Enhancement of G-CSF-induced stem cell mobilization by antibodies against the beta 2 integrins LFA-1 and Mac-1

Kmt2c restricts G-CSF-driven HSC mobilization and granulocyte production in a methyltransferase-independent manner

Granulocyte colony-stimulating factor (G-CSF) is widely used to enhance myeloid recovery after chemotherapy and to mobilize hematopoietic stem cells (HSCs) for transplantation. Unfortunately, through the course of chemotherapy, cancer patients can acquire leukemogenic mutations that cause therapy-related myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). This raises the question of whether therapeutic G-CSF might potentiate therapy-related MDS/AML by disproportionately stimulating mutant HSCs and other myeloid progenitors. A common mutation in therapy-related MDS/AML involves chromosome 7 deletions that inactivate many tumor suppressor genes, including KMT2C. Here, we show that Kmt2c deletions hypersensitize murine HSCs and myeloid progenitors to G-CSF, as evidenced by increased HSC mobilization and enhanced granulocyte production from granulocyte-monocyte progenitors (GMPs). Furthermore, Kmt2c attenuates the G-CSF response independently from its SET methyltransferase function. Altogether, the data raise concerns that monosomy 7 can hypersensitize progenitors to G-CSF, such that clinical use of G-CSF may amplify the risk of therapy-related MDS/AML.

Comparison of the efficacy of hematopoietic stem cell mobilization regimens: a systematic review and network meta-analysis of preclinical studies

BACKGROUND

Mobilization failure may occur when the conventional hematopoietic stem cells (HSCs) mobilization agent granulocyte colony-stimulating factor (G-CSF) is used alone, new regimens were developed to improve mobilization efficacy. Multiple studies have been performed to investigate the efficacy of these regimens via animal models, but the results are inconsistent. We aim to compare the efficacy of different HSC mobilization regimens and identify new promising regimens with a network meta-analysis of preclinical studies.

METHODS

We searched Medline and Embase databases for the eligible animal studies that compared the efficacy of different HSC mobilization regimens. Primary outcome is the number of total colony-forming cells (CFCs) in per milliliter of peripheral blood (/ml PB), and the secondary outcome is the number of Lin^- Sca1⁺ Kit⁺ (LSK) cells/ml PB. Bayesian network meta-analyses were performed following the guidelines of the National Institute for Health and Care Excellence Decision Support Unit (NICE DSU) with WinBUGS version 1.4.3. G-CSF-based regimens were classified into the SD (standard dose, 200-250 μg/kg/day) group and the LD (low dose, 100-150 μg/kg/day) group based on doses, and were classified into the short-term (2-3 days) group and the long-term (4-5 days) group based on administration duration. Long-term SD G-CSF was chosen as the reference treatment. Results are presented as the mean differences (MD) with the associated 95% credibility interval (95% CrI) for each regimen.

RESULTS

We included 95 eligible studies and reviewed the efficacy of 94 mobilization agents. Then 21 studies using the poor mobilizer mice model (C57BL/6 mice) to investigate the efficacy of different mobilization regimens were included for network meta-analysis. Network meta-analyses indicated that compared with long-term SD G-CSF alone, 14 regimens including long-term SD G-CSF + Me6, long-term SD G-CSF + AMD3100 + EP80031, long-term SD G-CSF + AMD3100 + FG-4497, long-term SD G-CSF + ML141, long-term SD G-CSF + desipramine, AMD3100 + meloxicam, long-term SD G-CSF + reboxetine, AMD3100 + VPC01091, long-term SD G-CSF + FG-4497, Me6, long-term SD G-CSF + EP80031, POL5551, long-term SD G-CSF + AMD3100, AMD1300 + EP80031 and long-term LD G-CSF + meloxicam significantly increased the collections of total CFCs. G-CSF + Me6 ranked first among these regimens in consideration of the number of harvested CFCs/ml PB (MD 2168.0, 95% CrI 2062.0-2272.0). In addition, 7 regimens including long-term SD G-CSF + AMD3100, AMD3100 + EP80031, long-term SD G-CSF + EP80031, short-term SD G-CSF + AMD3100 + IL-33, long-term SD G-CSF + ML141, short-term LD G-CSF + ARL67156, and long-term LD G-CSF + meloxicam significantly increased the collections of LSK cells compared with G-CSF alone. Long-term SD G-CSF + AMD3100 ranked first among these regimens in consideration of the number of harvested LSK cells/ml PB (MD 2577.0, 95% CrI 2422.0-2733.0).

CONCLUSIONS

Considering the number of CFC and LSK cells in PB as outcomes, G-CSF plus AMD3100, Me6, EP80031, ML141, FG-4497, IL-33, ARL67156, meloxicam, desipramine, and reboxetine are all promising mobilizing regimens for future investigation.

