Organoids cured of Leber's amaurosis
A group of researchers from the National Eye Institute, part of the US National Institutes of Health, has developed a promising strategy for gene therapy of a rare form of Leber congenital amaurosis, which causes irreversible vision loss in childhood. This disease is caused by autosomal dominant mutations in the CRX gene, which encodes a protein necessary for the normal functioning of photoreceptors. Such mutations are difficult to eliminate with the help of gene therapy.
The researchers developed a new approach and tested it on retinal organoids – retinal tissues created in the laboratory from patient cells. The method consists in including copies of a normal gene under its natural control mechanism and partially restoring CRX function.
An organoid of the human retina.
The U.S. Food and Drug Administration approved the drug Luxturna in 2017 for the treatment of patients with Leber congenital amaurosis with mutations in the RPE65 gene. Being a major achievement in gene therapy, luxturna is still ineffective against other forms of Leber congenital amaurosis, including those caused by autosomal dominant mutations in the CRX gene.
The CRX gene encodes a cone-rod homeobox protein that binds to DNA and instructs retinal photoreceptors to produce photosensitive opsin pigments. Without the functional CRX protein, photoreceptors lose their ability to detect light and eventually die.
Disorders such as Leber's autosomal dominant congenital amaurosis are difficult to treat with gene therapy because adding a large amount of a normal gene does not always restore function. People with autosomal dominant mutations retain a normal copy of the gene, but the mutant version of the protein interferes with the normal protein. Sometimes simply adding more normal protein instead of restoring function can worsen the disease in an unpredictable way.
To study how adding copies of a normal gene will affect Leber's autosomal dominant congenital amaurosis, a group of researchers led by Anand Swarup developed retinal organoids from cells taken from two volunteers with amaurosis and from healthy members of their families. Scientists built complex retinal-like tissues in several stages, inducing the transformation of skin cells into mature photoreceptors and other retinal cells with the genetic profile of each of the volunteers. As expected, the organoids of participants with Leber's congenital amaurosis produced much less of the photosensitive pigment opsin than organoids from healthy family members.
In order to carefully determine how much of the CRX gene will be expressed by recipient photoreceptors, the group remade the CRX promoter, and as part of gene therapy it was injected together with the CRX gene. A promoter is a DNA sequence that controls when and how genes are expressed. The researchers placed the gene and its modified promoter inside the virus, which delivered them to the photoreceptors of the organoids.
The gene copy augmentation strategy restored the function of the CRX protein in retinal organoids with Leber's amaurosis by controlling the expression of opsins in both types of photoreceptors: rods and cones.
The authors believe that the new strategy of increasing gene copies may also be an effective method of treating Leber congenital amaurosis caused by other autosomal dominant mutations.
Article by K.Kruczek et al. Gene therapy of dominant CRX-Leber genital amaurosis using patient stem cell-derived retinal organoids is published in the journal Stem Cell Reports.
Aminat Adzhieva, portal "Eternal Youth" http://vechnayamolodost.ru According to NIH NEI: Researchers use patients' cells to test gene therapy for rare eye disease.