The prospects and challenges of universal vaccines for influenza

mRNA vaccines encoding influenza virus hemagglutinin (HA) elicits immunity in mice from influenza A virus challenge

Influenza viruses cause epidemics and can cause pandemics with substantial morbidity with some mortality every year. Seasonal influenza vaccines have incomplete effectiveness and elicit a narrow antibody response that often does not protect against mutations occurring in influenza viruses. Thus, various vaccine approaches have been investigated to improve safety and efficacy. Here, we evaluate an mRNA influenza vaccine encoding hemagglutinin (HA) proteins in a BALB/c mouse model. The results show that mRNA vaccination elicits neutralizing and serum antibodies to each influenza virus strain contained in the current quadrivalent vaccine that is designed to protect against four different influenza viruses including two influenza A viruses (IAV) and two influenza B (IBV), as well as several antigenically distinct influenza virus strains in both hemagglutination inhibition assay (HAI) and virus neutralization assays. The quadrivalent mRNA vaccines had antibody titers comparable to the antibodies elicited by the monovalent vaccines to each tested virus regardless of dosage following an mRNA booster vaccine. Mice vaccinated with mRNA encoding an H1 HA had decreased weight loss and decreased lung viral titers compared to mice not vaccinated with an mRNA encoding an H1 HA. Overall, this study demonstrates the efficacy of mRNA-based seasonal influenza vaccines are their potential to replace both the currently available split-inactivated, and live-attenuated seasonal influenza vaccines.

Assessing the Intense Influenza A(H1N1)pdm09 Epidemic and Vaccine Effectiveness in the Post-COVID Season in the Russian Federation

The COVID-19 pandemic had a profound impact on influenza activity worldwide. However, as the pandemic progressed, influenza activity resumed. Here, we describe the influenza epidemic of high intensity of the 2022-2023 season. The epidemic had an early start and peaked in week 51.2022. The extremely high intensity of the epidemic may have been due to a significant decrease in herd immunity. The results of PCR-testing of 220,067 clinical samples revealed that the influenza A(H1N1)pdm09 virus dominated, causing 56.4% of positive cases, while A(H3N2) influenza subtype accounted for only 0.6%, and influenza B of Victoria lineage-for 34.3%. The influenza vaccine was found to be highly effective, with an estimated effectiveness of 92.7% in preventing admission with laboratory-confirmed influenza severe acute respiratory illness (SARI) cases and 54.7% in preventing influenza-like illness/acute respiratory illness (ILI/ARI) cases due to antigenic matching of circulated viruses with influenza vaccine strains for the season. Full genome next-generation sequencing of 1723 influenza A(H1N1)pdm09 viruses showed that all of them fell within clade 6B.1A.5.a2; nine of them possessed H275Y substitution in the NA gene, a genetic marker of oseltamivir resistance. Influenza A(H3N2) viruses belonged to subclade 3C.2a1b.2a.2 with the genetic group 2b being dominant. All 433 influenza B viruses belonged to subclade V1A.3a.2 encoding HA1 substitutions A127T, P144L, and K203R, which could be further divided into two subgroups. None of the influenza A(H3N2) and B viruses sequenced had markers of resistance to NA inhibitors. Thus, despite the continuing circulation of Omicron descendant lineages, influenza activity has resumed in full force, raising concerns about the intensity of fore coming seasonal epidemics.

Development of functional antibodies against influenza B virus by activation-induced cytidine deaminase in hybridoma cells

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Class-switch recombination was mimicked in hybridomas by controllable expression of activation-induced cytidine deaminase.

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IgG antibodies were generated through this system in an anti-Flu B IgM hybridoma 7G1.

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IgG1 and IgG2a subtypes of 7G1 present improved antiviral activity in vitro and in vivo.

Characterization of key amino acid substitutions and dynamics of the influenza virus H3N2 hemagglutinin

The annual epidemics of seasonal influenza is partly attributed to the continued virus evolution. It is challenging to evaluate the effect of influenza virus mutations on evading population immunity. In this study, we introduce a novel statistical and computational approach to measure the dynamic molecular determinants underlying epidemics using effective mutations (EMs), and account for the time of waning mutation advantage against herd immunity by measuring the effective mutation periods (EMPs). Extensive analysis is performed on the sequencing and epidemiology data of H3N2 epidemics in ten regions from season to season. We systematically identified 46 EMs in the hemagglutinin (HA) gene, in which the majority were antigenic sites. Eight EMs were located in immunosubdominant stalk domain, an important target for developing broadly reactive antibodies. The EMs might provide timely information on key substitutions for influenza vaccines antigen design. The EMP suggested that major genetic variants of H3N2 circulated in Southeast Asia for an average duration of 4.5 years (SD 2.4) compared to a significantly shorter 2.0 years (SD 1.0) in temperate regions. The proposed method bridges population epidemics and molecular characteristics of infectious diseases, and would find broad applications in various pathogens mutation estimations.

Exploiting Pan Influenza A and Pan Influenza B Pseudotype Libraries for Efficient Vaccine Antigen Selection

We developed an influenza hemagglutinin (HA) pseudotype library encompassing Influenza A subtypes HA1-18 and Influenza B subtypes (both lineages) to be employed in influenza pseudotype microneutralization (pMN) assays. The pMN is highly sensitive and specific for detecting virus-specific neutralizing antibodies against influenza viruses and can be used to assess antibody functionality in vitro. Here we show the production of these viral HA pseudotypes and their employment as substitutes for wildtype viruses in influenza neutralization assays. We demonstrate their utility in detecting serum responses to vaccination with the ability to evaluate cross-subtype neutralizing responses elicited by specific vaccinating antigens. Our findings may inform further preclinical studies involving immunization dosing regimens in mice and may help in the creation and selection of better antigens for vaccine design. These HA pseudotypes can be harnessed to meet strategic objectives that contribute to the strengthening of global influenza surveillance, expansion of seasonal influenza prevention and control policies, and strengthening pandemic preparedness and response.

