8-K: Cullinan Therapeutics Unveils Promising CLN-049 AML Data

Cullinan Therapeutics announced new positive Phase 1 clinical data for CLN-049 in relapsed/refractory AML and MDS patients, to be presented at the ASH Annual Meeting.

Summary

• Cullinan Therapeutics presented new Phase 1 clinical data for CLN-049, a FLT3xCD3 T cell engager, in patients with relapsed/refractory (r/r) acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS).
• The updated data will be presented at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition, held December 6-9, 2025.
• As of the June 2025 data cutoff, 40 patients (34 AML, 6 MDS) were enrolled across 7 cohorts with a target dose range of 1.5-12 g/kg.
• 29 AML patients were efficacy evaluable, having received a median of two prior therapies.
• At target doses ≥6 g/kg (n=23 AML patients), a composite complete response (CRc) rate of 30% and an overall response rate (ORR) of 57% were observed.
• At the highest target dose studied thus far of 12 g/kg (n=13), the CRc rate was 31% and ORR was 69%.
• Responses were observed in AML patients regardless of baseline genetic risk, including 4 responses (2 CRh, 2 MLFS) among 5 TP53-mutated AML patients treated at 12 g/kg.
• In 9/23 patients achieving bone marrow blasts <5%, 33% (n=3) were MRD negative by flow cytometry, with no relapse observed in MRD-negative patients.
• CLN-049 demonstrated a manageable safety profile; common treatment-emergent adverse events (TEAEs) included cytokine release syndrome (CRS) (40%), infusion-related reaction (35%), and febrile neutropenia, pneumonia, stomatitis, white blood cell count decrease (17.5% each).
• All CRS events were limited to Grade 1 or 2, and neither CRS nor ICANS led to treatment discontinuation.

Sentiment

Score: 8

Explanation: The clinical data presented for CLN-049 shows promising efficacy in a difficult-to-treat patient population (relapsed/refractory AML, including TP53-mutated patients) with a manageable safety profile. This represents a significant positive step for the program and addresses an unmet medical need, indicating strong potential for future development and commercialization.

Positives

• Promising anti-leukemic activity observed in a heavily pretreated relapsed/refractory AML population.
• High composite complete response (CRc) rate of 30% and overall response rate (ORR) of 57% at target doses ≥6 g/kg.
• Even higher ORR of 69% at the highest target dose of 12 g/kg, with a 31% CRc rate.
• Responses were observed regardless of baseline genetic risk, including 4 responses in 5 high-risk TP53-mutated AML patients treated at 12 g/kg.
• 33% of patients achieving bone marrow blasts <5% were MRD negative, with no observed relapse in this subgroup, indicating deep and durable responses.
• Manageable safety profile with all cytokine release syndrome (CRS) events limited to Grade 1 or 2, and no treatment discontinuations due to CRS or ICANS.
• CLN-049 targets both mutated and non-mutated FLT3, suggesting broad applicability across a wide patient population.

Negatives

• Common treatment-emergent adverse events (TEAEs) included cytokine release syndrome (CRS) (40%), infusion-related reaction (35%), febrile neutropenia (17.5%), pneumonia (17.5%), stomatitis (17.5%), and white blood cell count decrease (17.5%).
• Grade 3 TEAEs occurring in >10% of patients included febrile neutropenia (17.5%), white blood cell count decrease (17.5%), and pneumonia (12.5%).

Risks

• Uncertainty regarding the timing and results of regulatory submissions for CLN-049.
• Risk that any NDAs, INDs, or other global regulatory submissions may not be cleared or approved on expected timelines, or at all.
• The success of clinical trials and preclinical studies is not guaranteed, and future results may differ from initial findings.
• Risks related to the company's ability to protect and maintain its intellectual property position for CLN-049.
• Risks related to manufacturing, supply, and distribution of product candidates.
• Risk that CLN-049, or any other product candidate, will not be successfully developed and commercialized.
• The success of any collaboration, partnership, license, or similar agreements related to CLN-049 is not guaranteed.

