financial information reflects the consolidated results of operations of the Company as if the Merger had taken place on January 1, 2022. The unaudited pro forma financial information is not necessarily indicative of the results of operations as they would have been had the transactions been effected on the assumed date (in thousands):


	Year Ended December 31,
	2023
Revenue	$	26,004
Net loss	$	(232,259)

Revenue Arrangements

12 Months Ended

Dec. 31, 2024

Revenue from Contract with Customer [Abstract]

Revenue Arrangements

Collaboration and license revenue

Astellas Gene Therapies

In January 2023, the Company entered into the License and Development Agreement, or the Astellas Agreement, with Audentes Therapeutics, Inc., or Astellas. Under the Astellas Agreement, the Company granted Astellas an exclusive license to the Company’s IdeXork technology arising from Xork, to develop and commercialize Xork for use in Pompe disease in combination with an Astellas gene therapy investigational or authorized product. Xork, Genovis’ IgG Protease, was licensed pursuant to an Exclusive License Agreement, or the Genovis Agreement, with Genovis AB (publ.), or Genovis, as described in Note 16 to these consolidated financial statements. Astellas paid a $10.0 million upfront payment to the Company upon signing of the Astellas Agreement, and the Company was entitled to receive up to $340.0 million in future additional payments over the course of the partnership that were contingent on the achievement of various development and regulatory milestones and, if commercialized, sales thresholds for annual net sales where Xork is used as a pre-treatment for an Astellas investigational or authorized product. The Company was also eligible for tiered royalty payments ranging from low to high single digits. Any proceeds received from milestone payments or royalties relating to Xork would have been required to be distributed to holders of CVRs, net of certain deductions.

Pursuant to the Astellas Agreement, the Company would have had the exclusive right and responsibility to complete research and development of Xork products and to conduct all preclinical studies and clinical trials for Xork for use in Pompe disease with an Astellas gene therapy investigational or authorized product, or the Xork Development Services. Astellas reimbursed the Company for 25% of all budgeted costs incurred to complete the development of Xork for use in Pompe disease with an Astellas gene therapy investigational or authorized product. The Company would have had control and responsibility over regulatory filings, including any investigational drug applications, biologics license applications, and marketing authorization applications relating to the licensed product. Astellas would have had the exclusive right and responsibility to research, develop, and commercialize Astellas products used in combination with Xork and would have had control and responsibility over all regulatory filings, including any investigational drug applications, biologics license applications, and marketing authorization applications, relating to Astellas products and Astellas products used in combination with Xork.

The Company determined the Astellas Agreement represented a service arrangement under the scope of ASC 606. The Company determined that the sublicense of Xork to Astellas, the licensed know-how, and the Xork Development Services represented a single promise and performance obligation to be transferred to Astellas over time due to the nature of the promises in the contract. As such, the Company recognized the transaction price as revenue utilizing the input method to measure the progress of satisfying the single performance obligation to Astellas.

In determining the transaction price, the Company concluded the upfront payment of $10.0 million and development cost reimbursements of $5.5 million would be included in the initial transaction price. All other development milestones would be fully constrained and would only have been included in the transaction price when the applicable milestone was deemed probable of achievement. Each of these variable consideration items were evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should have been constrained until

they became probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt and timing of such development milestones was outside the control of the Company and probability of success criteria was estimated. The Company re-evaluated the transaction price in each reporting period, as uncertain events were resolved, or as other changes in circumstances occurred. In accordance with ASC 606, the Company would have only recognized revenue associated with sales-based milestones and royalties when the subsequent sales thresholds were reached and underlying sales occurred, respectively. The Company determined that a significant financing component did not exist in its arrangement with Astellas. The Company also determined the options to negotiate additional fields, enter into a clinical supply agreement, and enter into a commercial supply agreement did not represent material rights under the Astellas Agreement. Astellas had the right to terminate the Astellas Agreement in its entirety or on a field-by-field basis, upon 90 days’ written notice to the Company.

In March 2024, the Company was notified by Astellas of its intention to terminate the Astellas Agreement, which occurred effective June 6, 2024.

As of December 31, 2024, there were no unsatisfied performance obligations related to the Astellas Agreement. As of December 31, 2023, the Company recorded $2.3 million as a short-term contract liability and $3.5 million as a long-term contract liability, representing deferred revenue associated with the Astellas Agreement. As of December 31, 2024 and 2023, the Company recorded a receivable of $0.1 million and $0.3 million, respectively, representing billings for the Xork Development Services that were subject to reimbursement by Astellas. Revenue of $6.3 million related to the Astellas Agreement was recognized during the year ended December 31, 2024, inclusive of $3.2 million of revenue recognized from performance obligations related to prior periods as a result of the change in transaction price during the year ended December 31, 2024. Revenue of $5.5 million related to the Astellas Agreement was recognized during the year ended December 31, 2023.

Takeda Pharmaceuticals USA, Inc.

License and Development Agreement

On October 1, 2021, the Company entered into a License Agreement, or the Takeda Agreement, with Takeda Pharmaceuticals USA, Inc., or Takeda. Under the Takeda Agreement, the Company granted Takeda an exclusive license to the Company’s ImmTOR technology initially for two specified disease indications within the field of lysosomal storage disorders. Takeda paid a $3.0 million upfront payment to the Company upon signing of the Takeda Agreement, and the Company was entitled to receive up to $1.124 billion in future additional payments over the course of the partnership that were contingent on the achievement of development or commercial milestones or Takeda’s election to continue its activities at specified development stages. The Company was also eligible for tiered royalties on future commercial sales of any licensed products.

Pursuant to the Takeda Agreement, the Company determined the Takeda Agreement represented a service arrangement under the scope of ASC 606, and given the reversion of the rights under the Takeda Agreement represented a penalty in substance for a termination by Takeda, the contract term would remain the stated term of the Takeda Agreement. The Company determined that the research license, the licensed know-how, and the manufactured supply and delivery of materials represented a single promise and performance obligation to be transferred to Takeda over time due to the nature of the promises in the contract. The delivery of the manufactured supply was the predominant promise within the arrangement, as it was essential to the utility of the licensed intellectual property. The material supplied by the Company to Takeda was unique to the Company and cannot be obtained by other vendors. As such, consideration in the initial transaction price was allocated to the single performance obligation and the recognition period would not extend beyond the initial contractual period. The Company recognized the revenue associated with the upfront payment and combined single performance obligation utilizing the output method over the term that manufactured supply was delivered to Takeda.

In determining the transaction price, the Company concluded the payment associated with all the performance milestones was fully constrained and only included in the transaction price when the respective milestone was deemed probable of achievement. Each of these variable consideration items were evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt and timing of such study milestones is outside the control of the Company and probability of success criteria is estimated. The Company re-evaluated the transaction price in each reporting period, as uncertain events were resolved, or as other changes in circumstances occurred. Takeda had the right to exercise covenant release rights on a field-by-field basis. If Takeda exercised its covenant release rights, the Company could have received exercise payments per indication and would have been entitled to significant development and commercial milestone payments and tiered royalties on commercial sales. The Company determined that a significant financing component did not exist in its arrangement with Takeda. The Company also determined the options to negotiate additional fields, pursue other products, enter into a supply agreement explore additional fields, and pursue additional development under the initial fields did not represent material rights under the agreement. Takeda had the right to terminate the Takeda Agreement in its entirety or on a field-by-field basis, upon 90 days’ written notice to the Company.

On March 9, 2023, the Company was notified by Takeda of the achievement of the milestone event related to the completion of a non-clinical milestone for one of the specified disease indications within the field of lysosomal storage

disorders under the Takeda Agreement. Accordingly, the Company received a milestone payment of $0.5 million during the year ended December 31, 2023.

The Takeda Agreement was terminated effective July 25, 2023, following Takeda’s decision to discontinue discovery and preclinical activities in adeno-associated virus, or AAV, gene therapy.

As of December 31, 2024 and 2023, there were no unsatisfied performance obligations related to the Takeda Agreement. No revenue and revenue of $0.6 million related to the Takeda Agreement was recognized during the years ended December 31, 2024 and 2023, respectively.

Swedish Orphan Biovitrum AB (publ.)

License and Development Agreement

On June 11, 2020, the Company and Sobi entered into a License and Development Agreement. Pursuant to the Sobi License, the Company agreed to grant Sobi an exclusive, worldwide (except as to Greater China) license to develop, manufacture and commercialize the SEL-212 drug candidate, which is currently in development for the treatment of chronic refractory gout. The SEL-212 drug candidate is a pharmaceutical composition containing a combination of SEL-037, or the Compound, and ImmTOR. Pursuant to the Sobi License, in consideration of the license, Sobi agreed to pay the Company a one-time, upfront payment of $75.0 million. Sobi has also agreed to make milestone payments totaling up to $630.0 million to the Company upon the achievement of various development and regulatory milestones and, if commercialized, sales thresholds for annual net sales of SEL-212, and tiered royalty payments ranging from the low double digits on the lowest sales tier to the high teens on the highest sales tier. Any proceeds received from milestone payments or royalties relating to the Sobi License would be required to be distributed to holders of CVRs, net of certain deductions.

Pursuant to the Sobi License, the Company agreed to supply (at cost) quantities of the Compound and ImmTOR as necessary for completion of the two Phase 3 clinical trials of SEL-212 (DISSOLVE I and DISSOLVE II) and a six-month placebo extension. The Company was required to supply quantities of the Compound until all rights to the Compound and any materials needed to manufacture the Compound were transferred to Sobi, which transfer occurred upon the execution of Amendment No. 1 to the License and Development Agreement on October 31, 2023. Sobi has agreed to reimburse the Company for all budgeted costs incurred to complete development of SEL-212, including but not limited to costs incurred while conducting and completing the Phase 3 DISSOLVE trials, except for any costs of additional development activities required that are related to ImmTOR and that are unrelated to SEL-212. Sobi will have control and responsibility over all regulatory filings, including any investigational drug applications (IND), biologics license applications (BLA), and marketing authorization applications (MAA) relating to the licensed product.

The transactions contemplated by the Sobi License were consummated on July 28, 2020. Sobi may terminate the Sobi License for any reason upon 180 days’ written notice to the Company, whereby all rights granted under the Sobi License would revert back to the Company. In addition, if Sobi were to terminate the Sobi License, the Company has the option to obtain a license to all patents and know-how necessary to exploit SEL-212 in existence as of the termination date from Sobi in return for making an equitable royalty payment to Sobi.

Additionally, on June 11, 2020, the Company entered into the Sobi Purchase Agreement in connection with the Sobi License. The closing of the Sobi Private Placement occurred on July 31, 2020, following the closing of the transactions contemplated under the Sobi License. See Note 12 for details.

The Company determined that the Sobi License represents a service arrangement under the scope of ASC 606. In addition, given the Sobi License and Sobi Purchase Agreement were executed contemporaneously and negotiated as a package with a single commercial objective, the Company will account for the two agreements as a single contract. The term of the Sobi License commenced upon the effective date of July 28, 2020 and will continue on a product-by-product basis until the royalty terms for each country have expired. The royalty term for a given product begins upon the first commercial sale of the product in a country and ends at the later of ten years from the first commercial sale, expiration of the last valid patent claim covering the product and expiration of all regulatory exclusivity periods for the product in a country. Given the reversion of the rights under the Sobi License represents a penalty in substance for a termination by Sobi, the contract term would remain the stated term of the Sobi License.

The Company determined that the Sobi License contained three distinct performance obligations due to the nature of the promises in the contract, which includes conducting the Phase 3 DISSOLVE trials, Sobi’s option to set-up a second source supplier, and a combined obligation comprised of the delivery of the license to SEL-212, transfer of the know-how and the manufacturing and delivery of SEL-212 supply for development, or the Combined License Obligation. As the set-up of a second source supplier was optional for Sobi and the Company was to be reimbursed at cost for its efforts in the subsequent set-up and technology transfer, the option for this future service was determined to be at a significant and incremental discount to its standalone selling price and treated as a material right in the arrangement, namely a distinct performance obligation.

In determining the transaction price, the Company concluded the upfront payment of $75.0 million and the $5.0 million development milestone associated with the dosing of the first patient in the Phase 3 DISSOLVE trials were included in the

transaction price. All other development milestones will be fully constrained and only be included in the transaction price when the respective milestone is deemed probable of achievement. Each of these variable consideration items was evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should be constrained until they become probable. As part of the evaluation of the constraint, the Company considered numerous factors, including that receipt of such milestones is outside the control of the Company and probability of success criteria is estimated. The Company re-evaluates the transaction price in each reporting period, as uncertain events are resolved. In accordance with ASC 606, the Company will only recognize revenue associated with sales-based milestones and royalties when the subsequent sales thresholds are reached and underlying sales occur, respectively. In connection with the Sobi Purchase Agreement, the Company determined that the gross proceeds of $25.0 million from the Sobi Private Placement included a premium to the fair value of the Company’s shares as of July 28, 2020 equal to approximately $14.5 million. The premium amount is included in the transaction price for revenue recognition. The Company estimates and includes in the transaction price the total reimbursements to be received from Sobi for both the manufacturing and delivery of the Compound and ImmTOR as well as conducting the Phase 3 DISSOLVE trials. The Company determined that a significant financing component does not exist in its arrangement with Sobi.

The Company allocated the transaction price based on the relative standalone selling prices of the three distinct performance obligations. The Company estimated the standalone selling price of conducting the Phase 3 DISSOLVE trials by forecasting its anticipated costs and applying a margin reflective of the industry. The Company determined the standalone selling price of the second source supplier option by determining the discount given to Sobi multiplied by the likelihood that Sobi would have exercised the option in the future. Similar to the Phase 3 program estimate, the Company estimated the discount of the option by forecasting the set-up costs and applying a margin that is reflective of the industry. As the Company was to provide the set-up and technology transfer services and the future supply at cost, the discount of the option was equal to the margin amount. The Company considered discussions with Sobi as well as probability of regulatory success of SEL-212 in determining the likelihood of exercise. The Company estimated the standalone selling price of the Combined License Obligation by utilizing a discounted cash flow model.

The Company determined that the delivery of the supply to Sobi best represented the pattern of delivery of the Combined License Obligation as the supply was essential to the utility of the license and know-how. The Company recognized the revenue allocated to the Combined License Obligation by utilizing the output method. The Company estimated the total supply of the Compound and ImmTOR required during the clinical trial period and recognized revenue as this supply was shipped for use in the clinical trials. The Company recognized the revenue allocated to the conducting of the Phase 3 DISSOLVE trials obligation by utilizing the input method. The Company estimated the total budgeted costs to be incurred over the Phase 3 DISSOLVE trials and recognized revenue as these costs were incurred. The Company’s costs best represented the pattern of transfer as these captured all performance of the trials completed to date and were readily able to be measured. The Company was to recognize the revenue allocated to the second source supplier option when the future services and goods were transferred.

On June 29, 2022, the Company completed enrollment of the DISSOLVE II trial. The completion of enrollment of the DISSOLVE II trial resulted in the achievement of a development milestone and a $10.0 million payment obligation from Sobi to the Company. This amount was added to the overall transaction price and payment was received during the year ended December 31, 2022.

On October 31, 2023, the Company and Sobi entered into Amendment No. 1 to the License and Development Agreement, pursuant to which the Company granted Sobi an exclusive license to manufacture ImmTOR solely in connection with Sobi’s development of SEL-212 under the License and Development Agreement and transferred certain contracts and manufacturing equipment to Sobi. Additionally, Sobi’s option to set-up a second source supplier was removed as a result of the amendment. Further, in connection with entry into the amendment, Sobi agreed to make employment offers to certain of the Company’s employees engaged in ImmTOR manufacturing activities on or prior to a specified date, and the Company agreed not to terminate the employment of such employees prior to such specified date. The Company maintains no responsibilities to Sobi to manufacture, or supply Sobi with, ImmTOR under the Sobi License.

On June 28, 2024, Sobi initiated a rolling biologics license application to the FDA for SEL-212 for the potential treatment of chronic refractory gout which resulted in the achievement of a development milestone and a $30.0 million payment obligation from Sobi to the Company. As a result, the development milestone was no longer constrained and $30.0 million was recognized as revenue during the year ended December 31, 2024 as there were no remaining performance obligations under the Sobi License. The proceeds from the achievement of the development milestone were received from Sobi in July 2024 and are expected to be included, net of deductions as specified in the CVR Agreement, in the next scheduled distribution to holders of the CVRs in March 2025.

As of December 31, 2024 and 2023, the Company recorded a total outstanding receivable of $0.1 million and $4.6 million, respectively, representing billings for the Phase 3 DISSOLVE program that are subject to reimbursement by Sobi. Additionally, as of December 31, 2023, the Company recorded a total unbilled receivable of $3.0 million representing revenue earned but not yet billed for the Phase 3 DISSOLVE program. As of December 31, 2024, there was no unbilled receivable outstanding. Revenue of $31.9 million, inclusive of the $30.0 million development milestone, related to the Sobi License was

recognized during the year ended December 31, 2024, and $1.9 million of revenue recognized from performance obligations related to prior periods as a result of the change in transaction price during the year ended December 31, 2024. Revenue of $19.4 million related to the Sobi License was recognized during the year ended December 31, 2023, inclusive of $1.1 million of revenue recognized from performance obligations related to prior periods as a result of the change in transaction price during the year ended December 31, 2023.

Sarepta Therapeutics, Inc.

Research License and Option Agreement

In June 2020, the Company and Sarepta Therapeutics, Inc., or Sarepta, entered into a Research License and Option Agreement, or the Sarepta Agreement. Pursuant to the Sarepta Agreement, the Company agreed to grant Sarepta a license under the Company’s intellectual property rights covering the Company’s antigen-specific biodegradable nanoparticle encapsulating ImmTOR to research and evaluate ImmTOR in combination with Sarepta’s adeno-associated virus gene therapy technology, or gene editing technology, using viral or non-viral delivery, to treat Duchenne Muscular Dystrophy and certain Limb-Girdle Muscular Dystrophy subtypes, or the Indications. Sarepta initially had an option term of 24 months during which it could opt-in to obtain an exclusive license to further develop and commercialize the product to treat at least one Indication, with a potential to extend the option term for an additional fee. The Company agreed to supply ImmTOR to Sarepta for clinical supply on a cost-plus basis under the Sarepta Agreement.

Sarepta paid a $2.0 million upfront payment to the Company upon signing of the Sarepta Agreement, and the Company was eligible to receive additional preclinical payments during the option term. If Sarepta opted in to an exclusive license agreement, the Company could have received option exercise payments per Indication upon execution of the exclusive license, and the Company would have been entitled to significant development and commercial milestone payments and tiered royalties ranging from the mid-to-high single digits based on net sales.

Pursuant to the Sarepta Agreement, the Company determined the Sarepta Agreement represented a service arrangement under the scope of ASC 606, with a 24-month contract duration. Given the reversion of the rights under the Sarepta Agreement represents a penalty in substance for a termination by Sarepta, the contract term would remain the stated term of the Sarepta Agreement.

The Company determined that the Sarepta Agreement and supply obligation including the delivery of the research license, the licensed know-how, the manufactured supply and delivery of materials represented a single promise and performance obligation to be transferred to Sarepta over time due to the nature of the promises in the contract. The delivery of the manufactured supply was the predominant promise within the arrangement, as it was essential to the utility of the licensed intellectual property. As such, consideration in the initial transaction price was allocated to the single performance obligation based on the contractual price.

In determining the transaction price, the Company concluded the payment associated with all the performance milestones was fully constrained and would only be included in the transaction price when the respective milestone was deemed probable of achievement. Each of these variable consideration items was evaluated under the most likely amount method to determine whether such amounts were probable of occurrence, or whether such amounts should have been constrained until they became probable. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of such study milestones was outside the control of the Company and probability of success criteria was estimated.

The Company also determined the option to enter into a future commercial license agreement and extend the term of the option did not represent a material right since it was not priced at an incremental discount. Sarepta had the right to terminate the Sarepta Agreement for any reason upon 30 days’ written notice to the Company. The Sarepta Agreement contained other customary terms and conditions, including representations and warranties, covenants, termination, and indemnification obligations in favor of each party.

On April 13, 2021, the Company was notified by Sarepta of the achievement of the milestone event related to the completion of a non-clinical study for Duchenne muscular dystrophy and certain limb-girdle muscular dystrophies under the Sarepta Agreement. Accordingly, the Company received a milestone payment of $3.0 million during the three months ended June 30, 2021.

On June 10, 2022, the Company was notified by Sarepta that Sarepta would be extending their options under the Sarepta Agreement. In exchange for a nine-month extension to Sarepta’s options to both Duchenne muscular dystrophy and certain limb-girdle muscular dystrophies, the Company received a milestone payment of $2.0 million during the year ended December 31, 2022.

On June 15, 2022, the Company was notified by Sarepta of the achievement of a milestone event related to certain preclinical study milestones under the Sarepta Agreement. Accordingly, the Company received a milestone payment of $4.0 million during the year ended December 31, 2022.

On March 13, 2023, the Company was notified by Sarepta that Sarepta would not be exercising its exclusive option under the Sarepta Agreement. The Sarepta Agreement terminated upon the expiration of the option in March 2023.

As of December 31, 2024 and 2023, there were no unsatisfied performance obligations related to the Sarepta Agreement. No revenue and revenue of $0.5 million related to the Sarepta Agreement was recognized during the years ended December 31, 2024 and 2023, respectively.

Transaction Price Allocated to Future Performance Obligations

Remaining performance obligations represent the transaction price of contracts for which work has not been performed, or has been partially performed. As of December 31, 2024, there were no unsatisfied performance obligations from contracts with customers.

Contract Balances from Contracts with Customers

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2024 (in thousands):


	Balance at						Balance at
	beginning of period		Additions		Deductions		end of period
Contract liabilities:
Deferred revenue	$	5,849	$	—	$	(5,849)	$	—
Total contract liabilities	$	5,849	$	—	$	(5,849)	$	—

Grant revenue

National Institute of Neurological Disorders and Stroke of the National Institutes of Health

In June 2024, the Company received funding approval from the National Institute of Neurological Disorders and Stroke of the National Institutes of Health, or NINDS, for an award of $1.5 million granted for the budget period, which runs from June 2024 through May 2025. Subject to the availability of funds and satisfactory progress of the project, an additional $1.5 million has been recommended by NINDS to be awarded for the budget period June 2025 through May 2026. The initial $1.5 million funding was provided by NINDS to further the Company’s use of RNA-based CAR-T cells to combat autoantibody-associated autoimmune disorders. Grant funding is to be used solely for manufacturing of RNA-based CAR-T cells and analysis of samples to inform mechanism of action. The award period runs through May 31, 2026. The Company will recognize grant revenue when expenses reimbursable under the grant have been incurred.

As of December 31, 2024, the Company recorded a receivable of $0.6 million that is subject to reimbursement by NINDS. Accordingly, the Company recognized grant revenue of $0.6 million during the year ended December 31, 2024.

