New method may suit other organsLab-grown tissue mends eye damage
Paris, Friday, July 14, 2000
WASHINGTON - Surgeons in Taiwan and the United States have restored vision to people with previously untreatable eye damage by transplanting tissue grown in a laboratory.
In a pair of new studies, researchers report that the transplants improved vision in all six Taiwanese patients and in 10 of 14 U.S. patients treated, although doctors warn that the procedure's long-term success is uncertain.
Researchers may be able to adapt the method to grow tissue for transplantation to other "wet" body surfaces, such as the lining of the lungs and intestines, said Ivan Schwab, professor of ophthalmology at the University of California at Davis Medical School, who led the U.S. study.
"We think this is the beginning of a very exciting change in terms of how we manage surface disease of many kinds, not just in the eye," Dr. Schwab said.
Both groups of researchers removed cells known as stem cells from the limbus, a circular area on the eye's surface that surrounds the cornea, the clear, window-like tissue over the iris and pupil. They induced the cells to multiply on a piece of amniotic membrane, the thin covering that envelops a fetus in the womb. In 16 cases, the stem cells used to grow the tissue were taken from one of the patient's own eyes; in four, they were obtained from a relative's eye.
"It is important and they seem to have good results. The idea of using the amniotic membrane is different," said Nancy Parenteau, chief scientific officer at Organogenesis Inc. of Canton, Mass. The company makes Apligraf, a bioengineered skin that is the only live, manufactured human tissue approved by the Food and Drug Administration.
Efforts to grow tissues and organs for transplantation are the focus of intense scientific and commercial interest. Patients can have their cells used to make custom-grown skin or joint cartilage by Genzyme Corp., another Massachusetts company, and several medical centers culture skin cells from burn patients for skin grafts. Factory-grown nerve cells have been experimentally implanted in the brains of stroke victims. Laboratory-grown blood vessels and heart valves are being tested in animals, and researchers are working on other tissues, ranging from heart muscle and breast implants to artificial livers.
The patients who received the laboratory-grown eye tissue would not have been helped by a conventional corneal transplant, a procedure performed about 40,000 times annually in the United States, Dr. Schwab said. The transparent cornea is composed of three layers of cells. The outermost layer must be constantly renewed by stem cells in the nearby limbus. Most people who receive corneal transplants still have enough stem cells to do this.
Patients treated in the studies had suffered injuries or diseases that had not only scarred the cornea, but also destroyed the stem cells in the affected eyes. Causes of such scarring can include chemical burns, inflammation from severe misuse of contact lenses, and various degenerative or immune system disorders. Between 2,000 and 4,000 U.S. patients annually might be candidates for the new procedure, Dr. Schwab said.
The Taiwanese group's results appeared Thursday in the New England Journal of Medicine; the U.S. group's results appeared this month in the journal Cornea.
In the Taiwanese patients, a tiny piece of tissue was taken from a healthy area of the limbus and its cells were grown on amniotic membrane, a protein sheet that does not provoke rejection by the immune system and that shows promise as a scaffold for growing transplantable tissues. The membrane, obtained after infants' birth, is processed and sterilized.
After two to three weeks, the cells formed a layer about an inch (2.5 centimeters) across from which doctors could cut a piece of the size needed.
The U.S. researchers used a similar technique, except that they first cultured large numbers of cells in the laboratory, freezing some for possible use later.