Targeting VLA4 integrin and CXCR2 mobilizes serially repopulating hematopoietic stem cells

Mobilized peripheral blood has become the primary source of hematopoietic stem and progenitor cells (HSPCs) for stem cell transplantation, with a five-day course of granulocyte colony stimulating factor (G-CSF) as the most common regimen used for HSPC mobilization. The CXCR4 inhibitor, plerixafor, is a more rapid mobilizer, yet not potent enough when used as a single agent, thus emphasizing the need for faster acting agents with more predictable mobilization responses and fewer side effects. We sought to improve hematopoietic stem cell transplantation by developing a new mobilization strategy in mice through combined targeting of the chemokine receptor CXCR2 and the very late antigen 4 (VLA4) integrin. Rapid and synergistic mobilization of HSPCs along with an enhanced recruitment of true HSCs was achieved when a CXCR2 agonist was co-administered in conjunction with a VLA4 inhibitor. Mechanistic studies revealed involvement of CXCR2 expressed on BM stroma in addition to stimulation of the receptor on granulocytes in the regulation of HSPC localization and egress. Given the rapid kinetics and potency of HSPC mobilization provided by the VLA4 inhibitor and CXCR2 agonist combination in mice compared to currently approved HSPC mobilization methods, it represents an exciting potential strategy for clinical development in the future.

Cytokine-induced hematopoietic stem and progenitor cell mobilization: unraveling interactions between stem cells and their niche

Peripheral blood hematopoietic stem and progenitor cells (HSPCs), mobilized by granulocyte colony‐stimulating factor, are widely used as a source for both autologous and allogeneic stem cell transplantation. The use of mobilized HSPCs has several advantages over traditional bone marrow–derived HSPCs, including a less invasive harvesting process for the donor, higher HSPC yields, and faster hematopoietic reconstitution in the recipient. For years, the mechanisms by which cytokines and other agents mobilize HSPCs from the bone marrow were not fully understood. The field of stem cell mobilization research has advanced significantly over the past decade, with major breakthroughs in the elucidation of the complex mechanisms that underlie stem cell mobilization. In this review, we provide an overview of the events that underlie HSPC mobilization and address the relevant cellular and molecular components of the bone marrow niche. Furthermore, current and future mobilizing agents will be discussed.

Expression of adhesion molecules on CD34+ cells from steady-state bone marrow before and after mobilization and their association with the yield of CD34+ cells

Background

Cell adhesion molecules (CAMs) expressed on hematopoietic progenitor cells (HPCs), endothelial cells, and stromal cells play a pivotal role in the mobilization of CD34+ cells. Herein, we conducted a non-randomized peripheral blood stem cell (PBSC) mobilization study aimed to compare the potential differences in the expressions of several CAMs and chemokines on CD34+ cells obtained from bone marrow aspirate before and after HPC mobilization from patients with hematologic malignancies and healthy donors.

Methods

Three-color cytofluorometric analysis was used to compare the expressions of CAMs and chemokines in the bone marrow before and after mobilization.

Results

For all studied groups, CAM expression among those with good and poor yields of CD34+ cells was significantly correlated with VCAM-1 (P=0.007), CD44 (P=0.027), and VLA-4 (P=0.014) expressions. VCAM-1 (P=0.001), FLT-3 (P=0.001), CD44 (P=0.011), VLA-4 (P=0.001), and LFA-1 (P=0.001) expressions were higher before HPC mobilization than after HPC mobilization. By contrast, the expression of CXCR4 significantly varied before and after mobilization only among those with successful PBSC mobilization (P=0.002).

Conclusion

We attempted to identify particular aspects of CAMs involved in CD34+ cell mobilization, which is a highly complex mechanism that involves adhesion molecules and matrix metalloproteases. The mechanism by which CD34+ cell mobilization is activated through proteolytic enzymes is not fully understood. We believe that CXCR4, VLA-4, CD44, and VCAM-1 are the most important molecules implicated in HPC mobilization, particularly because they show a correlation with the yield of CD34+ cells collected via large volume leukapheresis.

Five Days Granulocyte Colony-Stimulating Factor Treatment Increases Bone Formation and Reduces Gap Size of a Rat Segmental Bone Defect: A Pilot Study

Bone is an organ with high natural regenerative capacity and most fractures heal spontaneously when appropriate fracture fixation is provided. However, additional treatment is required for patients with large segmental defects exceeding the endogenous healing potential and for patients suffering from fracture non-unions. These cases are often associated with insufficient vascularization. Transplantation of CD34+ endothelial progenitor cells (EPCs) has been successfully applied to promote neovascularization of bone defects, however including extensive ex vivo manipulation of cells. Here, we hypothesized, that treatment with granulocyte colony-stimulating factor (G-CSF) may improve bone healing by mobilization of CD34+ progenitor cells into the circulation, which in turn may facilitate vascularization at the defect site. In this pilot study, we aimed to characterize the different cell populations mobilized by G-CSF and investigate the influence of cell mobilization on the healing of a critical size femoral defect in rats. Cell mobilization was investigated by flow cytometry at different time points after five consecutive daily G-CSF injections. In a pilot study, bone healing of a 4.5-mm critical femoral defect in F344 rats was compared between a saline-treated control group and a G-CSF treatment group. In vivo microcomputed tomography and histology were applied to compare bone formation in both treatment groups. Our data revealed that leukocyte counts show a peak increase at the first day after the last G-CSF injection. In addition, we found that CD34+ progenitor cells, including EPCs, were significantly enriched at day 1, and further increased at day 5 and day 11. Upregulation of monocytes, granulocytes and macrophages peaked at day 1. G-CSF treatment significantly increased bone volume and bone density in the defect, which was confirmed by histology. Our data show that different cell populations are mobilized by G-CSF treatment in cell specific patterns. Although in this pilot study no bridging of the critical defect was observed, significantly improved bone formation by G-CSF treatment was clearly shown.

