Flagellin in fusion with human rotavirus structural proteins exerts an adjuvant effect when delivered with replicating but non-disseminating adenovectors through the intrarectal route.

Human rotavirus (HRV) is the worldwide leading cause of gastroenteritis in young children. Two live attenuated HRV vaccines have been approved since 2006. However, these live vaccines still have potential risks including reversion of virulence. Adenoviruses are suitable vectors for mucosal administration of subunit vaccines. In addition to the adjuvant effect of certain adenovirus components, the use of an adjuvant like flagellin is also another means to increase the immune response to the immunogen. The aim of this study was to determine whether flagellin in fusion with HRV structural proteins stimulates the innate immune response and enhances the HRV-specific immune response when delivered through the intrarectal route with replicating but non-disseminating adenovector (R-AdV). Salmonella typhimurium flagellin B (FljB) in fusion with HRV VP4Δ::VP7 protein induced IL-1β production in J774A.1 macrophages exposed to the R-AdV. Intrarectal administration of R-AdVs expressing either VP4Δ::VP7 or VP4Δ::VP7::FljB in BALB/c mice resulted in HRV-specific mixed Th1/Th2 immune responses. The HRV-specific antibody response elicited with the use of R-AdV expressing VP4Δ::VP7::FljB was higher than that with R-AdV expressing VP4Δ::VP7. The results also show that the replication capability of R-AdVs contributed to enhance the HRV-specific immune response as compared with that obtained with non-replicative AdVs. This work lays the foundation for using the R-AdV system and FljB-adjuvanted formulation to elicit a mucosal immune response specific to HRV.