DPP4 and malignant mesothelioma: In the one follow-up study of cancer under biological therapy that we know of, a phase I trial with humanized anti-CD26 mAb [120], serum sCD26/DPP4 titers were reduced following YS110 administration in patients with solid-tumor renal cell carcinoma (RCC), malignant mesothelioma (MM), and one urothelial carcinoma (UTC) and later gradually recovered until the next infusion.