- 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
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-9

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-10

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-15

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-12

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-13

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org/606/tableOfContent

+ Details

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Cash Equivalents, Marketable Securities and Investments Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Marketable securities consist of securities with remaining maturities greater than 90 days when purchased. The Company classifies these marketable securities as available-for-sale and records them at fair value in the accompanying consolidated balance sheets. Marketable securities with less than one year until maturity are classified as short term, while marketable securities with maturities greater than one year are classified as long term. Unrealized gains or losses are included in accumulated other comprehensive loss. Premiums or discounts from par value are amortized to interest income over the life of the underlying investment. Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined based on the specific identification method for purposes of recording realized gains and losses. The Company has also in the past invested in equity securities of a company whose securities are not publicly traded and where fair value is not readily available. This investment is recorded using cost minus impairment adjusted for changes in observable prices, depending on our ownership percentage and other factors that suggest we have significant influence. The Company monitors this investment to evaluate whether any increase or decline in its value has occurred, based on the implied value of recent company financings, public market prices of comparable companies and general market conditions. This investment is included in investments in the consolidated balance sheets. Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash, cash equivalents, short-term deposits, investments, accounts receivable, and unbilled receivables. Cash and cash equivalents are deposited with federally insured financial institutions in the United States and may, at times, exceed federally insured limits. Management believes that the financial institutions that hold the Company’s deposits are financially creditworthy and, accordingly, minimal risk exists with respect to those balances. Fair Value of Financial Instruments The Company’s financial instruments consist mainly of cash equivalents, restricted cash, accounts receivable, accounts payable, accrued expenses and other current liabilities, investments, warrants to purchase common stock, forward contract liabilities, and contingent value rights. The carrying amounts of cash equivalents, restricted cash, accounts receivable, accounts payable, and accrued expenses and other current liabilities approximate their estimated fair value due to their short-term maturities. Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three-level hierarchy is used to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements), and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy are described below: Level 1—Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2—Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. If the asset or liability has a specified (contractual) term, a Level 2 input must be observable for substantially the full term of the asset or liability. Level 3—Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair value of warrant liabilities and contingent value rights are determined using Level 3 inputs. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may change for many instruments. This condition could cause an instrument to be reclassified within levels in the fair value hierarchy. The carrying amounts reflected in the consolidated balance sheet for investments approximate fair value and are assessed for impairment quarterly. Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, generally seven years for furniture and fixtures, five years for laboratory equipment, software and office equipment and three years for computer equipment. Leasehold improvements are amortized over their useful life or the life of the lease, whichever is shorter. Major additions and betterments are capitalized. Maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to operations as incurred. Costs incurred for construction in progress are recorded as assets and are not amortized until the construction is substantially complete and the assets are ready for their intended use. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. In order to determine if assets have been impaired, assets are tested at the lowest level for which identifiable independent cash flows are available. An impairment loss is recognized when the sum of projected undiscounted cash flows is less than the carrying value of the asset group. The measurement of the impairment loss to be recognized is based on the difference between the fair value and the carrying value of the asset group. The Company recognized an impairment charge on its right of use assets and related furniture and fixtures during the year ended December 31, 2024 and on a right-of-use asset during the year ended December 31, 2023. Debt Issuance Costs Debt issuance costs and fees paid to lenders are recorded as a direct deduction from the face amount of the related debt. Debt issuance costs are amortized over the term of the related debt using the effective interest method and recorded as interest expense. Accumulated Other Comprehensive Loss Comprehensive loss is defined as the change in the equity of a business entity during a period from transactions and other events and circumstances from non-owner sources. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners. Comprehensive loss consists of: (i) all components of net loss and (ii) all components of comprehensive loss other than net loss, referred to as other comprehensive loss. Other comprehensive loss is comprised of unrealized gains and losses on debt securities and foreign currency translation adjustments. Collaboration and License Revenue Recognition Revenue is recognized when a 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. Pursuant to ASC Topic 606, Revenue from Contracts with Customers (ASC 606), a customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract, including whether they are distinct in the context of the contract; (iii) determine the transaction price, including the constraint on variable consideration; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. If a promised good or service is not distinct, it is combined with other promised goods or services into a performance obligation. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaboration and License Revenue: The Company currently generates its revenue through collaboration and license agreements with strategic collaborators for the development and commercialization of product candidates. Collaboration and license agreements with customers are generally accounted for in accordance with ASC 606. The Company analyzes collaboration arrangements by first assessing whether they are within the scope of ASC Topic 808, Collaborative Arrangements (ASC 808), and evaluates whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. Collaboration agreements with customers that are not within the scope of ASC 808 are accounted for in accordance with ASC 606. To the extent the collaboration agreement is within the scope of ASC 808, the Company also assesses whether any aspects of the agreement are within the scope of other accounting literature (specifically ASC 606). If the Company concludes that some or all aspects of the agreement are distinct and represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606. The Company recognizes the shared costs incurred that are not within the scope of other accounting literature as a component of the related expense in the period incurred by analogy to ASC Topic 730, Research and Development (ASC 730), and records reimbursements from counterparties as an offset to the related research and development costs. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements in accordance with ASC 606, the Company performs the five steps above. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. The terms of the Company’s arrangements typically include one or more of the following: (i) upfront fees; (ii) milestone payments related to the achievement of development, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) reimbursements or cost-sharing of research and development expenses; and (v) profit/loss sharing arising from co-promotion arrangements. Licenses of Intellectual Property: If the license to the Company’s intellectual property is determined to be distinct from the other promised goods and services identified in the arrangement, the Company recognizes revenues 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. If not distinct, the license is combined with other promised goods and services in the contract. For licenses that are combined with other promised goods and services, the Company assesses 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. Optional licenses are evaluated to determine if they are issued at a discount, and therefore, represent material rights and accounted for as separate performance obligations. Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. The Company also evaluates the milestone to determine whether they are considered probable of being reached 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 to be allocated, otherwise, such amounts are constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are evaluated to determine if they are distinct and optional. For optional services that are distinct, the Company assesses if they are priced at a discount, and therefore, provide a material right to the licensee to be accounted for as separate performance obligations. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint. Grant Revenue The Company has contracts with government-sponsored organizations for research and development related activities that provide for payments for reimbursable costs. The Company recognizes grant revenue from these contracts as it performs services under these arrangements when the funding is committed. Expenses associated with these contracts are recognized when incurred as research and development expense. Grant revenue and related expenses are presented gross in the consolidated statements of operations and comprehensive loss as the Company has determined it is the primary obligor under the arrangements relative to the research and development services it performs as lead technical expert. Amounts incurred that are subject to reimbursement from the sponsor are recorded as accounts receivable on the consolidated balance sheets. Research and Development Costs Costs incurred in the research and development of the Company’s products are expensed as incurred. Research and development expenses include costs incurred in performing research and development activities, including salaries and benefits, stock-based compensation expenses, facilities cost, overhead costs, contract services, supplies and other outside costs. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Clinical Trial Costs Clinical trial expenses are a significant component of research and development expenses, and the Company outsources a significant portion of these costs to third-parties. Third-party clinical trial expenses include patient costs, clinical research organization costs and costs for data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through costs. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as a prepaid asset or accrued clinical trial cost. These third-party agreements are generally cancellable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future research and development activities are recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. The Company also records accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical clinical accrual estimates made by the Company have not been materially different from the actual costs. Income Taxes The Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax assets to the amount that will more-likely-than-not be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more-likely-than-not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. To date, the Company has not incurred interest and penalties related to uncertain tax positions. Warrants The Company determines the accounting classification of warrants that are issued, as either liability or equity, by first assessing whether the warrants meet liability classification in accordance with ASC 480-10, Accounting for Certain Financial Instruments with Characteristics of both Liabilities and Equity, and then in accordance with ASC 815-40, Accounting for Derivative Financial Instruments Indexed to, and Potentially Settled in, a Company’s Own Stock. Under ASC 480, warrants are considered liability classified if the warrants are mandatorily redeemable, obligate the issuer to settle the warrants or the underlying shares by paying cash or other assets, or must or may require settlement by issuing variable number of shares. If warrants do not meet liability classification under ASC 480-10, the Company assesses the requirements under ASC 815-40, which states that contracts that require or may require the issuer to settle the contract for cash are liabilities recorded at fair value, irrespective of the likelihood of the transaction occurring that triggers the net cash settlement feature. If the warrants do not require liability classification under ASC 815-40, in order to conclude equity classification, the Company assesses whether the warrants are indexed to its common stock and whether the warrants are classified as equity under ASC 815-40 or other applicable U.S. GAAP. After all relevant assessments are made, the Company concludes whether the warrants are classified as liability or equity. Liability classified warrants are required to be accounted for at fair value both on the date of issuance and on subsequent accounting period ending dates, with all changes in fair value after the issuance date recorded in the statements of operations as a gain or loss. Equity classified warrants are accounted for at fair value on the issuance date with no changes in fair value recognized after the issuance date. Stock-Based Compensation The Company accounts for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value and is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis, net of estimated forfeitures. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were adjusted. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that ultimately vest. Net Loss Per Share The Company applies the two-class method to compute basic and diluted net income (loss) per share attributable to common stockholders when it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income (loss) for the period had been distributed. The Company’s Series A Preferred Stock, Series B Preferred Stock and 2022 Warrants participate in any dividends declared by the Company and are therefore considered to be participating securities. The participating securities are not required to participate in the losses of the Company, and therefore during periods of loss there is no allocation required under the two-class method. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potentially dilutive common shares. For purposes of this calculation, outstanding options to purchase common stock and Series A Preferred Stock, forward contracts to issue Series A Preferred Stock, restricted stock units, warrants to purchase common stock, employee stock purchase plan stock, contingently issuable shares, Series A Preferred Stock, and Series B Preferred Stock are considered potential dilutive common shares. Contingent Liabilities The Company accounts for its contingent liabilities in accordance with ASC Topic 450, Contingencies (ASC 450). A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. Leases The Company accounts for its leases in accordance with ASC Topic 842, Leases (ASC 842), and determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Most leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company elected not to recognize leases with an original term less than one year on its balance sheet. Operating lease right-of-use assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow, on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASC 842, the fixed and in-substance fixed contract consideration must be allocated to lease and non-lease components based on their relative fair values. Non-components of a contract (e.g., administrative tasks that do not transfer a good or service to the Company, reimbursement or payment of a lessor’s cost, etc.) do not receive an allocation of the consideration in the contract. Although allocation of consideration of lease and non-lease components is required, the Company elected the practical expedient to not separate lease components (e.g. land, building, etc.) and non-lease components (e.g., common area maintenance, consumables, etc.). The lease component results in an operating right-of-use asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense. Right-of-use assets and operating lease liabilities are remeasured upon certain modifications to leases using the present value of remaining lease payments and the estimated incremental borrowing rate upon lease modification. The Company enters into lease agreements with terms generally ranging from two to eight years. Some of the Company’s lease agreements include Company options to either extend and/or early terminate the lease, the costs of which are included in its operating lease liabilities to the extent that such options are reasonably certain of being exercised. Leases with renewal options allow the Company to extend the lease term typically between one and five years. When determining the lease term, renewal options reasonably certain of being exercised are included in the lease term. When determining if a renewal option is reasonably certain of being exercised, the Company considers several economic factors, including but not limited to, the significance of leasehold improvements incurred on the property, whether the asset is difficult to replace, underlying contractual obligations, or specific characteristics unique to that particular lease that would make it reasonably certain that the Company would exercise such option. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases. Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Company recognizes lease expense for these leases on a straight-line basis over the lease term. Acquisitions The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If the screen is met, the transaction is accounted for as an asset acquisition. If the screen is not met, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the requirements of a business. If determined to be a business combination, the Company accounts for the transaction under the acquisition method of accounting which requires the acquiring entity in a business combination to recognize the fair value of all assets acquired, liabilities assumed, and any non-controlling interest in the acquiree and establishes the acquisition date as the fair value measurement point. Accordingly, the Company recognizes assets acquired and liabilities assumed in business combinations based on the fair value estimates as of the date of acquisition. In accordance with ASC Topic 805, Business Combinations (ASC 805) the Company recognizes and measures goodwill as of the acquisition date, as the excess of the fair value of the consideration paid over the fair value of the identified net assets acquired. Goodwill Goodwill represents the amount of consideration paid in excess of the fair value of the identified net assets acquired as a result of the Company’s business acquisitions accounted for using the acquisition method of accounting. Goodwill is not amortized and is subject to impairment testing at a reporting unit level on an annual basis or when a triggering event occurs that may indicate the carrying value of the goodwill is impaired. An entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Such qualitative factors include macroeconomic conditions, industry and market considerations, cost factors, overall financial performance and other relevant events. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. The Company evaluates goodwill for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable. For the years ended December 31, 2024 and 2023, the Company determined that there was no impairment to goodwill. Indefinite-Lived Intangible Assets Indefinite-lived intangible assets consist of in-process research and development, or IPR&D. The fair values of IPR&D assets acquired in business combinations are capitalized. These assets are treated as indefinite-lived intangible assets until completion or abandonment of the projects, at which time the assets are amortized over the remaining useful life or written off, as appropriate. Intangible assets with indefinite lives, including IPR&D, are tested for impairment if impairment indicators arise and, at a minimum, annually. However, an entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more likely than not that an indefinite-lived intangible asset’s fair value is less than its carrying amount. Otherwise, no further impairment testing is required. The indefinite-lived intangible asset impairment test consists of a one-step analysis that compares the fair value of the intangible asset with its carrying amount. If the carrying amount of an intangible asset exceeds its fair value, an impairment loss is recognized in an amount equal to that excess. The Company considers many factors in evaluating whether the value of its intangible assets with indefinite lives may not be recoverable, including, but not limited to, expected growth rates, the cost of equity and debt capital, general economic conditions, the Company’s outlook and market performance of the Company’s industry and recent and forecasted financial performance. The Company evaluates indefinite-lived intangible assets for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable. For the years ended December 31, 2024 and 2023, the Company determined that there was no impairment to the IPR&D assets. Convertible Preferred Stock The Company records its convertible preferred stock upon issuance at its fair value. The fair value includes the original issuance price, the settlement of any related forward contract, and is less issuance costs. The Company classifies its convertible preferred stock outside of stockholders’ deficit if the redemption of such shares is outside the Company’s control. For shares classified outside of stockholders’ deficit, the Company does not adjust the carrying value of its convertible preferred stock to redemption value until it is probable of becoming redeemable. As of December 31, 2024, there were no conditions that could have required cash redemption of the convertible preferred stock and therefore, all convertible preferred stock were classified within stockholders’ deficit. Series A Preferred Stock Options The Company classifies a portion of the fair value of the vested stock options for Series A Preferred Stock equal to the estimated redemption value on the measurement date outside of stockholders’ deficit, if the redemption of the shares underlying the options are outside the Company’s control. Any fair value in excess of the estimated redemption value is recognized as additional paid-in capital. The estimated redemption value is based on the intrinsic value of the option. The Company does not adjust the carrying value of the stock options for Series A Preferred Stock until the underlying Series A Preferred Stock is probable of becoming redeemable. The Company records the stock options for Series A Preferred Stock based on the intrinsic value of the vested options. Variable Interest Entities The Company evaluates its variable interests in variable interest entities, or VIEs, and consolidates VIEs when the Company is the primary beneficiary. The Company determines whether it is the primary beneficiary of a VIE based on its assessment of whether the Company possesses both (i) the power to direct the activities that most significantly affect the VIE’s economic performance and (ii) the obligation to absorb losses that could be significant to the VIE or the right to receive benefits that could be significant to the VIE. The Company reevaluates the accounting for its VIEs upon the occurrence of events that could change the primary beneficiary conclusion. Contingent Value Right Liability The CVRs distributed by the Company pursuant to the terms of the CVR Agreement (as defined below) represent financial instruments that are accounted for under the fair value option election in ASC Topic 825, Financial Instruments (ASC 825). Under the fair value option election, the CVRs are initially measured at the aggregate estimated fair value of the CVRs and will be subsequently remeasured at estimated fair value on a recurring basis at each reporting period date. The estimated fair value of the CVR liability was determined using a discounted cash flow methodology as of December 31, 2023 and a Monte Carlo simulation method as of December 31, 2024 to estimate future cash flows associated with the legacy assets, including the expected milestone and royalty payments under the Sobi License, net of deductions. Changes in fair value of the liability are presented in the consolidated statements of operations and comprehensive loss. The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of success, expected volatilities of revenues (Monte Carlo simulation) and risk-adjustment discount rate (discounted cash flow methodology), which represent a Level 3 measurement within the fair value hierarchy. Forward Contract Liabilities The Company accounts for contracts related to the future issuance of its convertible preferred stock as a liability if the underlying shares include a redemption feature that may require the Company to settle the instrument by transferring an asset. The forward contract liability is carried at fair value through the date the underlying shares are issued. The fair value of the Series A Preferred Stock forward contract liability was initially measured based on the fair value of the Series A Preferred Stock issued in the 2023 Private Placement (see Note 11), less the purchase price, if any. Subsequent measurement of the fair value of the Series A Preferred Stock forward contract liability was based on the market price of the Company’s common stock, which represented the redemption and conversion value of the Series A Preferred Stock, less the purchase price, if any, on an as-converted basis. The remeasurement of the forward contract liability is based on Level 2 inputs within the fair value hierarchy as it’s based on observable market data. Changes in fair value of the liability are presented within change in fair value of forward contract liabilities in the consolidated statements of operations and comprehensive loss. Recent Accounting Pronouncements Recently Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07), which requires an enhanced disclosure of significant segment expenses on an annual and interim basis. This guidance is effective for the annual period beginning the year ended December 31, 2024, and for interim periods beginning January 1, 2025, with early adoption permitted. The Company adopted the new standard during the year ended December 31, 2024 and the amendments have be applied retrospectively to all prior periods presented in the consolidated financial statements. See Note 21 for additional information. Not Yet Adopted In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09), which improves the transparency of income tax disclosures by requiring consistent categories and greater disaggregation of information in the effective tax rate reconciliation and income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. This guidance will be effective for the annual period beginning the year ended December 31, 2025. Early adoption is permitted. Upon adoption, the guidance can be applied prospectively or retrospectively. The Company is currently in the process of evaluating the impact of the standard’s adoption on its consolidated financial statements and related disclosures In November 2024, the FASB issued ASU 2024-03, Income Statement Reporting- Comprehensive Income- Expense Disaggregation Disclosures (ASU 2024-03), which requires public companies to disclose, in interim and annual reporting periods, additional information about certain expenses in notes to financial statements, including purchases of inventory, employee compensation, depreciation, amortization of intangible assets, and selling expenses. This guidance will be effective for the annual period beginning the year ended December 31, 2027 and for interim periods beginning January 1, 2028, with early adoption permitted. The Company is currently in the process of evaluating the impact of the standard’s adoption on its consolidated financial statements and related disclosures.

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2024

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following tables present the Company’s assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2024 and 2023 (in thousands):


	December 31, 2024
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds (included in cash equivalents)	$	39,088	$	39,088	$	—	$	—






Total assets	$	39,088	$	39,088	$	—	$	—

Liabilities:
Warrant liabilities	$	3,836	$	—	$	—	$	3,836
Contingent value right liability	395,500		—		—		395,500

Total liabilities	$	399,336	$	—	$	—	$	399,336


	December 31, 2023
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds (included in cash equivalents)	$	41,161	$	41,161	$	—	$	—






Total assets	$	41,161	$	41,161	$	—	$	—

Liabilities:
Warrant liabilities	$	6,394	$	—	$	—	$	6,394
Contingent value right liability	358,600		—		—		358,600
Forward contract liabilities	28,307		—		28,307		—
Total liabilities	$	393,301	$	—	$	28,307	$	364,994

Schedule of Cash and Cash Equivalents

The Company’s consolidated statement of cash flows includes the following as of December 31, 2024 and 2023 (in thousands):


	Year Ended December 31,
		2024		2023
Cash and cash equivalents		$	212,610	$	76,911

Long-term restricted cash		1,669		1,377
Total cash, cash equivalents, and restricted cash		$	214,279	$	78,288

Schedule of Restricted Cash

The Company’s consolidated statement of cash flows includes the following as of December 31, 2024 and 2023 (in thousands):


	Year Ended December 31,
		2024		2023
Cash and cash equivalents		$	212,610	$	76,911

Long-term restricted cash		1,669		1,377
Total cash, cash equivalents, and restricted cash		$	214,279	$	78,288

Schedule of Fair Value Measurement Inputs and Valuation Techniques for 2019 Warrants Liability and CVR Liability

A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2019 Warrants liability as of December 31, 2023 is as follows:


	December 31,
	2023
Risk-free interest rate	4.79	%
Dividend yield	—
Expected life (in years)	0.98
Expected volatility	83.67	%

A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2022 Warrants liability is as follows:


	December 31,
	2024		2023
Risk-free interest rate	4.25	%	4.01	%
Dividend yield	—		—
Expected life (in years)	2.28		3.28
Expected volatility	92.92	%	84.09	%

The significant inputs used to estimate the fair value of the CVR liability, which represented a financial instrument being accounted for under the fair value option, were as follows:


	December 31,
	2024
Estimated cash flow dates	2025 - 2038
Estimated probability of success	95.0% - 100.0%
Expected volatility of future revenues	22.0	%


	December 31,
	2023
Estimated cash flow dates	2024 - 2038
Estimated probability of success	95.0	%
Risk-adjusted discount rate	13.7	%

Schedule of Roll-Forward of Fair Value for the Company’s Level 3 Warrant Liabilities, CVR Liability and Forward Contract Liabilities

The following table reflects a roll-forward of fair value for the Company’s Level 3 warrant liabilities (see Note 12), for the year ended December 31, 2024 (in thousands):


	Warrant liabilities
Fair value as of December 31, 2023	$	6,394



Change in fair value	(2,558)

Fair value as of December 31, 2024	$	3,836

The following table reflects a roll-forward of fair value for the Company’s Level 3 CVR liability for the year ended December 31, 2024 (in thousands):


	CVR liability
Fair value as of December 31, 2023	$	358,600

Change in fair value	36,900
Fair value as of December 31, 2024	$	395,500

The following table presents changes in the forward contract liabilities for the periods presented (in thousands):


	Forward contract liabilities
Fair value as of December 31, 2023	$	28,307

Settlements	(35,197)
Change in fair value	6,890
Fair value as of December 31, 2024	$	—

Basis of Presentation	12 Months Ended
Basis of Presentation	Dec. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Selecta (RUS), LLC, or Selecta (RUS), a Russian limited liability corporation, Selecta Biosciences Security Corporation, a Massachusetts securities corporation which the Company dissolved in December 2024, and Cartesian Bio, LLC, a Delaware limited liability company, which is a variable interest entity for which the Company is the primary beneficiary. All significant intercompany accounts and transactions have been eliminated. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company’s management considers many factors in selecting appropriate financial accounting policies and controls, and bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. In preparing these consolidated financial statements, management used significant estimates in the following areas, among others: estimated fair value of the intangible assets acquired in connection with the Merger, estimated fair value of the CVRs, deferred income taxes, revenue recognition, estimated accrued research and development expenses, stock-based compensation expense, estimated fair value of the liability-classified warrants, and impairment of long-lived assets. The Company assesses the above estimates on an ongoing basis; however, actual results could materially differ from those estimates. Segment Information Operating segments are defined as components of an enterprise for which separate and discrete information is available for evaluation by the chief operating decision maker, or the CODM, for the purposes of assessing performance and allocating resources. The Company views its operations and manages its business in one operating segment, which prior to the Merger related to the research and development of nanoparticle immunomodulatory drugs for the treatment and prevention of human diseases and subsequent to the Merger relates to the research and development of cell therapy product candidates. The Company’s CODM function is fulfilled by its Chief Executive Officer. The CODM function assesses performance for the segment and decides how to allocate resources based on consolidated net loss that is also reported on the consolidated statements of operations and comprehensive loss. The CODM function uses net loss to monitor budget versus actual results to assess performance of the segment. Segment assets are the same as total assets on the Company’s consolidated balance sheets. All long-lived assets are located in the United States. Long-lived assets consist of property and equipment, net, and operating lease right-of-use assets.

Revenue Arrangements (Tables)

12 Months Ended

Dec. 31, 2024

Revenue from Contract with Customer [Abstract]

Schedule of Changes in Contract Liabilities

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2024 (in thousands):


	Balance at						Balance at
	beginning of period		Additions		Deductions		end of period
Contract liabilities:
Deferred revenue	$	5,849	$	—	$	(5,849)	$	—
Total contract liabilities	$	5,849	$	—	$	(5,849)	$	—

Restructuring - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended		21 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2024
Restructuring and Related Activities [Abstract]
Employee workforce, termination percentage			90.00%
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 798	$ 6,431
Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 200	$ 5,600
Restructuring charges, location	Research and development	Research and development
General and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 600	$ 800
Restructuring charges, location	General and administrative	General and administrative

- 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 + Details

Leases - 704 Quince Orchard Road Leases (Narrative) (Details) - operating_lease	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating Leased Assets [Line Items]
Weighted-average discount rate	11.70%	9.90%
704 Quince Orchard Road Leases
Operating Leased Assets [Line Items]
Number of acquired operating leases	2
Weighted-average discount rate	11.50%

Merger - Schedule of Pro Forma Financial Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Revenue	$ 26,004
Net loss	$ (232,259)

Net Loss Per Share Allocable to Common Stockholders

12 Months Ended

Dec. 31, 2024

Earnings Per Share [Abstract]

Net Loss Per Share Allocable to Common Stockholders

The Company reported a net loss for the years ended December 31, 2024 and 2023. The Company used the treasury stock method to determine the number of dilutive shares for the year ended December 31, 2024. The following table sets forth the computation of basic and diluted net loss per share allocable to common stockholders (in thousands, except share and per-share data):


	Year Ended December 31,
		2024		2023
Numerator:
Net loss		$	(77,424)	$	(219,710)
Less: CVR distribution to participating securities		—		(37,550)
Net loss allocable to shares of common stock - basic		(77,424)		(257,260)
Less: Change in fair value of forward contract liability settled in February 2024		(446)		—
Net loss allocable to shares of common stock - diluted		$	(77,870)	$	(257,260)
Denominator:
Weighted-average common shares outstanding - basic		17,276,822		5,170,319
Plus: Dilutive effect of forward contract liability settled in February 2024		81,121		—
Weighted-average common shares outstanding - diluted		17,357,943		5,170,319
Net loss per share:
Basic		$	(4.48)	$	(49.76)
Diluted		$	(4.49)	$	(49.76)


	Year Ended December 31,
	2024	2023
Common stock options and RSUs	2,150,273	776,865
Warrants to purchase common stock	692,523	1,040,813
Series A Preferred Stock	4,026,346	14,503,993
Series B Preferred Stock	437,927	—
Forward contract to issue Series A Preferred Stock	—	3,304,677
Series A Preferred Stock options	—	470,403
Total	7,307,069	20,096,751

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2024

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table reconciles the federal statutory income tax rate to the Company’s effective income tax rate:


	Year Ended December 31,
	2024		2023
Statutory U.S. federal rate	21.0	%	21.0	%
State income taxes - net of federal benefit	10.5	%	2.3	%
Permanent items	1.0	%	(1.6)	%
Research tax credits	0.3	%	0.6	%


Change in fair value of contingent value right liability	127.9	%	—	%
Change in fair value of forward contract liabilities	(1.9)	%	(13.2)	%
Valuation allowance, net	(160.1)	%	2.8	%
Stock-based compensation	0.9	%	(3.9)	%
Effective income tax rate	(0.4)	%	8.0	%

Schedule of Deferred Tax Assets and Liabilities

The tax effects of temporary differences that give rise to the Company’s net deferred tax assets are as follows (in thousands):


