The hyped ability of adult stem cells to sprout numerous different cell types is questioned by two Nature (Vol. 416, No. 6877, 14 Mar 2002) reports published this week. They may instead be fusing with existing cells, say two new reports, creating cells with double the dose of chromosomes and unknown health consequences.
Recent studies have shown that adult stem cells from one tissue such as blood, can give rise to other cell types, such as nerve and muscle. The adult cells are thought to revert to a state similar to embryonic stem cells, able to make many other cell types in the body.
Austin Smith of the University of Edinburgh, UK, and Naohiro Terada of the University of Florida in Gainesville suggest that spontaneous cell fusion could be occurring instead. They found that adult cells from either bone marrow or brain grown in the same dish as embryonic stem cells fused spontaneously to make hybrid cells, which were able to produce muscle, nerve and other cell types.
Smith and Terada only tested whether this could occur in a petri dish. Animal studies will be required to confirm that spontaneous cell fusion occurs in vivo, and that it provides an alternative explanation for recent demonstrations of adult stem cell plasticity.
If confirmed by animal studies, the findings could be a reality check for those hoping to use adult stem cells clinically. Fused cells carry double the normal amount of DNA, and may be unhealthy. "It might be a precautionary tale for stem cell research," says Terada.
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