Immune-checkpoint inhibitors (ICIs), including monoclonal antibodies against programmed cell death protein 1 (PD-1), programmed cell death-ligand 1 (PD-L1), and cytotoxic T lymphocyte-associated protein 4 (CTLA-4), have achieved great advances in cancer therapies for immunologically activated tumors (also called inflamed or hot tumors) across multiple cancer types20–23. This evidence concerns the gene PDCD1 and cancer.