Tumor necrosis factor-alpha (TNF-alpha) potently enhances in vitro macrophage production from primitive murine hematopoietic progenitor cells in combination with stem cell factor and interleukin-7: novel stimulatory role of p55 TNF receptors

Tumor necrosis factor-alpha (TNF-alpha) is a bifunctional regulator of hematopoiesis, and its cellular responses are mediated by two distinct cell surface receptors. TNF-alpha generally inhibits the growth of primitive murine hematopoietic progenitor cells (Lin-Scal+) in response to multiple cytokine combinations, and the p75 TNF receptor is essential in signaling such inhibition. In the present study we show the reverse phenomenon in that TNF-alpha on the same progenitor cell population in combination with stem cell factor (SCF) and interleukin-7 (IL-7) through the p55 TNF receptor can recruit additional progenitors to proliferate. In contrast, TGF-beta 1, another bifunctional regulator of hematopoietic progenitor cell growth, completely blocked SCF plus IL-7-induced proliferation. TNF-alpha increased the number of responding progenitors, as well as the size of the colonies formed. The synergistic effects of TNF-alpha were seen at the single cell level, suggesting that its effects are directly mediated. Finally, whereas SCF plus IL-7 promoted primarily granulopoiesis, the addition of TNF-alpha switched the differentiation toward the production of almost exclusively macrophages.

Stem cell factor and interleukin-7 synergize to enhance early myelopoiesis in vitro

Interleukin-7 (IL-7) has been shown to be a critical factor in murine lymphoid development. It stimulates pre-B cells to divide in the absence of stroma cells and it is an important growth regulator of immature and mature T cells. IL-7 has been shown to synergize with stem cell factor (SCF) to provide a potent growth stimulus for pre-B cells. However, the combined effects of IL-7 and SCF on murine primitive hematopoietic cells in vitro have not been established. In the present study, the effects of recombinant rat (rr) SCF and recombinant human (rh) IL-7 on primitive murine bone marrow progenitors (Lin-Sca1+) were investigated in single-cell cloning experiments. rhIL-7 alone had no proliferative effect on Lin-Sca1+ cells, but in a dose-dependent manner directly enhanced rrSCF-induced colony formation, with an average increase in colony numbers of 2.7-fold. Interestingly, the cells formed in response to SCF and IL-7 were predominantly mature granulocytes. Thus, SCF and IL-7 synergize to stimulate early myelopoiesis in vitro.

In vivo synergy between recombinant human stem cell factor and recombinant human granulocyte colony-stimulating factor in baboons enhanced circulation of progenitor cells

Recombinant human stem cell factor (rhSCF) and recombinant human granulocyte colony-stimulating factor (rhG-CSF) are synergistic in vitro in stimulating the proliferation of hematopoietic progenitor cells and their precursors. We examined the in vivo synergy of rhSCF with rhG-CSF for stimulating hematopoiesis in vivo in baboons. Administration of low-dose (LD) rhSCF (25 micrograms/kg) alone did not stimulate changes in circulating WBCs. In comparison, administration of LD rhSCF in combination with rhG-CSF at 10 micrograms/kg or 100 micrograms/kg stimulated increases in circulating WBCs of multiple types up to twofold higher than was stimulated by administration of the same dose of rhG-CSF alone. When the dose of rhG-CSF is increased to 250 micrograms/kg, the administration of LD rhSCF does not further increase the circulating WBC counts. Administration of LD rhSCF in combination with rhG-CSF also stimulated increased circulation of hematopoietic progenitors. LD rhSCF alone stimulated less of an increase in circulating progenitors, per milliliter of blood, than did administration of rhG-CSF alone at 100 micrograms/kg. Baboons administered LD rhSCF together with rhG-CSF at 10, 100, or 250 micrograms/kg had 3.5- to 16-fold higher numbers per milliliter of blood of progenitors cells of multiple types, including colony-forming units granulocyte/macrophage (CFU-GM), burst-forming unit-erythroid (BFU-E), and colony-forming and burst-forming units-megakaryocyte (CFU-MK and BFU-MK) compared with animals given the same dose of rhG-CSF without rhSCF, regardless of the rhG-CSF dose. The increased circulation of progenitor cells stimulated by the combination of rhSCF plus rhG-CSF was not necessarily directly related to the increase in WBCs, as this effect on peripheral blood progenitors was observed even at an rhG-CSF dose of 250 micrograms/kg, where coadministration of LD rhSCF did not further increase WBC counts. Administration of very-low-dose rhSCF (2.5 micrograms/kg) with rhG-CSF, 10 micrograms/kg, did not stimulate increases in circulating WBCs, but did increase the number of megakaryocyte progenitor cells in blood compared with rhG-CSF alone. LD rhSCF administered alone for 7 days before rhG-CSF did not result in increased levels of circulating WBCs or progenitors compared with rhG-CSF alone. Thus, the synergistic effects of rhSCF with rhG-CSF were both dose- and time-dependent. The doses of rhSCF used in these studies have been tolerated in vivo in humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulation of hematopoiesis in vivo by stem cell factor

