New Stem Cell Workshop

STEM CELLS 2001;19:260-262 www.StemCells.com On September 18 and 19, 2000, more than 120 scientists from all over the world convened in Leiden, the Netherlands, to participate in a workshop on the plasticity of stem cells from adult tissues. The occasion was in celebration of the completion of the new building of the Dutch biotech company, Crucell. This meeting included wet workshops, i.e., demonstrations in the laboratory of the various quite sensational recent discoveries. The opportunity to organize such demonstrations arose from the availability of equipped but not occupied laboratories just prior to the move from the old premises. The meeting was funded jointly by Crucell and the Comprehensive Cancer Center at Rotterdam. P. Quesenberry (Boston) described changes in engraftment properties with various stages of the cell cycle of mouse hematopoietic stem cells. Bone marrow from male mice was cultured in the presence of growth factors and used at various intervals for competitive engraftment experiments in irradiated female recipients. The cycle parameters were determined for lineage-rhodaminelow Hoechstlow stem cells that were purified and then cultured separately under identical conditions. Competitive grafting capacity of the bone marrow as determined by Southern blot analysis revealed a decrease during late S and M phases and an increase again during G1 and early S phases. These findings are highly suggestive of reversible changes in the phenotype of stem cells as they move through the cell cycle, but some uncertainty remains because the two properties that were compared had to be determined in separate cell populations. S. Knaan-Shanzer (Leiden) provided evidence for a reversal of differentiation of primitive hematopoietic stem cells as defined by current surface markers using human cord-blood-derived cells. Within the CD34 population, the early lineage markers’ negative (ELM–) subpopulation, defined by these authors as CD34++, CD33, CD38, CD71–, can repopulate the bone marrow of non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice, while the ELM+ population cannot, and was therefore considered to be more differentiated. Following culturing on stroma in the absence of serum, the latter cells generated ELM– cells and acquired repopulating ability. The authors consider that this finding challenges the concept of hierarchy within the primitive stem cell compartment and favors the idea of stem cell plasticity. Under different conditions (fetal bovine serum and growth factors), C. Dorrell and F. Mazurier from John Dick’s laboratory in Toronto demonstrated a large expansion of CD34+38– cells in cord blood cultures without an increase in NOD/SCID repopulating capacity. These observations suggest a dissociation between surface markers and functional phenotype but would also fit the hypothesis that repopulating stem cells constitute an as yet unidentified subpopulation of lineage– cells. The session on neural stem cells focused on the isolation of these cells from adult mouse brain. These cells are most prevalent in the walls of the lateral ventricles and may form colonies in vitro, the so-called neurospheres. After a certain period of culture, the neural cells derived from Rosa mice (these mice are transgenic for LacZ, which encodes for the marker E. coli beta-galactosidase) were grafted into chicken or mouse embryos by J. Frisen et al. (Copenhagen). They demonstrated their grafting technique into the amniotic cavity Meeting Report Stem Cells

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