CTLA4 and cancer: Indeed, the blockage of immune checkpoints, including programmed cell death protein 1 (PD-1), programmed cell death 1 ligand 1 (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), improves clinical outcomes in subsets of patients with cancers previously considered to be essentially untreatable [2–4].