CTLA4 and cancer: CTLA-4 binds with B7 to represses T cells at the G1 phase and decreases the expression of interleukin-2 (IL-2) and the IL-2 receptor.[5] CTLA-4 can also induce Fas cell surface death receptor-independent apoptosis of activated T lymphocytes, and then further restrain T cells.[6] It has been proposed that, during the development of malignancy, CTLA-4 may attenuate the T-cell activation threshold, thereby decreasing the antitumor response and conferring susceptibility to cancer.