Harnessing bone marrow resident regulatory T cells to improve allogeneic stem cell transplant outcomes

Regulatory T cells (Treg) are a suppressive T cell population which play a crucial role in the establishment of tolerance after stem cell transplantation (SCT) by controlling the effector T cell responses that drive acute and chronic GVHD. The BM compartment is enriched in a highly suppressive, activated/memory autophagy-dependent Treg population, which contributes to the HSC engraftment and the control of GVHD. G-CSF administration releases Treg from the BM through disruption of the CXCR4/SDF-1 axis and further improves Treg survival following SCT through the induction of autophagy. However, AMD3100 is more efficacious in mobilizing these Treg highlighting the potential for optimized mobilization regimes to produce more tolerogenic grafts. Notably, the disruption of adhesive interaction between integrins and their ligands contributes to HSC mobilization and may be relevant for BM Treg. Importantly, the Tregs in the BM niche contribute to maintenance of the HSC niche and appear required for optimal control of GVHD post-transplant. Although poorly studied, the BM Treg appear phenotypically and functionally unique to Treg in the periphery. Understanding the requirements for maintaining the enrichment, function and survival of BM Treg needs to be further investigated to improve therapeutic strategies and promote tolerance after SCT.

Therapeutic targeting and rapid mobilization of endosteal HSC using a small molecule integrin antagonist

The inherent disadvantages of using granulocyte colony-stimulating factor (G-CSF) for hematopoietic stem cell (HSC) mobilization have driven efforts to identify alternate strategies based on single doses of small molecules. Here, we show targeting α₉β₁/α₄β₁ integrins with a single dose of a small molecule antagonist (BOP (N-(benzenesulfonyl)-L-prolyl-L-O-(1-pyrrolidinylcarbonyl)tyrosine)) rapidly mobilizes long-term multi-lineage reconstituting HSC. Synergistic engraftment augmentation is observed when BOP is co-administered with AMD3100. Impressively, HSC in equal volumes of peripheral blood (PB) mobilized with this combination effectively out-competes PB mobilized with G-CSF. The enhanced mobilization observed using BOP and AMD3100 is recapitulated in a humanized NODSCIDIL2Rγ^−/− model, demonstrated by a significant increase in PB CD34⁺ cells. Using a related fluorescent analogue of BOP (R-BC154), we show that this class of antagonists preferentially bind human and mouse HSC and progenitors via endogenously primed/activated α₉β₁/α₄β₁ within the endosteal niche. These results support using dual α₉β₁/α₄β₁ inhibitors as effective, rapid and transient mobilization agents with promising clinical applications.

Mobilizing haematopoietic stem cells to the peripheral blood has largely replaced bone marrow transplants as a strategy in the clinic. Here, Cao et al. report the use of an α₉β₁/α₄β₁ integrin antagonist to induce rapid mobilization of blood stem cells from the bone marrow in a humanized mouse model.

CD11a is essential for normal development of hematopoietic intermediates

The process of lymphopoiesis begins in the bone marrow (BM) and requires multiple cellular intermediates. For T cell production, lymphoid progenitors exit the BM and home to the thymus where maturation and selection ensue. These processes are dependent on a number of factors, including chemokines and adhesion molecules. Although the β2 integrin CD11a plays an important role in the migration of lymphocytes to lymph nodes, the role of CD11a in T cell development is largely undefined. Our studies now show that, in CD11a(-/-) mice, thymic cellularity was decreased and early T cell development was partially impaired. Remarkably, CD11a was critical for generation of common lymphoid progenitors (CLPs) and lymphoid-primed multipotent progenitors. However, in intact CD11a(-/-) mice, peripheral B and T cell subsets were only modestly altered, suggesting that compensatory mechanisms were operating. In contrast, competitive BM-reconstitution assays revealed an essential role for CD11a in the generation of thymocytes and mature T and B cells. This defect was linked to the requirement for CD11a in the development of CLPs. Furthermore, our results identified CLPs, and not lymphoid-primed multipotent progenitors, as the requisite CD11a-dependent precursor for lymphocyte development. Thus, these findings established a key role for CD11a in lymphopoiesis.

