Granulocyte colony-stimulating factor enhances interleukin 3-dependent proliferation of multipotential hemopoietic progenitors

Involvement of G-CSF, IL-6, and cortisol in transient neutrophilia after marathon races

OBJECTIVES

The aim of this study was to clarify the mechanisms of the transient increase in neutrophils after running standard marathon races by measurement of cytokines involved in the production and survival of neutrophils, and cortisol.

METHODS

Fourteen male runners who participated in the Hokkaido Marathon, which is the sole marathon race held in summer in Japan, and finished the standard marathon were analyzed sequentially from the start until a maximum of 8 days after the finish.

RESULTS

Neutrophilia was observed in all runners just after they reached the goal (mean neutrophils: 13 226/μL). IL-6, G-CSF, and cortisol, but not GM-CSF, increased at the same time. Time-course studies with complete blood counts, biochemical markers, cytokines, and cortisol showed transient increases in neutrophils, monocytes, myoglobin, high-sensitivity C-reactive protein (hsCRP), G-CSF, IL-6, and cortisol. The increase in hsCRP was delayed 6 hours from the first increase in neutrophils. Correlations were observed between the neutrophil count and G-CSF, IL-6, and cortisol (G-CSF; r = .667, IL-6; r = .667, cortisol; r = .623).

CONCLUSION

These results suggest that G-CSF is directly involved, and IL-6 is involved via cortisol in the transient neutrophilia that occurs after marathon races.

Protective effects of cytokine combinations against the apoptotic activity of glucocorticoids on CD34+ hematopoietic stem/progenitor cells

Haematopoietic stem cells can self-renew and produce progenitor cells, which have a high proliferation capacity. Chemotherapeutic drugs are toxic to normal cells as well as cancer cells, and glucocorticoids (GCs), which are essential drugs for many chemotherapeutic protocols, efficiently induce apoptosis not only in malignant cells but also in normal haematopoietic cells. Studies have shown that haematopoietic cytokines can prevent the apoptosis induced by chemotherapy and decrease the toxic effects of these drugs. However, the apoptosis induction mechanism of GCs in CD34⁺ haematopoietic cells and the anti-apoptotic effects of cytokines have not been well elucidated. In this study, we investigated the apoptotic effects of GCs on CD34⁺, a haematopoietic stem/progenitor cell (HSPC) population, and demonstrated the protective effects of haematopoietic cytokines. We used a cytokine cocktail containing early-acting cytokines, namely, interleukin-3 (IL-3), thrombopoietin, stem cell factor and flt3/flk2 ligand, and dexamethasone and prednisolone were used as GCs. Apoptotic mechanisms were assessed by immunohistochemical staining and quantified using H-scoring. Dexamethasone and prednisolone induced apoptosis in CD34⁺ HSPCs. GC treatment caused a significant increase in apoptotic Fas, caspase-3, cytochrome c and Bax, but a significant decrease in anti-apoptotic Bcl-2. Furthermore, as expected, cytokines caused a significant decrease in all apoptotic markers and a significant increase in Bcl-2. Thus, our findings suggest that CD34⁺ HSPCs are an extremely sensitive target for GCs and that cytokines protect these cells from GC-induced apoptosis.

Role of lipegfilgrastim in the management of chemotherapy-induced neutropenia

Chemotherapy, irradiation, and other agents are widely used to target the process of cell division in neoplastic cells. However, while these therapies are effective against most cancers, the high proliferative rate of the cells of the hematopoietic system that produce billions of blood cells needed daily throughout life is extremely sensitive to these agents, resulting in loss of blood cell populations, which can be life threatening. Neutropenia is the most serious hematologic toxicity of chemotherapy, which can result in patient morbidity and mortality due to opportunistic infection and often is the limiting factor in dose escalation or duration of chemotherapeutic administration. Neutropenic patients often require hospitalization and incur substantial medical costs associated with anti-infective therapy. Treatment of iatrogenic and congenic neutropenia was changed in the early 1990s with the introduction of filgrastim (Neupogen^®) and pegfilgrastim (Neulasta^®). With the expiration of patent lives of both of these drugs, biosimilars have begun to emerge. In this review, we will summarize the chemical characteristics, pharmacokinetics, safety and efficacy of lipegfilgrastim (Lonquex^®), the first long-acting biosimilar filgrastim to receive regulatory approval and enter the marketplace.

Concise review: Sowing the seeds of a fruitful harvest: hematopoietic stem cell mobilization

Hematopoietic stem cell transplantation is the only curative option for a number of malignant and nonmalignant diseases. As the use of hematopoietic transplant has expanded, so too has the source of stem and progenitor cells. The predominate source of stem and progenitors today, particularly in settings of autologous transplantation, is mobilized peripheral blood. This review will highlight the historical advances which led to the widespread use of peripheral blood stem cells for transplantation, with a look toward future enhancements to mobilization strategies.

Hematopoietic stem cells give rise to osteo-chondrogenic cells

Repair of bone fracture requires recruitment and proliferation of stem cells with the capacity to differentiate to functional osteoblasts. Given the close association of bone and bone marrow (BM), it has been suggested that BM may serve as a source of these progenitors. To test the ability of hematopoietic stem cells (HSCs) to give rise to osteo-chondrogenic cells, we used a single HSC transplantation paradigm in uninjured bone and in conjunction with a tibial fracture model. Mice were lethally irradiated and transplanted with a clonal population of cells derived from a single enhanced green fluorescent protein positive (eGFP+) HSC. Analysis of paraffin sections from these animals showed the presence of eGFP+ osteocytes and hypertrophic chondrocytes. To determine the contribution of HSC-derived cells to fracture repair, non-stabilized tibial fracture was created. Paraffin sections were examined at 7 days, 2 weeks and 2 months after fracture and eGFP+ hypertrophic chondrocytes, osteoblasts and osteocytes were identified at the callus site. These cells stained positive for Runx-2 or osteocalcin and also stained for eGFP demonstrating their origin from the HSC. Together, these findings strongly support the concept that HSCs generate bone cells and suggest therapeutic potentials of HSCs in fracture repair.

CBLB613: a TLR 2/6 agonist, natural lipopeptide of Mycoplasma arginini , as a novel radiation countermeasure

To date, there are no safe and effective drugs available for protection against ionizing radiation damage. Therefore, a great need exists to identify and develop non-toxic agents that will be useful as radioprotectors or postirradiation therapies under a variety of operational scenarios. We have developed a new pharmacological agent, CBLB613 (a naturally occurring Mycoplasma-derived lipopeptide ligand for Toll-like receptor 2/6), as a novel radiation countermeasure. Using CD2F1 mice, we investigated CBLB613 for toxicity, immunogenicity, radioprotection, radiomitigation and pharmacokinetics. We also evaluated CBLB613 for its effects on cytokine induction and radiation-induced cytopenia in unirradiated and irradiated mice. The no-observable-adverse-effect level of CBLB613 was 1.79 mg/kg and 1 mg/kg for single and repeated doses, respectively. CBLB613 significantly protected mice against a lethal dose of (60)Co γ radiation. The dose reduction factor of CBLB613 as a radioprotector was 1.25. CBLB613 also mitigated the effects of (60)Co γ radiation on survival in mice. In both irradiated and unirradiated mice, the drug stimulated induction of interleukin-1β (IL-1β), IL-6, IL-10, IL-12, keratinocyte-derived chemokine, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor-1α. CBLB613 also reduced radiation-induced cytopenia and increased bone marrow cellularity in irradiated mice. Our immunogenicity study demonstrated that CBLB613 is not immunogenic in mice, indicating that it could be developed as a radioprotector and radiomitigator for humans against the potentially lethal effects of radiation exposure.

