The threat of avian influenza A (H5N1). Part IV: Development of vaccines

A review-plant medicine and its extraction components inhibit influenza virus

Influenza is a highly prevalent and highly contagious lung disease caused by influenza viruses. The main anti-influenza strategies are vaccination and antiviral drugs. Vaccination is an effective means of prevention, but the time lag in research and development makes it difficult to respond immediately to an outbreak. Approved drugs are mainly inhibitors of neuraminidase and M2 ion channels, but, due to the variability of influenza viruses, resistance to these drugs may emerge. Botanicals and their extracts have shown unique advantages in influenza treatment and are widely used in clinics across China. However, there are few reviews on the prevention and treatment of influenza with herbal medicines. We undertook a review of relevant literature in recent years to analyze the research progress of various botanicals and their extracts in the prevention and treatment of influenza. Our review provides theoretical support for the prevention and treatment of influenza by plant-based medicines, as well as new ideas for the development of novel low-toxicity and multi-target drugs.

Inhibitory Activity of Honeysuckle Extracts against Influenza A Virus In Vitro and In Vivo

Honeysuckle has been used in the treatment of influenza virus infection for thousands of years in China. However, its main active components and the functional mechanisms remain to be elucidated. Here, four honeysuckle extracts, including acids extract, flavonoids extract, total extract and acids-flavonoids mixture, were prepared to clarify the main active antiviral components. The cytopathic effect reduction assay showed that all the four extracts inhibited the replication of influenza viruses H1N1, H3N2 and the oseltamivir-resistant mutant strain H1N1-H275Y. The acids-flavonoids mixture had the strongest inhibitory effects in vitro with EC₅₀ values of 3.8, 4.1, and > 20 μg/mL against H1N1, H3N2 and H1N1-H275Y, respectively, showing competitive antiviral activity with oseltamivir and ribavirin. Honeysuckle acids extract also showed the most significant antiviral activity in vivo. Oral administration of the acids extract at a dosage of 600 mg/kg/d effectively alleviated viral pneumonia, maintained body weight and improved the survival rate to 30% of the mice infected with a lethal dose of H1N1. The results of time-of-drug addition experiment and neuraminidase (NA) inhibition assay showed that honeysuckle extracts had a broad-spectrum inhibitory effect against influenza virus NAs. The flavonoid extract showed the strongest inhibitory effect on the NA of influenza virus H7N9 with an IC₅₀ of 24.7 μg/mL. These results suggested that these extracts might exert their antiviral activity by suppressing the release of influenza viruses. Briefly, our findings demonstrate that acids and flavonoids extracts of honeysuckle are the major antiviral active components, and the acids extract has the potential to be developed into an antiviral agent against influenza virus, especially for oseltamivir-resistant viruses.

Non-viral Vector for Muscle-Mediated Gene Therapy

Non-viral gene delivery to skeletal muscle was one of the first applications of gene therapy that went into the clinic, mainly because skeletal muscle is an easily accessible tissue for local gene transfer and non-viral vectors have a relatively safe and low immunogenic track record. However, plasmid DNA, naked or complexed to the various chemistries, turn out to be moderately efficient in humans when injected locally and very inefficient (and very toxic in some cases) when injected systemically. A number of clinical applications have been initiated however, based on transgenes that were adapted to good local impact and/or to a wide physiological outcome (i.e., strong humoral and cellular immune responses following the introduction of DNA vaccines). Neuromuscular diseases seem more challenging for non-viral vectors. Nevertheless, the local production of therapeutic proteins that may act distantly from the injected site and/or the hydrodynamic perfusion of safe plasmids remains a viable basis for the non-viral gene therapy of muscle disorders, cachexia, as well as peripheral neuropathies.

High accumulation in tobacco seeds of hemagglutinin antigen from avian (H5N1) influenza

Tobacco seeds can be used as a cost effective system for production of recombinant vaccines. Avian influenza is an important respiratory pathogen that causes a high degree of mortality and becomes a serious threat for the poultry industry. A safe vaccine against avian flu produced at low cost could help to prevent future outbreaks. We have genetically engineered tobacco plants to express extracellular domain of hemagglutinin protein from H5N1 avian influenza virus as an inexpensive alternative for production purposes. Two regulatory sequences of seed storage protein genes from Phaseolus vulgaris L. were used to direct the expression, yielding 3.0 mg of the viral antigen per g of seeds. The production and stability of seed-produced recombinant HA protein was characterized by different molecular techniques. The aqueous extract of tobacco seed proteins was used for subcutaneous immunization of chickens, which developed antibodies that inhibited the agglutination of erythrocytes after the second application of the antigen. The feasibility of using tobacco seeds as a vaccine carrier is discussed.

