Proliferation of Haemopoietic Stem Cells in Vitro

S ummary . A liquid culture system for murine haemopoietic cells is described where proliferation of granulocytes (G‐cultures) or mononuclear cells (M‐cultures) can be maintained for many weeks. In M‐cultures there is a rapid loss of spleen colony forming cells (CFUs). Agar colony forming cells (CFUc) are present for 6 weeks, then decline rapidly. Colonies formed from these CFUc contain only large mononuclear cells. In G‐cultures there is proliferation of CFUs, grafts of which (after 7‐9 weeks in culture) protect lethally irradiated mice from haemopoietic death. Similarly, there is proliferation of CFUc, which form colonies in agar consisting of granulocytes, in all stages of differentiation.