TMIC-30. Tumor-specific response to armed-oncolytic herpesvirus targeting cDC1 DC-CD8 T cell axis in glioblastoma mouse models

Abstract Recent advances in immunotherapy have paved the way for the development of strategies to target solid tumors, such as glioblastoma (GBM), which are immunologically cold in nature. Potentiation of dendritic cells to activate naïve CD8 T cells against tumors is one such strategy that could further enhance the outcome of oncolytic virotherapy against GBM. To this end, we have developed an oncolytic herpes simplex virus armed with the cytokines mXCL1 and mFLT3L, named rQ1-XF. mXCL1 acts as a chemoattractant to recruit dendritic cells to the tumor microenvironment, while mFLT3L is critical for the expansion and maturation of recruited conventional type I dendritic cells (cDC1s) to uptake tumor-specific antigens. We tested rQ1-XF in four different murine GBM lines, including one genetically engineered mouse model (GEMM) expressing human EGFR. GBM cells infected with rQ1-XF successfully expressed and secreted mXCL1 and mFLT3L in conditioned media. Secretion of pro-inflammatory and immunogenic cell-death markers was also observed from the infected cells. Conditioned media from infected cells successfully expanded mature bone marrow-derived cDC1s (CD45⁺CD11c⁺CD11b⁻B220⁻) with increased expression of XCR1 and CD135, validating the functionality of the secreted mFLT3L. In vivo, mouse GBM models showed expansion of cDC1s in the tumor-draining lymph nodes three days post rQ1-XF administration. However, infiltration of activated (CD25⁺IFNγ⁺) CD8 T cells into the tumor microenvironment was observed only in GL261N4 and CT2A tumors, where CT2A also had an increased infiltration of NK-like T cells following rQ1-XF administration. Furthermore, rQ1-XF enhanced survival only for the GL261N4 and CT2A murine models but failed to do so in the 1620 GEMM murine model suggesting that the adaptive immune response in the GEMM tumor microenvironment was reduced. Interestingly, bulk mRNA sequencing revealed a cell-type-specific response to rQ1-XF compared to the parent oHSV, reflecting the differential outcomes observed in preclinical in vivo models.