PD ligand (PD-L1) binding or cytotoxic T lymphocyte-associatedprotein-4 (CTLA-4) binding to CD80 (B7-1) activates tumor immune responses, but only about 20–30% of patients receive long-lasting effects with a single immunotherapy drug because cancer cells use a variety of ways to block the immune response and lead to immune escape. The gene discussed is CTLA4; the disease is cancer.