Pre-existing immunity to influenza aids ferrets in developing stronger and broader H3 vaccine-induced antibody responses.

Influenza seasons occur annually, building immune history for individuals, but the influence of this history on subsequent influenza vaccine protection remains unclear. We extracted data from an animal trial to study its potential impact. The trial involved 80 ferrets, each receiving either one type of infection or a placebo before vaccination. We quantified the vaccine protection by evaluating hemagglutination inhibition (HAI) antibody titer responses. We tested whether hosts with different infection histories exhibited similar level of responses when receiving the same vaccine for all homologous and heterologous outcomes. We observed that different pre-existing immunities were generally beneficial to vaccine induced responses, but varied in magnitude. Without pre-immunity, post-vaccination HAI titers after the 1st dose of the vaccine were less likely to be above 1:40, and a booster shot was needed. Our study suggests that pre-existing immunity may strengthen and extend the homologous and heterologous vaccine responses.

Longitudinal assessment of human antibody binding to hemagglutinin elicited by split-inactivated influenza vaccination over six consecutive seasons.

Participants between the ages of 10-86 years old were vaccinated with split-inactivated influenza vaccine (Fluzone®) in six consecutive influenza seasons from 2016-2017 to 2021-2022. Vaccine effectiveness varies from season to season as a result of both host immune responses as well as evolutionary changes in the influenza virus surface glycoproteins that provide challenges to vaccine manufacturers to produce more effective annual vaccines. Next generation influenza vaccines are in development and may provide protective immune responses against a broader number of influenza viruses and reduce the need for annual vaccination. An improved understanding how current influenza vaccines are influenced by human host immune responses in people of different ages and co-morbidities is necessary for designing the next-generation of 'universal' or broadly-protective influenza vaccines. Overall, pre-existing immune responses to previous influenza virus exposures, either by past infections or vaccinations, is a critical factor influencing host responses to seasonal influenza vaccination. Participants vaccinated in consecutive seasons had reduced serum hemagglutination-inhibition (HAI) activity against strains included in the vaccine compared to participants that had not been vaccinated in the preceding 1-2 years prior to entering this study. The magnitude and breadth of these antibody responses were also modulated by the age of the participant. Elderly participants over 65 years of age, in general, had lower pre-existing HAI titers each season prior to vaccination with lower post-vaccination titers compared to children or young adults under the age of 35. The administration of higher doses (HD) of the split-inactivated vaccine enhanced the antibody titers in the elderly. This report showcases 6 consecutive years of antibody HAI activity in human subjects receiving seasonal split-inactivated influenza vaccine.

mRNA vaccines encoding computationally optimized hemagglutinin elicit protective antibodies against future antigenically drifted H1N1 and H3N2 influenza viruses isolated between 2018-2020.

Background: The implementation of mRNA vaccines against COVID-19 has successfully validated the safety and efficacy of the platform, while at the same time revealing the potential for their applications against other infectious diseases. Traditional seasonal influenza vaccines often induce strain specific antibody responses that offer limited protection against antigenically drifted viruses, leading to reduced vaccine efficacy. Modern advances in viral surveillance and sequencing have led to the development of in-silico methodologies for generating computationally optimized broadly reactive antigens (COBRAs) to improve seasonal influenza vaccines. Methods: In this study, immunologically naïve mice were intramuscularly vaccinated with mRNA encoding H1 and H3 COBRA hemagglutinins (HA) or wild-type (WT) influenza HAs encapsulated in lipid nanoparticles (LNPs). Results: Mice vaccinated with H1 and H3 COBRA HA-encoding mRNA vaccines generated robust neutralizing serum antibody responses against more antigenically distinct contemporary and future drifted H1N1 and H3N2 influenza strains than those vaccinated with WT H1 and H3 HA-encoding mRNA vaccines. The H1 and H3 COBRA HA-encoding mRNA vaccines also prevented influenza illness, including severe disease in the mouse model against H1N1 and H3N2 viruses. Conclusions: This study highlights the potential benefits of combining universal influenza antigen design technology with modern vaccine delivery platforms and exhibits how these vaccines can be advantageous over traditional WT vaccine antigens at eliciting superior protective antibody responses against a broader number of influenza virus isolates.

