Myeloid-derived suppressor cells and tumor immune escape.

Myeloid-derived suppressor cells(MDSCs) are heterogeneous cells derived from myeloid progenitor cells and immature myeloid cells(IMCs) in bone marrow;they are the progenitors of dendritic cells(DCs),macrophages and granulocytes.MDSCs proliferate in the blood,spleen,and tumor tissues in tumor-bearing mice and in the peripheral blood and tumor tissues in patients with cancer.MDSCs prevent tumors from attacks by body immunosurveillance and promote tumors progression through inhibiting both innate and adaptive antitumor immunity by a variety of pathways;they are recruited to the peripheral tissues from bone marrow and exert their inhibitory effects on antitumor immunity after activation in peripheral tissues.Chronic inflammation-related cytokines produced by tumors play crucial roles in the recruitment and activation of MDSCs.Progress has been made in antitumor therapies targeting MDSCs.But it has only been 10 years since the discovery of MDSCs,and many questions remain to be answered through experimental and clinical investigations.This review focuses on progress in MDSCs and its subsets,the recruitment and activation of MDSCs,the mechanisms of MDSCs-mediated immunosurveillance and antitumor treatment targeting MDSCs.