	Year Ended December 31,
	2024		2023
Deferred Tax Assets
Net operating loss carryforwards	$	44,062	$	29,841
Research and development credits	6,024		5,649
Stock-based compensation expense	1,070		8
Other expenses	—		705
Deferred revenue	75,567		84,626
Operating lease liabilities	3,848		2,718
Contingent value right liability	108,832		—
R&E Capitalization	26,863		19,778
Patent and license costs	8,540		9,140
Gross deferred tax assets	274,806		152,465
Deferred Tax Liabilities
Intangible assets	$	(41,441)	$	(41,144)
Depreciation	(115)		(128)
Operating lease right-of-use assets	(1,523)		(2,751)
Gross deferred tax liabilities	(43,079)		(44,023)
Net deferred tax assets before valuation allowance	231,727		108,442
Valuation allowance	(247,867)		(124,295)
Net deferred tax assets/(liabilities)	$	(16,140)	$	(15,853)

Equity - Common Stock (Narrative) (Details)	12 Months Ended
Equity - Common Stock (Narrative) (Details)	Dec. 31, 2024 USD ($) vote $ / shares shares	Dec. 31, 2023 $ / shares shares	Nov. 13, 2023 $ / shares
Equity [Abstract]
Common Stock, Shares Authorized	350,000,000	350,000,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, shares issued (in shares)	25,767,369	5,397,597
Common stock, shares outstanding (in shares)	25,767,369	5,397,597
Number of votes per share that common stockholders are entitled to \| vote	1
Dividends declared or paid on common stock \| $	$ 0

Collaboration and License Agreements - Shenyang Sunshine Pharmaceutical Co., Ltd (Narrative) (Details) - 3SBio License $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate amount of upfront and milestone-based payments	$ 7.0
Aggregate amount for future payments upon achievement of clinical and regulatory approval milestones for products containing ImmTOR platform	$ 15.0

Convertible Preferred Stock - Conversion (Narrative) (Details)	Dec. 31, 2024	Mar. 27, 2024
Class of Stock [Line Items]
Preferred stock, convertible, conversion ratio	33.333	33.333
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, convertible, conversion ratio	1
Minimum
Class of Stock [Line Items]
Beneficially holders owned percentage	0.00%
Minimum \| Series B Preferred Stock
Class of Stock [Line Items]
Beneficially holders owned percentage	0.00%
Maximum
Class of Stock [Line Items]
Beneficially holders owned percentage	19.90%
Maximum \| Series B Preferred Stock
Class of Stock [Line Items]
Beneficially holders owned percentage	19.90%

- 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

+ Details

Insider Trading Arrangements	3 Months Ended	12 Months Ended
Insider Trading Arrangements	Dec. 31, 2024 shares	Dec. 31, 2024 shares
Trading Arrangements, by Individual
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Christopher Jewell [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On December 23, 2024, Christopher Jewell, our Chief Scientific Officer, adopted a trading plan intended to satisfy the conditions under Rule 10b5-1(c) of the Exchange Act. Dr. Jewell’s plan provides for the exercise of vested stock options and the potential associated sale of up to 15,000 shares of our common stock until and including December 31, 2025. The foregoing exercises or sales, if any, will be made in accordance with the prices and formulas set forth in the plan and such plan terminates on the earlier of the date all the shares under the plan are sold and December 31, 2025.
Name	Christopher Jewell
Title	Chief Scientific Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	December 23, 2024
Expiration Date	December 31, 2025
Arrangement Duration	373 days
Aggregate Available	15,000	15,000

Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 12,269	$ 7,841
Less accumulated depreciation	(2,357)	(5,728)
Property and equipment, net	9,912	2,113
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	7,295	6,280
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	415	702
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,427	61
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	268	452
Office equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	169	196
Construction in process
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 695	$ 150

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 212,610	$ 76,911
Accounts receivable	872	5,870
Unbilled receivables	0	2,981
Prepaid expenses and other current assets	3,144	4,967
Total current assets	216,626	90,729
Non-current assets:
Property and equipment, net	9,912	2,113
Right-of-use asset, net	5,535	10,068
In-process research and development assets	150,600	150,600
Goodwill	48,163	48,163
Long-term restricted cash	1,669	1,377
Investments	2,000	2,000
Other assets	518	0
Total assets	435,023	305,050
Current liabilities:
Accounts payable	288	3,150
Accrued expenses and other current liabilities	12,076	15,572
Lease liability	2,851	2,166
Deferred revenue	0	2,311
Warrant liabilities	0	720
Contingent value right liability	7,761	15,983
Forward contract liabilities	0	28,307
Total current liabilities	22,976	68,209
Non-current liabilities:
Lease liability, net of current portion	11,133	8,789
Deferred revenue, net of current portion	0	3,538
Warrant liabilities, net of current portion	3,836	5,674
Contingent value right liability, net of current portion	387,739	342,617
Deferred tax liabilities, net	16,141	15,853
Total liabilities	441,825	444,680
Commitments and contingencies (Note 19)
Series A Preferred Stock, $0.0001 par value; no and 548,375 shares authorized as of December 31, 2024 and December 31, 2023, respectively; no and 435,120.513 shares issued and outstanding as of December 31, 2024 and December 31, 2023, respectively	0	296,851
Options for Series A Preferred Stock	0	3,703
Stockholders’ deficit:
Preferred stock, value, issued	0	0
Common stock, $0.0001 par value; 350,000,000 shares authorized as of December 31, 2024 and December 31, 2023; 25,767,369 and 5,397,597 shares issued and outstanding as of December 31, 2024 and December 31, 2023, respectively	3	1
Additional paid-in capital	689,887	179,062
Accumulated deficit	(692,071)	(614,647)
Accumulated other comprehensive loss	(4,621)	(4,600)
Total stockholders’ deficit	(6,802)	(440,184)
Total liabilities, convertible preferred stock, and stockholders’ deficit	435,023	305,050
Series A Preferred Stock
Stockholders’ deficit:
Preferred stock, value, issued	0	0
Series B Preferred Stock
Stockholders’ deficit:
Preferred stock, value, issued	$ 0	$ 0

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events through the date on which the consolidated financial statements were issued. The Company has concluded that no subsequent events have occurred that require disclosure, except as disclosed within these consolidated financial statements.

Convertible Preferred Stock	12 Months Ended
Convertible Preferred Stock	Dec. 31, 2024
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	Convertible Preferred Stock Series B Preferred Stock The Certificate of Designation of Preferences, Rights, and Limitations of the Series B Non-Voting Convertible Preferred Stock, or the Series B Certificate of Designation, was filed with the Secretary of State of the State of Delaware on July 2, 2024, and provided for the designation of shares of Series B Preferred Stock and authorized the issuance of 2,937,903 shares of Series B Preferred Stock. Additionally, on July 2, 2024, the Company entered into the 2024 Securities Purchase Agreement with certain institutional and accredited investors, or the Purchasers. The Purchasers included (i) Dr. Timothy A. Springer, a member of the Company’s Board of Directors; (ii) TAS Partners LLC, an affiliate of Dr. Springer, and (iii) Dr. Chafen Lu, Dr. Springer’s wife. Pursuant to the 2024 Securities Purchase Agreement, the Company agreed to issue and sell an aggregate of 3,563,247 shares of common stock and 2,937,903 shares of Series B Preferred Stock for an aggregate purchase price of $130.0 million in the 2024 Private Placement. Each share of Series B Preferred Stock is convertible into one share of the Company’s common stock subject to stockholder approval of a proposal to issue such shares of common stock upon conversion of such shares of Series B Preferred Stock in accordance with the Listing Rules of the Nasdaq Stock Market LLC, or the Series B Conversion Proposal. Under the 2024 Securities Purchase Agreement, the Company issued 3,563,247 shares of common stock and 578,403 shares of Series B Preferred Stock for an aggregate purchase price of $82.8 million to the Purchasers other than Dr. Springer, TAS Partners LLC, and Dr. Lu. The Company also issued (i) 1,636,832 shares of Series B Preferred Stock to Dr. Springer, (ii) 721,361 shares of Series B Preferred Stock to TAS Partners LLC, and (iii) 1,307 shares of Series B Preferred Stock to Dr. Lu for an aggregate purchase price of $47.2 million. Pursuant to the 2024 Securities Purchase Agreement, the Company agreed to submit to its stockholders the approval of the Series B Conversion Proposal, at a special meeting of stockholders, which was held on September 20, 2024. On September 20, 2024, at such special meeting, the Company’s stockholders approved the Series B Conversion Proposal, among other matters. On September 25, 2024, pursuant to the terms of the Series B Certificate of Designation, 2,499,976 shares of Series B Preferred Stock automatically converted into 2,499,976 shares of common stock; 437,927 shares of Series B Preferred Stock did not automatically convert at such time due to beneficial ownership limitations. The Series B Preferred Stock were classified in permanent equity as there were no conditions that could have required cash redemption of the shares. The Series B Preferred Stock has the following rights and preferences: Conversion Prior to the stockholder approval of the Series B Conversion Proposal the Series B Preferred Stock were not convertible into shares of common stock. Following the stockholder approval of the Series B Conversion Proposal, each share of Series B Preferred Stock automatically converted into one share of common stock, subject to certain limitations, including that a holder of Series B Preferred Stock is prohibited from converting shares of Series B Preferred Stock into shares of common stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than a specified percentage (to be established by the holder between 0.0% and 19.9%) of the total number of shares of common stock issued and outstanding immediately after giving effect to such conversion; provided, however, that such beneficial ownership limitation does not apply to Dr. Springer, TAS Partners LLC, or any of their respective affiliates. Each share of Series B Preferred Stock outstanding that was not automatically converted into common stock as a result of the stockholder approval of the Series B Conversion Proposal shall be convertible at any time at the option of the holder following stockholder approval of the Series B Conversion Proposal, only to the extent the beneficial ownership limitation does not apply to the shares of Series B Preferred Stock to be converted. Redemption The Series B Preferred Stock is not redeemable. Dividends Holders of Series B Preferred Stock are entitled to receive dividends on shares of Series B Preferred Stock on an as-converted basis (without regard to the beneficial ownership limitation) equal to the dividends paid on shares of the common stock. Voting Except as otherwise required by law, the Series B Preferred Stock does not have voting rights. However, as long as any shares of Series B Preferred Stock are outstanding, the Company will not, without the affirmative vote of the holders of a majority of the then-outstanding shares of the Series B Preferred Stock, (a) alter or change adversely the powers, preferences or rights given to the Series B Preferred Stock, (b) alter or amend the Series B Certificate of Designation, or (c) amend the Charter or other organizational documents in any manner that alters or changes the preferences, rights, privileges, or powers of, or restrictions provided for the benefit of the holders of Series B Preferred Stock. Liquidation The holders of Series B Preferred Stock shall rank on parity with the holders of common stock and the holders of Series A Preferred Stock as to distributions of assets upon liquidation, dissolution or winding up of the Company, whether voluntarily or involuntarily. Upon any liquidation, dissolution or winding-up of the Company, whether voluntary or involuntary, each holder of Series B Preferred Stock shall be entitled to receive out of the assets of the Company, whether capital or surplus, the same amount that a holder of common stock would receive if the Series B Preferred Stock were fully converted, which shall be paid pari passu with holders of common stock and holders of Series A Preferred Stock, plus an amount equal to any dividends declared but unpaid. If the assets available for distribution are not sufficient to pay the holders of the Series B Preferred Stock pursuant to the preceding sentence, all remaining assets will be distributed ratably to the holders of the Series A Preferred Stock, Series B Preferred Stock and common stock. Series A Preferred Stock The Certificate of Designation of Preferences, Rights, and Limitations of the Series A Non-Voting Convertible Preferred Stock, or the Series A Certificate of Designation, was filed on November 13, 2023, which provided for the designation of shares of the Series A Preferred Stock and authorized the issuance of 548,375 shares of Series A Preferred Stock. Additionally on November 13, 2023, the Company entered into the 2023 Securities Purchase Agreement with (i) Dr. Timothy A. Springer, a member of the Company’s Board of Directors; (ii) TAS Partners LLC, an affiliate of Dr. Springer, and (iii) Seven One Eight Three Four Irrevocable Trust, a trust associated with Dr. Murat Kalayoglu, a co-founder and the former chief executive officer of Old Cartesian, who joined the Company’s Board of Directors effective immediately after the effective time of the Merger, or the Investors. Pursuant to the 2023 Securities Purchase Agreement, the Company agreed to issue and sell an aggregate of 149,330.115 shares of Series A Preferred Stock for an aggregate purchase price of $60.25 million in the 2023 Private Placement. In the 2023 Private Placement, Dr. Timothy A. Springer agreed to settle his purchases in three tranches of shares of Series A Preferred Stock, the first for a purchase price of $10.0 million and each thereafter for a purchase price of approximately $20.0 million, with the three tranches settling 30, 60, and 90 days, respectively, following the Closing Date. TAS Partners LLC agreed to settle its purchase for approximately $10.0 million within 30 days following the Closing Date. The first, second and third tranches were settled on December 13, 2023, January 12, 2024 and February 11, 2024, respectively, under which (i) 24,785.081 shares of Series A Preferred Stock were issued to each of TAS Partners LLC and Dr. Timothy A. Springer in the first tranche, (ii) 49,570.163 shares of Series A Preferred Stock were issued to Dr. Timothy A. Springer in the second tranche, and (iii) 49,570.163 shares of Series A Preferred Stock were issued to Dr. Timothy A. Springer in the third tranche. On November 15, 2023, the Company issued 619.627 shares of Series A Preferred Stock to Seven One Eight Three Four Irrevocable Trust for $0.25 million. The Company determined the obligation to issue 148,710.488 shares of Series A Preferred Stock to Dr. Springer and TAS Partners LLC represented a forward contract and was accounted for as a liability with changes in fair value recorded in earnings. A portion of the liability was settled with the initial issuance of 49,570.162 shares of Series A Preferred Stock on December 13, 2023. The remaining portion of the forward contract liability was settled upon the issuance of 49,570.163 shares of Series A Preferred Stock each on January 12, 2024 and February 11, 2024, respectively (see Note 6). On December 5, 2023, the Company issued 384,930.724 shares of Series A Preferred Stock as part of its consideration transferred in connection with the Merger which settled the related forward contract liability (see Note 6). On March 26, 2024, the Company, with the consent of the requisite holders of Series A Preferred Stock, amended the Series A Certificate of Designation such that the automatic conversion of the Series A Preferred Stock into common stock, or the Automatic Conversion, would occur eight business days following stockholder approval of the Conversion Proposal. On March 27, 2024, the Company’s stockholders approved the Conversion Proposal, among other matters, at the Special Meeting. On April 8, 2024, pursuant to the terms of the Series A Certificate of Designation, as amended, 367,919.247 shares of Series A Preferred Stock automatically converted into 12,263,951 shares of common stock, including the non-cash reclassification of an amount equal to the increase in par value of common stock from additional paid-in capital; 166,341.592 shares of Series A Preferred Stock did not automatically convert at such time due to beneficial ownership limitations. On October 11, 2024, pursuant to a Notice of Optional Conversion delivered to the Company by a holder of Series A Preferred Stock pursuant to the Series A Certificate of Designation, 45,551.190 shares of Series A Preferred Stock held by such holder were converted into 1,518,373 newly issued shares of common stock. In accordance with the guidance in ASC Topic 480, Distinguishing Liabilities from Equity (ASC 480) the Series A Preferred Stock was classified outside of stockholders’ deficit upon issuance and as of December 31, 2023 because the shares of Series A Preferred Stock contained redemption features that were not solely within the control of the Company. The Series A Preferred Stock was not currently redeemable, nor was it probable that the instrument would become redeemable, as it was only redeemable upon the occurrence of a contingent event. Accordingly, no accretion was recognized for the Series A Preferred Stock. As a result of the approval of the Conversion Proposal, all conditions that could have required cash redemption of the Series A Preferred Stock were removed. Since the Series A Preferred Stock was no longer redeemable, the associated balances of the Series A Preferred Stock were reclassified to permanent equity during the first quarter of 2024. The Series A Preferred Stock has the following rights and preferences: Conversion Prior to the stockholder approval of the Conversion Proposal, the Series A Preferred Shares were not convertible. Following the stockholder approval of the Conversion Proposal, each share of Series A Preferred Stock automatically converted into 33.333 shares of common stock, subject to certain limitations, including that a holder of Series A Preferred Stock is prohibited from converting shares of Series A Preferred Stock into shares of common stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than a specified percentage (to be established by the holder between 0% and 19.9%) of the total number of shares of common stock issued and outstanding immediately after giving effect to such conversion; provided, however, that such beneficial ownership limitation does not apply to Dr. Springer, TAS Partners LLC, or any of their respective affiliates. Each share of Series A Preferred Stock outstanding that was not otherwise automatically converted into common stock as a result of the beneficial ownership limitation shall be convertible at any time at the option of the holder following stockholder approval of the Conversion Proposal, only to the extent the beneficial ownership limitation does not apply to the shares of Series A Preferred Stock to be converted. Redemption Prior to the stockholder approval of the Conversion Proposal, each share of Series A Preferred Stock was redeemable at the option of the holder at any time following the date that was 18 months after the initial issuance date of the Series A Preferred Stock, other than any shares of Series A Preferred Stock that would not have been convertible into shares of common stock as a result of the beneficial ownership limitation referred to above. The amount payable upon redemption would have been equal to the average closing sale price of the common stock listed over the ten consecutive trading days ending on, and including, the day immediately prior to the redemption date multiplied by the number of shares of common stock the Series A Preferred Stock would have been convertible into. Following the Conversion Proposal, the Series A Preferred Stock is not redeemable. Dividends Holders of Series A Preferred Stock are entitled to receive dividends on shares of Series A Preferred Stock on an as-converted basis equal to the dividends paid on shares of the common stock; provided, however, that holders of Series A Preferred Stock (or any shares of common stock into which the Series A Preferred Stock are convertible) are not entitled to any CVRs or any amounts paid under the CVR Agreement. Voting Except as otherwise required by law, the Series A Preferred Stock does not have voting rights. However, as long as any shares of Series A Preferred Stock are outstanding, the Company will not, without the affirmative vote of the holders of a majority of the then-outstanding shares of the Series A Preferred Stock, (a) alter or change adversely the powers, preferences or rights given to the Series A Preferred Stock, (b) alter or amend the Series A Certificate of Designation, (c) amend the Charter or other organizational documents in any manner that adversely affects any rights of the holders of Series A Preferred Stock, (d) issue further shares of Series A Preferred Stock (other than in connection with the exercise of the stock options to purchase Series A Preferred Stock) or increase or decrease (other than by conversion) the number of authorized shares of Series A Preferred Stock, (e) prior to the stockholder approval of the Conversion Proposal or at any time while at least 30% of the originally issued Series A Preferred Stock remains issued and outstanding, consummate either (A) a Fundamental Transaction (as defined in the Series A Certificate of Designation) or (B) any merger or consolidation of the Company or other business combination in which the stockholders of the Company immediately before such transaction do not hold at least a majority of the capital stock of the Company immediately after such transaction, (f) amend or fail to comply with, in any manner that would be reasonably likely to prevent, impede or materially delay the conversion (or the stockholder approval thereof), or terminate, any of the stockholder support agreements entered into in connection with the Merger, or the Support Agreements, or agree to any transfer, sale or disposition of such shares subject to the Support Agreements (except for such transfers, sales or dispositions with respect to which the approval of the Company is not required pursuant to the applicable Support Agreement) or (g) enter into any agreement with respect to any of the foregoing. Liquidation The holders of Series A Preferred Stock shall rank on parity with the common stockholders and the holders of Series B Preferred Stock as to distributions of assets upon liquidation, dissolution or winding up of the Company, whether voluntarily or involuntarily. Upon any liquidation, dissolution or winding-up of the Company, whether voluntary or involuntary each holder of Series A Preferred Stock shall be entitled to receive out the assets of the Company equal to of the same amount that a holder of common stock would receive if the Series A Preferred Stock were fully converted, which shall be paid pari passu with holders of common stock and holders of Series B Preferred Stock, plus an amount equal to any dividends declared but unpaid. If the assets available for distribution are not sufficient to pay the holders of the Series A Preferred Stock pursuant to the preceding sentence, the assets will be distributed ratably to the holders of the Series A Preferred Stock, Series B Preferred Stock and common stock. As of December 31, 2024, the Company had 120,790.402 shares of Series A Preferred Stock and 437,927 shares of Series B Preferred Stock issued and outstanding, respectively, which are convertible into a total of 4,464,273 shares of common stock.

Debt	12 Months Ended
Debt	Dec. 31, 2024
Debt Disclosure [Abstract]
Debt	Debt 2020 Term Loan On August 31, 2020, the Company entered into a Loan and Security Agreement with Oxford Finance LLC, or Oxford, and Silicon Valley Bank, or the Loan and Security Agreement, and such facility, the 2020 Term Loan. On March 10, 2023, Silicon Valley Bank was closed by the California Department of Financial Protection and Innovation, and the Federal Deposit Insurance Corporation, or the FDIC, was appointed as receiver. On March 13, 2023, the FDIC announced that all of Silicon Valley Bank’s deposits and substantially all of its assets had been transferred to a newly created, full-service, FDIC-operated bridge bank, Silicon Valley Bridge Bank, N.A., or SVBB. SVBB assumed all loans that were previously held by Silicon Valley Bank. On March 27, 2023, First-Citizens Bank & Trust Company assumed all of SVBB’s customer deposits and certain other liabilities and acquired substantially all of SVBB’s loans and certain other assets from the FDIC, including the 2020 Term Loan. On September 11, 2023, the Company entered into a payoff letter with Oxford and SVB, pursuant to which the Company paid all outstanding amounts under the 2020 Term Loan, together with accrued interest and a prepayment penalty, resulting in the full extinguishment of the 2020 Term Loan. The total payoff amount was $22.3 million, consisting of the remaining principal amount due of $19.8 million, the final payment fee of $2.3 million, the prepayment penalty of $0.2 million, and less than $0.1 million of accrued interest. During the year ended December 31, 2023, the Company recorded a loss of $0.7 million on the extinguishment of the 2020 Term Loan, consisting of the prepayment penalty of $0.2 million and the write-off of $0.5 million of unamortized debt issuance costs and venture debt termination fee, which was included within interest expense in the consolidated statements of operations and comprehensive loss. As of December 31, 2024 and 2023, the Company had no outstanding borrowings. During the year ended December 31, 2024, the Company recognized no interest expense. During the year ended December 31, 2023, the Company recognized $2.1 million of interest expense related to the 2020 Term Loan.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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-Name Accounting Standards Codification
-Section 50
-Paragraph 6
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1C

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481139/470-20-50-1I

+ Details

Restructuring (Tables)

12 Months Ended

Dec. 31, 2024

Restructuring and Related Activities [Abstract]

Schedule of Change in Accrued Restructuring Balance

The following table summarizes the change in the Company’s accrued restructuring balance included in accrued expenses and other current liabilities on its consolidated balance sheets (in thousands):


	December 31, 2022		Charges		Cash Payments		December 31, 2023
Severance liability	$	—	$	6,431	$	(2,535)	$	3,896

	December 31, 2023		Charges		Cash Payments		December 31, 2024
Severance liability	$	3,896	$	798	$	(4,614)	$	80

Restructuring

12 Months Ended

Dec. 31, 2024

Restructuring and Related Activities [Abstract]

Restructuring

In April 2023, in light of current market conditions, the Board of Directors took steps to extend the Company’s cash runway by pausing further development of the Company’s product candidate, SEL-302, for the treatment of methylmalonic acidemia and conducting a targeted headcount reduction. On August 17, 2023, the Company announced additional steps to extend cash runway and maximize value for stockholders by continuing to prioritize development of the Company’s product candidate, SEL-212, and support of its collaboration with Astellas for Xork, and pausing further development of all of the Company’s other clinical and preclinical product candidates that it was no longer actively advancing.

As a result of these measures, the Company implemented a restructuring plan that resulted in an approximate 90% reduction of the Company’s existing headcount as of December 31, 2024.


	December 31, 2022		Charges		Cash Payments		December 31, 2023
Severance liability	$	—	$	6,431	$	(2,535)	$	3,896

	December 31, 2023		Charges		Cash Payments		December 31, 2024
Severance liability	$	3,896	$	798	$	(4,614)	$	80

The Company recognized restructuring expenses consisting of one-time cash severance payments and other employee-related costs. The Company recorded these restructuring charges based on each employee’s role to the respective research and development and general and administrative operating expense categories on its consolidated statements of operations and comprehensive loss. For the years ended December 31, 2024 and 2023, the Company recognized $0.2 million and $5.6 million in research and development expenses, respectively, and $0.6 million and $0.8 million in general and administrative expenses, respectively. Payments for the restructuring plan were substantially complete by June 30, 2024.

Property and Equipment - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1.2	$ 0.7

Equity

12 Months Ended

Dec. 31, 2024

Equity [Abstract]

Equity

Equity Financings

2024 Private Placement

On July 2, 2024, the Company and the Purchasers entered into the 2024 Securities Purchase Agreement for the 2024 Private Placement.

Pursuant to the 2024 Securities Purchase Agreement, the Purchasers agreed to purchase an aggregate of 3,563,247 shares of common stock and 2,937,903 shares of Series B Preferred Stock, inclusive of 2,359,500 shares of Series B Preferred Stock purchased by directors and executive officers of the Company, and related parties thereto, each at a price per share of $20.00. The 2024 Private Placement resulted in gross proceeds of approximately $130.0 million before deducting placement agent fees and other offering expenses. See Note 11.

Merger

On December 5, 2023, the Company issued 224,099 shares of common stock as part of its consideration transferred in connection with the Merger which settled the related equity-classified forward contract (see Note 4).

