Insider filing report for Changes in Beneficial Ownership
- Schedule 13G & 13D forms are used to report a party's ownership of stock which exceeds 5% of a company's total stock issue.
- Schedule 13G is a shorter version of Schedule 13D with fewer reporting requirements.
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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549 |
SCHEDULE 13D
Under the Securities Exchange Act of 1934
(Amendment No. 3)*
|
Cartesian Therapeutics, Inc. (Name of Issuer) |
Common Stock (Title of Class of Securities) |
816212104 (CUSIP Number) |
Daniel S. Clevenger Foley Hoag LLP, 155 Seaport Boulevard Boston, MA, 02210 617-832-1000 (Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications) |
03/31/2026 (Date of Event Which Requires Filing of This Statement) |
If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.


The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the
Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other
provisions of the Act (however, see the Notes).
SCHEDULE 13D
|
| CUSIP No. | 816212104 |
| 1 |
Name of reporting person
Murat Kalayoglu | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
PF, OO | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
![]() | ||||||||
| 6 | Citizenship or place of organization
UNITED STATES
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
5,833,971.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
![]() | ||||||||
| 13 | Percent of class represented by amount in Row (11)
19.9 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
IN |
SCHEDULE 13D
|
| CUSIP No. | 816212104 |
| 1 |
Name of reporting person
Seven One Eight Three Four Irrevocable Trust | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
AF, OO | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
![]() | ||||||||
| 6 | Citizenship or place of organization
UNITED STATES
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
5,313,261.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
![]() | ||||||||
| 13 | Percent of class represented by amount in Row (11)
18.1 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
OO |
SCHEDULE 13D
|
| CUSIP No. | 816212104 |
| 1 |
Name of reporting person
Elizabeth Hoge | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
AF, OO | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
![]() | ||||||||
| 6 | Citizenship or place of organization
UNITED STATES
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
5,313,261.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
![]() | ||||||||
| 13 | Percent of class represented by amount in Row (11)
18.1 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
HC, IN |
SCHEDULE 13D
|
| CUSIP No. | 816212104 |
| 1 |
Name of reporting person
Sinan Kalayoglu | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
AF, OO | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
![]() | ||||||||
| 6 | Citizenship or place of organization
UNITED STATES
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
5,313,261.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
![]() | ||||||||
| 13 | Percent of class represented by amount in Row (11)
18.1 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
HC, IN |
SCHEDULE 13D
|
| Item 1. | Security and Issuer |
| (a) | Title of Class of Securities:
Common Stock |
| (b) | Name of Issuer:
Cartesian Therapeutics, Inc. |
| (c) | Address of Issuer's Principal Executive Offices:
7495 New Horizon Way, Frederick,
MARYLAND
, 21703. |
| Item 2. | Identity and Background |
| (a) | N/A |
| (b) | N/A |
| (c) | Item 2 of the Schedule 13D is hereby amended by deleting section (c) thereof and replacing it with the following: (c) The present principal occupation of Murat Kalayoglu is as a private investor and the Founder and Chief Executive Officer of SOAR Bio LLC. The Trust is a trust for the benefit of Murat Kalayoglu's family members. Elizabeth Hoge, Murat Kalayoglu's spouse, is a beneficiary of the Trust, and each of the Trustees is a trustee of the Trust. The present principal occupation of Elizabeth Hoge is as a Professor and the Director of the Anxiety Disorders Research Program at Georgetown University Medical Center, located at 2115 Wisconsin Avenue, NW, Suite 140, Washington, DC 20007. The present principal occupation of Sinan Kalayoglu is as a Trial Attorney for the United States Department of Justice, located at 1400 New York Avenue, NW, Washington, DC 20005. |
| (d) | N/A |
| (e) | N/A |
| (f) | N/A |
| Item 3. | Source and Amount of Funds or Other Consideration |
Item 3 of the Schedule 13D is hereby supplemented as follows: On April 2, 2026, pursuant to a Notice of Optional Conversion delivered to the Issuer by the Trust pursuant to Section 6.02 of the Certificate of Designation, as amended by the Amendment to the Certificate of Designation, 22,740.030 shares of Series A Preferred Stock held by the Trust were converted into 758,001 shares of Common Stock. | |
| Item 4. | Purpose of Transaction |
