CTLA4 and neoplasm: Using H11-Cy5, we confirmed higher levels of CTLA-4 expression on intratumoral Tregs than on splenic Tregs (Fig. 2D) as a possible mechanism for the tumor-specific depletion of Tregs.45 Using FcgR-deficient and complement-deficient mice, we demonstrate that Treg depletion is mediated by FcgR.