Recombinant viruses expressing the foot-and-mouth disease virus capsid precursor polypeptide (P1) induce cellular but not humoral antiviral immunity and partial protection in pigs

Defining correlates of protection for mammalian livestock vaccines against high-priority viral diseases

Enhancing livestock biosecurity is critical to safeguard the livelihoods of farmers, global and local economies, and food security. Vaccination is fundamental to the control and prevention of exotic and endemic high-priority infectious livestock diseases. Successful implementation of vaccination in a biosecurity plan is underpinned by a strong understanding of correlates of protection-those elements of the immune response that can reliably predict the level of protection from viral challenge. While correlates of protection have been successfully characterized for many human viral vaccines, for many high-priority livestock viral diseases, including African swine fever and foot and mouth disease, they remain largely uncharacterized. Current literature provides insights into potential correlates of protection that should be assessed during vaccine development for these high-priority mammalian livestock viral diseases. Establishment of correlates of protection for biosecurity purposes enables immune surveillance, rationale for vaccine development, and successful implementation of livestock vaccines as part of a biosecurity strategy.

A Novel Live Attenuated Vaccine Candidate Protects Against Heterologous Senecavirus A Challenge

Senecavirus A (SVA) is an emerging picornavirus causing vesicular disease (VD) clinically indistinguishable from foot-and-mouth disease (FMD) in pigs. Currently there are no vaccines currently available for SVA. Here we developed a recombinant SVA strain (rSVAm SacII) using reverse genetics and assessed its immunogenicity and protective efficacy in pigs. In vivo characterization of the rSVAm SacII strain demonstrated that the virus is attenuated, as evidenced by absence of lesions, decreased viremia and virus shedding in inoculated animals. Notably, while attenuated, rSVA mSacII virus retained its immunogenicity as high neutralizing antibody (NA) responses were detected in inoculated animals. To assess the immunogenicity and protective efficacy of rSVA mSacII, 4-week-old piglets were sham-immunized or immunized with inactivated or live rSVA mSacII virus-based formulations. A single immunization with live rSVA mSacII virus via the intramuscular (IM) and intranasal (IN) routes resulted in robust NA responses with antibodies being detected between days 3-7 pi. Neutralizing antibody responses in animals immunized with the inactivated virus via the IM route were delayed and only detected after a booster on day 21 pi. Immunization with live virus resulted in recall T cell proliferation (CD4⁺, CD8⁺, and CD4⁺/CD8⁺ T cells), demonstrating efficient stimulation of cellular immunity. Notably, a single dose of the live attenuated vaccine candidate resulted in protection against heterologous SVA challenge, as demonstrated by absence of overt disease and reduced viremia, virus shedding and viral load in tissues. The live attenuated vaccine candidate developed here represents a promising alternative to prevent and control SVA in swine.

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.

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.

Immunogenicity and protective efficacy of a novel foot-and-mouth disease virus empty-capsid-like particle with improved acid stability

Foot-and-mouth disease virus (FMDV) is the etiological agent of a highly contagious disease that affects cloven-hoofed animal species. The FMDV capsid is highly acid labile and viral particles lose their immunogenicity when they disassemble at mildly acidic pHs. The viral capsid of FMDV serotype O is more sensitive than those of other serotypes, making it more difficult to acquire enough empty-capsid-like particles in the acidic insect cell environment for research. In this study, novel FMDV mutants with increased acid resistance were isolated using BHK-21 cell cultured under low-pH conditions. Amino acid substitutions Q25R, K41E, and N85A in the VP1 capsid protein and K154Q in the VP3 capsid protein were detected in all six mutants. Based on these amino acid replacements, empty-capsid-like particles of FMDV serotype O, which were resistant to the acid-induced dissociation of the capsid into pentameric subunits, were produced in insect cells. We characterized the protective immunity induced by these acid-resistant empty capsid particles. Significant humoral and cellular immune responses were elicited in mice after immunization with the acid-resistant empty capsid particles. The acid-resistant empty-capsid-like particles also induced strong neutralizing antibodies in guinea pigs and protected all the guinea pigs from FMDV challenge. Our results suggest that these acid-resistant empty-capsid-like particles have potential utility as a vaccine against serotype O FMDV infection.

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.

