Purified recombinant (r) macrophage inflammatory proteins (MIPs) 1 alpha, 1 beta, and 2 were assessed for effects on murine (mu) and human (hu) marrow colony-forming unit-granulocyte-macrophage (CFU-GM) and burst-forming unit-erythroid (BFU-E) colonies. Recombinant MIP-1 alpha, -1 beta, and -2 enhanced muCFU-GM colonies above that stimulated with 10 to 100 U natural mu macrophage-colony-stimulating factor (M-CSF) or rmuGM-CSF, with enhancement seen on huCFU-GM colony formation stimulated with suboptimal rhuM-CSF or rhuGM-CSF; effects were neutralized by respective MIP-specific antibodies. Macrophage inflammatory proteins had no effects on mu or huBFU-E colonies stimulated with erythropoietin (Epo). However, natural MIP-1 and rMIP-1 alpha, but not rMIP-1 beta or -2, suppressed muCFU-GM stimulated with pokeweed mitogen spleen-conditioned medium (PWMSCM), huCFU-GM stimulated with optimal rhuGM-CSF plus rhu interleukin-3 (IL-3), muBFU- E and multipotential progenitors (CFU-GEMM) stimulated with Epo plus PWMSCM, and huBFU-E and CFU-GEMM stimulated with Epo plus rhuIL-3 or rhuGM-CSF. The suppressive effects of natural MIP-1 and rMIP-1 alpha were also apparent on a population of BFU-E, CFU-GEMM, and CFU-GM present in cell-sorted fractions of human bone marrow (CD34 HLA-DR+) highly enriched for progenitors with cloning efficiencies of 42% to 75%. These results, along with our previous studies, suggest that MIP-1 alpha, -1 beta, and -2 may have direct myelopoietic enhancing activity for mature progenitors, while MIP-1 alpha may have direct suppressing activity for more immature progenitors.
The replating capability of human umbilical cord blood (CB) multipotential (CFU-GEMM) progenitors was assessed in vitro as an estimate of self-renewal using erythropoietin (Epo), steel factor (SLF), and either fetal bovine serum (FBS) or CB plasma. This study found a much higher replating efficiency for CB CFU-GEMM than previously reported, in terms of the percentage of colonies that could be replated, the number of secondary colonies per replated primary colony, and the size of secondary colonies. Moreover, the majority of secondary colonies were CFU-GEMM-derived. Although the percentages of bone marrow CFU-GEMM that replate was similar to that for CB CFU-GEMM and the sizes of secondary bone marrow and CB CFU-GEMM were also similar, replated CB CFU-GEMM gave rise to far greater numbers of secondary colonies. No tertiary colonies were observed when secondary CFU-GEMM were replated. Detection of extensive secondary replating potential was enhanced by the addition of CB plasma to the cultures. This activity was not found in either adult blood (PB) plasma, umbilical cord vein endothelial cell-conditioned medium (ECCM), FBS plus ECCM, or FBS plus the combination of interleukin-1 (IL-1), IL-3, IL-6, IL-11, granulocyte colony-stimulating factor, and granulocyte- macrophage colony-stimulating factor. Whether the CB plasma-enhancing activity for CFU-GEMM replating capacity is attributable to a novel factor or factors, or represents effects of other known cytokines, alone or in combination, remains to be determined. Of particular relevance, these studies suggest that human CFU-GEMM have some degree of stemness and perhaps should be classified as a subset of stem cells.
The replating capability of human multipotential (colony-forming unit- granulocyte-erythrocyte-macrophage-megakaryocyte [CFU-GEMM]) and erythroid (burst-forming unit-erythroid [BFU-E]) progenitors was assessed in vitro as a potential measure of self-renewal using purified, recombinant (r) human (hu) or murine (mu) mast cell growth factor (MGF), a ligand for the c-kit proto-oncogene receptor. Primary cultures of human umbilical cord blood or adult human bone marrow cells were initiated in methylcellulose with erythropoietin (Epo) alone or in combination with rhu interleukin-3 (IL-3) or MGF. Individual day 14 to 18 CFU-GEMM or BFU-E colonies were removed from primary cultures and reseeded into secondary methylcellulose cultures containing a combination of Epo, MGF, and rhu granulocyte-macrophage colony- stimulating factor (GM-CSF). The data showed a high replating efficiency of cord blood and bone marrow CFU-GEMM in response to Epo + MGF in terms of the percentage of colonies that could be replated and the number of secondary colonies formed per replated primary colony. The average number of hematopoietic colonies and clusters apparent from replated cultures of cord blood or bone marrow CFU-GEMM stimulated by Epo + MGF was greater than with Epo + rhuIL-3 or Epo alone. Replated cord blood CFU-GEMM gave rise to CFU-GEMM, BFU-E, and GM colony-forming units (CFU-GM) in secondary cultures. Replated bone marrow CFU-GEMM gave rise mainly to CFU-GM in secondary cultures. A more limited capacity for replating of cord blood and bone marrow BFU-E was observed. These studies show that CFU-GEMM responding to MGF have an enhanced replating potential, which may be promoted by MGF. These studies also support the concept that MGF acts on more primitive progenitors than IL-3.
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