CD33 and neoplasm: Myeloid-derived suppressor cells (MDSC), a heterogenous population of CD11b+ CD33+ HLA-DR- myeloid cells found in the peripheral blood and tumor mass of GBM patients, have also emerged as a potential target for sensitizing the tumor microenvironment to immunotherapy given their myriad immunosuppressive functions associated with poor prognosis (Almand et al., 2001; Alban et al., 2018).