The ligand for c-kit, known as stem cell factor, mast cell growth factor, or kit ligand, plays a central role in normal hematopoietic stem cell, melanocyte, and gametocyte development and function during embryogenesis and in adult life. In vitro, stem cell factor promotes the survival of hematopoietic progenitors and enhances their proliferation in response to specific growth factors. Administration of recombinant soluble stem cell factor to rodents, dogs, and baboons produces a broad array of effects on hematopoiesis, though not all lineages are equally stimulated. At doses of more than 100 micrograms/kg/d stem cell factor stimulates neutrophilia, lymphocytosis, basophilia, and reticulocytosis and increases mast cells in multiple tissues. In vivo mast cell activation can occur. Marrow cellularity is increased and progenitor cells are increased in marrow, spleen, and blood, and marrow-repopulating cells are increased in the circulation of stem cell factor-treated animals. Stem cell factor synergizes with other hematopoietic growth factors in vivo. Low-dose stem cell factor, 25 micrograms/kg/d, that does not elicit a detectable biological response, enhances the effects of granulocyte colony-stimulating factor in vivo, increasing the neutrophilia and circulation of progenitor and marrow-repopulating cells above that which is achieved with either factor alone. In phase I human trials, dose-limiting toxicities, related to mast cell activation, were reached at 25 to 50 micrograms/kg/d of recombinant human stem cell factor. At these doses, progenitor and long-term culture-initiating cells are increased in marrow and increases in circulating levels of progenitor cells of multiple types are observed. Phase I-II trials of low-dose stem cell factor in combination with granulocyte colony-stimulating factor show that the combination increases the circulation of CD34+ cells and colony-forming progenitor cells. Further studies are needed to determine the therapeutic role of stem cell factor and its effects on expansion and maintenance of hematopoietic stem cells in vivo.

The role of stem cell factor in mobilization of peripheral blood progenitor cells: synergy with G-CSF

The use of cytokine mobilized peripheral blood progenitor cells (PBPC) in transplantation following chemotherapy has led to enhanced engraftment. Granulocyte-colony stimulating factor (G-CSF) has been shown in a number of clinical studies to be an effective mobilizer of PBPC. Preclinical data in mice and primates have demonstrated a potential role for the use of stem cell factor (SCF) in mobilization of PBPC. In the studies presented here, low doses of SCF are shown to synergize with optimal doses of G-CSF to enhance the number and quality of PBPC compared to G-CSF alone. Phase I studies using r-metHuSCF demonstrated mast cell-related dose limiting effects. The data presented here have led to Phase I/II studies to evaluate the potential use of low doses of SCF in combination with G-CSF for mobilization of PBPC.

Recombinant rat stem cell factor synergizes with recombinant human granulocyte colony-stimulating factor in vivo in mice to mobilize peripheral blood progenitor cells that have enhanced repopulating potential

Splenectomized mice treated for 7 days with pegylated recombinant rat stem cell factor (rrSCF-PEG) showed a dose-dependent increase in peripheral blood progenitor cells (PBPC) that have enhanced in vivo repopulating potential. A dose of rrSCF-PEG at 25 micrograms/kg/d for 7 days produced no significant increase in PBPC. However, when this dose of rrSCF-PEG was combined with an optimal dose of recombinant human granulocyte colony-stimulating factor (rhG-CSF; 200 micrograms/kg/d), a synergistic increase in PBPC was observed. Compared with treatment with rhG-CSF alone, the combination of rrSCF-PEG plus rhG-CSF resulted in a synergistic increase in peripheral white blood cells, in the incidence and absolute numbers of PBPC, and in the incidence and absolute numbers of circulating cells with in vivo repopulating potential. These data suggest that low doses of SCF, which would have minimal, if any, effects in vivo, can synergize with optimal doses of rhG-CSF to enhance the mobilization of PBPC stimulated by rhG-CSF alone.

Stem cell factor enhances in vivo effects of granulocyte colony stimulating factor for stimulating mobilization of peripheral blood progenitor cells

Granulocyte colony stimulating factor (G-CSF) has been shown to increase peripheral blood progenitor cells (PBPC) which have an enhanced engraftment potential in autologous transplantation compared with bone marrow cells. The data presented in this study demonstrate the ability of low doses of stem cell factor (SCF) to synergize with G-CSF to enhance the mobilization of PBPC, compared with G-CSF alone, in both mouse and primate models. In the mouse model the combination of SCF plus G-CSF stimulated an absolute increase in cells with in vivo repopulating potential. These studies suggest a possible role for SCF plus G-CSF in the clinical setting for increased mobilization of PBPC, giving rise to increased phoresis yields and enhanced engraftment for support of high-dose chemotherapy.

Accelerated establishment of murine long-term bone marrow cultures by addition of stem cell factor

The effect of stem cell factor (SCF) on the establishment of hematopoietic activity in murine long-term bone marrow cultures (LTBMC) was investigated by addition of SCF to (a) normal LTBMC from the onset of culture and (b) pre-established irradiated bone marrow stroma inoculated with lineage negative (Lin-) primitive hematopoietic progenitor cells enriched on the basis of low rhodamine-123 uptake (Rh-dull). Hematopoietic activity was established more rapidly in LTBMC grown in the presence of SCF (70 ng/mL), and the typical decline in cellularity and progenitor cell content during the first weeks of culture was not observed. SCF also promoted the rapid expansion of progenitor cells derived from Lin-, Rh-dull primitive hematopoietic cells inoculated onto irradiated preestablished bone marrow stroma. The data demonstrate that exogenous SCF augments hematopoietic activity in LTBMC, and that the levels of endogenous SCF elaborated in LTBMC may be suboptimal for expansion of hematopoietic cells.