Discovery and Characterization of a Pan-betacoronavirus S2-binding antibody.

Three coronaviruses have spilled over from animal reservoirs into the human population and caused deadly epidemics or pandemics. The continued emergence of coronaviruses highlights the need for pan-coronavirus interventions for effective pandemic preparedness. Here, using LIBRA-seq, we report a panel of 50 coronavirus antibodies isolated from human B cells. Of these antibodies, 54043-5 was shown to bind the S2 subunit of spike proteins from alpha-, beta-, and deltacoronaviruses. A cryo-EM structure of 54043-5 bound to the pre-fusion S2 subunit of the SARS-CoV-2 spike defined an epitope at the apex of S2 that is highly conserved among betacoronaviruses. Although non-neutralizing, 54043-5 induced Fc-dependent antiviral responses, including ADCC and ADCP. In murine SARS-CoV-2 challenge studies, protection against disease was observed after introduction of Leu234Ala, Leu235Ala, and Pro329Gly (LALA-PG) substitutions in the Fc region of 54043-5. Together, these data provide new insights into the protective mechanisms of non-neutralizing antibodies and define a broadly conserved epitope within the S2 subunit.

Bivalent H1 and H3 COBRA Recombinant Hemagglutinin Vaccines Elicit Seroprotective Antibodies against H1N1 and H3N2 Influenza Viruses from 2009 to 2019.

Commercial influenza virus vaccines often elicit strain-specific immune responses and have difficulties preventing illness caused by antigenically drifted viral variants. In the last 20 years, the H3N2 component of the annual vaccine has been updated nearly twice as often as the H1N1 component, and in 2019, a mismatch between the wild-type (WT) H3N2 vaccine strain and circulating H3N2 influenza strains led to a vaccine efficacy of ∼9%. Modern methods of developing computationally optimized broadly reactive antigens (COBRAs) for H3N2 influenza viruses utilize current viral surveillance information to design more broadly reactive vaccine antigens. Here, 7 new recombinant hemagglutinin (rHA) H3 COBRA hemagglutinin (HA) antigens were evaluated in mice. Subsequently, two candidates, J4 and NG2, were selected for further testing in influenza-preimmune animals based on their ability to elicit broadly reactive antibodies against antigenically drifted H3N2 viral isolates. In the preimmune model, monovalent formulations of J4 and NG2 elicited broadly reactive antibodies against recently circulating H3N2 influenza viruses from 2019. Bivalent mixtures of COBRA H1 and H3 rHA, Y2 + J4, and Y2 + NG2 outperformed multiple WT H1+H3 bivalent rHA mixtures by eliciting seroprotective antibodies against H1N1 and H3N2 isolates from 2009 to 2019. Overall, the newly generated COBRA HA antigens, namely, Y2, J4, and NG2, had the ability to induce broadly reactive antibodies in influenza-naive and preimmune animals in both monovalent and bivalent formulations, and these antigens outperformed H1 and H3 WT rHA vaccine antigens by eliciting seroprotective antibodies against panels of antigenically drifted historical H1N1 and H3N2 vaccine strains from 2009 to 2019. IMPORTANCE Standard-of-care influenza virus vaccines are composed of a mixture of antigens from different influenza viral subtypes. For the first time, lead COBRA H1 and H3 HA antigens, formulated as a bivalent vaccine, have been investigated in animals with preexisting immunity to influenza viruses. The cocktail of COBRA HA antigens elicited more broadly reactive anti-HA antibodies than those elicited by a comparator bivalent wild-type HA vaccine against H1 and H3 influenza viruses isolated between 2009 and 2019.

Evaluation of Next-Generation H3 Influenza Vaccines in Ferrets Pre-Immune to Historical H3N2 Viruses.

