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Remarkable Advance with Adult Stem Cells
E-Newsletter No. 32
Despite some ethical objections, proponents of using embryonic stem cells for medical therapy have argued that the alternative-adult stem cells-simply does not have sufficient developmental potential. A new report from researchers at the University of Minnesota challenges that assumption.
The team identified rare cells, called multipotent adult progenitor cells (MAPCs), in bone marrow of adult mice and rats. These cells are very similar to the more common mesenchymal stem cells in appearance and in the cell markers that they express. However, like embryonic stem cells, they can proliferate through at least 80 cell doublings. In vitro, single MAPCs can be coaxed to form mesenchymal1 cells, as well as mesoderm2, neuroectoderm3, and endoderm4 cells and tissues. When MAPCs were injected into early blastocysts, they contributed to nearly all cell types. When MAPCs were transplanted into immunocompetent animals, they homed to various organs __ blood, liver, lung, and gut __ and differenciated into tissue specific to those organs; in immunodeficient animals, engraftment was even greater, and the transplanted cells did not form tumors.
Comment: This report, described as "stunning" by editorialist, may herald a brighter future for adult-stem-cell therapy for various inherited or degenerative diseases. These results need to be confirmed, and it remains to be shown that transplanted cells function properly in the various tissues to which they home.
1&2) Mesenchyme is a diffuse network of cells forming the embryonic mesoderm (middle layer) and giving rise to connective tissues, blood and blood vessels, the lymphatic system and cells of the surrounding spaces between these structures.
3) Neuroectoderm is the outer layer of cells in a developing embryo. From it are developed skin structures, the nervous system, organs of special sense, the pineal and part of the pituitary and adrenal glands.
4) Endoderm is the inner layer of cells of an embryo. From it are derived the linings of the oral cavity, intestinal tract, vagina, urethra, nasopharynx, liver, kidney, spleen, prostate, ovaries and uterus.
Jiang Y et al. Pluripotency of mesenchymal stem cells derived from adult marrow. Nature 2002 Jul 4, 418:41-9.
Orkin SH and Morrison SJ. Stem-cell competition. Nature 2002 Jul 4; 418:25-7.
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