A novel intranasal virus-like particle (VLP) vaccine designed to protect against the pandemic 1918 influenza A virus (H1N1)

Nanoadjuvants: Promising Bioinspired and Biomimetic Approaches in Vaccine Innovation

Adjuvants are the important part of vaccine manufacturing as they elicit the vaccination effect and enhance the durability of the immune response through controlled release. In light of this, nanoadjuvants have shown unique broad spectrum advantages. As nanoparticles (NPs) based vaccines are fast-acting and better in terms of safety and usability parameters as compared to traditional vaccines, they have attracted the attention of researchers. A vaccine nanocarrier is another interesting and promising area for the development of next-generation vaccines for prophylaxis. This review looks at the various nanoadjuvants and their structure-function relationships. It compiles the state-of-art literature on numerous nanoadjuvants to help domain researchers orient their understanding and extend their endeavors in vaccines research and development.

Self-Assembled Proteinaceous Nanoparticles for Co-Delivery of Antigens and Cytosine Phosphoguanine (CpG) Adjuvants: Implications for Nanovaccines

Nanotechnology has developed rapidly, giving rise to "nanovaccinology". In particular, protein-based nanocarriers have gained widespread attention because of their excellent biocompatibility. As the development of flexible and rapid vaccines is challenging, modular extensible nanoparticles are urgently needed. In this study, a multifunctional nanocarrier capable of delivering various biomolecules (including polysaccharides, proteins, and nucleic acids) was designed by fusing the cholera toxin B subunit with streptavidin. Then, the nanocarrier was used to prepare a bioconjugate nanovaccine against S. flexneri by co-delivery of antigens and CpG adjuvants. Subsequent experimental results indicated that the nanovaccine with multiple components could stimulate both adaptive and innate immunity. Moreover, combining nanocarriers and CpG adjuvants with glycan antigens could improve the survival of vaccinated mice during the interval of two vaccination injections. The multifunctional nanocarrier and the design strategy demonstrated in this study could be utilized in the development of many other nanovaccines against infectious diseases.

Biosynthesis of a VLP-type nanocarrier specific to cancer cells using the BEVS expression system for targeted drug delivery

OBJECTIVE

Canine parvovirus (CPV) is a small virus without an envelope that consists of three viral proteins including VP1, VP2, and VP3. Exclusively, the VP2 can form a typically CPV-sized virus-like particle (CPV-VLP) that can be used as a biological nanocarrier for diagnostic and therapeutic purposes since these VLPs can target cancer cells specially through the transferrin surface receptors (TFRs). Consequently, we aimed to produce these nanocarriers to be used for specific targeting of cancer cells.

METHODS

Sf9 insect cells were transfected with constructed recombinant bacmid shuttle vector encoding an enhanced green fluorescent protein (EGFP) and CPV-VP2 by the cationic lipids of Cellfectin II. Subsequently, two recombinant baculoviruses expressing EGFP and VP2 were produced and expression of VP2 was increased under the optimal condition. In consequence, the CPV-VLP nanoparticles composed of recombinant VP2 subunits were extracted. The purity of VLPs was then evaluated by SDS-PAGE, and the structural integrity and quality of the final product were evaluated by TEM and HA methods. Eventually, the size distribution of the produced biological nanoparticles and their uniformity were determined by the DLS method.

RESULTS

The expression of EGFP protein was confirmed by fluorescent microscopy, and the expression of VP2 protein was evaluated by SDS-PAGE and western blotting. Infected Sf9 insect cells also showed cytopathic effects (CPEs), and the maximum expression of VP2 occurred at MOI of 10 (pfu/cell) at the harvest time of 72 h post-infection (hpi). After performing various stages of purification, buffer exchange, and concentration, the quality and structural integrity of the VLP product were confirmed. The results of the DLS technique showed the presence of uniform particles (PdI below 0.5) with an approximate size of 25 nm.

CONCLUSION

The results indicate BEVS as an appropriate and efficient system for generating CPV-VLPs, and the used method based on two-stage ultracentrifugation was appropriate for purifying these nanoparticles. Produced nanoparticles can be used as the biologic nano-carriers in future studies.

