Immunogenicity and T cell recognition in swine of foot-and-mouth disease virus polymerase 3D

Deciphering Molecular Dynamics of Foot and Mouth Disease Virus (FMDV): A Looming Threat to Pakistan’s Dairy Industry

Milk is seen as a chief source of protein and other biologically available nutrients for human beings. Pakistan, the fourth largest milk-producing country, is badly affected by the contagious transboundary apthoviral disease of ungulate animals; the foot and mouth disease (FMD) virus. FMD is endemic in Pakistan and has caused significant economic loss to the dairy industry in the form of a profound decrease in milk production and increased morbidity and deaths of dairy animals. Inclusively, the case fatality ratio of FMD was 15.11%. Of the seven FMDV serotypes, (O, A, C, Asia 1, SAT 1, SAT2, and SAT 3), three serotypes (O, A, and Asia-1) are endemic in Pakistan. Rapid and highly sensitive diagnostic tools are required for efficient control of this disease. Presently, FMD in the laboratory is diagnosed via ELISA and molecular approaches, i.e., RT-PCR. Serotype-specific RT-PCR analysis not only confirms ELISA serotyping results but can also be used for the screening of ELISA negative samples. Genotypically, FMDV serotype O has a topotype (Middle East–South Asia (ME–SA) and lineage PanAsia-2) that is reported frequently from different areas of Pakistan. Confirmed cases of serotype A and Asia-1 are also reported. The information gathered can be used for understanding the molecular epidemiology of FMD in Pakistan. Further studies on the molecular dynamics of FMD could be useful for ensuring the timely diagnosis of this deadly pathogen, which would ultimately be beneficial for the mass vaccination programs of FMD in Pakistan.

An Adenovirus Vector Expressing FMDV RNA Polymerase Combined with a Chimeric VLP Harboring a Neutralizing Epitope as a Prime Boost Strategy to Induce FMDV-Specific Humoral and Cellular Responses

Foot and mouth disease is a highly contagious disease affecting cattle, sheep, and swine among other cloven-hoofed animals that imposes serious economic burden by its direct effects on farm productivity as well as on commerce of farmed produce. Vaccination using inactivated viral strains of the different serotypes is an effective protective measure, but has several drawbacks including a lack of cross protection and the perils associated with the large-scale growth of infectious virus. We have previously developed chimeric virus-like particles (VLPs) bearing an FMDV epitope which induced strong specific humoral responses in vaccinated pigs but conferred only partial protection against homologous challenge. While this and other FMD vaccines under development mostly rely on the induction of neutralizing responses, it is thought that induction of specific T-cell responses might improve both cross protective efficacy as well as duration of immunity. Therefore, we here describe the development of a recombinant adenovirus expressing the highly conserved nonstructural FMDV 3D protein as well as its capacity to induce specific T-cell responses in a murine model. We further describe the generation of an FMDV serotype C-specific chimeric VLP and analyze the immunogenicity of two different prime-boost strategies combining both elements in mice. This combination can effectively induce both humoral and cellular FMDV-specific responses eliciting high titers of ELISA and neutralizing antibodies anti-FMDV as well as a high frequency of IFNγ-secreting cells. These results provide the basis for further testing of this anti FMD vaccination strategy in cattle or pig, two of the most relevant natural host of this pathogen.

Swine T-Cells and Specific Antibodies Evoked by Peptide Dendrimers Displaying Different FMDV T-Cell Epitopes

Dendrimeric peptide constructs based on a lysine core that comprises both B- and T-cell epitopes of foot-and-mouth disease virus (FMDV) have proven a successful strategy for the development of FMD vaccines. Specifically, B₂T dendrimers displaying two copies of the major type O FMDV antigenic B-cell epitope located on the virus capsid [VP1 (140–158)], covalently linked to a heterotypic T-cell epitope from either non-structural protein 3A [3A (21–35)] or 3D [3D (56–70)], named B₂T-3A and B₂T-3D, respectively, elicit high levels of neutralizing antibodies (nAbs) and IFN-γ-producing cells in pigs. To assess whether the inclusion and orientation of T-3A and T-3D T-cell epitopes in a single molecule could modulate immunogenicity, dendrimers with T epitopes juxtaposed in both possible orientations, i.e., constructs B₂TT-3A3D and B₂TT-3D3A, were made and tested in pigs. Both dendrimers elicited high nAbs titers that broadly neutralized type O FMDVs, although B₂TT-3D3A did not respond to boosting, and induced lower IgGs titers, in particular IgG2, than B₂TT-3A3D. Pigs immunized with B_2, a control dendrimer displaying two B-cell epitope copies and no T-cell epitope, gave no nABs, confirming T-3A and T-3D as T helper epitopes. The T-3D peptide was found to be an immunodominant, as it produced more IFN-γ expressing cells than T-3A in the in vitro recall assay. Besides, in pigs immunized with the different dendrimeric peptides, CD4⁺ T-cells were the major subset contributing to IFN-γ expression upon in vitro recall, and depletion of CD4⁺ cells from PBMCs abolished the production of this cytokine. Most CD4⁺IFN-γ⁺ cells showed a memory (CD4⁺2E3⁻) and a multifunctional phenotype, as they expressed both IFN-γ and TNF-α, suggesting that the peptides induced a potent Th1 pro-inflammatory response. Furthermore, not only the presence, but also the orientation of T-cell epitopes influenced the T-cell response, as B₂TT-3D3A and B₂ groups had fewer cells expressing both cytokines. These results help understand how B₂T-type dendrimers triggers T-cell populations, highlighting their potential as next-generation FMD vaccines.

