Recombinant human granulocyte-colony stimulating factor and recombinant human macrophage-colony stimulating factor synergize in vivo to enhance proliferation of granulocyte-macrophage, erythroid, and multipotential progenitor cells in mice

Stress and Non-Stress Roles of Inflammatory Signals during HSC Emergence and Maintenance

Hematopoietic stem cells (HSCs) are a rare population that gives rise to almost all cells of the hematopoietic system, including immune cells. Until recently, it was thought that immune cells sense inflammatory signaling and HSCs respond only secondarily to these signals. However, it was later shown that adult HSCs could directly sense and respond to inflammatory signals, resulting in a higher output of immune cells. Recent studies demonstrated that inflammatory signaling is also vital for HSC ontogeny. These signals are thought to arise in the absence of pathogens, are active during development, and indispensable for HSC formation. In contrast, during times of stress and disease, inflammatory responses can be activated and can have devastating effects on HSCs. In this review, we summarize the current knowledge about inflammatory signaling in HSC development and maintenance, as well as the endogenous molecular cues that can trigger inflammatory pathway activation. Finally, we comment of the role of inflammatory signaling in hematopoietic diseases.

Diverse isoforms of colony-stimulating factor-1 have different effects on the development of stroma-dependent hematopoietic cells

Maintenance and differentiation of hematopoietic stem and progenitor cells are controlled by complex interactions with the stroma microenvironment. Stroma-cell interactions can be supported by locally expressed membrane-spanning cell-surface (cs) growth factors. CSF-1 is expressed by stroma as a soluble glycoprotein, as proteoglycan, or as a membrane-spanning cs glycoprotein. CSF-1 regulates the survival, proliferation, and differentiation of mononuclear phagocytes. Whereas the biological role of soluble CSF-1 is well characterized, the function of the membrane-spanning cell-surface CSF-1 (csCSF-1) remains unclear. To analyze the biological significance of csCSF-1 in vitro, we used an epithelial cell line to ectopically express the different CSF-1 isoforms. In co-cultures of CSF-1 transduced epithelial cells with primary, early hematopoietic progenitor cells we examined whether interaction between csCSF-1 and its receptor mediates cell proliferation, self-renewal, or differentiation. csCSF-1 induces long-lasting proliferation of stimulated cells and furthermore supports self-renewal. Ectopic secretion of soluble CSF-1 does not permit long-term growth of progenitor cells but induces differentiation of monocytes into macrophages. Previously, we showed that the soluble and cs isoforms of stroma-encoded SCF differently affect the development of hematopoietic cells. Cell-surface SCF (csSCF) promotes self-renewal of stimulated cells whereas soluble SCF causes clonal extinction. These results and those presented here for CSF-1 provide evidence for diverse functions of the isoforms of the ligands SCF and CSF-1 for two tyrosine kinase receptors of the subclass III both regulating hematopoiesis on stroma.

Regulation of hematopoiesis by chemokine family members

Chemokines, originally designated as chemoattractant cytokines, comprise a large family of molecules that have been implicated in a number of different functions mediated through chemokine receptors. Among these functions are regulatory roles in hematopoiesis that encompass effects on the proliferation, survival, and homing/migration of myeloid progenitor cells. This article reviews the field of chemokine regulation of hematopoiesis at the level of myeloid progenitor cells.

A comparison of macrophage colony-stimulating factor (M-CSF) gene expression in primary and immortalized endothelial cells

M-CSF is produced by a wide variety of cell types, including EC, fibroblasts, and monocyte/macrophages, where it functions as a survival factor and a chemotactic agent for monocytes. An early event in the development of atherosclerosis is the infiltration of monocytes into the artery wall. Local expression of M-CSF by EC lining the blood vessels is thought to promote the growth and survival of lesional monocytes and macrophages, thus enhancing lesion development and disease progression. Primary cultures of EC are difficult to maintain for long periods of time, which complicates their use for biochemical and molecular analysis. As a step toward identifying a representative endothelial-like cell line, serum-dependent and IL-1-dependent changes in M-CSF gene expression in two endothelial-like cell lines were compared to that detected in primary EC cultures. The data presented here demonstrate that the two endothelial-like cell lines, like primary cultures of EC, express the M-CSF gene under basal conditions. In both types of cell cultures, IL-1alpha stimulation increased M-CSF mRNA levels 2-7-fold, whereas serum stimulation elicited a more modest effect (2-3-fold increase). The IL-1alpha-induced change in M-CSF gene expression is mediated at the transcriptional level, and M-CSF promoter activity is, in part, dependent on the activity of the NF-kappaB-inducing kinase. Collectively, our results demonstrate that either endothelial-like cell line would be a representative model in which endothelial-specific changes in M-CSF gene expression could be identified.

Biopharmaceutical drug development: Filgrastim (r-metHuG-CSF) use in patients with HIV infection

Hematopoietic growth factors are well known to increase neutrophil counts and support the administration of myelotoxic and myelosuppressive therapies, especially chemotherapies. Filgrastim (r-metHuG-CSF) has been used in the setting of HIV disease to treat neutropenia and HIV-associated neutrophil defects. This article reviews the biology, product characteristics, and preclinical and clinical development of Filgrastim. Emphasis is given on the use of Filgrastim in the setting of HIV infection and AIDS.

