Given that Tbet is an important regulator of Treg stability and function during Th1 immunity,43 that ICOS is an important survival factor for tumor-infiltrating Tregs,44 and that CD25, CTLA-4, and CD39 are all involved in Treg-mediated immunosuppression,45 our results suggested that 9D9 reduces the activation, stability, and function of Tregs in MCAprog tumors. Here, ICOS is linked to neoplasm.