TNFSF9 and neoplasm: Notably, we did not detect any expression of CD137 and PD-1 molecules and their respective ligands CD137L and PD-L1/PD-L2 on the surface of ID8 ovarian cancer cells (data not shown), excluding the possibility that inhibition of ID8 tumor growth in vivo is directly mediated by the anti-CD137 plus anti-PD-1 mAbs.