A human GM-CSF receptor expressed in transgenic mice stimulates proliferation and differentiation of hemopoietic progenitors to all lineages in response to human GM-CSF

Divergent effects of Wnt5b on IL-3- and GM-CSF-induced myeloid differentiation

The multiple specialized cell types of the hematopoietic system originate from differentiation of hematopoietic stem cells and progenitors (HSPC), which can generate both lymphoid and myeloid lineages. The myeloid lineage is preferentially maintained during ageing, but the mechanisms that contribute to this process are incompletely understood. Here, we studied the roles of Wnt5a and Wnt5b, ligands that have previously been linked to hematopoietic stem cell ageing and that are abundantly expressed by both hematopoietic progenitors and bone-marrow derived niche cells. Whereas Wnt5a had no major effects on primitive cell differentiation, Wnt5b had profound and divergent effects on cytokine-induced myeloid differentiation. Remarkably, while IL-3- mediated myeloid differentiation was largely repressed by Wnt5b, GM-CSF-induced myeloid differentiation was augmented. Furthermore, in the presence of IL-3, Wnt5b enhanced HSPC self-renewal, whereas in the presence ofGM-CSF, Wnt5b accelerated differentiation, leading to progenitor cell exhaustion. Our results highlight discrepancies between IL-3 and GM-CSF, and reveal novel effects of Wnt5b on the hematopoietic system.

Eosinophils and Mast Cells in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) involves overexpression of proinflammatory mediators, including 5-lipoxygenase and leukotriene C₄ synthase (LTC₄S), resulting in constitutive overproduction of cysteinyl leukotrienes. Mast cells and eosinophils have roles in mediating many of the observed effects. Increased levels of both interleukin-4 (IL-4) and interferon (IFN)-γ are present in the tissue of patients with AERD. Previous studies showed that IL-4 is primarily responsible for the upregulation of LTC₄S by mast cells. Our studies show that IFN-γ, but not IL-4, drives this process in eosinophils. This article examines the overall role that eosinophils and mast cells contribute to the pathophysiology of AERD.

Oncolytic and immunostimulatory efficacy of a targeted oncolytic poxvirus expressing human GM-CSF following intravenous administration in a rabbit tumor model

Targeted oncolytic poxviruses hold promise for the treatment of cancer. Arming these agents with immunostimulatory cytokines (for example, granulocyte-monocyte colony-stimulating factor; GM-CSF) can potentially increase their efficacy and/or alter their safety. However, due to species-specific differences in both human GM-CSF (hGM-CSF) activity and poxviruses immune avoidance proteins, the impact of hGM-CSF expression from an oncolytic poxvirus cannot be adequately assessed in murine or rat tumor models. We developed a rabbit tumor model to assess toxicology, pharmacodynamics, oncolytic efficacy and tumor-specific immunity of hGM-CSF expressed from a targeted oncolytic poxvirus JX-963. Recombinant purified hGM-CSF protein stimulated a leukocyte response in this model that paralleled effects of the protein in humans. JX-963 replication and targeting was highly tumor-selective after i.v. administration, and intratumoral replication led to recurrent, delayed systemic viremia. Likewise, hGM-CSF was expressed and released into the blood during JX-963 replication in tumors, but not in tumor-free animals. hGM-CSF expression from JX-963 was associated with significant increases in neutrophil, monocyte and basophil concentrations in the peripheral blood. Finally, tumor-specific cytotoxic T lymphocytes (CTL) were induced by the oncolytic poxvirus, and expression of hGM-CSF from the virus enhanced both tumor-specific CTL and antitumoral efficacy. JX-963 had significant efficacy against both the primary liver tumor as well as metastases; no significant organ toxicity was noted. This model holds promise for the evaluation of immunostimulatory transgene-armed oncolytic poxviruses, and potentially other viral species.

Activation of mitogen-activated protein kinase kinase (MEK)/extracellular signal regulated kinase (ERK) signaling pathway is involved in myeloid lineage commitment

Common lymphoid progenitors (CLPs) are lymphoid-lineage-committed progenitor cells. However, they maintain a latent myeloid differentiation potential that can be initiated by stimulation with interleukin-2 (IL-2) via ectopically expressed IL-2 receptors. Although CLPs express IL-7 receptors, which share the common gamma chain with IL-2 receptors, IL-7 cannot initiate lineage conversion in CLPs. In this study, we demonstrate that the critical signals for initiating lineage conversion in CLPs are delivered via IL-2 receptor beta (IL-2R beta) intracellular domains. Fusion of the A region of the IL-2R beta cytoplasmic tail to IL-7R alpha enables IL-7 to initiate myeloid differentiation in CLPs. We found that Shc, which associates with the A region, mediates lineage conversion signals through the mitogen activated protein kinase (MAPK) pathway. Because mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) inhibitors completely blocked IL-2-mediated lineage conversion, MAPK activation, specifically via the MEK/ERK pathway, is critically involved in the initiation of this event. Furthermore, formation of granulocyte/macrophage (GM) colonies by hematopoietic stem cells, but not by common myeloid progenitors (CMPs), was severely reduced in the presence of MEK/ERK inhibitors. These results demonstrate that activation of MEK/ERK plays an important role in GM lineage commitment.

Expression of CCL20 and granulocyte-macrophage colony-stimulating factor, but not Flt3-L, from modified vaccinia virus ankara enhances antiviral cellular and humoral immune responses

While modified vaccinia virus Ankara (MVA) is currently in clinical development as a safe vaccine against smallpox and heterologous infectious diseases, its immunogenicity is likely limited due to the inability of the virus to replicate productively in mammalian hosts. In light of recent data demonstrating that vaccinia viruses, including MVA, preferentially infect antigen-presenting cells (APCs) that play crucial roles in generating antiviral immunity, we hypothesized that expression of specific cytokines and chemokines that mediate APC recruitment and activation from recombinant MVA (rMVA) vectors would enhance the immunogenicity of these vectors. To test this hypothesis, we generated rMVAs that express murine granulocyte-macrophage colony-stimulating factor (mGM-CSF), human CCL20/human macrophage inflammatory protein 3alpha (hCCL20/hMIP-3alpha), or human fms-like tyrosine kinase 3 ligand (hFlt3-L), factors predicted to increase levels of dendritic cells (DCs), to recruit DCs to sites of immunization, or to promote maturation of DCs in vivo, respectively. These rMVAs also coexpress the well-characterized, immunodominant lymphocytic choriomeningitis virus nucleoprotein (NP) antigen that enabled sensitive and quantitative assessment of antigen-specific CD8(+) T-cell responses following immunization of BALB/c mice. Our results demonstrate that immunization of mice with rMVAs expressing mGM-CSF or hCCL20, but not hFlt3-L, results in two- to fourfold increases of cellular immune responses directed against vector-encoded antigens and 6- to 17-fold enhancements of MVA-specific antibody titers, compared to those responses elicited by nonadjuvanted rMVA. Of note, cytokine augmentation of cellular immune responses occurs when rMVAs are given as primary immunizations but not when they are used as booster immunizations, suggesting that these APC-modulating proteins, when used as poxvirus-encoded adjuvants, are more effective at stimulating naïve T-cell responses than in promoting recall of preexisting memory T-cell responses. Our results demonstrate that a strategy to express specific genetic adjuvants from rMVA vectors can be successfully applied to enhance the immunogenicity of MVA-based vaccines.

