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. Author manuscript; available in PMC: 2010 Mar 1.
Published in final edited form as: Nat Rev Immunol. 2009 Mar;9(3):162–174. doi: 10.1038/nri2506

Figure 1. The origin of MDSCs.

Figure 1

Immature myeloid cells (IMCs) are part of the normal process of myelopoiesis, which takes place in the bone marrow and is controlled by a complex network of soluble factors that include cytokines such as granulocyte/macrophage colony-stimulating factor (GM-CSF), stem-cell factor (SCF), interleukin-3 (IL-3), FMS-related tyrosine kinase 3 (FLT-3), macrophage colony-stimulating factor (M-CSF) and cell-expressed molecules including Notch (not shown). Haematopoietic stem cells (HSCs) differentiate into common myeloid progenitor (CMP) cells and then into IMCs. Normally, IMCs migrate to different peripheral organs, where they differentiate into dendritic cells, macrophages and/or granulocytes. However, factors produced in the tumour microenvironment and/or during acute or chronic infections, trauma or sepsis, promote the accumulation of IMCs at these sites, prevent their differentiation and induce their activation. These cells exhibit immunosuppressive functions and are therefore known as myeloid-derived suppressor cells (MDSCs). MDSCs can also differentiate into tumor-associated macrophages (TAMs) within the tumour environment, which are cells that have a phenotype and function that is distinct from MDSCs.