ICOS and neoplasm: In addition to co-inhibitory immune checkpoint molecules, tumor-infiltrating Tregs also express TNFRs on the surface, such as glucocorticoid-induced TNFR-related protein (GITR), OX40, 4-1BB, inducible co-stimulator (ICOS), TNFR superfamily member 1B (TNFR2), and CD27.