CAMBRIDGE, Mass. — December 8, 2025 — Leads & Copy — Cullinan Therapeutics, Inc. (Nasdaq: CGEM) shared updated clinical data from its Phase 1 study of CLN-049 in patients with relapsed/refractory (R/R) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS).
The data, which will be presented at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition, demonstrated promising efficacy, including multiple complete responses and encouraging response durability, in a heavily pretreated all-comer population of patients with R/R AML.
At the highest target dose tested to date, CLN-049 monotherapy demonstrated a 31% CR/CRh rate. Initial dose escalation results in 45 patients demonstrated a favorable safety profile across all doses assessed. The U.S. Food and Drug Administration (FDA) recently granted CLN-049 Fast Track designation.
Jeffrey Jones, MD, MBA, Chief Medical Officer at Cullinan Therapeutics, said the promising clinical data demonstrates the potential for CLN-049 to expand treatment options for a broad population of people with AML, including patients with TP53-mutated AML who currently face a particularly poor prognosis.
Mohammad Maher Abdul Hay, MD, Director, Clinical Leukemia Program, Perlmutter Cancer Center, and Director, Blood & Marrow Transplantation and Cellular Therapy Program, NYU Langone Health, said that CLN-049 represents a novel approach to target AML as it binds to the extracellular domain of FLT3, redirecting a patient’s own T cells to recognize and eliminate leukemic cells. He added that the compelling early efficacy data, including durability data, shows the potential impact a FLT3-targeted T cell engager could have for AML patients in need of new options.
As of the August 2025 data cutoff, 45 patients (39 AML, 3 MDS/AML, and 3 MDS) were enrolled without regard to FLT3 cell surface expression across 8 cohorts (target dose range 1.5-12 µg/kg). Of those, 41 patients were efficacy evaluable.
At the highest target dose studied thus far of 12 µg/kg (n=16), the CR/CRh rate was 31% (5/16) and CRc rate was 31% (5/16). Anti-leukemic activity was observed at target doses ≥6 µg/kg (n=32), with a CR/CRh rate of 25% (8/32) and a CRc rate of 28% (9/32).
At efficacious doses (≥6 µg/kg), in the patients achieving a CR/CRh response, 63% (5/8) of patients had a duration of response of >16 weeks, and two additional patients were able to proceed to allogeneic hematopoietic stem cell transplant.
In 10/32 patients achieving bone marrow blasts <5% at a target dose of ≥6 µg/kg, 30% (n=3) patients were MRD negative by flow cytometry, and 1 MRD-negative patient has had an ongoing response for >36 weeks.
Notably, among the 8 patients with TP53-mutated AML treated at 12 µg/kg, 50% (4/8) of patients achieved a CR/CRh response: 3 patients achieved a CRh response and 1 patient achieved a CR; 3/4 patients with CR/CRh had responses that were durable >16 weeks.
Responses were observed in patients with AML independent of baseline FLT3 expression and regardless of baseline genetic risk.
As of the August 2025 data cutoff, the most common treatment-emergent adverse events (TEAEs) included cytokine release syndrome (CRS) (35.6%), infusion-related reaction (33.3%), febrile neutropenia (20.0%), white blood cell count decrease and pneumonia (17.8% each), diarrhea, hypomagnesemia, stomatitis, and hypokalemia (15.6% each).
Nearly all CRS events limited to Grade 1 or 2, and the majority occurred after a step-up dose (SUD) or target dose 1. No Grade 3 CRS was observed with two step-up doses. CRS did not lead to treatment discontinuation.
Grade ≥3 TEAEs occurring in >10% of patients included febrile neutropenia (20.0%), white blood cell count decrease (17.8%), pneumonia and neutrophil count decrease (11.1% each).
Cullinan Therapeutics will host an in-person event for analysts and institutional investors on Monday, December 8, at 8:00 p.m. ET. Investors and analysts are invited to register to attend in person by emailing Nick Smith, Head of Investor Relations (nsmith@cullinantx.com).
Cullinan Therapeutics, Inc. is a biopharmaceutical company developing potential first- or best-in-class, high-impact therapies for autoimmune diseases and cancer.
CLN-049 is being studied in a Phase 1, open-label, multicenter, first-in-human, multiple ascending dose study evaluating safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and preliminary efficacy of intravenously (IV) administered CLN-049 in patients with relapsed/refractory AML or MDS (NCT05143996) and in a parallel Phase 1, open-label, dose escalation and dose expansion study for the treatment of patients with AML with measurable residual disease (MRD) (EUCT 2023-506572-27-00). CLN-049 has received Fast Track designation from the U.S. FDA for the treatment of relapsed/refractory AML.
Nick Smith
+1 401.241.3516
Nsmith@cullinantx.com
Rose Weldon
+1 215.801.7644
Rweldon@cullinantx.com
Source: Cullinan Therapeutics
