Harnessing CRISPR/Cas9 to reverse the effects of a harmful genetic mutation in an animal model

A new pre-clinical proof-of-concept study from AstraZeneca brings therapeutic assessment of gene editing a step closer  


Scientists at the AstraZeneca IMED Biotech Unit have successfully reversed symptoms of genetic disease in a mouse model using CRISPR/Cas9 gene editing. In the recent issue of EBioMedicine, the authors describe how they eliminated harmful effects of a mutant form of the human α1-antitrypsin (AAT) gene in mice, by cutting the mutation out of the genome.

AAT is a protein secreted by the liver and, in its normal form, is transported to the lungs where it serves a protective function against elastase-associated tissue damage. Inheritance of two copies of the mutated form of the AAT gene results in a rare genetic condition known as α1-antitrypsin deficiency (AATD). Over 100,000 people are affected by this condition in the US, and sufferers experience a range of symptoms ranging from undetectable to potentially fatal lung and liver damage.

The mutation either prevents production of AAT, or encodes a misfolded version of AAT that accumulates in the liver. AATD has two main pathological features: first, in 10–20% of people with the disease, the aggregated protein increases the risk of liver disease including cirrhosis and liver cancer. Second, since the protein is either not produced or its transport to the lungs is impaired, its protective effect is lost. Lung tissue is left open to elastase degradation, eventually resulting in lung disease including emphysema.

Using the CRISPR/Cas9 gene editing system, the group was able to remove the faulty DNA in mice expressing the mutant human sequence, preventing production of the defective protein. Injecting a viral vector containing CRISPR/Cas9 into the mice led to significant decreases in the amount of aggregated protein in the liver, effectively eliminating one of the two main symptoms of this mutation.

These results pave the way for future studies in which the mutated DNA could not only be removed, but be replaced with the wild-type sequence, potentially ameliorating the harmful effects of this mutation on the lungs as well.

This is an early example of the use of CRISPR/Cas9 to reverse pathology in vivo in a humanised mouse model of genetic disease, and represents an exciting development.

John Wiseman, the senior author of the article, said: “The scientific community is working hard to harness CRISPR/Cas9 technology and identify opportunities to develop future therapeutic applications. These pre-clinical results support the potential future testing of CRISPR in patients with rare genetic disorders."

There remain technological challenges to improve the effective and safe delivery of CRISPR/Cas9 gene editing for use in the clinical setting. Still, these findings represent an important milestone being able to reverse the effects of a genetic disease in an animal model.



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