They were hailed as an “ethical” alternative to embryonic stem cells – adult stem cells that can turn into any of the body’s tissues. Doubts have grown, but now a prominent sceptic has shown that one claim seems true: they can form all of the cell types found in blood.
Catherine Verfaillie and colleagues at the University of Minnesota, US, described the "multipotent" adult progenitor cells (MAPCs) in 2002. Isolated from mammalian bone marrow, they belonged to a class called mesenchymal stem cells, which normally form muscle and bone. However, MAPCs seemed much more versatile, able to form any of the body’s tissues (see Is this the one?).
Other teams have since struggled to repeat the results (see Stem cells' miracle postponed). But now Verfaillie has teamed up with Irving Weissman of Stanford University in California, US, to transplant MAPCs into mice that had been irradiated, wiping out their haematopoetic stem cells (HSCs) – another class of marrow cells that give rise to blood. “From the beginning I was very, very sceptical that MAPCs could contribute to blood formation,” says Weissman.Jury out
Now he has changed his tune: the transplanted MAPCs were able to form all blood cell types. “Mouse MAPCs can make normal blood, and we need to understand how they do it,” Weissman says.
MAPCs were much less efficient than HSCs in engrafting into the marrow and giving rise to blood, however. “This needs to be resolved before we would use [human MAPCs] to engraft in humans,” says Verfaillie, who is now at the Catholic University of Leuven in Belgium.
And the jury is still out over other claims made for MAPCs. Although the latest experiment was designed specifically to investigate blood formation, Weissman notes that the doses of radiation used caused damage throughout the animals’ bodies. This would have triggered repair mechanisms, giving MAPCs an opportunity to form a range of tissues. “I was disappointed to see that only blood cells were derived,” Weissman admits.
Journal reference: Journal of Experimental Medicine (vol 204, p 129) New Scientist