Vascular cell adhesion molecule-1 (CD106) is cleaved by neutrophil proteases in the bone marrow following hematopoietic progenitor cell mobilization by granulocyte colony-stimulating factor

Detection and quantification of functionally defined hematopoietic progenitor cells and tissue specific mRNA within the peripheral blood of myeloma patients after administration of granulocyte colony-stimulating factor and erythropoietin

OBJECTIVE

Hematopoietic progenitor cells (HPC) as well as tissue committed stem cells expressing mRNA specific to various somatic tissues are thought to be part of the CD34+ bone marrow compartment. In this study, we explore and quantify their mobilization in patients with multiple myeloma undergoing chemotherapy upon administration of granulocyte colony-stimulating factor (G-CSF) plus/minus erythropoietin (EPO).

PATIENTS AND METHODS

HPC were quantified by flow cytometry and functional assays within the blood of healthy donors and myeloma patients before and after chemotherapy followed by G-CSF or G-CSF + EPO given subcutaneously. The mRNA expression was studied by quantitative polymerase chain reaction (PCR). Cytokines and peripheral blood protease levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

EPO did not significantly alter the number of HPC mobilized by G-CSF alone, and mRNA specific for liver, brain, muscle and kidney was detected in both treatment groups. Quantitative PCR analysis revealed a 2.7-fold increased expression of glial fibrillary acidic protein after G-CSF + EPO administration compared to G-CSF alone (P = 0.003). The concentration of G-CSF rose from 62 +/- 22 pg/mL and 48 +/- 10 pg/mL to 28 +/- 9 ng/mL and 85 +/- 10 ng/mL after 10 d of treatment with G-CSF and G-CSF + EPO, respectively. The concentration of neutrophil elastase (NE) rose only in the G-CSF group by a factor 1.5.

CONCLUSION

The alteration of G-CSF and NE levels as well as the expression of tissue committed RNA after the administration of EPO in addition to G-CSF indicate that different growth factors mobilize different stem cells that might potentially be used for the support of tissue repair in future treatment protocols.

The human-sheep chimeras as a model for human stem cell mobilization and evaluation of hematopoietic grafts' potential

OBJECTIVE

To investigate whether the sheep xenograft model of human hematopoiesis can be used to mimic mobilization of human hematopoietic stem cells in vivo.

MATERIAL AND METHODS

Sheep transplanted with 3.6 x 10(6) CD34+ from human adult bone marrow were mobilized 1.5 years posttransplantation with human granulocyte colony-stimulating factor for 5 days. At day 3 and 4 of mobilization, human cells were harvested from peripheral blood (PB) and bone marrow (BM) and were injected into secondary sheep recipients (n = 6) and these animals were analyzed for the presence of human cells in their BM and PB, starting at 3.5 months posttransplantation.

RESULTS

Maximum mobilization of human cells in PB occurred at day 3, with a 21-fold increase in total numbers of human cells, and a recovery of 5.5 x 10(4)/mL CD34+. In the BM, maximal numbers of human cells were achieved at day 4, with a 6.3-fold increase and a recovery of 1.5 x 10(4)/mL CD34+ cells. PB and BM mobilized human cells were then transplanted into new sheep recipients, and analysis at 3.5 months posttransplantation demonstrated that levels of human cell engraftment in BM of the group transplanted with mobilized PB were significantly lower than those transplanted with BM cells (0.6% +/- 0.1% vs 8.0% +/- 1.8%). Furthermore, in sheep transplanted with mobilized PB, the levels of human cells in circulation remained 2.5-fold higher than the levels of human cells found in their BM.

CONCLUSION

Mobilization of human cells in the sheep model parallels human PB and BM hematopoietic stem cells (HSC) mobilization in healthy human donors in their ability to engraft, differentiate, and repopulate secondary hosts. Thus, this model can become a useful tool to study mobilization regimens, mechanisms, and quality of products obtained.

Bone marrow-derived cells and arterial disease

This article reviews the association between bone and artery disease, with particular relevance to progenitor cells. The review was based on insight gained by analysis of previous publications and on-going work by the authors. A large number of studies have demonstrated a correlation between bone pathology, particularly osteoporosis, and atherosclerosis. In this review we highlight the particular aspect of bone marrow progenitor cells in the bone-artery link. Progenitor cells, primarily those believed to give rise to endothelial cells, have been inversely correlated with atherosclerosis severity and risk factors. Therapeutic approaches aimed at manipulating progenitor cells in revascularization and vascular repair have demonstrated some promising results. Subtypes of progenitor cells have also been linked with vascular pathology, however, and further studies are required to assess relative beneficial and pathologic effects of bone marrow-derived progenitors. Further understanding of the link between bone and artery pathophysiology is likely to be of significant value in developing new therapies for vascular disease.

Hematopoietic growth factors for hematopoietic stem cell mobilization and expansion

During inflammation and cytopenia, increased levels of hematopoietic growth factors (HPGFs) induce mobilization and proliferation of hematopoietic stem cells and hematopoietic progenitor cells (HPCs), resulting in spatial and quantitative in vivo expansion of the hematopoietic tissue. Exogenous administration of recombinant HPGFs, particularly granulocyte colony-stimulating factor (G-CSF), is routine for mobilization of stem cells, followed by collection and transplantation of autologous or allogeneic stem cells. In this review, we summarize experience using different HPGFs and HPGF combinations for stem cell mobilization, such as G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), stem cell factor (SCF), and others. Preclinical and clinical studies of so-called early- and late-acting HPGFs for ex vivo expansion of HPCs are discussed, also with respect to the unresolved question whether expansion of repopulating stem cells can be achieved in vitro.

A novel role of complement in mobilization: immunodeficient mice are poor granulocyte-colony stimulating factor mobilizers because they lack complement-activating immunoglobulins

Complement (C) and innate immunity emerge as important and underappreciated modulators of mobilization of hematopoietic stem/progenitor cells (HSPC). We reported that (a) C becomes activated in bone marrow (BM) during granulocyte-colony-stimulating factor (G-CSF)-induced mobilization by the classic immunoglobulin (Ig)-dependent pathway and that (b) C3 cleavage fragments increase the responsiveness of HSPC to a stromal derived factor-1 gradient. Since patients suffering from severe combined immunodeficiency (SCID) mobilize poorly, we hypothesized that this could be directly linked to the lack of C activating Ig in these patients. In the current study to better elucidate the role of C activation in HSPC mobilization, we mobilized mice that lack Ig (RAG2, SCID, and Jh) by G-CSF or zymosan, compounds that activate C by the classic Ig-dependent and the alternative Ig-independent pathways, respectively. In addition, we evaluated mobilization in C5-deficient animals. Mobilization was evaluated by measuring the number of colony-forming unit-granulocyte macrophage and leukocytes circulating in peripheral blood. We found that (a) G-CSF- but not zymosan-induced mobilization was severely reduced in RAG2, SCID, and Jh mice; (b) impaired G-CSF-induced mobilization was restored after infusion of purified wild-type Ig; and (c) mobilization was severely reduced in C5-deficient mice. These data provide strong evidence that the C system plays a pivotal role in mobilization of HSPC and that egress of HSPC from BM occurs as part of an immune response. Disclosure of potential conflicts of interest is found at the end of this article.

Neutrophil elastase converts human immature dendritic cells into transforming growth factor-beta1-secreting cells and reduces allostimulatory ability

During microbial infection, neutrophils (polymorphonuclear leukocytes; PMNs) activate dendritic cells (DCs). However, early reports illustrated that neutrophil-derived mediators may suppress responses to mitogens. In the present study, we investigated the mechanism used by PMNs to modulate the immunostimulatory ability of DCs. Autologous syngeneic PMNs decreased T-cell proliferation induced by allogeneic DCs. Culture supernatant (CS) derived from PMNs also decreased allostimulation ability of immature DCs and increased the expression of transforming growth factor (TGF)-beta1 on DCs. A TGF-beta1 monoclonal antibody, a CD40 monoclonal antibody, or a serine protease inhibitor reversed the effect of PMN CS on DC allostimulatory ability. Furthermore, elastase reproduced the inhibitory effect of PMN CS on DC allostimulatory ability and the TGF-beta1 production. The role of elastase was confirmed by examining PMN CS from two patients with cyclic neutropenia, a disease due to mutations in the neutrophil elastase gene. These PMN CS samples had reduced elastase activity and were unable to increase DC TGF-beta1 production. Moreover, elastase and PMN CS induced IkappaBalpha degradation in DCs. We conclude that PMNs decrease DC allostimulatory ability via production of elastase leading to a switch of immature DCs into TGF-beta1-secreting cells.

