Prime Editing Shows Early Promise for Treating Cystic Fibrosis

Swelling response of patient derived mini-guts. Collapsed organoids (left) show active swelling response that is mediated by the CFTR ion channel after one hour incubation with forskolin (right). Green staining shows complete cells (Calcein green) and DNA is shown in Blue.
Swelling response of patient derived mini-guts. Collapsed organoids (left) show active swelling response that is mediated by the CFTR ion channel after one hour incubation with forskolin (right). Green staining shows complete cells (Calcein green) and DNA is shown in Blue. (Credit: Eyleen de Poel, UMC Utrecht)

An experimental type of gene editing known as ‘prime editing’ can correct mutations that cause cystic fibrosis in human cell lines and organoids in the lab, shows research from the Hubrecht Institute in the Netherlands.

While this research is very early stage, it shows that this kind of gene editing could potentially be used to create treatments for individuals with cystic fibrosis and other similar inherited diseases in the future.

“We have for the first time demonstrated that this technique really works and can be safely applied in human stem cells to correct cystic fibrosis,” say the researchers.

Prime editing has hit the headlines in recent years due to its potential for creating treatments for genetic diseases. The method involves fusing a type of Cas9 enzyme to a reverse transcriptase enzyme and combines it with a prime editing guide RNA that can identify the site being targeted and provide information to replace the faulty DNA with a functional sequence.

Cystic fibrosis is one of the most prevalent genetic diseases affecting around 30,000 young people in the U.S. with around 1000 new cases diagnosed each year. Symptoms are caused by a defective CFTR protein that makes sweat and mucus thicker than normal and affects the lungs and gastrointestinal system. Although mitigation treatments have improved, there is no cure for cystic fibrosis and people with this condition have a significantly reduced lifespan, usually not living beyond around 44 years.

Gene therapy has been tried before for treating cystic fibrosis, with limited success. CRISPR-Cas9 has previously been used in the lab to correct CFTR gene mutations in cell lines and organoids, but there are known limitations to this technique such as the risk of unintended damage to other areas of the DNA.

Prime editing is essentially the next generation of CRISPR gene editing and is more precise. In this study, which was published in the journal Life Science Alliance, the researchers used a nickase-cas9 fused to a reverse transcriptase to repair common cystic fibrosis mutations in colonic and hepatocyte organoids in the lab.

The team tested if the editing had correctly repaired the gene defect by adding a substance called forskolin that causes healthy CFTR channels to swell. “We applied prime editing to the mutations, after which the treated organoids demonstrated the same response as the healthy organoids: they became swollen. That provided us with proof that our technique worked and replaced the mutated DNA,” says Maarten Geurts, a researcher at the Hubrecht Institute and first author on the publication.

While editing efficiency varied, no off-target effects were observed in the cells and organoids used. “In our study, prime editing proves to be a safer technique than the conventional CRISPR/Cas9. It can build in a new piece of DNA without causing damage elsewhere in the DNA. That makes the technique promising for application in patients,” says Maarten Geurts, a researcher at the Hubrecht Institute and first author on the publication.

The technique needs to be refined before it could be used in humans, but definitely shows promise for the future. “Prime editing is a versatile tool that can be used for disease modeling and clinical repair of most types of disease-causing mutations in human adult stem cells. Yet, it will require further improvement to allow widespread use as a technique for mutational modeling and for gene repair,” conclude the authors.

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