CTLA4 and neoplasm: In addition, CTLA-4 inhibitors can also reduce the number of regulatory T cells (Tregs) that highly express CTLA-4 in the tumor microenvironment by blocking CTLA-4, thereby relieving the immunosuppressive effects of Treg cells and promoting the activation and proliferation of effector T cells.222–225 These two types of inhibitors target different immune checkpoint proteins, but their mechanisms of action are similar, both working by blocking immune checkpoint proteins to activate the immune system.