14-Deoxy-11,12-dehydroandrographolide exerts anti-influenza A virus activity and inhibits replication of H5N1 virus by restraining nuclear export of viral ribonucleoprotein complexes

The highly pathogenic avian influenza H5N1 virus has become a worldwide public health threat, and current antiviral therapies have limited activity against the emerging, resistant influenza viruses. Therefore, effective drugs with novel targets against influenza A viruses, H5N1 strains in particular, should be developed. In the present study, 14-deoxy-11,12-dehydroandrographolide (DAP), a major component of the traditional Chinese medicine Andrographis paniculata, exerted potent anti-influenza A virus activity against A/chicken/Hubei/327/2004 (H5N1), A/duck/Hubei/XN/2007 (H5N1), A/PR/8/34 (H1N1), A/NanChang/08/2010 (H1N1) and A/HuNan/01/2014 (H3N2) in vitro. To elucidate the underlying mechanisms, a series of experiments was conducted using A/chicken/Hubei/327/2004 (H5N1) as an example. Our results demonstrated that DAP strongly inhibited H5N1 replication by reducing the production of viral nucleoprotein (NP) mRNA, NP and NS1proteins, whereas DAP had no effect on the absorption and release of H5N1 towards/from A549 cells. DAP also effectively restrained the nuclear export of viral ribonucleoprotein (vRNP) complexes. This inhibitory effect ought to be an important anti-H5N1 mechanism of DAP. Meanwhile, DAP significantly reduced the upregulated expression of all the tested proinflammatory cytokines (TNF-α, IL-6, IL-8, IFN-α, IL-1β and IFN-β) and chemokines (CXCL-10 and CCL-2) stimulated by H5N1. Overall results suggest that DAP impairs H5N1 replication at least in part by restraining nuclear export of vRNP complexes, and the inhibition of viral replication leads to a subsequent decrease of the intense proinflammatory cytokine/chemokine expression. In turn, the effect of modification of the host excessive immune response may contribute to overcoming H5N1. To our knowledge, this study is the first to reveal the antiviral and anti-inflammatory activities of DAP in vitro against H5N1 influenza A virus infection.

Vaccination against infectious diseases: what is promising?

Vaccination has proven to be one of the best weapons protecting the mankind against infectious diseases. Along with the huge progress in microbiology, numerous highly efficacious and safe vaccines have been produced by conventional technology (cultivation), by the use of molecular biology (genetic modification), or by synthetic chemistry. Sterilising prevention is achieved by the stimulation of antibody production, while the stimulation of cell-mediated immune responses may prevent the outbreak of disease in consequence of an acute or reactivated infection. From several examples, two rules are deduced to evaluate the perspectives of future vaccine developments: They are promising, if (1) the natural infectious disease induces immunity or (2) passive immunisation (transfer of antibodies, adoptive transfer of lymphocytes) is successful in preventing infection.

N-acetyl-l-cystine (NAC) protects against H9N2 swine influenza virus-induced acute lung injury

The antioxidant N-acetyl-l-cysteine (NAC) had been shown to inhibit replication of seasonal human influenza A viruses. Here, the effects of NAC on H9N2 swine influenza virus-induced acute lung injury (ALI) were investigated in mice. BALB/c mice were inoculated intranasally with 10⁷ 50% tissue culture infective doses (TCID₅₀) of A/swine/HeBei/012/2008/(H9N2) viruses with or without NAC treatments to induce ALI model. The result showed that pulmonary inflammation, pulmonary edema, MPO activity, total cells, neutrophils, macrophages, TNF-α, IL-6, IL-1β and CXCL-10 in BALF were attenuated by NAC. Moreover, our data showed that NAC significantly inhibited the levels of TLR4 protein and TLR4 mRNA in the lungs. Pharmacological inhibitors of TLR4 (E5564) exerted similar effects like those determined for NAC in H9N2 swine influenza virus-infected mice. These results suggest that antioxidants like NAC represent a potential additional treatment option that could be considered in the case of an influenza A virus pandemic.