Src family kinase-mediated negative regulation of hematopoietic stem cell mobilization involves both intrinsic and microenvironmental factors

OBJECTIVE

The intracellular signals that contribute to granulocyte colony-stimulating factor (G-CSF) receptor induced stem cell mobilization are poorly characterized.

METHODS

We show enhanced G-CSF induced mobilization of stem cells in mice deficient in expression of Src family kinases (SFK-/-), which is associated with hypersensitivity of SFK-/- bone marrow cells to G-CSF as well as sustained activation of signal transducer and activator of transcription-3.

RESULTS

A proteome map of the bone marrow fluid derived from wild-type and SFK-/- mice revealed a significant global reduction in the number of proteins in SFK-/- mice compared to controls, which was associated with elevated matrix metalloproteinase-9 levels, reduced stromal-derived factor-1 expression, and enhanced breakdown of vascular cell adhesion molecule-1. Transplantation of wild-type or SFK-/- stem cells into wild-type mice and treatment with G-CSF recapitulated the G-CSF-induced increase in stem cell mobilization noted in SFK-/- nontransplanted mice; however, the increase was significantly less. G-CSF treatment of SFK-/- mice engrafted with wild-type stem cells also demonstrated a modest increase in stem cell mobilization compared to controls, however, the observed increase was greatest in mice completely devoid of SFKs.

CONCLUSIONS

These data suggest an involvement of both hematopoietic intrinsic and microenvironmental factors in Src kinase-mediated mobilization of stem cells and identify Src kinases as potential targets for modulating stem cell mobilization.

Cytokines and hematopoietic stem cell mobilization

Hematopoietic stem cell transplantation (HSCT) has become the standard of care for the treatment of many hematologic malignancies, chemotherapy sensitive relapsed acute leukemias or lymphomas, multiple myeloma; and for some non-malignant diseases such as aplastic anemia and immunodeficient states. The hematopoietic stem cell (HSC) resides in the bone marrow (BM). A number of chemokines and cytokines have been shown in vivo and in clinical trials to enhance trafficking of HSC into the peripheral blood. This process, termed stem cell mobilization, results in the collection of HSC via apheresis for both autologous and allogeneic transplantation. Enhanced understanding of HSC biology, processes involved in HSC microenvironmental interactions and the critical ligands, receptors and cellular proteases involved in HSC homing and mobilization, with an emphasis on G-CSF induced HSC mobilization, form the basis of this review. We will describe the key features and dynamic processes involved in HSC mobilization and focus on the key ligand-receptor pairs including CXCR4/SDF1, VLA4/VCAM1, CD62L/PSGL, CD44/HA, and Kit/KL. In addition we will describe food and drug administration (FDA) approved and agents currently in clinical development for enhancing HSC mobilization and transplantation outcomes.

Hematopoietic progenitor cell mobilization results in hypoxia with increased hypoxia-inducible transcription factor-1 alpha and vascular endothelial growth factor A in bone marrow

Despite the fact that many hypoxia-inducible genes are important in hematopoiesis, the spatial distribution of oxygen in the bone marrow (BM) has not previously been explored in vivo. Using the hypoxia bioprobe pimonidazole, we showed by confocal laser scanning microscopy that the endosteum at the bone-BM interface is hypoxic, with constitutive expression of hypoxia-inducible transcription factor-1alpha (HIF-1alpha) protein in steady-state mice. Interestingly, at the peak of hematopoietic stem and progenitor cell (HSPC) mobilization induced by either granulocyte colony-stimulating factor or cyclophosphamide, hypoxic areas expand through the central BM. Furthermore, we found that HSPC mobilization leads to increased levels of HIF-1alpha protein and increased expression of vascular endothelial growth factor A (VEGF-A) mRNA throughout the BM, with an accumulation of VEGF-A protein in BM endothelial sinuses. VEGF-A is a cytokine known to induce stem cell mobilization, vasodilatation, and vascular permeability in vivo. We therefore propose that the expansion in myeloid progenitors that occurs during mobilization depletes the BM hematopoietic microenvironment of O(2), leading to local hypoxia, stabilization of HIF-1alpha transcription factor in BM cells, increased transcription of VEGF-A, and accumulation of VEGF-A protein on BM sinuses that increases vascular permeability. Disclosure of potential conflicts of interest is found at the end of this article.

Expression of mineralization markers in dental pulp cells

There is an increasing interest in the utility of dental pulp stem cells (DPSCs) for dentin regeneration. The mechanisms involved in DPSC differentiation remain poorly understood. The purpose of the study was to investigate the mineralization capacity of human dental pulp cells (DPCs) and identify potential markers for odontoblast differentiation. The isolated DPCs expressed mesenchymal stem-cell markers as shown by flow cytometry and could differentiate in vitro into odontogenic, adipogenic, and chondrogenic lineages. Alkaline phosphatase activity of DPCs elevated over time, with significant upregulation on day 21 in odontogenic induction. Quantitative RT-PCR revealed that osteocalcin, dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoglycoprotein (MEPE) expression also increased time dependently in the induction cultures. In conclusion, we isolated DPCs with stem cell characteristics. MEPE and DSPP showed a similar regulatory pattern of DPCs mineralization. MEPE along with DSPP may be potential odontogenetic differentiation markers.

Effects of AMD3100 on transmigration and survival of acute myelogenous leukemia cells

Acute myelogenous leukaemia (AML) blasts transmigrate in response to SDF-1alpha. AMD3100, a novel bicyclam molecule which inhibits stromal-derived factor (SDF)-1alpha/CXCR4 interactions, inhibited the transmigration of AML blasts and inhibited outgrowth of leukemia colony forming units. AMD3100 did not abrogate stroma-mediated protection from cytarabine-mediated apoptosis, except in the case of one promyelocytic leukemic sample tested, and it did not influence adhesion of blasts to endothelial monolayers. When AML blasts were pretreated with AMD3100, the positive effects of SDF-1alpha on NOD/SCID engraftment were diminished. This work confirms that AML is influenced by the SDF-1alpha/CXCR4 axis and demonstrates that disruption of this axis by the bicyclam AMD3100 can influence AML microenvironmental interactions.

Granulocyte colony-stimulating factor and an RARalpha specific agonist, VTP195183, synergize to enhance the mobilization of hematopoietic progenitor cells

BACKGROUND

Failure to mobilize adequate numbers of hematopoietic stem and progenitor cells (HSPC) is an important clinical problem. Since bone marrow (BM) neutrophils play a central role in HSPC mobilization, we hypothesized that granulocyte colony-stimulating factor (G-CSF)-mediated mobilization would be enhanced by further expanding the size of the BM granulocyte pool.

METHODS

We tested the potential of the retinoic acid receptor alpha (RARalpha) specific agonist VTP195183, and the pan-RAR agonist all-trans retinoic acid (ATRA), to enhance G-CSF-mediated mobilization of HSPC, in two mouse strains.

RESULTS

Pretreatment of mice with VTP195183 significantly increased the number of leukocytes, colony-forming cells, and early engrafting hematopoietic stem cells (HSC) mobilized in the blood in response to G-CSF. In contrast, ATRA had only a marginal effect on G-CSF-induced mobilization. HSPC mobilization synergy between VTP195183 and G-CSF occurred only when mice were preconditioned with VTP195183 prior to G-CSF. This preconditioning was shown to increase the numbers of granulocyte/macrophage progenitors in the BM. Treatment with VTP195183 and G-CSF was accompanied by enhanced levels of active neutrophil proteases in the BM extracellular fluid compared to G-CSF treatment alone.

CONCLUSIONS

VTP195183 treatment increases the numbers of immature granulocyte progenitors in BM and subsequently synergizes to enhance G-CSF-mediated mobilization of HSPC. These data demonstrate a novel approach to improve G-CSF-induced mobilization by accelerating granulocyte maturation in the BM. These findings are currently being tested in a clinical trial of VTP195183 plus G-CSF for mobilization of HSPC in human patients.

