PDCD1 and neoplasm: In the present study, the addition of αCD8 to TI/PDT/αPD-1 leads to rapid tumor regrowth and wholly removes the beneficial effect of PDT and of PD-1 inhibition after TI for both AB12 tumors (TI/PDT/αPD-1 vs. TI/PDT/αPD-1/αCD8; P < 0.001; Fig. 7E) and AE17O tumors (TI/PDT/αPD-1 vs. TI/PDT/αPD-1/αCD8; P = 0.032; Fig. 7F).