Healthy Myeloid-Derived Suppressor Cells Express the Surface Ectoenzyme Vanin-2 (VNN2)

Study of human monocytic Myeloid-Derived Suppressor cells Mo-MDSC (CD14+ HLA-DRneg/low) has been hampered by the lack of positive cell-surface markers. In order to identify positive markers for Mo-MDSC, we performed microarray analysis comparing Mo-MDSC cells from healthy subjects versus CD14+ HLA-DRhigh monocytes. We have identified the surface ectoenzyme Vanin-2(VNN2) protein as a novel biomarker highly-enriched in healthy subjects Mo-MDSC. Indeed, healthy subjects Mo-MDSC cells expressed 68% VNN2, whereas only 9% VNN2 expression was observed on CD14+ HLA-DRhigh cells (n=4 p<0.01). The top 10 percent positive VNN2 monocytes expressed CD33 and CD11b while being negative for HLA-DR, CD3, CD15, CD19 and CD56, consistent with a Mo-MDSC phenotype. CD14+VNN2high monocytes were able to inhibit CD8 T cell proliferation comparably to traditional Mo-MDSC at 51% and 48% respectively. However, VNN2 expression on CD14+ monocytes from glioma patients was inversely correlated to their grade. CD14+VNN2high monocytes thus appear to mark a monocytic population similar to Mo-MDSC only in healthy subjects, which may be useful for tumor diagnoses. Myeloid-Derived Suppressor Cells (MDSC) are identified by upregulated expression of the cell surface ectoenzyme Vanin-2 in healthy subjects PBMC were isolated from fresh blood from three independent healthy donor by density centrifugation. CD14+ cells were isolated manually using CD14 microbeads (Miltenyi), and then stained with CD14 and HLA-DR antibodies. Mo-MDSC and CD14+ HLADR+ monocytes cells were sorted as CD14+ HLA-DR-neg/low (bottom 10%) and CD14+HLA-DR-high (top 10%) cells respectively. The sorted two populations were immediately frozen for RNA isolation and further microarray.