Progress in the development of virus-like particle vaccines against respiratory viruses

Introduction: Influenza virus, human respiratory syncytial virus (RSV), and human metapneumovirus (HMPV) are important human respiratory pathogens. Recombinant virus-like particle (VLP) vaccines are suggested to be potential promising platforms to protect against these respiratory viruses. This review updates important progress in the development of VLP vaccines against respiratory viruses.Areas Covered: This review summarizes progress in developing VLP and nanoparticle-based vaccines against influenza virus, RSV, and HMPV. The PubMed was mainly used to search for important research articles published since 2010 although earlier key articles were also referenced. The research area covered includes VLP and nanoparticle platform vaccines against seasonal, pandemic, and avian influenza viruses as well as RSV and HMPV respiratory viruses. The production methods, immunogenic properties, and vaccine efficacy of respiratory VLP vaccines in preclinical animal models and clinical studies were reviewed in this article.Expert opinion: Previous and current preclinical and clinical studies suggest that recombinant VLP and nanoparticle vaccines are expected to be developed as promising alternative platforms against respiratory viruses in future. Therefore, continued research efforts are warranted.

Development of experimental pneumococcal vaccine for mucosal immunization

Streptococcus pneumonia is an important human pathogen that causes various severe diseases such as pneumonia, otitis and meningitis. Vaccination against S. pneumoniae is implemented in many developed countries. The presently used vaccines are safe, well tolerated but relatively expensive and require modification due to the immunological changes of the epidemic strains. This paper describes the development of a new pneumococcal vaccine candidate for immunization on mucosal surfaces. For this purpose the antigens of chimeric protein PSPF, previously suggested for an injectable S. pneumoniae vaccine, were expressed on the surface of the live probiotic strain Enterococcus faecium L3. Experiments on laboratory mice vaccinated with live bacteria demonstrated the appearance of the specific IgA and IgG which provide protection against the lethal S. pneumoniae infection.

Nanoparticle Vaccines Against Infectious Diseases

Due to emergence of new variants of pathogenic micro-organisms the treatment and immunization of infectious diseases have become a great challenge in the past few years. In the context of vaccine development remarkable efforts have been made to develop new vaccines and also to improve the efficacy of existing vaccines against specific diseases. To date, some vaccines are developed from protein subunits or killed pathogens, whilst several vaccines are based on live-attenuated organisms, which carry the risk of regaining their pathogenicity under certain immunocompromised conditions. To avoid this, the development of risk-free effective vaccines in conjunction with adequate delivery systems are considered as an imperative need to obtain desired humoral and cell-mediated immunity against infectious diseases. In the last several years, the use of nanoparticle-based vaccines has received a great attention to improve vaccine efficacy, immunization strategies, and targeted delivery to achieve desired immune responses at the cellular level. To improve vaccine efficacy, these nanocarriers should protect the antigens from premature proteolytic degradation, facilitate antigen uptake and processing by antigen presenting cells, control release, and should be safe for human use. Nanocarriers composed of lipids, proteins, metals or polymers have already been used to attain some of these attributes. In this context, several physico-chemical properties of nanoparticles play an important role in the determination of vaccine efficacy. This review article focuses on the applications of nanocarrier-based vaccine formulations and the strategies used for the functionalization of nanoparticles to accomplish efficient delivery of vaccines in order to induce desired host immunity against infectious diseases.

Adjuvant formulations for virus-like particle (VLP) based vaccines

The development of virus-like particle (VLP) technology has had an enormous impact on modern vaccinology. In order to optimize the efficacy and safety of VLP-based vaccines, adjuvants are included in most vaccine formulations. To date, most licensed VLP-based vaccines utilize the classic aluminum adjuvant compositions. Certain challenging pathogens and weak immune responder subjects may require further optimization of the adjuvant formulation to maximize the magnitude and duration of the protective immunity. Indeed, novel classes of adjuvants such as liposomes, agonists of pathogen recognition receptors, polymeric particles, emulsions, cytokines and bacterial toxins, can be used to further improve the immunostimulatory activity of a VLP-based vaccine. This review describes the current advances in adjuvant technology for VLP-based vaccines directed at viral diseases, and discusses the basic principles for designing adjuvant formulations for enhancing the vaccine immunogenicity.

Nasal Vaccine Delivery

The mucosal surfaces represent the major site of entry of many pathogens, and major challenges in vaccine development include safety and stability in a suitable dosage form. Micro- and nanocarrier-based delivery systems as nasal vaccines induce humoral, cellular, and mucosal immunity. The nasal route of vaccination could also offer immunity at several distant mucosal sites (oral, rectal, vaginal, and pulmonary), which is considered a simplified and cost-effective mode of vaccination with enhanced patient compliance. Most of the nasal vaccine delivery systems in the form of microparticulates, nanoparticulates, and liposomes are currently under development and prove to offer immunity in animal models. The importance and potential of the nasal route of administration for vaccines is unexplored, and this chapter outlines the opportunities, challenges, and potential delivery solutions to facilitate the development of improved nasal vaccines for infectious diseases.

