The role of cytokines and adhesion molecules for mobilization of peripheral blood stem cells

Engineered Zinc Finger Protein Targeting 2LTR Inhibits HIV Integration in Hematopoietic Stem and Progenitor Cell-Derived Macrophages: In Vitro Study

Human hematopoietic stem/progenitor cell (HSPC)-based gene therapy is a promising direction for curing HIV-1-infected individuals. The zinc finger protein (2LTRZFP) designed to target the 2-LTR-circle junction of HIV-1 cDNA was previously reported as an intracellular antiviral molecular scaffold that prevents HIV integration. Here, we elucidate the efficacy and safety of using 2LTRZFP in human CD34⁺ HSPCs. We transduced 2LTRZFP which has the mCherry tag (2LTRZFPmCherry) into human CD34⁺ HSPCs using a lentiviral vector. The 2LTRZFPmCherry-transduced HSPCs were subsequently differentiated into macrophages. The expression levels of pro-apoptotic proteins of the 2LTRZFPmCherry-transduced HSPCs showed no significant difference from those of the non-transduced control. Furthermore, the 2LTRZFPmCherry-transduced HSPCs were successfully differentiated into mature macrophages, which had normal phagocytic function. The cytokine secretion assay demonstrated that 2LTRZFPmCherry-transduced CD34⁺ derived macrophages promoted the polarization towards classically activated (M1) subtypes. More importantly, the 2LTRZFPmCherry transduced cells significantly exhibited resistance to HIV-1 integration in vitro. Our findings demonstrate that the 2LTRZFPmCherry-transduced macrophages were found to be functionally and phenotypically normal, with no adverse effects of the anti-HIV-1 scaffold. Our data suggest that the anti-HIV-1 integrase scaffold is a promising antiviral molecule that could be applied to human CD34⁺ HSPC-based gene therapy for AIDS patients.

The healthy donor profile of immunoregulatory soluble mediators is altered by stem cell mobilization and apheresis

BACKGROUND

Peripheral blood stem cells from healthy donors mobilized by granulocyte colony-stimulating factor (G-CSF) and thereafter harvested by leukapheresis are commonly used for allogeneic stem cell transplantation.

METHODS

Plasma levels of 38 soluble mediators (cytokines, soluble adhesion molecules, proteases, protease inhibitors) were analyzed in samples derived from healthy stem cell donors before G-CSF treatment and after 4 days, both immediately before and after leukapheresis.

RESULTS

Donors could be classified into two main subsets based on their plasma mediator profile before G-CSF treatment. Seventeen of 36 detectable mediators were significantly altered by G-CSF; generally an increase in mediator levels was seen, including pro-inflammatory cytokines, soluble adhesion molecules and proteases. Several leukocyte- and platelet-released mediators were increased during apheresis. Both plasma and graft mediator profiles were thus altered and showed correlations to graft concentrations of leukocytes and platelets; these concentrations were influenced by the apheresis device used. Finally, the mediator profile of the allotransplant recipients was altered by graft infusion, and based on their day +1 post-transplantation plasma profile our recipients could be divided into two major subsets that differed in overall survival.

DISCUSSION

G-CSF alters the short-term plasma mediator profile of healthy stem cell donors. These effects together with the leukocyte and platelet levels in the graft determine the mediator profile of the stem cell grafts. Graft infusion also alters the systemic mediator profile of the recipients, but further studies are required to clarify whether such graft-induced alterations have a prognostic impact.

VEGF gene therapy cooperatively recruits molecules from the immune system and stimulates cell homing and angiogenesis in refractory angina

BACKGROUND

New vessels are formed in response to stimuli from angiogenic factors, a process in which paracrine signaling is fundamental.

OBJECTIVE

To investigate the cooperative paracrine signaling profile in response to Vascular Endothelial Growth Factor (VEGF) gene therapy in patients with coronary artery disease (CAD) and refractory angina.

METHOD

A cohort study was conducted in which plasma was collected from patients who underwent gene therapy with a plasmid expressing VEGF 165 (10) and from surgical procedure controls (4). Blood samples were collected from both groups prior to baseline and on days 3, 9 and 27 after the interventions and subjected to systemic analysis of protein expression (Interleukin-6, IL-6; Tumor Necrosis Factor-α, TNF-α; Interleukin-10, IL-10; Stromal Derived Factor-1 α, SDF-1α; VEGF; Angiopoietin-1, ANGPT-1; and Endothelin-1, ET-1) using the enzyme-linked immunosorbent assay (ELISA).

RESULTS

Analysis showed an increase in proinflammatory IL-6 (p=0.02) and ET-1 (p=0.05) on day 3 after gene therapy and in VEGF (p=0.02) on day 9. A strong positive correlation was found between mobilization of endothelial progenitor cells and TNF-α on day 9 (r=0.71; p=0.03). Furthermore, a strong correlation between β-blockers, antiplatelets, and vasodilators with SDF-1α baseline in the group undergoing gene therapy was verified (r=0.74; p=0.004).

CONCLUSION

Analysis of cooperative paracrine signaling after VEGF gene therapy suggests that the immune system cell and angiogenic molecule expression as well as the endothelial progenitor cell mobilization are time-dependent, influenced by chronic inflammatory process and continuous pharmacological treatment.

Homing in hematopoietic stem cells: focus on regulatory role of CXCR7 on SDF1a/CXCR4 axis

Hematopoietic stem cells (HSCs) form a rare population of multipotent stem cells, which give rise to all hematopoietic lineages. HSCs home to bone marrow niches and circulate between blood and bone marrow. Many factors, especially SDF1a, affect the circulation of HSCs, but these have not been fully recognized. SDF1a has been shown to bind CXCR7 in addition to CXCR4 and can also function as SDF1a/CXCR4 modulator. CXCR7 plays a role in HSCs homing via SDF1a gradient and is a mediator of CXCR4/SDF1a axis. This review describes the current concepts and questions concerning CXCR7/CXCR4/SDF1a axis as an important key in hematopoietic stem cells homing with particular emphasis on CXCR7 receptor. Homing of HSCs is an essential step for successful hematopoietic stem cell transplantation.

Cell Therapy in Ischemic Heart Disease: Interventions That Modulate Cardiac Regeneration

The incidence of severe ischemic heart disease caused by coronary obstruction has progressively increased. Alternative forms of treatment have been studied in an attempt to regenerate myocardial tissue, induce angiogenesis, and improve clinical conditions. In this context, cell therapy has emerged as a promising alternative using cells with regenerative potential, focusing on the release of paracrine and autocrine factors that contribute to cell survival, angiogenesis, and tissue remodeling. Evidence of the safety, feasibility, and potential effectiveness of cell therapy has emerged from several clinical trials using different lineages of adult stem cells. The clinical benefit, however, is not yet well established. In this review, we discuss the therapeutic potential of cell therapy in terms of regenerative and angiogenic capacity after myocardial ischemia. In addition, we addressed nonpharmacological interventions that may influence this therapeutic practice, such as diet and physical training. This review brings together current data on pharmacological and nonpharmacological approaches to improve cell homing and cardiac repair.

