Improving the Delivery of Genes to Restore Sight

Researchers have produced an improvement in methods of gene therapy used to treat some rare forms of blindness, and which may allow the use of gene therapy in the treatment of more common forms of degenerative blindness that occur in old age:

Three groups of researchers have successfully restored some sight to more than a dozen people with a rare disease called Leber's congenital amaurosis. [They] achieved this by inserting a corrective gene into adeno-associated viruses (AAV), a common but benign respiratory virus, and injecting the viruses directly into the retina. The photoreceptor cells take up the virus and incorporate the functional gene into their chromosomes to make a critical protein that the defective gene could not, rescuing the photoreceptors and restoring sight.

Unfortunately, the technique cannot be applied to most blinding diseases because the needle often causes retinal detachment, making the situation worse. Yet the standard AAV used in eye and other types of gene therapy cannot penetrate into tissue to reach the photoreceptors and other cells, such as retinal pigment epithelium, that need to be fixed.

[Researchers] set out to find a way to "evolve" AAV to penetrate tissues, including eye and liver, as a way to deliver genes to specific cells. [They have] generated 100 million variants of AAV - each carrying slightly different proteins on its coat - [and] selected five that were effective in penetrating the retina. "Building upon 14 years of research, we have now created a virus that you just inject into the liquid vitreous humor inside the eye and it delivers genes to a very difficult-to-reach population of delicate cells in a way that is surgically non-invasive and safe. It's a 15-minute procedure, and you can likely go home that day."

The engineered virus works far better than current therapies in rodent models of two human degenerative eye diseases, and can penetrate photoreceptor cells in the eyes of monkeys, which are like those of humans. [This] could greatly expand gene therapy to help restore sight to patients with blinding diseases ranging from inherited defects like retinitis pigmentosa to degenerative illnesses of old age, such as macular degeneration.

Link: http://www.eurekalert.org/pub_releases/2013-06/uoc--rde061213.php

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