In line with a slight downregulation of HLA-DR on circulating monocytes of glioblastoma patients observed in the present study, it has previously been reported that patients with newly diagnosed glioblastoma show an increased number of circulating CD33+ HLA-DR− myeloid-derived suppressor cells (MDSCs) comprised of immature, monocytic and neutrophilic subsets [21]. Here, CD33 is linked to glioblastoma.