Plasmids encoding foot-and-mouth disease virus VP1 epitopes elicited immune responses in mice and swine and protected swine against viral infection

Oral immunization against foot-and-mouth disease virus using recombinant Saccharomyces cerevisiae with the improved expression of the codon-optimized VP1 fusion protein

VP1, a major immunogenic protein of foot-and-mouth disease virus (FMDV), facilitates viral attachment and entry into host cells. VP1 possesses critical epitope sequences responsible for inducing neutralizing antibodies but its expression using Saccharomyces cerevisiae has been hampered despite evidence that the presence of VP1 does not negatively impact the yeast's biology. In this study, we fused proteins to enhance VP1 expression using S. cerevisiae. Among short P1 chimeras containing VP1 including VP3-VP1 and VP2-VP1, VP3-VP1 fusion proteins showed higher expression levels than VP2-VP1. We subsequently designed new fusion proteins, of which 20 amino acids of N-terminal VP3 fused with VP1-Co1 (referred to 20aaVP3-VP1-Co1) showed the highest expression level. Lowering the culture temperature from 30 ⁰C to 20 ⁰C further enhanced fusion protein production. The highest expression level of 20aaVP3-VP1-Co1 was estimated to be 7.7 mg/L, which is comparable to other heterologous proteins produced using our S. cerevisiae expression system. Oral administration of the cell expressing 20aaVP3-VP1-Co1 induced VP1-specific IgG and IgA responses in mice. The S. cerevisiae-expressed 20aaVP3-VP1-Co1 fusion protein induced a significant immune response to the FMDV structural epitope protein, which opens the possibility of an oral FMDV vaccine.

Chimeric Porcine Parvovirus VP2 Virus-like Particles with Epitopes of South African Serotype 2 Foot-and-Mouth Disease Virus Elicits Specific Humoral and Cellular Responses in Mice

Southern Africa Territories 2 (SAT2) foot-and-mouth disease (FMD) has crossed long-standing regional boundaries in recent years and entered the Middle East. However, the existing vaccines offer poor cross-protection against the circulating strains in the field. Therefore, there is an urgent need for an alternative design approach for vaccines in anticipation of a pandemic of SAT2 Foot-and-mouth disease virus (FMDV). The porcine parvovirus (PPV) VP2 protein can embed exogenous epitopes into the four loops on its surface, assemble into virus-like particles (VLPs), and induce antibodies and cytokines to PPV and the exogenous epitope. In this study, chimeric porcine parvovirus VP2 VLPs (chimeric PPV-SAT2-VLPs) expressing the T-and/or B-cell epitopes of the structural protein VP1 of FMDV SAT2 were produced using the recombinant pFastBac™ Dual vector of baculoviruses in Sf9 and HF cells We used the Bac-to-Bac system to construct the recombinant baculoviruses. The VP2-VLP--SAT2 chimeras displayed chimeric T-cell epitope (amino acids 21-40 of VP1) and/or the B-cell epitope (amino acids 135-174) of SAT FMDV VP1 by substitution of the corresponding regions at the N terminus (amino acids 2-23) and/or loop 2 and/or loop 4 of the PPV VP2 protein, respectively. In mice, the chimeric PPV-SAT2-VLPs induced specific antibodies against PPV and the VP1 protein of SAT2 FMDV. The VP2-VLP-SAT2 chimeras induced specific antibodies to PPV and the VP1 protein specific epitopes of FMDV SAT2. In this study, as a proof-of-concept, successfully generated chimeric PPV-VP2 VLPs expressing epitopes of the structural protein VP1 of FMDV SAT2 that has a potential to prevent FMDV SAT2 and PPV infection in pigs.

Evaluation of immunogenicity and cross-reactive responses of vaccines prepared from two chimeric serotype O foot-and-mouth disease viruses in pigs and cattle

Foot-and-mouth disease (FMD) remains a very serious barrier to agricultural development and the international trade of animals and animal products. Recently, serotype O has been the most prevalent FMDV serotype in China, and it has evolved into four different lineages: O/SEA/Mya-98, O/ME-SA/PanAsia, O/ME-SA/Ind-2001 and O/Cathay. PanAsia-2, belonging to the O/ME-SA topotype, is prevalent in neighbouring countries and poses the risk of cross-border spread in China. This study aimed to develop a promising vaccine candidate strain that can not only provide the best protection against all serotype O FMDVs circulating in China but also be used as an emergency vaccine for the prevention and control of transboundary incursion of PanAsia-2. Here, two chimeric FMDVs (rHN/TURVP1 and rHN/NXVP1) featuring substitution of VP1 genes of the O/TUR/5/2009 vaccine strain (PanAsia-2) and O/NXYCh/CHA/2018 epidemic strain (Mya98) were constructed and evaluated. The biological properties of the two chimeric FMDVs were similar to those of the wild-type (wt) virus despite slight differences in plaque sizes observed in BHK-21 cells. The structural protein-specific antibody titres induced by the rHN/TURVP1 and wt virus vaccines in pigs and cows were higher than those induced by the rHN/NXVP1 vaccine at 28–56 dpv. The vaccines prepared from the two chimeric viruses and wt virus all induced the production of protective cross-neutralizing antibodies against the viruses of the Mya-98, PanAsia and Ind-2001 lineages in pigs and cattle at 28 dpv; however, only the animals vaccinated with the rHN/TURVP1 vaccine produced a protective immune response to the field isolate of the Cathay lineage at 28 dpv, whereas the animals receiving the wt virus and the rHN/NXVP1 vaccines did not, although the wt virus and O/GXCX/CHA/2018 both belong to the Cathay topotype. This study will provide very useful information to help develop a potential vaccine candidate for the prevention and control of serotype O FMD in China.

Foot-and-mouth disease virus VP1 target the MAVS to inhibit type-I interferon signaling and VP1 E83K mutation results in virus attenuation

VP1, a pivotal capsid protein encoded by the foot-and-mouth disease virus (FMDV), plays an important role in receptor-mediated attachment and humoral immune responses. Previous studies show that amino acid changes in the VP1 protein of cell culture-adapted strains of FMDV alter the properties of the virus. In addition, FMDV VP1 modulates host IFN signal transduction. Here, we examined the ability of cell culture-adapted FMDV VP1(83K) and wild-type FMDV VP1(83E) to evade host immunity by blocking mitochondrial antiviral signaling protein (MAVS)/TNF Receptor Associated Factor 3 (TRAF3) mediated cellular innate responses. Wild-type FMDV VP1(83E) interacted specifically with C-terminal TRAF3-binding site within MAVS and this interaction inhibited binding of TRAF3 to MAVS, thereby suppressing interferon-mediated responses. This was not observed for cell culture-adapted FMDV VP1(83K). Finally, chimeric FMDV harboring VP1(83K) showed very low pathogenicity in pigs. Collectively, these data highlight a critical role of VP1 with respect to suppression of type-I IFN pathway and attenuation of FMDV by the E83K mutation in VP1.

