Pandemic Influenza Vaccine Development Research Articles

Composition and mode of action of adjuvants in licensed viral vaccines

The immunogenicity and efficacy of vaccines is largely governed by nature and the amount of antigen(s) included. Specific immune-stimulating substances, so-called adjuvants, are added to vaccine formulations to enhance and modulate the induced immune response.Adjuvants are very different in their physicochemical nature and are primarily characterized by their immune-enhancing effects. In this report, adjuvants that are components of vaccines licensed in the EU will be presented and their mode of action will be discussed.Aluminum salts have been used for almost acentury as vaccine adjuvants. In recent years numerous novel immune-stimulating substances have been developed and integrated into licensed human vaccines. These novel adjuvants are not only intended to generally increase the vaccine-induced antibody titers, but are also aimed at modulating and triggering aspecific immune response. The search for innovative adjuvants was considerably stimulated during development of pandemic influenza vaccines. By using squalene-containing oil-in-water adjuvants (namely AS03 and MF59), pandemic influenza vaccines were developed that were efficacious despite asignificant reduction of the antigen content.The development of novel adjuvants is ahighly dynamic and essential area in modern vaccine design. Some years ago, vaccines for prevention of HPV-induced cervix carcinoma and hepatitisB were licensed that contained the toll-like receptor4 agonist 3‑O-desacyl-monophosphoryl lipidA (MPL), adetoxified LPS version, as the adjuvant. Quite recently, aherpes zoster vaccine was licensed in Europe with acombination of MPL and the saponin QS21 as adjuvant. This combination of immune enhancers is also used in the formulations of the same manufacturer's malaria and hepatitisB vaccine.

Multi-subtype influenza virus-like particles incorporated with flagellin and granulocyte-macrophage colony-stimulating factor for vaccine design

Virus-like particle (VLP) technology is an attractive platform for seasonal and pandemic influenza vaccine development. We previously showed that influenza VLPs can be modified using M2 fusion with molecular adjuvants such as Salmonella typhimurium flagellin (FliC) to enhance VLP immunogenicity. For this study, three types of chimeric VLPs were incorporated with FliC, granulocyte-macrophage colony-stimulating factor (GM-CSF), or both GM-CSF and FliC (GM-CSF/FliC) to enhance anti-influenza immunogenicity. Our results indicate that immunizations with the chimeric FliC VLPs and GM-CSF/FliC H5N1 VLPs elicited more potent and broadly neutralizing antibodies and neuraminidase-inhibiting antibodies in sera, and induced higher numbers of hemagglutinin-specific antibody-secreting cells and germinal center B cell subsets in splenoctyes. Immunization with the chimeric GM-CSF H5N1 VLPs induced stronger Th1 and Th2 cellular responses. The chimeric GM-CSF/FliC H5N1 VLP constructs were further obtained to include H7 or H1H7 bi- or tri-subtype. It is our hope that these findings provide useful information for developing multi-subtype influenza vaccines.

Development of high-yield influenza A virus vaccine viruses

Vaccination is one of the most cost-effective ways to prevent infection. Influenza vaccines propagated in cultured cells are approved for use in humans, but their yields are often suboptimal. Here, we screened A/Puerto Rico/8/34 (PR8) virus mutant libraries to develop vaccine backbones (defined here as the six viral RNA segments not encoding haemagglutinin and neuraminidase) that support high yield in cell culture. We also tested mutations in the coding and regulatory regions of the virus, and chimeric haemagglutinin and neuraminidase genes. A combination of high-yield mutations from these screens led to a PR8 backbone that improved the titres of H1N1, H3N2, H5N1 and H7N9 vaccine viruses in African green monkey kidney and Madin–Darby canine kidney cells. This PR8 backbone also improves titres in embryonated chicken eggs, a common propagation system for influenza viruses. This PR8 vaccine backbone thus represents an advance in seasonal and pandemic influenza vaccine development.

Refining the approach to vaccines against influenza A viruses with pandemic potential.

Vaccination is the most effective strategy for prevention and control of influenza. Timely production and deployment of seasonal influenza vaccines is based on an understanding of the epidemiology of influenza and on global disease and virologic surveillance. Experience with seasonal influenza vaccines guided the initial development of pandemic influenza vaccines. A large investment in pandemic influenza vaccines in the last decade has resulted in much progress and a body of information that can now be applied to refine the established paradigm. Critical and complementary considerations for pandemic influenza vaccines include improved assessment of the pandemic potential of animal influenza viruses, proactive development and deployment of pandemic influenza vaccines, and application of novel platforms and strategies for vaccine production and administration.

