# Evaluation of Aav Capsids and Delivery Approaches for Hereditary Hemorrhagic Telangiectasia Gene Therapy

## TL;DR

This study evaluates different AAV capsids and delivery methods for gene therapy in hereditary hemorrhagic telangiectasia, focusing on reducing brain arteriovenous malformations with minimal side effects.

## Contribution

The study identifies AAV.cc84 as a promising vector for targeted gene delivery to brain and nasal tissues in HHT gene therapy.

## Key findings

- AAV.cc84 delivered intravenously transduced a high percentage of brain endothelial cells with minimal hepatocyte transduction.
- Intranasal delivery of AAV.cc84 transduced nasal epithelial and skeletal muscle cells with minimal liver impact.
- AAV.cc84-Alk1 delivery reduced brain arteriovenous malformation severity in a mouse model.

## Abstract

Nosebleeds and intracranial hemorrhage from brain arteriovenous malformations (bAVMs) are among the most devastating symptoms of patients with hereditary hemorrhagic telangiectasis (HHT). All available managements have limitations. We showed that intravenous delivery of soluble FMS-related tyrosine kinase 1 using an adeno-associated viral vector (AAV9-sFLT1) reduced bAVM severity of endoglin deficient mice. However, minor liver inflammation and growth arrest in young mice were observed. To identify AAV variants and delivery methods that can best transduce brain and nasal tissue with an optimal transduction profile, we compared 3 engineered AAV capsids (AAV.cc47, AAV.cc84 and AAV1RX) with AAV9. A single-stranded CBA promoter driven tdTomato transgene was packaged in these capsids and delivered intravenously (i.v.) or intranasally (i.n.) to wild-type mice. A CMV promoter driven Alk1 transgene was packaged into AAV.cc84 and delivered to PdgfbiCre;Alk1f/f mice through i.v. injection followed by brain AVM induction. Transduced cells in different organs, vessel density and abnormal vessels in the bAVMs, and liver inflammation were analyzed histologically. Liver and kidney function were measured enzymatically. Compared to other viral vectors, AAV.cc84, after i.v. delivery, transduced a high percentage of brain ECs and few hepatocytes; whereas after i.n. delivery, AAV.cc84 transduced ECs and perivascular cells in the brain, and ECs, epithelial cells, and skeletal muscles in the nose with minimum hepatocyte transduction. No changes to liver or kidney function were detected. Delivery of AAV.cc84-Alk1 through i.v. to PdgfbiCre;Alk1f/f mice reduced bAVM severity. In summary, we propose that AAV.cc84-Alk1 is a promising candidate for developing gene therapy in HHT patients.