Retroviral transduction of IL-7Rα into IL-7Rα−/− bone marrow progenitors: correction of lymphoid deficiency and induction of neutrophilia

Defects in the gene for the IL-7 receptor (R) alpha chain are one cause of severe combined immunodeficiency disease (SCID) based on a strict requirement for IL-7 in T lymphoid development and survival. We tested the feasibility and potentially undesirable consequences of IL-7Ralpha gene transfer as a therapy for this genetic defect. The murine IL-7Ralpha gene was introduced into IL-7Ralpha(-/-) bone marrow progenitors using retrovirus and transplanted into Rag(-/-) recipient mice. Both alphabeta and gammadelta T cells were reconstituted in thymus and spleen showing proof of principle. B-cell development was also restored in some mice, but their numbers were much lower than in the T-cell compartment. Splenomegaly was observed due to an increase in neutrophils. We showed that hematopoietic progenitors, after transfection with IL-7Ralpha, could respond to IL-7 in vitro by a striking production of neutrophils and other myeloid cells. These data indicate that although IL-7 is a critical lymphopoietin, ectopic expression of its receptor on multipotential progenitors can also induce production of myeloid cells, presumably through survival and proliferation signals that are not restricted to lymphoid cells. This supports the stochastic model of progenitor differentiation, in which cytokines give permissive and not instructive signals.

Distinctive and indispensable roles of PU.1 in maintenance of hematopoietic stem cells and their differentiation

The PU.1 transcription factor is a key regulator of hematopoietic development, but its role at each hematopoietic stage remains unclear. In particular, the expression of PU.1 in hematopoietic stem cells (HSCs) could simply represent "priming" of genes related to downstream myelolymphoid lineages. By using a conditional PU.1 knock-out model, we here show that HSCs express PU.1, and its constitutive expression is necessary for maintenance of the HSC pool in the bone marrow. Bone marrow HSCs disrupted with PU.1 in situ could not maintain hematopoiesis and were outcompeted by normal HSCs. PU.1-deficient HSCs also failed to generate the earliest myeloid and lymphoid progenitors. PU.1 disruption in granulocyte/monocyte-committed progenitors blocked their maturation but not proliferation, resulting in myeloblast colony formation. PU.1 disruption in common lymphoid progenitors, however, did not prevent their B-cell maturation. In vivo disruption of PU.1 in mature B cells by the CD19-Cre locus did not affect B-cell maturation, and PU.1-deficient mature B cells displayed normal proliferation in response to mitogenic signals including the cross-linking of surface immunoglobulin M (IgM). Thus, PU.1 plays indispensable and distinct roles in hematopoietic development through supporting HSC self-renewal as well as commitment and maturation of myeloid and lymphoid lineages.

GATA-1 Converts Lymphoid and Myelomonocytic Progenitors into the Megakaryocyte/Erythrocyte Lineages

GATA-1 is an essential transcription factor for megakaryocyte and erythrocyte (MegE) development. Here we show that hematopoietic progenitors can be reprogrammed by the instructive action of GATA-1. Enforced expression of GATA-1 in hematopoietic stem cells led to loss of self-renewal activity and the exclusive generation of MegE lineages. Strikingly, ectopic GATA-1 reprogrammed common lymphoid progenitors as well as granulocyte/monocyte (GM) progenitors to differentiate into MegE lineages, while inhibiting normal lymphoid or GM differentiation. GATA-1 upregulated critical MegE-related transcription factors such as FOG-1 and GATA-2 in lymphoid and GM progenitors, and their MegE development did not require "permissive" erythropoietin signals. Furthermore, GATA-1 induced apoptosis of proB and myelomonocytic cells, which could not be prevented by enforced permissive Bcl-2 or myeloid cytokine signals. Thus, GATA-1 specifically instructs MegE commitment while excluding other fate outcomes in stem and progenitor cells, suggesting that regulation of GATA-1 is critical in maintaining multilineage homeostasis.

Enforced granulocyte/macrophage colony-stimulating factor signals do not support lymphopoiesis, but instruct lymphoid to myelomonocytic lineage conversion

We evaluated the effects of ectopic granulocyte/macrophage colony-stimulating factor (GM-CSF) signals on hematopoietic commitment and differentiation. Lineage-restricted progenitors purified from mice with the ubiquitous transgenic human GM-CSF receptor (hGM-CSFR) were used for the analysis. In cultures with hGM-CSF alone, hGM-CSFR-expressing (hGM-CSFR+) granulocyte/monocyte progenitors (GMPs) and megakaryocyte/erythrocyte progenitors (MEPs) exclusively gave rise to granulocyte/monocyte (GM) and megakaryocyte/erythroid (MegE) colonies, respectively, providing formal proof that GM-CSF signals support the GM and MegE lineage differentiation without affecting the physiological myeloid fate. hGM-CSFR transgenic mice were crossed with mice deficient in interleukin (IL)-7, an essential cytokine for T and B cell development. Administration of hGM-CSF in these mice could not restore T or B lymphopoiesis, indicating that enforced GM-CSF signals cannot substitute for IL-7 to promote lymphopoiesis. Strikingly, >50% hGM-CSFR+ common lymphoid progenitors (CLPs) and >20% hGM-CSFR+ pro-T cells gave rise to granulocyte, monocyte, and/or myeloid dendritic cells, but not MegE lineage cells in the presence of hGM-CSF. Injection of hGM-CSF into mice transplanted with hGM-CSFR+ CLPs blocked their lymphoid differentiation, but induced development of GM cells in vivo. Thus, hGM-CSF transduces permissive signals for myeloerythroid differentiation, whereas it transmits potent instructive signals for the GM differentiation to CLPs and early T cell progenitors. These data suggest that a majority of CLPs and a fraction of pro-T cells possess plasticity for myelomonocytic differentiation that can be activated by ectopic GM-CSF signals, supporting the hypothesis that the down-regulation of GM-CSFR is a critical event in producing cells with a lymphoid-restricted lineage potential.

