Virus-like particle vaccine induces protective immunity against homologous and heterologous strains of influenza virus

Residual baculovirus in insect cell-derived influenza virus-like particle preparations enhances immunogenicity

Influenza virus-like particles are currently evaluated in clinical trials as vaccine candidates for influenza viruses. Most commonly they are produced in baculovirus- or mammalian- expression systems. Here we used different vaccination schemes in order to systematically compare virus-like particle preparations generated in the two systems. Our work shows significant differences in immunogenicity between the two, and indicates superior and broader immune responses induced by the baculovirus-derived constructs. We demonstrate that these differences critically influence protection and survival in a mouse model of influenza virus infection. Finally, we show that the enhanced immunogenicity of the baculovirus-derived virus-like particles is caused by contamination with residual baculovirus which activates the innate immune response at the site of inoculation.

Protective efficacy of baculovirus-derived influenza virus-like particles bearing H5 HA alone or in combination with M1 in chickens

Since 2003, the highly pathogenic avian influenza (HPAI) H5N1 has become a serious problem in animals and an increasing threat to public health. To develop effective vaccines for H5 HPAI in chickens, virus-like particles (VLP) were produced using a baculovirus expression system. The particles comprised hemagglutinin (HA) alone (HA-VLP) or HA in combination with a matrix protein (M1; HAM-VLP) derived from a recent clade 2.3.2.1 H5N1 HPAI virus. To compare the immunogenicity and protective efficacy of these VLPs, 10 μg HAM-VLP, the equivalent amounts of HA incorporated HA-VLP or whole inactivated virus (WIV), were emulsified with mineral oil and used to immunize chickens. The serum hemagglutination inhibition antibody levels induced by HA-VLP and HAM-VLP were comparable to WIV. Antibodies to nucleoprotein were detected only in the WIV group. Immunized chickens in each group survived and were protected against a lethal homologous virus challenge, showing no clinical signs of infection. The challenge virus was detected intermittently in some oropharyngeal swabs, but not in cloacal swabs or various organs, which means that VLPs and WIV provide protection against systemic but not local virus replication in chickens. After the challenge, the HA-VLP group showed significantly increased serum antibody levels compared to the HAM-VLP and WIV groups, and some chickens in the HA-VLP group seroconverted with respect to nucleoprotein. Taken together, these results suggest that VLPs may be an effective method for controlling HPAI in chickens. They could be applied to a differentiating infected from vaccinated animals (DIVA) strategy. In addition, it is likely that HAM-VLP is more efficacious than HA-VLP in chickens.

Protection against a lethal H5N1 influenza challenge by intranasal immunization with virus-like particles containing 2009 pandemic H1N1 neuraminidase in mice

Highly pathogenic H5N1 influenza shares the same neuraminidase (NA) subtype with the 2009 pandemic (H1N1pdm09), and cross-reactive NA immunity might protect against or mitigate lethal H5N1 infection. In this study, mice were either infected with a sublethal dose of H1N1pdm09 or were vaccinated and boosted with virus-like particles (VLP) consisting of the NA and matrix proteins, standardized by NA activity and administered intranasally, and were then challenged with a lethal dose of HPAI H5N1 virus. Mice previously infected with H1N1pdm09 survived H5N1 challenge with no detectable virus or respiratory tract pathology on day 4. Mice immunized with H5N1 or H1N1pdm09 NA VLPs were also fully protected from death, with a 100-fold and 10-fold reduction in infectious virus, respectively, and reduced pathology in the lungs. Human influenza vaccines that elicit not only HA, but also NA immunity may provide enhanced protection against the emergence of seasonal and pandemic viruses.

Long-term vaccine-induced heterologous protection against H5N1 influenza viruses in the ferret model

Please cite this paper as: Ducatez et al. (2012) Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model. Influenza and Other Respiratory Viruses 7(4), 506–512.

Background  Highly pathogenic H5N1 influenza viruses reemerged in humans in 2003 and have caused fatal human infections in Asia and Africa as well as ongoing outbreaks in poultry. These viruses have evolved substantially and are now so antigenically varied that a single vaccine antigen may not protect against all circulating strains. Nevertheless, studies have shown that substantial cross‐reactivity can be achieved with H5N1 vaccines. These studies have not, however, addressed the issue of duration of such cross‐reactive protection.

Objectives  To directly address this using the ferret model, we used two recommended World Health Organization H5N1 vaccine seed strains – A/Vietnam/1203/04 (clade 1) and A/duck/Hunan/795/02 (clade 2.1) – seven single, double, or triple mutant viruses based on A/Vietnam/1203/04, and the ancestral viruses A and D, selected from sequences at nodes of the hemagglutinin and neuraminidase gene phylogenies to represent antigenically diverse progeny H5N1 subclades as vaccine antigens.

Results  All inactivated whole‐virus vaccines provided full protection against morbidity and mortality in ferrets challenged with the highly pathogenic H5N1 strain A/Vietnam/1203/04 5 months and 1 year after immunization.

Conclusion  If an H5N1 pandemic was to arise, and with the hypothesis that one can extrapolate the results from three doses of a whole‐virion vaccine in ferrets to the available split vaccines for use in humans, the population could be efficiently immunized with currently available H5N1 vaccines, while the homologous vaccine is under production.

Protective effect of Korean red ginseng extract on the infections by H1N1 and H3N2 influenza viruses in mice

Ginseng has been used in humans for thousands of years and is known to have multiple biological and immunomodulatory effects. In this study, we investigated whether Korean red ginseng extract would have preventive and antiviral effects on influenza virus infection. Oral administration to mice of red ginseng extract prior to infection significantly increased survival after infection with the 2009 pandemic H1N1 virus. Daily oral treatment of vaccinated mice with red ginseng extract provided enhanced cross-protection against antigenically distinct H1N1 and H3N2 influenza viruses. Naive mice that were infected with virus mixed with red ginseng extract showed significantly enhanced protection, lower levels of lung viral titers and interleukin-6, but higher levels of interferon-γ compared with control mice having virus infections without red ginseng extract, indicating an antiviral effect of ginseng. In addition, ginseng extract exhibited inhibitory effects on the growth of influenza virus in vitro. This study provides evidence that intake of ginseng extract will have beneficial effects on preventing lethal infection with newly emerging influenza viruses.