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NAC protects against H9N2 swine influenza virus-induced acute lung injury (ALI).

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NAC protects against acute lung injury by inactivation of TLR4.

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Eritoran (E5564), a TLR4 antagonist, also protects against acute lung injury.

Prevalence of antibodies against influenza A and B viruses in children in Germany, 2008 to 2010

The prevalence of influenza A and B virus-specific IgG was determined in sera taken between 2008 and 2010 from 1,665 children aged 0-17 years and 400 blood donors in Germany. ELISA on the basis of whole virus antigens was applied. Nearly all children aged nine years and older had antibodies against influenza A. In contrast, 40% of children aged 0-4 years did not have any influenza A virus-specific IgG antibodies. Eightysix percent of 0-6 year-olds, 47% of 7-12 year-olds and 20% of 13-17 year-olds were serologically naïve to influenza B viruses. By the age of 18 years, influenza B seroprevalence reached approximately 90%. There were obvious regional differences in the seroprevalence of influenza B in Germany. In conclusion, seroprevalences of influenza A and influenza B increase gradually during childhood. The majority of children older than eight years have basal immunity to influenza A, while comparable immunity against influenza B is only acquired at the age of 18 years. Children aged 0-6 years, showing an overall seroprevalence of 67% for influenza A and of 14% for influenza B, are especially at risk for primary infections during influenza B seasons.

Differential antiviral and anti-inflammatory mechanisms of the flavonoids biochanin A and baicalein in H5N1 influenza A virus-infected cells

From a panel of 22 flavonoids, we identified six compounds (apigenin, baicalein, biochanin A, kaempferol, luteolin, naringenin) that inhibited influenza A nucleoprotein production in human lung epithelial (A549) cells infected with the highly pathogenic avian influenza H5N1 virus strain A/Thailand/Kan-1/04 in non-toxic concentrations. Baicalein (IC(50): 18.79±1.17μM, selectivity index 5.82) and biochanin A (IC(50) 8.92±1.87μM, selectivity index 5.60) were selected for further experiments. Both compounds reduced H5N1 infectious titres (baicalein 40μM: 29-fold reduction, biochanin A 40μM: 55-fold reduction after infection at MOI 0.01), virus-induced caspase 3 cleavage, nuclear export of viral RNP complexes, and enhanced the effects of the neuraminidase inhibitor zanamivir. Biochanin A and baicalein also inhibited the replication of the H5N1 strain A/Vietnam/1203/04. Time of addition experiments indicated that both compounds interfere with H5N1 replication after the adsorption period. Further mechanistic investigations revealed clear differences between these two flavonoids. Only baicalein interfered with the viral neuraminidase activity (39±7% inhibition at 100μM, the maximum concentration tested). In contrast to baicalein, biochanin A affected cellular signalling pathways resulting in reduced virus-induced activation of AKT, ERK 1/2, and NF-kB. Moreover, biochanin A inhibited the virus-induced production of IL-6, IL-8, and IP-10 while baicalein inhibited IL-6 and IL-8 production without affecting IP-10 levels. In primary human monocyte-derived macrophages, only baicalein but not biochanin A impaired H5N1 virus replication. Both flavonoids interfered with the H5N1-induced production of IL-6, IP-10, and TNF-α but not of IL-8 in macrophages. These findings indicate that closely related flavonoids can exert anti-H5N1 effects by different molecular mechanisms.

Recent publications in medical microbiology and immunology: a retrospective

A look back is done to some clinical and basic research activities recently published in medical microbiology and immunology. The review covers clinical experiences and in vitro experiments to understand the emergency, pathogenicity, epidemic spread, and vaccine-based prevention of avian and swine-origin flu. Some new developments and concepts in diagnosis, (molecular) epidemiology, and therapy of AIDS, viral hepatitis C, and herpesvirus-associated diseases are outlined. Regulation of immune system has been discussed in a special issue 2010 including some aspects of CNS affections (measles). Mycobacterial infection and its prevention by modern recombinant vaccines have reached new interest, as well as new concepts of vaccination and prophylaxis against several other bacteria. Adaptation to host niches enables immune escape (example brucella) and determines virulence (example N. meningitidis). Chlamydia pneumoniae, previously considered to trigger atherosclerosis, is hypothetically associated to Alzheimer disease, while CMV, another putative trigger of atherosclerosis, gains evidence of oncomodulation in CNS tumor diseases. In terms of globalization, exotic virus infections are increasingly imported from southern countries.

