A triclade DNA vaccine designed on the basis of a comprehensive serologic study elicits neutralizing antibody responses against all clades and subclades of highly pathogenic avian influenza H5N1 viruses

Status and Challenges for Vaccination against Avian H9N2 Influenza Virus in China

In China, H9N2 avian influenza virus (AIV) has become widely prevalent in poultry, causing huge economic losses after secondary infection with other pathogens. Importantly, H9N2 AIV continuously infects humans, and its six internal genes frequently reassort with other influenza viruses to generate novel influenza viruses that infect humans, threatening public health. Inactivated whole-virus vaccines have been used to control H9N2 AIV in China for more than 20 years, and they can alleviate clinical symptoms after immunization, greatly reducing economic losses. However, H9N2 AIVs can still be isolated from immunized chickens and have recently become the main epidemic subtype. A more effective vaccine prevention strategy might be able to address the current situation. Herein, we analyze the current status and vaccination strategy against H9N2 AIV and summarize the progress in vaccine development to provide insight for better H9N2 prevention and control.

Human Organotypic Airway and Lung Organoid Cells of Bronchiolar and Alveolar Differentiation Are Permissive to Infection by Influenza and SARS-CoV-2 Respiratory Virus

The ongoing coronavirus disease 2019 (COVID-19) pandemic has led to the initiation of unprecedented research efforts to understand the pathogenesis mediated by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). More knowledge is needed regarding the cell type-specific cytopathology and its impact on cellular tropism. Furthermore, the impact of novel SARS-CoV-2 mutations on cellular tropism, alternative routes of entry, the impact of co-infections, and virus replication kinetics along the respiratory tract remains to be explored in improved models. Most applied virology models are not well suited to address the remaining questions, as they do not recapitulate the histoarchitecture and cellular composition of human respiratory tissues. The overall aim of this work was to establish from single biopsy specimens, a human adult stem cell-derived organoid model representing the upper respiratory airways and lungs and explore the applicability of this model to study respiratory virus infection. First, we characterized the organoid model with respect to growth pattern and histoarchitecture, cellular composition, and functional characteristics. Next, in situ expression of viral entry receptors, including influenza virus-relevant sialic acids and SARS-CoV-2 entry receptor ACE2 and TMPRSS2, were confirmed in organoids of bronchiolar and alveolar differentiation. We further showed successful infection by pseudotype influenza A H7N1 and H5N1 virus, and the ability of the model to support viral replication of influenza A H7N1 virus. Finally, successful infection and replication of a clinical isolate of SARS-CoV-2 were confirmed in the organoids by TCID50 assay and immunostaining to detect intracellular SARS-CoV-2 specific nucleocapsid and dsRNA. The prominent syncytia formation in organoid tissues following SARS-CoV-2 infection mimics the findings from infected human tissues in situ. We conclude that the human organotypic model described here may be particularly useful for virology studies to evaluate regional differences in the host response to infection. The model contains the various cell types along the respiratory tract, expresses respiratory virus entry factors, and supports successful infection and replication of influenza virus and SARS-CoV-2. Thus, the model may serve as a relevant and reliable tool in virology and aid in pandemic preparedness, and efficient evaluation of antiviral strategies.

Matrix M Adjuvanted H5N1 Vaccine Elicits Broadly Neutralizing Antibodies and Neuraminidase Inhibiting Antibodies in Humans That Correlate With In Vivo Protection

The highly pathogenic avian influenza H5N1 viruses constantly evolve and give rise to novel variants that have caused widespread zoonotic outbreaks and sporadic human infections. Therefore, vaccines capable of eliciting broadly protective antibody responses are desired and under development. We here investigated the magnitude, kinetics and protective efficacy of the multi-faceted humoral immunity induced by vaccination in healthy adult volunteers with a Matrix M adjuvanted virosomal H5N1 vaccine. Vaccinees were given escalating doses of adjuvanted vaccine (1.5μg, 7.5μg, or 30μg), or a non-adjuvanted vaccine (30μg). An evaluation of sera from vaccinees against pseudotyped viruses covering all (sub)clades isolated from human H5N1 infections demonstrated that the adjuvanted vaccines (7.5μg and 30μg) could elicit rapid and robust increases of broadly cross-neutralizing antibodies against all clades. In addition, the adjuvanted vaccines also induced multifaceted antibody responses including hemagglutinin stalk domain specific, neuraminidase inhibiting, and antibody-dependent cellular cytotoxicity inducing antibodies. The lower adjuvanted dose (1.5µg) showed delayed kinetics, whilst the non-adjuvanted vaccine induced overall lower levels of antibody responses. Importantly, we demonstrate that human sera post vaccination with the adjuvanted (30μg) vaccine provided full protection against a lethal homologous virus challenge in mice. Of note, when combining our data from mice and humans we identified the neutralizing and neuraminidase inhibiting antibody titers as correlates of in vivo protection.

Acceptance of seasonal influenza vaccination and associated factors among pregnant women in the context of COVID-19 pandemic in China: a multi-center cross-sectional study based on health belief model

Background

Seasonal influenza can circulate in parallel with coronavirus disease (COVID-19) in winter. In the context of COVID-19 pandemic, the risk of co-infection and the burden it poses on healthcare system calls for timely influenza vaccination among pregnant women, who are the priority population recommended for vaccination. We aimed to evaluate the acceptance of influenza vaccination and associated factors among pregnant women during COVID-19 pandemic, provide evidence to improve influenza vaccination among pregnant women, help reduce the risk of infection and alleviate the burden of healthcare system for co-infected patients.

Methods

We conducted a multi-center cross-sectional study among pregnant women in China. Sociodemographic characteristics, health status, knowledge on influenza, attitude towards vaccination, and health beliefs were collected. Locally weighted scatterplot smoothing regression analysis was used to evaluate the trends in the acceptance of influenza vaccine. Logistic regression was applied to identify factors associated with vaccination acceptance.

