Evaluation of swinepox virus as a vaccine vector in pigs using an Aujeszky's disease (pseudorabies) virus gene insert coding for glycoproteins gp50 and gp63

Skin-Based Vaccination: A Systematic Mapping Review of the Types of Vaccines and Methods Used and Immunity and Protection Elicited in Pigs

The advantages of skin-based vaccination include induction of strong immunity, dose-sparing, and ease of administration. Several technologies for skin-based immunisation in humans are being developed to maximise these key advantages. This route is more conventionally used in veterinary medicine. Skin-based vaccination of pigs is of high relevance due to their anatomical, physiological, and immunological similarities to humans, as well as being a source of zoonotic diseases and their livestock value. We conducted a systematic mapping review, focusing on vaccine-induced immunity and safety after the skin immunisation of pigs. Veterinary vaccines, specifically anti-viral vaccines, predominated in the literature. The safe and potent skin administration to pigs of adjuvanted vaccines, particularly emulsions, are frequently documented. Multiple methods of skin immunisation exist; however, there is a lack of consistent terminology and accurate descriptions of the route and device. Antibody responses, compared to other immune correlates, are most frequently reported. There is a lack of research on the underlying mechanisms of action and breadth of responses. Nevertheless, encouraging results, both in safety and immunogenicity, were observed after skin vaccination that were often comparable to or superior the intramuscular route. Further research in this area will underlie the development of enhanced skin vaccine strategies for pigs, other animals and humans.

Vaccines against pseudorabies virus (PrV)

Aujeszkýs disease (AD, pseudorabies) is a notifiable herpesvirus infection of pigs causing substantial economic losses to swine producers. AD in pigs is controlled by the use of vaccination with inactivated and attenuated live vaccines. Starting with classically attenuated live vaccines derived from low virulent field isolates, AD vaccination has pioneered novel strategies in animal disease control by the first use of genetically engineered live virus vaccines lacking virulence-determining genes, and the concept of DIVA, i.e. the serological differentiation of vaccinated from field-virus infected animals by the use of marker vaccines and respective companion diagnostic tests. The basis for this concept has been the molecular characterization of PrV and the identification of so-called nonessential envelope glycoproteins, e.g. glycoprotein E, which could be eliminated from the virus without harming viral replication or immunogenicity. Eradication of AD using the strategy of vaccination-DIVA testing has successfully been performed in several countries including Germany and the United States. Furthermore, by targeted genetic modification PrV has been developed into a powerful vector system for expression of foreign genes to vaccinate against several infectious diseases of swine, while heterologous vector systems have been used for expression of major immunogens of PrV. This small concise review summarizes the state-of-the-art information on PrV vaccines and provides an outlook for the future.

Animal poxvirus vaccines: a comprehensive review

The family Poxviridae includes several viruses of medical and veterinary importance. Global concerted efforts combined with an intensive mass-vaccination campaign with highly efficaceious live vaccine of vaccinia virus have led to eradication of smallpox. However, orthopoxviruses affecting domestic animals continue to cause outbreaks in several endemic countries. Different kinds of vaccines starting from conventional inactivated/attenuated to recombinant protein-based vaccines have been used for control of poxvirus infections. Live virus homologous vaccines are currently in use for diseases including capripox, parapox, camelpox and fowlpox, and these vaccines are highly effective in eliciting (with the exception of parapoxviruses) long-lasting immunity. Attenuated strains of poxviruses have been exploited as vectored vaccines to deliver heterologous immunogens, many of them being licensed for use in animals. Worthy of note are vaccinia virus, fowlpox virus, capripoxvirus, parapoxvirus and canary pox, which have been successfully used for developing new-generation vaccines targeting many important pathogens. Remarkable features of these vaccines are thermostability and their ability to engender both cellular and humoral immune responses to the target pathogens. This article updates the important vaccines available for poxviruses of livestock and identifies some of the research gaps in the present context of poxvirus research.

