CD34 and plasma cell myeloma: However, when we monitored MDSCs during the course of the treatment we observed a remarkably depletion of these cell populations in the group of patients that had vitamin D levels >15 ng/mL, while MDSC populations were broadly unchanged in the group with deficit of vitamin D. Lenalidomide has inhibited MDSC-mediated immunosuppression in multiple myeloma [51] and vitamin D was demonstrated to promote the differentiation of MDSCs into mature cells without suppressive activities [52], as this vitamin reduces the levels of CD34+ immature myeloid cells, which are precursors of MDSCs [29].