Results

The total acceptance rate was 76.5% (95%CI: 74.8–78.1%) among 2568 pregnant women enrolled. Only 8.3% of the participants had a history of seasonal influenza vaccination. In the logistic regression model, factors associated with the acceptance of influenza vaccine were western region, history of influenza vaccination, high knowledge of influenza infection and vaccination, high level of perceived susceptibility, perceived benefit, cues to action and low level of perceived barriers. Among 23.5% of the participants who had vaccine hesitancy, 48.0% of them were worried about side effect, 35.6% of them lacked confidence of vaccine safety.

Conclusions

Our findings highlighted that tailored strategies and publicity for influenza vaccination in the context of COVID-19 pandemic are warranted to reduce pregnant women’s concerns, improve their knowledge, expand vaccine uptake and alleviate pressure for healthcare system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-04224-3.

Broadly Reactive IgG Responses to Heterologous H5 Prime-Boost Influenza Vaccination Are Shaped by Antigenic Relatedness to Priming Strains

Prime-boost vaccinations of humans with different H5 strains have generated broadly protective antibody levels. However, the effect of an individual’s H5 exposure history on antibody responses to subsequent H5 vaccination is poorly understood. To investigate this, we analyzed the IgG responses to H5 influenza A/Indonesia/5/2005 (Ind05) virus vaccination in three cohorts: (i) a doubly primed group that had received two H5 virus vaccinations, namely, against influenza A/Vietnam/203/2004 (Vie04) virus 5 years prior and A/Hong Kong/156/1997 (HK97) 11 years prior to the Ind05 vaccination; (ii) a singly primed group that had received a vaccination against Vie04 virus 5 years prior to the Ind05 vaccination; and (iii) an H5-naive group that received two doses of the Ind05 vaccine 28 days apart. Hemagglutinin (HA)-reactive IgG levels were estimated by a multiplex assay against an HA panel that included 21 H5 strains and 9 other strains representing the H1, H3, H7, and H9 subtypes. Relative HA antibody landscapes were generated to quantitatively analyze the magnitude and breadth of antibody binding after vaccination. We found that short-interval priming and boosting with the Ind05 vaccine in the naive group generated a low anti-H5 response. Both primed groups generated robust antibody responses reactive to a broad range of H5 strains after receiving a booster injection of Ind05 vaccine; IgG antibody levels persisted longer in subjects who had been doubly primed years ago. Notably, the IgG responses were strongest against the first priming H5 strain, which reflects influenza virus immune imprinting. Finally, the broad anti-H5 IgG response was stronger against strains having a small antigenic distance from the initial priming strain.

Ebola-GP DNA Prime rAd5-GP Boost: Influence of Prime Frequency and Prime/Boost Time Interval on the Immune Response in Non-human Primates

Heterologous prime-boost immunization regimens are a common strategy for many vaccines. DNA prime rAd5-GP boost immunization has been demonstrated to protect non-human primates against a lethal challenge of Ebola virus, a pathogen that causes fatal hemorrhagic disease in humans. This protection correlates with antibody responses and is also associated with IFNγ⁺ TNFα⁺ double positive CD8⁺ T-cells. In this study, we compared single DNA vs. multiple DNA prime immunizations, and short vs. long time intervals between the DNA prime and the rAd5 boost to evaluate the impact of these different prime-boost strategies on vaccine-induced humoral and cellular responses in non-human primates. We demonstrated that DNA/rAd5 prime-boost strategies can be tailored to induce either CD4⁺ T-cell or CD8⁺ T-cell dominant responses while maintaining a high magnitude antibody response. Additionally, a single DNA prime immunization generated a stable memory response that could be boosted by rAd5 3 years later. These results suggest DNA/rAd5 prime-boost provides a flexible platform that can be fine-tuned to generate desirable T-cell memory responses.

Contribution of Fc-dependent cell-mediated activity of a vestigial esterase-targeting antibody against H5N6 virus infection

The highly pathogenic avian influenza A (H5N6) virus has caused sporadic human infections with a high case fatality rate. Due to the continuous evolution of this virus subtype and its ability to transmit to humans, there is an urgent need to develop effective antiviral therapeutics. In this study, a murine monoclonal antibody 9F4 was shown to display broad binding affinity against H5Nx viruses. Furthermore, 9F4 can neutralize H5N6 pseudotyped particles and prevent entry into host cells. Additionally, ADCC/ADCP deficient L234A, L235A (LALA) and CDC deficient K322A mutants were generated and displayed comparable binding affinity and neutralizing activity as wild type 9F4 (9F4-WT). Notably, 9F4-WT, 9F4-LALA and 9F4-K322A exhibit in vivo protective efficacies against H5N6 infections in that they were able to reduce viral loads in mice. However, only 9F4-WT and 9F4-K322A but not 9F4-LALA were able to reduce viral pathogenesis in H5N6 challenged mice. Furthermore, depletion of phagocytic cells in mice lungs nullifies 9F4-WT's protection against H5N6 infections, suggesting a crucial role of the host's immune cells in 9F4 antiviral activity. Collectively, these findings reveal the importance of ADCC/ADCP function for 9F4-WT protection against HPAIV H5N6 and demonstrate the potential of 9F4 to confer protection against the reassortant H5-subtype HPAIVs.

Sequential DNA immunization of chickens with bivalent heterologous vaccines induce highly reactive and cross-specific antibodies against influenza hemagglutinin

Vaccines against avian influenza are mostly based on hemagglutinin (HA), which is the main antigen of this virus and a target for neutralizing antibodies. Traditional vaccines are known to be poorly efficient against newly emerging strains, which is an increasing worldwide problem for human health and for the poultry industry. As demonstrated by research and clinical data, sequential exposure to divergent influenza HAs can boost induction of universal antibodies which recognize conserved epitopes. In this work, we have performed sequential immunization of laying hens using monovalent or bivalent compositions of DNA vaccines encoding HAs from distant groups 1 and 2 (H5, H1, and H3 subtypes, respectively). This strategy gave promising results, as it led to induction of polyclonal antibodies against HAs from both groups. These polyclonal antibodies showed cross-reactivity between different HA strains in ELISA, especially when bivalent formulations were used for immunization of birds. However, cross-reactivity of antibodies induced against H3 and H5 HA subtypes was rather limited against each other after homologous immunization. Using a cocktail of HA sequences and/or sequential DNA vaccination with different strains presents a good strategy to overcome the limited effectiveness of vaccines and induce broader immunity against avian influenza. Such a strategy could be adapted for vaccinating laying hens or parental flocks of different groups of poultry.

