Antibody Recognition of a Highly Conserved Influenza Virus Epitope

Abstract

Influenza virus presents a significant and persistent threat to public health worldwide and current vaccines provide immunity to viral isolates similar to the vaccine strain. High affinity antibodies against a conserved epitope could provide immunity to the diverse influenza subtypes and protection against future pandemic viruses. Co-crystal structures were determined at 2.2 and 2.7 Å resolutions for broadly neutralizing human antibody CR6261 Fab in complexes with the major surface antigen (hemagglutinin, HA) from viruses responsible for the 1918 H1N1 influenza pandemic and a recent lethal case of H5N1 avian influenza. In contrast to all other structurally characterized influenza antibodies, CR6261 recognizes a highly conserved helical region in the membrane-proximal stem of HA1/HA2. The antibody neutralizes the virus by blocking conformational rearrangements associated with membrane fusion. The CR6261 epitope identified here should accelerate the design and implementation of improved vaccines that can elicit CR6261-like antibodies, as well as antibodybased therapies for the treatment of influenza.Over the past century, three human influenza A pandemics (1918 H1N1 Spanish, 1957 H2N2 Asian, and 1968 have killed ∼50-100 million people worldwide. Each pandemic virus was derived, at least in part, from an avian influenza virus by direct interspecies transmission or exchange of genetic material between avian and human viruses (1-4). In each case, a novel hemagglutinin (HA) envelope glycoprotein was acquired that was antigenically distinct from the HAs of the human viruses in circulation at that time. HA is the primary target of neutralizing antibodies and rapidly and continuously accumulates mutations to escape recognition by the immune system. In pandemic years, HAs are shuffled from the vast reservoir of 16 HA subtypes in avian viruses into a circulating human virus to evade prevailing immunity in the human population. Thus, while many factors likely contribute to virulence and transmissibility, immune evasion is critical for the rapid spread of pandemic and epidemic viruses.Several small molecules are in use for treatment of influenza. Most notable are neuraminidase (NA) inhibitors, oseltamivir (Tamiflu) and zanamivir (Relenza), that prevent release of nascent virions, and amantadine (5) that interferes with the M2 channel proton conducting activity. However, excessive use leads to resistant viruses (6-8) that often show surprisingly little attenuation from the escape mutations, thereby contributing to rapid spread worldwide (6).

Crystal structure of the swine-origin A (H1N1)-2009 influenza A virus hemagglutinin (HA) reveals similar antigenicity to that of the 1918 pandemic virus

“…The soluble 09H1 (A/California/04/2009) was prepared based on the method described by Stevens et al in a baculovirus expression system (Stevens et al, , 2006Ekiert et al, 2009). The construct incorporated a C-terminal thrombin cleavage site, a trimerizing sequence ('foldon') and a hexa His-tag at the extreme C terminus of the construct to enable protein purification.…”

“…Methods for the cloning, expression and purification of secreted 09H1 were based on those reported by Stevens et al (2004Stevens et al ( , 2006 and Ekiert et al (2009). Briefly, cDNA encoding amino acid residues 11-505 (11-329 (HA1) and 1-176 (HA2)) from the A/California/04/ 2009 HA ectodomain was amplified and cloned into the baculovirus transfer vector pAcGP67-B (BD Biosciences), containing a thrombin cleavage site, a trimerizing 'foldon' sequence and a his-tag.…”

Cross-protective immunity against influenza pH1N1 2009 viruses induced by seasonal influenza A (H3N2) virus is mediated by virus-specific T-cells

“…To demonstrate that virus-specific T-cell responses not only correlated with protection but were also directly responsible for heterosubtypic immunity, we performed adoptive transfer experiments. Although protective antibodies have been described that are specific for conserved epitopes in the stem region of the HA molecule (Corti et al, 2010;Ekiert et al, 2009;Steel et al, 2010;Wang et al, 2010), the matrix-2 protein (Fan et al, 2004;Heinen et al, 2002;Slepushkin et al, 1995;Song et al, 2011;Tompkins et al, 2007) and the nucleoprotein LaMere et al, 2011a, b;RangelMoreno et al, 2008), the transfer of serum obtained from mice infected with sH3N2 virus failed to protect against infection with heterologous pH1N1 virus. Either antibodies to these conserved epitopes were not induced or the titres were too low to be protective.…”

Vers un vaccin universel contre la grippe ?

“…Différentes équipes de recherche, dont la nôtre, ont récemment décrit des anticorps monoclonaux humains capables de neutraliser différents sous-types du groupe 1 et/ou du groupe 2 des virus influenza A (Figure 1) [2,[4][5][6]8]. Jusqu'à aujourd'hui, moins d'attention avait été portée aux virus influenza B, probablement parce qu'ils n'infectent pas les oiseaux aquatiques, réservoir clé pour l'émergence des pandémies.…”

“…Les virus influenza B ne ségrègent pas en sous-types, mais leur évolution est caractérisée par la cocirculation de deux lignées possé-dant des caractéristiques génétiques et antigéniques différentes ( Figure 1B) [7]. L'HA, une glycoprotéine antigé-nique présente à la surface du virus de la grippe, est nécessaire à l'atta-A (bnAb, broadly neutralizing antibodies) [2][3][4][5][6] [2,4,6]. Cette région hautement conservée se situe au niveau de la partie de l'HA proche de la membrane appelée stem 1 (Figure 3).…”