Construction and immunogenicity of a recombinant fowlpox virus containing the capsid and 3C protease coding regions of foot-and-mouth disease virus

Genomic characteristics of an avipoxvirus 282E4 strain

Avipoxvirus 282E4 strain was extensively applied into recombinant vaccine vector to prevent other infectious diseases. However, little information on the genomic background, functional and genetic evolutionary of the isolate 282E4 strain was clarified. The results showed that the linear genome of avipoxvirus 282E4 was 308,826 bp, containing 313 open reading frames (ORFs) and 12 new predicted ORFs. The 282E4 strain appears to encode two novel thymidine kinase proteins and two TGF-beta-like proteins that may be associated with the suppression of the host's antiviral response. Avipoxvirus 282E4 also encodes 57 ankyrin repeat proteins and 5 variola B22R-like proteins, which composed 7% of the avipoxvirus 282E4 genome. GO and KEGG analysis further revealed that 12 ORFs participate in viral transcription process, 7 ORFs may function during DNA repair, replication and biological synthesis, and ORF 208 is involved in the process of virus life cycle. Interestingly, phylogenetic analysis based on concatenated sequences p4b and DNA polymerase of avipoxviruses gene demonstrates that avipoxvirus 282E4 strain is divergent from known FWPV isolates and is similar to shearwater poxvirus (SWPV-1) that belongs to the CNPV-like virus. Sequencing avipoxvirus 282E4 is a significant step to judge the genetic position of avipoxviruses within the larger Poxviridae phylogenetic tree and provide a new insight into the genetic background of avipoxvirus 282E4 and interspecies transmission of poxviruses, meanwhile, explanation of gene function provides theoretical foundation for vaccine design with 282E4 strain as skeleton.

In silico T cell epitope identification for SARS-CoV-2: Progress and perspectives

Growing evidence suggests that T cells may play a critical role in combating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, COVID-19 vaccines that can elicit a robust T cell response may be particularly important. The design, development and experimental evaluation of such vaccines is aided by an understanding of the landscape of T cell epitopes of SARS-CoV-2, which is largely unknown. Due to the challenges of identifying epitopes experimentally, many studies have proposed the use of in silico methods. Here, we present a review of the in silico methods that have been used for the prediction of SARS-CoV-2 T cell epitopes. These methods employ a diverse set of technical approaches, often rooted in machine learning. A performance comparison is provided based on the ability to identify a specific set of immunogenic epitopes that have been determined experimentally to be targeted by T cells in convalescent COVID-19 patients, shedding light on the relative performance merits of the different approaches adopted by the in silico studies. The review also puts forward perspectives for future research directions.

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

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

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.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

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

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

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.

Construction and evaluation of a new triple-gene expression cassette vaccinia virus shuttle vector

A vaccinia virus shuttle vector pSTKE with a triple-gene expression cassette was designed, and the derived recombinant virus could express at least three different target genes. A vaccinia virus and its mutant as the original viruses and EGFP as the reporter gene were used to verify the three expression cassettes. Two recombinant viruses containing EGFP were obtained by homologous recombination and plaque screening. The expression and genetic stability of the recombinant virus and foreign genes were analyzed using PCR, real-time PCR, and Western blot. And then EGFP, RFP and BFP were inserted into MCS1, MCS2 and MCS3 of pSTKE respectively, resulting in the generation of recombinant expressing three fluorescent proteins mentioned above, and the recombinant was continuously passaged 20 times. The results showed that EGFP, RFP and BFP were highly expressed in vaccinia virus, and no interaction between the three expression cassettes was observed. Recombinant viruses were stable genetically. The shuttle vector pSTKE can be used for efficient and stable gene expression to address problems in recombinant vaccinia viruses, such as low expression efficiency, limited number of inserted genes. In addition, this study provides a solid foundation for the development of a new genetically engineered vaccine.

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.