Protective efficacy of crude virus-like particle vaccine against HPAI H5N1 in chickens and its application on DIVA strategy

Background  Currently, Asian lineage highly pathogenic avian influenza (HPAI) H5N1 has become widespread across continents. These viruses are persistently circulating among poultry populations in endemic regions, causing huge economic losses, and raising concerns about an H5N1 pandemic. To control HPAI H5N1, effective vaccines for poultry are urgently needed.

Objective  In this study, we developed HPAI virus‐like particle (VLP) vaccine as a candidate poultry vaccine and evaluated its protective efficacy and possible application for differentiating infected from vaccinated animals (DIVA).

Methods  Specific pathogen‐free chickens received a single injection of HPAI H5N1 VLP vaccine generated using baculovirus expression vector system. Immunogenicity of VLP vaccines was determined using hemagglutination inhibition (HI), neuraminidase inhibition (NI), and ELISA test. Challenge study was performed to evaluate efficacy of VLP vaccines.

Results and Conclusions  A single immunization with HPAI H5N1 VLP vaccine induced high levels of HI and NI antibodies and protected chickens from a lethal challenge of wild‐type HPAI H5N1 virus. Viral excretion from the vaccinated and challenged group was strongly reduced compared with a mock‐vaccinated control group. Furthermore, we were able to differentiate VLP‐vaccinated chickens from vaccinated and then infected chickens with a commercial ELISA test kit, which offers a promising strategy for the application of DIVA concept.

Immunogenicity and protection of oral influenza vaccines formulated into microparticles

Influenza is a deadly disease affecting humans and animals. It is recommended that every individual should be vaccinated annually against influenza. Considering the frequency of administration of this vaccine, we have explored the oral route of vaccination with a microparticulate formulation. Microparticles containing inactivated influenza A/PR/34/8 H1N1 virus with Eudragit S and trehalose as a matrix were prepared using the Buchi spray dryer. Particle size distribution of microparticles was measured and the bioactivity of vaccine in a microparticle form was analyzed using a hemagglutination activity test. Furthermore, the efficacy of microparticle vaccines was evaluated in vivo in Balb/c mice. Analysis of serum samples showed that microparticles resulted in enhanced antigen-specific immunoglobulin G (IgG), IgG1, and IgG2a antibodies. Upon challenge with homologous and heterologous influenza viruses, microparticle vaccines showed significantly increased levels of protection. Use of microparticles to deliver vaccines could be a promising tool for the development of an oral influenza vaccine.

Influenza M1 VLPs containing neuraminidase induce heterosubtypic cross-protection

Influenza virus like particles (VLPs) containing hemagglutinin were previously demonstrated to induce protection against the homologous strains. However, little information is available on the protective role of neuraminidase (NA), the second major glycoprotein. In this study, we developed VLPs (NA VLPs) containing NA and M1 derived from A/PR/8/34 (H1N1) influenza virus, and investigated their ability to induce protective immunity. Intranasal immunization with NA VLPs induced serum antibody responses to H1N1 and H3N2 influenza A viruses as well as significant neuraminidase inhibition activity. Importantly, mice immunized with NA VLPs were 100% protected against lethal infection by the homologous A/PR/8/34 (H1N1) as well as heterosubtypic A/Philippines/82 (H3N2) virus, although body weight loss was observed after lethal challenge with heterosubtypic H3N2 virus. The present study therefore provides evidence that influenza VLPs containing M1 and NA are capable of inducing immunity to homologous as well as antigenically distinct influenza A virus strains.

Developments of subunit and VLP vaccines against influenza A virus

Influenza virus is a continuous and severe global threat to mankind. The continuously re-emerging disease gives rise to thousands of deaths and enormous economic losses each year, which emphasizes the urgency and necessity to develop high-quality influenza vaccines in a safer, more efficient and economic way. The influenza subunit and VLP vaccines, taking the advantage of recombinant DNA technologies and expression system platforms, can be produced in such an ideal way. This review summarized the recent advancements in the research and development of influenza subunit and VLP vaccines based on the recombinant expression of hemagglutinin antigen (HA), neuraminidase antigen (NA), Matrix 2 protein (M2) and nucleocapsid protein (NP). It would help to get insight into the current stage of influenza vaccines, and suggest the future design and development of novel influenza vaccines.

Enhanced influenza virus-like particle vaccines containing the extracellular domain of matrix protein 2 and a Toll-like receptor ligand

The extracellular domain of matrix protein 2 (M2e) is conserved among influenza A viruses. The goal of this project is to develop enhanced influenza vaccines with broad protective efficacy using the M2e antigen. We designed a membrane-anchored fusion protein by replacing the hyperimmunogenic region of Salmonella enterica serovar Typhimurium flagellin (FliC) with four repeats of M2e (4.M2e-tFliC) and fusing it to a membrane anchor from influenza virus hemagglutinin (HA). The fusion protein was incorporated into influenza virus M1-based virus-like particles (VLPs). These VLPs retained Toll-like receptor 5 (TLR5) agonist activity comparable to that of soluble FliC. Mice immunized with the VLPs by either intramuscular or intranasal immunization showed high levels of systemic M2-specific antibody responses compared to the responses to soluble 4.M2e protein. High mucosal antibody titers were also induced in intranasally immunized mice. All intranasally immunized mice survived lethal challenges with live virus, while intramuscularly immunized mice showed only partial protection, revealing better protection by the intranasal route. These results indicate that a combination of M2e antigens and TLR ligand adjuvants in VLPs has potential for development of a broadly protective influenza A virus vaccine.

