Bell, Michael

Abstract One limitation to the development of targeted tumor immunity is the availability of safe vectors that can drive strong T-cell responses capable of eradicating tumors. We have designed viral vectors using Theiler’s murine encephalomyelitis virus (TMEV) that effectively inhibit melanoma outgrowth. By cloning the TMEV genome into a eukaryotic expression vector that can easily be manipulated we were able to generate several novel tumor specific virus vaccines. We find that incorporation of defined MHC class I epitopes into sites within the leader protein of the virus can drive strong CD8+ T-cell responses against these target peptides. Further, we find that the site of incorporation can change the elicited cytokine profile and the virulence of the virus. Incorporation of the ovalbumen peptide after the third amino acid of the L protein (p3) generates a strong IFNβ response, whereas insertion within the downstream XhoI restriction site elicits a strong IL6 response similar to wild-type TMEV. Further, the p3 virus is not lethal to RAG-deficient mice, where the XhoI and wild-type TMEV virus are. However, p3 virus persists and kills IFNα/β receptor-deficient mice, suggesting that innate immune responses are responsible for viral clearance. In spite of these differences the p3 and XhoI viruses can stimulate antigen specific T-cell responses and inhibit tumor outgrowth equivalently, demonstrating the efficacy of TMEV and its potential as a therapeutic intervention.