In one aspect, the invention is directed to methods of expanding hematopoietic stem cells (HSCs) comprising culturing the HSCs with Wharton's Jelly mesenchymal stem cells (WJSCs), a cell culture medium that has been conditioned with WJSCs, or a combination thereof, thereby producing a HSC culture； and maintaining the HSC culture under conditions in which the HSCs expand in the culture, thereby expanding the HSCs. In another aspect, the invention is directed to a method of transplanting the expanded HSCs in an individual in need thereof. In yet another aspect, the invention is directed to compositions comprising HSCs and Wharton's Jelly mesenchymal stem cells (WJSCs). The composition can further comprise a cell culture medium that has been conditioned with WJSCs.
