# EDGAR Filing Document

**Accession Number:** 0002000002
**File Stem:** 0001193125-26-140633
**Filing Date:** 2026-4
**Character Count:** 14410
**Document Hash:** 78f19e9682018ac37812a5854acb3afd
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-140633.hdr.sgml**: 20260402

**ACCESSION NUMBER**: 0001193125-26-140633

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260402

**DATE AS OF CHANGE**: 20260402

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Cartesian Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001453687
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-89550
- **FILM NUMBER:** 26835691

**BUSINESS ADDRESS:**
- **STREET 1:** 7495 NEW HORIZON WAY
- **CITY:** FREDERICK
- **STATE:** MD
- **ZIP:** 21703
- **BUSINESS PHONE:** 301-348-8698

**MAIL ADDRESS:**
- **STREET 1:** 7495 NEW HORIZON WAY
- **CITY:** FREDERICK
- **STATE:** MD
- **ZIP:** 21703

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** SELECTA BIOSCIENCES INC
- **DATE OF NAME CHANGE:** 20090109
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Kalayoglu Murat
- **CENTRAL INDEX KEY:** 0002000002

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**MAIL ADDRESS:**
- **STREET 1:** C/O CARTESIAN THERAPEUTICS, INC.
- **STREET 2:** 704 QUINCE ORCHARD RD
- **CITY:** GAITHERSBURG
- **STATE:** MD
- **ZIP:** 20878

### UNITED STATES 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)*

**—**

*(CUSIP Number)*

**Daniel S. Clevenger**<br>Foley Hoag LLP<br>155 Seaport Boulevard<br>Boston MA 02210<br>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)*

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Murat Kalayoglu** | Name of reporting person<br>**Murat Kalayoglu** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**PF** | Source of funds (See Instructions)<br>**PF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**5833971.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**5833971.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5833971.00** | Aggregate amount beneficially owned by each reporting person<br>**5833971.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**19.9%** | Percent of class represented by amount in Row (11)<br>**19.9%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Seven One Eight Three Four Irrevocable Trust** | Name of reporting person<br>**Seven One Eight Three Four Irrevocable Trust** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**5313261.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**5313261.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**18.1%** | Percent of class represented by amount in Row (11)<br>**18.1%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Elizabeth Hoge** | Name of reporting person<br>**Elizabeth Hoge** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**5313261.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**5313261.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**18.1%** | Percent of class represented by amount in Row (11)<br>**18.1%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**HC** | Type of Reporting Person (See Instructions)<br>**HC** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Sinan Kalayoglu** | Name of reporting person<br>**Sinan Kalayoglu** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**5313261.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**5313261.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | Aggregate amount beneficially owned by each reporting person<br>**5313261.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**18.1%** | Percent of class represented by amount in Row (11)<br>**18.1%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**HC** | Type of Reporting Person (See Instructions)<br>**HC** | |

---

**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, MD, 21703

**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.

**Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.**

N/A

### 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.

**Reporting Person:** Murat Kalayoglu

**Signature:** /s/ Murat Kalayoglu

**Name/Title:** Murat Kalayoglu

**Date:** 04/02/2026

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.

**Reporting Person:** Seven One Eight Three Four Irrevocable Trust

**Signature:** /s/ Murat Kalayoglu

**Name/Title:** Murat Kalayoglu, Authorized Person

**Date:** 04/02/2026

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.

**Reporting Person:** Elizabeth Hoge

**Signature:** /s/ Murat Kalayoglu

**Name/Title:** Murat Kalayoglu, Authorized Person

**Date:** 04/02/2026

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.

**Reporting Person:** Sinan Kalayoglu

**Signature:** /s/ Murat Kalayoglu

**Name/Title:** Murat Kalayoglu, Authorized Person

**Date:** 04/02/2026