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Conserved epitope on influenza-virus hemagglutinin head defined by a vaccine-induced antibody.

ABSTRACT: Circulating influenza viruses evade neutralization in their human hosts by acquiring escape mutations at epitopes of prevalent antibodies. A goal for next-generation influenza vaccines is to reduce escape likelihood by selectively eliciting antibodies recognizing conserved surfaces on the viral hemagglutinin (HA). The receptor-binding site (RBS) on the HA "head" and a region near the fusion peptide on the HA "stem" are two such sites. We describe here a human antibody clonal lineage, designated CL6649, members of which bind a third conserved site ("lateral patch") on the side of the H1-subtype, HA head. A crystal structure of HA with bound Fab6649 shows the conserved antibody footprint. The site was invariant in isolates from 1977 (seasonal) to 2012 (pdm2009); antibodies in CL6649 recognize HAs from the entire period. In 2013, human H1 viruses acquired mutations in this epitope that were retained in subsequent seasons, prompting modification of the H1 vaccine component in 2017. The mutations inhibit Fab6649 binding. We infer from the rapid spread of these mutations in circulating H1 influenza viruses that the previously subdominant, conserved lateral patch had become immunodominant for individuals with B-cell memory imprinted by earlier H1 exposure. We suggest that introduction of the pdm2009 H1 virus, to which most of the broadly prevalent, neutralizing antibodies did not bind, conferred a selective advantage in the immune systems of infected hosts to recall of memory B cells that recognized the lateral patch, the principal exposed epitope that did not change when pdm2009 displaced previous seasonal H1 viruses.

SUBMITTER: Raymond DD

PROVIDER: S-EPMC5776812 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Conserved epitope on influenza-virus hemagglutinin head defined by a vaccine-induced antibody.

Raymond Donald D DD Bajic Goran G Ferdman Jack J Suphaphiphat Pirada P Settembre Ethan C EC Moody M Anthony MA Schmidt Aaron G AG Harrison Stephen C SC

Proceedings of the National Academy of Sciences of the United States of America 20171218 1

Circulating influenza viruses evade neutralization in their human hosts by acquiring escape mutations at epitopes of prevalent antibodies. A goal for next-generation influenza vaccines is to reduce escape likelihood by selectively eliciting antibodies recognizing conserved surfaces on the viral hemagglutinin (HA). The receptor-binding site (RBS) on the HA "head" and a region near the fusion peptide on the HA "stem" are two such sites. We describe here a human antibody clonal lineage, designated ...[more]

PMID: 29255041

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Project description:UnlabelledNeutralizing antibodies that target the hemagglutinin of influenza virus either inhibit binding of hemagglutinin to cellular receptors or prevent the low-pH-induced conformational change in hemagglutinin required for membrane fusion. In general, the former type of antibody binds to the globular head formed by HA1 and has narrow strain specificity, while the latter type binds to the stem mainly formed by HA2 and has broad strain specificity. In the present study, we analyzed the epitope and function of a broadly neutralizing human antibody against H3N2 viruses, F005-126. The crystal structure of F005-126 Fab in complex with hemagglutinin revealed that the antibody binds to the globular head, spans a cleft formed by two hemagglutinin monomers in a hemagglutinin trimer, and cross-links them. It recognizes two peptide portions (sites L and R) and a glycan linked to asparagine at residue 285 using three complementarity-determining regions and framework 3 in the heavy chain. Binding of the antibody to sites L (residues 171 to 173, 239, and 240) and R (residues 91, 92, 270 to 273, 284, and 285) is mediated mainly by van der Waals contacts with the main chains of the peptides in these sites and secondarily by hydrogen bonds with a few side chains of conserved sequences in HA1. Furthermore, the glycan recognized by F005-126 is conserved among H3N2 viruses. F005-126 has the ability to prevent low-pH-induced conformational changes in hemagglutinin. The newly identified conserved epitope, including the glycan, should be immunogenic in humans and may induce production of broadly neutralizing antibodies against H3 viruses.ImportanceAntibodies play an important role in protection against influenza virus, and hemagglutinin is the major target for virus neutralizing antibodies. It has long been believed that all effective neutralizing antibodies bind to the surrounding regions of the sialic acid-binding pocket and inhibit the binding of hemagglutinin to the cellular receptor. Since mutations are readily introduced into such epitopes, this type of antibody shows narrow strain specificity. Recently, however, broadly neutralizing antibodies have been isolated. Most of these bind either to conserved sites in the stem region or to the sialic acid-binding pocket itself. In the present study, we identified a new neutralizing epitope in the head region recognized by a broadly neutralizing human antibody against H3N2. This epitope may be useful for design of vaccines.

