IMMU-70. GLIOBLASTOMA DERIVED IL-8 INSTRUCTS IMMUNE CELL IDENTITY IN LATERAL VENTRICLE CONTACTING TUMORS

Abstract Adult IDH-wildtype glioblastoma (GBM) is an aggressive brain tumor with no established immunotherapy. Glioblastoma tumors that contact the ventricular-subventricular zone (V-SVZ) stem cell niche have especially poor clinical outcomes (PMC5771712, PMC5262526) and abnormal immune microenvironments filled with CD32+ HLA-DRhi macrophages that have displaced resident microglia (PMC10371245). Identifying the origin and role of these CD32+ macrophages is likely critical to developing successful GBM immunotherapies. Here, we present a mechanistic origin for these CD32+ cells as M_IL-8 macrophages. In ex vivo experiments with conditioned medium from primary human tumor cells, IL-8 was sufficient and necessary for tumor cells to instruct healthy macrophages, and inhibitory antibodies to IL-8 blocked the generation of CD32+ CD163+ M_IL-8 cells. Additionally, IL-8 protein was present in GBM tumor cells in vivo and especially common in tumors contacting the V-SVZ (p<0.0001, N=192 cores from 73 patients). Surface proteins CXCR1 and CXCR2, the primary receptors for IL-8, were detected on cells that were spatially separated from IL-8+ glioblastoma cells in tumors contacting the V-SVZ. These results suggest the hypothesis that glioblastoma-cell IL-8 instructs incoming CXCR1+ hematopoietic macrophages to adopt a suppressive M_IL-8 identity in V-SVZ-contacting GBM. Abundant HLA-DR (MHC II) observed on the CD32+ M_IL-8 cells closely matched the signature phenotype of cells in human tumors (PMC10371245) and contrasted with lower surface MHC II expression typically observed on human myeloid derived suppressor cells (PMC6608074). M_IL-8 cells might especially target CD4+ helper T cells required for effective cancer immunotherapy (PMC5312823). IL-8 and CD32+ macrophages should now be explored as targets in combination with GBM immunotherapies, especially for patients whose tumors present with radiographic contact with the V-SVZ stem cell niche. Some results here have been shared in a bioRxiv preprint by the these authors (PMC10996638).