Broad cross protection by recombinant live attenuated influenza H3N2 seasonal virus expressing conserved M2 extracellular domain in a chimeric hemagglutinin

Hemagglutinin (HA)-based current vaccines provide suboptimum cross protection. Influenza A virus contains an ion channel protein M2 conserved extracellular domain (M2e), a target for developing universal vaccines. Here we generated reassortant influenza virus rgH3N2 4xM2e virus (HA and NA from A/Switzerland/9715293/2013/(H3N2)) expressing chimeric 4xM2e-HA fusion proteins with 4xM2e epitopes inserted into the H3 HA N-terminus. Recombinant rgH3N2 4xM2e virus was found to retain equivalent growth kinetics as rgH3N2 in egg substrates. Intranasal single inoculation of mice with live rgH3N2 4xM2e virus was effective in priming the induction of M2e specific IgG antibody responses in mucosal and systemic sites as well as T cell responses. The rgH3N2 4xM2e primed mice were protected against a broad range of different influenza A virus subtypes including H1N1, H3N2, H5N1, H7N9, and H9N2. The findings support a new approach to improve the efficacy of current vaccine platforms by recombinant influenza virus inducing immunity to HA and cross protective M2e antigens.

Future epidemiological and economic impacts of universal influenza vaccines

The efficacy of influenza vaccines, currently at 44%, is limited by the rapid antigenic evolution of the virus and a manufacturing process that can lead to vaccine mismatch. The National Institute of Allergy and Infectious Diseases (NIAID) recently identified the development of a universal influenza vaccine with an efficacy of at least 75% as a high scientific priority. The US Congress approved $130 million funding for the 2019 fiscal year to support the development of a universal vaccine, and another $1 billion over 5 y has been proposed in the Flu Vaccine Act. Using a model of influenza transmission, we evaluated the population-level impacts of universal influenza vaccines distributed according to empirical age-specific coverage at multiple scales in the United States. We estimate that replacing just 10% of typical seasonal vaccines with 75% efficacious universal vaccines would avert ∼5.3 million cases, 81,000 hospitalizations, and 6,300 influenza-related deaths per year. This would prevent over $1.1 billion in direct health care costs compared to a typical season, based on average data from the 2010-11 to 2018-19 seasons. A complete replacement of seasonal vaccines with universal vaccines is projected to prevent 17 million cases, 251,000 hospitalizations, 19,500 deaths, and $3.5 billion in direct health care costs. States with high per-hospitalization medical expenses along with a large proportion of elderly residents are expected to receive the maximum economic benefit. Replacing even a fraction of seasonal vaccines with universal vaccines justifies the substantial cost of vaccine development.

Isolation of Neutralizing Human Single Chain Antibodies Against Conserved Hemagglutinin Epitopes of Influenza a Virus H3N2 Strain

BACKGROUND

Immunotherapies using monoclonal antibodies against influenza A hemagglutinin (HA) has been an effective means for controlling Influenza spread. An alternative method for viral prophylaxis and treatment is the development of human single-chain variable fragment (scFv) antibodies with no human anti-mouse antibody (HAMA) response and high specificity. In the present study, two highly conserved sequences of HA were used to select specific neutralizing scFvs against H3N2 strain of influenza A virus.

METHODS

Biopanning process was performed to isolate specific scFv antibodies against highly conserved HA sequences, aa173-181 and 227-239, of the influenza A H3N2 strain from a scFv library. The peptide-binding specificity of the selected clones was examined via phage ELISA. The soluble forms of the clones were prepared and assessed using western blot analysis and neutralization efficiency of the selected clones were examined by TCID50 neutralizing assay and real-time PCR.

RESULTS

scFv 1 and scFv 2 were selected against HA of H3N2 influenza A virus with frequencies of 95% and 30% in the panning process, respectively. Western blot analysis confirmed the scFv band size. Significant neutralization in the presence of scFv 1 and scFv 2 were obtained. Real time PCR revealed significant decrease in viral copy number.

CONCLUSION

Two specific neutralizing scFvs against two highly conserved neutralizing epitopes of the influenza A virus HA glycoprotein were selected. A strong neutralization effect of scFv1, showed the potential of this antibody for H3N2 influenza A controlling in the viral spread.

Public Health-Driven Research and Innovation for Next-Generation Influenza Vaccines, European Union

Influenza virus infections are a major public health threat. Vaccination is available, but unpredictable antigenic changes in circulating strains require annual modification of seasonal influenza vaccines. Vaccine effectiveness has proven limited, particularly in certain groups, such as the elderly. Moreover, preparedness for upcoming pandemics is challenging because we can predict neither the strain that will cause the next pandemic nor the severity of the pandemic. The European Union fosters research and innovation to develop novel vaccines that evoke broadly protective and long-lasting immune responses against both seasonal and pandemic influenza, underpinned by a political commitment to global public health.

Co-Delivery of M2e Virus-Like Particles with Influenza Split Vaccine to the Skin Using Microneedles Enhances the Efficacy of Cross Protection

It is a high priority to develop a simple and effective delivery method for a cross-protective influenza vaccine. We investigated skin immunization by microneedle (MN) patch with human influenza split vaccine and virus-like particles containing heterologous M2 extracellular (M2e) domains (M2e5x virus-like particles (VLP)) as a cross-protective influenza vaccine candidate. Co-delivery of influenza split vaccine and M2e5x VLP to the skin by MN patch was found to confer effective protection against heterosubtypic influenza virus by preventing weight loss and reducing lung viral loads. Compared to intramuscular immunization, MN-based delivery of combined split vaccine and M2e5x VLPs shaped cellular immune responses toward T helper type 1 responses increasing IgG2a isotype antibodies as well as IFN-γ producing cells in mucosal and systemic sites. This study provides evidence that potential immunological and logistic benefits of M2e5x VLP with human influenza split vaccine delivered by MN patch can be used to develop an easy-to-administer cross-protective influenza vaccine.

