An agonistic antibody targeting GITR was shown to attenuate the activity of Treg cells, reduce their numbers, decrease their stability in tumors, and promote tumor regression in mice,818 particularly when combined with treatment with CTLA-4 or PD-1 inhibitors.819–821 Similar to CTLA-4 or PD-1 blockade, GITR ligation also improved the functions of Teff cells.822 In addition, OX40, another TNF receptor family member, showed similar patterns of expression and function to GITR. This evidence concerns the gene TNFRSF18 and neoplasm.