Underwritten Offering

On April 6, 2022, the Company entered into an underwriting agreement with SVB Securities LLC (now known as Leerink Partners LLC), as representative of the several underwriters named therein, relating to an underwritten offering of 914,285 shares of the Company’s common stock and 2022 Warrants to purchase up to 685,712 shares of common stock, or the 2022 Offering. Each share and accompanying 2022 Warrant to purchase 0.75 shares of common stock was sold at a combined offering price of $42.30. The exercise price for the 2022 Warrants is $46.50 per share. The Company received net proceeds from the 2022 Offering of approximately $36.9 million.

The 2022 Warrants are subject to adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the Company’s common stock and also upon any distributions for no consideration of assets to the Company’s stockholders. Each 2022 Warrant is exercisable at any time and from time to time after issuance. In the event of certain corporate transactions, the holders of the 2022 Warrants will be entitled to receive the kind and amount of securities, cash or other property that the holders would have received had they exercised the warrants immediately prior to such transaction. Therefore, the Company is required to account for the 2022 Warrants as liabilities and record the 2022 Warrants at fair value. The 2022 Warrants do not entitle the holders thereof to any voting rights or any of the other rights or privileges to which holders of common stock are entitled.

“At-the-Market” Offerings

2024 Sales Agreement

On December 13, 2024, the Company entered into a Sales Agreement, or the 2024 Sales Agreement, with Leerink Partners to sell shares of the Company’s common stock, from time to time, through an “at the market” equity offering program under which Leerink Partners will act as sales agent. The shares of common stock sold pursuant to the 2024 Sales Agreement will be issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-283803), filed on December 13, 2024 with the SEC and related prospectus supplement, filed on January 8, 2025 with the SEC, for aggregate gross sales proceeds of up to $100.0 million.

2021 Sales Agreement

On October 25, 2021, the Company entered into a Sales Agreement, or the 2021 Sales Agreement, with Leerink Partners LLC (then known as SVB Leerink LLC), or Leerink Partners, pursuant to which the Company may sell shares of the Company’s common stock, from time to time, through an “at the market” equity offering program under which Leerink Partners will act as sales agent. The shares of common stock sold pursuant to the 2021 Sales Agreement, if any, would be issued and sold pursuant to a registration statement to be filed by the Company with the SEC, for aggregate remaining gross sales proceeds of up to $51.0 million. During the years ended December 31, 2024 and 2023, the Company sold no shares of its common stock pursuant to the 2021 Sales Agreement. The 2024 Sales Agreement supersedes the 2021 Sales Agreement, which is no longer in effect.

June 2020 Sobi Stock Purchase

On June 11, 2020, the Company entered into a stock purchase agreement with Sobi, pursuant to which the Company sold an aggregate of 180,546 shares of its common stock at a purchase price equal to $138.4680 per share, which represented 120% of the 10-day volume-weighted average price of the Company’s common stock prior to signing, for aggregate gross proceeds of $25.0 million, or the Sobi Private Placement. The closing of the Sobi Private Placement occurred on July 31, 2020.

In accordance with ASC 815, this forward sale treatment qualified as equity classification as the shares are not within the scope of ASC 480. The gross proceeds of $25.0 million were determined to include a premium to the fair value of the Company’s shares as of July 28, 2020 of approximately $14.5 million. As a result, such amount was included in the transaction price for revenue recognition of the Sobi License. See Note 14 for details.

Also on June 11, 2020, the Company entered into a registration rights agreement, as amended by that certain letter agreement, dated as of November 4, 2020, or the Sobi Registration Rights Agreement, with Sobi, pursuant to which the Company agreed to prepare and file a registration statement with respect to the resale of the shares of common stock acquired in the Sobi Private Placement. The Company will be required to file this resale registration statement within 30 days following receipt by the Company of a written request from Sobi to file such resale registration statement, and to have the registration statement declared effective within ten business days after the SEC informs the Company that no review of such resale registration statement will be made or that the SEC has no further comments on such resale registration statement.

December 2019 Financing

On December 18, 2019, the Company entered into a securities purchase agreement, or the 2019 Securities Purchase Agreement, with a group of institutional investors and certain members of the Board of Directors. Pursuant to the 2019 Securities Purchase Agreement, the Company sold an aggregate of 1,254,496 shares of its common stock at a purchase price of $43.80 per share, warrants to purchase an aggregate of 766,275 shares of common stock at a purchase price of $3.75 per share underlying each common warrant, and pre-funded warrants to purchase an aggregate of 278,070 shares of common stock at a purchase price of $43.80 per share, all with five year terms, or the 2019 Private Placement. The closing of the 2019 Private Placement occurred on December 23, 2019. The exercise price of the pre-funded warrants is $0.003 per share and the exercise price for the common warrants is $43.80 per share. In the event of a certain sale of the Company, the terms of the common warrants require us to make a payment to such common warrant holders based on a Black-Scholes valuation (using variables as specified in the warrants). This provision does not apply to the pre-funded warrants. Therefore, the Company is required to account for the common warrants as liabilities and record them at fair value, while the pre-funded warrants met the criteria to be classified as permanent equity.

The Company recorded the fair value of the 2019 Warrants of $40.7 million upon issuance using the Black-Scholes valuation model. Issuance costs were allocated between the equity component with an offset to additional paid-in capital and the liability component recorded as expense on a relative fair value basis. Total net proceeds from the equity offering was $65.6 million, after deducting transaction costs and commissions of $4.4 million.

As discussed in Note 6, the Company remeasured the Amended 2019 Warrants at the fair value of $0.8 million on December 20, 2022 and reclassified this amount to additional paid-in capital.

The outstanding 2019 Warrants expired on December 23, 2024 in accordance with their terms. The remaining 2022 Warrants liability was revalued as of December 31, 2024 at $3.8 million. During the years ended December 31, 2024 and 2023, the Company recorded a decrease of $2.6 million and $12.7 million, respectively, in the fair value of the warrants in the consolidated statements of operations and comprehensive loss.

Warrants

The following is a summary of warrant activity for the years ended December 31, 2024 and 2023:


	Number of Warrants
	Equity classified	Liability classified	Total	Weighted average exercise price
Outstanding at December 31, 2022	74,539	966,393	1,040,932	$	46.03


Expired	(119)	—	(119)	$	503.10

Outstanding at December 31, 2023	74,420	966,393	1,040,813	$	45.98
Exercises	(65,681)	—	(65,681)	43.80

Expired	(1,928)	(280,681)	(282,609)	44.09

Outstanding at December 31, 2024	6,811	685,712	692,523	$	46.96

Common Stock

As of December 31, 2024, the Company had 350,000,000 shares of common stock authorized for issuance, $0.0001 par value per share, with 25,767,369 shares issued and outstanding. The voting, dividend and liquidation rights of the common stockholders are subject to and qualified by the rights, powers and preferences of the preferred stock. The common stock has the following characteristics:

Voting

Common stockholders are entitled to one vote for each share of common stock held with respect to all matters voted on by the stockholders of the Company.

Dividends

Common stockholders are entitled to receive dividends, if and when declared by the Board of Directors. Through December 31, 2024, no cash dividends have been declared or paid on common stock.

Liquidation

Upon liquidation of the Company, common stockholders are entitled to receive all assets of the Company available for distribution to such stockholders.

Reserved Shares

The Company has authorized shares of common stock for future issuance as follows:


			As of
			December 31, 2024
Exercise of warrants			692,523
Shares available for future stock incentive awards			4,205,199

Unvested restricted stock units			444,238
Outstanding common stock options			1,706,035
Series A Preferred Stock			4,026,346
Series B Preferred Stock			437,927
Total			11,512,268

- 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)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477968/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478448/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-18

+ Details

Collaboration and License Agreements - Cyrus Biotechnology, Inc. (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 07, 2021	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity securities without readily determinable fair value, amount		$ 2,000	$ 2,000
Cyrus Biotechnology, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payment	$ 1,500,000
Equity securities, stock purchase agreement, shares purchased (in shares)	2,326,934
Equity securities without readily determinable fair value, amount	$ 2,000	$ 2,000
Cyrus Biotechnology, Inc. \| Series B Preferred Stock Purchase Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity securities, stock purchase agreement, par value per share (in dollars per share)	$ 0.0001
Equity securities, stock purchase agreement, purchase price per share (in dollars per share)	$ 0.8595

Employee Benefit Plans (Details) - USD ($)	12 Months Ended
Employee Benefit Plans (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023	Jun. 30, 2016
Retirement Benefits [Abstract]
Vesting period	2 years
Employer contribution made	$ 200,000	$ 300,000
Defined Benefit Plan Disclosure [Line Items]
Common stock authorized and reserved for future issuance (in shares)	11,512,268
Stock‑based compensation expense	$ 6,582,000	25,778,000
ESPP
Defined Benefit Plan Disclosure [Line Items]
Common stock authorized and reserved for future issuance (in shares)	45,795		5,769
Stock‑based compensation expense	$ 0	$ 100,000

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2024

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):


	December 31,
	2024		2023
Payroll and employee related expenses	$	3,534	$	4,390

Accrued patent fees	813		472
Accrued external research and development costs	2,987		4,896
Accrued professional and consulting services	3,674		4,331
Property and equipment	782		128

Other	286		516
Accrued expenses	$	12,076	$	14,733

Revenue Arrangements - Narrative (Details)							1 Months Ended		3 Months Ended	12 Months Ended
Revenue Arrangements - Narrative (Details)	Jun. 28, 2024 USD ($)	Jun. 29, 2022 USD ($)	Jun. 10, 2022	Oct. 01, 2021 USD ($)	Jul. 28, 2020 USD ($)	Jun. 11, 2020 USD ($) obligation	Jan. 31, 2023 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2024 USD ($)
Disaggregation of Revenue [Line Items]
Short-term contract liability										$ 0	$ 2,311,000
Long-term contract liability										0	3,538,000
Accounts receivable										872,000	5,870,000
Revenue recognized										5,849,000
Collaboration and license revenue										38,275,000	26,004,000
Remaining performance obligation										$ 0
Government Assistance Current Statement Of Financial Position Extensible Enumeration Not Disclosed Flag										receivable
Grant revenue										$ 638,000	0
National Institute of Neurological Disorders and Stroke of the National Institutes of Health Funding
Disaggregation of Revenue [Line Items]
Government assistance, award amount													$ 1,500,000
Government assistance, potential additional award amount													$ 1,500,000
Government assistance, asset, current										600,000
Grant revenue										600,000
SOBI Purchase Agreement
Disaggregation of Revenue [Line Items]
Sale common stock						$ 25,000,000
Redemption premium					$ 14,500,000
Astellas Gene Therapies
Disaggregation of Revenue [Line Items]
Collaboration and license agreements upfront payment							$ 10,000,000
Development and commercial milestones plus royalties							$ 340,000,000
Reimbursement percentage, budgeted costs incurred to complete the development							25.00%
License and option agreement, development cost reimbursements							$ 5,500,000
License and option agreement, written notice period before cancellation							90 days
Short-term contract liability										0	2,300,000
Long-term contract liability											3,500,000
Accounts receivable										100,000	300,000
Customer, liability, revenue recognized, including opening balance										6,300,000
Revenue, remaining performance obligation recognized										3,200,000
Revenue recognized											5,500,000
Sarepta Therapeutics, Inc.
Disaggregation of Revenue [Line Items]
License and option agreement, written notice period before cancellation								30 days
Short-term contract liability										0	0
Upfront cash payment								$ 2,000,000.0
Sales milestone payments									$ 3,000,000
Collaboration and license revenue										0	500,000
Option term								24 months
Extension term			9 months
Milestone receivable for certain dystrophies												$ 2,000,000
Milestone receivable												$ 4,000,000
Takeda Agreement
Disaggregation of Revenue [Line Items]
License and option agreement, written notice period before cancellation				90 days
Short-term contract liability										0	0
Contract with customer, asset, reclassified to receivable											500,000
Customer, liability, revenue recognized, including opening balance										0	600,000
Upfront cash payment				$ 3,000,000
Future additional payments, expected				$ 1,124,000,000
Collaborative Arrangement \| Swedish Orphan Biovitrum AB (SOBI)
Disaggregation of Revenue [Line Items]
License and option agreement, written notice period before cancellation						180 days
Accounts receivable										100,000	4,600,000
Revenue, remaining performance obligation recognized										1,900,000	1,100,000
Upfront cash payment						$ 75,000,000
Sales milestone payments						$ 630,000,000
Period after first commercial sale when the Company is eligible to receive royalties						10 years
Number of obligations \| obligation						3
Development milestone						$ 5,000,000
Collaborative arrangement, payment obligation		$ 10,000,000
Revenue recognized	$ 30,000,000									30,000,000
Collaboration and license revenue										31,900,000	19,400,000
Collaborative Arrangement \| Billed Revenues \| Swedish Orphan Biovitrum AB (SOBI)
Disaggregation of Revenue [Line Items]
Accounts receivable										$ 0	$ 3,000,000.0

Fair Value Measurements

12 Months Ended

Dec. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following tables present the Company’s assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2024 and 2023 (in thousands):


	December 31, 2024
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds (included in cash equivalents)	$	39,088	$	39,088	$	—	$	—






Total assets	$	39,088	$	39,088	$	—	$	—

Liabilities:
Warrant liabilities	$	3,836	$	—	$	—	$	3,836
Contingent value right liability	395,500		—		—		395,500

Total liabilities	$	399,336	$	—	$	—	$	399,336


	December 31, 2023
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds (included in cash equivalents)	$	41,161	$	41,161	$	—	$	—






Total assets	$	41,161	$	41,161	$	—	$	—

Liabilities:
Warrant liabilities	$	6,394	$	—	$	—	$	6,394
Contingent value right liability	358,600		—		—		358,600
Forward contract liabilities	28,307		—		28,307		—
Total liabilities	$	393,301	$	—	$	28,307	$	364,994

There were no transfers within the fair value hierarchy during the years ended December 31, 2024 or 2023.

Cash, Cash Equivalents, and Restricted Cash

As of December 31, 2024 and 2023, money market funds were classified as cash and cash equivalents on the accompanying consolidated balance sheets as they mature within 90 days from the date of purchase.

As of December 31, 2024, the Company had restricted cash balances relating to secured letters of credit in connection with its real estate leases (see Note 9). The Company’s consolidated statement of cash flows includes the following as of December 31, 2024 and 2023 (in thousands):


	Year Ended December 31,
		2024		2023
Cash and cash equivalents		$	212,610	$	76,911

Long-term restricted cash		1,669		1,377
Total cash, cash equivalents, and restricted cash		$	214,279	$	78,288

Warrants to Purchase Common Stock

In December 2019, the Company issued warrants to purchase common stock in connection with a private placement, or the 2019 Warrants. The outstanding 2019 Warrants expired on December 23, 2024 in accordance with their terms. Pursuant to the terms of the 2019 Warrants, the Company could have been required to settle the 2019 Warrants in cash in the event of certain acquisitions of the Company and, as a result, the 2019 Warrants were required to be measured at fair value and reported as a liability on the balance sheet. On December 20, 2022, the Company amended the terms of the outstanding 2019 Warrants held by certain members of the Board of Directors, or the Amended 2019 Warrants, to remove the cash settlement provision. As a result, the Amended 2019 Warrants were remeasured at fair value on December 20, 2022 and reclassified from a liability to equity on the balance sheet. See Note 12 for further discussion on the equity-classified Amended 2019 Warrants.

In April 2022, the Company issued warrants in connection with an underwritten offering, or the 2022 Warrants. Pursuant to the terms of the 2022 Warrants, the Company could be required to settle the 2022 Warrants in cash in the event of an acquisition of the Company under certain circumstances and, as a result, the 2022 Warrants are required to be measured at fair value and reported as a liability on the balance sheet.

The Company recorded the fair value of the 2019 Warrants and the 2022 Warrants upon issuance using the Black-Scholes valuation model and is required to revalue the 2019 Warrants and the 2022 Warrants at each reporting date, with any changes in fair value recorded in the consolidated statements of operations and comprehensive loss. The valuations of the 2019 Warrants and the 2022 Warrants are classified as Level 3 of the fair value hierarchy due to the need to use assumptions in the valuations that are both significant to the fair value measurement and unobservable, including the stock price volatility and the expected life of the 2019 Warrants and the 2022 Warrants. Generally, increases (decreases) in the fair value of the underlying stock and estimated term would result in a directionally similar impact to the fair value measurement. The changes in the fair values of the warrants are reflected in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2024 and 2023.

The estimated fair values of the 2019 Warrants and the 2022 Warrants were determined using the following inputs to the Black-Scholes simulation valuation:

Estimated fair value of the underlying stock. The Company estimates the fair value of the common stock based on the closing stock price at the end of each reporting period.

Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury at the valuation date commensurate with the expected remaining life assumption.

Dividend rate. The dividend rate is based on the historical rate, which the Company anticipates will remain at zero.

Expected life. The expected life of the 2019 Warrants was assumed to be equivalent to their remaining contractual term which expired on December 23, 2024. The expected life of the 2022 Warrants is assumed to be equivalent to their remaining contractual term which expire on April 11, 2027.

Volatility. The Company estimates stock price volatility based on the Company’s historical volatility for a period of time commensurate with the expected remaining life of the warrants.

The 2019 Warrants expired on December 23, 2024 and therefore, there were no 2019 Warrants outstanding as of December 31, 2024. A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2019 Warrants liability as of December 31, 2023 is as follows:


	December 31,
	2023
Risk-free interest rate	4.79	%
Dividend yield	—
Expected life (in years)	0.98
Expected volatility	83.67	%

A summary of the Black-Scholes pricing model assumptions used to record the fair value of the 2022 Warrants liability is as follows:


	December 31,
	2024		2023
Risk-free interest rate	4.25	%	4.01	%
Dividend yield	—		—
Expected life (in years)	2.28		3.28
Expected volatility	92.92	%	84.09	%

The following table reflects a roll-forward of fair value for the Company’s Level 3 warrant liabilities (see Note 12), for the year ended December 31, 2024 (in thousands):


	Warrant liabilities
Fair value as of December 31, 2023	$	6,394



Change in fair value	(2,558)

Fair value as of December 31, 2024	$	3,836

Contingent Value Right

On December 6, 2023, as contemplated by the Merger Agreement, the Company entered into a contingent value rights agreement, or the CVR Agreement, pursuant to which each holder of common stock or a 2022 Warrant as of December 4, 2023 was distributed a CVR, issued by the Company for each share of common stock held directly or underlying a 2022 Warrant held by such holder as of December 4, 2023. Holders of warrants other than the 2022 Warrants will be entitled to receive, upon

exercise of such warrants and in accordance with the terms of the warrants, 30 CVRs per each share of common stock underlying such warrants.

Each CVR entitles its holder to distributions of the following, pro-rated on a per-CVR basis, during the period ending on the date on which the Royalty Term (as defined in the Sobi License) ends, or the Termination Date:

•100% of all milestone payments, royalties and other amounts paid to the Company or its controlled affiliates, or the Company Entities, under the Sobi License or, following certain terminations of the Sobi License, any agreement a Company Entity enters into that provides for the development and commercialization of SEL-212; and

•100% of all cash consideration and the actual liquidation value of any and all non-cash consideration of any kind that is paid to or is actually received by any Company Entity prior to the Termination Date pursuant to an agreement relating to a sale, license, transfer or other disposition of any transferable asset of the Company existing as of immediately prior to the Merger, other than those exclusively licensed under the Sobi License or which the Company Entities are required to continue to own in order to comply with the Sobi License.

The distributions in respect of the CVRs will be made on a semi-annual basis, and will be subject to a number of deductions, subject to certain exceptions or limitations, including for (i) certain taxes payable on the proceeds subject to the CVR distribution, (ii) certain out of pocket costs incurred by the Company Entities, including audit and accounting fees incurred in connection with reporting obligations relating to the CVRs and other expenses incurred in the performance of their obligations and other actions under the CVR Agreement, (iii) a fixed semi-annual amount of $0.75 million for general and administrative overhead, (iv) payments made and remaining obligations on lease liabilities of Selecta immediately prior to the Merger and (v) amounts paid and remaining obligations with regard to the Xork product candidate. Each of the deductions described in (iv) and (v) will be made only if certain milestone payments under the Sobi License are made and are also subject to certain adjustments as contemplated in the CVR Agreement. Upon the achievement of a development milestone in June 2024, Sobi became obligated to make a $30.0 million payment to the Company and made such payment in July 2024. The proceeds from this payment, net of deductions specified in the CVR Agreement, is expected to be included in the next scheduled distribution to the holders of the CVR in March 2025.

The CVRs represent financial instruments that are accounted for under the fair value option election in ASC 825. Under the fair value option election, the CVRs are initially measured at the aggregate estimated fair value of the CVRs and will be subsequently remeasured at estimated fair value on a recurring basis at each reporting period date. The liability was recorded at the date of approval, November 13, 2023, as a dividend. The estimated fair value of the CVR liability was determined using a discounted cash flow methodology as of December 31, 2023 and a Monte Carlo simulation model as of December 31, 2024 to estimate future cash flows associated with the legacy assets, including the expected milestone and royalty payments under the Sobi License, net of deductions. Changes in fair value of the CVR liability are presented in the consolidated statements of operations and comprehensive loss. The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of success, expected volatility of future revenues (Monte Carlo simulation model) and risk-adjustment discount rate (discounted cash flow methodology), which represent a Level 3 measurement within the fair value hierarchy. The significant inputs used to estimate the fair value of the CVR liability, which represented a financial instrument being accounted for under the fair value option, were as follows:


	December 31,
	2024
Estimated cash flow dates	2025 - 2038
Estimated probability of success	95.0% - 100.0%
Expected volatility of future revenues	22.0	%


	December 31,
	2023
Estimated cash flow dates	2024 - 2038
Estimated probability of success	95.0	%
Risk-adjusted discount rate	13.7	%

The following table reflects a roll-forward of fair value for the Company’s Level 3 CVR liability for the year ended December 31, 2024 (in thousands):


	CVR liability
Fair value as of December 31, 2023	$	358,600

Change in fair value	36,900
Fair value as of December 31, 2024	$	395,500

Forward Contract Liabilities

Merger Consideration

In connection with the Merger, the Company entered into a contract for the issuance of 384,930.724 shares of Series A Preferred Stock as part of the consideration transferred. The fair value of the forward contract at the Closing Date was $155.3 million. The non-cash settlement of this liability occurred on December 5, 2023 with the issuance of the Series A Preferred Stock for $261.8 million.

2023 Private Placement

The Company entered into a contract for the issuance of 149,330.115 shares of Series A Preferred Stock as part of the 2023 Private Placement which was settled in multiple tranches. The Company determined the obligation to issue 148,710.488 shares of Series A Preferred Stock to Dr. Timothy A. Springer, a member of the Company’s Board of Directors, and TAS Partners LLC, an affiliate of Dr. Springer, represented a forward contract. See Note 11. The initial fair value of the forward contract liability on November 13, 2023 was insignificant as the fair value of the underlying Series A Preferred Stock was equal to the purchase price of the Series A Preferred Stock as agreed upon in the 2023 Private Placement. Subsequent measurement of the fair value of the forward contract liability was based on the market price of the Company’s common stock, which represented the redemption and conversion value of the Series A Preferred Stock, less the purchase price, on an as-converted basis. The non-cash settlement of a portion of the liability occurred on December 13, 2023 with the issuance of the first tranche of the Series A Preferred Stock for $14.8 million. The non-cash settlement of the remaining second and third tranches occurred on January 12, 2024 and February 11, 2024, respectively, for a total of $35.2 million.

