Neutralizing epitopes of influenza virus hemagglutinin: target for the development of a universal vaccine against H5N1 lineages

Epitopes in the HA and NA of H5 and H7 avian influenza viruses that are important for antigenic drift

Avian influenza viruses evolve antigenically to evade host immunity. Two influenza A virus surface glycoproteins, the haemagglutinin and neuraminidase, are the major targets of host immunity and undergo antigenic drift in response to host pre-existing humoral and cellular immune responses. Specific sites have been identified as important epitopes in prominent subtypes such as H5 and H7, which are of animal and public health significance due to their panzootic and pandemic potential. The haemagglutinin is the immunodominant immunogen, it has been extensively studied, and the antigenic reactivity is closely monitored to ensure candidate vaccine viruses are protective. More recently, the neuraminidase has received increasing attention for its role as a protective immunogen. The neuraminidase is expressed at a lower abundance than the haemagglutinin on the virus surface but does elicit a robust antibody response. This review aims to compile the current information on haemagglutinin and neuraminidase epitopes and immune escape mutants of H5 and H7 highly pathogenic avian influenza viruses. Understanding the evolution of immune escape mutants and the location of epitopes is critical for identification of vaccine strains and development of broadly reactive vaccines that can be utilized in humans and animals.

Vaccines against Major Poultry Viral Diseases: Strategies to Improve the Breadth and Protective Efficacy

The poultry industry is the largest source of meat and eggs for human consumption worldwide. However, viral outbreaks in farmed stock are a common occurrence and a major source of concern for the industry. Mortality and morbidity resulting from an outbreak can cause significant economic losses with subsequent detrimental impacts on the global food supply chain. Mass vaccination is one of the main strategies for controlling and preventing viral infection in poultry. The development of broadly protective vaccines against avian viral diseases will alleviate selection pressure on field virus strains and simplify vaccination regimens for commercial farms with overall savings in husbandry costs. With the increasing number of emerging and re-emerging viral infectious diseases in the poultry industry, there is an urgent need to understand the strategies for broadening the protective efficacy of the vaccines against distinct viral strains. The current review provides an overview of viral vaccines and vaccination regimens available for common avian viral infections, and strategies for developing safer and more efficacious viral vaccines for poultry.

Evolutionary Dynamics of Mexican Lineage H5N2 Avian Influenza Viruses

We have demonstrated for the first time a comprehensive evolutionary analysis of the Mexican lineage H5N2 avian influenza virus (AIV) using complete genome sequences (n = 189), from its first isolation in 1993 until 2019. Our study showed that the Mexican lineage H5N2 AIV originated from the North American wild bird gene pool viruses around 1990 and is currently circulating in poultry populations of Mexico, the Dominican Republic, and Taiwan. Since the implementation of vaccination in 1995, the highly pathogenic AIV (HPAIV) H5N2 virus was eradicated from Mexican poultry in mid-1995. However, the low pathogenic AIV (LPAIV) H5N2 virus has continued to circulate in domestic poultry populations in Mexico, eventually evolving into five distinct clades. In the current study, we demonstrate that the evolution of Mexican lineage H5N2 AIVs involves gene reassortments and mutations gained over time. The current circulating Mexican lineage H5N2 AIVs are classified as LPAIV based on the amino acid sequences of the hemagglutinin (HA) protein cleavage site motif as well as the results of the intravenous pathogenicity index (IVPI). The immune pressure from vaccinations most likely has played a significant role in the positive selection of antigenic drift mutants within the Mexican H5N2 AIVs. Most of the identified substitutions in these viruses are located on the critical antigenic residues of the HA protein and as a result, might have contributed to vaccine failures. This study highlights and stresses the need for vaccine updates while emphasizing the importance of continued molecular monitoring of the HA protein for its antigenic changes compared to the vaccines used.

RNA-dependent assembly of chimeric antigen nanoparticles as an efficient H5N1 pre-pandemic vaccine platform

Highly pathogenic avian influenza viruses (HPAIVs) pose a significant threat to human health, with high mortality rates, and require effective vaccines. We showed that, harnessed with novel RNA-mediated chaperone function, hemagglutinin (HA) of H5N1 HPAIV could be displayed as an immunologically relevant conformation on self-assembled chimeric nanoparticles (cNP). A tri-partite monomeric antigen was designed including: i) an RNA-interaction domain (RID) as a docking tag for RNA to enable chaperna function (chaperna: chaperone + RNA), ii) globular head domain (gd) of HA as a target antigen, and iii) ferritin as a scaffold for 24 mer-assembly. The immunization of mice with the nanoparticles (~46 nm) induced a 25-30 fold higher neutralizing capacity of the antibody and provided cross-protection from homologous and heterologous lethal challenges. This study suggests that cNP assembly is conducive to eliciting antibodies against the conserved region in HA, providing potent and broad protective efficacy.

Efficacy of recombinant Marek's disease virus vectored vaccines with computationally optimized broadly reactive antigen (COBRA) hemagglutinin insert against genetically diverse H5 high pathogenicity avian influenza viruses

The genetic and antigenic drift associated with the high pathogenicity avian influenza (HPAI) viruses of Goose/Guangdong (Gs/GD) lineage and the emergence of vaccine-resistant field viruses underscores the need for a broadly protective H5 influenza A vaccine. Here, we tested experimental vector herpesvirus of turkey (vHVT)-H5 vaccines containing either wild-type clade 2.3.4.4A-derived H5 inserts or computationally optimized broadly reactive antigen (COBRA) inserts with challenge by homologous and genetically divergent H5 HPAI Gs/GD lineage viruses in chickens. Direct assessment of protection was confirmed for all the tested constructs, which provided clinical protection against the homologous and heterologous H5 HPAI Gs/GD challenge viruses and significantly decreased oropharyngeal shedding titers compared to the sham vaccine. The cross reactivity was assessed by hemagglutinin inhibition (HI) and focus reduction assay against a panel of phylogenetically and antigenically diverse H5 strains. The COBRA-derived H5 inserts elicited antibody responses against antigenically diverse strains, while the wild-type-derived H5 vaccines elicited protection mostly against close antigenically related clades 2.3.4.4A and 2.3.4.4D viruses. In conclusion, the HVT vector, a widely used replicating vaccine platform in poultry, with H5 insert provides clinical protection and significant reduction of viral shedding against homologous and heterologous challenge. In addition, the COBRA-derived inserts have the potential to be used against antigenically distinct co-circulating viruses and future drift variants.