DNA immunization of pigs with foot-and-mouth disease virus minigenes: from partial protection to disease exacerbation

Despite several attempts to design new vaccines, there are as of yet no available alternatives to the conventional FMDV vaccines. Here, we present the divergent results obtained in pigs after immunization with two experimental DNA vaccines encoding one B and two T cell FMDV epitopes, either expressed alone (pCMV-BTT) or fused to a strong signal peptide (pCMV-spBTT). While all pigs vaccinated with pCMV-spBTT showed both a delay in the disease onset and reduced severity of signs and lesions after FMDV challenge, pigs immunized with pCMV-BTT showed an exacerbation of the disease and most of the pigs remained viremic at 10 days post-infection, the end-point of the experiment, thus opening concerns about FMDV-suboptimal immunization. Interestingly, only one of the four pigs vaccinated with pCMV-spBTT showed neutralizing antibodies before challenge, demonstrating that partial protection against FMDV could be afforded in the absence of preexisting neutralizing antibodies.

Immune responses to the oral administration of recombinant Bacillus subtilis expressing multi-epitopes of foot-and-mouth disease virus and a cholera toxin B subunit

Bacillus subtilis has been engineered successfully to express heterologous antigens for use as a vaccine vehicle that can elicit mucosal and systemic immunity response. In this study, a recombinant B. subtilis expressing the B subunit of cholera toxin (CT-B) and an epitope box constituted with antigen sites from foot-and-mouth disease virus (FMDV) type Asia 1 was constructed and named 1A751/CTB-TEpiAs. Its capability to induce mucosal, humoral, and cellular responses in mice and guinea pigs was evaluated after oral administration with vegetative cells of 1A751/CTB-TEpiAs. In addition, its capability to protect guinea pigs against homologous virus challenge was examined. All animals were given booster vaccination at day 21 after initial inoculation and guinea pigs were challenged 3 weeks after booster vaccination. The control groups were inoculated with a commercial vaccine or administered orally with 1A751/pBC38C or an oral buffer. All animals vaccinated with 1A751/CTB-TEpiAs developed specific anti-FMDV IgA in lung and gut lavage fluid, serum ELISA antibody, neutralizing antibody as well as T lymphocyte proliferation, and IFN-γ secretory responses. Three of the five guinea pigs vaccinated with 1A751/CTB-TEpiAs were protected completely from the viral challenge. The results demonstrate the potential viability of a B. subtilis-based recombinant vaccine for the control and prevention of FMDV infections.

Effect of foot-and-mouth disease virus capsid precursor protein and 3C protease expression on bovine herpesvirus 1 replication

Several reports have previously shown that expression of the foot-and-mouth disease virus (FMDV) capsid precursor protein encoding region P1-2A together with the 3C protease (P1-2A/3C) results in correct processing of the capsid precursor into VP0, VP1 and VP3 and formation of FMDV capsid structures that are able to induce a protective immune response against FMDV challenge after immunization using naked DNA constructs or recombinant viruses. To elucidate whether bovine herpesvirus 1 (BHV-1) might also be suitable as a viral vector for empty capsid generation, we aimed to integrate a P1-2A/3C expression cassette into the BHV-1 genome, which, however, failed repeatedly. In contrast, BHV-1 recombinants that expressed an inactive 3C protease or the P1-2A polyprotein alone could be easily generated, although the recombinant that expressed P1-2A exhibited a defect in direct cell-cell spread and release of infectious particles. These results suggested that expression of the original, active FMDV 3C protease is not compatible with BHV-1 replication. This conclusion is supported by the isolation of recombinant BHV-1/3C*, which contained mutations within the 3C ORF (3C* ORF)--probably introduced spontaneously during generation of BHV-1/3C*--instead of the authentic 3C ORF contained in the transfer plasmids. Within the 3C* ORF, the codons for glycine 38 and phenylalanine 48 were both substituted by codons for serine. The resulting 3C* protease exhibits a highly reduced activity for proteolytic processing of the P1-2A polyprotein and thus might be a good candidate for the generation of live attenuated FMDV variants.

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.

Technical transformation of biodefense vaccines

Biodefense vaccines are developed against a diverse group of pathogens. Vaccines were developed for some of these pathogens a long time ago but they are facing new challenges to move beyond the old manufacturing technologies. New vaccines to be developed against other pathogens have to determine whether to follow traditional vaccination strategies or to seek new approaches. Advances in basic immunology and recombinant DNA technology have fundamentally transformed the process of formulating a vaccine concept, optimizing protective antigens, and selecting the most effective vaccine delivery approach for candidate biodefense vaccines.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

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.