Chemokine CCL20 plasmid improves protective efficacy of the Montanide ISA™ 206 adjuvanted foot-and-mouth disease vaccine in mice model

This study aimed to investigate the chemokine CCL20, a macrophage inflammatory protein-3 alpha, for adjuvant potential in inactivated foot-and-mouth disease (FMD) vaccine. Groups of mice were injected intramuscularly with either murine CCL20 DNA or CCL20 protein two days ahead of the immunization with Montanide ISA206 adjuvanted inactivated FMD vaccine and humoral and cellular immune responses were measured in post-vaccinal sera. We demonstrated that the mice immunized with CCL20 plasmid plus FMD vaccine showed earlier and significantly (p < 0.05) higher neutralizing antibody responses compared to the mice vaccinated with CCL20 protein plus FMD vaccine. In fact, CCL20 as a protein did not show any adjuvant effect and the immune responses induced in this group were comparable to that of the mice vaccinated with FMD vaccine alone. All the vaccination groups showed serum IgG1 and IgG2 antibody responses; however, the mice vaccinated with CCL20 plasmid plus FMD vaccine showed significantly (p < 0.05) higher IgG1 and IgG2 responses and the responses remained high at all-time points post vaccination, although not always statistically significant. Upon restimulation of the vaccinated splenocytes with the inactivated FMD viral antigen, significantly (p < 0.05) higher IFN-γ and IL-2 levels in culture supernatants were found in animals vaccinated with the CCL20 plasmid plus FMD vaccine, which is indicative of the T_H1 type of cellular immunity. On challenge with the homologous FMD virus on 28th day post immunization, CCL20 plasmid plus FMD vaccine showed complete protection (100%) while animals immunized with CCL20 protein plus FMD vaccine or FMD vaccine alone showed 66% protection. In summary, we show that prior injection of CCL20 plasmid improved protective efficacy of the inactivated FMD vaccine and thus offers a valuable strategy to modulate the efficacy and polarization of specific immunity against inactivated vaccines.

A canine adenovirus type 2 vaccine vector confers protection against foot-and-mouth disease in guinea pigs

Vaccination is a key element in the control of foot-and-mouth disease (FMD). The majority of the antigenic sites that induce protective immune responses are localized on the FMD virus (FMDV) capsid that is formed by four virus-encoded structural proteins, VP1 to VP4. In the present study, recombinant canine adenovirus type 2 (CAV2)-based FMD vaccines, Cav-P1/3C R° and Cav-VP1 R°, respectively expressing the structural P1 precursor protein along with the non-structural 3C protein or expressing the structural VP1 protein of the FMDV strain O/FRA/1/2001, were evaluated as novel vaccines against FMD. A strong humoral immune response was elicited in guinea pigs (GP) following immunization with Cav-P1/3C R°, while administration of Cav-VP1 R° did not induce a satisfying antibody response in GP or mice. GP were then used as an experimental model for the determination of the protection afforded by the Cav-P1/3C R° vaccine against challenge with the FMDV strain O₁ Manisa/Turkey/1969. The Cav-P1/3C R° vaccine protected GP from generalized FMD to a similar extent as a high potency double-oil emulsion O₁ Manisa vaccine. The results of the present study show that CAV2-based vector vaccines can express immunogenic FMDV antigens and offer protection against generalized FMD in GP. This suggest that Cav-P1/3C R° FMDV vaccine may protect natural host species from FMD. In combination with an appropriate diagnostic test, the Cav-P1/3C R° FMDV vaccine may also serve as a marker vaccine to differentiate vaccinated from infected animals.

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.

A Recombinant Adenovirus Expressing P12A and 3C Protein of the Type O Foot-and-Mouth Disease Virus Stimulates Systemic and Mucosal Immune Responses in Mice

Foot-and-mouth disease (FMD) is a highly contagious livestock disease of cloven-hoofed animals which causes severe economic losses. The replication-deficient, human adenovirus-vectored FMD vaccine has been proven effective against FMD. However, the role of T-cell-mediated antiviral responses and the mucosae-mediated antiviral responses induced by the adenovirus-vectored FMD vaccine was rarely examined. Here, the capsid protein precursor P1-2A and viral protease 3C of the type O FMDV were expressed in replicative-deficient human adenovirus type 5 vector. BALB/c mice immunized intramuscularly and intraperitoneally with recombinant adenovirus rAdv-P12A3C elicited higher FMDV-specific IgG antibodies, IFN-γ, and IL-4 cytokines than those in mice immunized with inactivated FMDV vaccine. Moreover, BALB/c mice immunized with recombinant adenovirus rAdv-P12A3C by oral and intraocular-nasal immunization induced high FMDV-specific IgA antibodies. These results show that the recombinant adenovirus rAdv-P12A3C could resist FMDV comprehensively. This study highlights the potential of rAdv-P12A3C to serve as a type O FMDV vaccine.