DNA aptamers against the receptor binding region of hemagglutinin prevent avian influenza viral infection

The entrance of influenza virus into host cells is facilitated by the attachment of the globular region of viral hemagglutinin to the sialic acid receptors on host cell surfaces. In this study, we have cloned the cDNA fragment encoding the entire globular region (residues 101-257) of hemagglutinin of the H9N2 type avian influenza virus (A/ck/Korea/ms96/96). The protein segment (denoted as the H9 peptide), which was expressed and purified in E. coli, was used for the immunization of BALB/c mice to obtain the anti-H9 antiserum. To identify specific DNA aptamers with high affinity to H9 peptide, we conducted the SELEX method; 19 aptamers were newly isolated. A random mixture of these aptamers showed an increased level of binding affinity to the H9 peptide. The sequence alignment analysis of these aptamers revealed that 6 aptamers have highly conserved consensus sequences. Among these, aptamer C7 showed the highest similarity to the consensus sequences. Therefore, based on the C7 aptamer, we synthesized a new modified aptamer designated as C7-35M. This new aptamer showed strong binding capability to the viral particles. Furthermore, it could prevent MDCK cells from viral infection by strong binding to the viral particles. These results suggest that our aptamers can recognize the hemagglutinin protein of avian influenza virus and inhibit the binding of the virus to target receptors required for the penetration of host cells.

Glycyrrhizin exerts antioxidative effects in H5N1 influenza A virus-infected cells and inhibits virus replication and pro-inflammatory gene expression

Glycyrrhizin is known to exert antiviral and anti-inflammatory effects. Here, the effects of an approved parenteral glycyrrhizin preparation (Stronger Neo-Minophafen C) were investigated on highly pathogenic influenza A H5N1 virus replication, H5N1-induced apoptosis, and H5N1-induced pro-inflammatory responses in lung epithelial (A549) cells. Therapeutic glycyrrhizin concentrations substantially inhibited H5N1-induced expression of the pro-inflammatory molecules CXCL10, interleukin 6, CCL2, and CCL5 (effective glycyrrhizin concentrations 25 to 50 µg/ml) but interfered with H5N1 replication and H5N1-induced apoptosis to a lesser extent (effective glycyrrhizin concentrations 100 µg/ml or higher). Glycyrrhizin also diminished monocyte migration towards supernatants of H5N1-infected A549 cells. The mechanism by which glycyrrhizin interferes with H5N1 replication and H5N1-induced pro-inflammatory gene expression includes inhibition of H5N1-induced formation of reactive oxygen species and (in turn) reduced activation of NFκB, JNK, and p38, redox-sensitive signalling events known to be relevant for influenza A virus replication. Therefore, glycyrrhizin may complement the arsenal of potential drugs for the treatment of H5N1 disease.

Comparison of adjuvant efficacy of chitosan and aluminum hydroxide for intraperitoneally administered inactivated influenza H5N1 vaccine

A safe and effective adjuvant is important to develop vaccines against highly pathogenic avian influenza virus. Chitosan, a derivative from the natural amino polysaccharide chitin, has been proved to be an effective adjuvant for inactivated influenza virus vaccine. In this study, protective immunity in mice provided by chitosan-adjuvanted inactivated H5N1 vaccine was compared with that from an aluminum hydroxide-adjuvanted one. Mice were injected intraperitoneally once or twice with various dosages of inactivated vaccine alone or in combination with an adjuvant (chitosan or aluminum hydroxide). To test the immunization effect, mice were challenged with a lethal dose of H5N1 virus. The results showed that the adjuvanted vaccines were more effective than adjuvant-free ones in inducing humoral immune responses and protecting mice against lethal challenge. Chitosan was comparable to the alum adjuvant in efficacy. These findings indicated that chitosan might be a candidate adjuvant for parenteral administration of inactivated influenza vaccines.