Radioprotection of mice by recombinant rat stem cell factor

Treatment with recombinant rat stem cell factor (rSCF) protects mice from the lethal effects of irradiation. Mice treated with a single dose of rSCF prior to irradiation of up to 1150 rads [given as a split dose (1 rad = 0.01 Gy)] resulted in > 80% long-term survival, whereas a single injection given after the last dose of irradiation was not radioprotective. The combination of pre- and posttreatment (-20 h, -2 h, and +4 h) with rSCF resulted in 100% survival of otherwise lethally irradiated mice. Using this optimum schedule of rSCF administration, a radioprotective factor of 1.3-1.35 was achieved. The major cause of death in the control animals was massive bacteremia consisting of enteric organisms. The rSCF-treated animals had a much lower frequency of septicemia, due primarily to a rapid hematopoietic recovery of bone marrow function not evident in control animals.

Synergism of hematopoietic colony-stimulating factors

In this article, I have attempted to summarize many studies that clearly demonstrate a major role of combinations of growth factors in the development of blood cells. Clearly, the most striking effects are seen on primitive cells that do not reach full proliferative potential when stimulated by single factors. The treatment of patients with combination growth factor therapy has high potential in the areas of chemotherapy and bone marrow transplantation. In these patients, more rapid regeneration of primitive cells will lead to more rapid and effective recovery. Also, combinations of factors are essential for optimal retrovirus-mediated gene transfer in repopulating stem cells for use in gene replacement therapy. Stem cell factor has been shown to protect burst-forming units-erythroid from the toxic effects of zidovudine (AZT). This is an example where combinations of factors may enable patients to continue treatment regimens for extended periods. The side effects resulting from some factors may be overcome using combination therapy. When combinations of factors are given, greatly reduced doses of each factor can produce results similar to those seen with high doses of a single factor.

Transforming growth factor β inhibits the action of stem cell factor on mouse and human hematopoietic progenitors

In agar culture of post 5-fluorouracil mouse bone marrow cells (FUBM), recombinant rat stem cell factor (rrSCF) synergizes with granulocyte colony-stimulating factor (G-CSF), interleukin-3 (IL-3) or interleukin-6 (IL-6) to stimulate primitive progenitor cells (HPP-CFCs). The addition of recombinant human transforming growth factor beta (rhTGF-beta) to cultures of FUBM containing rrSCF plus rhG-CSF, rrSCF plus recombinant murine (rm)IL-3, or rrSCF plus rhIL-6 resulted in 100% inhibition of colony formation. Highly enriched populations of primitive bone marrow cells were obtained by isolating lineage negative (Lin-), Sca-1-positive (Sca-1+) cells from normal mouse bone marrow. RhTGF-beta inhibited 90% of colony formation stimulated by rrSCF plus rmIL-3 in agar culture of the Sca-1+ cells. RhTGF-beta also inhibited colony formation in agar culture of post FU human bone marrow cells. The synergistic increase in colony formation obtained with recombinant human SCF (rhSCF) plus rhGM-CSF and rhSCF plus rhIL-3 was inhibited by rhTGF-beta (approx. 60% and 87% inhibition, respectively). RhTGF-beta also totally inhibited the erythroid colony formation stimulated by rhSCF plus recombinant human erythropoietin (rhEpo). These data demonstrate that TGF-beta inhibits SCF-stimulated colony formation of mouse and human BM. This inhibition on progenitor cells appears to be a direct action of TGF-beta and is consistent with the target cells of SCF being more primitive progenitors than the CFCs stimulated by the CSFs alone.

Stem cell factor in combination with granulocyte colony-stimulating factor (CSF) or granulocyte-macrophage CSF synergistically increases granulopoiesis in vivo

Recombinant rat stem cell factor (rrSCF) and recombinant human granulocyte colony-stimulating factor (G-CSF) coinjected for 1 week in rats cause a synergistic increase in mature marrow neutrophils accompanied by a striking decrease in erythroid and lymphoid marrow elements. The spleens of the same rats show increased granulopoiesis as well as increased erythropoiesis as compared with the spleens of rats treated with either growth factor alone. Splenic extramedullary erythropoiesis may act to compensate for the decrease in marrow erythropoiesis. The coinjection of rrSCF and G-CSF causes an increase in marrow mast cells at the end of 1 week, but the increase is much less than in rrSCF-alone-treated rats. The combination of rrSCF and G-CSF increases the rate of release of marrow neutrophils into the circulation and causes a dramatic synergistic peripheral neutrophilia, beginning especially after 4 days of treatment. Colony-forming assays of all experimental groups showed a synergistic increase in colony-forming unit granulocyte-macrophage (CFU-GM) in the marrow, but not in peripheral blood, after coincubation with SCF plus granulocyte-macrophage CSF (GM-CSF) as opposed to GM-CSF alone, showing anatomic compartmentalization between a more primitive marrow CFU-GM subset and a more mature peripheral blood CFU-GM subset. In vivo daily administration of SCF plus GM-CSF results in a synergistic increase in marrow neutrophils, but not the striking synergistic increase in circulating neutrophils that is observed with SCF plus G-CSF.