Foot-and-Mouth disease (FMD), a highly contagious viral disease of cloven-hoofed animals, causes huge economic losses. To generate a FMD vaccine, cell culture-adapted strains of FMDV that show improved growth properties and allow repeated passage are needed. Generally, adaptation of field-isolated FMDV is accompanied by changes in viral properties, including amino acid mutations. A VP1 E83K mutation in cell culture-adapted FMDV was identified previously; here, we examined the impact of VP1 E83K on virus pathogenicity and type-I IFN pathway. Cell culture-adapted FMDV O1 Manisa, and highly virulent strain of O/Andong/SKR/2010, acquired the E83K mutation in the VP1 protein, which attenuated the virus via disposing VP1 mediate negative regulation ability of host cellular IFN responses. The data suggest a rational approach to viral propagation in cell culture and virus attenuation, which could be utilized for future development of FMDV vaccines.

Foot-and-Mouth Disease Virus: Immunobiology, Advances in Vaccines and Vaccination Strategies Addressing Vaccine Failures-An Indian Perspective

A mass vaccination campaign in India seeks to control and eventually eradicate foot-and-mouth disease (FMD). Biosanitary measures along with FMD monitoring are being conducted along with vaccination. The implementation of the FMD control program has drastically reduced the incidence of FMD. However, cases are still reported, even in regions where vaccination is carried out regularly. Control of FMD outbreaks is difficult when the virus remains in circulation in the vaccinated population. Various FMD risk factors have been identified that are responsible for FMD in vaccinated areas. The factors are discussed along with strategies to address these challenges. The current chemically inactivated trivalent vaccine formulation containing strains of serotype O, A, and Asia 1 has limitations including thermolability and induction of only short-term immunity. Advantages and disadvantages of several new-generation alternate vaccine formulations are discussed. It is unfeasible to study every incidence of FMD in vaccinated animals/areas in such a big country as India with its huge livestock population. However, at the same time, it is absolutely necessary to identify the precise reason for vaccination failure. Failure to vaccinate is one reason for the occurrence of FMD in vaccinated areas. FMD epidemiology, emerging and re-emerging virus strains, and serological status over the past 10 years are discussed to understand the impact of vaccination and incidences of vaccination failure in India. Other factors that are important in vaccination failure that we discuss include disrupted herd immunity, health status of animals, FMD carrier status, and FMD prevalence in other species. Recommendations to boost the search of alternate vaccine formulation, strengthen the veterinary infrastructure, bolster the real-time monitoring of FMD, as well as a detailed investigation and documentation of every case of vaccination failure are provided with the goal of refining the control program.

Development of a recombinant vaccine against foot and mouth disease utilizing mutant attenuated Listeria ivanovii strain as a live vector

The drawbacks of conventional inactivated Foot and Mouth Disease (FMD) vaccine, such as escaping of the virus during manufacture processes prompted researchers to explore novel types of vaccine to overcome these disadvantages. Listeria ivanovii (LI) is an intracellular microorganism that possesses immune-stimulatory properties, making it appropriate for use as a live bacterial vaccine vector. The Foot and mouth disease virus (FMDV) VP1 protein is the most immunogenic part of FMDV capsid, it has most of the antigenic sites for viral neutralization. The expression of antigen gene cassette in vitro was confirmed by Western blot analysis. Mice were able to eliminate LI△actAplcB-vp1 from the liver and spleen within few days revealed a safety of the candidate vaccine. Two doses of LI△actAplcB-vp1 with 14 days of interval were injected into mice. High levels of specific IgG antibodies and CD8⁺ and CD4⁺ T cells secreted cytokines including IFN-γ, TNF-α and IL-2 against FMDV-VP1 were achieved. Based on the obtained results, LI△actAplcB-vp1 candidate vaccine utilizing Listeria ivanovii as a live vector-based vaccine could enhance a specific cellular and humoral immune responses against the inserted FMDV-vp1 heterologous genes. LI△actAplcB-vp1 candidate vaccine could be a modern tool to overcome the disadvantages of the traditional inactivated FMD vaccine.

Virus-Like Particles as an Instrument of Vaccine Production

The paper discusses the techniques which are currently implemented for vaccine production based on virus-like particles (VLPs). The factors which determine the characteristics of VLP monomers assembly are provided in detail. Analysis of the literature demonstrates that the development of the techniques of VLP production and immobilization of target antigens on their surface have led to the development of universal platforms which make it possible for virtually any known antigen to be exposed on the particle surface in a highly concentrated form. As a result, the focus of attention has shifted from the approaches to VLP production to the development of a precise interface between the organism's immune system and the peptides inducing a strong immune response to pathogens or the organism's own pathological cells. Immunome-specified methods for vaccine design and the prospects of immunoprophylaxis are discussed. Certain examples of vaccines against viral diseases and cancers are considered.

Foot-and-mouth disease vaccines: recent updates and future perspectives

Foot-and-mouth disease (FMD) is a major worldwide viral disease in animals, affecting the national and international trade of livestock and animal products and leading to high economic losses and social consequences. Effective control measures of FMD involve prevention through vaccination with inactivated vaccines. These inactivated vaccines, unfortunately, require short-term protection and cold-chain and high-containment facilities. Major advances and pursuit of hot topics in vaccinology and vectorology are ongoing, involving peptide vaccines, DNA vaccines, live vector vaccines, and novel attenuated vaccines. DIVA capability and marker vaccines are very important in differentiating infected animals from vaccinated animals. This review focuses on updating the research progress of these novel vaccines, summarizing their merits and including ideas for improvement.

