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Stem Cell Eye Implants Safe, Stop Visual Function Loss

Retinal cells from stem cells

Scanning electron microscope image of retinal pigment epithelial cells derived from stem cells (Roski Eye Institute, University of Southern California)

5 April 2018. Early results from a clinical trial show implants of replacement retina cells grown from stem cells are safe for people with a form of age-related macular degeneration, and at least stop the loss of visual function. A description of the implants and report of the findings appear in yesterday’s issue of the journal Science Translational Medicine (paid subscription required).

Age-related macular degeneration, or AMD, is a common disorder and the leading cause of vision loss in people over the age of 50. The condition  occurs in the macula, the part of the retina with light-sensing cells at the back of the eye. When the macula is damaged, the retina’s ability to turn the sensed light into electrical signals for the brain is impaired. The disorder usually begins with blurry or dark spots in the central vision view, and can progress at varying speeds, leading in some advanced cases to complete vision loss.

About 90 percent of AMD cases are non-neovascular or “dry” AMD, since no leakage from blood vessels occurs. In late stages of dry AMD, large sections of the retina stop functioning, a condition called geographic atrophy. With geographic atrophy, the retinal pigment epithelium, a thin layer of cells beneath photoreceptors in the retina are damaged. This cell layer supports the photoreceptors with nutrients and oxygen, as well as supporting conversion of sensed light to electrical signals.

The implants in this study are designed to treat patients with geographic atrophy, with human embryonic stem cells used to grow replacement cells implanted in the retina to replace the damaged retinal pigment epithelium. The stem cells are seeded and grown into retinal pigment epithelium cells on an ultra-thin patch made of parylene, a stable and chemically inert biocompatible polymer used in protective coatings. The patch implants were designed and developed by researchers at University of Southern California in Los Angeles and University of California in Santa Barbara, led by Mark Humayun and David Hinton at USC, and Dennis Clegg at UC-Santa Barbara.

The clinical trial is an early- and intermediate-stage study mainly of the implants’ safety, but also looking for indicators of efficacy such as electrical responses of photoreceptor cells, as well as visual field and acuity. The trial is recruiting 20 patients with geographic atrophy, implanting a set of stem cells in one of the patient’s eyes, and comparing the results with the untreated eyes. The clinicians and researchers followed up with participants up to a year after the procedures.

The paper reports on the first 5 patients in the trial. Of those 5 participants, surgeons successfully implanted the stem cell patches in 4 of the patients. One of the participants was found to have debris in the proposed surgical site, making it too risky to continue the procedure. Using an imaging technique known as optical coherence tomography, the team found the retinal pigment epithelium cells in the implants integrated with their photoreceptor cells in the remaining 4 participants.

The researchers and clinicians found no safety concerns related to the implants, affecting the participants eyes or their overall health. One patient developed a hemorrhage in the implanted eye following the surgery, which later healed and did not affect the person’s vision. Two participants encountered health problems during the trial unrelated to the surgery or their implants.

The participants’ visual function in the implanted eyes remained stable after the surgery, halting the vision loss that occurred earlier. Two of the 4 participants were able to fix on objects in their field of view more like normal eyes. And one of the patients was able to read 17 more letters on the standard visual acuity eye chart with the implanted eye.

The authors conclude the implants are safe and well tolerated, and for at least some of their recipients help improve visual functioning. The trial was sponsored by Regenerative Patch Technologies in Menlo Park, California, a company founded by the implant’s inventors Mark Humayun, David Hinton, and Dennis Clegg. The company has an exclusive license from the universities to develop and commercialize the implants. California Institute for Regenerative Medicine also funded the trial.

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