Scientists have made a long-awaited breakthrough in human cloning, by using human skin cells to create early-stage embryos.
In what is being described as a "significant milestone" for medicine, the team from Oregon Health and Science University successfully used a technique which utilised a human skin cell and a woman's egg to produce an embryo which was a genetic copy of the original skin cell.
The resulting embryos were then used as a source of stem cells, which can be used to create specialised tissue cells for transplant operations.
But scientists say they do not think the technique could be used to clone humans for reproductive purposes.
"We still believe that the stem cells that we create don't actually have the potential to become embryos and [be] used for reproductive cloning," Oregon team member Dr Shoukhrat Mitalipov told ABC News Breakfast.
"They're basically charged with the ability to make any other cells and tissues, and even organs."
Years of research on monkey cells using the same technique have not successfully produced any monkey clones.
But 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.
Dr Mitalipov said that since the reprogrammed cells use genetic material from the patient, there was no concern about transplant rejection.
And he said the team had been surprised by how successful they had been.
"It's been a really exciting project to start and we actually accomplished it very quickly. We hadn't been expecting it to be that successful," he said.
"We started last year in September and by mid-December we had already established some stem cell lines."
The study, published in the journal Cell, used cloning techniques like those used to produce Dolly the sheep in Scotland in 1996.
However, unlike Dolly, the human embryos were destroyed when their stem cells were extracted.
But the breakthrough will still raise ethical concerns about the creation of human embryos for medical purposes.
Researchers say other stem cell sources may be easier and less controversial.
Trials are already taking place using stem cells from donated embryos to restore people's sight.
Professor of Stem Cell Sciences at the University of Melbourne, Martin Pera, says the discovery is enormously exciting.
"Although it was possible to do cloning and make stem cell lines using cloning in other species, it proved very, very difficult to do in humans," he told AM.
"And what this group was able to do, by fine-tuning the technology and using detailed knowledge of human reproduction, was to make this technique workable in man.
"And that’s a very significant achievement indeed."
And he said Australian scientists should look at using the technique to treat patients.
"I think in the scientific community, and in the medical community, and for patients suffering from these disorders, there'll be a lot of excitement around it," he said.
"Of course this approach is permissible in Australia, so Australian scientists could pursue the same avenue.
"I think in general, where we look at the potential for alleviating disease, and when that potential becomes real, then some of the objections I think tend to diminish."