Immune checkpoint inhibition is a recently introduced, innovative form of cancer immunotherapy that aims to eliminate inhibitory costimulatory signals from T cells, mainly tumor-specific cytotoxic CD8+ T cells, via blockade of cytotoxic T-lymphocyte associated protein-4 (CTLA-4), and/or programmed death protein-1 (PD-1)/PD-ligand 1 (PD-L1) (32–34). Here, PDCD1 is linked to neoplasm.