Development of an enzyme-linked immunoassay for the quantitation of influenza haemagglutinin: an alternative method to single radial immunodiffusion

Please cite this paper as: Bodle et al. (2013) Development of an enzyme‐linked immunoassay for the quantitation of influenza haemagglutinin: an alternative method to single radial immunodiffusion. Influenza and Other Respiratory Viruses 7(2) 191–200.

Background  The current method used to measure haemagglutinin (HA) content for influenza vaccine formulation, single radial immunodiffusion (SRID), is lengthy and relies on the availability of matched standardised homologous reagents. The 2009 influenza pandemic highlighted the need to develop alternate assays that are able to rapidly quantitate HA antigen for vaccine formulation.

Objectives  The aim of this work was to develop an enzyme‐linked immunoassay (EIA) for the rapid quantitation of H1, H3, H5 and B influenza HA antigens.

Methods  Monoclonal antibodies (mAbs) selected for haemagglutination inhibition (HAI) activity were conjugated with horseradish peroxidase and used to establish a capture–detection EIA for the quantitation of HA antigen. Results were compared with the appropriate reference SRID assays to investigate assay performance and utility.

Results  Quantitation of HA antigen by EIA correlated well with current reference SRID assays. EIA results showed equivalent precision and exhibited a similar capacity to detect HA antigen in virus samples that had been used in either stability or splitting studies, or subjected to physical or chemical stresses. EIA exhibited greater sensitivity than SRID and has the potential to be used in high‐throughput applications.

Conclusions  We demonstrated the utility of EIA as a suitable alternative to SRID for HA antigen quantitation and stability assessment. This approach would lead to earlier availability of both seasonal and pandemic vaccines, because of the extended cross‐reactivity of reagents.

DNA vaccination in the skin using microneedles improves protection against influenza

In this study, we tested the hypothesis that DNA vaccination in the skin using microneedles improves protective immunity compared to conventional intramuscular (i.m.) injection of a plasmid DNA vaccine encoding the influenza hemagglutinin (HA). In vivo fluorescence imaging demonstrated the expression of a reporter gene delivered to the skin using a solid microneedle patch coated with plasmid DNA. Vaccination at a low dose (3 µg HA DNA) using microneedles generated significantly stronger humoral immune responses and better protective responses post-challenge compared to i.m. vaccination at either low or high (10 µg HA DNA) dose. Vaccination using microneedles at a high (10 µg) dose further generated improved post-challenge protection, as measured by survival, recall antibody-secreting cell responses in spleen and bone marrow, and interferon (IFN)-γ cytokine T-cell responses. This study demonstrates that DNA vaccination in the skin using microneedles induces higher humoral and cellular immune responses as well as improves protective immunity compared to conventional i.m. injection of HA DNA vaccine.

Increased immunogenicity of avian influenza DNA vaccine delivered to the skin using a microneedle patch

Effective public health responses to an influenza pandemic require an effective vaccine that can be manufactured and administered to large populations in the shortest possible time. In this study, we evaluated a method for vaccination against avian influenza virus that uses a DNA vaccine for rapid manufacturing and delivered by a microneedle skin patch for simplified administration and increased immunogenicity. We prepared patches containing 700-μm long microneedles coated with an avian H5 influenza hemagglutinin DNA vaccine from A/Viet Nam/1203/04 influenza virus. The coating DNA dose increased with DNA concentration in the coating solution and the number of dip-coating cycles. Coated DNA was released into the skin tissue by dissolution within minutes. Vaccination of mice using microneedles induced higher levels of antibody responses and hemagglutination inhibition titers, and improved protection against lethal infection with avian influenza as compared to conventional intramuscular delivery of the same dose of the DNA vaccine. Additional analysis showed that the microneedle coating solution containing carboxymethylcellulose and a surfactant may have negatively affected the immunogenicity of the DNA vaccine. Overall, this study shows that DNA vaccine delivery by microneedles can be a promising approach for improved vaccination to mitigate an influenza pandemic.

H5N1 influenza virus-like particles produced by transient expression in mammalian cells induce humoral and cellular immune responses in mice

Vaccination is an effective way to protect from influenza virus infection. Among the new candidates of influenza vaccines, influenza virus-like particles (VLPs) seem to be promising. Here, we generated 2 types of H5N1 influenza VLPs by co-expressing influenza virus Env (envelope protein) and murine leukemia virus (MLV) Gag–Pol. VLPs generated by co-transfection of pHCMV-wtH5 or pHCMV-mtH5 with pSV-Mo-MLVgagpol and pHCMV-N1 were named as wtH5N1 VLPs or mtH5N1 VLPs. The plasmid of pHCMV-wtH5 encoded the wild-type hemagglutinin (HA) (wtH5) from A/swine/Anhui/ca/2004 (H5N1) with a multibasic cleavage site, while pHCMV-mtH5 encoded the modified mutant-type (mtH5) with a monobasic cleavage site. Influenza virus HA VLPs were characterized and equal amounts of them were used to immunize mice subcutaneously, intraperitoneally, or intramuscularly. The levels of HA-specific IgG1, IFN-γ, and neutralization antibodies were significantly induced in mice immunized with wtH5N1 VLPs or mtH5N1 VLPs via all 3 routes, while HA-specific IgG2a was barely detectable. IL-4 secretion was detected in mice subcutaneously immunized with wtH5N1 VLPs or mtH5N1 VLPs, or intramuscularly immunized with mtH5N1 VLPs. Our results indicated that both H5N1 influenza VLPs could induce specific humoral and cellular immune responses in immunized mice. In conclusion, our study provides helpful information for designing new candidate vaccines against H5N1 influenza viruses.

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.