The following table presents changes in the forward contract liabilities for the periods presented (in thousands):


	Forward contract liabilities
Fair value as of December 31, 2023	$	28,307

Settlements	(35,197)
Change in fair value	6,890
Fair value as of December 31, 2024	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 107
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-107

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Description of the Business	12 Months Ended
Description of the Business	Dec. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Business	Description of the Business Cartesian Therapeutics, Inc., or the Company, (formerly known as Selecta Biosciences, Inc., or Selecta) was incorporated in Delaware on December 10, 2007, and is headquartered in Frederick, Maryland. The Company is a clinical-stage biotechnology company pioneering mRNA cell therapy for the treatment of autoimmune diseases leveraging its proprietary technology and manufacturing platform to introduce one or more mRNA molecules into cells to enhance their function. The Company believes its mRNA cell therapies have the potential to deliver deep, durable clinical benefit to a broad group of patients with autoimmune diseases because they can be administered over a short period of time, in an outpatient setting, and without pre-treatment chemotherapy. On November 13, 2023, the Company acquired, in accordance with the terms of the Agreement and Plan of Merger, or the Merger Agreement, the assets of the Delaware corporation which, immediately prior to the Merger (as defined below), was known as Cartesian Therapeutics, Inc., or Old Cartesian, as disclosed in Note 4. The transaction was structured as a stock-for-stock transaction pursuant to which all of Old Cartesian’s outstanding shares of capital stock were exchanged based on a fixed exchange ratio for consideration of 224,099 shares of the common stock, par value $0.0001 per share, of the Company, or the common stock, and 384,930.724 shares of the newly designated Series A Non-Voting Convertible Preferred Stock, par value $0.0001 per share, or the Series A Preferred Stock. The Series A Preferred Stock is intended to have economic rights similar to the common stock, but with only limited voting rights. Additionally, the Company assumed all outstanding stock options of Old Cartesian. The common stock and Series A Preferred Stock related to the Merger were issued on December 5, 2023. For additional information, see Note 4. In connection with the Merger, the Company entered into a definitive agreement, or the 2023 Securities Purchase Agreement, for a private investment in public equity transaction, or the 2023 Private Placement, with the Investors (as defined below). The 2023 Securities Purchase Agreement provides for the issuance to the Investors of an aggregate of 149,330.115 shares of Series A Preferred Stock for an aggregate purchase price of approximately $60.25 million. For additional information, see Note 11. In connection with the Merger, a contractual contingent value right, or CVR, was distributed to the holders of record of the Company’s common stock and 2022 Warrants (as defined below) as of the close of business on December 4, 2023, but was not distributed to holders of shares of common stock or Series A Preferred Stock issued to stockholders of Old Cartesian or the Investors in the transactions. Holders of the CVRs will be entitled to receive certain payments from proceeds received by the Company, if any, related to the disposition or monetization of the Company’s legacy assets following the issuance of the CVRs. For additional information, see Note 6. On March 27, 2024, the Company’s stockholders approved the Conversion Proposal (as defined below). For additional information, see Note 11. Additionally, on March 27, 2024, the Company’s stockholders approved an amendment to the Company’s restated certificate of incorporation, as amended, or the Charter, to effect a reverse stock split of the Company’s issued and outstanding common stock, at a ratio in the range of 1-for-20 and 1-for-30, with such ratio to be determined at the discretion of the Company’s board of directors, or the Board of Directors. The Board of Directors subsequently approved a final reverse stock split ratio of 1-for-30, and the Company effected the Reverse Stock Split on April 4, 2024. As a result of the Reverse Stock Split, all figures in this Annual Report on Form 10-K relating to shares of the Company’s common stock (such as share amounts, per share amounts, and conversion rates and prices), have been adjusted to reflect the Reverse Stock Split for all periods presented, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. Shares of common stock underlying outstanding stock options, restricted stock units and warrants were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with their terms. Additionally, the conversion ratio of the Company’s Series A Preferred Stock was proportionally adjusted. Stockholders entitled to fractional shares as a result of the Reverse Stock Split received a cash payment in lieu of receiving fractional shares. On July 2, 2024, the Company entered into a securities purchase agreement, or the 2024 Securities Purchase Agreement, for a private investment in public equity financing, or the 2024 Private Placement, which provided for the issuance of 3,563,247 shares of common stock and 2,937,903 shares of Series B Non-Voting Convertible Preferred Stock, par value $0.0001 per share, or the Series B Preferred Stock, each at a purchase price of $20.00 per share. The 2024 Private Placement resulted in gross proceeds of approximately $130.0 million before deducting placement agent fees and other offering expenses. On September 20, 2024, the Company’s stockholders approved the Series B Conversion Proposal (as defined below). For additional information, see Note 11. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. The Company’s product candidates are in preclinical and clinical development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. Liquidity and Management’s Plan As of December 31, 2024, the Company had an accumulated deficit of $692.1 million. The Company anticipates operating losses to continue for the foreseeable future due to, among other things, costs related to research and development of its product candidates and its administrative organization. As of December 31, 2024, the Company’s cash, cash equivalents, and restricted cash were $214.3 million, of which $1.7 million was restricted cash related to lease commitments. The Company believes the cash, cash equivalents and restricted cash as of December 31, 2024 will enable it to fund its current planned operations for at least the next 12 months from the date of issuance of these financial statements, though it may pursue additional cash resources through public or private equity or debt financings or by establishing collaborations with other companies. However, there is no guarantee that any of these strategic or financing opportunities will be executed on favorable terms, and some could be dilutive to existing stockholders. Further, the liability associated with the CVR Agreement (as defined below) will be settled solely through cash flow received under the Company’s License and Development Agreement, or as so amended, the Sobi License, with Swedish Orphan Biovitrum AB (publ.), or Sobi, and any other Gross Proceeds (as defined in the CVR Agreement) net of certain agreed deductions. Under the CVR Agreement, 100% of all milestone payments, royalties and other amounts paid to the Company or controlled entities under the Sobi License, and any other Gross Proceeds will be distributed, net of specified deductions, to holders of the CVRs. There is no obligation to the Company to fund any amount related to the CVR liability. See Note 6. If the Company is unable to obtain additional funding on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations or otherwise capitalize on its commercialization of its product candidates.

Summary of Significant Accounting Policies (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2023	Dec. 31, 2024	Dec. 31, 2023
Lessee, Lease, Description [Line Items]
Impairment to goodwill		$ 0	$ 0
Impairment of intangible assets		$ 0
Furniture and fixtures
Lessee, Lease, Description [Line Items]
Estimated useful life		7 years
Laboratory Equipment, Software and Office Equipment
Lessee, Lease, Description [Line Items]
Estimated useful life		5 years
Computer equipment and software
Lessee, Lease, Description [Line Items]
Estimated useful life		3 years
Astellas Gene Therapies
Lessee, Lease, Description [Line Items]
Reimbursement percentage, budgeted costs incurred to complete the development	25.00%
Minimum
Lessee, Lease, Description [Line Items]
Lease term		2 years
Lease renewal term		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term		8 years
Lease renewal term		5 years

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities
Net loss	$ (77,424)	$ (219,710)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,151	843
Amortization of premiums and discounts on marketable securities	0	(79)
Non-cash lease expense	2,437	1,754
Impairment of long-lived assets	7,579	710
Loss on disposal of property and equipment	273	477
Stock-based compensation expense	6,582	22,524
Non-cash interest expense	0	455
Warrant liabilities revaluation	(2,558)	(12,746)
Contingent value right liability revaluation	36,900	18,300
Forward contract liabilities revaluation	6,890	149,600
Loss on extinguishment of debt	0	740
Provision (benefit) for deferred taxes	287	(19,000)
Changes in operating assets and liabilities:
Accounts receivable	4,998	726
Unbilled receivable	2,981	181
Prepaid expenses, deposits and other assets	1,747	(1,265)
Accounts payable	(2,927)	2,834
Deferred revenue	(5,849)	5,256
Accrued expenses and other liabilities	(6,741)	(2,761)
Net cash used in operating activities	(23,674)	(51,161)
Cash flows from investing activities
Cash assumed in acquisition of Old Cartesian	0	6,561
Proceeds from maturities of marketable securities	0	28,254
Purchases of property and equipment	(9,093)	(206)
Proceeds from the sale of property and equipment	351	0
Net cash (used in) provided by investing activities	(8,742)	34,609
Cash flows from financing activities
Proceeds from issuance of Series A Preferred Stock, gross in private placement	40,000	20,250
Repayments of principal, final payment fee, and prepayment penalty on debt	0	(27,457)
Net proceeds from issuance of common stock and Series B Preferred Stock in private placement	124,438	0
Equity offering costs	(66)	0
Proceeds from exercise of common warrants	2,877	0
Settlement of outstanding equity awards at Merger	0	(6,169)
Proceeds from exercise of stock options	1,179	0
Proceeds from issuance of common stock under Employee Stock Purchase Plan	0	231
Net cash provided by (used in) financing activities	168,428	(13,145)
Effect of exchange rate changes on cash	(21)	(53)
Net change in cash, cash equivalents, and restricted cash	135,991	(29,750)
Cash, cash equivalents, and restricted cash at beginning of period	78,288	108,038
Cash, cash equivalents, and restricted cash at end of period	214,279	78,288
Supplement cash flow information
Cash paid for interest	0	1,853
Non-cash investing and financing activities
Issuance of common stock, license agreement in stock-based compensation expense	0	1,500
Purchase of property and equipment not yet paid	847	128
Equity offering costs in accrued liabilities	$ 451	$ 0

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Pay vs Performance Disclosure
Net loss	$ (77,424)	$ (219,710)

- Definition

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

+ References

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+ Details

Collaboration and License Agreements	12 Months Ended
Collaboration and License Agreements	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Collaboration and License Agreements	Collaboration and License Agreements Biogen MA, Inc. On September 8, 2023, the Company entered into a non-exclusive, sublicensable, worldwide, perpetual patent license agreement, or the Biogen Agreement, with Biogen MA, Inc., or Biogen to research, develop, make, use, offer, sell and import products or processes containing or using an engineering T-cell modified with an mRNA comprising, or encoding a protein comprising, certain sequences licensed under the Biogen Agreement for the prevention, treatment, palliation and management of autoimmune diseases and disorders, excluding cancers, neoplastic disorders, and paraneoplastic disorders. The Company is not obligated to pay Biogen any expenses, fees, or royalties. The Company may terminate the Biogen Agreement for any reason or no reason, and Biogen may terminate the agreement after a notice-and-cure period of 30 days if the Company fails to pay a fee owed to Biogen or for any other material breach of the agreement. The Biogen Agreement will otherwise expire when all claims of all issued patents within the patents and patent applications licensed to the Company under the Biogen Agreement have expired or been finally rendered revoked, invalid or unenforceable by a decision of a court or government agency. The Biogen Agreement encompasses patents and patent applications in the PCT/US2010/026825 patent family, which was filed March 10, 2010. In general, all patents that issue in this family have an expected expiration date of March 10, 2030, subject to potential patent term adjustments and/or extensions. For the U.S. patents and applications in this family, U.S. Patent 9,034,324 was awarded 677 days of patent term adjustment, which would extend the expiration date of this patent to January 16, 2032, absent any challenges to the patent term. The other issued patent in this family was not awarded any patent term adjustment, so its expected expiration date is March 10, 2030. National Cancer Institute of the National Institutes of Health Effective September 16, 2019, the Company entered into a nonexclusive, worldwide license agreement, or the NCI Agreement, with the U.S. Department of Health and Human Services, represented by the National Cancer Institute of the National Institutes of Health, or NCI. Under the NCI Agreement, the Company was granted a license under certain NCI patents and patent applications designated in the agreement, to make, use, sell, offer and import products and processes within the scope of the patents and applications licensed under the NCI Agreement when developing and manufacturing anti-BCMA CAR-T cell products for the treatment of myasthenia gravis, pemphigus vulgaris, and immune thrombocytopenic purpura according to methods designated in the NCI Agreement. In connection with the Company’s entry into the NCI Agreement, Old Cartesian paid to NCI a one-time $0.1 million license royalty payment. Under the NCI Agreement, the Company is further required to pay NCI a low five-digit annual royalty. The Company must also pay earned royalties on net sales in a low single-digit percentage and pay up to $0.8 million in benchmark royalties upon the Company’s achievement of designated benchmarks that are based on the commercial development plan agreed between the parties. Under the NCI Agreement, the Company must use reasonable commercial efforts to bring licensed products and licensed processes to the point of Practical Application (as defined in the NCI Agreement). Upon the Company’s first commercial sale, the Company must use reasonable commercial efforts to make licensed products and licensed processes reasonably accessible to the United States public. After the Company’s first commercial sale, the Company must make reasonable quantities of licensed products or materials produced via licensed processes available to patient assistance programs and develop educational materials detailing the licensed products. Unless the Company obtains a waiver from NCI, the Company must have licensed products and licensed processes manufactured substantially in the United States. Prior to the first commercial sale, upon NCI’s request, the Company is obligated to provide NCI with commercially reasonable quantities of licensed products made through licensed processes to be used for in vitro research. Additionally, the Company must use reasonable commercial efforts to initiate a Phase 3 clinical trial of a licensed product by the fourth quarter of 2024, submit a BLA with respect to a licensed product by the fourth quarter of 2026, and make a first commercial sale of a licensed product by the fourth quarter of 2028. The NCI Agreement terminates upon the expiration of the last to expire of the patent rights licensed thereunder, if not sooner terminated. The NCI Agreement encompasses patents and patent applications in the PCT/US2013/032029 patent family, which was filed March 15, 2013. In general, all patents that issue in this family have an expected expiration of March 15, 2033, subject to potential patent term adjustments and/or extensions. For the U.S. patents and applications in this family, only two patents were awarded patent term adjustments. U.S. Patent 9,765,342 was awarded 297 days of patent term adjustment, which would extend the expiration date of this patent to January 6, 2034, absent any challenges to the patent term. The other patent, U.S. Patent 10,876,123, was awarded three days of patent term adjustment, but this patent is subject to terminal disclaimers filed against other family members, so this patent will not extend beyond the March 15, 2033 date. The other issued patents in this family were not awarded any patent term adjustment, so the expected expiration date for these patents also remains March 15, 2033. There is also a pending patent application which, if issued, will expire on March 15, 2033, but could also be subject to patent term adjustment and to any potential future terminal disclaimers. NCI has the right to terminate the NCI Agreement, after giving written notice and providing a cure period in accordance with its terms, if the Company is in default of a material obligation. The Company has the unilateral right to terminate the agreement in any country or territory by giving NCI 60 days’ written notice. The Company agreed to indemnify NCI against any liability arising out of the Company’s, sublicensees’ or third-parties’ use of the licensed patent rights and licensed products or licensed processes developed in connection with the licensed patent rights. Ginkgo Bioworks Holdings, Inc. Collaboration and License Agreements On October 25, 2021, the Company entered into a Collaboration and License Agreement, or the First Ginkgo Agreement, with Ginkgo. Under the First Ginkgo Agreement, Ginkgo will design next generation IgA proteases with potentially transformative therapeutic potential. In return, Ginkgo is eligible to earn both upfront research and development fees and milestone payments, including certain milestone payments for fixed fair values in the form of the Company’s common stock, clinical and commercial milestone payments of up to $85.0 million in cash. The First Ginkgo Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the First Ginkgo Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company is accounting for the contingently issuable shares to be issued in exchange for the license obtained from Ginkgo as a liability classified stock-based compensation arrangement with a non-employee which will be recognized when achievement of the milestones is probable. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Ginkgo tiered royalties ranging from low-single digit to high-single digit percentages of annual net sales of collaboration products which will be expensed as the commercial sales occur. On January 3, 2022, the Company entered into a Collaboration and License Agreement, or the Second Ginkgo Agreement, with Ginkgo. Under this agreement, the Company will engage with Ginkgo to develop AAV capsids designed to enhance transduction efficiency and transgene expression. In return, Ginkgo is eligible to earn both upfront research and development fees and milestone payments, including certain milestone payments in the form of shares of the Company’s common stock, clinical and commercial milestone payments of up to $207 million in cash. The Second Ginkgo Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company will expense costs related to the Second Ginkgo Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company is accounting for the contingently issuable shares of common stock to be issued in exchange for the license obtained from Ginkgo as a liability-classified, stock-based compensation arrangement with a non-employee which will be recognized when achievement of the milestones is probable. The Company will assess the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, will amortize these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company is also obligated to pay Ginkgo tiered royalties ranging from low-single digit to high-single digit percentages of annual net sales of collaboration products which will be expensed as the commercial sales occur. On June 13, 2022, the Company was notified of the achievement of the midpoint of the technical development plan under the First Ginkgo Agreement by Ginkgo. This milestone resulted in the payment of $0.5 million and issuance of 29,761 shares of the Company’s common stock then-valued at $1.0 million to Ginkgo during the year ended December 31, 2022. On July 19, 2023, the Company and Ginkgo mutually agreed that the completion of the technical development plan’s midpoint task under the Second Ginkgo Agreement had been achieved as of June 30, 2023. This milestone resulted in the payment of $1.0 million and issuance of 44,642 shares of the Company’s common stock then-valued at $1.5 million to Ginkgo during the year ended December 31, 2023. Genovis AB (publ.) License Agreement On October 21, 2021, the Company entered into the Genovis Agreement with Genovis. Under the Genovis Agreement, the Company paid to Genovis an upfront payment in exchange for an exclusive license to the Xork enzyme technology across all therapeutic uses in humans, excluding research, preclinical, diagnostic and other potential non-therapeutic applications of the enzyme. Genovis was eligible to earn from the Company development and sales-based milestones and sublicensing fees. The Genovis Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company was to expense costs related to the Genovis Agreement as incurred until regulatory approval was received in accordance with ASC 730. The Company would have assessed the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, would have amortized these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company was also obligated to pay Genovis tiered royalties of low double digit percentages of worldwide annual net sales of collaboration products which would have been expensed as the commercial sales occurred. In February 2023, the Company made a $4.0 million payment to Genovis as a result of the sublicense of Xork to Astellas. See Note 14 to these consolidated financial statements for further discussion on the Astellas Agreement. In March 2024, the Company notified Genovis of its intention to terminate the Genovis Agreement, which occurred effective September 13, 2024. Cyrus Biotechnology, Inc. Collaboration and License Agreement On September 7, 2021, the Company and Cyrus Biotechnology, Inc., or Cyrus, entered into a collaboration and license agreement, or the Cyrus Agreement. Pursuant to the Cyrus Agreement, Cyrus agreed to grant the Company an exclusive, worldwide license to certain intellectual property to form a protein engineering collaboration combining the Company’s ImmTOR platform with Cyrus’ ability to redesign protein therapeutics. The lead program was a proprietary interleukin-2, or IL-2, protein agonist designed to selectively promote expansion of regulatory T cells for treatment of patients with autoimmune diseases and other deleterious immune conditions. In return for the licensed intellectual property, the Company made an upfront payment and was obligated to pay certain discovery, development, and sales-based milestones which could have potentially totaled up to approximately $1.5 billion across multiple programs. The Cyrus Agreement was assessed for collaboration components and was determined not to be within the scope of ASC 808 as the risk and rewards are not shared by both parties. The Company expensed costs related to the Cyrus Agreement as incurred until regulatory approval is received in accordance with ASC 730. The Company assessed the capitalization of costs incurred after the receipt of regulatory approval and, if applicable, would have amortized these payments based on the expected useful life of each asset, typically based on the expected commercial exclusivity period. The Company was also obligated to pay Cyrus tiered royalties ranging from mid-single digit to low-double digit percentages of annual net sales of collaboration products which would have been expensed as commercial sales occur. On June 13, 2022, the Company and Cyrus mutually agreed that the preclinical key in-vitro success milestone had been achieved. In October 2023, the Company notified Cyrus of its termination of the Cyrus Agreement, effective December 29, 2023. Stock Purchase Agreement Additionally, on September 7, 2021, the Company entered into a stock purchase agreement, or the Series B Preferred Stock Purchase Agreement, in connection with the Cyrus Agreement. Pursuant to the Series B Preferred Stock Purchase Agreement, the Company purchased 2,326,934 shares of Cyrus’ Series B Preferred Stock, par value $0.0001 per share, at a purchase price of $0.8595 per share for $2.0 million. In accordance with ASC 810, the Company has a variable interest in Cyrus resulting from its equity investment. The Company will share in Cyrus’ expected losses or receive a portion of its expected returns and absorb the variability associated with changes in the entity’s net assets. However, the Company is not the primary beneficiary as it does not have the power to direct the activities most significant to Cyrus, and therefore it is not required to consolidate Cyrus. The Company has recognized the $2.0 million investment of Cyrus’ Series B Preferred Stock at cost on the purchase date. As of December 31, 2024, no impairment indicators are present and there were no observable price changes. Therefore, the carrying value of the investment in Cyrus is $2.0 million on the accompanying consolidated balance sheets. The Company’s maximum exposure to loss related to this VIE is limited to the carrying value of the investment. The Company has not provided financing to Cyrus other than the amount contractually required by the Series B Preferred Stock Purchase Agreement. Asklepios Biopharmaceutical, Inc. Feasibility Study and License Agreement In August 2019, the Company entered into a feasibility study and license agreement, or the AskBio Collaboration Agreement, with Asklepios Biopharmaceutical, Inc., or AskBio. Pursuant to the AskBio Collaboration Agreement, the Company and AskBio agreed to license intellectual property rights to each other as part of a collaboration to research, develop, and commercialize certain AAV gene therapy products utilizing the Company’s ImmTOR platform to enable re-dosing of such AAV gene therapy products to treat serious rare and orphan genetic diseases for which there is a significant unmet medical need. Pursuant to the AskBio Collaboration Agreement, the Company and AskBio agreed to conduct proof of concept studies to potentially validate the use of ImmTOR in conjunction with AskBio’s AAV gene therapy, or SEL-302, (previously disclosed as MMA-101, in combination with ImmTOR) for the treatment of methylmalonic acidemia, or MMA, to mitigate the formation of neutralizing anti-AAV capsid antibodies. On April 29, 2021, the Company was notified by AskBio that it intended to opt-out of development of the MMA indication. The Company and AskBio shared responsibility for the research, development and commercialization of products developed under the SEL-399 program collaboration. The parties also shared research, development, and commercialization costs equally for all collaboration products, but with a right of either party to opt out of certain products, and thereby not be required to share costs for such products. Each party would have received a percentage of net profits under the collaboration equal to the percentage of shared costs borne by such party in the development of such product. Pursuant to the AskBio Collaboration Agreement, AskBio was responsible for manufacturing the AAV capsids and AAV vectors and the Company was responsible for manufacturing ImmTOR. The Company and AskBio mutually agreed to the termination of the AskBio Collaboration Agreement, effective December 13, 2023. For the years ended December 31, 2024 and 2023, the Company recognized no and $0.1 million, respectively, of collaboration expense under the AskBio Collaboration Agreement in which actual costs incurred by both parties approximate a 50% cost share. Shenyang Sunshine Pharmaceutical Co., Ltd In May 2014, the Company entered into a license agreement, or the 3SBio License, with Shenyang Sunshine Pharmaceutical Co., Ltd., or 3SBio. The Company has paid to 3SBio an aggregate of $7.0 million in upfront and milestone-based payments under the 3SBio License as of December 31, 2024. The Company is required to make future payments to 3SBio contingent upon the occurrence of events related to the achievement of clinical and regulatory approval milestones of up to an aggregate of $15.0 million for products containing the Company’s ImmTOR platform.

Stock Incentive Plans - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2024 $ / shares shares
Number of shares
Unvested at beginning of period (in shares) \| shares	0
Grants in period (in shares) \| shares	477,037
Forfeited in period (in shares) \| shares	(32,799)
Unvested at end of period (in shares) \| shares	444,238
Weighted average grant date fair value ($)
Unvested at beginning of period (in dollars per share) \| $ / shares	$ 0
Grants in period (in dollars per share) \| $ / shares	19.86
Forfeited in period (in dollars per share) \| $ / shares	19.80
Unvested at end of period (in dollars per share) \| $ / shares	$ 19.86

Stock Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2024

Share-Based Payment Arrangement [Abstract]

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive loss, including $1.5 million recognized as stock-based compensation expense upon the achievement of a technical milestone by Ginkgo Bioworks Holdings, Inc., or Ginkgo, during the year ended December 31, 2023 as described in Note 16, was as follows (in thousands):


	Year Ended December 31,
		2024		2023
Research and development		$	3,217	$	12,985
General and administrative		3,365		12,793
Total stock-based compensation expense		$	6,582	$	25,778

Schedule of Weighted Average Assumptions Used

The fair value of the stock options assumed in connection with the Merger was calculated using a Black-Scholes option pricing model based on the following weighted-average assumptions:


	Common Stock			Series A Preferred Stock
Risk-free interest rate	4.83		%	4.92		%
Dividend yield	—			—
Expected term	3.59			3.29
Expected volatility	83.77		%	83.87		%
Weighted-average fair value of common stock or Series A Preferred Stock, as applicable	$	12.00		$	403.47

The estimated grant date fair values of stock option awards granted under the 2016 Plan and the 2018 Inducement Incentive Award Plan were calculated using the Black-Scholes option pricing model based on the following weighted-average assumptions:


	Year Ended December 31,
		2024			2023
Risk-free interest rate		4.02		%	3.95		%
Dividend yield		—			—
Expected term		6.21			5.94
Expected volatility		95.21		%	94.64		%
Weighted-average fair value of common stock		$	19.63		$	34.54

Schedule of Stock Option Activity

The following table summarizes the stock option activity under the 2016 Plan, the 2018 Inducement Incentive Award Plan, and the Old Cartesian Plan for options for common stock:


				Weighted-average
	Number of			remaining	Aggregate
	common stock	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)









Outstanding at December 31, 2023	776,865	$	2.97	6.50	$	13,760
Granted	1,000,092	$	19.63
Converted from options for Series A Preferred Stock	470,403	$	2.40
Exercised	(458,544)	$	2.57
Forfeited	(82,781)	$	17.28
Outstanding at December 31, 2024	1,706,035	$	11.99	7.59	$	12,025

Vested at December 31, 2024	656,258	$	3.22	5.36	$	9,674
Vested and expected to vest at December 31, 2024	1,564,044	$	11.31	7.44	$	11,961

The following table summarizes the stock option activity under the Old Cartesian Plan for options for Series A Preferred Stock:


	Number of			Weighted-average
	Series A			remaining	Aggregate
	Preferred Stock	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)









Outstanding at December 31, 2023	14,112.299	$	79.94	5.91	$	8,601
Converted to options for common stock	(14,112.299)	$	79.94
Outstanding at December 31, 2024	—	$	—

Schedule of Restricted Stock Units Activity

The following table summarizes the Company’s restricted stock units under the 2016 Plan and the Old Cartesian Plan:


	Number of shares	Weighted average grant date fair value ($)
Unvested at December 31, 2023	—	$	—
Granted	477,037	19.86


Forfeited	(32,799)	19.80
Unvested at December 31, 2024	444,238	$	19.86

Collaboration and License Agreements - Ginkgo Bioworks Holdings, Inc. (Narrative) (Details) - Ginkgo Agreement - USD ($) $ in Millions					12 Months Ended
	Jul. 19, 2023	Jun. 13, 2022	Jan. 03, 2022	Oct. 25, 2021	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Clinical and commercial milestone payment, expected			$ 207.0	$ 85.0
Milestone payment	$ 1.0	$ 0.5
Collaborative arrangement, number of shares issued for milestone achievement (in shares)					44,642	29,761
Collaborative arrangement, shares issued for milestone achievement, amount					$ 1.5	$ 1.0

