PDCD1 and neoplasm: In pancreatic cancer, an increased accumulation of CD8+ T cells in tumor tissue and close proximity to tumor cells correlate with a better survival [139,140,143]; however, many CD8+ T cells express checkpoint inhibitors, including PD1 and other inhibitory receptors, and in tumors, PD-ligand 1 (PD-L1) is detectable [136,138] (Figure 4).