Protective effect of ginseng polysaccharides on influenza viral infection

Ginseng polysaccharide has been known to have multiple immunomodulatory effects. In this study, we investigated whether Panax ginseng polysaccharide (GP) would have a preventive effect on influenza infection. Administration of mice with GP prior to infection was found to confer a survival benefit against infection with H1N1 (A/PR/8/34) and H3N2 (A/Philippines/82) influenza viruses. Mice infected with the 2009 H1N1 virus suspended in GP solution showed moderately enhanced survival rates and lower levels of lung viral titers and the inflammatory cytokine (IL-6). Daily treatment of vaccinated mice with GP improved their survival against heterosubtypic lethal challenge. This study demonstrates the first evidence that GP can be used as a remedy against influenza viral infection.

Virus-like particle (VLP)-based vaccines for pandemic influenza: performance of a VLP vaccine during the 2009 influenza pandemic

The influenza pandemic of 2009 demonstrated the inability of the established global capacity for egg-based vaccine production technology to provide sufficient vaccine for the population in a timely fashion. Several alternative technologies for developing influenza vaccines have been proposed, among which non-replicating virus-like particles (VLPs) represent an attractive option because of their safety and immunogenic characteristics. VLP vaccines against pandemic influenza have been developed in tobacco plant cells and in Sf9 insect cells infected with baculovirus that expresses protein genes from pandemic influenza strains. These technologies allow rapid and large-scale production of vaccines (3-12 weeks). The 2009 influenza outbreak provided an opportunity for clinical testing of a pandemic influenza VLP vaccine in the midst of the outbreak at its epicenter in Mexico. An influenza A(H1N1)2009 VLP pandemic vaccine (produced in insect cells) was tested in a phase II clinical trial involving 4,563 healthy adults. Results showed that the vaccine is safe and immunogenic despite high preexisting anti-A(H1N1)2009 antibody titers present in the population. The safety and immunogenicity profile presented by this pandemic VLP vaccine during the outbreak in Mexico suggests that VLP technology is a suitable alternative to current influenza vaccine technologies for producing pandemic and seasonal 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.

Stability of influenza vaccine coated onto microneedles

A microneedle patch coated with vaccine simplifies vaccination by using a patch-based delivery method and targets vaccination to the skin for superior immunogenicity compared to intramuscular injection. Previous studies of microneedles have demonstrated effective vaccination using freshly prepared microneedles, but the issue of long-term vaccine stability has received only limited attention. Here, we studied the long-term stability of microneedles coated with whole inactivated influenza vaccine guided by the hypothesis that crystallization and phase separation of the microneedle coating matrix damages influenza vaccine coated onto microneedles. In vitro studies showed that the vaccine lost stability as measured by hemagglutination activity in proportion to the degree of coating matrix crystallization and phase separation. Transmission electron microscopy similarly showed damaged morphology of the inactivated virus vaccine associated with crystallization. In vivo assessment of immune response and protective efficacy in mice further showed reduced vaccine immunogenicity after influenza vaccination using microneedles with crystallized or phase-separated coatings. This work shows that crystallization and phase separation of the dried coating matrix are important factors affecting long-term stability of influenza vaccine-coated microneedles.

Co-expression vs. co-infection using baculovirus expression vectors in insect cell culture: Benefits and drawbacks

The baculovirus expression vector system (BEVS) is a versatile and powerful platform for protein expression in insect cells. With the ability to approach similar post-translational modifications as in mammalian cells, the BEVS offers a number of advantages including high levels of expression as well as an inherent safety during manufacture and of the final product. Many BEVS products include proteins and protein complexes that require expression from more than one gene. This review examines the expression strategies that have been used to this end and focuses on the distinguishing features between those that make use of single polycistronic baculovirus (co-expression) and those that use multiple monocistronic baculoviruses (co-infection). Three major areas in which researchers have been able to take advantage of co-expression/co-infection are addressed, including compound structure-function studies, insect cell functionality augmentation, and VLP production. The core of the review discusses the parameters of interest for co-infection and co-expression with time of infection (TOI) and multiplicity of infection (MOI) highlighted for the former and the choice of promoter for the latter. In addition, an overview of modeling approaches is presented, with a suggested trajectory for future exploration. The review concludes with an examination of the gaps that still remain in co-expression/co-infection knowledge and practice.

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.

Baculovirus-produced influenza virus-like particles in mammalian cells protect mice from lethal influenza challenge

Influenza virus-like particles (VLPs) are effective vaccines against influenza infection, which can be produced either in insect cells by recombinant baculovirus (BV) infection or in mammalian cells by DNA plasmid transfection. However, VLPs produced from baculovirus/insect cells are difficult to purify due to baculovirus contamination; VLPs produced by plasmid transfection are limited by scale-up capability. In this study, a BacMam BV, in which three CMV-promoters drive the hemagglutinin, neuraminidase, and matrix of influenza virus was constructed. This baculovirus can deliver these genes into mammalian cells/hosts and subsequently influenza VLPs can be produced and secreted from transduced cells. Transduction conditions were optimized and influenza VLPs were purified from transduced 293T cells. Mice were vaccinated with BV transduction-produced VLPs, plasmid transfection-produced VLPs, and BacMam BV. Two vaccinations of each vaccine induced high hemagglutination-inhibition (HAI) titers and prevented influenza virus infection. In contrast, following a single vaccination, all mice vaccinated with each vaccine had significantly lower lung viral titers compared to unvaccinated mice. Remarkably, mice vaccinated with a single dose of BV transduction-produced VLPs survived challenge, whereas mice vaccinated with one dose of BacMam BV- or plasmid transfection-produced VLPs had 60-80% survival. This finding is particularly significant for producing easily purified VLPs. The BacMam system is an alternative strategy for VLP production, which is easy to scale up and purify. Besides, BacMam BV can be used as a gene delivery vector to produce VLPs in vivo, to stimulate immune responses.