A single cycle influenza virus coated in H7 haemagglutinin generates neutralizing antibody responses to haemagglutinin and neuraminidase glycoproteins and protection from heterotypic challenge

A non-replicating form of pseudotyped influenza virus, inactivated by suppression of the haemagglutinin signal sequence (S-FLU), can act as a broadly protective vaccine. S-FLU can infect for a single round only, and induces heterotypic protection predominantly through activation of cross-reactive T cells in the lung. Unlike the licensed live attenuated virus, it cannot reassort a pandemic haemagglutinin (HA) into seasonal influenza. Here we present data on four new forms of S-FLU coated with H7 HAs from either A/Anhui/1/2013, A/Shanghai/1/2013, A/Netherlands/219/2003 or A/New York/107/2003 strains of H7 virus. We show that intranasal vaccination induced a strong local CD8 T cell response and protected against heterosubtypic X31 (H3N2) virus and highly virulent PR8 (H1N1), but not influenza B virus. Intranasal vaccination also induced a strong neutralizing antibody response to the encoded neuraminidase. If given at higher dose in the periphery with intraperitoneal administration, H7 S-FLU induced a specific neutralizing antibody response to H7 HA coating the particle. Polyvalent intraperitoneal vaccination with mixed H7 S-FLU induced a broadly neutralizing antibody response to all four H7 strains. S-FLU is a versatile vaccine candidate that could be rapidly mobilized ahead of a new pandemic threat.

Efficacy of recombinant measles virus expressing highly pathogenic avian influenza virus (HPAIV) antigen against HPAIV infection in monkeys

Highly pathogenic avian influenza virus (HPAIV) is a serious threat not only to domestic fowls but also to humans. Vaccines inducing long-lasting immunity against HPAIV are required. In the present study, we generated recombinant measles virus (MV) expressing the hemagglutinin protein of HPAIV without the multibasic site necessary for its pathogenicity in chickens using the backbone of an MV vaccine strain (rMV-Ed-H5HA) or a wild-type MV-derived mutant (rMV-HL-Vko-H5HA). We examined protective efficacy of the candidate vaccines in the monkey infection model by the challenge with a HPAIV (H5N1). Cynomolgus monkeys inoculated with the candidate vaccines produced both anti-H5 HA and anti-MV antibodies. They recovered earlier from influenza symptoms than unvaccinated monkeys after the challenge with the HPAIV strain. Chest radiography and histopathological analyses confirmed less severe pneumonia in the vaccinated monkeys. Vaccination tended to suppress viral shedding and reduced the interleukin-6 levels in the lungs. Furthermore, the vaccination with rMV-Ed-H5HA of monkeys with pre-existing anti-MV immunity induced the production of anti-H5 HA antibodies. These results suggest that both candidate vaccines effectively reduce disease severity in naïve hosts, and that rMV-Ed-H5HA is a particularly good candidate vaccine against HPAIV infection.

Combination of the immunization with the sequence close to the consensus sequence and two DNA prime plus one VLP boost generate H5 hemagglutinin specific broad neutralizing antibodies

Hemagglutinin (HA) head has long been considered to be able to elicit only a narrow, strain-specific antibody response as it undergoes rapid antigenic drift. However, we previously showed that a heterologous prime-boost strategy, in which mice were primed twice with DNA encoding HA and boosted once with virus-like particles (VLP) from an H5N1 strain A/Thailand/1(KAN)-1/2004 (noted as TH DDV), induced anti-head broad cross-H5 neutralizing antibody response. To explain why TH DDV immunization could generate such breadth, we systemically compared the neutralization breadth and potency between TH DDV sera and immune sera elicited by TH DDD (three times of DNA immunizations), TH VVV (three times of VLP immunizations), TH DV (one DNA prime plus one VLP boost) and TK DDV (plasmid DNA and VLP derived from another H5N1 strain, A/Turkey/65596/2006). Then we determined the antigenic sites (AS) on TH HA head and the key residues of the main antigenic site. Through the comparison of different regiments, we found that the combination of the immunization with the sequence close to the consensus sequence and two DNA prime plus one VLP boost caused that TH DDV immunization generate broad neutralizing antibodies. Antigenic analysis showed that TH DDV, TH DV, TH DDD and TH VVV sera recognize the common antigenic site AS1. Antibodies directed to AS1 contribute to the largest proportion of the neutralizing activity of these immune sera. Residues 188 and 193 in AS1 are the key residues which are responsible for neutralization breadth of the immune sera. Interestingly, residues 188 and 193 locate in classical antigen sites but are relatively conserved among the 16 tested strains and 1,663 HA sequences from NCBI database. Thus, our results strongly indicate that it is feasible to develop broad cross-H5 influenza vaccines against HA head.

A Bivalent Heterologous DNA Virus-Like-Particle Prime-Boost Vaccine Elicits Broad Protection against both Group 1 and 2 Influenza A Viruses

