Synergistic Interaction between Notch ligand Delta-1 and IL-6/Soluble IL-6 Receptor Fusion Protein in the Generation of BFU-E from Primitive Hematopoietic Progenitors.

We have previously reported that Notch ligand Delta-1 may enhance the generation of NOD/SCID-repopulating hematopoietic stem cells and thymus-repopulating T cell precursors from cord blood [CB] CD34+CD38- cells. A complex of IL-6/soluble IL-6 receptor is shown to induce the expansion and proliferation of primitive hematopoietic progenitors that express gp130 but not the IL-6 receptor α chain, in mobilized peripheral blood (MPB) as well as in CB. In this study, we explored the interaction between Delta-1 and IL-6/soluble IL-6 receptor fusion protein [FP] in the generation of hematopoietic progenitors from MPB- and CB-derived primitive hematopoietic progenitors. MPB CD34+ Thy-1+ cells were cultured in serum-free medium with SCF, flt-3 ligand, TPO, and IL-3 [4GF], 4GF plus Delta-1, 4GF plus FP, and 4GF plus FP plus Delta-1. Delta-1 was used after immobilized to the culture plates. Freshly isolated cells and cultured cells were assessed for colony-forming ability by replating cells into semisolid medium containing SCF, flt-3 ligand, TPO, IL-3, IL-6, G-CSF, GM-CSF, and EPO. Colonies were counted at day 14. The numbers of BFU-E, CFU-Mix, and CFU-GM were 37-fold, 18-fold, and 135-fold increased, respectively, in cultures with 4GF plus FP, as compared with those in freshly isolated cells. The addition of both Delta-1 and FP to cultures resulted in 216-fold, 22-fold, and 132-fold increases in the numbers of BFU-E, CFU-Mix, and CFU-GM, respectively, relative to freshly isolated cells. Delta-1 did not affect the generation of colony-forming cells in cultures without FP. Thus, Delta-1 and FP synergistically enhanced the generation of BFU-E from primitive hematopoietic progenitors in MPB. In the cultures of CB CD34+CD38- cells with SCF, flt-3 ligand, TPO [3GF], 3GF plus Delta-1, 3GF plus FP, and 3GF plus FP plus Delta-1, the synergistic enhancement by Delta-1 and FP was observed in the generation of BFU-E and CFU-Mix. These data suggest a novel role for interaction between Notch and gp130 signalings in the generation of erythroid progenitors from primitive hematopoietic progenitors.