CTLA4 and neoplasm: Furthermore, in two other distinct syngeneic tumor models, blunted anti-tumor immunity was observed when FcγR-null animals were treated with either anti-CTLA-4 mIgG2b (clone 9D9) alone or in combination with an irradiated B16-BL6 tumor cell-based vaccine that secretes GM-CSF (GVAX).