Transcriptional profiling of the hematopoietic support of interleukin-stimulated human umbilical vein endothelial cells (HUVECs)

Endothelial cells can be successfully used to maintain or increase the number of hematopoietic stem cells in vitro. Previously we identified hematopoietic progenitor cell (HPC) expansion or survival benefit induced by IL-1β-, IL-3-, and IL-6-stimulated human umbilical vein endothelial cell (HUVEC) supernatants. In order to identify molecular mechanisms that support hematopoiesis, we examined the time-dependent expression profiles of IL-1β-, IL-3-, and IL-6-stimulated HUVECs via microarray. Here, we present 24 common upregulated elements and three common downregulated elements of IL-1β- and IL-3-stimulated HUVECs, with these factors exhibiting great potential for the observed HPC expansion. Furthermore, metabolic pathway analysis resulted in the identification of nonproteinogenic factors such as prostaglandin E(2) (PGE(2)) and nitric oxide (NO) and determined their HPC expansion potential via delta, methylcellulose, and cobblestone assays. We confirmed PGE(2) and spermine as hematopoietic expansion factors. Furthermore, we identified several factors such as SSAT, extracellular matrix components, microRNA21, and a microvesicle-mediated cross-talk between the endothelium and HPCs that may play a crucial role in determining stem cell fate. Our results suggest that microarray in combination with functional annotations is a convenient method to identify novel factors with great impact on HPC proliferation and differentiation.

Hematopoietic stem cell origin of connective tissues

Connective tissue consists of "connective tissue proper," which is further divided into loose and dense (fibrous) connective tissues and "specialized connective tissues." Specialized connective tissues consist of blood, adipose tissue, cartilage, and bone. In both loose and dense connective tissues, the principal cellular element is fibroblasts. It has been generally believed that all cellular elements of connective tissue, including fibroblasts, adipocytes, chondrocytes, and bone cells, are generated solely by mesenchymal stem cells. Recently, a number of studies, including those from our laboratory based on transplantation of single hematopoietic stem cells, strongly suggested a hematopoietic stem cell origin of these adult mesenchymal tissues. This review summarizes the experimental evidence for this new paradigm and discusses its translational implications.

An efficient method for single hematopoietic stem cell engraftment in mice based on cell-cycle dormancy of hematopoietic stem cells

OBJECTIVE

To develop an efficient method for single hematopoietic stem cell (HSC) transplantation for high-level hematopoietic engraftment.

MATERIALS AND METHODS

We combined single-cell sorting with short-term culture of putative HSCs. Mouse bone marrow cells that had been highly enriched for HSCs were individually deposited into a 96-well culture plate and incubated in the presence of mouse c-kit ligand and either mouse interleukin-11 or human recombinant granulocyte colony-stimulating factor. One week later, the resulting clones of cells were individually transplanted into lethally irradiated recipients. We also carried out time-course analysis of proliferation of the individual clones. Finally, we used micromanipulation of the paired progenies of the single cells and studied self-renewal and differentiation potentials of HSCs again in combination with transplantation.

RESULTS

There was a correlation between clone size at day 7 of culture and engraftment at 2 months post-transplantation. Small clones, such as those consisting of <15 cells, often showed high-level multilineage engraftment, while clones consisting of > or =40 cells showed very low levels of engraftment. Daily observation of cell divisions of individual clones revealed that some HSCs are in the G(0) state for as long as 1 week, despite the presence of permissive cytokines. Studies using micromanipulation of paired progenies documented the ability of an HSC to generate two HSCs, as well as asymmetric cell divisions.

CONCLUSIONS

Single-cell sorting combined with short-term culture of individual putative HSCs provides an efficient method for single HSC transplantation. Analyses of the kinetics of individual HSCs provided direct evidence for HSC cell-cycle dormancy, self-renewal, and expansion.

Hematopoietic stem cell origin of mesenchymal cells: opportunity for novel therapeutic approaches

There has been a general belief that there are two types of adult stem cells, i.e., hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), each with distinctly different functions. According to this dogma, HSCs produce blood cells, while MSCs are thought to generate a number of non-hematopoietic cells including fibroblasts, adipocytes, chondrocytes and bone cells. Recently, a number of studies, including those in our laboratory based on single HSC transplantation, blurred the clear distinction between HSCs and MSCs and strongly suggested an HSC origin of the adult mesenchymal tissues. This review summarizes the experimental evidence for this new paradigm and the literature pointing out the vagary in the stem cell nature of MSCs. The concept of the HSC origin of mesenchymal cells will have many immediate and long-term impacts on the therapies of diseases and injuries of the connective tissues.

MCP1 directs trafficking of hematopoietic stem cell-derived fibroblast precursors in solid tumor

Our previous studies have demonstrated that hematopoietic stem cells (HSCs) are a novel source of carcinoma-associated fibroblasts. However, the mechanisms regulating recruitment and homing of HSC-derived carcinoma-associated fibroblasts or their precursors to the tumor microenvironment are unknown. Herein, we demonstrate using a single cell transplantation model that circulating fibroblast precursors (CFPs) are of HSC origin. This population increased with tumor burden in vivo and functional in vitro studies showed that CFPs preferentially migrated and differentiated into fibroblasts in response to tumor, suggesting that HSC-derived CFPs serve as an intermediate between the bone marrow and tumor. Based on this chemotactic ability and our demonstration of a monocyte lineage origin for CFPs, we investigated the role of monocyte chemoattractant protein (MCP1) in mediating CFP recruitment/homing. Blocking tumor-produced MCP1 inhibited in vitro migration of CFPs in response to multiple tumor types, indicating broad biological significance for this CFP/chemokine interaction. In vivo, CCR2-expressing CFPs increased in circulation during the period of active tumor growth and stromal development. Inhibition of MCP1 during tumor development resulted in decreased tumor volume in tumor-bearing mice. Together these findings confirm an HSC origin for CFPs, demonstrate a role for MCP1 in regulating their contribution to the tumor microenvironment, and suggest a potential therapeutic target for limiting tumor growth.

The effects of benzene and other leukaemogenic agents on haematopoietic stem and progenitor cell differentiation

A characteristic shared by a diverse group of myelotoxic compounds and leukaemogens is the ability to act synergistically with granulocyte-macrophage colony stimulating factor (GM-CSF) in increasing clonogenic response. Pretreatment of murine or human bone marrow cells with the benzene metabolite, hydroquinone, but not phenol, catechol or trans, trans-muconaldehyde, results in a selective enhancement of GM-CSF but not an interleukin-3 (IL-3)-mediated clonogenic response. Clonal enhancement is preserved and magnified in enriched populations of CD34+ cells (> 95% purity), suggesting an intrinsic effect on haematopoietic progenitor cell (HPC) recruitment rather than a secondary effect involving accessory cytokines. Clonogenic enhancement of murine HPCs is not accompanied by alterations in GM-CSF receptor expression or ligand affinity and appears to be mediated via a p53-independent mechanism. These observations suggest that hydroquinone treatment alters recruitment and differentiation in a primitive subpopulation of CD34+ cells and are consistent with a role for altered stem cell differentiation in the development of chemically induced myelodysplasias.

Pharmacologic rationale for early G-CSF prophylaxis in cancer patients and role of pharmacogenetics in treatment optimization

The use of recombinant human granulocyte colony stimulating factors (G-CSF) has become an integral part of supportive care during cytotoxic chemotherapy. Current guidelines recommend the use of G-CSF in patients with substantial risk of febrile neutropenia. However, little consensus exists about optimal timing and tailoring of this therapy. Based on the known effects of chemotherapy and G-CSF on bone marrow compartments, we propose a model that supports the prophylactic rather than therapeutic use of G-CSF therapy. In addition, several genetic alterations in G-CSF signalling pathway have been described. These genetic variants may predict the risk of febrile neutropenia and response to G-CSF. Thus, future pharmacogenetic/omics studies in this field are warranted. Through the identification of patients at risk and the knowledge of biological basis for optimal timing, hopefully we should soon be able to improve the application of the existing guidelines for G-CSF therapy and patient's prognosis.