Immune responses and protective efficacy of a recombinant swinepox virus co-expressing HA1 genes of H3N2 and H1N1 swine influenza virus in mice and pigs

The recombinant swine poxvirus rSPV/H3-2A-H1 co-expressing HA1 genes of H3N2 and H1N1 subtype SIV has been constructed and identified. Inoculations of rSPV/H3-2A-H1 yielded ELISA and neutralization antibodies against SIV H1N1 and H3N2, and elicited potent H1N1 and H3N2 SIV-specific INF-γ response from T-lymphocytes in mice and pigs in this study. Complete protection against SIV H1N1 or H3N2 challenge in pigs was observed.

Immune responses and protection efficacy of a recombinant swinepox virus expressing HA1 against swine H3N2 influenza virus in mice and pigs

Swine influenza virus (SIV) is not only an important respiratory pathogen in pigs but also a potent threat to human health. Even though immunization with recombinant vaccinia poxviruses expressing protective antigens as a vaccination strategy has been widely used for many infectious diseases, development of recombinant swinepox virus (rSPV) vector for this purpose has been less successful. Here, we report the construction of a recombinant swinepox virus (rSPV) expressing hemagglutinin (HA1) of H3N2 SIV (rSPV-H3). Immune responses and protection efficacy of the vaccination vector were assessed in both mouse and pig models. Prime and boost inoculations of rSPV-H3 yielded neutralization antibody against SIV and elicited potent H3N2 SIV-specific INF-γ response from T-lymphocytes. Complete protection of pigs against H3N2 SIV challenge was achieved. No pigs showed severe systemic and local reactions and no SIV was found shed from the pigs vaccinated with rSPV-H3 after challenge. The data suggest that the SPV-based recombinant vector expressing HA1 of H3N2 SIV might serve as a promising SIV vaccine for protection against SIV infection.

Immune responses and protective efficacy of a recombinant swinepox virus expressing HA1 against swine H1N1 influenza virus in mice and pigs

Swine influenza virus (SIV) is not only an important respiratory pathogen in pigs but also a potent threat to human health. Although immunization with recombinant poxviruses expressing protective antigens as vaccines has been widely used for against many infectious diseases, development of recombinant swinepox virus (rSPV) vector for the purpose has been less successful. Here, we report the construction of a recombinant swinepox virus (rSPV-HA1) expressing hemagglutinin (HA1) of H1N1 SIV. Immune responses and protection efficacy of the vaccination vector were evaluated in both the mouse model and the natural host: pig. Prime and boost inoculations of rSPV-HA1 yielded high levels of neutralization antibody against SIV and elicited potent H1N1 SIV-specific IFN-γ response from T-lymphocytes. Complete protection of pigs against H1N1 SIV challenge was observed. No pigs showed evident systemic and local reactions to the vaccine and no SIV shedding was detected from pigs vaccinated with rSPV-HA1 after challenge. Our data demonstrated that the recombinant swinepox virus encoding HA1 of SIV H1N1 may serve as a promising SIV vaccine for protection against SIV infection.

A novel vaccine against Streptococcus equi ssp. zooepidemicus infections: the recombinant swinepox virus expressing M-like protein

To develop a safer, more immunogenic and efficacious vaccine against Streptococcus equi ssp. zooepidemicus (SEZ) infections, the gene of M-like protein (SzP) was placed under the strong vaccinia virus promoter P28 and then inserted into swinepox virus (SPV) genome. The recombinant swinepox virus (rSPV-szp) was isolated in a non-selective medium by the co-expression of Escherichia coli LacZ gene and verified by PCR, western blotting and immunofluorescence assays. To evaluate the immunogenicity of this rSPV-szp, ICR mice were immunized with the rSPV-szp, inactivated SEZ vaccine (positive control), wild type SPV (negative control), or PBS (challenge control). All mice were intraperitoneally challenged with 5 LD(50) of homogenous ATCC 35246 strain 14 days post-vaccination. The results showed that at least 70% mice in rSPV-szp-vaccinated group were protected against homogenous ATCC 35246 challenge, the survival rate was significantly higher compared with mice in the negative control group and the challenge control group (P<0.001). The antibody titers of the rSPV-szp-vaccinated group were significantly higher (P<0.05) than the other three groups. Passive immune protection assays showed that the hyperimmune sera against M-like protein could provide mice with complete protection against challenge of ATCC 35246. Semi-quantitative RT-PCR analysis showed a marked increased in levels of IL-4 and IFN-γ mRNA in immunized mice. The results suggested that the recombinant rSPV-szp provided mice with significant protection from the SEZ infections. It is a promising candidate for the vaccine development against SEZ infections.