Cross-Protection by Inactivated H5 Prepandemic Vaccine Seed Strains against Diverse Goose/Guangdong Lineage H5N1 Highly Pathogenic Avian Influenza Viruses

The highly pathogenic avian influenza virus (HPAIV) H5N1 A/goose/Guangdong/1996 lineage (Gs/GD) is endemic in poultry across several countries in the world and has caused sporadic lethal infections in humans. Vaccines are important in HPAIV control both for poultry and in prepandemic preparedness for humans. This study assessed inactivated prepandemic vaccine strains in a One Health framework across human and agricultural and wildlife animal health, focusing on the genetic and antigenic diversity of field H5N1 Gs/GD viruses from the agricultural sector and assessing cross-protection in a chicken challenge model. Nearly half (47.92%) of the 48 combinations of vaccine and challenge viruses examined had bird protection of 80% or above. Most vaccinated groups had prolonged mean death times (MDT), and the virus-shedding titers were significantly lower than those of the sham-vaccinated group (P ≤ 0.05). The antibody titers in the prechallenge sera were not predictive of protection. Although vaccinated birds had higher titers of hemagglutination-inhibiting (HI) antibodies against the homologous vaccine antigen, most of them also had lower or no antibody titer against the challenge antigen. The comparison of all parameters and homologous or closely related vaccine and challenge viruses gave the best prediction of protection. Through additional analysis, we identified a pattern of epitope substitutions in the hemagglutinin (HA) of each challenge virus that impacted protection, regardless of the vaccine used. These changes were situated in the antigenic sites and/or reported epitopes associated with virus escape from antibody neutralization. As a result, this study highlights virus diversity, immune response complexity, and the importance of strain selection for vaccine development to control H5N1 HPAIV in the agricultural sector and for human prepandemic preparedness. We suggest that the engineering of specific antigenic sites can improve the immunogenicity of H5 vaccines.IMPORTANCE The sustained circulation of highly pathogenic avian influenza virus (HPAIV) H5N1 A/goose/Guangdong/1996 (Gs/GD) lineage in the agricultural sector and some wild birds has led to the evolution and selection of distinct viral lineages involved in escape from vaccine protection. Our results using inactivated vaccine candidates from the human pandemic preparedness program in a chicken challenge model identified critical antigenic conformational epitopes on H5 hemagglutinin (HA) from different clades that were associated with antibody recognition and escape. Even though other investigators have reported epitope mapping in the H5 HA, much of this information pertains to epitopes reactive to mouse antibodies. Our findings validate changes in antigenic epitopes of HA associated with virus escape from antibody neutralization in chickens, which has direct relevance to field protection and virus evolution. Therefore, knowledge of these immunodominant regions is essential to proactively develop diagnostic tests, improve surveillance platforms to monitor AIV outbreaks, and design more efficient and broad-spectrum agricultural and human prepandemic vaccines.

Modification of neutralizing epitopes of hemagglutinin for the development of broadly protective H9N2 vaccine

The H9N2 avian influenza viruses cause significant economic losses in poultry worldwide and could potentially cause human pandemic. Currently, the available vaccines have limited efficacy due to antigenic drift of H9N2. To improve vaccine efficacy, we developed monovalent vaccine strain via the modification of neutralizing epitopes on hemagglutinin (HA) to broaden the protection against H9N2 viruses. In this study, single and multiple mutation were introduced to amino acid at position 148, 150 (site I) and 183, 186, 188 (site II) on the full-length HA gene of H9N2 strain (A/Hong Kong/33982/2009). These mutant HA constructs were displayed on the baculovirus surface (BacH9), and evaluated for their cross-protective efficacy against H9N2 viruses in a mouse model. Our findings indicate that mice immunized with multiple BacH9 mutant constructs (148-150 183 and 186) induced cross-protective immunity against circulating H9N2 in the viral challenge study and prove to be a promising vaccine candidate for H9N2.

Amino acid substitutions in antigenic region B of hemagglutinin play a critical role in the antigenic drift of subclade 2.3.4.4 highly pathogenic H5NX influenza viruses

As one of the important control strategies for highly pathogenic avian influenza (HPAI) in China, vaccination has been implemented compulsively in poultry flocks since 2004. However, the emergence and dominance of the circulating antigenic variants require the update of vaccines periodically. In order to investigate the key molecular sites responsible for the antigenic drift, a total of 13 amino acid positions divergent between clade 2.3.4 H5 viruses and their descendent subclade 2.3.4.4 variants in or around the recognized antigenic epitopes A-E were initially identified through inspecting a comprehensive HA sequence alignment of the H5 subtype HPAI viruses. Subsequently, a panel of single-site or multi-site HA mutants was constructed by reverse genetics with two H5N1 viruses of S (clade 2.3.4) and QD1 (subclade 2.3.4.4) as the HA backbone to study their antigenic variations, respectively. The hemagglutination-inhibition assay revealed an evident impact of mutations at sites 88, 156, 205, 208, 239 and 289 to the HA antigenicity and highlighted that the amino acid substitutions located in the antigenic region B, especially the combined mutations at sites 205 and 208, were the major antigenic determinant which was also consistent with results from flow cytometry and antigenic mapping. Our findings provided more insights into the molecular mechanism of antigenic drift of the H5 subtype HPAI virus, which would be helpful for the selection of vaccine candidates and accordingly for the prevention and control of this devastating viral agent.

Synthetic biology for bioengineering virus-like particle vaccines

Vaccination is the most effective method of disease prevention and control. Many viruses and bacteria that once caused catastrophic pandemics (e.g., smallpox, poliomyelitis, measles, and diphtheria) are either eradicated or effectively controlled through routine vaccination programs. Nonetheless, vaccine manufacturing remains incredibly challenging. Viruses exhibiting high antigenic diversity and high mutation rates cannot be fairly contested using traditional vaccine production methods and complexities surrounding the manufacturing processes, which impose significant limitations. Virus-like particles (VLPs) are recombinantly produced viral structures that exhibit immunoprotective traits of native viruses but are noninfectious. Several VLPs that compositionally match a given natural virus have been developed and licensed as vaccines. Expansively, a plethora of studies now confirms that VLPs can be designed to safely present heterologous antigens from a variety of pathogens unrelated to the chosen carrier VLPs. Owing to this design versatility, VLPs offer technological opportunities to modernize vaccine supply and disease response through rational bioengineering. These opportunities are greatly enhanced with the application of synthetic biology, the redesign and construction of novel biological entities. This review outlines how synthetic biology is currently applied to engineer VLP functions and manufacturing process. Current and developing technologies for the identification of novel target-specific antigens and their usefulness for rational engineering of VLP functions (e.g., presentation of structurally diverse antigens, enhanced antigen immunogenicity, and improved vaccine stability) are described. When applied to manufacturing processes, synthetic biology approaches can also overcome specific challenges in VLP vaccine production. Finally, we address several challenges and benefits associated with the translation of VLP vaccine development into the industry.