Viruslike particle vaccine induces protection against respiratory syncytial virus infection in mice

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral death in infants. Despite decades of research with traditional or subunit vaccine approaches, there are no approved RSV vaccines. New approaches are therefore urgently needed to develop effective RSV vaccines.

METHODS

We developed viruslike particles (VLPs) consisting of an influenza virus matrix (M1) protein core and RSV-F or -G on the surface. We tested the immunogenicity and vaccine efficacy of these VLPs (RSV-F, RSV-G) in a mouse model.

RESULTS

Intramuscular vaccination with RSV-F or RSV-G VLPs elicited IgG2a dominant RSV-specific immunoglobulin G (IgG) antibody responses against RSV-A2 viruses in both serum and lung extract. Mice immunized with VLPs (RSV-F or RSV-G) showed higher viral neutralizing antibodies in vitro and significantly decreased lung virus loads in vivo after live RSV-A2 challenge. RSV-G VLPs showed better protective efficacy than RSV-F VLPs as determined by the levels of lung virus loads and morbidity postchallenge.

CONCLUSIONS

This study demonstrates that VLP vaccination provides effective protection against RSV infection. VLPs containing RSV-F and/or RSV-G are potential vaccine candidates against RSV.

Oral vaccination with inactivated influenza vaccine induces cross-protective immunity

Oral vaccination would provide an easy and safe measure to prevent infectious diseases by facilitating mass immunization. We investigated the feasibility of oral vaccination with inactivated whole influenza virus (A/PR8/34). Oral vaccination of mice induced high levels of serum IgG and IgA antibodies specific to the homologous virus (A/PR8) as well as cross reactive to heterologous (A/California/04/09) and heterosubtypic viruses (A/Philippines/2/82). IgG1 isotype antibodies were found to be induced at significantly higher levels than IgG2a antibodies. These antibodies induced by oral vaccination exhibited hemagglutination inhibition activities. High levels of both IgG and IgA antibodies were induced in vagina and lungs. Mucosal IgA antibodies were also elicited in other sites including saliva, urine, and fecal samples. Orally vaccinated mice were completely protected against challenge with homologous or heterologous viruses, and partially protected against heterosubtypic virus. Importantly, high recall antibody secreting cell (ASC) responses were induced in spleen, indicating the generation of memory B cells by oral vaccination. The present study therefore presents new findings of cross-reactive antibodies at systemic and diverse mucosal sites, recall antibody responses, and cross-protective efficacies by oral vaccination, thus supporting a proof-of-concept that oral delivery of vaccines can be developed as an effective vaccination route.

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.

Understanding original antigenic sin in influenza with a dynamical system

Original antigenic sin is the phenomenon in which prior exposure to an antigen leads to a subsequent suboptimal immune response to a related antigen. Immune memory normally allows for an improved and rapid response to antigens previously seen and is the mechanism by which vaccination works. I here develop a dynamical system model of the mechanism of original antigenic sin in influenza, clarifying and explaining the detailed spin-glass treatment of original antigenic sin. The dynamical system describes the viral load, the quantities of healthy and infected epithelial cells, the concentrations of naïve and memory antibodies, and the affinities of naïve and memory antibodies. I give explicit correspondences between the microscopic variables of the spin-glass model and those of the present dynamical system model. The dynamical system model reproduces the phenomenon of original antigenic sin and describes how a competition between different types of B cells compromises the overall effect of immune response. I illustrate the competition between the naïve and the memory antibodies as a function of the antigenic distance between the initial and subsequent antigens. The suboptimal immune response caused by original antigenic sin is observed when the host is exposed to an antigen which has intermediate antigenic distance to a second antigen previously recognized by the host's immune system.

MyD88 plays an essential role in inducing B cells capable of differentiating into antibody-secreting cells after vaccination

We investigated the roles of MyD88, an innate adaptor signaling molecule, in inducing protective humoral immunity after vaccination with influenza virus-like particles (VLPs). MyD88 knockout C57BL/6 mice (MyD88(-/-) mice) vaccinated with influenza VLPs showed significant defects in inducing IgG2a/c isotype antibodies and in generating splenic recall memory B cell responses and antibody-secreting plasma cells in the bone marrow. The protective efficacy of influenza VLP vaccination was lower in MyD88(-/-) mice than in the wild-type mice. Our findings indicate that MyD88-mediated innate signaling pathways are important for effectively inducing primary and boost immune responses, T helper type 1 isotype-switched antibodies, and gamma interferon (IFN-γ)-secreting T cell responses. In particular, the results in this study demonstrated for the first time that MyD88-mediated immune activation is likely an essential pathway for effective generation of long-lived antibody-secreting plasma cells and highly protective immunity after vaccination with influenza VLPs. This study provides insight into mechanisms by which recombinant viral vaccines induce protective immunity via the MyD88-mediated innate immune signaling pathway.

Natural killer cell memory

Natural killer (NK) cells are bone marrow–derived granular lymphocytes that have a key role in immune defense against viral and bacterial infections and malignancies. NK cells are traditionally defined as cells of the innate immune response because they lack RAG recombinase–dependent clonal antigen receptors. However, evidence suggests that specific subsets of mouse NK cells can nevertheless develop long-lived and highly specific memory to a variety of antigens. Here we review published evidence of NK cell–mediated, RAG-independent adaptive immunity. We also compare and contrast candidate mechanisms for mammalian NK cell memory and antigen recognition with other examples of RAG-independent pathways that generate antigen receptor diversity in non-mammalian species and discuss NK cell memory in the context of lymphocyte evolution.

