CTLA4 and cancer: Monoclonal antibodies have been developed against PD-1/PD-L1 (e.g., pembrolizumab, nivolumab, tezolizumab, aurumab and durvalumab) and CTLA-4 (e.g., ipilimumab and tremelimumab), and their clinical application has launched a new era of cancer treatment [11, 12].