DPP8 and plasma cell myeloma: In order to determine whether DPP8 or DPP9 is particularly responsible for the anti-myeloma activity of 1G244, we employed small interfering RNAs (siRNAs) specific to either DPP8 or DPP9, due to unavailability of specific chemical inhibitors to either DPP8 or DPP9 since these two DPPs closely resemble each other in structure39,40.