News of the Week

Data on Adult Stem Cells Questioned

Science  02 Mar 2007:
Vol. 315, Issue 5816, pp. 1207a
DOI: 10.1126/science.315.5816.1207a

Just as her team is preparing some long-awaited follow-up papers on multipotent adult progenitor (MAP) cells, stem cell researcher Catherine Verfaillie is dealing with accusations that her landmark study, published in Nature in 2002, contains “flaws” that could jeopardize its conclusions. Nature has decided to rereview the work. Verfaillie, now at the Catholic University of Leuven, Belgium, says that although some data are puzzling, the problems do not affect her findings.

Hot seat.

Catherine Verfaillie sticks up for her cells.


The accusations were raised last summer but became widely known only last week following an article in New Scientist. They've received a flurry of attention because of the big splash Verfaillie made when she originally reported that her team had cultivated a new type of cell that appeared to have the potential to grow into most cell types in the body (Science, 9 February, p. 760).

Last year, two New Scientist reporters noticed that the Nature paper and another the team published at the same time in the Journal of Experimental Hematology contained identical data on flow cytometry—a technique for identifying cells—even though the two papers described different cell populations. They notified Verfaillie, who in turn notified the journal editors and the University of Minnesota (UMN), Twin Cities, where she did the research.

At Verfaillie's request, UMN convened three experts to review the flow-cytometry data. They concluded last August that the duplication was an “honest error.” Verfaillie subsequently had an erratum published in the hematology journal.

However, the panel also said it had reservations about the “validity” of the flow-cytometric analysis data in the Nature paper. Flow cytometry involves the use of antibodies to recognize proteins on cell membranes. Some of the fluorescent signatures generated by antibodies showed a variability “far outside what would be expected for this kind of experiment,” said the panel. If those data are unreliable, it could mean that the MAP cells do not have all the characteristics described in the paper.

The experts said they couldn't judge whether the problem would affect the paper's conclusions about the versatility of MAP cells. One of them told Science that “problems are rampant” in flow cytometry, and it would be hard to find a paper without some flaw.

UMN then asked two unnamed stem cell experts to address the validity of the conclusions of the Nature paper. Their comments have not been made public, but the university's vice president for research, Tim Mulcahy, says that one of the experts felt the problematic data “weakened” the paper. The other said the data were “not critical” to the conclusions. Mulcahy says the university plans no further action and will let the scientific community judge the matter for itself.

Verfaillie says her team has “no explanation for why” the data turned out as they did. “I personally don't think it affects the conclusion of the paper, and I've spoken to many people who personally don't think so,” she says. But it's “up to Nature to decide.”

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