U.S. and Japanese scientists who reported that they'd found a startlingly simple way to make stem cells withdrew that claim Wednesday, admitting to "extensive" errors in the research.

In two papers published in January in the journal Nature, the researchers said that they'd been able to transform ordinary mouse cells into versatile stem cells by exposing them to a mildly acidic environment. Someday, scientists hope to harness stem cells to grow replacement tissue for treating a variety of diseases.

While researchers have long been able to perform such transformations with a different method, the newly reported technique was far simpler, and the papers caused a sensation and some skepticism in the research community. They were also widely reported in the media, including by The Associated Press.

But before long, the government-funded Riken Center for Developmental Biology in Japan accused one of its scientists, Haruko Obokata, of falsifying data in the research. Obokata, the key author of the papers, defended the results during a televised news conference in April while apologizing for using wrong and altered images in the published reports. She also said she opposed withdrawing the papers, a process called retraction, and the 30-year-old attributed her mistakes to inexperience.

On Wednesday, Nature released a statement from Obokata and the other authors of the papers that retracted the papers, a rare occurrence for the prestigious journal. The scientists acknowledged "extensive" errors that meant "we are unable to say without a doubt" that the method works. They noted that studies of the simpler method are still going on by other researchers.

The Riken center also said on its website Wednesday that it expected a separate statement from Obokata and would post it when available.

Dr. Charles Vacanti of the Harvard-affiliated Brigham and Women's Hospital in Boston, another main author, issued his own statement in which he said he believes the further studies will vindicate the method, which produced what the authors called STAP cells.

But another author, Yoshiki Sasai, deputy director of the Riken center, said the errors in the papers meant "it has become increasingly difficult to call the STAP phenomenon even a promising hypothesis." In a statement issued by Riken, he said he was "deeply ashamed" of the problems in the papers.

The Riken investigation that led to allegations against Obokata also focused on Sasai and two other employees, but they were not accused of research misconduct.

Retractions of papers in major scientific journals like Nature are unusual. They can come about because of fraud or the discovery of honest mistakes that undercut the conclusions of research. Publications like Nature routinely have experts review papers submitted by scientists to look for problems. But in an editorial released Wednesday, Nature concluded that its editors and reviewers "could not have detected the fatal faults in this work."

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Scientists Withdraw Report on Simpler Stem Cells - ABC News