Development of Langat virus infectious clones as a platform for live-attenuated tick-borne encephalitis vaccine.

Tick-borne encephalitis (TBE) is one of the most important tick-transmitted diseases in Europe and Asia. With no specific antiviral treatment available, vaccination remains the most effective protective strategy for TBE. Unlike currently available inactivated TBE vaccines that require repeated boosters, live-attenuated vaccines could offer lifelong immunity with a single dose. Langat virus (LGTV) is a naturally attenuated strain of TBE virus (TBEV). In this study, we engineered and rescued four infectious clones (ICs) of LGTV using RNA- and DNA-based reverse genetics methods. The ICs rescued by DNA-based method showed higher genetic stability in cell culture. One of the ICs rescued by DNA-based method was further evaluated in vitro and in vivo, which exhibited growth kinetics and immune profile comparable to the LGTV strain in our laboratory. This reverse genetics platform will be utilized to introduce targeted mutations within the LGTV genome to develop a live-attenuated TBE vaccine.