Expression of the VP1 protein of FMDV integrated chromosomally with mutant Listeria monocytogenes strain induced both humoral and cellular immune responses

Live vector-based vaccine is a modern approach to overcome the drawbacks of inactivated foot-and-mouth disease (FMD) vaccines such as improper inactivation during manufacture. Listeria monocytogenes (LM), an intracellular microorganism with immune-stimulatory properties, is appropriate to be utilized as a live bacterial vaccine vector. FMDV-VP1 protein has the capability to induce both cellular and humoral immune responses since it is considered the most immunogenic part of FMDV capsid and has the most of antigenic sites for viral neutralization. The codon-optimized vp1 gene was ligated to the integrative pCW702 plasmid to construct the target cassette. The antigen cassette was integrated successfully into the chromosome of mutant LM strain via homologous recombination for more stability to generate a candidate vaccine strain LM△actAplcB-vp1. Safety evaluation of recombinant LM△actAplcB-vp1 revealed it could be eliminated from the internal organs within 3 days as a safe candidate vaccine. Mice groups were immunized I.V. twice with the recombinant LM△actAplcB-vp1 at an interval of 2 weeks. Antigen-specific IgG antibodies and the level of CD4+- and CD8+-specific secreted cytokines were estimated to evaluate the immunogenicity of the candidate vaccine. The rapid onset immune response was detected, strong IgG humoral immune response within 14 days post immunization and augmented again after the booster dose. Cellular immunity data after 9 days post the prime dose indicated elevation in CD4+ and CD8+ secreted cytokine level with another elevation after the booster dose. This is the first report to explain the ability of attenuated mutant LM to be a promising live vector for FMDV vaccine.

Foot-and-mouth disease vaccines

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease affects many areas of the world, often causing extensive epizootics in livestock, mostly farmed cattle and swine, although sheep, goats and many wild species are also susceptible. In countries where food and farm animals are essential for subsistence agriculture, outbreaks of FMD seriously impact food security and development. In highly industrialized developed nations, FMD endemics cause economic and social devastation mainly due to observance of health measures adopted from the World Organization for Animal Health (OIE). High morbidity, complex host-range and broad genetic diversity make FMD prevention and control exceptionally challenging. In this article we review multiple vaccine approaches developed over the years ultimately aimed to successfully control and eradicate this feared disease.

Challenges of Generating and Maintaining Protective Vaccine-Induced Immune Responses for Foot-and-Mouth Disease Virus in Pigs

Vaccination can play a central role in the control of outbreaks of foot-and-mouth disease (FMD) by reducing both the impact of clinical disease and the extent of virus transmission between susceptible animals. Recent incursions of exotic FMD virus lineages into several East Asian countries have highlighted the difficulties of generating and maintaining an adequate immune response in vaccinated pigs. Factors that impact vaccine performance include (i) the potency, antigenic payload, and formulation of a vaccine; (ii) the antigenic match between the vaccine and the heterologous circulating field strain; and (iii) the regime (timing, frequency, and herd-level coverage) used to administer the vaccine. This review collates data from studies that have evaluated the performance of foot-and-mouth disease virus vaccines at the individual and population level in pigs and identifies research priorities that could provide new insights to improve vaccination in the future.

A novel delivery platform based on Bacteriophage MS2 virus-like particles

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Here we reviewed Bacteriophage MS2 virus-like particles, including introduction to their structure, their potential as a delivery platform, and their expected use in medicine and other fields.

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Bacteriophage MS2 virus-like particles represent the novel delivery platform.

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Bacteriophage MS2 virus-like particles possess promising application prospect.

Our objective here is to review the novel delivery platform based on Bacteriophage MS2 virus-like particles (VLPs), including introduction to their structure, their potential as a delivery platform, and their expected use in medicine and other fields. Bacteriophage MS2 VLPs are nanoparticles devoid of viral genetic material and can self-assemble from the coat protein into an icosahedral capsid. As a novel delivery platform, they possess numerous features that make them suitable and attractive for targeted delivery of RNAs or DNAs, epitope peptides, and drugs within the protein capsid. In short, as a novel delivery platform, MS2 VLPs are suitable for delivery of targeted agents and hold promise for use in diagnostics, vaccines, and therapeutic modalities.

Promising MS2 mediated virus-like particle vaccine against foot-and-mouth disease

Foot-and-mouth disease (FMD) has caused severe economic losses to millions of farmers worldwide. In this work, the coding genes of 141-160 epitope peptide (EP141-160) of VP1 were inserted into the coat protein (CP) genes of MS2 in prokaryotic expression vector, and the recombinant protein self-assembled into virus-like particles (VLP). Results showed that the CP-EP141-160 VLP had a strong immunoreaction with the FMD virus (FMDV) antigen in vitro, and also had an effective immune response in mice. Further virus challenge tests were carried out on guinea pigs and swine, high-titer neutralizing antibodies were produced and the CP-EP141-160 VLP vaccine could protect most of the animals against FMDV.

Challenges and prospects for the control of foot-and-mouth disease: an African perspective

The epidemiology of foot-and-mouth disease (FMD) in Africa is unique in the sense that six of the seven serotypes of FMD viruses (Southern African Territories [SAT] 1, SAT2, SAT3, A, O, and C), with the exception of Asia-1, have occurred in the last decade. Due to underreporting of FMD, the current strains circulating throughout sub-Saharan Africa are in many cases unknown. For SAT1, SAT2, and serotype A viruses, the genetic diversity is reflected in antigenic variation, and indications are that vaccine strains may be needed for each topotype. This has serious implications for control using vaccines and for choice of strains to include in regional antigen banks. The epidemiology is further complicated by the fact that SAT1, SAT2, and SAT3 viruses are maintained and spread by wildlife, persistently infecting African buffalo in particular. Although the precise mechanism of transmission of FMD from buffalo to cattle is not well understood, it is facilitated by direct contact between these two species. Once cattle are infected they may maintain SAT infections without the further involvement of buffalo. No single strategy for control of FMD in Africa is applicable. Decision on the most effective regional control strategy should focus on an ecosystem approach, identification of primary endemic areas, animal husbandry practices, climate, and animal movement. Within each ecosystem, human behavior could be integrated in disease control planning. Different regions in sub-Saharan Africa are at different developmental stages and are thus facing unique challenges and priorities in terms of veterinary disease control. Many science-based options targeting improved vaccinology, diagnostics, and other control measures have been described. This review therefore aims to emphasize, on one hand, the progress that has been achieved in the development of new technologies, including research towards improved tailored vaccines, appropriate vaccine strain selection, vaccine potency, and diagnostics, and how it relates to the conditions in Africa. On the other hand, we focus on the unique epidemiological, ecological, livestock farming and marketing, socioeconomic, and governance issues that constrain effective FMD control. Any such new technologies should have the availability of safe livestock products for trade as the ultimate goal.

