Abstract
Hematopoietic stem cells are defined by their ability to self-renew and to generate the multiple hematopoietic mature cells (multipotency) through a various types of hematopoietic progenitors. Normal hematopoiesis is regulated by a complex network of soluble physiological regulatory factors, stromal cells and the extracellular matrix. In the present study, we investigated whether X-irradiated hematopoietic stem cells can be generated to normal hematopoieis in vitro using mesenchymal stem cells (MSC) prepared from human placental/umbilical cord blood (CB) that have been demonstrated to be effective for supporting of hematopoiesis. The CD34+ cells were highly purified from CB, and the adherent MSC were expanded from CB mononuclear cells except CD34+ cells. The non-irradiated or 2 Gy irradiated CD34+ cells were cultured onto MSC supplemented with a combination of thrombopoietin + interleukine-3 + stem cell factor. An assay for the clonogenic potential of hematopoietic progenitor cells was evaluated using a methylcellulose culture for CFU-GM, BFU-E and CFU-Mix, and a plasma clot culture for CFU-Meg. After co-culture of non-irradiated or X-irradiated CD34+ cells with MSC, no significant differences in the total number of cells were observed in the cultures with, or without MSC. In the generated cells harvested from each culture, the significant increase of total CFU-GM numbers was observed in the co-culture of X-irradiated CD34+ cells with MSC in comparison to the control. These results suggest that MSC can induce nearly normal hematopoiesis from X-irradiated hematopoietic stem cells.
