CTLA4 and cancer: Immune checkpoint molecules expressed on the surface of immune cells (for example, CTLA-4 on T cells) regulate cell activity by transducing stimulatory or inhibitory signals upon ligation with cognate molecules (for example, CD80/B7-1 expressed on the surface of antigen presenting cells), and many cancer therapies target inhibitory immune checkpoint molecules to achieve T cell (re)activation and tumor cell killing (for example, by blocking CTLA-4 on T cells) [70].