Cells of the retina, which detect light from the back of the eye, are a part of the central nervous system (CNS).  Unlike other parts of the body, the CNS cannot heal itself once it is damaged by injury or disease. This makes degenerative eye diseases like retinitis pigmentosa (RP)—a  genetic disorder that causes progressive damage to retinal cells—incurable. RP can cause blindness, and symptoms typically begin to appear during adolescence.


At least 100,000 Americans are afflicted by this orphan disease. Many more suffer from RP in China, where Jing Yang, MD, PhD, regularly  encountered retinal diseases in her patients at one of the top ophthalmology practices in the country. “After six years in the clinic, I realized that retinal degeneration is a common and serious problem, with millions of people around the world suffering and going blind,” Dr. Yang recollects. “RP was adversely impacting my patients’ lives, and I had to inform them that there was no cure.


“I chose to enter into the field of stem cell research to work on a cure for these challenging retinal diseases. During three years of research in  Denmark, I made a number of valuable stem cell discoveries. That inspired me to become a full-time researcher with the goal of using stem  cells to help blind patients regain their sight.”


Seeing Eye to Eye
Retinal progenitor cells are comparable to stem cells that have become restricted to only differentiating into cells of the retina. When  transplanted into a diseased eye, these cells are capable of producing new photoreceptors, thereby restoring retinal function. In addition,
progenitor cells can save the host photoreceptors from degeneration in the first place, thus providing a method to preserve vision.


As Dr. Yang researched retinal progenitor cells in Denmark, she met Henry Klassen, MD, PhD, who was working on a similar project in the
United States. “At that point, we were early on in the development of progenitor cells. I met Dr. Klassen in the cell culture lab to discuss our progress.  Like me, he had also trained as an ophthalmologist, so we had a lot in common. We both felt like this research was not just a job, that it was our mission to use this advanced science to help patients.”


Dr. Yang has worked closely with Dr. Klassen on stem cell therapy research for the treatment of retinal degeneration since she joined his lab
at the Gavin Herbert Eye Institute in 2006. They married in 2010. “We are currently collaborating on using retinal progenitor cells as a therapy for RP,” says Dr. Yang. “We are pioneers—our research could lead to one of the first approved stem cell therapies in eye care and pave the  way for the treatments of otherwise incurable diseases of the brain and spinal cord. Clinical trials could start as early as next year.”


Under Watchful Care
Progenitor cells need a lot of attention in the lab. “Great skill is required because the cells are viable for a limited time,” explains Dr. Yang. “Other researchers with similar projects have failed in culturing these cells. I developed cell culture methods to keep the cells happy, and put in so much time feeding and caring for them that I call them my babies.


“Once the cells have grown, we test them to verify that they are the right kind of cells and then perform many additional tests for safety. We use an animal model to make sure no tumors form over time, and then also test for visual efficacy in an animal model of retinal degeneration. Once all of our animal tests are successful, we must repeat all of our work using cells manufactured at a pharmaceutical-grade level and  again test for safety and therapeutic potency. From there, we can apply to the FDA to start a clinical trial that will help to turn these progenitor cells into an easily injectable drug for patients.”

Progenitor cells could eventually be used to treat other retinal conditions including age-related macular degeneration and glaucoma. Dr. Yang
has already begun gathering the preliminary efficacy data. “Dr. Klassen and I are fully committed to developing stem cell therapy for patients with RP and eventually treatments for other retinal diseases,” asserts Dr. Yang. “It will be very validating once we can start helping patients to see again.”



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