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“The
fact they are doing it in a model of a human disease is very canny,
and certainly this will have a big impact on the public debate.” |
Therapeutic
cloning suggests power to treat disease BOSTON (AP) — 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 that affect people. Most of the steps in the work have already been accomplished individually in lab animals. Scientists have used so-called 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. 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,” said Dr. 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. “Putting it all together in sequence is dramatic,” said Dr. Neil Theise, a stem cell biologist at New York University. “The fact they are doing it in a model of a human disease is very canny, and certainly this will have a big impact on the public debate.” Therapeutic cloning starts with cells derived from test-tube embryos that are genetic twins of the recipient. Many, including President Bush and some members of Congress, are opposed to cloning of all forms, including the therapeutic variety. Some scientists, including Daley, have proposed calling the procedure “nuclear transplantation therapy” to avoid confusion with reproductive cloning, which is intended to produce a whole person. 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 comprised about 3 percent. |
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