PDCD1 and prostate carcinoma: In conjunction with our own finding that a potent MR-1 ligand and pembrolizumab can co-operate to enhance MR-1-dependent cytotoxicity against a prostate cancer cell line, this raises the possibility of rationally combining PD-1 blockade with prostate-directed (intraurethral or transrectal) administration of MR-1 ligands.