Space constraints govern fate of hematopoietic stem and progenitor cells in vitro

Deciphering exogenous cues that determine stem cell fate decisions is a persisting challenge of cell biology and bioengineering. In an effort to unravel the role of spatial constraints in the cell-instructive characteristics of bone marrow microenvironments, murine hematopoietic stem and progenitor cells (HSPC) were exposed to fibronectin-coated microcavities in vitro. Microcavity sizes were chosen to allow for the inclusion of either individual or multiple cells. Repopulation experiments using lethally irradiated mice showed that the maintenance of functional HSPC in culture critically depends on cavity dimensions. Short-term repopulating hematopoietic stem cells (ST-HSC) were found to be best supported within single-cell sized compartments while long-term repopulating HSC (LT-HSC) were maintained within both cavity sizes. In sum, the reported data reveal spatial restriction to be a simple but powerful means for directing HSPC fate ex vivo.

Release of matrix metalloproteinase-8 during physiological trafficking and induced mobilization of human hematopoietic stem cells

Previous studies indicate that the release of proteases, including the gelatinase matrix metalloproteinase (MMP)-9, from mature granulocytes plays a crucial role in cytokine-induced hematopoietic stem and progenitor cell (HSPC) mobilization. However, studies with MMP-9-deficient mice revealed that HSPC mobilization was normal in these animals, suggesting that additional proteases must be active at clinically relevant cytokine concentrations. In the present study, we provide evidence that the collagenase MMP-8 is involved in stem cell mobilization. A rapid release of MMP-8 from isolated neutrophil granulocytes can be observed during an in vitro culture. During granulocyte colony-stimulating factor-induced HSPC mobilization, highly elevated serum concentrations of MMP-8 were observed on days 4 to 6 of the mobilization regimen, concomitantly with elevated MMP-9 serum levels and higher numbers of circulating CD34(+) cells. Elevated serum concentrations of both proteases were also found in umbilical cord blood serum. In functional assays, adhesion of HSPC to osteoblasts as an essential component of the endosteal stem cell niche is negatively influenced by MMP-8. The chemokine CXCL12, which is critically involved in stem cell trafficking, can be proteolytically processed by MMP-8 treatment. This degradation has a strong inhibitory influence on HSPC migration. Taken together, our data strongly suggest that MMP-8 can be directly involved in hematopoietic stem cell mobilization and trafficking.

Enabling stem cell therapies for tissue repair: current and future challenges

Stem cells embody the tremendous potential of the human body to develop, grow, and repair throughout life. Understanding the biologic mechanisms that underlie stem cell-mediated tissue regeneration is key to harnessing this potential. Recent advances in molecular biology, genetic engineering, and material science have broadened our understanding of stem cells and helped bring them closer to widespread clinical application. Specifically, innovative approaches to optimize how stem cells are identified, isolated, grown, and utilized will help translate these advances into effective clinical therapies. Although there is growing interest in stem cells worldwide, this enthusiasm must be tempered by the fact that these treatments remain for the most part clinically unproven. Future challenges include refining the therapeutic manipulation of stem cells, validating these technologies in randomized clinical trials, and regulating the global expansion of regenerative stem cell therapies.

Differences in surface marker expression and chondrogenic potential among various tissue-derived mesenchymal cells from elderly patients with osteoarthritis

Mesenchymal stem cells (MSCs) are self-renewing, multipotent cells that could potentially be used to repair injured cartilage in diseases such as osteoarthritis (OA). In this study we used bone marrow, adipose tissue from articular and subcutaneous locations, and synovial fluid samples from 18 patients with knee OA to find a suitable alternative source for the isolation of MSCs with high chondrogenic potential. MSCs from all tissues analysed had a fibroblastic morphology, but their rates of proliferation varied. Subcutaneous fat-derived MSCs proliferated faster than bone marrow- and Hoffa's fat pad-derived MSCs, while synovial fluid-derived MSCs grew more slowly. CD36 and CD54 expression was similar across all groups of MSCs with several minor differences. High expression of these surface markers in subcutaneous fat-derived MSCs was correlated with poor differentiation into hyaline cartilage. Synovial fluid-derived MSCs presented a relatively small chondrogenic differentiation capacity while Hoffa's fat pad-derived MSCs had strong chondrogenic potential. In conclusion, MSCs from elderly patients with OA may still display significant chondrogenic potential, depending on their origin.

Hematopoietic cytokines for cardiac repair: mobilization of bone marrow cells and beyond

Hematopoietic cytokines, traditionally known to influence cellular proliferation, differentiation, maturation, and lineage commitment in the bone marrow, include granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor, stem cell factor, Flt-3 ligand, and erythropoietin among others. Emerging evidence suggests that these cytokines also exert multifarious biological effects on diverse nonhematopoietic organs and tissues. Although the precise mechanisms remain unclear, numerous studies in animal models of myocardial infarction (MI) and heart failure indicate that hematopoietic cytokines confer potent cardiovascular benefits, possibly through mobilization and subsequent homing of bone marrow-derived cells into the infarcted heart with consequent induction of myocardial repair involving multifarious mechanisms. In addition, these cytokines are also known to exert direct cytoprotective effects. However, results from small-scale clinical trials of G-CSF therapy as a single agent after acute MI have been discordant and largely disappointing. It is likely that cardiac repair following cytokine therapy depends on a number of known and unknown variables, and further experimental and clinical studies are certainly warranted to accurately determine the true therapeutic potential of such therapy. In this review, we discuss the biological features of several key hematopoietic cytokines and present the basic and clinical evidence pertaining to cardiac repair with hematopoietic cytokine therapy.

Efficient removal of platelets from peripheral blood progenitor cell products using a novel micro-chip based acoustophoretic platform

Background

Excessive collection of platelets is an unwanted side effect in current centrifugation-based peripheral blood progenitor cell (PBPC) apheresis. We investigated a novel microchip-based acoustophoresis technique, utilizing ultrasonic standing wave forces for the removal of platelets from PBPC products. By applying an acoustic standing wave field onto a continuously flowing cell suspension in a micro channel, cells can be separated from the surrounding media depending on their physical properties.

Study Design and Methods

PBPC samples were obtained from patients (n = 15) and healthy donors (n = 6) and sorted on an acoustophoresis-chip. The acoustic force was set to separate leukocytes from platelets into a target fraction and a waste fraction, respectively. The PBPC samples, the target and the waste fractions were analysed for cell recovery, purity and functionality.