Construction and characterization of recombinant human adenovirus type 5 expressing foot-and-mouth disease virus capsid proteins of Indian vaccine strain, O/IND/R2/75

AIM

Generation of recombinant human adenovirus type 5 expressing foot-and-mouth disease virus (FMDV) capsid protein genes along with full-length 2B, 3B and 3C(pro) and its characterization.

MATERIALS AND METHODS

FMD viral RNA isolation, cDNA synthesis, and polymerase chain reaction were performed to synthesize expression cassettes (P1-2AB3BC(wt) and P1-2AB3BC(m)) followed by cloning in pShuttle-CMV vector. Chemically competent BJ5183-AD-1 cells were transformed with the recombinant pShuttle-CMV to produce recombinant adenoviral plasmids. HEK-293 cells were transfected with the recombinant adenoviral plasmids to generate recombinant adenoviruses (hAd5/P1-2AB3BC(wt) and hAd5/P1-2AB3BC(m)). Expression of the target proteins was analyzed by sandwich ELISA and indirect immunofluorescence assay. The recombinant adenoviruses were purified and concentrated by CsCl density gradient ultracentrifugation. Growth kinetics and thermostability of the recombinant adenoviruses were compared with that of non-recombinant replication-defective adenovirus (dAd5).

RESULTS

The recombinant adenoviruses containing capsid protein genes of the FMDV O/IND/R2/75 were generated and amplified in HEK-293 cells. The titer of the recombinant adenoviruses was approximately 10(8), 10(9.5) and 10(11) TCID50/ml in supernatant media, cell lysate and CsCl purified preparation, respectively. Expression of the FMDV capsid protein was detectable in sandwich ELISA and confirmed by immunofluorescence assay. Growth kinetics of the recombinant adenoviruses did not reveal a significant difference when compared with that of dAd5. A decrement of up to 10-fold at 4°C and 21-fold at 37°C was recorded in the virus titers during 60 h incubation period and found to be statistically significant (p<0.01).

CONCLUSION

Recombinant adenoviruses expressing capsid proteins of the FMDV O/IND/R2/75 were constructed and produced in high titers. In vitro expression of the target proteins in the adenovirus vector system was detected by sandwich ELISA and immunofluorescence assay.

Supplementation of dietary germanium biotite enhances induction of the immune responses by foot-and-mouth disease vaccine in cattle

Background

After the recent outbreak of foot-and-mouth disease (FMD) in Korea, a vaccination policy has been applied to control the disease. In addition, several non-specific immune stimulators have been used without any scientific evidence that they would enhance the immune response after FMD vaccination and/or protect against FMD. Based on the current situation, the aim of this study was to evaluate the effect of the non-specific immune stimulator germanium biotite on FMD vaccination and immune responses in cattle. To achieve our goal, immune responses to FMD vaccination, such as levels of IgG and IgA, antibody duration, and virus-neutralizing titers were investigated after germanium biotite feeding. The PBMC typing and proliferative response after stimulation with mitogens, the cytokines expression level of PBMC, and the lysozyme activity in the serum were measured to evaluate the immune enhancing effects of germanium biotite following its administration.

Results

Following the first vaccination, high level of IgG (at 4 weeks) and IgA (at 2 and 31 weeks) titers in serum and saliva were observed in the germanium biotite-feeding group (p < 0.05). The germanium biotite group also showed high and longstanding inhibition percentage value in ELISA assay at 31 weeks (p < 0.05). Generally, higher virus-neutralizing antibody titers were observed in the feeding group at 20 and 31 weeks after vaccination. Following the feeding germanium biotite, the germanium biotite group showed increased subpopulation of CD4⁺ lymphocytes and MHC I⁺II⁺ cells in PBMCs at 23 week, responding to stimulation of ConA. The levels of IFN-γ (at 3 and 8 weeks), IL-1α (at 3, 11, and 23 weeks), IL-1β (at 3, 8, and 11 weeks), and IL-4 (at 8 and 11 weeks) gene expression were also significantly increased in the feeding group (p < 0.01 and p < 0.05). Feeding with germanium biotite increased the lymphocytes’ proliferative response to the stimulation of ConA and LPS at 23 weeks and lysozyme activity at 9 weeks after feeding.

Conclusions

These results suggest that germanium biotite feeding could increase the protection against FMD virus infection via the induction of higher humoral and cellular immune responses in cattle.

