Immune checkpoint, a mechanism that regulates the normal activation of the immune system, inhibit the function of effector T cells upon encountering cancer cells containing ligands, such as programmed cell death ligand-1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), thereby promoting the escape of cancer cells from immune surveillance [92]. The gene discussed is CTLA4; the disease is cancer.