Researchers at the University of California at Berkeley have come up with a new version of an adeno-associated virus (AAV) vector that can deliver genes deep into the vitreous of the retina using an intravitreal injection. This less-invasive technique provides, for the first time, a viable alternative to an intraretinal injection below the surface of the retina, which is the usual way gene therapy is currently delivered.
The study, ‘In Vivo–Directed Evolution of a New Adeno-Associated Virus for Therapeutic Outer Retinal Gene Delivery from the Vitreous’ was published online in Science Translational Medicine.
Lead researcher Dr. David Schaffer said current AAV vectors are incapable of penetrating deep into the retina where the target cells for retinal diseases are located. “AAV is a respiratory virus and so it evolved to infect lung epithelial cells,” explained Prof. Schaffer, “It never evolved to penetrate deep into tissue.”
He said the new procedure “delivers genes to a very difficult-to-reach population of delicate cells in a way that is surgically non-invasive and safe. It’s a15-minute procedure, and you can likely go home that day.
AAV is a respiratory virus and so it evolved to infect lung epithelial cells
Able to Restore and Knock out Genes
He predicts the viruses can be used not only to insert genes that restore function to non-working genes, but can knock out genes or halt processes that are actively killing retinal cells, which may be the case in age-related macular degeneration.
AAVs are currently used for gene delivery in several retinal gene therapy clinical trials, including those that have restored vision in children and young adults with LCA (RPE65). AAVs are attractive for gene delivery because of their natural ability to penetrate a variety of cells. In addition, humans are exposed to the virus in nature and, therefore, tolerate it well.
Professor Schaffer said he and his team are now collaborating with other investigators to identify patients most likely to benefit and, after some preclinical development, hope soon to head into clinical trials.