[Hematopoietic stem cells mobilization: state of the art in 2011 and perspectives]

High-dose chemotherapy with stem cells support has largely improved in terms of hematopoietic stem and progenitor cells harvest procedures as well as in those, which target or manipulate the cellular composition of autologous graft. Optimal preparative regimens and supportive care had lead to better use of autologous transplantation procedure. For other patients assigned to hematopoietic transplantation, availability of allogeneic donors appears to be an interesting alternative source of hematopoietic stem cells. Since three decades, hematopoietic growth factors development has allowed mobilization optimization and collection of peripheral hematopoietic stem cells leading to reduced days of hospitalization and less blood products requirements, being more cost-effective for patients in autologous transplantation settings and for stem cell collection facilities in allogeneic ones. New perspectives include, besides ex vivo manipulation of graft, development of mobilizing drugs in order to perform transplantation even in poor mobilizers patients. An important goal is achieved with the description of genetic polymorphisms related to optimal mobilization of stem cells. New approach using more promising and selective agents called chemokines, such as plerixafor the main leader among these agents are now available and appear complementary for alternative approach using cytokines alone (G-CSF, GM-CSF, SCF). The aim of this review is to assess the evolution of theses biotechnologies and their role in different steps of autologous transplantation and allogeneic stem cells collection.

Hematopoietic stem and progenitor cell trafficking

Migration of hematopoietic stem cells (HSCs) is essential during embryonic development and throughout adult life. During embryogenesis, trafficking of HSCs is responsible for the sequential colonization of different hematopoietic organs by blood-producing cells. In adulthood, circulation of HSCs maintains homeostasis of the hematopoietic system and participates in innate immune responses. HSC trafficking is also crucial in clinical settings such as bone marrow (BM) and stem cell transplantation. This review provides an overview of the molecular and cellular signals that control and fine-tune trafficking of HSCs and hematopoietic progenitor cells in embryogenesis and during postnatal life. We also discuss the potential clinical utility of therapeutic approaches to modulate HSC trafficking in patients.

Modulation of beta1-integrins on hemopoietic progenitor cells after allergen challenge in asthmatic subjects

BACKGROUND

Mobilization of hemopoietic progenitor cells from the bone marrow (BM) is a feature of inflammatory asthmatic responses. Understanding the mechanisms regulating progenitor cell mobilization and trafficking to the peripheral circulation might be important for the development of effective asthma therapies.

OBJECTIVE

We investigated the role of adhesion molecules in the mobilization of hemopoietic progenitor cells from the BM during an allergen-induced asthmatic response.

METHODS

BM and peripheral blood samples were obtained from dual-responders with mild asthma before and at several time points after allergen challenge. Fluctuations in expression and adhesive properties of beta1- and beta2-integrins on CD34(+)CD45(+) progenitor cells were assessed by using flow cytometry and adhesion to protein-coated wells, respectively.

RESULTS

On BM-derived CD34(+)CD45(+) cells, expression of very late antigen (VLA) 4, but not VLA-5 or Mac-1, decreased significantly 24 hours after allergen challenge and had begun to recover by 48 hours after challenge. In peripheral blood allergen challenge induced a significant decrease in VLA-4 levels after 6 hours, which had not recovered by 96 hours after challenge. Similarly, VLA-5 expression decreased, most prominently at 72 to 96 hours after allergen challenge. In contrast, Mac-1 levels did not change. Chemokine-stimulated adhesion of BM-derived CD34(+)CD45(+) cells to fibronectin was significantly attenuated 24 hours after challenge. Furthermore, adhesion to fibronectin and vascular cell adhesion molecule 1 was greatly reduced by anti-VLA-4 or anti-VLA-5 antibodies.

CONCLUSIONS

Preferential downregulation of beta1-integrin expression on progenitor cells can reduce the tethering forces to BM components, thus facilitating their egress to the peripheral circulation during an allergic inflammatory response.

In vivo Activity of the Cleaved Form of Soluble Urokinase Receptor: A New Hematopoietic Stem/Progenitor Cell Mobilizer

Cleaved forms of soluble urokinase receptor (c-suPAR) have been detected in body fluids from patients affected by various tumors. We recently reported increased c-suPAR levels in sera of healthy donors during granulocyte colony-stimulating factor (G-CSF)-induced mobilization of CD34(+) hematopoietic stem cells (HSC). In vitro, c-suPAR or its derived chemotactic peptide (uPAR(84-95)) stimulated migration of human CD34(+) HSCs and inactivated CXCR4, the chemokine receptor primarily responsible for HSC retention in bone marrow. These results suggested that c-suPAR could potentially contribute to regulate HSC trafficking from and to bone marrow. Therefore, we investigated uPAR(84-95) effects on mobilization of mouse CD34(+) hematopoietic stem/progenitor cells (HSC/HPC). We first showed that uPAR(84-95) stimulated in vitro dose-dependent migration of mouse CD34(+) M1 leukemia cells and inactivated murine CXCR4. uPAR(84-95) capability to induce mouse HSC/HPC release from bone marrow and migration into the circulation was then investigated in vivo. uPAR(84-95) i.p. administration induced rapid leukocytosis, which was associated with an increase in peripheral blood CD34(+) HSCs/HPCs. In vitro colony assays confirmed that uPAR(84-95) mobilized hematopoietic progenitors, showing an absolute increase in circulating colony-forming cells. uPAR(84-95) mobilizing activity was comparable to that of G-CSF; however, neither synergistic nor additive effect was observed in combining the two molecules. These findings show for the first time in vivo biological effects of c-suPAR. Its capability to mobilize HSCs suggests potential clinical applications in HSC transplantation.