The role of recombinant stem cell factor in early B cell development. Synergistic interaction with IL-7

The cDNA for stem cell factor was recently isolated from Buffalo rat liver cells (BRL-3A) and recombinant rat stem cell factor produced from Escherichia coli (rrSCF164). rrSCF164 synergizes with rhIL-7 to stimulate pre-B clonal growth in agar culture of mouse bone marrow cells, and in this study we have characterized the role of rrSCF164 in B cell development. The combination of rrSCF164 plus rhIL-7 stimulated increased colony numbers compared with the sum of colonies stimulated by rrSCF164 and rhIL-7 alone. Also, increased cell proliferation per colony was stimulated by the combination of rrSCF164 plus rhIL-7 compared with rhIL-7 or rrSCF164 alone. The colonies formed with rrSCF164 plus rhIL-7 and rhIL-7 alone contained exclusively pre-B cells, which expressed B220 Ag and cytoplasmic mu-chain, but were negative for surface Ig expression. Morphological examination of the cells in the colonies showed blast-like characteristics. rrSCF164 alone and in combination with rhIL-7 stimulated generation of B220+ cells in liquid culture of B220- cells, whereas rhIL-7 alone had no stimulatory effect on B220- cells. Both stem cell factor mRNA and bioactivity were detected in a mouse bone marrow-derived stromal cell line, termed OZ-11. We propose that stem cell factor is a stromal-derived factor that synergizes with IL-7 to stimulate the proliferation and differentiation of pro-B cells to pre-B cells, which become responsive to IL-7 alone.

The role of recombinant stem cell factor in early B cell development. Synergistic interaction with IL-7

The cDNA for stem cell factor was recently isolated from Buffalo rat liver cells (BRL-3A) and recombinant rat stem cell factor produced from Escherichia coli (rrSCF164). rrSCF164 synergizes with rhIL-7 to stimulate pre-B clonal growth in agar culture of mouse bone marrow cells, and in this study we have characterized the role of rrSCF164 in B cell development. The combination of rrSCF164 plus rhIL-7 stimulated increased colony numbers compared with the sum of colonies stimulated by rrSCF164 and rhIL-7 alone. Also, increased cell proliferation per colony was stimulated by the combination of rrSCF164 plus rhIL-7 compared with rhIL-7 or rrSCF164 alone. The colonies formed with rrSCF164 plus rhIL-7 and rhIL-7 alone contained exclusively pre-B cells, which expressed B220 Ag and cytoplasmic mu-chain, but were negative for surface Ig expression. Morphological examination of the cells in the colonies showed blast-like characteristics. rrSCF164 alone and in combination with rhIL-7 stimulated generation of B220+ cells in liquid culture of B220- cells, whereas rhIL-7 alone had no stimulatory effect on B220- cells. Both stem cell factor mRNA and bioactivity were detected in a mouse bone marrow-derived stromal cell line, termed OZ-11. We propose that stem cell factor is a stromal-derived factor that synergizes with IL-7 to stimulate the proliferation and differentiation of pro-B cells to pre-B cells, which become responsive to IL-7 alone.

Recombinant human stem cell factor synergises with GM-CSF, G-CSF, IL-3 and epo to stimulate human progenitor cells of the myeloid and erythroid lineages

The cDNA for human stem cell factor (hSCF) has been cloned and expressed in mammalian and bacterial hosts and recombinant protein purified. We have examined the stimulatory effect of recombinant human SCF (rhSCF) on human bone marrow cells alone and in combination with recombinant human colony stimulating factors (CSFs) and erythropoietin (rhEpo). RhSCF alone resulted in no significant colony formation, however, in the presence of rhGM-CSF, rhG-CSF or rhIL-3, rhSCF stimulated a synergistic increase in colony numbers. In addition, increased colony size was stimulated by all combinations. The morphology of cells in the colonies obtained with the CSFs plus rhSCF was identical to the morphology obtained with rhGM-CSF, rhG-CSF or rhIL-3 alone. RhEpo also synergised with rhSCF to stimulate the formation of large compact hemoglobinized colonies which stained positive for spectrin and transferrin receptor and had a morphological appearance consistent with normoblasts. RhSCF stimulation of low density non-adherent, antibody depleted, CD34+ cells suggests that rhSCF directly stimulates progenitor cells capable of myeloid and erythroid differentiation.

Multifactor stimulation of megakaryocytopoiesis: effects of interleukin 6

We have previously demonstrated that interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and granulocyte colony-stimulating factor (G-CSF) stimulate various aspects of megakaryocytopoiesis. We have investigated the capacity of interleukin 6 (IL-6) to stimulate megakaryocyte colony formation from both normal Balb/C marrow and light-density marrow extensively depleted of adherent, pre-B, B and T cells. Human recombinant IL-6 (167 ng/ml) stimulated megakaryocyte colony formation from normal marrow (8.6 +/- 1 megakaryocyte colony-forming units [CFU-meg]/10(5) cells) as compared to control (1.5 +/- 4 CFU-meg/10(5) cells) in 16 determinations (p less than 0.01). IL-6 (167 ng/ml) also stimulated CFU-meg formation from depleted marrow (control, 10.8 +/- 4 CFU-meg/10(5) cells versus IL-6, 68 +/- 19 CFU-meg/10(5) cells in 12 determinations, p less than 0.01). IL-6 synergistically augmented IL-3-induced colony formation (139% IL-3 control, 120% calculated IL-3 plus IL-6 control, n = 11, p less than 0.01) in normal marrow and showed an additive effect in depleted marrow (133% IL-3 control, p less than 0.01, 114% of IL-3 plus IL-6, value not significant [NS] at 0.05 level). Studies with recombinant murine IL-6 gave similar results. There was an increasing level of megakaryocyte colony-stimulating activity from G-CSF (16,667 U/ml, 2.47 +/- 0.6 CFU-meg/10(5) cells, n = 17), to IL-6 (167 ng/ml, 8.47 +/- 0.96 CFU-meg/10(5) cells, n = 19), to GM-CSF (52 U/ml, 23 +/- 4 CFU-meg/10(5) cells, n = 14), to IL-3 (167 U/ml, 48 +/- 5 CFU-meg/10(5) cells, n = 20) as compared to media-stimulated marrow (range 1.29-1.86 CFU-meg/10(5) cells). A similar hierarchy was seen with depleted marrow. Combinations of factors (including IL-3, GM-CSF, G-CSF, and IL-6) tested against normal unseparated murine marrow did not further augment CFU-meg numbers over IL-3 plus IL-6 but did increase colony size. These data suggest that IL-6 is an important megakaryocyte regulator, that at least four growth factors interact synergistically or additively to regulate megakaryocytopoiesis, and that combinations of growth factors, possibly in physical association, might be critical in stimulating megakaryocyte stem cells.