Analysis of the 5' promoters for human IL-3 and GM-CSF receptor alpha genes

The receptors for human interleukin-3 (hIL-3R) and granulocyte-macrophage colony-stimulating factor (hGM-CSFR) consist of an alpha subunit, specific for each cytokine, and a beta subunit, common to IL-3, GM-CSF, and IL-5. We cloned genomic DNA covering 1.5 kb of the 5' flanking region of the hIL-3R alpha gene and identified multiple transcription start sites by 5(')-RACE and primer extension analyses. By use of transient transfection experiments, two regions (nt -363 to -331 and -106 to -92) of the hIL-3R alpha promoter appeared to have significant transcription-enhancing activities. Electrophoresis mobility shift assays revealed the binding of Sp1 and unidentified proteins to these regions. Deletion of a putative PU.1 binding site did not affect the promoter activity. We then analyzed 2.5 kb of the hGM-CSFR alpha gene and found the proximal PU.1 binding site to be important for transcription-enhancing activity, as previously reported. These results suggest that different transcriptional activation mechanisms are employed for the transcriptional regulation of hIL-3 and hGM-CSF receptor alpha genes.

Interleukin-7 inhibits pre-T-cell differentiation induced by the pre-T-cell receptor signal and the effect is mimicked by hGM-CSF in hGM-CSF receptor transgenic mice

We have previously reported that human granulocyte-macrophage colony-stimulating factor (hGM-CSF) causes a stage-specific inhibition of T-cell receptor (TCR) alphabeta cell development in the thymus of transgenic mice constitutively expressing the hGM-CSF receptor. Since it has been reported that the addition of interleukin-7 (IL-7) to fetal thymic organ culture (FTOC) has similar effects, we compared the effects of IL-7 and hGM-CSF on TCR(alphabeta) cell development in hGM-CSF receptor transgenic mice. We reconstituted fetal lobes with sorted pre-T, or post pre-T CD4(-)CD8(-) precursor cells. The addition of either IL-7 or hGM-CSF to these cultures suppressed further differentiation of pre-T cells but not post pre-T cells. At the same time, the cell number was increased, suggesting that pre-T-cell proliferation is stimulated by these cytokines. Furthermore, the differentiation of recombination-activating gene-1 (RAG-1)-deficient pre-T cells in response to anti-CD3 antibody stimulation was suppressed by either IL-7 or hGM-CSF, suggesting that these cytokines inhibit the pre-T-cell receptor (pre-TCR) signal. This inhibition is unexpected because the pre-TCR signal and the IL-7 signal have previously been considered to be co-operative. Recent analysis of the downstream events of IL-7 receptor and GM-CSF receptor revealed that they share common signal transduction molecules. Our results show that IL-7 is able to promote pre-T cell proliferation and to suppress differentiation induced by the pre-TCR signal. GM-CSF can mimic these biological activities of IL-7 when the pre-T cells express GM-CSF receptors. Our data suggest that both timing and level of activation of the IL-7 signalling pathway must be precisely regulated to facilitate the differentiation of thymocytes.

Megakaryocytic Maturation is Regulated by Maintaining a Balance Against Cytokine Induced-cell Proliferation: Steel Factor Retards Thrombopoietin-induced Megakaryocytic Differentiation While Synergistically Stimulating Mitogenesis; Hematopoiesis

Using a factor-dependent cell line MO7ER, which contains a stably transduced human erythropoietin (EPO) receptor gene in human megakaryoblastic cell line MO7e and which resulted in concomitant expression of EPO receptor, c-Mpl and c-Kit, we investigated the biological effects of these cytokines in terms of cell growth and differentiation. Thrombopoietin (TPO), EPO and Steel factor (SLF) all stimulated MO7ER cell proliferation in a dose-dependent manner. Combined stimulation of cells with SLF plus either TPO or EPO resulted in striking synergistic enhancement of MO7ER cell growth as compared with each cytokine alone, whereas combination of TPO plus EPO showed only an additive effect on cell proliferation. With regards to cell differentiation, either TPO or EPO treatment induced enhancement of platelet glycoprotein (GP) IIb/IIIa and GPIb expression. SLF induced GPIIb/IIIa and GPIb expression, but the effect was much weaker than that of EPO or TPO. However, addition of SLF to either TPO- or EPO- containing cultures (which induced potent mitogenesis in MO7ER cells) resulted in suppression of these megakaryocyte specific antigens. Addition of low-dose cytosine arabinoside (Ara-C)(1 to 10 ng/ml) enhanced TPO- or EPO- induced megakaryocytic differentiation in MO7ER cells while mildly suppressing cell growth. Treatment the cells with low-dose Ara-C plus TPO plus SLF overrode the proliferative enhancing effects of SLF and induced GPIIb/IIIa and GPIb expression as efficient as TPO alone. Retardation of TPO-induced megakaryocytic maturation was also observed in normal murine bone marrow cells by combined stimulation with TPO and SLF as assessed by the numbers of acetylcholinesterase staining-positive cells and megakaryocyte nuclear polyploidy. These results suggest that megakaryocytic maturation is, at least in part, regulated by countering cytokine-induced cell proliferation.

The granulocyte colony-stimulating factor receptor supports erythroid differentiation in the absence of the erythropoietin receptor or Stat5

To evaluate the functional conservation of signal transduction mechanisms between haematopoietic receptors and to characterize the molecules activated in this phenomenon, we introduced granulocyte colony-stimulating factor receptor (G-CSFR) cDNA into mouse fetal liver cells using a retroviral vector. In semi-solid medium assays, G-CSFR-infected cells gave rise to all types of colonies [granulocyte-macrophage (GM), megakaryocyte (MK) and mixed lineage (GEMM) colony-forming units (CFU) and erythroid burst-forming units (BFU-E)] in the presence of G-CSF alone. The direct effect of G-CSF on erythroid differentiation of G-CSFR-transduced erythroid progenitors was demonstrated by the development of erythroid colonies using G-CSFR-expressing Lin- cells cloned at one cell per well in liquid culture in the presence of G-CSF. Interestingly, while Stat5, but not Stat3, was activated in erythroid cells in response to erythropoietin (EPO), both were activated in erythroid and granulocytic cells stimulated by G-CSF. Furthermore, G-CSF induced the growth of erythroid colonies from G-CSFR-expressing fetal liver cells from EPO receptor-/- (EPO-R-/-) or Stat5a-/- Stat5b-/- mice, demonstrating that erythroid differentiation can occur in the absence of EPO-R or Stat5. These data show that forced expression of G-CSFR allows G-CSF-dependent multilineage proliferation and differentiation of haematopoietic progenitors and rescues EPO-R-/- erythroid cells. While G-CSF induces Stat5 activation in G-CSFR-expressing erythroid cells, this activation is not necessary for the terminal erythroid differentiation induced by G-CSF.

