Autologous T cell therapy for PRAME⁺ advanced solid tumors in HLA-A*02⁺ patients: a phase 1 trial

In contrast to chimeric antigen receptor T cells, T cell receptor (TCR)-engineered T cells can target intracellular tumor-associated antigens crucial for treating solid tumors. However, most trials published so far show limited clinical activity. Here we report interim data from a first-in-human, multicenter, open-label, 3 + 3 dose-escalation/de-escalation phase 1 trial studying IMA203, an autologous preferentially expressed antigen in melanoma (PRAME)-directed TCR T cell therapy in HLA-A*02⁺ patients with PRAME⁺ recurrent and/or refractory solid tumors, including melanoma and sarcoma. Primary objectives include the evaluation of safety and tolerability and the determination of the maximum tolerated dose (MTD) and/or recommended dose for extension. Secondary objectives include the evaluation of IMA203 TCR-engineered T cell persistence in peripheral blood, tumor response as well as duration of response. A total of 27 patients were enrolled in the phase 1a dose escalation and 13 patients in the phase 1b dose extension. IMA203 T cells were safe, and the MTD was not reached. Of the 41 patients receiving treatment (that is, who started lymphodepletion), severe cytokine release syndrome was observed in 4.9% (2/41), and severe neurotoxicity did not occur. In the 40 patients treated with IMA203, an overall response rate consisting of patients with unconfirmed or confirmed response (u/cORR) of 52.5% (21/40) and a cORR of 28.9% (11/38) was observed with a median duration of response of 4.4 months (range, 2.4-23.0, 95% confidence interval: 2.6-not reached) across multiple indications. Rapid T cell engraftment and long-term persistence of IMA203 T cells were observed. IMA203 T cells trafficked to all organs, and confirmed responses were more frequent in patients with higher dose. T cell exhaustion was not observed in the periphery; deep responses were enriched at higher PRAME expression; and higher T cell infiltration resulted in longer progression-free survival. Overall, IMA203 showed promising anti-tumor activity in multiple solid tumors, including refractory melanoma. ClinicalTrials.gov identifier: NCT03686124 .