Researchers Discover New Gene-Editing Technique to Treat Leber Congenital Amaurosis

A team led by researchers at UW–Madison successfully used a new experimental technique to fix faulty eye cells, addressing a gene mutation responsible for a specific form childhood blindness, namely Leber congenital amaurosis.

This innovative approach demonstrated its effectiveness in both lab-grown cells derived from a patient afflicted with the currently untreatable inherited condition known as LCA and in a mouse model that accurately mimics this disease.

The core of this method relies on the delivery of the gene-editing tool CRISPR base editor to retinal cells through the use of silica nanocapsules. In a proof-of-concept study, this approach managed to restore the functionality of a crucial protein responsible for regulating the flow of potassium ions within retinal tissue. This restoration, in turn, enables light-detecting cells to function as they should.

“Our goal is to design a package that will carry CRISPR base editors to the retina,” said Bikash Pattnaik, co-investigator and associate professor of pediatrics at the UW School of Medicine and Public Health. “It will be able to introduce nanoparticles in the eye, and those nanoparticles will be designed to target the cell types identified for therapy.”

Pattnaik, who is affiliated with the Department of Ophthalmology and Visual Sciences, led a collaborative effort involving scientists and engineers from UW–Madison, Harvard, and MIT.The primary focus of their research is the development of treatments for two forms of childhood blindness stemming from retinal gene mutations: LCA (Leber congenital amaurosis) and Best disease, also referred to as Best vitelliform macular dystrophy.

LCA typically manifests in infancy, causing severe farsightedness, sensitivity to light, and involuntary eye movements. In contrast, Best disease, usually diagnosed in childhood, leads to macular degeneration and the loss of central vision, visual acuity, and color perception.

While these diseases are relatively rare, affecting only 3 to 4 individuals per 100,000 people, the research team believes that their innovative nanoparticle-packaged CRISPR technology could potentially be applied to treat other inherited eye conditions.

What sets their approach apart is the departure from the conventional gene editing method. Since the discovery of the CRISPR gene editing technique known as CRISPR/Cas9 in 2012, the use of modified viruses for delivering gene-correction materials has become standard practice. However, this viral delivery method has limitations in terms of precision, the scope of cell targeting, and the potential for unpredictable side effects.

In an experimental technique, researchers delivered genome editors to the eye to correct a gene deficit that causes Leber congenital amaurosis, rescuing vision in an animal model.

The team's rationale behind using silica nanocapsules lies in their minimal interaction with the body, thus reducing the potential for troublesome and unpredictable immune system reactions often associated with viral delivery methods. Additionally, this technique boasts a high degree of specificity. Research associate Meha Kabra emphasized this point, stating, " The swift advancements in genetic diagnosis have enabled precise identification of disease-causing mutations. Leveraging base editing, we successfully rectified a specific DNA sequence error in patients, surmounting various challenges through a collaborative team effort in scientific research."

Demonstrating the therapy's effectiveness within a living organism presented challenges due to the fact that mice carrying two copies of the LCA-causing mutation do not survive beyond infancy, whereas in humans, having two copies of homozygous mutations is not fatal. To address this issue, the researchers created mice with one copy of the mutation. They then employed gene editing techniques to disrupt the second normal copy in retinal cells, facilitating the testing of the therapy.

“The clinical relevance and efficacy of any potential new therapy requires studies using laboratory animal models,” said scientist Pawan Shahi. “Without an existing animal model for this specific form of blindness, we used genome editing to first create the model and then deliver the base editor and demonstrate therapeutic value.”

“Typically, drug development can take more than 30 years,” Pattnaik said. “But with a multidisciplinary approach that brings together people with different expertise, we can cut this timeline significantly.” He says that this work, which demonstrates the feasibility of repairing genetic defects in ion channel proteins, is a critical first step toward restoring the sight of affected young patients.

The study has been published in the Journal of Clinical Investigation.