The role of mesenchymal stem cells in hematopoiesis

The dynamics of the hematopoietic system in steady state requires precise tuning to maintain the pool of deeply dormant hematopoietic stem cells (HSCs), while allowing the more proliferative HSCs to actively regenerate hematopoietic tissue. This chapter reviews some recent advances in dissecting the interactions between mesenchymal stem cells (MSCs) and HSCs firstly in mice and then in humans. More refined flow cytometry and 3D confocal fluorescent microscopy analyses of Nes-green fluorescent protein (GFP) transgenic mice revealed GFP positivity did not define a single population of bone marrow MSCs. Despite the complexity of HSC niches in the mouse bone marrow and the fact that exquisitely sensitive genetic studies with conditional gene induction or ablation in vivo in mice cannot be repeated in humans, progress has been made to better characterize genuine clonal multipotent MSCs and their HSC-supportive role in human bone marrow.