CTLA4 and cancer: Immune checkpoint blockade constitutes one of the most widely used immunotherapeutic modalities, aiming at three significant molecular targets: (i) the programmed death-ligand 1 (PD-L1), presented on the surface of cancer cells and antigen-presenting cells (APCs), (ii) the programmed cell death protein (PD-1) on the surface of lymphocytes, and (iii) the cytotoxic T-lymphocyte associated protein-4 (CTLA-4) on the surface of regulatory T cells (Tregs).