Immunotherapy with immune checkpoint inhibitors (ICIs), including anti-programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1) antibodies and anti-cytotoxic T lymphocyte-associated protein 4 (CTLA-4), were recently demonstrated to improve the clinical outcome of certain cancers.2 The gene discussed is CTLA4; the disease is cancer.