Treatment of severe aplastic anemia with antithymocyte globulin and cyclosporin A with or without G-CSF in adults: a multicenter randomized study in Japan

We report the results of a randomized study to elucidate whether addition of granulocyte colony-stimulating factor (G-CSF) to immunosuppressive therapy is valuable for the treatment of severe aplastic anemia (SAA) in adults. A total of 101 previously untreated patients (median age, 54 years; range, 19 to 75 years) were randomized to receive antithymocyte globulin (ATG) and cyclosporin A (CyA) (G-CSF- group) or ATG, CyA, and G-CSF (G-CSF+ group). In the G-CSF+ group, the hematologic response rate at 6 months was higher (77% vs 57%; P = .03) than in the G-CSF- group. No differences were observed between the groups in terms of the incidence of infections and febrile episodes. There were no differences between the G-CSF- group and the G-CSF+ group in terms of survival (88% vs 94% at 4 years), and the development of myelodysplastic syndrome (MDS)/acute leukemia (AL) (1 patient vs 2 patients). However, the relapse rate was lower in the G-CSF+ group compared with the G-CSF- group (42% vs 15% at 4 years; P = .01). Further follow-up is required to elucidate the role of G-CSF in immunosuppressive therapy for adult SAA.

Effects of whole-body gamma irradiation and 5-androstenediol administration on serum G-CSF

5-Androstenediol (5-AED) is a natural circulating adrenocortical steroid hormone that interconverts in vivo with other members of the 5-androstene family of steroids: dehydroepiandrosterone and 5-androstenetriol. These steroids stimulate immune responses and resistance to infection. 5-AED has been identified as a systemic radiation countermeasure that enhances survival in mice exposed to gamma irradiation and ameliorates radiation-induced neutropenia in mice and nonhuman primates. 5-AED mitigates radiation-induced decreases in platelets, natural killer (NK) cells, red blood cells, and monocytes. Administration of 5-AED causes functional activation of circulating granulocytes (phagocytic ability), monocytes (oxidative burst), and NK cells (surface CD11b expression). The effects of 5-AED on survival and hematological parameters are consistent with induction of hematopoietic cytokines. To test this hypothesis, we measured serum cytokines by ELISA, Luminex, and a cytokine array. A cytokine array was used for 62 different cytokines, chemokines, growth factors, and soluble receptors. 5-AED caused significant increases in circulating granulocyte colony-stimulating factor (G-CSF) in irradiated and unirradiated animals as observed with ELISA and Luminex. The cytokine array results suggest induction of G-CSF and additional cytokines, and related molecules. Since G-CSF is an important hematopoietic cytokine, the results support our hypothesis that the previously observed increases in numbers of hematopoietic progenitors, circulating innate immune cells and platelets, and functional activation of granulocytes, monocytes, and NK cells result from a cytokine cascade induced by 5-AED.

Recent advances in understanding extrinsic control of hematopoietic stem cell fate

PURPOSE OF REVIEW

Hematopoietic stem cells are responsible for generating all types of blood cells. As such they are under a high degree of regulation, both internal and external. With the identification of the hematopoietic stem cell niche, there has been increased investigation into extrinsic regulation of hematopoietic stem cells with emphasis on developmental signaling pathways. The purpose of this review is to discuss recent advances and findings in how these different pathways interact to achieve a balanced control of these stem cells.

RECENT FINDINGS

Studies indicating the importance of pathways such as Wnt, Notch, bone morphogenic protein, Sonic hedgehog and fibroblast growth factor in controlling the fate of hematopoietic stem cells are the most significant recent findings. These pathways have been implicated to affect various aspects of hematopoietic stem cells, including self-renewal, proliferation and lineage determination. Equally important are studies showing, by inactivation of various pathway components, the complexity of signal integration at the stem cell level in vivo. Additionally, some recent reports have provided evidence for direct interaction or cross-talk between different signaling pathways in this regulation.

SUMMARY

We review highlights of the recent advances made toward resolving the mechanisms of external regulation of hematopoietic stem cells. Understanding the interaction of different signaling pathways in the context of the hematopoietic stem cell niche is essential for increasing their therapeutic potential.

Hematopoietic origin of fibroblasts/myofibroblasts: Its pathophysiologic implications

Tissue fibroblasts/myofibroblasts play a key role in growth factor secretion, matrix deposition, and matrix degradation, and therefore are important in many pathologic processes. Regarding the origin of tissue fibroblasts/myofibroblasts, a number of recent in vivo transplantation studies have suggested the bone marrow as the source of fibroblasts/myofibroblasts in liver, intestine, skin, and lung. Because bone marrow cells are thought to contain 2 types of stem cells (ie, hematopoietic stem cells [HSCs] and mesenchymal stem cells), it is important to determine which type of stem cells is the source of fibroblasts/myofibroblasts. To address this issue, we have carried out a series of studies of tissue reconstitution by single HSCs. By transplanting clones derived from single HSCs expressing transgenic enhanced green fluorescent protein, we found that fibroblasts/myofibroblasts in many organs and tissues are derived from HSCs. This brief note summarizes these findings and discusses clinical and experimental perspectives generated by this newly identified differentiation pathway of HSCs.

Contribution of bone marrow hematopoietic stem cells to adult mouse inner ear: mesenchymal cells and fibrocytes

Bone marrow (BM)-derived stem cells have shown plasticity with a capacity to differentiate into a variety of specialized cells. To test the hypothesis that some cells in the inner ear are derived from BM, we transplanted either isolated whole BM cells or clonally expanded hematopoietic stem cells (HSCs) prepared from transgenic mice expressing enhanced green fluorescent protein (EGFP) into irradiated adult mice. Isolated GFP(+) BM cells were also transplanted into conditioned newborn mice derived from pregnant mice injected with busulfan (which ablates HSCs in the newborns). Quantification of GFP(+) cells was performed 3-20 months after transplant. GFP(+) cells were found in the inner ear with all transplant conditions. They were most abundant within the spiral ligament but were also found in other locations normally occupied by fibrocytes and mesenchymal cells. No GFP(+) neurons or hair cells were observed in inner ears of transplanted mice. Dual immunofluorescence assays demonstrated that most of the GFP(+) cells were negative for CD45, a macrophage and hematopoietic cell marker. A portion of the GFP(+) cells in the spiral ligament expressed immunoreactive Na, K-ATPase, or the Na-K-Cl transporter (NKCC), proteins used as markers for specialized ion transport fibrocytes. Phenotypic studies indicated that the GFP(+) cells did not arise from fusion of donor cells with endogenous cells. This study provides the first evidence for the origin of inner ear cells from BM and more specifically from HSCs. The results suggest that mesenchymal cells, including fibrocytes in the adult inner ear, may be derived continuously from HSCs.

Hematopoietic origins of fibroblasts: I. In vivo studies of fibroblasts associated with solid tumors

OBJECTIVE

Recent studies have reported that bone marrow cells can give rise to tissue fibroblasts. However, the bone marrow cell(s) that gives rise to fibroblasts has not yet been identified. In the present study, we tested the hypothesis that tissue fibroblasts are derived from hematopoietic stem cells (HSCs) in vivo.

METHODS

These studies were conducted using mice whose hematopoiesis had been reconstituted by transplantation of a clonal population of cells derived from a single enhanced green fluorescent protein (EGFP)-positive HSC in conjunction with murine tumor models.

RESULTS

When tumors propagated in the transplanted mice were evaluated for the presence of EGFP(+) HSC-derived cells, two prominent populations of EGFP(+) cells were found. The first were determined to be fibroblasts within the tumor stromal capsule, a subset of which expressed type I collagen mRNA and alpha-smooth muscle actin. The second population was a perivascular cell associated with the CD31(+) tumor blood vessels.

CONCLUSION

These in vivo findings establish an HSC origin of fibroblasts.

Hematopoietic origins of fibroblasts: II. In vitro studies of fibroblasts, CFU-F, and fibrocytes

OBJECTIVE

Using transplantation of a clonal population of cells derived from a single hematopoietic stem cell (HSC) of transgenic enhanced green fluorescent protein (EGFP) mice, we have documented the hematopoietic origin of myofibroblasts, such as kidney mesangial cells and brain microglial cells. Because myofibroblasts are thought to be an activated form of fibroblasts, we tested the hypothesis that fibroblasts are derived from HSCs.

