It was recently reported that transplantation of clonally derived murine neurosphere cells into sublethally irradiated allogeneic hosts leads to a donor-derived hematopoietic reconstitution. The confirmation of the existence of a common neurohematopoietic stem cell in the human brain will have a significant effect on stem cell research and on clinical transplantation. Here, it is demonstrated that the human fetal brain contains separate but overlapping epidermal growth factor (EGF)-responsive and basic fibroblast growth factor (FGF-2)-responsive neural stem cells. The majority (> 85%) of cells within these EGF-and/or FGF-2-generated neurospheres express characteristic neural stem/progenitor cell markers including nestin, EGF receptor, and FGF-2 receptor. These neural stem cells can be continuously passaged in vitro, and demonstrate a constant 20-fold expansion in every passage for up to the fifth passage (the longest period that has been carried out in the authors' laboratory). These neural stem cells are multipotential for neurons, astrocytes, and oligodendrocytes. After transplantation into SCID-hu mice, all neural stem cells, regardless of passages, culture conditions, and donors, are able to establish long-term hematopoietic reconstitution in the presence of an intact human bone marrow microenvironment.(
IntroductionHematopoietic stem cell transplantation (HSCT) has been shown to provide a definitive benefit for a variety of malignant and nonmalignant hematologic diseases and myelopoietic support for patients undergoing high-dose chemotherapy. 1,2 Several inherent limitations associated with HSCT, however, have restricted its general use. 3,4 These include (1) a lack of sufficient donors for all recipients, (2) a requirement of either operative bone marrow (BM) harvests or pheresis procedures to obtain sufficient stem cells necessary for benefit after transplantation, and (3) the potential for tumor contamination in autologous HSCT. A straightforward strategy to overcome these limitations is to develop culture systems for ex vivo expansion of transplantable hematopoietic stem cells (HSCs). 5 Ex vivo-generated and -expanded HSCs could support multiple cycles of chemotherapy, provide transplantation options for patients without matched donors, facilitate transduction of vectors into HSCs for gene therapy, and provide a tumor-free product for transplantation. During the last 10 years, better ways to identify and purify HSCs and the availability of various cytokines have facilitated and improved the development of ex vivo stem cell expansion technology. Expansion of HSCs in vitro is still limited in extent and duration, and the expansion technology has not yet reached a stage where ex vivo-expanded hematopoietic progenitors and stem cells can be used routinely for replacement therapy. [6][7][8][9] Another alternative strategy to overcome those limitations associated with HSCT is to identify and use stem cells from nonlymphoid tissues, which might be easier to maintain and expand in vitro and which possess hemat...