One mechanism for tumor-induced immunosuppression is based on the expression of immune checkpoint molecules acting as receptor/ligand, including PD-L1/PD-1, galectin-9/TIM-3, IDO1, lymphocyte-activation gene 3 (LAG-3), and cytotoxic T-lymphocyte-associated protein 4 (CTLA4), which can inhibit the activation of effector lymphocytes. The gene discussed is CTLA4; the disease is neoplasm.