Safety, Immunogenicity, and Effectiveness of Defective Viral Particles Arising in Mast Cells Against Influenza in Mice

Mast cells play pivotal roles in the pathogenesis of influenza A virus (IAV) infections. Defective viral particles (DPs) often arise during IAV replication, which can interfere with the replication of infectious viruses and stimulate the antiviral response of host cells. Therefore, DPs are expected to have immune-protective functions in clinic. However, the potent immunogenicity and effectiveness of DPs arising in mast cells during IAV replication have not been reported. In the present study, we showed that DPs generated in the human mastocytoma cell line HMC-1 following H1N1 infection were safe to mice after vaccination. Compared with lung adenocarcinoma cells, A549, DPs generated in infected mast cells had much better immunostimulatory activity, enhancing both humoral and cellular immunity of hosts. Notably, they could significantly increase the expression of immune-associated cytokines, especially the IFN-γ. Due to the robust immunogenicity, thus DPs generated in infected mast cells could stimulate the robust protective immune reaction effectively to fight against lethal IAV re-challenge after vaccination, which result in the high survival, decreased lung injury as well as inhibition of viral replication and inflammatory response in lungs. This study is the first to illustrate and explore the safety, immunogenicity, and effectiveness of DPs arising in mast cells against influenza as favorable potential vaccination. The results provide insight into the advances of new prophylactic strategies to fight influenza by focusing on DPs generated in mast cells.

Association of Porcine Swine Leukocyte Antigen (SLA) Haplotypes with B- and T-Cell Immune Response to Foot-and-Mouth Disease Virus (FMDV) Peptides

Dendrimer peptides are promising vaccine candidates against the foot-and-mouth disease virus (FMDV). Several B-cell epitope (B₂T) dendrimers, harboring a major FMDV antigenic B-cell site in VP1 protein, are covalently linked to heterotypic T-cell epitopes from 3A and/or 3D proteins, and elicited consistent levels of neutralizing antibodies and IFN-γ-producing cells in pigs. To address the contribution of the highly polymorphic nature of the porcine MHC (SLA, swine leukocyte antigen) on the immunogenicity of B₂T dendrimers, low-resolution (Lr) haplotyping was performed. We looked for possible correlations between particular Lr haplotypes with neutralizing antibody and T-cell responses induced by B₂T peptides. In this study, 63 pigs immunized with B₂T dendrimers and 10 non-immunized (control) animals are analyzed. The results reveal a robust significant correlation between SLA class-II Lr haplotypes and the T-cell response. Similar correlations of T-cell response with SLA class-I Lr haplotypes, and between B-cell antibody response and SLA class-I and SLA class-II Lr haplotypes, were only found when the sample was reduced to animals with Lr haplotypes represented more than once. These results support the contribution of SLA class-II restricted T-cells to the magnitude of the T-cell response and to the antibody response evoked by the B₂T dendrimers, being of potential value for peptide vaccine design against FMDV.

A Wide-Ranging Antiviral Response in Wild Boar Cells Is Triggered by Non-coding Synthetic RNAs From the Foot-and-Mouth Disease Virus Genome

Foot-and-mouth disease virus (FMDV) is the causative agent of a highly contagious viral disease that affects multiple cloven-hooved hosts including important livestock (pigs, cattle, sheep and goats) as well as several wild animal species. Crossover of FMDV between domestic and wildlife populations may prolong virus circulation during outbreaks. The wild boar (Sus scrofa) is considered a reservoir of various pathogens that can infect other wildlife, domestic animals, and humans. As wild boar and domestic pigs are susceptible to the same pathogens and can infect each other, infected wild boar populations may represent a threat to the pig industry and to international trade. The ncRNAs are synthetic non-coding RNA transcripts, mimicking structural domains in the FMDV genome, known to exert a broad-spectrum antiviral and immunomodulatory effect in swine, bovine and mice cells. Here, we show the type I interferon-dependent, robust and broad range antiviral activity induced by the ncRNAs in a cell line derived from wild boar lung cells (WSL). Transfection of WSL cells with the ncRNAs exerted a protective effect against infection with FMDV, vesicular stomatitis virus (VSV), swine vesicular disease virus (SVDV) and African swine fever virus (ASFV). Our results prove the biological activity of the ncRNAs in cells of an FMDV wild animal host species against a variety of viruses affecting pigs, including relevant viral pathogens of epizootic risk.

Immunogenicity of a Dendrimer B2T Peptide Harboring a T-Cell Epitope From FMDV Non-structural Protein 3D

Synthetic dendrimer peptides are a promising strategy to develop new FMD vaccines. A dendrimer peptide, termed B₂T-3A, which harbors two copies of the major FMDV antigenic B-cell site [VP1 (140–158)], covalently linked to a heterotypic T-cell from the non-structural protein 3A [3A (21–35)], has been shown to protect pigs against viral challenge. Interestingly, the modular design of this dendrimer peptide allows modifications aimed at improving its immunogenicity, such as the replacement of the T-cell epitope moiety. Here, we report that a dendrimer peptide, B₂T-3D, harboring a T-cell epitope from FMDV 3D protein [3D (56–70)], when inoculated in pigs, elicited consistent levels of neutralizing antibodies and high frequencies of IFN-γ-producing cells upon in vitro recall with the homologous dendrimers, both responses being similar to those evoked by B₂T-3A. Lymphocytes from B₂T-3A-immunized pigs were in vitro-stimulated by T-3A peptide and to a lesser extent by B-peptide, while those from B₂T-3D- immunized animals preferentially recognized the T-3D peptide, suggesting that this epitope is a potent inducer of IFN-γ producing-cells. These results extend the repertoire of T-cell epitopes efficiently recognized by swine lymphocytes and open the possibility of using T-3D to enhance the immunogenicity and the protection conferred by B₂T-dendrimers.

