DPP4 and plasma cell myeloma: Based on previous work showing that vildagliptin and saxagliptin were classified into the same category (Class 1) of DPP4 inhibitors34 and had non-negligible off-target effects on DPP8/9 activity35, we hypothesized that vildagliptin and saxagliptin-induced inhibitory effects on DPP8/9 were the causal factor for their anti-myeloma activity.