Current seasonal influenza vaccines are efficacious when vaccine strains are matched with circulating strains. However, they do not protect antigenic variants and newly emerging pandemic and outbreak strains. Thus, there is a critical need for developing so-called "universal" vaccines that protect against all influenza viruses. In the present study, we developed a bivalent heterologous DNA virus-like particle prime-boost vaccine strategy. We show that mice immunized with this vaccine were broadly protected against lethal challenge from group 1 (H1, H5, and H9) and group 2 (H3 and H7) viruses, with 94% aggregate survival. To determine the immune correlates of protection, we performed passive immunizations and in vitro assays. We show that this vaccine elicited antibody responses that bound HA from group 1 (H1, H2, H5, H6, H8, H9, H11, and H12) and group 2 (H3, H4, H7, H10, H14, and H15) and neutralized homologous and intrasubtypic H5 and H7 and heterosubtypic H1 viruses and hemagglutinin-specific CD4 and CD8 T cell responses. As a result, passive immunization with immune sera fully protected mice against H5, H7, and H1 challenge, whereas with both immune sera and T cells the mice survived heterosubtypic H3 and H9 challenge. Thus, it appears that (i) neutralizing antibodies alone fully protect against homologous and intrasubtypic H5 and H7 and (ii) neutralizing and binding antibodies are sufficient to protect against heterosubtypic H1, (iii) but against heterosubtypic H3 and H9, binding antibodies and T cells are required for complete survival. We believe that this vaccine regimen could potentially be a candidate for a "universal" influenza vaccine.IMPORTANCE Influenza virus infection is global health problem. Current seasonal influenza vaccines are efficacious only when vaccine strains are matched with circulating strains. However, these vaccines do not protect antigenic variants and newly emerging pandemic and outbreak strains. Because of this, there is an urgent need to develop so-called "universal" influenza vaccines that can protect against both current and future influenza strains. In the present study, we developed a bivalent heterologous prime-boost vaccine strategy. We show that a bivalent vaccine regimen elicited broad binding and neutralizing antibody and T cell responses that conferred broad protection against diverse challenge viruses in mice, suggesting that this bivalent prime-boost strategy could practically be a candidate for a "universal" influenza vaccine.

The Optimisation of Pseudotyped Viruses for the Characterisation of Immune Responses to Equine Influenza Virus

Pseudotyped viruses (PVs) produced by co-transfecting cells with plasmids expressing lentiviral core proteins and viral envelope proteins are potentially powerful tools for studying various aspects of equine influenza virus (EIV) biology. The aim of this study was to optimise production of equine influenza PVs. Co-transfection of the HAT protease to activate the haemagglutinin (HA) yielded a higher titre PV than TMPRSS2 with the HA from A/equine/Richmond/1/2007 (H3N8), whereas for A/equine/Newmarket/79 (H3N8), both proteases resulted in equivalent titres. TMPRSS4 was ineffective with the HA of either strain. There was also an inverse relationship between the amount of protease-expression plasmids and the PV titre obtained.  Interestingly, the PV titre obtained by co-transfection of a plasmid encoding the cognate N8 NA was not as high as that generated by the addition of exogenous neuraminidase (NA) from Clostridium perfringens to allow the release of nascent PV particles. Finally, initial characterisation of the reliability of PV neutralisation tests (PVNTs) demonstrated good intra-laboratory repeatability. In conclusion, we have demonstrated that equine influenza PV production can be readily optimised to provide a flexible tool for studying EIV.

Epitope-focused vaccine design against influenza A and B viruses

The threat of influenza A and B variants via antigenic drift and emerging novel influenza A and B strains in the human population via antigenic shift has spurred research efforts to improve upon current seasonal influenza vaccines. In recent years, a wave of novel technological breakthroughs has lead to the identification of many broadly anti-influenza hemagglutinin (HA) monoclonal antibodies (mAbs) and the elucidation of the conserved epitopes recognized by these mAbs in both the head and the stem of HA as well as the mechanisms of inhibition. These discoveries along with an improved understanding of how the immune system responds to influenza infection and vaccination has spurred great efforts on stem-based cross-subtype ('universal') vaccine design as well as RBS-based HA subtype-specific vaccine design.

Immunopotentiators Improve the Efficacy of Oil-Emulsion-Inactivated Avian Influenza Vaccine in Chickens, Ducks and Geese

Combination of CVCVA5 adjuvant and commercial avian influenza (AI) vaccine has been previously demonstrated to provide good protection against different AI viruses in chickens. In this study, we further investigated the protective immunity of CVCVA5-adjuvanted oil-emulsion inactivated AI vaccine in chickens, ducks and geese. Compared to the commercial H5 inactivated vaccine, the H5-CVCVA5 vaccine induced significantly higher titers of hemaglutinin inhibitory antibodies in three lines of broiler chickens and ducks, elongated the antibody persistence periods in geese, elevated the levels of cross serum neutralization antibody against different clade and subclade H5 AI viruses in chicken embryos. High levels of mucosal antibody were detected in chickens injected with the H5 or H9-CVCA5 vaccine. Furthermore, cellular immune response was markedly improved in terms of increasing the serum levels of cytokine interferon-γ and interleukine 4, promoting proliferation of splenocytes and upregulating cytotoxicity activity in both H5- and H9-CVCVA5 vaccinated chickens. Together, these results provide evidence that AI vaccines supplemented with CVCVA5 adjuvant is a promising approach for overcoming the limitation of vaccine strain specificity of protection.

Cross-protection of newly emerging HPAI H5 viruses by neutralizing human monoclonal antibodies: A viable alternative to oseltamivir

Newly emerging highly pathogenic avian influenza (HPAI) H5N2, H5N3, H5N5, H5N6, H5N8 and H5N9 viruses have been spreading in poultry and wild birds. The H5N6 viruses have also caused 10 human infections with 4 fatal cases in China. Here, we assessed the cross-neutralization and cross-protection of human and mouse monoclonal antibodies against 2 viruses: a HPAI H5N8 virus, A/chicken/Netherlands/14015526/2014 (NE14) and a HPAI H5N6 virus, A/Sichuan/26221/2014 (SC14). The former was isolated from an infected chicken in Netherlands in 2014 and the latter was isolated from an infected human patient in Sichuan, China. We show that antibodies FLA5.10, FLD21.140, 100F4 and 65C6, but not AVFluIgG01, AVFluIgG03, S139/1 and the VRC01 control, potently cross-neutralize the H5N8 NE14 and H5N6 SC14 viruses. Furthermore, we show that a single injection of >1 mg/kg of antibody 100F4 at 4 hours before, or 20 mg/kg antibody 100F4 at 72 hours after, a lethal dose of H5N8 NE14 enables mice to withstand the infection. Finally, we show that a single injection of 0.5 or 1 mg/kg antibody 100F4 prophylactically or 10 mg/kg 100F4 therapeutically outperforms a 5-day course of 10 mg/kg/day oseltamivir treatment against lethal H5N8 NE14 or H5N6 SC14 infection in mice. Our results suggest that further preclinical evaluation of human monoclonal antibodies against newly emerging H5 viruses is warranted.

