PRAME-Targeted T-Cell Therapy Achieves the Highest Reported Response Rate in Uveal Melanoma: 67%

Why Is This Study Important?

Metastatic melanomastill presents a major treatment gap, particularly after checkpoint inhibitors (anti–PD-1/PD-L1) in patients whose disease has progressed. Patients who do not respond to standard treatments generally face rapid disease progression and limited survival.

The outlook is particularly poor for treatment-resistant subtypes such as ocular melanoma (uveal melanoma) .

Developed to address this difficult clinical situation, IMA203 is a cellular therapy targeting PRAME , a tumor-associated antigen . It is a patient-specific (autologous) T-cell receptor-engineered (TCR-T) cell therapy. PRAME is highly expressed in more than 50 cancer types, including melanoma. Updated Phase 1b data presented at ASCO 2025 suggest that this treatment can produce strong, durable tumor responses.

What Is PRAME, and Why Does It Matter?

PRAME (PReferentially expressed Antigen in MElanoma):

• Highly expressed in almost all cutaneous melanomas (90–95%)
• An intracellular antigen that can be targeted only by specialized treatments such as TCR-T
• Because it is detected in more than 50 cancer types, it is viewed as a potential platform target .

💡 How Does IMA203 Treatment Work?

1. T cells are collected from the patient's blood.

2. In the laboratory, these cells are genetically reprogrammed to recognize PRAME , a tumor antigen (a PRAME-specific TCR gene is inserted into the cells).

3. The modified T cells are expanded and returned to the patient by intravenous infusion .

4. These “equipped T cells” can now recognize and destroy cancer cells carrying PRAME.

❗️Is This Different from CAR T?

Yes. The differences can be summarized as follows:

👉 Details of the ACTengine® IMA203-101 Clinical Trial

Who Received This Treatment?

• Total number of patients (Phase 1b): 33 patients with advanced melanoma
• Subgroups:
  • Cutaneous melanoma: 14 patients
  • Uveal (ocular) melanoma: 16 patients
  • Other subtypes (mucosal, unknown primary): 3 patients
• Median number of prior treatments: 2
• Proportion previously treated with anti-PD-1: 100%

Clinical Efficacy: How Strong Were the Responses?

Results after a single IMA203 infusion:

📌 Noteworthy finding: A 67% response rate is striking even in a treatment-resistant subgroup such as uveal melanoma.

📌 Deep responses (more than 50% tumor shrinkage) were achieved in 14 patients. Median progression-free survival in this group was 12.9 months.

Safety Profile: Are the Side Effects Manageable?

Treatment was generally well tolerated. The most common adverse effects were:

• Cytopenias: 100% (due to lymphodepleting chemotherapy)
• Cytokine release syndrome (CRS):
  • Grade 1–2: 84%
  • Grade 3: 11%
  • Grade 4–5: 0%
• ICANS (neurotoxicity):
  • Grade 1–3: 13% (mostly mild)
  • Grade 4–5: Not observed

These findings indicate a better-tolerated profile, particularly compared with TIL and CAR-T treatments.

The Phase 3 SUPRAME Study Is Underway

Following positive Phase 1b data, the Phase 3 SUPRAME study was initiated.

• Participants: 360 patients with cutaneous melanoma previously treated with checkpoint inhibitors
• Comparison: IMA203 vs physician's choice of available treatment (e.g., nivolumab, ipilimumab, pembrolizumab, lifileucel, etc.)
• Primary endpoint: Progression-free survival (PFS)
• Secondary endpoints: Overall survival (OS), response rate, quality of life

✅ This treatment has received FDA RMAT (Regenerative Medicine Advanced Therapy) designation, and a BLA submission is planned for the first quarter of 2027.

Conclusion and Future Outlook

IMA203 stands out as a cellular immunotherapy option that produces deep, durable, and manageable responses in patients with advanced melanoma. These findings suggest broad potential not only in melanoma but also in other PRAME-positive solid tumors.

🔬 Commentary: PRAME-targeted TCR-T cell therapies offer new hope, particularly for patients who do not respond to PD-1 treatment. IMA203 should be watched closely as one of the leading candidates in this field.