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Statutory U.S. federal rate	21.00%	21.00%
State income taxes - net of federal benefit	10.50%	2.30%
Permanent items	1.00%	(1.60%)
Research tax credits	0.30%	0.60%
Change in fair value of contingent value right liability	127.90%	0.00%
Change in fair value of forward contract liabilities	(1.90%)	(13.20%)
Valuation allowance, net	(160.10%)	2.80%
Stock-based compensation	0.90%	(3.90%)
Effective income tax rate	(0.40%)	8.00%

Leases - Schedule of Components of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Operating lease cost	$ 3,856	$ 2,828
Variable lease cost	1,609	965
Short-term lease cost	28	8
Less sublease income	(1,099)	(1,172)
Total lease cost	$ 4,394	$ 2,629

Cover Page - USD ($)	12 Months Ended
Cover Page - USD ($)	Dec. 31, 2024	Feb. 28, 2025	Jun. 28, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2024
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-37798
Entity Registrant Name	Cartesian Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1622110
Entity Address, Address Line One	7495 New Horizon Way
Entity Address, City or Town	Frederick
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	21703
City Area Code	301
Local Phone Number	348-8698
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	RNAC
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 Smaller Reporting Company	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			$ 193,901,954
Entity Common Stock, Shares Outstanding		25,907,101
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement relating to its 2025 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission are incorporated by reference into Part III of this Annual Report on Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Entity Central Index Key	0001453687

Leases - 65 Grove Street Lease (Narrative) (Details) $ in Thousands			1 Months Ended	12 Months Ended
	Oct. 31, 2023 USD ($) ft²	Sep. 01, 2022 USD ($) ft²	Jul. 31, 2019 USD ($) ft²	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jul. 17, 2023 USD ($)	Dec. 31, 2022 USD ($)	Oct. 24, 2022 USD ($)	Oct. 06, 2022 ft²
Operating Leased Assets [Line Items]
Lessee-paid construction costs				$ 4,394	$ 2,629
Weighted-average discount rate				11.70%	9.90%
Right-of-use asset, net				$ 5,535	$ 10,068
Lease liabilities				13,984
Asset impairment charges				7,579	710
Right-of-use asset impairment expense				7,400
Impairment of long-lived assets				$ 200
Impairment of long-lived assets, location				Asset impairment charges
65 Grove Street, Watertown,MA
Operating Leased Assets [Line Items]
Area of office space leased \| ft²	5,600	7,216	25,078						7,216
Lessee-paid construction costs			$ 800
Lease term		5 years 8 months 12 days	8 years
Weighted-average discount rate		11.30%	8.90%					11.90%
Base rent		$ 100
Right-of-use asset, net					700		$ 3,200	$ 100
Lease liabilities							$ 3,200	$ 100
Letters of credit outstanding, amount						$ 1,600
Upfront rental payment	$ 1,000
Deferred rent				$ 800
65 Grove Street, Watertown,MA \| Letter of Credit
Operating Leased Assets [Line Items]
Restricted cash					1,600
Restricted cash, noncurrent				$ 1,400	$ 1,400

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Income Tax Examination [Line Items]
Income tax expense (benefit)	$ 0.3	$ (19.0)
Valuation allowance, deferred tax asset, increase (decrease), amount	123.6		$ (3.5)
Tax benefit related to the CVR liability	108.8
Operating loss carryforwards, not subject to expiration	74.4
Operating loss carryforwards, subject to expiration	113.4
Capitalized research and experimental costs, tax purposes	45.1	$ 43.9
Federal
Income Tax Examination [Line Items]
Operating loss carryforwards	152.6
Tax credit carryforward, amount	5.2
State
Income Tax Examination [Line Items]
Operating loss carryforwards	187.8
Tax credit carryforward, amount	$ 1.0

Merger

12 Months Ended

Dec. 31, 2024

Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]

Merger

On November 13, 2023, the Company merged with Old Cartesian in accordance with the terms of the Merger Agreement, by and among Selecta, Sakura Merger Sub I, Inc., a wholly owned subsidiary of Selecta, or First Merger Sub, Sakura Merger Sub II, LLC, a wholly owned subsidiary of Selecta, or Second Merger Sub, and Old Cartesian. Pursuant to the Merger Agreement, First Merger Sub merged with and into Old Cartesian, pursuant to which Old Cartesian was the surviving corporation and became a wholly owned subsidiary of Selecta, or the First Merger. Immediately following the First Merger, Old Cartesian merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving entity, or the Second Merger and, together with the First Merger, the Merger. In connection with the Second Merger, Old Cartesian changed its name to Cartesian Bio, LLC.

The Merger was intended to qualify as a tax-free reorganization for U.S. federal income tax purposes. As a result of the Merger, Selecta changed its corporate name to Cartesian Therapeutics, Inc. and its common stock began trading on the Nasdaq Global Market under the new trading symbol “RNAC” beginning on November 14, 2023.

The Merger Agreement was unanimously approved by the board of directors, or the Board of Directors, of Selecta and the board of directors of Old Cartesian. The Merger was consummated substantially concurrently with the entry into the Merger Agreement and was not subject to approval of the Company’s stockholders.

Under the terms of the Merger Agreement, following the consummation of the Merger on November 13, 2023, or the Closing Date, in exchange for 100% of the outstanding shares of capital stock of Old Cartesian immediately prior to the effective time of the First Merger, the Company agreed to issue to the stockholders of Old Cartesian (i) 224,099 shares of the Company’s common stock and (ii) 384,930.724 shares of Series A Preferred Stock. The issuance of the shares of common stock and Series A Preferred Stock occurred on December 5, 2023 which was after the December 4, 2023 record date for the distribution of the CVRs (see Note 6); as such, the Old Cartesian stockholders did not have rights as holders of common stock or holders of Series A Preferred Stock until such issuance on December 5, 2023. In addition, all outstanding stock options to purchase Old Cartesian common stock were assumed by the Company and converted into stock options to purchase (i) shares of the Company’s common stock or (ii) shares of the Company’s Series A Preferred Stock on terms substantially identical to those in effect prior to Merger Agreement, except for adjustments to the underlying number of shares and the exercise price based on the Merger Agreement exchange ratio.

Pursuant to the Merger Agreement, the Company agreed to hold a stockholders’ meeting, or the Special Meeting, to submit the following proposals to a vote of its stockholders: (i) the approval of the conversion of shares of Series A Preferred Stock into shares of common stock, or the Conversion Proposal, and (ii) either or both of (A) the approval of an amendment to the Charter to increase the number of shares of common stock authorized under the Charter and (B) the approval of an amendment to the Charter to effect a reverse stock split of all outstanding shares of common stock, in either case (A) or (B) by a number of authorized shares or at a stock split ratio, as the case may be, sufficient to allow the conversion of all shares of Series A Preferred Stock issued in the Merger. The Special Meeting was held on March 27, 2024, during which the Company’s stockholders approved the Conversion Proposal, among other matters (see Note 11).

The Company concluded the acquisition resulted in the Company obtaining a controlling financial interest in a VIE in accordance with ASC Topic 810, Consolidation (ASC 810). The Company determined that Old Cartesian was considered to be a VIE as it did not have sufficient equity to finance its activities without additional subordinated financial support. Prior to the Closing Date, the primary source of funding for Old Cartesian had been preferred stock financings. The Company acquired all of the outstanding shares of Old Cartesian and, therefore, is the sole equity holder and primary beneficiary. The Company has the obligation to absorb the losses and right to receive the benefits of Old Cartesian, and the power to direct the activities that most significantly affect the economic performance of Old Cartesian which the Company considers to be its development

activities. Therefore, the Company is the primary beneficiary. Further, the Company concluded the VIE qualified as a business and accounted for the transaction as the acquisition of a business in accordance with ASC 805. As the primary beneficiary, the Company was the acquirer in the transaction.

The Company exchanged the right to receive shares of common stock and Series A Preferred Stock for all of the outstanding equity of Old Cartesian. The Company determined the rights to receive shares exchanged in the Merger represent a forward contract. The fair value of the forward contracts was determined based on the fair value of shares of common stock and Series A Preferred Stock underlying the forward contracts as of the acquisition date. The total purchase price consists of the fair value of the forward contracts in addition to a portion of the fair value of options exchanged in the transaction related to prior service. Under the acquisition method, the total purchase price of the acquisition was allocated to the net tangible and identifiable intangible assets acquired and liabilities assumed based on their estimated fair values as of the date of the acquisition.

The total fair value of the consideration of $168.5 million as of the Closing Date is summarized as follows (in thousands):


Forward contract to issue common stock	$	2,713
Forward contract to issue Series A Preferred Stock	155,308
Stock options allocated to consideration paid	10,444
Total consideration	$	168,465

The Company recorded the assets acquired and liabilities assumed as of the Closing Date based on the information available at that date. The following table presents the allocation of the purchase price to the estimated fair values of the assets acquired and liabilities assumed as of the Closing Date (in thousands):


Assets acquired:	As of November 13, 2023
Cash and cash equivalents	$	6,561
Prepaid expenses and other current assets	309
Property and equipment, net	215
Right-of-use asset, net	915
In-process research and development assets	150,600
Goodwill	48,163
	$	206,763
Liabilities assumed
Accrued expenses and other current liabilities	$	2,530
Lease liability	292
Lease liability, net of current portion	623
Deferred tax liability	34,853
	$	38,298

Net assets acquired	$	168,465

The fair value of the IPR&D assets were capitalized as of the Closing Date and are accounted for as indefinite-lived intangible assets until completion or disposition of the assets or abandonment of the associated research and development efforts. Upon successful completion of the development efforts, the carrying value of each respective IPR&D asset will be amortized over its estimated useful life. Until that time, the IPR&D assets will be subject to impairment testing and will not be amortized. The goodwill recorded related to the Merger is the excess of the fair value of the consideration transferred by the acquirer over the fair value of tangible assets, identifiable intangible assets and assumed liabilities as of the Closing Date and is not deductible for tax purposes. The goodwill balance is primarily attributable to the value of the assembled workforce and deferred tax liabilities associated with the transaction.

The following summarizes the Company’s intangible assets acquired in the Merger (in thousands):


	Acquisition Date Fair Value
Descartes-08 for MG	$	93,900
Descartes-08 for SLE	56,700
Total in-process research and development assets	$	150,600

The fair value of the intangible assets was estimated using the income approach in which the after-tax cash flows were discounted to present value. The cash flows are based on estimates used to price the transaction, and the discount rates applied

were benchmarked with reference to the implied rate of return from the transaction model as well as the weighted average cost of capital.

For the period from November 13, 2023 to December 31, 2023, Old Cartesian’s revenue and net loss within the consolidated statements of operations and comprehensive loss were $0.0 million and $1.6 million, respectively.


	Year Ended December 31,
	2023
Revenue	$	26,004
Net loss	$	(232,259)

The Company’s transaction costs of $4.9 million were expensed as incurred and included in general and administrative expense in the consolidated statements of operations and comprehensive loss during the year ended December 31, 2023.

The forward contract related to the common stock was recorded as additional paid-in capital as the instrument is indexed to the Company’s common stock. The forward contract related to the Series A Preferred Stock was recorded as a liability as the underlying Series A Preferred Stock had a redemption feature that may have required the Company to settle the instrument by transferring an asset. The forward contract was measured at fair value through the date of settlement through the issuance of the shares of Series A Preferred Stock on December 5, 2023.

Convertible Preferred Stock - Series B Preferred Stock (Narrative) (Details) - USD ($) $ in Thousands							1 Months Ended	12 Months Ended
	Oct. 11, 2024	Sep. 25, 2024	Jul. 02, 2024	Apr. 08, 2024	Mar. 26, 2024	Nov. 13, 2023	Jul. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)								9,427,168.437	9,451,625
Convertible preferred stock, shares that did not automatically convert (in shares)				166,341.592
Related Party
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)					65,681
Common stock
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)	1,518,373	2,499,976		12,263,951
2024 Securities Purchase Agreement
Class of Stock [Line Items]
Gross proceeds			$ 130,000
Sale of stock, consideration received on transaction							$ 82,800
2024 Securities Purchase Agreement \| Timothy A. Springer, Ph.D. \| Related Party
Class of Stock [Line Items]
Sale of stock, consideration received on transaction								$ 32,737
2024 Securities Purchase Agreement \| TAS Partners, LLC \| Related Party
Class of Stock [Line Items]
Sale of stock, consideration received on transaction								14,427
2024 Securities Purchase Agreement \| Dr. Chafen Lu \| Related Party
Class of Stock [Line Items]
Sale of stock, consideration received on transaction								$ 26
2024 Securities Purchase Agreement \| Common stock
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)							3,563,247
2023 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)						149,330.115
Sale of stock, consideration received on transaction						$ 60,250
2023 Securities Purchase Agreement \| Related Party
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)						149,330.115
Sale of stock, consideration received on transaction						$ 60,250
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			2,937,903					437,927	0
Convertible preferred stock, shares issued upon conversion (in shares)			1
Conversion of Series A and Series B preferred stock to common stock (in shares)		(2,499,976)
Convertible preferred stock, shares that did not automatically convert (in shares)		437,927
Series B Preferred Stock \| Common stock
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)								2,499,976
Series B Preferred Stock \| 2024 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)			2,937,903				578,403
Series B Preferred Stock \| 2024 Securities Purchase Agreement \| Timothy A. Springer, Ph.D. \| Related Party
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)								1,636,832
Series B Preferred Stock \| 2024 Securities Purchase Agreement \| TAS Partners, LLC \| Related Party
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)								721,361
Series B Preferred Stock \| 2024 Securities Purchase Agreement \| Dr. Chafen Lu \| Related Party
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)								1,307
Sale of stock, consideration received on transaction							$ 47,200
Common stock \| 2024 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)			3,563,247

Merger - Schedule of Fair Value of Consideration (Details) - Old Cartesian $ in Thousands	Nov. 13, 2023 USD ($)
Business Acquisition [Line Items]
Total consideration	$ 168,465
Common stock
Business Acquisition [Line Items]
Forward contract to issue stock and options	2,713
Preferred Stock
Business Acquisition [Line Items]
Forward contract to issue stock and options	155,308
Stock Options
Business Acquisition [Line Items]
Forward contract to issue stock and options	$ 10,444

Net Loss Per Share Allocable to Common Stockholders - Schedule of Potential Dilutive Shares of Common Stock Excluded from the Computation of the Diluted Net Loss Per Share Allocable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Potential common shares
Total (in shares)	7,307,069	20,096,751
Common stock options and RSUs
Potential common shares
Total (in shares)	2,150,273	776,865
Warrants to purchase common stock
Potential common shares
Total (in shares)	692,523	1,040,813
Preferred Stock \| Series A Preferred Stock
Potential common shares
Total (in shares)	4,026,346	14,503,993
Preferred Stock \| Series B Preferred Stock
Potential common shares
Total (in shares)	437,927	0
Forward contract to issue Series A Preferred Stock
Potential common shares
Total (in shares)	0	3,304,677
Series A Preferred Stock options
Potential common shares
Total (in shares)	0	470,403

Related-party Transactions - Schedule of Related Party Transactions (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Nov. 15, 2023	Jul. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
2024 Securities Purchase Agreement
Related Party Transaction [Line Items]
Total aggregate purchase price		$ 82,800
2023 Private Placement
Related Party Transaction [Line Items]
Shares issued (in shares)	619.627
Total aggregate purchase price	$ 250
Timothy A. Springer, Ph.D. \| Related Party \| 2024 Securities Purchase Agreement
Related Party Transaction [Line Items]
Total aggregate purchase price			$ 32,737
Timothy A. Springer, Ph.D. \| Related Party \| 2023 Private Placement
Related Party Transaction [Line Items]
Shares issued (in shares)			99,140.326	24,785.081
Total aggregate purchase price			$ 40,000	$ 10,000
TAS Partners, LLC \| Related Party \| 2024 Securities Purchase Agreement
Related Party Transaction [Line Items]
Total aggregate purchase price			14,427
TAS Partners, LLC \| Related Party \| 2023 Private Placement
Related Party Transaction [Line Items]
Shares issued (in shares)				24,785.081
Total aggregate purchase price				$ 10,000
Dr. Chafen Lu \| Related Party \| 2024 Securities Purchase Agreement
Related Party Transaction [Line Items]
Total aggregate purchase price			$ 26
Seven One Eight Three Four Irrevocable Trust (affiliate of Murat Kalayoglu, MD, Ph.D.) \| Related Party \| 2023 Private Placement
Related Party Transaction [Line Items]
Shares issued (in shares)				619.627
Total aggregate purchase price				$ 250

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2024
Audit Information [Abstract]
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	Boston, Massachusetts

Convertible Preferred Stock - Voting (Narrative) (Details)	Dec. 31, 2024
Temporary Equity Disclosure [Abstract]
Preferred stock, convertible, transaction restrictions, percentage of originally issued stock issued and outstanding	30.00%

Stock Incentive Plans - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Number of Options
Exercised (in shares)		0
2008 Plan, 2016 Plan, and 2018 Inducement Incentive Award Plan
Number of Options
Beginning balance (in shares)	776,865
Granted (in shares)	1,000,092
Converted from options for Series A preferred stock (in shares)	470,403
Exercised (in shares)	(458,544)
Forfeited (in shares)	(82,781)
Ending balance (in shares)	1,706,035	776,865
Vested (in shares)	656,258
Vested and expected to vest (in shares)	1,564,044
Weighted-Average Exercise Price
Beginning balance (in dollars per share)	$ 2.97
Granted (in dollars per share)	19.63
Converted from options for Series A preferred stock (in dollars per share)	2.40
Exercised (in dollars per share)	2.57
Forfeited (in dollars per share)	17.28
Ending balance (in dollars per share)	11.99	$ 2.97
Vested (in dollars per share)	3.22
Vested and expected to vest (in dollars per share)	$ 11.31
Weighted-Average Remaining Contractual Term
Outstanding, term	7 years 7 months 2 days	6 years 6 months
Vested, term	5 years 4 months 9 days
Vested and expected to vest, term	7 years 5 months 8 days
Aggregate Intrinsic Value
Outstanding	$ 12,025	$ 13,760
Vested	9,674
Vested and expected to vest	$ 11,961
Old Cartesian Plan
Number of Options
Beginning balance (in shares)	14,112.299
Converted to options for common stock (in shares)	(14,112.299)
Ending balance (in shares)	0	14,112.299
Weighted-Average Exercise Price
Beginning balance (in dollars per share)	$ 79.94
Converted to options for common stock (in dollars per share)	79.94
Ending balance (in dollars per share)	$ 0	$ 79.94
Weighted-Average Remaining Contractual Term
Outstanding, term		5 years 10 months 28 days
Aggregate Intrinsic Value
Outstanding		$ 8,601

Income Taxes

12 Months Ended

Dec. 31, 2024

Income Tax Disclosure [Abstract]

Income Taxes

The Company provides for income taxes under ASC 740. Under ASC 740, the Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax bases of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse.

On November 13, 2023, the Company acquired, in accordance with the terms of the Merger Agreement, the assets of Old Cartesian. In accordance with ASC 805-740-25-3, recognition of deferred tax assets and liabilities is required for substantially all temporary differences and acquired tax carryforwards and credits. The Company has computed estimated temporary differences and acquired tax carryforwards and credits as of the transaction date. The Company will not have tax basis in IPR&D booked as part of the purchase accounting. For accounting purposes, the IPR&D will not be amortized and only subject to impairment review and testing. Though the tax effects may be delayed indefinitely, ASC 740-10-55-63 states that “deferred tax liabilities may not be eliminated or reduced because a reporting entity may be able to delay the settlement of those liabilities by delaying the events that would cause taxable temporary differences to reverse.” The Company can potentially only utilize indefinite-lived assets as it relates to this indefinite lived intangible deferred tax liability reversal. As such, the Company has booked a deferred tax liability for the portion of the liability that cannot be reduced based on scheduling. Additionally, a portion of this target deferred tax liability is offset with the Company’s pre-Merger deferred tax assets on a combined basis, and as such the portion of deferred tax liability reduced by the Company’s pre-Merger deferred tax assets has been charged to income rather than to goodwill.

For the year ended December 31, 2024, the Company recognized a current tax expense of $0.3 million. For the year ended December 31, 2023, the Company recognized a current tax benefit of $19.0 million. The following table reconciles the federal statutory income tax rate to the Company’s effective income tax rate:


	Year Ended December 31,
	2024		2023
Statutory U.S. federal rate	21.0	%	21.0	%
State income taxes - net of federal benefit	10.5	%	2.3	%
Permanent items	1.0	%	(1.6)	%
Research tax credits	0.3	%	0.6	%


Change in fair value of contingent value right liability	127.9	%	—	%
Change in fair value of forward contract liabilities	(1.9)	%	(13.2)	%
Valuation allowance, net	(160.1)	%	2.8	%
Stock-based compensation	0.9	%	(3.9)	%
Effective income tax rate	(0.4)	%	8.0	%

The tax effects of temporary differences that give rise to the Company’s net deferred tax assets are as follows (in thousands):


	Year Ended December 31,
	2024		2023
Deferred Tax Assets
Net operating loss carryforwards	$	44,062	$	29,841
Research and development credits	6,024		5,649
Stock-based compensation expense	1,070		8
Other expenses	—		705
Deferred revenue	75,567		84,626
Operating lease liabilities	3,848		2,718
Contingent value right liability	108,832		—
R&E Capitalization	26,863		19,778
Patent and license costs	8,540		9,140
Gross deferred tax assets	274,806		152,465
Deferred Tax Liabilities
Intangible assets	$	(41,441)	$	(41,144)
Depreciation	(115)		(128)
Operating lease right-of-use assets	(1,523)		(2,751)
Gross deferred tax liabilities	(43,079)		(44,023)
Net deferred tax assets before valuation allowance	231,727		108,442
Valuation allowance	(247,867)		(124,295)
Net deferred tax assets/(liabilities)	$	(16,140)	$	(15,853)

The Company has provided a full valuation allowance against its net deferred tax assets, outside of the indefinite tax liability booked as part of the Merger. The Company believes that it is more likely than not that the net deferred tax assets will not be realized.

Realization of future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets and concluded that it is more likely than not that the Company will not realize the benefit of its net deferred tax assets. The valuation allowance increased by $123.6 million for the year ended December 31, 2024, primarily as a result of tax loss in the current year and the recognition of a $108.8 million tax benefit related to the Company’s CVR liability. The valuation allowance decreased by $3.5 million for the year ended December 31, 2023, primarily as a result of a tax benefit booked as part of the Merger. As of December 31, 2024, the Company is in the process of winding down operations in Russia and does not expect any tax liability relating to such operations.

At December 31, 2024, the Company has federal net operating loss carryforward of $152.6 million, which can be carried forward indefinitely, subject to an 80% limitation and state net operating loss carryforward of $187.8 million, of which $74.4 million has an unlimited carryforward and the remaining $113.4 million will expire at various times through 2044. The Company has $5.2 million and $1.0 million, respectively, of federal and state research and development tax credit carryforwards, which will expire at various times through 2044. Utilization of the NOL carryforwards and research and orphan drug credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, and similar state law due to ownership changes that could occur in the future.

These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. If the Company experiences a change of control, as defined by Section 382 of the Code and similar state law, utilization of the NOL carryforwards or research and orphan drug credit carryforwards may be subject to an annual limitation under Section 382 of the Code, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the NOL carryforwards or research and orphan drug credit carryforwards before utilization. The Company performed an analysis of ownership changes through December 31, 2023. Based on this analysis, the Company does not believe that any of its tax attributes through December 31, 2023 will expire unutilized due to Section 382 limitations. To the extent the Company enters into future equity transactions, there could be a limitation on the Company’s tax attributes.

The Company applies ASC 740, Income Taxes to uncertain tax positions. As of the adoption date on January 1, 2010 and through December 31, 2024, the Company had no unrecognized tax benefits or related interest and penalties accrued.

As of December 31, 2024, the Company has not completed a detailed study of its research and development and orphan drug credits for the tax years ending December 31, 2023 and December 31, 2024. As a result, the Company will adjust its deferred tax asset balances and include the impacts in the research tax credits and state income taxes – net of federal benefit lines in the effective rate reconciliation next year, once the updated study has been completed.

The Tax Cuts and Jobs Act requires taxpayers to capitalize and amortize, rather than deduct, research and experimental, or R&E, expenditures under Section 174 for tax years beginning after December 31, 2021. These rules became effective for the Company during the year ended December 31, 2022. As a result, the Company has capitalized R&E costs of $45.1 million and $43.9 million for the years ended December 31, 2024 and December 31, 2023, respectively. The Company will amortize these costs for tax purposes over five years if the R&E was performed in the United States and over 15 years if the R&E was performed outside the United States.

Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statement of operations. As of December 31, 2024, the Company had no accrued interest related to uncertain tax positions.

The statute of limitations for assessment by the Internal Revenue Service and state tax authorities is open for tax years 2020 to the present. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, or state tax authorities to the extent utilized in a future period. The Company files income tax returns in the United States, Massachusetts, and Maryland. There are currently no federal, state or foreign audits in progress.