Identification, purification, and biological characterization of hematopoietic stem cell factor from buffalo rat liver--conditioned medium

We have identified a novel growth factor, stem cell factor (SCF), for primitive hematopoietic progenitors based on its activity on bone marrow cells derived from mice treated with 5-fluorouracil. The protein was isolated from the medium conditioned by Buffalo rat liver cells. It is heavily glycosylated, with both N-linked and O-linked carbohydrate. Amino acid sequence following removal of N-terminal pyroglutamate is presented. The protein has potent synergistic activities in semisolid bone marrow cultures in conjunction with colony-stimulating factors. It is also a growth factor for mast cells. In two companion papers, we present the sequences of partial SCF cDNAs, identify SCF as a c-kit ligand, and map the SCF gene to the Sl locus of the mouse.

Primary structure and functional expression of rat and human stem cell factor DNAs

Partial cDNA and genomic clones of rat stem cell factor (SCF) have been isolated. Using probes based on the rat sequence, partial and full-length cDNA and genomic clones of human SCF have been isolated. Based on the primary structure of the 164 amino acid protein purified from BRL-3A cells, truncated forms of the rat and human proteins have been expressed in E. coli and mammalian cells and have been shown to possess biological activity. SCF is able to augment the proliferation of both myeloid and lymphoid hematopoietic progenitors in bone marrow cultures. SCF exhibits potent synergistic activities in conjunction with colony-stimulating factors, resulting in increased colony numbers and colony size.

Further studies on growth factor production by the TC-1 stromal cell line: pre-B stimulating activity

Adherent murine stromal cells support long-term in vitro lymphopoiesis or myelopoiesis dependent on the culture conditions used. A cell line, TC-1, isolated from long-term liquid murine marrow cultures under conditions approaching those permissive for lymphoid growth, has been found to produce an activity that acts synergistically with interleukin-3 (IL-3) or colony-stimulating factor-1 (CSF-1) to stimulate in vitro myeloid colonies, but which has no intrinsic colony-stimulating activity. We report here the presence of multiple growth factors in conditioned medium (CM) from the TC-1 line, including granulocyte-macrophage colony-stimulating factor (GM-CSF) (bioassay with antibody blocking and messenger RNA [mRNA] analysis), granulocyte CSF (G-CSF) and IL-4 (factor-dependent cell line bioassay), and CSF-1 (radioimmunoassay, mRNA) along with a pre-B cell inducing activity, which appears separate from these CSFs and segregates with the myeloid synergizing activity through anion exchange, sizing, and Conconavalin A chromatography. Because these activities are not yet purified to homogeneity, their identity or lack of identity remains an open question. Assays of TC-1 CM or cellular mRNA analysis have given negative results for IL-1, IL-2, IL-3, IL-6, and IL-7, and IL-6 does not stimulate pre-B cells in this assay. However, IL-4 and G-CSF do stimulate in vitro induction of pre-B cells from pre-B and B-cell-depleted Balb/C marrow and are present in CM by selective cell line assay. A monoclonal antibody to IL-4 that inhibited its pre-B inducing activity did not inhibit pre-B inducing activity of TC-1 CM. These data suggest the existence of a unique synergizing and pre-B inducing factor(s) in TC-1 CM. Given the known capacity of subliminal levels of growth factors to act synergistically, an alternate possibility is that these biologic phenomena represent the actions of low concentrations of growth factors acting synergistically and possibly associated with some core protein.

Colony-forming cells with high proliferative potential (HPP-CFC)

Colony-forming cells with a high proliferative potential (HPP-CFC) have been defined by their ability to form large colonies in vitro (diameters greater than 0.5 mm and containing approximately 50,000 cells) in bone marrow cell cultures. The HPP-CFC have been characterized by: 1) a relative resistance to treatment in vivo with the cytotoxic drug 5-fluorouracil, 2) a high correlation with cells capable of repopulating the bone marrow of lethally irradiated mice, 3) their multipotential ability to generate cells of the macrophage, granulocyte, megakaryocyte and erythroid lineages, and 4) their multifactor responsiveness. The HPP-CFC have been described in both mouse and human bone marrow. These properties suggest that the HPP-CFC represent an important cell type in hematopoiesis and provide a model system, particularly in the human, for studying the properties of primitive progenitor cells in vitro.