A New Cage-Like Particle Adjuvant Enhances Protection of Foot-and-Mouth Disease Vaccine

Foot-and-Mouth Disease (FMD) is an acute viral disease that causes important economy losses. Vaccines with new low-cost adjuvants that stimulate protective immune responses are needed and can be assayed in a mouse model to predict their effectiveness in cattle. Immunostimulant Particle Adjuvant (ISPA), also known as cage-like particle adjuvant, consisting of lipid boxes of dipalmitoyl-phosphatidylcholine, cholesterol, sterylamine, alpha-tocopherol, and QuilA saponin, was shown to enhance protection of a recombinant vaccine against Trypanosoma cruzi in a mouse model. Thus, in the present work, we studied the effects on the magnitude and type of immunity elicited in mice and cattle in response to a vaccine based on inactivated FMD virus (iFMDV) formulated with ISPA. It was demonstrated that iFMDV–ISPA induced protection in mice against challenge and elicited a specific antibody response in sera, characterized by a balanced Th1/Th2 profile. In cattle, the antibody titers reached corresponded to an expected percentage of protection (EPP) higher than 80%. EPP calculates the probability that livestock would be protected against a 10,000 bovine infectious doses challenge after vaccination. Moreover, in comparison with the non-adjuvanted iFMDV vaccine, iFMDV–ISPA elicited an increased specific T-cell response against the virus, including higher interferon gamma (IFNγ)+/CD8+ lymphocyte production in cattle. In this work, we report for first time that an inactivated FMDV serotype A vaccine adjuvanted with ISPA is capable of inducing protection against challenge in a murine model and of improving the specific immune responses against the virus in cattle.

Designing Functionally Versatile, Highly Immunogenic Peptide-Based Multiepitopic Vaccines against Foot-and-Mouth Disease Virus

A broadly protective and biosafe vaccine against foot-and-mouth disease virus (FMDV) remains an unmet need in the animal health sector. We have previously reported solid protection against serotype O FMDV afforded by dendrimeric peptide structures harboring virus-specific B- and T-cell epitopes, and also shown such type of multivalent presentations to be advantageous over simple B-T-epitope linear juxtaposition. Chemically, our vaccine platforms are modular constructions readily made from specified B- and T-cell epitope precursor peptides that are conjugated in solution. With the aim of developing an improved version of our formulations to be used for on-demand vaccine applications, we evaluate in this study a novel design for epitope presentation to the immune system based on a multiple antigen peptide (MAP) containing six immunologically relevant motifs arranged in dendrimeric fashion (named B₂T-TB₂). Interestingly, two B₂T units fused tail-to-tail into a single homodimer platform elicited higher B- and T-cell specific responses than former candidates, with immunization scores remaining stable even after 4 months. Moreover, this macromolecular assembly shows consistent immune response in swine, the natural FMDV host, at reduced dose. Thus, our versatile, immunogenic prototype can find application in the development of peptide-based vaccine candidates for various therapeutic uses using safer and more efficacious vaccination regimens.

A bivalent B-cell epitope dendrimer peptide can confer long-lasting immunity in swine against foot-and-mouth disease

Foot-and-mouth disease virus (FMDV) causes a widely extended contagious disease of livestock. We have previously reported that a synthetic dendrimeric peptide, termed B₂ T(mal), consisting of two copies of a B-cell epitope [VP1(140-158)] linked through maleimide groups to a T-cell epitope [3A(21-35)] of FMDV, elicits potent B- and T-cell-specific responses and confers solid protection in pigs to type O FMDV challenge. Longer duration of the protective response and the possibility of inducing protection after a single dose are important requirements for an efficient FMD vaccine. Herein, we show that administration of two doses of B₂ T(mal) elicited high levels of specific total IgGs and neutralizing antibodies that lasted 4-5 months after the peptide boost. Additionally, concomitant levels of IFN-γ-producing specific T cells were observed. Immunization with two doses of B₂ T(mal) conferred a long-lasting reduced susceptibility to FMDV infection, up to 136 days (19/20 weeks) post-boost. Remarkably, a similar duration of the protective response was achieved by a single dose of B₂ T(mal). The effect on the B₂ T(mal) vaccine of RNA transcripts derived from non-coding regions in the FMDV genome, known to enhance the immune response and protection induced by a conventional inactivated vaccine, was also analysed. The contribution of our results to the development of FMD dendrimeric vaccines is discussed.

A Single Dose of Dendrimer B2T Peptide Vaccine Partially Protects Pigs against Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hoofed animals whose control relies on efficient vaccination. We have reported that dendrimer peptide B₂T, with two copies of FMDV B-cell epitope VP1 (136–154) linked through maleimide units to T-cell epitope 3A (21–35)], elicits potent B- and T-cell specific responses and confers solid protection in pigs to type-O FMDV challenge after two doses of peptide. Herein we now show that B₂T evokes specific protective immune responses after administration of a single dose of either 2 or 0.5 mg of peptide. High titers of ELISA and neutralizing antibodies against FMDV were detectable at day 15 post-immunization. Likewise, activated T cells and induced IFN-γ response to in vitro recall with FMDV peptides were also detected by the same day. Further, in 70% of B₂T-vaccinated pigs, full protection—no clinical signs of disease—was observed upon virus challenge at day 25 post-immunization. These results strengthen the potential of B₂T as a safe, cost-effective candidate vaccine conferring adequate protection against FMDV with a single dose. The finding is particularly relevant to emergency scenarios permitting only a single shot immunization.

Evaluation of modified Vaccinia Ankara-based vaccines against foot-and-mouth disease serotype A24 in cattle