Mobilizing stem cells from normal donors: is it possible to improve upon G-CSF?

Currently, granulocyte colony stimulating factor (G-CSF) remains the standard mobilizing agent for peripheral blood stem cell (PBSC) donors, allowing the safe collection of adequate PBSCs from the vast majority of donors. However, G-CSF mobilization can be associated with some significant side effects and requires a multi-day dosing regimen. The other cytokine approved for stem cell mobilization, granulocyte-macrophage colony stimulating factor (GM-CSF), alters graft composition and may reduce the development of graft-versus-host disease, but a significant minority of donors fails to provide sufficient CD34+ cells with GM-CSF and some experience unacceptable toxicity. AMD3100 is a promising new mobilizing agent, which may have several advantages over G-CSF for donor mobilization. As it is a direct antagonist of the interaction between the chemokine stromal-derived factor-1 and its receptor CXCR4, AMD3100 mobilizes PBSCs within hours rather than days. It is also well tolerated, with no significant side effects reported in any of the clinical trials to date. Studies of autologous and allogeneic transplantation of AMD3100 mobilized grafts have demonstrated prompt and stable engraftment. Here, we review the current state of stem cell mobilization in normal donors and discuss novel strategies for donor stem cell mobilization.

Differentiation potential of adult human mesenchymal stem cells

Human mesenchymal stem cells (HMSCs) which are isolated from bone marrow stroma, peripheral blood, dermis, muscle and adipose tissue have the advantage of potential autologous transplantation ability. They can be differentiated into chondrogenic, osteogenic, adipogenic and myogenic lineages. Problems of stem cells from bone marrow are low cell numbers, low isolated volumes, pain, and to some extent ethical concerns. The isolation of mesenchymal stem cells from human adipose tissue was recently identified as an alternative source, since these cells are easy to obtain in big cell numbers. Adipose tissue is derived from embryonic mesoderm and contains a heterogeneous stromal cell population. To achieve lineage-specific differentiation of these cells they have to be cultured in media supplemented with appropriate factors. Inductions of the cells into multiple mesenchymal lineages resulted in the expression of several lineage-specific genes, proteins and specific metabolic activity. In conclusion, the potential benefit of the multi-germline capacity of HMSCs seems to be a promising approach for allogenic cell therapy and human tissue engineering.

Stage specific gene expression of serpins and their cognate proteases during myeloid differentiation

Proteases and their serpin inhibitors are abundantly expressed in haemopoietic and peripheral blood cells. There is, however, relatively little information about the role played by serpins in the control of protease activity within these cells and in the pericellular region. The observation that mutations in the neutrophil elastase gene, which cause cyclic and severe congenital neutropenia, are associated with protease maldistribution gives some clue as to the potential importance of inhibitor proteins. To begin to address the role of protease/inhibitor balance in blood cells we used reverse transcription polymerase chain reaction to examine protease and serpin gene expression in mature peripheral blood cells, differentiating haemopoietic progenitors, leukaemic blasts and haemopoietic cell lines. The results demonstrate stage-specific expression of proteases together with widespread expression of intra- and extra-cellular serpins. The elastase inhibitors monocyte neutrophil elastase inhibitor (MNEI) and antitrypsin (AT) showed overlapping expression. MNEI is predominantly expressed in early haemopoietic progenitors while antitrypsin is mainly expressed in more mature myeloid precursors, peripheral blood granulocytes and mononuclear cells. Our results give an overall picture of serpin and protease gene expression and draws attention to the potential importance of elastase regulators at all stages of myelopoiesis.

Repeated hematopoietic stem and progenitor cell mobilization without depletion of the bone marrow stem and progenitor cell pool in mice after repeated administration of recombinant murine G-CSF

Administration of recombinant-human G-CSF (rhG-CSF) is highly efficient in mobilizing hematopoietic stem and progenitor cells (HSC/HPC) from the bone marrow (BM) toward the peripheral blood. This study was designed to investigate whether repeated G-CSF-induced HSC/HPC mobilization in mice could lead to a depletion of the bone marrow HSC/HPC pool with subsequent loss of mobilizing capacity. To test this hypothesis Balb/c mice were treated with a maximum of 12 repeated 5-day cycles of either 10 microg rhG-CSF/day or 0.25 microg rmG-CSF/day. Repeated administration of rhG-CSF lead to strong inhibition of HSC/HPC mobilization toward the peripheral blood and spleen after >4 cycles because of the induction of anti-rhG-CSF antibodies. In contrast, after repeated administration of rmG-CSF, HSC/HPC mobilizing capacity remained intact for up to 12 cycles. The number of CFU-GM per femur did not significantly change for up to 12 cycles. We conclude that repeated administration of G-CSF does not lead to depletion of the bone marrow HSC/HPC pool.

Thrombocytopenia in association with splenomegaly during granulocyte-colony-stimulating factor treatment in mice is not caused by hypersplenism and is resolved spontaneously

BACKGROUND

Granulocyte-colony-stimulating factor (G-CSF) is used for hematopoietic progenitor cell (HPC) mobilization. Platelet (PLT) counts decrease during G-CSF administration. The mechanisms have not been determined, however. Because splenic pooling of PLTs caused thrombocytopenia in patients with splenomegaly and splenic enlargement was observed in G-CSF-treated donors, it was hypothesized that hypersplenism might cause G-CSF-induced thrombocytopenia.

STUDY DESIGN AND METHODS

Mice were treated with several concentrations of G-CSF, and PLT count was measured. Because transfused PLTs should be cleared rapidly from the blood stream under hypersplenic state, PLT life span was studied. To determine direct role of spleen on thrombocytopenia, G-CSF was given to splenectomized mice. Because PLT count did not decrease in G-CSF-expressing transgenic mice, G-CSF was given to mice for a longer period of time and PLT count was investigated.

RESULTS

PLT counts decreased while spleen weight increased in a dose-dependent manner by G-CSF treatment. No significant difference in PLT life span was found between G-CSF-treated and control mice. Histologic analysis showed no significant increase in PLT numbers trapped in either spleen or other tissue after PLT transfusion in G-CSF-treated mice. In splenectomized mice as well as in normal mice, G-CSF caused thrombocytopenia. When G-CSF was given to mice for a longer period of time, PLT counts decreased during the first 7 days and thereafter began to increase followed by returning to baseline on Day 15.

CONCLUSION

Thrombocytopenia coincided with splenomegaly during G-CSF treatment, but hypersplenism was not responsible for thrombocytopenia. G-CSF-induced thrombocytopenia was a transient event and improved spontaneously despite continual G-CSF treatment.

Soluble adhesion molecules and angiotensin-converting enzyme in dementia

We aimed to determine plasma and cerebrospinal fluid (CSF) levels of angiotensin-converting enzyme (ACE) and the soluble forms of intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1) and platelet endothelial cell adhesion molecule-1 (sPECAM-1) as surrogate markers for endothelial cell activation in clinically diagnosed patients with Alzheimer's disease (AD, n=260), dementia with Lewy bodies (DLB, n=39) and non-demented controls (n=34). Plasma sICAM-1 and sPECAM-1 were higher and CSF sVCAM-1 were lower in AD and DLB patients than in controls (p<0.001). DLB patients had higher CSF sICAM-1, but lower CSF sVCAM-1 (p<0.001). No difference in ACE levels was found between the dementia groups and controls. In controls and AD patients CSF sICAM and sVCAM-1 strongly correlated with each other and with blood barrier permeability whereas in DLB group these correlations were weaker. The observed patterns in adhesion molecules may reflect distinctions in the pathophysiological basis of their generation in dementia patients.

Regulation of neutrophil homeostasis

PURPOSE OF REVIEW

Neutrophils are an essential component of the innate immune response and a major contributor to inflammation. Consequently, neutrophil number in the blood is tightly regulated. Herein, we review recent studies that have greatly advanced our understanding of the mechanisms controlling neutrophil homeostasis.

RECENT FINDINGS

Accumulating evidence shows that stromal derived factor-1 (CXCL12) through interaction with its major receptor CXCR4 provides a key retention signal for neutrophils in the bone marrow. Granulocyte colony-stimulating factor induces neutrophil release from the bone marrow, in major part, by disrupting stromal derived factor-1/CXCR4 signaling. Granulocyte colony-stimulating factor expression is regulated by a novel feedback loop that senses neutrophil emigration into tissues. Specifically, engulfment of apoptotic neutrophils by tissue phagocytes initiates a cytokine cascade that includes interleukin-23, interleukin-17, and ultimately granulocyte colony-stimulating factor.

