DPP4 and plasma cell myeloma: Namely, epigenetic modification with isoform-selective (class I or class IIb) HDACi not only shows anti-myeloma activity in itself but also acts as a chemosensitizer by resensitizing CD26neg myeloma cells or those with CD26 antigen loss to CD26mAb, thereby eliciting superior anti-myeloma cytotoxicity that may lead to restore the refractoriness to mAb in RRMM.