Progress in developing virus-like particle influenza vaccines

Recombinant vaccines based on virus-like particles (VLPs) or nanoparticles have been successful in their safety and efficacy in preclinical and clinical studies. The technology of expressing enveloped VLP vaccines has combined with molecular engineering of proteins in membrane-anchor and immunogenic forms mimicking the native conformation of surface proteins on the enveloped viruses. This review summarizes recent developments in influenza VLP vaccines against seasonal, pandemic, and avian influenza viruses from the perspective of use in humans. The immunogenicity and efficacies of influenza VLP vaccine in the homologous and cross-protection were reviewed. Discussions include limitations of current influenza vaccination strategies and future directions to confer broadly cross protective new influenza vaccines as well as vaccination.

Incorporation of conserved nucleoprotein into influenza virus-like particles could provoke a broad protective immune response in BALB/c mice and chickens

We engineered influenza A/goose/GD/1996 (H5N1) (clade 0) virus-like particles (VLPs) by coinfecting Sf9 cells with triple/quadruple recombinant baculovirus that expressed hemagglutinin (HA), neuraminidase (NA), and matrix 1 (M1) with or without nucleoprotein (NP). VLP3 (HA, NA, and M1) and VLP4 (HA, NA, M1, and NP) vaccines (containing 1 μg HA) with oil emulsion were administered to mice and chickens by intramuscular injection, and the immune responses were analyzed. The VLP-vaccinated mice demonstrated high antigen specific antibody titers and effective cellular immune responses. The mice and chickens vaccinated with VLP4 demonstrated more robust humoral and cellular immune responses than those vaccinated with VLP3. The VLP4 vaccine afforded 100% protection against a heterologous lethal influenza virus challenge (clade 2.3.4) whereas the VLP3 vaccine conferred 50% protection in chickens. These results implied that the incorporation of conserved NP protein into the VLPs could elicit a broad protective immune response in BALB/c mice and chickens. To the best of our knowledge, this study is the first report describing the immunological profile of the NP-containing VLPs vaccines in mice and chicken models, and the results demonstrate that the non-infectious, genome less VLPs, particularly those containing NP, represent a promising strategy for the development of a safe and effective vaccine to control pandemic influenza.

Prevention and Control of Influenza Viruses

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

An evaluation of the emerging vaccines against influenza in children

BACKGROUND

Influenza is an under-appreciated cause of acute lower respiratory infections (ALRI) in children. It is estimated to cause approximately 20 million new episodes of ALRI in children annually, 97% of these occurring in developing countries. It is also estimated to result in 28000 to 112000 deaths annually in young children. Apart from hospitalisations and deaths, influenza has significant economic consequences. The current egg-based inactivated influenza vaccines have several limitations: annual vaccination, high production costs, and cannot respond adequately to meet the demand during pandemics.

METHODS

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In Stage I, we systematically reviewed the literature related to emerging cross-protective vaccines against influenza relevant to several criteria of interest: answerability; cost of development, production and implementation; efficacy and effectiveness; deliverability, affordability and sustainability; maximum potential impact on disease burden reduction; acceptability to the end users and health workers; and effect on equity. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies). They answered questions from the CHNRI framework and their "collective optimism" towards each criterion was documented on a scale from 0 to 100%.

RESULTS

The experts expressed very high level of optimism for deliverability, impact on equity, and acceptability to health workers and end users. However, they expressed concerns over the criteria of answerability, low development cost, low product cost, low implementation cost, affordability and, to a lesser extent sustainability. In addition they felt that the vaccine would have higher efficacy and impact on disease burden reduction on overall influenza-associated disease rather than specifically influenza-associated pneumonia.

CONCLUSION

Although the landscape of emerging influenza vaccines shows several promising candidates, it is unlikely that the advancements in the newer vaccine technologies will be able to progress through to large scale production in the near future. The combined effects of continued investments in researching new vaccines and improvements of available vaccines will hopefully shorten the time needed to the development of an effective seasonal and pandemic influenza vaccine suitable for large scale production.

Bacterium-like particles for efficient immune stimulation of existing vaccines and new subunit vaccines in mucosal applications

The successful development of a mucosal vaccine depends critically on the use of a safe and effective immunostimulant and/or carrier system. This review describes the effectiveness and mode of action of an immunostimulating particle, derived from bacteria, used in mucosal subunit vaccines. The non-living particles, designated bacterium-like particles are based on the food-grade bacterium Lactococcus lactis. The focus of the overview is on the development of intranasal BLP-based vaccines to prevent diseases caused by influenza and respiratory syncytial virus, and includes a selection of Phase I clinical data for the intranasal FluGEM vaccine.