Results

The median separation efficiency of leukocytes to the target fraction was 98% whereas platelets were effectively depleted by 89%. PBPC samples and corresponding target fractions were similar in the percentage of CD34+ hematopoetic progenitor/stem cells as well as leukocyte/lymphocyte subset distributions. Median viability was 98%, 98% and 97% in the PBPC samples, the target and the waste fractions, respectively. Results from hematopoietic progenitor cell assays indicated a preserved colony-forming ability post-sorting. Evaluation of platelet activation by P-selectin (CD62P) expression revealed a significant increase of CD62P+ platelets in the target (19%) and waste fractions (20%), respectively, compared to the PBPC input samples (9%). However, activation was lower when compared to stored blood bank platelet concentrates (48%).

Conclusion

Acoustophoresis can be utilized to efficiently deplete PBPC samples of platelets, whilst preserving the target stem/progenitor cell and leukocyte cell populations, cell viability and progenitor cell colony-forming ability. Acoustophoresis is, thus, an interesting technology to improve current cell processing methods.

Identification and functional characterization of ion channels in CD34(+) hematopoietic stem cells from human peripheral blood

Hematopoietic stem cells (HSCs) are used therapeutically for hematological diseases and may also serve as a source for nonhematopoietic tissue engineering in the future. In other cell types, ion channels have been investigated as potential targets for the regulation of proliferation and differentiation. However, the ion channels of HSCs remain elusive. Here, we functionally characterized the ion channels of CD34(+) cells from human peripheral blood. Using fluorescence-activated cell sorting, we confirmed that the CD34(+) cells also express CD45 and CD133. In the CD34(+)/CD45(+)/CD133(high) HSCs, RT-PCR of 58 ion channel mRNAs revealed the coexpression of Kv1.3, Kv7.1, Nav1.7, TASK2, TALK2, TWIK2, TRPC4, TRPC6, TRPM2, TRPM7, and TRPV2. Whole-cell patch clamp recordings identified voltage-gated K(+) currents (putatively Kv1.3), pH-sensitive TASK2-like back-ground K(+) currents, ADP-ribose-activated TRPM2 currents, temperature-sensitive TRPV2-like currents, and diacylglycerol-analogue-activated TRPC6-like currents. Our results lend new insight into the physiological role of ion channels in HSCs, the specific implications of which require further investigation.

Clozapine mobilizes CD34+ hematopoietic stem and progenitor cells and increases plasma concentration of interleukin 6 in patients with schizophrenia

The blood of 8 European patients with schizophrenia without manifest comorbidity was studied whether the classical atypical antipsychotic drug clozapine altered the amount of circulating CD34(+) hematopoietic cells. As assessed by flow cytometry, the number of CD34(+) cells increased by 433% (from 1.49 ± 1.07 × 10(6)/L, mean ± SD pretreatment, to a peak of 6.45 ± 3.47 × 10(6)/L) following first-time therapy with clozapine for 12 weeks. The increase of CD34(+) cell, neutrophil, and leukocyte counts was statistically significant (P = 0.012). A transversal investigation of 23 long-term patients and 58 controls showed elevated neutrophil counts in the clozapine-monotreated group, whereas CD34(+) cell numbers were unaltered. A transversal investigation of 12 clozapine-monotreated long-term patients and 10 controls revealed a 1.3-fold elevation of plasma interleukin 6 levels in patients on clozapine (P = 0.017). In conclusion, clozapine treatment results in an initial mobilization of CD34(+) stem and progenitor cells into the peripheral blood and in a slight long-term elevation of interleukin 6.

Adipose tissue: a new source for cardiovascular repair

Along with angiogenesis and gene therapy, stem cell transplantation is one of the newest treatment modalities proposed to improve the outcome of patients with heart failure or infarction. In this context, much interest has stemmed from experimental studies showing that cardiac transfer of unfractionated or partially purified bone marrow cells, or stem cells and progenitor cells derived from the bone marrow or peripheral blood, can enhance functional recovery after an acute myocardial infarction. On the basis of these data, stem cells and progenitor cells derived from the bone marrow have been proposed for use in the repair of cardiac tissue after acute myocardial infarction in patients. However, the relatively low abundance, small tissue volume, difficult accessibility and disease-related malfunction of bone marrow-derived stem cells make their clinical usefulness difficult in some situations. Recently it has been shown that adipose tissue contains a population of adult multipotent mesenchymal stem cells and endothelial progenitor cells that, in cell culture conditions, have extensive proliferative capacity and are able to differentiate into several lineages, including endothelial cells, smooth muscle cells and cardiomyocytes. The similarities between stem cells extracted from the bone marrow and the adipose tissue suggest the potential for the adipose tissue to act as an alternative, and perhaps preferable, cell source for repairing damaged tissues, such as the ischemic or infarcted heart. In this review we discuss molecular and functional characterization, preclinical results and currently ongoing clinical trials using adipose-derived stem cells in cardiovascular repair.

Redox regulation of stem cell mobilizationThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

A growing body of evidence supports the role of redox signaling in the mechanisms of hematopoietic stem cell mobilization and homing. Cytokines and adhesion molecules control stem cell mobilization through a redox-regulated process. The FoxO–SirT network appears to be intimately involved in redox-regulated stem cell homeostasis, whereas the process of stem cell differentiation is regulated by redox effector factor-1 (Ref-1) protein. Lack of oxygen (hypoxia), specifically controlled hypoxia, can stimulate the growth of the stem cells in their niche, and hypoxia-inducible factor (HIF)-1α appears to play a significant role in their maintenance and homing mechanism.

The beneficial effects of postinfarct cytokine combination therapy are sustained during long-term follow-up

We have previously reported that administration of granulocyte colony-stimulating factor (G-CSF)+Flt-3 ligand (FL) or G-CSF+stem cell factor (SCF) improves left ventricular (LV) function and halts LV remodeling at 35 d after myocardial infarction (MI). In the current study, we investigated whether these beneficial effects are sustained in the long term - an issue of fundamental importance for clinical translation. Mice undergoing a 30-min coronary occlusion followed by reperfusion received vehicle (group I), G-CSF+FL (group II), G-CSF+SCF (group III), or G-CSF alone (group IV) starting 4 h after reperfusion and were euthanized 48 wk later. LV structure and function were assessed by serial echocardiography before and at 48 h and 4, 8, 16, 32, and 48 wk after MI. During follow-up, mice in group I exhibited worsening of LV function and progressive LV remodeling. Compared with group I, both groups II and III exhibited improved LV EF at 4 wk after MI; however, only in group II was this improvement sustained at 48 wk. Group II was also the only group in which the decrease in infarct wall thickening fraction, the LV dilatation, and the increase in LV mass were attenuated vs. group I. We conclude that the beneficial effect of G-CSF+FL on postinfarction LV dysfunction and remodeling is sustained for at least 11 months, and thus is likely to be permanent. In contrast, the effect of G-CSF+SCF was not sustained beyond the first few weeks, and G-CSF alone is ineffective. To our knowledge, this is the first long-term study of cytokines in postinfarction LV remodeling. The results reveal heretofore unknown differential actions of cytokines and have important translational implications.