Life-course immunization as a gateway to health

INTRODUCTION

Extending the benefits of vaccination against infectious diseases from childhood throughout the entire life-span is becoming an increasingly urgent priority in view of the world's aging population, emergence and reemergence of infectious diseases, and the necessity to invest more on prevention versus cure in global healthcare. Areas covered: This perspective discusses how life-course immunization could benefit human health at all stages of life. To achieve this, the current vaccination paradigm should be changed and all stakeholders have a role to play. Expert commentary: To enhance immunization confidence in the population, it is essential that stakeholders eliminate complacency toward infectious diseases, improve vaccination convenience, remove barriers among different healthcare specialties, and address prevention as a single entity. They must also consider societal and cultural mindsets by understanding and including public viewpoints. A new "4Cs' model encompassing convenience, confidence, complacency, and cultural acceptance is proposed to convert 'vaccine availability' to 'vaccination acceptance' throughout life. Life-course vaccination should become the new social norm of a healthy life-style, along with a healthy diet, adequate physical exercise, and not smoking. We are 'all in' to make life-course immunization a gateway for all people to lead longer, healthier lives.

An IgM antibody targeting the receptor binding site of influenza B blocks viral infection with great breadth and potency

Broadly neutralizing antibodies (bnAbs) targeting the receptor binding site (RBS) of hemagglutinin (HA) have potential for developing into powerful anti-influenza agents. Several previously reported influenza B bnAbs are nevertheless unable to neutralize a portion of influenza B virus variants. HA-specific bnAbs with hemagglutination inhibition (HI) activity may possess the ability to block virus entry directly. Polymeric IgM antibodies are expected to more effectively inhibit virus attachment and entry into target cells due to their higher avidity and/or steric hindrance. We therefore hypothesized that certain RBS-targeted IgM antibodies with strong cross-lineage HI activity might display broader and more potent antiviral activity against rapidly evolving influenza B viruses.

Methods: In this study, we generated IgM and IgG bnAbs targeting the RBS of influenza B virus using the murine hybridoma technique. IgM and IgG versions of the same antibodies were then developed by isotype switching and characterized in subsequent in vitro and in vivo experiments.

Results: Two IgM and two IgG bnAbs against influenza B virus HA were identified. Of these, one IgM subtype antibody, C7G6-IgM, showed strong HI and neutralization activities against all 20 representative influenza B strains tested, with higher potency and broader breadth of anti-influenza activity in vitro than the IgG subtype variant of itself, or other previously-reported influenza B bnAbs. Furthermore, C7G6-IgM conferred excellent cross-protection against distinct lineages of influenza B viruses in mice and ferrets, performing better than the anti-influenza drug oseltamivir, and showed an additive antiviral effect when administered in combination with oseltamivir. Mechanistically, C7G6-IgM potently inhibits infection with influenza B virus strains from different lineages by blocking viral entry.

Conclusion: In summary, our study highlights the potential of IgM subtype antibodies in combatting pathogenic microbes. Moreover, C7G6-IgM is a promising candidate for the development of prophylactics or therapeutics against influenza B infection.

Eliciting unnatural immune responses by activating cryptic epitopes in viral antigens

Antigenic variation in viral surface antigens is a strategy for escaping the host's adaptive immunity, whereas regions with pivotal functions for infection are less subject to antigenic variability. We hypothesized that genetically invariable and immunologically dormant regions of a viral surface antigen could be exposed to the host immune system and activated by rendering them susceptible to antigen-processing machinery in professional antigen-presenting cells (APCs). Considering the frequent antigen drift and shift in influenza viruses, we identified and used structural modeling to evaluate the conserved regions on the influenza hemagglutinin (HA) surface as potential epitopes. Mutant viruses containing the cleavage motifs of cathepsin S within HA were generated. Immunization of mice showed that the mutant, but not the wild-type virus, elicited specific antibodies against the cryptic epitope. Those antibodies were purified, and specific binding to HA was confirmed. These results suggest that an unnatural immune response can be elicited through the processing of target antigens in APCs, followed by presentation via the major histocompatibility complex, if not subjected to regulatory pathways. By harnessing the antigen-processing machinery, our study shows a proof-of-principle for designer vaccines with increased efficacy and safety by either activating cryptic, or inactivating naturally occurring, epitopes of viral antigens.-Lee, Y. J., Yu, J. E., Kim, P., Lee, J.-Y., Cheong, Y. C., Lee, Y. J., Chang, J., Seong, B. L. Eliciting unnatural immune responses by activating cryptic epitopes in viral antigens.

Recombinant M2e-HA2 fusion protein induced immunity responses against intranasally administered H9N2 influenza virus

Influenza is a highly contagious respiratory tract disease and is considered a serious community health problem. Influenza viruses possess multiple conserved epitopes which are used for designing universal vaccines. To this aim, the gene coding for N-terminal part of M2e (SLLTEVET) and HA2 (GLFGAIAGF), was synthesized, linked by a (Gly4Ser)₄ peptide linker, and cloned into pGS-21a vector. Afterwards, the construct was transferred into E. coli BL21 (DE3) cells to produce the designed antigenic protein called M2e-HA2. Immunization of mice with these peptides significantly induced humoral immune responses against the influenza virus. Three weeks after the last booster, mice were inoculated intranasally with 1 × 10⁶ EID₅₀ of H9N2 virus. The results indicated that the recombinant M2e-HA2 fusion protein could protect mice against H9N2 virus.