Cocktail of H5N1 COBRA HA vaccines elicit protective antibodies against H5N1 viruses from multiple clades

Pandemic outbreaks of influenza are caused by the emergence of a pathogenic and transmissible virus to which the human population is immunologically naïve. Recent outbreaks of highly pathogenic avian influenza (HPAI) of the H5N1 subtype are of particular concern because of the high mortality rate (60% case fatality rate) and novel subtype. In this study, we have engineered an influenza virus-like particle (VLP) that contains a synthetic, consensus-based HA molecule using a new methodology, computationally optimized broadly reactive antigen (COBRA). Three COBRA H5N1 HA proteins have been engineered based upon (1) human clade 2 H5N1 sequences, (2) human and avian clade 2 sequences, and (3) all H5N1 influenza sequences recorded between 2005-2008. Each hemagglutinin protein retained the ability to bind the appropriate receptors, as well as the ability to mediate particle fusion, following purification from a mammalian expression system. COBRA VLP vaccines were administered to mice and the humoral immune responses were compared to those induced by VLPs containing an HA derived from a primary viral isolate. Using a single vaccination (0.6 ug HA dose with an adjuvant) all animals vaccinated with COBRA clade 2 HA H5N1 VLPs had protective levels of HAI antibodies to a representative isolate from each subclade of clade 2, but lower titers against other clades. The addition of avian sequences from other clades expanded breadth of HAI antibodies to the divergent clades, but still not all of the 25 H5N1 viruses in the panel were recognized by antibodies elicited any one H5N1 COBRA VLP vaccine. Vaccination of mice with a cocktail of all 3 COBRA HA VLP vaccines, in a prime-boost regimen, elicited an average HAI titer greater than 1:40 against all 25 viruses. Collectively, our findings indicate that the elicited antibody response following VLP vaccination with all 3 COBRA HA vaccine simultaneously elicited a broadly-reactive set of antibodies that recognized H5N1 viruses from 11 H5N1 clades/subclades isolated over a 12-year span.

DNA-based influenza vaccines as immunoprophylactic agents toward universality

Influenza is an illness of global public health concern. Influenza viruses have been responsible for several pandemics affecting humans. Current influenza vaccines have proved satisfactory safety; however, they have limitations and do not provide protection against unexpected emerging influenza virus strains. Therefore, there is an urgent need for alternative approaches to conventional influenza vaccines. The development of universal influenza vaccines will help alleviate the severity of influenza pandemics. Influenza DNA vaccines have been the subject of many studies over the past decades due to their ability to induce broad-based protective immune responses in various animal models. The present review highlights the recent advances in influenza DNA vaccine research and its potential as an affordable universal influenza vaccine.

Repeated Low-Dose Influenza Virus Infection Causes Severe Disease in Mice: a Model for Vaccine Evaluation

Influenza infection causes severe disease and death in humans. In traditional vaccine research and development, a single high-dose virus challenge of animals is used to evaluate vaccine efficacy. This type of challenge model may have limitations. In the present study, we developed a novel challenge model by infecting mice repeatedly in short intervals with low doses of influenza A virus. Our results show that compared to a single high-dose infection, mice that received repeated low-dose challenges showed earlier morbidity and mortality and more severe disease. They developed higher vial loads, more severe lung pathology, and greater inflammatory responses and generated only limited influenza A virus-specific B and T cell responses. A commercial trivalent influenza vaccine protected mice against a single high and lethal dose of influenza A virus but was ineffective against repeated low-dose virus challenges. Overall, our data show that the repeated low-dose influenza A virus infection mouse model is more stringent and may thus be more suitable to select for highly efficacious influenza vaccines.

IMPORTANCE

Influenza epidemics and pandemics pose serious threats to public health. Animal models are crucial for evaluating the efficacy of influenza vaccines. Traditional models based on a single high-dose virus challenge may have limitations. Here, we describe a new mouse model based on repeated low-dose influenza A virus challenges given within a short period. Repeated low-dose challenges caused more severe disease in mice, associated with higher viral loads and increased lung inflammation and reduced influenza A virus-specific B and T cell responses. A commercial influenza vaccine that was shown to protect mice from high-dose challenge was ineffective against repeated low-dose challenges. Overall, our results show that the low-dose repeated-challenge model is more stringent and may therefore be better suited for preclinical vaccine efficacy studies.

Pseudotype-based neutralization assays for influenza: a systematic analysis

The use of vaccination against the influenza virus remains the most effective method of mitigating the significant morbidity and mortality caused by this virus. Antibodies elicited by currently licensed influenza vaccines are predominantly hemagglutination-inhibition (HI)-competent antibodies that target the globular head of hemagglutinin (HA) thus inhibiting influenza virus entry into target cells. These antibodies predominantly confer homosubtypic/strain specific protection and only rarely confer heterosubtypic protection. However, recent academia or pharma-led R&D toward the production of a “universal vaccine” has centered on the elicitation of antibodies directed against the stalk of the influenza HA that has been shown to confer broad protection across a range of different subtypes (H1–H16). The accurate and sensitive measurement of antibody responses elicited by these “next-generation” influenza vaccines is, however, hampered by the lack of sensitivity of the traditional influenza serological assays HI, single radial hemolysis, and microneutralization. Assays utilizing pseudotypes, chimeric viruses bearing influenza glycoproteins, have been shown to be highly efficient for the measurement of homosubtypic and heterosubtypic broadly neutralizing antibodies, making them ideal serological tools for the study of cross-protective responses against multiple influenza subtypes with pandemic potential. In this review, we will analyze and compare literature involving the production of influenza pseudotypes with particular emphasis on their use in serum antibody neutralization assays. This will enable us to establish the parameters required for optimization and propose a consensus protocol to be employed for the further deployment of these assays in influenza vaccine immunogenicity studies.

