Immunogenicity in Aujeszky's disease virus structural glycoprotein gVI (gp50) in swine

A self-assembled nanoparticle vaccine based on pseudorabies virus glycoprotein D induces potent protective immunity against pseudorabies virus infection

Pseudorabies virus (PRV) mainly causes pseudorabies (PR) or Aujeszky's disease in pigs and can infect humans, raising public health concerns about zoonotic and interspecies transmission of PR. With the emergence of PRV variants in 2011, the classic attenuated PRV vaccine strains have failed to protect many swine herds against PR. Herein, we developed a self-assembled nanoparticle vaccine that induces potent protective immunity against PRV infection. PRV glycoprotein D (gD) was expressed using the baculovirus expression system and further presented on the lumazine synthase (LS) 60-meric protein scaffolds via the SpyTag003/SpyCatcher003 covalent coupling system. In mouse and piglet models, LSgD nanoparticles emulsified with the ISA 201VG adjuvant elicited robust humoral and cellular immune responses. Furthermore, LSgD nanoparticles provided effective protection against PRV infection and eliminated pathological symptoms in the brain and lungs. Collectively, the gD-based nanoparticle vaccine design appears to be a promising candidate for potent protection against PRV infection.

Efficacy of a gB + gD-based subunit vaccine and the adjuvant granulocyte-macrophage colony stimulating factor for pseudorabies virus in rabbits

Pseudorabies (PR), which is caused by the pseudorabies virus (PRV), is a severe infectious disease that causes abortions in adult sows and fatal encephalitis in piglets; the disease can occur in pigs of all ages and other mammals, which can lead to significant economic loss around the worldwide. The new PRV variant invalidated the available commercial attenuated and inactivated vaccines. Consequently, subunit vaccines have been suggested as novel strategies for PR control, while they are usually formulated with adjuvants due to their lower immunogenicity. We aimed to select a safe and efficient adjuvant for subunit vaccines for PR. In our study, glycoprotein B (gB) and glycoprotein D (gD) were expressed based on a baculovirus expression system, and granulocyte-macrophage colony-stimulating factor (GM-CSF) was expressed using an Escherichia coli (E. coli) expression system; subsequently, a gB + gD subunit vaccine adjuvanted by GM-CSF was constructed. A rabbit model infected with a PRV SD-2017 strain was established, the TCID₅₀ and LD₅₀ were measured, and the typical clinical symptoms were observed. After a lethal challenge of 5 LD₅₀ with a PRV SD-2017 strain, the rabbits exhibited typical clinical symptoms, including itching and high temperature, and histopathology revealed severe inflammation in the brain, which is the dominant target organ of PRV. Rabbits immunized with the gB + gD + GM-CSF subunit vaccines produced higher levels of antibodies than those immunized with gB + gD + ISA 201, which was adjuvanted with a frequently used oil adjuvant. The survival rate of rabbits vaccinated with gB + gD + GM-CSF was 100%, which was superior to that of rabbits vaccinated with gB + gD + ISA 201 (80%), inactivated PRV + GM-CSF (60%) and commercial inactivated vaccine (60%) after challenge with PRV SD-2017. These data suggested that the gB + gD + GM-CSF-based subunit vaccine had good protective efficacy against the PRV SD-2017 strain in rabbits and that GM-CSF could be developed as a candidate adjuvant for use in a vaccine regimen to prevent and even eradicate PR.

A poly(dimethylsiloxane)-based solid-phase microchip platform for dual detection of Pseudorabies virus gD and gE antibodies

Pseudorabies caused by pseudorabies virus (PRV) infection is still a major disease affecting the pig industry; its eradication depends on effective vaccination and antibody (Ab) detection. For a more rapid and accurate PRV detection method that is suitable for clinical application, here, we established a poly(dimethylsiloxane)-based (efficient removal of non-specific binding) solid-phase protein chip platform (blocking ELISA) for dual detection of PRV gD and gE Abs. The purified gD and gE proteins expressed in baculovirus were coated into the highly hydrophobic nanomembrane by an automatic spotter, and the gray values measured by a scanner were used for the S/N (sample/negative) value calculation (gD and gE Abs standard, positive: S/N value ≤0.6; negative: S/N value >0.7; suspicious: 0.6 < S/N ≤ 0.7). The method showed an equal sensitivity in the gD Ab test of immunized pig serum samples compared to the neutralization test and higher sensitivity in the gE Ab test compared to the commercial gE Ab detection kit. In the clinical evaluation, we found an agreement of 100% (122/122) in the gD Ab detection compared to the neutralization test and an agreement of 97.5% (119/122) in the gE Ab detection compared to the commercial PRV gE Ab detection kit. In summary, the protein chip platform for dual detection of PRV gD and gE Abs showed high sensitivity and specificity, which is suitable for PRV immune efficacy evaluation and epidemic monitoring.

