EXTH-76. REDIRECTING STROMAL CELLS TO IGNITE ANTI-TUMOR IMMUNITY AGAINST GLIOBLASTOMA

Abstract BACKGROUND The dismal prognosis of high-grade gliomas demands novel treatment approaches. Through the development of a novel mRNA lipid particle aggregate (RNA-LPA) vaccine, our lab has shown anti-tumor efficacy in preclinical murine studies and promising immunological responses in canine glioma models and human studies (Cell. 2024 May 9;187(10):2521-2535.e21). The translational potential necessitates further investigating the immune activation mechanism to allow greater applicability of this therapy in the future. OBJECTIVE We sought to unravel mechanistic cross-talk for immune initiation following intravenous administration of RNA-LPAs. METHODS We used Ai14 reporter mice to determine RNA-LPA transfected cellular subsets and dual reporter mice to assess cellular infiltration into murine glioma models. Murine gliomas were generated via implantation of K2 or KR158b-luc cell lines. RESULTS Following intravenous administration, we found fibroblastic reticular cells in secondary lymphoid organs take up RNA-LPAs. We show that FRCs have direct contact with antigen presenting cells and mediate release of full-length proteins following RNA-LPA transfection. Similar to the periphery, there is transfection of stromal cells in the brain tumor microenvironment (TME) and recruitment of infiltrating leukocytes. In response to RNA-LPAs, transfected stromal cells release type I interferon (IFN-I), which is requisite for anti-tumor efficacy. IFN-I mediates upregulation of CD69 on lymphocytes leading to sequestration following co-localization with RNA-LPAs. IFN-I is necessary for LFA-I expression on T cells, which is important for T cell trafficking across the blood-brain barrier. In preclinical models to track antigen specific immunity, we find systemic RNA administration elicits an increase in tumor reactive T cells with decreased S1P1 expression suggestive of a ‘locked-in’ response within the TME. CONCLUSION While stromal cells are regulatory niches in glioblastoma ecosystems, we show they can be leveraged for immunologic cross-talk that facilitates T cell recruitment, trafficking and sequestration in the TME critical for immunologic reprogramming and long-lasting immunotherapy.