SUMMARY

Granulocyte colony-stimulating factor plays a central role in the dynamic regulation of neutrophil production and release from the bone marrow in response to environmental stresses. Recent studies have begun to elucidate both the pathways linking neutrophil clearance to granulocyte colony-stimulating factor expression and the mechanisms by which the factor induces neutrophil release from the bone marrow. These studies may lead to novel strategies to modulate neutrophil responses in host defense and inflammation.

Mobilization of bone marrow-derived progenitors

Bone marrow (BM) is a source of various stem and progenitor cells in the adult, and it is able to regenerate a variety of tissues following transplantation. In the 1970s the first BM stem cells identified were hematopoietic stem cells (HSCs). HSCs have the potential to differentiate into all myeloid (including erythroid) and lymphoid cell lineages in vitro and reconstitute the entire hematopoietic and immune systems following transplantation in vivo. More recently, nonhematopoietic stem and progenitor cells have been identified that can differentiate into other cell types such as endothelial progenitor cells (EPCs), contributing to the neovascularization of tumors as well as ischemic tissues, and mesenchymal stem cells (MSCs), which are able to differentiate into many cells of ectodermal, endodermal, and mesodermal origins in vitro as well as in vivo. Following adequate stimulation, stem and progenitor cells can be forced out of the BM to circulate into the peripheral blood, a phenomenon called "mobilization." This chapter reviews the molecular mechanisms behind mobilization and how these have led to the various strategies employed to mobilize BM-derived stem and progenitor cells in experimental and clinical settings. Mobilization of HSCs will be reviewed first, as it has been best-explored--being used extensively in clinics to transplant large numbers of HSCs to rescue cancer patients requiring hematopoietic reconstitution--and provides a paradigm that can be generalized to the mobilization of other types of BM-derived stem and progenitor cells in order to repair other tissues.

Effects of Granulocyte Colony Stimulating Factor on Functional Activities of Endothelial Progenitor Cells in Patients With Chronic Ischemic Heart Disease

OBJECTIVE

Bone marrow-derived circulating endothelial progenitor cells (EPCs) may contribute to regeneration of infarcted myocardium and enhance neovascularization. Granulocyte colony-stimulating factor (G-CSF) is well-established to mobilize hematopoietic stem cells (HSCs) and might, thereby, also increase the pool of endogenously circulating EPC. Therefore, we investigated the effects of G-CSF administration on mobilization and functional activities of blood-derived EPC in patients with chronic ischemic heart disease (CIHD).

METHODS AND RESULTS

Sixteen patients with CIHD received 10 microg/kg per day subcutaneous G-CSF injection for 5 days. Leukocyte counts, the number of HSCs and EPCs, and the migratory response to VEGF and SDF-1 were analyzed before and after G-CSF-therapy. At day 5 of G-CSF treatment, the number of circulating leukocytes, CD34+ CD45+ and CD34+ CD133+ cells was significantly increased. Likewise, G-CSF treatment augmented the numbers of colony forming units with endothelial cell morphology (EC-CFU). However, the functional activity of the EPC as assessed by the migratory response to VEGF and SDF-1 was significantly reduced after G-CSF treatment (P<0.01). Because G-CSF was previously shown to cleave the CXCR4 receptor, we determined the surface expression of the 6H8 epitope of the CXCR4 receptor by fluorescence-activated cell sorter (FACS) analysis. Consistent with the reduced migratory capacity, the surface expression of the functionally active CXCR4 receptor was significantly reduced. To test the functional activity of the cultivated EPCs in vivo, cells were intravenously infused in nude mice after hind limb ischemia. EPCs, which were cultivated before G-CSF administration, increased blood flow recovery and prevented limb necrosis. However, infusion of EPCs, which were isolated 5 days after G-CSF treatment from the same patient, showed a reduced capacity to augment blood flow recovery and to prevent necrosis by 27%.

CONCLUSIONS

G-CSF treatment effectively mobilizes HSCs and EPCs. However, the migratory response to SDF-1 and in vivo capacity of G-CSF-mobilized EPCs was significantly reduced.

Understanding hematopoietic stem-cell microenvironments

The hematopoietic system is the paradigm for adult mammalian stem-cell research. Recent advances have improved our understanding of the cellular and molecular components of the microenvironment - or niche - that regulates hematopoietic stem cells (HSCs). Here, we summarize the molecular and cellular properties of two types of niche, namely the osteoblastic and the vascular niche, in homeostatic regulation of HSC behavior, including its maintenance, proliferation, differentiation, mobilization and homing. We highlight the most recent findings and point to an important trend to the study of niche activity in cancers. Knowledge of the basic features of the HSC niches, including physical location, cell type and various signaling pathways, should provide insights into other stem-cell systems and benefit clinical applications.

Placental Growth Factor-1 Potentiates Hematopoietic Progenitor Cell Mobilization Induced by Granulocyte Colony-Stimulating Factor in Mice and Nonhuman Primates

The complex hematopoietic effects of placental growth factor (PlGF) prompted us to test in mice and nonhuman primates the mobilization of peripheral blood progenitor cells (PBPCs) elicited by recombinant mouse PlGF-2 (rmPlGF-2) and recombinant human PlGF-1 (rhPlGF-1). PBPC mobilization was evaluated by assaying colony-forming cells (CFCs), high-proliferative potential-CFCs (HPP-CFCs), and long-term culture-initiating cells (LTC-ICs). In mice, both rmPlGF-2 and rhPlGF-1 used as single agents failed to mobilize PBPCs, whereas the combination of rhPlGF-1 and granulocyte colony-stimulating factor (rhG-CSF) increased CFCs and LTC-ICs per milliliter of blood by four- and eightfold, respectively, as compared with rhG-CSF alone. rhPlGF-1 plus rhG-CSF significantly increased matrix metalloproteinase-9 plasma levels over rhG-CSF alone, suggesting a mechanistic explanation for rhPlGF-1/rhG-CSF synergism. In rhesus monkeys, rhPlGF-1 alone had no mobilization effect, whereas rhPlGF-1 (260 microg/kg per day) plus rhG-CSF (100 microg/kg per day) increased rhG-CSF-elicited mobilization of CFCs, HPP-CFCs, and LTC-ICs per milliliter of blood by 5-, 7-, and 15-fold, respectively. No specific toxicity was associated with the administration of rhPlGF-1 alone or in combination. In conclusion, our data demonstrate that rhPlGF-1 significantly increases rhG-CSF-elicited hematopoietic mobilization and provide a preclinical rationale for evaluating rhPlGF-1 in the clinical setting.

Cathepsin G: the significance in rheumatoid arthritis as a monocyte chemoattractant

Human cathepsin G (EC 3.4.21.20) has been reported to have the in vitro chemotactic activity for human monocytes. In this study, we examined the role of cathepsin G in monocyte involvement in joint inflammation of rheumatoid arthritis (RA) as a monocyte chemoattractant. Eighteen patients with RA and four patients with osteoarthritis (OA) were used in this study. Thiobenzylester substrate, Succ-Phe-Leu-Phe-S-Bzl, was used to measure the activity of cathepsin G in synovial fluids. Monocyte migration induced by cathepsin G and synovial fluids was assessed by a 48-well microchemotaxis chamber technique. Immunohistochemical staining was performed to determine the cellular origin of cathepsin G in RA synovial tissue. A very low activity of cathepsin G was detected in synovial fluids from patients with OA. On the other hand, significantly increased activity of cathepsin G was detected in patients with RA when compared with the value of OA patients. A considerable monocyte chemotactic activity was detected in the synovial fluid of RA patients, and the activity was partially decreased by the treatment with inhibitors for cathepsin G, alpha1-antichymotrypsin and phenylmethylsulfonyl fluoride. The activity of cathepsin G was significantly correlated with the neutrophil counts in synovial fluids and the concentration of interleukin-6. Immunohistochemical studies showed that cathepsin G was strongly expressed by synovial lining cells, and weakly expressed by macrophages and neutrophils in synovial tissues. This study indicates that the monocyte chemotactic activity of cathepsin G may have a role in the pathogenesis of RA synovial inflammation.

