PDCD1 and neoplasm: Cytotoxic T lymphocyte antigen-4 (CTLA-4) receptor, programmed cell death-1 (PD-1) receptor, both expressed on the T cell surface, and the PD-1 ligands, PD-L1/L2, expressed on the APCs and the tumor cell surface, represent potential targets of the novel immuno-checkpoint inhibitors.