GLA-AF, an Emulsion-Free Vaccine Adjuvant for Pandemic Influenza

The ongoing threat from Influenza necessitates the development of new vaccine and adjuvant technologies that can maximize vaccine immunogenicity, shorten production cycles, and increase global vaccine supply. Currently, the most successful adjuvants for Influenza vaccines are squalene-based oil-in-water emulsions. These adjuvants enhance seroprotective antibody titers to homologous and heterologous strains of virus, and augment a significant dose sparing activity that could improve vaccine manufacturing capacity. As an alternative to an emulsion, we tested a simple lipid-based aqueous formulation containing a synthetic TLR4 ligand (GLA-AF) for its ability to enhance protection against H5N1 infection. GLA-AF was very effective in adjuvanting recombinant H5 hemagglutinin antigen (rH5) in mice and was as potent as the stable emulsion, SE. Both adjuvants induced similar antibody titers using a sub-microgram dose of rH5, and both conferred complete protection against a highly pathogenic H5N1 challenge. However, GLA-AF was the superior adjuvant in ferrets. GLA-AF stimulated a broader antibody response than SE after both the prime and boost immunization with rH5, and ferrets were better protected against homologous and heterologous strains of H5N1 virus. Thus, GLA-AF is a potent emulsion-free adjuvant that warrants consideration for pandemic influenza vaccine development.

Intranasal c-di-GMP-adjuvanted plant-derived H5 influenza vaccine induces multifunctional Th1 CD4+ cells and strong mucosal and systemic antibody responses in mice

Vaccination is the best available measure of limiting the impact of the next influenza pandemic. Ideally, a candidate pandemic influenza vaccine should be easy to administer and should elicit strong mucosal and systemic immune responses. Production of influenza subunit antigen in transient plant expression systems is an alternative to overcome the bottleneck in vaccine supply during influenza pandemic. Furthermore, a needle-free intranasal influenza vaccine is an attractive approach, which may provide immunity at the portal of virus entry.The present study investigated the detailed humoral and cellular immune responses in mice vaccinated intranasally or intramuscularly with plant-derived influenza H5N1 (A/Anhui/1/05) antigen alone or formulated with bis-(3′,5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) as adjuvant. The use of c-di-GMP as intramuscular adjuvant did not enhance the immune response to plant-derived influenza H5 antigen. However, intranasal c-di-GMP-adjuvanted vaccine induced strong mucosal and systemic humoral immune responses. Additionally, the intranasal vaccine elicited a balanced Th1/Th2 profile and, most importantly, high frequencies of multifunctional Th1 CD4+ cells. Our results highlight that c-di-GMP is a promising mucosal adjuvant for pandemic influenza vaccine development.

Progress in the development of pandemic influenza vaccines and their production technologies.

This article analyzes the current situation in the field of construction and production of pandemic influenza vaccines. The main task of protecting the population against influenza pandemics requires state-of-the-art approaches to the construction of influenza vaccines to be based on reassortment and genetic engineering techniques, including the analysis of primary structures of influenza viral genes, synthesis and cloning of the main viral genes, reverse genetics techniques, and banks of plasmids bearing basic viral genes. Reassortant technologies are now giving way to new approaches for objective reasons. The state-of-the-art technologies provide safety not only at the laboratories where vaccine viruses are constructed but also make the production process wholly safe. We are using the following approaches to the development of industrial production: use of nanoparticles and nanoemulsions as functional adjuvants, construction of totally-safe strains for live attenuated influenza vaccines with deletions of molecular determinants of pathogenicity, application of protein and chemical chaperones to provide self-assembly of haemagglutinin molecules of the H1N1v-2009 virus, and impregnation of whole-virion preparations with nanoparticles to enhance antigenicity.

Emulsified nanoparticles containing inactivated influenza virus and CpG oligodeoxynucleotides critically influences the host immune responses in mice.

