EXTH-68. SYSTEMIC NEUTRALIZATION OF IL6 SENSITIZES IDH-WILDTYPE GLIOBLASTOMA PRECLINICAL MODELS TO IMMUNE CHECKPOINT INHIBITION

Abstract

Abstract IDH-wildtype glioblastomas are resistant to immune checkpoint inhibition (ICI). Here we integrate spatial and single-cell approaches across paired human glioblastomas before or after ICI with functional studies in immunocompetent intracranial mouse glioblastoma models to reveal mechanisms and therapeutic vulnerabilities underlying glioblastoma resistance to ICI. Spatial proteomic and transcriptomic approaches were used to identify biochemical and gene expression programs underlying ICI response or resistance in paired human glioblastoma samples (n = 7). Intracranial SB28 glioblastoma allografts were implanted in C57BL/6J mice and treated with (1) convection enhanced delivery (CED) of AAV9 gene therapy vectors encoding cytokines that reprogram the tumor immune microenvironment (TIME) in other cancers (Il1b, Ccl4, Apoa1), (2) systemic anti-PD1, (3) local anti-IL6, (4) systemic anti-IL6, or (5) combination systemic treatment with anti-PD1 and anti-IL6. Histological, mass cytometry (CyTOF), and multiplexed cytokine assays were used to assess the glioblastoma TIME in response to treatment over time. Mice were monitored for survival and tumor growth was measured using intracranial bioluminescence. Human glioblastomas with radiographic responses to ICI had lower pre-treatment IL6 levels on spatial profiling than glioblastomas resistant to ICI. Intratumor IL6 was suppressed by all AAV9 cytokine conditions compared to AAV9-GFP in mice. Mouse survival was improved by combination systemic treatment with anti-PD1 and anti-IL6, but was not improved by either antibody alone, or by anti-IL6 CED. CyTOF revealed combination systemic therapy reprogrammed the glioblastoma TIME by increasing activated immune cell types such as MHCII+ monocytes, CD103+ migratory dendritic cells (DCs), CD11b+ conventional DCs, and effector CD8+ T cells, and by decreasing immunosuppressive Tregs. In summary, systemic anti-IL6 in combination with systemic anti-PD1 reprograms the glioblastoma TIME to sensitize preclinical models to ICI. These results provide mechanistic validation of findings from human glioblastomas that respond to ICI and shed light on a therapeutic vulnerability underlying the glioblastoma TIME.