Immunogenicity of low-pH treated whole viral influenza vaccine

Low pH treatment of influenza virus hemagglutinin (HA) exposes its relatively conserved stalk domain, suggesting a potential immunogen with capability to induce broader immune responses. Here, we describe characterization, immunogenicity, antigenicity, and protective immunity induced by low pH treated inactivated whole viral vaccine in comparison with the untreated vaccine. The acidic pH treated viral vaccine showed high susceptibility to proteolytic cleavage and low hemagglutination activity indicating conformational changes. Immunization of mice with low pH treated viral vaccine induced lower levels of homologous or heterologous virus-specific binding and neutralizing antibodies compared to the untreated vaccine. Also, low pH treated influenza viral antigen showed lower antigenicity compared to the untreated influenza viral antigen. Lower efficacy of cross-protection against heterosubtypic virus was observed in the low-pH treated vaccine group. The results provide evidence that there is a correlation between protective efficacy and the stability of vaccines.

Yellow fever virus envelope protein expressed in insect cells is capable of syncytium formation in lepidopteran cells and could be used for immunodetection of YFV in human sera

BACKGROUND

Yellow fever is an haemorrhagic disease caused by a virus that belongs to the genus Flavivirus (Flaviviridae family) and is transmitted by mosquitoes. Among the viral proteins, the envelope protein (E) is the most studied one, due to its high antigenic potencial. Baculovirus are one of the most popular and efficient eukaryotic expression system. In this study a recombinant baculovirus (vSynYFE) containing the envelope gene (env) of the 17D vaccine strain of yellow fever virus was constructed and the recombinant protein antigenicity was tested.

RESULTS

Insect cells infected with vSynYFE showed syncytium formation, which is a cytopathic effect characteristic of flavivirus infection and expressed a polypeptide of around 54 kDa, which corresponds to the expected size of the recombinant E protein. Furthermore, the recombinant E protein expression was also confirmed by fluorescence microscopy of vSynYFE-infected insect cells. Total vSynYFE-infected insect extracts used as antigens detected the presence of antibodies for yellow fever virus in human sera derived from yellow fever-infected patients in an immunoassay and did not cross react with sera from dengue virus-infected patients.

CONCLUSIONS

The E protein expressed by the recombinant baculovirus in insect cells is antigenically similar to the wild protein and it may be useful for different medical applications, from improved diagnosis of the disease to source of antigens for the development of a subunit vaccine.

H9N2 avian influenza virus-like particle vaccine provides protective immunity and a strategy for the differentiation of infected from vaccinated animals

In the present study, virus-like particles (VLPs) were evaluated as a candidate poultry vaccine against avian influenza virus (AIV) subtype H9N2. Specific pathogen-free chickens received a single injection of the VLP vaccine expressing HA and M1 protein of AIV H9N2 (H9 HA VLP) at escalating doses in the presence or absence of ISA70 water-in-oil adjuvant. At 3 weeks post vaccination, we performed hemagglutination inhibition (HI) test and enzyme-linked immunosorbent assay (ELISA) to determine serological immune responses, and challenge studies using SPF chickens. A single dose of H9 HA VLP vaccine induced high levels of HI antibodies and lowered frequencies of virus isolation after the wild-type virus challenge. The addition of ISA70 adjuvant significantly increased the immunogenicity of H9 HA VLP vaccines. Furthermore, it allows differentiation of AIV-infected chickens from vaccinated chickens with an ELISA using nucleocapsid antigen, which offers a promising strategy to differentiate infected from vaccinated animals (DIVA). These results provide support for continued development of the VLP as an animal vaccine against influenza virus.

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.

Enhanced mucosal immune responses to HIV virus-like particles containing a membrane-anchored adjuvant

Previously, a modified HIV Env protein with a heterologous membrane anchor was found to be incorporated into HIV virus-like particles (VLPs) at 10-fold-higher levels than those of unmodified Env. To further improve the immunogenicity of such VLPs, membrane-anchored forms of bacterial flagellin (FliC) or a flagellin with a truncated variable region (tFliC) were constructed to be incorporated into the VLPs as adjuvants. HIV-specific immune responses induced by the resulting VLPs were determined in a guinea pig model. The VLPs induce enhanced systemic antibody responses by either systemic or mucosal vaccination and enhanced mucosal immunity by a mucosal immunization route, as demonstrated by high levels of HIV-specific serum IgG and mucosal IgG and IgA. The quality of the antibody responses was also improved, as shown by enhanced neutralization capacity. VLPs incorporating FliC were more effective in inducing systemic responses, while VLPs containing tFliC were more effective in inducing mucosal IgA responses. The IgG titers in sera were found to last for at least 5 months without a significant drop. These results indicate that HIV VLPs incorporating high levels of Env and a molecular adjuvant have excellent potential for further development as a prophylactic HIV vaccine.

A prophylactic vaccine is urgently needed to control the spread of HIV/AIDS. Antigens inducing strong systemic and mucosal immune responses are promising as vaccines for this mucosally transmitted disease. We found that novel HIV virus-like particles (VLPs) presenting a high level of Env in its native membrane-bound form and coincorporating an innate immune-signaling adjuvant in the same particles were effective in inducing enhanced systemic and mucosal immunity. As new HIV vaccine candidates, these VLPs bridge the gaps of the innate and adaptive, as well as systemic and mucosal, immune responses, providing a new approach for HIV vaccine development.

Progress towards a universal influenza vaccine

Seasonal influenza is a common and highly transmissible disease, characterized by frequent and unpredictable mutations occurring in the viral envelope glycoproteins. Owing to this high variability, annual reformulation and immunization are required and still, the vaccine is not effective enough when there is an antigenic mismatch with circulating strains. A solution could come from the construction of a universal vaccine that would be based on highly conserved antigens and would be effective against many strains: some universal vaccine developers focus on the Matrix 2 protein, whereas others use additional conserved proteins, such as the nucleoprotein and Matrix 1, or even a range of peptides from these proteins and others to induce cross-strain immunity. This article aims to highlight recent significant advances in the development of a universal vaccine against influenza and focuses mainly on studies using the epitope-based approach that have also entered the clinical trial stage; it includes a brief summary of current vaccines against influenza as well as the ongoing efforts to develop a universal vaccine.

