Fetal tissue restores lost sight
THREE years ago Elisabeth Bryant believed she would be blind for the rest of her life. "I couldn't see anything," she says. Now, although her vision is not perfect, she can see well enough to read, play computer games and check emails. Bryant has retinitis pigmentosa, an eye disease that has blinded four generations of her family. What has saved the sight in one of her eyes is a transplant of a sheet of retinal cells. The vision in this eye has improved from 20:800 to 20:84 in the two-and-a-half years since the transplant- a remarkable transformation. So far, six patients with either advanced retinitis pigmentosa or macular degeneration have had similar transplants.
Together, these degenerative diseases are the biggest cause of blindness in rich countries, affecting tens of millions of people. While Bryant's improvement is the most dramatic, four other patients have also had good results. When New Scientist reported the initial results of these retinal transplants last year (1 February 2003, p 14), experts cautioned that the results could be due to the rescue effect: a short-term improvement triggered by the release of growth factors after eye surgery. That appears increasingly unlikely, because the rescue effect usually lasts only months. "We have shown the way," says Robert Aramant at the University of Louisville in Kentucky, who developed the transplant technique with his colleague Magdalene Seiler. "It is possible to reverse these incurable diseases." No other technique has come close to achieving this. The team has received approval from the US Food and Drug Administration to carry out further transplants on people with less advanced disease, and Aramant believes the results will be even better.
There is a catch, of course. The sheets of retinal cells used by the team are harvested from aborted fetuses, which some people find objectionable. There is also a practical problem. Although millions of terminations are performed each year in the US alone, the fetal tissue is rarely donated. If further trials are successful and the technique starts to be widely used, there will not be enough tissue to meet demand. One accusation of those opposed to using fetal tissue is that women might be tempted to have abortions to provide tissue to restore their own sight or that of relatives. "People are going to claim that we are promoting abortion," says Norman Radtke, the surgeon who carried out the transplants at the Norton Audubon Hospital in Louisville, Kentucky. A few countries, such as the UK, already have clear guidelines to ensure this does not happen. "The guidelines are meant to prevent the deliberate conception and termination for treatment of a particular person," says Stephen Minger, head of the stem cell laboratory at King's College London. In the US no such guidelines exist. Some of the other groups trying to develop treatments for degenerative eye diseases are pinning their hopes on stem cells.
Various kinds can be turned into retinal cells, and this week it was reported that the eyes of people as old as 60 contain specific stem cells capable of forming all the different cell types in the retina. But the few attempts to treat degenerative eye diseases with stem cells in animals have failed, as have attempts to transplant unstructured groups of cells into the retina. Aramant and Seiler think the key to their success is that they transplant intact, 2-millimetre-square sheets of the upper retinal layer. This preserves the circuitry of the light-sensing cells, as well as the supporting cells that nourish them. Aramant is dismissive of the stem-cell work, pointing out that no one is anywhere near recreating the complex structure of the retina using stem cells. Instead, his team is examining the possibility of transplanting retinal sheets from pigs genetically engineered to reduce the chances of immune rejection.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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