CTLA4 and cancer: Immune checkpoint inhibitors (anti-PD-1/PD-L1 and anti-CTLA-4 mAbs), dendritic cell (DC)-based vaccines, cytokine-induced killer (CIK) cells, cytotoxic T lymphocytes (CTLs) and CAR-engineered T cells are approved as monotherapies or combination treatments for different types of cancer [29].