PDCD1 and neoplasm: The blockage of the protein-protein interaction (PPI) between programmed cell death protein 1 (PD-1) and programmed cell death 1 ligand 1 (PD-L1) can reactivate the effector functions of T cell and eliminate tumor phenotypes with significant PD-L1 expression (Gatalica et al., 2014; Patel and Kurzrock, 2015; Sharma and Allison, 2015a,b).