CTLA4 and cancer: Cancer cells are able to block immune cell activity by exposing on their surface the programmed cell death ligand (PDL-1, CD274) that interacts with receptors, called immune checkpoints, present on the surface of T-cells, like the B- and T-lymphocyte attenuator (BTLA), the programmed death protein 1 (PD-1), and the cytotoxic T-lymphocyte-associated protein 4 (CTLA4) [17].