Computationally-driven identification of antibody epitopes

Understanding where antibodies recognize antigens can help define mechanisms of action and provide insights into progression of immune responses. We investigate the extent to which information about binding specificity implicitly encoded in amino acid sequence can be leveraged to identify antibody epitopes. In computationally-driven epitope localization, possible antibody–antigen binding modes are modeled, and targeted panels of antigen variants are designed to experimentally test these hypotheses. Prospective application of this approach to two antibodies enabled epitope localization using five or fewer variants per antibody, or alternatively, a six-variant panel for both simultaneously. Retrospective analysis of a variety of antibodies and antigens demonstrated an almost 90% success rate with an average of three antigen variants, further supporting the observation that the combination of computational modeling and protein design can reveal key determinants of antibody–antigen binding and enable efficient studies of collections of antibodies identified from polyclonal samples or engineered libraries.

Immunogenicity and efficacy of replication-competent recombinant influenza virus carrying multimeric M2 extracellular domains in a chimeric hemagglutinin conjugate

Current influenza vaccines provide hemagglutinin (HA) strain-specific protection. To improve cross protection, we engineered replication-competent influenza A virus to express tandem repeats of heterologous M2 extracellular (M2e) domains in a chimeric HA. M2e epitopes conjugated to HA glycoproteins (M2e4x-HA) were found to be expressed on the surfaces of a replicable influenza virus as examined by electron microscopy. The recombinant influenza virus containing M2e4x-HA was moderately attenuated but superior to the parental virus in inducing M2e specific antibodies without compromising HA immunogenicity. Recombinant influenza virus immune mice showed better cross protection than parental virus immune mice. Immune sera from the mice with inoculation of live recombinant influenza virus expressing M2e4x-HA were effective in conferring protection against H1, H3, and H5 subtype influenza viruses. This study indicates that recombinant influenza virus expressing conserved protective epitopes in an HA chimeric form can provide a new approach for improving the efficacy of influenza vaccines.

Roles of antibodies to influenza A virus hemagglutinin, neuraminidase, and M2e in conferring cross protection

Although neuraminidase (NA) is the second major viral glycoprotein of influenza virus, its immune mechanism as a vaccine target has been less considered. Here we compared the properties of antibodies and the efficacy of cross protection by N1 and N2 NA proteins, inactivated split influenza vaccines (split), and tandem repeat extracellular domain M2 on virus-like particles (M2e5x VLP). Anti-NA immune sera could confer better cross-protection against multiple heterologous influenza viruses correlating with NA inhibition activity compared to split vaccine immune sera. Whereas split vaccine was superior to NA in conferring homologous protection. NA and M2e immune sera each showed comparable survival protection. Protective efficacy by NA immune sera was lower in Fc receptor common γ-chain deficient mice but comparable in C3 complement deficient mice compared to that in wild type mice, suggesting a role of Fc receptor in NA immunity.

Expression of surface-bound nonstructural 1 (NS1) protein of influenza virus A H5N1 on Lactobacillus casei strain C1

The study aimed to construct a recombinant Lactobacillus casei expressing the nonstructural (NS) 1 protein of influenza A virus H5N1 on its cell wall. The NS1 gene was first amplified and fused to the pSGANC332 expression plasmid. The NS1 protein expression was carried out by Lact. casei strain C1. PCR screening and DNA sequencing confirmed the presence of recombinant pSG-NS1-ANC332 plasmid in Lact. casei. The plasmid was stably maintained (98·94 ± 1·65%) by the bacterium within the first 20 generations without selective pressure. The NS1 was expressed as a 49-kDa protein in association with the anchoring peptide. The yield was 1·325 ± 0·065 μg mg^-1 of bacterial cells. Lactobacillus casei expressing the NS1 on its cell wall was red-fluorescently stained, but the staining was not observed on Lact. casei carrying the empty pSGANC332. The results implied that Lact. casei strain C1 is a promising host for the expression of surface-bound NS1 protein using the pSGANC332 expression plasmid.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study has demonstrated, for the first time, the expression of nonstructural 1 (NS1) protein of influenza A virus H5N1 on the cell wall of Lactobacillus casei using the pSGANC332 expression plasmid. Display of NS1 protein on the bacterial cell wall was evident under an immunofluorescence microscopic observation. Lactobacillus casei carrying the NS1 protein could be developed into a universal oral influenza vaccine since the NS1 is highly conserved among influenza viruses.

Evaluating influenza vaccines: progress and perspectives

Severe influenza infections are responsible for 3–5 million cases worldwide and 250,000–500,000 deaths per year. Although vaccination is the primary and most effective means of inducing protection against influenza viruses, it also presents limitations. This review outlines the promising steps that have been taken toward the development of a broadly protective influenza virus vaccine through the use of new technologies. The future challenge is to develop a broadly protective vaccine that is able to induce long-term protection against antigenically variant influenza viruses, regardless of antigenic shift and drift, and thus to protect against seasonal and pandemic influenza viruses.