Dissecting the hematopoietic microenvironment. VII. The production of an autostimulatory factor as well as a CSF by unstimulated murine marrow fibroblasts

Purified normal murine bone marrow-derived fibroblasts were shown to produce a factor that stimulates the in vitro growth of fibroblastic colony-forming unit (CFU-F) colonies. Conditioned medium from the purified fibroblasts (F-CM) also stimulated pure marrow fibroblasts themselves. Analysis of the F-CM detected the presence of macrophage colony-stimulating factor (M-CSF), and low levels of interleukin 1 (IL-1) and interleukin 6 (IL-6), but no detectable levels of interleukin 3 (IL-3), interleukin 5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), or granulocyte colony-stimulating factor (G-CSF). Macrophages and endothelial cells, freed from other bone marrow components, required the F-CM if no other growth factors were added. We conclude that F-CM contains an autocrine factor, which the evidence suggests is IL-1, for bone marrow fibroblasts, and a paracrine factor (CSF-1) for macrophages and/or endothelial cells.

Acute and subacute hematologic effects of multi-colony stimulating factor in combination with granulocyte colony-stimulating factor in vivo

Multi-colony stimulating factor (Multi-CSF, interleukin-3, IL-3) and granulocyte-CSF (G-CSF) administered concurrently as an intravenous (IV) injection induce a peripheral neutrophilia that is approximately additive in comparison with the neutrophilia induced by IL-3 and G-CSF individually. The bone marrow (BM) at 12 hours is depleted of mature neutrophils and shows a left-shifted myeloid hyperplasia, consistent with the neutrophil-releasing and myeloproliferative activities of both IL-3 and G-CSF individually. The BM at 24 hours shows a replenished reserve of mature neutrophils and a synergistic left-shifted myeloid hyperplasia as compared with IL-3 and G-CSF alone. Daily IV injections of IL-3 plus G-CSF for 1 week also induce an approximately additive daily peripheral neutrophilia. The BM after a week's administration of IL-3 plus G-CSF shows a generalized myeloid hyperplasia with a synergistic increase in mature neutrophils as compared with IL-3 or G-CSF alone. Daily injection of IL-3 plus G-CSF induced a significant decrease in erythroid, lymphoid, and eosinophilic marrow precursors, possibly owing to a myelophthisic effect of the myeloid hyperplasia and despite the fact that IL-3 alone induced a significant erythroid hyperplasia.

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.

Studies on the myeloid synergistic factor from 5637: comparison with interleukin-1 alpha

A synergistic factor that is produced by the human bladder carcinoma cell line 5637 (SF-1) stimulates primitive bone marrow progenitor cells, termed high proliferative-potential colony-forming cells (HPP-CFC), in the presence of an optimal dose of macrophage colony stimulating factor (CSF-1). Recent reports have demonstrated that interleukin-1 alpha (IL-1) is identical to hemopoietin 1 and have suggested that IL-1 is the synergistic factor present in 5637 conditioned medium (cm). We have compared the ability of recombinant human IL-1 alpha and partially purified preparations of SF-1 to synergize with optimal doses of CSF-1 to stimulate HPP-CFC. In all experiments performed the numbers of HPP-CFC colonies formed with IL-1 were significantly less than with SF-1. Replating experiments demonstrated that SF-1 plus CSF-1 generated HPP-CFC (responsive to IL-3 plus CSF-1); however, IL-1 plus CSF-1 resulted in no generation of HPP-CFC. Multiple factor combinations of IL-1 and SF-1 with G-CSF, GM-CSF, and CSF-1 also resulted in less HPP-CFC colony formation in cultures containing IL-1 compared with SF-1. Incubation of SF-1 with an antibody to IL-6 had no effect on HPP-CFC colony formation and IL-6 did not synergize with IL-1 plus CSF-1 or SF-1 plus CSF-1. These data suggest the presence of a factor in 5637 cm, which is distinct from G-CSF, GM-CSF, and IL-6, which synergizes with IL-1 to produce the SF-1 effect.

Granulocyte colony-stimulating factor augments in vitro megakaryocyte colony formation by interleukin-3

Granulocyte colony-stimulating factor (G-CSF) has been purified to homogeneity and the cDNA isolated. The reported properties of G-CSF have suggested that it is specific for the granulocytic lineage and only forms pure granulocyte colonies in in vitro cultures of murine bone marrow. We have demonstrated in this report that G-CSF augments the effect of interleukin 3 (IL3) on megakaryocyte formation. G-CSF alone had no stimulatory effect on megakaryocyte colony formation, however, the addition of G-CSF to IL3 in cultures of normal murine bone marrow increased the number of megakaryocyte colonies to 176% compared to cultures containing IL3 alone. Also, the combination of G-CSF plus IL3 stimulated the formation of larger megakaryocyte colonies than those formed in cultures of IL3 alone. In contrast, G-CSF had no effect on the number or size of megakaryocyte colonies stimulated by granulocyte-macrophage CSF. These results demonstrate that G-CSF augments the megakaryocyte colony formation of IL3, but not GM-CSF, and expands the lineage potential of G-CSF.