Superior neutralizing antibody response and protection in mice vaccinated with heterologous DNA prime and virus like particle boost against HPAI H5N1 virus

BACKGROUND

Although DNA plasmid and virus-like particle (VLP) vaccines have been individually tested against highly pathogenic avian influenza (HPAI) H5N1 viruses, the combination of both vaccines into a heterologous prime-boost strategy against HPAI H5N1 viruses has not been reported before.

METHODOLOGY/PRINCIPAL FINDINGS

We constructed DNA plasmid encoding H5HA (A/Shenzhen/406H/06, subclade 2.3.4) and generated VLP expressing the same H5HA and N1NA. We then compared neutralizing antibody responses and immune protection elicited with heterologous DNA-VLP, homologous DNA-DNA and VLP-VLP prime-boost strategies against HPAI H5N1 viruses in mice. We demonstrate that DNA-VLP elicits the highest neutralizing antibody titers among the three prime-boost strategies, whereas DNA-DNA elicits higher neutralizing antibody titers than VLP-VLP. We show that although all three prime-boost strategies protect mice from death caused by 10 MLD(50) of homologous and heterologous H5N1 challenge, only DNA-VLP and DNA-DNA protect mice from infection as manifested by no weight loss and no lung pathology. In addition, we show that although DNA-VLP and DNA-DNA protect mice from death caused by 1,000 MLD(50) of homologous H5N1 challenge, only DNA-VLP protects mice from infection. Moreover, we show that after 1,000 MLD(50) of heterologous H5N1 challenge, while all mice in PBS, VLP-VLP and DNA-DNA died, 3 of 6 mice in DNA-VLP actually survived. Finally, we show that DNA-VLP completely protects mice from infection after 1,000 MLD(50) of homologous H5N1 challenge even when the challenge was administrated at 60 days post the boost.

CONCLUSIONS/SIGNIFICANCE

These results provide strong support for clinical evaluation of heterologous DNA-VLP prime-boost strategy as a public health intervention against a possible H5N1 pandemic.

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.

Influenza virus-like particles containing M2 induce broadly cross protective immunity

Background

Current influenza vaccines based on the hemagglutinin protein are strain specific and do not provide good protection against drifted viruses or emergence of new pandemic strains. An influenza vaccine that can confer cross-protection against antigenically different influenza A strains is highly desirable for improving public health.

Methodology/Principal Findings

To develop a cross protective vaccine, we generated influenza virus-like particles containing the highly conserved M2 protein in a membrane-anchored form (M2 VLPs), and investigated their immunogenicity and breadth of cross protection. Immunization of mice with M2 VLPs induced anti-M2 antibodies binding to virions of various strains, M2 specific T cell responses, and conferred long-lasting cross protection against heterologous and heterosubtypic influenza viruses. M2 immune sera were found to play an important role in providing cross protection against heterosubtypic virus and an antigenically distinct 2009 pandemic H1N1 virus, and depletion of dendritic and macrophage cells abolished this cross protection, providing new insight into cross-protective immune mechanisms.

Conclusions/Significance

These results suggest that presenting M2 on VLPs in a membrane-anchored form is a promising approach for developing broadly cross protective influenza vaccines.

Vaccination inducing broad and improved cross protection against multiple subtypes of influenza A virus

Development of an influenza vaccine that provides broadly cross-protective immunity has been a scientific challenge for more than half a century. This study presents an approach to overcome strain-specific protection by supplementing conventional vaccines with virus-like particles (VLPs) containing the conserved M2 protein (M2 VLPs) in the absence of adjuvants. We demonstrate that an inactivated influenza vaccine supplemented with M2 VLPs prevents disease symptoms without showing weight loss and confers complete cross protection against lethal challenge with heterologous influenza A viruses including the 2009 H1N1 pandemic virus as well as heterosubtypic H3N2 and H5N1 influenza viruses. Cross-protective immunity was long-lived, for more than 7 mo. Immune sera from mice immunized with M2 VLP supplemented vaccine transferred cross protection to naive mice. Dendritic and macrophage cells were found to be important for this cross protection mediated by immune sera. The results provide evidence that supplementation of seasonal influenza vaccines with M2 VLPs is a promising approach for overcoming the limitation of strain-specific protection by current vaccines and developing a universal influenza A vaccine.

Intranasal immunization with influenza VLPs incorporating membrane-anchored flagellin induces strong heterosubtypic protection

We demonstrated previously that the incorporation of a membrane-anchored form of flagellin into influenza virus-like particles (VLPs) improved the immunogenicity of VLPs significantly, inducing partially protective heterosubtypic immunity by intramuscular immunization. Because the efficacy of mucosal vaccination is highly dependent on an adjuvant, and is particularly effective for preventing mucosal infections such as influenza, we determined whether the membrane-anchored flagellin is an efficient adjuvant for VLP vaccines by a mucosal immunization route. We compared the adjuvant effect of membrane-anchored and soluble flagellins for immunization with influenza A/PR8 (H1N1) VLPs by the intranasal route in a mouse model. The results demonstrate that membrane-anchored flagellin is an effective adjuvant for intranasal (IN) immunization, inducing enhanced systemic and mucosal antibody responses. High cellular responses were also observed as shown by cytokine production in splenocyte cultures when stimulated with viral antigens. All mice immunized with flagellin-containing VLPs survived challenge with a high lethal dose of homologous virus as well as a high dose heterosubtypic virus challenge (40 LD₅₀ of A/Philippines/82, H3N2). In contrast, no protection was observed with a standard HA/M1 VLP group upon heterosubtypic challenge. Soluble flagellin exhibited a moderate adjuvant effect when co-administered with VLPs by the mucosal route, as indicated by enhanced systemic and mucosal responses and partial heterosubtypic protection. The membrane-anchored form of flagellin incorporated together with antigen into influenza VLPs is effective as an adjuvant by the mucosal route and unlike standard VLPs, immunization with such chimeric VLPs elicits protective immunity to challenge with a distantly related influenza A virus.