Microneedle delivery of trivalent influenza vaccine to the skin induces long-term cross-protection

A painless self-immunization method with effective and broad cross-protection is urgently needed to prevent infections against newly emerging influenza viruses. In this study, we investigated the cross-protection efficacy of trivalent influenza vaccine containing inactivated A/PR/8/34 (H1N1), A/Hong Kong/68 (H3N2) and B/Lee/40 after skin vaccination using microneedle patches coated with this vaccine. Microneedle vaccination of mice in the skin provided 100% protection against lethal challenges with heterologous pandemic strain influenza A/California/04/09, heterogeneous A/Philippines/2/82 and B/Victoria/287 viruses 8 months after boost immunization. Cross-reactive serum IgG antibody responses against heterologous influenza viruses A/California/04/09, A/Philippines/2/82 and B/Victoria/287 were induced at high levels. Hemagglutination inhibition titers were also maintained at high levels against these heterogeneous viruses. Microneedle vaccination induced substantial levels of cross-reactive IgG antibody responses in the lung and cellular immune responses, as well as cross-reactive antibody-secreting plasma cells in the spleen. Viral loads in the lung were significantly (p < 0.05) reduced. All mice survived after viral challenges. These results indicate that skin vaccination with trivalent vaccine using a microneedle array could provide protection against seasonal epidemic or new pandemic strain of influenza viruses.

High-Yield Expression of M2e Peptide of Avian Influenza Virus H5N1 in Transgenic Duckweed Plants

Avian influenza is a major viral disease in poultry. Antigenic variation of this virus hinders vaccine development. However, the extracellular domain of the virus-encoded M2 protein (peptide M2e) is nearly invariant in all influenza A strains, enabling the development of a broad-range vaccine against them. Antigen expression in transgenic plants is becoming a popular alternative to classical expression methods. Here we expressed M2e from avian influenza virus A/chicken/Kurgan/5/2005(H5N1) in nuclear-transformed duckweed plants for further development of avian influenza vaccine. The N-terminal fragment of M2, including M2e, was selected for expression. The M2e DNA sequence fused in-frame to the 5' end of β-glucuronidase was cloned into pBI121 under the control of CaMV 35S promoter. The resulting plasmid was successfully used for duckweed transformation, and western analysis with anti-β-glucuronidase and anti-M2e antibodies confirmed accumulation of the target protein (M130) in 17 independent transgenic lines. Quantitative ELISA of crude protein extracts from these lines showed M130-β-glucuronidase accumulation ranging from 0.09-0.97 mg/g FW (0.12-1.96 % of total soluble protein), equivalent to yields of up to 40 μg M2e/g plant FW. This relatively high yield holds promise for the development of a duckweed-based expression system to produce an edible vaccine against avian influenza.

Infection

Virus infection of higher organisms is the cumulative result of all the processes of replication and gene expression described in the previous chapters. Together, these determine the overall course of each infection. Infections range in complexity and duration from a very brief, superficial interaction between the virus and its host to infections that may span the entire life of the host organism, from before birth to its eventual death. A common misconception is that virus infection inevitably results in disease. In reality, the reverse is true—only a small minority of virus infections gives rise to any disease symptoms. This chapter provides an overview of the numerous patterns of virus infection and forms an introduction to the discussion of virus pathogenesis in Chapter 7. Unlike previous and subsequent chapters, this chapter deals primarily with the interaction of viruses with intact organisms rather than with the molecular biologist’s usual concern about the interaction between a virus and the cell.

Hemagglutinin Stalk Immunity Reduces Influenza Virus Replication and Transmission in Ferrets

We assessed whether influenza virus hemagglutinin stalk-based immunity protects ferrets against aerosol-transmitted H1N1 influenza virus infection. Immunization of ferrets by a universal influenza virus vaccine strategy based on viral vectors expressing chimeric hemagglutinin constructs induced stalk-specific antibody responses. Stalk-immunized ferrets were cohoused with H1N1-infected ferrets under conditions that permitted virus transmission. Hemagglutinin stalk-immunized ferrets had lower viral titers and delayed or no virus replication at all following natural exposure to influenza virus.

Influenza vaccines: challenges and solutions

Vaccination is the best method for the prevention and control of influenza. Vaccination can reduce illness and lessen severity of infection. This review focuses on how currently licensed influenza vaccines are generated in the U.S., why the biology of influenza poses vaccine challenges, and vaccine approaches on the horizon that address these challenges.

Viral vaccines and their manufacturing cell substrates: New trends and designs in modern vaccinology

Vaccination is one of the most effective interventions in global health. The worldwide vaccination programs significantly reduced the number of deaths caused by infectious agents. A successful example was the eradication of smallpox in 1979 after two centuries of vaccination campaigns. Since the first variolation administrations until today, the knowledge on immunology has increased substantially. This knowledge combined with the introduction of cell culture and DNA recombinant technologies revolutionized vaccine design. This review will focus on vaccines against human viral pathogens, recent developments on vaccine design and cell substrates used for their manufacture. While the production of attenuated and inactivated vaccines requires the use of the respective permissible cell substrates, the production of recombinant antigens, virus‐like particles, vectored vaccines and chimeric vaccines requires the use – and often the development – of specific cell lines. Indeed, the development of novel modern viral vaccine designs combined with, the stringent safety requirements for manufacture, and the better understanding on animal cell metabolism and physiology are increasing the awareness on the importance of cell line development and engineering areas. A new era of modern vaccinology is arriving, offering an extensive toolbox to materialize novel and creative ideas in vaccine design and its manufacture.

