Scientists have found a way to create embryonic stem cells by converting mature cells to an earlier state, according to a study to be released Wednesday.

The breakthrough, found by genetically manipulating mature skin cells in mice into a so-called pluripotent state, would allow the reprogrammed cells to grow into any cell-type, and they could grow into living mice.

Before the discovery of the new technique, embryonic stem cells were created by implanting DNA into an egg, which would then grow to provide a supply of stem cells. But to harvest them, the viable embryo would have to be destroyed.

The findings of scientists at the Whitehead Institute for Biomedical Research at the Massachusetts Institute of Technology in Cambridge, Mass., were to be published online Wednesday in the science journal Nature.

"These reprogrammed cells, by all criteria that we can apply, are indistinguishable from embryonic stem cells," Rudolf Jaenisch, the paper's senior author said in a written statement.

But Jaenisch, an MIT professor of biology who works at the Whitehead Institute, cautioned that it is premature to assume that the technique means treatments for spinal cord injuries or other ailments in people are around the corner.

"All these results are preliminary and proof of principle. It will be a while before we know what can and can't be done in humans," he said.

Co-researcher Marius Wernig echoed Jaenisch's statement but expressed hope that the research could eventually lead to new medical treatments.

"We are optimistic that this can one day work in human cells," Wernig said. "We just need to find new strategies to reach that goal. For now, it would simply be premature and irresponsible to claim that we no longer need eggs for embryonic stem cell research."

Two other papers reported findings similar to the Whitehead team's. One, by Shinya Yamanaka of Kyoto University in Kyoto, Japan, was to be published in the same online edition of Nature.

Another, by Konrad Hochedlinger of the Center for Regenerative Medicine at Massachusetts General Hospital and Harvard Stem Cell Institute, is to be published in the new journal Cell Stem Cells.