Preclinical evaluation of the efficacy of an H5N8 vaccine candidate (IDCDC-RG43A) in mouse and ferret models for pandemic preparedness

Because H5N1 influenza viruses continuously threaten the public health, the WHO has prepared various clades of H5N1 mock-up vaccines as one of the measures for pandemic preparedness. The recent worldwide outbreak of H5Nx virus which belongs to clade 2.3.4.4 and of which H5N6 subtype belongs and already caused human infection also increases the need of pandemic vaccine for such novel emerging viruses. In this study, we evaluated the protective efficacy and immunogenicity of an egg-based and inactivated whole-virus H5N8 (IDCDC-RG43A) developed by CDC containing HA and NA gene of the parent virus A/gyrfalcon/Washington/41088-6/2014. Mice vaccinated two times elicited low to moderate antibody titer in varying amount of antigen doses against the homologous H5N8 vaccine virus and heterologous intra-clade 2.3.4.4 H5N6 (A/Sichuan/26221/2014) virus. Mice immunized with at least 3.0 µg/dose of IDCDC-RG43A with aluminum hydroxide adjuvant were completely protected from lethal challenge with the mouse-adapted H5N8 (A/Environment/Korea/ma468/2015, maH5N8) as well as cleared the viral replication in tissues including lung, brain, spleen, and kidney. Vaccinated ferrets induced high antibody titers against clade 2.3.4.4 H5N8/H5N6 viruses and the antibody showed high cross-reactivity to clade 2.2 H5N1 but not to clade 1 and 2.3.4 viruses as measured by hemagglutinin inhibition and serum neutralization assays. Furthermore, administration of the vaccine in ferrets resulted in attenuation of clinical disease signs and virus spread to peripheral organs including lung, spleen, and kidney from high dose challenge with maH5N8 virus. The protective and immunogenic characteristic of the candidate vaccine are essential attributes to be considered for further clinical trials as a pre-pandemic vaccine for a potential pandemic virus.

Complementary recognition of the receptor-binding site of highly pathogenic H5N1 influenza viruses by two human neutralizing antibodies

The highly pathogenic avian influenza virus H5N1 is a major threat to global public health and therefore a high-priority target of current vaccine development. The receptor-binding site (RBS) on the globular head of hemagglutinin (HA) in the viral envelope is one of the major target sites for antibody recognition against H5N1 and other influenza viruses. Here, we report the identification and characterization of a pair of human RBS-specific antibodies, designated FLD21.140 and AVFluIgG03, that are mutually complementary in their neutralizing activities against a diverse panel of H5N1 viruses. Crystallographic analysis and site-directed mutagenesis revealed that the two antibodies share a similar RBS-binding mode, and their individual specificities are governed by residues at positions 133a, 144, and 145. Specifically, FLD21.140 preferred Leu-133a/Lys-144/Ser-145, whereas AVFluIgG03 favored Ser-133a/Thr-144/Pro-145 residue triplets, both of which perfectly matched the most prevalent residues in viruses from epidemic-originating regions. Of note, according to an analysis of 3758 H5 HA sequences available in the Influenza Virus Database at the National Center for Biotechnology Information, the residues Leu-133a/Ser-133a and Ser-145/Pro-145 constituted more than 87.6 and 99.3% of all residues at these two positions, respectively. Taken together, our results provide a structural understanding for the neutralizing complementarity of these two antibodies and improve our understanding of the RBS-specific antibody response against H5N1 infection in humans.

Avian Influenza A Virus Pandemic Preparedness and Vaccine Development

Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses.

Baculovirus Surface Display of Immunogenic Proteins for Vaccine Development

Vaccination is an efficient way to prevent the occurrence of many infectious diseases in humans. To date, several viral vectors have been utilized for the generation of vaccines. Among them, baculovirus-categorized as a nonhuman viral vector-has been used in wider applications. Its versatile features, like large cloning capacity, nonreplicative nature in mammalian cells, and broad tissue tropism, hold it at an excellent position among vaccine vectors. In addition to ease and safety during swift production, recent key improvements to existing baculovirus vectors (such as inclusion of hybrid promoters, immunostimulatory elements, etc.) have led to significant improvements in immunogenicity and efficacy of surface-displayed antigens. Furthermore, some promising preclinical results have been reported that mirror the scope and practicality of baculovirus as a vaccine vector for human applications in the near future. Herein, this review provides an overview of the induced immune responses by baculovirus surface-displayed vaccines against influenza and other infectious diseases in animal models, and highlights the strategies applied to enhance the protective immune responses against the displayed antigens.

Broadening the H5N3 Vaccine Immunogenicity against H5N1 Virus by Modification of Neutralizing Epitopes

The highly pathogenic avian influenza (HPAI) H5N1 virus remains to be one of the world's largest pandemic threats due to the emergence of new variants. The rapid evolution of new sub-lineages is currently the greatest challenge in vaccine development. In this study, we developed an epitope modified non-pathogenic H5N3 (A/duck/Singapore/97) vaccine for broad protection against influenza H5 subtype. H5N3 hemagglutinin (HA) mutant reassortant viruses with A/Puerto Rico/8/34 (PR8) backbone were generated by mutating amino acids at the 140th loop and 190th α-helix of hemagglutinin. The cross-neutralizing efficacy of reverse genetics-derived H5N3HA (RG-H5N3HA) mutants was confirmed by testing reactivity with reference chicken anti-H5N1 clade 2 virus sera. Furthermore, RG-H5N3HA mutant immunized mice induced cross-neutralizing antibodies and cross-protection against distinct H5N1 viral infection. Our findings suggest that the use of non-pathogenic H5 viruses antigenically related to HPAI-H5N1 allows for the development of broadly protective vaccines and reduces the need for biosafety level 3 (BSL3) containment facilities.

Visualization of Alternative Functional Configurations of Influenza Virus Hemagglutinin Facilitates Rapid Selection of Complementing Vaccines in Emergency Situations

Successful immunization against avian influenza virus (AIV) requires eliciting an adequate polyclonal response to AIV hemagglutinin (HA) subunit 1 (HA1) epitopes. Outbreaks of highly-pathogenic (HP) AIV subtype H5N1 can occur in vaccinated flocks in many endemic areas. Protection against emerging AIV is partly hindered by the limitations of vaccine production and transport, the use of leaky vaccines, and the use of multiple, and often antigenically-diverse, vaccines. It was hypothesized that the majority of alternative functional configurations (AFC) within the AIV HA1 can be represented by the pool of vaccine seed viruses currently in production because only a finite number of AFC are possible within each substructure of the molecule. Therefore, combinations of commercial vaccines containing complementing structural units (CSU) to each HA1 substructure can elicit responses to the totality of a given emerging AIV HA1 substructure isoforms. Analysis of homology-based 3D models of vaccine seed and emerging viruses facilitated the definition of HA1 AFC isoforms. CSU-based plots were used to predict which commercial vaccine combinations could have been used to cover nine selected AFC isoforms on recent Egyptian HP AIV H5N1 outbreak viruses. It is projected that expansion of the vaccine HA1 3D model database will improve international emergency responses to AIV.

