Stem Cell Breakthrough Defuses Debate

"It's a bit like learning how to turn lead into gold," said Lanza, while cautioning that the work is far from providing medical payoffs.

"It's a huge deal," agreed Rudolf Jaenisch, a prominent stem cell scientist at the Whitehead Institute in Cambridge, Mass. "You have the proof of principle that you can do it."

There is a catch. At this point, the technique disrupts the DNA of the skin cells, and that creates the potential for developing cancer. So it would be unacceptable for transplanting into a patient.

But the DNA disruption is just a byproduct of the technique, and experts said they believe it can be avoided.

For the new work, the two scientific teams chose different cell types from a tissue supplier. Yamanaka reprogrammed skin cells from the face of an unidentified 36-year-old woman, and Thomson's team worked with foreskin cells from a newborn. Thomson's team, which was working its way from embryonic to fetal to adult cells, is still analyzing its results with adult cells.

Both labs did basically the same thing. Each used viruses to ferry four genes into the skin cells. These particular genes were known to turn other genes on and off, but just how they produced cells that mimic embryonic stem cells is a mystery.

Both Thomson, 48, and Yamanaka, 45, had already produced notable achievements. Thomson made headlines in 1998 when he announced that his team had isolated human embryonic stem cells.

And Yamanaka gained scientific notice in 2006 by reporting that direct reprogramming in mice had produced cells resembling embryonic stem cells, although with significant differences. In June, his group and two others announced they'd created mouse cells that were virtually indistinguishable from stem cells.

Zoloth, the ethicist at Northwestern, noted that direct reprogramming avoids not only embryo destruction, but also the need for unfertilized human eggs to create embryos. Eggs are hard to obtain for research, and collecting them subjects women to drug treatment and surgery. Using eggs also raises the ethical question of whether women should be paid for them.

The embryo and egg issues were "show-stopping ethical problems," she said.

Another advantage of direct reprogramming is that it would qualify for federal research funding, unlike projects that seek to extract stem cells from human embryos, noted Doug Melton, co-director of the Harvard Stem Cell Institute.

Still, scientific questions remain about the cells produced by direct reprogramming, called "iPS" cells. One is how the cells compare to embryonic stem cells in their behavior and potential. Eventually, iPS cells might prove better for some scientific uses and cloned stem cells preferable for other uses. For example, scientists want to study the roots of genetic disease and screen potential drug treatments in their laboratories.