The monoclonal anti-VLA-4 antibody natalizumab mobilizes CD34+ hematopoietic progenitor cells in humans

We investigated the role of adhesion molecule VLA-4 in CD34+ blood stem-cell mobilization. Therefore, we examined 20 patients with multiple sclerosis (MS) who were treated with the anti-VLA-4 antibody natalizumab. Treated patients had received a median number of 4 natalizumab infusions (range: 2-9 infusions). Blood samples were taken 4 weeks following the last infusion. With a median proportion of 7.6 CD34+ cells/microL (range: 2.2-30.4 cells/microL), these patients had a significantly higher (P=.003) amount of circulating CD34+ cells compared with 5 healthy volunteers (median: 1.4/microL; range: 0.6-2.4/microL) and 5 untreated MS patients (median: 1.0/microL; range: 0.5-1.7/microL) (P=.001). Serial measurements in 4 patients receiving their first natalizumab infusion showed a maximal significant increase in circulating CD34+ cells from 3.3/microL (range: 1.6-4.8/microL) to 10.4/microL (range: 7.5-12.04/microL) 72 hours following natalizumab infusion (P=.001), including pluripotent cells in colony-forming assays. This mobilizing ability of natalizumab might be useful for patients with poor response to granulocyte colony-stimulating factor (G-CSF)-based protocols.

Rho GTPases and regulation of hematopoietic stem cell localization

Bone marrow engraftment in the context of hematopoietic stem cell and progenitor (HSC/P) transplantation is based on the ability of intravenously administered cells to lodge in the medullary cavity and be retained in the appropriate marrow space, a process referred to as homing. It is likely that homing is a multistep process, encompassing a sequence of highly regulated events that mimic the migration of leukocytes to inflammatory sites. In leukocyte biology, this process includes an initial phase of tethering and rolling of cells to the endothelium via E- and P-selectins, firm adhesion to the vessel wall via integrins that appear to be activated in an "inside-out" fashion, transendothelial migration, and chemotaxis through the extracellular matrix (ECM) to the inflammatory nidus. For HSC/P, the cells appear to migrate to the endosteal space of the bone marrow. A second phase of engraftment involves the subsequent interaction of specific HSC/P surface receptors, such as alpha(4)beta(1) integrin receptors with vascular cell-cell adhesion molecule-1 and fibronectin in the ECM, and interactions with growth factors that are soluble, membrane, or matrix bound. We have utilized knockout and conditional knockout mouse lines generated by gene targeting to study the role of Rac1 and Rac2 in blood cell development and function. We have determined that Rac is activated via stimulation of CXCR4 by SDF-1, by adhesion via beta(1) integrins, and via stimulation of c-kit by the stem cell factor-all of which involved in stem cell engraftment. Thus Rac proteins are key molecular switches of HSC/P engraftment and marrow retention. We have defined Rac proteins as key regulators of HSC/P cell function and delineated key unique and overlapping functions of these two highly related GTPases in a variety of primary hematopoietic cell lineages in vitro and in vivo. Further, we have begun to define the mechanisms by which each GTPase leads to specific functions in these cells. These studies have led to important new understanding of stem cell bone marrow retention and trafficking in the peripheral circulation and to the development of a novel small molecule inhibitor that can modulate stem cell functions, including adhesion, mobilization, and proliferation. This chapter describes the biochemical footprint of stem cell engraftment and marrow retention related to Rho GTPases. In addition, it reviews abnormalities of Rho GTPases implicated in human immunohematopoietic diseases and in leukemia/lymphoma.

Future investigations in stem cell activation with granulocyte-colony-stimulating factor after myocardial infarction

Experimental data indicate that stem cell mobilization with granulocyte colony-stimulating factor (G-CSF) might have potential as a novel therapeutic strategy for acute myocardial infarction. The prospective beneficial effects of G-CSF can be attributed mainly to a direct action on injured myocardium rather than on differentiation of mobilized bone marrow stem cells into cardiac myocytes. This article reviews the evidence for the potential cardioprotective effects of G-CSF and discusses future investigations regarding pharmacologic stem cell activation and mobilization with G-CSF in the setting of acute myocardial infarction.

Bone-marrow-derived mesenchymal stem cells as a target for cytomegalovirus infection: implications for hematopoiesis, self-renewal and differentiation potential

Mesenchymal stem cells (MSCs) in bone marrow (BM) regulate the differentiation and proliferation of adjacent hematopoietic precursor cells and contribute to the regeneration of mesenchymal tissues, including bone, cartilage, fat and connective tissue. BM is an important site for the pathogenesis of human cytomegalovirus (HCMV) where the virus establishes latency in hematopoietic progenitors and can transmit after reactivation to neighboring cells. Here we demonstrate that BM-MSCs are permissive to productive HCMV infection, and that HCMV alters the function of MSCs: (i) by changing the repertoire of cell surface molecules in BM-MSCs, HCMV modifies the pattern of interaction between BM-MSCs and hematopoietic cells; (ii) HCMV infection of BM-MSCs undergoing adipogenic or osteogenic differentiation impaired the process of differentiation. Our results suggest that by altering BM-MSC biology, HCMV may contribute to the development of various diseases.

The metastasis-associated 67-kDa laminin receptor is involved in G-CSF–induced hematopoietic stem cell mobilization

The 67-kDa laminin receptor (67LR) is a nonintegrin cell-surface receptor with high affinity for laminin, which plays a key role in tumor invasion and metastasis. We investigated the role of 67LR in granulocyte colony-stimulating factor (G-CSF)–induced mobilization of CD34+ hematopoietic stem cells (HSCs) from 35 healthy donors. G-CSF–mobilized HSCs, including CD34+/CD38– cells, showed increased 67LR expression as compared with unstimulated marrow HSCs; noteworthy, also, is the fact that the level of 67LR expression in G-CSF–mobilized HSCs correlated significantly with mobilization efficiency. During G-CSF–induced HSC mobilization, the expression of laminin receptors switched from α6 integrins, which mediated laminin-dependent adhesion of steady-state human marrow HSCs, to 67LR, responsible for G-CSF–mobilized HSC adhesion and migration toward laminin. In vitro G-CSF treatment, alone or combined with exposure to marrow-derived endothelial cells, induced 67LR up-regulation in marrow HSCs; moreover, anti-67LR antibodies significantly inhibited transendothelial migration of G-CSF–stimulated marrow HSCs. Finally, G-CSF–induced mobilization in mice was associated with 67LR up-regulation both in circulating and marrow CD34+ cells, and anti-67LR antibodies significantly reduced HSC mobilization, providing the first in vivo evidence for 67LR involvement in stem-cell egress from bone marrow after G-CSF administration. In conclusion, 67LR up-regulation in G-CSF–mobilized HSCs correlates with their successful mobilization and reflects its increase in marrow HSCs, which contributes to the egress from bone marrow by mediating laminin-dependent cell adhesion and transendothelial migration.