Stimulation of murine colony-forming cells with high proliferative potential by the combination of GM-CSF and CSF-1

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has previously been shown to stimulate granulocyte, macrophage, and megakaryocyte lineages to act as an erythroid burst-promoting activity and to stimulate limited replication of spleen colony-forming cells. Here we demonstrate that murine GM-CSF alone or in combination with macrophage colony-stimulating factor (CSF-1) can stimulate colony-forming cells in bone marrow (BM) that have a high proliferative capacity. In cultures of BM from mice treated with 5-fluorouracil (FU) eight days before sampling, GM-CSF alone or in combination with CSF-1 stimulated the formation of large macrophage colonies with diameters greater than 0.5 mm. CSF-1 alone, at 800 units or greater, also stimulated larger colonies; however, these colonies were always less than 1.1 mm in diameter, whereas GM-CSF in combination with CSF-1 stimulated many colonies with diameters between 1 and 4 mm. At all doses of CSF-1 tested, the combination of factors resulted in a synergistic increase in colonies with diameters greater than 1.0 or 2.0 mm. Analysis of the incidence of colony-forming cells in the BM of normal mice and mice 2, 4, 6, and 8 days after FU treatment demonstrated that the progenitor cells stimulated by GM-CSF alone or in combination with CSF-1 were depleted by FU treatment in vivo and regenerated more rapidly than did the macrophage progenitors (M-CFC) stimulated by CSF-1 alone. This is similar to the properties of the previously described high-proliferative potential, colony-forming cell (HPP-CFC) that is responsive to interleukin-3 plus CSF-1 but not the HPP-CFC stimulated by hematopoietin 1 plus CSF-1. These data suggest that GM-CSF plus CSF-1 act synergistically to stimulate a population of progenitor cells that have a high proliferative potential and have properties similar to those of the population of HPP-CFC stimulated by interleukin-3 plus CSF-1.

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.

A colorimetric liquid culture assay of a growth factor for primitive murine macrophage progenitor cells

Synergistic factors from media conditioned (CM) by human placentas or the 5637 human bladder carcinoma cell line (SFH-HPCM and SFH-5637 respectively) have the ability to stimulate early progenitor cells in mouse bone marrow to form large colonies in agar cultures after 12-14 days, in the presence of CSF-1. Culture conditions have been examined and a quicker and more convenient liquid culture assay has been developed for this factor, using a tetrazolium salt to quantitate cell proliferation. The use of flat-bottomed vessels, high cell density, supra-optimal doses of CSF-1 or the addition of WEHI-3-CM to these cultures, all resulted in a decrease in the required incubation time. In combination, these modifications reduced the assay time to 4 days.

Generation of murine hematopoietic precursor cells from macrophage high-proliferative-potential colony-forming cells

High-proliferative-potential colony-forming cells (HPP-CFC) have been described as primitive murine macrophage progenitors. We have previously demonstrated the existence of two populations of HPP-CFC: one population, termed HPP-CFC-1, is stimulated by the combination of macrophage colony-stimulating factor (CSF-1) plus haemopoietin-1 (H-1) and actively generates a second population of HPP-CFC, termed HPP-CFC-2. HPP-CFC-2 are stimulated by CSF-1 plus interleukin-3 and generate macrophage CFC that differentiate to form mature macrophages. In this study, we have demonstrated that HPP-CFC-1, when stimulated by CSF-1 plus H-1, generate colony-forming cells (CFC) for the megakaryocyte and granulocyte lineages in addition to HPP-CFC-2 and M-CFC. No CFC were detected with erythroid potential. In addition, HPP-CFC-1 generated cells that formed day-13 spleen colonies, cells that repopulated the bone marrow, cells with platelet-repopulating ability, and cells with erythroid-repopulating ability in lethally irradiated mice. These data support previous data that the HPP-CFC-1 represent a primitive hemopoietic cell population and demonstrate the multipotentiality but not totipotentiality of these cells.

Detection of murine hemopoietin-1 in media conditioned by EMT6 cells

We have previously reported replating experiments which demonstrated the existence of subpopulations of murine high-proliferative-potential colony-forming cells (HPP-CFC). One population of HPP-CFC, termed HPP-CFC-1, is stimulated by the combination of macrophage colony-stimulating factor (CSF-1) plus hemopoietin-1 (H-1), and actively generate a second population of HPP-CFC, termed HPP-CFC-2, which is responsive to CSF-1 plus interleukin-3 (IL-3). These reclonal experiments represent an assay system that discriminates between the two types of synergistic factors, namely H-1 and IL-3. To date H-1 has only been detected in medium conditioned by human cells. In this paper we have utilized these recloning experiments to study the synergistic factor(s) present in media conditioned by the murine mammary carcinoma cell line EMT6. Colony formation in secondary cultures containing cells picked up from primary cultures incubated in CSF-1 plus EMT6-conditioned medium was identical to that seen in secondary cultures containing cells picked up from primary cultures incubated in CSF-1 plus a source of H-1. Both sets of cultures demonstrated the generation of HPP-CFC-2 in the primary cultures, indicating the presence of a molecule in EMT6-conditioned medium that is the murine equivalent of H-1.

