Evaluation of Foot-and-Mouth Disease (FMD) Virus Asia1 Genotype-V as an FMD Vaccine Candidate: Study on Vaccine Antigen Production Yield and Inactivation Kinetics

Abstract

South Korea has experienced outbreaks of foot-and-mouth disease (FMD) of serotypes O and A, leading to nationwide vaccination with a bivalent vaccine. Since the FMD virus (FMDV) Asia1 group-V genotype occurred in North Korea in 2007, an Asia1/MOG/05 vaccine strain belonging to the Asia1 group-V genotype was developed using a genetic recombination method (Asia1/MOG/05-R). This study aimed to evaluate the antigen productivity and viral inactivation kinetics of Asia1/MOG/05-R to assess its commercial viability. The antigen yield of Asia1/MOG/05-R produced in flasks and bioreactors was approximately 4.0 μg/mL. Binary ethylenimine (BEI) inactivation kinetics of Asia1/MOG/05-R showed that 2 mM and 1.0 mM BEI treatment at 26 °C and 37 °C, respectively, resulted in a virus titer <10^-7 TCID₅₀/mL within 24 h, meeting the inactivation kinetics criteria. During incubation at 26 °C and 37 °C, 10% antigen loss occurred, but not due to BEI treatment. When pigs were inoculated twice with the Asia1/MOG/05-R antigen, the virus neutralization titer increased to approximately 1:1000; therefore, it can sufficiently protect against Asia1/MOG/05-R and Asia1 Shamir viruses. The Asia1/MOG/05-R will be useful as a vaccine strain for domestic antigen banks.

Keywords: Asia1/MOG/05; antigen; foot-and-mouth disease; inactivation; vaccine.

Figure 1

Optimization of the conditions for producing the Asia1/MOG/05-R antigen. The BHK-21 cells were inoculated with Aisa1/MOG/05-R at different virus infection doses and cultivation times, and then antigen yield and titers were measured. Data are presented as the mean ± standard deviation from three independent experiments. hpi: hours post-infection, ** p < 0.01, and **** p < 0.001.

Figure 2

Determination of optimal pH for producing the Asia1/MOG/05-R antigen. The antigen yield was measured according to the medium pH at the virus inoculation stage. Data are presented as the mean ± standard deviation from three independent experiments. * p < 0.05, ** p < 0.01.

Figure 3

Comparison of antigen yield according to the production scale. Asia1/MOG/05-R was produced by progressively increasing the culture volume 5-fold, and antigen yield and titer were measured at each step. Data are presented as the mean ± standard deviation from three independent experiments. ns: not significant.

Figure 4

Inactivation kinetics of Asia1/MOG/05-R. The supernatant obtained after the Asia1/MOG/05-R was inoculated in the BHK-21 suspension cells was inactivated by each binary ethyleneimine (BEI) concentration, with samples taken at intervals of 1 h up to 6 h and 24 h. The individual graph was extrapolated with a linear line for the analysis of inactivation kinetics.

Figure 5

Virus neutralization antibody titers post-immunization with the Asia1/MOG/05-R vaccine. Virus neutralization tests against the Asia1/MOG/05-R and Asia1 Shamir viruses were performed using sera collected weekly from pigs immunized twice with the Asia1/MOG/05-R vaccine at the four-week interval. Data are presented as the mean ± standard deviation from three independent experiments. The dotted line indicates 1.65 log10 (1:45) virus neutralization (VN) titer. * p < 0.05, ns: not significant.