The role of chemokine activation of Rac GTPases in hematopoietic stem cell marrow homing, retention, and peripheral mobilization

Signaling downstream from the chemokine receptor CXCR4, the tyrosine kinase receptor c-kit and beta1-integrins has been shown to be crucial in the regulation of migration, homing, and engraftment of hematopoietic stem cells and progenitors. Each of these receptors signal through Rac-type Rho guanosine triphosphatases (GTPases). Rac GTPases play a major role in the organization of the actin cytoskeleton and also in the control of gene expression and the activation of proliferation and survival pathways. Here we review the specific roles of the members of the Rac subfamily of the Rho GTPase family in regulating the intracellular signaling of hematopoietic cells responsible for regulation of homing, marrow retention, and peripheral mobilization.

Granulocyte Colony-Stimulating Factor Mediates Cardioprotection Against Ischemia/Reperfusion Injury via Phosphatidylinositol-3-Kinase/Akt Pathway in Canine Hearts

PURPOSE

Recent studies suggest that G-CSF prevents cardiac remodeling following myocardial infarction (MI) likely through regeneration of the myocardium and coronary vessels. However, it remains unclear whether G-CSF administered at the onset of reperfusion prevents ischemia/reperfusion injury in the acute phase. We investigated acute effects of G-CSF on myocardial infarct size and the incidence of lethal arrhythmia and evaluated the involvement of the phosphatidylinositol-3 kinase (PI3K) in the in vivo canine models.

METHODS

In open-chest dogs, left anterior descending coronary artery (LAD) was occluded for 90 minutes followed by 6 hours of reperfusion. We intravenously administered G-CSF (0.33 micro/kg/min) for 30 minutes from the onset of reperfusion. Wortmannin, a PI3K inhibitor, was selectively administered into the LAD after the onset of reperfusion.

RESULTS

G-CSF significantly (p<0.05) reduced myocardial infarct size (38.7+/-4.3% to 15.7+/-5.3%) and the incidence of ventricular fibrillation during reperfusion periods (50% to 0%) compared with the control. G-CSF enhanced Akt phospholylation in ischemic canine myocardium. Wortmannin blunted both the infarct size-limiting and anti-arrhythmic effects of G-CSF. G-CSF did not change myeloperoxidase activity, a marker of neutrophil accumulation, in the infarcted myocardium.

CONCLUSION

An intravenous administration of G-CSF at the onset of reperfusion attenuates ischemia/reperfusion injury through PI3K/Akt pathway in the in vivo model. G-CSF administration can be a promising candidate for the adjunctive therapy for patients with acute myocardial infarction.

Postinfarct cytokine therapy regenerates cardiac tissue and improves left ventricular function

We systematically investigated the comparative efficacy of three different cytokine regimens, administered after a reperfused myocardial infarction, in regenerating cardiac tissue and improving left ventricular (LV) function. Wild-type (WT) mice underwent a 30-minute coronary occlusion followed by reperfusion and received vehicle, granulocyte colony-stimulating factor (G-CSF)+Flt-3 ligand (FL), G-CSF+stem cell factor (SCF), or G-CSF alone starting 4 hours after reperfusion. In separate experiments, chimeric mice generated by reconstitution of radioablated WT mice with bone marrow from enhanced green fluorescent protein (EGFP) transgenic mice underwent identical protocols. Mice were euthanized 5 weeks later. Echocardiographically, LV function was improved in G-CSF+FL- and G-CSF+SCF-treated but not in G-CSF-treated mice, whereas LV end-diastolic dimensions were smaller in all three groups. Morphometrically, cytokine-treated hearts had smaller LV diameter and volume. Numerous EGFP-positive cardiomyocytes, capillaries, and arterioles were noted in the infarcted region in cytokine-treated chimeric mice treated with G-CSF+FL or G-CSF+SCF, but the numbers were much smaller in G-CSF-treated mice. G-CSF+FL therapy mobilized bone marrow-derived cells exhibiting increased expression of surface antigens (CD62L and CD11a) that facilitate homing. We conclude that postinfarct cytokine therapy with G-CSF+FL or G-CSF+SCF limits adverse LV remodeling and improves LV performance by promoting cardiac regeneration and probably also by exerting other beneficial actions unrelated to regeneration, and that G-CSF alone is less effective.

Fat tissue: an underappreciated source of stem cells for biotechnology

Adipose tissue can be harvested in large amounts with minimal morbidity. It contains numerous cells types, including adipocytes, preadipocytes, vascular endothelial cells and vascular smooth muscle cells; it also contains cells that have the ability to differentiate into several lineages, such as fat, bone, cartilage, skeletal, smooth, and cardiac muscle, endothelium, hematopoietic cells, hepatocytes and neuronal cells. Cloning studies have shown that some adipose-derived stem cells (ADSCs) have multilineage differentiation potential. ADSCs are also capable of expressing multiple growth factors, including vascular endothelial growth factor and hepatocyte growth factor. Early, uncontrolled, non-randomized clinical research, applying fresh adipose-derived cells into a cranial defect or undifferentiated ADSCs into fistulas in Crohn's disease, has shown healing and an absence of side effects. The combination of these properties, and the large quantity of cells that can be obtained from fat, suggests that this tissue will be a useful tool in biotechnology.

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

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

Contribution of alpha6 integrins to hematopoietic stem and progenitor cell homing to bone marrow and collaboration with alpha4 integrins

The laminin receptor integrin alpha6 chain is ubiquitously expressed in human and mouse hematopoietic stem and progenitor cells. We have studied its role for homing of stem and progenitor cells to mouse hematopoietic tissues in vivo. A function-blocking anti-integrin alpha6 antibody significantly reduced progenitor cell homing to bone marrow (BM) of lethally irradiated mice, with a corresponding retention of progenitors in blood. Remarkably, the anti-integrin alpha6 antibody profoundly inhibited BM homing of long-term multilineage engrafting stem cells, studied by competitive repopulation assay and analysis of donor-derived lymphocytes and myeloid cells in blood 16 weeks after transplantation. A similar profound inhibition of long-term stem cell homing was obtained by using a function-blocking antibody against alpha4 integrin, studied in parallel. Furthermore, the anti-integrin alpha6 and alpha4 antibodies synergistically inhibited homing of short-term repopulating stem cells. Intravenous injection of anti-integrin alpha6 antibodies, in contrast to antibodies against alpha4 integrin, did not mobilize progenitors or enhance cytokine-induced mobilization by G-CSF. Our results provide the first evidence for a distinct functional role of integrin alpha6 receptor during hematopoietic stem and progenitor cell homing and collaboration of alpha6 integrin with alpha4 integrin receptors during homing of short-term stem cells.

