Broadly cross-reactive antibodies dominate the human B cell response against 2009 pandemic H1N1 influenza virus infection

Broadly reactive antibodies targeting the conserved hemagglutinin (HA) stalk region are elicited following sequential infection or vaccination with influenza viruses belonging to divergent subtypes and/or expressing antigenically distinct HA globular head domains. Here, we demonstrate, through the use of novel chimeric HA proteins and competitive binding assays, that sequential infection of ferrets with antigenically distinct seasonal H1N1 (sH1N1) influenza virus isolates induced an HA stalk-specific antibody response. Additionally, stalk-specific antibody titers were boosted following sequential infection with antigenically distinct sH1N1 isolates in spite of preexisting, cross-reactive, HA-specific antibody titers. Despite a decline in stalk-specific serum antibody titers, sequential sH1N1 influenza virus-infected ferrets were protected from challenge with a novel H1N1 influenza virus (A/California/07/2009), and these ferrets poorly transmitted the virus to naive contacts. Collectively, these findings indicate that HA stalk-specific antibodies are commonly elicited in ferrets following sequential infection with antigenically distinct sH1N1 influenza virus isolates lacking HA receptor-binding site cross-reactivity and can protect ferrets against a pathogenic novel H1N1 virus. IMPORTANCE The influenza virus hemagglutinin (HA) is a major target of the humoral immune response following infection and The influenza virus is highly contagious and causes an acute respiratory illness, with seasonal epidemics in the human population. Despite global vaccination efforts, influenza remains a major medical issue and is responsible for substantial morbidity and mortality annually. It is estimated that 5 to 20% of the people in the United States contract influenza virus annually, and more than 200,000 people require hospitalization due to influenza-related complications (according to the Centers for Disease Control and Prevention, Atlanta, GA [http://www.cdc.gov/flu/about/qa /disease.htm; accessed 1 September 2015]). The young, the elderly, pregnant females, and those with certain medical conditions are at an increased risk for influenza-associated complications.Current vaccination approaches primarily rely on the induction of antibodies recognizing hemagglutinin (HA) (1). The HA glycoprotein is expressed as a trimeric complex of identical subunits on the surface of influenza virus virions. HA mediates virus attachment and subsequent membrane fusion with target cells (2, 3). Individual HA monomers can be further segregated into the membrane-distal globular head and membrane-proximal stalk domains. The globular head encodes the receptor-binding site (RBS), and the stalk domain encodes the fusion peptide (2).Antibodies directed against HA and, more specifically, to epitopes in close proximity to the RBS within the globular head region are elicited following infection or vaccination (4). These antibodies possess a potent neutralization capacity through the ability to interfere with viral attachment to target cells and a...

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confidence: 99%

Sequential Infection in Ferrets with Antigenically Distinct Seasonal H1N1 Influenza Viruses Boosts Hemagglutinin Stalk-Specific Antibodies

Kirchenbaum

Carter

Ross

2016

“…The stalk domain shows conservation within these groups, and the binding pattern of broadly neutralizing antibodies-with some exceptions (11,12)-usually resembles this phylogeny (4)(5)(6)(7)(13)(14)(15). It has been hypothesized that exposure to HAs with divergent head domains and conserved stalk domains could refocus the immune response to the immunosubdominant conserved stalk domain of the HA by boosting antibodies to shared epitopes (16)(17)(18)(19)(20)(21)(22). A universal influenza virus vaccine based on this hypothesis using chimeric HAs (cHAs) is currently in late-stage preclinical development (10,19,20,23).…”

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confidence: 99%

Induction of Broadly Reactive Anti-Hemagglutinin Stalk Antibodies by an H5N1 Vaccine in Humans

