U.S. scientists say they have, for the first time, returned adult mouse cells to their embryonic pluripotent state, meaning they can become any cell type.

The University of California-San Francisco researchers said they used tiny molecules called microRNAs to reprogram the cells.

The achievement suggests scientists will soon be able to replace retroviruses and even genes currently used in laboratory experiments to induce pluripotency in adult cells. The researchers said that would make potential stem cell-based therapies safer by eliminating risks posed to humans by these DNA-based methods, including alteration of the genome and risk of cancer.

"Using small molecules such as microRNAs to manipulate cells will play a major role in the future of stem cell biology," said Dr. Robert Blelloch, the study's senior author.

Scientists are interested in reprogramming because it would offer a way to create cells that provide a genetic match for individual patients.

The study appears online in the journal Nature Biotechnology and is scheduled to appear in the journal's May 8 print edition.