Transcription factors that regulate growth and differentiation of myeloid cells

Recently much progress has been made in our understanding of how myeloid progenitor cells undergo commitment and become mature granulocytes or monocytes/macrophages. Studies of normal and leukemic myeloid cells as well as those of cells derived from mice with targeted disruption showed that a series of transcription factors play a major role in both commitment and maturation of myeloid cells. This is primarily because these transcription factors direct an ordered pattern of gene expression according to a well-defined developmental program. PU.1, an Ets family member, is one of the master transcription factors identified to regulate development of both granulocytes and monocytes/macrophages. Further, C/EBPalpha and C/EBPvarepsilon of the bZip family have important roles in directing granulocytic maturation. A number of additional transcription factors such as AML1, RARalpha, MZF-1, Hox and STAT families of transcription factors, Egr-1 and c-myb etc are shown to play roles in myeloid cell differentiation. Our laboratory has recently obtained evidence that ICSBP, a member of the IRF family, is involved in lineage commitment during myeloid cell differentiation and stimulates maturation of functional macrophages. Future elucidation of pathways and networks through which these transcription factors act in various stages of development would provide a more definitive picture of myeloid cell commitment and maturation.

Combination of granulocyte colony-stimulating factor and low-dose cytosine arabinoside further enhances myeloid differentiation in leukemia cells in vitro

We examined the differentiation-inducing effect on freshly isolated myeloid leukemia cells in liquid suspension culture by combined treatment with granulocyte colony-stimulating factor (G-CSF) plus low-dose cytosine arabinoside (Ara-C; 5-10 ng/ml) in 25 patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) in leukemic transformation. Culture with G-CSF alone showed leukemic cell growth stimulation in 15 out of the 25 cases (60%) and induction of cell differentiation in 19 out of the 25 cases (76%), respectively. In 23 cases (92%), either growth stimulation and/or differentiation induction of leukemia cells was observed in response to G-CSF. This suggests that most myeloid leukemia cells are able to respond to G-CSF stimulation. In addition, treatment of cells with low-dose Ara-C alone resulted in the enhancement of myeloid specific antigens expression in 16 cases (64%). Treatment of leukemia cells with higher concentrations of Ara-C (over 50 ng/ml) alone resulted in cytocidal effects but not in the induction of differentiation. Furthermore, 15 cases (60%) showed pronounced myeloid differentiation of leukemia cells after combined exposure to G-CSF plus low-dose Ara-C as compared with cells treated with either G-CSF or Ara-C alone. The enhanced effect of differentiation induction by combining G-CSF plus low-dose Ara-C was also observed in a murine myeloid leukemia cell line WEHI-3B in vitro. These data suggest that treatment with G-CSF plus low-dose Ara-C is capable of inducing differentiation of leukemic cells in vitro, and also appears to be useful for the differentiation-based therapy of patients with AML and MDS.

Analysis of signals and functions of the chimeric human granulocyte-macrophage colony-stimulating factor receptor in BA/F3 cells and transgenic mice

Receptors for GM-CSF, IL-3, and IL-5 are composed of two subunits: alpha, which is specific for each cytokine, and betac, which is shared by all. Although the role of betac in signal transduction has been extensively studied, the role of the alpha subunit has remained to be clarified. To analyze the role of the human (h) GM-CSF receptor alpha subunit, we constructed a chimeric receptor subunit composed of extracellular and transmembrane regions of alpha fused with the cytoplasmic region of betac, designated alpha/beta. In BA/F3 cells, chimeric receptor composed of alpha/beta,beta can transduce signals for mitogen-activated protein kinase cascade activation and proliferation in response to hGM-CSF. Although phosphorylation of Jak1 but not of Jak2 occurred with stimulation of hGM-CSF, the dominant-negative Jak2 but not the dominant-negative Jak1 suppresses c-fos promoter activation. To determine whether the chimeric receptor alpha/beta,beta is functional in vivo, we developed transgenic mice expressing the chimeric receptor alpha/beta,beta. Bone marrow cells from the transgenic mice expressing the alpha/beta,beta receptor form not only GM colonies but also various lineages of colonies in response to GM-CSF. In addition, mast cells were produced when bone marrow cells of the transgenic mouse were cultured with hGM-CSF. Thus, it appears that the cytoplasmic region of the alpha subunit is not required for hGM-CSF promoting activities, even in bone marrow cells.

Chimeric cytokine receptor can transduce expansion signals in interleukin 6 receptor alpha (IL-6Ralpha)-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors

We generated transgenic mice expressing chimeric receptors, which comprise extracellular domains of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) receptor and transmembrane and cytoplasmic domains of the mouse leukemia inhibitory factor receptor. In suspension cultures of lineage-negative (Lin(-)), 5-fluorouracil-resistant bone marrow cells of the transgenic mice, a combination of hGM-CSF and stem cell factor (SCF) induced exponential expansions of mixed colony-forming unit. The combination of hGM-CSF and SCF was effective on enriched, Lin(-)Sca-1(+)c-kit(+) progenitors and increased either mixed colony-forming unit or cobblestone area-forming cells. In case of stimulation with hGM-CSF and SCF, interleukin-6 (IL-6) and SCF, or IL-11 and SCF, the most efficient expansion was achieved with hGM-CSF and SCF. When Lin(-)Sca-1(+)c-kit(+)CD34(-) further enriched progenitors were clone sorted and individually incubated in the presence of SCF, hGM-CSF stimulated a larger number of cells than did IL-6, IL-6 and soluble IL-6 receptor (IL-6R), or IL-11. These data suggest the presence of IL-6Ralpha-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors. Such primitive progenitors are equipped with signal transduction molecules and can expand when these chimeric receptors are genetically introduced into the cells and stimulated with hGM-CSF in the presence of SCF.

Differential Effects of Human Granulocyte Colony-Stimulating Factor (hG-CSF) and Thrombopoietin on Megakaryopoiesis and Platelet Function in hG-CSF Receptor-Transgenic Mice

Granulocyte-colony stimulating factor (G-CSF) has been found to act on the neutrophilic lineage. We recently showed that human G-CSF (hG-CSF) has effects similar to early-acting cytokines such as interleukin-3 (IL-3) in the development of multipotential hematopoietic progenitors in transgenic (Tg) mice expressing receptors (R) for hG-CSF. In the present study, we examined the effects of hG-CSF on more mature hematopoietic cells committed to megakaryocytic lineage in these Tg mice. The administration of hG-CSF to the Tg mice increased the numbers of both platelets in peripheral blood and megakaryocytes in the spleen, indicating that hG-CSF stimulates megakaryopoiesis in the Tg mice in vivo. The stimulatory effect of hG-CSF was also supported by the results of studies in vitro. hG-CSF supported megakaryocyte colony formation in a dose-dependent fashion in clonal cultures of bone marrow cells derived from the Tg mice. Direct effects of hG-CSF on megakaryocytic progenitors in the Tg mice were confirmed by culture of single-cell sorted from bone marrow cells. hG-CSF showed a stronger effect on maturation of megakaryocytes in the Tg mice than that of IL-3 alone, but weaker than that of TPO alone. In addition, hG-CSF induced phosphorylation of STAT3 but not Jak2 or STAT5, while TPO induced phosphorylation of both. In contrast to TPO, hG-CSF did not enhance ADP-induced aggregation. Thus, hG-CSF has a wide variety of functions in megakaryopoiesis of hG-CSFR-Tg mice, as compared with other megakaryopoietic cytokines, but the activity of hG-CSF in megakaryocytes and platelets does not stand up to a comparison with that of TPO. Specific signals may be required for the full maturation and activation of platelets.

