Once upon a time, there was a little girl named Anna Kuehl who loved exploring the nature surrounding her home in the Bavarian Forest. Located northeast of Munich not far from the German-Czech border, this verdant landscape, called Bayerischer Wald, is a wooded, low-mountain region. Kuehl’s childhood took place in this idyllic setting, a beautiful playground where she spent many happy hours. Oftentimes, Kuehl would pick wild blackberries and hazelnuts in the foothills that birthed characters like Red Riding Hood, Rapunzel and Snow White.
As an adult, Kuehl moved to the United States and settled in Los Angeles in the early 1960s. At 22, she landed a job as an administrative assistant to USC engineering legend Zohrab Kaprielian. She met and married Hans Kuehl, a dapper and earnest electrical engineering professor, and had two children. While Hans continued his teaching and research, Anna completed her bachelor’s degree in accounting at USC and earned her CPA.
Yet Kuehl remained that same girl from the now-faraway forest who found time to appreciate nature. She took frequent hikes in the Palos Verdes Hills of Southern California. On the trails, her favorite plant was the Santa Catalina mariposa lily, a colorful native flower that is white on the outside with a brightly hued interior. On clear days, she saw all the way to Santa Catalina Island, just south in the cobalt blue waters of the Pacific.
Little Girl Lost
As Kuehl grew older, she couldn’t marvel at nature’s beauty in the same way. Unfortunately, her sight began to deteriorate.
In her mid-30s, Kuehl was diagnosed with dry macular degeneration, an age-related condition that results in the loss of central vision over time. The condition is characterized by the loss of a single-cell layer in the back of the eye called the retinal pigment epithelium (RPE).
At the onset, Kuehl didn’t notice anything, but her eye doctor observed an early sign of dry macular degeneration — yellow deposits in the eye called drusen. These deposits form under the retina and are one of the first signs of the condition, often occurring years or decades before the onset of visual symptoms.
Her eye doctor recommended that Kuehl monitor her vision at home using an Amsler grid, a tool ophthalmologists use to detect vision problems resulting from damage to the macula, the central part of the retina. Instead of seeing one black dot in the center of the grid, patients with macular degeneration see an unfocused, larger black area with no distinct shape — essentially a large blind spot.
Eventually, Kuehl found it impossible to see the black dot in the center of the grid.
While her peripheral vision remained intact, she realized she was losing the central vision in her left eye. She could no longer make out people’s faces clearly, drive a car or read the time on her watch. Even her beloved hiking excursions became cumbersome.
“I couldn’t read the trail names on the posts anymore,” said Kuehl, now 78. “I always had to take so many things with me — my magnifying glass, my reading glasses — and I always printed out a big map.”
A New Hope
In the Brothers Grimm’s fairy tale “Rapunzel,” the sight of a blind prince is a restored by the heroine’s tears.
Fortunately, Kuehl’s eye doctor at the time, Dr. Lisa Olmos, had a different idea: the first human trial of a novel stem cell-based retinal implant that would bring Kuehl all the way back to the doors of her alma mater.
In fact, the USC Roski Eye Institute, part of the Keck School of Medicine of USC, had collaborated for more than a decade with other California institutions to develop a stem cell-based retinal implant for people with advanced dry age-related macular degeneration.
Funded in part by the California Institute for Regenerative Medicine, the phase I/IIa study treatment involved implanting an ultra-thin scaffold layered with stem cell-derived RPE cells into the patient’s eye. The hope was that implanting RPE cells would halt the progression of the disease. In the best-case scenario, the patient’s vision could even improve.
Led at USC by Dr. Mark Humayun, a University Professor of ophthalmology, biomedical engineering and integrative anatomical sciences; Dr. Amir Kashani, an assistant professor of clinical ophthalmology at the Keck School of Medicine; and David Hinton, a professor of pathology also at Keck, the research involved collaboration with other engineers and scientists including Dennis Clegg, co-director of the Center for Stem Cell Biology and Engineering at the University of California, Santa Barbara.
According to Humayun, a renowned eye doctor and USC Viterbi biomedical engineer, macular degeneration affects 14 million people worldwide. The condition can be inherited or age-related, typically showing up in patients aged 55 or older. Age-related macular degeneration has two primary forms: neovascular, meaning the creation of new blood vessels, called “wet” form; and non-neovascular, meaning no new blood vessels, also called “dry” form.
Humayun had watched his grandmother go blind due to diabetes. She, like Kuehl, had loved nature and all the roses in her garden. That experience helped inform his life’s work: restoring sight to the blind. “The loss of one’s vision can be extremely devastating,” said Humayun, holder of the Cornelius J. Pings Chair in Biomedical Sciences. “And it can rob one of his or her independence.”
In 2013, the Food and Drug Administration approved a device that Humayun co-invented. The Argus II, a retinal implant, was the world’s first commercially available “bionic eye” designed to help patients with genetic retinitis pigmentosa, a condition that causes vision loss as the light-sensing cells of the retina gradually deteriorate.
In wet macular degeneration, bleeding and swelling occur in the retina due to the formation of new blood vessels. Treatment consists of injecting drugs into the eye that prevent the new blood vessels from growing. In effect, the medicine alone has the power to stop the disease progression and even reverse vision loss.