Induction of protective immune response against both PPRV and FMDV by a novel recombinant PPRV expressing FMDV VP1

Peste des petits ruminants (PPR) and foot-and-mouth disease (FMD) are both highly contagious diseases of small domestic and wild ruminants caused by the PPR virus (PPRV) and the FMD virus (FMDV). In this study, a recombinant PPRV expressing the FMDV VP1 gene (rPPRV/VP1) was generated and FMDV VP1 expression did not impair replication of the recombinant virus in vitro and immunogenicity in inducing neutralizing antibody against PPR in goats. Vaccination with one dose of rPPRV/VP1 induced FMDV neutralizing antibody in goats and protected them from challenge with virulent FMDV. Our results suggest that the recombinant PPRV expressing the FMDV VP1 protein is a potential dual live vectored vaccine against PPRV and FMDV.

Transmission of foot-and-mouth disease virus from experimentally infected Indian buffalo (Bubalus bubalis) to in-contact naïve and vaccinated Indian buffalo and cattle

This study investigated the transmission of foot-and-mouth disease virus (FMDV) from experimentally infected Indian buffalo to in-contact naïve and vaccinated cattle and buffalo. In each of six rooms, two donor buffalo that had been inoculated with FMDV were housed for five days with four recipient animals, comprising one vaccinated buffalo, one vaccinated calf, one unvaccinated buffalo and one unvaccinated calf. Vaccination was carried out with current Indian vaccine strain (O/IND/R2/75) and challenged on 28 days post-vaccination with an antigenically similar strain (O/HAS/34/05). All 12 donor buffalo and the six unvaccinated cattle and six unvaccinated calves developed clinical signs of foot-and-mouth disease (FMD). In contrast, all six vaccinated cattle (100%) and four out of six vaccinated buffalo (66.6%) were protected from disease but all became infected with FMDV. This confirms that buffalo have the potential to spread FMD by direct contact and that vaccination can block this spread. The numbers of animals in the study were too small to determine if the differences in clinical protection afforded by vaccination of cattle and buffalo are significant and warrant a different dose regime.

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.

Transient gene expression in serum-free suspension-growing mammalian cells for the production of foot-and-mouth disease virus empty capsids

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. It produces severe economic losses in the livestock industry. Currently available vaccines are based on inactivated FMD virus (FMDV). The use of empty capsids as a subunit vaccine has been reported to be a promising candidate because it avoids the use of virus in the vaccine production and conserves the conformational epitopes of the virus. In this report, we explored transient gene expression (TGE) in serum-free suspension-growing mammalian cells for the production of FMDV recombinant empty capsids as a subunit vaccine. The recombinant proteins produced, assembled into empty capsids and induced protective immune response against viral challenge in mice. Furthermore, they were recognized by anti-FMDV bovine sera. By using this technology, we were able to achieve expression levels that are compatible with the development of a vaccine. Thus, TGE of mammalian cells is an easy to perform, scalable and cost-effective technology for the production of a recombinant subunit vaccine against FMDV.

Characterization of cytotoxic T lymphocyte function after foot-and-mouth disease virus infection and vaccination

The induction of neutralizing antibodies specific for foot-and-mouth disease virus (FMDV) has been the central goal of vaccination efforts against this economically important disease of cloven-hoofed animals. Although these efforts have yielded much success, challenges remain, including little cross-serotype protection and inadequate duration of immunity. Commonly, viral infections are characterized by induction of cytotoxic T lymphocytes (CTL), yet the function of CTL in FMDV immunity is poorly defined. We developed an assay for detection of CTL specific for FMDV and reported that a modified adenovirus-vectored FMDV vaccine could induce CTL activity. This allowed us to determine whether FMDV-specific CTL responses are induced during infection and to test further whether vaccine-induced CTL could protect against challenge with FMDV. We now show the induction of antigen-specific CTL responses after infection of swine with FMDV strain A24 Cruizero. In addition, we developed a vaccination strategy that induces FMDV-specific CTL in the absence of significant neutralizing antibody. Animals vaccinated using this protocol showed delayed clinical disease and significantly suppressed viremia compared to control animals, suggesting a role for CTLs in the control of virus shedding. These results provide new insights showing induction of CTL responses to FMDV following infection or vaccination, and create the potential for improving vaccine performance by targeting cellular immunity.