- Definition

The entire disclosure for income tax.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
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-Name Accounting Standards Codification
-Section 55
-Paragraph 231
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-231

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 12C
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-12C

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Paragraph 12B
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477891/740-270-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Publisher FASB
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 14
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 2
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482603/740-30-50-2

+ Details

Accrued Expenses

12 Months Ended

Dec. 31, 2024

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses consist of the following (in thousands):


	December 31,
	2024		2023
Payroll and employee related expenses	$	3,534	$	4,390

Accrued patent fees	813		472
Accrued external research and development costs	2,987		4,896
Accrued professional and consulting services	3,674		4,331
Property and equipment	782		128

Other	286		516
Accrued expenses	$	12,076	$	14,733

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2024	Dec. 31, 2023
Temporary equity, par value (in dollars per share)	$ 0.0001	$ 0.0001
Temporary equity, shares authorized (in shares)	0	548,375
Temporary equity, shares issued (in shares)	0	435,120.513
Temporary equity, shares outstanding (in shares)	0	435,120.513
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	9,427,168.437	9,451,625
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	350,000,000	350,000,000
Common stock, shares issued (in shares)	25,767,369	5,397,597
Common stock, shares outstanding (in shares)	25,767,369	5,397,597
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	134,904.563	0
Preferred stock, shares issued (in shares)	120,790.402	0
Preferred stock, shares outstanding (in shares)	120,790.402	0
Series B Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	437,927	0
Preferred stock, shares issued (in shares)	437,927	0
Preferred stock, shares outstanding (in shares)	437,927	0

Collaboration and License Agreements - Asklepios Biopharmaceutical, Inc. (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration expense	$ 82,810,000	$ 112,420,000
AskBio License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration expense	$ 0	$ 100,000
Cost share percentage	50.00%	50.00%

Related-Party Transactions (Tables)

12 Months Ended

Dec. 31, 2024

Schedule of Related Party Transactions

The below issuances and sales to related parties of the Company were made during the year ended December 31, 2024.


Name	Shares of Series B Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	1,636,832	$	32,737
TAS Partners LLC, affiliate of Timothy A. Springer, Ph.D.	721,361	$	14,427
Chafen Lu, Ph.D., wife of Timothy A. Springer, Ph.D.	1,307	$	26

The 2023 Private Placement included a delayed settlement mechanism, and as a result, the below issuances and sales to related parties of the Company were made during the year ended December 31, 2024.


Name	Shares of Series A Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	99,140.326	$	40,000

The below issuances and sales to related parties of the Company were made subject to the 2023 Private Placement during the year ended December 31, 2023.


Name	Shares of Series A Preferred Stock purchased	Total aggregate purchase price (in thousands)
Timothy A. Springer, Ph.D.	24,785.081	$	10,000
TAS Partners LLC (affiliate of Timothy A. Springer, Ph.D.)	24,785.081	$	10,000
Seven One Eight Three Four Irrevocable Trust (affiliate of Murat Kalayoglu, MD, Ph.D.)	619.627	$	250

Revenue Arrangements - Schedule of Changes in Contract Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($)
Contract liabilities:
Deferred revenue, beginning of period	$ 5,849
Deferred revenue, additions	0
Deferred revenue, deductions	(5,849)
Deferred revenue, end of period	0
Contract liabilities, beginning of period	5,849
Additions	0
Deductions	(5,849)
Contract liabilities, end of period	$ 0

Segment Reporting (Details) - USD ($) $ in Thousands	12 Months Ended
Segment Reporting (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Revenue:
Collaboration and license revenue	$ 38,275	$ 26,004
Grant revenue	638	0
Total revenue	38,913	26,004
Operating expenses:
General and administrative	30,126	40,450
Net loss	(77,424)	(219,710)
Reporting Segments
Revenue:
Collaboration and license revenue	38,275	26,004
Grant revenue	638	0
Total revenue	38,913	26,004
Operating expenses:
Research and development employee expenses	11,952	18,363
Research and development stock-based compensation expense	3,217	12,985
Research and development facilities and other expenses	10,616	7,148
General and administrative	30,126	40,450
Impairment of long-lived assets	7,579	710
Other expense, net	33,527	133,294
Net loss	(77,424)	(219,710)
Reporting Segments \| Legacy Selecta programs
Operating expenses:
Medical expenses, operating	6,150	31,826
Reporting Segments \| Descartes-08 for MG
Operating expenses:
Medical expenses, operating	12,142	343
Reporting Segments \| Early stage programs
Operating expenses:
Medical expenses, operating	$ 1,028	$ 595

Equity - Underwritten Offering (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 06, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Exercise price (in dollars per share)		$ 46.96	$ 45.98	$ 46.03
2022 Offering
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	914,285
Class of warrant or right, number of securities called by warrants or rights (in shares)	685,712
Class of warrant or right, number of securities called by each warrant or right (in shares)	0.75
Share price (in dollars per share)	$ 42.30
Exercise price (in dollars per share)	$ 46.50
Sale of stock, consideration received on transaction	$ 36.9

- 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

+ Details

Collaboration and License Agreements - National Cancer Institute of the National Institutes of Health (Narrative) (Details) - NCI Agreement $ in Millions	Sep. 16, 2019 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License and option agreement, royalty payment	$ 0.1
License and option agreement, benchmark royalties, maximum	$ 0.8
Written notice for agreement termination	60 days

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2024

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consists of the following (in thousands):


	December 31,
	2024		2023
Laboratory equipment	$	7,295	$	6,280
Computer equipment and software	415		702
Leasehold improvements	3,427		61
Furniture and fixtures	268		452
Office equipment	169		196
Construction in process	695		150
Total property and equipment	12,269		7,841
Less accumulated depreciation	(2,357)		(5,728)
Property and equipment, net	$	9,912	$	2,113

Fair Value Measurements - Schedule of Roll-Forward of Fair Value for the Forward Contract Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 28,307
Settlements	(35,197)
Change in fair value	6,890
Ending balance	$ 0
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Change in fair value of forward contract liabilities

Stock Incentive Plans - Narrative (Details) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Nov. 13, 2023 USD ($) $ / shares shares	Jun. 30, 2024 shares	Jan. 31, 2024 shares	Jan. 31, 2023 shares	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Mar. 27, 2024	Mar. 31, 2019 shares	Sep. 30, 2018 shares	Jun. 30, 2016 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares) \| shares					11,512,268
Stock‑based compensation expense					$ 6,582	$ 25,778
Share based compensation arrangement by share based payment award, settlement of awards, amount (in dollars per share) \| $ / shares	$ 61.80
Share-based payment arrangement, accelerated cost	$ 13,100
Total cash payment made to the holders of stock options and restricted stock units	9,400
Adjustments to additional paid in capital, settlement of outstanding equity awards at merger						6,169
Excess over fair value recognized as additional stock-based compensation expense						$ 3,200
Weighted average grant date fair value of stock options (in dollars per share) \| $ / shares					$ 15.63	$ 26.90
Intrinsic value of stock options exercised					$ 7,000
Issuance of common stock upon exercise of options (in shares) \| shares						0
Preferred stock, convertible, conversion ratio					33.333		33.333
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock‑based compensation expense					$ 3,217	$ 12,985
Share-based payment arrangement, accelerated cost	5,900
Excess over fair value recognized as additional stock-based compensation expense						1,500
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock‑based compensation expense					$ 3,365	12,793
Share-based payment arrangement, accelerated cost	7,200
Excess over fair value recognized as additional stock-based compensation expense						1,700
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares) \| shares					1,706,035
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting term					4 years
Weighted average period for recognition					2 years 10 months 24 days
Grants in period (in shares) \| shares					477,037
Grants in period (in dollars per share) \| $ / shares					$ 19.86
Estimated forfeitures rate					10.00%
Vested in period (in shares) \| shares					0
Aggregate fair value of RSU awards vested						$ 700
Unrecognized compensation expense					$ 5,400
Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock upon exercise of options (in shares) \| shares					458,544
Common stock \| Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested employee stock options					$ 10,300
Weighted average period for recognition					2 years 10 months 24 days
2016 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grants (in shares) \| shares										40,341
Number of shares authorized, increase (in shares) \| shares		3,466,544	215,903	204,056
Common stock authorized and reserved for future issuance (in shares) \| shares					3,520,174
Employment Inducement Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grants (in shares) \| shares					611,960
Common stock authorized and reserved for future issuance (in shares) \| shares		360,000			450,000	60,833		66,667	39,166
Old Cartesian Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grants (in shares) \| shares					27,270
Award vesting term					4 years
Award expiration term					10 years
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) \| shares					0	14,112.299
Unrecognized compensation expense related to unvested employee stock options	$ 2,600
Stock‑based compensation expense					$ 1,300	$ 200
Old Cartesian Plan \| Common stock \| Old Cartestian
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) \| shares	776,865
Old Cartesian Plan \| Preferred Stock \| Old Cartestian
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) \| shares	14,112.299

Equity - Merger (Narrative) (Details) - shares	Dec. 05, 2023	Nov. 13, 2023
Old Cartesian \| Common stock
Class of Stock [Line Items]
Issuance of shares (in shares)	224,099	224,099

- 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

+ Details

Employee Benefit Plans	12 Months Ended
Employee Benefit Plans	Dec. 31, 2024
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Defined Contribution Plan The Company maintains a defined contribution plan, or the 401(k) Plan, under Section 401(k) of the Internal Revenue Code. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. The 401(k) Plan provides for matching contributions on a portion of participant contributions pursuant to the 401(k) Plan’s matching formula. All matching contributions vest ratably over two years and participant contributions vest immediately. Contributions by the Company totaled $0.2 million and $0.3 million during the years ended December 31, 2024 and 2023, respectively. Employee Stock Purchase Plan In June 2016, the Company approved the 2016 Employee Stock Purchase Plan, or the ESPP, which initially authorized 5,769 shares of common stock for future issuance under the ESPP to participating employees. As of December 31, 2024, 45,795 shares remain available for future issuance under the ESPP. In connection with the Merger, the Board of Directors suspended offerings under the ESPP. The Company recognized no stock-based compensation expense under the ESPP for the year ended December 31, 2024 and $0.1 million of stock-based compensation expense under the ESPP for the year ended December 31, 2023.

Convertible Preferred Stock - Series A Preferred Stock (Narrative) (Details) $ in Thousands										1 Months Ended	12 Months Ended
	Oct. 11, 2024 shares	Sep. 25, 2024 shares	Apr. 08, 2024 shares	Feb. 11, 2024 shares	Jan. 12, 2024 shares	Dec. 13, 2023 shares	Dec. 05, 2023 shares	Nov. 15, 2023 USD ($) shares	Nov. 13, 2023 USD ($) shares	Nov. 30, 2023 USD ($)	Dec. 31, 2024 shares	Feb. 11, 2025 shares	Jan. 12, 2025 shares	Mar. 26, 2024 business_day	Dec. 31, 2023 shares
Class of Stock [Line Items]
Temporary equity, shares authorized (in shares)									548,375		0				548,375
Derivative liability, shares (in shares)						49,570.162			148,710.488
Number of business days \| business_day														8
Convertible preferred stock, shares that did not automatically convert (in shares)			166,341.592
Subsequent Event
Class of Stock [Line Items]
Derivative liability, shares (in shares)												49,570.163	49,570.163
Common stock
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)	1,518,373	2,499,976	12,263,951
Series A Preferred Stock
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)	45,551.19		367,919.247
Series A Preferred Stock \| Common stock
Class of Stock [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)											13,782,324
Old Cartesian \| Preferred Stock
Class of Stock [Line Items]
Issuance of shares (in shares)							384,930.724
Old Cartesian \| Preferred Stock \| Series A Preferred Stock
Class of Stock [Line Items]
Issuance of shares (in shares)									384,930.724
2023 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)									149,330.115
Sale of stock, consideration received on transaction \| $									$ 60,250
2023 Private Placement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)								619.627
Sale of stock, consideration received on transaction \| $								$ 250
2023 Private Placement, Tranche One
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)						24,785.081
Sale of stock, consideration received on transaction \| $										$ 10,000
Sale of stock, settlement term										30 days
2023 Private Placement, Tranche Three
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)				49,570.163
Sale of stock, consideration received on transaction \| $										$ 20,000
Sale of stock, settlement term										90 days
2023 Private Placement, Tranche Two
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)					49,570.163
Sale of stock, consideration received on transaction \| $										$ 20,000
Sale of stock, settlement term										60 days

Property and Equipment

12 Months Ended

Dec. 31, 2024

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consists of the following (in thousands):


	December 31,
	2024		2023
Laboratory equipment	$	7,295	$	6,280
Computer equipment and software	415		702
Leasehold improvements	3,427		61
Furniture and fixtures	268		452
Office equipment	169		196
Construction in process	695		150
Total property and equipment	12,269		7,841
Less accumulated depreciation	(2,357)		(5,728)
Property and equipment, net	$	9,912	$	2,113

See Note 9 for details regarding the impairment loss the Company recognized for certain furniture and fixtures during the year ended December 31, 2024.

Depreciation expense was $1.2 million and $0.7 million for the years ended December 31, 2024 and 2023, respectively.

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred Tax Assets
Net operating loss carryforwards	$ 44,062	$ 29,841
Research and development credits	6,024	5,649
Stock-based compensation expense	1,070	8
Other expenses	0	705
Deferred revenue	75,567	84,626
Operating lease liabilities	3,848	2,718
Contingent value right liability	108,832	0
R&E Capitalization	26,863	19,778
Patent and license costs	8,540	9,140
Gross deferred tax assets	274,806	152,465
Deferred Tax Liabilities
Intangible assets	(41,441)	(41,144)
Depreciation	(115)	(128)
Operating lease right-of-use assets	(1,523)	(2,751)
Gross deferred tax liabilities	(43,079)	(44,023)
Net deferred tax assets before valuation allowance	231,727	108,442
Valuation allowance	(247,867)	(124,295)
Net deferred tax assets/(liabilities)	$ (16,140)	$ (15,853)

Restructuring - Schedule of Change in Accrued Restructuring Balance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Beginning balance	$ 3,896	$ 0
Charges	798	6,431
Cash Payments	(4,614)	(2,535)
Ending balance	$ 80	$ 3,896

Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Preferred Stock	Series B Preferred Stock	Private Placement One	Private Placement Two	Preferred Stock Series A Preferred Stock	Preferred Stock Series B Preferred Stock	Common stock	Common stock Series A Preferred Stock	Common stock Series B Preferred Stock	Additional Paid-in Capital	Additional Paid-in Capital Series A Preferred Stock	Additional Paid-in Capital Series B Preferred Stock	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2022	0
Beginning balance at Dec. 31, 2022	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A preferred stock forward in connection with private placement and settlement of related forward contract (in shares)				619.627	49,570.162
Issuance of Series A Preferred Stock in connection with the Merger and settlement of related forward contract				$ 250	$ 34,848
Issuance of Series A preferred stock in connection with the merger and settlement of related forward contract (in shares)	384,930.724
Issuance of Series A Preferred Stock in connection with the Merger and settlement of related forward contract	$ 261,753
Ending balance (in shares) at Dec. 31, 2023	435,120.513
Ending balance at Dec. 31, 2023	$ 296,851
Beginning balance at Dec. 31, 2022	0
Increase (Decrease) In Temporary Equity, Option, Roll Forward [Roll Forward]
Issuance of replacement options in Merger	3,643
Stock-based compensation expense	60
Ending balance at Dec. 31, 2023	3,703
Preferred stock, beginning balance (in shares) at Dec. 31, 2022						0	0
Beginning balance at Dec. 31, 2022	93,828					$ 0	$ 0	$ 1			$ 493,322			$ (394,937)	$ (4,558)
Common stock, beginning balance (in shares) at Dec. 31, 2022								5,101,459
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock purchase plan (in shares)								6,171
Issuance of common stock under Employee Stock Purchase Plan	$ 231										231
Issuance of common stock upon exercise of options (in shares)	0
Issuance of vested restricted stock units (in shares)								21,226
Issuance of common stock forward in connection with the Merger	$ 2,713										2,713
Issuance of common stock in connection with the merger and settlement of related forward contract (in shares)								224,099
Issuance of replacement options in Merger	6,801										6,801
Issuance of common stock, license agreement (in shares)								44,642
Issuance of common stock, license agreement	1,500										1,500
Settlement of outstanding equity awards at Merger	(6,169)										(6,169)
Distribution of contingent value rights	(340,300)										(340,300)
Stock-based compensation expense	20,964										20,964
Currency translation adjustment	(53)														(53)
Unrealized gain on marketable securities	11														11
Net income (loss)	$ (219,710)													(219,710)
Preferred stock, ending balance (in shares) at Dec. 31, 2023	0	0	0			0	0
Ending balance at Dec. 31, 2023	$ (440,184)					$ 0	$ 0	$ 1			179,062			(614,647)	(4,600)
Common stock, ending balance (in shares) at Dec. 31, 2023	5,397,597							5,397,597
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A preferred stock forward in connection with private placement and settlement of related forward contract (in shares)	99,140.326
Issuance of Series A Preferred Stock in connection with the Merger and settlement of related forward contract	$ 75,197
Transfer of Series A preferred stock and options for Series A preferred stock to permanent equity (in shares)	(534,260.839)
Transfer of Series A Preferred Stock and options for Series A Preferred Stock to permanent equity	$ (372,048)
Ending balance (in shares) at Dec. 31, 2024	0
Ending balance at Dec. 31, 2024	$ 0
Increase (Decrease) In Temporary Equity, Option, Roll Forward [Roll Forward]
Transfer of Series A Preferred Stock and options for Series A Preferred Stock to permanent equity	(3,703)
Ending balance at Dec. 31, 2024	0
Increase (Decrease) in Stockholders' Equity
Transfer of Series A preferred stock and options for Series A preferred stock to permanent equity (in shares)						534,260.839
Transfer of Series A Preferred Stock and options for Series A Preferred Stock to permanent equity	375,751										$ 375,751
Conversion of Series A and Series B preferred stock to common stock (in shares)						(413,470.437)	(2,499,976)		13,782,324	2,499,976
Conversion of Series A Preferred Stock to common stock		$ 0							$ 2			$ (2)
Issuance of Series B preferred stock and common stock in connection with private placement, net (in shares)							2,937,903			3,563,247
Issuance of Series B Preferred Stock and common stock in connection with private placement, net of issuance costs of $5,585			$ 124,438										$ 124,438
Issuance of common stock upon exercise of options (in shares)								458,544			1,179,000
Issuance of common stock upon exercise of options	1,179
Issuance of common stock upon exercise of common warrants (in shares)								65,681
Issuance of common stock upon exercise of warrants	2,877										$ 2,877
Stock-based compensation expense	6,582										6,582
Currency translation adjustment	(21)														(21)
Unrealized gain on marketable securities	0
Net income (loss)	$ (77,424)													(77,424)
Preferred stock, ending balance (in shares) at Dec. 31, 2024	0	120,790.402	437,927			120,790.402	437,927
Ending balance at Dec. 31, 2024	$ (6,802)					$ 0	$ 0	$ 3			$ 689,887			$ (692,071)	$ (4,621)
Common stock, ending balance (in shares) at Dec. 31, 2024	25,767,369							25,767,369

Related-Party Transactions - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Mar. 26, 2024	Nov. 13, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Exercise price (in dollars per share)			$ 46.96	$ 45.98	$ 46.03
Proceeds from exercise of common warrants			$ 2,877	$ 0
Related Party
Related Party Transaction [Line Items]
Conversion of Series A and Series B preferred stock to common stock (in shares)	65,681
Issuance of CVRs upon exercise of warrants (in shares)	1,970,443
Related Party \| 2019 Warrants
Related Party Transaction [Line Items]
Warrants exercised (in shares)	65,681
Exercise price (in dollars per share)	$ 43.80
Proceeds from exercise of common warrants	$ 2,900
2023 Securities Purchase Agreement
Related Party Transaction [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		149,330.115
Total aggregate purchase price		$ 60,250
2023 Securities Purchase Agreement \| Related Party
Related Party Transaction [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		149,330.115
Total aggregate purchase price		$ 60,250

Leases - 7495 New Horizon Way Leases (Narrative) (Details) $ in Thousands	Aug. 30, 2024 USD ($) ft²	May 07, 2024 USD ($) ft²	May 01, 2024 USD ($) extension_option	Feb. 28, 2024 USD ($) ft²	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Operating Leased Assets [Line Items]
Lease liabilities					$ 13,984
Right-of-use asset, net					$ 5,535	$ 10,068
Weighted-average discount rate					11.70%	9.90%
Minimum
Operating Leased Assets [Line Items]
Lease term					2 years
Lease renewal term					1 year
Maximum
Operating Leased Assets [Line Items]
Lease term					8 years
Lease renewal term					5 years
7495 New Horizon Way Lease
Operating Leased Assets [Line Items]
Area of office space leased \| ft²	2,009	7,842		19,199
Lease term			7 years 2 months 12 days
Number of options to extend lease \| extension_option			1
Lease renewal term			5 years
Lease agreement, monthly base rent			$ 900
Lessee, operating lease, base rent, annual upward adjustment percentage after year one	3.00%	3.00%	3.00%
Lessee, operating lease, first month rent paid on execution of lease agreement				$ 100
Lease liabilities	$ 300	$ 1,200	$ 3,600
Right-of-use asset, net	300	1,200	3,700
Tenant improvement allowance		$ 100	$ 700
Weighted-average discount rate		14.00%	14.00%
Lessee, operating lease, additional annual base rent, year one	$ 100	$ 300
Letters of credit outstanding, amount					$ 300
7495 New Horizon Way Lease \| Minimum
Operating Leased Assets [Line Items]
Operating lease, cost percentage			100.00%
7495 New Horizon Way Lease \| Maximum
Operating Leased Assets [Line Items]
Operating lease, cost percentage			103.00%

Stock Incentive Plans

12 Months Ended

Dec. 31, 2024

Share-Based Payment Arrangement [Abstract]

Stock Incentive Plans

The Company maintained the 2008 Stock Incentive Plan, or the 2008 Plan, for employees, consultants, advisors, and directors. The 2008 Plan provided for the granting of incentive and non-qualified stock option and restricted stock awards as determined by the Board of Directors. In connection with the Merger, all outstanding awards issued under the 2008 Plan were cancelled, and the Board of Directors formally terminated the 2008 Plan.

In June 2016, the Company’s stockholders approved the 2016 Incentive Award Plan, or the 2016 Plan, which authorized 40,341 shares of common stock for future issuance under the 2016 Plan and the Company ceased granting awards under the 2008 Plan. Upon the effective date of the 2016 Plan, awards issued under the 2008 Plan remained subject to the terms of the 2008 Plan. Awards granted under the 2008 Plan that expired, lapsed or terminated became available under the 2016 Plan as shares available for future grants.

Additionally, pursuant to the terms of the 2016 Plan, the Board of Directors is authorized to grant awards with respect to common stock, and may delegate to a committee of one or more members of the Board of Directors or executive officers of the Company the authority to grant options and restricted stock units. On December 9, 2020, the Board of Directors established a Stock Option Committee authorized to grant awards to certain employees and consultants subject to conditions and limitations within the 2016 Plan. In January 2024 and 2023, the number of shares of common stock that may be issued under the 2016 Plan was increased by 215,903 and 204,056 shares, respectively. In June 2024, the Company’s stockholders approved an amendment and restatement of the 2016 Plan to reserve an additional 3,466,544 shares of the Company’s common stock for issuance. As of December 31, 2024, 3,520,174 shares remain available for future issuance under the 2016 Plan.

In September 2018, the Company’s 2018 Employment Inducement Incentive Award Plan, or the 2018 Inducement Incentive Award Plan was adopted by the Board of Directors without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Stock Market LLC listing rules, which authorized 39,166 shares of its common stock for issuance. In March 2019, the Board of Directors approved an amendment and restatement of the 2018 Inducement Incentive Award Plan to reserve an additional 66,667 shares of the Company’s common stock for issuance thereunder. In December 2023, the Board of Directors approved an amendment and restatement of the 2018 Inducement Incentive Award Plan to reserve an additional 60,833 shares of the Company’s common stock for issuance thereunder. In June and December 2024, the Board of Directors approved amendments and restatements of the 2018 Inducement Incentive Award Plan to reserve an additional 360,000 and 450,000 shares, respectively, of the Company’s common stock for issuance thereunder. As of December 31, 2024, there are 611,960 shares available for future grant under the 2018 Inducement Incentive Award Plan.

In accordance with the Merger Agreement, the Company assumed Old Cartesian’s 2016 Stock Incentive Plan, or the Old Cartesian Plan. The Old Cartesian Plan permits the granting of options or restricted stock to employees, officers, directors, consultants and advisors to the Company. The unvested common stock options and Series A Preferred Stock options assumed by the Company in connection with the Merger generally vest over a four-year period. Additionally, the stock options granted have a contractual term of ten years and only full shares can be exercised as per the individual award agreements. As of December 31, 2024, there are 27,270 shares available for future grant under the Old Cartesian Plan.

In connection with the Merger, the outstanding stock options to purchase Old Cartesian common stock were converted into stock options to purchase 776,865 shares of common stock and 14,112.299 shares of Series A Preferred Stock of the Company. These replacement awards were revalued at their acquisition-date fair value and then attributed to pre and post-combination service. This resulted in $2.6 million attributed to post-combination service to be recognized as stock-based compensation expense over the remaining terms of the replacement awards, of which $1.3 million and $0.2 million was recognized as research and development expense in the consolidated statements of operations and comprehensive loss during the years ended December 31, 2024 and 2023, respectively. Following the Automatic Conversion, the options exercisable for shares of Series A Preferred Stock became exercisable for shares of common stock.