To prepare foot-and-mouth disease (FMD) recombinant vaccines in response to newly emerging FMD virus (FMDV) field strains, we evaluated Modified Vaccinia virus Ankara-Bavarian Nordic (MVA-BN®) as an FMD vaccine vector platform. The MVA-BN vector has the capacity to carry and express numerous foreign genes and thereby has the potential to encode antigens from multiple FMDV strains. Moreover, this vector has an extensive safety record in humans. All MVA-BN-FMD constructs expressed the FMDV A24 Cruzeiro P1 capsid polyprotein as antigen and the FMDV 3C protease required for processing of the polyprotein. Because the FMDV wild-type 3C protease is detrimental to mammalian cells, one of four FMDV 3C protease variants were utilized: wild-type, or one of three previously reported mutants intended to dampen protease activity (C142T, C142L) or to increase specificity and thereby reduce adverse effects (L127P). These 3C coding sequences were expressed under the control of different promoters selected to reduce 3C protease expression. Four MVA-BN-FMD constructs were evaluated in vitro for acceptable vector stability, FMDV P1 polyprotein expression, processing, and the potential for vaccine scale-up production. Two MVA-BN FMD constructs met the in vitro selection criteria to qualify for clinical studies: MVA-mBN360B (carrying a C142T mutant 3C protease and an HIV frameshift for reduced expression) and MVA-mBN386B (carrying a L127P mutant 3C protease). Both vaccines were safe in cattle and elicited low to moderate serum neutralization titers to FMDV following multiple dose administrations. Following FMDV homologous challenge, both vaccines conferred 100% protection against clinical FMD and viremia using single dose or prime-boost immunization regimens. The MVA-BN FMD vaccine platform was capable of differentiating infected from vaccinated animals (DIVA). The demonstration of the successful application of MVA-BN as an FMD vaccine vector provides a platform for further FMD vaccine development against more epidemiologically relevant FMDV strains.

Deciphering foot-and-mouth disease (FMD) virus-host tropism

The pattern of interactions between foot and mouth disease (FMD) viral protein 1 (VP1) with susceptible and resistant host integrins were deciphered. The putative effect of site-directed mutation on alteration of interaction is illustrated using predicted and validated 3D structures of VP1, mutated VP1 and integrins of Bos taurus, Gallus and Canis. Strong interactions were observed between FMDV-VP1 protein motifs at conserved tripeptide, Arg-Gly-Asp ¹⁴³RGD¹⁴⁵ and at domain ⁶⁷⁶SIPLQ⁶⁸⁰ in alpha-integrin of B. taurus. Notably, in-silico site-directed mutation in FMDV-VP1 protein led to complete loss of interaction between FMD-VP1 protein and B. taurus integrin, which confirmed the active role of arginine-glycine-aspartic acid (RGD) domain. Interestingly, in-vitro analysis demonstrates the persistence of the putative tropism site 'SIPLQ' in different cattle breeds undertaken. Thus, the attempt to decipher the tropism of FMDV at host receptor level interaction might be useful for future FMD control strategies through development of mimetic marker vaccines and/or host receptor manipulations. Communicated by Ramaswamy H. Sarma.

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.

Development and validation of an epitope prediction tool for swine (PigMatrix) based on the pocket profile method

Background

T cell epitope prediction tools and associated vaccine design algorithms have accelerated the development of vaccines for humans. Predictive tools for swine and other food animals are not as well developed, primarily because the data required to develop the tools are lacking. Here, we overcome a lack of T cell epitope data to construct swine epitope predictors by systematically leveraging available human information. Applying the “pocket profile method”, we use sequence and structural similarities in the binding pockets of human and swine major histocompatibility complex proteins to infer Swine Leukocyte Antigen (SLA) peptide binding preferences.

We developed epitope-prediction matrices (PigMatrices), for three SLA class I alleles (SLA-1*0401, 2*0401 and 3*0401) and one class II allele (SLA-DRB1*0201), based on the binding preferences of the best-matched Human Leukocyte Antigen (HLA) pocket for each SLA pocket. The contact residues involved in the binding pockets were defined for class I based on crystal structures of either SLA (SLA-specific contacts, Ssc) or HLA supertype alleles (HLA contacts, Hc); for class II, only Hc was possible. Different substitution matrices were evaluated (PAM and BLOSUM) for scoring pocket similarity and identifying the best human match. The accuracy of the PigMatrices was compared to available online swine epitope prediction tools such as PickPocket and NetMHCpan.

Results

PigMatrices that used Ssc to define the pocket sequences and PAM30 to score pocket similarity demonstrated the best predictive performance and were able to accurately separate binders from random peptides. For SLA-1*0401 and 2*0401, PigMatrix achieved area under the receiver operating characteristic curves (AUC) of 0.78 and 0.73, respectively, which were equivalent or better than PickPocket (0.76 and 0.54) and NetMHCpan version 2.4 (0.41 and 0.51) and version 2.8 (0.72 and 0.71). In addition, we developed the first predictive SLA class II matrix, obtaining an AUC of 0.73 for existing SLA-DRB1*0201 epitopes. Notably, PigMatrix achieved this level of predictive power without training on SLA binding data.

Conclusion

Overall, the pocket profile method combined with binding preferences from HLA binding data shows significant promise for developing T cell epitope prediction tools for pigs. When combined with existing vaccine design algorithms, PigMatrix will be useful for developing genome-derived vaccines for a range of pig pathogens for which no effective vaccines currently exist (e.g. porcine reproductive and respiratory syndrome, influenza and porcine epidemic diarrhea).

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0724-8) contains supplementary material, which is available to authorized users.

Synthetic RNAs Mimicking Structural Domains in the Foot-and-Mouth Disease Virus Genome Elicit a Broad Innate Immune Response in Porcine Cells Triggered by RIG-I and TLR Activation

The innate immune system is the first line of defense against viral infections. Exploiting innate responses for antiviral, therapeutic and vaccine adjuvation strategies is being extensively explored. We have previously described, the ability of small in vitro RNA transcripts, mimicking the sequence and structure of different domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome (ncRNAs), to trigger a potent and rapid innate immune response. These synthetic non-infectious molecules have proved to have a broad-range antiviral activity and to enhance the immunogenicity of an FMD inactivated vaccine in mice. Here, we have studied the involvement of pattern-recognition receptors (PRRs) in the ncRNA-induced innate response and analyzed the antiviral and cytokine profiles elicited in swine cultured cells, as well as peripheral blood mononuclear cells (PBMCs).

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.

