In one aspect the present invention is concerned with a method of cell culture, comprising the steps of (i) obtaining a stem or progenitor cell sample, (ii) culturing the stem or progenitor cell sample in media and under closed conditions appropriate to cause proliferation or differentiation of the stem or progenitor cells, wherein the media comprises a vEPO protein variant, (iii) purifying the stem or progenitor cells ex vivo. The invention relates to a method of increasing the number and survival of stem and progenitor cells in vitro and in vivo using a vEPO protein variant. The invention also relates to improved differentiation of stem and progenitor cells in vitro and in vivo using a vEPO protein variant.
