- 18:00 23 March 2008
- NewScientist.com news service
- Peter Aldhous
Therapeutic cloning works – in mice, at least. An international team has restored mice with a condition similar to Parkinson's disease back to health, using neurons grown in the lab that were made from their own cloned skin cells.
This is the first time that a disease has been successfully treated using cloned cells that had been derived from the recipient animals. "It is the proof of concept," says Lorenz Studer of the Sloan-Kettering Institute in New York, US, who led the research. But he warns that is too early to say whether the technique can be developed into a practical therapy for human patients.
Studer's team first gave mice a drug to kill neurons that make the neurotransmitter dopamine. This caused movement problems similar to those seen in people with Parkinson's disease. Then the researchers took biopsies from the tails of these mice and shipped them to Teruhiko Wakayama, a specialist in cloning at the RIKEN Center for Developmental Biology in Kobe, Japan.
Wakayama's team transferred the nuclei from skin cells taken from these biopsies into mouse eggs stripped of their chromosomes, to create embryos. The Japanese researchers extracted embryonic stem (ES) cells from these cloned embryos, creating a total 187 ES cell lines from 24 mice.
Back in New York, Studer's team took the ES cells, coaxed them to develop into dopamine-secreting neurons, and then transplanted these neurons into mice with symptoms of Parkinson's.
All six mice that had been given grafts of neurons derived from their own skin cells got significantly better, scoring well on tests of movement.
This is similar to results obtained by a team led by Ron McKay of the US National Institute of Neurological Disorders and Stroke in Bethesda, Maryland. That team transplanted neurons grown from conventional mouse ES cells into the brains of rats with the symptoms of Parkinson's. But unlike McKay, Studer did not have to suppress the immune systems of his animals to allow the grafts to survive.
Studer had less successful results, however, when he transplanted cloning-derived neurons into seven totally unrelated mice with Parkinson's-like symptoms, again without immune suppression. They showed little improvement, and autopsies conducted 11 weeks later revealed chronic inflammation in their brains. In three of them, none of the transplanted cells had survived.
"There's a major difference in the immune response depending on whether the cells are genetically identical," observes Alan Trounson, president of the California Institute for Regenerative Medicine in San Francisco, US.
While Studer's study shows the value of achieving genetic matching by cloning, it is unclear whether the technique will prove viable in people. For one thing, nobody has yet managed to create a single human ES cell line by cloning. Even if this can be done, human eggs are in very short supply, which would limit the number of patients who could be treated.
Also, Studer points out that his success in mice required a partnership between two research teams, one highly skilled in neural grafting, the other a world leader in cloning.
"It was a very challenging project," he says. "You need a special set of expertise that is typically not available in an individual lab."
If the process cannot be made less technically demanding, any treatment for human patients is likely to be extremely costly.
This is why many researchers are excited about the possibility of using a simpler genetic reprogramming technique pioneered by Shinya Yamanaka of Kyoto University in Japan. This can turn skin cells into cells that have similar properties to ES cells.
But Yamanaka's technique leaves behind active copies of genes that can induce cancer. This problem would need to be solved before such cells could be considered for use in human patients.
Stem Cells - Learn more about the promise and the controversy in our cutting-edge special report .
Journal reference: Nature Medicine (DOI: 10.1038/nm1732)
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