IL-8 Reprograms Monocyte-derived Macrophages into M2-like States in Human Glioblastoma

Glioblastoma (GBM), the most common primary brain tumor in adults, remains incurable and has not yet benefitted from immunotherapies.  Microglial and hematopoietic macrophages are the most abundant immune cells in GBM and play contrasting roles in the disease. Our prior studies revealed a signature of CD32 and HLA-DR protein expression and STAT3 signaling in hematopoietic macrophages associated with poor GBM patient survival and neural stem cell niche contact (PMC10371245). We hypothesized that GBM cells may secrete factors to remodel the cellular microenvironment and generate this signature macrophage subset from myeloid cells.  In a series of experiments, 1) IL-8 was the primary cytokine expressed in vivo and ex vivo by human GBM cells (immunohistochemistry, cytokine arrays), 2) IL-8 was sufficient to instruct healthy monocytes to adopt the CD32⁺ HLA-DR⁺ signature of in vivo GBM macrophages (spectral flow cytometry, mass cytometry), and 3) IL-8 was required for primary GBM cell supernatant to polarize healthy macrophages into CD163⁺ CD206⁺ CD32⁺ HLA-DR⁺ M2-like cells in ex vivo 6-day cultures (α-IL-8 blocking antibodies, spectral flow cytometry). This ex vivo system will now be used to test the function of the GBM signature macrophages and to explore targeting of IL-8 to improve GBM therapy.