Immatics Updates IMA203CD8 Clinical Data, Shows Anti-Tumor Activity

Immatics announced updated Phase 1a dose escalation data from its second-generation PRAME cell therapy, IMA203CD8, in heavily pre-treated patients with solid tumors. Based on the enhanced pharmacology of IMA203CD8 reported previously, IMA203CD8 provides the potential to address difficult-to-treat solid tumors expressing PRAME beyond melanoma, such as ovarian cancer. The data from the ongoing Phase 1a trial will be presented at the European Society for Medical Oncology Immuno-Oncology Congress 2025 during a Mini Oral Presentation by Prof. Dr. med. Antonia Busse, Charite, Berlin, Germany. Patient Population: Heavily pre-treated patient population with limited treatment options: As of the data cutoff on October 27, 2025, 781 heavily pre-treated patients with advanced and/or metastatic solid tumors expressing PRAME were enrolled in the ongoing Phase 1a dose escalation clinical trial. The median total infused dose across seven escalating dose levels was 1.6x109 TCR T cells. The efficacy-evaluable patient population included 69 patients: 42 with melanoma, 11 with ovarian carcinoma, 11 with synovial sarcoma and 5 with other tumor types. Safety: Treatment with IMA203CD8 showed manageable tolerability: IMA203CD8 showed manageable tolerability in the 78 patients enrolled. The most frequent treatment-emergent adverse events were anticipated cytopenias associated with lymphodepletion. Expected and manageable cytokine release syndrome was mostly Grade 1 to 2 and was consistent with the mechanism of action: Grade 1: 35%, Grade 2: 50%, Grade 3: 9%, Grade 4: 1%. Immune effector cell-associated neurotoxicity syndrome and hemophagocytic lymphohistiocytosis were infrequently observed. No IMA203CD8-related Grade 5 events occurred. Based on the manageable tolerability profile, dose escalation is ongoing at dose level 7 and on track to determine the recommended Phase 2 dose. Anti-tumor Activity and Durability: Deep and durable objective responses in PRAME-positive advanced solid tumors during ongoing dose escalation. A one-time infusion of IMA203CD8 PRAME cell therapy showed promising initial anti-tumor activity during dose escalation across various PRAME-expressing indications at a low median dose of 1.6x109 total IMA203CD8 TCR T cells: Confirmed Objective Response Rate: 36%; Objective Response Rate: 46%; Tumor reduction: 78%; Disease Control Rate at week 6: 84%; Median Duration of Response: 9.2 months at a median follow-up of 14 months. Deep and durable objective responses were observed for up to 3+ years. The data also showed three complete responses in addition to two confirmed partial responses with -100% reduction of target lesions across indications. 66% of responders exhibited deep responses with tumor reduction of greater than or equal to 50%, and seven responses remained ongoing for greater than or equal to 1 year post infusion. In patients with ovarian carcinoma, a promising, dose-dependent signal was observed, including deep, confirmed objective responses at higher dose levels. Among the five patients with ovarian carcinoma treated with IMA203CD8 at greater than or equal toDL5, two confirmed partial responses were observed, one of which is an ongoing metabolic complete response in the patient treated at the highest dose in the ovarian carcinoma efficacy population to date, and an additional unconfirmed PR. All responders were resistant to previous platinum-based chemotherapy. All responses were observed in patients who did not receive post-infusion low-dose IL-2. In addition, tolerability in ovarian carcinoma was generally consistent with the full IMA203CD8 tolerability profile. Within Immatics' PRAME franchise, its lead PRAME cell therapy, anzu-cel, showed a cORR of 19% during dose escalation. With enhanced pharmacology, IMA203CD8 is designed to build on the potential of anzu-cel in additional tumor types across a broad spectrum of PRAME expression levels and characterized by a more complex tumor microenvironment than melanoma, such as ovarian carcinoma. Immatics aims to position IMA203CD8 in the tumor-agnostic setting of advanced PRAME cancers beyond melanoma, starting with gynecologic cancers. In addition, the Phase 1 trial could support the positioning of IMA203CD8 without the requirement of post-infusion low-dose IL-2 in the future. The Company believes the early proof-of-concept data in ovarian carcinoma presented today support this strategy. The Company is on track to complete Phase 1a dose escalation and determine RP2D in 2026, including data on the two highest dose levels, to unlock the full clinical potential of IMA203CD8.