Advances in novel influenza vaccines: a patent review

The threat of a major human influenza pandemic such as the avian H5N1 or the 2009 new H1N1 has emphasized the need for effective prevention strategies to combat these pathogens. Although egg based influenza vaccines have been well established for a long time, it remains an ongoing public health need to develop alternative production methods that ensures improved safety, efficacy, and ease of administration compared with conventional influenza vaccines. This article is intended to cover some of the recent advances and related patents on the development of influenza vaccines including live attenuated, cell based, genomic and synthetic peptide vaccines.

Oral Delivery of a Novel Attenuated Salmonella Vaccine Expressing Influenza A Virus Proteins Protects Mice against H5N1 and H1N1 Viral Infection

Attenuated strains of invasive enteric bacteria, such as Salmonella, represent promising gene delivery agents for nucleic acid-based vaccines as they can be administrated orally. In this study, we constructed a novel attenuated strain of Salmonella for the delivery and expression of the hemagglutinin (HA) and neuraminidase (NA) of a highly pathogenic H5N1 influenza virus. We showed that the constructed Salmonella strain exhibited efficient gene transfer activity for HA and NA expression and little cytotoxicity and pathogenicity in mice. Using BALB/c mice as the model, we evaluated the immune responses and protection induced by the constructed Salmonella-based vaccine. Our study showed that the Salmonella-based vaccine induced significant production of anti-HA serum IgG and mucosal IgA, and of anti-HA interferon-γ producing T cells in orally vaccinated mice. Furthermore, mice orally vaccinated with the Salmonella vaccine expressing viral HA and NA proteins were completely protected from lethal challenge of highly pathogenic H5N1 as well as H1N1 influenza viruses while none of the animals treated with the Salmonella vaccine carrying the empty expression vector with no viral antigen expression was protected. These results suggest that the Salmonella-based vaccine elicits strong antigen-specific humoral and cellular immune responses and provides effective immune protection against multiple strains of influenza viruses. Furthermore, our study demonstrates the feasibility of developing novel attenuated Salmonella strains as new oral vaccine vectors against influenza viruses.

A novel humanized antibody neutralizes H5N1 influenza virus via two different mechanisms

Highly pathogenic avian influenza virus subtype H5N1 continues to be a severe threat to public health, as well as the poultry industry, because of its high lethality and antigenic drift rate. Neutralizing monoclonal antibodies (MAbs) can serve as a useful tool for preventing, treating, and detecting H5N1. In the present study, humanized H5 antibody 8A8 was developed from a murine H5 MAb. Both the humanized and mouse MAbs presented positive activity in hemagglutination inhibition (HI), virus neutralization, and immunofluorescence assays against a wide range of H5N1 strains. Interestingly, both human and murine 8A8 antibodies were able to detect H5 in Western blot assays under reducing conditions. Further, by sequencing of escape mutants, the conformational epitope of 8A8 was found to be located within the receptor binding domain (RBD) of H5. The linear epitope of 8A8 was identified by Western blotting of overlapping fragments and substitution mutant forms of HA1. Reverse genetic H5N1 strains with individual mutations in either the conformational or the linear epitope were generated and characterized in a series of assays, including HI, postattachment, and cell-cell fusion inhibition assays. The results indicate that for 8A8, virus neutralization mediated by RBD blocking relies on the conformational epitope while binding to the linear epitope contributes to the neutralization by inhibiting membrane fusion. Taken together, the results of this study show that a novel humanized H5 MAb binds to two types of epitopes on HA, leading to virus neutralization via two mechanisms.

IMPORTANCE

Recurrence of the highly pathogenic avian influenza virus subtype H5N1 in humans and poultry continues to be a serious public health concern. Preventive and therapeutic measures against influenza A viruses have received much interest in the context of global efforts to combat the current and future pandemics. Passive immune therapy is considered to be the most effective and economically prudent preventive strategy against influenza virus besides vaccination. It is important to develop a humanized neutralizing monoclonal antibody (MAb) against all of the clades of H5N1. For the first time, we report in this study that a novel humanized H5 MAb binds to two types of epitopes on HA, leading to virus neutralization via two mechanisms. These findings further deepen our understanding of influenza virus neutralization.

Identification of a neutralizing epitope within antigenic domain 5 of glycoprotein B of human cytomegalovirus

Human cytomegalovirus (HCMV) is an important, ubiquitous pathogen that causes severe clinical disease in immunocompromised individuals, such as organ transplant recipients and infants infected in utero. The envelope glycoprotein B (gB) of HCMV is a major antigen for the induction of virus-neutralizing antibodies. We have begun to define target structures within gB that are recognized by virus-neutralizing antibodies. Antigenic domain 5 (AD-5) of gB has been identified as an important target for neutralizing antibodies in studies using human monoclonal antibodies (MAbs). Anti-AD-5 MAbs share a target site on gB, despite originating from different, healthy, HCMV-infected donors. Mutational analysis of AD-5 identified tyrosine 280 in combination with other surface-exposed residues (the YNND epitope) as critical for antibody binding. The YNND epitope is strictly conserved among different HCMV strains. Recombinant viruses carrying YNND mutations in AD-5 were resistant to virus-neutralizing MAbs. Competition enzyme-linked immunosorbent assays (ELISAs) with human HCMV-convalescent-phase sera from unselected donors confirmed the conserved antibody response for the YNND epitope in HCMV-infected individuals and, because a significant fraction of the gB AD-5 response was directed against the YNND epitope, further argued that this epitope is a major target of anti-AD-5 antibody responses. In addition, affinity-purified polyclonal anti-AD-5 antibodies prepared from individual sera showed reactivity to AD-5 and neutralization activity toward gB mutant viruses that were similar to those of AD-5-specific MAbs. Taken together, our data indicate that the YNND epitope represents an important target for anti-gB antibody responses as well as for anti-AD-5 virus-neutralizing antibodies.

IMPORTANCE

HCMV is a major global health concern, and a vaccine to prevent HCMV disease is a widely recognized medical need. Glycoprotein B of HCMV is an important target for neutralizing antibodies and hence an interesting molecule for intervention strategies, e.g., vaccination. Mapping the target structures of neutralizing antibodies induced by naturally occurring HCMV infection can aid in defining the properties required for a protective capacity of vaccine antigens. The data presented here extend our knowledge of neutralizing epitopes within gB to include AD-5. Collectively, our data will contribute to optimal vaccine design and development of antibody-based therapies.

