EXTH-39. HEXON SWAPPING MITIGATES ANTI-VIRAL IMMUNE RESPONSE DURING BRAIN TUMOR VIROTHERAPY

Abstract Cancer virotherapy is a paradigm-shifting treatment modality based on the capabilities of virus-mediated oncolysis to elicit an anti-tumor immune response. Phase 1 and 2 clinical trials have demonstrated the safety and efficacy of our oncolytic adenovirus DNX-2401 (Delta-24-RGD) for patients with recurrent malignant gliomas. While a subset of the patients showed significant benefits, our goal is to improve the response rate. Clearance of the therapeutic virus by dominant anti-viral immune responses may contribute to the observed limits of the virotherapy. Adenovirus serotype 5 that provides the backbone of most oncolytic adenoviruses is highly prevalent in the human population and neutralizing antibodies against the capsid protein hexon may inhibit viral infection and replication. In this study, we showed using immunofluorescence that in mice bearing orthotopic syngeneic glioblastoma GSC005 treated with Delta-24-RGD, IgG antibodies crossed the disrupted blood-brain barrier and infiltrated the brain tumor parenchyma to colocalize with the viral hexon, suggesting that the systemic immune response may eradicate the virus within the infected tumor. To overcome this obstacle, we generated a chimeric virus called Delta-24-RGD-H43m with hexon hypervariable regions replaced with those from a lesser prevalent serotype 43 to avoid recognition by antibodies generated against serotype 5. The molecular swapping of the hexon did not significantly interfere with virion assembly nor attenuate its anti-glioma effect. Thus, the two viruses showed comparable efficacy in vitro (P= 0.568) and in vivo for animals without prior virus exposures (P= 0.228). Importantly, Delta-24-RGD-H43m evaded neutralizing antibodies generated against Delta-24-RGD and maintained its oncolytic ability (P< 0.0001). We conclude that hexon swapping strategies may improve virotherapy by alleviating the dominant immune response against the virus. Despite limited understanding of the interaction between oncolytic viruses and the host immune system, further research on strategies to circumvent virus-specific immune responses should aid the development of enhanced, glioma-targeted virotherapies.