Although, higher doses of RG2833 at 5.0 μmol/L or entinostat at 500 μmol/L further reduced the viability of myeloma cells, these doses did not induce greater CD26 expression in myeloma cells anymore (Fig. 1C; Supplementary Fig. S1) Collectively, HDACi by both broad and isoform-selective inhibitors exposure-time dependently as well as dose-dependently induced the upregulation of CD26 protein expression on myeloma cells. This evidence concerns the gene DPP4 and plasma cell myeloma.