Induction of neutralizing antibody (NAb) responses is the ultimate goal for the successful prevention of HCV infection. HCV envelope glycoproteins E1 and E2, are clear targets for NAbs and are thus attractive immunogens for the development of a prophylactic vaccine. DNA vaccines are cost-effective to manufacture on a global scale, but DNA vaccines encoding E1/E2 proteins have not been highly immunogenic in the past. Furthermore, the ideal mode of processing and presenting these immunogens for effective vaccination is yet to be determined. We now report a novel strategy that incorporates E1 and E2 into heptamers by fusion with the oligomerisation domain of the C4 binding protein (IMX313P). As the adjuvanticity of IMX313P requires efficient secretion of the oligomerised protein, a TPA leader sequence was introduced upstream of the E1 or E2 proteins (tE1 or tE2) from which the transmembrane domains were removed. The use of tE1 and tE2 proteins as separate immunogens or as a single tE1tE2 polyprotein was assessed in vaccination studies in Balb/c mice using prime-boost intra-dermal DNA immunisations.
Animals vaccinated with tE2IMX313P or tE1tE2IMX313P or a cocktail of tE1IMX313P+tE2IMX313P elicited significantly higher E1 and/or E2-specific antibody responses (mean titers in ELISA of 1:1707, 1:1343 and 1:1994 for tE2IMX313P, tE1tE2IMX313P and tE1IMX313P+tE2IMX313P respectively) when compared to animals vaccinated with DNA encoding tE2 (titer 1:6) or a cocktail of tE1+tE2 (titer 1:9). No significant differences in E1/E2-specific antibody titers were observed between mice vaccinated with DNA encoding tE1 (titer 1:2) or tE1IMX313P (titer 1:6). The ability of the antibodies induced by immunisation with the cocktail to cross-neutralise HCV-pseudoparticles will be investigated using a neutralising assay.
Our study shows HCV E1 and E2 proteins are much more immunogenic when fused to the IMX313P domain, thus making IMX313P domain an effective adjuvant that enhances the immunogenicity of HCV-E1E2 based DNA vaccines.