BackgroundAntigen sparing and cross-protective immunity are regarded as crucial in pandemic influenza vaccine development. Both targets can be achieved by adjuvantation strategy to elicit a robust and broadened immune response. We assessed the immunogenicity of an inactivated H5N1 whole-virion vaccine (A/Vietnam/1194/2004 NIBRG-14, clade 1) formulated with emulsified nanoparticles and investigated whether it can induce cross-clade protecting immunity.Methodology/Principal FindingsAfter formulation with PELC, a proprietary water-in-oil-in-water nanoemulsion comprising of bioresorbable polymer/Span®85/squalene, inactivated virus was intramuscularly administered to mice in either one-dose or two-dose schedule. We found that the antigen-specific serum antibody responses elicited after two doses of non-adjuvanted vaccine were lower than those observed after a single dose of adjuvanted vaccine, PELC and the conventional alum adjuvant as well. Moreover, 5 µg HA of PELC-formulated inactivated virus were capable of inducing higher antibodies than those obtained from alum-adjuvanted vaccine. In single-dose study, we found that encapsulating inactivated virus into emulsified PELC nanoparticles could induce better antibody responses than those formulated with PELC-adsorbed vaccine. However, the potency was rather reduced when the inactivated virus and CpG (an immunostimulatory oligodeoxynucleotide containing unmethylated cytosine-guanosine motifs) were co-encapsulated within the emulsion. Finally, the mice who received PELC/CpG(adsorption)-vaccine could easily and quickly reach 100% of seroprotection against a homologous virus strain and effective cross-protection against a heterologous virus strain (A/Whooper swan/Mongolia/244/2005, clade 2.2).Conclusions/SignificanceEncapsulating inactivated H5N1 influenza virus and CpG into emulsified nanoparticles critically influences the humoral responses against pandemic influenza. These results demonstrated that the use of PELC could be as antigen-sparing in preparation for a potential shortage of prophylactic vaccines against local infectious diseases, in particular pandemic influenza. Moreover, the cross-clade neutralizing antibody responses data verify the potential of such adjuvanted H5N1 candidate vaccine as an effective tool in pre-pandemic preparedness.

H5N1 Avian Influenza: Preventive and Therapeutic Strategies Against a Pandemic

Avian influenza H5N1 viruses that have spread to a number of countries in Asia, the Middle East, and Africa have the potential to cause a pandemic. The most effective public health intervention strategy is to combine preventive vaccination with nonpharmaceutical intervention strategies and enhanced surveillance activities. H5N1 vaccines are poorly immunogenic even at high doses; an adjuvant is needed for enhancement of immunogenicity and for dose-sparing. Lack of effective, yet safe, adjuvants is the limiting factor for candidate vaccines that utilize egg-dependent or egg-independent manufacturing technologies. Hence, developing novel adjuvants is crucial for pandemic influenza vaccine development. Although the use of antiviral drugs is also an important public health countermeasure for preventing and treating influenza, the emergence of drug-resistant strains of avian H5N1 viruses underscores the need to develop not only new drugs but other novel preventive and therapeutic strategies such as vaccines.

Safety and immunogenicity of a 2009 pandemic influenza A H1N1 vaccine when administered alone or simultaneously with the seasonal influenza vaccine for the 2009–10 influenza season: a multicentre, randomised controlled trial

With the ongoing 2009 pandemic of influenza A H1N1, development of pandemic influenza vaccines has generated much interest. We investigated the safety and immunogenicity of a whole-virion, inactivated, adjuvanted pandemic H1N1 vaccine in adult and elderly volunteers, given without or simultaneously with the 2009-10 seasonal trivalent influenza vaccine. This prospective, randomised study was undertaken in two centres in Hungary. 355 participants, including 203 adults (18-60 years) and 152 elderly people (>60 years), were assigned by stratified randomisation to either 0.5 mL of the pandemic vaccine (Fluval P, a monovalent vaccine with 6 microg haemagglutinin per 0.5 mL content and aluminium phosphate gel adjuvant; n=178) or 0.5 mL of the pandemic vaccine and 0.5 mL of the seasonal trivalent vaccine (Fluval AB, a trivalent inactivated whole-virion influenza vaccine; n=177). All vaccinations were done by specific study personnel, who did not take part in the assessment of safety or immunogenicity. Co-primary objectives were safety and immunogenicity by haemagglutinin inhibition testing. All analyses were done according to a pre-established analysis plan. This study is registered with ClinicalTrials.gov, number NCT01010893. Two participants receiving the pandemic vaccine only (group 1) and one receiving pandemic and seasonal vaccines (group 2) were lost to follow-up. Participants in both groups developed antibody responses against the pandemic influenza A H1N1 virus (group 1: seroconversion for adults 74.3%, 95% CI 64-6-82.4 and for elderly people 61.3%, 49.1-72.4; group 2: 76.8%, 67.2-84.7 and 81.8%, 71.4-89.7, respectively). Single doses of 6 microg fulfilled European Union and US licensing criteria for interpandemic and pandemic influenza vaccines. Simultaneously, participants in group 2 developed the immune responses needed for licensing for all three seasonal strains in the seasonal vaccine for the 2009-10 season. All adverse events were rare, mild, and transient; the most frequent were pain at injection site (eight cases in group 1 vs 18 in group 2) and fatigue for 1-2 days after vaccination (three vs five cases). The present pandemic vaccine is safe and immunogenic in healthy adult and elderly patients, and needs low doses and only one injection to trigger immune responses to comply with licensing criteria. It can be safely co-administered with the 2009-10 seasonal influenza vaccine. Omninvest, Hungary.

