8-K: Cullinan's CLN-049 Shows Promising AML/MDS Data

Cullinan Therapeutics presented updated positive Phase 1 clinical data for CLN-049 in relapsed/refractory acute myeloid leukemia and myelodysplastic syndrome at the 67th ASH Annual Meeting.

Summary

• Updated clinical data from the Phase 1 study of CLN-049 in patients with relapsed/refractory (r/r) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) were presented at the 67th American Society of Hematology (ASH) Annual Meeting.
• As of the August 2025 data cutoff, 45 patients (39 AML, 3 MDS/AML, and 3 MDS) were enrolled across eight cohorts, with 41 patients efficacy evaluable.
• Promising monotherapy activity was observed in heavily pretreated AML patients at clinically active target doses.
• At the highest target dose of 12 g/kg (n=16), the complete response (CR)/complete remission with partial hematologic recovery (CRh) rate was 31% (5/16) and the composite complete response (CRc) rate was 31% (5/16).
• At target doses of 6 g/kg (n=32), the CR/CRh rate was 25% (8/32) and the CRc rate was 28% (9/32).
• Initial durability in responders was promising, with 63% (5/8) of patients achieving a CR/CRh response at 6 g/kg having a duration of response of >16 weeks; two additional patients proceeded to allogeneic hematopoietic stem cell transplant.
• Measurable residual disease (MRD) negativity was observed in 30% (3/10) of patients achieving bone marrow blasts <5% at 6 g/kg, with one MRD-negative patient having an ongoing response for >36 weeks.
• Encouraging responses were seen in difficult-to-treat AML patients with high-risk genetic features, including 50% (4/8) of TP53-mutated AML patients treated at 12 g/kg achieving a CR/CRh response, with three out of four responses durable >16 weeks.
• Responses were observed in AML patients independent of baseline FLT3 expression and regardless of baseline genetic risk.
• The data demonstrate a favorable safety profile (N=45), with common treatment-emergent adverse events (TEAEs) including cytokine release syndrome (CRS) (35.6%), infusion-related reaction (33.3%), and febrile neutropenia (20.0%).
• Nearly all CRS events were limited to Grade 1 or 2, and 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).
• CLN-049 development will proceed under U.S. Food and Drug Administration (FDA) Fast Track designation.
• Dose escalation continues in the ongoing Phase 1 study, with expansion cohorts planned in early 2026.

Sentiment

Score: 8

Explanation: The clinical data for CLN-049 in relapsed/refractory AML and MDS are highly encouraging, demonstrating significant efficacy, including complete responses and durability, in a heavily pretreated patient population. The strong responses in high-risk TP53-mutated AML patients are particularly noteworthy given the poor prognosis for this group. The favorable safety profile and FDA Fast Track designation further enhance the positive outlook for this novel therapeutic candidate.

Positives

• Promising monotherapy efficacy, including multiple complete responses, observed in heavily pretreated patients with relapsed/refractory AML.
• High CR/CRh rate of 31% at the highest target dose (12 g/kg) and 25% at 6 g/kg, indicating significant anti-leukemic activity.
• Encouraging initial durability of response, with 63% of CR/CRh responders at 6 g/kg maintaining response for over 16 weeks, and some proceeding to stem cell transplant.
• Achievement of measurable residual disease (MRD) negativity in a subset of patients, with one MRD-negative patient showing an ongoing response for over 36 weeks.
• Significant responses (50% CR/CRh) observed in difficult-to-treat TP53-mutated AML patients, a population with particularly poor prognosis and limited treatment options.
• Responses were independent of baseline FLT3 expression and genetic risk, suggesting broad applicability of CLN-049.
• Favorable safety profile with nearly all cytokine release syndrome (CRS) events being Grade 1 or 2, and no treatment discontinuations due to CRS.
• CLN-049 has received FDA Fast Track designation for the treatment of relapsed/refractory AML, potentially accelerating its development and review process.

Negatives

• Common treatment-emergent adverse events (TEAEs) included cytokine release syndrome (35.6%), infusion-related reaction (33.3%), and febrile neutropenia (20.0%).
• Grade 3 TEAEs occurring in more than 10% of patients included febrile neutropenia (20.0%), white blood cell count decrease (17.8%), pneumonia, and neutrophil count decrease (11.1% each).

Risks

• Uncertainty regarding the timing and results of regulatory submissions.
• The risk that any NDAs, INDs, or other global regulatory submissions may not be approved or cleared on expected timelines, or at all.
• The success of clinical trials and preclinical studies is not guaranteed.
• Risks related to the ability to protect and maintain intellectual property position.
• Risks related to manufacturing, supply, and distribution of product candidates.
• The risk that any one or more product candidates, including those that are co-developed, will not be successfully developed and commercialized.
• The risk that the results of preclinical studies or clinical studies will not be predictive of future results in connection with future studies.
• The effect of changes in global economic conditions, including uncertainties related to international trade policies, tariffs, and supply chain dynamics on business and operations.
• The success of any collaboration, partnership, license, or similar agreements.

