Myeloid-derived suppressor cells and tumor growth

The tumour microenvironment is a heterogeneous and complex environment, characterized by the presence of malignant cells and non-neoplastic cellular elements, including immune and stromal cells, as well as blood vessels. Tumour progression is associated with profound alteration of myelopoiesis, which gives origin to myeloid-derived suppressor cells (MDSCs) from immature myeloid progenitors. MDSCs accumulate in the blood, secondary lymphoid organs, bone marrow, and at tumour sites, as has been observed in different cancer patients and experimental tumour models in response to pro-inflammatory cytokines and growth factors released by tumour. Upon recruitment, MDSCs exert various immunosuppressive effects to block innate and adaptive anti-tumour responses. This chapter reviews the origin and features of MDSCs, as well as the immunosuppressive mechanisms used by these cells in order to promote tumour progression.