Adjuvant effects of L. acidophilus LW1 on immune responses to the foot-and-mouth disease virus DNA vaccine in mice

The adjuvant effects of Lactobacillus acidophilus on DNA vaccination are not fully understood. It has been hypothesized that swine-derived Lactobacillus acidophilus SW1 (LASW1) could function as an immune adjuvant to enhance antigen-specific immune responses after foot-and-mouth disease (FMD) DNA vaccination in mice. To evaluate the effect of oral LASW1 on the immune response to a DNA vaccine (pRC/CMV-vp1) harboring FMD VP1 gene, anti-FMDV antibody and its isotypes, T-cell proliferation, and cytokine detection were investigated. The results showed that LASW1 was able to enhance FMDV-specific antibody levels and FMDV-neutralizing antibodies. After a booster vaccine, the anti-FMDV antibody titers and FMDV-neutralizing antibodies levels induced by pRC/CMV-vp1 were higher in mice treated with LSAW1 than in the group immunized with pRC/CMV-vp1 alone (the control). Using T-cell proliferation, the stimulation index of the LASW1 group was significantly higher in response to ConA and 146S antigen (P<0.05) than in the control group. Importantly, higher concentrations of IFN-γ and IFN-γ-producing cells were also observed in splenocytes isolated from the experimental LASW1 mice, indicating that INF-γ secretion is important to the immune response to LASW1. The results indicate that LASW1 is a promising immune adjuvant in DNA vaccination against FMD when administrated orally.

DNA vaccination with VP2 gene fragment confers protection against Infectious Bursal Disease Virus in chickens

Infectious Bursal Disease Virus (IBDV) causes immunosuppression in young chickens by destruction of antibody producing B cells in the Bursa of Fabricius and poses a potential threat to the poultry industry. We have examined the protective efficacy of a subunit DNA vaccine against IBDV infection in chickens in this study. An immunodominant VP2 gene fragment (VP252-417) was cloned into CMV promoter based DNA vaccine vector pVAX1 and in vitro expression of the DNA encoded antigens was confirmed by transfection of CHO cells with vaccine constructs followed by RT-PCR and western blot analysis using IBDV-antiserum. Two weeks old chickens were immunized intramuscularly with pVAXVP252-417 and the in vivo transcription of the plasmid DNA was confirmed by RT-PCR analysis of DNA injected muscle tissue at different intervals of post immunization. Tissue distribution analysis revealed that the plasmid DNA was extensively distributed in muscle, spleen, kidney, liver, and bursa tissues. Chickens immunized with pVAXVP252-417 developed high titer (1:12,000) of anti-VP252-417 antibodies. Further, chicken splenocytes from pVAXVP252-417 immunized group showed a significantly high proliferation to the whole viral and recombinant antigen (P<0.01) compared to control groups, which implies that pVAXVP252-417 codes for immunogenic fragment which has epitopes capable of eliciting both B and T cell responses. This is evident by the fact that, pVAXVP252-417 immunized chicken conferred 75% protection against virulent IBDV (vIBDV) challenge compared to the control group. Thus, the present study confirms that the immunodominant VP2 fragment can be used as a potential DNA vaccine against IBDV infection in chickens.

Protection to homologous and heterologous challenge in pigs immunized with vaccine against foot-and-mouth disease type O caused an epidemic in East Asia during 2010/2011

Foot-and-mouth disease (FMD) is a highly contagious infectious disease, and the use of vaccines is known to be effective for its prevention. In 2010/2011, there was an epidemic of the South East Asia (SEA) topotype in East Asian countries. We adapted the SEA topotype virus isolated in November 2010 in Korea in cells to analyze the characteristics of the virus and evaluate its possibility as a vaccine. After cell culture adaptation, the FMD virus particle 146S was purified to develop an inactivated oil vaccine for SEA or other topotypes. To measure its immunogenicity, pigs were inoculated with the experimental vaccine at different concentrations of the antigen. The results indicated that the groups immunized with at least 7.5 μg antigen were protected from homologous challenge. The immunized pigs were also protected against heterologous virus (ME-SA topotype) challenge. The genetic variations between the two field isolates and the adapted vaccine strains were identified in six amino acids by complete genome sequencing.

New approaches to rapidly control foot-and-mouth disease outbreaks

Economically, foot-and-mouth disease is the most important viral-induced livestock disease worldwide. The disease is highly contagious and foot-and-mouth disease virus replicates and spreads extremely rapidly. Recent outbreaks in previously foot-and-mouth disease-free countries and the potential use of foot-and-mouth disease virus by terrorist groups have demonstrated the vulnerability of countries and the need to develop control strategies that can rapidly inhibit or limit spread of the disease. The current vaccine, an inactivated whole-virus preparation, has a number of limitations for use in outbreaks in disease-free countries. This review discusses the potential of the antiviral agent, Type I interferon, to produce rapid protection and proposes a combination strategy of an antiviral agent and a foot-and-mouth disease vaccine to induce both immediate and long-lasting protective responses.

Development of porcine respiratory and reproductive syndrome virus replicon vector for foot-and-mouth disease vaccine

PURPOSE

Foot-and-mouth disease (FMD) is an economically important global animal disease. To control FMD virus (FMDV) outbreaks, a lot of different novel approaches have been attempted. In this study, we proposed a novel porcine reproductive and respiratory syndrome virus (PRRSV) as a replicon vector to express FMDV structural protein.

MATERIALS AND METHODS

PRRSV infectious clone (PRRSVK418DM) was used to develop an expression vector through the reverse genetic manipulation of PRRSV; FMDVP12A3C gene of serotype O was synthesized and used for an antigen. MARC-145 cells (African green monkey kidney epithelial cell line) were used for electroporation mediated transfection. The transfection or the expression of P12A3C and N protein of PRRSV was analyzed by either replicon containing PRRSV alone or by co-infection of helper PRRSV.

