Figure 2.

MDSC population could differentiate into TAMs, in tumor microenvironment, they suppress NK cells, CD8⁺ cells and other immune cells synergistically. The cytokines exist in tumor microenvironment mediate the interaction between TAMs and MDSCs with CSCs. TAMs activates NFκB and STAT3 pathways through TNF-α, IL-6 and TGF-β. In addition to IL-6, MDSCs utilize NO to activate STAT3 and NOTCH pathways. By means of these signal pathways, TAMs and MDSCs drive CSCs development, enhance the invasion and migration. CSCs, cancer stem cells; STAT, signal transducer and activator of transcription; TNF, tumor necrosis factor; NFκB; nuclear factor κB; IL, interleukin; MDSCs, myeloid-derived suppressor cells; TAMs, tumor-associated macrophages; TGF, transforming growth factor.