Comparative immunogenicity of recombinant adenovirus-vectored vaccines expressing different forms of hemagglutinin (HA) proteins from the H5 serotype of influenza A viruses in mice

Recent outbreaks of highly pathogenic avian influenza (HPAI) H5N1 viruses in poultry and their subsequent transmission to humans have highlighted an urgent need to develop preventive vaccines in the event of a pandemic. In this paper we constructed recombinant adenovirus (rAd)-vectored influenza vaccines expressing different forms of H5 hemagglutinin (HA) from the A/Vietnam/1194/04 (VN/1194/04) virus, a wild-type HA, a sequence codon-optimized HA and a transmembrane (TM) domain-truncated HA. Compared to the rAd vectors expressing the wild-type HA (rAd-04wtHA) and the TM-truncated form of HA (rAd-04optHA-dTM), the rAd vectored vaccine with the sequence codon-optimized HA (rAd-04optHA) showed a tendency to induce much higher hemagglutinin inhibition (HI) antibody titers in mice immunized with a prime-boost vaccine. Furthermore, administration of the rAd-04optHA vaccine to mice could elicit cross-reactive immune responses against the antigenically distinct HK/482/97 virus. Additionally, we constructed another vector containing the codon-optimized HA of the A/Hong Kong/482/97 (HK/482/97) virus. Administration of a bivalent immunization formulation including the rAd-04optHA and rAd-97optHA vaccines to mice induced a stronger immune response against HK/482/97 virus than the monovalent formulation. Taken together, these findings may have some implications for the development of rAd-vectored vaccines in the event of the pandemic spread of HPAI.

Glycyrrhizin inhibits highly pathogenic H5N1 influenza A virus-induced pro-inflammatory cytokine and chemokine expression in human macrophages

Hypercytokinaemia is thought to contribute to highly pathogenic H5N1 influenza A virus disease. Glycyrrhizin is known to exert immunomodulatory and anti-inflammatory effects and therefore a candidate drug for the control of H5N1-induced pro-inflammatory gene expression. Here, the effects of an approved parenteral glycyrrhizin preparation were investigated on H5N1 virus replication, H5N1-induced pro-inflammatory responses, and H5N1-induced apoptosis in human monocyte-derived macrophages. Glycyrrhizin 100 μg/ml, a therapeutically achievable concentration, impaired H5N1-induced production of CXCL10, interleukin 6, and CCL5 and inhibited H5N1-induced apoptosis but did not interfere with H5N1 replication. Global inhibition of immune responses may result in the loss of control of virus replication by cytotoxic immune cells including natural killer cells and cytotoxic CD8(+) T-lymphocytes. Notably, glycyrrhizin concentrations that inhibited H5N1-induced pro-inflammatory gene expression did not affect cytolytic activity of natural killer cells. Since H5N1-induced hypercytokinaemia is considered to play an important role within H5N1 pathogenesis, glycyrrhizin may complement the arsenal of potential drugs for the treatment of H5N1 disease.

Two novel HLA-A*0201 T-cell epitopes in avian H5N1 viral nucleoprotein induced specific immune responses in HHD mice

The influenza A nucleoprotein (NP) is an attractive target for avian flu vaccine development because of its high conversancy in the evolutionary chain of the virus. Here we identified two novel HLA-A*0201 restricted NP epitopes, named H5N1 NP373-381 AMDSNTLEL (NP373) and NP458-466 FQGRGVFEL (NP458), using computational bioinformatic analysis. The NP peptides showed a high binding affinity to HLA-A*0201 on T2 cells, and were able to induce the activation of the cytotoxic T cells in the human peripheral blood mononuclear cells. We examined the potential of using NP373 and NP458 peptide sequences supplemented with a single-chain trimer as potential DNA vaccine candidates in an HHD transgenic mouse model. A gene gun delivery system was used for administrating the vaccine candidates into the animals. The results from cytotoxicity and ELISPOT assays indicated that a significant amount of IFN-γ was secreted by the T cells of the vaccinated mice, and the T cells were able to eliminate the corresponding peptide-loaded T2 cells. The discovery of these novel immunogenic NP peptides provides valuable information for avian flu vaccine design and construction.

An influenza A H1N1 virus revival - pandemic H1N1/09 virus

In April 2009, a novel H1N1 influenza A virus, the so-called pandemic H1N1/09 virus (former designations include swine influenza, novel influenza, swine-origin influenza A [H1N1] virus [S-OIV], Mexican flu, North American Flu) was identified in Mexico. The virus has since spread throughout the world and caused an influenza pandemic as defined by the criteria of the World Health Organization. This represents the first influenza A virus pandemic since the emergence of H3N2 (''Hong Kong'' Flu) in 1968. Vaccine production has started, and vaccines are expected to become available during the course of 2009. Although the pandemic H1N1/09 virus originates from the triple-reassortant swine influenza (H1) virus circulating in North American pigs, it is not epidemic in pigs. Although the H1N1/09 virus pandemic is currently mild, concerns remain that it may become more aggressive during spreading. The distribution of proper information to the public on the status of the H1N1/09 virus pandemic will be important to achieve a broad awareness of the potential risks and the optimum code of behavior during the pandemic. Here, the features of pandemic H1N1/09 virus are discussed within the framework of knowledge gained from previous influenza A virus pandemics.

