CD38 and neoplasm: Several cellular elements of the bone marrow (BM) microenvironment in MM patients contribute to the immune evasion, proliferation, and drug resistance of MM cells [4,5,6], including myeloid-derived suppressor cells (MDSCs), tumor-associated M2-like, “alternatively activated”, macrophages, CD38+ regulatory B-cells (Bregs), and regulatory T-cells (Tregs) [4,5,6] (Figure 1A).