CTLA4 and neoplasm: Mouse and human FcγR systems significantly differ,53 and although the role of Fc effector function in the antitumor activity of mouse anti-CTLA-4 antibodies has been clearly demonstrated in mouse tumor models,27,28,29,30,31,32,37 its importance in patients is controversial,34 especially because human anti-CTLA-4 antibodies fail to induce Fc-dependent depletion of intratumoral Tregs.33