New techniques regrow lens, cornea tissue

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Human cells reprogrammed to become stem cells can form cornea tissue in lab dishes, researchers in Japan and Wales report March 9 in Nature. The stem cell tissue was used to repair the damaged outer layer of the cornea in rabbits. In a separate study also published March 9 in Nature, researchers in China and the United States coaxed stem cells in the eyes of a dozen babies born with cataracts to regrow clear lenses.  

While both studies are technically proficient and provide new approaches to treating cataracts or corneal injuries, neither will soon be ready for widespread use in the clinic, says Henry Klassen, an ophthalmologist at the University of California, Irvine School of Medicine. The United States would require more extensive testing before human studies are approved (both studies report results from small numbers of animals). Klassen also doubts that lens regeneration would be useful for adults with cataracts, “but it is promising in infants,” he says.

In the first study, Kohji Nishida of Osaka University in Japan and colleagues grew eyelike structures in lab dishes using reprogrammed human cells, known as induced pluripotent stem cells. The proto-eyes grew in a target pattern with each ring of the target containing cells that correspond to a different layer of the eye. The researchers then isolated cells that could grow into corneal epithelial cells, the outer skin of the eye. When transplanted to the eyes of rabbits with cornea damage, the human cells repaired the wound, the researchers report.

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Nishida says the researchers hope to start clinical trials within two to three years to repair corneas damaged by injury or diseases.

But it remains to be seen how useful this approach will be, Klassen says. “I can see the beauty of this, but I don’t think it’s all sorted out yet.”

In the second study, researchers took a different approach to restoring the eye. Instead of transplanting stem cells, Kang Zhang, a stem cell biologist at the University of California, San Diego, and colleagues prodded the tissue to repair itself. The researchers took advantage of a complication of cataract surgery: Stem cells in the lens start to grow when the lens is injured by the surgery or other means, but pile up in disorderly pearls instead of making orderly, clear crystals. In about half of patients, the pearls can cloud vision again and must be removed with laser surgery. By manipulating levels of proteins that control growth of the stem cells, Zhang and colleagues regenerated clear lenses in rabbits and monkeys.

In human babies, lenses could regrow without the help of growth proteins, Zhang and colleagues found. The researchers studied 37 babies who were born with cataracts. Regular cataract surgery, which involves removing the cloudy lens and replacing it with a plastic one, was done for 25 of the babies. In the remaining 12 babies, doctors made a small incision in the side of the sack containing the lens and extracted the cataract, but didn’t replace the lens. Stem cells in the sack generated a new lens within about three months of surgery.

Zhang thinks it may be possible to stimulate stem cells in other organs to regenerate and rejuvenate the organs. But at this point, such applications are still dreams, other researchers say.

Even when eye surgeons learn of the study, “I can guarantee the first reaction is going to be disbelief,” says J. Fielding Hejtmancik, an ophthalmic geneticist at the National Eye Institute in Rockville, Md. The work in both studies is exciting but exploratory, and must be followed up with much more detailed clinical studies, he says.

Ophthalmologist Manuel Datiles, also at the National Eye Institute, thinks lens regeneration has bigger problems. Babies in the study were still legally blind after either the conventional surgery or the new lens regeneration surgery, so the new technique does not initially improve the outcome. The regeneration surgery had fewer complications, though, and may have long-term benefits, he says.

But Datiles is skeptical that regenerated lenses would help adults. It takes months to regrow a lens in babies and may take even longer for adults. Patients probably won’t wait around, especially since artificial lenses inserted after cataracts are removed restore vision almost immediately, Datiles says. “How can you compare it with the current treatment where the patient can see 20/20 the very next day?”