To Örebro University

Tick-borne encephalitis (TBE) is a significant disease in Europe and Asia, with a risingincidence due to the spread of the TBE virus (TBEV) and its vectors. Current TBE vaccinesprovide good protection, but they have a complex immunization schedule and lower efficacy inthe elderly, leading to occasional vaccine failures. We aim to develop a novel TBE vaccine toprovide better protection with fewer doses through mucosal immunization. The current workcovers a pilot study that evaluates live-attenuated TBE vaccine in vivo, using Langat virus(LGTV) platform that we developed based on a rescued LGTV infectious clone (LGTV IC).In the current mouse study, LGTV IC was administered via intranasal and intramuscular routesat two doses (10³ and 10⁵ PFU). The study assessed tolerability, viremia profile, and inducedimmunogenicity.As a result, we show that intranasal immunization with LGTV IC induced strong immuneresponses and revealed a favorable safety profile in a dose-dependent manner. Low-doseintranasal administration was well tolerated, with no clinical signs, weight loss, or viral presencein the central nervous system. It elicited robust anti-TBEV IgG antibodies that successfullyneutralized both LGTV and TBEV and induced strong cellular immunity, characterized byTBEV NS3-specific IFNγ and IL-2 secreting cells. Notably, low-dose mucosal immunizationoutperformed both high-dose intranasal and intramuscular administration in generating abalanced immune response. In contrast, high-dose intranasal immunization caused significantweight loss and minimal viral detection in CSF, indicating potential adverse effects at elevateddoses.These findings support the potential of low-dose mucosal immunization with LGTV IC as a safeand effective TBE vaccination strategy. Further attenuation of LGTV IC is underway to enhancesafety for future development.