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.

Towards a unique and transmissible vaccine against myxomatosis and rabbit haemorrhagic disease for rabbit populations

Currently available vaccines against myxomatosis and rabbit hemorrhagic disease virus (RHDV) are not suited to immunise wild rabbit populations, as vaccines need to be delivered individually by conventional veterinary practices. As an alternative approach, research in Spain has focused on the development of a transmissible vaccine. A recombinant virus has been constructed based on a naturally attenuated myxoma virus (MV) field strain, expressing the RHDV capsid protein (VP60). Following inoculation of rabbits, the recombinant virus (MV-VP60) induced specific antibody responses against MV and RHDV, conferring protection against lethal challenges with both viruses. Furthermore, the recombinant MV-VP60 virus showed a limited horizontal transmission capacity, either by direct contact or in a flea-mediated process, promoting immunisation of contact uninoculated animals. Efficacy and safety of the vaccine have been extensively evaluated under laboratory conditions and in a limited field trial. The development of the transmissible vaccine strategy and the steps being taken to obtain the marketing authorisation for the vaccine in the European Union are presented in this review.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin

The host range of swinepox virus (SPV) is restricted to swine, although SPV has been shown to infect mammalian, non-swine cells, without recovery of infectious virus. SPV is a reasonable candidate for development as a non-productively replicating viral vector for use in non-swine, mammalian species, such as the cat. A novel SPV gene deletion (SPV 043) was created and found to be non-attenuating. This deletion was utilized to generate a stable recombinant virus expressing the Gag-Pro and Env proteins of feline leukemia virus (FeLV). Expression and replication of this vector was studied in embryonic swine kidney cells (ESK-4), and two feline cell lines, Crandell feline kidney cells (CRFK) and feline skin fibroblasts (FSF). Our results showed that feline cells were susceptible to infection by SPV and supported expression of foreign genes driven by synthetic poxvirus promoters, however, SPV viral DNA was not replicated in feline cells and infectious virus was not recovered. In addition, FeLV Gag virus-like particles were produced from both ESK-4 and CRFK cells and foreign antigens were incorporated into infectious SPV intracellular mature virions (IMV). These results suggest that SPV may have potential as a safe vaccine delivery vector for cats.

Construction of recombinant swinepox viruses and expression of the classical swine fever virus E2 protein

To explore the swinepox virus (SPV) as a potential live vector for immunization, a vector was developed for the construction of a recombinant SPV carrying foreign genes. In this system, a foreign gene placed under the strong vaccinia virus promoter P(11) can be inserted into the viral thymidine kinase (TK) gene, and the recombinant virus can be isolated in a non-selective medium by the co-expression of E. coli lacZ gene. Compared with the wild type virus, the TK(-)recombinant SPV showed a modest level of attenuation in porcine cells while more attenuation was observed in monkey or human cells. Using this system, a recombinant virus expressing the E2 glycoprotein of classical swine fever virus (CSFV) was produced. Engineered with the gX signal sequence of the pseudorabies virus, and transmembrane domain of E2, the E2 protein was expressed as a dimeric form in the cytoplasm of the infected cells.

