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Safety and immunogenicity of an attenuated Chinese pseudorabies variant by dual deletion of TK&gE genes.

ABSTRACT: BACKGROUND:Since the outbreak of a new emerging virulent pseudorabies virus mutant in Chinese pig herds, intensive research has been focused on the construction of novel gene deletion vaccine based on the variant virulent viruses. An ideal vaccine candidate is expected to have a balanced safety and immunogenicity. RESULTS:From the infectious clone of PRV AH02LA strain, a TK deletion mutant was generated through two-step Red mutagenesis. After homologous recombination with a transfer vector, a TK&gE dual deficient mutant PRV (PRV?TK&gE-AH02) was generated, and its structure verified by PCR, RFLP and sequencing. Growth kinetics test showed that PRV?TK&gE-AH02 reached a titer of 107.5 TCID50 /mL on ST cells. The PRV?TK&gE-AH02 at a dose of 106.0 TCID50 /animal was not virulent in mice or 1-day-old piglets with maternal PRV antibodies. No clinical signs or virus shedding were detected in 28~?35-day-old piglets without maternal PRV antibodies after nasal or intramuscular administration with a dose of 106.0 TCID50, although it caused one death of four 1-day-old piglets without maternal PRV antibodies. In the efficiency test of PRV?TK&gE-AH02, all four 28~?35-day-old piglets without PRV antibody in the challenge control showed typical clinical symptoms and virus shedding, and two died at 4~?5 days post challenge. All piglets in 105.0, 104.0 and 103.0 TCID50/dose PRV?TK&gE-AH02 groups provided complete protection against challenge at only 7 days post intramuscular vaccination. More importantly, PRV?TK&gE-AH02 stopped virus shedding in these piglets. In contrast, all four piglets in PRV Bartha K61 vaccine group developed high body temperature (?40.5 °C) and viral shedding, despite they had mild or even no clinical symptoms. CONCLUSIONS:The constructed TK&gE dual deletion mutant PRV?TK&gE-AH02 can reach high titers on ST cells. The live vaccine of PRV?TK&gE-AH02 is highly safe, and can not only provide clinical protection but also stops virus shedding. This study suggests that PRV?TK&gE-AH02 might work as a promising vaccine candidate to combat the PRV variant emerging in Chinese herds since 2011.

SUBMITTER: Wang J

PROVIDER: S-EPMC6150974 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Safety and immunogenicity of an attenuated Chinese pseudorabies variant by dual deletion of TK&gE genes.

Wang Jichun J Song Zengcai Z Ge Aimin A Guo Rongli R Qiao Yongfeng Y Xu Mengwei M Wang Zhisheng Z Liu Yamei Y Zheng Yating Y Fan Hongjie H Hou Jibo J

BMC veterinary research 20180921 1

<h4>Background</h4>Since the outbreak of a new emerging virulent pseudorabies virus mutant in Chinese pig herds, intensive research has been focused on the construction of novel gene deletion vaccine based on the variant virulent viruses. An ideal vaccine candidate is expected to have a balanced safety and immunogenicity.<h4>Results</h4>From the infectious clone of PRV AH02LA strain, a TK deletion mutant was generated through two-step Red mutagenesis. After homologous recombination with a transf ...[more]

PMID: 30241529

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Project description:Since 2011, pseudorabies based on the pseudorabies virus (PRV) variant has emerged as a serious health issue in pig farms in China. The PRV gE/TK or gE/gI/TK deletion strains protect against emerging PRV variants. However, these variants may cause lethal infections in newborn piglets without PRV antibodies. Previous studies have shown that codon deoptimization of a virulence gene causes virus attenuation. Accordingly, we deoptimized US3-S (US3 gene encoding a short isoform that represents approximately 95% of the total US3 transcription) and UL56 genes (first 10 or all codons) of PRV gE/TK deletion strain (PRVΔTK&gE-AH02) to generate six recombinant PRVs through bacterial artificial chromosome technology. In swine testicular cells, recombinant PRVs with all codon deoptimization of US3-S or UL56 genes were grown to lower titers than the parental virus. Notably, US3-S or UL56 with all codon deoptimization reduced mRNA and protein expressions. Subsequently, the safety and immunogenicity of recombinant PRVs with codon deoptimization of US3-S or UL56 are evaluated as vaccine candidates in mice and piglets. The mice inoculated with recombinant PRVs with codon deoptimization of US3-S or UL56 showed exceptional survival ability without severe clinical signs. All codons deoptimized (US3-S and UL56) significantly decreased virus load and attenuated pathological changes in the brains of the mice. Moreover, the protection efficiency offered by recombinant PRVs with codon deoptimization of US3-S or UL56 showed similar effects to PRVΔTK&gE-AH02. Remarkably, the 1-day-old PRV antibody-negative piglets inoculated with PRVΔTK&gE-US3-ST-CD (a recombinant PRV with all codon deoptimization of US3-S) presented no abnormal clinical symptoms, including fever. The piglets inoculated with PRVΔTK&gE-US3-ST-CD showed a high serum neutralization index against the PRV variant. In conclusion, these results suggest using codon deoptimization to generate innovative live attenuated PRV vaccine candidates.

Project description:BackgroundSince the end of 2011 an outbreak of pseudorabies affected Chinese pig herds that had been vaccinated with the commercial vaccine made of Bartha K61 strain. It is now clear that the outbreak was caused by an emergent PRV variant. Even though vaccines made of PRV Bartha K61 strain can confer certain cross protection against PRV variants based on experimental data, less than optimal clinical protection and virus shedding reduction were observed, making the control or eradication of this disease difficult.ResultsAn infectious clone of PRV AH02LA strain was constructed to generate a gE deletion mutant PRV(LA-AB) strain. PRV(LA-AB) strain can reach a titer of 108.43 TCID50 /mL (50% tissue culture infectious dose) on BHK-21 cells. To evaluate the efficiency of the inactivated vaccine made of PRV(LA-AB) strain, thirty 3-week-old PRV-negative piglets were divided randomly into six groups for vaccination and challenge test. All five piglets in the challenge control showed typical clinical symptoms of pseudorabies post challenge. Sneezing and nasal discharge were observed in four and three piglets in groups C(vaccinated with inactivated PRV Bartha K61 strain vaccine) and D(vaccinated with live PRV Bartha K61 strain vaccine) respectively. In contrast, piglets in both groups A(vaccinated with inactivated PRV LA-AB strain vaccine) and B(vaccinated with inactivated PRV LA-AB strain vaccine with adjuvant) presented mild or no clinical symptoms. Moreover, viral titers detected via nasal swabs were approximately 100 times lower in group B than in the challenge control, and the duration of virus shedding (3-4 days) was shorter than in either the challenge control (5-10 days) or groups C and D (5-6 days).ConclusionsThe infectious clone constructed in this study harbors the whole genome of the PRV variant AH02LA strain. The gE deletion mutant PRV(LA-AB)strain generated from PRV AH02LA strain can reach a high titer on BHK-21 cells. An inactivated vaccine of PRV LA-AB provides clinical protection and significantly reduces virus shedding post challenge, especially if accompanied by the adjuvant CVC1302. While Inactivated or live vaccines made of PRV Barth K61 strain can provide only partial protection in this test.

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Safety and immunogenicity of an attenuated Chinese pseudorabies variant by dual deletion of TK&gE genes.

Publications

Safety and immunogenicity of an attenuated Chinese pseudorabies variant by dual deletion of TK&gE genes.

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