Progress toward a universal H5N1 vaccine: a recombinant modified vaccinia virus Ankara-expressing trivalent hemagglutinin vaccine

Background

The rapid evolution of new sublineages of H5N1 influenza poses the greatest challenge in control of H5N1 infection by currently existing vaccines. To overcome this, an MVAtor vector expressing three H5HA antigens A/Vietnam/1203/04, A/Indonesia/669/06 and A/Anhui/01/05 (MVAtor-tri-HA vector) was developed to elicit broad cross-protection against diverse clades by covering amino acid variations in the major neutralizing epitopes of HA among H5N1 subtypes.

Methods

BALB/c mice and guinea pigs were immunized i.m. with 8×10⁷ TCID₅₀/animal of MVAtor-tri-HA vector. The immunogenicity and cross-protective immunity of the MVAtor-tri-HA vector was evaluated against diverse clades of H5N1 strains.

Results

The results showed that mice immunized with MVAtor-tri-HA vector induced robust cross-neutralizing immunity to diverse H5N1 clades. In addition, the MVAtor-tri-HA vector completely protected against 10 MLD₅₀ of a divergent clade of H5N1 infection (clade 7). Importantly, the serological surveillance of post-vaccinated guinea pig sera demonstrated that MVAtor-tri-HA vector was able to elicit strong cross-clade neutralizing immunity against twenty different H5N1 strains from six clades that emerged between 1997 and 2012.

Conclusions

The present findings revealed that incorporation of carefully selected HA genes from divergent H5N1 strains within a single vector could be an effective approach in developing a vaccine with broad coverage to prevent infection during a pandemic situation.

Genetic characterization of an H5N1 avian influenza virus from a vaccinated duck flock in Vietnam

This study reports the genetic characterization of a highly pathogenic avian influenza virus subtype H5N1 isolated from a moribund domestic duck in central Vietnam during 2012. In the moribund duck's flock, within 6 days after vaccination with a commercial H5N1 vaccine (Re-5) to 59-day-old birds, 120 out of 2,000 ducks died. Genetic analysis revealed a substantial number of mutations in the HA gene of the isolate in comparison with the vaccine strains, Re-1 and Re-5. Similar mutations were also found in selected Vietnamese H5N1 strains isolated since 2009. Mutations in the HA gene involved positions at antigenic sites associated with antibody binding and also neutralizing epitopes, with some of the mutations resulting in the modification of N-linked glycosylation of the HA. Those mutations may be related to the escape of virus from antibody binding and the infection of poultry, interpretations which may be confirmed through a reverse genetics approach. The virus also carried an amino acid substitution in the M2, which conferred a reduced susceptibility to amantadine, but no neuraminidase inhibitor resistance markers were found in the viral NA gene. Additional information including vaccination history in the farm and the surrounding area is needed to fully understand the background of this outbreak. Such understanding and expanded monitoring of the H5N1 influenza viruses circulating in Vietnam is an urgent need to provide updated information to improve effective vaccine strain selection and vaccination protocols, aiding disease control, and biosecurity to prevent H5N1 infection in both poultry and humans.

Monovalent H5 vaccine based on epitope-chimeric HA provides broad cross-clade protection against variant H5N1 viruses in mice

H5N1 HPAI virus continues to be a severe threat for public health, as well as for the poultry industry, due to its high mortality and antigenic drift rate. There is no monovalent vaccine available which provides broad protection against those major circulating strains. In the present study, a monovalent H5 vaccine strain was developed with antigenic sequence analysis and epitope mutations. H5 from Indonesia strain (A/Indonesia/CDC669/2006) was used as backbone sequence. Three amino acids were mutated to express immunogenic epitopes from other circulating H5N1s in the backbone. RG influenza virus expressing the epitope-chimeric H5 can react in HI with multiple H5 monoclonal antibodies which fail to neutralize wild type CDC669. High titers in HI and virus neutralization against different clades H5N1s (clade 1, 2, 4 and 7) were detected using sera from mice immunized with the epitope-chimeric H5N1. The monovalent vaccine with RG-epitope-chimeric H5N1 protected mice from lethal challenge with H5N1s of different clades, including clade 1.0, 2.1, 2.2 and 2.3. This study indicates that the broad immune response elicited by this single H5N1 virus allows it to be a promising candidate for a monovalent H5 universal vaccine.

Antigenic analyses of highly pathogenic avian influenza a viruses

In response to the ongoing threat to animal and human health posed by HPAI endemic in poultry, Asia (H5N1) and North America (H7N3) have revived efforts to reduce pandemic risk by disease control at the source and improved pandemic vaccines. Discovery of conserved neutralization epitopes in the HA, which mediate broad protection within and across HA subtypes have changed the paradigm of "broadly reactive" or "universal" vaccine design. Development of such vaccines would benefit from comparative antigenic analysis of viruses with increasing divergence within (and between) HA subtypes. A review of recent work to define the antigenic properties of HPAI viruses revealed data generated through an array of experimental approaches. This information has supported diagnostics and vaccine development for animal and human health. Further harmonization of analytical methods is needed to determine the antigenic relationships among multiple lineages of rapidly evolving HPAI viruses.

Development of dual-function ELISA for effective antigen and antibody detection against H7 avian influenza virus

Background

Outbreaks in poultry involving influenza virus from H7 subtype have resulted in human infections, thus causing a major concern for public health, as well as for the poultry industry. Currently, no efficient rapid test is available for large-scale detection of either antigen or antibody of H7 avian influenza viruses.

Results

In the present study, a dual function ELISA was developed for the effective detection of antigen and antibody against H7 AIVs. The test was established based on antigen-capture-ELISA and epitope blocking ELISA. The two Mabs 62 and 98 which were exploited in the assay were identified to recognize two conformational neutralizing epitopes on H7 HA1. Both of the epitopes exist in all of the human H7 strains, including the recent H7N9 strain from China and > 96.6% of avian H7 strains. The dual ELISA was able to detect all of the five H7 antigens tested without any cross reaction to other influenza subtypes. The antigen detection limit was less than 1 HA unit of H7. For antibody detection, the sensitivity and specificity of the dual ELISA was evaluated and compared to HI and microneutralization using immunized animal sera to different H7 strains and different subtypes of AIVs. Results indicated that antibodies to H7 were readily detected in immunized animal sera by the dual ELISA whereas specimens with antibodies to other AIVs yielded negative results.

Conclusions

This is the first dual-function ELISA reported for either antigen or antibody detection against H7 AIVs. The assay was highly sensitive and 100% specific in both functions rendering it effective for H7 diagnosis.

