Cartesian Therapeutics, Inc.

1. 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 cell therapy for the treatment of autoimmune diseases. Unlike DNA cell therapies, the Company’s cell therapy method degrades naturally over time without integrating into the cell’s genetic material. Therefore, the Company’s cell therapy is distinguished by its capacity to be dosed repeatedly like conventional drugs, administered in an outpatient setting, and given without pre-treatment chemotherapy required with many conventional cell therapies.

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, “Merger” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024. 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.

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 provided 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. See Note 11, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024 for further discussion of the 2023 Private Placement.

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 7, “Fair Value Measurements” to these unaudited consolidated financial statements.

On March 27, 2024, the Company’s stockholders approved the conversion of shares of Series A Preferred Stock into shares of common stock. For additional information, see Note 11, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024.

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 Quarterly Report on Form 10-Q relating to shares of the Company’s common stock (such as share amounts, per share amounts, and conversion rates and prices), 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 conversion of shares of Series B Preferred Stock into shares of common stock. For additional information, see Note 11, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024.

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.

Unaudited Interim Financial Information

The accompanying unaudited consolidated financial statements for the three and nine months ended September 30, 2025 and 2024 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC, for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America, or U.S. GAAP, have been condensed or omitted pursuant to such rules and regulations. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2024 included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 13, 2025. The unaudited interim financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of management, the accompanying unaudited interim consolidated financial statements contain all adjustments that are necessary for a fair statement of the Company’s financial position as of September 30, 2025, the consolidated results of operations for the three and nine months ended September 30, 2025, and cash flows for the nine months ended September 30, 2025. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2025.

Liquidity and Management’s Plan

The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain and sustain profitable operations. The Company is subject to a number of risks similar to other early-stage life science companies, including, but not limited to, successful development of its product candidates, raising additional capital with favorable terms, protection of proprietary technology and market acceptance of any approved future products. The successful development of product candidates requires substantial working capital, which may not be available to the Company on favorable terms or at all.

To date, the Company has financed its operations primarily through public offerings and private placements of its securities, funding received from research grants, collaboration and license arrangements and a credit facility. The Company currently has no source of product revenue, and it does not expect to generate product revenue for the foreseeable future. To date, the Company’s revenue has primarily been from collaboration agreements. The Company has devoted substantially all of its financial resources and efforts to developing its existing product candidates, identifying potential product candidates and conducting preclinical studies and clinical trials. The Company is in the early stages of development of its product candidates, and it has not completed development of any product candidates.

As of September 30, 2025, the Company’s cash, cash equivalents, and restricted cash were $145.1 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 September 30, 2025 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. Management’s expectations with respect to its ability to fund current and long term planned operations are based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional strategic or financing opportunities sooner than would otherwise be expected. 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 flows 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 7, “Fair Value Measurement”, for more information on the CVR.

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. As of September 30, 2025, the Company had an accumulated deficit of $729.8 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.

2. 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: fair value of the intangible assets acquired in connection with the Merger, fair value of the CVRs, deferred income taxes, revenue recognition, accrued research and development expenses, stock-based compensation expense, 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 inone 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 income (loss) that is also reported on the consolidated statements of operations and comprehensive income (loss). The CODM function uses net income (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.

3. Summary of Significant Accounting Policies

The Company disclosed its significant accounting policies in Note 3, “Summary of Significant Accounting Policies” included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024. There have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2025.

Recent Accounting Pronouncements

Not Yet Adopted

In December 2023, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or 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 periods beginning with 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.

4. Goodwill and Intangible Assets

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. As a result of the Merger, Selecta changed its corporate name to Cartesian Therapeutics, Inc. See Note 4, “Merger” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024 for further discussion of the Merger.

Goodwill

The Merger resulted in goodwill of approximately $48.2 million. There were no changes to the carrying value of the Company’s goodwill during the nine months ended September 30, 2025.

Intangible Assets

The Merger resulted in total indefinite-lived intangible assets of $150.6 million, of which $93.9 million is related to Descartes-08 for myasthenia gravis, or MG and $56.7 million is related to Descartes-08 for systematic lupus erythematosus. There were no changes to the carrying value of the Company’s indefinite-lived intangible assets during the nine months ended September 30, 2025.

