Immatics N.V.

On May 31, 2026, the Company announced extended data from the ongoing Phase 1 clinical trial evaluating its TCR bispecific (TCER®) candidate IMA401 targeting MAGEA4/8 in heavily pretreated patients with solid tumors, including head and neck cancer and lung cancer.

Patient Population. As of the March 2, 2026 data cutoff, 61 heavily pretreated patients with recurrent and/or refractory solid tumors across more than 15 different tumor types were treated with IMA401 with or without pembrolizumab, an immune checkpoint inhibitor (“ICI”). Patients had a median of three prior lines of systemic therapy (range: 1 – 8). 44 patients were treated at RP2D (1 – 2 mg), with 32 receiving monotherapy and 12 receiving the combination of IMA401 and pembrolizumab. Among these patients, head and neck cancer represented the largest subgroup treated at RP2D (n=14).

Safety Data. IMA401 demonstrated manageable tolerability. The tolerability profile of IMA401 with or without pembrolizumab was consistent across patient populations. The most frequent treatment-related adverse events (“TRAEs”) were expected and manageable CRS and transient lymphopenia, consistent with the mechanism of action, as well as neutropenia, mostly transient and manageable. No patient experienced ICANS. Five DLTs occurred (which were manageable in four cases) but no DLTs occurred at RP2D with dexamethasone premedication, and the MTD was not reached. Tolerability of IMA401 at RP2D in combination with pembrolizumab was consistent with IMA401 as a monotherapy at RP2D, with no overlapping and/or additive toxicity observed. At RP2D, tolerability was observed to be favorable, supporting broad combinability of IMA401. The following table shows TRAEs for IMA401 as monotherapy and IMA401 at RP2D with and without pembrolizumab:

a All TRAEs at least possibly related to IMA401 infusion and/or pembrolizumab infusion with grade 1-2 occurring in at least 10% of all patients, all events with ≥ Grade 3; bin patients with and without dexamethasone pre-medication; ALT, alanine aminotransferase; AST, aspartate aminotransferase; GGT, gamma-glutamyltransferase.

a All TRAEs at least possibly related to IMA401 infusion and/or pembrolizumab infusion with grade 1-2 occurring in at least 10% of all patients, all events with ≥ grade 3 and typical ICI-associated toxicities; b IMA401 dose in pembrolizumab expansion cohorts were 1 mg (n=8) or 1.5 mg (n=4).

Anti-Tumor Activity. Patients treated with IMA401 at RP2D as a monotherapy or in combination with pembrolizumab demonstrated clinical activity across multiple solid tumor indications, including melanoma, sqNSCLC, head and neck cancer and others:

a Two patients not shown in plot due to clinical progression before post-infusion scan. b One patient not shown in plot due to clinical progression before post-infusion scan. BL, Baseline; BOR, Best overall response; (c)PR, (confirmed) partial response; H&N, head and neck cancer; PD, progressive disease; RECIST, response evaluation criteria in solid tumors; SD, stable disease.

Preclinical Data. Target expression data from analyzed tumor samples showed that > 90% of patients with sqNSCLC are positive for PRAME and/or MAGEA4/8, and ~60% of patients with sqNSCLC are positive for both

targets, suggesting that a combination therapy against both targets could boost anti-tumor activity and counteract potential tumor escape mechanisms. IMA401/IMA402 combination demonstrated synergistic anti-tumor activity in MAGEA4/8 and PRAME double-positive tumor cell lines.