Transgene distribution and immune response after ultrasound delivery of rAAV9 and PHP.B to the brain in a mouse model of amyloidosis.

Efficient disease-modifying treatments for Alzheimer disease, the most common form of dementia, have yet to be established. Gene therapy has the potential to provide the long-term production of therapeutic in the brain following a single administration. However, the blood-brain barrier poses a challenge for gene delivery to the adult brain. We investigated the transduction efficiency and immunological response following non-invasive gene-delivery strategies to the brain of a mouse model of amyloidosis. Two emerging technologies enabling gene delivery across the blood-brain barrier were used to establish the minimal vector dosage required to reach the brain: (1) focused ultrasound combined with intravenous microbubbles, which increases the permeability of the blood-brain barrier at targeted sites and (2) the recombinant adeno-associated virus (rAAV)-based capsid named rAAV-PHP.B. We found that equal intravenous dosages of rAAV9 combined with focused ultrasound, or rAAV-PHP.B, were required for brain gene delivery. In contrast to rAAV9, focused ultrasound did not decrease the rAAV-PHP.B dosage required to transduce brain cells in a mouse model of amyloidosis. The non-invasive rAAV delivery to the brain using rAAV-PHP.B or rAAV9 with focused ultrasound triggered an immune reaction including major histocompatibility complex class II expression, complement system and microglial activation, and T cell infiltration.

Introduction

Purpose Drug delivery with BBB opening

Study Objective To compare the ability of rAAV-PHP.B and rAAV9 (with or without MRI-guided focused ultrasound) to transduce the brain and elicit immune responses in a mouse model of amyloidosis.

Animal model / Human subject Mouse; strain: mouse model of amyloidosis (None); age: None; sex: None

Disease model Alzheimer's disease

Cargo name and characteristics Recombinant adeno-associated virus (rAAV) gene therapy vectors — specifically rAAV9 and the rAAV-PHP.B capsid variant, used for systemic (intravenous) gene delivery to the brain.

Route of administration intravenous

Outcomes and Safety

Summary of Outcomes Systemic rAAV-PHP.B at 1×10^11 GC produced widespread brain transduction, while MRI-guided focused ultrasound (MRIgFUS) with intravenous microbubbles enabled targeted transduction of rAAV9 (1×10^11 GC) but did not lower the PHP.B dose required (1×10^10 GC PHP.B was ineffective); both delivery methods induced neuroinflammation (microglial and complement activation, increased MHC class II expression, and T cell infiltration). MRIgFUS parameters that were effective for rAAV9 delivery were MRI-guided targeting of two cortical/striatal and two thalamic spots with microbubbles and cavitation-feedback control (hydrophone trigger set to a 50% pressure drop) to open the BBB.

Duration of biological effect 3 weeks

Safety-related matter Delivery of GFP-expressing rAAVs to the brain (i.v. PHP.B at 1E11 GC or i.v. rAAV9 with MRIgFUS at 1E11 GC) induced immune reactions including microglial and complement activation, increased MHC class II expression and T cell infiltration — localized to MRIgFUS-targeted spots for rAAV9 but widespread for high-dose PHP.B. The paper also cites prior reports of serious systemic adverse events (e.g., liver toxicity and deaths) at very high systemic rAAV doses in non-human primates/clinical trials, while MRIgFUS alone produces a benign, transient microglial activation that resolves by ~15 days.

Brain Region

Visualization unavailable

Ultrasound Parameters

Focal Characteristics Focal depth: None; Focal length: None; Aperture size: None

Treatment frequency single

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