IMMU-06. SYSTEMIC MRNA VACCINES RESET IMMUNOGENICITY AGAINST DIFFUSE MIDLINE GLIOMA

Abstract BACKGROUND DIPG remains a uniformly fatal disease in dire need of new therapies. There are currently no systemic therapies with proven efficacy against these tumors. To overcome these barriers, we developed a systemic mRNA lipid particle (LP) vaccine that localizes to tumors and reticuloendothelial (RE) organs to modulate both innate and adaptive immunity against poorly immunogenic tumors like DIPG. OBJECTIVE We sought to assess whether RNA-LPs encoding for model antigens (e.g. H3K27M) would reprogram innate immunity and simultaneously elicit sustained adaptive immunity against diffuse midline glioma (DMG). RESULTS RNA-LP encoding for model antigens elicit massive recruitment of nearly all monocytes and lymphocytes to RE organs secondary to a danger response mediated by release of orchestrated cytokines (IL-12, TNF-α, IFN-α) and chemokines (CCL2, CCL4, CXCL9-10). This corresponds to increases in absolute numbers of activated DCs and T cells in the RE organs of mice and reprogramming the glioma tumor microenvironment in canines (pet dogs with spontaneous disease). In neonatal mice inoculated midline with established murine K2 gliomas, we observed that RNA-LP vaccines encoding for H3K27M (beginning at ~day 30) elicit significant long-term survivorship, which appears curative in the bulk of animals treated. While H3K27M specific constructs appeared superior, we observed improved survivorship with irrelevant mRNA species (i.e. pp65 and GFP) suggesting these tumors to be particularly sensitive to innate immune modulation. In mice with DMGs, we observed clinical symptomatology of edema/hydrocephalus followed by improvement in many animals suggesting pseudoprogression from intratumoral inflammation and remodeling. CONCLUSION RNA-LPs reprogram the tumor microenvironment of poorly immunogenic tumors in effect making them ‘hot.’ Treatment responses in murine models of advanced DMGs are encouraging. We are advancing a final RNA-LP formulation for FDA-IND submission and early phase clinical trials for DIPG through multi-institutional consortia.