Specificity of signaling by hematopoietic cytokine receptors: instructive versus permissive effects

The helical cytokines constitute a family of proteins with a common three-dimensional structure. They exert a wide variety of biological effects with a preference for the hematopoietic system. The effects of helical cytokines are mediated by cell surface receptors, which belong to the cytokine receptor superfamily and signal by activating cytoplasmic tyrosine kinases of the Janus kinase (Jak) family and other downstream signaling pathways. The relevance of each of these pathways for eliciting a specific cellular response remains to be determined. This review will focus on cytokine receptors which play a role in the regulation of hematopoiesis and summarize data the address the question how specificity of signaling is achieved.

Human Granulocyte Colony-Stimulating Factor (G-CSF) Stimulates the In Vitro and In Vivo Development But Not Commitment of Primitive Multipotential Progenitors From Transgenic Mice Expressing the Human G-CSF Receptor

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and restricted differentiation of hematopoietic progenitors into neutrophils. To clarify the effects of G-CSF on hematopoietic progenitors, we generated transgenic (Tg) mice that had ubiquitous expression of the human G-CSF receptor (hG-CSFR). In clonal cultures of bone marrow and spleen cells obtained from these mice, hG-CSF supported the growth of myelocytic as well as megakaryocytic, mast cell, mixed, and blast cell colonies. Single-cell cultures of lineage-negative (Lin−)c-Kit+Sca-1+ or Sca-1− cells obtained from the Tg mice confirmed the direct effects of hG-CSF on the proliferation and differentiation of various progenitors. hG-CSF also had stimulatory effects on the formation of blast cell colonies in cultures using 5-fluorouracil–resistant hematopoietic progenitors and clone-sorted Lin−c-Kit+Sca-1+ primitive hematopoietic cells. These colonies contained different progenitors in proportions similar to those obtained when mouse interleukin-3 was used in place of hG-CSF. Administration of hG-CSF to Tg mice led to significant increases in spleen colony-forming and mixed/blast cell colony-forming cells in bone marrow and spleen, but did not alter the proportion of myeloid progenitors in total clonogenic cells. These results show that, when functional G-CSFR is present on the cell surface, hG-CSF stimulates the development of primitive multipotential progenitors both in vitro and in vivo, but does not induce exclusive commitment to the myeloid lineage.

Human Granulocyte Colony-Stimulating Factor (G-CSF) Stimulates the In Vitro and In Vivo Development But Not Commitment of Primitive Multipotential Progenitors From Transgenic Mice Expressing the Human G-CSF Receptor

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and restricted differentiation of hematopoietic progenitors into neutrophils. To clarify the effects of G-CSF on hematopoietic progenitors, we generated transgenic (Tg) mice that had ubiquitous expression of the human G-CSF receptor (hG-CSFR). In clonal cultures of bone marrow and spleen cells obtained from these mice, hG-CSF supported the growth of myelocytic as well as megakaryocytic, mast cell, mixed, and blast cell colonies. Single-cell cultures of lineage-negative (Lin−)c-Kit+Sca-1+ or Sca-1− cells obtained from the Tg mice confirmed the direct effects of hG-CSF on the proliferation and differentiation of various progenitors. hG-CSF also had stimulatory effects on the formation of blast cell colonies in cultures using 5-fluorouracil–resistant hematopoietic progenitors and clone-sorted Lin−c-Kit+Sca-1+ primitive hematopoietic cells. These colonies contained different progenitors in proportions similar to those obtained when mouse interleukin-3 was used in place of hG-CSF. Administration of hG-CSF to Tg mice led to significant increases in spleen colony-forming and mixed/blast cell colony-forming cells in bone marrow and spleen, but did not alter the proportion of myeloid progenitors in total clonogenic cells. These results show that, when functional G-CSFR is present on the cell surface, hG-CSF stimulates the development of primitive multipotential progenitors both in vitro and in vivo, but does not induce exclusive commitment to the myeloid lineage.

Cytokine dependent growth of human TF-1 leukemic cell line in human GM-CSF and IL-3 producing transgenic SCID mice

Although severe combined immunodeficient (SCID) mice are considered useful as an animal model for human hematopoietic diseases, the complete reconstruction of human hematopoietic cells can not be established even in these mice. This appears to be because human cytokines, adhesion molecules and extracellular matrices which support differentiation and growth of human hematopoietic cells differ from those in animals. To improve this animal model, we attempted to produce transgenic (Tg) mice producing human interleukin 3 (hIL-3) and human granulocyte macrophage colony stimulating factor (hGM-CSF) with the homozygote of the scid gene. We established two Tg mouse lines, one releasing both 0.5-1 ng/ml of hIL-3 and 0.05-0.2 ng/ml of hGM-CSF in their sera and another releasing only high (2-10 ng/ml) levels of hGM-CSF. When human cytokine-dependent myeloid cell line, TF-1, was subcutaneously transplanted into these two Tg-SCID mouse lines, TF-1 could be successfully engrafted and grew in all lines of Tg-SCID mice but not in control mice. We also observed that TF-1 grows in GM-CSF Tg-SCID mice in a dose dependent manner in vivo and IL-3 shows an additive effect on its growth. These results indicated that these Tg-SCID mice were an useful in vivo model for investigating human leukemogenesis, especially the role of IL-3 and GM-CSF in leukemogenesis.

