Systemic accumulation of Tregs in tumor-bearing mice and cancer patients is associated with poor prognosis [338], Treg depletion in animal models allowed tumor control [339], while the blockade of Treg function with anti-CTLA-4 antibodies allowed tumor control in animal models [329,340,341] and in a subset of patients with advanced melanoma [342]. This evidence concerns the gene CTLA4 and cancer.