Item 4 of the Schedule 13D is supplemented as follows: On March 31, 2026, Murat Kalayoglu resigned as a member of the Issuer's board of directors. On April 2, 2026, pursuant to a Notice of Optional Conversion delivered to the Issuer by the Trust pursuant to Section 6.02 of the Certificate of Designation, as amended by the Amendment to the Certificate of Designation, 22,740.030 shares of Series A Preferred Stock held by the Trust were converted into 758,001 shares of Common Stock. | |
| Item 5. | Interest in Securities of the Issuer |
| (a) | Item 5 of the Schedule 13D is hereby amended and restated in full as follows: The percentages of beneficial ownership reported in this Item 5, and on each Reporting Person's cover page to this Schedule 13D, are based on a total of 28,544,728 shares of Common Stock issued and outstanding as of March 31, 2026, as advised by the Issuer. All of the share numbers reported herein are as of April 2, 2026, unless otherwise indicated. Each Reporting Person's cover page to this Schedule 13D is incorporated by reference into this Item 5(a, b). In aggregate, the Reporting Persons have voting and dispositive power over 5,833,971 shares of Common Stock, representing approximately 19.9% of such class of securities. The securities reported herein exclude 1,122,074 shares of Common Stock issuable upon conversion of shares of Series A Preferred Stock held by the Trust, but which would exceed the Conversion Limit. The beneficial ownership of each Reporting Person is as follows: (i) Murat Kalayoglu beneficially owns 5,833,971 shares of Common Stock representing approximately 19.9% of the class; (ii) the Trust beneficially owns 5,313,261 shares of Common Stock representing approximately 18.1% of the class; (iii) Elizabeth Hoge beneficially owns 5,313,261 shares of Common Stock representing approximately 18.1% of the class; and (iv) Sinan Kalayoglu beneficially owns 5,313,261 shares of Common Stock representing approximately 18.1% of the class. |
| (b) | Pursuant to a right of substitution, Murat Kalayoglu has the right to acquire from the Trust the shares of Common Stock and Series A Preferred Stock held by the Trust in exchange for assets with an equal value to such shares. Accordingly, the shares of Common Stock beneficially owned by the Trust are included in his holdings. Murat Kalayoglu has the sole power to vote and dispose of the shares of Common Stock beneficially owned by him (as described above). The Trust has the sole power to vote and dispose of the shares of Common Stock beneficially owned by it (as described above). Each of Elizabeth Hoge and Sinan Kalayoglu has the shared power to vote and dispose of the shares of Common Stock beneficially owned by such person (as described above). |
| (c) | No Reporting Person effected any transaction in the Common Stock from February 1, 2026 (the date 60 days prior to the filing of this Schedule 13D) to April 2, 2026. |
| (d) | No person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from or the proceeds from the sale of shares of the Common Stock. |
| (e) | N/A |
| Item 6. | Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer |
N/A | |
| Item 7. | Material to be Filed as Exhibits. |
1. Item 7 of the Schedule 13D is hereby amended and restated in full as follows: Item 7. Material to be Filed as Exhibits Exhibit 1 Joint Filing Agreement by and among Murat Kalayoglu, Seven One Eight Three Four Irrevocable Trust, Elizabeth Hoge and Sinan Kalayoglu dated November 22, 2023 (incorporated by reference to Exhibit 1 of the Reporting Persons' Schedule 13D filed with the SEC on November 22, 2023). Exhibit 2 Confirming Statement of Seven One Eight Three Four Irrevocable Trust dated November 22, 2023(incorporated by reference to Exhibit 2 of the Reporting Persons' Schedule 13D filed with the SEC on November 22, 2023). Exhibit 3 Confirming Statement of Elizabeth Hoge dated November 22, 2023 (incorporated by reference to Exhibit 3 of the Reporting Persons' Schedule 13D filed with the SEC on November 22, 2023). Exhibit 4 Confirming Statement of Sinan Kalayoglu dated November 22, 2023 (incorporated by reference to Exhibit 4 of the Reporting Persons' Schedule 13D filed with the SEC on November 22, 2023). Exhibit 5 Agreement and Plan of Merger, dated November 13, 2023, by and among Selecta Biosciences, Inc. Sakura Merger Sub I, Inc., Sakura Merger Sub II, LLC and Cartesian Therapeutics, Inc. (incorporated by reference to Exhibit 2.1 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on November 13, 2023). Exhibit 6 Certificate of Designation of Series A Non-Voting Convertible Preferred Stock (incorporated by reference to Exhibit 3.4 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on November 13, 2023). Exhibit 7 Securities Purchase Agreement, dated November 13, 2023, by and among Selecta Biosciences, Inc. and the Purchasers named therein (incorporated by reference to Exhibit 10.1 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on November 13, 2023). Exhibit 8 Registration Rights Agreement, dated November 13, 2023, by and among Selecta Biosciences, Inc. and the Purchasers named therein (incorporated by reference to Exhibit 10.2 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on November 13, 2023). |
| SIGNATURE | |
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
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