Specific Signals Generated by the Cytoplasmic Domain of the Granulocyte Colony-Stimulating Factor (G-CSF) Receptor Are Not Required for G-CSF–Dependent Granulocytic Differentiation

Granulocyte colony-stimulating factor (G-CSF) is the principal growth factor regulating the production of neutrophils, yet its role in lineage commitment and terminal differentiation of hematopoietic progenitor cells is controversial. In this study, we describe a system to study the role of G-CSF receptor (G-CSFR) signals in granulocytic differentiation using retroviral transduction of G-CSFR–deficient, primary hematopoietic progenitor cells. We show that ectopic expression of wild-type G-CSFR in hematopoietic progenitor cells supports G-CSF–dependent differentiation of these cells into mature granulocytes, macrophages, megakaryocytes, and erythroid cells. Furthermore, we show that two mutant G-CSFR proteins, a truncation mutant that deletes the carboxy-terminal 96 amino acids and a chimeric receptor containing the extracellular and transmembrane domains of the G-CSFR fused to the cytoplasmic domain of the erythropoietin receptor, are able to support the production of morphologically mature, chloroacetate esterase-positive, Gr-1/Mac-1–positive neutrophils in response to G-CSF. These results demonstrate that ectopic expression of the G-CSFR in hematopoietic progenitor cells allows for multilineage differentiation and suggest that unique signals generated by the cytoplasmic domain of the G-CSFR are not required for G-CSF–dependent granulocytic differentiation.

Specific Signals Generated by the Cytoplasmic Domain of the Granulocyte Colony-Stimulating Factor (G-CSF) Receptor Are Not Required for G-CSF–Dependent Granulocytic Differentiation

Granulocyte colony-stimulating factor (G-CSF) is the principal growth factor regulating the production of neutrophils, yet its role in lineage commitment and terminal differentiation of hematopoietic progenitor cells is controversial. In this study, we describe a system to study the role of G-CSF receptor (G-CSFR) signals in granulocytic differentiation using retroviral transduction of G-CSFR–deficient, primary hematopoietic progenitor cells. We show that ectopic expression of wild-type G-CSFR in hematopoietic progenitor cells supports G-CSF–dependent differentiation of these cells into mature granulocytes, macrophages, megakaryocytes, and erythroid cells. Furthermore, we show that two mutant G-CSFR proteins, a truncation mutant that deletes the carboxy-terminal 96 amino acids and a chimeric receptor containing the extracellular and transmembrane domains of the G-CSFR fused to the cytoplasmic domain of the erythropoietin receptor, are able to support the production of morphologically mature, chloroacetate esterase-positive, Gr-1/Mac-1–positive neutrophils in response to G-CSF. These results demonstrate that ectopic expression of the G-CSFR in hematopoietic progenitor cells allows for multilineage differentiation and suggest that unique signals generated by the cytoplasmic domain of the G-CSFR are not required for G-CSF–dependent granulocytic differentiation.

The making of an erythroid cell. Molecular control of hematopoiesis

The number of circulating red cells is regulated by the daily balance between two processes: the destruction of the old red cells in the liver and the generation of new cells in the bone marrow. The process during which hematopoietic stem cells generate new red cells is called erythropoiesis. This manuscript will describe the molecular mechanisms involved in the process of erythroid differentiation as we understand them today. In particular it will review how erythroid specific growth factor-receptor interactions activate specific transcription factors to turn on the expression of the genes responsible for the establishment of the erythroid phenotype.

Mammalian granulocyte-macrophage colony-stimulating factor receptor expressed in primary avian hematopoietic progenitors: lineage-specific regulation of proliferation and differentiation

The cytokine Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) regulates proliferation, differentiation, and apoptosis during myelopoiesis and erythropoiesis. Structure-function relationships of GM-CSF interactions with its receptor (GM-R), the biochemistry of GM-R signal transduction, and GM-CSF action in vivo are relatively well understood. Much less is known, however, about GM-R function in primary hematopoietic cells. In this paper we show that expression of the human GM-R in a heterologous cell system (primary avian erythroid and myeloid cells) confirms respective results in murine or human cell lines, but also provides new insights how the GM-R regulates progenitor proliferation and differentiation. As expected, the hGM-CSF stimulated myeloid progenitor proliferation and differentiation and enhanced erythroid progenitor proliferation during terminal differentiation. In the latter cells, however, the hGM-R only partially substituted for the activities of the erythropoietin receptor (EpoR). It failed to replace the EpoR in its cooperation with c-Kit to induce long-term proliferation of erythroid progenitors. Furthermore, the hGM-R alpha chain specifically interfered with EpoR signaling, an activity neither seen for the betac subunit of the receptor complex alone, nor for the alpha chain of the closely related Interleukin-3 receptor. These results point to a novel role of the GM-R alpha chain in defining cell type-specific functions of the GM-R.

Thymocyte proliferation and differentiation in human granulocyte-macrophage colony-stimulating factor receptor transgenic mice

Thymocytes display varying responses to cytokines depending on their stage of differentiation. Whether these responses are due to stage-specific cytokine receptor expression or to downstream signaling mechanisms is unknown. We examined the relationship between receptor expression and thymocyte proliferation or differentiation by using thymocytes from transgenic mice that constitutively expressed the human granulocyte-macrophage colony stimulating factor (hGM-CSF) receptor. Transgenic CD4-CD8-, CD4+CD8-, and CD4-CD8+ thymocyte populations expressing the hGM-CSF receptor proliferated when cultured with hGM-CSF, whereas CD4+CD8+ cells failed to proliferate despite expressing this receptor. We next examined the effect of hGM-CSF receptor signaling on thymocyte differentiation in fetal thymic organ culture supporting a full program of T cell development in vitro. Addition of hGM-CSF to the transgenic fetal thymic organ culture resulted in failure of CD4-CD8- cells to differentiate into CD4+CD8+ cells. To investigate this maturational inhibition more closely, we repopulated wild-type fetal lobes with sorted pro-T, pre-T or post pre-T precursor cells from hGM-CSF receptor transgenic mice. In these cultures hGM-CSF blocked both pro-T and pre-T cell differentiation, whereas the more mature post pre-T cells differentiated normally. These results suggest that hGM-CSF receptor signaling during thymocyte differentiation causes stage-specific inhibition of precursor cell maturation. In addition, repopulation studies of transgenic fetal lobes with sorted wild-type thymocyte precursors indicated that hGM-CSF inhibited proliferation and differentiation of the wild-type precursors, suggesting a secondary effect via transgenic stromal cells.

