The authors injected the NSCs into a second group of mice whose hematopoietic stem cells (these cells reside primarily in the bone marrow where they produce the different varieties of blood cells) had been destroyed by a near-lethal dose of radiation. Once in the blood stream, the NSCs seeded the mice's bone marrow (and the spleen, another site of blood production). There, they took over the job of the hematopoietic stem cells and churned out a fresh supply of blood cells. Apparently, during their development as NSCs, the stem cells had not undergone any irrevocable changes that made them unable to specialize as other types of stem cells as well.
"It took us a while to believe our own data. The tissue of the body has always been seen as unchangeable," Vescovi said.
Vescovi and his colleagues speculate that it may be possible in the future to perform bone marrow transplants using adult stem cells to create a new supply of healthy blood in patients with cancers of the hematopoietic system such as leukemia. To reach that point, however, researchers will have to confirm that human stem cells behave the same way the mouse stem cells do. And they will have to accomplish the daunting task of isolating and growing adult human stem cells.
More directly, the evidence from Vescovi and his colleagues' study indicates
that neural stem cells, or "NSCs," were able to revert to their unspecialized,
embryonic state and then re-specialize as hematopoietic stem cells. To further
investigate whether this process was in fact occurring, the researchers also
injected a second group of irradiated mice with foreign hematopoietic stem
cells. Because these cells had been producing blood cells originally, it took
them less time to produce blood cells after being transplanted than it did the
NSCs. The NSCs may have taken more time b
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Contact: Diane Dondershine or Kathy Wren
ddonders@aaas.org
202-326-7088
American Association for the Advancement of Science
22-Jan-1999