Requirements for improved vaccines against foot-and-mouth disease epidemics

Inactivated foot-and-mouth disease (FMD) vaccines are currently used worldwide. With the emergence of various FMD virus serotypes and subtypes, vaccines must become more suitable for field-based uses under the current circumstances in terms of the fast and proper selection of vaccine strains, an extended vaccine development period for new viruses, protecting against the risk of virus leakage during vaccine manufacture, counteracting the delayed onset of immune response, counteracting shorter durations of immunity, and the accurate serological differentiation of infected and vaccinated animals and multiple vaccination. The quality of vaccines should then be improved to effectively control FMD outbreaks and minimize the problems that can arise among livestock after vaccinations. Vaccine improvement should be based on using attenuated virus strains with high levels of safety. Moreover, when vaccines are urgently required for newly spread field strains, the seed viruses for new vaccines should be developed for only a short period. Improved vaccines should offer superior immunization to all susceptible animals including cattle and swine. In addition, they should have highly protective effects without persistent infection. In this way, if vaccines are developed using new methods such as reverse genetics or vector vaccine technology, in which live viruses can be easily made by replacing specific protective antigens, even a single vaccination is likely to generate highly protective effects with an extended duration of immunity, and the safety and stability of the vaccines will be assured. We therefore reviewed the current FMD vaccines and their adjuvants, and evaluated if they provide superior immunization to all susceptible animals including cattle and swine.

Time-dependent biodistribution and transgene expression of a recombinant human adenovirus serotype 5-luciferase vector as a surrogate for rAd5-FMDV vaccines in cattle

Replication-defective recombinant adenovirus 5 (rAd5) vectors carrying foot-and-mouth disease virus (FMDV) transgenes elicit a robust immune response to FMDV challenge in cattle; however mechanistic functions of vaccine function are incompletely understood. Recent efforts addressing critical interactions of rAd5 vectors with components of the bovine immune system have elucidated important aspects of induction of protective immunity against FMDV. In the current study, a rAd5-Luciferase (rAd5-Luc) surrogate vector was utilized for indirect assessment of rAd5-FMDV distribution during the first 48 hours post inoculation (hpi). To compare vector distribution dynamics and time-dependent transgene expression, bovine cells were inoculated in vitro with rAd5-FMDV and rAd5-Luc vectors. Superior transgene expression was detected in cells infected with rAd5-Luc compared to rAd5-FMDV. However, both vectors behaved remarkably similar in demonstrating elevated mRNA transcription at 24 and 48 hpi with peak occurrence of transgene expression at 48 hpi. Injection sites of cattle inoculated with rAd5-Luc contained mononuclear inflammatory infiltrates with hexon and transgene proteins associated with antigen-presenting cells. Luciferase activity, as well as microscopic detection of luciferase antigens, peaked at 24 hpi. Presence of viral mRNA also peaked at 24 hpi but unlike luciferase, remained strongly detected at 48 hpi. Cell-associated luciferase antigens were detected as early as 6 hpi at the cortical interfolicullar areas of local LN, indicating rapid trafficking of antigen-presenting cells to lymphoid tissues. This work provides mechanistic insights on rAd5-mediated immunity in cattle and will contribute to ongoing efforts to enhance rAd5-FMDV vaccine efficacy.

Interferon-γ induced by in vitro re-stimulation of CD4+ T-cells correlates with in vivo FMD vaccine induced protection of cattle against disease and persistent infection

The immune defense against FMDV has been correlated to the antibody mediated component. However, there are occasions when some animals with high virus neutralising (VN) antibody are not protected following challenge and some with low neutralising antibody which do not succumb to disease. The importance of cell mediated immunity in clinical protection is less clear and so we investigated the source and production of interferon-gamma (IFN-γ) in re-stimulated whole blood of FMDV immunized cattle and its correlation to vaccine induced protection and FMDV persistence. We were able to show a positive correlation between IFN-γ response and vaccine induced protection as well as reduction of long term persistence of FMD virus. When combining this IFN-γ response in re-stimulated blood with virus neutralizing antibody titer in serum on the day of challenge, a better correlation of vaccine-induced protection with IFN-γ and VN antibody was predicted. Our investigations also showed that CD4+ T-cells are the major proliferating phenotype and IFN-γ producing cells.

A DNA vaccine encoding foot-and-mouth disease virus B and T-cell epitopes targeted to class II swine leukocyte antigens protects pigs against viral challenge

Development of efficient and safer vaccines against foot-and-mouth disease virus (FMDV) is a must. Previous results obtained in our laboratory have demonstrated that DNA vaccines encoding B and T cell epitopes from type C FMDV, efficiently controlled virus replication in mice, while they did not protect against FMDV challenge in pigs, one of the FMDV natural hosts. The main finding of this work is the ability to improve the protection afforded in swine using a new DNA-vaccine prototype (pCMV-APCH1BTT), encoding FMDV B and T-cell epitopes fused to the single-chain variable fragment of the 1F12 mouse monoclonal antibody that recognizes Class-II Swine Leukocyte antigens. Half of the DNA-immunized pigs were fully protected upon viral challenge, while the remaining animals were partially protected, showing a delayed, shorter and milder disease than control pigs. Full protection in a given vaccinated-pig correlated with the induction of specific IFNγ-secreting T-cells, detectable prior to FMDV-challenge, together with a rapid development of neutralizing antibodies after viral challenge, pointing towards the relevance that both arms of the immune response can play in protection. Our results open new avenues for developing future FMDV subunit vaccines.

