Vaccination of pigs with replication-defective adenovirus vectored vaccines: the example of pseudorabies

The Development of Classical Swine Fever Marker Vaccines in Recent Years

Classical swine fever (CSF) is a severe disease that has caused serious economic losses for the global pig industry and is widely prevalent worldwide. In recent decades, CSF has been effectively controlled through compulsory vaccination with a live CSF vaccine (C strain). It has been successfully eradicated in some countries or regions. However, the re-emergence of CSF in Japan and Romania, where it had been eradicated, has brought increased attention to the disease. Because the traditional C-strain vaccine cannot distinguish between vaccinated and infected animals (DIVA), this makes it difficult to fight CSF. The emergence of marker vaccines is considered to be an effective strategy for the decontamination of CSF. This paper summarizes the progress of the new CSF marker vaccine and provides a detailed overview of the vaccine design ideas and immunization effects. It also provides a methodology for the development of a new generation of vaccines for CSF and vaccine development for other significant epidemics.

Current status of virus-vectored vaccines against pathogens that affect poultry

The most effective strategies for the control of disease in poultry are vaccination and biosecurity. Vaccines useful against pathogens affecting poultry must be safe, effective with a single dose, inexpensive, applicable by mass vaccination methods, and able to induce a protective immune response in the presence of maternal antibodies. Viral vector meet some of these characteristics and if the attenuated virus used as vector infects birds, the vaccine will have the advantage of being bivalent. Thus, viral vectors are currently a tool of choice for the development of new poultry vaccines. This review describes the main viruses used as vectors for the delivery and in vivo expression of antigens of poultry pathogens. It also presents the methodologies most frequently used to obtain recombinant viral vectors and summarizes the state-of-the-art related to vectored vaccines in poultry (some of them currently licensed), the pathogens targeted and their antigens, and the ability of these vaccines to induce an effective immune response. Finally, the review discusses the results of a few studies comparing recombinant viral vector vaccines and live-attenuated vaccines in vaccine matching challenges, and mentions strategies and future researches that can help to improve the efficacy of vectored vaccines in poultry birds.

Generation and efficacy evaluation of a recombinant adenovirus expressing the E2 protein of classical swine fever virus

Classical swine fever virus (CSFV) is the causative agent of classical swine fever (CSF), which causes significant economic losses to the pig industry worldwide. The E2 glycoprotein of CSFV is the main target for neutralizing antibodies. This study was aimed to develop a recombinant human adenovirus type 5 expressing the CSFV E2 gene (rAdV-E2) and evaluate its efficacy in rabbits and pigs. The results showed that the rabbits and the pigs immunized with the rAdV-E2 developed high-level CSFV-specific neutralizing antibodies. The rAdV-E2-immunized rabbits were protected from fever induced by infection with C-strain, which is pathogenic to the rabbit, and the rAdV-E2-immunized pigs were protected from lethal challenge with highly virulent Shimen strain. This indicates that the recombinant adenovirus can be an attractive candidate vaccine for preventing CSF.

Targeting the porcine immune system--particulate vaccines in the 21st century

During the last decade, the propagation of immunological knowledge describing the critical role of dendritic cells (DC) in the induction of efficacious immune responses has promoted research and development of vaccines systematically targeting DC. Based on the promise for the rational design of vaccine platforms, the current review will provide an update on particle-based vaccines of both viral and synthetic origin, giving examples of recombinant virus carriers such as adenoviruses and biodegradable particulate carriers. The viral carriers carry pathogen-associated molecular patterns (PAMP), used by the original virus for targeting DC, and are particularly efficient and versatile gene delivery vectors. Efforts in the field of synthetic vaccine carriers are focussing on decorating the particle surface with ligands for DC receptors such as heparan sulphate glycosaminoglycan structures, integrins, Siglecs, galectins, C-type lectins and toll-like receptors. The emphasis of this review will be placed on targeting the porcine immune system, but reference will be made to advances with murine and human vaccine delivery systems where information on DC targeting is available.

Growth characteristics of human adenoviruses on porcine cell lines

Human adenoviruses (hAdV) have been recognized as a highly prevalent virus family causing severe disease in immunocompromised patients. In xenotransplantation the xenograft therefore will be exposed to these viruses, which in case of its infection might contribute to posttransplant complications. To evaluate the susceptibility of porcine cells for hAdV, we infected the porcine cell line POEK with seven serotypes representing all six hAdV species. Additionally, a second porcine cell line (ST) was infected with two serotypes. Viral replication of serotypes varied: porcine cells were fully permissive for serotypes 1, 4 and 17, semi-permissive for 11 and 21, and non-permissive for 31 and 40. Furthermore, we demonstrated the interaction of serotype 1 with the porcine homologue of the coxsackie-adenovirus receptor, the receptor used by many hAdV serotypes for cell attachment. Thus, various adenovirus types of different hAdV species may be capable of infecting different porcine tissue types.

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.

Vaccination of pigs with a recombinant porcine adenovirus expressing the gD gene from pseudorabies virus

Five week old, commercially available large white pigs were vaccinated with either a single dose or two doses of a recombinant porcine adenovirus expressing the glycoprotein D gene from pseudorabies virus (PRV). Pigs were monitored for the development of serum neutralizing antibodies to PRV and challenged 3 weeks after final vaccination. Prior to challenge, pigs given 2 doses of the vaccine demonstrated boosted levels of antibody compared with those given a single dose, and all surviving pigs had increased neutralization titres over pre-challenge levels. Following challenge, pigs were monitored for clinical signs of disease, with blood and nasal swabs collected for virus isolation. All control animals became sick with elevated temperatures for 6 days post challenge, whereas; vaccinated animals displayed an increase in body temperature for only 2-3 days. Control pigs and those given a single dose all lost condition, but the group given 2 doses remained healthy. At postmortem, gross lesions of pneumonia only occurred in control animals and those given a single dose of vaccine. Histology carried out on the brains of all animals demonstrated a difference in severity of infection and frequency of immunohistochemical antigen detection between test animals, with control and single dose groups being most severely affected and pigs given 2 doses the least. Virus isolation studies demonstrated that no viraemia could be detected, but virus was found in nasal swabs from some animals in both groups of vaccinates following challenge.