Immune responses to baculovirus-displayed enterovirus 71 VP1 antigen

The increased distribution and neurovirulence of enterovirus 71 is an important health threat for young children in Asia Pacific. Vaccine design has concentrated on inactivated virus with the most advanced undergoing Phase III clinical trials. By using a subunit vaccine approach, production costs could be reduced by lowering the need for biocontainment. In addition, novel mutations could be rapidly incorporated to reflect the emergence of new enterovirus 71 subgenogroups. To circumvent the problems associated with conventional subunit vaccines, the antigen can be displayed on a viral vector that conveys stability and facilitates purification. Additional advantages of viral-vectored subunit vaccines are their ability to stimulate the innate immune system by transducing cells and the possibility of oral or nasal delivery, which dispenses with the need for syringes and medical personnel. Baculovirus-displayed VP1 combines all these benefits with protection that is as efficient as inactivated virus.

Recombinant baculovirus displayed vaccine: a novel tool for the development of a cross-protective influenza H5N1 vaccine

The rapid evolution of new sublineages of H5N1 influenza in Asia poses the greatest challenge in vaccine development for pre-pandemic preparedness. To overcome the antigenic diversity of H5N1 strains, multiple vaccine strains can be designed based on the distribution of neutralizing epitopes in the globular head of H5 hemagglutinin (HA). Recently, we selected two different HAs of H5N1 strains based on the neutralizing epitopes and reactivity with different neutralizing antibodies. The HAs of selected vaccine strains were individually expressed on the baculovirus envelope (bivalent-BacHA) with its native antigenic configuration. Further, oral delivery of live bivalent-BacHA elicited broadly reactive humoral, mucosal and cell-mediated immune responses and showed complete protection against antigenically distinct H5N1 strains in mice. The strategy for the vaccine strain selection, vaccine design and route of administration will provide an idea for development of a widely protective vaccine against highly pathogenic H5N1 for pre-pandemic preparedness.

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.

Monoclonal Antibody Targeting Neutralizing Epitope on H5N1 Influenza Virus of Clade 1 and 0 for Specific H5 Quantification

H5N1 influenza viruses cause high mortality in avian and mammalian species, including humans. Antigenic drift in H5 sequence poses challenges in the development of vaccine and therapeutic antibody. In this study, a monoclonal antibody 11G12 was produced from inactivated H5N1 immunized mice. Results from IFA, ELISA, HI, and virus neutralization indicated that Mab 11G12 can specifically recognize and neutralize H5 type hemagglutinin from clade 1 and 0 without any cross-reaction to any other clades of H5N1 viruses. Mab 11G12 was used to differentiate and quantify the expression of H5N1 strain A/VietNam/1203/04 from a trivalent vaccine mix in ELISA. Sequencing of escape mutants identified that Mab 11G12 targets a major neutralizing epitope of influenza H5 hemagglutinin. The study indicated that some major neutralizing epitopes in H5s of early strains were mutated due to antigenic drift.

Cross-protective efficacy of bivalent recombinant baculoviral vaccine against heterologous influenza H5N1 challenge

The present study demonstrates the cross-protective efficacy of baculovirus displayed HAs of A/Indonesia/669/06 and A/Anhui/01/05 against heterologous H5N1 challenges in a mouse model. Mice orally or subcutaneously immunized with live bivalent-BacHA vaccine significantly induced higher HA-specific humoral and cellular immune responses when compared with inactivated bivalent-BacHA. In addition, oral administration of live bivalent-BacHA vaccine was able to induce significant level of antigen-specific mucosal IgA levels. Microneutralization assay indicated that live bivalent-BacHA vaccine was able to induce strong cross-clade neutralization titer against distinct H5N1 clades (1, 2.1.3, 2.2.1.1, 2.3.2, 2.3.4, 4, 7 and 9). The production of both interferon-gamma (IFN-γ) and interleukin-4 (IL-4) by splenocytes from vaccinated mice indicated that mice vaccinated orally or subcutaneously with live bivalent-BacHA stimulated both IFN-γ secreting Th1 cells and IL-4 secreting Th2 cells, whereas mice immunized subcutaneously with inactive adjuvanted bivalent-BacHA stimulated only IL-4 secreting Th2 cells. Cross-protective immunity study also showed that mice immunized either orally or subcutaneously with live bivalent-BacHA were completely protected against 5MLD50 of clade 1 and clade 2.2.1.1 H5N1 viral infections. The protective immune response elicited by bivalent-BacHA vaccine against H5N1 variants demonstrates the possibility of protection against a broad range of H5N1 strains.

Reverse engineering the antigenic architecture of the haemagglutinin from influenza H5N1 clade 1 and 2.2 viruses with fine epitope mapping using monoclonal antibodies

The induction of neutralising antibodies to the viral surface glycoprotein, haemagglutinin (HA) is considered the cornerstone of current seasonal and pandemic influenza vaccines. Mapping of neutralising epitopes using monoclonal antibodies (mAbs) helps define mechanisms of antigenic drift, neutralising escape and facilitates pre-pandemic vaccine design. In the present study we reverse engineered the antigenic structure of the HAs of two highly pathogenic H5N1 vaccine strains representative of currently circulating clade 1 and 2.2 H5N1 viruses. The HA sequence of the A/Vietnam/1194/04 clade 1 virus was progressively mutated into the HA sequence of the clade 2.2 virus, A/Bar-headed Goose/Qinghai/1A/05. Fine mapping of clade-specific neutralising epitopes was performed by examining the cross-reactivity of mAbs raised against the native HA of each parent virus. The reactivity across all clade specific mAbs centred around a constellation of mutations at positions 140, 145, 171 and 172, all of which are proximal to the receptor binding site on the membrane distal globular head of the HA. Overlapping cross-reactivity of these antigenic sites suggests that these amino acid positions relate to the antigenic evolution of the H5 clade 1 and 2.2 viruses. This finding may prove useful for the design of vaccines with broader neutralising cross-reactivity against the different H5 HA sublineages currently in circulation. These findings provide important information about the amino acid changes involved in the cross-clade evolution of H5N1 viruses and their potential for human to human transmission; and facilitates a greater understanding of the pandemic potential of H5N1 isolates.

