Restore the sight of the blind. Regenerative medicine offers new hope for retinitis pigmentosa

Imagine what retinitis pigmentosa looks like. Imagine gradually losing your vision over the course of forty years, waking up each morning with just a little more of your peripheral vision dimmed, until you succumb to complete blindness as more and more photoreceptor cells begin to fail. in your eyes. RP is considered a rare disease. Although current statistics are not available, it is generally estimated that the disorder affects about 1 in 4,000 people, in the United States and around the world. It was the life of a 58-year-old man until a team of scientists restored useful eyesight by injecting genetically engineered viruses into his eyes. From the lack of vision over the past two decades (due to the inability of defective photoreceptors to transmit visual information from the eyes to the brain), to the ability to see small objects such as a notebook and a box of With staples using light-stimulating glasses, the breakthrough described in an article published in the journal Nature Medicine was based on optogenetics. While he could identify the notebook 92% of the time, he could only touch the smaller box of staples 36% of the time and it was even reported that he could see the white stripes of a crosswalk.

The team of international scientists found that activity in his brain’s visual cortex changed depending on whether or not an element was present, demonstrating its relationship to the retina, using non-invasive electroencephalography (EEG) readings. The results were described as “remarkable”. “I think a new field is emerging,” Botond Roska, professor and researcher at the University of Basel, said on a recent conference call announcing the team’s results.

Optogenetic therapies to restore vision have been used for more than a decade by scientists to treat people with degenerative eye diseases, such as retinitis pigmentosa. It combines optics and genetics to allow researchers to regulate individual neurons in vitro using visible light. Brain cells are first exposed to photosensitive molecules, which are then activated by light pulses from fiber optic wires. The chemical turns light into an electrical impulse, also triggering the neuron. This allows researchers to stimulate specific neurons on demand, potentially affecting the subject’s behavior and responses. The method is based on algae proteins that move in response to light sources. During the therapy, the scientists injected these genes into the remaining functional ganglion cells in the retina, causing them to create the light-sensitive protein ChrimsonR.

“It’s exciting. It’s really good to watch it work and get precise answers from patients,” says David Birch, retinal degeneration expert at the Retina Foundation of the Southwest in Dallas. Birch led. clinical trials on other optogenetic therapies, but did not participate in this study.

As part of their PIONEER 1 / 2a investigation, the University of Basel-UPMC team used GenSight Biologics technology to apply fundamental theories of optogenetics to the retina. The two-pronged approach was adopted using both biological and technological components. The biological aspect addressed the problem of RA as researchers targeted the patient’s retinal ganglion cells to receive gene therapy that would make them photoactivatable. Normally the rods and cones are photosensitive, but since the RP had essentially damaged and destroyed the patient’s rods and cones, the ganglion cells (which mainly focus on carrying the electrical charges generated by these photoreceptor cells) should be changed. To do this, the researchers isolated a gene from a species of photosensitive green algae in one of the patient’s eyes. This leads to the gene encoding a photoactivatable protein called ChrimsonR.

“These proteins are very special,” said Dr José-Alain Sahel, professor emeritus and chair of the ophthalmology department at the University of Pittsburgh School of Medicine, co-founder of Gensight Biologics and co-principal investigator of the PIONEER study. Committed. “They were discovered in the late 90s and early 2000s. These proteins exist in algae, capturing light and triggering an electrical response that allows algae to move closer to or withdraw from the light, and c ‘is a unique protein so it’s a very quick response.

After a few months, the lymph nodes produced sufficient amounts of ChrimsonR. Since ChrimsonR is most sensitive to light in the 590nm (amber) wavelength, this is when the technological aspect came into play. As it is much brighter than this. that ambient lighting can typically produce, Gensight (founded by Dr Sahel and colleagues) has developed an exclusive set of glasses that collect image data from a built-in event camera and project high wave light intensity of 590 nm directly into the patient’s eyes. “We have developed a bio-inspired camera that operates at every pixel by detecting any change in light sensitivity,” Sahel explained. “These cameras can detect very low levels of change, can operate at low applied levels and high light levels. We work pixel by pixel and we process the image in real time.

This is the first reported case of partial functional recovery in neurodegenerative disease after optogenetic therapy. However, this current PIONEER study is a very preliminary start to this form of therapy. Before optogenetics can become a standard treatment for some forms of blindness, more positive clinical trial results are needed. For now, Dr Sahel and his colleagues are bringing in additional volunteers for training, as well as to test higher doses of the virus and update their glasses to thin glasses which are more comfortable and provide more information to the retina. Compared to the Orion Visual Cortical Prosthesis System, which requires leads to implant a control unit chip into your skull, optogenetic therapy may be a less invasive approach. Sahel and Roska stress that therapy is not a cure for blindness. “For now, all we can say is that there is a patient… with a functional difference,” says Roska. Sahel adds: “This is an important step on the road to even better results. “

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