5. Investments

In September 2021, the Company and Cyrus Biotechnology, Inc., or Cyrus, entered into a stock purchase agreement, or the Series B Preferred Stock Purchase 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.

During the nine months ended September 30, 2025 and the year ended December 31, 2024, 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 variable interest entity 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.

6. 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 for the three and nine months ended September 30, 2025 and 2024 (in thousands, except share and per-share data):

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:

7. 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 September 30, 2025 and December 31, 2024 (in thousands):

There wereno transfers within the fair value hierarchy during the nine months ended September 30, 2025 or the year ended December 31, 2024.

Cash, Cash Equivalents, and Restricted Cash

As of September 30, 2025 and December 31, 2024, 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 September 30, 2025, the Company had restricted cash balances relating to secured letters of credit in connection with its real estate leases. The Company’s consolidated statements of cash flows include the following as of September 30, 2025 and 2024 (in thousands):

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.

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 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 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 atzero.

•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 expires 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 or September 30, 2025.

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

The following table reflects a roll-forward of fair value for the Company’s Level 3 warrant liabilities (see Note 11, “Equity” to these unaudited consolidated financial statements) for the nine months ended September 30, 2025 (in thousands):

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, were included in the 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, Financial Instruments, or 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 Monte Carlo simulation model 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, and expected volatility of future revenues, 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:

The following table reflects a roll-forward of fair value for the Company’s Level 3 CVR liability for the nine months ended September 30, 2025 (in thousands):

Forward Contract Liabilities

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, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024. 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.

8. Property and Equipment

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

Depreciation expense was $0.6 million and $0.3 million for the three months ended September 30, 2025 and 2024, respectively, and $1.8 million and $0.7 million for the nine months ended September 30, 2025 and 2024, respectively.

9. Accrued Expenses

Accrued expenses consist of the following (in thousands):

10. 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 haveone option to extend the term of the Frederick Lease Agreement for a period offive 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 September 1, 2024 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 and the First Frederick Lease Agreement Amendment. The rent commencement date was September 1, 2024.

The Company assessed the classification of the lease at the September 1, 2024 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.

On March 13, 2025, the Company and the Landlord entered into the third amendment to the Frederick Lease Agreement, or the Third Frederick Lease Agreement Amendment, providing for the expansion of the premises leased pursuant to the Frederick Lease Agreement by approximately 6,439 square feet. In connection with the expansion of the leased premises, the Company is obligated to pay $0.2 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 November 1, 2025, 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 First Frederick Lease Agreement Amendment and the Second Frederick Lease Agreement Amendment.

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 September 30, 2025 and 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 on-reimbursable construction costs. The lease began in March 2020, when the Company took control of the office space, and the lease term iseight 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.

On September 1, 2022, the Company entered into an amendment to the Watertown Lease, or the Watertown Lease Agreement Amendment, to expand the Company’s laboratory and office space located at 65 Grove Street, Watertown, Massachusetts by approximately 7,216 square feet. The lease term began on September 1, 2022, consistent with when the Company took control of the office space and 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 during such year.

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. The term of the sublease expired on March 31, 2024 with no option to extend the sublease term. Sublease income is included within other (expense) income, net in the consolidated statements of operations and comprehensive loss.

As a result of the sublease agreement, 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 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 September 30, 2025 and December 31, 2024, and renews automatically each year.

On October 31, 2023, in connection with entering into Amendment No. 1 to the Sobi License as described in Note 13, “Revenue Arrangements”, 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. The term of this sublease expired on November 5, 2024. Sublease income is included within other (expense) income, net in the consolidated statements of operations and comprehensive loss.

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 generate 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 acquiredtwo 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.

For the three and nine months ended September 30, 2025 and 2024, the components of lease costs were as follows (in thousands):

The maturity of the Company’s operating lease liabilities as of September 30, 2025 were as follows (in thousands):

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

Other than the initial recording of the right-of-use assets and lease liabilities for the Frederick Lease Agreement and Amended Frederick Lease Agreement, which were non-cash, the changes in the Company’s right-of-use assets and lease liabilities for the nine months ended September 30, 2025 and 2024 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 operating leases:

11. Equity

Equity Financings

2024 Private Placement

On July 2, 2024, the Company and certain institutional and accredited investors, or 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.

