IL6 Supports Development of an Immunosuppressive Microenvironment and Resistance to Therapy in Glioblastoma

The glioblastoma tumor-immune microenvironment (TIME) is an immunosuppressive barrier to therapy that encumbers glioblastoma responses to immune checkpoint inhibition (ICI). Immunosuppressive cytokines, protumor macrophages and myeloid cells, and exhausted T cells are all hallmarks of the glioblastoma TIME. In this study, we integrated spatial and single-cell analyses of patient-matched human glioblastoma samples before and after ICI treatment with genetic, immunologic, single-cell, and pharmacologic studies in preclinical models to show that interleukin 6 (IL6) neutralization reprograms the glioblastoma TIME to sensitize mouse glioblastoma allografts to ICI and radiotherapy. Rare human glioblastomas that achieved clinical responses to ICI had lower pretreatment IL6 levels compared with glioblastomas that did not respond to ICI. Diverse immunostimulatory gene therapies suppressed local IL6 levels in mouse glioblastoma allografts, and IL6 from glioblastoma cells and the tumor microenvironment was associated with reduced survival in preclinical models and in patients. IL6 blockade with a neutralizing antibody transiently sensitized mouse glioblastoma allografts to ICI by decreasing immunosuppressive regulatory T cells and increasing MHCII+ monocytes, CD103+ migratory dendritic cells (DC), CD11b+ conventional DCs, and effector CD8+ T cells. IL6 blockade plus ICI sensitized mouse glioblastoma allografts to immunostimulatory ablative radiotherapy. Together, these data suggest that IL6 signaling contributes to ICI resistance in glioblastoma and provides a combination treatment strategy that could be used for patients. SIGNIFICANCE: Integration of spatial and single-cell analyses of glioblastoma samples with immunologic, single-cell, and pharmacologic studies showed that IL6 neutralization reprograms the immune microenvironment to sensitize glioblastomas to ICI and radiotherapy.