The prospect of using a patient's skin to generate healthy heart, liver or nerve cells for transplant operations has moved a step closer after a scientists' breakthrough.
Using the cloning technique which produced Dolly the sheep in 1996, researchers for the first time turned human skin cells into "embryonic" stem cells, which can grow into any type of tissue in the body.
The discovery reopened an ethical debate about "reproductive cloning" yesterday, with critics claiming the "irresponsible" technology opened the door to the cloning of human babies.
But researchers insisted the technique, which involves the creation and destruction of early-stage embryos, is intended solely to lead to new treatments for disease and injury.
Dr Shoukhrat Mitalipov, who led the study at Oregon Health & Science University, said human cloning "is not our focus, nor do we believe our findings might be used by others to advance the possibility".
Opponents of the research insisted the technique inevitably brought the prospect of cloned IVF babies a step nearer.
Stem cell therapies could help patients with conditions such as Parkinson's disease, multiple sclerosis, cardiac disease and spinal cord injuries. The study is published in the Cell journal.
Professor Robin Lovell-Badge, head of developmental genetics at Britain's National Institute for Medical Research, said the new work "at last brings the topic of therapeutic cloning in humans back into the realm of good science rather than controversy".
How it works
• The nucleus is extracted from the egg cell and the skin-cell nucleus is inserted into the empty egg cell.
• Electric shock fuses the skin-cell nucleus inside the egg and cell division begins. The embryo develops into a blastocyst with stem cells.
• Stem cells are cultured into specialised cells, such as beating heart muscles.
- additional reporting, Independent