N-acetyl-L-cysteine (NAC) inhibits virus replication and expression of pro-inflammatory molecules in A549 cells infected with highly pathogenic H5N1 influenza A virus

The antioxidant N-acetyl-L-cysteine (NAC) had been shown to inhibit replication of seasonal human influenza A viruses. Here, the effects of NAC on virus replication, virus-induced pro-inflammatory responses and virus-induced apoptosis were investigated in H5N1-infected lung epithelial (A549) cells. NAC at concentrations ranging from 5 to 15 mM reduced H5N1-induced cytopathogenic effects (CPEs), virus-induced apoptosis and infectious viral yields 24 h post-infection. NAC also decreased the production of pro-inflammatory molecules (CXCL8, CXCL10, CCL5 and interleukin-6 (IL-6)) in H5N1-infected A549 cells and reduced monocyte migration towards supernatants of H5N1-infected A549 cells. The antiviral and anti-inflammatory mechanisms of NAC included inhibition of activation of oxidant sensitive pathways including transcription factor NF-kappaB and mitogen activated protein kinase p38. Pharmacological inhibitors of NF-kappaB (BAY 11-7085) or p38 (SB203580) exerted similar effects like those determined for NAC in H5N1-infected cells. The combination of BAY 11-7085 and SB203580 resulted in increased inhibitory effects on virus replication and production of pro-inflammatory molecules relative to either single treatment. NAC inhibits H5N1 replication and H5N1-induced production of pro-inflammatory molecules. Therefore, antioxidants like NAC represent a potential additional treatment option that could be considered in the case of an influenza A virus pandemic.

Novel swine-origin influenza A virus in humans: another pandemic knocking at the door

Influenza A viruses represent a continuous pandemic threat. In April 2009, a novel influenza A virus, the so-called swine-origin influenza A (H1N1) virus (S-OIV), was identified in Mexico. Although S-OIV originates from triple-reassortant swine influenza A (H1) that has been circulating in North American pig herds since the end of the 1990s, S-OIV is readily transmitted between humans but is not epidemic in pigs. After its discovery, S-OIV rapidly spread throughout the world within few weeks. In this review, we sum up the current situation and put it into the context of the current state of knowledge of influenza and influenza pandemics. Some indications suggest that a pandemic may be mild but even "mild" pandemics can result in millions of deaths. However, no reasonable forecasts how this pandemic may develop can be made at this time. Despite stockpiling by many countries and WHO, antiviral drugs will be limited in case of pandemic and resistances may emerge. Effective vaccines are regarded to be crucial for the control of influenza pandemics. However, production capacities are restricted and development/production of a S-OIV vaccine will interfere with manufacturing of seasonal influenza vaccines. The authors are convinced that S-OIV should be taken seriously as pandemic threat and underestimation of the menace by S-OIV to be by far more dangerous than its overestimation.

Prevalence of influenza A and B antibodies in pregnant women and their offspring

BACKGROUND

Influenza is associated with substantial morbidity and mortality in pregnant women and neonates, but few countries offer annual influenza vaccination with the inactivated vaccine to all women who are, or intend to become, pregnant.

OBJECTIVES

To provide seroepidemiological information on influenza A and B antibodies in pregnant women and their offspring in Germany.

STUDY DESIGN

Anti-influenza antibodies were determined using commercially available enzyme-linked immunosorbent assays (ELISA) on serum obtained from 209 women and their newborns at delivery.

RESULTS

The prevalence of antibodies against influenza A virus was 93.8% [89.6-96.6%] in the mothers and 96.7% [93.2-98.6%] in the newborns. The prevalence of antibodies against influenza B virus was 42.1% [35.3-49.1%] in the mothers and 78.5% [72.3-83.8%] in their newborns, which was a significant difference. The antibody concentrations against both influenza A and influenza B viruses were significantly lower in mother than in their newborns.

