Bell, Michael

Abstract We have engineered an attenuated picornavirus vaccine using Theiler’s murine encephalomyelitis virus (TMEV) and are exploring its usefulness in immunotherapy. We find that two different insertion sites within the leader protein of the TMEV genome allow for effective production of virus vaccine strains. One site is at the amino terminal end of the protein after the third amino acid position (p3); the other is at the XhoI restriction site further downstream. We find that vaccine antigen insertion at p3 disrupts the ability of the virus to inhibit type I interferon production by infected cells, whereas XhoI insertion does not. Further, the p3 modified virus can be cleared from animals lacking functional T and B-cells but replicates to high titer in IFNα/β receptor knockout mice, suggesting that innate immune mechanisms are sufficient for viral clearance. In spite of rapid clearance, p3 vaccines readily stimulate proliferation of transgenic T-cells and induce de novo responses to T-cell antigens in wild-type mice, although to a lesser extent than the XhoI modified vaccines strains. The use of either vaccine however effectively delays tumor growth and enhances survival in mice bearing melanoma and breast tumors. This vaccine provides a safe and effective vaccine strategy for the induction of CD8+ T-cell immunity directed towards cancer and provides support for the development of picornaviruses as vaccine vectors for treating human disease.