Human corneas regrown to restore vision

A team of scientists from several Harvard-affiliated centers in Boston, MA, has grown human corneal tissue in mice using adult-derived human stem cells. They believe their breakthrough will bring hope to people who have impaired or lost vision due to burns, chemical injuries, or eye diseases that damage the cornea.

Dr. Bruce Ksander, associate professor of ophthalmology at Harvard Medical School, and also of Massachusetts Eye & Ear Infirmary, and colleagues write about their work - the first known example of tissue grown from a human stem cell - in the journal Nature.

The cells that make up the cornea - the transparent "window" of tissue at the front of the eye - are constantly damaged from blinking and exposure to the outside world. To repair the damage, the eye maintains a small number of "limbal stem cells" at the edge of the cornea.

Rare limbal stem cells are essential for corneal growth and repair
The limbal stem cells replenish corneal cells as they become damaged. However, injury or disease can lead to loss of these stem cells, and the eye loses its ability to keep the cornea transparent and clear, resulting in significant loss of vision and eventually, blindness.
The only treatment option for patients who have lost their limbal stem cells is transplantation. However, this is complicated by the fact limbal stem are not easy to identify, so eye surgeons cannot be sure if the grafts are rich or poor in the essential stem cells.

Prof. Ksander says, "Limbal stem cells are very rare, and successful transplants are dependent on these rare cells."

In their study, he and his colleagues found that the gene ABCB5 acts as a marker for hard-to-find limbal stem cells, and is also essential for maintaining the stem cells and growing and repairing the cornea.

They found mice lacking a functional ABCB5 gene lost their limbal stem cells, and their corneas healed poorly after injury.

Mice receiving human ABCB5-positive limbal stem cells restored their corneas
But, mice deficient in limbal stem cells developed fully functioning, restored corneas, that were kept clear and normal, after receiving transplants of human ABCB5-positive limbal stem cells.

In contrast, control mice that received either no limbal stem cells, or received ABCB5-negative limbal stem cells, failed to restore their corneas.

The researchers used antibodies to detect ABCB5 and confirm that tissue from deceased human donors contained limbal stem cells before transplanting them into the mice.

They say ABCB5 keeps the stem cells alive, and protects them from programmed cell death or apoptosis. The study in mice is thought to be the first to show how the gene behaves in normal development.

"This finding will now make it much easier to restore the corneal surface," says Prof. Ksander. "It's a very good example of basic research moving quickly to a translational application."

Meanwhile, Medical News Today recently reported how researchers at Oxford University in the UK have started testing newly developed "smart glasses" that help people with poor vision boost their awareness of what is around them. With the help of volunteers, the team is measuring how well their invention can help the near-blind navigate around shopping malls and avoid walking into obstacles.

Written by Catharine Paddock PhD