Enhanced Myeloid Progenitor Cell Cycling and Apoptosis in Mice Lacking the Chemokine Receptor, CCR2

Chemokines regulate hematopoiesis in part by influencing the proliferative status of myeloid progenitor cells (MPC). Human MCP-1/murine JE, a myelosuppressive chemokine, specifically binds C-C chemokine receptor 2 (CCR2). Transgenic mice containing a targeted disruption in CCR2 that prevents expression of CCR2 mRNA and protein and have MPC that are insensitive to inhibition by MCP-1 and JE in vitro were assessed for potential abnormalities in growth of bone marrow (BM) and spleen MPC. MPC in both unseparated and c-kit+lin− populations of BM from CCR2-deficient (−/−) mice were in a greatly increased proliferation state compared with CCR2 littermate control (+/+) mice, an effect not apparent with progenitors from spleens of CCR2 (−/−) mice. Increased cycling status of CCR2 (−/−) BM MPC did not result in increased numbers of nucleated cells or MPC in BM or spleens of CCR2 (−/−) mice. Possible reasons for this apparent discrepancy were highlighted by flow cytometric analysis of c-kit+lin− BM cells and colony formation by MPC subjected to delayed addition of growth factors. The c-kit+lin− population of BM cells from CCR2 (−/−) mice had a significantly higher percentage of apoptotic cells than those from CCR2 (+/+) BM. However, elevated apoptosis was not associated with decreased numbers of c-kit+lin− cells. The increased percentage of apoptotic c-kit+lin− cells was due to elevated apoptosis within the c-kitdimlin−, but not the c-kitbrightlin−, subpopulations of cells. Consistent with enhanced apoptosis of phenotypically defined cells, MPC from CCR2 (−/−) BM and purified c-kit+lin− cells demonstrated decreased cell survival in vitro upon delayed addition of growth factors. The data suggest that signals received by CCR2 limit proliferation of progenitor cells in the BM, but also enhance survival of these cells.

Enhanced Myeloid Progenitor Cell Cycling and Apoptosis in Mice Lacking the Chemokine Receptor, CCR2

Chemokines regulate hematopoiesis in part by influencing the proliferative status of myeloid progenitor cells (MPC). Human MCP-1/murine JE, a myelosuppressive chemokine, specifically binds C-C chemokine receptor 2 (CCR2). Transgenic mice containing a targeted disruption in CCR2 that prevents expression of CCR2 mRNA and protein and have MPC that are insensitive to inhibition by MCP-1 and JE in vitro were assessed for potential abnormalities in growth of bone marrow (BM) and spleen MPC. MPC in both unseparated and c-kit+lin− populations of BM from CCR2-deficient (−/−) mice were in a greatly increased proliferation state compared with CCR2 littermate control (+/+) mice, an effect not apparent with progenitors from spleens of CCR2 (−/−) mice. Increased cycling status of CCR2 (−/−) BM MPC did not result in increased numbers of nucleated cells or MPC in BM or spleens of CCR2 (−/−) mice. Possible reasons for this apparent discrepancy were highlighted by flow cytometric analysis of c-kit+lin− BM cells and colony formation by MPC subjected to delayed addition of growth factors. The c-kit+lin− population of BM cells from CCR2 (−/−) mice had a significantly higher percentage of apoptotic cells than those from CCR2 (+/+) BM. However, elevated apoptosis was not associated with decreased numbers of c-kit+lin− cells. The increased percentage of apoptotic c-kit+lin− cells was due to elevated apoptosis within the c-kitdimlin−, but not the c-kitbrightlin−, subpopulations of cells. Consistent with enhanced apoptosis of phenotypically defined cells, MPC from CCR2 (−/−) BM and purified c-kit+lin− cells demonstrated decreased cell survival in vitro upon delayed addition of growth factors. The data suggest that signals received by CCR2 limit proliferation of progenitor cells in the BM, but also enhance survival of these cells.

Granulocyte colony-stimulating factor and drugs elevating extracellular adenosine synergize to enhance haematopoietic reconstitution in irradiated mice

The activation of adenosine receptors has recently been demonstrated to stimulate haematopoiesis. In the present study, we investigated the ability of drugs elevating extracellular adenosine to influence curative effects of granulocyte colony-stimulating factor (G-CSF) in mice exposed to a sublethal dose of 4 Gy of 60Co radiation. Elevation of extracellular adenosine in mice was induced by the combined administration of dipyridamole, a drug inhibiting the cellular uptake of adenosine, and adenosine monophosphate (AMP), an adenosine prodrug. The effects of dipyridamole plus AMP, and G-CSF, administered either alone or in combination, were evaluated. The drugs were injected to mice in a 4-d treatment regimen starting on d 3 after irradiation and the haematopoietic response was evaluated on d 7, 10, 14, 18 and 24 after irradiation. While the effects of G-CSF on the late maturation stages of blood cells, appearing shortly after the completion of the treatment, were not influenced by dipyridamole plus AMP, positive effects of the combination therapy occurred in the post-irradiation recovery phase which is dependent on the repopulation of haematopoietic stem cells. This was indicated by the significant elevation of counts of granulocyte-macrophage progenitor cells (GM-CFC) and granulocytic cells in the bone marrow (d 14), of GM-CFC (d 14), granulocytic and erythroid cells (d 14 and 18) in the spleen, and of neutrophils (d 18), monocytes (d 14 and 18) and platelets (d 18) in the peripheral blood. These effects suggest that the repopulation potential of the combination therapy lies in a common multilineage cell population. The results of this study implicate the promising possibility to enhance the curative effects of G-CSF under conditions of myelosuppressive states induced by radiation exposure.