Each person has a unique immune history to past influenza virus infections. Exposure to influenza viruses early in life establishes memory B cell populations that influence future immune responses to influenza vaccination. Current influenza vaccines elicit antibodies that are typically strain specific and do not offer broad protection against antigenically drifted influenza strains in all age groups of people. This is particularly true for vaccine antigens of the A(H3N2) influenza virus subtype, where continual antigenic drift necessitates frequent vaccine reformulation. Broadly-reactive influenza virus vaccine antigens offer a solution to combat antigenic drift, but they also need to be equally effective in all populations, regardless of prior influenza virus exposure history. This study examined the role that pre-existing immunity plays on influenza virus vaccination. Ferrets were infected with historical A(H3N2) influenza viruses isolated from either the 1970's, 1980's, or 1990's and then vaccinated with computationally optimized broadly reactive antigens (COBRA) or wild-type (WT) influenza virus like particles (VLPs) expressing hemagglutinin (HA) vaccine antigens to examine the expansion of immune breadth. Vaccines with the H3 COBRA HA antigens had more cross-reactive antibodies following a single vaccination in all three pre-immune regimens than vaccines with WT H3 HA antigens against historical, contemporary, and future drifted A(H3N2) influenza viruses. The H3 COBRA HA vaccines also induced antibodies capable of neutralizing live virus infections against modern drifted A(H3N2) strains at higher titers than the WT H3 HA vaccine comparators.

Next Generation of Computationally Optimized Broadly Reactive HA Vaccines Elicited Cross-Reactive Immune Responses and Provided Protection against H1N1 Virus Infection.

Vaccination is the best way to prevent influenza virus infections, but the diversity of antigenically distinct isolates is a persistent challenge for vaccine development. In order to conquer the antigenic variability and improve influenza virus vaccine efficacy, our research group has developed computationally optimized broadly reactive antigens (COBRAs) in the form of recombinant hemagglutinins (rHAs) to elicit broader immune responses. However, previous COBRA H1N1 vaccines do not elicit immune responses that neutralize H1N1 virus strains in circulation during the recent years. In order to update our COBRA vaccine, two new candidate COBRA HA vaccines, Y2 and Y4, were generated using a new seasonal-based COBRA methodology derived from H1N1 isolates that circulated during 2013-2019. In this study, the effectiveness of COBRA Y2 and Y4 vaccines were evaluated in mice, and the elicited immune responses were compared to those generated by historical H1 COBRA HA and wild-type H1N1 HA vaccines. Mice vaccinated with the next generation COBRA HA vaccines effectively protected against morbidity and mortality after infection with H1N1 influenza viruses. The antibodies elicited by the COBRA HA vaccines were highly cross-reactive with influenza A (H1N1) pdm09-like viruses isolated from 2009 to 2021, especially with the most recent circulating viruses from 2019 to 2021. Furthermore, viral loads in lungs of mice vaccinated with Y2 and Y4 were dramatically reduced to low or undetectable levels, resulting in minimal lung injury compared to wild-type HA vaccines following H1N1 influenza virus infection.

Human neutralizing antibodies against SARS-CoV-2 require intact Fc effector functions for optimal therapeutic protection.

SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here, we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes and CD8+ T cells for optimal clinical and virological benefit. Thus, potently neutralizing mAbs utilize Fc effector functions during therapy to mitigate lung infection and disease.

Next generation methodology for updating HA vaccines against emerging human seasonal influenza A(H3N2) viruses.

While vaccines remain the best tool for preventing influenza virus infections, they have demonstrated low to moderate effectiveness in recent years. Seasonal influenza vaccines typically consist of wild-type influenza A and B viruses that are limited in their ability to elicit protective immune responses against co-circulating influenza virus variant strains. Improved influenza virus vaccines need to elicit protective immune responses against multiple influenza virus drift variants within each season. Broadly reactive vaccine candidates potentially provide a solution to this problem, but their efficacy may begin to wane as influenza viruses naturally mutate through processes that mediates drift. Thus, it is necessary to develop a method that commercial vaccine manufacturers can use to update broadly reactive vaccine antigens to better protect against future and currently circulating viral variants. Building upon the COBRA technology, nine next-generation H3N2 influenza hemagglutinin (HA) vaccines were designed using a next generation algorithm and design methodology. These next-generation broadly reactive COBRA H3 HA vaccines were superior to wild-type HA vaccines at eliciting antibodies with high HAI activity against a panel of historical and co-circulating H3N2 influenza viruses isolated over the last 15 years, as well as the ability to neutralize future emerging H3N2 isolates.