Current status and progress of prepandemic and pandemic influenza vaccine development

H5N1 viruses are widely considered to be a probable cause of the next influenza pandemic. Influenza vaccines are considered to form the main prophylactic measure against pandemic influenza. The world’s population is expected to have no pre-existing immunity against the pandemic virus strain and will need two vaccine doses to acquire protective immunity. A pandemic outbreak will spread much faster than it will take for pandemic vaccines to be produced and distributed. Therefore, increasing efforts are being made to develop prepandemic vaccines that can induce broad cross-protective responses and that can be administered as soon as a pandemic is declared or even before, in order to successfully prime the immune system and allow for a rapid and protective antibody response with one dose of the pandemic vaccine. Several vaccine manufacturers have developed candidate pandemic and prepandemic vaccines, predominantly based on reverse-genetics reference strains and have improved the immunogenicity by formulating these vaccines with different adjuvants. Clinical studies with inactivated split-virion or whole-virion vaccines based on H5N1 indicate that two immunizations appear necessary to elicit the level of immunity required to meet licensure criteria. A detailed overview is given of the most successful candidate vaccines developed by seven vaccine manufacturers.

Pandemic influenza vaccine development: time is of the essence

Pandemic influenza vaccine development: time is of the essence

Regulatory issues in pandemic influenza vaccine development

The Therapeutic Goods Administration (TGA) is responsible for the licensing of vaccines used in Australia. This includes pre-market evaluation aspects (such as assessing the quality, efficacy and safety of vaccines) and post-market aspects (such as batch release testing and the monitoring of adverse reactions). For inter-pandemic and pandemic influenza vaccines, TGA is also involved in the selection of appropriate vaccine viruses and the calibration and supply of reagents for the production of influenza vaccines. Together with industry, TGA has a responsibility to ensure that all regulatory and good manufacturing requirements (GMP) are met to ensure vaccine safety and efficacy.

Influenza vaccines generated by reverse genetics.

Influenza viruses cause annual epidemics and occasional pandemics of acute respiratory disease. Vaccination is the primary means to prevent and control the disease. However, influenza viruses undergo continual antigenic variation, which requires the annual reformulation of trivalent influenza vaccines, making influenza unique among pathogens for which vaccines have been developed. The segmented nature of the influenza virus genome allows for the traditional reassortment between two viruses in a coinfected cell. This technique has long been used to generate strains for the preparation of either inactivated or live attenuated influenza vaccines. Recent advancements in reverse genetics techniques now make it possible to generate influenza viruses entirely from cloned plasmid DNA by cotransfection of appropriate cells with 8 or 12 plasmids encoding the influenza virion sense RNA and/or mRNA. Once regulatory issues have been addressed, this technology will enable the routine and rapid generation of strains for either inactivated or live attenuated influenza vaccine. In addition, the technology offers the potential for new vaccine strategies based on the generation of genetically engineered donors attenuated through directed mutation of one or more internal genes. Reverse genetics techniques are also proving to be important for the development of pandemic influenza vaccines, because the technology provides a means to modify genes to remove virulence determinants found in highly pathogenic avian strains. The future of influenza prevention and control lies in the application of this powerful technology for the generation of safe and more effective influenza vaccines.