For example, immune checkpoint blockade is a hot therapeutic strategy, such as programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) inhibitors exhibiting a favorable performance in cancer immunotherapy (Borghaei et al., 2015; Herbst et al., 2016; Jain et al., 2018). Here, PDCD1 is linked to cancer.