The 2010 outbreak of poliomyelitis in Tajikistan: epidemiology and lessons learnt

A large outbreak of poliomyelitis, with 463 laboratory-confirmed and 47 polio-compatible cases, took place in 2010 in Tajikistan. Phylogenetic analysis of the viral VP1 gene suggested a single importation of wild poliovirus type 1 from India in late 2009, its further circulation in Tajikistan and expansion into neighbouring countries, namely Kazakhstan, Russia, Turkmenistan and Uzbekistan. Whole-genome sequencing of 14 isolates revealed recombination events with enterovirus C with cross-overs within the P2 region. Viruses with one class of recombinant genomes co-circulated with the parental virus, and representatives of both caused paralytic poliomyelitis. Serological analysis of 327 sera from acute flaccid paralysis cases as well as from patients with other diagnoses and from healthy people demonstrated inadequate immunity against polio in the years preceding the outbreak. Evidence was obtained suggesting that vaccination against poliomyelitis, in rare cases, may not prevent the disease. Factors contributing to the peculiarities of this outbreak are discussed. The outbreak emphasises the necessity of continued vaccination against polio and the need, at least in risk areas, of quality control of this vaccination through well planned serological surveillance.

Chronic heat stress inhibits immune responses to H5N1 vaccination through regulating CD4⁺ CD25⁺ Foxp3⁺ Tregs

Chronic heat stress (CHS) is known to have negative impacts on the immune responses in animals and increases their susceptibility to infections including the highly pathogenic avian influenza virus H5N1. However, the role of regulatory T cells (Tregs) in CHS immunosuppression remains largely undefined. In this study, we demonstrated a novel mechanism by which CHS suppressed both Th1 and Th2 immune responses and dramatically decreased the protective efficacy of the formalin-inactivated H5N1 vaccine against H5N1 influenza virus infection. This suppression was found to be associated with the induced generation of CD4⁺CD25⁺FoxP3⁺ Tregs and the increased secretions of IL-10 and TGF-β in CD4⁺ T cells. Adoptive transfer of the induced Tregs also suppressed the protective efficacy of formalin-inactivated H5N1 virus immunization. Collectively, this study identifies a novel mechanism of CHS immunosuppression mediated by regulating CD4⁺CD25⁺Foxp3⁺ Tregs.

Use of replication-defective adenoviruses to develop vaccines and biotherapeutics against foot-and-mouth disease

We have developed a replication-defective human adenovirus (Ad5) vectored foot-and-mouth disease (FMD) vaccine platform that protects both swine and cattle from subsequent challenge with homologous virus after a single immunization. This Ad5-FMD vaccine has undergone testing following the requirements of the Center for Veterinary Biologics of the Animal Plant and Health Inspection Service, US Department of Agriculture, and has recently been granted a conditional license for inclusion of the vaccine in the US National Veterinary Vaccine Stockpile. In this review, we will describe the approaches we have taken to improve the potency and efficacy of this vaccine platform. Furthermore, we will discuss the development of Ad5 vector-based biotherapeutics to generate rapid protection against FMD virus prior to vaccine-induced adaptive immunity and describe the use of a combination of these approaches to stimulate both fast and long-lasting immunity.

Inoculation of swine with foot-and-mouth disease SAP-mutant virus induces early protection against disease

Foot-and-mouth disease virus (FMDV) leader proteinase (L(pro)) cleaves itself from the viral polyprotein and cleaves the translation initiation factor eIF4G. As a result, host cell translation is inhibited, affecting the host innate immune response. We have demonstrated that L(pro) is also associated with degradation of nuclear factor κB (NF-κB), a process that requires L(pro) nuclear localization. Additionally, we reported that disruption of a conserved protein domain within the L(pro) coding sequence, SAP mutation, prevented L(pro) nuclear retention and degradation of NF-κB, resulting in in vitro attenuation. Here we report that inoculation of swine with this SAP-mutant virus does not cause clinical signs of disease, viremia, or virus shedding even when inoculated at doses 100-fold higher than those required to cause disease with wild-type (WT) virus. Remarkably, SAP-mutant virus-inoculated animals developed a strong neutralizing antibody response and were completely protected against challenge with WT FMDV as early as 2 days postinoculation and for at least 21 days postinoculation. Early protection correlated with a distinct pattern in the serum levels of proinflammatory cytokines in comparison to the levels detected in animals inoculated with WT FMDV that developed disease. In addition, animals inoculated with the FMDV SAP mutant displayed a memory T cell response that resembled infection with WT virus. Our results suggest that L(pro) plays a pivotal role in modulating several pathways of the immune response. Furthermore, manipulation of the L(pro) coding region may serve as a viable strategy to derive live attenuated strains with potential for development as effective vaccines against foot-and-mouth disease.

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.

Prophylactic, therapeutic and immune enhancement effect of liposome-encapsulated PolyICLC on highly pathogenic H5N1 influenza infection

BACKGROUND

In view of the magnitude and severity of outbreaks of the highly pathogenic H5N1 influenza virus (H5N1-HPIV) and the threat to public health, there is an urgent need to develop broad-spectrum prophylactic and therapeutic agents against infection by H5N1-HPIV and other subtypes.

METHODS AND RESULTS

In the present study, we explored the use of LE-PolyICLC, a liposome encapsulated double-stranded RNA, as a possible prophylactic, therapeutic and immune enhancement agent. In a mouse infection model, we showed that the administration of LE-PolyICLC intranasally before or shortly after infection could inhibit virus replication, leading to a significant reduction in pulmonary viral titres and a higher survival rate of infected mice. When used as a molecular adjuvant, LE-PolyICLC significantly enhanced both the humoral and cellular responses elicited by inactivated H5N1 vaccine and augmented the protective efficacy provided by vaccination. Most importantly, the data also demonstrate that LE-PolyICLC could effectively attenuate the development of pulmonary fibrosis during the restoration period at day 14 after H5N1 infection.

CONCLUSIONS

Taken together, the data obtained in the present study suggest that strong consideration should be given for the use of LE-PolyICLC as prophylactic and therapeutic agents and also as a vaccination adjuvant to combat highly pathogenic influenza infection and its associated complications such as pulmonary fibrosis.