Future Outlook

Dose escalation continues in the ongoing Phase 1 study of CLN-049, with expansion cohorts planned for early 2026. The company is committed to rapidly advancing CLN-049, especially given its FDA Fast Track designation, to expand treatment options for patients with relapsed/refractory AML.

Management Comments

• "These promising clinical data, including multiple complete responses and encouraging initial data for response durability, demonstrate 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." Jeffrey Jones, MD, MBA, Chief Medical Officer, Cullinan Therapeutics.
• "Coupled with recent Fast Track designation from the FDA, which underscores the promise of CLN-049 to help patients with AML, Cullinan is committed to rapidly advancing this potential new treatment option for a devastating disease." Jeffrey Jones, MD, MBA, Chief Medical Officer, Cullinan Therapeutics.
• "CLN-049 represents a novel approach to target AML as it binds to the extracellular domain of FLT3, both wildtype and mutated forms, redirecting a patients own T cells to recognize and eliminate leukemic cells. FLT3 is a particularly promising target for this therapeutic approach since it is expressed by AML blasts in more than 80% of patients. The compelling early efficacy including durability data shared today show the potential impact a FLT3-targeted T cell engager could have for AML patients in need of new options." Mohammad Maher Abdul Hay, MD, Director, Clinical Leukemia Program, Perlmutter Cancer Center, and Director, Blood & Marrow Transplantation and Cellular Therapy Program, NYU Langone Health.

Industry Context

Acute myeloid leukemia (AML) remains an aggressive blood cancer with limited options for durable response, particularly for patients with relapsed or refractory disease, where five-year survival is 10% or less. Patients with high-risk genetic features, such as TP53 mutations, face especially limited options. FLT3 is a promising target as it is expressed by AML blasts in over 80% of patients. Currently, there are no approved immunotherapies for AML, underscoring a significant unmet medical need. CLN-049, as a novel FLT3xCD3 bispecific T cell engager, offers a new immunotherapeutic approach by redirecting a patient's own T cells to recognize and eliminate leukemic cells, regardless of FLT3 mutational status, addressing a broad patient population.

Comparison to Industry Standards

• Outcomes for patients with relapsed or refractory AML remain poor, with five-year survival rates of 10% or less, highlighting the significant unmet need CLN-049 aims to address.
• Patients with high-risk genetic features, such as TP53 mutations, face particularly limited treatment options and poor prognoses, making CLN-049's 50% CR/CRh rate in this subgroup at 12 g/kg a notable achievement.
• The mechanism of action of CLN-049 as a FLT3xCD3 bispecific T cell engager represents a novel immunotherapeutic approach, as there are currently no approved immunotherapies for AML.
• The broad applicability of CLN-049, binding to both mutated and non-mutated FLT3 and showing responses independent of baseline FLT3 expression or genetic risk, positions it favorably against therapies with more restricted patient populations.

Stakeholder Impact

• Shareholders: Positive impact due to promising clinical data, potential for future drug development success, and FDA Fast Track designation, which could lead to accelerated approval pathways.
• Patients (r/r AML/MDS): Potential for a new, effective treatment option, especially for those with high-risk genetic features like TP53 mutations who currently have limited options and poor prognoses.
• Medical Community: Provides a novel immunotherapeutic approach (FLT3xCD3 T cell engager) for AML, potentially expanding the treatment paradigm.
• Employees: Positive impact on morale and company direction due to successful clinical progress.

Next Steps

• Continue dose escalation in the ongoing Phase 1 study of CLN-049.
• Plan expansion cohorts for the CLN-049 study in early 2026.
• Rapidly advance CLN-049 development under FDA Fast Track designation.

Key Dates

Recommendation

The updated Phase 1 clinical data for CLN-049 are highly compelling, demonstrating significant efficacy, including complete responses and encouraging durability, in a heavily pretreated and difficult-to-treat relapsed/refractory AML population. The 50% CR/CRh rate in TP53-mutated AML patients is particularly impressive given the severe prognosis for this subgroup and the lack of effective current treatments. Coupled with a favorable safety profile (mostly low-grade CRS, no discontinuations due to CRS) and the FDA Fast Track designation, CLN-049 shows strong potential to become a firstor best-in-class therapy. The broad applicability regardless of FLT3 expression or genetic risk further enhances its market potential. These results significantly de-risk the program and suggest a high probability of success in later-stage trials, making Cullinan Therapeutics an attractive investment.

Keywords

Cullinan Therapeutics, CGEM, CLN-049, Acute Myeloid Leukemia, AML, Myelodysplastic Syndrome, MDS, FLT3xCD3, T cell engager, Phase 1 clinical trial, ASH Annual Meeting, Oncology, Biopharmaceutical, FDA Fast Track, Relapsed/Refractory, TP53-mutated AML, Complete Response, MRD negativity, Cytokine Release Syndrome