| Summary: | Influenza virus causes a highly contagious respiratory disease whose morbidity and mortality is best prevented by vaccination and the need for a rapid and scalable vaccine response to emerging influenza virus strains is widely recognised. In this study, the haemagglutinins (HAs) of human HI and H3 influenza viruses and avian H5 influenza virus were produced as recombinant fusion proteins with the human immunoglobulin Fe domain. Recombinant HA-human immunoglobulin Fe domain (HA-HuFc) proteins were secreted from baculovirus-infected insect cells as glycosylated oligomeric HAs of the anticipated molecular mass, which agglutinated red blood cells and were purified by protein A chromatography. Purified protein was used to immunise mice in the absence of adjuvant. Immunogenicity was demonstrated for all subtypes, with the serum samples demonstrating subtype- specific haemagglutination inhibition. A degree of heterosubtypic cross reaction between H5 antibodies and HI HA was also shown in this study, plausibly due to structural relatedness of the HAI domains. A Th2 immune response was dominant with some ThI response, typical of the immune responses described for other influenza vaccines and for soluble oligomeric HA. Dose ranging immunisation studies demonstrated significant seroconversion down to 100ng per dose, the human equivalent dose of 24ugs as calculated by body surface area, which is lower than that observed for a recombinant HA in human studies. The polyvalent serum response was directed to the RBS of the HA as reported for experimental influenza infection and included neutralising antibodies. Mutations introduced into the RBS of the H5 HA altered the antigenicity of the virus protein and appeared to elicit antibodies more efficient for binding to human origin influenza subtypes. Epitope specificity studies identified the top of the HAl domain as the target of the induced antibodies, which broadly correlated with the epitope mapping for the H5 HA of several influenza strains. Thus, HuFc-tagged HAs expressed in insect cells are potential candidates for gene-to-vaccine approaches to influenza vaccination.
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