Apr 14, 2002
It has long been thought that the liver was the only organ capable of regenerating itself. Now, doctors are rethinking the idea in light of studies showing that the pancreas and the heart may be able to do the same thing.
"Isn't it fascinating?" said Dr. Denise Faustman, a diabetes researcher at Massachusetts General Hospital, whose study in mice last year discovered, by accident, that the insulin-producing cells of the pancreas could regenerate.
"It's not what we were taught," she said.
In another study published in January, researchers at New York Medical College in Valhalla, N.Y., reported that human hearts appear to be able to grow new cells.
"It opens up new avenues for therapy and hope for many diseases that were considered end-stage," Faustman said.
The studies, while different, suggest the body has a surprising ability to repair itself, although it could be a long time before any of the research makes it from the lab bench to the bedside.
Faustman, however, is hoping her work can make it into clinical trials within a couple of years.
"Clinical trials are not that far off," she said.
Although her work involves Type I diabetes, she said it has broader implications.
"The treatment could be broadbased for all autoimmune diseases," she said.
Besides diabetes, Faustman said autoimmune diseases such as lupus, scleroderma, multiple sclerosis and Crohn's disease could be cured this way.
In her study, she was able to cure Type I diabetes in mice - the first time an autoimmune disease has been reversed in an animal model.
The treatment involves retraining the immune system to stop the disease that causes the destruction of pancreatic islet cells that secrete insulin.
In the mice studies, Faustman said, "we permanently reversed the disease within 40 days of starting therapy. A miracle really occurs."
The reversal of the disease allows the body to remake insulin from the pancreas by the regrowth of islet cells that are no longer under attack by the body's immune system.
Faustman's experiment sought to find out why the body, through the white blood cells, was attacking its own pancreas.
The plan was to train immune system cells in the blood not to attack islet cells.
"Our highest hopes were that we'd eliminate the autoimmune disease in these animals and have to come back and do an islet cell transplant," she said in a recent radio interview.
But what happened was a huge surprise - and much better.
"The surprise was the animal . . . once the autoimmune disease was eliminated, effectively regrew its islets in the pancreas," she said. "So they regrew the missing organ that had originally been destroyed."
The animal used its own adult stem cells to regrow the islets. Such stem cells exist in adult humans, Faustman said.
So if a way can be found to stop the underlying autoimmune disorder, the body might well be able to regenerate what has been destroyed.
"But you have to get rid of the underlying disease," she said. "It's not easy."
That's how hearts were able to repair themselves in the New York experiments.
The study, published in the New England Journal of Medicine, looked at eight hearts transplanted from female donors to male patients.
What appeared to be stem cells of the recipients were seen forming new tissue in the transplanted hearts. The cells that grew to help the new hearts formed both muscle and blood vessels - the two cell types found in the heart.
"If you get rid of the disease, the host comes in and starts the repair process," Faustman said.
Heart study author Dr. Piero Anversa found stem cells in both the donor and recipient hearts, and also in the hearts of 10 control patients who had no transplants. The study suggests all hearts contain stem cells.
The findings prompted the NEJM editors to gush over the possibilities of better therapies for heart disease.
"Such approaches to therapy, which previously were only pipe dreams, are now realistic goals that may soon be within reach," they wrote.
The idea got another boost when a new study showed that stem cells circulating in the bloodstream can grow new tissue in the liver, gut and skin.
At the University of Texas M.D. Anderson Cancer Center in Houston, researchers looked at tissue samples collected from 12 cancer patients after stem cell transplants and found evidence they made new tissue in unexpected places.
Six women received transplants from their brothers, so the researchers looked for male cells in tissue taken from the women's liver, gastrointestinal tract and skin. They found cells with a male Y chromosome accounted for up to 7 percent of the samples from the females.
"The school of thought for many years was that stem cells only make cells of their own tissue. This has changed and things are pretty much upside down now," said Dr. Martin Korbling, one of the Texas researchers.
But two new studies cast doubt on the whole idea that adult stem cells can serve as the body's all-around repairmen.
In the two studies, embryonic stem cells from mice were put in lab dishes with mouse bone marrow and brain cells. But instead of transforming into their neighboring cells, the stem cells simply merged their genetic material with the marrow and brain cells.
The researchers said the same phenomenon might have occurred in studies involving adult stem cells and might have fooled scientists into thinking the cells had transformed themselves.
Dr. Robert Lanza, medical director at Advanced Cell Technology, a Worcester biotech firm that has worked with the New York heart researchers and is pushing Congress to allow embryonic stem cell research, said the findings don't rule out adult stem cells working in some cases.
"There is no question the adult body harbors cells that have regenerative abilities," he said.
But the heart study findings must be examined more closely, Lanza said.
"Adult stem cells may be useful for the treatment of some diseases,
but not others," he said. "We're just not sure of the extent of their regenerative
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