Development of new tools for foreign antigen expression in live Vibrio cholerae vaccine strains

Abstract

Live, attenuated Vibrio cholerae vaccines can induce potent immune responses after only a single oral dose. The strategy of harnessing these strains to present antigens from heterologous pathogens to the mucosal immune system in vivo shows great promise. To fully realize this possibility, strains must be created which stably express antigens in vivo in sufficient quantity to generate an immune response. In vivo-induced promoters have been shown to increase stability and immunogenicity of foreign antigens expressed from multicopy plasmids. A recent in vivo expression technology study conducted in humans has identified several potential V. cholerae in vivo-induced promoters, including PargC, PfhuC, and Pvca1008. This study explores the use of these and other promoters in the expression of heterologous proteins from the live attenuated V. cholerae vaccine strain CVD103-HgR. Strains were constructed that express and secrete the D4 subunit of Protective Antigen from Bacillus anthracis and these strains were tested for immunogenicity in vivo. A major roadblock in the testing of new V. cholerae vector vaccines is the lack of a convenient small animal model. Several attempts were made to develop such a model, without great success. However, it was possible to quantify in vivo induction of the promoters using the well characterized suckling mouse model. Indeed, this study used real-time bioluminescent imaging of suckling mice to directly demonstrate high levels of in vivo induction of the V. cholerae promoters, PargC, PfhuC, and Pvca1008.