“At-the-Market” Offering

On December 13, 2024, the Company entered into a Sales Agreement, or the Sales Agreement, with Leerink Partners LLC 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 LLC will act as sales agent. The shares of common stock sold pursuant to the 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.

During the nine months ended September 30, 2025 and the year ended December 31, 2024, the Company soldno shares of its common stock pursuant to the Sales Agreement.

Warrants

During the nine months ended September 30, 2025, there wereno warrants issued, exercised, or cancelled. The following is a summary of the Company’s warrants as of September 30, 2025:

See Note 12, “Equity” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024 for further discussion of the terms related to the Company’s warrants.

Common Stock

On April 4, 2024, the Company implemented the Reverse Stock Split. The Reverse Stock Split became effective at 4:30 p.m. Eastern Time on April 4, 2024. On April 5, 2024, the Company’s common stock began trading on The Nasdaq Global Market on a split-adjusted basis under the symbol “RNAC” with a new CUSIP number, 816212302. As a result of the Reverse Stock Split, every 30 shares of common stock outstanding were combined, automatically and without any action on the part of the Company or its stockholders, into one share of common stock. Stockholders entitled to fractional shares as a result of the Reverse Stock Split received a cash payment in lieu of receiving fractional shares. The Reverse Stock Split did not change the number of authorized shares or par value of the Company’s common or preferred stock.

Preferred Stock

As of September 30, 2025, 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 4,464,273 shares of common stock.

Reserved Shares

The Company has authorized shares of common stock for future issuance as of September 30, 2025 as follows:

12. 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 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. In January 2025, the number of shares of common stock that may be issued under the 2016 Plan was increased by 1,030,694. As of September 30, 2025,3,614,406 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 September 30, 2025, there are 496,639 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 afour-year period. Additionally, the stock options granted have a contractual term often years and only full shares can be exercised as per the individual award agreements. As of September 30, 2025, there are 36,179 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 $0.1 million and $0.3 million was recognized during the three months ended September 30, 2025 and 2024, respectively, and $0.5 million and $1.0 million was recognized during the nine months ended September 30, 2025 and 2024, respectively, as research and development expense in the consolidated statements of operations and comprehensive loss. Following the stockholder approval of the conversion of the Series A Preferred Stock into shares of common stock, the options exercisable for shares of Series A Preferred Stock became exercisable for shares of common stock.

Stock-Based Compensation Expense

In April 2025, the Company entered into a separation agreement and release, or the Separation Agreement, with the Company’s former Chief Technology Officer, Metin Kurtoglu. Dr. Kurtoglu’s employment with the Company ended effective May 2025, and Dr. Kurtoglu will serve as a consultant to the Company from May 2025 through April 2026, or the Consulting Period. Pursuant to the Separation Agreement, certain of Dr. Kurtoglu’s stock options and restricted stock unit awards were modified to accelerate the vesting of a portion of the awards, continue the vesting of the remaining awards during the Consulting Period, and extend the post-termination exercise period of the modified stock options. The services performed during the Consulting Period do not qualify as substantive services under ASC 718 and therefore, the continued vesting of these awards represents a modification to the original award. The modification resulted in the recognition of $0.7 million of stock- compensation expense during the nine months ended September 30, 2025 which is reflected in research and development expenses on the consolidated statements of operations and comprehensive loss.

Stock-based compensation expense by classification included within the consolidated statements of operations and comprehensive loss, was as follows (in thousands):

Stock Options

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:

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 three months ended September 30, 2025 and 2024 was $9.82 and $14.23, respectively, and $13.54 and $15.75 during the nine months ended September 30, 2025 and 2024, respectively.

As of September 30, 2025, total unrecognized compensation expense related to unvested common stock options was $13.7 million, which is expected to be recognized over a weighted average period of 2.8 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:

Restricted Stock Units

During the nine months ended September 30, 2025, the Company granted 256,790 restricted stock unit awards with a weighted-average fair value of $16.93 per share based on the closing price of the Company’s common stock on the date of grant under the 2016 Plan, which generally vest over afour-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.

