Regulation of the proliferative potential of cord blood long-term culture-initiating cells (LTC-IC) by different stromal cell lines: implications forLTC-IC measurement

Background and Objective. Long-term culture-initiating cells (LTC-IC) are t he best available approximation to an in vitro assay of stem cells in human s although they still represent a heterogeneous population in terms of prol iferative capacity and sensitivity to different growth factors. Human umbil ical cord blood (CB) is rich in hemopoietic progenitor cells, as measured b y clonogenic assays and contains stem cells capable of reconstituting the m arrow after ablation in clinical transplantation. We evaluated the influenc e of culture conditions on the in vitro behavior of LTC-IC from On. Design and Methods. LTC-IC were evaluated in longterm cultures, comparing t wo types of murine stromal cell lines: M2-10B4 and M2-10B4 transfected with cDNAs for human G-CSF and IL-3. Results. Two and five fold higher numbers of terminally differentiated cell s were produced during nine weeks of culture of On mononuclear or CD34(+) c ells respectively, in cultures containing a M2-10B4 IL-3 G-CSF cell line co mpared to cultures containing the parental cell line. Likewise, a higher nu mber of colony-forming cells (CFC) were detected in the supernatant of cult ures with the transfected cell line. In contrast, the number of CFC generat ed within the stromal layer, after 5 or 9 weeks of culture, was significant ly higher in cultures on M2-10B4 cells than those on M2-10B4 IL-3 G-CSF. Interpretation and Conclusions. Our results show that the proliferative cap acity of CB LTC-IC can be strongly Influenced by culture conditions and tha t the frequency of LTC-IC estimated using these cell lines as stromal suppo rt is not identical. (C) 1998, Ferrata Storti Foundation.