AAV-mediated delivery of an anti-BACE1 VHH alleviates pathology in an Alzheimer's disease model

Single domain antibodies (VHHs) are potentially disruptive therapeutics, with important biological value for treatment of several diseases, including neurological disorders. However, VHHs have not been widely used in the central nervous system (CNS), largely because of their restricted blood-brain barrier (BBB) penetration. Here, we propose a gene transfer strategy based on BBB-crossing adeno-associated virus (AAV)-based vectors to deliver VHH directly into the CNS. As a proof-of-concept, we explored the potential of AAV-delivered VHH to inhibit BACE1, a well-characterized target in Alzheimer's disease. First, we generated a panel of VHHs targeting BACE1, one of which, VHH-B9, shows high selectivity for BACE1 and efficacy in lowering BACE1 activity in vitro. We further demonstrate that a single systemic dose of AAV-VHH-B9 produces positive long-term (12 months plus) effects on amyloid load, neuroinflammation, synaptic function, and cognitive performance, in the AppNL-G-F Alzheimer's mouse model. These results constitute a novel therapeutic approach for neurodegenerative diseases, which is applicable to a range of CNS disease targets. We want to thank the collaborators of the VIB Nanobody Core and VIB Protein Core for their valuable contribution to the research presented in this paper. We thank Joost Schymkowitz, Frederic Rousseau, and Roosmarijn Vandenbroucke for discussions and advice. We thank Jeason Haughton for expert support with mouse husbandry. MM was supported by a predoctoral fellowship from the Fonds Wetenschappelijk Onderzoek (FWO) (SB/ 1S48018N). MYR received a postdoctoral fellowship from the FWO (133722/ 1204517N) and acknowledges the continuous support of the Fundacion Cardiovascular de Colombia. SID was supported by The Foundation for Alzheimer Research (SAO-FRA) (P#14006). MGH was supported by the Thierry Latran Foundation (SOD-VIP), FWO (Grant 1513616N), and European Research Council (ERC) (Starting Grant 281961—AstroFunc; Proof of Concept Grant 713755—AD-VIP). He is currently the ERANet Chair (NCBio) at i3S Porto funded by the European Commission (H2020-WIDESPREAD-2018- 2020-6; NCBio; 951923). Work in the BDS Lab is supported by the Opening the Future campaign of the KU Leuven, SAO-FRA (P#16017), FWO, KU Leuven, VIB, a Methusalem grant from KU Leuven and the Flemish Government, the Flanders Network for Dementia Research (VIND, Strategic Basic Research Grant 135043) and the Alzheimer’s Association. BDS is supported by the Geneeskundige Stichting Koningin Elisabeth and the Bax-Vanluffelen Chair for Alzheimer’s disease. The synopsis image was produced by David Pennington (@PenningtonArt.co.uk).