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Edited Stem Cells Offer Hope Of Precision Therapy For Blindness

Skin cells from a patient with X-linked Retinitis Pigmentosa were transformed into induced pluripotent stem cells and the blindness-causing point mutation in the RPGR gene was corrected using CRISPR/Cas9 (Image credit: Vinit Mahajan)

A team of University of Iowa and Columbia University Medical Center researchers have corrected a blindness-causing gene mutation in stem cells derived from an affected patient. The result offers hope that eye diseases might one day be treated with patients’ own edited tissue.

With the aim of repairing deteriorating retinas in patients with the inherited blinding disease X-linked retinitis pigmentosa (XLRP), Alexander Bassuk and Vinit Mahajan led a team of researchers who generated stem cells from a patient’s skin cells and then repaired the damaged gene, RPGR, using CRISPR/Cas9, a new gene-editing technology. The technique is so precise it corrected a single DNA change that had damaged the RPGR gene. And because the corrected tissue had been derived from the patient’s own cells, it could potentially be transplanted without the need for anti-rejection drugs.

The research was published Jan. 27 in the journal Scientific Reports.

“With CRISPR gene editing of human stem cells, we can theoretically transplant healthy new cells that come from the patient after having fixed their specific gene mutation,” says Mahajan, clinical assistant professor of ophthalmology and visual sciences in the UI Carver College of Medicine. “And retinal diseases are a perfect model for stem-cell therapy because we have the advanced surgical techniques to implant cells exactly where they are needed.”

This proof-of-concept experiment showed that it is possible not only to repair a rare gene mutation, but also to do so with a patient’s stem cells. The use of stem cells is key because they can be reprogrammed into retinal cells. The CRISPR technology was able to correct the RPGR mutation in 13 percent of the stem cells, which is a practically workable correction rate.

Bassuk, associate professor in the Stead Family Department of Pediatrics at University of Iowa Children’s Hospital, notes this result is particularly encouraging because the gene mutation sits in a highly repetitive sequence of the RPGR gene where it can be tricky to discriminate one region from another. Determining the DNA sequence in this part of the gene was itself challenging, and it was not clear that CRISPR/Cas9 would be able to home in on and correct the targeted “point mutation.”

“We didn’t know before we started if we were going to be able to fix the mutation,” says Bassuk.

Developed just three years ago, CRISPR/Cas9 has been heralded as a major breakthrough in genetic engineering, allowing scientists to easily, precisely, and relatively cheaply make specific alterations to the DNA of experimental cells and animals.

The technology has not yet been used in humans, so questions remain about the potential for unanticipated genetic changes. There are also ethical concerns about the technique’s ability to permanently alter sperm and egg cells. Nevertheless, the possibility of repairing genes has tremendous potential.

“There is still work to do,” says Stephen Tsang, associate professor of ophthalmology at Columbia University Medical Center and a collaborator on the study. “Before we go into patients, we want to make sure we are only changing that particular, single mutation and we are not making other alterations to the genome.”

Bassuk adds, “I think there is hope in real time for patients with this particular retinal degenerative disease.”

In addition to Bassuk, Mahajan, and Tsang, the research team included Andrew Zheng and Yao Li at Columbia University Medical Center.

The study was funded in part by grants from the National Institutes of Health, the Doris Duke Charitable Foundation, and Research to Prevent Blindness.

The University of Iowa Foundation has established a fund to support the CURE RPGR research project, a collaborative effort currently being conducted by Bassuk and Mahajan.

Source: The University of Iowa