Isolation and Characterization of a Variant Psedorabies Virus HNXY and Construction of rHNXY-∆TK/∆gE

The outbreak of pseudorabies in China, caused by more virulent pseudorabies virus (PRV) than the classical strains, has led to considerable economic losses. In this study, PRV strain HNXY was isolated from the Henan province of China in 2015 from the pig farm with severe reproductive failure in sows and a high mortality in piglets. The 50% tissue culture infectious doses (TCID50) of HNXY in Vero cells were examined to be 106.5/mL, and the neutralisation titer against Bartha-K61 was significantly higher than against HNXY when tested with the serum from Bartha-K61 vaccinated pigs. The 50% lethal doses (LD50) of HNXY to six-week-old BALB/c mice and two-month-old PRV-free pigs were both 102.3 TCID50. HNXY was classified as genotype II, and numerous amino acid variations were found in gB, gE, gC, gD, TK, and RR1 proteins, compared with PRV from other countries or those prevalent in China before 2012. The attenuated rHNXY-∆TK/∆gE was further constructed, which presented significantly smaller plaques than HNXY, as well as the similar growth kinetics. rHNXY-∆TK/∆gE was confirmed to be non-pathogenic to six-week-old BALB/c mice and zero-day-old piglets. This study isolated updated PRV promising to develop into a new vaccine candidate.

A single dose glycoprotein D-based subunit vaccine against pseudorabies virus infection

Pseudorabies Virus (PRV) is the causative agent of Pseudorabies (PR), also known as Aujeszky's Disease, one of the most important infectious diseases in swine, resulting in huge economic losses to the swine industry globally. The emergence of mutant PRV strains after 2011 resulted in a sharp decrease in the efficacy of available commercial vaccines. To develop a more effective vaccine that can prevent the spread of PRV, glycoprotein B (gB), glycoprotein C (gC) and glycoprotein D (gD) from recent PRV isolates were expressed in a baculovirus system and their protective efficacy was tested in mice and piglets. Neutralizing antibody titers (NAs) in mice vaccinated with gB, gC and gD peaked at 28 days after immunization and then slowly declined. NAs in the mice immunized with gD were remarkably higher than other groups. After a lethal challenge of 5 LD₅₀ with mutant PRV-HNLH strain, the survival rates of gB and gD were 100% and 87.5% respectively, which was significantly higher than gC group (50%). Piglets vaccinated with the gD and gB + D vaccines developed the highest NAs 7 days post immunization. No piglets in these two groups exhibited clinical symptoms, high body temperature or virus shedding following challenge with 10^6.6 TCID₅₀ with the mutant PRV-HNLH strain. Histopathology and immunohistochemistry showed remarkably reduced pathological damage and viral loads in gD and gB + D groups. Furthermore, the duration of the NAs induced by gD vaccine could maintain as long as four months after a single dose. The current study indicates that a gD-based vaccine could be developed for the efficient control of PRV.

Fusion of pseudorabies virus glycoproteins to IgG Fc enhances protective immunity against pseudorabies virus

Molecular adjuvants are vaccine delivery vehicle to increase specific antigens effectiveness. Herein, we concentrated on IgG Fc, an effective molecular adjuvant, to develop novel pseudorabies virus (PRV) subunit vaccines. Two major protective antigen genes of PRV were constructed and linked into the mouse IgG Fc fragment. The gD, gD-IgG2aFc, gB and gB-IgG2aFc proteins were expressed using a baculovirus system. Mice intranasally immunized with gD-IgG2aFc or gB-IgG2aFc subunit vaccine exhibited significantly higher PRV-specific antibodies, neutralizing antibodies and intracellular cytokines than the mice intranasally immunized with gD or gB subunit vaccine. Moreover, no histopathological lesions were observed in mice immunized with gB-IgG2aFc subunit vaccine via histopathology examination. Further, the gB-IgG2aFc subunit vaccine was efficient for PRV infection compared with live attenuated vaccine. Overall, these results suggest that IgG2a Fc fragment, as a potential molecular adjuvant, fused with PRV antigen might be a promising and efficient PRV vaccine candidate.