Breaking up the tie: Disintegrin-like metalloproteinases as regulators of cell migration in inflammation and invasion

Cell adhesion and cell migration are essential for a variety of important events in both embryonic development and in the adult organism. Cell adhesion molecules (CAM) like selectins, immunoglobulin superfamily members, integrins, and cadherins undergo diverse mechanisms of regulation. Dysregulation of adhesion can lead to pathological processes, including inflammatory diseases or tumor metastasis either by disrupting the normal anchorage, thereby altering cell movement and regulatory signalling, or by promoting inappropriate temporal and spatial adhesion. An increasing body of evidence has emerged showing that members of the a disintegrin and metalloproteinase (ADAM) family critically contribute to the regulation of CAM functions. While the disintegrin domain can interact with integrins and mediate adhesion, the metalloproteinase domain can mediate anti-adhesive functions by cleaving the membrane bound adhesion molecules. This "shedding" process leads to the release of often still functional soluble ectodomains and can additionally influence intracellular cell signalling pathways. Several soluble CAMs have been detected in vitro and in vivo. Some of them are strongly increased in inflammatory diseases or in the serum of cancer patients. Therefore the level of soluble CAMs but also the expression of the metalloproteinases responsible for their release might provide prognostic information. It could also be useful for monitoring malignant disease stages and for evaluating the effectiveness of various therapeutic approaches. Moreover, metalloproteases of the ADAM family are emerging as promising targets for new therapeutic options.

Neutrophil serine proteases: specific regulators of inflammation

Neutrophils are essential for host defence against invading pathogens. They engulf and degrade microorganisms using an array of weapons that include reactive oxygen species, antimicrobial peptides, and proteases such as cathepsin G, neutrophil elastase and proteinase 3. As discussed in this Review, the generation of mice deficient in these proteases has established a role for these enzymes as intracellular microbicidal agents. However, I focus mainly on emerging data indicating that, after release, these proteases also contribute to the extracellular killing of microorganisms, and regulate non-infectious inflammatory processes by activating specific receptors and modulating the levels of cytokines.

Mechanisms of hematopoietic stem cell mobilization: When innate immunity assails the cells that make blood and bone

Mobilization is now used worldwide to collect large numbers of hematopoietic stem and progenitor cells (HSPCs) for transplantation. Although the first mobilizing agents were discovered largely by accident, discovery of more efficient mobilizing agents will require a better understanding of the molecular mechanisms responsible. During the past 5 years, a number of mechanisms have been identified, shedding new light on the dynamics of the hematopoietic system in vivo and on the intricate relationship between hematopoiesis, innate immunity, and bone. After briefly reviewing the mechanisms by which circulating HSPCs home into the bone marrow and what keeps them there, the current knowledge of mechanisms responsible for HSPC mobilization in response to hematopoietic growth factors such as granulocyte colony-stimulating factor, chemotherapy, chemokines, and polyanions will be discussed together with current strategies developed to further increase HSPC mobilization.

Functional regulatory T cells are collected in stem cell autografts by mobilization with high-dose cyclophosphamide and granulocyte colony-stimulating factor

High-dose cyclophosphamide (Cy) and G-CSF are widely used to mobilize hemopoietic stem cells for treating patients with high-dose chemotherapy and autologous stem cell transplantation (ASCT). Because lymphocyte count in the graft collected after Cy-G-CSF treatment is an independent survival factor after ASCT for patients with multiple myeloma, our purpose was to study how Cy-G-CSF treatment affects the phenotype and function of T cells in patients with multiple myeloma. Cy induced a 3-fold decrease of T cell counts with a slow and partial T cell recovery of one-third at the time of hemopoietic stem cell collection. Cy-G-CSF treatment did not affect the relative ratios of central memory, effector memory, and late effector CD4+ or CD8+ T cells, but a decrease in the percentage of naive CD4+ cells was observed. The percentages of CD25+ cells increased 2- to 3-fold in CD4+ and CD8+ T cells, the former including both activated CD25low and CD25high cells. CD4+CD25high cells were regulatory T cells (Treg) that expressed high levels of FOXP3, CTLA-4, and GITR and displayed in vitro suppressive properties. The recovery of Treg absolute counts after Cy-G-CSF treatment was higher than the recovery of other lymphocyte subpopulations. In conclusion, Cy-G-CSF treatment induces a severe T cell count decrease without deleting Treg, which are potent inhibitors of antitumor response. The present data encourage novel therapeutic strategies to improve T cell recovery following ASCT while limiting Treg expansion.

Multiple sources of non-embryonic multipotent stem cells: processed lipoaspirates and dermis as promising alternatives to bone-marrow-derived cell therapies

A body of evidence points to the existence of stem cell stores in adult tissues, in addition to the well-known hematopoietic stem cells from bone marrow. Many reports describe the ability of these multipotent cells (developmentally non-compromised with their organs of origin) to give rise to many different cell types in response to specific stimuli. This apparent plasticity provides new perspectives in tissue engineering and suggests the usefulness of these cells in future protocols of autologous transplantation, gene therapy, and tissue reconstitution in a number of pathological processes. Lipoaspirates and dermis represent accessible sources for obtaining such cells, with minimal discomfort to the donor, and might be promising candidates for cell therapy procedures once their features are experimentally accessed. The intention of the present work has been to gather reports on the phenotypic characteristics, profile, and plastic potential of these stem cells.

Contrasting Roles for Domain 4 of VCAM-1 in the Regulation of Cell Adhesion and Soluble VCAM-1 Binding to Integrin α4β1

Cell adhesion mediated by the interaction between integrin alpha4beta1 and VCAM-1 is important in normal physiologic processes and in inflammatory and autoimmune disease. Numerous studies have mapped the alpha4beta1 binding sites in VCAM-1 that mediate cell adhesion; however, little is known about the regions in VCAM-1 important for regulating soluble binding. In the present study, we demonstrate that 6D VCAM-1 (an alternatively spliced isoform of VCAM-1 lacking Ig-like domain 4) binds alpha4beta1 with a higher relative affinity than does the full-length form of VCAM-1 containing 7 Ig-like extracellular domains (7D VCAM-1). In indirect binding assays, the EC50 of soluble 6D VCAM-1 binding to alpha4beta1 on Jurkat cells (in 1 mM MnCl2) was 2 x 10(-9) M, compared with 7D VCAM-1 at 11 x 10(-9) M. When used in solution to inhibit alpha4beta1 mediated cell adhesion, the IC50 of 6D VCAM-1 was 13 x 10(-9) M, compared with 7D VCAM-1 measured at 150 x 10(-9) M. Removal of Ig-like domains 4, 5, or 6, or simply substituting Asp328 in domain 4 of 7D VCAM-1 with alanine, caused increased binding of soluble 7D VCAM-1 to alpha4beta1. In contrast, cells adhered more avidly to 7D VCAM-1 under shear force, as it induced cell spreading at lower concentrations than did 6D VCAM-1. Finally, soluble 6D VCAM-1 acts as an agonist through alpha4beta1 by augmenting cell migration and inducing cell aggregation. These results indicate that the domain 4 of VCAM-1 plays a contrasting role when VCAM-1 is presented in solution or as a cell surface-expressed adhesive substrate.

G-CSF down-regulation of CXCR4 expression identified as a mechanism for mobilization of myeloid cells

CXCR4 receptor expression is required for the retention of granulocyte precursors and mature neutrophils within the bone marrow, and disruption of the SDF-1/CXCR4 axis in the bone marrow results in the mobilization of myeloid lineage cells to the peripheral circulation. We report that G-CSF down-regulates CXCR4 expression in bone marrow-derived murine and human myeloid lineage cells. When exposed to G-CSF, murine Gr1(+) bone marrow myeloid cells display a time-dependent reduction of cell-surface CXCR4 and respond poorly to SDF-1 in attachment and migration assays. Bone marrow-derived cells of nonmyeloid lineage display no change in surface CXCR4 expression upon exposure to G-CSF. Compared with controls, mice treated with G-CSF for mobilization of hematopoietic progenitor cells display reduced levels of CXCR4 selectively in bone marrow Gr1(+) myeloid cells. Since bone marrow myeloid cells express G-CSF receptors and G-CSF rapidly reduces CXCR4 expression in purified Gr1(+) cells populations, these results provide evidence that G-CSF acts directly on myeloid lineage cells to reduce CXCR4 expression. By down-regulating CXCR4 expression in bone marrow myeloid cells and attenuating their responsiveness to SDF-1, G-CSF promotes their mobilization from the bone marrow to the peripheral blood.

