PDCD1 and neoplasm: The addition of immune checkpoint inhibitors to RT has been shown to enhance tumor response compared to controls across several mouse tumor models through reinvigoration of exhausted CD8+ TILs characterized by increased Ki67+ GzmB+ T-cells within the exhausted PD-1+ Eomes+ T-cell pool, increased CD8+ CD44+ TILs, and increased CD8+/Treg ratio [61, 77, 85].