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

Because of their rapid evolution, genetic diversity, broad host range, ongoing circulation in birds, and potential human-to-human transmission, H5N1 influenza viruses remain a major global health concern. Their high degree of genetic diversity also poses enormous burdens and uncertainties in developing effective vaccines. To overcome this, we took a new approach, i.e., the development of immunogens based on a comprehensive serologic study. We constructed DNA plasmids encoding codon-optimized hemagglutinin (HA) from 17 representative strains covering all reported clades and subclades of highly pathogenic avian influenza H5N1 viruses. Using DNA plasmids, we generated the corresponding H5N1 pseudotypes and immune sera. We performed an across-the-board pseudotype-based neutralization assay and determined antigenic clusters by cartography. We then designed a triclade DNA vaccine and evaluated its immunogenicity and protection in mice. We report here that (sub)clades 0, 1, 3, 4, 5, 6, 7.1, and 9 were grouped into antigenic cluster 1, (sub)clades 2.1.3.2, 2.3.4, 2.4, 2.5, and 8 were grouped into another antigenic cluster, with subclade 2.2.1 loosely connected to it, and each of subclades 2.3.2.1 and 7.2 was by itself. Importantly, the triclade DNA vaccine encoding HAs of (sub)clades 0, 2.3.2.1, and 7.2 elicited broadly neutralizing antibody responses against all H5 clades and subclades and protected mice against high-lethal-dose heterologous H5N1 challenge. Thus, we conclude that broadly neutralizing antibodies against all H5 clades and subclades can indeed be elicited with immunogens on the basis of a comprehensive serologic study. Further evaluation and optimization of such an approach in ferrets and in humans is warranted.

New strategies for the development of H5N1 subtype influenza vaccines: progress and challenges

The emergence and spread of highly pathogenic avian influenza (H5N1) viruses among poultry in Asia, the Middle East, and Africa have fueled concerns of a possible human pandemic, and spurred efforts towards developing vaccines against H5N1 influenza viruses, as well as improving vaccine production methods. In recent years, promising experimental reverse genetics-derived H5N1 live attenuated vaccines have been generated and characterized, including vaccines that are attenuated through temperature-sensitive mutation, modulation of the interferon antagonist protein, or disruption of the M2 protein. Live attenuated influenza virus vaccines based on each of these modalities have conferred protection against homologous and heterologous challenge in animal models of influenza virus infection. Alternative vaccine strategies that do not require the use of live virus, such as virus-like particle (VLP) and DNA-based vaccines, have also been vigorously pursued in recent years. Studies have demonstrated that influenza VLP vaccination can confer homologous and heterologous protection from lethal challenge in a mouse model of infection. There have also been improvements in the formulation and production of vaccines following concerns over the threat of H5N1 influenza viruses. The use of novel substrates for the growth of vaccine virus stocks has been intensively researched in recent years, and several candidate cell culture-based systems for vaccine amplification have emerged, including production systems based on Madin-Darby canine kidney, Vero, and PerC6 cell lines. Such systems promise increased scalability of product, and reduced reliance on embryonated chicken eggs as a growth substrate. Studies into the use of adjuvants have shown that oil-in-water-based adjuvants can improve the immunogenicity of inactivated influenza vaccines and conserve antigen in such formulations. Finally, efforts to develop more broadly cross-protective immunization strategies through the inclusion of conserved influenza virus antigens in vaccines have led to experimental vaccines based on the influenza hemagglutinin (HA) stem domain. Such vaccines have been shown to confer protection from lethal challenge in mouse models of influenza virus infection. Through further development, vaccines based on the HA stem have the potential to protect vaccinated individuals against unanticipated pandemic and epidemic influenza virus strains. Overall, recent advances in experimental vaccines and in vaccine production processes provide the potential to lower mortality and morbidity resulting from influenza infection.

A computationally optimized hemagglutinin virus-like particle vaccine elicits broadly reactive antibodies that protect nonhuman primates from H5N1 infection

BACKGROUND

Highly pathogenic H5N1 avian influenza viruses continue to spread via waterfowl, causing lethal infections in humans. Vaccines can prevent the morbidity and mortality associated with pandemic influenza isolates. Predicting the specific isolate that may emerge from the 10 different H5N1 clades is a tremendous challenge for vaccine design.

METHODS

In this study, we generated a synthetic hemagglutinin (HA) on the basis of a new method, computationally optimized broadly reactive antigen (COBRA), which uses worldwide sequencing and surveillance efforts that are specifically focused on sequences from H5N1 clade 2 human isolates.

RESULTS

Cynomolgus macaques vaccinated with COBRA clade 2 HA H5N1 virus-like particles (VLPs) had hemagglutination-inhibition antibody titers that recognized a broader number of representative isolates from divergent clades as compared to nonhuman primates vaccinated with clade 2.2 HA VLPs. Furthermore, all vaccinated animals were protected from A/Whooper Swan/Mongolia/244/2005 (WS/05) clade 2.2 challenge, with no virus detected in the nasal or tracheal washes. However, COBRA VLP-vaccinated nonhuman primates had reduced lung inflammation and pathologic effects as compared to those that received WS/05 VLP vaccines.

CONCLUSIONS

The COBRA clade 2 HA H5N1 VLP elicits broad humoral immunity against multiple H5N1 isolates from different clades. In addition, the COBRA VLP vaccine is more effective than a homologous vaccine against a highly pathogenic avian influenza virus challenge.

Both the unique and repeat regions of the Porphyromonas gingivalis hemagglutin A are involved in adhesion and invasion of host cells

Porphyromonas gingivalis is one of the major etiologic agents of adult periodontitis and has been associated with cardiovascular diseases. It expresses multiple hemagglutinins that are significant virulence factors and play an important role in bacterial attachment and invasion of host cells. The objective of this study was to determine the impact of P. gingivalis hemagglutinin A (HagA) on the attachment to and invasion of human coronary artery endothelial cells (HCAEC) and gingival epithelial cells (GEC). Bacterial strains expressing the HagA protein (or subunits), including Escherichia coli carrying plasmid pEKS5, E. coli carrying plasmid ST2, and Salmonella enterica serovar Typhimurium with plasmid pNM1.1 were used in this study. The strains were tested for their ability to attach to and invade HCAEC and GEC using antibiotic protection assays. In addition, the unique 5' N-terminal non-repeated segment of HagA was purified in recombinant form and a monoclonal antibody was created against the polypeptide. The monoclonal antibody against the unique portion of HagA was tested for inhibitory activity in these assays. The attachment of both E. coli strains expressing HagA fragment to host cells was significantly increased compared to their respective controls. However, they did not invade GEC or HCAEC. Interestingly, HagA expression in the Salmonella strain increased both adherence to and invasion of HCAEC, which may be due to the presence of the entire hagA ORF. A monoclonal antibody against the unique 5' N-terminal portion of HagA reduced invasion. Further experiments are needed to determine the role of the unique and the repeat segments of P. gingivalis HagA.

