Stem cells could help treat people with cataracts and even some who are blind by regenerating eye tissue and replacing flawed lenses, according to new experiments in children and rabbits.
In order for people to see properly, both the lens of the eye and the cornea — the layer of tissue that covers the eye in front of the lens — must be transparent. Current treatments for people who have clouding in the lens or cornea involve artificial implants or donor transplants, respectively, but these surgical procedures can be risky, researchers said.
In the new research, scientists performed minimally invasive surgeries on 12 infants under age 2 who all had congenital cataracts — a major cause of childhood blindness. They removed the children's cataracts, but carefully spared certain cells in their eyes, called lens epithelial stem/progenitor cells (LECs), which could then go on to regenerate lenses.
They found that the infants' incisions healed within one month, and the transparency of their line of vision was more than 20 times better, compared to infants with congenital cataracts who received the current, standard treatment. [5 Amazing Technologies That Are Revolutionizing Biotech]
The finding shows that "we can harness our own stem cells to regenerate a tissue or organ," Dr. Kang Zhang, who led the study and is an ophthalmologist at the University of California, San Diego, told Live Science.
Researchers had not previously shown that LECs could be used to regenerate human lenses.
Cataracts involve clouding of the lens, and are the leading cause of blindness worldwide. The current treatment for cataracts involves surgically removing the clouded lens of the eye from its supporting capsule and replacing it with an artificial lens. More than 20 million cataract patients worldwide now undergo this procedure each year.
Zhang noted that only 4 in 10,000 cataract patients are infants. Still, "in principle, this approach should work for any age, because lens stem cells are present through life," he said. The stem cells of older patients may need a bit of a boost to regenerate lenses, he added.
The current treatment for cataracts is artificial lens implantation, which requires a cut about 6 millimeters wide to the lens capsule. The treatment can lead to inflammation and the destruction of the LECs, which normally help protect the lens from damage. Moreover, this surgery can lead to scars or the abnormal growth of lens cells — either of which can result in cloudiness in a patient's line of vision.
In early experiments, Zhang and his colleagues showed they could isolate LECs from mice, and that these cells could form transparent, lenslike structures. The scientists reasoned that minimally invasive surgeries, involving cuts of only 1 to 1.5 millimeters wide, could remove cataracts while also preserving LECs that could then go on to regenerate lenses, Zhang said. They achieved successful lens regeneration in rabbits and monkeys, before attempting the procedure in children.
In the study, the infants' surgical wounds were only about 4.3 percent the size of those created by the current method. The scientists also moved the site of the incision to the periphery of the lens rather than its center, according to the findings published online March 9 in the journal Nature. [Top 3 Techniques for Creating Organs in the Lab]
The researchers noted that they only tested a small number of patients with their new method. They will need "much larger and longer-term clinical trials to show its safety and efficacy," Zhang said.
When it comes to treating blindness due to problems with the cornea, the gold-standard treatment involves corneal transplants from donors. However, the immune systems of recipients can reject a transplanted cornea.
In a separate finding, also published March 9 in Nature, researchers tested out a promising strategy for avoiding such rejection that involves growing corneas from the cells of patients.
Researcher Kohji Nishida at Osaka University in Japan and his colleagues used induced pluripotent stem cells (iPSCs), which are mature cells that are chemically reprogrammed with the ability to become any tissue in the body, to grow new corneas.
During embryonic development, eye tissue is formed from three layers, and the cornea and lens emerge from the topmost layer. In the experiments, the scientists grew human iPSCs with a chemical that promoted the creation of a structure that resembled the developing eye. The researchers harvested stem cells from this structure, which generated molecules one might expect of the cornea. They grew sheets of corneal tissue from these cells, and found they could restore vision in rabbits that had corneal blindness.
It seems unlikely that growing a structure mimicking the embryonic eye is an economically viable strategy for treating corneal blindness, noted Julie Daniels, a professor of regenerative medicine and cellular therapy at the University of College London Institute of Ophthalmology, who was not involved in the study.
The real value of this research is how experiments with this kind of structure will help better understand eye development, and "such an understanding might eventually enable in situ manipulation of stem-cell populations throughout the eye" as Zhang and his colleagues accomplished, Daniels wrote in a commentary on this research.