Mouse Stem Cells Repair Sheeps' Hearts

Opinions differ on whether cross-species transplants would work in humans

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By Ed Edelson
HealthDay Reporter

FRIDAY, Sept. 16, 2005 (HealthDay News) -- French scientists say they've used embryonic stem cells from one animal species to repair heart damage in another species.

But the researchers themselves disagree about what the achievement may mean in terms of the use of animal stem cells in humans.

Implanting embryonic stem cells from mice resulted in healthier heart tissue in nine sheep with damaged cardiac muscle, according to a report in the Sept. 17 issue of The Lancet by researchers at the National Center for Scientific Research in Montpellier and the Hopital Europeen Georges Pompidou in Paris. No such response was seen in nine sheep with similar damage who did not get the transplants.

Asked whether animal stem cells might someday be used to repair human heart damage, Michel Puceat, a scientist at the research center and a co-author of the paper said, "We are on the road to that."

Use of animal cells in medicine would overcome the major ethical issue in stem cell research: the need to create embryos to produce human stem cells needed for treatment. Embryonic stem cells are valued because they can be transformed into almost every kind of cell. Adult stem cells have a much more limited ability to be transformed.

Puceat said his group is taking the next step toward using animal stem cells to treat human heart disorders. "We will graft these stem cells into nonhuman primates," he said. "We are planning such experiments in the near future."

But Puceat acknowledged that the ability of the human immunological system to accept such animal cells is "a very controversial issue," with some researchers saying it can be done and others saying it can't.

A member of the skeptical group is Dr. Philippe Menasche, a clinical cardiac surgeon at the Pompidou Hospital, and the senior author on the paper.

"Xenografts [transplants from an animal to a human], in particular of mice and even other species, really raise major immunological problems," he said. "What is interesting is that when you graft mouse cells into the sheep heart, they are not rejected. But the immune system of humans is different, and I am not sure that a xenograft would be successful."

To Menasche, the important point of the study is that it shows the value of embryonic stem cells to repair damaged hearts.

"This is the first study done in a more clinically relevant live animal model," he said. "These stem cells were able to become heart cells and improve heart function. It is an additional step, not toward a clinical application, but in favor of the concept that it is probably worthwhile to consider embryonic stem cells for clinical repair."

Another important point of the study is that it eases the fear that stem cells might become cancerous, growing endlessly in a disorganized manner, he said. The treatment given to the mouse stem cells in this experiment prevented that, Menasche said.

"We have pre-committed them toward growth in the cardiac pathway," he said.

More information

Stem cell research and its potential are outlined by the National Institutes of Health.

SOURCES: Michel Puceat, Ph.D, scientist, National Center for Scientific Research, Montpelier, France; Phillippe Menasche, M.D., Ph.D, clinical cardiac surgeon, Hopital Europeen Georges Pompidou, Paris; Sept. 17, 2005, The Lancet

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