It has become clear that adult mammalian bone marrow contains not one but two ostensibly
discrete populations of adult stem cells. The first and by far the most fully characterized are
the hematopoietic stem cells responsible for maintaining lifelong production of blood cells.
The biological characteristics and properties of the second marrow resident population of
stem cells, variously termed bone marrow stromal cells or mesenchymal stem cells, are in
contrast much less well understood. In vitro, cultures established from single-cell …