Stem cells might cause brain tumors - MSNBC.com
Injecting human embryonic stem cells into the brains of Parkinson’s disease patients may cause tumors to form, U.S. researchers reported Sunday.

Steven Goldman and colleagues at the University of Rochester Medical Center in New York said human stem cells injected into rat brains turned into cells that looked like early tumors.

Writing in the journal Nature Medicine, the researchers said the transplants clearly helped the rats, but some of the cells started growing in a way that could eventually lead to a tumor.

Goldman’s team used human embryonic stem cells. Taken from days-old embryos, these cells can form any kind of cell in the body. This batch had been cultured in substances aimed at making them become brain cells.


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Previous groups have tried to coax stem cells into becoming dopamine-releasing cells.

Goldman’s team apparently succeeded and transplanted them into the rats with an equivalent of Parkinson’s damage. The animals did get better.

Dividing cells
But the grafted cells started to show areas that no longer consisted of dopamine-releasing neurons, but of dividing cells that had the potential to give rise to tumors.

The researchers killed the animals before they could know for sure, and said any experiments in humans would have to be done very cautiously.

Scientists have long feared that human embryonic stem cells could turn into tumors, because of their pliability.

Opponents of embryonic stem cell research cite such threats. Many opponents, including President Bush and some members of Congress, believe it is immoral to destroy human embryos to obtain their stem cellsMORE - MSNBC.com