Scientists use monkey clones for stem cells
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Researchers in Oregon are reporting that they used cloning to produce monkey embryos and then extracted stem cells from the embryos.
Not only is this the first time such cells have been produced in any animal other than a mouse, but the method, the researchers say, should also work in humans. In 2004, South Korean researchers reported making stem cells from cloned human embryos, but the claim turned out fraudulent.
"We hope the technology will be useful for other labs that are working on human eggs and human cells," the lead researcher of the group, Shoukhrat Mitalipov at Oregon Health and Science University in Beaverton, said in a telephone interview. "I am quite sure it will work in humans."
The monkey stem cells were genetically identical to an adult monkey, Semos, whose cells were cloned. They are a sort of universal cell that can, in theory, develop into any tissue or organ.
Medical researchers and patient advocacy groups have long hoped to use human embryonic stem cells to study diseases and supply replacement cells to treat them. So far, though, stem cell research has not yielded cures, and many obstacles lie ahead.
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An advantage of using cloning to obtain stem cells is that they would genetically match a patient's cells, making it unnecessary to suppress the immune system if the stem cells are used in treatment. Cloning could also produce stem cells that genetically match patients with complex diseases like Alzheimer's. That might let scientists study those cells and understand how the diseases progress.
With the monkey work, some researchers say, cloned human embryonic stem cells seem more feasible. There is no way to know, of course, whether it will be harder or easier to repeat the work with humans. "I'm very enthusiastic," said Dr. Leonard Zon, director of the stem cell program at Harvard's Children's Hospital. "The next step is definitely doing it in humans."
Groups opposing human cloning and the destruction of human embryos to extract stem cells say the report makes it more urgent than ever to draw a moral line.
"I certainly think that this represents a new threshold in the entire discussion," said the Rev. Tadeusz Pacholczyk, director of education at the National Catholic Bioethics Center. "At this point, it becomes essential to ask a question as a society: Are there ever going to be circumstances where it is morally justifiable to clone human beings?"
The report on cloned stem cells, which appears in the Nov. 22 issue of Nature, was published online Wednesday, after some details of the work had filtered into the news media.
Mitalipov said his team showed that the cloned cells had features characteristic of universal cells. For instance, they developed into monkey heart cells and nerve cells.
The team also put the cells in mice, where they turned into a wide array of cell types.
The stem cells, Mitalipov says, "can contribute to any cell of the body."
The scientists began by removing skin cells from a 9-year-old adult male rhesus macaque and inserted them, along with all their genes, into monkey eggs whose genetic material had been removed.
The egg, in a part of the cloning process that remains mysterious, reprogrammed the genes from the skin cells, bringing them back to the state they were in when embryo development begins.
The reprogrammed genes took over developing the eggs. A result was monkey embryos that were genetically identical — clones — of the adult male monkey. A few days later, the investigators extracted stem cells from the embryo clones, destroying the embryos in the process.
Most attempts at cloning failed. The investigators started with 304 egg cells from 14 female macaques and ended up with two stem cell lines. One line had an abnormal Y chromosome. The other, Mitalipov said, appeared normal.
But, he speculates, one reason for the success was finding a gentle way to take the genetic material out of monkey eggs.
In previous attempts, the investigators had used a method that worked well in mice. They marked the egg's chromosomes with a dye that glowed under ultraviolet light. That let them see the chromosomes and be sure that they were removed before they inserted the adult cell with its genes into the egg.
The dye and ultraviolet light, the researchers surmised, might damage the egg. So they used a new method that shines polarized light through the egg, allowing them to see the chromosomes directly, without dyes.
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