Orally delivered foot-and-mouth disease virus capsid protomer vaccine displayed on T4 bacteriophage surface: 100% protection from potency challenge in mice

An orally delivered foot-and-mouth disease (FMD) vaccine has not previously been reported. By using a T4 bacteriophage nanoparticle surface gene-protein display system (T4-S-GPDS), we created a foot-and-mouth disease virus (FMDV) entire capsid protein vaccine candidate. On the T4 phage surface SOC site, a full length FMDV capsid precursor polyprotein (P1, 755 aa) and proteinase 3C (213 aa) derived from an infected pig of serotype O strain GD-10 (1999), were separately displayed on different T4 phage particle surfaces through inserting their coding region DNAs into the T4 phage genome, yielding phage strains T4-P1 and T4-3C. We also constructed a series of FMDV sub-full length capsid structural protein (subunit) containing T4 phage recombinant vaccines. Both sucking and young BALB/c mice were used as two kinds of FMDV vaccine potency evaluation models. Many groups of both model mice were vaccinated orally or by subcutaneous injection with varying FMDV-T4 phage recombinant vaccines, with and without addition of adjuvant, then challenged with a lethal dose of cattle source virulent FMDV. In the case of immunization with a mixture of phage T4-P1 and phage T4-3C particles without any adjuvant added, all mice were 100% protected following either oral or injection immunization, whereas 100% of the control, non-immunized mice and mice immunized with only T4 phage vector Z1/Zh(-) or wild-type T4(+)D phage died; in contrast, with FMDV subunit vaccine, less than 75% protection followed the same potency challenge in both mice model groups. In addition, two pigs immunized with a phage T4-P1 and phage T4-3C mix were protected upon housing together with infected pigs. This study represents a clear example of how FMD and other pathogenic disease vaccines can be prepared by a simple and efficient bacteriophage route.

Immune responses of swine inoculated with a recombinant fowlpox virus co-expressing P12A and 3C of FMDV and swine IL-18

Two recombinant fowlpox viruses (rFPV-P1 and rFPV-IL18-2AP12A) containing foot-and-mouth disease virus (FMDV) capsid polypeptide, 3C coding regions of O/NY00 were evaluated to determine their abilities to induce humoral and cellular responses in the presence or absence of swine IL-18 as genetic adjuvant. The ability to protect swine against homologous virus challenge was examined. All swine were given booster vaccinations at 21 days after the initial inoculation and were challenged 10 days after the booster vaccination. Control groups were inoculated with wild-type fowlpox virus (wtFPV). All animals vaccinated with rFPV-P12A and rFPV-IL18-P12A developed specific anti-FMDV ELISA antibody and neutralizing antibody and T-lymphocyte proliferation was observed. Cellular immune function was evaluated via examination of IFN-gamma production in swine peripheral blood serum. The results demonstrate the potential viability of a fowlpox virus-based recombinant vaccine in the control and prevention of FMDV infections.

Immune responses of pigs inoculated with a recombinant fowlpox virus coexpressing GP5/GP3 of porcine reproductive and respiratory syndrome virus and swine IL-18

Two recombinant fowlpox viruses (rFPV-ORF5-ORF3 and rFPV-IL-18-ORF5-ORF3) containing the ORF5/ORF3 cDNAs of PRRSV (strain Chang Chun) and IL-18 of swine were constructed and evaluated for theirs abilities to induce humoral and cellular responses in piglets. In addition, their abilities to protect piglets against homologous virus challenge were examined. All piglets were given booster vaccinations at 21 days after the initial inoculation, and all piglets were challenged at 60 after the initial inoculation. Control groups were inoculated with wild-type fowlpox virus (wtFPV). All animals vaccinated with rFPV-ORF5-ORF3 and rFPV-IL-18-ORF5-ORF3 developed specific anti-PRRSV ELISA antibody and neutralizing antibody, as well as T-lymphocyte proliferation response. To evaluate the cellular immune function, IFN-gamma production in pigs serum and T-lymphocytes (CD4 and CD8 T cells) in peripheral blood were examined. Following challenge with a pathogenic strain of PRRSV (strain Chang Chun), piglets inoculated with recombinant fowlpox virus (rFPV) showed lower (P<0.05) temperature, viremia and virus load in bronchial lymph nodes than control animals, suggesting the establishment of partial protection against PRRSV infection. The results demonstrated the potential use of a fowlpox virus-based recombinant vaccine in the control and prevention of PRRSV infections.