Like MDSCs, high concentration of tumor-infiltrating Tregs is associated with poor prognosis in many solid tumors.81 Tregs suppress T cell responses in large part by binding IL-2 with high affinity, thereby limiting IL-2 availability for effector cells.82 They also express CTLA-4 and produce immunosuppressive cytokines, including IL-10.81 Indeed, murine models indicate that CTLA-4 blockade selectively depletes Tregs in the tumor microenvironment via antibody-dependent cellular toxicity.83,84 This may be an important mechanism by which CTLA-4 blockade exerts anti-tumor effects. Here, CTLA4 is linked to neoplasm.