CTLA4 and cancer: While chemotherapy primarily targets cancer cells to inhibit the cell cycle, ICIs consist of antibodies directed against programmed death 1 (PD-1), programmed death-ligand (PD-L1), or cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), thus intercepting crucial regulatory signals that suppress immune responses within the tumor microenvironment (4–7).