Single-Dose CpG Immunization Protects Against a Heterosubtypic Challenge and Generates Antigen-Specific Memory T Cells

Despite extensive research, influenza A virus (IAV) remains a major cause of morbidity, mortality, and healthcare expenditure. Emerging pandemics from highly pathogenic IAV strains, such as H5N1 and pandemic H1N1, highlight the need for universal, cross-protective vaccines. Current vaccine formulations generate strain-specific neutralizing antibodies primarily against the outer coat proteins, hemagglutinin and neuraminidase. In contrast to these highly mutable proteins, internal proteins of IAV are more conserved and are a favorable target for developing vaccines that induce strong T cell responses in addition to humoral immunity. Here, we found that intranasal administration with a single dose of CpG and inactivated x31 (H3N2) reduced viral titers and partially protected mice from a heterosubtypic challenge with a lethal dose of PR8 (H1N1). Early after immunization, vaccinated mice showed increased innate immune activation with high levels of MHCII and CD86 expression on dendritic cells in both draining lymph nodes and lungs. Three days after immunization, CD4 and CD8 cells in the lung upregulated CD69, suggesting that activated lymphocytes are present at the site of vaccine administration. The ensuing effector Th1 responses were capable of producing multiple cytokines and were present at least 30 days after immunization. Furthermore, functional memory responses were observed, as antigen-specific IFN-γ⁺ and GrB⁺ cells were detected early after lethal infection. Together, this work provides evidence for using pattern recognition receptor agonists as a mucosal vaccine platform for inducing robust T cell responses capable of protecting against heterologous IAV challenges.

Microneedle Vaccination Elicits Superior Protection and Antibody Response over Intranasal Vaccination against Swine-Origin Influenza A (H1N1) in Mice

Influenza is one of the critical infectious diseases globally and vaccination has been considered as the best way to prevent. In this study, immunogenicity and protection efficacy between intranasal (IN) and microneedle (MN) vaccination was compared using inactivated swine-origin influenza A/H1N1 virus vaccine. Mice were vaccinated by MN or IN administration with 1 μg of inactivated H1N1 virus vaccine. Antigen-specific antibody responses and hemagglutination-inhibition (HI) titers were measured in all immunized sera after immunization. Five weeks after an immunization, a lethal challenge was performed to evaluate the protective efficacy. Furthermore, mice were vaccinated by IN administration with higher dosages (> 1 μg), analyzed in the same manner, and compared with 1 μg-vaccine-coated MN. Significantly higher antigen-specific antibody responses and HI titer were measured in sera in MN group than those in IN group. While 100% protection, slight weight loss, and reduced viral replication were observed in MN group, 0% survival rate were observed in IN group. As vaccine dose for IN vaccination increased, MN-immunized sera showed much higher antigen-specific antibody responses and HI titer than other IN groups. In addition, protective immunity of 1 μg-MN group was similar to those of 20- and 40 μg-IN groups. We conclude that MN vaccination showed more potential immune response and protection than IN vaccination at the same vaccine dosage.

Microneedle patch delivery to the skin of virus-like particles containing heterologous M2e extracellular domains of influenza virus induces broad heterosubtypic cross-protection

A broadly cross-protective influenza vaccine that can be administrated by a painless self-immunization method would be a value as a potential universal mass vaccination strategy. This study developed a minimally-invasive microneedle (MN) patch for skin vaccination with virus-like particles containing influenza virus heterologous M2 extracellular (M2e) domains (M2e5x VLPs) as a universal vaccine candidate without adjuvants. The stability of M2e5x VLP-coated microneedles was maintained for 8weeks at room temperature without losing M2e antigenicity and immunogenicity. MN skin immunization induced strong humoral and mucosal M2e antibody responses and conferred cross-protection against heterosubtypic H1N1, H3N2, and H5N1 influenza virus challenges. In addition, M2e5x VLP MN skin vaccination induced T-helper type 1 responses such as IgG2a isotype antibodies and IFN-γ producing cells at higher levels than those by conventional intramuscular injection. These potential immunological and logistic advantages for skin delivery of M2e5x VLP MN vaccines could offer a promising approach to develop an easy-to-administer universal influenza vaccine.

Vaccines against influenza A viruses in poultry and swine: Status and future developments

Influenza A viruses are important pathogens with a very broad host spectrum including domestic poultry and swine. For preventing clinical disease and controlling the spread, vaccination is one of the most efficient tools. Classical influenza vaccines for domestic poultry and swine are conventional inactivated preparations. However, a very broad range of novel vaccine types ranging from (i) nucleic acid-based vaccines, (ii) replicon particles, (iii) subunits and virus-like particles, (iv) vectored vaccines, or (v) live-attenuated vaccines has been described, and some of them are now also used in the field. The different novel approaches for vaccines against avian and swine influenza virus infections are reviewed, and additional features like universal vaccines, novel application approaches and the "differentiating infected from vaccinated animals" (DIVA)-strategy are summarized.

A human monoclonal antibody derived from a vaccinated volunteer recognizes heterosubtypically a novel epitope on the hemagglutinin globular head of H1 and H9 influenza A viruses

Most neutralizing antibodies elicited during influenza virus infection or by vaccination have a narrow spectrum because they usually target variable epitopes in the globular head region of hemagglutinin (HA). In this study, we describe a human monoclonal antibody (HuMAb), 5D7, that was prepared from the peripheral blood lymphocytes of a vaccinated volunteer using the fusion method. The HuMAb heterosubtypically neutralizes group 1 influenza A viruses, including seasonal H1N1, 2009 pandemic H1N1 (H1N1pdm) and avian H9N2, with a strong hemagglutinin inhibition activity. Selection of an escape mutant showed that the HuMAb targets a novel conformational epitope that is located in the HA head region but is distinct from the receptor binding site. Furthermore, Phe114Ile substitution in the epitope made the HA unrecognizable by the HuMAb. Amino acid residues in the predicted epitope region are also highly conserved in the HAs of H1N1 and H9N2. The HuMAb reported here may be a potential candidate for the development of therapeutic/prophylactic antibodies against H1 and H9 influenza viruses.

