Gene Therapy Surprise (and Sight Restored)



Cool things going on in the medical field. Specifically in the field of gene therapy. The Economist reports on a new study published in Science Translational Medicine by a group of researchers led by Patrick Yu-Wai-Man, an ophthalmologist at Cambridge University.


Dr. Yu-Wai-Man’s team were trying to restore vision to those with a genetic condition. Specifically, people with Leber hereditary optic neuropathy (LHON) have DNA that is missing a gene involved in keeping the mitochondria in their retinal cells functioning. Since mitochondria make the energy that keeps a cell alive, the retinal cells in patients with LHON (which affects about 1 in 40,000 people) die suddenly sometimes over the course of less than a year.


To fix this problem, Dr. Yu-Wai-Man’s team loaded the correct gene sequence into a modified virus and then injected these viruses into patients’ eyes. Normally, viruses inject genes into healthy cells that instruct the healthy cell to produce more copies of the virus. However, the team’s viruses were modified not to reproduce, but only to cause the cell to repair the defective LHON gene.


However, in order to ensure a proper experimental study, the team only injected the virus into one eye and injected a placebo into the other eye.


The team was expecting the eye injected with the modified virus would have better vision than the eye injected with the placebo. However, the results surprised them: the patients’ vision improved in both eyes.


Follow-up monkey studies demonstrated that the modified virus was travelling from the injected eye to the other eye probably via the optic nerve.


This does raise a new concern for gene therapy, namely that gene therapy viruses can travel to unintended places.


At least in this instance it does not look as if there were any bad side effects and the virus did not travel to other tissues like the brain. Therefore, “GenSight Biologics, the company that has developed the treatment, has already sent its results to Europe’s medical regulator. It hopes to hear back by the end of 2021.”


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