Sequence and analysis of a swinepox virus homologue of the vaccinia virus major envelope protein P37 (F13L)

P37 (F13L gene product), the most abundant protein in the envelope of the extracellular virus form of the prototype poxvirus, vaccinia virus (VV), is a crucial player in the process leading to acquisition of the envelope, virus egress and transmission. We have cloned and sequenced a swinepox virus (SPV) gene homologous to VV F13L. The SPV gene product, termed P42, was 54% identical to P37, the VV F13L gene product, and, among the poxviruses, was most similar (73% identity) to the myxoma virus homologue. The SPV P42 gene contained late transcription signals and was expressed only at late times during infection. The protein was palmitylated, and showed an intracellular distribution similar to that of VV P37, both by immunofluorescence and by subcellular fractionation. As with VV P37, SPV P42 was incorporated in extracellular enveloped SPV particles, but was absent from the intracellular mature virus form. To check the ability of SPV P42 to function in the context of VV infection, we inserted the SPV gene into a VV deficient in P37, which is severely blocked in virus envelopment and cell-to-cell transmission. Despite correct expression of SPV P42, the resulting recombinant VV showed no rescue of extracellular virus formation or cell-to-cell virus spread. The lack of function of SPV P42 in the VV genetic background suggests that specific interactions between SPV P42 or VV P37 and other viral proteins is required to drive the envelopment process.

Horizontal transmissible protection against myxomatosis and rabbit hemorrhagic disease by using a recombinant myxoma virus

We have developed a new strategy for immunization of wild rabbit populations against myxomatosis and rabbit hemorrhagic disease (RHD) that uses recombinant viruses based on a naturally attenuated field strain of myxoma virus (MV). The recombinant viruses expressed the RHDV major capsid protein (VP60) including a linear epitope tag from the transmissible gastroenteritis virus (TGEV) nucleoprotein. Following inoculation, the recombinant viruses induced specific antibody responses against MV, RHDV, and the TGEV tag. Immunization of wild rabbits by the subcutaneous and oral routes conferred protection against virulent RHDV and MV challenges. The recombinant viruses showed a limited horizontal transmission capacity, either by direct contact or in a flea-mediated process, promoting immunization of contact uninoculated animals.

Swinepox virus as a vaccine vector for swine pathogens

Several small and large viruses (e.g., adenovirus, poxvirus, and herpesviruses) have been investigated as vaccine vectors. Each viral system has its advantages and disadvantages. One major advantage for viral vector vaccines is their ability to elicit a protective cell-mediated immunity as well as a humoral response to the antigen delivered by the vector. One major problem to using recombinant viruses as vaccines is the pathogenic potential of the parent virus. Therefore, it is important that along with the optimal expression of the foreign genes and ability to provide protection, the pathogenicity of the vector virus must be reduced during genetic manipulation without affecting its multiplication. The requirements to develop a viral vector, for example, swinepox virus, are a cell culture system that will support the growth of the virus, a suitable nonessential region(s) in the virus genome for insertion of foreign DNA so that virus replication is not affected, a foreign gene(s) that encodes for an immunogenic protein of a swine pathogen, strong transcriptional regulatory elements (promoters) necessary for optimal expression of the foreign genes, a procedure for delivering the foreign gene(s) into the nonessential locus, and a convenient method of distinguishing the recombinant viruses from the parent wild-type virus. Using this methodology, recombinant swinepox virus vaccines expressing pseudorabies virus antigens have been developed and shown to provide protection against challenge. These studies and evidence of local infection of the oral tract by swinepox virus indicate its potential as a recombinant vector for providing immunity against various swine pathogens including those that infect the respiratory and gastrointestinal tracts.

Viral vectors for veterinary vaccines

Whatever strategy is adopted for the development of viral vectors for delivery of veterinary vaccines there are several key points to consider: (1) Will the vectored vaccine give a delivery advantage compared to what's already available? (2) Will the vectored vaccine give a manufacturing advantage compared to what's already available? (3) Will the vectored vaccine provide improved safety compared to what's already available? (5) Will the vectored vaccine increase the duration of immunity compared to what's already available? (6) Will the vectored vaccine be more convenient to store compared to what's already available? (7) Is the vectored vaccine compatible with other vaccines? If there is no other alternative available then the answer to these questions is easy. However, if there are alternative vaccines available then the answers to these questions become very important because the answers will determine whether a vectored vaccine is merely a good laboratory idea or a successful vaccine.