Transplantation of Undifferentiated, Bone Marrow‐Derived Stem Cells

Stem cell research has known an enormous development, and cellular transplantation holds great promise for regenerative medicine. However, some aspects, such as the mechanisms underlying stem cell plasticity (cell fusion vs true transdifferentiation) and the functional improvement after stem cell transplantation, are highly debated. Furthermore, the great variability in methodology used by several groups, sometimes leads to confusing, contradicting results. In this chapter, we review a number of studies in this area with an eye on possible technical and other difficulties in interpretation of the obtained results.

Bone marrow-induced tolerance in the era of pancreas and islets transplantation

Enormous progress has been made in the field of solid organ adaptation recently because of the improvement in immunosuppression. Although powerful immunosuppressive drugs decrease the rate of acute rejection significantly, the long-term functional graft survival and tolerance induction remains poor. Chronic rejection is the main cause of graft failure. An electronic search was performed for articles on chimerism, tolerance, and immunologic perspectives of islet and pancreas transplantation along with referrals to our experience. Infusion of donor bone marrow-derived cells to create a chimeric state continue to be tested in clinical protocols intended to induce specific immunologic tolerance. The proposed mechanisms of immunologic engagement and the emergence of a tolerant state through mixed chimerism include central depletion of alloreactive cells, induction of T-cell anergy, and generation of suppressor cells by interactions between donor and host cells. In this setting, depletion of recipient T cells by different strategies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion are prerequisites for tolerance induction. Many efforts have aimed to establish mixed chimerism along with tolerance in solid organ transplantation including pancreas and islets to facilitate engraftment. A review of the more important advances in the field and the future prospects combined with our experience to induce tolerance in the clinic and the laboratory is presented in this article.

Role of CXCR4 chemokine receptor blockade using AMD3100 for mobilization of autologous hematopoietic progenitor cells

G-CSF mobilization of hematopoietic progenitor cells (HPCs) is mediated through enzyme release from maturing myeloid cells, leading to digestion of adhesion molecules, trophic chemokines and their receptors, and the extracellular matrix. HPCs traffic to and are retained in the marrow through the trophic effects of the chemokine SDF-1alpha/CXCL12 binding to its receptor, CXCR4. AMD3100 reversibly inhibits SDF-1alpha/CXCR4 binding, and AMD3100 administration mobilizes CD34+ cells into the circulation. AMD3100 has been tested in several clinical trials which demonstrate that it improves the number of CD34+ cells mobilized including patients failing to mobilize with G-CSF alone. Engraftment of AMD3100-mobilized cells is prompt and durable. Toxicities are mild and infrequent. Lymphoma and myeloma cells do not appear to be mobilized. AMD3100 appears to be a promising agent for HPC mobilization.

Low CXCR4 membrane expression on CD34+ cells characterizes cells mobilized to blood

SUMMARY

In this work, association between the presence and membrane density of CXCR4 and the effectiveness of mobilization was studied. Ninety G-CSF mobilized PBPC and 28 native BM (nBM) preparations obtained from healthy individuals for transplantation and BM obtained after G-CSF mobilized PBPC collection in 10 donors were investigated. Positivity for CD34, HLA-DR and CXCR4 were analysed in the three colour fluorescence. The cellular profile of PBPC differed from nBM preparations with respect to lower: (i) proportion of CD34(+) cells (0.64%+/-0.04 vs 0.92+/-0.07) and CD34(+)CXCR4(+) cells (0.30%+/-0.02 vs 0.61+/-0.07); (ii) contribution of CXCR4(+) cells to CD34(+) cells (52.2%+/-2.5 vs 62.2%+/-4.2); (iii) CXCR4 epitope density in CD34(+) cells (48.9+/-5.5 vs 94.7+/-10.4). PBPC yield for CD34(+) cells was correlated with the content of CD34(+) cells lacking CXCR4 in the leukapheresis product (R=0.38). In contrast, nBM harvested for transplantation was poor in CD34(+) cells if these cells were frequently CXCR4- (R=-0.49). The present study shows that CD34(+) cells mobilized to blood were characterized with a low proportion of CXCR4 and this associated with CD34(+) cell content in PBPC.

HOXB4-induced self-renewal of hematopoietic stem cells is significantly enhanced by p21 deficiency

Enforced expression of the HOXB4 transcription factor and downregulation of p21(Cip1/Waf) (p21) can each independently increase proliferation of murine hematopoietic stem cells (HSCs). We asked whether the increase in HSC self-renewal generated by overexpression of HOXB4 is enhanced in p21-deficient HSCs. HOXB4 was overexpressed in hematopoietic cells from wild-type (wt) and p21-/- mice. Bone marrow (BM) cells were transduced with a retroviral vector expressing HOXB4 together with GFP (MIGB4), or a control vector containing GFP alone (MIG) and maintained in liquid culture for up to 11 days. At day 11 of the expansion culture, the number of primary CFU-GM (colony-forming unit granulocyte-macrophage) colonies and the repopulating ability were significantly increased in MIGB4 p21-/- BM (p21B4) cells compared with MIGB4-transduced wt BM (wtB4) cells. To test proliferation of HSCs in vivo, we performed competitive repopulation experiments and obtained significantly higher long-term engraftment of expanded p21B4 cells compared with wtB4 cells. The 5-day expansion of p21B4 HSCs generated 100-fold higher numbers of competitive repopulating units compared with wtMIG and threefold higher numbers compared with wtB4. The findings demonstrate that increased expression of HOXB4, in combination with suppression of p21 expression, could be a useful strategy for effective and robust expansion of HSCs.

