Generation Of A GE/gI/TK Gene-deleted Pseudorabies Virus Variant Expressing The E2 Protein Of Classical Swine Fever Virus And Evaluation Of Its Efficacy In Pigs

Classical swine fever (CSF) is an economically important infectious disease of pigs, which caused by classical swine fever virus (CSFV). At present, the modified live vaccine (MLV) C-strain was widely used to prevent and control the CSFV in the world, although this vaccine harbored high safety and immunogenicity in pigs, it did not allow differentiation of infected from vaccinated animals (DIVA) and the immune efficacy was affected by maternally derived antibodies (MDA), which often led to immune failure and low efficacy. Therefore, it is very significant to develop a new CSF vaccine that allowed DIVA to effectively control and eradicate CSF in China.Pseudorabies (PR) is an acute infectious disease, characterized by fever, itching, encephalomyelitis, respiratory and nervous system disorders in many livestock and wild animals. The etiologic agent of PR is pseudorabies virus (PRV). The Bartha-K61 strain is a well-known MLV that has played a key role in the control and eradication of PR in the world. Since late 2011, however, PR outbreaks have been frequently reported in many Bartha-K61-vaccinated pig farms in China, which caused serious economic losses to the pig industry. Subsequently, many studies demonstrated that PRV have undergone mutations in our country, the virulence of the PRV variant has been significantly enhanced compared with the classic PRV strain (Shuangcheng strain), and the Batha-K61 vaccine did not provide complete protection against challenge with the PRV variant. Therefore, in order to effectively control the spread or outbreak of the emerging PR, it is necessary to develop a safe and effective PR vaccine.Previously, we isolated a PRV variant (PRV TJ) from Bartha-K61-vaccinated pig farms and generated a new recombinant virus rPRVTJ-delgE/gI/TK, a gE/gI/TK-deleted PRV mutant based on PRV variant. The results showed that the recombinant virus rPRVTJ-delgE/gI/TK is safe for natural hosts (pigs) and non-natural hosts (mice and sheep) and provided complete protection against lethal challenge with the PRV variant. In order to develop a bivalent vaccine against CSFV and emerging PRV, here, we generated a recombinant virus rPRVTJ-delgE/gI/TK-E2 expressing the E2 protein of CSFV based on rPRVTJ-delgE/gI/TK and evaluated the safety and immunogenicity in pigs. The results indicated that the recombinant virus rPRVTJ-delgE/gI/TK-E2 harbored genetic stability and the propagation properties of rPRVTJ-delgE/gI/TK-E2 were similar to those of the vector virus rPRVTJ-delgE/gI/TK in vitro. The vaccinated piglets did not show any clinical signs after immunization with rPRVTJ-delgE/gI/TK-E2 and were completely protected against the lethal CSFV Shimen strain and PRV variant TJ strain challenge. These findings suggest that rPRVTJ-delgE/gI/TK-E2 is a promising bivalent DIVA vaccine candidate against CSFV and PRV coinfections.