CTLA4 and cancer: Monoclonal antibodies (mAbs) against 3 of these immune checkpoints; cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) (e.g. ipilimumab), programmed cell death protein 1 (PD-1) (e.g. pembrolizumab and nivolumab) and its ligand PD-L1 (e.g. atezolizumab, durvalumab and avelumab) are now standard and effective anticancer agents serving as the backbone of cancer therapy for a wide range of cancer types (1, 4–6).