Construction and immunogenicity of serotype O recombinant foot-and-mouth disease virus

Abstract:

[Objective] To construct a recombinant food-and-mouth disease virus (FMDV) strain carrying the genes encoding three topotypes of immunodominant structural proteins of serotype O FMDV by reverse genetic manipulation and evaluate the potential of the recombinant strain serving as a vaccine candidate for porcine food-and-mouth disease (FMD) type O. [Methods] Based on the gene of the recombinant FMDV with the replacement of the VP1 structural protein of O/NXYCh/CHA/2018 epidemic strain, the recombinant full-length plasmid featuring substitution of G-H loop genes of the structural protein VP1 of O/TUR/5/2009 vaccine strain was constructed by gene synthesis. The recombinant virus was rescued after transfection of the linearized recombinant plasmid into BSR/T7 cells expressing T7 RNA polymerase, and then identified by RT-PCR, sequencing, and indirect immunofluorescence. The plaque assay and one-step growth curve building were employed to characterize the recombinant virus. Pigs were vaccinated with the vaccines prepared from the recombinant virus and the parental virus, and then virus neutralization tests were carried out to examine the cross-reactive responses against the epidemic serotype O FMDV isolates of three topotypes. [Results] The recombinant FMDV strain carrying the structural protein genes of three topotypes was successful rescued. The recombinant strain showed similar biological properties to the parental virus. Pigs vaccinated with the vaccines prepared from the recombinant virus and the parental virus produced protective neutralizing antibodies with the mean titer of >1.65log₁₀ against the viruses of the Middle East-South Asia (ME-SA) and South-East Asia (SEA) topotypes. The pigs did not produce protective neutralizing antibodies against the Cathay topotype (<1.65log₁₀). The substitution of O/TUR/5/2009 G-H loop gene improved the cross-reactivity against the viruses of ME-SA and SEA topotypes compared with the parental virus (p<0.05). [Conclusion] This study has guiding significance for the design of FMD vaccines in the future.