After more than 15 years of failures, biologists have finally created human stem cells by the same technique that produced Dolly the cloned sheep in 1996. They transplanted genetic material from an adult cell into an egg whose own DNA had been removed.
The result is a harvest of human embryonic stem cells, the seemingly magic cells capable of morphing into any of the 200-plus kinds that make up a person.
The feat, reported on Wednesday in the journal Cell, could re-ignite stem-cell medicine, hobbled by technical challenges and ethical issues.
Until now, the most natural sources of human stem cells have been human embryos, whose use in research poses ethical quandaries. The technique by scientists at Oregon Health & Science University and the Oregon National Primate Research Center, uses unfertilised human eggs.
Eliminating the need for human embryos could boost attempts to use stem cells and their progeny to replace cells damaged or destroyed in heart disease, Parkinson’s disease, multiple sclerosis, spinal cord injuries and other devastating conditions.
But the achievement could also revive fears of reproductive cloning, or producing genetic copies of living (or dead) individuals.
Even before the study was published, a British watchdog ‘Human Genetics Alert’ protested the research. “Scientists have finally delivered the baby that would-be human cloners have been waiting for: a method for reliably creating cloned human embryos,” said Dr David King, the group’s director.
“This makes it imperative that we create an international legal ban on human cloning before any more research like this takes place. It is irresponsible in the extreme to have published this research.”
Among scientists, however, the accomplishment is being hailed as an unparalleled achievement.
If the Oregon achievement holds up and replicated in other labs, it would offer a third, and potentially superior way of producing embryonic stem cells.
The field of stem cells took off in 1998, when scientists led by Jamie Thomson at the University of Wisconsin announced that they had harvested the cells from days-old human embryos, called blastocysts, obtained from fertility clinics.
The fact that the blastocysts are destroyed when their stem cells are removed ignited a furor from groups that believe life begins at conception. In 2001, President George W. Bush banned federal funding for research that would create more blastocysts, but stem cells already produced from them were fair game.
Those cell lines turned out to be fewer and of poorer quality than scientists had hoped. The next breakthrough came in 2007, when Shinya Yamanaka of Kyoto University produced human embryonic stem cells in a way that did not require eggs or embryos. That turned attention away from a third technique for producing embryonic stem cells: the method that created Dolly the sheep in 1996.
Scientists in Scotland had started with a sheep oocyte (egg), removed its DNA and replaced it with DNA from a sheep mammary gland cell.
They zapped the egg with electricity to make it grow and divide like a fertilised embryo.
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No sperm were necessary.
If the embryo is implanted inside a surrogate mother, as the Dolly team did, the result is reproductive cloning, which has also been done for mice, cows and other animals.
The Oregon scientists, led by Shoukhrat Mitalipov, used a variation of the Dolly technique.
They carefully inserted an adult skin cell into a donated human egg whose DNA had been removed. The unfertilised eggs, stimulated by electric pulses to start dividing, developed to about the 150-cell stage.
The cells were all true embryonic stem cells; they have “ability to convert just like normal embryonic stem cells, into several different cell types, including nerve cells, liver cells and heart cells,” said Mitalipov.
In succeeding with humans, the Oregon team toppled the dogma that there is something odd about human eggs or embryos.
Published data said there was a difference in principle between humans, mice and other animals that had been cloned, a difference that presented an insurmountable barrier to human cloning” for either reproduction or stem cells.
The team figured out how to get the egg to act as if it had been fertilised. The secret was to keep the eggs in the phase of their growth cycle called “metaphase,” which is when DNA aligns in the middle of the cell before the cell divides. They got the best results when they grew the eggs in a little of a substance that tends to be abundant in labs: caffeine.
-Reuters