CD33 and glioblastoma: The MDSCs observed in the blood of patients with GBM consisted mainly of CD33+/CD15+/CD14−/HLA-DR− neutrophilic subset with very few CD33+/CD15−/CD14−/HLA-DR− negative lineage as well as CD33+/CD15−/CD14+/HLA-DR− monocytic subtypes [13, 29].