Immune checkpoint inhibitors such as cytotoxic T lymphocyte antigen‐4 (CTLA‐4), programmed cell death protein 1 (PD‐1), and PD‐1 ligand (PD‐L1) antibodies have shown significant antitumor activity in several human cancers (Le et al., 2015a; Reck et al., 2016; Wolchok et al., 2013) . Here, PDCD1 is linked to cancer.