Novel liquid-phase blocking ELISA using single-domain antibody M8 and virus-like particles for in-vitro potency assessment of foot-and-mouth disease virus-like particle vaccine

Potency tests for inactivated foot-and-mouth disease (FMD) vaccines involve either in vivo challenge trials in target animals or in vitro tests. However, evaluating potency of FMD virus-like particle (VLP) vaccines currently lack in vitro tools. We developed a liquid-phase blocking ELISA (LPBE) using a broadly neutralizing single-domain antibody (M8) and FMD VLPs to assess antibody titers in animals vaccinated with FMD serotype O VLPs. We utilized 505 negative sera and 32 sera of pigs infected or vaccinated with other viruses than FMDV to validate the M8 LPBE detection limit. The M8 LPBE was compared to virus neutralizing test and conventional LPBE using 338 sera from PD₅₀ potency tests in cattle and pigs. The results were analyzed using logistic models. The M8 LPBE showed superior correlation with protection, with an average titer of 1.7 log₁₀ corresponding to a potency of 3 PD₅₀/dose.