And now: primates.
Since Dolly the sheep was cloned in 1997, biologists have cloned at least 16 other species, from mice and goats to pigs, cats, dogs and ferrets. For a couple of years starting in 2004, it looked like scientists in South Korea had followed the same basic recipe in humans: take an ovum, remove its DNA, replace that DNA with DNA from an adult cell, and grow it in the laboratory until a days-old embryo develops, from which (they said) they derived stem cells, but did not allow development to continue. They stopped well short of producing a human clone, of course. But within two years that work was exposed as a fraud. (The South Koreans did, however, clone a dog.) And so it has stood, with zero successes in using “somatic cell nuclear transfer” to reprogram an egg from a primate to develop into an embryo.
This morning the journal Nature, citing widespread speculation, confirmed that it will soon publish the first report that scientists have used cloning technology with a primate, producing custom-made stem cells. Scientists at Oregon Health & Science University describe injecting the nucleus, which contains a cell’s DNA, of an adult rhesus monkey’s fibroblast into an egg whose own nucleus was removed. They then manipulated the egg so that it developed into an early-stage embryo called a blastocyst, from which they teased out and grew, in lab dishes, embryonic stem cells.
Their success rate was less than stellar, but that’s not unusual in cloning: the Oregon team generated two embryonic stem cell lines from 304 eggs, a 0.7% efficiency. Still, even this level of success suggests the approach might work in humans, allowing scientists to finally generate stem cells that have the DNA of an individual patient. Those cells would develop into neurons and other cells that would be perfect genetic matches for that patient, eliminating the possibility that transplanting these cells—neurons to treat Parkinson’s disease, for instance—would trigger the immune system to reject them.
In a highly unusual step, and in reaction to the South Korean fraud, an independent team of scientists in Australia verified that the Oregon team had indeed produced stem cells through cloning. Their report is being published by Nature simultaneously with the Oregon paper.
Nature asked the scientist who cloned Dolly, Ian Wilmut, to discuss the potential of such cells. He and a colleague inject a much-needed dose of realism into the stem cell debate, which has led the public to expect these almost magical cells—able to develop into any kind of cell, from pancreatic to muscle to neuronal—to be primarily used for therapy, via transplants. But as Wilmut says, “In our haste to use patient-specific cells in therapy, however, we tend to overlook that they have great value for basic research and drug discovery. . . . Realistically, a careful examination of resources and the time required to produce differentiated cells for treatment purposes suggests that large-scale use of stem cells would be impractical.” It will be interesting to see whether a public torn by the ethics of stem-cell production will support research that is at least one step removed from directly yielding cures for terrible diseases.