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.

Self Replicating Gene Vaccine Carrying P1-2A Gene of FMDV Serotype O and its Effects on the Immune Responses of Cattle

DNA vaccines are considered as alternatives to live attenuated ones for those diseases like foot-and-mouth disease (FMD) where the production and application of live vaccines have been found unsuccessful. However, stability of DNA and the quantity of antigen expressed are the major limitation with naked DNA vaccines. To address these issues self replicating gene vaccine construct was made for foot-and-mouth disease virus (FMDV) type 'O' and studied. The vector for vaccine construct, designated as pSinCMVVac carried CMV promoter and Poly(A) signal sequences at 5' and 3' end of Sindbis replicase gene respectively. Gene for structural protein precursor (P1-2A) of FMDV serotype 'O' was inserted into pSinCMVVac under subgenomic promoter. 5'UTR (untranslated region) of FMDV was introduced upstream of P1-2A to enhance the level of expression of cloned gene. Functionality of the vaccine construct was confirmed in vitro and in vivo. The self-replicating gene vaccine construct was tested in cattle in comparison with naked DNA vaccine carrying P1-2A and 3CD (pUP3CD). Humoral immune response by ELISA and SNT and cellular response by lymphoproliferation assay using MTT were studied. The default approach of using self replicating gene vaccine in high dose and multiple injection in cattle as followed in our studies might result in immunosuppression as this was observed in our subsequent experiments in guinea pigs. Hence based on dose response studies, vaccine strategy needs to be decided. However, the approach of using Sindbis polymerase gene and UTR in FMDV vaccine is the first report and shows future scope of developing such vaccines.

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.

Induction of foot-and-mouth disease virus-specific cytotoxic T cell killing by vaccination

Foot-and-mouth disease (FMD) continues to be a significant threat to the health and economic value of livestock species. This acute infection is caused by the highly contagious FMD virus (FMDV), which infects cloven-hoofed animals, including large and small ruminants and swine. Current vaccine strategies are all directed toward the induction of neutralizing antibody responses. However, the role of cytotoxic T lymphocytes (CTLs) has not received a great deal of attention, in part because of the technical difficulties associated with establishing a reliable assay of cell killing for this highly cytopathic virus. Here, we have used recombinant human adenovirus vectors as a means of delivering FMDV antigens in a T cell-directed vaccine in pigs. We tested the hypothesis that impaired processing of the FMDV capsid would enhance cytolytic activity, presumably by targeting all proteins for degradation and effectively increasing the class I major histocompatibility complex (MHC)/FMDV peptide concentration for stimulation of a CTL response. We compared such a T cell-targeting vaccine with the parental vaccine, previously shown to effectively induce a neutralizing antibody response. Our results show induction of FMDV-specific CD8(+) CTL killing of MHC-matched target cells in an antigen-specific manner. Further, we confirm these results by MHC tetramer staining. This work presents the first demonstration of FMDV-specific CTL killing and confirmation by MHC tetramer staining in response to vaccination against FMDV.

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.

Improved immune response by ID-pVAC: a secretory DNA vaccine construct delivered by PLG micro particles against foot and mouth disease in guinea pigs

Foot and mouth disease (FMD) outbreaks usually have devastating effects on the economy of countries were disease is endemic due to direct and indirect cost; most of them related to international trade embargoes of animals and animal products. Although currently used inactivated vaccine provides protection, it has several drawbacks like short duration of immunity, and the requirement for containment facilities. A DNA vaccine construct which expresses the secretary antigens, delivered through micro particles could be one of the alternate approaches to overcome these limitations. Present study is envisaged to prepare a DNA vaccine construct containing the VP1 sequence of FMDV serotype O in pVAC vector. DNA vaccine was formulated by adsorbing plasmid DNA construct on cationic micro particles and administered in guinea pigs @25 μg DNA vaccine construct per animal intramuscularly. Sera samples collected were analyzed by sandwich ELISA and SNT, shown enhanced immune response in PLG adjuvanted DNA vaccine. MTT and 3H Thymidine incorporation have shown good CMI responses to PLG adjuvanted DNA. When challenged with 100 gpid50 of homologous virus 5 of the six animals were protected.

