Scientists may have found a safer way of giving a flake of skin the biologically alchemical powers of embryonic stem cells.

They turned adult cells into versatile, embryonic-like cells without causing permanent damage – potentially solving the central problem of a promising but uncertain field of stem cell science.

"This is certainly a major stem cell milestone," said Advanced Cell Technologies chief scientific officer Bob Lanza, who was not involved in the research. "It’s the first ray of light that iPS cells could soon be used to treat patients."

These iPS cells – short for induced pluripotent stem cell – debuted less than a year ago: By using viruses to insert key developmental genes, researchers coaxed human skin cells into an embryonic state, capable of growing into almost any other type of tissue.

It was the biggest stem cell breakthrough in a decade. No longer would tricky – and ethically controversial – manufacturing procedures be required to produce ultra-versatile stem cells. Cloning wouldn't be needed to produce personally customized embryonic stem cell lines, which remain as elusive as they are promising.

But there was a catch: Viruses used to reset the cells tended to fuse with their DNA, leading to unpredictable mutations and cancer. The cells were promising in principle, but couldn't be used medically.

The standard iPS technique was a blunt and damaging instrument.

The new technique doesn't cause permanent genetic alterations; it's a scalpel that leaves no scar behind. And though important caveats remain

\– the procedure, published today in Science, was performed on mice – it has made safe iPS cells a realistic possibility.

"Clinical translation of iPS technology has been dead in its tracks,"

said Lanza. "The use of iPS cells to treat – or even cure – human disease may not be far away."

To produce their iPS cells, the researchers added cell-reprogramming genes to adenoviruses, a type of virus that infects cells without affecting their DNA. The adenoviruses pumped out cell-reprogramming proteins, turning the cells embryonic, and then departed.

"You produce proteins for a while, but over time – with cell division

\– both DNA proteins are diluted out from the cell," said Konrad

Hochedlinger, a Harvard Medical School cell biologist and co-author of the study. "You end up with a genetically unmodified iPS cell."

Hochedlinger's team grew the cells into lung, brain and heart tissue – benchmark measurements of versatility – and used the cells to create mouse embryos, which they allowed to develop. Those mice remained cancer-free for four months. That's not long enough to be completely certain of their safety, but it's reassuring nonetheless.

"Some published reports on mice made with retrovirally produced iPS

cells succumbed to tumors as early as four weeks after birth," said

Hochedlinger.

Old-fashioned iPS cells, said Lanza, would never have been safe enough for FDA approval. But he warned that duplicating Hochedlinger's feat

"may be a challenge – and far more difficult – in the human system."

Some politicians and bioethicists, including Republican presidential candidate John McCain, have hoped that iPS cells would soon make embryonic stem cell research unnecessary. But stem cell scientists say it's too soon to compare embryonic stem cells, which have been studied for more than a decade, with iPS cells. It's also possible that both of types of cell, as well as adult stem cells, will provide therapies that the other types cannot.

"There are still a lot of unknowns, and we cannot afford to put all our eggs in one basket," said Lanza, while Hochedlinger called embryonic stem cells the

"gold standard."

But the findings are still a testament to the rapidly developing field of iPS research, which in less than a year has gone from proof-of-principle to mouse therapies to the latest refinement.

"I have never seen a field move forward as fast as this one," said Hochedlinger.

Induced Pluripotent Stem Cells Generated Without Viral Integration [Science] [not yet online]

*Images: Science. Different tissue types, and adult mice, produced through adenovirally modified iPS cells.

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