Critical role for the chemokine receptor CXCR6 in NK cell-mediated antigen-specific memory of haptens and viruses

Hepatic natural killer (NK) cells mediate antigen-specific contact hypersensitivity (CHS) in mice deficient in T cells and B cells. We report here that hepatic NK cells, but not splenic or naive NK cells, also developed specific memory of vaccines containing antigens from influenza, vesicular stomatitis virus (VSV) or human immunodeficiency virus type 1 (HIV-1). Adoptive transfer of virus-sensitized NK cells into naive recipient mice enhanced the survival of the mice after lethal challenge with the sensitizing virus but not after lethal challenge with a different virus. NK cell memory of haptens and viruses depended on CXCR6, a chemokine receptor on hepatic NK cells that was required for the persistence of memory NK cells but not for antigen recognition. Thus, hepatic NK cells can develop adaptive immunity to structurally diverse antigens, an activity that requires NK cell-expressed CXCR6.

Induction of a cross-reactive CD8(+) T cell response following foot-and-mouth disease virus vaccination

Foot-and-mouth disease virus (FMDV) causes a highly contagious infection in cloven-hoofed animals. Current inactivated FMDV vaccines generate short-term, serotype-specific protection, mainly through neutralizing antibody. An improved understanding of the mechanisms of protective immunity would aid design of more effective vaccines. We have previously reported the presence of virus-specific CD8(+) T cells in FMDV-vaccinated and -infected cattle. In the current study, we aimed to identify CD8(+) T cell epitopes in FMDV recognized by cattle vaccinated with inactivated FMDV serotype O. Analysis of gamma interferon (IFN-γ)-producing CD8(+) T cells responding to stimulation with FMDV-derived peptides revealed one putative CD8(+) T cell epitope present within the structural protein P1D, comprising residues 795 to 803 of FMDV serotype O UKG/2001. The restricting major histocompatibility complex (MHC) class I allele was N*02201, expressed by the A31 haplotype. This epitope induced IFN-γ release, proliferation, and target cell killing by αβ CD8(+) T cells, but not CD4(+) T cells. A protein alignment of representative samples from each of the 7 FMDV serotypes showed that the putative epitope is highly conserved. CD8(+) T cells from FMDV serotype O-vaccinated A31(+) cattle recognized antigen-presenting cells (APCs) loaded with peptides derived from all 7 FMDV serotypes, suggesting that CD8(+) T cells recognizing the defined epitope are cross-reactive to equivalent peptides derived from all of the other FMDV serotypes.

Improved protection against avian influenza H5N1 virus by a single vaccination with virus-like particles in skin using microneedles

To develop a more effective vaccination method against H5N1 virus, we investigated the immunogenicity and protective efficacy after skin vaccination using microneedles coated with influenza virus-like particles containing hemagglutinin derived from A/Vietnam/1203/04 H5N1 virus (H5 VLPs). A single microneedle vaccination of mice with H5 VLPs induced increased levels of antibodies and provided complete protection against lethal challenge without apparent disease symptoms. In contrast, intramuscular injection with the same vaccine dose showed low levels of antibodies and provided only partial protection accompanied by severe body weight loss. Post-challenge analysis suggested that improved protection was associated with lower lung viral titers and enhanced generation of recall antibody secreting cells by microneedle vaccination. Thus, this study provides evidence that skin delivery of H5 VLP vaccines using microneedles designed for self-administration induces improved protection compared to conventional intramuscular immunization.

Trichoplusia ni cells (High Five) are highly efficient for the production of influenza A virus-like particles: a comparison of two insect cell lines as production platforms for influenza vaccines

Virus-like particles (VLPs) consisting of the influenza A virus proteins haemagglutinin (HA) and matrix protein (M1) represent a new alternative approach for vaccine design against influenza virus. Influenza VLPs can be fast and easily produced in sufficient amounts in insect cells using the baculovirus expression system. Up to now, influenza VLPs have been produced in the Spodoptera frugiperda cell line Sf9. We compared VLP production in terms of yield and quality in two insect cell lines, namely Sf9 and the Trichoplusia ni cell line BTI-TN5B1-4 (High Five). Additionally we compared VLP production with three different HAs and two different M1s from influenza H1 and H3 strains including one swine-origin pandemic H1N1 strain. Comparison of the two cell lines showed dramatic differences in baculovirus background as well as in yield and particle density. Taken together, we consider the establishment of the BTI-TN5B1-4 cell line advantageous as production cell line for influenza VLPs.

Formulation of microneedles coated with influenza virus-like particle vaccine

Mortality due to seasonal and pandemic influenza could be reduced by increasing the speed of influenza vaccine production and distribution. We propose that vaccination can be expedited by (1) immunizing with influenza virus-like particle (VLP) vaccines, which are simpler and faster to manufacture than conventional egg-based inactivated virus vaccines, and (2) administering vaccines using microneedle patches, which should simplify vaccine distribution due to their small package size and possible self-administration. In this study, we coated microneedle patches with influenza VLP vaccine, which was released into skin by dissolution within minutes. Optimizing the coating formulation required balancing factors affecting the coating dose and vaccine antigen stability. Vaccine stability, as measured by an in vitro hemagglutination assay, was increased by formulation with increased concentration of trehalose or other stabilizing carbohydrate compounds and decreased concentration of carboxymethylcellulose (CMC) or other viscosity-enhancing compounds. Coating dose was increased by formulation with increased VLP concentration, increased CMC concentration, and decreased trehalose concentration, as well as increased number of dip coating cycles. Finally, vaccination of mice using microneedles stabilized by trehalose generated strong antibody responses and provided full protection against high-dose lethal challenge infection. In summary, this study provides detailed analysis to guide formulation of microneedle patches coated with influenza VLP vaccine and demonstrates effective vaccination in vivo using this system.