Functional diversity of myeloid-derived suppressor cells: The multitasking hydra of cancer

Myeloid-derived suppressor cells (MDSCs) are immature suppressive cells found in tumors and immunological niches. In this article, we highlight the ability of MDSCs to promote IL-17–producing T cells (Th17) and regulatory T cells in addition to suppressing cytotoxic T cells in different tumor models. These interactions between MDSCs and T cells support tumor growth because IL-17 is tumorigenic in many cancer types and regulatory T cells suppress antitumor T cells. Besides T cells, MDSCs promote regulatory B cells and suppress overall B cell function; however, tumor-evoked regulatory B cells also regulate MDSC function, suggesting cross-regulation between MDSCs and B cells. These multiple functions shed light on how MDSCs dysregulate several arms of host immune response. Moreover, MDSCs promote tumor cell survival and angiogenesis to support tumors. Therefore, the multifunctionalfeature of MDSCs make them attractive immunotherapeutictargets.