Stem-cell researchers worldwide have been dismayed and confused by the abrupt end of the highest-profile collaboration in their field.

Over the weekend, the University of Pittsburgh's Gerald Schatten suddenly accused Woo Suk Hwang of possible irregularities in the donation of eggs used for his research. Schatten cut all ties to Hwang and his team at Seoul National University in South Korea. Researchers in the field, many of whom were considering collaborating with Hwang through his World Stem Cell Hub, say their plans are now on hold.

Hwang and Schatten's 20-month collaboration produced two landmark papers — the first examples of patient-specific human embryonic stem cells (W. S. Hwang et al. Science 308, 1777–1783; 2005) and the first cloned dog (B. C. Lee et al. Nature 436, 641; 2005). But Schatten's accusations relate to the earlier work that shot Hwang to fame, in which he established the first stem-cell lines from a cloned human embryo (W. S. Hwang et al. Science 303, 1669–1674; 2004).

In a statement issued by the University of Pittsburgh, Pennsylvania, on 12 November, Schatten said: “Yesterday information came to my attention suggesting that misrepresentations might have occurred relating to [egg] donations. I have...accordingly suspended my collaboration with Professor Hwang.”

Hwang has yet to respond formally. On Tuesday, he e-mailed Nature stating: “I have begun an investigation to find out what happened. I will inform you of the result as soon as it comes.”

In May last year, an article in Nature presented claims that Hwang's procedures were ethically tainted by the use of eggs from two junior members of his lab (Nature 429, 3; 2004). One of them, a graduate student of Hwang's, told Nature that she had donated eggs for the lab's research at MizMedi Hospital in Seoul. She later retracted her statement.

Egg donation is a painful and invasive procedure that requires multiple hormone injections. Donation by junior researchers is ethically suspect, because it raises the possibility that senior researchers could pressure graduate students into undergoing the procedure.

Fractured: Woo Suk Hwang (left) and Gerald Schatten's close partnership has split over ethical concerns. Credit: H.-G. LEE/GETTY IMAGES

Last week, Korean newspapers reported that Sung Il Roh, a fertility doctor at MizMedi Hospital who has worked with Hwang since 1995, had used illegally traded eggs to treat infertile couples. Roh refused Nature's request for an interview, but has so far denied that any such eggs were used for Hwang's experiments.

Hwang himself has continuously denied using either illegally traded eggs or eggs from graduate students. And Schatten had staunchly defended him. In May 2005, Schatten told Nature that the internal review board overseeing Hwang's research “had made it clear that no students have ever donated”.

Support crumbles

Schatten's sudden statement regarding possible ethical irregularities in Hwang's work, and the fact that he has withheld related details, have shaken the world of stem-cell research. Jose Cibelli of Michigan State University in East Lansing was a co-author on the 2004 paper. He says he will await clarification of the allegations and a formal response from Hwang. But he is worried about the field. “This is a setback,” he says. “We are all very confused.”

Kevin Eggan, a developmental biologist at the Harvard Stem Cell Institute in Cambridge, Massachusetts, says the allegations are difficult to weigh, because they come without any public explanation of their origins. “We have to wait and see, because there is no evidence proving them.”

This has led to calls that Schatten present the reasons behind his charge. “At this stage, it is Dr Schatten's and others' responsibility to come forward with evidence,” says bioethicist Insoo Hyun of Case Western Reserve University in Cleveland, Ohio.

But the allegations themselves are sufficient to cast doubt on the future of the World Stem Cell Hub. This network, launched last month, is meant to serve as a stem-cell bank and a research facility where scientists from any country can study cell lines created to order by South Korea. Many scientists in the United States, Britain and elsewhere had planned to participate, but are reconsidering their position.

Eggan, for example, says his plans are now on hold. “The allegations are serious and would have to be completely resolved for us to continue to consider collaborating with them.”

And the Korean media is starting to criticize Hwang, who until now has been treated like an idol. An editorial in JoongAng Ilbo calls on Hwang to “prove that cloning is clean”.

Korean scientists are calling for an independent investigation, but it is not clear whether this will happen (see page 257). In the meantime, researchers are left wondering what caused Schatten's sudden change of heart.

Until recently, Hwang and Schatten had been getting on famously. “They seemed as close as they could be,” says Hyun, who spent this summer studying the Korean team's ethical practices. “Gerry kept referring to Dr Hwang as his brother, and Dr Hwang's public toast to Gerry at a formal dinner was so effusive, it was almost embarrassing.”

Eggan adds that just last week the two were as chummy as ever at a conference in New York. “They seemed to have every intention of continuing to collaborate in the future,” he says.

Evan Snyder, a neuroscientist from the Burnham Institute in La Jolla, California, says that he received an e-mail from Schatten just before he issued his statement. “Whatever prompted this he found so exceedingly disturbing, he could not sit on it,” says Snyder. “You have to realize this is a major part of his research programme as well, so to do something this precipitously, it must have been terribly shocking.”