TNFSF10 and cancer: In contrast, early research indicated that TRAIL, the ligand for both DR4 and DR5, and its recombinant derivative, recombinant soluble APO2L/TRAIL, were safe and did not cause systemic toxicity, while effective at inducing apoptosis in cell lines derived from a wide variety of cancers and promoting the regression of xenograft tumors in immunodeficient mice [16, 17].