Employing XIAP to enhance the duration of antigen expression and immunity against an avian influenza H5 DNA vaccine

DNA vaccine represents a powerful approach for prevention of avian H5N1 influenza infection. Yet, DNA vaccine-induced immune responses might be limited by the short duration of antigen expression. As a strategy to enhance adaptive immune responses elicited by a hemagglutinin 5 (H5) DNA vaccine, we explored the effect of co-administration of a DNA encoding X-linked inhibitor of apoptosis protein (XIAP) as a modulator of apoptosis and a stimulator of inflammatory signaling. In cultured cells as early as 24 hours (h), we found that the DNA vaccine encoded H5 antigen was a potent stimulator of apoptosis, and the H5 pro-apoptotic activity was significantly suppressed by the co-expression of full-length XIAP or mutant XIAP (ΔRING). However, full-length XIAP showed a higher potency than mutant XIAP (ΔRING) in the inhibition of H5-induced apoptosis. We also compared the immunizing ability of transmembrane and secretory forms of H5. Mice vaccinated (twice with 3-week intervals) with the secretory form of H5 showed higher hemagglutination inhibition (HI) antibody titers than mice vaccinated with the transmembrane form of H5. Furthermore, co-administration of XIAP with the secretory form of H5 resulted into a stronger antibody response than the transmembrane form of H5. Our findings suggest that in the design of DNA vaccines for a given pro-apoptotic antigen, using an anti-apoptotic molecular adjuvant and the secretory form of antigen may be a greater stimulus to induce immune responses.

Prospects of HA-based universal influenza vaccine

Current influenza vaccines afford substantial protection in humans by inducing strain-specific neutralizing antibodies (Abs). Most of these Abs target highly variable immunodominant epitopes in the globular domain of the viral hemagglutinin (HA). Therefore, current vaccines may not be able to induce heterosubtypic immunity against the divergent influenza subtypes. The identification of broadly neutralizing Abs (BnAbs) against influenza HA using recent technological advancements in antibody libraries, hybridoma, and isolation of single Ab-secreting plasma cells has increased the interest in developing a universal influenza vaccine as it could provide life-long protection. While these BnAbs can serve as a source for passive immunotherapy, their identification represents an important step towards the design of such a universal vaccine. This review describes the recent advances and approaches used in the development of universal influenza vaccine based on highly conserved HA regions identified by BnAbs.

Induction of cell-mediated immune responses in mice by DNA vaccines that express hepatitis C virus NS3 mutants lacking serine protease and NTPase/RNA helicase activities

Effective therapeutic vaccines against virus infection must induce sufficient levels of cell-mediated immune responses against the target viral epitopes and also must avoid concomitant risk factors, such as potential carcinogenic properties. The nonstructural protein 3 (NS3) of hepatitis C virus (HCV) carries a variety of CD4(+) and CD8(+) T cell epitopes, and induces strong HCV-specific T cell responses, which are correlated with viral clearance and resolution of acute HCV infection. On the other hand, NS3 possesses serine protease and nucleoside triphosphatase (NTPase)/RNA helicase activities, which not only play important roles in viral life cycle but also concomitantly interfere with host defense mechanisms by deregulating normal cellular functions. In this study, we constructed a series of DNA vaccines that express NS3 of HCV. To avoid the potential harm of NS3, we introduced mutations to the catalytic triad of the serine protease (H57A, D81A and S139A) and the NTPase/RNA helicase domain (K210N, F444A, R461Q and W501A) to eliminate the enzymatic activities. Immunization of BALB/c mice with each of the DNA vaccine candidates (pNS3[S139A/K210N], pNS3[S139A/F444A], pNS3[S139A/R461Q] and pNS3[S139A/W501A]) that expresses an NS3 mutant lacking both serine protease and NTPase/helicase activities induced T cell immune responses to the degree comparable to that induced by the wild type NS3 and the NS3/4A complex, as demonstrated by interferon-γ production and cytotoxic T lymphocytes activities against NS3. The present study has demonstrated that plasmids expressing NS3 mutants, NS3(S139A/K210N), NS3(S139A/F444A), NS3(S139A/R461Q) and NS3(S139A/W501A), which lack both serine protease and NTPase/RNA helicase activities, would be good candidates for safe and efficient therapeutic DNA vaccines against HCV infection.

Glycan masking of hemagglutinin for adenovirus vector and recombinant protein immunizations elicits broadly neutralizing antibodies against H5N1 avian influenza viruses

The highly pathogenic avian influenza (HPAI) H5N1 virus, a known trigger of diseases in poultry and humans, is perceived as a serious threat to public health. There is a clear need for a broadly protective H5N1 vaccine or vaccines for inducing neutralizing antibodies against multiple clades/subclades. We constructed single, double, and triple mutants of glycan-masked hemagglutiinin (HA) antigens at residues 83, 127 and 138 (i.e., g83, g127, g138, g83+g127, g127+g138, g83+g138 and g83+g127+g138), and then obtained their corresponding HA-expressing adenovirus vectors and recombinant HA proteins using a prime-boost immunization strategy. Our results indicate that the glycan-masked g127+g138 double mutant induced more potent HA-inhibition, virus neutralization antibodies, cross-clade protection against heterologous H5N1 clades, correlated with the enhanced bindings to the receptor binding sites and the highly conserved stem region of HA. The immune refocusing stem-specific antibodies elicited by the glycan-masked H5HA g127+g138 and g83+g127+g138 mutants overlapped with broadly neutralizing epitopes of the CR6261 monoclonal antibody that neutralizes most group 1 subtypes. These findings may provide useful information in the development of a broadly protective H5N1 influenza vaccine.

Avian influenza vaccines against H5N1 'bird flu'

H5N1 avian influenza viruses (AIVs) have spread widely to more than 60 countries spanning three continents. To control the disease, vaccination of poultry is implemented in many of the affected countries, especially in those where H5N1 viruses have become enzootic in poultry and wild birds. Recently, considerable progress has been made toward the development of novel avian influenza (AI) vaccines, especially recombinant virus vector vaccines and DNA vaccines. Here, we will discuss the recent advances in vaccine development and use against H5N1 AIV in poultry. Understanding the properties of the available, novel vaccines will allow for the establishment of rational vaccination protocols, which in turn will help the effective control and prevention of H5N1 AI.

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.

