It's one of the biggest milestones for stem cells since their discovery. Researchers yesterday published the first results of a clinical trial where doctors transplanted of stem cells into the eyes of patients suffering from a form of progressive blindness. And the preliminary results look very good.

Human embryonic stem cells (hESCs) were first discovered thirteen years ago. Since then, they have shown incredible potential for therapeutic applications in conditions ranging from Alzheimer's disease to diabetes — but no studies examining their effects in humans had ever been published. Now that's all changed.


The study was designed to examine the safety of hESC-transplantation in two human patients with sight-threatening diseases. The first patient suffers from age-related macular degeneration (AMD for short, age-related macular degeneration is the number one cause of blindness in people over 50), the second patient from Stargardt's macular dystrophy.

Both diseases are characterized by the gradual degeneration of a layer of cells in the eye known as the retinal pigment epithelium (RPE). If you've ever dissected a calf's eye, you've seen the RPE — it's the black-pigmented tissue lining the inside of the eye. As this cell layer wastes away, photoreceptors vital to eye sight are gradually lost, and blindness sets in. In the study published in yesterday's issue of The Lancet (no subscription required), a research team led by stem cell pioneer Robert Lanza examined how safely hESCs could be transplanted into the RPE of these two patients.

It's important to recognize that in early clinical trials, researchers are much more concerned with the safety of the treatment under investigation, and how well patients tolerate its administration, than they are with its efficacy. This trial was no different. Having said that, its findings are especially encouraging.


Four months after the transplants were performed, the researchers were able to verify that over 99% of the transplanted hESCs had successfully developed into RPE cells; neither patient had lost vision, as is typical of people with progressive blindness; and — perhaps most important of all — neither patient showed any signs of abnormal tissue growth (the risk of developing tumors has long been one of the biggest concerns attached to stem cell therapy).


In fact, both patients have described improvements to their vision. According to a piece published online in TIME, the patient suffering from macular dystrophy — a woman who goes by the assumed name "Rosemary" — has gone from seeing only vague hand gestures to being able to make out individual fingers; while Sue Freeman — the patient who suffers from AMD — is able to see seven more letters on a standard eye chart than she could before the treatment.

The researchers are confident that Rosemary's improvements are related to the stem cell transplants, but the fact that Freeman has reported a boost in vision in both of her eyes — even though only one was treated with stem cells — makes it harder to determine whether her improvement is due to the stem cells or a placebo effect.


Again: this trial is more about assessing the safety of the transplantation than its efficacy; but the ambiguity surrounding Freeman's improvements draws attention to the need for control groups and larger sample sizes in future trials. For now, however, these results are pretty much everything the researchers could have hoped for.

"This is very important for the field of human embryonic stem cell research," says Dr. Steven Schwartz, director of the Diabetic Eye Disease and Retinal Vascular Center at UCLA and lead author of the paper. "It opens the door for multiple strategies in the field, and hopefully for everyone investigating [this technique], it puts some wind in their sails." He continues:

The improvement in vision is a tiny biological signal. It could be disproven, or it could be the beginning of something fantastic. The important thing here is that at four months, we saw the cells transplanted successfully into the subretinal space, they engrafted, and there was no immune rejection and not tumors, so it appeared safe.


The researchers' findings are published in The Lancet (no subscription required). To learn more about the researchers, the patients, and their progress in this trial, check out this excellent piece by TIME's Alice Park.

Top image via mashe/Shutterstock; eye chart via Wikimedia Commons; RPE photo by Mark Fickett via Wikimedia Commons


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