RESULTS

We constructed PRRSVK418DM replicon vector containing FMDVP12A3C, and genome sequences were confirmed by subsequent sequence analysis. In vitro expression of P12A3C and PRRSV N protein was confirmed by immunofluorescence antibody assay using antibodies specific for PRRSV N protein (anti-PRRSV N MAb), FMDV-VP1 (anti-VP1 MAb).

CONCLUSION

The results indicate that PRRSV replicon vector can be a promising novel vector system to control FMDV and useful for vaccine development in the future.

High-yield production of the VP1 structural protein epitope from serotype O foot-and-mouth disease virus in Escherichia coli

For effective control of foot-and-mouth disease (FMD), the development of rapid diagnostic systems and vaccines are required against its etiological agent, FMD virus (FMDV). To accomplish this, efficient large-scale expression of the FMDV VP1 protein, with high solubility, needs to be optimized. We attempted to produce high levels of a serotype O FMDV VP1 epitope in Escherichia coli. We identified the subtype-independent serotype O FMDV VP1 epitope sequence and used it to construct a glutathione S-transferase (GST) fusion protein. For efficient production of the FMDV VP1 epitope fused to GST (VP1e-GST), four E. coli strains and three temperatures were examined. The conditions yielding the greatest level of VP1e-GST with highest solubility were achieved with E. coli BL21(DE3) at 25 °C. For high-level production, fed-batch cultures were conducted in 5-l bioreactors. When cells were induced at a high density and complex feeding solutions were supplied, approximately 11 g of VP1e-GST was obtained from a 2.9-l culture. Following purification, the VP1 epitope was used to immunize rabbits, and we confirmed that it induced an immune response.

Sindbis virus replicase-based DNA vaccine construct encoding FMDV-specific multivalent epitope gene: studies on its immune responses in guinea pigs

Foot-and-mouth disease (FMD) is still a perennial global menace affecting livestock health and production. It is imperative to figure out new ways to curb this disease. In this study, a sindbis virus replicase-based DNA vaccine, pSinCMV-Vac-MEG990, encoding a multivalent epitope gene (representing tandemly linked VP1 C-terminal halves of three foot-and-mouth disease virus (FMDV) serotypes) was constructed. In vitro transfection studies in BHK-21 cells revealed that the construct was able to express FMDV-specific antigen but does not overproduce the antigen. Immunization of guinea pigs with the construct at dose rate of 10, 5, 2 and 1 μg per animal through intramuscular route showed significant neutralizing antibody induction at all doses against all serotype tested as compared to non-immunized controls. On viral challenge of guinea pigs 4 week post-immunization with 1000 GPID(50) of FMDV serotype A, it was observed that the immunization not only delayed the appearance and reduced the severity of FMD lesions significantly (P < 0.05) but also provided complete protection in several guinea pigs. In fact, two of six and one of six guinea pigs were completely protected in 10 and 5 μg immunized groups, respectively. These results suggest that the development of the replicase-based DNA vaccine may provide a promising approach as an alternative vaccine strategy for controlling FMD.

Comparison of immune responses against FMD by a DNA vaccine encoding the FMDV/O/IRN/2007 VP1 gene and the conventional inactivated vaccine in an animal model

Foot-and-mouth disease virus (FMDV) is highly contagious and responsible for huge outbreaks among cloven hoofed animals. The aim of the present study is to evaluate a plasmid DNA immunization system that expresses the FMDV/O/IRN/2007 VP1 gene and compare it with the conventional inactivated vaccine in an animal model. The VP1 gene was sub-cloned into the unique Kpn I and BamH I cloning sites of the pcDNA3.1+ and pEGFP-N1 vectors to construct the VP(1) gene cassettes. The transfected BHKT7 cells with sub-cloned pEGFP-N1-VP1 vector expressed GFP-VP1 fusion protein and displayed more green fluorescence spots than the transfected BHKT7 cells with pEGFP-N1 vector, which solely expressed the GFP protein. Six mice groups were respectively immunized by the sub-cloned pcDNA3.1(+)-VP1 gene cassette as the DNA vaccine, DNA vaccine and PCMV-SPORT-GMCSF vector (as molecular adjuvant) together, conventional vaccine, PBS (as negative control), pcDNA3.1(+) vector (as control group) and PCMV-SPORT vector that contained the GMCSF gene (as control group). Significant neutralizing antibody responses were induced in the mice which were immunized using plasmid vectors expressing the VP1 and GMCSF genes together, the DNA vaccine alone and the conventional inactivated vaccine (P<0.05). Co-administration of DNA vaccine and GMCSF gene improved neutralizing antibody response in comparison with administration of the DNA vaccine alone, but this response was the most for the conventional vaccine group. However, induction of humeral immunity response in the conventional vaccine group was more protective than for the DNA vaccine, but T-cell proliferation and IFN-γ concentration were the most in DNA vaccine with the GMCSF gene. Therefore the group that was vaccinated by DNA vaccine with the GMCSF gene, showed protective neutralizing antibody response and the most Th1 cellular immunity.

Progress in the development of DNA vaccines against foot-and-mouth disease

DNA vaccines are, in principle, the simplest yet most versatile methods of inducing protective humoral and cellular immune responses. Research involving this type of vaccine against veterinary diseases began in the early 1990s and has since seen the evaluation of more than 30 important viral pathogens, including the economically important foot-and-mouth disease. With the demonstration that DNA vaccines protect against foot-and-mouth disease in sheep and pigs, and the advantages these DNA vaccines have over the conventional formulations, this approach may provide a better solution to the control of this disease. In this review, we provide a comprehensive overview of DNA vaccination strategies for foot-and-mouth disease reported in the literature, in which we highlight the studies that have reported protection in the key target species.

