DIFFUSIBLE FACTORS FROM THE MURINE CELL-LINE M2-10B4 SUPPORT HUMAN IN-VITRO HEMATOPOIESIS

Significantly more primitive human hematopoietic progenitors are maint ained and differentiate when cultured separately from the stroma by a microporous membrane (''stroma-noncontact'' cultures) than when cultur ed in direct contact with stromal layers (''stroma-contact'' cultures) . This suggests that diffusible stroma-derived factors may be sufficie nt for the in vitro induction of progenitor proliferation and differen tiation. To further characterize stroma-derived factors that maintain long-term bone marrow culture initiating cells (LTBMC-IC), we compared the hematopoietic supportive capacity of human marrow stroma with tha t of the murine marrow stroma-derived fibroblast cell line M2-10B4 as well as two embryonic fibroblast cell lines, the human FHS-173-WE and the murine NIH-3T3 cell lines. We demonstrate that LTBMC-IC, present i n human CD34(+)/HLA-DR(-) (DR(-) cells), are maintained equally well a nd give rise to similar numbers of committed progenitors, that is-colo ny-forming cells (CFC)-when cultured in contact with human marrow stro ma or any cell line feeder (stroma-contact cultures). LTBMC-IC, cultur ed in marrow stroma or M2-10B4 stroma-noncontact cultures, were mainta ined significantly better and gave rise to significantly more CFC than when cultured in human marrow stroma or M2-10B4 contact cultures. How ever, LTBMC-IC maintenance and differentiation in FHS-173-WE or NIH-3T 3 noncontact cultures was significantly less than in human marrow stro ma or M2-10B4 noncontact cultures. These studies indicate that systema tic comparison of diffusible growth stimulatory factors in conditioned media from M2-10B4 cells and FHS-173-WE may lead to the characterizat ion of growth regulatory factors required for in vitro maintenance and differentiation of human primitive LTBMC-IC. Since diffusible factors from the M2-10B4 cell line can support human hematopoiesis, our obser vations may also have important implications for in vitro stem cell ex pansion protocols.