THE HIGH-PROLIFERATIVE-POTENTIAL MEGAKARYOCYTE MIXED (HPP-MEG-MIX) CELL - A TRILINEAGE MURINE HEMATOPOIETIC PROGENITOR WITH MULTIPLE GROWTH-FACTOR RESPONSIVENESS

Megakaryocyte progenitors are notable for their response to synergisti c cytokine combinations and apparently early position in the hematopoi etic differentiation pathway. Although high-proliferative-potential mu rine megakaryocyte progenitors have been described, they have previous ly been primarily observed as unilineage colonies. We describe a subcl ass of agar-based high-proliferative-potential colony forming cells (H PP-CFC) derived from populations enriched for early hematopoietic prog enitors which, when stimulated with the combination of CSF-1, G-CSF, G M-CSF, IL-1 alpha, IL-3, and SCF, produces colonies with trilineage po tential for macrophages, granulocytes, and megakaryocytes. The high pr oliferative potential megakaryocyte mixed (HPP-Meg-Mix) colony-forming cell is defined as a cell meeting traditional criteria for HPP-CFC bu t additionally containing 20 or more megakaryocytes per colony. The co mbination of high-proliferative-potential, multilineage differentiatio n, and megakaryocytic lineage capacity suggests that the HPP-Meg-Mix m arks a very early hematopoietic progenitor cell.