Prime editing corrects a disease-causing mutation in blood stem cells

A genome editing technique has corrected a disease-causing mutation in blood stem cells taken from a patient with a rare and severe immune disorder.

GATA2 deficiency is a life-threatening genetic disorder caused by mutations in the GATA2 gene, which is needed for normal blood cell production. The condition can leave patients with too few immune cells, leading to repeated infections, bone marrow failure and an increased risk of blood cancers. The study, published in Science Translational Medicine, used an advanced genome editing technique called prime editing (see BioNews 1021, 1243 and 1285) to correct a seven-base-pair deletion in the GATA2 gene in blood stem cells from an affected patient.

'We have shown that it's possible to repair the genetic defect directly in a patient's own stem cells,' said Dr Jonas Holst Wolff, a postdoctoral researcher in the Department of Biomedicine at Aarhus University, Denmark, and first author of the study. 'This brings us one step closer to a treatment that addresses the underlying cause of the disease rather than simply treating its consequences.'

Unlike conventional CRISPR/Cas9 editing, which cuts both strands of DNA, prime editing makes a small nick in one strand and uses a specialised guide RNA containing a template for the corrected DNA sequence to rewrite the faulty section. The researchers optimised the prime editing approach to correct the mutation in the patient's cells, achieving an editing efficiency of up to 70 percent. The proportion of functional GATA2 gene copies increased from 50 to 77 percent. The proportion of cells producing the GATA2 protein was higher with the selected prime-editing approach, at nearly 70 percent, compared with around 45 percent using an alternative approach.

The researchers had previously developed conventional CRISPR/Cas9 editing for the same condition. Although this method also corrected the gene, it caused unwanted genetic changes and reduced the edited cells' ability to survive and multiply. Prime editing helped the cells survive better, and no off-target editing was detected at the 20 most likely predicted sites. However, the researchers did find limited unintended genetic damage at the intended editing site.

The only established curative treatment for GATA2 deficiency at present is a stem cell transplant from a donor. This can cause serious complications, including graft-versus-host disease, in which donor immune cells attack the patient's tissue. The alternative approach explored in this study, however, is not yet ready for patients. Further studies are needed to establish how many corrected stem cells would be required to provide lasting benefits and whether the treatment can restore normal blood cell production.

'This shows that we do not necessarily need to correct every gene copy,' said Dr Wolff. 'What matters is whether we can improve the cells' function enough to make a difference for the patient.' He added that, in principle, the same strategy could be applied to other inherited diseases where the precise genetic defect is known.