PCNA and neoplasm: Given that IR alone led to reduced collagen deposition, increased cleaved caspase-3+ apoptotic cells, and reduced numbers of PCNA+ cells compared to non-irradiated tumors in the absence of anti-PD-1 treatment (Supplementary Fig. 5), it appears that the combination of irradiation and PD-1 blockade exerts a synergistic effect by facilitating infiltration of anti-PD-1-activated immune cells into the tumor microenvironment.