Immune checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA4) and programmed cell death protein 1 (PD1) and its ligand-programmed death ligand 1 (PDL1) axis appear to require a pre-existing, primed effector anti-tumor CD8+ T cell infiltration for optimum therapeutic effect (28, 40). The gene discussed is PDCD1; the disease is neoplasm.