# Preclinical Evaluation of the Systemic Safety, Efficacy, and Biodistribution of a Recombinant AAV8 Vector Expressing FIX-TripleL in Hemophilia B Mice: Implications for Human Gene Therapy

## TL;DR

This study shows that a gene therapy using AAV8-FIX-TripleL is safe and effective in treating hemophilia B in mice, with long-lasting benefits.

## Contribution

The study provides preclinical evidence of AAV8-FIX-TripleL's safety, efficacy, and biodistribution in hemophilia B mice.

## Key findings

- AAV8-FIX-TripleL increased FIX activity and protein levels in a dose-dependent manner.
- The therapy showed a favorable safety profile and minimal off-target effects.
- Vector persisted in the liver for up to 91 days post-injection.

## Abstract

Gene therapy for hemophilia B offers the advantage of a single administration with sustained therapeutic effects. This study evaluated the systemic safety, efficacy, biodistribution, and immunogenicity of AAV8-FIX-TripleL, a recombinant adeno-associated virus type 8 (AAV8) vector encoding a modified factor IX (FIX) variant with increased activity. In this good laboratory practice (GLP)-compliant study, 180 male FIX-knockout hemophilia B mice were randomized into 12 groups (n = 15) and received intravenous AAV8-FIX-TripleL at therapeutic (5 × 1011 VG/kg) or supraphysiological (5 × 1012 VG/kg) doses on Day 1. The mice were sacrificed on Days 2, 15, 28, and 91 for comprehensive evaluations, including hematological and biochemical assessments, histopathological examination, FIX protein/activity analysis, immunogenicity assessment, and vector biodistribution via quantitative polymerase chain reaction (qPCR) in major organs. AAV8-FIX-TripleL demonstrated dose-dependent increases in FIX activity and protein levels, with FIX activity exceeding physiological levels and the maintenance of a favorable safety profile. Biodistribution analysis confirmed predominant hepatic accumulation and vector persistence up to 91 days post-injection, with minimal off-target distribution. These findings indicate that AAV8-FIX-TripleL is a promising gene therapy candidate for hemophilia B, as it has robust expression, sustained efficacy, and a favorable safety profile, and that further translational studies are warranted.