The Inactivated gE/TK Gene-Deleted Vaccine Against Pseudorabies Virus Type II Confers Effective Protection in Mice and Pigs

Immunological characteristics of a recombinant alphaherpesvirus with an envelope-embedded Cap protein of circovirus

Introduction

Variant pseudorabies virus (PRV) is a newly emerged zoonotic pathogen that can cause human blindness. PRV can take advantage of its large genome and multiple non-essential genes to construct recombinant attenuated vaccines carrying foreign genes. However, a major problem is that the foreign genes in recombinant PRV are only integrated into the genome for independent expression, rather than assembled on the surface of virion.

Methods

We reported a recombinant PRV with deleted gE/TK genes and an inserted porcine circovirus virus 2 (PCV2) Cap gene into the extracellular domain of the PRV gE gene using the Cre-loxP recombinant system combined with the CRISPR-Cas9 gene editing system. This recombinant PRV (PRV-Cap), with the envelope-embedded Cap protein, exhibits a similar replication ability to its parental virus.

Results

An immunogenicity assay revealed that PRV-Cap immunized mice have 100% resistance to lethal PRV and PCV2 attacks. Neutralization antibody and ELISPOT detections indicated that PRV-Cap can enhance neutralizing antibodies to PRV and produce IFN-γ secreting T cells specific for both PRV and PCV2. Immunological mechanistic investigation revealed that initial immunization with PRV-Cap stimulates significantly early activation and expansion of CD69+ T cells, promoting the activation of CD4 Tfh cell dependent germinal B cells and producing effectively specific effector memory T and B cells. Booster immunization with PRV-Cap recalled the activation of PRV-specific IFN-γ+IL-2+CD4+ T cells and IFN-γ+TNF-α+CD8+ T cells, as well as PCV2-specific IFN-γ+TNF-α+CD8+ T cells.

Conclusion

Collectively, our data suggested an immunological mechanism in that the recombinant PRV with envelope-assembled PCV2 Cap protein can serve as an excellent vaccine candidate for combined immunity against PRV and PCV2, and provided a cost-effective method for the production of PRV- PCV2 vaccine.

A Comprehensive Review of Our Understanding and Challenges of Viral Vaccines against Swine Pathogens

Pig farming has become a strategically significant and economically important industry across the globe. It is also a potentially vulnerable sector due to challenges posed by transboundary diseases in which viral infections are at the forefront. Among the porcine viral diseases, African swine fever, classical swine fever, foot and mouth disease, porcine reproductive and respiratory syndrome, pseudorabies, swine influenza, and transmissible gastroenteritis are some of the diseases that cause substantial economic losses in the pig industry. It is a well-established fact that vaccination is undoubtedly the most effective strategy to control viral infections in animals. From the period of Jenner and Pasteur to the recent new-generation technology era, the development of vaccines has contributed significantly to reducing the burden of viral infections on animals and humans. Inactivated and modified live viral vaccines provide partial protection against key pathogens. However, there is a need to improve these vaccines to address emerging infections more comprehensively and ensure their safety. The recent reports on new-generation vaccines against swine viruses like DNA, viral-vector-based replicon, chimeric, peptide, plant-made, virus-like particle, and nanoparticle-based vaccines are very encouraging. The current review gathers comprehensive information on the available vaccines and the future perspectives on porcine viral vaccines.

Generation and Characterization of Recombinant Pseudorabies Virus Delivering African Swine Fever Virus CD2v and p54

African swine fever (ASF) leads to high mortality in domestic pigs and wild boar, and it is caused by the African swine fever virus (ASFV). Currently, no commercially available vaccine exists for its prevention in China. In this study, we engineered a pseudorabies recombinant virus (PRV) expressing ASFV CD2v and p54 proteins (PRV-∆TK-(CD2v)-∆gE-(p54)) using CRISPR/Cas9 and homologous recombination technology. PRV-∆TK-(CD2v)-∆gE-(p54) effectively delivers CD2v and p54, and it exhibits reduced virulence. Immunization with PRV-∆TK-(CD2v)-∆gE-(p54) neither induces pruritus nor causes systemic infection and inflammation. Furthermore, a double knockout of the TK and gE genes eliminates the depletion of T, B, and monocytes/macrophages in the blood caused by wild-type viral infection, decreases the proliferation of granulocytes to eliminate T-cell immunosuppression from granulocytes, and enhances the ability of the immune system against PRV infection. An overexpression of CD2v and p54 proteins does not alter the characteristics of PRV-∆TK/∆gE. Moreover, PRV-∆TK-(CD2v)-∆gE-(p54) successfully induces antibody production via intramuscular (IM) vaccination and confers effective protection for vaccinated mice upon challenge. Thus, PRV-∆TK-(CD2v)-∆gE-(p54) demonstrates good immunogenicity and safety, providing highly effective protection against PRV and ASFV. It potentially represents a suitable candidate for the development of a bivalent vaccine against both PRV and ASFV infections.