CONCLUSIONS

Because of active placental transport of IgG antibodies, neonates have higher prevalence and/or concentrations of influenza A and B virus-specific antibodies induced by natural infections than their mothers. Considering these serological findings, especially the lower prevalence of maternal antibody against influenza B virus, annual influenza vaccination may improve the protection of pregnant women and their offspring against influenza.

Baculovirus vector as a delivery vehicle for influenza vaccines

The baculovirus vector has emerged as an efficient delivery vehicle for influenza vaccines. In addition to the ease and safety in expeditious production, recent improvements in baculovirus engineering to display foreign proteins on the surface and to express transgenes with suitable promoters in various cell lines have become milestones in the development of the baculovirus expression system. Surface-displayed and shuttle promoter-mediated baculovirus vaccines for influenza present advantages in immunogenicity and safety, as studied in several animal models. A variety of strategies, including the modification of envelope proteins for surface display, the selection of novel promoters for in vivo transductions and advancements in downstream processing, aid the improvement of baculovirus-based influenza vaccines and represent progress toward next-generation vaccines for influenza.

A gene-based avian influenza vaccine in poultry

Highly pathogenic avian influenza A (HPAI) viruses, specifically H5N1 strains, cause widespread morbidity and mortality in domestic and wild bird populations, and recent outbreaks have resulted in severe economic losses. Although still largely confined to birds, more than 300 human cases resulting in deaths have been reported to the World Health Organization. These sporadic human cases result from direct transmission from infected birds; however, a sustained outbreak of HPAI H5N1 increases the potential for the emergence of a human pandemic strain. One approach to the containment of HPAI H5N1 is the development of vaccines for use in poultry. Currently, the majority of avian influenza vaccines for poultry are traditional whole-virus vaccines produced in eggs. Although highly efficacious, these vaccines are hindered by long production times, inflexibility in quickly altering antigenic composition, and limited breadth of protection. Newer vaccines with more efficient manufacturing processes, enhanced efficacy, and cross-protection against multiple strains would improve preparedness. Reverse genetics technology has provided one such method, and emerging gene-based vaccines offer another approach that reduces dependence on egg-based production and human exposure to pathogenic viruses. Gene-based vaccines also provide rapid manufacturing, enhanced precision and versatility, and the capacity to protect against a broad range of viral subtypes. Vectors for these vaccines include replication-defective viruses, bacterial vectors, and DNA. Here we review the features of gene-based vaccination that may facilitate the control of HPAI H5N1 in poultry, and highlight the development of a hemagglutinin-based multivalent DNA vaccine that confers protection in mice and chickens.

Development of a vaccine against pandemic influenza viruses: current status and perspectives

The constant threat of a new influenza pandemic, which may be caused by a highly pathogenic avian influenza virus, necessitates the development of a vaccine capable of providing efficient, long-term, and cost-effective protection. Proven avenues for the development of vaccines against seasonal influenza as well as novel approaches have been explored over the past decade. Whereas significant insights are consistently being made, the generation of a highly efficient and cross-protective vaccine against the future pandemic influenza strain remains as the ultimate goal in the field. In this review, we re-examine these efforts and outline the scientific, political, and economic problems that befall this area of biotechnological research.

Structural and functional bases for broad-spectrum neutralization of avian and human influenza A viruses

Influenza virus remains a serious health threat, owing to its ability to evade immune surveillance through rapid genetic drift and reassortment. Here we used a human non-immune antibody phage-display library and the H5 hemagglutinin ectodomain to select ten neutralizing antibodies (nAbs) that were effective against all group 1 influenza viruses tested, including H5N1 'bird flu' and the H1N1 'Spanish flu'. The crystal structure of one such nAb bound to H5 shows that it blocks infection by inserting its heavy chain into a conserved pocket in the stem region, thus preventing membrane fusion. Nine of the nAbs employ the germline gene VH1-69, and all seem to use the same neutralizing mechanism. Our data further suggest that this region is recalcitrant to neutralization escape and that nAb-based immunotherapy is a promising strategy for broad-spectrum protection against seasonal and pandemic influenza viruses.

