CD8A and neoplasm: In addition, the expression of PD-1 in CD8+T cells of irradiated primary tumor was increased in PD-L1 wt mice and more significantly elevated in PD-L1−/− mice (Figure 4E), but the expression of PD-1 was only obviously increased in the distal tumor of irradiated PD-L1−/− mice (Figure 4F).