Effect of erythroid differentiation factor on maintenance of human hematopoietic cells in co-cultures with allogenic stromal cells.

The effect of erythroid differentiation factor (EDF) on the maintenance of human hematopoietic progenitors in a microenvironment was examined by co-culture of adherent- and E rosette-depleted mononuclear cells from the bone marrow (BM) or peripheral blood (PB) with allogenic stromal cells. EDF had no effect on colony formation of erythroid burst-forming units (BFU-E) from the BM cultured without a stromal layer. The number of BFU-E cultured with the stromal layer was decreased less in the presence of EDF than in its absence. This activity of EDF was also observed when the mononuclear cells were separated from the stromal layer by a filter membrane. These data suggest that EDF facilitates maintenance of the number of BFU-E through a humoral factor(s) secreted by the stromal layer. The number of BM erythroid colony-forming units (CFU-E) was decreased on addition of EDF, which promotes differentiation of CFU-E. The number of PB CFU-E was increased irrespective of the presence or absence of EDF over 2 weeks, suggesting that BFU-E, which are more abundant in PB than in BM, differentiate to supply CFU-E. However, the addition of EDF resulted in less increase of PB CFU-E, indicating that it inhibited the proliferation of CFU-E progenitors to suppress colony formation. On the other hand, CFU-GM was consistently decreased by addition of EDF to this culture system. These data indicate that EDF acts as a commitment factor and/or a promoter of erythroid progenitors in a hematopoietic microenvironment.