Antibody breadth and protective efficacy are increased by vaccination with computationally optimized hemagglutinin but not with polyvalent hemagglutinin-based H5N1 virus-like particle vaccines

One of the challenges for developing an H5N1 influenza vaccine is the diversity of antigenically distinct isolates within this subtype. Previously, our group described a novel hemagglutinin (HA) derived from a methodology termed computationally optimized broadly reactive antigen (COBRA). This COBRA HA, when used as an immunogen, elicits a broad antibody response against H5N1 isolates from different clades. In this report, the immune responses elicited by the COBRA HA virus-like particle (VLP) vaccine were compared to responses elicited by a mixture of VLPs expressing representative HA molecules from clade 2.1, 2.2, and 2.3 primary H5N1 isolates (polyvalent). The COBRA HA VLP vaccine elicited higher-titer antibodies to a panel of H5N1 HA proteins than did the other VLPs. Both COBRA and polyvalent vaccines protected vaccinated mice and ferrets from experimental infection with highly lethal H5N1 influenza viruses, but COBRA-vaccinated animals had decreased viral replication, less inflammation in the lungs of mice, and reduced virus recovery in ferret nasal washes. Both vaccines had similar cellular responses postchallenge, indicating that higher-titer serum antibodies likely restrict the duration of viral replication. Furthermore, passively transferred immune serum from the COBRA HA VLP-vaccinated mice protected recipient animals more efficiently than immune serum from polyvalent-vaccinated mice. This is the first report comparing these two vaccine strategies. The single COBRA HA antigen elicited a broader antibody response and reduced morbidity and viral titers more effectively than a polyvalent mixture of primary H5N1 HA antigens.

Influenza research database: an integrated bioinformatics resource for influenza research and surveillance

Please cite this paper as: Squires et al. (2012) Influenza research database: an integrated bioinformatics resource for influenza research and surveillance. Influenza and Other Respiratory Viruses 6(6), 404–416.

Background  The recent emergence of the 2009 pandemic influenza A/H1N1 virus has highlighted the value of free and open access to influenza virus genome sequence data integrated with information about other important virus characteristics.

Design  The Influenza Research Database (IRD, http://www.fludb.org) is a free, open, publicly‐accessible resource funded by the U.S. National Institute of Allergy and Infectious Diseases through the Bioinformatics Resource Centers program. IRD provides a comprehensive, integrated database and analysis resource for influenza sequence, surveillance, and research data, including user‐friendly interfaces for data retrieval, visualization and comparative genomics analysis, together with personal log in‐protected ‘workbench’ spaces for saving data sets and analysis results. IRD integrates genomic, proteomic, immune epitope, and surveillance data from a variety of sources, including public databases, computational algorithms, external research groups, and the scientific literature.

Results  To demonstrate the utility of the data and analysis tools available in IRD, two scientific use cases are presented. A comparison of hemagglutinin sequence conservation and epitope coverage information revealed highly conserved protein regions that can be recognized by the human adaptive immune system as possible targets for inducing cross‐protective immunity. Phylogenetic and geospatial analysis of sequences from wild bird surveillance samples revealed a possible evolutionary connection between influenza virus from Delaware Bay shorebirds and Alberta ducks.

Conclusions  The IRD provides a wealth of integrated data and information about influenza virus to support research of the genetic determinants dictating virus pathogenicity, host range restriction and transmission, and to facilitate development of vaccines, diagnostics, and therapeutics.

Protective immunity elicited by a pseudotyped baculovirus-mediated bivalent H5N1 influenza vaccine

The development of novel H5N1 influenza vaccines to elicit a broad immune response is a priority in veterinary and human public health. In this report, a baculovirus vector was used to construct bivalent recombinant baculovirus vaccine encoding H5N1 influenza virus hemagglutinin proteins (BV-HAs) from clade 2.3.4 and clade 9 influenza viruses. Mice immunized with 5×10(7) IFU BV-HAs developed significantly high levels of H5-specific neutralizing antibodies and cellular immunity that conferred 100% protection against infection with H5N1 influenza viruses. This study suggests that baculovirus-delivered multi-hemagglutinin proteins might serve as a candidate vaccine for the prevention of pre-pandemic and pandemic H5N1 influenza viruses.

Display of VP1 on the surface of baculovirus and its immunogenicity against heterologous human enterovirus 71 strains in mice

BACKGROUND

Human Enterovirus 71 (EV71) is a common cause of hand, foot and mouth disease (HFMD) in young children. It is often associated with severe neurological diseases and has caused high mortalities in recent outbreaks across the Asia Pacific region. Currently, there is no effective vaccine and antiviral agents available against EV71 infections. VP1 is one of the major immunogenic capsid protein of EV71 and plays a crucial role in viral infection. Antibodies against VP1 are important for virus neutralization.

METHODOLOGY/PRINCIPAL FINDING

In the present study, infectious EV71 viruses were generated from their synthetic complementary DNA using the human RNA polymerase I reverse genetics system. Secondly, the major immunogenic capsid protein (VP1) of EV71-Fuyang (subgenogroup C4) was displayed on the surface of recombinant baculovirus Bac-Pie1-gp64-VP1 as gp64 fusion protein under a novel White Spot Syndrome Virus (WSSV) immediate early ie1 promoter. Baculovirus expressed VP1 was able to maintain its structural and antigenic conformity as indicated by immunofluorescence assay and western blot analysis. Interestingly, our results with confocal microscopy revealed that VP1 was able to localize on the plasma membrane of insect cells infected with recombinant baculovirus. In addition, we demonstrated with transmission electron microscopy that baculovirus successfully acquired VP1 from the insect cell membrane via the budding process. After two immunizations in mice, Bac-Pie1-gp64-VP1 elicited neutralization antibody titer of 1∶64 against EV71 (subgenogroup C4) in an in vitro neutralization assay. Furthermore, the antisera showed high cross-neutralization activities against all 11 subgenogroup EV71 strains.

CONCLUSION

Our results illustrated that Bac-Pie1-gp64-VP1 retained native epitopes of VP1 and acted as an effective EV71 vaccine candidate which would enable rapid production without any biosafety concerns.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.

A computationally optimized broadly reactive antigen (COBRA) based H5N1 VLP vaccine elicits broadly reactive antibodies in mice and ferrets

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 order to develop a vaccine that elicits broadly reactive antibody responses against emerging H5N1 isolates, we utilized a novel antigen design technique termed computationally optimized broadly reactive antigen (COBRA). The COBRA HA sequence was based upon HA amino acid sequences from clade 2 H5N1 human infections and the expressed protein retained the ability to bind the receptor, as well as mediate particle fusion. Non-infectious recombinant VLP vaccines using the COBRA HA were purified from a mammalian expression system. Mice and ferrets vaccinated with COBRA HA H5N1 VLPs had protective levels of HAI antibodies to a representative isolates from each subclade of clade 2. Furthermore, VLP vaccinated animals were completely protected from a lethal challenge of the clade 2.2 H5N1 virus A/Whooper Swan/Mongolia/244/2005. This is the first report describing the use of COBRA-based antigen design. The COBRA HA H5N1 VLP vaccine elicited broadly reactive antibodies and is an effective influenza vaccine against HPAI virus.