A DNA vaccination regime including protein boost and electroporation protects cattle against foot-and-mouth disease

Protection against foot-and-mouth disease (FMD) using DNA technology has been documented for sheep and pigs but not for the highly susceptible species of cattle. Twenty-five Holstein Friesian cross-bred cattle were vaccinated twice, 21 days apart, with a DNA vaccine containing the capsid coding region (P1) along with the non-structural proteins 2A, 3C and 3D (pcDNA3.1/P1-2A3C3D) of O(1) Kaufbeuren alone or coated onto PLG (d,l-lactide-co-glycolide) microparticles. In some pcDNA3.1/P1-2A3C3D was also combined with an adjuvant plasmid expressing bovine granulocyte macrophage colony stimulating factor (GM-CSF). DNA vaccinations were administered intramuscularly with, or without, the use of electroporation and at 42 days post primary vaccination cattle received a protein boost of 146S FMD virus (FMDV) antigen and non-structural protein 3D. For comparison, four cattle were vaccinated with a conventional FMD vaccine and two more included as unvaccinated controls. Apart from those immunised with PLG microparticles all cattle were challenged with 10(5) TCID(50) cattle adapted O(1) Lausanne FMDV virus at day 93 post primary vaccination. All DNA vaccinated cattle regardless of regime developed good humoral and cell mediated responses prior to challenge. The best overall virus neutralising antibody, IFN-γ and clinical protection (75%) were seen in the cattle whereby the DNA was delivered by electroporation. In contrast, only 25% of cattle vaccinated with the DNA vaccine without electroporation were clinically protected. The addition of GM-CSF in combination with electroporation further improved the efficacy of the vaccine, as demonstrated from the reduction of clinical disease and virus excretions in nasal swabs. We thus demonstrate for the first time that cattle can be clinically protected against FMDV challenge following a DNA prime-protein boost strategy, and particularly when DNA vaccine is combined with GM-CSF and delivered by electroporation.

Foot-and-mouth disease virus particles inactivated with binary ethylenimine are efficiently internalized into cultured cells

Conventional foot-and-mouth disease (FMD) vaccines are produced from virus grown in cell culture that is chemically inactivated by using binary ethylenimide (BEI). Here, we show that BEI treatment preserves both the architecture of FMDV particles, as inactivated viral particles showed by electron microscopy characteristics similar to those of infectious virions, as well as the general features of infectious virus internalization. Binding of inactivated particles to BHK-21 cells was blocked by preincubation with either a FMDV-specific monoclonal antibody or a synthetic peptide spanning the integrin-binding viral motif Arg-Gly-Asp (RGD). In addition, these particles were internalized into cultured cells through endocytosis, being directed to early endosomes, as indicated by their colocalization with the marker protein Rab5. When purified BEI-inactivated virions were labelled and their interaction with live cultured cells analyzed by time-lapse fluorescence microscopy, a major subpopulation of virus particles, about 80%, was shown to undergo internalization into a static endosome population, insensitive to the microtubule depolymerization exerted by nocodazole, while the remaining subpopulation (about 20%) was dynamic and sensitive to this drug. Thus, BEI-inactivated particles provide an interesting tool to study early steps in FMDV-cell interactions enabling a distinction between FMDV internalization and productive infection. Possible implications for FMDV immune response elicited following vaccine administration are discussed.

Identification of H-2d restricted T cell epitope of foot-and-mouth disease virus structural protein VP1

Background

Foot-and-mouth disease (FMD) is a highly contagious and devastating disease affecting livestock that causes significant financial losses. Therefore, safer and more effective vaccines are required against Foot-and-mouth disease virus(FMDV). The purpose of this study is to screen and identify an H-2d restricted T cell epitope from the virus structural protein VP1, which is present with FMD. We therefore provide a method and basis for studying a specific FMDV T cell epitope.

Results

A codon-optimized expression method was adopted for effective expression of VP1 protein in colon bacillus. We used foot-and-mouth disease standard positive serum was used for Western blot detection of its immunogenicity. The VP1 protein was used for immunizing BALB/c mice, and spleen lymphocytes were isolated. Then, a common in vitro training stimulus was conducted for potential H-2Dd, H-2Kd and H-2Ld restricted T cell epitope on VP1 proteins that were predicted and synthesized by using a bioinformatics method. The H-2Kd restricted T cell epitope pK1 (AYHKGPFTRL) and the H-2Dd restricted T cell epitope pD7 (GFIMDRFVKI) were identified using lymphocyte proliferation assays and IFN-γ ELISPOT experiments.

Conclusions

The results of this study lay foundation for studying the FMDV immune process, vaccine development, among other things. These results also showed that, to identify viral T cell epitopes, the combined application of bioinformatics and molecular biology methods is effective.

Research in advance for FMD novel vaccines

Foot-and-Mouth Disease (FMD), as a major global animal disease, affects millions of animals worldwide and remains the main sanitary barrier to the international and national trade of animals and animal products. Inactivated vaccination is the most effective measure for prevention of FMD at present, but fail to induce long-term protection and content new requires for production of FMD vaccines. As a number of Researchers hope to obtain satisfactory novel vaccines by new bio-technology, novel vaccines have been studied for more than thirty years. Here reviews the latest research progress of new vaccines, summarizes some importance and raises several suggestions for the future of FMD vaccine.

B cell epitopes within VP1 of type O foot-and-mouth disease virus for detection of viral antibodies

In this study, the coding region of type O FMDV capsid protein VP1 and a series of codon optimized DNA sequences coding for VP1 amino acid residues 141-160 (epitope1), tandem repeat 200-213 (epitope2 (+2)) and the combination of two epitopes (epitope1-2) was genetically cloned into the prokaryotic expression vector pP(RO)ExHTb and pGEX4T-1, respectively. VP1 and the fused epitopes GST-E1, GST-E2 (+2) and GST-E1-2 were successfully solubly expressed in the cytoplasm of Escherichia coli and Western blot analysis demonstrated they retained antigenicity. Indirect VP1-ELISA and epitope ELISAs were subsequently developed to screen a panel of 80 field pig sera using LPB-ELISA as a standard test. For VP1-ELISA and all the epitope ELISAs, there were clear distinctions between the FMDV-positive and the FMDV-negative samples. Cross-reactions with pig sera positive to the viruses of swine vesicular disease virus that produce clinically indistinguishable syndromes in pigs or guinea pig antisera to FMDV strains of type A, C and Asia1 did not occur. The relative sensitivity and specificity for the GST-E1 ELISA, GST-E2 (+2), GST-E1-2 ELISA and VP1-ELISA in comparison with LPB-ELISA were 93.3% and 85.0%, 95.0% and 90%, 100% and 81.8%, 96.6% and 80.9% respectively. This study shows the potential use of the aforementioned epitopes as alternatives to the complex antigens used in current detection for antibody to FMDV structural proteins.