Human neutralizing antibodies against SARS-CoV-2 require intact Fc effector functions and monocytes for optimal therapeutic protection.

SARS-CoV-2 has caused the global COVID-19 pandemic. Although passively delivered neutralizing antibodies against SARS-CoV-2 show promise in clinical trials, their mechanism of action in vivo is incompletely understood. Here, we define correlates of protection of neutralizing human monoclonal antibodies (mAbs) in SARS-CoV-2-infected animals. Whereas Fc effector functions are dispensable when representative neutralizing mAbs are administered as prophylaxis, they are required for optimal protection as therapy. When given after infection, intact mAbs reduce SARS-CoV-2 burden and lung disease in mice and hamsters better than loss-of-function Fc variant mAbs. Fc engagement of neutralizing antibodies mitigates inflammation and improves respiratory mechanics, and transcriptional profiling suggests these phenotypes are associated with diminished innate immune signaling and preserved tissue repair. Immune cell depletions establish that neutralizing mAbs require monocytes for therapeutic efficacy. Thus, potently neutralizing mAbs require Fc effector functions for maximal therapeutic benefit during therapy to modulate protective immune responses and mitigate lung disease.

Elicitation of Protective Antibodies against 20 Years of Future H3N2 Cocirculating Influenza Virus Variants in Ferrets Preimmune to Historical H3N2 Influenza Viruses.

The vast majority of people already have preexisting immune responses to influenza viruses from one or more subtypes. However, almost all preclinical studies evaluate new influenza vaccine candidates in immunologically naive animals. Recently, our group demonstrated that priming naive ferrets with broadly reactive H1 COBRA HA-based vaccines boosted preexisting antibodies induced by wild-type H1N1 virus infections. These H1 COBRA hemagglutinin (HA) antigens induced antibodies with HAI activity against multiple antigenically different H1N1 viral variants. In this study, ferrets, preimmune to historical H3N2 viruses, were vaccinated with virus-like particle (VLP) vaccines expressing either an HA from a wild-type H3 influenza virus or a COBRA H3 HA antigen (T6, T7, T10, or T11). The elicited antisera had the ability to neutralize virus infection against either a panel of viruses representing vaccine strains selected by the World Health Organization or a set of viral variants that cocirculated during the same time period. Preimmune animals vaccinated with H3 COBRA T10 HA antigen elicited sera with higher hemagglutination inhibition (HAI) antibody titers than antisera elicited by VLP vaccines with wild-type HA VLPs in preimmune ferrets. However, while the T11 COBRA vaccine did not elicit HAI activity, the elicited antibodies did neutralize antigenically distinct H3N2 influenza viruses. Overall, H3 COBRA-based HA vaccines were able to neutralize both historical H3 and contemporary, as well as future, H3N2 viruses with higher titers than vaccines with wild-type H3 HA antigens. This is the first report demonstrating the effectiveness of a broadly reactive H3N3 vaccine in a preimmune ferret model.IMPORTANCE After exposure to influenza virus, the host generates neutralizing anti-hemagglutinin (anti-HA) antibodies against that specific infecting influenza strain. These antibodies can also neutralize some, but not all, cocirculating strains. The goal of next-generation influenza vaccines, such as HA head-based COBRA, is to stimulate broadly protective neutralizing antibodies against all strains circulating within a subtype, in particular those that persist over multiple influenza seasons, without requiring an update to the vaccine. To mimic the human condition, COBRA HA virus-like particle vaccines were tested in ferrets that were previously exposed to historical H3N2 influenza viruses. In this model, these vaccines elicited broadly protective antibodies that neutralized cocirculating H3N2 influenza viruses isolated over a 20-year period. This is the first study to show the effectiveness of H3N3 COBRA HA vaccines in a host with preexisting immunity to influenza.

Correction: Split inactivated COBRA vaccine elicits protective antibodies against H1N1 and H3N2 influenza viruses.

