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

Abstract

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...

Influenza preimmunity increases vaccination efficacy by influencing antibody longevity, neutralization activity, and epitope specificity

“…We previously reported that primary infection induced pre-existing non-HA antibodies during 2009 H1N1 virus challenge due to sequence homology with the less immunogenic internal viral proteins. Other reports showed this sequential infection leads to the generation of both HA head and stalk directed antibodies and that stalk antibodies may be responsible for a more broadly protective antibody response [31][32][33]47]. Together, these reports suggest that antibodies generated toward internal proteins and/or the HA stem may also play a role in the clinical outcome we observed.…”

“…Future investigation of the antibodies elicited toward the HA stem and viral internal proteins using the long recovery model should also be done similarly to the live viral sequential infection studies [32,33] to gain a more complete picture of the humoral immune responses in the preimmune host during vaccination.…”

“…Previously, sequential infections with divergent influenza viruses leads to the elicitation of the antibodies that are more broadly reactive toward a larger spectrum of antigenically distinct influenza strains [31][32][33].…”

Design and Characterization of a Computationally Optimized Broadly Reactive Hemagglutinin Vaccine for H1N1 Influenza Viruses

“…8). In contrast to head-based universal strategies, anti-HA stembased approaches elicit antibodies that recognize the stem portion of HA in isolates across several strains within a subtype (37) and multiple subtypes within a group (38). Stem-induced antibodies, just as head-based elicited antibodies, may function through disease modulation.…”

Passive immunization with influenza haemagglutinin specific monoclonal antibodies

“…Multiple successive exposures to chimeric HAs bearing antigenically distinct heads and conserved stems has been proposed to preferentially boost antibody responses to the conserved stem. 14,30,58,59 Studies in mice have shown that sequential administration of DNA vaccines encoding different H3 HAs or vaccination with only the stem portion of the HA were successful in inducing HA stem bNAbs. 60,61 However, the effectiveness of these strategies in human vaccinees is yet to be demonstrated.…”