Variations in glycoprotein B contribute to immunogenic difference between PRV variant JS-2012 and Bartha-K61

A newly emerged pseudorabies virus (PRV) variant has been identified in many Bartha-K61-vaccinated pig farms. This variant has caused great economic losses to the swine industry in China since 2011. Sequence analysis demonstrated that the gB gene of the emerging PRV variant JS-2012 had multiple variations compared with the vaccine strain Bartha-K61. In the study, a specific CRISPR/Cas9 system combined with homologous recombination was used to construct two recombinant viruses, BJB (Bartha-K61+JS-2012gB) and JBJ (JS-2012-ΔgE/gI+Bartha-K61gB), by interchanging the full-length gB genes between Bartha-K61 and JS-2012-ΔgE/gI. The two recombinant viruses showed similar characteristics in growth kinetics in vitro and similar pathogenicity in mice, as compared to their parental strains. Immunization of mice with inactivated BJB or JBJ followed by challenge of JS-2012 showed that BJB could increase protective efficacy to 80%, compared to only 40% protection by the parental Bartha-K61 strain. JBJ had a decreased protective efficacy of 65%, as compared to 90% protection by its parental JS-2012-ΔgE/gI strain. Exchange of the gB gene markedly altered the immunogenicity of the recombinant PRV. These data suggest that variations in gB might play an important role in the virulence of the reemergent PRV variant in China. Our results demonstrate the importance of gB in protective immunity and suggest that the recombinant virus BJB could be a promising vaccine candidate for eradication of the PRV variant.

New baculovirus recombinants expressing Pseudorabies virus (PRV) glycoproteins protect mice against lethal challenge infection

The present study demonstrates the protective potential of novel baculovirus recombinants, which express the glycoproteins gB, gC, or gD of Pseudorabies virus (PRV; Alphaherpesvirus of swine) and additionally contain the glycoprotein G of Vesicular Stomatitis Virus (VSV-G) in the virion (Bac-G-PRV). To evaluate the protective capacity, mixtures of equal amounts of the PRV gB-, gC-, and gD-expressing baculoviruses were used for immunization. Three intramuscular immunizations with that Bac-G-PRV mixture could protect mice against a lethal PRV challenge infection. To achieve complete protection high titers of Bac-G-PRV and three immunizations were necessary. This immunization with Bac-G-PRV resulted in the induction of high titers of PRV-specific serum antibodies of the IgG2a subclass and of interferon (IFN)-gamma, indicating a Th1-type immune response. Moreover, splenocytes of immunized mice exhibited natural killer cell activity accompanied by the production of IFN-alpha and IFN-gamma. Collectively, the presented data demonstrate for the first time that co-expression of VSV-G in baculovirus recombinant vaccines can improve the induction of a protective immune response against foreign antigens.

Molecular biology of pseudorabies virus: impact on neurovirology and veterinary medicine

Pseudorabies virus (PRV) is a herpesvirus of swine, a member of the Alphaherpesvirinae subfamily, and the etiological agent of Aujeszky's disease. This review describes the contributions of PRV research to herpesvirus biology, neurobiology, and viral pathogenesis by focusing on (i) the molecular biology of PRV, (ii) model systems to study PRV pathogenesis and neurovirulence, (iii) PRV transsynaptic tracing of neuronal circuits, and (iv) veterinary aspects of pseudorabies disease. The structure of the enveloped infectious particle, the content of the viral DNA genome, and a step-by-step overview of the viral replication cycle are presented. PRV infection is initiated by binding to cellular receptors to allow penetration into the cell. After reaching the nucleus, the viral genome directs a regulated gene expression cascade that culminates with viral DNA replication and production of new virion constituents. Finally, progeny virions self-assemble and exit the host cells. Animal models and neuronal culture systems developed for the study of PRV pathogenesis and neurovirulence are discussed. PRV serves asa self-perpetuating transsynaptic tracer of neuronal circuitry, and we detail the original studies of PRV circuitry mapping, the biology underlying this application, and the development of the next generation of tracer viruses. The basic veterinary aspects of pseudorabies management and disease in swine are discussed. PRV infection progresses from acute infection of the respiratory epithelium to latent infection in the peripheral nervous system. Sporadic reactivation from latency can transmit PRV to new hosts. The successful management of PRV disease has relied on vaccination, prevention, and testing.

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.

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.

