It is one of the best-known stem cell papers in the past five years, describing adult cells that seemed to hold the same promise as embryonic stem cells. Now, following inquiries by New Scientist, some of the data contained within the papers is being questioned.
In 2002, a team led by Catherine Verfaillie of the University of Minnesota, Minneapolis, described 鈥渕ultipotent adult progenitor cells鈥� or MAPCs, isolated from the bone marrow of rodents (). These cells seemed able to develop into most of the body鈥檚 tissues.
Previously, only embryonic stem cells (ESCs) had proved so versatile, and the work was seized upon by opponents of ESC research, who claimed it showed similarly versatile cells could be harvested without destroying human embryos.
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The results proved hard to repeat, and for more than six months from late 2003 even Verfaillie鈥檚 own group was unable to isolate the cells. When New Scientist looked more closely, we found that six plots from the Nature paper and its supplementary information were duplicated in a second paper, published at about the same time in Experimental Hematology (), even though they were supposed to refer to different cells, taken from different mice. The plots described 鈥渕arker鈥� molecules on the surface of the cells, supposedly characteristic of MAPCs.
鈥淐onsensus opinion鈥�
After New Scientist questioned the results, a panel of experts reviewed the data. Verfaillie, now at the Catholic University of Leuven (KUL) in Belgium, has since written to the two journals informing them of problems with data within the two papers, stating: 鈥淚t was [the experts鈥橾 consensus opinion that the data were flawed and should not be relied upon as accurate representation of MAPC marker profiles.鈥�
The flaws she refers to do not relate to the duplications in the papers. These duplications, Verfaillie told New Scientist, were a simple mix-up. She stands by the claim that MAPCs can develop into most of the body鈥檚 tissues, and argues that later papers have described reliable methods for identifying them. In her most recent paper, Verfaillie and Irving Weissman, a stem cell biologist at Stanford University in California, showed that MAPCs can give rise to all the cell types found in blood, but it is still unclear whether MAPCs are as versatile as she claimed in the original Nature paper.
Many researchers are unable even to isolate them. 鈥淭hey鈥檙e very testy cells,鈥� observes Amy Wagers of Harvard University, who spent a week in Verfaillie鈥檚 lab trying in vain to learn the technique.
The problems with the marker profiles may help explain these difficulties. 鈥淚f I had been following this recipe since 2002, I鈥檇 be extremely angry,鈥� says Jeanne Loring, a stem cell biologist at the Burnham Institute for Medical Research in La Jolla, California.
鈥淲e are contacting the author for more details of the problems she mentions and will then decide how to respond, probably with the help of external advice,鈥� says Philip Campbell, editor-in-chief of Nature.