CTLA4 and neoplasm: More recently, a third anti-mouse Ctla-4 mAb, 9D9, was reported to have therapeutic effect in tumor-bearing mice and cause local depletion of Treg cells in tumor microenvironment.10 We therefore set out to test all three commercially available anti-mouse Ctla-4 mAbs that had been shown to induce tumor rejection for their ability to block the B7-Ctla-4 interaction under physiologically relevant conditions.