Tregs express CTLA-4, PD-1, inducible T-cell costimulator (ICOS), glucocorticoid-induced TNFR-related protein (GITR), tumor necrosis factor receptor 4 (OX40), vascular endothelial growth factor receptor-2 (VEGFR2), chemokine receptor 4 (CCR4) and CCR8 receptors, which can mediate tumor immunosuppression (128); and participate in co-stimulatory receptors on the surface of APCs to modulate APC activity, leading to weaken or abrogated signals from APC to naive/effector cells. Here, ICOS is linked to neoplasm.