CD226 and plasma cell myeloma: Chemotherapeutics like melphalan, etoposide, and doxorubicin, or the proteasome inhibitor bortezomib trigger the upregulation of activating ligands for the receptors NKG2D and DNAX accessory molecule-1 (DNAM-1) on multiple myeloma cells, thus sensitizing them to NK cell-mediated killing [30].