TMIC-29. Neutrophil-Macrophage Crosstalk Drives Immunosuppression in Glioblastoma Microenvironment

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, hallmarked by a high degree of inter- and intratumoral heterogeneity, which we have shown is partially driven by tumor genotype. The myeloid compartment, which constitutes approximately 30-50% of GBM cell population, contributes to the substantial immunosuppressive tumor microenvironment (TME) lending to challenges for standard-of-care and emerging immunotherapies. Previous studies have primarily focused on elucidating the role of tumor-associated macrophages (TAMs) in the TME, with limited focus on other myeloid cell types, including neutrophils. However, recent research has suggested that neutrophils are emerging as a crucial player in brain tumor pathology. Their importance was further highlighted with our recent work showing compensatory neutrophil recruitment in response to macrophage targeting therapies, rendering them ineffective. In this study, we aim to investigate the tumor-genotype dependent roles of neutrophils in GBM. Our previous work has shown GBM subtype specific differential macrophage and neutrophil recruitment. Here, we show that MES-like tumors have higher infiltration of myeloperoxidase (MPO+) neutrophils as compared to PN-like tumors, and they predominantly localize in the hypoxic niche in the tumor core in both murine and human GBM. Further, in vitro bone marrow-derived neutrophil-tumor cell co-cultures show that neutrophils in hypoxic conditions release increased MPO via rapidly undergoing NETosis (neutrophil extracellular traps). Macrophages take up NET-derived MPO, which further promotes an immunosuppressive phenotype in macrophages by upregulating arginase1 expression. To better understand the biological significance of MPO in GBM progression in vivo, we generated tumors in MPO-ablated (MPO-/-) GEMMs using RCAS/Nestin Tv-a gene transfer system. As compared to wild type, MPO-deficient mice showed distinct TME with reduced infiltration of TAMs and extended survival in GBM-bearing mice. Together, our study indicates that NETs are actively involved in TME modulation and suggests their potential as a therapeutic target for glioblastoma.