PDCD1 and neoplasm: Immune checkpoint blockade (ICB) therapy is designed to target immune checkpoint receptors on tumors and immune cells, such as programmed cell death-1 (PD-1), programmed death ligand-1 (PD-L1) or cytotoxic associated lymphocyte antigen-4 (CTLA-4), to restore CD8+ T cell-induced anti-tumor immune activity (2, 3, 60).