The generation and activation of myeloid-derived suppressor cells in multiple myeloma.

Multiple Myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells, which are predominantly localized in the bone marrow. The presence of an immunosuppressive bone marrow microenvironment and dysfunction of immune cells are both described in MM patients; however the mechanisms controlling this immunosuppression are not well defined. Recently, a heterogeneous population of immature myeloid cells, the so called myeloid-derived suppressor cells (MDSCs), were identified to be present and active in MM (Van Valckenborgh et al, Leukemia. 2012;26(11):2424-8. E-pub April 23). MDSCs are thought to promote cancer progression by their T-cell suppressive capacity, however in MM little is known about the generation and activation of these MDSCs. In this study we investigated the effects of the myeloma microenvironment on the total MDSC population using the 5T33MM mouse model.