Stem cell cultures Mouse embryonic fibroblast cells: Mitotically inactivated by irradiation or mitomycin C ES cells: Medium with 15% FCS 1000u/mILIF CO2:7-10% LiF (leukaemia inhibitory factor): Maintains stem cells in an undifferentiated stateStem cell cultures Mouse Embryonic Fibroblast Cells: Mitotically inactivated by irradiation or mitomycin C ES cells: Medium with 15% FCS 1000u/ml LIF CO2 : 7-10% LIF (leukaemia inhibitory factor) ： Maintains stem cells in an undifferentiated state