Signals from the sympathetic nervous system regulate hematopoietic stem cell egress from bone marrow

Hematopoietic stem and progenitor cells (HSPC), attracted by the chemokine CXCL12, reside in specific niches in the bone marrow (BM). HSPC migration out of the BM is a critical process that underlies modern clinical stem cell transplantation. Here we demonstrate that enforced HSPC egress from BM niches depends critically on the nervous system. UDP-galactose ceramide galactosyltransferase-deficient (Cgt(-/-)) mice exhibit aberrant nerve conduction and display virtually no HSPC egress from BM following granulocyte colony-stimulating factor (G-CSF) or fucoidan administration. Adrenergic tone, osteoblast function, and bone CXCL12 are dysregulated in Cgt(-/-) mice. Pharmacological or genetic ablation of adrenergic neurotransmission indicates that norepinephrine (NE) signaling controls G-CSF-induced osteoblast suppression, bone CXCL12 downregulation, and HSPC mobilization. Further, administration of a beta(2) adrenergic agonist enhances mobilization in both control and NE-deficient mice. Thus, these results indicate that the sympathetic nervous system regulates the attraction of stem cells to their niche.

Trafficking from the bone marrow to the thymus: a prerequisite for thymopoiesis

T-cell development in the thymus requires periodic importation of hematopoietic progenitors from the bone marrow. Such thymus settling progenitors arise from hematopoietic stem cells (HSCs) that are retained in a specific bone marrow microenvironmental niche. Vacation of this niche is required for HSC proliferation and differentiation into downstream progenitors. In order to reach the thymus, progenitors must then be mobilized from bone marrow to blood. Finally, progenitors in blood must settle in the thymus. Here we review signals and molecular interactions that are likely to play a role in trafficking from the bone marrow to the thymus, focusing on how these interactions may regulate which progenitors physiologically contribute to thymopoiesis.

Serpina1 is a potent inhibitor of IL-8-induced hematopoietic stem cell mobilization

Here, we report that cytokine-induced (granulocyte colony-stimulating factor and IL-8) hematopoietic stem cell (HSC) and hematopoietic progenitor cell (HPC) mobilization is completely inhibited after low-dose (0.5 Gy) total-body irradiation (TBI). Because neutrophil granular proteases are regulatory mediators in cytokine-induced HSC/HPC mobilization, we considered a possible role for protease inhibitors in the induction of HSC/HPC mobilization. Bone marrow (BM) extracellular extracts that were obtained from murine femurs after 0.5 Gy of TBI contained an inhibitor of elastase. Also, after low-dose TBI, both Serpina1 mRNA and protein concentrations were increased in BM extracts, compared with extracts that were obtained from controls. The inhibitory activity in BM extracts of irradiated mice was reversed by addition of an Ab directed against Serpina1. To further study a possible in vivo role of Serpina1 in HSC/HPC mobilization, we administered Serpina1 before IL-8 injection. This administration resulted in an almost complete inhibition of HSC/HPC mobilization, whereas heat-inactivated Serpina1 had no effect. These results indicate that low-dose TBI inhibits cytokine-induced HSC/HPC mobilization and induces Serpina1 in the BM. Because exogenous administration of Serpina1 inhibits mobilization, we propose that radiation-induced Serpina1 is responsible for the inhibition of HSC/HPC mobilization. Also, we hypothesize that cytokine-induced HSC/HPC mobilization is determined by a critical balance between serine proteases and serine protease inhibitors.

Comparative analysis of mesenchymal stem cells from bone marrow, umbilical cord blood, or adipose tissue

Mesenchymal stem cells (MSCs) represent a promising tool for new clinical concepts in supporting cellular therapy. Bone marrow (BM) was the first source reported to contain MSCs. However, for clinical use, BM may be detrimental due to the highly invasive donation procedure and the decline in MSC number and differentiation potential with increasing age. More recently, umbilical cord blood (UCB), attainable by a less invasive method, was introduced as an alternative source for MSCs. Another promising source is adipose tissue (AT). We compared MSCs derived from these sources regarding morphology, the success rate of isolating MSCs, colony frequency, expansion potential, multiple differentiation capacity, and immune phenotype. No significant differences concerning the morphology and immune phenotype of the MSCs derived from these sources were obvious. Differences could be observed concerning the success rate of isolating MSCs, which was 100% for BM and AT, but only 63% for UCB. The colony frequency was lowest in UCB, whereas it was highest in AT. However, UCB-MSCs could be cultured longest and showed the highest proliferation capacity, whereas BM-MSCs possessed the shortest culture period and the lowest proliferation capacity. Most strikingly, UCB-MSCs showed no adipogenic differentiation capacity, in contrast to BM- and AT-MSCs. Both UCB and AT are attractive alternatives to BM in isolating MSC: AT as it contains MSCs at the highest frequency and UCB as it seems to be expandable to higher numbers.

Involvement of Proteases in Cytokine-Induced Hematopoietic Stem Cell Mobilization

The number of circulating stem cells and progenitor cells can be increased by physiological stress, such as exercise, stress, and infections. The process of shifting the stem cells from the bone marrow into the peripheral blood is referred to as "mobilization" or "egress." Cytokine-mobilized hematopoietic progenitor cells (HPCs) are currently used for autologous or allogeneic stem cell transplantation in a variety of malignant and nonmalignant diseases. In spite of the wide-spread use of mobilized peripheral blood stem cells for transplantation, the mechanisms underlying mobilization are still incompletely understood. Here we discuss the role of neutrophils and proteases as mediators of stem cell mobilization.

Functional disruption of alpha4 integrin mobilizes bone marrow-derived endothelial progenitors and augments ischemic neovascularization

The cell surface receptor α4 integrin plays a critical role in the homing, engraftment, and maintenance of hematopoietic progenitor cells (HPCs) in the bone marrow (BM). Down-regulation or functional blockade of α4 integrin or its ligand vascular cell adhesion molecule-1 mobilizes long-term HPCs. We investigated the role of α4 integrin in the mobilization and homing of BM endothelial progenitor cells (EPCs). EPCs with endothelial colony-forming activity in the BM are exclusively α4 integrin–expressing cells. In vivo, a single dose of anti–α4 integrin antibody resulted in increased circulating EPC counts for 3 d. In hindlimb ischemia and myocardial infarction, systemically administered anti–α4 integrin antibody increased recruitment and incorporation of BM EPCs in newly formed vasculature and improved functional blood flow recovery and tissue preservation. Interestingly, BM EPCs that had been preblocked with anti–α4 integrin ex vivo or collected from α4 integrin–deficient mice incorporated as well as control cells into the neovasculature in ischemic sites, suggesting that α4 integrin may be dispensable or play a redundant role in EPC homing to ischemic tissue. These data indicate that functional disruption of α4 integrin may represent a potential angiogenic therapy for ischemic disease by increasing the available circulating supply of EPCs.

Polymorphisms in cytokine and cellular adhesion molecule genes and susceptibility to hematotoxicity among workers exposed to benzene

Benzene is a recognized hematotoxin and leukemogen but its mechanism of action and the role of genetic susceptibility are still unclear. Cytokines, chemokines, and cellular adhesion molecules are soluble proteins that play an important regulatory role in hematopoiesis. We therefore hypothesized that variation in these genes could influence benzene-induced hematotoxicity. We analyzed common, well-studied single-nucleotide polymorphisms (SNPs) in 20 candidate genes drawn from these pathways in a study of 250 workers exposed to benzene and 140 unexposed controls in China. After accounting for multiple comparisons, SNPs in five genes were associated with a statistically significant decrease in total WBC counts among exposed workers [IL-1A (-889C>T), IL-4 (-1098T>G), IL-10 (-819T>C), IL-12A (8685G>A), and VCAM1 (-1591T>C)], and one SNP [CSF3 (Ex4-165C>T)] was associated with an increase in WBC counts. The adhesion molecule VCAM1 variant was particularly noteworthy as it was associated with a decrease in B cells, natural killer cells, CD4+ T cells, and monocytes. Further, VCAM1 (-1591T>C) and CSF3 (Ex4-165C>T) were associated, respectively, with decreased (P = 0.041) and increased (P = 0.076) CFU-GEMM progenitor cell colony formation in 29 benzene-exposed workers. This is the first report to provide evidence that SNPs in genes that regulate hematopoiesis influence benzene-induced hematotoxicity.

