PDCD1 and cancer: Based on the cancer immunosurveillance hypothesis postulating that evasion from immune control is an essential feature of cancer, immune checkpoint molecules including PD-1, PD-L1, and CTLA-4 were further studied (Brahmer et al., 2010; 2012; Pardoll, 2012; Topalian et al., 2012; Zitvogel et al., 2016a; Zitvogel et al., 2016b).