Effects of different CpG oligodeoxynucleotides with inactivated avian H5N1 influenza virus on mucosal immunity of chickens

Oligodeoxynucleotide containing unmethylated CpG motifs (CpG-ODN) has been proved to be a potent and safe vaccine adjuvant. However, the application of CpG-ODN in poultry vaccines was limited because of its high cost to benefit ratio. The objective of this study was to identify the CpG-ODN with efficient adjuvant activity and low cost in chickens. Four sequences of CpG-ODN were designed based on CpG-ODN 2006, which was used as a template and positive sequence in our study. In the current study, in vitro observations revealed that the designed CpG-ODN had efficient immunostimulatory effects on chicken splenic lymphocytes. The in vivo results showed that the mRNA expressions of IL-6, IL-12, interferon-γ, and Toll-like receptor (TLR) 21 in upper respiratory tract tissues increased significantly in the early period after intranasal immunization with inactivated avian H5N1 influenza virus (IAIV) and CpG-ODN (P < 0.01). In addition, the avian influenza virus (AIV)-specific secretory IgA antibody level in the lavage fluid of upper respiratory tract increased significantly after intranasal immunization with IAIV and CpG-ODN, so did AIV-specific IgG in serum (P < 0.01). Among all the designed CpG-ODN, CpG-ODN F3 with an addition of poly-guanosine strings at the 3'-end not only had the best enhancement on local mucosal immune response but also showed an effective induction of systemic immune response. Most importantly, the virus challenge study showed that prior administration of IAIV with CpG-ODN F3 could protect chickens effectively against live AIV H5N1 challenge. Additionally, among all the CpG-ODN in our study, the cost of the designed CpG-ODN F3 was the lowest because of the partially phosphorothioate backbone. Therefore, we speculated that CpG-ODN F3 with efficient adjuvant activity and a big cost advantage over CpG-ODN F1 (CpG-ODN 2006) might serve as an efficient and affordable nasal adjuvant for inactivated AIV vaccine in chicken.

Immune responses of chickens inoculated with recombinant Lactobacillus expressing the haemagglutinin of the avian influenza virus

AIMS

To develop a safe, effective and convenient vaccine for the prevention of highly pathogenic avian influenza (HPAI), we have successfully constructed a recombinant lactobacillus (LDL17-pH) that expresses the foreign HPAI protein, haemagglutinin 1 (HA1 ).

METHODS AND RESULTS

The mucosal and systemic immune responses that are triggered by LDL17-pH following the oral administration to 10-day-old chickens were evaluated. The results showed that LDL17-pH could significantly increase the specific anti-HA1 IgA antibody level in the mucosa and the anti-HA1 IgG level in sera. Tissues were isolated from trachea and Peyer's patches(PPs)and caecal tonsils of chickens, and gene expression was analysed via real-time quantitative PCR.

CONCLUSIONS

The results showed that LDL17-pH could significantly induce the specific anti-HA1 IgA antibody level in the trachea and intestine and the specific anti-HA1 IgG antibody level in the serum (P < 0·05). Additionally, LDL17-pH was in the capacity to induce the expression of cytokines IFN-γ, TLR-2 and AvBD-9 in the PPs and caecal tonsils. Most importantly, the chickens that were immunized with LDL17-pH were protected against lethal challenge of the H5N1 virus to some extent.

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, LDL17-pH could be a promising oral vaccine candidate against HPAI.

DNA vaccine that targets hemagglutinin to MHC class II molecules rapidly induces antibody-mediated protection against influenza

New influenza A viruses with pandemic potential periodically emerge due to viral genomic reassortment. In the face of pandemic threats, production of conventional egg-based vaccines is time consuming and of limited capacity. We have developed in this study a novel DNA vaccine in which viral hemagglutinin (HA) is bivalently targeted to MHC class II (MHC II) molecules on APCs. Following DNA vaccination, transfected cells secreted vaccine proteins that bound MHC II on APCs and initiated adaptive immune responses. A single DNA immunization induced within 8 d protective levels of strain-specific Abs and also cross-reactive T cells. During the Mexican flu pandemic, a targeted DNA vaccine (HA from A/California/07/2009) was generated within 3 wk after the HA sequences were published online. These results suggest that MHC II-targeted DNA vaccines could play a role in situations of pandemic threats. The vaccine principle should be extendable to other infectious diseases.

The antigenic architecture of the hemagglutinin of influenza H5N1 viruses

Human infection with the highly pathogenic avian influenza A virus H5N1 is associated with a high mortality and morbidity. H5N1 continues to transmit from poultry to the human population, raising serious concerns about its pandemic potential. Current influenza H5N1 vaccines are based upon the elicitation of a neutralizing antibody (Ab) response against the major epitope regions of the viral surface glycoprotein, hemagglutinin (HA). However, antigenic drift mutations in immune-dominant regions on the HA structure allow the virus to escape Ab neutralization. Epitope mapping using neutralizing monoclonal antibodies (mAb) helps define mechanisms of antigenic drift, neutralizing escape and can facilitate pre-pandemic vaccine design. This review explores the current knowledge base of the antigenic sites of the H5N1 HA molecule. The relationship between the epitope architecture of the H5N1 HA, antigenic evolution of the different H5N1 lineages and the antigenic complexity of the H5N1 virus lineages that constitute potential pandemic strains are discussed in detail.

Antigenic characterization of H3N2 influenza A viruses from Ohio agricultural fairs

The demonstrated link between the emergence of H3N2 variant (H3N2v) influenza A viruses (IAVs) and swine exposure at agricultural fairs has raised concerns about the human health risk posed by IAV-infected swine. Understanding the antigenic profiles of IAVs circulating in pigs at agricultural fairs is critical to developing effective prevention and control strategies. Here, 68 H3N2 IAV isolates recovered from pigs at Ohio fairs (2009 to 2011) were antigenically characterized. These isolates were compared with other H3 IAVs recovered from commercial swine, wild birds, and canines, along with human seasonal and variant H3N2 IAVs. Antigenic cartography demonstrated that H3N2 IAV isolates from Ohio fairs could be divided into two antigenic groups: (i) the 2009 fair isolates and (ii) the 2010 and 2011 fair isolates. These same two antigenic clusters have also been observed in commercial swine populations in recent years. Human H3N2v isolates from 2010 and 2011 are antigenically clustered with swine-origin IAVs from the same time period. The isolates recovered from pigs at fairs did not cross-react with ferret antisera produced against the human seasonal H3N2 IAVs circulating during the past decade, raising the question of the degree of immunity that the human population has to swine-origin H3N2 IAVs. Our results demonstrate that H3N2 IAVs infecting pigs at fairs and H3N2v isolates were antigenically similar to the IAVs circulating in commercial swine, demonstrating that exhibition swine can function as a bridge between commercial swine and the human population.