Synergy in cytokine and chemokine networks amplifies the inflammatory response

The inflammatory response is a highly co-ordinated process involving multiple factors acting in a complex network as stimulators or inhibitors. Upon infection, the sequential release of exogenous agents (e.g. bacterial and viral products) and induction of endogenous mediators (e.g. cytokines and chemokines) contribute to the recruitment of circulating leukocytes to the inflamed tissue. Microbial products trigger multiple cell types to release cytokines, which in turn are potent inducers of chemokines. Primary cytokines act as endogenous activators of the immune response, whereas inducible chemokines act as secondary mediators to attract leukocytes. Interaction between exogenous and endogenous mediators thus enhances the inflammatory response. In this review, the synergistic interaction between cytokines to induce chemokine production and the molecular mechanisms of the cooperation amongst co-induced chemokines to further increase leukocyte recruitment to the site of inflammation are discussed.

G-CSF potently inhibits osteoblast activity and CXCL12 mRNA expression in the bone marrow

Accumulating evidence indicates that interaction of stromal cell-derived factor 1 (SDF-1/CXCL12 [CXC motif, ligand 12]) with its cognate receptor, CXCR4 (CXC motif, receptor 4), generates signals that regulate hematopoietic progenitor cell (HPC) trafficking in the bone marrow. During granulocyte colony-stimulating factor (G-CSF)-induced HPC mobilization, CXCL12 protein expression in the bone marrow decreases. Herein, we show that in a series of transgenic mice carrying targeted mutations of their G-CSF receptor and displaying markedly different G-CSF-induced HPC mobilization responses, the decrease in bone marrow CXCL12 protein expression closely correlates with the degree of HPC mobilization. G-CSF treatment induced a decrease in bone marrow CXCL12 mRNA that closely mirrored the fall in CXCL12 protein. Cell sorting experiments showed that osteoblasts and to a lesser degree endothelial cells are the major sources of CXCL12 production in the bone marrow. Interestingly, osteoblast activity, as measured by histomorphometry and osteocalcin expression, is strongly down-regulated during G-CSF treatment. However, the G-CSF receptor is not expressed on osteoblasts; accordingly, G-CSF had no direct effect on osteoblast function. Collectively, these data suggest a model in which G-CSF, through an indirect mechanism, potently inhibits osteoblast activity resulting in decreased CXCL12 expression in the bone marrow. The consequent attenuation of CXCR4 signaling ultimately leads to HPC mobilization.

A prospective randomized study on the mobilization of CD34+ cells comparing continuous intravenous vs subcutaneous administration of rhG-CSF in normal donors

The efficacy of mobilizing peripheral blood progenitor cells (PBPC) with continuous intravenous (c.i.v.) administration of rhG-CSF was randomly compared to subcutaneous (s.c.) administration, in 15 normal donors in each arm of the study for 6 days. The percentage and absolute numbers of CD34+ cells in the c.i.v. and s.c. groups increased maximally at day 3 and 5, respectively, when compared with the steady-state (day 0) level. Peak CD34+ cell levels were achieved on day 3 in the c.i.v. group, with more rapid results than in the s.c. group (49.3/microl vs 35.9/microl, P=0.043). Plasma rhG-CSF levels declined progressively during mobilization in each group as the WBC increased. The serum level of rhG-CSF did not correlate with CD34+ cell counts in the peripheral blood. Toxicity profiles in the c.i.v. and s.c. groups were similar. Each regimen was effective in successfully mobilizing the target CD34 cell number.

CpG-oligodeoxynucleotides induce mobilization of hematopoietic progenitor cells into peripheral blood in association with mouse KC (IL-8) production

The immune system of vertebrates detects bacterial DNA as a "danger signal" based on the presence of unmethylated CpG motifs. We examined whether oligodeoxynucleotides (ODNs) with CpG motifs (CpG-ODNs) also induce mobilization of hematopoietic progenitor cells (HPCs). Mice challenged with CpG-ODNs showed an increase in peripheral blood colony-forming units (CFU) with a peak at day 4 after treatment, associated with an increase, starting 30 min after CpG treatment, in serum levels of mouse keratinocyte-derived chemokine (mKC), a functional homolog of human interleukin (IL) 8; production of granulocyte-colony-stimulating factor (CSF) was also detected. Mobilization and mKC induction were sequence-specific and dose-dependent occurring even with low doses of CpG-ODNs. Interestingly, intestinal cells were involved in mKC production. HPC mobilization by CpG-ODNs was dependent on peripheral blood mononuclear cells since mobilization was reduced in neutrophil-depleted mice. Moreover, CpG-ODN treatment significantly increased G-CSF mobilizing capacity. Finally, pretreatment with an anti-mKC neutralizing antibody significantly reduced CpG-induced mobilization, further supporting a role for mKC. Thus, bacterial DNA is a "danger signal" not only for immune cells but also for hematopoietic cells, communicating the need for increased hematopoiesis during infections and for the renewal of the immune system. The HPC mobilization activity of CpG-ODNs will need to be considered in the design of treatment regimens for cancer clinical trials using CpG-ODNs in association with chemotherapy.

Multicellular spheroids of bone marrow stromal cells: a three-dimensional in vitro culture system for the study of hematopoietic cell migration

Cell fate decisions are governed by a complex interplay between cell-autonomous signals and stimuli from the surrounding tissue. In vivo cells are connected to their neighbors and to the extracellular matrix forming a complex three-dimensional (3-D) microenvironment that is not reproduced in conventional in vitro systems. A large body of evidence indicates that mechanical tension applied to the cytoskeleton controls cell proliferation, differentiation and migration, suggesting that 3-D in vitro culture systems that mimic the in vivo situation would reveal biological subtleties. In hematopoietic tissues, the microenvironment plays a crucial role in stem and progenitor cell survival, differentiation, proliferation, and migration. In adults, hematopoiesis takes place inside the bone marrow cavity where hematopoietic cells are intimately associated with a specialized three 3-D scaffold of stromal cell surfaces and extracellular matrix that comprise specific niches. The relationship between hematopoietic cells and their niches is highly dynamic. Under steady-state conditions, hematopoietic cells migrate within the marrow cavity and circulate in the bloodstream. The mechanisms underlying hematopoietic stem/progenitor cell homing and mobilization have been studied in animal models, since conventional two-dimensional (2-D) bone marrow cell cultures do not reproduce the complex 3-D environment. In this review, we will highlight some of the mechanisms controlling hematopoietic cell migration and 3-D culture systems.

Modification of the content of plasma protein carbonyl groups in donors after granulocyte colony stimulating factor-induced stem cell mobilization

Granulocyte-colony stimulating factor (G-CSF), the most established agent for the mobilization of stem cells in current clinical practice, could induce a condition of oxidative stress. Herein plasmatic levels of protein carbonyl groups (a biomarker of oxidative stress) were measured in a group of donors given recombinant human G-CSF (rHuG-CSF) at different times: (1) before starting rHuG-CSF administration, (2) on day 5 of rHuG-CSF administration, (3) on the same day immediately after the end of the first leukapheresis procedure and (4) one week after rHuG-CSF withdrawal. Plasma levels of protein carbonyl groups enhanced significantly in donors after 5 days of rHuG-CSF treatment and appeared further slightly increased following leukapheresis procedure; 7 days following rHuG-CSF withdrawal, they showed a tendency to normalization. These findings may contribute to better understand the oxidative reactions following rHuG-CSF treatment and leukapheresis.

