Immune checkpoint inhibitors [e.g., programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4)] and chimeric antigen receptor (CAR)-T-cell therapies have made significant progress in extending cancer patients’ lives.3 The gene discussed is PDCD1; the disease is cancer.