MATERIALS AND METHODS

Clones of cells derived from single cells of EGFP Ly-5.2 C57Bl/6 mice were transplanted into lethally irradiated Ly-5.1 mice. Using bone marrow and peripheral blood cells from mice showing high-level multilineage hematopoietic reconstitution, we induced growth of fibroblasts in vitro.

RESULTS

Culture of EGFP(+) bone marrow cells from clonally engrafted mice revealed adherent cells with morphology typical of fibroblasts. Flow cytometric analysis revealed that the majority of these cells are CD45(-) and express collagen-I and the collagen receptor, discoidin domain receptor 2 (DDR2). Reverse transcriptase polymerase chain reaction analysis of cultured cells demonstrated expression of procollagen 1-alpha1, DDR2, fibronectin, and vimentin mRNA. Fibroblast colonies consisting of EGFP(+) cells were observed in cultures of bone marrow cells from clonally engrafted mice, indicating an HSC origin of fibroblast colony-forming units. Culture of peripheral blood nucleated cells from clonally engrafted mice revealed EGFP(+) cells expressing collagen-I and DDR2, indicating that fibrocytes are also derived from HSCs.

CONCLUSION

We conclude that a population of fibroblasts and their precursors are derived from HSCs.

Granulocyte/Macrophage Origin of Glomerular Mesangial Cells

We previously demonstrated the ability of hematopoietic stem cells (HSCs) to generate glomerular mesangial cells by trans-planting clonal populations of cells derived from a single enhanced green fluorescent protein (EGFP)-positive HSC into lethally irradiated mice. To define more precisely the hematopoietic differentiation pathway through which mesangial cells are derived, we studied the relationship between mesangial cell expression and individual hematopoietic lineages by means of a transplantation strategy. In a series of clonal HSC transplantation experiments, we generated 3 mice engrafted predominantly by granulocytes and macrophages (GMs) and 4 mice engrafted with B-cells or with B-cells and T-cells. When the kidneys of these mice were analyzed, the mice exhibiting high GM lineage engraftment revealed much higher levels of EGFP-positive mesangial cells than those with predominantly lymphocyte engraftment. Fluorescence in situ hybridization analysis of the kidneys from a male recipient of an EGFP-positive female donor excluded cell fusion as the cause for the observed differentiation. These results support the notion that glomerular mesangial cells share their origin with GMs.

Lineage-specific growth factors can compensate for stem and progenitor cell deficiencies at the postprogenitor cell level: an analysis of doubly TPO- and G-CSF receptor-deficient mice

Multiple lines of evidence indicate that thrombopoietin (TPO) substantially impacts the number of hematopoietic stem cells and progenitors of all myeloid lineages. Nevertheless, tpo knock-out mice (T(-)) display thrombocytopenia only; blood erythroid and neutrophil levels are normal despite 60% to 85% reductions in stem and progenitor cells. The compensatory mechanism(s) for these deficiencies remains uncertain; lineage-specific cytokines such as erythropoietin or granulocyte colony-stimulating factor (G-CSF) have been postulated but never proven to be responsible. To directly test whether G-CSF can compensate for the myeloid progenitor cell reduction in the T(-) model of hematopoietic deficiency, T(-) and G-CSF-receptor knock-out (GR(-)) mice were crossed, and F1 animals bred to obtain doubly nullizygous mice (T(-)GR(-)). This experiment also allowed us to test the hypothesis that G-CSF contributes to the residual platelet production in T(-) mice. We found that T(-)GR(-) F2 mice displayed similar blood platelet levels as that seen in T(-) mice, indicating that G-CSF does not account for the residual megakaryopoiesis in T(-) mice. However, we also noted excessive perinatal mortality of T(-)GR(-) animals, caused by infection due to a profound and significant decrease in marrow and peripheral blood neutrophils, far greater than that seen in either T(-) or GR(-) mice. These data indicate that in the additional absence of GR, T(-) mice cannot compensate for their 62% reduction in myeloid progenitors and become profoundly neutropenic, supporting the hypothesis that G-CSF can compensate for the myeloid effects of TPO deficiency by expanding the pool of cells between the granulocyte-macrophage colony-forming unit and mature neutrophil stages of granulopoiesis.

Liver-derived DEC205+B220+CD19- dendritic cells regulate T cell responses

Leukocytes resident in the liver may play a role in immune responses. We describe a cell population propagated from mouse liver nonparenchymal cells in IL-3 and anti-CD40 mAb that exhibits a distinct surface immunophenotype and function in directing differentiation of naive allogeneic T cells. After culture, such cells are DEC-205(bright)B220+CD11c-CD19-, and negative for T (CD3, CD4, CD8alpha), NK (NK 1.1) cell markers, and myeloid Ags (CD11b, CD13, CD14). These liver-derived DEC205+B220+ CD19- cells have a morphology and migratory capacity similar to dendritic cells. Interestingly, they possess Ig gene rearrangements, but lack Ig molecule expression on the cell surface. They induce low thymidine uptake of allogeneic T cells in MLR due to extensive apoptosis of activated T cells. T cell proliferation is restored by addition of the common caspase inhibitor peptide, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk). T cells stimulated by liver-derived DEC205+B220+D19- cells release both IL-10 and IFN-gamma, small amounts of TGF-beta, and no IL-2 or IL-4, a cytokine profile resembling T regulatory type 1 cells. Expression of IL-10 and IFN-gamma, but not bioactive IL-12 in liver DEC205+B220+CD19- cells was demonstrated by RNase protection assay. In vivo administration of liver DEC205+B220+CD19- cells significantly prolonged the survival of vascularized cardiac allografts in an alloantigen-specific manner.

The combined administration of daniplestim and Mpl ligand augments the hematopoietic reconstitution observed with single cytokine administration in a nonhuman primate model of myelosuppression

This study evaluated the ability of daniplestim, a high affinity interleukin 3 receptor agonist, to enhance the hematopoietic response of Mpl ligand (Mpl-L) administration in nonhuman primates following severe, radiation-induced myelosuppression. Rhesus monkeys were total body x-irradiated (TBI) to 600 cGy, midline tissue dose. Beginning on day 1 post-TBI, animals were s.c. administered daniplestim (100 microg/kg bid; n = 4), Mpl-L (10 microg/kg qd; n = 3), daniplestim (100 microg/kg bid) plus Mpl-L (10 microg/kg qd) (n = 4) or 0.1% autologous serum (AS) (n = 11) for 18 days. CBCs were monitored for 60 d after TBI. The duration of thrombocytopenia (platelet count; PLT <20,000/microl) was significantly decreased by the administration of daniplestim (6.5 d, p = .01), Mpl-L (3.0 d, p = .003) and the coadministered daniplestim/Mpl-L (1.3 d, p = .001) compared to controls (10.4 d). As monotherapy Mpl-L but not daniplestim significantly improved the PLT nadir (21,000/microl, p = .023 and 5,000/microl, p = .266, respectively) compared to the control (3,000/microl). The combined administration of daniplestim and Mpl-L significantly improved the PLT nadir (28,000/microl, p = .007) compared to both the control cohort (3,000/microl) and the daniplestim only cohort (5,000/microl, p = .043). Recovery of PLT to preirradiation values occurred earlier in the daniplestim only (d 21) or the daniplestim/Mpl-L cohorts (d 18) than in the Mpl-L only or control cohorts (d 28, d 29, respectively). The administration of daniplestim or Mpl-L alone neither shortened the duration of neutropenia (ANC<500/microl) compared to the controls (15.8 d, 16.0 d versus 16.2 d, respectively), nor improved the recovery time of neutrophils to baseline values (d 22, d 25, and d 23, respectively). The ANC nadir was significantly improved by daniplestim alone but not Mpl-L administration (76/microl, p = .001 and 50/microl, p = .093, respectively) compared to the controls (8/microl). Coadministration of daniplestim and Mpl-L significantly improved the ANC nadir (196/microl, p = .001) compared to either the AS- or the monotherapy-treated cohorts. Also the duration of neutropenia observed in the AS-controls (16.2 d) was significantly reduced in the daniplestim/Mpl-L cohort (10.8 d, p = .002). The combined administration of daniplestim and Mpl-L significantly improved hematopoietic recovery and further enhanced the stimulatory effect of cytokine monotherapy, as well as reducing clinical support requirements after radiation-induced bone marrow myelosuppression.

