The notion that stem cell fate is dictated by the tissue of origin has been challenged by recent work published in Science (283, 534–537, 1999 ). In collaboration with colleagues from NeuroSpheres (Calgary, Alberta, Canada) and Istituto di Mutagenesi (Pisa, Italy), Angelo Vescovi of the Istituto Nazionale Neurologico Carlo Besta (Milan, Italy) have shown that neural stem cells (NSCs) can adopt hematopoietic identity when injected into mice. By tagging the NSCs with lacZ, the authors were able to confirm that donor DNA was present in the spleen of recipient mice and that transplanted NSCs were capable of producing B cells, T cells, and myeloid cells. What's more, hematopoietic antigens were detected on these cells that were distinctly absent in NSCs before transplantation. According to Vescovi, "The inherent plasticity of highly undifferentiated stem cells is probably wider than what was originally thought. This allows them to respond to the environmental cues in which they find themselves." It remains to be determined whether human stem cells show the same plasticity and broad specificity as mouse NSCs. If the results prove comparable, large batches of stem cells for use in leukemia could be grown, providing an alternative to stem cells derived from human embryos, which pose ethical problems.