TNFRSF9 and neoplasm: Bcl-xL and 4-1BB are two key regulators in the TRAF1 signaling pathway. TRAF1 has a prosurvival effect in CD8 T cells via the 4-1BB–mediated upregulation of Bcl-xL [14]. Bcl-xL, an antiapoptotic member of the Bcl-2 family, is involved in modulating the angiogenic phenotype of human tumor cells [15, 16].