RNA structural domains in noncoding regions of the foot-and-mouth disease virus genome trigger innate immunity in porcine cells and mice

The induction of type I interferons (alpha/beta interferon [IFN-α/β]) in response to viral infection is a crucial step leading to the antiviral state in the host. Viruses produce double-stranded RNA (dsDNA) during their replication cycle that is sensed as nonself by host cells through different receptors. A signaling cascade then is activated to block viral replication and spread. Foot-and-mouth disease virus (FMDV) is a picornavirus that is highly sensitive to IFN, and it causes one of the world's most important animal diseases. In this study, we showed the ability of structural domains predicted to enclose stable dsRNA regions in the 5'- and 3'-noncoding regions (NCRs) of the FMDV genome to trigger an IFN-α/β response in porcine kidney cultured cells and newborn mice. These RNAs, generated by in vitro transcription, were able to stimulate IFN-β transcription and induce an antiviral state in SK-6 cells. The induction levels elicited by the different NCR RNAs were compared. Among them, the 3'NCR was identified as a potent IFN activator, and the features in this region involved in signaling have been analyzed. To address whether the FMDV NCR transcripts were able to trigger the innate immune response in vivo, Swiss suckling mice were inoculated intraperitoneally with the RNAs. All transcripts induced the innate response in transfected animals, measured as IFN-α/β protein levels, antiviral activity in sera, and reduced susceptibility to FMDV infection. Our work provides new insight into innate responses against FMDV and identifies these small noninfectious RNA molecules as potential adjuvants for vaccine improvement and antiviral strategies against picornaviruses.

Evidence of activation and suppression during the early immune response to foot-and-mouth disease virus

Foot-and-mouth disease virus causes a serious disease of livestock species, threatening free global trade and food security. The disease spreads rapidly between animals, and to ensure a window of opportunity for such spread, the virus has evolved multiple mechanisms to subvert the early immune response. The cycle of infection in the individual animal is very short, infection is initiated, disseminated throughout the body and infectious virus produced in <7 days. Foot-and-mouth disease virus has been shown to disrupt the innate response in vitro and also interacts directly with antigen-presenting cells and their precursors. This interaction results in suboptimal immune function, favouring viral replication and the delayed onset of specific adaptive T-cell responses. Detailed understanding of this cycle is crucial to effectively control disease in livestock populations. Knowledge-based vaccine design would specifically target and induce the immunological mechanisms of early protection and of robust memory induction. Specifically, information on the contribution of cytokines and interferon, innate immune cells as well as humoral and cellular immunity can be employed to design vaccines promoting such responses. Furthermore, understanding of viral escape mechanisms of immunity can be used to create attenuated viruses that could be used to develop novel vaccines and to study viral pathogenesis.

Foot and mouth disease virus polyepitope protein produced in bacteria and plants induces protective immunity in guinea pigs

The goal of this project was to develop an alternative foot and mouth disease (FMD) vaccine candidate based on a recombinant protein consisting of efficient viral epitopes. A recombinant gene was designed that encodes B-cell epitopes of proteins VP1 and VP4 and T-cell epitopes of proteins 2C and 3D. The polyepitope protein (H-PE) was produced in E. coli bacteria or in N. benthamiana plants using a phytovirus expression system. The methods of extraction and purification of H-PE proteins from bacteria and plants were developed. Immunization of guinea pigs with the purified H-PE proteins induced an efficient immune response against foot and mouth disease virus (FMDV) serotype O/Taiwan/99 and protection against the disease. The polyepitope protein H-PE can be used as a basis for developing a new recombinant vaccine against FMD.

A pseudotype baculovirus expressing the capsid protein of foot-and-mouth disease virus and a T-cell immunogen shows enhanced immunogenicity in mice

Background

Foot-and-mouth disease (FMD) is a highly contagious disease of livestock which causes severe economic loss in cloven-hoofed animals. Vaccination is still a major strategy in developing countries to control FMD. Currently, inactivated vaccine of FMDV has been used in many countries with limited success and safety concerns. Development of a novel effective vaccine is must.

Methods

In the present study, two recombinant pseudotype baculoviruses, one expressing the capsid of foot-and-mouth disease virus (FMDV) under the control of a cytomegalovirus immediate early enhancer/promoter (CMV-IE), and the other the caspid plus a T-cell immunogen coding region under a CAG promoter were constructed, and their expression was characterized in mammalian cells. In addition, their immunogenicity in a mouse model was investigated. The humoral and cell-mediated immune responses induced by pseudotype baculovirus were compared with those of inactivated vaccine.

Results

Indirect immunofluorescence assay (IFA) and indirect sandwich-ELISA (IS-ELISA) showed both recombinant baculoviruses (with or without T-cell epitopes) were transduced efficiently and expressed target proteins in BHK-21 cells. In mice, intramuscular inoculation of recombinants with 1 × 10⁹ or 1 × 10¹⁰ PFU/mouse induced the production of FMDV-specific neutralizing antibodies and gamma interferon (IFN-γ). Furthermore, recombinant baculovirus with T-cell epitopes had better immunogenicity than the recombinant without T-cell epitopes as demonstrated by significantly enhanced IFN-γ production (P < 0.01) and higher neutralizing antibody titer (P < 0.05). Although the inactivated vaccine produced the highest titer of neutralizing antibodies, a lower IFN-γ expression was observed compared to the two recombinant pseudotype baculoviruses.

Conclusions

These results indicate that pseudotype baculovirus-mediated gene delivery could be a alternative strategy to develop a new generation of vaccines against FMDV infection.

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.

Inhibition of enveloped virus infection of cultured cells by valproic acid

Valproic acid (VPA) is a short-chain fatty acid commonly used for treatment of neurological disorders. As VPA can interfere with cellular lipid metabolism, its effect on the infection of cultured cells by viruses of seven viral families relevant to human and animal health, including eight enveloped and four nonenveloped viruses, was analyzed. VPA drastically inhibited multiplication of all the enveloped viruses tested, including the zoonotic lymphocytic choriomeningitis virus and West Nile virus (WNV), while it did not affect infection by the nonenveloped viruses assayed. VPA reduced vesicular stomatitis virus infection yield without causing a major blockage of either viral RNA or protein synthesis. In contrast, VPA drastically abolished WNV RNA and protein synthesis, indicating that this drug can interfere the viral cycle at different steps of enveloped virus infection. Thus, VPA can contribute to an understanding of the crucial steps of viral maturation and to the development of future strategies against infections associated with enveloped viruses.

