Abstract: The protein NM23 is disclosed as an agent for the maintenance of undifferentiated biological cells in culture. The NM23 protein may act as a survival factor for such cultured cells, or to prevent the differentiation and maturation of the cultured cells. The use of NM23 protein is applicable to culture of stem and/or progenitor cells, and particularly to such cells cultured and adapted for therapeutic use. The invention provides methods, media and media supplements for use in the culture of biological cells, and further provides methods of preparing biological cells for therapeutic use, as well as methods of therapy utilising biological cells and medicaments comprising biological cells adapted for therapeutic use.