The Role of Myeloid-Derived Suppressor Cells in Immunosuppression in Brain Tumors

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells with impaired ability to differentiate into macrophages, granulocytes, or dendritic cells. MDSCs have been identified in peripheral blood and tumor microenvironment of glioma-bearing mice and glioblastoma (GBM) patients. MDSCs together with M2-polarized microglia/macrophages play a crucial role in suppression of innate and adaptive antitumor immunity. MDSCs utilize multiple of mechanisms to suppress T cell function; however their interactions with other myeloid cell have not yet been fully elucidated. In this chapter, we describe the origin of the myeloid population, the mechanism of activation and expansion of MDSCs, suppressive mechanisms mediated by MDSCs, and the role of MDSCs in GBM development, with a primary focus on potential therapeutic strategies targeting MDSCs in GBM.