S100A9 a new marker for monocytic human myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of cells that negatively regulate the immune response during tumour progression, inflammation and infection. Only limited data are available on human MDSC because of the lack of specific markers. We have identified members of the S100 protein family S100A8, S100A9 and S100A12 specifically expressed in CD14+ HLA-DR-/low MDSC. S100A9 staining in combination with anti-CD14 could be used to identify MDSC in whole blood from patients with colon cancer. An increase in the population of CD14+ S100A9high MDSC was observed in the peripheral blood from colon cancer patients in comparison with healthy controls. Finally, nitric oxide synthase expression, a hallmark of MDSC, was induced in CD14+ S100A9high upon lipopolysaccharide/interferon-? stimulation. We propose S100 proteins as useful markers for the analysis and further characterization of human MDSC.