Virus-like particles as a highly efficient vaccine platform: diversity of targets and production systems and advances in clinical development

Virus-like particles (VLPs) are a class of subunit vaccines that differentiate themselves from soluble recombinant antigens by stronger protective immunogenicity associated with the VLP structure. Like parental viruses, VLPs can be either non-enveloped or enveloped, and they can form following expression of one or several viral structural proteins in a recombinant heterologous system. Depending on the complexity of the VLP, it can be produced in either a prokaryotic or eukaryotic expression system using target-encoding recombinant vectors, or in some cases can be assembled in cell-free conditions. To date, a wide variety of VLP-based candidate vaccines targeting various viral, bacterial, parasitic and fungal pathogens, as well as non-infectious diseases, have been produced in different expression systems. Some VLPs have entered clinical development and a few have been licensed and commercialized. This article reviews VLP-based vaccines produced in different systems, their immunogenicity in animal models and their status in clinical development.

Production and characterization of mammalian virus-like particles from modified vaccinia virus Ankara vectors expressing influenza H5N1 hemagglutinin and neuraminidase

Several studies have described the production of influenza virus-like particles (VLP) using a variety of platform systems. These VLPs are non-replicating particles that spontaneously self-assemble from expressed influenza virus proteins and have been proposed as vaccine candidates for both seasonal and pandemic influenza. Although still in the early stages of development and evaluation as influenza vaccines, influenza VLPs have a variety of other valuable uses such as examining and understanding correlates of protection against influenza and investigating virus-cell interactions. The most common production system for influenza VLPs is the baculovirus-insect cell expression which has several attractive features including the ease in which new gene combinations can be constructed, the immunogenicity elicited and protection afforded by the produced VLPs, and the scalability offered by the system. However, there are differences between the influenza VLPs produced by baculovirus expression systems in insect cells and the influenza viruses produced for use as current vaccines or the virus produced during a productive clinical infection. We describe here the development of a modified vaccinia virus Ankara (MVA) system to generate mammalian influenza VLPs containing influenza H5N1 proteins. The MVA vector system is flexible for manipulating and generating various VLP constructs, expresses high level of influenza hemagglutinin (HA), neuraminidase (NA), and matrix (M) proteins, and can be scaled up to produce VLPs in quantities sufficient for in vivo studies. We show that mammalian VLPs are generated from recombinant MVA vectors expressing H5N1 HA alone, but that increased VLP production can be achieved if NA is co-expressed. These mammalian H5N1 influenza VLPs have properties in common with live virus, as shown by electron microscopy analysis, their ability to hemagglutinate red blood cells, express neuraminidase activity, and to bind influenza specific antibodies. Importantly, these VLPs are able to elicit a protective immune response in a mouse challenge model, suggesting their utility in dissecting the correlates of immunity in such models. Mammalian derived VLPs may also provide a useful tool for studying virus-cell interactions and may have potential for development as pandemic vaccines.

Developments in virus-like particle-based vaccines for infectious diseases and cancer

Virus-like particles hold great promise for the development of effective and affordable vaccines. Indeed, virus-like particles are suitable for presentation and efficient delivery of linear as well as conformational antigens to antigen-presenting cells. This will ultimately result in optimal B-cell activation and cross-presentation with both MHC class I and II molecules to prime CD4(+) T-helper as well as CD8(+) cytotoxic T cells. This article provides an update on the development and use of virus-like particles as vaccine approaches for infectious diseases and cancer.

Pandemic H1N1 influenza virus-like particles are immunogenic and provide protective immunity to pigs

The outbreak of the 2009 influenza pandemic underscored the important role of swine in influenza virus evolution and the emergence of novel viruses with pandemic potential. Vaccination is the most common practice to control swine influenza in swine industry. Influenza virus-like particle (VLP) vaccines are an alternative approach and have been demonstrated to be immunogenic and confer protection against influenza virus challenge in chickens, mice and ferrets. In this study, we generated VLPs consisting of HA, NA and M1 proteins derived from pandemic virus A/California/04/2009 in insect cells. The immunogenicity and efficacy following vaccination of VLPs were evaluated in swine. Our data showed that vaccination using VLPs elicited robust levels of serum IgG, mucosal IgA, and viral neutralizing antibodies against A/Sw/Manitoba/MAFRI32/2009 H1N1. Following challenge with pandemic H1N1 2009, vaccinated pigs were protected, displaying reduced lung lesions, virus shedding and inhibition of virus replication in the lungs compared to non-vaccinated control pigs. Thus, VLPs can serve as a promising vaccination strategy to control influenza in swine.

