PDCD1 and cancer: The aim of immune checkpoint blockade is to restore and strengthen the anticancer response by suppressing the intrinsic immuno-inhibitory pathways, which are commonly utilized by tumor cells to develop immune resistance.35 Enormous efforts have been invested to exploit the efficacy of treating cancer patients with fully-humanized monoclonal antibodies against two of the most-studied immune checkpoint regulators – cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and programmed cell death protein-1 (PD-1) or its ligand PD-1-ligand 1 (PD-L1).