But, about four years ago, this fundamental idea received a serious jolt when scientists reported inducing a small percentage of adult stem cells from the brain to switch into cells from the blood. This led to a series of confirmatory findings that seemed to have settled the question, when two teams of researchers last year dropped the small bombshell that, in their laboratory studies, some stem cells physically fused with other cells. This finding suggested that maybe the brain-to-blood and other stem cell switches, a process that scientists call transdifferentiation, weren't what they seemed. Maybe the stem cells had fused with cells from other tissues all along.

Now, in the current issue of The Lancet, a team of scientists at the National Institutes of Health offers a key piece of new evidence to advance the debate. In a study of five women who had received bone marrow transplants from their brothers several years earlier, the team reports finding cheek cells that contained the male Y chromosome, a sign that some transplanted stem cells had differentiated into cheek cells. Moreover, the group found almost no evidence of fusion among the cells in the cheek.

Because the researchers analyzed cells extracted directly from patients, which previous studies did not for various technical reasons, these data offer strong evidence that transdifferentiation does occur. The study also shows the power of using oral tissues to pursue complex biological questions, an idea that is gaining wider favor among biologists.

"Being so accessible, the mouth is one of the best 'laboratories' in the body to study many issues in human biology that go beyond dental research," said Dr. Bruce Bau
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Contact: Bob Kuska
kuskar@nidcr.nih.gov
301-594-7560
NIH/National Institute of Dental and Craniofacial Research
27-Mar-2003