Modulation of the SDF-1-CXCR4 axis by the third complement component (C3)--implications for trafficking of CXCR4+ stem cells

Several organs including hematopoietic ones may regenerate by attracting stem cells that are mobilized from their niches in response to stress related to tissue/organ damage and after mobilization circulate in the peripheral blood. The trafficking of these cells is regulated by alpha-chemokine stromal derived factor-1 (SDF-1) that is upregulated in damaged organs and binds to seven-transmembrane-span G-protein-coupled CXCR4 receptor that is expressed on circulating stem cells. In parallel, evidence has accumulated that the complement (C) system, which is part of innate immunity, may also orchestrate regeneration. C becomes activated with the release of the third complement component (C3) cleavage fragments (e.g., C3a, desArgC3a, and iC3b) during tissue/organ injury. Our recent work demonstrated that these fragments modulate responsiveness of CXCR4+ stem cells to an SDF-1 gradient. Thus the high concentration of both SDF-1 and C3 cleavage fragments in damaged organs results in the formation of an optimal gradient for chemoattracting circulating CXCR4+ stem cells. In this review we will focus on interactions between the SDF-1-CXCR4 axis and the C3 cleavage fragments in a model of mobilization, trafficking, and homing of hematopoietic stem/progenitor cells (HSPC).

G-CSF-induced evacuation of sinusoidal NK cells and the facilitation of liver regeneration in a partial hepatectomy☆

Since liver regeneration after partial hepatectomy (PHx) is known to improve by pretreatment with recombinant human G-CSF (rhG-CSF), we investigated the mechanism by evaluating the distribution and activity of sinusoidal NK cells. F344 rats were treated with rhG-CSF (250 microg/kg/day) for 5 days before PHx. Pretreatment with rhG-CSF improved the serum ALT levels and DNA biosynthesis of the remnant liver tissues at 20 h after PHx. Notably, the rhG-CSF pretreatment decreased the number of NK cells in the liver determined by immunohistochemistry using anti-NKR-P1A mAb before and at 20 h after PHx with no significant change in the NK activity per cell base, while also increasing the number of NK cells in the peripheral blood detected by flow cytometry. The rhG-CSF induced a pre-PHx downregulation of the IL-12p70 protein levels, while also promoting the post-PHx reduction of the protein levels of IL-12p70 and IFN-gamma. Conversely, rhG-CSF had no effect on the pre-PHx mRNA levels or the PHx-induced upregulation of mRNA levels of TNF-alpha, IL-1beta, IL-6, TGF-beta, IL-10, HGF, and c-Met determined by real-time RT-PCR. These results strongly suggest that rhG-CSF-induced facilitation of liver regeneration is achieved by immunoregulation through the intrahepatic IL-12 downregulation and evacuation of sinusoidal NK cells.

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.

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.

Beta-glucan enhances complement-mediated hematopoietic recovery after bone marrow injury

Myelotoxic injury in the bone marrow (BM) as a consequence of total body irradiation (TBI) or granulocyte colony-stimulating factor (G-CSF) mobilization results in the deposition of iC3b on BM stroma (stroma-iC3b). In the present study, we have examined how stroma-iC3b interacts with hematopoietic progenitor cells (HPCs) and the role of complement (C) and complement receptor 3 (CR3) in BM injury/repair. We demonstrate here that stroma-iC3b tethers HPCs via the inserted (I) domain of HPC complement receptor 3 (CR3, CD11b/CD18, Mac-1). Following irradiation, stroma-iC3b was observed in the presence of purified IgM and normal mouse serum (NMS), but not serum from Rag-2(-/-) mice, implicating a role for antibody (Ab) and the classic pathway of C activation. Furthermore, a novel role for soluble yeast beta-glucan, a ligand for the CR3 lectin-like domain (LLD), in the priming of CR3(+) HPC is suggested. Soluble yeast beta-glucan could enhance the proliferation of tethered HPCs, promote leukocyte recovery following sublethal irradiation, and increase the survival of lethally irradiated animals following allogeneic HPC transplantation in a CR3-dependent manner. Taken together, these observations suggest a novel role for C, CR3, and beta-glucan in the restoration of hematopoiesis following injury.

