Hematopoietic stem cell homing: The long, winding and adhesive road to the bone marow

In adult mammals, a rare population of cells that gives rise to the hematopoietic compartment dwells in niches within the bone marrow where they are nourished and protected. These blood stem cells can, however, exit these niches under physiological conditions and, in the context of bone marrow transplantation, migrate to the recipient's marrow to regenerate hematopoiesis. This review will address old and new discoveries regarding the mechanisms that allow these stem cells to find their way home through long and winding roads: From the peripheral circulation, through interactions with the vessel-lining endothelial cells in the bone marrow, and into their niches located in the intramedullary space. It will also address how these discoveries have provided us with new tools to manipulate stem cell trafficking.