Murine M2-10B4 and SL/SL cell lines differentially affect the balance between CD34+ cell expansion and maturation

The ability of bone marrow stroma to modulate hematopoietic progenitor cell expansion is of considerable interest for gene transfer strategies and transplantation of limited stem cell numbers. We compared the capacity of 2 murine stromal cell lines to affect the balance between maturation and proliferation of human CD34+ cells in short-term expansion cultures. In 7-day serum-free cultures, cytokine-induced amplification of granulocyte-macrophage colony-forming cells (CFC-GM), erythroid burst-forming units (BFU-E), and total cells was significantly increased by the presence of genetically engineered Sl/Sl and M2-10B4 stromal cells in a 1:1 ratio (Sl/M2 cells) compared with stroma-free cultures (P < .05). Sl/M2 cultures generated 21-fold more mature CD15+ cells than stroma-free cultures, without further amplifying the number of CD34+ cells. The addition of serum led to a further increase of CFC-GM, total cells, and CD15+ cells, whereas BFU-E were no longer maintained. Pure Sl/Sl stromal layers were likewise superior to stroma-free cultures in expansion of CD34+ cells and total cells when serum was present. However, the differentiation of CD34+ cells was less pronounced in Sl/Sl cultures compared with Sl/M2 layers, as demonstrated by a lower content of CD15+ cells. Neutralization experiments revealed differential contributions of Flt3 ligand and thrombopoietin to the support of total cell and CFC expansion by Sl/M2 and Sl/Sl stromal feeders.