TNFRSF9 and cancer: Ligation of co-stimulatory T cell receptors, such as OX40 (Tnfrsf4, CD134), 4-1BB (Tnfrsf9, CD137) and GITR (Tnfrsf18, CD357), with agonist mAbs has been shown to augment the anti-tumor immune response in numerous cancer models [12].