Evaluation of Tembusu virus single-round infectious particle as vaccine vector in chickens.

Orthoflaviviruses are single-stranded RNA viruses characterized by highly efficient self-amplification of RNA in host cells, which makes them attractive vehicles for vaccines. Numerous preclinical and clinical studies have demonstrated the efficacy and safety of orthoflavivirus replicon vectors for vaccine development. In this study, we constructed Tembusu virus (TMUV) replicon-based single-round infectious particles (SRIPs) as vaccine development platform. To evaluate the potential of TMUV SRIPs as vaccines, we generated SRIPs that express the heterologous Fowl adenovirus 4 (FAdV-4) fiber2 protein and fiber2 head domain, named TMUVRP-fiber2 and TMUVRP-fiber2H, respectively. To assess the immunogenicity of the TMUV SRIPs, SPF chicks were intramuscularly inoculated twice. Our results showed that the TMUVRP-fiber2 vaccines elicited high levels of neutralizing antibodies. Challenge experiments showed that TMUVRP-fiber2 provided full protection against virulent FAdV-4 and significantly reduced viral shedding. Moreover, the immunogenicity of TMUVRP-fiber2H was significantly lower than that of TMUVRP-fiber2, which was reflected in the neutralizing antibody titer, survival rate, and virus shedding after challenge. Therefore, our results suggested that TMUV SRIPs are a promising novel platform for the development of vaccines for existing and emerging poultry diseases.