Project description:UnlabelledA human monoclonal heterosubtypic antibody, MAb 3.1, with its heavy chain encoded by VH3-30, was isolated using phage display with immobilized hemagglutinin (HA) from influenza virus A/Japan/305/1957(H2N2) as the target. Antibody 3.1 potently neutralizes influenza viruses from the H1a clade (i.e., H1, H2, H5, H6) but has little neutralizing activity against the H1b clade. Its crystal structure in complex with HA from a pandemic H1N1 influenza virus, A/South Carolina/1/1918(H1N1), revealed that like other heterosubtypic anti-influenza virus antibodies, MAb 3.1 contacts a hydrophobic groove in the HA stem, primarily using its heavy chain. However, in contrast to the closely related monoclonal antibody (Mab) FI6 that relies heavily on HCDR3 for binding, MAb 3.1 utilizes residues from HCDR1, HCDR3, and framework region 3 (FR3). Interestingly, HCDR1 of MAb 3.1 adopts an ?-helical conformation and engages in hydrophobic interactions with the HA very similar to those of the de novo in silico-designed and affinity-matured synthetic protein HB36.3. These findings improve our understanding of the molecular requirements for binding to the conserved epitope in the stem of the HA protein and, therefore, aid the development of more universal influenza vaccines targeting these epitopes.ImportanceInfluenza viruses rapidly evade preexisting immunity by constantly altering the immunodominant neutralizing antibody epitopes (antigenic drift) or by acquiring new envelope serotypes (antigenic shift). As a consequence, the majority of antibodies elicited by immunization or infection protect only against the immunizing or closely related strains. Here, we describe a novel monoclonal antibody that recognizes the conserved heterosubtypic epitope in the stem of influenza A virus hemagglutinin. This antibody, referred to as MAb 3.1, recognizes its epitope in a manner that resembles recognition of a similar epitope by the de novo in silico-designed and affinity-matured synthetic protein HB36.3. Thus, besides providing novel insights into the molecular interactions between heterosubtypic antibodies and influenza virus hemagglutinin, MAb 3.1 demonstrates that de novo in silico-designed and affinity-matured synthetic proteins can foretell naturally selected antibody binding. This knowledge will aid development of a pan-influenza virus vaccine.

Project description:Despite the availability of seasonal vaccines and antiviral medications, influenza virus continues to be a major health concern and pandemic threat due to the continually changing antigenic regions of the major surface glycoprotein, hemagglutinin (HA). One emerging strategy for the development of more efficacious seasonal and universal influenza vaccines is structure-guided design of nanoparticles that display conserved regions of HA, such as the stem. Using the H1 HA subtype to establish proof of concept, we found that tandem copies of an alpha-helical fragment from the conserved stem region (helix-A) can be displayed on the protruding spikes structures of a capsid scaffold. The stem region of HA on these designed chimeric nanoparticles is immunogenic and the nanoparticles are biochemically robust in that heat exposure did not destroy the particles and immunogenicity was retained. Furthermore, mice vaccinated with H1-nanoparticles were protected from lethal challenge with H1N1 influenza virus. By using a nanoparticle library approach with this helix-A nanoparticle design, we show that this vaccine nanoparticle construct design could be applicable to different influenza HA subtypes. Importantly, antibodies elicited by H1, H5, and H7 nanoparticles demonstrated homosubtypic and heterosubtypic cross-reactivity binding to different HA subtypes. Also, helix-A nanoparticle immunizations were used to isolate mouse monoclonal antibodies that demonstrated heterosubtypic cross-reactivity and provided protection to mice from viral challenge via passive-transfer. This tandem helix-A nanoparticle construct represents a novel design to display several hundred copies of non-trimeric conserved HA stem epitopes on vaccine nanoparticles. This design concept provides a new approach to universal influenza vaccine development strategies and opens opportunities for the development of nanoparticles with broad coverage over many antigenically diverse influenza HA subtypes.

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Conserved epitope on influenza-virus hemagglutinin head defined by a vaccine-induced antibody.

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Conserved epitope on influenza-virus hemagglutinin head defined by a vaccine-induced antibody.

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