Options and obstacles for designing a universal influenza vaccine

Since the discovery of antibodies specific to a highly conserved stalk region of the influenza virus hemagglutinin (HA), eliciting such antibodies has been considered the key to developing a universal influenza vaccine that confers broad-spectrum protection against various influenza subtypes. To achieve this goal, a prime/boost immunization strategy has been heralded to redirect host immune responses from the variable globular head domain to the conserved stalk domain of HA. While this approach has been successful in eliciting cross-reactive antibodies against the HA stalk domain, protective efficacy remains relatively poor due to the low immunogenicity of the domain, and the cross-reactivity was only within the same group, rather than among different groups. Additionally, concerns are raised on the possibility of vaccine-associated enhancement of viral infection and whether multiple boost immunization protocols would be considered practical from a clinical standpoint. Live attenuated vaccine hitherto remains unexplored, but is expected to serve as an alternative approach, considering its superior cross-reactivity. This review summarizes recent advancements in the HA stalk-based universal influenza vaccines, discusses the pros and cons of these approaches with respect to the potentially beneficial and harmful effects of neutralizing and non-neutralizing antibodies, and suggests future guidelines towards the design of a truly protective universal influenza vaccine.

Challenges of selecting seasonal influenza vaccine strains for humans with diverse pre-exposure histories

Seasonal influenza vaccine strains are routinely updated when influenza viruses acquire mutations in exposed regions of the hemagglutinin and neuraminidase glycoproteins. Ironically, although thousands of viral isolates are sequenced each year, today's influenza surveillance community places less emphasis on viral genetic information and more emphasis on classical serological assays when choosing vaccine strains. Here, I argue that these classical serological assays are oversimplified and that they fail to detect influenza mutations that facilitate escape of particular types of human antibodies. I propose that influenza vaccine strains should be updated more frequently even when classical serological assays fail to detect significant antigenic alterations.

Human monoclonal antibodies derived from a patient infected with 2009 pandemic influenza A virus broadly cross-neutralize group 1 influenza viruses

Influenza viruses are a continuous threat to human public health because of their ability to evolve rapidly through genetic drift and reassortment. Three human monoclonal antibodies (HuMAbs) were generated in this study, 1H11, 2H5 and 5G2, and they cross-neutralize a diverse range of group 1 influenza A viruses, including seasonal H1N1, 2009 pandemic H1N1 (H1N1pdm) and avian H5N1 and H9N2. The three HuMAbs were prepared by fusing peripheral blood lymphocytes from an H1N1pdm-infected patient with a newly developed fusion partner cell line, SPYMEG. All the HuMAbs had little hemagglutination inhibition activity but had strong membrane-fusion inhibition activity against influenza viruses. A protease digestion assay showed the HuMAbs targeted commonly a short α-helix region in the stalk of the hemagglutinin. Furthermore, Ile45Phe and Glu47Gly double substitutions in the α-helix region made the HA unrecognizable by the HuMAbs. These two amino acid residues are highly conserved in the HAs of H1N1, H5N1 and H9N2 viruses. The HuMAbs reported here may be potential candidates for the development of therapeutic antibodies against group 1 influenza viruses.

MVA vectors expressing conserved influenza proteins protect mice against lethal challenge with H5N1, H9N2 and H7N1 viruses

Background

The availability of a universal influenza vaccine able to induce broad cross-reactive immune responses against diverse influenza viruses would provide an alternative to currently available strain-specific vaccines. We evaluated the ability of vectors based on modified vaccinia virus Ankara (MVA) expressing conserved influenza proteins to protect mice against lethal challenge with multiple influenza subtypes.

Methods

Mice were immunized with MVA vectors expressing H5N1-derived nucleoprotein (NP), the stem region of hemagglutinin (HA), matrix proteins 1 and 2 (M1 and M2), the viral polymerase basic protein 1 (PB1), or the HA stem fused to a quadrivalent matrix protein 2 extracellular domain (M2e). Immunized mice were challenged with lethal doses of H5N1, H7N1 or H9N2 virus and monitored for disease symptoms and weight loss. To investigate the influence of previous exposure to influenza virus on protective immune responses induced by conserved influenza proteins, mice were infected with pandemic H1N1 virus (H1N1pdm09) prior to immunization and subsequently challenged with H5N1 virus. Antibody and T cell responses were assessed by ELISA and flow cytometry, respectively.

Results

MVA vectors expressing NP alone, or co-expressed with other conserved influenza proteins, protected mice against lethal challenge with H5N1, H7N1 or H9N2 virus. Pre-exposure to H1N1pdm09 increased protective efficacy against lethal H5N1 challenge. None of the other conserved influenza proteins provided significant levels of protection against lethal challenge. NP-expressing vectors induced high numbers of influenza-specific CD4⁺ and CD8⁺ T cells and high titer influenza-specific antibody responses. Higher influenza-specific CD4⁺ T cell responses and NP-specific CD8⁺ T cell responses were associated with increased protective efficacy.

Conclusions

MVA vectors expressing influenza NP protect mice against lethal challenge with H5N1, H7N1 and H9N2 viruses by a mechanism involving influenza-specific CD4⁺ and CD8⁺ T cell responses.

Advances in universal influenza virus vaccine design and antibody mediated therapies based on conserved regions of the hemagglutinin

The threat of novel influenza viruses emerging into the human population from animal reservoirs, as well as the short duration of protection conferred by licensed vaccines against human seasonal strains has spurred research efforts to improve upon current vaccines and develop novel therapeutics against influenza viruses. In recent years these efforts have resulted in the identification of novel, highly conserved epitopes for neutralizing antibodies on the influenza virus hemagglutinin protein, which are present in both the stalk and globular head domains of the molecule. The existence of such epitopes may allow for generation of novel therapeutic antibodies, in addition to serving as attractive targets of novel vaccine design. The aims of developing improved vaccines include eliciting broader protection from drifted strains, inducing long-lived immunity against seasonal strains, and allowing for the rational design of vaccines that can be stockpiled for use as pre-pandemic vaccines. In addition, an increased focus on influenza virus vaccine research has prompted an improved understanding of how the immune system responds to influenza virus infection.