Vaccination against foot-and-mouth disease virus: strategies and effectiveness

Although present conventional foot-and-mouth disease (FMD) vaccines can prevent clinical disease, protection is short lived ( approximately 6 months), often requiring frequent revaccination for prophylactic control, and vaccination does not induce rapid protection against challenge or prevent the development of the carrier state. Furthermore, it is clear that the clinical protection depends upon the length of immunization and the duration of exposure/challenge methods. This review summarizes the present and future strategies for FMD control in endemic and FMD-free countries, the effectiveness of FMD vaccines in cattle, sheep and pigs, new methods for selecting vaccine strains, suggestions for alternative methods of vaccine testing, suggestions for the development of new-generation efficacious vaccines and their companion tests to differentiate infection in vaccinated animals.

Dramatic improvement in FMD DNA vaccine efficacy and cross-serotype antibody induction in pigs following a protein boost

To overcome the low and slow development of humoral antibody often observed with DNA vaccines we applied a prime-boost strategy. When FMD DNA vaccine P1-2A3C3D and pGM-CSF primed pigs were boosted with inactivated foot-and-mouth disease virus (FMDV) antigen and recombinant 3D (without adjuvant) an average 36-fold increase in the FMDV antibody response was observed compared to conventional vaccination, that included a log(10) virus neutralising titre increase. Most remarkably, a significant level of cross-serotype reactivity was observed against A, C and Asia1 in the virus neutralisation and ELISA tests. This prime-boost strategy fully protected pigs from a heterologous challenge.

Induction of T-cell response by a DNA vaccine encoding a novel HLA-A*0201 severe acute respiratory syndrome coronavirus epitope

The severe acute respiratory syndrome coronavirus nucleocapsid protein (SARS-CoV N) is one of the major targets for SARS vaccine due to its high potency in triggering immune responses. In this study, we have identified a novel HLA-A*0201 restricted epitope, N220 (LALLLLDRL), of the SARS-CoV N-protein through bioinformatics analysis. The N-protein peptide N220 shows a high binding affinity towards human MHC class I in T2-cells, and is capable of activating cytotoxic T-cells in human peripheral blood mononuclear cells (PBMCs). The application of using the N220 peptide sequence with a single-chain-trimer (SCT) approach to produce a potential DNA vaccine candidate was investigated in HLA-A2.1K(b) transgenic mice. Cytotoxicity assay clearly showed that the T-cells obtained from the vaccinated animals were able to kill the N-protein expressing cells with a cytotoxicity level of 86% in an effector cells/target cells ratio of 81:1 one week after the last vaccination, which is significantly higher than other N-protein peptides previously described. The novel immunogenic N-protein peptide revealed in the present study provides valuable information for therapeutic SARS vaccine design.

DNA immunization with 2C FMDV non-structural protein reveals the presence of an immunodominant CD8+, CTL epitope for Balb/c mice

Outbreaks of foot and mouth disease virus (FMDV) have devastating economic consequences in affected areas. The presence of multiple serotypes and virus variants makes vaccination complicated. A better understanding of protective immune mechanisms may help in development of novel vaccines with cross protective capacity. While much attention has been devoted to humoral responses to FMDV, less is known about the role of cell-mediated responses in protective immunity. Predictions of potential CTL epitopes by two different computer algorithms identified the viral 2C protein as containing a potential murine H2-Kd CTL epitope located in its amino-terminal half. DNA vaccination of mice with a plasmid expressing the 2C protein and a fragment thereof confirmed that this was indeed a CTL epitope, as shown by interferon gamma (IFN-gamma) induction in CD8+, CD44(hi) splenocytes after in vitro stimulation with peptides containing the amino acid sequence KYKDAKEWL, predicted for the CTL epitope. A peptide with the variant sequence KYKEAKEWL induced similar responses, indicating tolerability towards a conservative substitution at the altered residue. Virus infection likewise induced a measurable CTL response against KYKDAKEWL, although less clear due to a higher background of IFN-gamma production in splenocytes from infected mice. Challenge of vaccinated mice showed that the CTL response induced by the 2C protein was not protective, since viremia and mortality were unaffected by vaccination. The implications for vaccine development are discussed in the context of cross-serotype reactive responses.

DNA vaccines expressing B and T cell epitopes can protect mice from FMDV infection in the absence of specific humoral responses

Despite foot-and-mouth disease virus (FMDV) being responsible for one of the most devastating animal diseases, little is known about the cellular immune mechanisms involved in protection against this virus. In this work we have studied the potential of DNA vaccines based on viral minigenes corresponding to three major B and T-cell FMDV epitopes (isolate C-S8c1) originally identified in natural hosts. The BTT epitopes [VP1 (133-156)-3A (11-40)-VP4 (20-34)] were cloned into the plasmid pCMV, either alone or fused to ubiquitin, the lysosomal targeting signal from LIMPII, a soluble version of CTLA4 or a signal peptide from the human prion protein, to analyze the effect of processing through different antigenic presentation pathways on the immunogenicity of the FMDV epitopes. As a first step in the analysis of modulation exerted by these target signals, a FMDV infection inhibition assay in Swiss outbred mice was developed and used to analyze the protection conferred by the different BTT-expressing plasmids. Only one of the 37 mice immunized with minigene-bearing plasmids developed specific neutralizing antibodies prior to FMDV challenge. As expected, this single mouse that had been immunized with the BTT tandem epitopes fused to a signal peptide (pCMV-spBTT) was protected against FMDV infection. Interestingly, nine more of the animals immunized with BTT-expressing plasmids did not show viremia at 48 h post-infection (pi), even in the absence of anti-FMDV antibodies prior to challenge. The highest protection (50%, six out of 12 mice) was observed with the plasmid expressing BTT alone, indicating that the targeting strategies used did not result in an improvement of the protection conferred by BTT epitopes. Interestingly, peptide specific CD4+ T-cells were detected for some of the BTT-protected mice. Thus, a DNA vaccine based on single FMDV B and T cell epitopes can protect mice, in the absence of specific antibodies at the time of challenge. Further work must be done to elucidate the mechanisms involved in protection and to determine the protective potential of these vaccines in natural FMDV hosts.

Extract from Agaricus blazei Murill can enhance immune responses elicited by DNA vaccine against foot-and-mouth disease

The fungus Agaricus blazei Murill (ABM) is particularly rich in polysaccharides, which have shown particularly strong results in treating and preventing cancers. The goal of this study was to investigate whether co-administration of the ABM extract with foot-and-mouth disease virus (FMDV) DNA vaccine could increase the immune responses. Compared with the control mice, which received FMDV DNA vaccine alone, significant increase in not only the FMDV-specific antibody response but also T cell proliferation was observed in mice which received FMDV DNA vaccine plus the ABM extract. Taken together, these results demonstrated that application of the ABM extract might provide a strategy to improve the efficacy of DNA vaccines.