More than just proliferation: Myc function in stem cells

Adult stem cells are essential to maintain regenerative tissues such as skin epidermis, gastrointestinal mucosa or the hematopoietic system. Recent studies in mice suggest that the transcription factor and oncoprotein c-Myc has unexpected functions during both self-renewal and the differentiation of stem and early progenitor cells, particularly in interactions between stem cells and the local microenvironment or "niche". By incorporating recent findings on Myc and hematopoietic stem cells we propose a model in which "resting" hematopoietic stem cells are "activated" to self-renew and to differentiate at the interface between the niche and non-niche microenvironments.

Bone marrow stem cell transplantation for cardiac repair

Cardiomyocytes respond to physiological or pathological stress only by hypertrophy and not by an increase in the number of functioning cardiomyocytes. However, recent evidence suggests that adult cardiomyocytes have the ability, albeit limited, to divide to compensate for the cardiomyocyte loss in the event of myocardial injury. Similarly, the presence of stem cells in the myocardium is a good omen. Their activation to participate in the repair process is, however, hindered by some as-yet-undetermined biological impediments. The rationale behind the use of adult stem cell transplantation is to supplement the inadequacies of the intrinsic repair mechanism of the heart and compensate for the cardiomyocyte loss in the event of injury. Various cell types including embryonic, fetal, and adult cardiomyocytes, smooth muscle cells, and stable cell lines have been used to augment the declining cardiomyocyte number and cardiac function. More recently, the focus has been shifted to the use of autologous skeletal myoblasts and bone marrow-derived stem cells. This review is a synopsis of some interesting aspects of the fast-emerging field of bone marrow-derived stem cell therapy for cardiac repair.

Cyclosporine and mycophenolate mofetil prophylaxis with fludarabine and melphalan conditioning for unrelated donor transplantation: a prospective study of 22 patients with hematologic malignancies

In an attempt to decrease toxicity in high-risk patients undergoing unrelated donor hematopoietic stem cell transplantation (URD HSCT), we tested a combination of cyclosporine (CSP) and mycophenolate mofetil (MMF) as graft-versus-host disease (GVHD) prophylaxis with the reduced-intensity conditioning regimen fludarabine/melphalan (Flu/Mel). A total of 22 adult patients with advanced myeloid (n=15) and lymphoid (n=7) malignancies were treated. All patients received Flu 25 mg/m2 for 5 days and Mel 140 mg/m2, with CSP 3 mg/kg daily and MMF 15 mg/kg three times a day. The median age was 49 years (range 18-66). Durable engraftment was seen in all but one patient with myelofibrosis. The 1-year nonrelapse mortality was 32%, 27% from GVHD. The cumulative incidence of acute GVHD grade 2-4 and 3-4 was 63 and 41%, respectively. With a median follow-up of 18 months, the disease-free survival (DFS) and overall survival (OS) are 55 and 59%, respectively. For patients with AML and MDS (n=14), the DFS and OS is 71%. For patients undergoing a second transplant (n=14), the DFS and OS is 57%. In conclusion, this regimen is associated with acceptable toxicity but high rates of GVHD in high-risk patients undergoing URD HSCT. Encouraging disease control for patients with advanced myeloid malignancies was observed.

c-Myc controls the balance between hematopoietic stem cell self-renewal and differentiation

The activity of adult stem cells is essential to replenish mature cells constantly lost due to normal tissue turnover. By a poorly understood mechanism, stem cells are maintained through self-renewal while concomitantly producing differentiated progeny. Here, we provide genetic evidence for an unexpected function of the c-Myc protein in the homeostasis of hematopoietic stem cells (HSCs). Conditional elimination of c-Myc activity in the bone marrow (BM) results in severe cytopenia and accumulation of HSCs in situ. Mutant HSCs self-renew and accumulate due to their failure to initiate normal stem cell differentiation. Impaired differentiation of c-Myc-deficient HSCs is linked to their localization in the differentiation preventative BM niche environment, and correlates with up-regulation of N-cadherin and a number of adhesion receptors, suggesting that release of HSCs from the stem cell niche requires c-Myc activity. Accordingly, enforced c-Myc expression in HSCs represses N-cadherin and integrins leading to loss of self-renewal activity at the expense of differentiation. Endogenous c-Myc is differentially expressed and induced upon differentiation of long-term HSCs. Collectively, our data indicate that c-Myc controls the balance between stem cell self-renewal and differentiation, presumably by regulating the interaction between HSCs and their niche.

