CRISPR/Cas9 Gene-Editing Strategy Successfully Used in Hemophilia B Mice

Researchers have successfully applied a potential gene therapy for hemophilia B based on the genome editing properties of the CRISPR/Cas9 system. The results of this study using mice were presented recently at the 58^th Annual American Society of Hematology Meeting and Exposition in San Diego, Calif.

Hemophilia B is a disease caused by different mutations (defects in the DNA sequence) of a single gene, leading to the lack or defective clotting protein factor IX.

A team of researchers at the Perelman School of Medicine, University of Pennsylvania developed a preclinical proof-of-concept study using the powerful gene-editing CRISPR/Cas9 gene targeting tool to target the different mutations causing the disease.

“Basically, we cured the mice,” first author Lili Wang, PhD, a research associate professor in the Penn Gene Therapy Program (GTP) said in a press release . James M Wilson, MD, PhD, a professor of medicine and GTP director, is the lead author of the study.

Specifically, researchers used a mouse model where the gene coding for the clotting factor IX was “knocked out” (eliminated) from the mice. They then generated what is called a two-vector approach: Mice would receive a vehicle (vector) that carries the Cas9 and is targeted specifically to the liver, because that is where the clotting factor IX is produced.

The researchers then introduced a second vehicle (vector 2). It was here that their approach was different from other CRISPR-based-gene-therapy studies, because they introduced both a mouse and human sequence to be delivered to mice, which would increase the strategy for potency and accuracy. Simply put, the second vector inserted the human sequence of factor IX into the mouse genome.

“The targeted insertion leads to the expression of a chimeric hyperactive factor IX protein under the control of the native mouse factor IX promoter,” Wang explained.

Injecting this two component system (vector 1 and vector 2) into newborn and adult “knock-out” mice at increasing doses led to expression and activity of stable factor IX activity at normal (or even higher) levels for over four months.

“This study provides convincing evidence for efficacy in a hemophilia B mouse model following in vivo genome editing by CRISPR/Cas9,” Wang concluded.