DNA vaccines against influenza viruses

As an attractive alternative to conventional vaccines, DNA vaccines play a critical role in inducing protection against several infectious diseases. In this review, we discuss the advantages that DNA vaccines offer in comparison to conventional protein-based vaccines. We discuss strategies to improve the potency and efficacy of DNA vaccines. Specifically, we focus on the potential use of DNA-based vaccines to elicit broad-spectrum humoral and cellular immunity against influenza virus. Finally, we discuss the advances made in the use of DNA vaccines to prevent avian H5N1 influenza.

Anti-influenza drugs: the development of sialidase inhibitors

Viruses, particularly those that are harmful to humans, are the 'silent terrorists' of the twenty-first century. Well over four million humans die per annum as a result of viral infections alone. The scourge of influenza virus has plagued mankind throughout the ages. The fact that new viral strains emerge on a regular basis, particularly out of Asia, establishes a continual socio-economic threat to mankind. The arrival of the highly pathogenic avian influenza H5N1 heightened the threat of a potential human pandemic to the point where many countries have put in place 'preparedness plans' to defend against such an outcome. The discovery of the first designer influenza virus sialidase inhibitor and anti-influenza drug Relenza, and subsequently Tamiflu, has now inspired a number of continuing efforts towards the discovery of next generation anti-influenza drugs. Such drugs may act as 'first-line-of-defence' against the spread of influenza infection and buy time for necessary vaccine development particularly in a human pandemic setting. Furthermore, the fact that influenza virus can develop resistance to therapeutics makes these continuing efforts extremely important. An overview of the role of the virus-associated glycoprotein sialidase (neuraminidase) and some of the most recent developments towards the discovery of anti-influenza drugs based on the inhibition of influenza virus sialidase is provided in this chapter.

Incorporation of membrane-anchored flagellin into influenza virus-like particles enhances the breadth of immune responses

We have designed a membrane-anchored form of the Toll-like receptor 5 ligand flagellin, the major proinflammatory determinant of enteropathogenic Salmonella, which was found to be glycosylated and expressed on cell surfaces. A chimeric influenza virus-like particle (cVLP) vaccine candidate containing A/PR8/34 (H(1)N(1)) hemagglutinin (HA), matrix protein (M1), and the modified flagellin as a molecular adjuvant was produced. The immunogenicity, including the serum antibody levels and cellular immune responses, and the protective efficacy against homologous and heterologous live virus challenge of the resulting VLPs were tested after intramuscular administration in a mouse model. The results demonstrated that flagellin-containing VLPs elicited higher specific immunoglobulin G (IgG) responses than standard HA and M1 VLPs, indicating the adjuvant effect of flagellin. Enhanced IgG2a and IgG2b but not IgG1 responses were observed with flagellin-containing VLPs, illuminating the activation of Th1 class immunity. The adjuvant effects of flagellin were also reflected by enhanced specific cellular responses revealed by the secretion of cytokines by freshly isolated splenocyte cultures when stimulated with pools of major histocompatibility complex class I or II peptides. When immunized mice were challenged with homologous live PR8 virus, complete protection was observed for both the standard and cVLP groups. However, when a heterosubtypic A/Philippines (H(3)N(2)) virus was used for challenge, all of the standard VLP group lost at least 25% of body weight, reaching the experimental endpoint. In contrast, for the cVLP group, 67% of mice survived the challenge infection. These results reveal that cVLPs designed by incorporating flagellin as a membrane-anchored adjuvant induce enhanced cross-protective heterosubtypic immune responses. They also indicate that such cVLP vaccines are a promising new approach for protection against pandemic influenza viruses.

New pre-pandemic influenza vaccines: an egg- and adjuvant-independent human adenoviral vector strategy induces long-lasting protective immune responses in mice

Highly pathogenic avian H5N1 influenza viruses that are currently circulating in southeast Asia may acquire the potential to cause the next influenza pandemic. A number of alternate approaches are being pursued to generate cross-protective, dose-sparing, safe, and effective vaccines, as traditional vaccine approaches, i.e., embryonated egg-grown, are not immunogenic. We developed a replication-incompetent adenoviral vector-based, adjuvant- and egg-independent pandemic influenza vaccine strategy as a potential alternative to conventional egg-derived vaccines. In this paper, we address suboptimal dose and longevity of vaccine-induced protective immunity and demonstrate that a vaccine dose as little as 1 x 10(6) plaque-forming unit (PFU) is sufficient to induce protective immune responses against a highly pathogenic H5N1 virus. Furthermore, the vaccine-induced humoral and cellular immune responses and protective immunity persisted at least for a year.