Elicitation of anti-1918 influenza virus immunity early in life prevents morbidity and lower levels of lung infection by 2009 pandemic H1N1 influenza virus in aged mice

The Spanish influenza virus pandemic of 1918 was responsible for 40 million to 50 million deaths and is antigenically similar to the swine lineage 2009 pandemic influenza virus. Emergence of the 2009 pandemic from swine into humans has raised the possibility that low levels of cross-protective immunity to past shared epitopes could confer protection. In this study, influenza viruslike particles (VLPs) were engineered to express the hemagglutinin (HA) and genes from the 1918 influenza virus to evaluate the duration of cross-protection to the H1N1 pandemic strain by vaccinating young mice (8 to 12 weeks) and then allowing the animals to age to 20 months. This immunity was long lasting, with homologous receptor-blocking antibodies detected throughout the lifespan of vaccinated mice. Furthermore, the 1918 VLPs fully protected aged mice from 2009 pandemic H1N1 virus challenge 16 months after vaccination. Histopathological assessment showed that aged vaccinated mice had significant protection from alveolar infection but less protection of the bronchial tissue than adult vaccinated mice. Additionally, passive transfer of immune serum from aged vaccinated mice resulted in protection from death but not morbidity. This is the first report describing the lifelong duration of cross-reactive immune responses elicited by a 1918 VLP vaccine in a murine model. Importantly, these lifelong immune responses did not result in decreased total viral replication but did prevent infection of the lower respiratory tract. These findings show that immunity acquired early in life can restrict the anatomical location of influenza viral replication, rather than preventing infection, in the aged.

Virus-like particle vaccine containing hemagglutinin confers protection against 2009 H1N1 pandemic influenza

Immunization of the world population before an influenza pandemic such as the 2009 H1N1 virus spreads globally is not possible with current vaccine production platforms. New influenza vaccine technologies, such as virus-like-particles (VLPs), offer a promising alternative. Here, we tested the immunogenicity and protective efficacy of a VLP vaccine containing hemagglutinin (HA) and M1 from the 2009 pandemic H1N1 influenza virus (H1N1pdm) in ferrets and compared intramuscular (i.m.) and intranasal (i.n.) routes of immunization. Vaccination of ferrets with VLPs containing the M1 and HA proteins from A/California/04/2009 (H1N1pdm) induced high antibody titers and conferred significant protection against virus challenge. VLP-vaccinated animals lost less weight, shed less virus in nasal washes, and had markedly lower virus titers in all organs tested than naïve controls. A single dose of VLPs, either i.m. or i.n., induced higher levels of antibody than did two doses of commercial split vaccine. Ferrets vaccinated with split vaccine were incompletely protected against challenge; these animals had lower virus titers in olfactory bulbs, tonsils, and intestines, but lost weight and shed virus in nasal washes to a similar extent as naïve controls. Challenge with heterologous A/Brisbane/59/07 (H1N1) virus revealed that the VLPs conferred minimal cross-protection to heterologous infection, as revealed by the lack of reduction in nasal wash and lung virus titers and slightly higher weight loss relative to controls. In summary, these experiments demonstrate the strong immunogenicity and protective efficacy of VLPs compared to the split vaccine and show that i.n. vaccination with VLPs has the potential for highly efficacious vaccination against influenza.

Current strategies for subunit and genetic viral veterinary vaccine development

Developing vaccines for livestock provides researchers with the opportunity to perform efficacy testing in the natural hosts. This enables the evaluation of different strategies, including definition of effective antigens or antigen combinations, and improvement in delivery systems for target antigens so that protective immune responses can be modulated or potentiated. An impressive amount of knowledge has been generated in recent years on vaccine strategies and consequently a wide variety of antigen delivery systems is now available for vaccine research. This paper reviews several antigen production and delivery strategies other than those based on the use of live viral vectors. Genetic and protein subunit vaccines as well as alternative production systems are considered in this review.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

Viruses and Virus-Like Particles in Biotechnology

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this article, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitorization, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Swine influenza vaccines: current status and future perspectives

Swine influenza is an important contagious disease in pigs caused by influenza A viruses. Although only three subtypes of influenza A viruses, H1N1, H1N2 and H3N2, predominantly infect pigs worldwide, it is still a big challenge for vaccine manufacturers to produce efficacious vaccines for the prevention and control of swine influenza. Swine influenza viruses not only cause significant economic losses for the swine industry, but are also important zoonotic pathogens. Vaccination is still one of the most important and effective strategies to prevent and control influenza for both the animal and human population. In this review, we will discuss the current status of swine influenza worldwide as well as current and future options to control this economically important swine disease.

