Dissecting human, ferret, and murine antibody and B cell responses to generate a broadly protective synthetic influenza virus hemagglutinin

Abstract

Abstract A major challenge in developing improved influenza vaccines is the identification of broadly reactive and protective epitopes. While it is generally believed that the specificity of the antibody response to hemagglutinin (HA) is relatively narrow, we and others have identified individuals that mount a cross-reactive neutralizing antibody response after natural infection. Using plasmablasts from one such individual we generated broadly cross-reactive HA-specific monoclonal antibodies (mAbs). Six of these mAbs bound to the globular head of the HA and one to the stalk region; all provided broad protection against multiple subtypes of influenza A viruses including zoonotic strains in passively immunized mice. Using a peptide ELISA approach, we identified the binding regions of each mAb and subsequently immunized mice with these peptides. Immunized mice showed less weight loss and significantly improved survival against challenges with multiple subtypes as compared with control mice. We next used a similar mapping approach with broadly reactive B cells from mice and ferrets. Based on all of the collected data we generated three different composite HA antigens (HF1, HF2 and HF3) that contained a different mix of broadly reactive epitopes in one native HA structure. Mice immunized with the HFs were protected from multiple challenges, including lethal doses of H1, H3, H5, H6, H7 and H9 viruses. We also showed the HFs protected ferrets from H1, H3, and H9 viruses. Overall, by combining data generated from an examination of B cell and antibody responses following infection and/or vaccination in humans, mice, and ferrets we were able to construct a composite HA that was able to induce broad protection against multiple subtypes of influenza virus.