Study finds little promise in adult blood stem cells: Cells have less ability than embryonic cells to morph into other tissues

By MARILYNN MARCHIONE
of the Journal Sentinel staff
Last Updated: Sept. 6, 2002

Adult blood stem cells have far less ability to produce other types of cells in the body than stem cells taken from embryos, one of the most rigorous studies to test this potential suggests.

Many people who oppose research involving human embryos hope that adult stem cells might be able to do what embryonic stem cells are hailed for - being able to make a wide variety of tissues, not just the kind they came from, such as blood or muscle.

Several recent studies have raised the intriguing possibility that in certain circumstances they can, and blood stem cells have shown particular promise.

But a study by Stanford University researchers, published Thursday in Science Express, the online version of the journal Science, suggests adult cells aren't very changeable.

The researchers did two experiments in mice that mimicked the conditions others have used to show adult blood cells' "plasticity," or ability to form other tissue, and found they basically formed only blood. The experiments used a tracing mechanism - a fluorescent protein - to document exactly what the blood stem cells did.

"It's a very carefully performed study which really gives a lot of pause to the idea that adult stem cells are going to do everything that everyone would like them to be able to do," said George Daley, a stem cell scientist at the Whitehead Institute at Massachusetts Institute of Technology who was not involved in the work.

"It reinforces our skepticism with hard data," he said, and "calls into question" whether the observations of other studies claiming to show blood stem cell plasticity "have been an artifact or a spurious or misleading finding."

The experiments were led by Stanford scientist Amy Wagers and included blood stem cell expert Irving Weissman, who headed a recent National Academy of Sciences committee on cloning and stem cells.

In one experiment, they transplanted a single blood stem cell with a fluorescent "tag" into mice whose own blood stem cells had been destroyed via radiation. The single transplanted cell made lots of blood cells, as would be expected, but only a few liver cells, one brain cell and no other cell types.

In a second experiment, they surgically joined pairs of mice to create a joint circulatory system between them so blood would be exchanged freely. One animal's blood stem cells were tagged so they could be tracked in the other animal, whose own cells were untagged.

In the untagged animal, the fluorescent marker showed that the other animal's blood stem cells made many blood cells but not one cell of any other type.

Adult blood stem cells morphing into other types of cells "is an extremely rare event, if it occurs at all," the researchers concluded.

Daley repeated what many scientists have said: that this and previous experiments underscore the need to continue research on all types of stem cells until their respective benefits and drawbacks are known.

"Most of us in the field think this push to define adult or embryonic cells as better than another is a lot of folly," he said.

Wisconsin has had a prominent place in stem cell research. Human embryonic stem cells were first isolated by University of Wisconsin-Madison scientist James Thomson.