updated 12/6/2007 5:04:03 PM ET 2007-12-06T22:04:03

U.S. scientists have the first evidence that those "reprogrammed stem cells" that made headlines last month really have the potential to treat disease: They used skin from the tails of sick mice to cure the rodents of sickle cell anemia.

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At issue: Turning adult cells into ones that mimic embryonic stem cells, master cells that can turn into any type of tissue. When scientists announced last month that they had successfully engineered embryo-like stem cells from human skin, it was hailed as a possible alternative to ethically fraught embryo research.

But no one yet knew whether those reprogrammed cells could create functioning tissue just like natural embryonic stem cells can.

Thursday, scientists reported a key next step when they used the technique to give mice with sickle cell anemia a healthy new blood supply.

The study, published in the journal Science, does not bring this potential therapy closer to people just yet. Big hurdles remain, including a risk of cancer from the reprogramming method.

But without the mouse work, scientists did not know "whether all the recombined machinery will work or not," explained lead researcher Tim Townes, molecular genetics chief at the University of Alabama, Birmingham. "It's the first example of actually completing the cycle and curing a disease."

Townes had created a strain of mice bearing the human genes for sickle cell, a devastating inherited disease of deformed red blood cells that can't carry enough oxygen.

Townes paired with prominent stem cell scientist Rudolf Jaenisch of the Whitehead Institute in Cambridge, Massachusetts, to reprogram skin from those mice into embryonic-like stem cells. They coaxed the newly engineered cells to grow into blood-producing cells. Then they replaced the sickle cell-causing gene with a healthy version and infused the new cells.

The mice started producing healthy blood, and their sickle cell symptoms vanished.

"What this paper shows for the first time is you can combine all these steps," said Konrad Hochedlinger, a researcher at the Harvard Stem Cell Institute and Massachusetts General Hospital. "It's an important proof of principle for the usefulness of this technology to treat disease."

Townes next is testing whether human skin cells from sickle cell patients can be similarly reprogrammed.

But it may take several years of additional research to create a safe enough reprogramming method to test such an approach in people.

Hochedlinger cited an even bigger challenge: Scientists know very little about how to direct an embryo-like stem cell to turn into the just the tissue they need, such as pancreas cells instead of nerve cells, for example.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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