Development of blood-brain barrier-penetrating antibodies for neutralizing tick-borne encephalitis virus in the brain

ABSTRACT Tick-borne encephalitis virus (TBEV) belongs to the genus Flavivirus and causes tick-borne encephalitis (TBE), a disease characterized by severe neurological symptoms with a high mortality rate. Currently, no specific antiviral treatments have been developed for TBE. The blood-brain barrier (BBB) restricts drug delivery to the central nervous system, posing a major challenge in developing effective therapies targeting TBEV in the brain. In this study, we developed recombinant anti-TBEV antibodies fused with BBB-penetrating rabies virus glycoprotein (RVG) peptides to facilitate their transport across the BBB. The fusion of RVG peptides to the C-terminus of the heavy chain of whole antibodies or single-chain variable fragment had minimal impact on their neutralizing ability against TBEV. The RVG fusion enhanced antibody binding to the surface of a human brain endothelial cell line and increased permeability in an in vitro BBB model. The RVG-fused antibodies exhibited a higher transport efficiency to the brain than the non-fused antibodies following peripheral injection in mice. Notably, the peripheral administration of the RVG-fused whole antibody after viral invasion into the brain significantly neutralized TBEV in the brains of infected mice. These findings suggest that RVG-fused antibodies represent a promising therapeutic strategy for treating TBE once the virus has entered the brain.IMPORTANCETick-borne encephalitis virus is a neuroinvasive pathogen that causes severe neurologic disease, significantly affecting patients' quality of life. No specific antiviral treatment is available for tick-borne encephalitis caused by virus multiplication in the brain. The delivery of drugs to the brain via peripheral administration is often obstructed by the blood-brain barrier. To develop targeted antiviral therapies for brain infections, we engineered recombinant antibodies capable of crossing the blood-brain barrier via brain-targeted ligands. These antibodies exhibited permeability across the blood-brain barrier in both in vitro and in vivo models and notably effectively neutralized the virus within the brain following peripheral administration. This study is the first to highlight the therapeutic potential of brain-targeted recombinant antibodies after viral entry into the brain, offering a promising pathway for the development of effective antiviral treatments for tick-borne encephalitis.