CTLA4 and neoplasm: CTLA-4 inhibitors efficiently bind CTLA-4 molecules, reducing the number of CTLA-4 molecules bound to B7 molecules, and inhibiting T cell activation by reducing the production of negative regulatory signals, enhancing T cell activation and the growth and infiltration of tumor-differentiated T cells in the tumor microenvironment, thereby achieving antitumor effects of the immune system.