There may be a safe way to turn human skin cells into stem cells with the potential to be steered toward the body's repair system, scientists said Thursday.

In Thursday's online issue of the journal Science, James Thomson and his colleagues at the University of Wisconsin said they've developed a way to create induced pluripotent stem cells, or iPS cells, without using viruses known as vectors that could introduce harmful genes and trigger cancer.

Pluripotent stem cells could offer the treatment potential of embryonic stem cells without destroying a human embryo.

"We believe this is the first time human-induced pluripotent stem cells have been created that are completely free of vector," and genetically engineered sequences, said study author Thomson.

Instead of using a virus to make the iPS cells, the researchers used a plasmid — a circular piece of DNA that carries the genes into the skin cell.

The plasmid eventually disappears from the cell population, avoiding the danger posed by using viruses and reprogrammed genes that also led to mutations and interfered with the function of induced cells in laboratory experiments.

"The recent discovery that adult cells could be reprogrammed to iPS cells that resemble embryonic stem cells opened up tremendous potential for regenerative medicine," said Marion Zatz of the National Institute of Health's National Institute of General Medical Sciences, which partially funded the research.

"This latest discovery by Thomson's group of a new method for generating iPS cells without inserting viral vectors into the cells' genetic material is a major advance toward safely reprogramming cells for clinical use."