CD226 and plasma cell myeloma: Chemotherapeutic drugs, including doxorubicin, melphalan and bortezomib, upregulate both the DNAX accessory molecule-1 (DNAM-1; CD226) ligand PVR (poliovirus receptor; CD155) and NKG2D ligands (MICA and MICB) on multiple myeloma cells presenting a senescent phenotype.