IMMU-72. TYPE I INTERFERON SIGNALING WITHIN GLIOBLASTOMA CELLS PROMOTES T-CELL EXHAUSTION AND RESISTANCE TO CHECKPOINT INHIBITORS

Abstract Glioblastoma (GBM) remains among the most fatal cancers with few treatment modalities and resistance to modern immunotherapeutic treatment paradigms including immune checkpoint inhibitors (ICI). ICIs neutralize the regulatory signals that disable T cells and have demonstrated remarkable efficacy against a variety of cancers, though not in GBM. The impotence of ICI in GBM has been linked to the tumor’s remarkable capacity to elicit T cell exhaustion, though the mechanism remains poorly understood. Chronic interferon (IFN) cytokine signaling is known to promote immunosuppression and Tex in several cancer types as well as resistance to ICI. However, the role of IFN in GBM has not been investigated despite evidence that IFN signatures exist within clinical samples of GBM. Syngeneic murine GBM cell lines CT2A and SB28 were utilized for in vivo and in vitro studies. Anti-mouse PD-1 and CD8 antibodies or PBS control were injected intraperitoneally. CRISPR editing was used to create validated knockouts (KO) of the type I IFN receptor (IFNAR1) in CT2A. Mice bearing IFNAR1 KO intracranial tumors have improved median survival (p < 0.05) and are exquisitely sensitive to checkpoint anti-PD-1 blockade (p < 0.05) with the majority of mice surviving. Furthermore, surviving mice reject the subsequent intracranial re-challenge with parental CT2A tumors compared to controls (p <0.05) suggesting central memory responses mediating rejection. We conclude that abrogation of Type I IFN signaling is sufficient to extend survival which is further enhanced by ICI. Work is ongoing to further elucidate the precise mechanism that mediates this response and to identify a therapeutic intervention that enables tumor-specific inhibition of the IFN pathway with preliminary work suggesting a CD8 T cell mediated response and reversal of the T cell exhaustion phenotype.