The potential of embryonic stem cells to develop into a wide variety of tissues and organs has been established, but it remains unclear how this can be achieved in practice. In 4 September Proceedings of the National Academy of Sciences, Dan Kaufman and colleagues at the University of Wisconsin-Madison show for the first time how undifferentiated human embryonic stem cells (ES) can be cultured to become blood cells.

Kaufman et al. cultured ES in flasks containing murine bone marrow cell line S17 or the yolk sac endothelial cell line C166. They found that in this medium, which required only additional foetal bovine serum, ES undergo haematopoietic differentiation and transform into haematopoietic precursor cells expressing the cell surface antigen CD34. When cultured on semisolid media with haematopoietic growth factors, these precursor cells formed characteristic myeloid, erythroid, and megakaryocyte colonies (Proc Natl Acad Sci USA 2001, 10.1073/pnas.191362598).

The authors...

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