Mobilization of Human Lymphoid Progenitors after Treatment with Granulocyte Colony-Stimulating Factor

Hemopoietic stem and progenitor cells ordinarily residing within bone marrow are released into the circulation following G-CSF administration. Such mobilization has a great clinical impact on hemopoietic stem cell transplantation. Underlying mechanisms are incompletely understood, but may involve G-CSF-induced modulation of chemokines, adhesion molecules, and proteolytic enzymes. We studied G-CSF-induced mobilization of CD34+ CD10+ CD19- Lin- and CD34+ CD10+ CD19+ Lin- cells (early B and pro-B cells, respectively). These mobilized lymphoid populations could differentiate only into B/NK cells or B cells equivalent to their marrow counterparts. Mobilized lymphoid progenitors expressed lymphoid- but not myeloid-related genes including the G-CSF receptor gene, and displayed the same pattern of Ig rearrangement status as their bone marrow counterparts. Decreased expression of VLA-4 and CXCR-4 on mobilized lymphoid progenitors as well as multipotent and myeloid progenitors indicated lineage-independent involvement of these molecules in G-CSF-induced mobilization. The results suggest that by acting through multiple trans-acting signals, G-CSF can mobilize not only myeloid-committed populations but a variety of resident marrow cell populations including lymphoid progenitors.

Hematopoietic Progenitor Cell Mobilization by Granulocyte Colony-Stimulating Factor and Erythropoietin in the Absence of Matrix Metalloproteinase-9

The use of mobilized hematopoietic progenitor cells (HPC) has largely replaced the use of bone marrow HPC for autologous and allogeneic transplantation; however, the mechanisms of HPC mobilization remain unclear. A better understanding of these mechanisms, may allow the development of improved (potentially more rapid and/or higher yield) HPC mobilization strategies, especially for patients who mobilize poorly using current mobilization protocols. Clinically, granulocyte colony-stimulating factor (G-CSF) is widely used to induce HPC mobilization, and evidence suggests that metalloproteinase enzymes released by activated granulocytes play an important role in the G-CSF-induced HPC mobilization. These enzymes may act to disrupt putative cell-cell and/or cell-extracellular matrix interactions within the hematopoietic microenvironment thereby releasing HPC into the blood. Matrix metalloproteinase-9 (MMP-9) appears to be important for G-CSF-induced mobilization. Using an MMP-9 knock-out (KO) mouse model, we investigated the role of MMP-9 in G-CSF and erythropoietin (EPO)-based HPC mobilization at clinically relevant cytokine doses. There were few hematologic or hematopoietic differences between the wild-type and MMP-9KO mice during steady-state hematopoiesis. When treated subcutaneously with EPO (500 U/kg per day) and G-CSF (15 microg/kg per day) for 5 days and assayed on day 6, similarly increased extramedullary hematopoiesis and numbers of HPC in the spleen and blood were observed for both the wild-type and MMP-9KO mice. These data demonstrate that MMP-9 is not required for EPO + G-CSF mobilization and that alternative mobilization mechanisms must be active at clinically relevant cytokine concentrations.

Constitutive mobilization of CD34+ cells into the peripheral blood in idiopathic myelofibrosis may be due to the action of a number of proteases

Idiopathic myelofibrosis (IM) is characterized by increased numbers of CD34+ cells in the peripheral blood (PB). We explored the possible mechanisms underlying this abnormal trafficking of CD34+ cells. Plasma levels of neutrophil elastase (NE), total and active matrix metalloproteinase 9 (MMP-9), and soluble vascular cell adhesion molecule-1 (sVCAM-1) were dramatically increased in IM. The absolute number of CD34+ cells in the PB was correlated with the levels of sVCAM-1. Marked elevations of the levels of NE but not total and active MMP-9 as well as MMP-2 were detected in media conditioned by IM mononuclear cells (MNCs) as compared with that of healthy volunteers. IM MNC-conditioned media, however, was shown by zymographic analysis to contain increased gelatinolytic activity corresponding to the molecular weight of MMP-9. IM MNC-conditioned media also exhibited a greater ability to cleave VCAM-1 and c-kit in vitro, consistent with the biologic actions of NE. In addition, the increased ability of IM PB CD34+ cells to migrate through a reconstituted basement membrane was diminished by several inhibitors of MMP-9 activity, indicating that these cells express increased levels of this MMP. These data indicate that a proteolytic environment exists in IM which might result in the sustained mobilization of CD34+ cells.

The CXCR4 agonist peptide, CTCE-0021, rapidly mobilizes polymorphonuclear neutrophils and hematopoietic progenitor cells into peripheral blood and synergizes with granulocyte colony-stimulating factor

OBJECTIVE

Mobilization of hematopoietic stem and progenitor cells (HSPC) by stromal cell-derived factor-1 (SDF-1) has been described; however, sustained adenoviral delivery or N-terminal modification was required for effect and could not be demonstrated with native protein. The aim of this study was to further investigate the SDF-1alpha/CXCR4 axis in HSPC mobilization using CTCE-0021, a cyclized CXCR4 agonist peptide, with comparable bioactivity and improved stability relative to SDF-1alpha.

METHODS

Peripheral blood cells and hematopoietic progenitor cells (HPC) were quantitated in mice administered single or multiple doses of CTCE-0021 or SDF-1alpha, or mobilized by granulocyte colony-stimulating factor (G-CSF) in combination with CTCE-0021. Proteases, cytokines, and receptors implicated in HSPC mobilization were evaluated to determine mechanism of action.

RESULTS

CTCE-0021 dose-dependently elevated blood neutrophils polymorphonuclear neutrophil [PMN] within 5 minutes that peaked after 1 hour and persisted for 24 hours. PMN mobilization could be maintained by daily dosing. CTCE-0021 mobilized colony-forming unit granulocyte macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), and CFU-granulocyte-erythrocyte-monocyte-megakaryocyte (CFU-GEMM) that peaked within 1 hour after administration, and synergistically enhanced both PMN and HSPC mobilization when combined with G-CSF. Mobilization induced by CTCE-0021 was associated with rapid downregulation of CXCR4 expression on HPC. No appreciable changes in proteases implicated in HPC mobilization were observed. Significantly elevated plasma SDF-1 was detected in mobilized mice, which likely represents CTCE-0021.

CONCLUSION

These studies indicate that CTCE-0021 is an efficient and rapid mobilizer of PMN and HPC when used alone and shows synergistic activity when used in combination with G-CSF. The mobilizing effect of this peptide appears to be mediated by downregulation of the CXCR4 receptor on HPC and altered chemokine gradient.

Aminopeptidase N/CD13 regulates the fetal liver microenvironment of hematopoiesis

Fetal liver (FL) hematopoiesis is thought to be important for expanding the cell number during ontogeny. In order to investigate the cellular interaction molecules among FL stromal and hematopoietic cells, we established a monoclonal antibody, Ndk-10, that reacts with FL stromal cells but not with dish non-adherent cells. When Ndk-10 was added to an FL stromal and hematopoietic cell-coculture, it inhibited the survival of c-kit+ cells. The inhibitory activity of Ndk-10 was also observed in the fetal liver organ culture. The Ndk-10 recognized a 150 kD molecule in the adherent cells of FL and kidney, and the N-terminal amino acid sequence was identical to that of mouse aminopeptidase N/CD13. The peptidase activity of CD13 was inhibited by Ndk-10, and addition of its specific inhibitor resulted in the same inhibitory activity as Ndk-10. We propose that aminopeptidase N/CD13 is a critical molecule that regulates the survival of c-kit+ cells in the FL microenvironment.

Serine protease inhibitors serpina1 and serpina3 are down-regulated in bone marrow during hematopoietic progenitor mobilization

Mobilization of hematopoietic progenitor cells into the blood involves a massive release of neutrophil serine proteases in the bone marrow. We hypothesize that the activity of these neutrophil serine proteases is regulated by the expression of naturally occurring inhibitors (serpina1 and serpina3) produced locally within the bone marrow. We found that serpina1 and serpina3 were transcribed in the bone marrow by many different hematopoietic cell populations and that a strong reduction in expression occurred both at the protein and mRNA levels during mobilization induced by granulocyte colony-stimulating factor or chemotherapy. This decreased expression was restricted to the bone marrow as serpina1 expression was maintained in the liver, leading to no change in plasma concentrations during mobilization. The down-regulation of serpina1 and serpina3 during mobilization may contribute to a shift in the balance between serine proteases and their inhibitors, and an accumulation of active neutrophil serine proteases in bone marrow extravascular fluids that cleave and inactivate molecules essential to the retention of hematopoietic progenitor cells within the bone marrow. These data suggest an unexpected role for serpina1 and serpina3 in regulating the bone marrow hematopoietic microenvironment as well as influencing the migratory behavior of hematopoietic precursors.