Clin Exp Vaccine Res.  2020 Jan;9(1):26-39. 10.7774/cevr.2020.9.1.26.

The potential efficacy of the E2-subunit vaccine to protect pigs against different genotypes of classical swine fever virus circulating in Vietnam

• Tran HT
• Truong DA
• Ly VD
• Vu HT
• Hoang TV
• Nguyen CT
• Chu NT
• Nguyen VT
• Nguyen DT
• Miyazawa K
• Kokuho T
• Dang HV

• KMID: 2470835
• DOI: http://doi.org/10.7774/cevr.2020.9.1.26

Abstract

PURPOSE
To date, many kinds of classical swine fever (CSF) vaccines have been developed to protect against this disease. However, the efficacy of these vaccines to protect the pig against field CSF strains needs to be considered, based on circulating strains of classical swine fever virus (CSFV).
MATERIALS AND METHODS
Recombinant E2-CSFV protein produced by baculovirus/insect cell system was analyzed by western blots and immunoperoxidase monolayer assay. The effect of CSFV-E2 subunit vaccines was evaluated in experimental pigs with three genotypes of CSFV challenge. Anti-E2 specific and neutralizing antibodies in experimental pigs were analyzed by blocking enzyme-linked immunosorbent assay and neutralization peroxidize-linked assay.
RESULTS
The data showed that CSFV VN91-E2 subunit vaccine provided clinical protection in pigs against three different genotypes of CSFV without noticeable clinical signs, symptoms, and mortality. In addition, no CSFV was isolated from the spleen of the vaccinated pigs. However, the unvaccinated pigs exhibited high clinical scores and the successful virus isolation from spleen. These results showed that the E2-specific and neutralizing antibodies induced by VN91-E2 antigen appeared at day 24 after first boost and a significant increase was observed at day 28 (p<0.01). This response reached a peak at day 35 and continued until day 63 when compared to controls. Importantly, VN91-E2 induced E2-specific and neutralizing antibodies protected experimental pigs against high virulence of CSFVs circulating in Vietnam, including genotype 1.1, 2.1, and 2.2.
CONCLUSION
These findings also suggested that CSFV VN91-E2 subunit vaccine could be a promising vaccine candidate for the control and prevention of CSFV in Vietnam.

Keyword

Classical swine fever; Genotype; Vaccine; Vietnam

MeSH Terms

Animals
Antibodies, Neutralizing
Blotting, Western
Classical swine fever virus*
Classical Swine Fever*
Enzyme-Linked Immunosorbent Assay
Genotype*
Mortality
Spleen
Swine*
Vaccines
Vaccines, Subunit
Vietnam*
Virulence
Antibodies, Neutralizing
Vaccines
Vaccines, Subunit

Figure

• 

  Fig. 1 Phylogenetic tree based on the gene sequences of three classical swine fever virus that are isolated from recently outbreak in Vietnam. The tree was constructed using the neighbor-joining method with a bootstrap value of 1,000 in the MEGA7 program.

• 

  Fig. 2 Production and characterization of recombinant CSFV VN91-E2 protein. (A) Sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis. From left to right: lane 1: protein marker; lane 2–7: Sf21AE cell culture supernatant was collected at day 0, 1, 2, 3, 4, and 5 after infected with baculovirus contained VN91-E2 gene. (B) Western blot of VN91-E2 protein. From left to right: lane 1–6: Sf21AE cell culture supernatant was collected at day 0, 1, 2, 3, 4, and 5 after infected with baculovirus contained VN91-E2 gene. E2-specific mAb CSFV was used for the western blot. (C) Identification of baculovirus contained E2 CSFV at 3 days in TN5 cell cultured by Immunoperoxidase Monolayer Assay (×200). Specific cytoplasmic was shown in the TN5 cells infected with baculovirus contained E2 CSFV (arrows). (D) Sf21AE infected baculovirus contained VN91-E2 at 5 days was inactivated by 10 nM BEI in 48 hours. CSFV, classical swine fever virus; BEI, binary ethylenimine.

• 

  Fig. 3 Pigs immunized with VN91-E2 subunit vaccine were protected clinically from CSFV challenge. Pigs were immunized with VN91-E2 on day 0 for the first dose group and a second dose on day 14. Five weeks after the second vaccination (D49), pigs were challenged with 5×105 TCID50 CSFV strain VN91, RAHO3/NA, and NAM DINH. (A) Body temperature was monitored daily after CSFV infection. Vaccinated pigs did not have body temperatures higher than 40℃. (B) Pigs vaccinated with VN91-E2 were protected from CSFV-induced white blood cells. Each symbol represents the mean±standard error. CSF, classical swine fever; CSFV, classical swine fever virus. The significant difference in the body temperatures, number of white blood cell between vaccinated and control groups were indicated with *p<0.01, **p<0.001, and ***p<0.0001.

• 

  Fig. 4 Clinical scores (A) and survived (B) recorded the classical swine fever virus challenge. Each symbol represents the mean±standard error. The significant difference in the body temperatures, number of white blood cell between vaccinated and control groups were indicated with *p<0.01, **p<0.001, and ***p<0.0001.

• 

  Fig. 5 Results obtained by blocking enzyme-linked immunosorbent assay and depicted as average OD% with a cut-off value of 40 (red dashed line). Results ≥40 are positive for CSFV antibodies and results <40 are negative for CSFV antibodies. Each symbol represents the mean±standard error. OD, optical density; CSF, classical swine fever; CSFV, classical swine fever virus. The significant difference in the OD% between vaccinated and control groups were indicated with *p<0.01, **p<0.001, and ***p<0.0001.

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