Generation of broad-spectrum vaccine platforms against tick-borne flaviviruses using ancestral sequence reconstruction

Tick-Borne Flaviviruses (TBFs) pose a significant global health threat, but few vaccines exist against these viral pathogens. Currently approved vaccines against TBFs are only protective against specific virus species, leaving the population at risk for infection by many existing and emerging TBFs. The development of vaccines that provide broad protection against a range of related TBFs has the potential of reducing disease burden against known and unknown viral pathogens. In this study we utilized ancestral sequence reconstruction (ASR) to design recombinant antigens of extinct ancestral viruses to serve as vaccines against multiple modern day TBFs. We reconstructed a common ancestral envelope (E) antigen that possesses high sequence and structural identity to several modern-day TBF pathogens and engineered this ancestral E antigen sequence into an attenuated Sindbis virus vaccine platform. We observed that this Sindbis virus was replication competent and generated sustained antigen expression in vitro. Immunizing mice with this vaccine candidate resulted in the production of significant neutralizing antibody active against virulent Powassan (POWV) and Langat (LGTV) viruses. Antibody neutralization correlated well with decreased clinical signs and increased survival from virulent POWV challenge. These data indicate that a common ancestral antigen from TBFs can provide protection against multiple modern day TBFs, and that the ASR approach may provide a valuable new pathway to safe and effective pan-TBF vaccines.