Adenovirus type 5-expressing Gn induces better protective immunity than Gc against SFTSV infection in mice

Severe fever with thrombocytopenia syndrome (SFTS) is caused by the SFTS virus (SFTSV) with high morbidity and mortality. The major immunodominant region of SFTSV surface glycoprotein (G) remains unclear. In this study, we constructed adenovirus type 5 (Ad5) vectored vaccine candidates expressing different regions of SFTSV G (Gn, Gc and Gn-Gc) and evaluated their immunogenicity and protective efficacy in mice. In wild-type mice, compared with Ad5-Gc or Ad5-Gn-Gc, Ad5-Gn recruited/activated more dendritic cells and B cells in lymph nodes or peripheral blood, causing Th1-/Th2-mediated responses in splenocytes and triggered a greater level of SFTSV-neutralizing antibodies. In IFNAR Ab-treated mice, immunization of Ad5-Gn exhibited better protection against SFTSV challenge than Ad5-Gc or Ad5-Gn-Gc. Furthermore, passive immunization revealed complete protective immunity of Gn-specific serum rather than Gc. Collectively, our data demonstrated that Gn is the immunodominant fragment of SFTSV G and could be a potential candidate for SFTSV vaccine development.