Immunobiology of pseudorabies (Aujeszky's disease)

Aujeszky's Disease (AD), a serious illness of pigs causing significant economic losses in the pig industry, is caused by Pseudorabies Virus (PrV). PrV belongs to the alphaherpesvirus subfamily of the herpesviruses with a double-stranded DNA genome in an enveloped capsid capable of encoding approximately 70 proteins. For disease control, vaccination with live and killed vaccines is performed. Recently, 'marked' vaccines have become available for use in eradication programs based on the differentiation between infected and vaccinated animals. PrV is also used as a viral vector for the development of multivalent vaccines. Despite the effectiveness of PrV vaccines, relatively little is known about the immune response against PrV infection. Several viral envelope glycoproteins have been shown to represent targets for antibody responses, and a number of isolated glycoproteins as well as genetically engineered proteins were able to elicit protective immunity. The nature of the cellular immune response is even less defined. Using viral mutants genetically engineered to lack specific antigens, it has been shown that glycoprotein C (gC) acts as a target for cytotoxic T-lymphocytes, and gB, gC, gD, and gH appear to be involved in stimulation of in vitro proliferation of PBMC from immune animals. In addition, gB and gC have been implicated in recognition of infected cells by lymphokine-activated killer (LAK) cells. In summary, the data indicate a prominent role for viral envelope glycoproteins in eliciting humoral and cellular immune responses in the animal host. A complicating factor is the ability of PrV to productively infect cells of the hematopoietic system, which may impair immune responses and might also play a role in persistent or latent infection.

A novel non-mineral oil-based adjuvant. II. Efficacy of a synthetic sulfolipopolysaccharide in a squalane-in-water emulsion in pigs

The adjuvanticity of a sulfolipopolysaccharide (SLP) incorporated into a squalane-in-water emulsion (SLP/S/W) was compared with that of a mineral oil-in-water (O/W) adjuvant currently used in commercial porcine vaccines. Groups of pigs were immunized twice with vaccines comprising either inactivated influenza virus (iFlu3 containing strains A/Swine, MRC-11 and X-79), inactivated pseudorabies virus (iPRV), live pseudorabies virus (PRV) or inactivated porcine parvovirus (iPPV) as antigen and SLP/S/W or O/W as adjuvant. Antibody titres in serum 2 or 3 weeks after the second immunization were measured by haemagglutination inhibition (HI) or serum neutralization (SN) assays. Both adjuvants significantly augmented the antibody responses against the antigens tested. Mean factors of increase obtained by SLP/S/W and O/W were: 315 and 91, respectively, for A/Swine; 478 and 137 for MRC-11; 362 and 128 for X-79; 69 and 49 for iPRV; and 23 and 7 for live PRV. Increased humoral immunity against live PRV was affirmed by reduced levels and duration of virus excreted by pigs after challenge with virulent PRV. Immunization of pigs with iPPV plus adjuvant SLP/S/W gave 36-fold higher titres than with O/W. It was concluded that SLP/S/W is more effective than O/W in stimulating humoral immunity against the viral antigens examined and that the two constituents SLP and S/W interact synergistically. Advantages of SLP/S/W over O/W include stronger adjuvanticity, better biocompatibility and lower doses of active substances.

Role of pseudorabies virus glycoprotein II in protection from lethal infection

A monoclonal antibody (mAb), named 1.21, with complement-dependent neutralizing activity was produced against glycoprotein II (gII) of pseudorabies virus (PRV). By immunoaffinity chromatography using a mAB 1.21 column, gII was purified from Nonidet P40-lysates of PRV infected BHK21/13 cells. When mice and pigs were immunized with purified gII, complement-dependent virus-neutralizing antibodies were produced. The immunized animals survived potentially lethal challenge with PRV. These results indicate that an immunological response against gII plays an important role in the protection from PRV infection.

A comparison of the efficacy of two commercial Aujeszky's disease vaccines with glycoprotein-I deletion in pigs

Two commercial Aujeszky's disease vaccines, a modified killed vaccine and a sub-unit vaccine, both carrying a deletion of glycoprotein-I, were evaluated in pigs. Each vaccine was administered to two groups of four pigs, twice at 4-week intervals, with two pigs held as unvaccinated controls. All pigs were challenged with a New Zealand field isolate of Aujeszky's disease virus 3 weeks after the second vaccination. The results indicate that the sub-unit vaccine was able to protect pigs against clinical Aujeszky's disease much better than the pigs vaccinated with the modified killed vaccine when challenged with a virulent virus. However, the amount and the duration of virulent virus excretion following challenge was greater with the sub-unit vaccine than the modified killed vaccine. Pigs vaccinated with the sub-unit vaccine were shown to be latently infected following challenge. Latent infection was demonstrated by excretion of Aujeszky's disease virus from the nasal cavity after dexamethasone treatment and seroconversion of a sentinel in contact pigs to Aujeszky's disease virus.