Effect of age on the frequency, cell cycle, and lineage maturation of rhesus monkey (Macaca mulatta) CD34+ and hematopoietic progenitor cells

The effects of maturation and aging on hematopoietic progenitor cells, blood and bone marrow from second- and third-trimester fetal, newborn, infant, adult, and aged rhesus monkeys (Macaca mulatta) were analyzed. CD34(+) cells were immunoselected and stained with propidium iodide for cell cycle analysis. Blood and bone marrow mononuclear cells were plated in methylcellulose, and erythroid and myeloid progenitors were grown and counted. A higher frequency of circulating CD34(+)CD38(-) and CD34(+)DR(-) cells was observed in second-trimester fetuses compared with the other age groups. The frequency of bone marrow CD34(+)CD38(-) and CD34(+)DR(-) cells declined in adult and aged animals when compared with the younger age groups. Cell-cycle analysis showed 4.5% second-trimester fetal bone marrow CD34(+) cells entering the G(2)/M phase, compared with 1.7% CD34(+) cells in aged animals. More than 95% of circulating CD34(+) cells remained quiescent for most age groups, except for second-trimester fetuses. Adult marrow myeloid progenitors were found in a lower quantity when compared with third-trimester fetuses, whereas erythroid progenitors were greatest in early-gestation fetuses and adults. The results of these studies suggest that 1) the greatest quantity of CD34(+)CD38(-) and CD34(+)DR(-) cells was found in fetal and infant bone marrow, 2) the frequency of cycling CD34(+) cells declines with maturation and aging, and 3) an age-dependent difference in lineage commitment occurs.

Whether modern cell technologies can break down biological limitations of tissue-specific regeneration of the myocardium

The paper reviews modern concepts of physiological and reparative regeneration of the myocardium as a highly specific and highly differentiated tissue system. Special attention was given to evaluation of the proliferative potential of cardiomyocytes, in particular, to the existence of a population of resident cardiac stem cells in the myocardium. Modern approaches to replenishment of massive cardiomyocyte loss via transplantation and transdifferentiation of adult and embryonic stem cells are discussed and the possibilities of using cell technologies for induction of tissue-specific regeneration of the myocardium are analyzed.

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.

Stem cells today: B1. Bone marrow stem cells

This review is the second in a series of four devoted to the analysis of recent studies on stem cells. The first considered embryo stem cells (ES). This review covers bone marrow stem cells. They are analysed initially in a historical perspective, and then in relation to foundation studies in the later 20th century before a detailed analysis is presented on very recent studies. Methods of identifying, culturing, expanding and grafting stem cells are described, including the separation of haemopoietic and mesenchyme cell lines (HSC and MSC) and recent more detailed analyses using numerous CD and other markers to identify very small subsets of stem cells such as multipotent adult progenitor cells (MAPC) and bone marrow stromal stem cells (BMSSC) from MSC. Queries arising on the immense potential of these stem cell lines due to the discovery of epigentic factors and cell fusions influencing their development and potency are described. A section on cord blood stem cells is followed by a detailed discussion on the modern situation regarding the clinical use of stem cells, its recent setbacks due to epigenetic factors, different approaches to the discovery of a highly multipotent bone marrow stem cell, and a brief description of embryological approaches to identifying the basic bone marrow stem cell in very early mammalian embryos.

Donor bone marrow transplantation: chimerism and tolerance

Infusion of donor bone marrow (DBM)-derived cells continue to be tested in clinical protocols intended to induce specific immunologic tolerance. Central clonal deletion of donor-specific alloreactive cells associated with mixed chimerism reliably produced long-term graft tolerance. In this setting, depletion of recipient T cells by antilymphocyte antibodies and subsequent repopulation by donor hematopoietic cells after donor bone marrow infusion (DBMI) are prerequisites for tolerance induction. Major advances have been made in animal models and in pilot clinical trials and the key questions with the future perspectives are presented in this article.

Phenotypic and functional characteristics of CD34+cells are related to their anatomical environment: is their versatility a prerequisite for their bio-availability"

Human CD34+ hematopoietic progenitors (HP) are mainly resident in adult bone marrow (BM). However, their recent revelation in nonhematopoietic tissues implies their circulation through peripheral blood (PB). The intimate mechanisms of this physiological process are not yet understood. Our results showed that steady-state CD34+ HP exhibit a differential phenotypic profile according to their BM versus PB localization. We demonstrated that this phenotype could be modulated by incubation in the presence of their counterpart mononuclear cells (MNC) through cell interactions and cytokine production. Such a modulation mainly concerns migration-mediated cytokine and chemokine receptors as well as some adhesion molecules and partly results from MNC specificity. These phenotypic profiles are associated with distinct cell-cycle position, cloning efficiency, and migration capacity of CD34+ cells from the different anatomical sources. We therefore propose a definition for a circulating versus resident CD34+ cell profile, which mostly depends on their cellular environment. We suggest that blood would represent a supply of cells for which phenotypic and functional characteristics would be a prerequisite for their bio-availability.

Hepatocytes derived from peripheral blood stem cells of granulocyte-colony stimulating factor treated F344 rats in analbuminemic rat livers

BACKGROUND

hematopoietic stem cells (SCs) mobilized from the bone marrow (BM) into peripheral blood (PB) are reported to have ability to differentiate into various cell types. We investigated whether PB-SCs mobilized by treatment with granulocyte-colony stimulating factor (G-CSF) in normal rats can raise albumin-producing hepatocytes after transplantation within the liver of analbuminemic rats.

MATERIALS AND METHODS

Fischer 344 rats (F344) were used as donors, and F344 congenic Nagase's analbuminemic rats (F344alb) as recipients. The donors were repeatedly treated with human recombinant G-CSF, and their PB mononuclear cells (MNCs) were infused into the portal veins of recipients immediately after 70% hepatectomy (PH).

RESULTS

Although a few single and small clusters (less than five cells) of albumin positive (alb+) hepatocytes were seen in the livers of untreated F344alb and of the animals undergoing PH alone or transplantation of PB-MNCs with or without the prior G-CSF treatment, clusters consisting of more than 6 alb+ hepatocytes were only detected in the livers of recipients that received transplantation of mobilized PB-MNCs or BM-MNCs under the regenerating condition induced by PH. Sry3, a Y chromosome marker, could be detected corresponding to the alb+ clusters by in situ hybridization when male donors and female recipients were used. Moreover, normal albumin gene sequences were demonstrated in the microdissected alb+ clusters by polymerase chain reaction, and the serum albumin levels were elevated in the recipients.

CONCLUSIONS

Hematopoietic SCs mobilized from BM into PB by the G-CSF treatment may raise hepatocyte colonies, when transplanted into regenerating livers.