Use of granulocyte colony-stimulating factor after high-dose chemotherapy and autologous peripheral blood stem cell transplantation: what is the optimal timing?

Administration of granulocyte colony-stimulating factor to patients undergoing high-dose chemotherapy and autologous peripheral blood stem cell transplantation accelerates neutrophil recovery and decreases hospitalization time. The optimal timing for granulocyte colony-stimulating factor infusion remains unknown. In this retrospective, case-controlled, two-armed study, we reviewed our experience at Hahnemann University Hospital to determine whether initiating granulocyte colony-stimulating factor infusions on posttransplant day 0 versus day 8 affects neutrophil recovery time, posttransplant discharge date, total hospital days after high-dose chemotherapy, and autologous peripheral blood stem cell transplantation. All patients hospitalized between 1994 and 1998 at Hahnemann University Hospital, Bone Marrow Transplantation Unit with breast cancer or non-Hodgkin's lymphoma, who underwent high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation and received granulocyte colony-stimulating factor either on posttransplant day 0 (16 patients) or day 8 (16 patients). The day 0 and day 8 groups had no statistically significant differences in age, sex, weight, height, body surface area, disease characteristics, pretransplant harvesting or conditioning regimens, or transplant CD34+ cell counts. Our main outcome measure was the mean time to reach absolute neutrophil count greater than or equal to 0.5 x 10(9)/l, the number of hospital days after transplant, and the total hospital days. The mean days to neutrophil recovery (10.56 versus 9.68, p = 0.48), posttransplant hospital days (13.62 versus 12.81, p = 0.39), and total hospital days (20.25 versus 20.25, p = 1.00) were not significantly different between day 8 and day 0 groups, respectively. No significant effects on neutrophil recovery time, posttransplant hospital days, or total hospital days were observed with the initial granulocyte colony-stimulating factor infusion on day 0 versus day 8 after transplant. Delayed administration may allow substantial cost savings (US$200 x 8 approximately equal to US $1,600 per patient) without affecting clinical outcome. More studies are needed to determine whether greater delay is feasible.

Disruption of nuclear factor-interleukin-6, a transcription factor, results in severe mycobacterial infection

Nuclear factor-interleukin-6 (NF-IL-6) is one of several nuclear transcription factors (NF-IL-6, NF-kappaB, PU.1, interferon-regulatory factor 1, Egr-1, and Stat-1). NF-IL-6 and NF-kappaB are expressed in macrophages and is induced by bacterial lipopolysaccharides. To evaluate whether NF-IL-6 is required for the inflammatory immune response to mycobacterial infection, in which epithelioid macrophages comprise the leading cell population, we generated NF-IL-6 knockout (KO) mutant mice. Airborne infection of these mice with Mycobacterium tuberculosis strains induced disseminated tuberculosis lacking granuloma formation, although interferon-gamma, tumor necrosis factor-alpha, and interleukin-12 mRNA expression levels were within the normal range compared with those of wild-type mice. Generation of O2- and mycobacterial killing by neutrophils from these mice were impaired severely compared with wild-type mice. We conclude that NF-IL-6 is a critical transcription factor in mycobacterial control as well as in granulocyte-colony stimulating factor induction resulting in neutrophil activation.

Coexpression of granulocyte colony stimulating factor and its receptor in primary ovarian carcinomas

Immunohistochemistry was used to determine the expression of granulocyte colony-stimulating factor (G-CSF) and its receptor (G-CSFR) in primary ovarian carcinomas. The expression of G-CSFR was observed in the malignant cells of each of the 46 primary carcinomas examined; G-CSF was coexpressed in both the malignant epithelial cells and the stroma of 56.5% of the specimens. Thus the majority of ovarian carcinomas harbor both potential autocrine and paracrine G-CSF axes. In 37% of the samples, G-CSF was expressed only within stromal cells, suggesting that only a potential paracrine system is in place. In a preliminary, retrospective, evaluation, the survival of patients whose tumors expressed only the apparent paracrine loop was significantly worse than patients whose tumors expressed both potential autocrine and paracrine G-CSF-based regulatory loops (14.5 vs. 42.5 months, respectively). Studies on the potential function of G-CSF were performed using the G-CSFR-expressing OVCAR-3 ovarian carcinoma line. As a single agent, rhG-CSF failed to stimulate [3H]-thymidine incorporation in these cells, but enhanced the mitogenic action of epidermal growth factor (EGF) in a dose-dependent manner. Thus, potential autocrine and/or paracrine loops involving G-CSF and its receptor occur in over 90% of primary ovarian carcinomas, and may act to modulate the action of growth factors.

Negative influence of IL3 on the expansion of human cord blood in vivo long-term repopulating stem cells

Identification of culture conditions that support expansion or even long-term maintenance of in vivo repopulating human hematopoietic stem cells is still a major challenge. Using a combination of FLT3 ligand (FL), Stem Cell Factor (SCF), Thrombopoietin (TPO) and Interleukin 6 (IL6), we cultured cord blood (CB) CD34+ cells for up to 12 weeks and transplanted their progeny into sublethally irradiated NOD/SCID mice. Bone marrow engraftment was considered successful when recipients contained measurable numbers of human CD45+, CD71+ and Glycophorin A+(GpA) cells 8 weeks after transplantation. Twelve-week expanded cells with FL+SCF+TPO+IL6 successfully engrafted all of the recipients and human CD45(+)+CD71(+)+GpA(+) cells represented 4.3 to 22.4% of bone marrow. Substitution of IL6 with IL3 led to an even better expansion of cells and a similar clonogenic progenitor output in the first 8 weeks of culture; however, LTC-IC output increased up to week 6 and then decreased and disappeared. By contrast, with FL+SCF+TPO+IL6, LTC-IC kept increasing up to week 12. Four-week cultured cells with FL+SCF+TPO+IL3 less efficiently engrafted NOD/SCID mice, both as measured by frequency of positive recipients (4 out of 10) and percentage of engrafted human cells (< or =2%). Six-week expanded cells failed to engraft. This study provides evidence that many, but not all, of the so-called "early acting" cytokines, can sustain long-term maintenance and even expansion of human primitive in vivo repopulating stem cells. In particular, in the culture conditions used in this study, the presence of IL3 greatly reduces the repopulating potential of expanded CD34+ CB cells.

A practical approach to evaluating and treating neutropenia in the neonatal intensive care unit

Neutropenia is a relatively common problem in the NICU, recognized in as many as 8% of patients at some time during their hospital stay. In most instances, neutropenia among NICU patients is of short duration and has little influence on outcome. In other cases it is prolonged and severe, and constitutes a serious antimicrobial defense deficiency. When a neonatologist discovers a low blood neutrophil count, choices must be made regarding further evaluation and treatment. The authors hope that the information provided in this article is useful in making these choices.

IL-3 increases production of B lymphoid progenitors from human CD34+CD38- cells

The effect of IL-3 on the B lymphoid potential of human hemopoietic stem cells is controversial. Murine studies suggest that B cell differentiation from uncommitted progenitors is completely prevented after short-term exposure to IL-3. We studied B lymphopoiesis after IL-3 stimulation of uncommitted human CD34+CD38- cells, using the stromal cell line S17 to assay the B lymphoid potential of stimulated cells. In contrast to the murine studies, production of CD19+ B cells from human CD34+CD38- cells was significantly increased by a 3-day exposure to IL-3 (p < 0.001). IL-3, however, did not increase B lymphopoiesis from more mature progenitors (CD34+CD38+ cells) or from committed CD34-CD19+ B cells. B cell production was increased whether CD34+CD38- cells were stimulated with IL-3 during cocultivation on S17 stroma, on fibronectin, or in suspension. IL-3Ralpha expression was studied in CD34+ populations by RT-PCR and FACS. High IL-3Ralpha protein expression was largely restricted to myeloid progenitors. CD34+CD38- cells had low to undetectable levels of IL-3Ralpha by FACS. IL-3-responsive B lymphopoiesis was specifically found in CD34+ cells with low or undetectable IL-3Ralpha protein expression. IL-3 acted directly on progenitor cells; single cell analysis showed that short-term exposure of CD34+CD38- cells to IL-3 increased the subsequent cloning efficiency of B lymphoid and B lymphomyeloid progenitors. We conclude that short-term exposure to IL-3 significantly increases human B cell production by inducing proliferation and/or maintaining the survival of primitive human progenitors with B lymphoid potential.

