TGFB1 and neoplasm: Although the mechanism behind MDSC generation, expansion, and suppressive function is not completely known, recent studies have suggested that MDSC accumulation is mediated by tumor-associated mediators, including granulocyte macrophage-colony stimulating factor (GM-CSF) [11], interleukin (IL)-1β [12], IL-6 [13], vascular endothelial growth factor (VEGF) [14] and transforming growth factor-β (TGF-β) [15].