TNFRSF18 and neoplasm: Treatment with agonist anti-GITR mAb leads to enhanced vaccine-induced and endogenous effector T cell responses and tumor rejection in multiple murine tumor models, and is associated with a marked reduction in Treg frequency within the tumor microenvironment, though the exact mechanism(s) by which GITR ligation modulates Tregs remains controversial (115, 130–133).