Summary Cytosine base editors and adenine base editors (ABE) can correct point mutations predictably and independently of Cas9-induced double-stranded DNA breaks (which cause substantial indel formation) and homology-directed repair ( which usually leads to low editing efficiency). Here, we show, in adult mice, that a subretinal injection of an adeno-associated virus expressing an ABE and a single guide RNA targeting a de novo missense mutation in the Rpe65 gene corrects the pathogenic mutation with up to 29% efficiency and with minimal indel formation and off-target mutations, despite the absence of the canonical NGG sequence as a motif adjacent to the protospacer. Mice treated with ABE showed restored RPE65 expression and retinoid isomerase activity, and near normal levels of retinal and visual functions. Our findings motivate further testing of ABE for the treatment of inherited retinal diseases and for the correction of pathological mutations with motifs adjacent to non-canonical protospacers. |
A groundbreaking study, led by researchers at the University of California, Irvine, results in the restoration of visual and retinal functions in mouse models suffering from an inherited retinal disease.
Published today in Nature Biomedical Engineering , the paper, titled "Restoration of visual function in adult mice with an inherited retinal disease by adenine base editing," illustrates the use of a next-generation CRISPR technology and lays the groundwork for the development of a new therapeutic modality for a wide range of inherited eye diseases caused by different genetic mutations.
"In this proof-of-concept study, we provide evidence of the clinical potential of base editors for correcting mutations that cause inherited retinal diseases and for restoring visual function," said Krzysztof Palczewski, PhD, Irving H. Leopold Chair and a distinguished professor at the Gavin Herbert Eye Institute, Department of Ophthalmology, UCI School of Medicine. "Our results demonstrate the most successful rescue from blindness to date using genome editing."
Inherited retinal diseases (IRDs) are a group of blinding conditions caused by mutations in more than 250 different genes. Previously, there was no avenue available to treat these devastating, blinding diseases. Recently, the FDA approved the first gene augmentation therapy for Leber congenital amaurosis (LCA), a common form of IRD that originates during childhood.
A mutation in a mouse model of inherited blindness abolishes the expression of RPE65, a key enzyme in a visual cycle, in RPE cells. Base editing treatment can correct the mutation and restore functional RPE65 (green), thereby restoring vision in mice.
"As an alternative to gene augmentation therapy, we applied a new generation of CRISPR technology, known as ’base editing’ , as a treatment for inherited retinal diseases," said first author Susie Suh, an assistant specialist in the Department of Medicine at the UCI Faculty of Medicine. Ophthalmology.
"We overcame some of the barriers of the CRISPR-Cas9 system, such as unpredictable off-target mutations and low editing efficiency, using cytosine and adenine base editors (CBE and ABE). Using these editors allowed us to correct point mutations in a precise and predictable manner while minimizing unintentional mutations that could cause unwanted side effects," said co-senior author Elliot Choi, also an assistant specialist in the UCI Department of Ophthalmology.
Using an LCA mouse model harboring a clinically relevant pathogenic mutation in the Rpe65 gene, the UCI team successfully demonstrated the therapeutic potential of base editing for the treatment of LCA and, by extension, other inherited diseases that cause blindness. Among other results, the base editing treatment restored visual and retinal function in LCA mice to near normal levels.
"After receiving the treatment, the mice in our study were able to discriminate visual changes in terms of direction, size, contrast, and spatial and temporal frequency," Palczewski said. "These results are extremely encouraging and represent a major step forward toward developing treatments for inherited retinal diseases."
Gene therapy approaches to treat inherited retinal diseases are of particular interest given the accessibility of the eye, its immune-privileged status, and the successful clinical trials of the RPE65 gene augmentation therapy that led to the first gene therapy approved by the US Administration. US Food and Drugs
Now, as demonstrated in this study, base editing technology may provide an alternative treatment model to gene augmentation therapy to permanently rescue the function of a key vision-related protein disabled by mutations.