Transplantation studies in C3-deficient animals reveal a novel role of the third complement component (C3) in engraftment of bone marrow cells

Mice deficient in complement C3 (C3(-/-)) are hematologically normal under steady-state conditions, and yet displayed a significant delay in hematopoietic recovery from either irradiation or transplantation of wild-type (WT) hematopoietic stem/progenitor cells (HSPC). Transplantation of histocompatible WT Sca-1(+) cells into C3(-/-) mice resulted in a (i) decrease in day 12 CFU-S, (ii) 5-7-day delay in platelet and leukocyte recovery, and (iii) reduced number of BM CFU-GM progenitors at day 16 after transplantation. Nevertheless, HSPC from C3(-/-) mice engrafted normally into irradiated WT mice, suggesting that there was a defect in the hematopoietic environment of C3(-/-) mice. Since C3(-/-) mice cannot activate/cleave C3, the C3 fragments C3a, C3a(des-Arg), and iC3b were examined for a role in HSPC engraftment. Liquid-phase C3a and C3a(des-Arg) increased CXCR4 incorporation into membrane lipid rafts (thus potentiating HSPC responses to SDF-1 gradients), whereas iC3b was deposited onto irradiated BM cells and functioned to tether CR3(CD11b/CD18)(+)HSPC to damaged stroma. The activity of C3a(des-Arg) suggested that C3aR(+)HSPC also expressed the C5L2 (receptor for C3a and C3a(des-Arg)) and this was confirmed. In conclusion, a novel mechanism for HSC engraftment was identified, which involves complement activation and specific C3 fragments that promote conditioning for transplantation and enhance HSPC engraftment.

The integrin alphaMbeta2 anchors hematopoietic progenitors in the bone marrow during enforced mobilization

The sulfated polysaccharide fucoidan can rapidly mobilize hematopoietic progenitor cells (HPCs) and long-term repopulating stem cells from the bone marrow (BM) to the circulation. While searching for mechanisms involved in this phenomenon we found that BM myeloid cells bound to fucoidan through the integrin alphaMbeta2 (macrophage antigen-1 [Mac-1]) and L-selectin resulting in alphaMbeta2-independent release of neutrophil elastase, but inhibition of elastase activity did not impair fucoidan-induced mobilization. Mobilization of HPCs by fucoidan was enhanced in animals deficient in alphaM (alphaM-/-) compared with wild-type (alphaM+/+) animals and higher plasma levels of the chemokine CXCL12/stromal cell-derived factor-1 (SDF-1) were achieved in alphaM-/- mice by fucoidan treatment. However, in chimeric animals harboring alphaM+/+ and alphaM-/- HPCs in the BM, alphaM-/- HPCs were preferentially mobilized by fucoidan, suggesting that the enhanced mobilization is cell intrinsic and does not result from altered microenvironment. Suboptimal doses of granulocyte colony-stimulating factor (G-CSF) or cyclophosphamide (CY) also resulted in enhanced HPC mobilization in alphaM-/- mice compared with alphaM+/+ controls, but this difference was overcome when standard doses of G-CSF or CY were administered. Taken together, these data suggest that the integrin alphaMbeta2 participates in the retention of HPCs in the BM.

Mobilization studies in mice deficient in either C3 or C3a receptor (C3aR) reveal a novel role for complement in retention of hematopoietic stem/progenitor cells in bone marrow

The mechanisms regulating the homing/mobilization of hematopoietic stem/progenitor cells (HSPCs) are not fully understood. In our previous studies we showed that the complement C3 activation peptide, C3a, sensitizes responses of HSPCs to stromal-derived factor 1 (SDF-1). In this study, mobilization was induced with granulocyte colony-stimulating factor (G-CSF) in both C3-deficient (C3–/–) and C3a receptor–deficient (C3aR–/–) mice as well as in wild-type (wt) mice in the presence or absence of a C3aR antagonist, SB 290157. The data indicated (1) significantly increased G-CSF–induced mobilization in C3–/– and C3aR–/– mice compared with wt mice, (2) significantly accelerated and enhanced G-CSF–induced mobilization in wt, but not in C3–/– or C3aR–/–, mice treated with SB 290157, and (3) deposition of C3b/iC3b fragments onto the viable bone marrow (BM) cells of G-CSF–treated animals. Furthermore, mobilization studies performed in chimeric mice revealed that wt mice reconstituted with C3aR–/– BM cells, but not C3aR–/– mice reconstituted with wt BM cells, are more sensitive to G-CSF–induced mobilization, suggesting that C3aR deficiency on graft-derived cells is responsible for this increased mobilization. Hence we suggest that C3 is activated in mobilized BM into C3a and C3b, and that the C3a-C3aR axis plays an important and novel role in retention of HSPCs (by counteracting mobilization) by increasing their responsiveness to SDF-1, the concentration of which is reduced in BM during mobilization. The C3a-C3aR axis may prevent an uncontrolled release of HSPCs into peripheral blood. These data further suggest that the C3aR antagonist SB 290157 could be developed as a drug to mobilize HSPCs for transplantation.

