WESTPORT, CT (Reuters Health) – Hematopoietic stem and progenitor cells can migrate to bone marrow niches before bone marrow ablation and may therefore play a role in bone marrow transplantation, California investigators report in the November 30th issue of Science.
To investigate these mechanisms, Dr. Irving L. Weissman, of the Stanford University School of Medicine, and colleagues surgically conjoined parabiotic mice and induced a common blood circulation. Blood chimerism reached approximately 50% after about a week.
Twenty-two weeks after separating the established pairs of mice, the animals all had partner-derived peripheral blood granulocytes and bone marrow long-term hematopoietic stem cells (HSCs). Removing the spleen from one mouse in one pair showed that the spleen is not required as a source of circulating stem cells for bone marrow cross engraftment, the investigators note.
Further work indicated that "the flux of HSCs into the blood from bone marrow and other tissues and the flux of HSCs out of the blood must be essentially the same," the authors add. Thus, at least some HSCs appear to be capable of re-engrafting bone marrow.
These findings imply, according to Dr. Weissman's team, that HSC engraftment of bone marrow may not require infusion of large numbers of cells.
The investigators point out that HSCs circulate widely and operate as a source of pluripotent stem cells for the repair of nonhematopoietic tissue. They caution that the recently observed generation of blood cells from nonhematopoietic tissue may be the result of HSC contamination rather than transdifferentiation of nonhematopoietic tissues.
Science 2001;294:1933-1936.
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