Vaccination of gallinaceous poultry for H5N1 highly pathogenic avian influenza: current questions and new technology

Vaccination of poultry for avian influenza virus (AIV) is a complex topic as there are numerous technical, logistic and regulatory aspects which must be considered. Historically, control of high pathogenicity (HP) AIV infection in poultry has been accomplished by eradication and stamping out when outbreaks occur locally. Since the H5N1 HPAIV from Asia has spread and become enzootic, vaccination has been used on a long-term basis by some countries to control the virus, other countries have used it temporarily to aid eradication efforts, while others have not used it at all. Currently, H5N1 HPAIV is considered enzootic in China, Egypt, Viet Nam, India, Bangladesh and Indonesia. All but Bangladesh and India have instituted vaccination programs for poultry. Importantly, the specifics of these programs differ to accommodate different situations, resources, and industry structure in each country. The current vaccines most commonly used are inactivated whole virus vaccines, but vectored vaccine use is increasing. Numerous technical improvements to these platforms and novel vaccine platforms for H5N1 vaccines have been reported, but most are not ready to be implemented in the field.

A critical HA1 neutralizing domain of H5N1 influenza in an optimal conformation induces strong cross-protection

The highly pathogenic avian influenza (HPAI) H5N1 viruses, especially the laboratory-generated H5N1 mutants, have demonstrated the potential to cross the species barrier and infect mammals and humans. Consequently, the design of an effective and safe anti-H5N1 vaccine is essential. We previously demonstrated that the full-length hemagglutinin 1 (HA1) could induce significant neutralizing antibody response and protection. Here, we intended to identify the critical neutralizing domain (CND) in an optimal conformation that can elicit strong cross-neutralizing antibodies and protection against divergent H5N1 strains. We thus constructed six recombinant proteins covering different regions of HA1 of A/Anhui/1/2005(H5N1), each of which was fused with foldon (Fd) and Fc of human IgG. We found that the critical fragment fused with Fd/Fc (HA-13–263-Fdc, H5 numbering) that could elicit the strongest neutralizing antibody response is located in the N-terminal region of HA1 (residues 13–263), which covers the receptor-binding domain (RBD, residues 112–263). We then constructed three additional recombinants fused with Fd plus His tag (HA-13–263-Fd-His), Fc only (HA-13–263-Fc), and His tag only (HA-13–263-His), respectively. We found that the HA-13–263-Fdc, which formed an oligomeric conformation, induced the strongest neutralizing antibody response and cross-protection against challenges of two tested H5N1 virus strains covering clade 1: A/VietNam/1194/2004 (VN/1194) or clade 2.3.4: A/Shenzhen/406H/06 (SZ/406H), while HA-13–263-Fc dimer and HA-13–263-Fd-His trimer elicited higher neutralizing antibody response and protection than HA-13–263-His monomer. These results suggest that the oligomeric form of the CND containing the RBD can be further developed as an effective and safe vaccine for cross-protection against divergent strains of H5N1 viruses.

Influenza B-cells protective epitope characterization: a passkey for the rational design of new broad-range anti-influenza vaccines

The emergence of new influenza strains causing pandemics represents a serious threat to human health. From 1918, four influenza pandemics occurred, caused by H1N1, H2N2 and H3N2 subtypes. Moreover, in 1997 a novel influenza avian strain belonging to the H5N1 subtype infected humans. Nowadays, even if its transmission is still circumscribed to avian species, the capability of the virus to infect humans directly from avian reservoirs can result in fatalities. Moreover, the risk that this or novel avian strains could adapt to inter-human transmission, the development of resistance to anti-viral drugs and the lack of an effective prevention are all incumbent problems for the world population. In this scenario, the identification of broadly neutralizing monoclonal antibodies (mAbs) directed against conserved regions shared among influenza isolates has raised hopes for the development of monoclonal antibody-based immunotherapy and "universal" anti-influenza vaccines.

Evaluation of mismatched immunity against influenza viruses

Prior immunity against influenza A viruses generates sterilizing immunity against matched (homologous) viruses and varying levels of protection against mismatched (heterologous) viruses of the same or different subtypes. Natural immunity carries the risk of high morbidity and mortality, therefore immunization offers the best preventative measure. Antibody responses against the viral hemagglutinin protein correlate with protection in humans and evidence increasingly supports a role for robust cellular immune responses. By exploiting mismatched immunity, current conventional and experimental vaccine candidates can improve the generation of cross-protective immune responses against heterologous viruses. Experimental vaccines such as virus-like particles, DNA vectors, viral vectors and broadly neutralizing antibodies are able to expand cross-protection through mismatched B- and T-cell responses. However, the generation of mismatched immune responses can also have the opposite effect and impair protective immunity. This review discusses mismatched immunity in the context of natural infection and immunization. Additionally, we discuss strategies to exploit mismatched immunity in order to improve current conventional and experimental influenza A virus vaccines.

Potential strategies and biosafety protocols used for dual-use research on highly pathogenic influenza viruses

Influenza A viruses (IAVs), particularly the highly pathogenic avian influenza H5N1, have posed a substantial threat to public health worldwide. Although the laboratory generation of the mutant influenza virus H5N1 with airborne transmissibility among mammals, which has been considered as a dual-use research, may benefit the development of effective vaccines and therapeutics against the emerging infectious agents, it may also pose threats to national biosecurity, laboratory biosafety, and/or public health. This review introduces the classification and characterization of IAVs, pinpoints historic pandemics and epidemics caused by IAVs, emphasizes the significance and necessity of biosafety, summarizes currently established biosafety-related protocols for IAV research, and provides potential strategies to improve biosafety protocols for dual-use research on the highly pathogenic avian influenza viruses and other emerging infectious agents.