One biotech startup wants to restore vision in blind patients with a gene therapy that gives light sensitivity to neurons that don’t normally possess it.
The attempt, by Ann Arbor, Michigan-based Retrosense Therapeutics, will use so-called optogenetics. Scientists have used the technique over the last few years as a research tool to study brain circuits and the neural control of behavior by directing neuron activity with flashes of light. But Retrosense and others groups are pushing to bring the technique to patients in clinical trials.
The idea behind Retrosense’s experimental therapy is to use optogenetics to treat patients who have lost their vision due to retinal degenerative diseases such as retinitis pigmentosa. Patients with retinitis pigmentosa experience progressive and irreversible vision loss because the rods and cones of their eyes die due to an inherited condition. If the company is successful, the treatment could also help patients with the most common form of macular degeneration, which affects nearly a million people in the United States. The U.S. Food and Drug Administration hasn’t approved any therapies for either condition.
Retrosense is developing a treatment in which other cells in the retina could take the place of the rods and cones, cells which convert light into electrical signals. The company is targeting a group of neurons in the eye called ganglion cells. Normally, ganglion cells don’t respond to light. Instead, they act as a conduit for electrical information sent from the retina’s rods and cones. The ganglion cells then transmit visual information directly to the brain.
Doctors would inject a non-disease causing virus into a patient’s eye. The virus would carry the genetic information needed to produce the light-sensitive channel proteins in the ganglion cells. Normally, rods, cones, and other cells translate light information into a code of neuron-firing patterns that is then transmitted via the ganglion cells into the brain. Since Retrosense’s therapy would bypass that information processing, it may require the brain to learn how to interpret the signals.
So far, Retrosense and its academic collaborators have shown that the treatment can restore some vision-evoked behaviors in rodents. The treatment also seems safe in nonhuman primates. The optogenetically modified ganglion cells of these primates are light-responsive, but behavioral tests aren’t possible, as there are no nonhuman primate models of retinal degeneration, says Retrosense CEO Sean Ainsworth.
Retrosense plans to begin its first clinical trial in 2013 with nine blind retinitis pigmentosa patients.