Pathogenesis of pandemic influenza A (H1N1) and triple-reassortant swine influenza A (H1) viruses in mice

The pandemic H1N1 virus of 2009 (2009 H1N1) continues to cause illness worldwide, primarily in younger age groups. To better understand the pathogenesis of these viruses in mammals, we used a mouse model to evaluate the relative virulence of selected 2009 H1N1 viruses and compared them to a representative human triple-reassortant swine influenza virus that has circulated in pigs in the United States for over a decade preceding the current pandemic. Additional comparisons were made with the reconstructed 1918 virus, a 1976 H1N1 swine influenza virus, and a highly pathogenic H5N1 virus. Mice were inoculated intranasally with each virus and monitored for morbidity, mortality, viral replication, hemostatic parameters, cytokine production, and lung histology. All 2009 H1N1 viruses replicated efficiently in the lungs of mice and possessed a high degree of infectivity but did not cause lethal disease or exhibit extrapulmonary virus spread. Transient weight loss, lymphopenia, and proinflammatory cytokine and chemokine production were present following 2009 H1N1 virus infection, but these levels were generally muted compared with a triple-reassortant swine virus and the 1918 virus. 2009 H1N1 viruses isolated from fatal cases did not demonstrate enhanced virulence in this model compared with isolates from mild human cases. Histologically, infection with the 2009 viruses resulted in lesions in the lung varying from mild to moderate bronchiolitis with occasional necrosis of bronchiolar epithelium and mild to moderate peribronchiolar alveolitis. Taken together, these studies demonstrate that the 2009 H1N1 viruses exhibited mild to moderate virulence in mice compared with highly pathogenic viruses.

Intranasal delivery of influenza subunit vaccine formulated with GEM particles as an adjuvant

Nasal administration of influenza vaccine has the potential to facilitate influenza control and prevention. However, when administered intranasally (i.n.), commercially available inactivated vaccines only generate systemic and mucosal immune responses if strong adjuvants are used, which are often associated with safety problems. We describe the successful use of a safe adjuvant Gram-positive enhancer matrix (GEM) particles derived from the food-grade bacterium Lactococcus lactis for i.n. vaccination with subunit influenza vaccine in mice. It is shown that simple admixing of the vaccine with the GEM particles results in a strongly enhanced immune response. Already after one booster, the i.n. delivered GEM subunit vaccine resulted in hemagglutination inhibition titers in serum at a level equal to the conventional intramuscular (i.m.) route. Moreover, i.n. immunization with GEM subunit vaccine elicited superior mucosal and Th1 skewed immune responses compared to those induced by i.m. and i.n. administered subunit vaccine alone. In conclusion, GEM particles act as a potent adjuvant for i.n. influenza immunization.

Effectiveness and cost-effectiveness of expanded antiviral prophylaxis and adjuvanted vaccination strategies for an influenza A (H5N1) pandemic

BACKGROUND

The pandemic potential of influenza A (H5N1) virus is a prominent public health concern of the 21st century.

OBJECTIVE

To estimate the effectiveness and cost-effectiveness of alternative pandemic (H5N1) mitigation and response strategies.

DESIGN

Compartmental epidemic model in conjunction with a Markov model of disease progression.

DATA SOURCES

Literature and expert opinion.

TARGET POPULATION

Residents of a U.S. metropolitan city with a population of 8.3 million.

TIME HORIZON

Lifetime.

PERSPECTIVE

Societal.

INTERVENTIONS

3 scenarios: 1) vaccination and antiviral pharmacotherapy in quantities similar to those currently available in the U.S. stockpile (stockpiled strategy), 2) stockpiled strategy but with expanded distribution of antiviral agents (expanded prophylaxis strategy), and 3) stockpiled strategy but with adjuvanted vaccine (expanded vaccination strategy). All scenarios assumed standard nonpharmaceutical interventions.

OUTCOME MEASURES

Infections and deaths averted, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness.

RESULTS OF BASE-CASE ANALYSIS

Expanded vaccination was the most effective and cost-effective of the 3 strategies, averting 68% of infections and deaths and gaining 404 030 QALYs at $10 844 per QALY gained relative to the stockpiled strategy.

RESULTS OF SENSITIVITY ANALYSIS

Expanded vaccination remained incrementally cost-effective over a wide range of assumptions.

LIMITATIONS

The model assumed homogenous mixing of cases and contacts; heterogeneous mixing would result in faster initial spread, followed by slower spread. We did not model interventions for children or older adults; the model is not designed to target interventions to specific groups.