Promising multiple-epitope recombinant vaccine against foot-and-mouth disease virus type O in swine

In order to develop a completely safe immunogen to replace the traditional inactivated vaccine, a tandem-repeat multiple-epitope recombinant vaccine against foot-and-mouth disease (FMD) virus (FMDV) type O was developed. It contained three copies each of residues 141 to 160 and 200 to 213 of VP1 of the O/China/99 strain of FMDV coupled with a swine immunoglobulin G heavy-chain constant region (scIgG). The data showed that the multiple-epitope recombinant vaccine elicited high titers of anti-FMDV specific antibodies in swine at 30 days postvaccination (dpv) and conferred complete protection against a challenge with 10³ 50% swine infective doses of the O/China/99 strain. The anti-FMDV specific antibody titers were not significantly different between the multiple-epitope recombinant vaccine and the traditional vaccine (t test, P > 0.05). The number of 50% pig protective doses was 6.47, which is higher than the number recommended by the World Organization for Animal Health. The multiple-epitope recombinant vaccine resulted in a duration of immunity of at least 6 months. We speculate that the multiple-epitope recombinant vaccine is a promising vaccine that may replace the traditional inactivated vaccine for the prevention and control of FMD in swine in the future.

RNA immunization can protect mice against foot-and-mouth disease virus

In previous work we have reported the immunization of swine using in vitro-transcribed foot-and-mouth disease virus (FMDV) RNA. With the aim of testing whether RNA-induced immunization can mediate protection against viral infection, a group of Swiss adult mice was inoculated with FMDV infectious transcripts. In most inoculated animals viral RNA was detected in serum at 48-72h postinoculation. A group of the RNA-inoculated mice (11 out of 19) developed significant titers of neutralizing antibodies against FMDV. Among those animals that were successfully challenged with infectious virus (15 out of 19), three out of the eight animals immunized upon RNA inoculation were protected, as infectious virus could not be isolated from sera but specific anti-FMDV antibodies could be readily detected. These results suggest the potential of the inoculation of genetically engineered FMDV RNA for virulence and protection assays in the murine model and allow to explore the suitability of RNA-based FMDV vaccination in natural host animals.

Theiler's virus infection induces a predominant pathogenic CD4+ T cell response to RNA polymerase in susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV)-induced immune-mediated demyelinating disease in susceptible mouse strains has been extensively investigated as a relevant model for human multiple sclerosis. Previous investigations of antiviral T-cell responses focus on immune responses to viral capsid proteins, while virtually nothing is reported on immune responses to nonstructural proteins. In this study, we have identified noncapsid regions recognized by CD4(+) T cells from TMEV-infected mice using an overlapping peptide library. Interestingly, a greater number of CD4(+) T cells recognizing an epitope (3D(21-36)) of the 3D viral RNA polymerase, in contrast to capsid epitopes, were detected in the CNS of TMEV-infected SJL mice, whereas only a minor population of CD4(+) T cells from infected C57BL/6 mice recognized this region. The effects of preimmunization and tolerization with these epitopes on the development of demyelinating disease indicated that capsid-specific CD4(+) T cells are protective during the early stages of viral infection, whereas 3D(21-36)-specific CD4(+) T cells exacerbate disease development. Therefore, protective versus pathogenic CD4(+) T-cell responses directed to TMEV appear to be epitope dependent, and the differences in CD4(+) T-cell responses to these epitopes between susceptible and resistant mice may play an important role in the resistance or susceptibility to virally induced demyelinating disease.

Attenuated foot-and-mouth disease virus RNA carrying a deletion in the 3' noncoding region can elicit immunity in swine

We constructed foot-and-mouth disease virus (FMDV) mutants bearing independent deletions of the two stem-loop structures predicted in the 3' noncoding region of viral RNA, SL1 and SL2, respectively. Deletion of SL2 was lethal for viral infectivity in cultured cells, while deletion of SL1 resulted in viruses with slower growth kinetics and downregulated replication associated with impaired negative-strand RNA synthesis. With the aim of exploring the potential of an RNA-based vaccine against foot-and-mouth disease using attenuated viral genomes, full-length chimeric O1K/C-S8 RNAs were first inoculated into pigs. Our results show that FMDV viral transcripts could generate infectious virus and induce disease in swine. In contrast, RNAs carrying the DeltaSL1 mutation on an FMDV O1K genome were innocuous for pigs but elicited a specific immune response including both humoral and cellular responses. A single inoculation with 500 microg of RNA was able to induce a neutralizing antibody response. This response could be further boosted by a second RNA injection. The presence of the DeltaSL1 mutation was confirmed in viruses isolated from serum samples of RNA-inoculated pigs or after transfection and five passages in cell culture. These findings suggest that deletion of SL1 might contribute to FMDV attenuation in swine and support the potential of RNA technology for the design of new FMDV vaccines.

Enhanced mucosal immunoglobulin A response and solid protection against foot-and-mouth disease virus challenge induced by a novel dendrimeric peptide

The successful use of a dendrimeric peptide to protect pigs against challenge with foot-and-mouth disease virus (FMDV), which causes the most devastating animal disease worldwide, is described. Animals were immunized intramuscularly with a peptide containing one copy of a FMDV T-cell epitope and branching out into four copies of a B-cell epitope. The four immunized pigs did not develop significant clinical signs upon FMDV challenge, neither systemic nor mucosal FMDV replication, nor was its transmission to contact control pigs observed. The dendrimeric construction specifically induced high titers of FMDV-neutralizing antibodies and activated FMDV-specific T cells. Interestingly, a potent anti-FMDV immunoglobulin A response (local and systemic) was observed, despite the parenteral administration of the peptide. On the other hand, peptide-immunized animals showed no antibodies specific of FMDV infection, which qualifies the peptide as a potential marker vaccine. Overall, the dendrimeric peptide used elicited an immune response comparable to that found for control FMDV-infected pigs that correlated with a solid protection against FMDV challenge. Dendrimeric designs of this type may hold substantial promise for peptide subunit vaccine development.

