The cloned embryonic stem cells could lead to new treatments for a range of medical conditions.
Scientists have previously produced embryonic stem cells using DNA taken from infants, but for medical purposes researchers also needed to prove they could do the same with adult DNA.
Now researchers in the US have reported they've extracted nuclear DNA from the skin cells of two men, aged 35 and 75, and injected it into human eggs. The women's nuclear DNA had been removed from the eggs before the man's DNA was injected.
The resulting cells can divide indefinitely and be grown into any tissue in the human body, all genetically-matched to the DNA donor. This makes the tissue perfect for transplanting into the donor's body, a procedure that could help treat a range of conditions, including Alzheimer's and heart disease.
It's the same process that was used to clone Dolly the sheep 18 years ago.
The results of the study are published in the journal Cell Stem Cell.
NPR reports: "What we show for the first time is that you can actually take skin cells, from a middle-aged 35-year-old male, but also from an elderly, 75-year-old male" and use the DNA from those cells in this cloning process," says Bob Lanza, the chief scientific officer of Advanced Cell Technology and co-author of the study.
Of course, these cells could potentially be used to clone a human embryo, which brings up a raft of ethical issues.