Subpopulations of mouse bone marrow high-proliferative-potential colony-forming cells

Bone marrow cells taken from mice treated eight days previously with 5-fluorouracil, formed colonies consisting of 10-100 cells after four days of incubation in methylcellulose cultures containing only 500 cells/dish, in the presence of partially purified synergistic factor from human placental-conditioned medium (SFHPlac) and macrophage colony-stimulating factor (CSF-1). Replating of these colonies revealed a high incidence (27%) of another class of high-proliferative-potential colony-forming cells (HPP-CFC) responsive only to the synergistic factor in WEHI-3B-conditioned medium (SFW, which appears to be identical to interleukin 3) plus CSF-1. These colonies contained no HPP-CFC responsive to SFHPlac plus CSF-1, although primary cultures incubated for 14 days in the presence of SFHPlac plus CSF-1 formed large colonies (diameter greater than 0.5 mm), indicating the presence of HPP-CFC responsive to SFHPlac plus CSF-1 in the starting marrow. Primary cultures containing SFW alone, or purified interleukin 3 alone, also gave rise to colonies consisting of 10-100 cells after four days of incubation in methylcellulose cultures; however, the cells from these colonies were unable to form large colonies on replating in the presence of either CSF-1 plus SFHPlac or CSF-1 plus SFW. These results suggest that two distinct populations of HPP-CFC exist and that the population of HPP-CFC stimulated by CSF-1 plus SFHPlac differentiates to form HPP-CFC that respond to CSF-1 plus SFW.

Isolation and analysis of primitive hemopoietic progenitor cells on the basis of differential expression of Qa-m7 antigen

In the presence of the hemopoietic growth factor CSF-1, the later committed cells of the macrophage lineage can be detected by their ability to form small colonies in clonal agar culture (CFCCSF-1). Synergistic factors have been described that in combination with CSF-1 stimulate developmentally early hemopoietic progenitor cells of high proliferative potential (HPP-CFC). By using a monoclonal antibody to the Qa-m7 antigenic determinant, we investigated and compared the expression of Qa-m7 on CFCCSF-1 and on HPP-CFC of two types that grow in response to either 1) CSF-1 plus synergistic factor from human placenta-conditioned medium (HPP-CFCHplac+CSF-1) or 2) CSF-1 plus synergistic factor from conditioned medium of the WEHI-3 myelomonocytic cell line (HPP-CFCW+CSF-1). We have shown that HPP-CFC of both types express relatively more Qa-m7 antigen than CFCCSF-1 and can be separated and enriched on this basis by discontinuous buoyant density centrifugation and fluorescence-activated cell sorting of normal bone marrow. Significant enrichments of HPP-CFCHPlac+CSF-1 (43.5-fold) and HPP-CFCW+CSF-1 (28.8-fold) have been achieved with cloning efficiencies of HPP-CFC in the most enriched fractions reaching 4 to 5%. These results clearly illustrate the fact that there are populations of progenitor cells from normal, unperturbed bone marrow that strictly require a combination of two hemopoietic growth factors (CSF-1 plus synergistic factor) in order to be detected.

Isolation and analysis of primitive hemopoietic progenitor cells on the basis of differential expression of Qa-m7 antigen

In the presence of the hemopoietic growth factor CSF-1, the later committed cells of the macrophage lineage can be detected by their ability to form small colonies in clonal agar culture (CFCCSF-1). Synergistic factors have been described that in combination with CSF-1 stimulate developmentally early hemopoietic progenitor cells of high proliferative potential (HPP-CFC). By using a monoclonal antibody to the Qa-m7 antigenic determinant, we investigated and compared the expression of Qa-m7 on CFCCSF-1 and on HPP-CFC of two types that grow in response to either 1) CSF-1 plus synergistic factor from human placenta-conditioned medium (HPP-CFCHplac+CSF-1) or 2) CSF-1 plus synergistic factor from conditioned medium of the WEHI-3 myelomonocytic cell line (HPP-CFCW+CSF-1). We have shown that HPP-CFC of both types express relatively more Qa-m7 antigen than CFCCSF-1 and can be separated and enriched on this basis by discontinuous buoyant density centrifugation and fluorescence-activated cell sorting of normal bone marrow. Significant enrichments of HPP-CFCHPlac+CSF-1 (43.5-fold) and HPP-CFCW+CSF-1 (28.8-fold) have been achieved with cloning efficiencies of HPP-CFC in the most enriched fractions reaching 4 to 5%. These results clearly illustrate the fact that there are populations of progenitor cells from normal, unperturbed bone marrow that strictly require a combination of two hemopoietic growth factors (CSF-1 plus synergistic factor) in order to be detected.

Identification of the "factor" in erythrocyte lysates which enhances colony growth in agar cultures

The activity in human erythrocyte lysates which enhances colony growth of mouse bone marrow (BM) and other cell types in agar culture, could not be separated from hemoglobin (Hb). This conclusion was reached after various procedures, including purification of Hb in human hemolysates by crystallisation, separation of Hb into its major (A0) and minor (A1 and A2) components by DEAE-Sephadex chromatography and separation of a hemolysate into a Hb fraction and a non-Hb protein fraction by DEAE-cellulose chromatography; all resulted in the enchancement activity remaining with the Hb fraction. Separation of globins from rat or human lysates by an acid acetone precipitation, resulted in an acetone powder (AP) which retained the enhancement activity towards both mouse BM and tumour cell lines. The AP was separated into alpha and beta globins by chromatography on Sephadex G100 in 20% formic acid followed by CM-cellulose chromatography in a 8 M urea system. Since the enhancement activity is associated with both the alpha and beta globin peaks even under these dissociating conditions, it has been concluded that the enhancement factor in erythrocyte lysates is Hb itself. The enhancement activity of an AP is abolished by treatment with N-ethylmaleimide, suggesting that sulfhydryl groups in Hb are required for the activity.