In the US, extensive reservoirs of the rabies virus exist in many diverse wild animal species that continue to pose a serious risk of lethal infection of humans and cause an economic burden exceeding $1 billion annually. Previous experience with rabies control in foxes in Europe has clearly demonstrated that oral immunization with live vaccines is the only practical approach to eradicating rabies in free-ranging animals. However, unlike Europe where vulpine rabies was the only major reservoir, the Americas harbor a variety of species including raccoons, skunks, coyotes, and bats that serve as the primary reservoirs of rabies. Each of these animal reservoirs carries an antigenically distinct virus variant. Because the currently available modified-live rabies virus vaccines have either safety problems or do not induce sufficient protective immunity, particularly in wildlife species, die overall goal of this proposal is the development of recombinant rabies virus vaccines that are very safe and highly effective in particular wildlife species. Based on preliminary data indicating that the potency of a vaccine is significantly increased if the G protein of the vaccine strain is identical to that of the target virus, we propose to use a reverse genetics approach to engineer viruses that contain G proteins from virus strains associated with relevant wildlife species. Our preliminary data also indicate that an increased ability of rabies virus to induce apoptosis leads to enhanced immunogenicity of the virus and to reduced pathogenicity. Moreover, our recent evidence indicates that the immunogenicity can also be enhanced by immunostimulatory cytokines. Thus, we will construct recombinant viruses that express genes encoding proapoptotic proteins and cytokines in order to stimulate immunity or otherwise interfere with viral pathogenesis in order to enhance their efficacy and safety. In addition to the practical implications of this approach for vaccine development, information derived from studying these viruses will provide a better understanding of factors that stimulate immunity against rabies and may provide a strategy based on co-expression of immunostimulatory proteins that finds broad application to other vaccines. ? ?
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