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF)-dependent in vitro and in vivo proliferation and differentiation of all hematopoietic progenitor cells in hGM-CSF receptor transgenic mice

To examine the relation between receptor expression and differentiation of hematopoietic cells, we produced transgenic mice that constitutively expressed the human granulocyte-macrophage colony stimulating factor (hGM-CSF) receptor at almost all stages of hematopoietic cell development. The high-affinity GM-CSF receptor is species specific, allowing analysis of the specific effects of hGM-CSF in our mouse model. Proliferation and differentiation of hematopoietic progenitor cells from transgenic mice were analyzed by means of methylcellulose colony-forming assay and in vivo treatment with hGM-CSF, respectively. We found that hGM-CSF supported various types of colonies, including granulocyte-macrophage, mast cell, megakaryocyte, blast cell, and mixed hematopoietic colonies, whereas mouse GM-CSF supported only granulocyte-macrophage colonies. In addition, hGM-CSF generated erythrocyte colonies in the absence of erythropoietin. Furthermore, in vivo administration of hGM-CSF to transgenic mice resulted in a dose-dependent increase in reticulocytes and white blood cells in the peripheral blood. The spleens of the mice showed gross enlargement, mainly caused by an increase of erythroid cells and their progenitors. Taken together, these results indicate that hGM-CSF receptor-mediated signals can support the growth of cells of all hematopoietic cell lineages if this receptor is present on the cell surface. This implies that the differentiation of hematopoietic progenitor cells is not determined by exogenous cytokine stimulation (instruction model) but by an intrinsic cell program in which cytokines simply select cells that express the appropriate receptor (stochastic model).

Expression of Activated Mutants of the Human Interleukin-3/Interleukin-5/Granulocyte-Macrophage Colony-Stimulating Factor Receptor Common β Subunit in Primary Hematopoietic Cells Induces Factor-Independent Proliferation and Differentiation

To date, several activating mutations have been discovered in the common signal-transducing subunit (hβc) of the receptors for human granulocyte-macrophage colony-stimulating factor, interleukin-3, and interleukin-5. Two of these, FIΔ and I374N, result in a 37 amino acid duplication and a single amino acid substitution in the extracellular domain of hβc, respectively. A third, V449E, results in a single amino acid substitution in the transmembrane domain. Previous studies comparing the activity of these mutants in different hematopoietic cell lines imply that the transmembrane and extracellular mutations act by different mechanisms and suggest the requirement for cell type-specific molecules in signalling. To characterize the ability of these mutant hβc subunits to mediate growth and differentiation of primary cells and hence investigate their oncogenic potential, we have expressed all three mutants in primary murine hematopoietic cells using retroviral transduction. It is shown that, whereas expression of either extracellular hβc mutant confers factor-independent proliferation and differentiation on cells of the neutrophil and monocyte lineages only, expression of the transmembrane mutant does so on these lineages as well as the eosinophil, basophil, megakaryocyte, and erythroid lineages. Factor-independent myeloid precursors expressing the transmembrane mutant display extended proliferation in liquid culture and in some cases yielded immortalized cell lines.

Expression of Activated Mutants of the Human Interleukin-3/Interleukin-5/Granulocyte-Macrophage Colony-Stimulating Factor Receptor Common β Subunit in Primary Hematopoietic Cells Induces Factor-Independent Proliferation and Differentiation

To date, several activating mutations have been discovered in the common signal-transducing subunit (hβc) of the receptors for human granulocyte-macrophage colony-stimulating factor, interleukin-3, and interleukin-5. Two of these, FIΔ and I374N, result in a 37 amino acid duplication and a single amino acid substitution in the extracellular domain of hβc, respectively. A third, V449E, results in a single amino acid substitution in the transmembrane domain. Previous studies comparing the activity of these mutants in different hematopoietic cell lines imply that the transmembrane and extracellular mutations act by different mechanisms and suggest the requirement for cell type-specific molecules in signalling. To characterize the ability of these mutant hβc subunits to mediate growth and differentiation of primary cells and hence investigate their oncogenic potential, we have expressed all three mutants in primary murine hematopoietic cells using retroviral transduction. It is shown that, whereas expression of either extracellular hβc mutant confers factor-independent proliferation and differentiation on cells of the neutrophil and monocyte lineages only, expression of the transmembrane mutant does so on these lineages as well as the eosinophil, basophil, megakaryocyte, and erythroid lineages. Factor-independent myeloid precursors expressing the transmembrane mutant display extended proliferation in liquid culture and in some cases yielded immortalized cell lines.

Hematopoietic and Lymphopoietic Responses in Human Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF ) Receptor Transgenic Mice Injected With Human GM-CSF

Using a clonal assay of bone marrow (BM) cells from transgenic mice (Tg-mice) expressing the human granulocyte-macrophage colony-stimulating factor receptor (hGM-CSFR), we found in earlier studies that hGM-CSF alone supported the development not only of granulocyte-macrophage colonies, but also of erythrocytes, megakaryocytes, mast cells, blast cells, and mixed hematopoietic colonies. In this report, we evaluated the in vivo effects of hGM-CSF on hematopoietic and lymphopoietic responses in the hGM-CSFR Tg-mice. Administration of this factor to Tg-mice resulted in dose-dependent increases in numbers of reticulocytes and white blood cells (WBCs) in the peripheral blood. Morphological analysis of WBCs showed that the numbers of all types of the cell, including neutrophils, eosinophils, monocytes, and lymphocytes increased; the most remarkable being in lymphocytes that contained a number of large granular lymphocytes (LGLs) in addition to mature T and B cells. However, total cellularity of the BM of the Tg-mice decreased in a dose-dependent manner when hGM-CSF was injected. In sharp contrast to the BM, spleens of the Tg-mice were grossly enlarged. Although all types of blood cells and hematopoietic progenitors increased in the spleen, erythroid cells and their progenitors showed the most significant increase. Increased numbers of megakaryocytes and LGLs were also observed in spleen and liver of the treated Tg-mice. Flow cytometric analysis showed that LGLs expanded in Tg-mice expressed Mac-1+CD3−NK1.1+. The thymus of Tg-mice treated with hGM-CSF exhibited a dose-dependent shrinkage and a remarkable decrease in CD4+CD8+ cells. Thus, hGM-CSF stimulated not only myelopoiesis but also erythropoiesis and megakaryopoiesis of hGM-CSFR Tg-mice in vivo, in accordance with our reported in vitro findings. In addition, hGM-CSF affected the development of lymphoid cells, including natural killer cells of these Tg-mice.