[This corrects the article DOI: 10.1371/journal.pone.0204284.].

Split inactivated COBRA vaccine elicits protective antibodies against H1N1 and H3N2 influenza viruses.

Development of broadly reactive or universal influenza vaccines will be a paradigm shifting event for the influenza vaccine field. These next generation vaccines could replace the current standard of care with vaccines that elicit broadly cross-protective immune responses. However, a variety of in vitro and in vivo models are necessary to make the best assessments of these vaccine formulations to determine their mechanisms of action, and allow for downselection of candidates prior to human clinical trials. Our group has developed the computationally optimized broadly reactive antigen (COBRA) technology to develop HA head-based strategies to elicit antibodies against H1, H3, and H5 influenza strains. These vaccines elicit broadly reactive antibody responses that neutralize not only historical and contemporary vaccine strains, but also co-circulating variants in mice. In this study, we used H1 and H3 HA antigens in a split, inactivated vaccine (IIV) formulation in combination with the AF03 squalene-in-water emulsion adjuvant in ferrets immunologically naïve to influenza virus. The H3 COBRA IIV vaccine T11 elicited antibodies with HAI activity against more H3N2 influenza strains compared to IIV expressing wild-type H3 HA antigens, except for IIV vaccines expressing the HA from A/Texas/50/2012 (Tx/12) virus. H1 COBRA IIV vaccines, P1 and X6, elicited antibodies that recognized a similar number of H1N1 viruses as those antibodies elicited by IIV expressing the A/California/07/2009 (CA/09) HA. Ferrets vaccinated with the P1 or X6 COBRA IIV were protected against CA/09 challege and cleared virus from the lungs of the ferrets, similar to ferrets vaccinated with the CA/09 IIV.

H3N2 influenza viruses in humans: Viral mechanisms, evolution, and evaluation.

Annual seasonal influenza vaccines are composed of two influenza A strains representing the H1N1 and H3N2 subtypes, and two influenza B strains representing the Victoria and Yamagata lineages. Strains from these Influenza A and Influenza B viruses currently co-circulate in humans. Of these, strains associated with the H3N2 subtype are affiliated with severe influenza seasons. H3N2 influenza viruses pre-dominated during 3 of the last 5 quite severe influenza seasons. During the 2016/2017 flu season, the H3N2 component of the influenza vaccine exhibited a poor protective efficacy (∼28-42%) against preventing infection of co-circulating strains. Since their introduction to the human population in 1968, H3N2 Influenza viruses have rapidly evolved both genetically and antigenically in an attempt to escape host immune pressures. As a result, these viruses have added numerous N-linked glycans to the viral hemagglutinin (HA), increased the overall net charge of the HA molecule, changed their preferences in receptor binding, and altered the ability of neuraminidase (NA) to agglutinate red blood cells prior to host entry. Over time, these adaptations have made characterizing these viruses increasingly difficult. This review investigates these recent changes in modern H3N2 influenza viruses and explores the methods that researchers are currently developing in order to study these viruses.

Impact of age and pre-existing influenza immune responses in humans receiving split inactivated influenza vaccine on the induction of the breadth of antibodies to influenza A strains.

Most humans have pre-existing immunity to influenza viruses. In this study, volunteers (ages of 18-85 years) were vaccinated with split, inactivated Fluzone™ influenza vaccine in four consecutive influenza seasons from 2013 to 2016 seasons. The impact of repeated vaccination on breadth and durability of antibodies was assessed as a result of vaccine strain changes. Total IgG anti-hemagglutinin (HA) binding antibodies and hemagglutination-inhibition (HAI) activity increased in all age groups against both influenza A HA components in the vaccine post-vaccination (day 21). However, younger subjects maintained seroprotective titers to the vaccine strains, which resulted in higher seroconversion rates in the elderly, since the HAI titers in elderly subjects were more likely to decline prior to the next season. Young subjects had significant HAI activity against historical, as well as contemporary H1 and H3 vaccine strains from the mid-1980s to present. In contrast, elderly subjects had HAI activity to H1 strains from all years, but were more likely to have HAI activity to older strains from 1918-1950s. They also had a more restricted HAI profile against H3 viruses compared to young subjects recognizing H3N2 influenza viruses from the mid-2000s to present. Vaccine recipients were then categorized by whether subjects seroconverted from a seronegative or seropositive pre-vaccination state. Regardless of age, immunological recall or 'back-boosting' to antigenically related strains were associated with seroconversion to the vaccine strain. Overall, both younger and older people have the ability to mount a breadth of immune responses following influenza vaccination. This report describes how imprinting exposure differs across age groups, influences antibody cross-reactivity to past hemagglutinin antigenic variants, and shapes immune responses elicited by current split inactivated influenza vaccines. Understanding how current influenza vaccines are influenced by pre-existing immunity in people of different ages is critical for designing the next-generation of 'universal' or broadly-protective influenza vaccines.

