CTLA4 and neoplasm: For example, the tumor and thesurrounding tissue can reduce the penetration of T cells into the tumor site,reduce granzyme B activity, suppress death receptor CD95 expression by T cells,and induce anergy of activated T cells by enhancing the expression of theinhibitory receptors CTLA-4 and PD-1 (the so-called immune checkpoints) on theT-cell surface [87].