DNA vaccination against foot-and-mouth disease via electroporation: study of molecular approaches for enhancing VP1 antigenicity

BACKGROUND

Foot-and-mouth disease virus (FMDV) affects susceptible livestock animals and causes disastrous economic impact. Immunization with plasmid expressing VP1 that contains the major antigenic epitope(s) of FMDV as cytoplasmic protein (cVP1) failed to elicit full protection against FMDV challenge.

MATERIALS AND METHODS

In this study, mice were immunized via electroporation with four cDNA expression vectors that were constructed to express VP1 of FMDV, as cytoplasmic (cVP1), secreted (sVP1), membrane-anchored (mVP1) or capsid precursor protein (P1), respectively, to evaluate whether expression of VP1 in specific subcellular compartment(s) would result in better immune responses.

RESULTS

Electroporation enhanced immune responses to vectors expressing cVP1 or P1 and expedited the immune responses to vectors expressing sVP1 or mVP1. Immunization of mice via electroporation with mVP1 cDNA was better than sVP1 or cVP1 cDNA in eliciting neutralizing antibodies and viral clearance protection. Vaccination with P1 cDNA, nonetheless, yielded the best immune responses and protection among all four cDNAs that we tested.

CONCLUSIONS

These results suggest that the antigenicity of a VP1 DNA vaccine can be significantly enhanced by altering the cellular localization of the VP1 antigen. Electroporation is a useful tool for enhancing the immune responses of vectors expressing VP1 or P1. By mimicking FMDV more closely than that of transgenic VP1 and eliciting immune responses favorably toward Th2, transgenic P1 may induce more neutralizing antibodies and better protection against FMDV challenge.

Enhanced immunogenicity of microencapsulated multiepitope DNA vaccine encoding T and B cell epitopes of foot-and-mouth disease virus in mice

The role of poly(D,L-lactic-co-glycolic acid, PLGA) microparticles on enhancing immune responses of multiepitope DNA vaccines was investigated in vitro and in vivo. pcDNA-SG encoding T and B cell epitopes of foot-and-mouth disease virus (FMDV) was encapsulated into PLGA microparticles. PLGA microparticles could protect themselves from nuclease degradation in vitro. PLGA-pcDNA-SG microparticles could be uptaken by cells and expressed His-tagged SG immunogen in vitro and in vivo. A prolonged expression and presentation of SG immunogen were observed by confocal laser scanning microscopy in the lymphocytes from the mice incubated with PLGA-pcDNA-SG microparticles, compared with the mice immunized with naked pcDNA-SG. PLGA-pcDNA-SG microparticles displayed a significant stronger immunogenicity than naked DNA vaccines with a higher titer of virus-specific antibody, elevated IFN-gamma production and enhanced lymphocyte proliferation. PLGA-DNA microparticle could elicit augmented humoral and cellular responses with reduced amounts and times of immunization.

Tissue distribution of a plasmid DNA containing epitopes of foot-and-mouth disease virus in mice

It is known that only the minority of plasmid DNAs effect a cure or prevention after intramuscular injection into host. But what is the fate of the majority? And indeed how many of the injected DNAs work? Till now, little is known about it. To answer these questions, two methods including PCR and autoradiography were used in distribution study in mice that had received a single muscular inoculation of plasmid DNA containing antigenic epitopes of foot-and-mouth disease virus. The results showed that the plasmid DNAs were distributed by blood circulation and degraded soon. The degradation ratio of super coiled plasmid DNA was 20.9% in 10 min, 34.1% in 1h, 86.8% in 1 day and 97.8% in 1 week in sera in vivo. And over a half of the whole were output in urine and faeces. The rest resided most in muscles as 'antigen pool', next in immune organs, kidney, liver, heart, lung and little in brain or gonad. About 40% or 0.5% of total plasmid DNAs, inferring to be effective, resided in muscles or immune organs, respectively. Collective results suggested that 'nude' DNA, as water injection, was characterized as quick absorbent, extensive distribution, but low utilization rate. Finally, the immune mechanism for the DNA vaccine was discussed.

Development of novel strategies to control foot-and-mouth disease: marker vaccines and antivirals

Foot-and-mouth disease (FMD) is economically the most important viral-induced livestock disease worldwide. The disease is highly contagious and FMD virus (FMDV) replicates and spreads extremely rapidly. Outbreaks in previously FMD-free countries, including Taiwan, the United Kingdom, and Uruguay, and the potential use of FMDV by terrorist groups have demonstrated the vulnerability of countries and the need to develop control strategies that can rapidly inhibit or limit disease spread. The current vaccine, an inactivated whole virus preparation, has a number of limitations for use in outbreaks in disease-free countries. We have developed an alternative approach using a genetically engineered FMD subunit vaccine that only contains the portions of the viral genome required for virus capsid assembly and lacks the coding region for most of the viral nonstructural (NS) proteins including the highly immunogenic 3D protein. Thus, animals inoculated with this marker vaccine can readily be differentiated from infected animals using diagnostic assays employing the NS proteins not present in the vaccine and production of this vaccine, which does not contain infectious FMDV, does not require expensive high-containment manufacturing facilities. One inoculation of this subunit vaccine delivered in a replication-defective human adenovirus vector can induce rapid, within 7 days, and relatively long-lasting protection in swine. Similarly cattle inoculated with one dose of this recombinant vector are rapidly protected from direct and contact exposure to virulent virus. Furthermore, cattle given two doses of this vaccine developed high levels of FMDV-specific neutralizing antibodies, but did not develop antibodies against viral NS proteins demonstrating the ability of FMD subunit vaccinated animals to be differentiated from infected animals. To stimulate early protection prior to the vaccine-induced adaptive immune response we inoculated swine with the antiviral agent, type I interferon, and induced complete protection within 1 day. Protection can last for 3-5 days. The combination of the FMD marker vaccine and type I interferon can induce immediate, within 1 day, and long-lasting protection against FMD. Thus, this combination approach successfully addresses a number of concerns of FMD-free countries with the current disease control plan. By rapidly limiting virus replication and spread this strategy may reduce the number of animals that need to be slaughtered during an outbreak.