# A Head-to-Head Comparison of AAV9 Biodistribution in Mice: Routes of Administration and Age Dependence

## TL;DR

This study compares how AAV9, a gene delivery vector, spreads in mice based on administration route and age, providing a benchmark for future gene therapy research.

## Contribution

The study provides a standardized benchmark for AAV9 biodistribution across tissues based on administration route and age in mice.

## Key findings

- Direct cerebrospinal fluid injections result in higher CNS transgene expression than intravenous administration.
- Combination injections do not significantly increase expression beyond single-route methods.
- Treatment age significantly affects AAV9 biodistribution in the brain, eye, and liver.

## Abstract

Background/Objectives: Adeno-associated virus serotype 9 (AAV9) can cross the blood–brain barrier, making it widely used as a gene delivery vector for central nervous system (CNS) applications. Despite extensive use of AAV9 in translational research, variability in study designs makes cross-comparisons difficult to interpret. We designed a study in mice to generate a resource of AAV9 biodistribution across tissues for commonly used routes of administration and treatment ages. Methods: Lumbar intrathecal, intracerebroventricular, lumbar intrathecal and intracerebroventricular combination, or intravenous injections of vehicle or AAV9/GFP were performed in C57BL/6J male and female mice on postnatal day 1, 5, 10, or 28. Organs were collected at postnatal day 56 and biodistribution of AAV9/GFP was evaluated by quantifying GFP protein expression and vector genome copy number. Results: Direct cerebrospinal fluid injections led to higher transgene expression levels in the brain and spinal cord compared to intravenous administration but did not de-target transgene expression in peripheral tissues. Lumbar intrathecal and intracerebroventricular combination injections resulted in expression throughout the CNS but did not substantially increase expression in either the spinal cord or brain beyond the levels obtained with the respective single routes. Treatment age had effects on AAV9 biodistribution regardless of the route of administration, especially in the brain, eye, and liver. Conclusions: Our results provide the necessary biodistribution data to establish a standardized benchmark for comparison of the current gold standard AAV9 to next generation viral vectors. Additionally, this body of work can provide valuable insights for the design of translational gene therapy studies.