CTLA4 and cancer: Immune checkpoints such as cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), and the programmed death protein-1 (PD-1)/programmed death ligand-1 (PD-L1) signaling axis are co-inhibitory pathways that physiologically prevent inappropriate activation of immune responses, but are often upregulated by cancers to prevent or dampen T-cell activation and thus suppress antitumor activity (4).