Sec Form 4 Filing - Kalayoglu Murat @ Cartesian Therapeutics, Inc. - 2024-04-08

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 Kalayoglu Murat 2. Issuer Name and Ticker or Trading Symbol Cartesian Therapeutics, Inc. [ RNAC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O CARTESIAN THERAPEUTICS, INC., 704 QUINCE ORCHARD ROAD 3. Date of Earliest Transaction (MM/DD/YY) 04/08/2024 (Street) GAITHERSBURG, MD20878 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 Common Stock 04/08/2024 M 491,853 A 506,377 ( 2 ) D Common Stock 04/08/2024 M 2,926,764 A 3,036,887 ( 2 ) I by trust ( 3 )

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 Series A Non-Voting Convertible Preferred Stock ( 1 ) 04/08/2024 M 14,755.609 ( 1 ) ( 1 ) Common Stock 491,853 ( 2 ) ( 4 ) 0 D Series A Non-Voting Convertible Preferred Stock ( 1 ) 04/08/2024 M 87,802.95 ( 1 ) ( 1 ) Common Stock 2,926,764 ( 2 ) ( 5 ) 101,953.444 I by trust ( 3 ) Stock Option (Right to Buy) $ 19.656 ( 6 ) 01/01/2034 Common Stock 7,600 ( 2 ) 7,600 ( 2 ) D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Kalayoglu Murat C/O CARTESIAN THERAPEUTICS, INC. 704 QUINCE ORCHARD ROAD GAITHERSBURG, MD20878 X X Signatures /s/ Matthew Bartholomae, Attorney-in-Fact for Murat Kalayoglu 04/10/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On March 27, 2024, issuer held a special meeting of stockholders (the "Special Meeting"). At the Special Meeting, the issuer's stockholders approved the Reverse Stock Split and the conversion of the issuer's Series A Non-Voting Convertible Preferred Stock ("Series A Preferred Stock") into shares of Common Stock. On April 8, 2024, the conversion of the majority of the shares of Series A Preferred Stock occurred automatically (the "Automatic Conversion"). The remaining shares of Series A Preferred Stock remain subject to certain beneficial ownership limitations described in issuer's filings with the Securities and Exchange Commission. At the time of the Automatic Conversion, the reporting person's shares of Series A Preferred Stock were limited to the extent that doing so would result in the reporting person beneficially owning greater than 19.9% of the issuer's outstanding Common Stock after giving effect to such conversion. ( 2 )On April 4, 2024, the issuer effected a 1-for-30 reverse stock split of its common stock (the "Reverse Stock Split"). The amount of securities reported on this Form 4 has been adjusted to reflect the Reverse Stock Split. ( 3 )Shares are held in a trust (the "Trust") for the benefit of the reporting person's spouse and children. The reporting person's spouse is a trustee of the Trust. ( 4 )On November 13, 2023, the issuer acquired the private Delaware corporation which was then known as Cartesian Therapeutics, Inc. in accordance with the terms of an Agreement and Plan of Merger, dated November 13, 2023 (the "Merger"). These securities represent merger consideration payable as a result of the closing of the Merger. ( 5 )These securities represent merger consideration payable as a result of the closing of the Merger and securities purchased in a private placement in November 2023. ( 6 )This award will vest in 36 equal monthly installments, so that it shall be fully vested on the third anniversary of the date of grant.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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