Sequence-function relationship of influenza broadly neutralizing antibodies

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PROJECT SUMMARY Influenza A virus continues to be a major global health concern due to antigenic drifts and shifts. Rapid antigenic drifts of circulating human influenza subtypes (H1N1 and H3N2), which are caused by point mutations, can drastically hamper vaccine effectiveness despite annual update of the seasonal influenza vaccine. On the other hand, antigenic shifts, which are caused by genetic reassortment between antigenically distinct strains, can result in devastating pandemic as exemplified by the 1918 Spanish flu. Human infections with different zoonotic subtypes, such as H5N1, H6N1, H7N9, H9N2, and H10N8 have also been reported. As a result, a universal influenza vaccine that can elicit broadly protective antibody responses to diverse influenza strains and subtypes is urgently needed. The discovery of broadly neutralizing antibodies (bnAbs) that target the conserved stem region of influenza hemagglutinin (HA) has raised the possibility of developing a universal influenza vaccine. A number of HA stem bnAbs are encoded by immunoglobulin heavy chain germline gene IGHV6-1. Since these IGHV6-1 HA stem bnAbs can be found in multiple individuals and can cross-react with both group 1 HAs (H1, H2, H5, H6, H8, H9, H11, H12, H13, and H16) and group 2 HAs (H3, H4, H7, H10, H14, and H15), they represent the type of antibody response that needs to be induced by a universal influenza vaccine. This proposed study will use innovative high-throughput experiments to define sequence features in the heavy-chain complementarity-determining region 3, light chain, and somatic hypermutations, that enable an IGHV6-1 antibody to be a cross-group HA stem bnAbs. The underlying molecular mechanisms will be further characterized by structural biology approach. The results will help accurately estimate the germline frequency of IGHV6-1 HA stem bnAbs and understand their affinity maturation pathway, which in turn will benefit the design of a universal influenza vaccine. Furthermore, the experimental framework established in this study will be applicable to characterize any antibody of interest.