Future Outlook

Dose escalation continues in the ongoing Phase 1 study of CLN-049. The company aims to expand treatment options for patients with relapsed/refractory AML through a unique FLT3-directed T cell engager approach, targeting both mutated and non-mutated FLT3 for broad applicability. The company looks forward to sharing updated data at the ASH Annual Meeting.

Management Comments

• Jeffrey Jones, MD, MBA, Chief Medical Officer, stated that AML is among the largest hematology indications for which a T cell engager is not available, and the new data for CLN-049 demonstrate compelling potential for patients with relapsed or refractory AML, a population urgently needing new treatment options.
• Dr. Jones also highlighted that initial Phase 1 study results showed clinically meaningful anti-leukemic activity, including complete responses, with a composite complete response (CRc) rate of 31% at the highest dose level explored, and importantly, responses were observed regardless of baseline genetic risk, even in TP53-mutated AML patients where prognosis is notably poor.
• Mohammad Maher Abdul Hay, MD, Director, Clinical Leukemia Program, Perlmutter Cancer Center, commented that CLN-049 has the potential to be widely applicable because it targets the extracellular domain of both mutated and non-mutated FLT3, expressed on malignant blasts in over 80% of AML patients.

Industry Context

Acute myeloid leukemia (AML) remains a devastating disease with a poor prognosis, particularly for relapsed or refractory patients, and currently lacks approved immunotherapies like T cell engagers. CLN-049 addresses a significant unmet medical need by offering a novel FLT3xCD3 bispecific T cell engager, potentially expanding treatment options for a broad AML patient population, including those with high-risk genetic features like TP53 mutations, for whom options are especially limited.

Comparison to Industry Standards

• AML is among the largest hematology indications for which a T cell engager is not available, positioning CLN-049 as a potential first-in-class therapy in this significant market.
• The ability of CLN-049 to induce responses in TP53-mutated AML patients is particularly notable, as this subgroup typically faces a notably poor prognosis and extremely limited treatment options compared to standard therapies.
• CLN-049's mechanism of targeting both mutated and non-mutated FLT3 offers broader applicability compared to existing FLT3 inhibitors that often target specific mutations, potentially reaching a larger patient population.

Stakeholder Impact

• Shareholders: Positive impact due to promising clinical data, potentially increasing company valuation and future revenue prospects.
• Patients: Offers a potential new, effective treatment option for relapsed/refractory AML and MDS, especially for those with high-risk genetic features and limited current options.
• Medical Community: Provides new data on a novel T cell engager for AML, potentially influencing future treatment paradigms and research directions.

Next Steps

• Presentation of updated data at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition on December 8, 2025.
• Continued dose escalation in the ongoing Phase 1 study of CLN-049.
• Host an in-person event for analysts and institutional investors on Monday, December 8, 2025, to discuss the CLN-049 data shared at the ASH Annual Meeting.

Key Dates

Recommendation

The clinical data for CLN-049 in relapsed/refractory AML and MDS is highly encouraging, demonstrating significant anti-leukemic activity (high CRc and ORR) and a manageable safety profile in a heavily pretreated patient population. The observed responses in high-risk TP53-mutated AML patients are particularly noteworthy, addressing a critical unmet need. The broad applicability of CLN-049, targeting both mutated and non-mutated FLT3, further enhances its market potential. This positive Phase 1 data significantly de-risks the program and suggests strong potential for future clinical success and commercialization, making it an attractive investment opportunity.

Keywords

Cullinan Therapeutics, CGEM, CLN-049, AML, Acute Myeloid Leukemia, MDS, Myelodysplastic Syndrome, FLT3xCD3, T Cell Engager, Phase 1 Clinical Trial, ASH Annual Meeting, Oncology, Hematology, Biopharmaceutical, Clinical Data, Cancer Treatment, Relapsed/Refractory