Unrecognized compensation expense related to the restricted stock units was $5.9 million as of September 30, 2025, which is expected to be recognized over a weighted-average period of 2.5 years.

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

13. Revenue Arrangements

Astellas Gene Therapies

License and Development Agreement

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 15, “Collaboration and License Agreements” to these unaudited 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. A more detailed description of the Astellas Agreement and the Company's evaluation of this agreement under ASC 606 can be found in Note 14, “Revenue Arrangements” to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024.

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 September 30, 2025, there wereno unsatisfied performance obligations andno receivable related to the Astellas Agreement. As of December 31, 2024, the Company recorded a receivable of $0.1 million, representing billings for the Xork Development Services (as defined in the Astellas Agreement) that are subject to reimbursement by Astellas. No revenue related to the Astellas Agreement was recognized during the three and nine months ended September 30, 2025 or the three months ended September 30, 2024. During the nine months ended September 30, 2024, revenue of $6.3 million related to the Astellas Agreement was recognized, 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 nine months ended September 30, 2024.

Swedish Orphan Biovitrum AB (publ.)

License and Development Agreement

In June 2020, the Company and Sobi entered into the Sobi License, which was subsequently amended in October 2023. 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. A more detailed description of the Sobi License and the Company’s evaluation of this agreement under ASC 606 can be found in Note 14, “Revenue Arrangements” to the consolidated financial statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024. 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.

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 were included, net of deductions as specified in the CVR Agreement, in the distribution to holders of the CVRs in March 2025.

As of each of September 30, 2025 and December 31, 2024, the Company recorded total outstanding receivables of $0.1 million, representing billings for the Phase 3 DISSOLVE program that are subject to reimbursement by Sobi. Additionally, as of September 30, 2025 and December 31, 2024, there was no unbilled receivable outstanding. No revenue was recognized during the three and nine months ended September 30, 2025 or the three months ended September 30, 2024. Revenue of $32.8 million, inclusive of the $30.0 million development milestone, related to the Sobi License was recognized during the nine months ended September 30, 2024.

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 September 30, 2025 and December 31, 2024, there wereno unsatisfied performance obligations from contracts with customers.

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 ran from June 2024 through May 2025. In June 2025, the Company received funding approval from NINDS for an additional award of $1.5 million granted for the budget period that runs from June 2025 through May 2026. The 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 September 30, 2025 and December 31, 2024, the Company recorded a receivable of $0.5 million and $0.6 million, respectively, that is subject to reimbursement by NINDS. The Company recognized grant revenue of $0.5 million and $1.4 million during the three and nine months ended September 30, 2025, respectively. The Company recognized grant revenue of $0.4 million and $0.6 million during the three and nine months ended September 30, 2024, respectively.

14. 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, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024 for further discussion of the 2024 Private Placement. The below issuances and sales to related parties of the Company were made during the nine months ended September 30, 2024.

2023 Securities Purchase Agreement

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 member of the Company’s Board of Directors, or the Investors, 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, “Convertible Preferred Stock” to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024 for further discussion of the 2023 Private Placement. 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 nine months ended September 30, 2024.

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.

During the three and nine months ended September 30, 2025, there were no related party transactions.

15. 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 MG 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 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.

Genovis AB (publ.)

License Agreement

In October 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.

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 13, “Revenue Arrangements” to these unaudited 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.

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 September 30, 2025. 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.

16. Income Taxes

As of September 30, 2025, the Company has not recorded any U.S. federal or state income tax benefits for either the net losses the Company has incurred or its earned research and orphan drug credits, due to the uncertainty of realizing a benefit from those items in the future.

17. Commitments and Contingencies

As of September 30, 2025, 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 September 30, 2025, 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 on the Company’s business, financial position, results of operations or cash flows.

18. Restructuring

In April 2023, in light of then-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 headcount as of April 2023.

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):

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 nine months ended September 30, 2025, the Company recognizedno restructuring charges. For the nine months ended September 30, 2024, the Company recognized $0.2 million in research and development expenses and $0.6 million in general and administrative expenses. Payments for the restructuring plan were completed in the first quarter of 2025.

19. Segment Information

The following table presents selected financial information with respect to the Company’s single operating segment for the three and nine months ended September 30, 2025 and 2024 (in thousands):

20. 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.