CONCLUSION

Expanded adjuvanted vaccination is an effective and cost-effective mitigation strategy for an influenza A (H5N1) pandemic. Expanded antiviral prophylaxis can help delay the pandemic while additional strategies are implemented.

PRIMARY FUNDING SOURCE

National Institutes of Health and Agency for Healthcare Research and Quality.

Virus-like particle vaccine comprised of the HA, NA, and M1 proteins of an avian isolated H5N1 influenza virus induces protective immunity against homologous and heterologous strains in mice

Highly pathogenic avian influenza H5N1 virus represents a growing threat for an influenza pandemic. Development of effective vaccines for H5N1 is a priority for pandemic preparedness. Focusing on influenza virus-like particles (VLPs) has been suggested as a promising vaccine approach. Recent VLP vaccination efforts have been concentrated on the H5N1 strains isolated from humans. Because all confirmed cases of human H5N1 infection were directly transmitted from infected poultry, it is of interest to develop VLP vaccines comprised of antigenic proteins of avian H5N1 strains in order to compare their efficacy in fighting diverse H5N1 strains with vaccines developed using human isolates. In this study, we generated a VLP vaccine composed of the HA, NA, and M1 proteins of the avian H5N1 influenza virus isolate A/chicken/Hubei/489/2004, which seems to occupy a unique phylogenetic position; it belongs to neither clade 1 nor clade 2. Upon infection of Sf9 insect cells using recombinant baculoviruses, the co-expressed HA, NA, and M1 proteins self-assembled and released into the culture medium as VLPs. In a mouse model, purified VLPs elicited an effective antibody response and conferred complete protection against heterologous human H5N1 influenza virus, as well as a homologous avian H5N1 influenza virus isolate. Our work provides further evidence that vaccination with influenza VLPs may be a productive approach to achieve protection against diverse H5N1 strains.

Preclinical efficacy of a virus-like particle-based vaccine against avian influenza H5N1

Evaluation of: Kang S-M, Yoo D-G, Lipatov AS et al.: Induction of long-term protective immune responses by influenza H5N1 virus-like particles. PLoS ONE 4, e4667 (2009). This article describes a long-term protective effect of a vaccine candidate against avian influenza H5N1 that is based on A/Viet Nam1203/04 proteins within nonreplicating virus-like particles. The protective effect is correlated with both humoral and cellular immune responses.

Influenza virus-like particle vaccines

Enveloped virus-like particle (VLP) vaccines containing influenza hemagglutinin (HA) and neuraminidase (NA) antigens are produced easily in insect or mammalian cells via the simultaneous expression of HA and NA along with a viral core protein, such as influenza matrix (M1) or a retroviral Gag protein. The size and shape of the resulting particles are dictated by the choice of the core component, but M1- and Gag-based VLPs are strongly immunogenic and protective in seasonal and highly pathogenic influenza challenge models. Current data are consistent with the hypothesis that influenza VLP vaccine efficacy is related to the particulate, multivalent composition coupled with the presence of correctly folded antigens with intact biological activities. This new influenza vaccine paradigm offers potential advantages over the conventional egg-based, split-vaccine platform in terms of enhanced immunogenicity and better breadth of protection.

Influenza vaccines based on virus-like particles

The simultaneous expression of structural proteins of virus can produce virus-like particles (VLPs) by a self-assembly process in a viral life cycle even in the absence of genomic material. Taking an advantage of structural and morphological similarities of VLPs to native virions, VLPs have been suggested as a promising platform for new viral vaccines. In the light of a pandemic threat, influenza VLPs have been recently developed as a new generation of non-egg based cell culture-derived vaccine candidates against influenza infection. Animals vaccinated with VLPs containing hemagglutinin (HA) or HA and neuraminidase (NA) were protected from morbidity and mortality resulting from lethal influenza infections. Influenza VLPs serve as an excellent model system of an enveloped virus for understanding the properties of VLPs in inducing protective immunity. In this review, we briefly describe the characteristics of influenza VLPs assembled with a lipid bilayer containing glycoproteins, and summarize the current progress on influenza VLPs as an alternative vaccine candidate against seasonal as well as pandemic influenza viruses. In addition, the protective immune correlates induced by vaccination with influenza VLPs are discussed.

