CTLA4 and cancer: By expressing immune checkpoint proteins such as cytotoxic T lymphocytes-associated protein-4 (CTLA-4), programmed cell death receptor 1 (PD-1), and programmed cell death ligand-1 (PDL-1), cancer cells can avoid the activation of a T lymphocyte-mediated immune response and survive in the immuno-suppressive niche [97,98].