TMIC-83. ABERRANT EGFR ACTIVATION SUPPORTS ENHANCED TUMOR-MYELOID CROSSTALK AND IMPAIRS EFFECTOR T CELL INFILTRATION AND FUNCTION IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is known to display a highly suppressive tumor immune microenvironment (TIME) dominated by myeloid cells with low T cell infiltration. Aberrant epidermal growth factor receptor (EGFR) activation is observed in ~50% of GBM patients via amplification and the constitutively active EGFRvIII variant, however the impact of EGFR activation on the brain TIME and T cell-mediated anti-tumor immunity remains poorly understood. Single cell transcriptomic and receptor-ligand interaction analyses of paired newly diagnosed GBM tumor and intratumoral CD45+ immune cells revealed increased crosstalk between EGFR activated tumors and EGFR ligand-expressing tumor-associated myeloid cells. Therefore, a novel orthotopic murine EGFRvIII-expressing glioma model wherein the mEGFRvIII gene is under a tetracycline-off system (MADR-mEGFRvIII) was leveraged to identify how EGFR signaling impacts overall TIME composition and the phenotype of intratumoral and systemic T cells in vivo. Temporal flow cytometric immunophenotyping following tumor or mock (saline) implantation identified no significant shift in T cell infiltration within the brain or cervical lymph nodes (cLNs). In contrast, one week of doxycycline-mediated genetic EGFR ablation conferred a significant survival benefit and was associated with enhanced intratumoral T cell infiltration as well as diminished tumor-associated F4/80+ myeloid cells compared to vehicle treated animals. Further characterization revealed genetic EGFR ablation enhanced recruitment of CXCR3+, TNFα+, and TIGIT+ CD4 T cells to the tumor, while the prevalence of these populations contracted in CD4 and CD8 T cells within the draining cLNs. In vitro, pharmacologic EGFR inhibition enhanced antigen-specific Pmel-1 T cell killing of gp100-expressing MADR-mEGFRvIII tumor cells and was associated with increased IFNγ secretion by ELISA. Collectively, our work demonstrates that aberrant EGFR signaling promotes an immunosuppressive brain TIME with reduced T cell infiltration potentially via tumor-myeloid signaling. Targeting this oncogenic axis may therefore reprogram the TIME and directly enable enhanced trafficking of effector T cells to the tumor.