UPDATE: Phase 1 Trial Early Results, Pasritamig + JNJ-87189401 dual T-cell engagement

Early results presented at SITC 2026 suggest encouraging activity for a novel dual-target immunotherapy combining pasritamig, a KLK2×CD3 T-cell engager, with JNJ-87189401, a PSMA×CD28 costimulatory antibody, in heavily pretreated metastatic castration-resistant prostate cancer (mCRPC).
Among 15 patients receiving the recommended regimen, 73.3% achieved a PSA reduction of at least 50% (PSA50), 46.7% achieved PSA90, and four patients (26.7%) reached PSA levels below 0.2 ng/mL.
No grade 3 or higher treatment-related adverse events occurred at the recommended dose, although higher doses were associated with reversible hepatic toxicity. Cytokine release syndrome occurred in 20% of patients, exclusively grade 1. These findings suggest that combining T-cell recruitment with a second costimulatory signal may produce substantial antitumour activity. The study is a small, non-randomised phase 1 trial with only 7.4 months of median follow-up, but the results are still very promising.

The ongoing phase 3 KLK2-comPAS trial is designed to investigate clinical benefit.

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