Sec Form 4 Filing - SPRINGER TIMOTHY A @ 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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person SPRINGER TIMOTHY A 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) 36 WOODMAN ROAD 3. Date of Earliest Transaction (MM/DD/YY) 04/08/2024 (Street) CHESTNUT HILL, MA02467 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 Series A Non-Voting Convertible Preferred Stock 04/08/2024 M 123,925.407 D 0 D Common Stock 04/08/2024 M 4,130,846 A 4,379,899 ( 2 ) D Series A Non-Voting Convertible Preferred Stock 04/08/2024 M 24,785.081 D 0 I See Footnote ( 3 ) Common Stock 04/08/2024 M 826,169 A 1,927,630 ( 2 ) I See Footnote ( 3 ) Common Stock 3,493 ( 2 ) I By wife

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) $ 19.656 ( 4 ) 01/01/2034 Common Stock 7,600 ( 2 ) 7,600 ( 2 ) D Warrant (Right to Buy) $ 46.5 04/11/2022 04/11/2027 Common Stock 167,040 ( 2 ) 167,040 ( 2 ) I See Footnote

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SPRINGER TIMOTHY A 36 WOODMAN ROAD CHESTNUT HILL, MA02467 X X Signatures /s/ Matthew Bartholomae, Attorney-in-Fact for Timothy A. Springer 04/10/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On March 27, 2024, the issuer held a special meeting of stockholders (the "Special Meeting"). At the Special Meeting, the stockholders of the issuer approved a 1-for-30 reverse stock split (the "Reverse Stock Split") of the issuer's common stock ("Common Stock") 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 the issuer's filings with the Securities and Exchange Commission. At the time of the Automatic Conversion, all of the reporting person's shares of Series A Preferred Stock converted into shares of Common Stock. ( 2 )On April 4, 2024, the issuer effected the "Reverse Stock Split". The amount of securities reported on this Form 4 has been adjusted to reflect the Reverse Stock Split. ( 3 )Held by TAS Partners LLC. The reporting person is the managing member of TAS Partners LLC. The reporting person disclaims beneficial ownership of the securities held by TAS Partners LLC except to the extent of his pecuniary interest therein, if any. ( 4 )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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.