On the other hand, 80 percent to 90 percent of age-related macular degeneration patients have the dry form, which doesn’t create new blood vessels. According to Kashani, a retinal specialist, the dry form is characterized by the loss of mature RPE cells that support the photoreceptors in the eye responsible for light sensing. Since the RPE cells die primarily in the macula, the retina’s mid-region responsible for the sharpest vision, a patient’s central vision would worsen over time.
“That led to the idea that we can make these mature RPE cells from stem cells and put them back in under the retina,” Kashani explained. “The idea is to replace this single-cell layer early enough in the disease process so that the overlying retina isn’t damaged and hopefully you can restore some vision, or at least prevent it from getting worse.”
Placement Is Everything
Even more challenging, this layer of RPE cells has to be oriented properly for specific placement in the eye. Past treatment efforts have involved injections of stem cell-derived RPE cells into the macula, a scattershot approach lacking an exact target.
Humayun stressed that placement was a crucial factor for the implant to heal specific, damaged regions of the macula. He made the polymer-based carrier for the RPE cells in collaboration with engineers at Caltech.
The engineering platform itself was another first-of-its-kind, according to Humayun. The substrate was made from parylene, a biocompatible piece of plastic that can be machined in extremely thin form. To engineer this sort of carrier, it needs to behave at the cellular level and seamlessly integrate with the tissue, yet it can’t dissolve or erode in the eye.
“In certain areas, it’s as thick as only two human hairs and needs to be very thin to allow the diffusion exchange of nutrients, but it also has to be strong enough to carry the RPE cells, so we can fold it and get it in through small, surgical incisions,” Humayun said.
Added Kashani, “It’s amazing that we can differentiate the RPE cells from human embryonic stem cells and get them to lay flat in a single sheet, which is the same way they exist in the retina. That’s a marvel of not only stem cell biology, but also engineering.”
Kashani, the eye surgeon for the trial, knew he would have to maneuver the carrier, only four to six microns thick, into the exact spot of the retina where RPE cells had already atrophied or died. After locating the damaged area, he would need to come up with a surgical plan to insert the implant without damaging the surrounding tissue.
After surgery, the RPE cells would need to be monitored, checking how they integrate and function in the patient’s eye over time.
Kuehl was selected as one of four patients for the clinical trial. She underwent the surgery for her left eye at Keck Medicine of USC on Oct. 10, 2017. Kashani performed the operation.
For outpatient care, Kuehl slept with a shield on her eye and went back to the doctor’s office the following morning. After the shield was removed, she was given a thorough vision test for about an hour, in both bright and dark conditions.
“I knew that [my vision] was getting better,” Kuehl said. “Using the Amsler grid, I could tell right away. I have used it every day of every year for both of my eyes, and I could tell the shape of the black area had changed after the implant and that [the black area] was getting smaller over time.”
Because the trial was part of a phase I/IIa study, Kashani admits the research team wasn’t prepared for the exceptionally positive results they saw.
“We weren’t really expecting anything significant since most of these patients had such severe disease,” Kashani said.
One patient’s vision was notably better when tested with an eye chart and measured an ability to read an impressive 17 more letters than before the implant. For two others, tests continue to show that their sight is improving, even if they aren’t able to see well enough to read yet.
For the next phase of the clinical trial, researchers will need to conduct a multi-centered trial with a larger cohort of subjects with more visual potential and less severe disease.
Extrapolating beyond the study, Humayun, also the director of the new USC Ginsburg Institute for Biomedical Therapeutics, hopes that one basic idea will have been proven: that stem cells can create replacement parts, organs, tissues and even cells.
“With the right kind of environment and support, you can actually treat very specific regions or diseases down to the cellular level,” Humayun said. “One aspect of that could be called precision medicine, and another aspect is that stem cell-based therapies are coming of age. This will be one of the first studies to land that point.”
Since the surgery, Kuehl notices little changes in her vision all the time. For example, she can make out the time on her watch again, and reading in general has become much easier. Often, she calls Kashani out of sheer excitement about something new she saw during the day. An avid fan of the opera, Kuehl says she can now read part or all of the subtitles during Metropolitan Opera screenings at local theaters. Remarkably, she can even see the whole faces of people again, whether in person or on television.
“I could only see half of people’s faces before on TV and couldn’t tell the characters apart,” Kuehl said. “But now that I can see better, I can follow the story.”
And with sparkling blue eyes filled with joy, she describes how excited she is to go hiking.
“I got my independence back, and I’m just so happy about it,” Kuehl said. “Now I don’t use a map on the trails, and I can read the trail names on the posts. I don’t need anything! I’m much more liberated.”
Disclosures: Regenerative Patch Technologies LLC was founded by Mark Humayun, M.D., Ph.D., and David R. Hinton, M.D., from the University of Southern California, and Dennis O. Clegg, Ph.D., from the University of California, Santa Barbara. The technology to produce the stem cell-based retinal implant is exclusively licensed to Regenerative Patch Technologies LLC from the University of Southern California, the California Institute of Technology and the University of California, Santa Barbara. Humayun and Hinton have an equity interest in and are consultants for Regenerative Patch Technologies LLC.