Settlement of Equity Compensation Awards

Upon consummation of the First Merger, the equity compensation awards of the Company outstanding as of the date of the Merger were settled as follows: (i) each unvested option to acquire shares of common stock and each unvested restricted stock unit award with respect to shares of common stock was accelerated and vested in full at the effective time of the First Merger; (ii) each option to acquire shares of common stock was canceled and in exchange therefore, former holders became entitled to receive an amount in cash equal to the product of (A) the total number of shares of common stock subject to the unexercised portion the stock option (determined after giving effect to the accelerated vesting) multiplied by (B) the excess, if any, of $61.80, or the Cash-out Amount, over the applicable exercise price per share of common stock under such stock option; and (iii) each restricted stock unit award with respect to shares of common stock was cancelled and the former holder of such canceled restricted stock unit became entitled, in exchange therefor, to receive an amount in cash equal to the product of (A) the total number of shares of common stock deliverable under such restricted stock unit (determined after giving effect to the accelerated vesting) multiplied by (B) the Cash-out Amount. Stock options with an exercise price in excess of the Cash-out Amount received no cash payment.

The modification to accelerate the vesting of all awards upon the Merger resulted in full recognition of unrecognized compensation of $13.1 million, of which $5.9 million and $7.2 million was classified as research and development expense and general and administrative expense, respectively, in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2023. In addition, with the exception of any options with an exercise price greater than $61.80 per share, all awards were settled in cash for an amount equal to $61.80 less any exercise price associated with the awards. The total cash payment made to the holders of stock options and restricted stock units was $9.4 million. The fair value of the awards prior to the settlement was recorded to additional paid-in capital in an amount of $6.2 million and the amount in excess of fair value was recognized as additional stock-based compensation expense in an amount of $3.2 million, of which $1.5 million and $1.7 million was classified as research and development expense and general and administrative expense, respectively, in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2023.

Stock-Based Compensation Expense


	Year Ended December 31,
		2024		2023
Research and development		$	3,217	$	12,985
General and administrative		3,365		12,793
Total stock-based compensation expense		$	6,582	$	25,778

Stock Options

The fair value of the stock options assumed in connection with the Merger was calculated using a Black-Scholes option pricing model based on the following weighted-average assumptions:


	Common Stock			Series A Preferred Stock
Risk-free interest rate	4.83		%	4.92		%
Dividend yield	—			—
Expected term	3.59			3.29
Expected volatility	83.77		%	83.87		%
Weighted-average fair value of common stock or Series A Preferred Stock, as applicable	$	12.00		$	403.47


	Year Ended December 31,
		2024			2023
Risk-free interest rate		4.02		%	3.95		%
Dividend yield		—			—
Expected term		6.21			5.94
Expected volatility		95.21		%	94.64		%
Weighted-average fair value of common stock		$	19.63		$	34.54

The expected term of the Company’s stock options granted has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Under the simplified method, the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. Expected volatilities are based on the Company’s historical volatility.

The weighted average grant date fair value of stock options granted during the years ended December 31, 2024 and 2023 was $15.63 and $26.90, respectively. The total intrinsic value of stock options exercised during the year ended December 31, 2024 was $7.0 million. No stock options were exercised during the year ended December 31, 2023.

As of December 31, 2024, total unrecognized compensation expense related to unvested common stock options was $10.3 million, which is expected to be recognized over a weighted average period of 2.9 years.

The following table summarizes the stock option activity under the 2016 Plan, the 2018 Inducement Incentive Award Plan, and the Old Cartesian Plan for options for common stock:


				Weighted-average
	Number of			remaining	Aggregate
	common stock	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)









Outstanding at December 31, 2023	776,865	$	2.97	6.50	$	13,760
Granted	1,000,092	$	19.63
Converted from options for Series A Preferred Stock	470,403	$	2.40
Exercised	(458,544)	$	2.57
Forfeited	(82,781)	$	17.28
Outstanding at December 31, 2024	1,706,035	$	11.99	7.59	$	12,025

Vested at December 31, 2024	656,258	$	3.22	5.36	$	9,674
Vested and expected to vest at December 31, 2024	1,564,044	$	11.31	7.44	$	11,961

The following table summarizes the stock option activity under the Old Cartesian Plan for options for Series A Preferred Stock:


	Number of			Weighted-average
	Series A			remaining	Aggregate
	Preferred Stock	Weighted-average		contractual term	intrinsic value
	options	exercise price ($)		(in years)	(in thousands)









Outstanding at December 31, 2023	14,112.299	$	79.94	5.91	$	8,601
Converted to options for common stock	(14,112.299)	$	79.94
Outstanding at December 31, 2024	—	$	—

As a result of the approval of the Conversion Proposal on March 27, 2024, all conditions that could have required cash redemption of the Series A Preferred Stock underlying the stock options were removed. Since the Series A Preferred Stock was no longer redeemable, the associated balances of the stock options to purchase Series A Preferred Stock were reclassified to additional paid-in capital during the first quarter of 2024.

Following the Automatic Conversion, all options to purchase Series A Preferred Stock were converted into options to purchase common stock with adjustments to the underlying number of shares of common stock determined by multiplying the number of shares of Series A Preferred Stock by 33.333 and rounding down to the nearest whole number of shares and the per-share exercise price by dividing the per-share exercise price of Series A Preferred Stock by 33.333 and rounding the resulting exercise price up to the nearest whole cent.

Restricted Stock Units

During the year ended December 31, 2024, the Company granted 477,037 restricted stock unit awards with a weighted average fair value of $19.86 per share based on the closing price of the Company’s common stock on the date of grant under the 2016 Plan and the Old Cartesian Plan, which generally vest over a four-year term. Forfeitures are estimated at the time of grant and are adjusted, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company has estimated a forfeiture rate of 10% for restricted stock unit awards based on historical experience.

No restricted stock unit awards vested during the year ended December 31, 2024. The aggregate fair value of restricted stock unit awards that vested during the year ended December 31, 2023 was $0.7 million.

Unrecognized compensation expense related to the restricted stock unit awards was $5.4 million as of December 31, 2024, which is expected to be recognized over a weighted-average period of 2.9 years.

The following table summarizes the Company’s restricted stock units under the 2016 Plan and the Old Cartesian Plan:


	Number of shares	Weighted average grant date fair value ($)
Unvested at December 31, 2023	—	$	—
Granted	477,037	19.86


Forfeited	(32,799)	19.80
Unvested at December 31, 2024	444,238	$	19.86

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies As of December 31, 2024, the Company was not a party to any litigation that could have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. Other As permitted under Delaware law, the Company indemnifies its officers, directors, consultants and employees for certain events or occurrences that happen by reason of the relationship with, or position held at, the Company. Through December 31, 2024, the Company had not experienced any losses related to these indemnification obligations, and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established. Additionally, as permitted under Delaware law, the Company indemnifies its directors for certain events or occurrences while the director is, or was, serving at the Company’s request in such capacity. The term of the indemnification is for the director’s lifetime. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ insurance coverage that limits its exposure and enables it to recover a portion of any future amounts paid. The Company also has indemnification arrangements under certain of its facility leases that require it to indemnify the landlord against certain costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from certain breaches, violations, or non-performance of any covenant or condition of the Company’s lease. The term of the indemnification is for the term of the related lease agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. To date, the Company had not experienced any material losses related to any of its indemnification obligations, and no material claims with respect thereto were outstanding. The Company is a party in various other contractual disputes and potential claims arising in the ordinary course of business. The Company does not believe that the resolution of these matters will have a material adverse effect the Company’s business, financial position, results of operations or cash flows.

Fair Value Measurements - Schedule of Fair Value Measurement Inputs and Valuation Techniques for CVR Liability (Details) - Level 3	Dec. 31, 2024	Dec. 31, 2023
Estimated probability of success
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right liability, measurement input		0.950
Estimated probability of success \| Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right liability, measurement input	0.950
Estimated probability of success \| Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right liability, measurement input	1.000
Expected volatility of future revenues
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right liability, measurement input	0.220
Risk-adjusted discount rate
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right liability, measurement input		0.137

Merger - Narrative (Details) - Old Cartesian - USD ($) $ in Millions			2 Months Ended	12 Months Ended
	Dec. 05, 2023	Nov. 13, 2023	Dec. 31, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Percentage acquired		100.00%
Revenues			$ 0.0
Net loss			$ 1.6
Transaction costs				$ 4.9
Common stock
Business Acquisition [Line Items]
Issuance of shares (in shares)	224,099	224,099
Preferred Stock
Business Acquisition [Line Items]
Issuance of shares (in shares)	384,930.724
Preferred Stock \| Series A Preferred Stock
Business Acquisition [Line Items]
Issuance of shares (in shares)		384,930.724

Fair Value Measurements - Schedule of Roll-Forward of Fair Value for the Company’s Level 3 Warrant Liabilities and CVR Liability (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($)
Warrant liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 6,394
Change in fair value	(2,558)
Ending balance	3,836
CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	358,600
Change in fair value	36,900
Ending balance	$ 395,500

Fair Value Measurements - Schedule of Fair Value Measurement Inputs and Valuation Techniques for Warrants Liability (Details) - Valuation Technique, Option Pricing Model	Dec. 31, 2024	Dec. 31, 2023
Risk-free interest rate \| 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input		0.0479
Risk-free interest rate \| 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.0425	0.0401
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0
Dividend yield \| 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input		0
Dividend yield \| 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0	0
Expected life (in years) \| 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, term		11 months 23 days
Expected life (in years) \| 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, term	2 years 3 months 10 days	3 years 3 months 10 days
Expected volatility \| 2019 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input		0.8367
Expected volatility \| 2022 Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, measurement input	0.9292	0.8409

Description of the Business (Details) $ / shares in Units, $ in Thousands							1 Months Ended	12 Months Ended
	Jul. 02, 2024 USD ($) $ / shares shares	Apr. 04, 2024	Mar. 27, 2024	Dec. 06, 2023	Dec. 05, 2023 shares	Nov. 13, 2023 USD ($) $ / shares shares	Jul. 31, 2024 USD ($) shares	Dec. 31, 2024 USD ($) $ / shares	Dec. 31, 2023 USD ($) $ / shares
Cash and Cash Equivalents [Line Items]
Common stock, par value (in dollars per share) \| $ / shares						$ 0.0001		$ 0.0001	$ 0.0001
Temporary equity, par value (in dollars per share) \| $ / shares						$ 0.0001		$ 0.0001	$ 0.0001
Stock split conversion ratio		0.0333
Accumulated deficit \| $								$ 692,071	$ 614,647
Cash, cash equivalents, restricted cash and marketable securities \| $								214,300
Restricted cash and cash equivalents \| $								$ 1,700
Minimum
Cash and Cash Equivalents [Line Items]
Stock split conversion ratio			0.05
Maximum
Cash and Cash Equivalents [Line Items]
Stock split conversion ratio			0.0333
Series B Preferred Stock
Cash and Cash Equivalents [Line Items]
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001
2023 Securities Purchase Agreement
Cash and Cash Equivalents [Line Items]
Sale of stock, number of shares issued in transaction (in shares) \| shares						149,330.115
Sale common stock \| $						$ 60,250
2024 Securities Purchase Agreement
Cash and Cash Equivalents [Line Items]
Sale common stock \| $							$ 82,800
Share price (in dollars per share) \| $ / shares	$ 20.00
Gross proceeds \| $	$ 130,000
2024 Securities Purchase Agreement \| Common stock
Cash and Cash Equivalents [Line Items]
Sale of stock, number of shares issued in transaction (in shares) \| shares	3,563,247
2024 Securities Purchase Agreement \| Series B Preferred Stock
Cash and Cash Equivalents [Line Items]
Sale of stock, number of shares issued in transaction (in shares) \| shares	2,937,903						578,403
Old Cartesian
Cash and Cash Equivalents [Line Items]
Contingent value right, percentage of milestone payments, royalties and other amounts to be distributed				100.00%				100.00%
Old Cartesian \| Common stock
Cash and Cash Equivalents [Line Items]
Issuance of shares (in shares) \| shares					224,099	224,099
Old Cartesian \| Preferred Stock
Cash and Cash Equivalents [Line Items]
Issuance of shares (in shares) \| shares					384,930.724
Old Cartesian \| Preferred Stock \| Series A Preferred Stock
Cash and Cash Equivalents [Line Items]
Issuance of shares (in shares) \| shares						384,930.724

Debt (Details) - USD ($)		12 Months Ended
Debt (Details) - USD ($)	Sep. 11, 2023	Dec. 31, 2024	Dec. 31, 2023
Line of Credit Facility [Line Items]
Total payoff amount of term loan		$ 0	$ 27,457,000
Loss on extinguishment of debt		0	740,000
Interest expense related to term loans		0	2,100,000
2020 Term Loans
Line of Credit Facility [Line Items]
Total payoff amount of term loan	$ 22,300,000
Extinguishment of debt, amount	19,800,000
Debt instrument, fee amount	2,300,000
Debt instrument, prepayment fee	200,000		200,000
Debt instrument, accrued interest	$ 100,000
Loss on extinguishment of debt			700,000
Deferred debt issuance cost, writeoff			500,000
Term loan facility		$ 0	$ 0

Leases (Tables)

12 Months Ended

Dec. 31, 2024

Leases [Abstract]

Schedule of Components of Lease Costs and Additional Information Related to Operating Leases

For the years ended December 31, 2024 and 2023, the components of lease costs were as follows (in thousands):


	Year Ended December 31,
	2024		2023
Operating lease cost	$	3,856	$	2,828
Variable lease cost	1,609		965
Short-term lease cost	28		8
Less sublease income	(1,099)		(1,172)
Total lease cost	$	4,394	$	2,629

The following summarizes additional information related to the Company’s operating leases:


	December 31,
	2024		2023
Weighted-average remaining lease term	4.5 years		4.3 years
Weighted-average discount rate	11.7	%	9.9	%

Schedule of Maturity of Operating Lease Liabilities

The maturity of the Company’s operating lease liabilities as of December 31, 2024 were as follows (in thousands):


	December 31,
	2024
2025	$	3,645
2026	4,538
2027	4,345
2028	2,314
2029	1,409
Thereafter	2,188
Total future minimum lease payments	18,439
Less: Imputed interest	4,455
Total operating lease liabilities	$	13,984

Schedule of Supplemental Disclosure for the Statement of Cash Flows Related to Operating Leases

The supplemental disclosure for the statement of cash flows related to operating leases were as follows (in thousands):


	December 31,
	2024		2023
Cash paid for amounts included in the measurement of lease liabilities:	$	3,559	$	2,696

Leases - Schedule of Maturity of Operating Lease Liabilities (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Leases [Abstract]
2025	$ 3,645
2026	4,538
2027	4,345
2028	2,314
2029	1,409
Thereafter	2,188
Total future minimum lease payments	18,439
Less: Imputed interest	4,455
Total operating lease liabilities	$ 13,984

Fair Value Measurements - Narrative (Details)					1 Months Ended		12 Months Ended
Fair Value Measurements - Narrative (Details)	Dec. 13, 2023 USD ($) shares	Dec. 06, 2023 USD ($) shares	Dec. 05, 2023 USD ($) shares	Nov. 13, 2023 USD ($) shares	Jun. 30, 2024 USD ($)	Feb. 11, 2024 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Disclosures [Abstract]
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, transfers, net							$ 0	$ 0
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability, transfers, net							$ 0	$ 0
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability, shares (in shares) \| shares	49,570.162			148,710.488
SOBI Purchase Agreement \| Collaborative Arrangement
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Revenue recognized					$ 30,000,000
2023 Securities Purchase Agreement
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Sale of stock, number of shares issued in transaction (in shares) \| shares				149,330.115
Issuance of stock for settlement of liability	$ 14,800,000					$ 35,200,000
Old Cartesian
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent value right, percentage of milestone payments, royalties and other amounts to be distributed		100.00%					100.00%
Fixed semi annual amount		$ 750,000
Old Cartesian \| Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuance of shares (in shares) \| shares			384,930.724
Forward contract to issue stock				$ 155,308,000
Settlement of forward contract liability			$ 261,800,000
Old Cartesian \| Preferred Stock \| Series A Preferred Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Issuance of shares (in shares) \| shares				384,930.724
Old Cartesian \| 2022 Warrants \| CVR liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Class of warrant or right, number of securities called by each warrant or right (in shares) \| shares		30
Dividend yield \| Valuation Technique, Option Pricing Model
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants and rights outstanding, measurement input							0
Dividend yield \| Valuation Technique, Option Pricing Model \| 2022 Warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Warrants and rights outstanding, measurement input							0	0

Convertible Preferred Stock - Liquidation (Narrative) (Details) - shares	Dec. 31, 2024	Dec. 31, 2023
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	120,790.402	0
Preferred stock, shares issued (in shares)	120,790.402	0
Convertible preferred stock, common stock issuable upon conversion (in shares)	4,464,273
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)	437,927	0
Preferred stock, shares issued (in shares)	437,927	0
Convertible preferred stock, common stock issuable upon conversion (in shares)	4,464,273

- 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

+ Details

Equity - 2024 Private Placement (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended
	Jul. 02, 2024	Jul. 31, 2024
2024 Securities Purchase Agreement
Class of Stock [Line Items]
Share price (in dollars per share)	$ 20.00
Gross proceeds	$ 130.0
Common stock \| 2024 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	3,563,247
Series B Preferred Stock
Class of Stock [Line Items]
Convertible preferred stock, shares issued upon conversion (in shares)	1
Series B Preferred Stock \| 2024 Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	2,937,903	578,403
Series B Preferred Stock \| 2024 Securities Purchase Agreement \| Directors and Executive Officers
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	2,359,500

- 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

+ Details

Stock Incentive Plans - Schedule of Weighted Average Assumptions Used (Details) - Stock Options - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	4.02%	3.95%
Dividend yield	0.00%	0.00%
Expected term	6 years 2 months 15 days	5 years 11 months 8 days
Expected volatility	95.21%	94.64%
Weighted-average fair value of common stock and preferred stock (in dollars per share)	$ 19.63	$ 34.54
Common stock \| Old Cartestian
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	4.83%
Dividend yield	0.00%
Expected term	3 years 7 months 2 days
Expected volatility	83.77%
Weighted-average fair value of common stock and preferred stock (in dollars per share)	$ 12.00
Preferred Stock \| Old Cartestian
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	4.92%
Dividend yield	0.00%
Expected term	3 years 3 months 14 days
Expected volatility	83.87%
Weighted-average fair value of common stock and preferred stock (in dollars per share)	$ 403.47

Equity - June 2020 Sobi Stock Purchase (Narrative) (Details) - SOBI Purchase Agreement - USD ($) $ / shares in Units, $ in Millions	Jul. 28, 2020	Jun. 11, 2020
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		180,546
Share price (in dollars per share)		$ 138.4680
Sale of stock, percentage of ten-day volume weighted average price of common stock		120.00%
Total aggregate purchase price		$ 25.0
Redemption premium	$ 14.5

- 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

+ Details

Merger - Schedule of Allocation of the Purchase Price to the Estimated Fair Values of the Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Nov. 13, 2023
Assets acquired:
Goodwill	$ 48,163	$ 48,163
Old Cartesian
Assets acquired:
Cash and cash equivalents			$ 6,561
Prepaid expenses and other current assets			309
Property and equipment, net			215
Right-of-use asset, net			915
In-process research and development assets			150,600
Goodwill			48,163
Total assets acquired			206,763
Liabilities assumed
Accrued expenses and other current liabilities			2,530
Lease liability			292
Lease liability, net of current portion			623
Deferred tax liability			34,853
Total liabilities assumed			38,298
Net assets acquired			$ 168,465

Net Loss Per Share Allocable to Common Stockholders - Schedule of Computation of Basic and Diluted Net Loss Per Share Allocable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Numerator:
Net loss	$ (77,424)	$ (219,710)
Less: CVR distribution to participating securities	0	(37,550)
Net loss allocable to shares of common stock - basic	(77,424)	(257,260)
Less: Change in fair value of forward contract liability settled in February 2024	(446)	0
Net loss allocable to shares of common stock - diluted	$ (77,870)	$ (257,260)
Denominator:
Weighted-average common shares outstanding - basic (in shares)	17,276,822	5,170,319
Plus: dilutive effect of forward contract liability settled in February 2024 (in shares)	81,121	0
Weighted-average common shares outstanding - diluted (in shares)	17,357,943	5,170,319
Net loss per share:
Basic (in dollars per share)	$ (4.48)	$ (49.76)
Diluted (in dollars per share)	$ (4.49)	$ (49.76)

Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2024

Segment Reporting [Abstract]

Schedule of Segment Reporting Information, by Segment

The following table presents selected financial information with respect to the Company’s single operating segment for the years ended December 31, 2024 and 2023 (in thousands):


	Year Ended December 31,
	2024		2023
Revenue:
Collaboration and license revenue	$	38,275	$	26,004
Grant revenue	638		—
Total revenue	38,913		26,004
Less
Operating expenses:
Legacy Selecta programs	6,150		31,826
Descartes-08 for MG	12,142		343
Early stage programs	1,028		595
Research and development employee expenses	11,952		18,363
Research and development stock-based compensation expense	3,217		12,985
Research and development facilities and other expenses	10,616		7,148
General and administrative	30,126		40,450
Impairment of long-lived assets	7,579		710
Other expense, net (1)	33,527		133,294
Net loss	$	(77,424)	$	(219,710)

(1) Includes impairment of long-lived assets, interest income, foreign currency transaction, net, interest expense, change in fair value of warrant liabilities, change in fair value of contingent value right liability, change in fair value of forward contract liabilities, other income, net, and income tax (expense) benefit.

Leases - Schedule of Supplemental Disclosure for the Statement of Cash Flows Related to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities:	$ 3,559	$ 2,696

Segment Reporting

12 Months Ended

Dec. 31, 2024

Segment Reporting [Abstract]

Segment Reporting

Factors used in determining the reportable segment include the nature of the Company’s operating activities, the organizational and reporting structure and the type of information reviewed by the CODM to allocate resources and evaluate financial performance. The accounting policies of the segment are the same as those described in Note 3.

The following table presents selected financial information with respect to the Company’s single operating segment for the years ended December 31, 2024 and 2023 (in thousands):


	Year Ended December 31,
	2024		2023
Revenue:
Collaboration and license revenue	$	38,275	$	26,004
Grant revenue	638		—
Total revenue	38,913		26,004
Less
Operating expenses:
Legacy Selecta programs	6,150		31,826
Descartes-08 for MG	12,142		343
Early stage programs	1,028		595
Research and development employee expenses	11,952		18,363
Research and development stock-based compensation expense	3,217		12,985
Research and development facilities and other expenses	10,616		7,148
General and administrative	30,126		40,450
Impairment of long-lived assets	7,579		710
Other expense, net (1)	33,527		133,294
Net loss	$	(77,424)	$	(219,710)

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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+ Details

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Liabilities:
Forward contract liabilities	$ 0	$ 28,307
Recurring
Assets:
Total assets	39,088	41,161
Liabilities:
Warrant liabilities	3,836	6,394
Contingent value right liability	395,500	358,600
Forward contract liabilities		28,307
Total liabilities	399,336	393,301
Recurring \| Level 1
Assets:
Total assets	39,088	41,161
Liabilities:
Warrant liabilities	0	0
Contingent value right liability	0	0
Forward contract liabilities		0
Total liabilities	0	0
Recurring \| Level 2
Assets:
Total assets	0	0
Liabilities:
Warrant liabilities	0	0
Contingent value right liability	0	0
Forward contract liabilities		28,307
Total liabilities	0	28,307
Recurring \| Level 3
Assets:
Total assets	0	0
Liabilities:
Warrant liabilities	3,836	6,394
Contingent value right liability	395,500	358,600
Forward contract liabilities		0
Total liabilities	399,336	364,994
Recurring \| Money market funds (included in cash equivalents)
Assets:
Money market funds (included in cash equivalents)	39,088	41,161
Recurring \| Money market funds (included in cash equivalents) \| Level 1
Assets:
Money market funds (included in cash equivalents)	39,088	41,161
Recurring \| Money market funds (included in cash equivalents) \| Level 2
Assets:
Money market funds (included in cash equivalents)	0	0
Recurring \| Money market funds (included in cash equivalents) \| Level 3
Assets:
Money market funds (included in cash equivalents)	$ 0	$ 0

Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parentheticals) $ in Thousands	12 Months Ended
	Dec. 31, 2024 USD ($)
Series B Preferred Stock \| Preferred Stock
Issuance costs	$ 5,585

Equity - Schedule of Authorized Shares of Common Stock for Future Issuance (Details)	Dec. 31, 2024 shares
Class of Stock [Line Items]
Total (in shares)	11,512,268
Shares available for future stock incentive awards
Class of Stock [Line Items]
Total (in shares)	4,205,199
Unvested restricted stock units
Class of Stock [Line Items]
Total (in shares)	444,238
Outstanding common stock options
Class of Stock [Line Items]
Total (in shares)	1,706,035
Series A Preferred Stock
Class of Stock [Line Items]
Total (in shares)	4,026,346
Series B Preferred Stock
Class of Stock [Line Items]
Total (in shares)	437,927
Warrant
Class of Stock [Line Items]
Total (in shares)	692,523

- 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

+ Details

Basis of Presentation (Details)	12 Months Ended
Basis of Presentation (Details)	Dec. 31, 2024 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	1

Collaboration and License Agreements - Biogen M.A., Inc. (Narrative) (Details)	Sep. 08, 2023
Biogen M.A., Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Written notice for agreement termination	30 days