# AAV‐PHP.eB Peripheral Delivery and Central Expression in Cre Mice

## TL;DR

This study shows that peripheral delivery of AAV-PHP.eB can reach neurons in multiple brain regions, but transduction efficiency varies and some non-specific expression occurs.

## Contribution

The study reveals variable transduction efficiency and nonspecific expression of PHP.eB in different Cre mouse strains after peripheral delivery.

## Key findings

- PHP.eB transduces neurons and astrocytes across brain regions with variable efficiency.
- Low levels of nonspecific Cre-independent expression were observed in all tested strains.
- Transduction patterns differ across Cre-driver mouse strains and brain regions.

## Abstract

Investigating the molecular and functional identity of specific neuronal populations is a critical component of neuroscience research. Specific brain regions can be targeted with stereotaxic injections of viral vectors that deliver recombinase‐dependent genetic tools, but this approach cannot target widely distributed neuronal populations. Peripheral injection is a potential strategy to access widely distributed populations, and unlike most viral vectors, PHP.eB penetrates the blood–brain barrier. However, many neurotropic viruses have tropism for specific neuronal subtypes, and it is unclear if PHP.eB transduces neurons equally across brain regions. To evaluate tropism and transduction efficiency, we examined the brain after retro‐orbital injections of a PHP.eB vector that delivers a Cre‐dependent reporter in a variety of Cre mice. We observed widely variable transduction efficiency across brain regions and cell types. Additionally, we found scattered neurons and astrocytes throughout the brain in all Cre‐driver strains, as well as Cre‐negative control mice, indicating that a low rate of spontaneous recombination had occurred. These results confirm that peripheral delivery of PHP.eB can transduce widely distributed neuronal populations. However, variations in tropism, sensitivity, and specificity merit careful consideration for each population of interest.

Retro‐orbital injection of AAV‐PHP.eB‐FLEX‐tdTomato into four different strains of Cre mice produced various and distinct patterns of transduction efficiency and tropism across brain regions and cell types. We found many target neurons expressing tdTomato in most but not all strains, along with a low level of nonspecific (Cre‐independent) expression across brain regions in every strain and in C57BL/6J mice.