Sec Form 4 Filing - Jewell Christopher M @ Cartesian Therapeutics, Inc. - 2023-11-13

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Jewell Christopher M 2. Issuer Name and Ticker or Trading Symbol Cartesian Therapeutics, Inc. [ RNAC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Scientific Officer (Last) (First) (Middle) C/O CARTESIAN THERAPEUTICS, INC., 65 GROVE STREET 3. Date of Earliest Transaction (MM/DD/YY) 11/13/2023 (Street) WATERTOWN, MA02472 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 107.59 11/13/2023 A 4,276.454 ( 1 ) 01/15/2033 Series A Non-Voting Convertible Preferred Stock ( 2 ) 4,276.454 ( 3 ) 4,276.454 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Jewell Christopher M C/O CARTESIAN THERAPEUTICS, INC. 65 GROVE STREET WATERTOWN, MA02472 Chief Scientific Officer Signatures /s/ Christopher M. Jewell 11/15/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Option is currently exercisable for 2,539.177 shares of Series A Non-Voting Convertible Preferred Stock of the issuer ("Series A Preferred Stock") and becomes exercisable for an additional 89.093 shares each month until it is fully exercisable. ( 2 )Following the approval by the stockholders of the issuer of the conversion of the Series A Preferred Stock into shares of common stock of the issuer ("Common Stock"), each share of Series A Preferred Stock will be convertible into 1,000 shares of Common Stock, subject to certain limitations, including that a holder of Series A Preferred Stock is prohibited from converting shares of Series Preferred Stock into shares of Common Stock if, as a result of such conversion, such holder, together with its affiliates, would beneficially own more than 19.9% of the total number of shares of Common Stock issued and outstanding immediately after giving effect to such conversion. ( 3 )On November 13, 2023, the issuer acquired Cartesian Therapeutics, Inc. ("Cartesian") in accordance with the terms of an Agreement and Plan of Merger, dated November 13, 2023. Options to purchase Cartesian common stock held by the reporting person were converted into options to purchase shares of Series A Preferred Stock in connection with the acquisition.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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