New baculovirus recombinants expressing Pseudorabies virus (PRV) glycoproteins protect mice against lethal challenge infection

The present study demonstrates the protective potential of novel baculovirus recombinants, which express the glycoproteins gB, gC, or gD of Pseudorabies virus (PRV; Alphaherpesvirus of swine) and additionally contain the glycoprotein G of Vesicular Stomatitis Virus (VSV-G) in the virion (Bac-G-PRV). To evaluate the protective capacity, mixtures of equal amounts of the PRV gB-, gC-, and gD-expressing baculoviruses were used for immunization. Three intramuscular immunizations with that Bac-G-PRV mixture could protect mice against a lethal PRV challenge infection. To achieve complete protection high titers of Bac-G-PRV and three immunizations were necessary. This immunization with Bac-G-PRV resulted in the induction of high titers of PRV-specific serum antibodies of the IgG2a subclass and of interferon (IFN)-gamma, indicating a Th1-type immune response. Moreover, splenocytes of immunized mice exhibited natural killer cell activity accompanied by the production of IFN-alpha and IFN-gamma. Collectively, the presented data demonstrate for the first time that co-expression of VSV-G in baculovirus recombinant vaccines can improve the induction of a protective immune response against foreign antigens.

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.

Kinetics of immune responses to influenza virus-like particles and dose-dependence of protection with a single vaccination

The format of influenza virus-like particles (VLPs) as a nonreplicating particulate vaccine candidate is a promising alternative to conventional egg-based vaccines. In this study, we have investigated the detailed kinetics of immune responses and protective efficacy after a single intranasal immunization with different doses of VLPs alone or in the presence of an Escherichia coli mutant heat-labile enterotoxin [mLT(R192G)] or cholera toxin subunit B as adjuvants. Analysis of immune responses showed differential kinetics in a VLP antigen dose-dependent manner and dynamic changes in the ratios of antibody immunoglobulin G isotypes over the time course. Protection against lethal challenge was observed with a single immunization with influenza VLPs even without adjuvant. The addition of adjuvant showed significant antigen-sparing effects with improved protective efficacy. The protective immune responses, efficacies of protection, and antigen-sparing effects were significantly improved by a second immunization as determined by the levels of neutralizing antibodies, morbidity postchallenge, lung viral titers, and inflammatory cytokines. Our results are informative for a better understanding of the protective immunity induced by a single dose or two doses of influenza VLPs, which is dependent on antigen dosage and the presence of adjuvant, and will provide insights into designing effective vaccines based on VLPs.

Influenza virus-like particles as pandemic vaccines

There is an urgent need to develop novel approaches for vaccination against emerging pathogenic avian influenza viruses as a priority for pandemic preparedness. Influenza virus-like particles (VLPs) have been suggested and developed as a new generation of non-egg-based cell culture-derived vaccine candidates against influenza infection. Influenza VLPs are formed by a self-assembly process incorporating structural proteins into budding particles composed of the hemagglutinin (HA), neuraminidase (NA) and M1 proteins, and may include additional influenza proteins such as M2. Animals vaccinated with VLPs were protected from morbidity and mortality resulting from lethal influenza infections. The protective mechanism of influenza VLP vaccines was similar to that of the currently licensed influenza vaccines inducing neutralizing antibodies and hemagglutination inhibition activities. Current studies demonstrate that influenza VLP approaches can be a promising alternative approach to developing a vaccine for pandemic influenza viruses. The first human clinical trial of a recombinant pandemic-like H5N1 influenza VLP vaccine was initiated in July 2007 (Bright et al., unpublished).

Influenza-pseudotyped Gag virus-like particle vaccines provide broad protection against highly pathogenic avian influenza challenge

Influenza-pseudotyped Gag virus-like particles (VLPs) were produced via the expression of influenza hemagglutinin (HA), neuraminidase (NA) and the murine leukemia virus Gag product in the baculovirus-insect cell expression system. Hemagglutination specific activities of sucrose gradient-purified VLPs were similar to those of egg-grown influenza viruses but particle morphologies were gamma retrovirus-like in the form of consistent 100nm spheres. Immunization of mice and ferrets demonstrated robust immunogenicity and protection from challenge with no measurable morbidity. Ferret data were striking in that immunization with H5N1 VLPs representing either A/Vietnam/1203/04 or A/Indonesia/5/05 resulted in solid protection against highly pathogenic A/Vietnam/1203/04 challenge with no detectable virus in the upper respiratory tract post-challenge in either group. H1N1 VLP immunization of ferrets resulted in partial protection against H5N1 challenge with markedly accelerated virus clearance from the upper respiratory tract relative to controls. The immunogenicity of influenza-pseudotyped VLPs was not dependent on the adjuvant properties of replication competent contaminating baculovirus. These data demonstrate robust vaccine protection of Gag-based, influenza-pseudotyped VLPs carrying a variety of influenza antigens and suggest applicability toward a number of additional respiratory viruses.

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.