CXCL12 and glioblastoma: In our studies, we observed that PMN-MDSCs expressed high levels of Csfr3, Ccr1, Cxcr2 and Cxcr4, whereas Cxcl12, the ligand for Cxcr4, was expressed preferentially in CD45− GBM endothelial cells, unraveling a previously unidentified mechanism for recruitment of immunosuppressive MDSC into the GBM microenvironment.