VTCN1 and glioblastoma: In GBM, B7-H4 expression on tumor cells and tumor-associated macrophages (TAMs) results in the maintenance of glioma progenitor cells and the formation of an immunosuppressive tumor microenvironment [29] while miRNA-21 contained in exosomes produced by TAMs increases the production of PDCD4, SOX2, STAT3, IL-6, and TGF-β1 in GBM cells that engenders TMZ resistance [112].