Cartesian Therapeutics, Inc.

Item 7.01 Regulation FD Disclosure. On September 29, 2026, Cartesian Therapeutics, Inc. (the “Company”) issued a press release announcing additional retreatment data from the Company’s Phase 2 trial of Descartes-08 in patients with myasthenia gravis (“MG”). A copy of the press release is attached hereto as Exhibit 99.1 and incorporated herein by reference. The information in Item 7.01 of this Form 8-K, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing. The Company undertakes no obligation to update, supplement or amend the materials attached hereto as Exhibit 99.1, except as required by law.

Item 8.01 Other Events. On September 29, 2026, the Company announced additional retreatment data from the Company’s Phase 2 trial of Descartes-08 in patients with MG. The data consisted of observations from five participants who experienced recurrence of MG symptoms (as measured by Myasthenia Gravis Activities of Daily Living (“MG-ADL”) ≥6) following 12-month follow-up from the initial course of Descartes-08 treatment in the Phase 2 trial. Key observations included: Efficacy • Patients retreated at a median of 16.6 months following completion of initial treatment course experienced greater improvement in MG symptoms compared to initial course of treatment; mean decrease in MG-ADL scores were sustained through 12 months following retreatment ◦ Retreated patients observed an average MG-ADL reduction of 6.6 (±4.2) points from baseline at Month 12. ◦ Retreated patients observed an average Myasthenia Gravis Composite (“MGC”) reduction of 15 (±6.2) points from baseline at Month 12. ◦ All retreated patients experienced a clinically meaningful reduction across MGC (≥3-point reduction) and MG-ADL scores (≥2-point reduction), and four patients maintained the clinically meaningful MG-ADL reduction through Month 12 following retreatment. Safety • Consistent safety data observed to date supports potential retreatment of Descartes-08 following recurrence of MG symptoms, as clinical benefit was observed with no new safety concerns ◦ Descartes-08 was observed to be generally well-tolerated through Month 12 following retreatment, and adverse events were transient and mild. No serious adverse events were reported during retreatment. Notably, there were no cases of cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, cytopenias, or hypogammaglobulinemia.