Participation of granulocyte colony-stimulating factor in the growth regulation of leukemia cells from Philadelphia chromosome-positive acute leukemia and blast crisis of chronic myeloid leukemia

Granulocyte colony-stimulating factor (G-CSF) has been shown to support the growth of multipotential hematopoietic stem cells in addition to the cells of neutrophilic lineage. Philadelphia chromosome (Ph1)-positive leukemia has its origin in the hematopoietic stem cell. In the present study, we demonstrated that the proliferation of leukemic cells from chronic myeloid leukemia in blast crisis (CML-BC) and Ph1-positive acute lymphoblastic leukemia (ALL) cases is frequently stimulated with G-CSF in vitro. We next studied a total of 12 leukemic cell lines established from CML-BC (n= 6) and Ph1-positive acute leukemia (n= 6): four 'myeloid', five 'biphenotypic', and three 'lymphoid' types. All cell lines expressed G-CSF receptor (G-CSFR) in flow cytometric analysis, but their proliferative response to G-CSF in 3H-thymidine incorporation assay varied. The 'biphenotypic' cell lines expressed G-CSFR at higher levels and showed the most pronounced response to G-CSF. The 'lymphoid' cell lines showed intermediate G-CSFR expression with the modest response to G-CSF. Unexpectedly, 'myeloid' cell lines showed lower G-CSFR expression and lower G-CSF response compared with 'biphenotypic' cell lines. In three of four 'myeloid' cell lines, proliferation was partially inhibited by an addition of anti-G-CSF neutralizing monoclonal antibody into culture medium. Further, the % inhibition of 3H-thymidine uptake of cell lines positively correlated with the amount of their intracellular G-CSF measured by enzyme immunoassay, suggesting an autocrine growth mechanism via the G-CSF/G-CSFR interaction. These results suggest that G-CSF play an important role in the growth regulation of leukemia cells from Ph1-positive acute leukemia and CML-BC.

Aclarubicin induces differentiation of leukemic progenitors in myelodysplastic syndrome cooperating with granulocyte colony-stimulating factor

We have reported that low-dose aclarubicin (ACR) therapy is effective in some patients with myelodysplastic syndrome (MDS). Here, we demonstrate that a low concentration of ACR induces the in vitro differentiation of leukemic progenitor cells from patients with MDS. ACR (0.1 ng/ml) significantly increased the number of granulocyte colony-stimulating factor (G-CSF)-dependent colonies from circulating blast cells in vitro in six out of seven MDS patients with refractory anemia with excess of blast in transformation or chronic myelomonocytic leukemia, but not in all four patients with primary acute myelogenous leukemia. In these MDS patients, the effect of ACR gradually disappeared along with the progression of MDS. Interestingly, the majority of G-CSF/ACR-dependent colonies consisted of rather differentiated myeloid cells such as myelocytes and metamyelocytes, whereas colonies formed by G-CSF alone were composed mainly of immature blastic cells. The number of G-CSF-responding progenitors significantly increased during a 24-48 h incubation with ACR alone. The circulating blasts in MDS patients expressed G-CSF receptors at unchanged levels before and after the incubation with ACR. It is suggested that ACR might increase clonogenic progenitor responsiveness to G-CSF in MDS, probably through modulating downstream signaling cascades associated with G-CSF receptors, and induce these progenitors to differentiate in response to G-CSF.

Defective Proliferation of Primitive Myeloid Progenitor Cells in Patients With Severe Congenital Neutropenia

Although several mechanisms have been proposed to explain the pathophysiology of severe congenital neutropenia (SCN), the precise defect responsible for SCN remains unknown. We studied the responsiveness of primitive myeloid progenitor cells to hematopoietic factors in 4 patients with SCN. The number of granulocyte-macrophage (GM) colonies formed in patients was decreased in response to granulocyte colony-stimulating factor (G-CSF) in both serum-supplemented and serum-deprived culture. The polymerase chain reaction–single-strand conformational polymorphism analysis of the G-CSF receptor gene showed no variance in structure conformation between the 4 patients and the normal subjects. In patients with SCN, the nonadherent light density bone marrow cells and cells that were purified on the basis of the expression of CD34 and Kit receptor (CD34+/Kit+ cells) showed the reduced response to the combination of steel factor (SF), the ligand for flk2/flt3 (FL), and interleukin-3 (IL-3) with or without G-CSF in serum-deprived culture. Furthermore, when individual CD34+/Kit+ cells from patients were cultured in the presence of SF, FL, and IL-3, with or without G-CSF for 10 days, the number of clones proliferated and the number of cells per each proliferating clone was significantly less than those in normal subjects. These results suggest that primitive myeloid progenitor cells of patients with SCN have defective responsiveness to not only G-CSF, but also the early- or intermediate-acting hematopoietic factors, SF, FL, and IL-3.

Defective Proliferation of Primitive Myeloid Progenitor Cells in Patients With Severe Congenital Neutropenia

Although several mechanisms have been proposed to explain the pathophysiology of severe congenital neutropenia (SCN), the precise defect responsible for SCN remains unknown. We studied the responsiveness of primitive myeloid progenitor cells to hematopoietic factors in 4 patients with SCN. The number of granulocyte-macrophage (GM) colonies formed in patients was decreased in response to granulocyte colony-stimulating factor (G-CSF) in both serum-supplemented and serum-deprived culture. The polymerase chain reaction–single-strand conformational polymorphism analysis of the G-CSF receptor gene showed no variance in structure conformation between the 4 patients and the normal subjects. In patients with SCN, the nonadherent light density bone marrow cells and cells that were purified on the basis of the expression of CD34 and Kit receptor (CD34+/Kit+ cells) showed the reduced response to the combination of steel factor (SF), the ligand for flk2/flt3 (FL), and interleukin-3 (IL-3) with or without G-CSF in serum-deprived culture. Furthermore, when individual CD34+/Kit+ cells from patients were cultured in the presence of SF, FL, and IL-3, with or without G-CSF for 10 days, the number of clones proliferated and the number of cells per each proliferating clone was significantly less than those in normal subjects. These results suggest that primitive myeloid progenitor cells of patients with SCN have defective responsiveness to not only G-CSF, but also the early- or intermediate-acting hematopoietic factors, SF, FL, and IL-3.

Shwachman-Diamond Syndrome: An Inherited Preleukemic Bone Marrow Failure Disorder With Aberrant Hematopoietic Progenitors and Faulty Marrow Microenvironment

Shwachman-Diamond syndrome (SD), an inherited disorder with varying cytopenias and a marked tendency for malignant myeloid transformation, is an important model for understanding genetic determinants in hematopoiesis. To define the basis for the faulty hematopoietic function, 13 patients with SD (2 of whom had myelodysplasia with a clonal cytogenetic abnormality) and 11 healthy marrow donors were studied. Patients with SD had significantly lower numbers of CD34+ cells on bone marrow aspirates. SD CD34+ cells plated directly in standard clonogenic assays showed markedly impaired colony production potential, underscoring an intrinsically aberrant progenitor population. To assess marrow stromal function, long-term marrow stromal cell cultures (LTCs) were established. Normal marrow CD34+ cells were plated over either SD stroma (N/SD) or normal stroma (N/N); SD CD34+cells were plated over either SD stroma (SD/SD) or normal stroma (SD/N). Nonadherent cells harvested weekly from N/SD LTCs were strikingly reduced compared with N/N LTCs; numbers of granulocyte-monocyte colony-forming units (CFU-GM) derived from N/SD nonadherent cells were also lower. SD/N showed improved production of nonadherent cells and CFU-GM colonies compared with SD/SD, but much less than N/N. Stem-cell and stromal properties from the 2 patients with SD and myelodysplasia did not differ discernibly from SD patients without myelodysplasia. We conclude that in addition to a stem-cell defect, patients with SD have also a serious, generalized marrow dysfunction with an abnormal bone marrow stroma in terms of its ability to support and maintain hematopoiesis. This dual defect exists in SD with and without myelodysplasia.

