TCR-Based Therapy Directed against Kallikrein-Related Peptidase 4 Is Safe and Effective against Prostate Cancer

The efficacy of most immunotherapies for prostate cancer is limited by poor tumor immunogenicity as evidenced by minimal T-cell infiltration. Treatment with T cells engineered to express T-cell receptors (TCR) targeting prostate-specific antigens offers a potential solution by bypassing endogenous T-cell repertoire limitations. Through differential gene expression analysis, we have identified kallikrein-related peptidases 2, 3, and 4 (KLK2, KLK3, and KLK4) and homeobox B13 (HOXB13) as strictly prostate lineage-specific genes with high expression in prostate cancer and no expression in healthy tissues of risk. Naturally processed peptides derived from these antigens were identified, enabling T-cell enrichment using peptide-MHC multimers. High-avidity T cells targeting these antigens were isolated from allogeneic HLA-mismatched donors. After screening for on-target tumor specificity and absence of off-target reactivity, TCRs recognizing KLK4 in HLA-A*02:01 and KLK3 in HLA-B*35:01 were sequenced and further tested. TCRs were expressed in T cells through TCR gene transfer and TCRs with best performance were selected. Using combinatorial peptide library scanning, the cross-reactive potential of the KLK4-A2 and KLK3-B35 TCRs was analyzed. The KLK3-B35 TCR exhibited cross-reactivity against two additional peptides derived from LOXHD1 and CDH23, with broad tissue expression, and was therefore excluded. The KLK4-A2 TCR was highly specific for the KLK4 peptide. Further testing confirmed effective cytotoxic killing potential of KLK4-A2 TCR in vitro and in vivo, underscoring its therapeutic potential. These findings highlight the promise of the KLK4-A2 TCR for prostate cancer immunotherapy and demonstrate that prostate-specific antigens can be effectively targeted using TCR gene transfer strategies.