Prevention and Control of Influenza Viruses

The 2003–2004 outbreaks of highly pathogenic avian influenza (HPAI) have proven to be disastrous to the regional poultry industry in Asia, and have raised serious worldwide public health apprehension regarding the steps that should be taken to urgently control HPAI. Control measures must be taken based on the principles of biosecurity and disease management and at the same time making public aware of the precautionary measures at the verge of outbreak. Creation of protection and surveillance zones, various vaccination strategies viz. routine, preventive, emergency, mass and targeted vaccination programmes using live, inactivated and recombinant vaccines are the common strategies adopted in different parts of the globe. The new generation vaccines include recombinant vaccines and recombinant fusion vaccine. The pro-poor disease control programmes, giving compensation and subsidies to the farmers along with effective and efficient Veterinary Services forms integral part of control of HPAI. Following biosecurity principles and vaccination forms integral part of control programme against swine and equine influenza as well. Use of neuraminidase (NA) inhibitors (Zanamivir and Oseltamivir) for the treatment of human influenza has been widely accepted worldwide. The threat of increasing resistance of the flu viruses to these antivirals has evoked interest in the development of novel antiviral drugs for influenza virus such as inhibitors of cellular factors and host signalling cascades, cellular miRNAs, siRNA and innate immune peptides (defensins and cathelicidins). Commercial licensed inactivated vaccines for humans against influenza A and B viruses are available consisting of three influenza viruses: influenza type A subtype H3N2, influenza type A subtype H1N1 (seasonal) virus strain and influenza type B virus strain. As per WHO, use of tetravaccine consisting of antigens of influenza virus serotypes H3N2, H1N1, B and H5 is the most promising method to control influenza pandemic. All healthy children in many countries are required to be vaccinated between 6 and 59 months of age. The seasonal vaccines currently used in humans induce strain-specific humoral immunity as the antibodies. Universal influenza virus vaccines containing the relatively conserved ectodomain of M2 (M2e), M1, HA fusion peptide and stalk domains, NA, NP alone or in combination have been developed which have been shown to induce cross-protection. The T cell-based vaccines are another recent experimental approach that has been shown to elicit broad-spectrum heterosubtypic immunity in the host. As far as HPAI is concerned, various pandemic preparedness strategies have been documented.

Genome-wide mutagenesis of influenza virus reveals unique plasticity of the hemagglutinin and NS1 proteins

The molecular basis for the diversity across influenza strains is poorly understood. To gain insight into this question, we mutagenized the viral genome and sequenced recoverable viruses. Only two small regions in the genome were enriched for insertions, the hemagglutinin head and the immune-modulatory nonstructural protein 1. These proteins play a major role in host adaptation, and thus need to be able to evolve rapidly. We propose a model in which certain influenza A virus proteins (or protein domains) exist as highly plastic scaffolds, which will readily accept mutations yet retain their functionality. This model implies that the ability to rapidly acquire mutations is an inherent aspect of influenza HA and nonstructural protein 1 proteins; further, this may explain why rapid antigenic drift and a broad host range is observed with influenza A virus and not with some other RNA viruses.

How will physicians respond to the next influenza pandemic?

The emergence of the H7N9 virus in China is another reminder of the threat of a global influenza pandemic. Many believe we could confront a pandemic by expanding our capacity to provide timely supplies of affordable pandemic vaccines and antiviral agents. Experience in 2009 demonstrated that this cannot and will not be done. Consequently, physicians may have little more to offer their patients than they had in the 1918 pandemic. Fortunately, several modern drugs (eg, statins, angiotensin II receptor blockers, angiotensin-converting enzyme inhibitors) can modify the host response to inflammatory illness, and laboratory and clinical studies suggest they might be used to treat pandemic patients. Unfortunately, little attention has been given to the research needed to support their use in patient care. There is no guarantee these drugs will work, but physicians will never know unless those responsible for pandemic preparedness recognize and act on the extraordinary possibility that they might save lives.

Immunologic consequences of chemotherapy for ovarian cancer: impaired responses to the influenza vaccine

OBJECTIVES

To examine the effect of chemotherapy for ovarian cancer on immunologic function and to define the effect on the serologic response to the influenza vaccine.

METHODS

Under IRB approved protocols, patients with ovarian cancer were administered seasonal trivalent killed influenza vaccines. Peripheral blood was collected for immunologic assessments. Serum was analyzed for hemagglutination inhibition (HAI) antibody titers. Peripheral blood mononuclear cells were isolated to characterize T and B cell populations and function.

RESULTS

Thirty-one patients were recruited: 13 in remission receiving a dendritic cell vaccine with or without a single dose of low-dose cyclophosphamide, 3 in remission not receiving treatment, and 15 undergoing standard therapy. Significant effects on T cell and B cell subset distributions were seen. Functional effects were also seen. Few patients were able to mount a 4-fold HAI antibody response. A 4-fold response was observed for H1N1 in 20%, for H3N2 in 26%, and for influenza B in 6%. Pre-existing exposure to influenza was predictive of responders.

CONCLUSIONS

Despite CDC recommendations that patients undergoing chemotherapy receive influenza vaccine, there is little evidence to support its serologic effectiveness in this population. Patients with ovarian cancer are almost uniformly unable to mount a meaningful antibody response. These findings have serious implications for future resource allocation for both seasonal and novel pandemic influenza outbreak and understanding the immunologic deficits as a result of chemotherapy may improve patient care.