CTLA4 and renal cell carcinoma: Numerous clinical trials have shown that ipilimumab, a fully human monoclonal antibody (Ab) directed against CTLA-4, has been successfully used as immunotherapy to treat many different types of cancers, including melanoma, renal cell carcinoma, prostate cancers, urothelial carcinoma, and ovarian cancer, and that the therapeutic effect correlates with selective depletion of Treg cells in the tumor microenvironment34,35.