Elicitation of Protective Antibodies against a Broad Panel of H1N1 Viruses in Ferrets Preimmune to Historical H1N1 Influenza Viruses.

Most preclinical animal studies test influenza vaccines in immunologically naive animal models, even though the results of vaccination may not accurately reflect the effectiveness of vaccine candidates in humans that have preexisting immunity to influenza. In this study, novel, broadly reactive influenza vaccine candidates were assessed in preimmune ferrets. These animals were infected with different H1N1 isolates before being vaccinated or infected with another influenza virus. Previously, our group has described the design and characterization of computationally optimized broadly reactive hemagglutinin (HA) antigens (COBRA) for H1N1 isolates. Vaccinating ferrets with virus-like particle (VLP) vaccines expressing COBRA HA proteins elicited antibodies with hemagglutination inhibition (HAI) activity against more H1N1 viruses in the panel than VLP vaccines expressing wild-type HA proteins. Specifically, ferrets infected with the 1986 virus and vaccinated with a single dose of the COBRA HA VLP vaccines elicited antibodies with HAI activity against 11 to 14 of the 15 H1N1 viruses isolated between 1934 and 2013. A subset of ferrets was infected with influenza viruses expressing the COBRA HA antigens. These COBRA preimmune ferrets had superior breadth of HAI activity after vaccination with COBRA HA VLP vaccines than COBRA preimmune ferrets vaccinated with VLP vaccines expressing wild-type HA proteins. Overall, priming naive ferrets with COBRA HA based viruses or using COBRA HA based vaccines to boost preexisting antibodies induced by wild-type H1N1 viruses, COBRA HA antigens elicited sera with the broadest HAI reactivity against multiple antigenic H1N1 viral variants. This is the first report demonstrating the effectiveness of a broadly reactive or universal influenza vaccine in a preimmune ferret model.IMPORTANCE Currently, many groups are testing influenza vaccine candidates to meet the challenge of developing a vaccine that elicits broadly reactive and long-lasting protective immune responses. The goal of these vaccines is to stimulate immune responses that react against most, if not all, circulating influenza strains, over a long period of time in all populations of people. Commonly, these experimental vaccines are tested in naive animal models that do not have anti-influenza immune responses; however, humans have preexisting immunity to influenza viral antigens, particularly antibodies to the HA and NA glycoproteins. Therefore, this study investigated how preexisting antibodies to historical influenza viruses influenced HAI-specific antibodies and protective efficacy using a broadly protective vaccine candidate.

Computationally Optimized Broadly Reactive Hemagglutinin Elicits Hemagglutination Inhibition Antibodies against a Panel of H3N2 Influenza Virus Cocirculating Variants.