An MHC-restricted CD8+ T-cell response is induced in cattle by foot-and-mouth disease virus (FMDV) infection and also following vaccination with inactivated FMDV

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease of cloven-hooved animals that carries enormous economic consequences. CD8(+) cytotoxic T lymphocytes play an important role in protection and disease outcome in viral infections but, to date, the role of the CD8(+) T-cell immune response to FMDV remains unclear. This study aimed to investigate major histocompatibility complex (MHC) class I-restricted CD8(+) T-cell responses to FMDV in vaccinated and in infected cattle. An in vitro assay was used to detect antigen-specific gamma interferon release by CD8(+) T cells in FMDV-infected cattle of known MHC class I genotypes. A significant MHC class I-restricted CD8(+) T-cell response was detected to both FMDV strain O1 BFS and a recombinant fowlpox virus expressing the structural proteins of FMDV. Antigen-specific MHC class I-restricted CD8(+) T-cell responses were also detected in cattle vaccinated with inactivated FMDV. These responses were shown to be directed, at least in part, to epitopes within the structural proteins (P12A region) of the virus. By using mouse cells expressing single cattle MHC class I alleles, it was possible to identify the restriction elements in each case. Identification of these epitopes will facilitate the quantitative and qualitative analysis of FMDV-specific memory CD8(+) T cells in cattle and help to ensure that potential vaccines induce a qualitatively appropriate CD8(+) T-cell response.

Guinea pig-adapted foot-and-mouth disease virus with altered receptor recognition can productively infect a natural host

We report that adaptation to infect the guinea pig did not modify the capacity of foot-and-mouth disease virus (FMDV) to kill suckling mice and to cause an acute and transmissible disease in the pig, an important natural host for this pathogen. Adaptive amino acid replacements (I(248)-->T in 2C, Q(44)-->R in 3A, and L(147)-->P in VP1), selected upon serial passages of a type C FMDV isolated from swine (biological clone C-S8c1) in the guinea pig, were maintained after virus multiplication in swine and suckling mice. However, the adaptive replacement L(147)-->P, next to the integrin-binding RGD motif at the GH loop in VP1, abolished growth of the virus in different established cell lines and modified its antigenicity. In contrast, primary bovine thyroid cell cultures could be productively infected by viruses with replacement L(147)-->P, and this infection was inhibited by antibodies to alphavbeta6 and by an FMDV-derived RGD-containing peptide, suggesting that integrin alphavbeta6 may be used as a receptor for these mutants in the animal (porcine, guinea pig, and suckling mice) host. Substitution T(248)-->N in 2C was not detectable in C-S8c1 but was present in a low proportion of the guinea pig-adapted virus. This substitution became rapidly dominant in the viral population after the reintroduction of the guinea pig-adapted virus into pigs. These observations illustrate how the appearance of minority variant viruses in an unnatural host can result in the dominance of these viruses on reinfection of the original host species.

Identification of a major antibody binding epitope in the non-structural protein 3D of foot-and-mouth disease virus in cattle and the development of a monoclonal antibody with diagnostic applications

Detection of FMDV non-structural protein 3D antibodies has been used as a complementary method for sero-epidemiological studies as an indirect indicator of FMDV infection. In order to develop a sensitive cELISA to detect FMDV antibodies, immune dominant epitopes in FMDV-3D protein were identified by peptide array analysis. Monoclonal antibodies were then raised to a selected epitope and used in cELISA. Ninety two peptides corresponding to the complete amino acid sequence of FMDV-3D were synthesized. The sera from 15 FMDV infected cows were tested for binding to the peptides in an indirect ELISA. One major peptide (3D-4) was recognized by antisera in 12 of the 15 infected cows (80%). The sequence was formed by amino acid residues 16-30 of FMDV-3D. The mAbs produced from the mice immunized with native 3D showed neither reactivity to this epitope nor competition with sera from FMDV infected cattle. However, the mAbs produced from the mice immunized with native 3D and boosted with the peptide 3D-4 showed reactivity with native 3D, recombinant 3D as well as competition with sera of FMDV infected cattle and sheep in ELISA assays. Immune response to FMDV-3D was determined using a cELISA. All cattle and sheep tested were positive at 9 dpi and remained positive until the end of the experiment on days 28-31 (>50% inhibition). This demonstrated that mAbs directed to the peptide 3D-4 were effective competitors to the polyclonal antibodies against 3D in infected sera. The approach described here provides a useful tool for specific mAb production in the development of new diagnostic tests.

Identification of novel foot-and-mouth disease virus specific T-cell epitopes in c/c and d/d haplotype miniature swine

To identify foot-and-mouth disease virus (FMDV) specific T-cell epitopes within the non-structural protein 3D in swine, pentadecapeptides were tested in proliferation and Interferon-gamma ELISPOT assays using lymphocytes from two strains of inbred miniature pigs (c/c and d/d haplotype) experimentally infected with FMDV. Lymphocytes of c/c pigs recognized peptides from three different regions in 3D, d/d lymphocytes recognized peptides from two regions, one of them being adjacent to an epitope of c/c pigs and comprising amino acid residues 346-370. Analyses of the response of d/d lymphocytes against peptides representing the structural protein 1A revealed another novel T-cell epitope. Investigation of the phenotype of responding lymphocytes showed a response of CD4(+)CD8(+)MHC-class-II(+) cells, identifying them as activated T-helper cells. This is the first report on FMDV specific T-cell epitopes recognized by swine leukocyte antigen (SLA) inbred swine and provides information useful for the design of novel vaccines against FMDV.

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.