X-Message-Number: 18728
From: "Peter Christiansen" <>
Date: Fri, 08 Mar 2002 13:47:16 -0600

Cloning Used To Treat Defect in Mice


washingtonpost.com  Daniel Q. Haney   03/08/2002

BOSTON, March 7 -- For the first time, scientists say they have used the 
ethically sensitive technology of therapeutic cloning to repair an inherited 
disease in a lab animal.

While still far from human use, experts say this demonstrates the potential 
power of the approach to correct many common ills.

Scientists have used therapeutic cloning to make embryonic stem cells that 
can develop into many different kinds of tissue, such as muscle or nerves. 
But until now, they have not been put back into an animal to treat a 
disease.

The experiments involved repairing an immune system defect in mice. First, 
they made clones of the animals to harvest embryonic stem cells. Then they 
fixed the genetic defect in these stem cells and put them 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," said George 
Daley. "We are the first to do this all the way."

The experiments were conducted by Daley and Rudolf Jaenisch at the Whitehead 
Institute for Biomedical Research in Cambridge, Mass. Two reports on the 
work were to be posted online Friday by the journal Cell.

Therapeutic cloning starts with cells derived from test-tube embryos that 
are genetic twins of the recipient. President Bush and some members of 
Congress are opposed to cloning of all forms.

Some scientists, including Daley, have proposed calling the procedure 
"nuclear transplantation therapy" to avoid confusion with reproductive 
cloning, which produces a whole individual.

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. 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 the adults, which are programmed to produce one kind of tissue, the 
embryonic stem cells can potentially grow into anything.

Since the embryonic stem cells were genetically identical to the mice, they 
carried the same genetic defect. Scientists 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 make up about 40 percent of the animals' blood. After the 
experiment, they made up 3 percent.

The results suggest that a combination of therapeutic cloning and gene 
therapy could be used to cure a variety of hereditary diseases, but they 
also show that significant hurdles will have to be overcome if the 
techniques are ever to result in total cures.

For more news, or to subscribe to the newspaper, please visit 
www.washingtonpost.com

Copyright 2002 The Washington Post Company



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