Financial Analysis

Commitments and Contingencies As of March 31, 2026, the Company was not a party to any litigation that could have a material adverse effect on the Companys 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 March 31, 2026, 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 Companys request in such capacity. The term of the indemnification is for the directors 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, cl …

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Stock Incentive Plans In June 2016, the Companys stockholders approved the 2016 Incentive Award Plan, or the 2016 Plan, which initially authorized 40,341 shares of common stock for future issuance under the 2016 Plan. 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. The Board of Directors established a Stock Option Committee which is authorized to grant awards to certain employees and consultants subject to conditions and limitations within the 2016 Plan. In January 2026, the number of shares of common stock that may be issued under the 2016 Plan was increased by 1,040,444. As of March 31, 2026, 3,044,044 shares remain available for future issuance under the 2016 Plan. In September 2018, the Companys 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 initially authorized 39,166 shares of its common stock for issuance. As of March 31, 2026, there are 502,296 shares available for future grant under the 2018 Inducement Incentive Award Plan. On November 2023, the Company assumed the 2016 Stock Incentive Plan, or the Old Cartesian Plan, of the then …

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Fair Value Measurements The following tables present the Companys assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2026 and December 31, 2025 (in thousands): March 31, 2026 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 117,674 $ 117,674 $ $ Total assets $ 117,674 $ 117,674 $ $ Liabilities: Warrant liability $ 47 $ $ $ 47 Contingent value right liability 405,900 405,900 Total liabilities $ 405,947 $ $ $ 405,947 December 31, 2025 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash equivalents) $ 122,724 $ 122,724 $ $ Total assets $ 122,724 $ 122,724 $ $ Liabilities: Warrant liability $ 141 $ $ $ 141 Contingent value right liability 392,100 392,100 Total liabilities $ 392,241 $ $ $ 392,241 There were no transfers within the fair value hierarchy during the three months ended March 31, 2026 or the year ended December 31, 2025. Cash, Cash Equivalents, and Restricted Cash As of March 31, 2026 and December 31, 2025, 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 March 31, 2026, the Company had restricted cash balances relating to secured letters of credit in connection with its real estate leases. The Companys consolidated statements of cash flows include the following as of March 31, 2026 and 2025 (in thousands): March 31, 2026 2025 Cash and cash eq …

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Goodwill and Indefinite-Lived Intangible Assets As of March 31, 2026, the Company has goodwill of approximately $48.2 million and an indefinite-lived intangible asset of $93.9 million related to Descartes-08 for MG. There were no changes to the carrying value of the Companys goodwill or in-process research and development asset related to Descartes-08 for MG during the three months ended March 31, 2026 and 2025. …

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Income Taxes As of March 31, 2026, 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.

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Leases The Company maintains operating leases for manufacturing, laboratory and office space located in Maryland and Massachusetts. In Frederick, Maryland, the Company occupies over 35,000 total square feet of integrated space under a lease agreement, or the Frederick Lease Agreement, and subsequent amendments entered into between February 2024 and June 2025, or the Amended Frederick Lease Agreement. The Amended Fredrick Lease Agreement is set to expire in 2031, carries an aggregate annual base rent of approximately $1.4 million and is subject to annual increases in accordance with the terms of the Amended Frederick Lease Agreement. See Note 9, Leases to the consolidated financial statements included in the Companys Annual Report on Form 10-K for the year ended December 31, 2025 for further discussion of the Companys leases. For the three months ended March 31, 2026 and 2025, the components of lease costs were as follows (in thousands): Three Months Ended March 31, 2026 2025 Operating lease cost $ 583 $ 584 Variable lease cost 431 406 Short-term lease cost 4 11 Total lease cost $ 1,018 $ 1,001 The maturity of the Companys operating lease liabilities as of March 31, 2026 were as follows (in thousands): March 31, 2026 2026 (remainder) $ 3,571 2027 4,554 2028 2,529 2029 1,630 2030 1,679 Thereafter 852 Total future minimum lease payments 14,815 Less: Imputed interest (2,960) Total operating lease liabilities $ 11,855 Other information related to operating leases was as follows: M …

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Recent Accounting Pronouncements Not Yet Adopted 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 evaluating the impact of the standards adoption on its consolidated financial statements and related disclosures. In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities (ASU 2025-10), which establishes authoritative guidance on the recognition, measurement, presentation, and disclosure of government grants. Under ASU 2025-10, government grants are recognized when it is probable that the entity will both comply with the conditions of the grant and the grant will be received. The ASU provides specific accounting models for grants related to assets and grants related to income, including options to recognize government grants as deferred income or as a reduction of the assets cost basis. The ASU also requires enha …

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Revenue Arrangements Collaboration and license revenue Swedish Orphan Biovitrum AB (publ.) 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 Nanoecapsulated Sirolimus plus Pegadricase, or NASP, formerly known as SEL-212, drug candidate , which is currently in development for the treatment of chronic refractory gout. The NASP drug candidate is a pharmaceutical composition containing a combination of a pegylated uricase known as SEL-037, or the Compound, and nanoparticle-encapsulated form of rapamycin, known as 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 NASP, 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 Companys evaluation of this agreement under ASC 606 can be found in Note 13, Revenue Arrangements to the consolidated financial statements in the Companys Annual Report on Form 10- …

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Segment Reporting The following table presents selected financial information with respect to the Companys single operating segment for the three months ended March 31, 2026 and 2025 (in thousands): Three Months Ended March 31, 2026 2025 Revenue: Collaboration and license revenue $ $ 400 Grant revenue 78 700 Total revenue 78 1,100 Less: Operating expenses: Descartes-08 for MG 12,135 7,036 Descartes-08 for dermatomyositis 227 Early stage programs 355 990 Research and development employee expenses 3,828 3,702 Research and development stock-based compensation expense 949 1,275 Research and development facilities and other expenses 1,969 1,671 General and administrative 7,114 8,315 Other expense (income), net (1) 12,683 (4,179) Net loss $ (39,182) $ (17,710) (1) Includes interest income; gain on change in fair value of warrant liabilities; (loss) gain on change in fair value of contingent value right liability; and other expense, net. …

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Summary of Significant Accounting Policies Basis of presentation and 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, and Cartesian Bio, LLC, a Delaware limited liability company, which is a variable interest entity for which the Company is the primary beneficiary and have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the relevant Accounting Standards Codification, or ASC and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB. All significant intercompany accounts and transactions have been eliminated. The accompanying unaudited consolidated financial statements for the three months ended March 31, 2026 and 2025 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 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 Companys audited co …

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Equity Equity Financings At the Market Sales Agreement On December 13, 2024, the Company entered into a Sales Agreement, or the Sales Agreement, with Leerink Partners LLC to sell shares of the Companys 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 Companys 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 three months ended March 31, 2026, the Company sold 2,270,712 shares of its common stock pursuant to the Sales Agreement for net proceeds of approximately $14.6 million after commissions and expenses. There were no shares sold pursuant to the Sales Agreement during the three months ended March 31, 2025. Warrants During the three months ended March 31, 2026, there were no warrants issued, exercised, or cancelled. The following is a summary of the Companys warrants as of March 31, 2026: Number of Warrants Equity classified Liability classified Total Weighted-average exercise price Outstanding at March 31, 2026 6,560 685,712 692,272 $ 46.76 See Note 11, Equity to the consolidated financial statements included in the Companys Annual Report on Form 10-K for the year ended December 31, 2025 for furth …

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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.

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