Adenovirus-mediated expression of interleukin-1 receptor antagonist in swine cells in vitro and in vivo

Adenovirus-mediated gene delivery of anticytokines is a powerful tool for modulating the cytokine environment under conditions of respiratory disease. In order to determine the feasibility of cytokine modulation in the context of respiratory disease in swine, nonreplicating E1- and E3-deficient adenovirus constructs expressing a model protein, beta-galactosidase, and an anticytokine, the IL-1 receptor antagonist (IL-1Ra), were evaluated for in vitro expression in porcine PK15 cells, and in vivo following endotracheal instillation into the lungs. beta-Galactosidase and IL-1Ra were readily expressed in vitro in swine cells. Endotracheal administration of lacZ-containing adenovirus demonstrated that endothelial and epithelial cells in the alveolar spaces and bronchi of the middle and lower lobes were the principal sites of infection and expression, whereas beta-galactosidase staining was not observed in the upper lobe. Endotracheal administration of IL-1Ra recombinant adenovirus resulted in sustained expression of IL-1Ra into the alveolar spaces, where it was recovered in a concentration of 660 pg/ml in 500 ml of lavage fluid, equivalent to 330 ng IL-1Ra, in the lungs 7 days after treatment. Moreover, in vivo instillation of nonreplicating adenovirus did not induce an inflammatory response in the 1-week time frame of the study period. Lung weight as a percent of body weight, serum zinc, serum amyloid A, leukocyte differentials, neutrophil activity, and TNF levels all were the same between untreated pigs and pigs treated with either recombinant adenovirus. The results indicate that the delivery of IL-1Ra to swine lungs via nonreplicating, recombinant adenovirus may be an effective method for in vivo modulation of IL-1 activity and investigation of cytokine involvement in respiratory disease pathogenesis.

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.

Efficacy of replication-defective adenovirus-vectored vaccines: protection following intramuscular injection is linked to promoter efficiency in muscle representative cells

To investigate the respective role of transduced cells in the induction of immune response following intramuscular inoculation of adenovirus-based vaccines, we generated several replication-defective adenoviruses expressing the glycoprotein D gene of pseudorabies virus under the control of four different promoters: major late promoter of adenovirus type 2, human cytomegalovirus immediate-early promoter/enhancer (CMV), Rous sarcoma virus-long terminal repeat promoter, and human desmin gene 5' regulatory region (DES). All the adenovirus constructs were able to fully protect mice, in the contrary of direct DNA inoculation of plasmids harboring the same transcription units. The far most effective adenovirus constructs, on the criterion of protective doses and specific antibody response induction, were those in which the foreign gene was driven by the DES or CMV promoter. Wide variations in promoter strength in vitro were evidenced in several cell culture types representative of putative target cells following muscular inoculation (myoblasts, myotubes, fibroblasts, macrophages, and endothelial cells). The level of efficacy in vivo, was not correlated with the level of expression in vitro in myotubes, but paralleled the level of expression in endothelial cells and in myoblasts. Together with previously published data, these results suggest that, following adenovirus injection, locally produced cytokines may induce myoblasts to act as local antigen presenting cells.

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.

Study of the delivery of the gD gene of pseudorabies virus to one-day-old piglets by adenovirus or plasmid DNA as ways to by-pass the inhibition of immune response by colostral antibodies

In the present study, it was shown that piglets with maternal antibodies, which had been primed with a replication-defective adenovirus that expresses the pseudorabies virus (PRV) glycoprotein gD and boosted with the Bartha vaccine strain at 10 weeks of age are equally protected clinically upon a challenge as piglets without maternal antibodies vaccinated with the same approach or with the Bartha vaccine strain alone. Priming with a plasmid that expresses gD was less efficient.

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.

Immunization trial of cats with a replication-defective adenovirus type 5 expressing the ENV gene of feline immunodeficiency virus

Our aim was to develop a recombinant replication-defective adenovirus suitable for the vaccination of cats against feline immunodeficiency virus. We first demonstrated that this vector was able to transfer a marker gene (E. coli beta-galactosidase) in feline cells in vitro. We then constructed an adenovirus type 5 expressing the Feline Immunodeficiency Virus (FIV) envelope (ENV) gene of the Wo isolate in the absence of the rev gene (Ad-ENV-Wo). Ad-ENV-Wo was then tested in four cats in a 3 injections scheme (at day 0, day 30 and day 210). Four other control cats received Ad-gp50, a similar recombinant adenovirus expressing gp50 (Ad-gp50) of pseudorabies virus (PRV). Viruses were formulated in two different kind of oil adjuvants (water/oil and water/oil/water), a protocol previously shown to enhance the immune response against the virus-induced protein. The control cats developed neutralizing antibodies against PRV, demonstrating the potency of recombinant human adenovirus 5 (Ad5) as a vector in cats. Antibody responses appeared after the first injection and were higher with the water/oil/water formulation than with the water/oil controls. However, none of the four cats vaccinated with Ad-ENV-Wo developed antibodies against two peptides of the envelope protein. Animals were challenged with 20 infectious doses 50% of the strain Wo. All of them developed antibodies against FIV within 4 to 5 weeks, and FIV virus could be isolated from all.