Shwachman-Diamond Syndrome: An Inherited Preleukemic Bone Marrow Failure Disorder With Aberrant Hematopoietic Progenitors and Faulty Marrow Microenvironment

Shwachman-Diamond syndrome (SD), an inherited disorder with varying cytopenias and a marked tendency for malignant myeloid transformation, is an important model for understanding genetic determinants in hematopoiesis. To define the basis for the faulty hematopoietic function, 13 patients with SD (2 of whom had myelodysplasia with a clonal cytogenetic abnormality) and 11 healthy marrow donors were studied. Patients with SD had significantly lower numbers of CD34+ cells on bone marrow aspirates. SD CD34+ cells plated directly in standard clonogenic assays showed markedly impaired colony production potential, underscoring an intrinsically aberrant progenitor population. To assess marrow stromal function, long-term marrow stromal cell cultures (LTCs) were established. Normal marrow CD34+ cells were plated over either SD stroma (N/SD) or normal stroma (N/N); SD CD34+cells were plated over either SD stroma (SD/SD) or normal stroma (SD/N). Nonadherent cells harvested weekly from N/SD LTCs were strikingly reduced compared with N/N LTCs; numbers of granulocyte-monocyte colony-forming units (CFU-GM) derived from N/SD nonadherent cells were also lower. SD/N showed improved production of nonadherent cells and CFU-GM colonies compared with SD/SD, but much less than N/N. Stem-cell and stromal properties from the 2 patients with SD and myelodysplasia did not differ discernibly from SD patients without myelodysplasia. We conclude that in addition to a stem-cell defect, patients with SD have also a serious, generalized marrow dysfunction with an abnormal bone marrow stroma in terms of its ability to support and maintain hematopoiesis. This dual defect exists in SD with and without myelodysplasia.

Humoral regulation of hematopoietic stem cells

During the last two decades, studies using primarily cell culture methods disclosed that a number of hematopoietic cytokines possess stimulatory effects on primitive hematopoietic progenitors. More recently, investigators in a number of laboratories, including ours, used murine transplantation models to characterize the cytokines regulating the hematopoietic stem cells. The results are in general agreement with the cytokine interactions defined in culture. The positive cytokines may be separated into two groups: one consisting of steel factor and flt3/flt2 ligand and the other consisting of interleukin (IL)-6, IL-11, IL-12, leukemia inhibitory factor, granulocyte colony-stimulating factor (G-CSF) and thrombopoietin. Interactions of two cytokines belonging to different groups appear necessary to positively regulate the kinetics of stem cells. Surprisingly, IL-3 and IL-1 proved to have profound negative effects on hematopoietic stem cells. Studies of human hematopoietic stem cells are now necessary.

Prolonged Expression of c-fos Suppresses Cell Cycle Entry of Dormant Hematopoietic Stem Cells

The proto-oncogene c-fos was transiently upregulated in primitive hematopoietic stem (Lin−Sca-1+) cells stimulated with stem cell factor, interleukin-3 (IL-3), and IL-6. To investigate a role of the c-fos in hematopoietic stem cells, we used bone marrow (BM) cells from transgenic mice carrying the c-fos gene under the control of the interferon-/β–inducible Mx-promoter (Mx–c-fos), and fetal liver cells from c-fos–deficient mice. Prolonged expression of the c-fos in Lin−Sca-1+ BM cells inhibited factor-dependent colony formation and hematopoiesis on a stromal cell layer by keeping them at G0/G1 phase of the cell cycle. These Lin−Sca-1+ BM cells on a stromal layer entered into the cell cycle whenever exogenous c-fos was downregulated. However, ectopic c-fos did not perturb colony formation by Lin−Sca-1+ BM cells after they entered the cell cycle. Furthermore, endogenous c-fos is not essential to cell cycle progression of hematopoietic stem cells because the factor-dependent and the stroma-dependent hematopoiesis by Lin−Sca-1+ fetal liver cells from c-fos–deficient mice was not impaired. These results suggest that the c-fos induced in primitive hematopoietic stem cells negatively controls cell cycle progression and maintains them in a dormant state.

Prolonged Expression of c-fos Suppresses Cell Cycle Entry of Dormant Hematopoietic Stem Cells

The proto-oncogene c-fos was transiently upregulated in primitive hematopoietic stem (Lin−Sca-1+) cells stimulated with stem cell factor, interleukin-3 (IL-3), and IL-6. To investigate a role of the c-fos in hematopoietic stem cells, we used bone marrow (BM) cells from transgenic mice carrying the c-fos gene under the control of the interferon-/β–inducible Mx-promoter (Mx–c-fos), and fetal liver cells from c-fos–deficient mice. Prolonged expression of the c-fos in Lin−Sca-1+ BM cells inhibited factor-dependent colony formation and hematopoiesis on a stromal cell layer by keeping them at G0/G1 phase of the cell cycle. These Lin−Sca-1+ BM cells on a stromal layer entered into the cell cycle whenever exogenous c-fos was downregulated. However, ectopic c-fos did not perturb colony formation by Lin−Sca-1+ BM cells after they entered the cell cycle. Furthermore, endogenous c-fos is not essential to cell cycle progression of hematopoietic stem cells because the factor-dependent and the stroma-dependent hematopoiesis by Lin−Sca-1+ fetal liver cells from c-fos–deficient mice was not impaired. These results suggest that the c-fos induced in primitive hematopoietic stem cells negatively controls cell cycle progression and maintains them in a dormant state.

Abnormal levels of proinflammatory cytokines in serum and monocyte cultures from patients with chronic myeloid leukemia in different stages, and their role in prognosis

Interleukin-1 (IL-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), primarily monocyte-derived cytokines, form a group of proinflammatory cytokines with related and overlapping spectra of activities. The role of these cytokines in chronic myeloid leukemia (CML) has been investigated. A distinctive pattern of cytokine secretion has been found in chronic myeloid leukemia in chronic phase (CML-CP), in blastic crisis (CML-BC) and in normal subjects. Serum IL-6 levels in CML-CP and CML-BC were significantly raised compared with normal controls (p = 0.0026 for CML-CP and p = 0.0011 for CML-BC). IL-6 was significantly elevated in blastic crisis of CML (103.5 +/- 20.77 pg ml-1) compared with CML-CP (37.35 +/- 10.88 pg ml-1; p = 0.014). IL-6 serum levels were found to correlate significantly with peripheral blood monocyte counts and bone marrow blast and basophil counts. We have analysed monocyte/macrophage function with respect to their ability to produce IL-1, IL-6 and TNF-alpha, spontaneously as well as in response to LPS, in comparison with normal controls. A direct correlation of IL-6 levels in unstimulated and stimulated cultures with bone marrow blast and basophil counts has been observed. From these results it is inferred that the monocyte function is impaired in CML patients, and the cytokine secretion is deficient. Our limited data suggest that serum IL-6 levels may play an important role as a prognostic marker for CML.

