- The Washington Times - Saturday, March 9, 2002

BOSTON (AP) The much-debated potential of so-called therapeutic cloning to cure disease has been demonstrated for the first time in a living creature with the partial repair of an immune system defect in lab mice.
The approach is controversial because it involves making test-tube embryos that are genetic twins of the recipient. The embryos would supply stem cells but would not be allowed to grow into a person.
Many, including President Bush, disapprove of all forms of cloning, including the therapeutic variety. However, some scientists who oppose cloning humans say they believe therapeutic cloning should be pursued because it could supply healthy new tissue to fix a variety of illnesses.
While still far from use for humans, experts say the latest advance demonstrates the disease-fighting potential of the method. The steps necessary to accomplish this had already been accomplished in lab animals, but the latest experiment is the first to carry the process through from beginning to end to fix a problem.
The experiments were conducted by Drs. George Daley and Rudolf Jaenisch at the Whitehead Institute for Biomedical Research in Cambridge, Mass. Two reports on the work were to be posted online yesterday by the journal Cell.
"The future is now," said Dr. Neil Theise, a stem-cell biologist at New York University. "It's not decades away. It's around the corner."
To repair the immune system defect, the scientists first made clones of the animals to harvest embryonic stem cells. Next, they fixed the genetic defect in these stem cells. Finally they put the repaired stem cells into the adult animals, where they partially overturned the immune defect.
"This really is a tremendous confluence of very, very challenging technology, wrapping them all together into a model therapy," Dr. Daley said. "We are the first to do this all the way."
The latest experiments were conducted on inbred mice that had severe immune deficiency because of a genetic defect that prevented them from manufacturing antibodies in response to infections.
The researchers started with skin cells from the adult mice's tails. Then they removed the nucleus from a mouse egg and replaced it with a nucleus from one of the skin cells.
In a lab dish, the egg grew into a blastocyst, an embryo containing about 100 cells, including embryonic stem cells. Unlike stem cells in adult creatures, which are generally programmed to produce just one kind of tissue, the embryonic stem cells can potentially grow into anything.
Since the embryonic stem cells were genetically identical to the immune deficient mice, they carried the same genetic defect. So the scientist used gene therapy to fix the bad gene and then put the stem cells into the animals.
The goal was to give them stem cells that would make healthy blood cells. The process worked, although not totally. Disease-fighting cells known as B cells and T cells ordinarily make up about 40 percent of the animals' blood. After the experiment, they made up about 3 percent.
"That was still enough to generate antibodies in these mice," Dr. Daley said. "We would expect this level of reconstitution would provide significant immune function and have significant benefit."
Dr. Daley said he believes the results will improve with more work. Used in humans, the procedure could potentially supply cells that would correct a variety of ills, such as muscular dystrophy and neurologic diseases.

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