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Adult stem cells may be redefinable

Deborah Josefson , San Francisco

New research indicates that adult neural stem cellspreviously thought to be committed to becoming either neurones, astrocytes, or oligodendrocytescan de-differentiate and reinvent themselves as haemopoietic precursors (Science 1999;283:471, 534-7).

This finding raises the possibility that adult human stem cells may some day be coached to grow into organs, regenerate damaged tissue, or reconstitute the immune system.

The problem of immune rejection may also be circumvented if an individual's own cells can be used.

It also means that the need for fetal cells as a source of stem cells for medical research may soon be eclipsed by the more readily available and less controversial adult stem cells.

Christopher Bjornson, of the University of Washington in Seattle, and Angelo Vescovi, of the National Neurological Institute in Milan, Italy, showed that both adult and embryonic murine neural stem cells can adopt a haemopoietic identity when transplanted into mice whose bone marrow has been destroyed by radiation.

The scientists irradiated BALB/c mice to destroy their bone marrow and then injected them with neural stem cells derived from another strain of mice known as ROSA26.

The donor ROSA26 mice were transgenic for the Escherichia coli lacZ gene, which encodes the enzyme B-galactosidase. The presence of this gene product served as a marker to identify which cells took up the injected neural precursors.

The scientists injected mice with both adult and embryonic neural stem cells. Five to 12 months later they detected strong lacZ signals in the irradiated BALB/c mice, indicating that the donated cells had taken up residence in the mice.

B-galactosidase was found in the bone marrow of mice that had received adult neural stem cells, indicating that some of the donated cells had redeveloped into haemopoietic cells.

The researchers found that adult stem cells were as effective in reconstituting the immune system as fetal neural stem cells. However, both fetal and adult neural stem cells took longer to repopulate the bone marrow than did a control group with injected foreign hemopoetic cells.

The difference may reflect the time it takes for neural stem cells to redefine themselves.

Astrocytes: can they reinvent themselves?