Researchers at Hubrecht Institute and University Medical Center at Utrecht University in the Netherlands have used a new version of the CRISPR-Cas9 gene editing tool to make edits to the CFTR gene to correct mutations that cause cystic fibrosis, without having to remove the affected part of the gene.
Cystic fibrosis affects more than 70,000 people worldwide and around 1,000 new cases are diagnosed each year. The disease is caused by a mutation on the CFTR gene that prevents the gene from producing an essential protein. Individuals with cystic fibrosis produce abnormally thick and sticky mucus that clogs the airways causing breathing difficulties. The disease also causes digestive problems. The disease can be fatal, although with management many individuals can live into adulthood. CRISPR-Cas9 offers hope to cystic fibrosis patients, as it could allow the mutation to be corrected, curing the disease.
Earlier versions of CRISPR-Cas9, which were developed in 2012, worked by removing a defective section of DNA from the genome. The latest version uses a technique called base-editing to repair defective sections of the DNA without making double-stranded cuts, which makes the technique much safer.
Assisted by cystic fibrosis centers in Europe, the researchers generated an organoid biobank using stem cells harvested from 664 patients. The biobank consisted of tiny three-dimensional cultures of intestinal cells, of which approximately 20% could potentially be used to test the new CRISPR-Cas9 gene editing tool. Four of the gut organoids were selected for the trial that the researchers could easily manipulate with CRISPR.
The researchers, led by Hans Clevers, PhD, group leader at the Hubrecht Institute for Developmental Biology and Stem Cell Research, and Jeffrey Beekman, PhD, professor, cellular disease models at UMC Utrecht, used an adenine base editor to convert A-T and G-C base pairs to repair the mutations in the faulty genes of the gut organoids.
After using CRISPR, the researchers report that the mutation was corrected, resulting in production of the CFTR protein without causing off-target effects – accidental alterations to non-targeted sections of the DNA. The research suggests the new base-editing CRISPR-Cas9 tool could potentially be safe to use in humans.
However, while effective in the lab, a method of delivering CRISPR to appropriate cells in the body would need to be developed and trials would need to be conducted to assess whether the tool is safe for use in humans. This research could help to accelerate the first clinical applications, which could be made available in the next five years.
You can read more about the study in the paper – CRISPR-Based Adenine Editors Correct Nonsense Mutations in a Cystic Fibrosis Organoid Biobank – which was recently published in the journal Cell Stem Cell. DOI: 10.1016/j.stem.2020.01.019