Development of Novel Pseudoinfectious Flavivirus Vaccines

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Viruses in the flavivirus family populate all three of NIAID's Category A, B, and C lists of viruses. Vaccines are needed for multiple flavivirus diseases. To address this need, we have engineered a capsid (C) gene-deleted flavivirus vaccine platform that we have named RepliVAX. RepliVAX can infect cells in vitro and in vivo, but cannot produce live virus. However, RepliVAX-infected cells produce a key viral immunogen, a sub-viral particle (SVP) that contains the flavivirus envelope proteins, prM/M and E. SVPs have known ability to provide flavivirus immunity in man. RepliVAX can be propagated using two different systems. The first method is based on growth in Cexpressing cell lines that produce large amounts of C protein from a non-cytopathic alphavirus vector. In this system, RepliVAX is grown in a format similar to that used for production of classical live attenuated vaccines. The second system for RepliVAX production involves the co-cultivation of RepliVAX with helper particles that encode a flavivirus genome expressing a functional form of C, but deleted for the prM and E genes. This second system, referred to throughout this proposal as the "two-component" genome system has the advantage that it permits RepliVAX production on any type of cell line. RepliVAX vaccines based on the genomes of yellow fever virus (YFV) and West Nile virus (WNV) can protect animals from YF and WN encephalitis. We have also applied the widely used "chimeric" flavivirus technology to generate a WNV-based RepliVAX encoding the prM/E structural proteins of Japanese encephalitis virus (JEV). This RepliVAX JE protects animals from JE, suggesting that using the highly efficient WNV replication "engine" to drive chimeric RepliVAX provides a breakthrough for flavivirus vaccine development. The goal of this 6-year project will be the development of RepliVAX as a platform, by extending it to the production of safe and effective vaccines for the most widely circulating emerging flavivirus disease (dengue) and two biodefense threat diseases with known high morbidity and a history of weaponization {Omsk hemorrhagic fever (OHF) and tick-borne encephalitis (TBE)}. To develop RepliVAX into a universal flavivirus vaccine platform, we have devised the following specific aims. 1: Determine if stable cells or the "two-component" system is best for RepliVAX production. 2. Determine which RepliVAX backbone is superior for producing effective TBE vaccines. 3: Generate RepliVAX chimeras with dengue virus (DENV) that grow to high titers. 4: Create chimeric RepliVAX expressing the prM/E and NS1 proteins and determine if these are superior to prM/E. 5. Determine if RepliVAX can be retargeted to enhance its efficacy.