Using mouse eyes as a setting for directed evolution, scientists have created a new version of the gene therapy vector adeno-associated virus (AAV) that can deliver genes deep into the retina, according to a paper published online today (June 12) in Science Translational Medicine. Such a vector could improve therapeutic gene delivery to target cells and lead to safer and less invasive gene therapy treatments.

Intravitreal injection, whereby a needle is pushed into the eye’s vitreous, or gel-like core, is a common drug delivery procedure performed under local anesthetic in a doctor’s office, explained Bennett. But using this routine injection technique in trials of gene therapy for retinal degeneration has thus far proven impossible.

The problem, explained David Schaffer, a professor of chemical and biomolecular engineering, bioengineering, and neuroscience at the University of California, Berkeley, who led the research, is that 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 Schaffer. “It never evolved to penetrate deep into tissue.”

Patients receiving gene therapy have therefore undergone a direct intraretinal injection, which requires hospitalization and general anesthetic, and can sometimes even damage the retina. If it were possible to inject AAV into the vitreous instead of the retina and still get gene delivery to the target cells, said Bennett, “one could envision the [doctor saying], ‘Ok, well just come into the office and get your gene therapy, tomorrow afternoon at two.’”


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