CTLA4 and cancer: As the mechanism of this protein is gradually revealed, many studies have disclosed its powerful suppressive role in regulating T cell activity, and a variety of CTLA-4 monoclonal antibodies, such as ipilimumab and tremelimumab, have been recommended by the US FDA for clinical trials and are moving towards clinical application in some cancers, suggesting that a major moment in cancer immunotherapy has emerged [20, 21].