Each influenza season, a set of wild-type viruses, representing one H1N1, one H3N2, and one to two influenza B isolates, are selected for inclusion in the annual seasonal influenza vaccine. In order to develop broadly reactive subtype-specific influenza vaccines, a methodology called computationally optimized broadly reactive antigens (COBRA) was used to design novel hemagglutinin (HA) vaccine immunogens. COBRA technology was effectively used to design HA immunogens that elicited antibodies that neutralized H5N1 and H1N1 isolates. In this report, the development and characterization of 17 prototype H3N2 COBRA HA proteins were screened in mice and ferrets for the elicitation of antibodies with HA inhibition (HAI) activity against human seasonal H3N2 viruses that were isolated over the last 48 years. The most effective COBRA HA vaccine regimens elicited antibodies with broader HAI activity against a panel of H3N2 viruses than wild-type H3 HA vaccines. The top leading COBRA HA candidates were tested against cocirculating variants. These variants were not efficiently detected by antibodies elicited by the wild-type HA from viruses selected as the vaccine candidates. The T-11 COBRA HA vaccine elicited antibodies with HAI and neutralization activity against all cocirculating variants from 2004 to 2007. This is the first report demonstrating broader breadth of vaccine-induced antibodies against cocirculating H3N2 strains compared to the wild-type HA antigens that were represented in commercial influenza vaccines.IMPORTANCE There is a need for an improved influenza vaccine that elicits immune responses that recognize a broader number of influenza virus strains to prevent infection and transmission. Using the COBRA approach, a set of vaccines against influenza viruses in the H3N2 subtype was tested for the ability to elicit antibodies that neutralize virus infection against not only historical vaccine strains of H3N2 but also a set of cocirculating variants that circulated between 2004 and 2007. Three of the H3N2 COBRA vaccines recognized all of the cocirculating strains during this era, but the chosen wild-type vaccine strains were not able to elicit antibodies with HAI activity against these cocirculating strains. Therefore, the COBRA vaccines have the ability to elicit protective antibodies against not only the dominant vaccine strains but also minor circulating strains that can evolve into the dominant vaccine strains in the future.

Infection of Ferrets with Influenza Virus Elicits a Light Chain-Biased Antibody Response against Hemagglutinin.

The domestic ferret (Mustela putorius furo) is a commonly used animal model for the study of influenza virus infection and vaccination. Recently, our group has developed murine mAbs with specificity for the κ (Igκ) and λ (Igλ) L chains of ferret Ig. These mAbs were used to quantify the abundance of Igκ and Igλ in serum and to evaluate L chain usage of the Ab response against the hemagglutinin (HA) protein elicited by influenza infection. After influenza A infection of immunologically naive ferrets with various H1N1 or H3N2 strains, the acute Ab response against HA exhibited an inherent bias toward λ L chain usage. In contrast, secondary infection of H1N1 preimmune ferrets with an antigenically distinct H1N1 virus elicited a recall response against the original HA that was no longer biased toward Igλ and possessed differential specificity. Moreover, sequential infection of ferrets with H1N1 influenza viruses elicited an Igκ-biased Ab response directed against the HA globular head and stem regions. Furthermore, sequential infection of ferrets with viral vectors expressing chimeric HA, aimed at boosting Ab reactivity against the HA stem region, also elicited an Igκ-biased response. Collectively, these findings suggest that ferret B cells expressing an Igκ or Igλ BCR possess differential specificities, and highlight the utility of our recently developed mAbs for studying the immune response to influenza virus infection and vaccination in the ferret model.

Broadened immunity and protective responses with emulsion-adjuvanted H5 COBRA-VLP vaccines.

A number of challenges for developing a protective pre-pandemic influenza A vaccine exists including predicting the target influenza strain and designing the vaccine for an immunologically naïve population. Manufacturing and supply of the vaccine would also require implementing ways to increase coverage for the largest number of people through dose-sparing methods, while not compromising the potency of the vaccine. Previously, our group described a novel hemagglutinin (HA) for H5N1 influenza derived from a methodology termed computationally optimized broadly reactive antigen (COBRA). This report describes a strategy combining a COBRA-based HA vaccine with an oil-in-water emulsion, resulting in a dose-sparing, immunologically broadened, and protective response against multiple H5N1 isolates. Here, we show that an emulsion-based adjuvant enhances the magnitude and breadth of antibody responses with both a wild-type H5HA (H5N1 WT) and the H5N1 COBRA HA VLP vaccines. The H5N1 COBRA HA VLP, combined with an emulsion adjuvant, elicited HAI specific antibodies against a larger panel of H5N1 viruses that resulted in protection against challenge as efficiently as the homologous, matched vaccine.