Foot-and-mouth disease vaccine with insertion of a 24-amino acid VP1 G-H loop epitope of the Cathay virus provides broad antigenic coverage.

Vaccination with inactivated whole-virus vaccines remains the most effective measure for controlling foot-and-mouth disease virus (FMDV) transmission and disease outbreaks. However, the existing type O FMDV vaccines show suboptimal efficacy and antigenic mismatch to the circulating Cathay viruses in China, thus requiring the development of a new vaccine. The VP1 G-H loop is a hypervariable region and plays a pivotal role in the protective immunity induced by FMDV vaccines. Here, we engineered four recombinant FMDVs with insertions of a 20-amino acid (aa) or a 24-aa G-H loop epitope of a prevalent Cathay strain upstream or downstream of the RGD (Arg-Gly-Asp) motif. The recombinant viruses with insertions upstream of the RGD motif retained parental virus-like plaque morphology and replication kinetics and maintained genetic stability even after 20 serial passages. In contrast, the downstream insertion variants exhibited small plaque morphology, reduced growth capacity, and acquired 1 or 2 aa mutations in the capsid proteins by passage 20. The parental virus vaccine induced high titer protective mean neutralizing antibodies (> 1:128) against viruses of the Mya98, PanAsia, and Ind-2001 lineages but failed to elicit protective mean neutralizing antibodies (< 1:22) to the Cathay virus after 28 days vaccination (dpv) in pigs. In contrast, vaccines containing upstream insertions both exhibited protective immune response to viruses of four lineages. Especially, pigs vaccinated with vaccine containing a 24-aa insertion produced significantly higher mean neutralizing antibody against the Cathay virus (p < 0.01), compared to those vaccinated with vaccine having a 20-aa insertion, indicating that the recombinant virus with 24-aa insertion has great potential as a vaccine candidate for serotype O FMD control. This study provides crucial insights for designing FMDV vaccines in the future. KEY POINTS: • This study firstly reported that FMDV can tolerate a 24-aa insertion in the VP1 G-H loop • The G-H loop insertions at different sites of FMDV VP1 have different impacts on viral replication capacity • Vaccines containing the G-H loop insertions can induce markedly high neutralizing antibodies to the Cathay virus.