Nachbagauer

Wohlbold

Hirsh

et al. 2014

135

124

Influenza virus infections are a major public health concern and cause significant morbidity and mortality worldwide. Current vaccines are effective but strain specific due to their focus on the immunodominant globular head domain of the hemagglutinin (HA). It has been hypothesized that sequential exposure of humans to hemagglutinins with divergent globular head domains but conserved stalk domains could refocus the immune response to broadly neutralizing epitopes in the stalk. Humans have preexisting immunity against H1 (group 1 hemagglutinin), and vaccination with H5 HA (also group 1)-which has a divergent globular head domain but a similar stalk domain-represents one such sequential-exposure scenario. To test this hypothesis, we used novel reagents based on chimeric hemagglutinins to screen sera from an H5N1 clinical trial for induction of stalk-specific antibodies by quantitative enzyme-linked immunosorbent assay (ELISA) and neutralization assays. Importantly, we also investigated the biological activity of these antibodies in a passive transfer in a mouse challenge model. We found that the H5N1 vaccine induced high titers of stalk-reactive antibodies which were biologically active and protective in the passive-transfer experiment. The induced response showed exceptional breadth toward divergent group 1 hemagglutinins but did not extend to group 2 hemagglutinins. These data provide evidence for the hypothesis that sequential exposure to hemagglutinins with divergent globular head domains but conserved stalk domains can refocus the immune response toward the conserved stalk domain. Furthermore, the results support the concept of a chimeric hemagglutinin universal influenza virus vaccine strategy that is based on the same principle.

“…Due to its role in facilitating the fusion of the viral and endosomal membranes, which subsequently releases the viral ribonucleoprotein (RNP) into the cytosol, the stalk is less susceptible to mutations and is relatively conserved across the divergent subtypes. Thus, stalk-directed antibodies are capable of neutralizing diverse influenza viruses (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27).…”

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confidence: 99%

“…The majority of the stalk-directed broadly neutralizing monoclonal antibodies (MAbs) that have been isolated and characterized to date bind and neutralize group 1 influenza A viruses (i.e., H1, H2, and H5 subtypes) (14)(15)(16)(17)(18)(19)(20)(21), while only a few MAbs recognize group 2 influenza A viruses (e.g., H3, H7, and H10 subtypes) (22)(23)(24). Of note, human MAb FI6v3 was described to bind group 1 and 2 influenza A viruses (25), whereas human MAb CR9114 was found to bind to influenza A and B viruses (26).…”

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confidence: 99%

Characterization of a Broadly Neutralizing Monoclonal Antibody That Targets the Fusion Domain of Group 2 Influenza A Virus Hemagglutinin

Tan

Lee

Hoffman

et al. 2014

112

Due to continuous changes to its antigenic regions, influenza viruses can evade immune detection and cause a significant amount of morbidity and mortality around the world. Influenza vaccinations can protect against disease but must be annually reformulated to match the current circulating strains. In the development of a broad-spectrum influenza vaccine, the elucidation of conserved epitopes is paramount. To this end, we designed an immunization strategy in mice to boost the humoral response against conserved regions of the hemagglutinin (HA) glycoprotein. Of note, generation and identification of broadly neutralizing antibodies that target group 2 HAs are rare and thus far have yielded only a few monoclonal antibodies (MAbs). Here, we demonstrate that mouse MAb 9H10 has broad and potent in vitro neutralizing activity against H3 and H10 group 2 influenza A subtypes. In the mouse model, MAb 9H10 protects mice against two divergent mouse-adapted H3N2 strains, in both pre-and postexposure administration regimens. In vitro and cell-free assays suggest that MAb 9H10 inhibits viral replication by blocking HA-dependent fusion of the viral and endosomal membranes early in the replication cycle and by disrupting viral particle egress in the late stage of infection. Interestingly, electron microscopy reconstructions of MAb 9H10 bound to the HA reveal that it binds a similar binding footprint to MAbs CR8020 and CR8043. IMPORTANCEThe influenza hemagglutinin is the major antigenic target of the humoral immune response. However, due to continuous antigenic changes that occur on the surface of this glycoprotein, influenza viruses can escape the immune system and cause significant disease to the host. Toward the development of broad-spectrum therapeutics and vaccines against influenza virus, elucidation of conserved regions of influenza viruses is crucial. Thus, defining these types of epitopes through the generation and characterization of broadly neutralizing monoclonal antibodies (MAbs) can greatly assist others in highlighting conserved regions of hemagglutinin. Here, we demonstrate that MAb 9H10 that targets the hemagglutinin stalk has broadly neutralizing activity against group 2 influenza A viruses in vitro and in vivo.