TMIC-120. Investigating EGFRvIII mRNA LNP vaccine-induced re-programming of the GBM TME using the 10x Genomics Visium HD platform

Abstract Glioblastoma (GBM) is a lethal brain tumor refractory to standard therapies, highlighting the need for alternative treatments. Immunotherapies, particularly cancer vaccines targeting neoantigens, offer a compelling approach to enhance anti-tumor immunity. To this end, we developed a preclinical mRNA lipid nanoparticle (LNP) vaccine designed to target human EGFRvIII, a GBM-specific oncogenic variant, and evaluated its impact on survival in an EGFRvIII-driven tumor model, utilizing EGFRvIII-OE/CDKN2A-KO/PTEN-KO syngeneic mice. Following vaccine administration on days 7, 10, 14, 21, and 36 post-tumor cell implantations, vaccinated mice showed complete tumor clearance by day 30, whereas controls exhibited significant tumor burden. To elucidate the vaccine’s therapeutic mechanisms and its impact on the tumor microenvironment (TME), we performed Visium HD spatial transcriptomic profiling on coronal brain sections from four mouse groups: buffer control and luciferase vaccine at day 21, and EGFRvIII mRNA-LNP vaccine-treated tumors at days 21 and 32. Using an unsupervised deconvolution approach, we identified 29 distinct transcriptional programs localized within the tumor lesion, comprising diverse glial, myeloid, and lymphocyte signatures. Notably, we observe a significant enrichment of pro-inflammatory and antigen-processing tumor-associated macrophage populations, alongside activated cytotoxic T-cells within the EGFRvIII vaccine-treated tumors compared to controls. Furthermore, a differential neighborhood analysis between the EGFRvIII vaccine-treated and control samples revealed a close spatial association of these activated immune signatures, indicating a vaccine-induced re-programming of the TME to facilitate a coordinated anti-tumor response. Our results thus demonstrate the EGFRvIII mRNA-LNP vaccine as a potent therapeutic that drives GBM regression in preclinical models by modulating the TME, paving the way for its clinical translation.