Optimized Recombinant Vaccinia Virus as a Potential Immunomodulatory Tool in Glioblastoma

Glioblastoma is a highly aggressive and currently incurable brain tumor. It is characterized by a pronounced immunosuppressive tumor microenvironment (TME), which limits the potential of any immunotherapy options. Targeted therapy with recombinant oncolytic viruses can modulate the properties of the TME, overcome the glioblastoma-mediated immunosuppression, and evoke an antitumor immune response. Recombinant vaccinia viruses are suitable for these tasks because they have a favorable safety profile and can be modified with cDNA of immunomodulatory factors for their expression in tumor cells. The aim of the study was to evaluate the impact of the recombinant vaccinia virus strain carrying the interleukin-15 cDNA (LIVP-mIL15) on the TME in the GL261 experimental glioma model. Materials and Methods. Using intravital fluorescence microscopy, in vivo bioluminescence imaging, brain magnetic resonance imaging, and flow cytometry of immune cell subpopulations, we evaluated the ability of the novel LIVP-mIL15 strains (LIVP-mIL15-RFP and LIVP-mIL15-FLuc) to affect GL261 glioma cells in 3D spheroids and in the syngeneic orthotopic GL261 glioma in C57BL/6 mice, as well as the dynamics of TME changes induced by immunotherapy. Results. The recombinant vaccinia virus strain LIVP-mIL15-RFP is capable of efficiently infecting GL261 glioma cells in 3D spheroids formed during cultivation in non-adherent plates and of inducing selective transgene expression in orthotopic glioma cells following a single stereotactic or intravenous administration. The bioluminescence signal of the recombinant vaccinia virus strain LIVP-mIL15-FLuc was detected in the tumor at 48, 72, and 144 h after stereotactic administration and at 72 h after intravenous virus administration. Stereotactic administration of LIVP-mIL15-RFP caused changes in the composition of immune cell subpopulations, with a relative increase in the proportion of IL-15-responsive NK cells and cytotoxic lymphocytes within the TME.