Recombinant swinepox virus expressing beta-galactosidase: investigation of viral host range and gene expression levels in cell culture

Swinepox virus (SPV) has been proposed as a potential vector for generating recombinant vaccines for swine. However, little is known about important aspects of SPV biology, such as the functionality of SPV promoters or the host range of SPV. Using a transient expression assay, well-characterized vaccinia virus promoters were shown to be active in cells infected with SPV. A recombinant SPV expressing beta-galactosidase (beta-gal) was constructed and characterized. The E. coli LacZ gene was placed under the control of a strong vaccinia synthetic early/late promoter and was inserted by homologous recombination in a noncoding region of the SPV genome. The recombinant SPV expressing beta-gal was used to characterize the host range of the virus by measuring protein expression and virus production in different cell lines. In general, SPV expressed more protein and grew more efficiently than vaccinia virus in porcine cell lines. Surprisingly, the recombinant SPV was able to infect and replicate in several cell lines of nonswine origin. The virus directed regulated early and late gene expression of beta-gal in those cells and formed blue plaques in cell monolayers in the presence of X-gal. Upon infection with the recombinant SPV, there was a significant level of viral replication, and the virus can be serially passaged in some nonswine cell lines. The data presented suggest that despite the strict host tropism of SPV, the virus exhibits a relatively broad host range in cell culture.

A synthetic vaccinia virus promoter with enhanced early and late activity

A synthetic vaccinia virus promoter (Psel) was constructed based upon sequences which increase activity of the P7.5 early/late promoter. Comparison of luciferase activity in lysates from cells infected with recombinant vaccinia viruses expressing the luciferase gene either under the control of the P7.5 promoter or Psel, demonstrated significantly enhanced activity mediated by Psel at both early and late times post infection. This promoter may be of considerable benefit in the construction of recombinant poxviruses where early foreign gene expression is important for generating a protective immune response in vaccinated animals, or in reporter/target gene expression in vitro.

Recombinant viral vector vaccines for the veterinary use

Recently, genetically engineering using recombinant DNA techniques has been applied to design new viral vaccines in order to reduce some problems which present viral vaccines have. Up to now, many viruses have been investigated for development of recombinant attenuated vaccines or live viral vectors for delivery of foreign immunogenic antigens. In this review, we introduced three kind of viruses; herpesviruses, vaccinia viruses, and adenoviruses, which have best widely been studied as recombinant vaccines or delivery vaccines for the veterinary use.

The role of biotechnologically engineered vaccines and diagnostics in pseudorabies (Aujeszky's disease) eradication strategies

Modern-day biotechnology has an almost unlimited number of possibilities for reducing the impact of hereditary and infectious diseases. To date one of its most visible and rewarding applications for veterinary medicine has been in the genetic engineering of vaccines and diagnostics to assist in the eventual eradication of pseudorabies (PR, Aujeszky's disease). In the following review we summarize some of the most pertinent issues relative to PR eradication and point out the present and potential role of biotechnology in achieving our goal.

Genetically engineered poxviruses for recombinant gene expression, vaccination, and safety

Vaccinia virus, no longer required for immunization against smallpox, now serves as a unique vector for expressing genes within the cytoplasm of mammalian cells. As a research tool, recombinant vaccinia viruses are used to synthesize and analyze the structure-function relationships of proteins, determine the targets of humoral and cell-mediated immunity, and investigate the types of immune response needed for protection against specific infectious diseases and cancer. The vaccine potential of recombinant vaccinia virus has been realized in the form of an effective oral wild-life rabies vaccine, although no product for humans has been licensed. A genetically altered vaccinia virus that is unable to replicate in mammalian cells and produces diminished cytopathic effects retains the capacity for high-level gene expression and immunogenicity while promising exceptional safety for laboratory workers and potential vaccine recipients.