Lab-Grown Cornea Cells Transplanted
For the first time, researchers have used cells grown in the laboratory to restore vision to people who suffer from conditions that damage the cornea, the clear covering of the eye.
In separate reports in today’s New England Journal of Medicine and this month’s issue of the journal Cornea, researchers in California and Taiwan report that they have successfully improved sight in 15 of 20 patients treated with the procedure.
The groups took a small number of corneal cells from a healthy eye--either from a patient or, in a few cases, a relative--and grew the cells in a laboratory dish to obtain enough tissue to provide a new layer of cornea for the patients’ damaged eyes.
“The procedure applies to a relatively small number of patients, but what is exciting is the bioengineering of mucus membranes, or ‘wet’ areas of the body,” said Dr. Ivan Schwab, who led the research group at UC Davis. The research shows “it can be done and that’s the promise of this work,” he said.
The experience of George Norman, 69, of Colusa, a town in the foothills north of Sacramento, shows how the new procedure can be used.
Norman lost most of his vision after a 1973 accident in which ammonia splashed into his eyes at an agricultural chemical company where he worked. “It was like looking through a piece of foggy plastic. I could see images but I couldn’t read,” he said.
Because both of Norman’s eyes were damaged, Schwab took a small number of donor cells from Norman’s son, Robert. “I was kind of nervous at first; the idea of someone scraping your eye with a scalpel is pretty nerve-racking. But, it was pretty simple, there was no pain whatsoever and just some redness for about a week,” said the younger Norman.
Now, he says, his father is doing more gardening and isn’t worried about crossing the street to go to the grocery store.
“It’s really brilliant now, I’ve got good color, and everything’s going according to plan,” said the elder Norman.
The work is “very exciting” although still “very preliminary,” said Richard Fisher, program director of Corneal Diseases at the National Eye Institute.
“We need longer follow-up to see how the tissue is maintained and what happens to the vision with time,” said Fisher. Studies of similar transplant techniques are being conducted by the Eye Institute, he said.
Corneal stem cells--cells that reproduce themselves to replace old, damaged corneal cells--are what allow the researchers to grow the tissue in the lab.
Both the UC Davis researchers and the group from Taiwan’s Chang Gung Memorial Hospital use a procedure removing a tiny 2-square-millimeter patch of corneal tissue. The cells grow on top of a membrane, which acts as a scaffold, in the lab for about two weeks. Then the damaged, cloudy corneal tissue is removed from the patient’s eye and the newly grown, clear tissue is sewn on.
“We learned from skin [studies] and translated that to the eye,” said Dr. Rivkah Isseroff, professor of dermatology at UC Davis. Isseroff used her knowledge of bioengineering skin replacements for burn patients to develop the technique for corneal tissue with Schwab.
Skin and cornea consist of a similar cell type, called epithelium, which covers or lines organs, Isseroff said. Each type of epithelium has its own set of stem cells that renews tissue as older cells die. Because the cornea, like skin, is exposed to the environment, it constantly replaces cells as they are shed or damaged.
Many of the patients treated had undergone conventional corneal transplants that had failed. In a conventional corneal transplant, a rather large area of cornea is taken from a cadaver and transferred to the patient. This procedure is widely effective for the 46,000 patients who receive corneal transplants each year. But in patients with damaged or deficient stem cells, scarred cells and blood vessels will eventually grow over the transplanted tissue, obscuring vision.
Using only a small number of cells and growing tissue from them in the laboratory offers important advantages, the researchers say. Removing only a tiny section of tissue does not put a healthy eye--of either the patient or a related donor--in jeopardy. Also, using cells that are genetically identical or similar to the patient lowers the risk of complications and increases the chances of success.
The UC Davis researchers also found that they can freeze some of the stem cells and “bank” them in case a patient needs a second procedure.
“It’s certainly a big step forward, but it also raises some other issues, which could go beyond this. What if you could bioengineer the epithelium so that it makes some immunosuppressant factor to create ‘super’ cells that are less likely to be rejected?” asked Dr. Jay Pepose, an ophthalmologist at Washington University in St. Louis.
Potentially, the technique could also be used to design tissues for each patient, reducing the chance of rejection or other complications that have been problems in skin transplants.
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Replacing Bad Corneas
1. A small piece of the cornea is collected with a scalpel from either the patient’s undamaged eye or a related donor’s eye.
2. The tissue is broken into individual cells, which are placed on top of a membrane in a lab dish.
3. After about 2 weeks, the cells have grown into a tissue about the size of a silver dollar. The surgeon cuts out the size of tissue needed.
4. The surgeon removes the damaged corneal tissue with a scalpel and stitches the piece of lab-grown tissue onto the eye. The membrane will eventually dissolve.
Sources: UC Davis, Chang Gung University
