For the first time US researchers have turned human skin cells into embryonic stem cells.
The method described Wednesday by Oregon State University scientists in the journal Cell, would not likely be able to create human clones, said Shoukhrat Mitalipov, senior scientist at the Oregon National Primate Research Center.
But it is an important step in research because it does not require the use of embryos in creating the type of stem cell capable of transforming into any other type of cell in the body.
The technique involves transplanting an individual's DNA into an egg cell that has been stripped of genetic material, a variation of a method called somatic cell nuclear transfer.
"A thorough examination of the stem cells derived through this technique demonstrated their ability to convert just like normal embryonic stem cells, into several different cell types, including nerve cells, liver cells and heart cells," said Mitalipov.
He added that since the reprogrammed cells use genetic material from the patient, there is no concern about transplant rejection.
"While there is much work to be done in developing safe and effective stem cell treatments, we believe this is a significant step forward in developing the cells that could be used in regenerative medicine," Mitalipov said.
Another advantage of this approach is that it does not use fertilized embryos to obtain stem cells, a technique that raises major ethical issues because the embryo is destroyed.
Since the birth of the sheep Dolly in 1996 in the United Kingdom, the first cloned animal, researchers have cloned some 20 species including goats and rabbits, but never monkeys or primates whose biologies and reproduction is more complex.
Years of research on monkey cells using the same technique have not successfully produced any monkey clones.
Since the human cells used in the study appeared even more fragile, researchers said it was unlikely that clones could be made.
"While nuclear transfer breakthroughs often lead to a public discussion about the ethics of human cloning, this is not our focus, nor do we believe our findings might be used by others to advance the possibility of human reproductive cloning," they said.
Scientists hope that stem cell research will offer new pathways in the fight against Parkinson's disease, multiple sclerosis, spinal cord injuries and blindness.
Nonetheless, the US Conference of Catholic Bishops warned that other researchers will use the new technique to try to clone people.
Cardinal Sean O'Malley of Boston said this way of making embryos will be taken up by people who want to produce cloned children as "copies" of other people.
"Whether used for one purpose or the other, human cloning treats human beings as products, manufactured to order to suit other people's wishes." He added, "A technical advance in human cloning is not progress for humanity but its opposite," he said in a statement.