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.

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.

Enhanced antiviral activity against foot-and-mouth disease virus by a combination of type I and II porcine interferons

Previously, we showed that type I interferon (alpha/beta interferon [IFN-alpha/beta]) can inhibit foot-and-mouth disease virus (FMDV) replication in cell culture, and swine inoculated with 10(9) PFU of human adenovirus type 5 expressing porcine IFN-alpha (Ad5-pIFN-alpha) were protected when challenged 1 day later. In this study, we found that type II pIFN (pIFN-gamma) also has antiviral activity against FMDV in cell culture and that, in combination with pIFN-alpha, it has a synergistic antiviral effect. We also observed that while each IFN alone induced a number of IFN-stimulated genes (ISGs), the combination resulted in a synergistic induction of some ISGs. To extend these studies to susceptible animals, we inoculated groups of swine with a control Ad5, 10(8) PFU of Ad5-pIFN-alpha, low- or high-dose Ad5-pIFN-gamma, or a combination of Ad5-pIFN-alpha and low- or high-dose Ad5-pIFN-gamma and challenged all groups with FMDV 1 day later. The control group and the groups inoculated with either Ad5-pIFN-alpha or a low dose of Ad5-pIFN-gamma developed clinical disease and viremia. However, the group that received the combination of both Ad5-IFNs with the low dose of Ad5-pIFN-gamma was completely protected from challenge and had no viremia. Similarly the groups inoculated with the combination of Ad5s with the higher dose of Ad5-pIFN-gamma or with only high-dose Ad5-pIFN-gamma were protected. The protected animals did not develop antibodies against viral nonstructural (NS) proteins, while all infected animals were NS protein seropositive. No antiviral activity or significant levels of IFNs were detected in the protected groups, but there was an induction of some ISGs. The results indicate that the combination of type I and II IFNs act synergistically to inhibit FMDV replication in vitro and in vivo.

Enhanced immunogenicity to food-and-mouth disease virus in mice vaccination with alphaviral replicon-based DNA vaccine expressing the capsid precursor polypeptide (P1)

Recently, alphavirus replicon-based DNA vaccines, also known as suicidal DNA vaccines, have emerged as an important strategy to enhance the potency of DNA vaccines. In this study, two different types of DNA vaccines encoding the capsid precursor polypeptide (P1) of foot-and-mouth disease virus (FMDV) were constructed and the immunogenicity were investigated and compared in mouse model. The first DNA vaccine, pcDP1, is a conventional plasmid DNA vaccine in which P1 was driven directly by a cytomegalovirus promoter. The second DNA vaccine, pSCAP1, is a Semliki Forest virus (SFV) replicon-based DNA vaccine encoding the same antigen. In vitro expression and characterization indicated that two vaccine vectors could correctly produce the P1 antigen. However, pSCAP1 could induce obvious apoptosis of the transfected cells. After immunization in BALB/c mice, the P1-specific ELISA antibodies, neutralizing antibodies, as well as lymphocyte proliferative responses induced by pSCAP1 were significantly higher than those obtained in mice immunized with pcDP1. Notably, mice immunized with the pSCAP1 had the determined ability of clearing virus in their sera after FMDV challenge. These results indicate that the SFV replicon-based DNA vaccine pSCAP1 are more effective than conventional DNA vaccine and it can be considered a promising approach for the development of a safety and efficacious vaccine against FMDV.

Expression of the Foot-and-Mouth Disease Virus VP1 protein using a replication-competent recombinant canine adenovirus type 2 elicits a humoral antibody response in a porcine model

To develop a new type vaccine for Foot-and-Mouth Disease (FMD) prevention by using canine adenovirus as vector, the VP1 cDNA of Foot-and-Mouth Disease Virus (FMDV) type O strain China 99 was amplified by RT-PCR and cloned into pEGFP-C1 by replacing the GFP gene with the VP1 cDNA, resulting in an expression plasmid pVP1-C1. The expression cassette of VP1 composed of the CMV promoter, the VP1 gene and the SV40 early mRNA polyadenylation signal was recovered by Nsi I / Mlu I digestion of pVP1-C1 and cloned into the Canine adenovirus type-2 (CAV-2) genome in which E3 region was partly deleted by removing the Ssp I- Ssp I fragment. The recombinant virus (CAV-2-VP1) was obtained by transfecting the recombinant CAV-2-VP1 genome into MDCK cells with Lipofectamine 2000. Immunization trial in pigs with the recombinant virus, CAV-2-VP1, showed that CAV-2-VP1 could stimulate a specific immune response to both FMDV and the vector virus. Immune response to the VP1 and FMDV after VP1 expression was confirmed by ELISA, western blotting analysis and neutralization test. It was indicated that CAV-2 may serve as a vector for FMD vaccine development in pigs.

