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Analysis: Mice Cloned From Adult Stem Cell

Posted on: Monday, 12 February 2007, 21:00 CST

By STEVE MITCHELL

Scientists, for the first time, have cloned mice from adult stem cells found in the skin, but cloning remains so inefficient it won't reach the clinic anytime soon.

Although the efficiency rate was higher than previous cloning attempts that used non-stem cells, it was still too low to be considered a viable technique for generating therapies for patients.

It's still a very inefficient procedure, Peter Mombaerts, senior author of the paper and a professor at Rockefeller University, told United Press International. If you ever want to do this in the clinic, you need high efficiency.

Therapeutic cloning holds the promise of using a patient's own cells to generate tissues for replacing those that are damaged or diseased. It would also help eliminate the chance of rejection since the new tissues would be genetically identical to the patient.

In the study, which was published in the online issue of the Proceedings of the National Academy of Sciences, the researchers isolated hair-follicle stem cells that are located just under the skin in mice. The nuclei from these cells were placed into mice egg cells, or oocytes, to produce cloned mice that were healthy and normal.

The highest efficiency the group received was with male cells and that came in at 5.4 percent. Mombaerts said to make the technique feasible for treating patients, the efficiency would have to be increased to 10, 20 or 30 percent at least.

He noted that the research required about 3,000 oocytes to produced the nine cloned mice that reached adulthood. If we tried to do that in humans, this would be about $3 million worth of oocytes, he said, noting that a human egg costs $1,000.

The efficiency of cloning has been a barrier since Dolly the sheep was cloned. Scientists thought that using adult stem cells might increase the efficiency, but attempts at using other adult stem cell types -- such as mesenchymal and neural -- did not pan out. Since the skin stem cell also didn't increase the efficiency significantly, it raises the issue of whether there is a biological threshold that can't be exceeded.

We're struggling to understand that, Mombaerts said. Is there a threshold that we can't overcome or is it just using the wrong cell types or is it that we just have to perfect our techniques?

However, the experiment does have some positives, Elaine Fuchs, co-author of the paper and also with Rockefeller University, told UPI. It shows that there is a readily available source of donor cells for cloning. In addition, these stem cells have been in use for years for treating burn patients, so their clinical utility is well established.

The next step for the field is to overcome the technical hurdles for nuclear transfer so it can be applied to humans, Fuchs said.

She said it's important to understand that use of adult stem cells in cloning is not a reason to stop supporting embryonic stem cell research.

We're still hampered by government restrictions along those lines, but I think there's been an increasing awareness of the public about the differences between reproductive versus therapeutic cloning, Fuchs said.

Robert Lanza, vice president of research and scientific development at Advanced Cell Technology, a company pursuing therapies based on embryonic stem cells, told UPI the findings indicate that adult stem cells are not going to be the silver bullet for improving the efficiency of cloning.

This paper is saying there's no easily solution here, Lanza said. We're still struggling with the same inefficiencies as when Dolly was cloned.

Lanza said his company recently developed a technique utilizing mice cells that dramatically increased the efficiency of cloning. He said he could not divulge the specific details of the strategy because he is writing it up for publication in a scientific journal, but he said it raised the efficiency to literally 100 percent.

Unfortunately, the technique did not work as well with human cells. But his group had to rely on older human egg cells. They may attempt it with fresh eggs to see if that makes a difference, he said.

Source: United Press International

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