Cullinan Therapeutics presented data from a Phase 1 study of its FLT3xCD3 bispecific T‑cell engager CL 049 at the 67th American Society of Hematology (ASH) Annual Meeting on December 8, 2025. The presentation highlighted a 31 % complete response/composite complete response (CR/CRh) rate at the highest dose tested (12 µg/kg) in a heavily pre‑treated cohort of 45 patients with relapsed or refractory acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS).
The study enrolled 39 AML and 6 MDS/AML patients, each with a median of two prior therapies. Among patients receiving doses of 6 µg/kg or higher, 63 % achieved durable responses lasting longer than 16 weeks, and measurable residual disease (MRD) negativity was observed in all responders. Activity was also noted in the TP53‑mutated AML subgroup, a population that historically has limited treatment options and poor prognosis.
Safety data were encouraging, with no new or unexpected adverse events. Cytokine release syndrome (CRS) and infusion reactions were the most common side effects, but most CRS events were Grade 1 or 2 and manageable with standard supportive care. The favorable safety profile supports continued dose escalation and expansion of the clinical program.
Cullinan’s FLT3xCD3 bispecific has already received FDA Fast Track designation, underscoring the regulatory momentum behind the program. The company plans to continue dose escalation and launch expansion cohorts in early 2026, positioning CL 049 as a potential treatment for patients with limited options in the relapsed/refractory AML and MDS space.
Chief Medical Officer Jeffrey Jones emphasized the urgency of new therapies for this patient population, noting that “the early data demonstrate meaningful efficacy, including complete responses, reinforcing the broad potential of CL 049 in a setting where effective treatment options are currently fragmented.” The results suggest that CL 049 could fill a critical unmet need and strengthen Cullinan’s pipeline in the competitive landscape of FLT3‑targeted immunotherapies.
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