Reduced stem cell mobilization in mice receiving antibiotic modulation of the intestinal flora: involvement of endotoxins as cofactors in mobilization

Since endotoxins are potent inducers of stem cell mobilization, we hypothesized that their presence in the gut may play a role in cytokine-induced mobilization. To address this possibility we added ciprofloxacin and polymyxin B to the drinking water of Balb/c mice mobilized with either interleukin-8 (IL-8), granulocyte colony-stimulating factor (G-CSF), or flt3 ligand (FL). The yield of colony-forming units (CFUs) was significantly reduced in all mice treated with these antibiotics when compared with controls (IL-8: 192 +/- 61 vs 290 +/- 64, P <.05; G-CSF: 1925 +/- 1216 vs 3371 +/- 1214, P <.05; FL: 562 +/- 213 vs 1068 +/- 528, P <.05). Treatment with ciprofloxacin eliminated only aerobic Gram-negative bacteria from the feces without effect on mobilization. Polymyxin B treatment did not result in decontamination but significantly reduced the number of mobilized hematopoietic progenitor cells (HPCs) most likely due to the endotoxin binding capacity of polymyxin B. More than 90% of the gastrointestinal flora consists of anaerobic bacteria. Elimination of the anaerobic flora by metronidazol led to a significantly reduced number of mobilized HPCs when compared with controls (IL-8: 55 +/- 66 vs 538 +/- 216, P <.05). Germ-free OF1 mice showed a significantly reduced mobilization compared with their wild-type controls (IL-8 controls: 378 +/- 182, IL-8 germ free: 157 +/- 53, P <.05). Finally, we performed reconstitution experiments adding Escherichia coli-derived endotoxins to the drinking water of decontaminated mice. This resulted in partial restoration of the IL-8-induced mobilization (67 +/- 28 vs 190 +/- 98.1, P <.01). Our results indicate that endotoxins serve as cofactors in cytokine-induced mobilization. Modification of the endotoxin content by antibiotic treatment may affect the yield of cytokine-induced mobilization.

Erythropoiesis and serum sVCAM-1 levels in adults with sickle cell disease

Sickle cell patients are characterized by stress erythropoiesis involving cytokines, growth factors, and adhesion molecules. We set out to determine whether serum soluble vascular cell adhesion molecule-1 (sVCAM-1) levels, which are inversely related to red blood cell counts in sickle cell disease (SCD), reflect erythropoietic activity in adult HbSS patients. Serum levels of sVCAM-1 were compared to erythropoietin (EPO), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and soluble transferrin receptor (sTfR) levels in 29 adults with HbSS, and their respective levels were also compared to 29 race- and age-matched HbAA controls. EPO and sTfR levels were increased as compared to healthy controls, whereas IL-3 and GM-CSF were not. No significant correlation of sVCAM-1 levels could be detected with any of the measured erythropoietic markers. Patients, but not controls, with detectable IL-3 levels had lower sTfR and GM-CSF levels as compared to patients with undetectable IL-3 levels. Even though a link of sVCAM-1 to erythropoiesis could not be established, it cannot be ruled out that sVCAM-1 levels reflect the release of young red blood cells into the circulation. IL-3 and GM-CSF levels suggest that different rates of erythropoiesis may be characterized by specific cytokine profiles in SCD. Further research should focus on the potential cytokines and adhesion molecules involved in sickle cell erythropoiesis, as this may increase our understanding of sickle cell complications and may provide us with potential markers for risk assessment in sickle cell disease as well.

Stem cell mobilization

Successful blood and marrow transplant (BMT), both autologous and allogeneic, requires the infusion of a sufficient number of hematopoietic progenitor/stem cells (HPCs) capable of homing to the marrow cavity and regenerating a full array of hematopoietic cell lineages in a timely fashion. At present, the most commonly used surrogate marker for HPCs is the cell surface marker CD34, identified in the clinical laboratory by flow cytometry. Clinical studies have shown that infusion of at least 2 x 10(6) CD34(+) cells/kg recipient body weight results in reliable engraftment as measured by recovery of adequate neutrophil and platelet counts approximately 14 days after transplant. Recruitment of HPCs from the marrow into the blood is termed mobilization, or, more commonly, stem cell mobilization. In Section I, Dr. Tsvee Lapidot and colleagues review the wide range of factors influencing stem cell mobilization. Our current understanding focuses on chemokines, proteolytic enzymes, adhesion molecules, cytokines and stromal cell-stem cell interactions. On the basis of this understanding, new approaches to mobilization have been designed and are now starting to undergo clinical testing. In Section II, Dr. Michele Cottler-Fox describes factors predicting the ability to mobilize the older patient with myeloma. In addition, clinical approaches to improving collection by individualizing the timing of apheresis and adjusting the volume of blood processed to achieve a desired product are discussed. Key to this process is the daily enumeration of blood CD34(+) cells. Newer methods of enumerating and mobilizing autologous blood HPCs are discussed. In Section III, Dr. John DiPersio and colleagues provide data on clinical results of mobilizing allogeneic donors with G-CSF, GM-CSF and the combination of both as relates to the number and type of cells collected by apheresis. Newer methods of stem cell mobilization as well as the relationship of graft composition on immune reconstitution and GVHD are discussed.