Negative Regulation by Interleukin-3 (IL-3) of Mouse Early B-Cell Progenitors and Stem Cells in Culture: Transduction of the Negative Signals by βc and βIL-3 Proteins of IL-3 Receptor and Absence of Negative Regulation by Granulocyte-Macrophage Colony-Stimulating Factor

The receptors for interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 share a common signaling subunit βc. However, in the mouse, there is an additional IL-3 signaling protein, βIL-3, which is specific for IL-3. We have previously reported that IL-3 abrogates the lymphoid potentials of murine lymphohematopoietic progenitors and the reconstituting ability of hematopoietic stem cells. We used bone marrow cells from βc- and βIL-3–knock-out mice to examine the relative contributions of the receptor proteins to the negative regulation by IL-3. First, we tested the effects of IL-3 on lymphohematopoietic progenitors by using lineage-negative (Lin−) marrow cells of 5-fluorouracil (5-FU)-treated mice in the two-step methylcellulose culture we reported previously. Addition of IL-3 to the combination of steel factor (SF, c-kit ligand) and IL-11 abrogated the B-lymphoid potential of the marrow cells of both types of knock-out mice as well as wild-type mice. Next, we investigated the effects of IL-3 on in vitro expansion of the hematopoietic stem cells. We cultured Lin−Sca-1–positive, c-kit–positive marrow cells from 5-FU–treated mice in suspension in the presence of SF and IL-11 with or without IL-3 for 7 days and tested the reconstituting ability of the cultured cells by transplanting the cells into lethally irradiated Ly-5 congenic mice together with “compromised” marrow cells. Presence of IL-3 in culture abrogated the reconstituting ability of the cells from both types of knock-out mice and the wild-type mice. In contrast, addition of GM-CSF to the suspension culture abrogated neither B-cell potential nor reconstituting abilities of the cultured cells of wild-type mice. These observations may have implications in the choice of cytokines for use in in vitro expansion of human hematopoietic stem cells and progenitors.

© 1998 by The American Society of Hematology.

Negative Regulation by Interleukin-3 (IL-3) of Mouse Early B-Cell Progenitors and Stem Cells in Culture: Transduction of the Negative Signals by βc and βIL-3 Proteins of IL-3 Receptor and Absence of Negative Regulation by Granulocyte-Macrophage Colony-Stimulating Factor

The receptors for interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 share a common signaling subunit βc. However, in the mouse, there is an additional IL-3 signaling protein, βIL-3, which is specific for IL-3. We have previously reported that IL-3 abrogates the lymphoid potentials of murine lymphohematopoietic progenitors and the reconstituting ability of hematopoietic stem cells. We used bone marrow cells from βc- and βIL-3–knock-out mice to examine the relative contributions of the receptor proteins to the negative regulation by IL-3. First, we tested the effects of IL-3 on lymphohematopoietic progenitors by using lineage-negative (Lin−) marrow cells of 5-fluorouracil (5-FU)-treated mice in the two-step methylcellulose culture we reported previously. Addition of IL-3 to the combination of steel factor (SF, c-kit ligand) and IL-11 abrogated the B-lymphoid potential of the marrow cells of both types of knock-out mice as well as wild-type mice. Next, we investigated the effects of IL-3 on in vitro expansion of the hematopoietic stem cells. We cultured Lin−Sca-1–positive, c-kit–positive marrow cells from 5-FU–treated mice in suspension in the presence of SF and IL-11 with or without IL-3 for 7 days and tested the reconstituting ability of the cultured cells by transplanting the cells into lethally irradiated Ly-5 congenic mice together with “compromised” marrow cells. Presence of IL-3 in culture abrogated the reconstituting ability of the cells from both types of knock-out mice and the wild-type mice. In contrast, addition of GM-CSF to the suspension culture abrogated neither B-cell potential nor reconstituting abilities of the cultured cells of wild-type mice. These observations may have implications in the choice of cytokines for use in in vitro expansion of human hematopoietic stem cells and progenitors.

© 1998 by The American Society of Hematology.

Thrombopoietin Promotes the Survival of Murine Hematopoietic Long-Term Reconstituting Cells: Comparison With the Effects of FLT3/FLK-2 Ligand and Interleukin-6

The effects of thrombopoietin (TPO; c-mpl ligand), FLT3/FLK-2 ligand (FL), and interleukin-6 (IL-6) on the survival of murine hematopoietic long-term reconstituting cells (LTRC) were studied by using lineage-negative, Sca-1–positive, c-kit–positive (Lin−Sca-1+c-kit+) marrow cells from 5-fluorouracil–treated mice. We tested the ability of these cytokines to maintain the viability of LTRC by transplanting the cultured cells to lethally irradiated Ly-5 congenic mice together with compromised marrow cells. As a single agent, only TPO could maintain the LTRC. Neither IL-6 nor FL was effective by itself, but they acted synergistically to maintain the LTRC. We examined whether the maintenance of LTRC by these cytokines was due to the survival of stem cells or was the result of active cell divisions and self-renewal. To monitor cell division, we used membrane dye PKH26. Enriched cells were stained with PKH26 on day 0 and incubated in suspension culture with TPO or with IL-6 and FL for 7 days. On day 7, PKH26low and PKH26high cells were prepared by sorting and their in vivo reconstituting abilities were tested by transplantation into lethally irradiated Ly-5 congenic mice together with compromised marrow cells. PKH26high populations cultured with both TPO alone and the combination of IL-6 and FL showed greater reconstitution activity than that of PKH26low populations. These data indicate that TPO alone and the combination of IL-6 and FL can support the survival of stem cells without stimulating their active cell proliferation.

Thrombopoietin Promotes the Survival of Murine Hematopoietic Long-Term Reconstituting Cells: Comparison With the Effects of FLT3/FLK-2 Ligand and Interleukin-6

The effects of thrombopoietin (TPO; c-mpl ligand), FLT3/FLK-2 ligand (FL), and interleukin-6 (IL-6) on the survival of murine hematopoietic long-term reconstituting cells (LTRC) were studied by using lineage-negative, Sca-1–positive, c-kit–positive (Lin−Sca-1+c-kit+) marrow cells from 5-fluorouracil–treated mice. We tested the ability of these cytokines to maintain the viability of LTRC by transplanting the cultured cells to lethally irradiated Ly-5 congenic mice together with compromised marrow cells. As a single agent, only TPO could maintain the LTRC. Neither IL-6 nor FL was effective by itself, but they acted synergistically to maintain the LTRC. We examined whether the maintenance of LTRC by these cytokines was due to the survival of stem cells or was the result of active cell divisions and self-renewal. To monitor cell division, we used membrane dye PKH26. Enriched cells were stained with PKH26 on day 0 and incubated in suspension culture with TPO or with IL-6 and FL for 7 days. On day 7, PKH26low and PKH26high cells were prepared by sorting and their in vivo reconstituting abilities were tested by transplantation into lethally irradiated Ly-5 congenic mice together with compromised marrow cells. PKH26high populations cultured with both TPO alone and the combination of IL-6 and FL showed greater reconstitution activity than that of PKH26low populations. These data indicate that TPO alone and the combination of IL-6 and FL can support the survival of stem cells without stimulating their active cell proliferation.

Timing of recombinant human granulocyte colony-stimulating factor administration on neutropenia induced by cyclophosphamide in normal mice

The effects of altering the timing of recombinant human granulocyte colony-stimulating factor (rhG-CSF) administration on neutropenia induced by cyclophosphamide (CPA) were studied experimentally in a mouse model. Experimental mice were divided into three groups: (a) treatment with rhG-CSF after CPA administration (post-treatment group); (b) treatment with rhG-CSF both before and after CPA administration (pre- and post-treatment group); and (c) treatment with saline after CPA administration (control group). The results were as follows. Mice receiving rhG-CSF on the 2 days preceding CPA treatment, in which progenitor cell counts outside the S-phase when CPA was administered were the lowest of all the groups, showed accelerated neutrophil recovery but decreased neutrophil nadirs compared with the control group despite rhG-CSF treatment. The pre- and post-treatment group, consisting of mice who received rhG-CSF treatment on days -4 and -3 before CPA treatment, and in which progenitor cell counts when CPA was administered were increased to greater levels than in the other groups, showed remarkably accelerated neutrophil recovery and the greatest increase in the neutrophil nadirs of all the groups. These results suggested that the kinetics of progenitor cell populations when chemotherapeutic agents were administered seemed to play an important role in neutropenia after chemotherapy, and that not only peripheral neutrophil cell and total progenitor cell counts but also progenitor cell kinetics should be taken into consideration when administering rhG-CSF treatment against the effects of chemotherapy.