A new variation of the gene-editing technology CRISPR-Cas9 can correct mutations in the CFTR gene — the genetic cause of cystic fibrosis (CF) — in stem cells from CF patients, a study shows.

The new approach has the ability to correct mutations without the need to excise the affected region, the researchers said.

The study, “CRISPR-Based Adenine Editors Correct Nonsense Mutations in a Cystic Fibrosis Organoid Biobank,” was published in the journal Cell Stem Cell.

CRISPR-Cas9, a system used by microbes to defend themselves against invading viruses, has been adapted and is currently at the forefront of many therapeutic approaches for human diseases. The technique allows for the correction of genetic defects associated with several human genetic diseases, including CF, sickle cell disease, and muscular dystrophy.

The first version of the CRISPR technology, developed in 2012, cuts a mutation out of a gene, but a 2018 version, called base editing, is able to repair a mutation without cutting the DNA.This makes the gene-editing tool more precise and safe.

Scientists at the Hubrecht Institute and University Medical Center Utrecht University in the Netherlands used the newer version of the gene-editing CRISPR-Cas9 technology to correct certain mutations in the CFTR gene in CF-patient derived stem cells. These stem cells are grown into “mini-guts,” called intestinal organoids, from patient tissue.

“In traditional CRISPR/Cas9 genome editing, a specific piece of the DNA is cut out, resulting in DNA damage,” the study’s first author, Maarten Geurts of the Hubrecht Institute, said in a press release.This is done with the aim that the cell repairs this cut using a lab-made piece of ‘healthy’ DNA.”

“However, in the new CRISPR technique, called base editing, the Cas part is altered in such a way that it no longer creates a cut, but still detects the mutation,” Geurts said. “So instead of creating a cut and replacing the faulty DNA, the mutation is directly repaired on site, making this a more effective genome editing tool.”

The Hubrecht Organoid Technology foundation and UMC Utrecht generated a CF intestinal organoid biobank representing 664 patients. The biobank was set up with the help of CF centers across Europe and the Dutch CF Foundation.

Scientists tested four CF intestinal organoids carrying a mutation in the CFTR gene amenable for manipulation with the new editing CRISPR.

Results showed that the technique was able to repair the CFTR mutation without causing additional errors in other parts of the genome. These so-called off-target effects are a known caveat in the standard CRISPR technology.

“With the new base-editing technique, the mutation in the CFTR gene can be detected and repaired without creating further damage in the genome,” said Geurts.

While the results are promising, more research is needed before the strategy is available to patients. To use the CRISPR technology, scientists must first design a way to deliver the CRISPR tools to the appropriate cells.

“This research represents a big step towards genetic repair of diseases in patients. However, a big question that remains is how to deliver the CRISPR enzyme to the appropriate organs in the patient,” said Eyleen de Poel of UMC Utrecht, one of the lead authors of the study.

“Further research is needed before the base editor can be used for clinical application,” de Poel said. “However, in part due to this study, the first clinical applications may already happen in the coming five years.”