Hematopoietic and Lymphopoietic Responses in Human Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF ) Receptor Transgenic Mice Injected With Human GM-CSF

Using a clonal assay of bone marrow (BM) cells from transgenic mice (Tg-mice) expressing the human granulocyte-macrophage colony-stimulating factor receptor (hGM-CSFR), we found in earlier studies that hGM-CSF alone supported the development not only of granulocyte-macrophage colonies, but also of erythrocytes, megakaryocytes, mast cells, blast cells, and mixed hematopoietic colonies. In this report, we evaluated the in vivo effects of hGM-CSF on hematopoietic and lymphopoietic responses in the hGM-CSFR Tg-mice. Administration of this factor to Tg-mice resulted in dose-dependent increases in numbers of reticulocytes and white blood cells (WBCs) in the peripheral blood. Morphological analysis of WBCs showed that the numbers of all types of the cell, including neutrophils, eosinophils, monocytes, and lymphocytes increased; the most remarkable being in lymphocytes that contained a number of large granular lymphocytes (LGLs) in addition to mature T and B cells. However, total cellularity of the BM of the Tg-mice decreased in a dose-dependent manner when hGM-CSF was injected. In sharp contrast to the BM, spleens of the Tg-mice were grossly enlarged. Although all types of blood cells and hematopoietic progenitors increased in the spleen, erythroid cells and their progenitors showed the most significant increase. Increased numbers of megakaryocytes and LGLs were also observed in spleen and liver of the treated Tg-mice. Flow cytometric analysis showed that LGLs expanded in Tg-mice expressed Mac-1+CD3−NK1.1+. The thymus of Tg-mice treated with hGM-CSF exhibited a dose-dependent shrinkage and a remarkable decrease in CD4+CD8+ cells. Thus, hGM-CSF stimulated not only myelopoiesis but also erythropoiesis and megakaryopoiesis of hGM-CSFR Tg-mice in vivo, in accordance with our reported in vitro findings. In addition, hGM-CSF affected the development of lymphoid cells, including natural killer cells of these Tg-mice.

A possible involvement of Stat5 in erythropoietin-induced hemoglobin synthesis

Erythropoietin (EPO) and its cell surface receptor (EPOR) play central roles in the proliferation and differentiation of mammalian erythroid progenitor cells. Recently both the tyrosine residues in the EPOR responsible for the activation of Stat5 and the role of Stat5 for EPO-dependent cell proliferation have been shown. Here, we describe the roles of Stat5 and of these tyrosine residues in the EPOR in the erythroid differentiation of murine hematopoietic cell line SKT6 which produces hemoglobin in response to EPO. Chimeric receptors carrying the extracellular domain of the EGF receptor and the intracellular domain of the EPOR were introduced into SKT6 cells. Like EPO, EGF equally activated Stat5 and induced hemoglobin. Activation of Stat5 and hemoglobin expression by EGF were markedly impaired in cells expressing the tyrosine mutated chimeric receptors. In addition, ectopic expression of the prolactin receptor, another cytokine receptor that activates Stat5, led to hemoglobin synthesis. Finally, hemoglobin synthesis was severely inhibited by overexpressing a dominant negative form of Stat5. These results collectively suggest that Stat5 plays a role in EPO-mediated hemoglobin synthesis in SKT6 cells.

Receptors That Induce Erythroid Differentiation of Ba/F3 Cells: Structural Requirements and Effect on STAT5 Binding

Ectopic expression of the erythropoietin receptor (EpoR) in the interleukin-3 (IL-3)–dependent cell line Ba/F3 results in growth and partial erythroid differentiation in Epo. In contrast, introduction and activation of the interleukin-5 receptor (IL-5R) or of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR) results in proliferation only. As this effect is specific to the EpoR, the role of its extracellular or cytoplasmic domain in differentiation was tested after construction of two chimeric receptors. One receptor contained the extracellular domain of EpoR fused to the endodomain of IL-3R β-chain (E/β), while the other contained the EpoR cytoplasmic region fused to the extracellular domain of GM-CSFR α-chain (GMER). Surprisingly, both receptors induced differentiation ruling out a strict specificity of the extracellular or cytoplasmic region of EpoR in this process. Instead the ability to signal differentiation correlated with structural features shared by the EpoR, GMER, and E/β receptors. Dimerization of all three receptors results in the pairing of two signal transducing chains in the cytoplasm, in contrast to the mitogenic receptors IL-3R, IL-5R, GM-CSFR, which assemble as αβ heterodimers. Two new chimeric receptors that fulfilled the structural requirement exemplified by EpoR, but lacked any part of EpoR, were designed to consolidate this model. They consisted of the ectodomains of the GMR-α and IL-5Rα, respectively, fused to the endodomain of IL-3R β-chain. Both receptors were as effective as EpoR in signaling differentiation in response to their cognate ligand. Another property of receptors fulfilling these structural requirements is that they cause a marked delay in signal transducers and activators of transcription 5 (STAT5) activation on ligand stimulation. Taken together our studies show that structural assembly of receptors dictates their potential to signal erythroid differentiation in Ba/F3 cells, that differentiation can take place in the absence of Epo and that a delay in STAT5 activation is highly predictive of this process.

Human Granulocyte-Macrophage Colony-Stimulating Factor (hGM-CSF) Induces Inhibition of Intrathymic T-Cell Development in hGM-CSF Receptor Transgenic Mice

Thymocytes show differential cytokine responses, depending on the stage of differentiation. Whether these responses are due to preferential cytokine receptor expression or due to downstream signaling mechanisms is unknown. In this study, we examined the relationship between receptor expression and T-cell proliferation or differentiation using thymocytes from transgenic mice constitutively expressing the human granulocyte-macrophage colony-stimulating factor (hGM-CSF ) receptor. Transgenic CD4−CD8−, CD4+CD8−, and CD4−CD8+ cells proliferated when cultured with hGM-CSF in vitro, whereas CD4+CD8+ cells failed to proliferate. To examine the effect of hGM-CSF receptor signaling on T-cell development, we used fetal thymic organ cultures. The addition of exogenous hGM-CSF resulted in the failure of CD4−CD8− cells to differentiate into CD4+CD8+ cells. To more closely identify this maturational inhibition, we reconstituted normal fetal lobes with sorted pro-T–, pre-T–, or post-pre-T–precursor cells from transgenic mice. The addition of hGM-CSF to these cultures led to a block in both pro-T– and pre-T–cell differentiation, whereas the more mature post-pre-T cells differentiated normally. We propose that hGM-CSF receptor signaling during T-cell development results in a stage-specific inhibition of thymic precursor maturation.

Effects of granulocyte-macrophage colony stimulating factor (GM-CSF) on biomaterial-associated staphylococcal infection in mice

Staphylococcal infections are a major complication in the usage of biomaterials. Different modifications of polymers have been made to reduce the incidence of such infections. We studied the effects of modifying heparinized polyethylene (H-PE) with mouse recombinant granulocyte-macrophage stimulating factor (rGM-CSF). The elimination of staphylococci (Staphylococcus aureus, S. epidermidis) from the peritoneum of mice implanted with rGM-CSF-coated H-PE was slightly more effective than the elimination of the bacteria from the peritoneum of animals implanted with uncoated H-PE. Most interestingly, the number of staphylococci present in the biofilms covering rGM-CSF-coated implants were significantly lower than the number of bacteria detected on the surface of H-PE not coated with rGM-CSF. In vitro, rGM-CSF restored the anti-bacterial potency of the phagocytes, which had been reduced by surface contact with H-PE. The results suggest that modification of biomaterials with rGM-CSF could be one way of preventing staphylococcal infections; especially in neutropenic disorders, which constitute the highest risk factor for foreign body-associated infections.