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 synergistic cytokine combinations and apparently early position in the hematopoietic differentiation pathway. Although high-proliferative-potential murine megakaryocyte progenitors have been described, they have previously been primarily observed as unilineage colonies. We describe a subclass of agar-based high-proliferative-potential colony forming cells (HPP-CFC) derived from populations enriched for early hematopoietic progenitors which, when stimulated with the combination of CSF-1, G-CSF, GM-CSF, IL-1 alpha, IL-3 and SCF, produces colonies with trilineage potential for macrophages, granulocytes, and megakaryocytes. The high proliferative potential megakaryocyte mixed (HPP-Meg-Mix) colony-forming cell is defined as a cell meeting traditional criteria for HPP-CFC but additionally containing 20 or more megakaryocytes per colony. The combination of high-proliferative-potential, multilineage differentiation, and megakaryocytic lineage capacity suggests that the HPP-Meg-Mix marks a very early hematopoietic progenitor cell.

Detection of a human CFC with a high proliferative potential.

Colony forming cells (CFC) with high proliferative potential have been detected in nutrient agar cultures of human bone marrow cells containing recombinant human interleukin-3 (IL-3) and granulocyte macrophage colony stimulating factor (GM-CSF). These CFC were detected by the formation of large colonies with diameters greater than 0.5 mm and containing approximately 50,000 cells after 28 days incubation. The incidence of these CFC was only two in 100,000 normal bone marrow cells; however, bone marrow from patients treated with 5-fluorouracil contained up to sevenfold higher numbers of these CFC. The characteristics of these CFC, multifactor-responsive progenitors with high proliferative potential, requiring a prolonged growth period in culture and showing a relative preservation in marrow from individuals pretreated with 5-fluorouracil, are consistent with a human cell type equivalent to the primitive murine progenitor termed HPP-CFC.

Synergistic interactions between hematopoietic growth factors as detected by in vitro mouse bone marrow colony formation.

We have investigated the proliferative effects of several combinations of hematopoietic growth factors in agar cultures of murine bone marrow cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) synergized with granulocyte colony-stimulating factor (G-CSF), while G-CSF also synergized with macrophage colony-stimulating factor (CSF-1) and interleukin 3 (IL3), resulting in colony numbers greater than the sum of the numbers of colonies formed with each factor alone. In addition, these combinations resulted in increased colony sizes, with the formation of day-14 colonies with diameters greater than 0.5 mm. The combination of GM-CSF plus IL3 showed an increase in numbers of colonies that approximated the sum of that seen with each factor alone, however, the size of the colonies was increased with a number of day-14 and day-21 colonies having diameters greater than 0.5 mm. These data add to the list of hematopoietic factors known to synergistically stimulate myeloid progenitors and suggest that some of these interactions may be on early progenitor cells with high proliferative potentials.