Japanese researchers have identified a factor that finally allows scientists to grow hematopoietic stem cells in test tubes. In the May issue of Nature Immunology, Hiroo Ueno of the National Cancer Research Institute in Tokyo, and colleagues, report the isolation of a mouse protein that keeps stem cells alive and capable of generating all normal cell types found in blood. This is good news for both basic researchers and for clinicians pursuing stem cell therapies to reconstitute immune systems and blood cell populations devastated by chemotherapy or inherited genetic diseases.
Finding the conditions in which stem cells can be grown was critical because hematopoietic stem cells are very rare in the bloodstream and normally reside in protective niches deep within bone marrow. The newly identified protein, called mKirre, is made and secreted by bone marrow stromal cells, which act as guardians of stem cells. Stem cells rapidly die or lose their potential to generate blood cells in the absence of this stromal support. mKirre can substitute for the stromal cells and is sufficient to keep stem cells alive outside the body. The discovery of mKirre provides a ‘missing link’ in the long search for the exact conditions that allow blood stem cells to flourish.
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