A method of expanding undifferentiated hemopoietic stem cells to increase the number of the hemopoietic stem cells is provided. The method comprising: (a) obtaining the undifferentiated hemopoietic stem cells; and (b) culturing the undifferentiated hemopoietic stem cells in a medium containing a stromal cell conditioned medium, the stromal cell conditioned medium being derived from a stationary phase plug-flow bioreactor in which a three dimensional stromal cell culture has been established under continuous flow of a culture medium on a substrate in the form of a sheet, the substrate including a non-woven fibrous matrix forming a physiologically acceptable three-dimensional network of fibers, thereby expanding the undifferentiated hemopoietic stem cells.