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.

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.

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.

Granulocyte-macrophage colony-stimulating factor does not increase the potency or efficacy of a foot-and-mouth disease virus subunit vaccine

Foot-and-mouth disease (FMD) is one of the most feared diseases of livestock worldwide. Vaccination has been a very effective weapon in controlling the disease, however a number of concerns with the current vaccine including the inability of approved diagnostic tests to reliably distinguish vaccinated from infected animals and the need for high containment facilities for vaccine production, have limited its use during outbreaks in countries previously free of the disease. A number of FMD vaccine candidates have been tested and a replication-defective human adenovirus type 5 (Ad5) vector containing the FMDV capsid (P1-2A) and 3C protease coding regions has been shown to completely protect pigs against challenge with the homologous virus (FMDV A12 and A24). An Ad5-P1-2A+3C vaccine for FMDV O1 Campos (Ad5-O1C), however, only induced a low FMDV-specific neutralizing antibody response in swine potency tests. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been successfully used to stimulate the immune response in vaccine formulations against a number of diseases, including HIV, hepatitis C and B. To attempt to improve the FMDV-specific immune response induced by Ad5-O1C, we inoculated swine with Ad5-O1C and an Ad5 vector containing the gene for porcine GM-CSF (pGM-CSF). However, in the conditions used in this trial, pGM-CSF did not improve the immune response to Ad5-O1C and adversely affected the level of protection of swine challenged with homologous FMDV.

Foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

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

Immunization of domestic pigs with a vaccinia virus (VV) recombinant expressing foot-and-mouth disease virus (FMDV) 3D protein conferred partial protection against challenge with infectious virus. The severity reduction of the clinical symptoms developed by the challenged animals occurred in the absence of significant levels of anti-3D circulating antibodies. This observation suggested that the partial protection observed was mediated by the induction of a 3D-specific cellular immune response. To gain information on the T cell recognition of FMDV 3D protein, we conducted in vitro proliferative assays using lymphocytes from outbred pigs experimentally infected with FMDV and 90 overlapping peptides spanning the complete 3D sequence. The use of pools of two to three peptides allowed the identification of T cell epitopes that were efficiently recognized by lymphocytes from at least four of the five animals analyzed. This recognition was heterotypic because anti-peptide responses increased upon reinfection of animals with a FMDV isolate from a different serotype. The results obtained with individual peptides confirmed the antigenicity observed with peptide pools. Detection of cytokine mRNAs by RT-PCR in lymphocytes stimulated in vitro by individual 3D peptides revealed that IFN-gamma mRNA was the most consistently induced, suggesting that the activated T cells belong to the Th 1 subset. These results indicate that 3D protein contains epitopes that can be efficiently recognized by porcine T lymphocytes from different infected animals, both upon primary and secondary (heterotypic) FMDV infection. These epitopes can extend the repertoire of viral T cell epitopes to be included in subunit and synthetic FMD vaccines.

Immediate protection of swine from foot-and-mouth disease: a combination of adenoviruses expressing interferon alpha and a foot-and-mouth disease virus subunit vaccine

We have previously shown that swine inoculated with recombinant, replication-defective human adenovirus type 5 containing the porcine interferon alpha gene (Ad5-pIFNalpha) are completely protected when challenged 1 day later with virulent foot-and-mouth disease virus (FMDV). In the current study, we examined the duration of protection afforded swine by Ad5-pIFNalpha and the ability of a combination of Ad5-pIFNalpha and a FMDV subunit vaccine delivered by Ad5-A24 (an Ad5 vector containing the capsid coding region of FMDV serotype A24 Cruzeiro and the 3C proteinase coding region of FMDV serotype A12) to induce immediate as well as long-lasting protection against homologous FMDV challenge. Groups of swine were inoculated with Ad5-pIFNalpha and challenged with virulent FMDV A24 1, 3, 5, and 7 days postinoculation (dpi) or 1 day preinoculation. All animals challenged 1 and 3dpi were completely protected from disease. The animals in the remaining groups had either no clinical signs of disease or clinical signs were delayed and less severe compared to the control group. Swine inoculated with a combination of Ad5-pIFNalpha and Ad5-A24 and challenged 5dpi were all completely protected from disease and developed a significant FMDV-specific neutralizing antibody response.