Involvement of the urokinase-type plasminogen activator receptor in hematopoietic stem cell mobilization

We investigated the involvement of the urokinase-type plasminogen-activator receptor (uPAR) in granulocyte-colony-stimulating factor (G-CSF)-induced mobilization of CD34+ hematopoietic stem cells (HSCs) from 16 healthy donors. Analysis of peripheral blood mononuclear cells (PBMNCs) showed an increased uPAR expression after G-CSF treatment in CD33+ myeloid and CD14+ monocytic cells, whereas mobilized CD34+ HSCs remained uPAR negative. G-CSF treatment also induced an increase in serum levels of soluble uPAR (suPAR). Cleaved forms of suPAR (c-suPAR) were released in vitro by PBMNCs and were also detected in the serum of G-CSF-treated donors. c-suPAR was able to chemoattract CD34+ KG1 leukemia cells and CD34+ HSCs, as documented by their in vitro migratory response to a chemotactic suPAR-derived peptide (uPAR84-95). uPAR84-95 induced CD34+ KG1 and CD34+ HSC migration by activating the high-affinity fMet-Leu-Phe (fMLP) receptor (FPR). In addition, uPAR84-95 inhibited CD34+ KG1 and CD34+ HSC in vitro migration toward the stromal-derived factor 1 (SDF1), thus suggesting the heterologous desensitization of its receptor, CXCR4. Finally, uPAR84-95 treatment significantly increased the output of clonogenic progenitors from long-term cultures of CD34+ HSCs. Our findings demonstrate that G-CSF-induced upregulation of uPAR on circulating CD33+ and CD14+ cells is associated with increased uPAR shedding, which leads to the appearance of serum c-suPAR. c-suPAR could contribute to the mobilization of HSCs by promoting their FPR-mediated migration and by inducing CXCR4 desensitization.

Homing-associated cell adhesion molecules and cell cycle status on the nucleated cells in the bone marrow, mobilized peripheral blood and cord blood

Homing-associated cell adhesion molecules (H-CAM) on the CD34+ cells play an important role for the engraftment process following hematopoietic stem cell transplantation (HSCT). However, it seems that not only CD34+ cells but also other nucleated cells (NCs) with H-CAM could be implicated in the engraftment process and the proliferation of hematopoietic stem cells. We investigated the differences of HCAM and cell cycle status on the NCs in cord blood (CB), bone marrow (BM), and mobilized peripheral blood (PB). The proportions of CXCR4+ cells within the NC populations were greater in CB than in PB or BM (p=0.0493), although the proportions of CXCR4+, CD44+, and CD49d+ cells within the CB CD34+ cell populations were same within BM or PB. A lower proportion of CD34+CD49d+ cells within the CD34+ cell populations was more noted in CB than in PB or BM (p=0.0085). There were no differences in cell cycle status between CB and BM or PB. Our results suggest that the migrating potential of CB would be enhanced with increased CXCR4 expression on the NCs, but the adhesion potential of CB CD34+ cells would be less than that of PB and BM. These findings may help explain why the lower cell dose is required and engraftment is delayed in cord blood stem cell transplantation.

Primary human CD34+ hematopoietic stem and progenitor cells express functionally active receptors of neuromediators

Recently, overlapping molecular phenotypes of hematopoietic and neuropoietic cells were described in mice. Here, we examined primary human CD34+ hematopoietic stem and progenitor cells applying specialized cDNA arrays, real-time reverse-transcriptase–polymerase chain reaction (RT-PCR), and fluorescent-activated cell sorter (FACS) analysis focusing on genes involved in neurobiologic functions. We found expression of vesicle fusion and motility genes, ligand- and voltage-gated ion channels, receptor kinases and phosphatases, and, most interestingly, mRNA as well as protein expression of G protein–coupled receptors of neuromediators (corticotropin-releasing hormone 1 [CRH 1] and CRH 2 receptors, orexin/hypocretin 1 and 2 receptors, GABAB receptor, adenosine A2B receptor, opioid κ1 and μ1 receptors, and 5-HT 1F receptor). As shown by 2-color immunofluorescence, the protein expression of these receptors was higher in the more immature CD38dim than in the CD38bright subset within the CD34+ population, and completely absent in fully differentiated blood cells, suggesting that those receptors play a role in developmentally early CD34+ stem and progenitor cells. The intracellular concentration of cyclic adenosine monophosphate (cAMP) in CD34+ cells was diminished significantly upon stimulation of either CRH or orexin receptors, indicating that those are functionally active and coupled to inhibitory G proteins in human hematopoietic cells. In conclusion, these findings suggest a molecular interrelation of neuronal and hematopoietic signaling mechanisms in humans.

Differential expression of stem cell mobilization-associated molecules on multi-lineage cells from adipose tissue and bone marrow

Our laboratory has characterized a population of stromal cells obtained from adipose tissue termed processed lipoaspirate cells (PLAs). PLAs, like bone-marrow derived mesenchymal stem cells (BM-MSCs), have the capacity to differentiate along the adipogenic, osteogenic, chondrogenic, and myogenic lineages, In order to better characterize these two multi-lineage populations, we examined the surface phenotype of both bone marrow and adipose tissue-derived cells from five patients undergoing surgery. PLA and BM-MSC cells were isolated, subcultivated, and evaluated for cell surface marker expression using flow cytometry. PLA and BM-MSC cells both expressed CD13, CD29, CD44, CD90, CD105, SH-3, and STRO-1. Differences in expression were noted for cell adhesion molecules CD49d (Integrin alpha4), CD54 (ICAM-1), CD34, and CD106 (VCAM-1). While markedly similar, the surface phenotypes of PLA and BM-MSC cells are distinct for several cell adhesion molecules implicated in hematopoietic stem cell homing, mobilization, and proliferation.

Bone marrow–derived hematopoietic cells generate cardiomyocytes at a low frequency through cell fusion, but not transdifferentiation

Recent studies have suggested that bone marrow cells might possess a much broader differentiation potential than previously appreciated. In most cases, the reported efficiency of such plasticity has been rather low and, at least in some instances, is a consequence of cell fusion. After myocardial infarction, however, bone marrow cells have been suggested to extensively regenerate cardiomyocytes through transdifferentiation. Although bone marrow-derived cells are already being used in clinical trials, the exact identity, longevity and fate of these cells in infarcted myocardium have yet to be investigated in detail. Here we use various approaches to induce acute myocardial injury and deliver transgenically marked bone marrow cells to the injured myocardium. We show that unfractionated bone marrow cells and a purified population of hematopoietic stem and progenitor cells efficiently engraft within the infarcted myocardium. Engraftment was transient, however, and hematopoietic in nature. In contrast, bone marrow-derived cardiomyocytes were observed outside the infarcted myocardium at a low frequency and were derived exclusively through cell fusion.

Soluble c-kit receptor mobilizes hematopoietic stem cells to peripheral blood in mice

OBJECTIVE

The mechanisms of mobilization of hematopoietic stem cells (HSC) from bone marrow to peripheral blood (PB) by cytokines are poorly understood. One hypothesis is that cytokines disrupt cytoadhesive interactions of stem cells with bone marrow stroma. The soluble portion of c-kit (s-kit) binds stem cell factor (SCF) and can specifically block the ability of SCF to bind HSC.

MATERIALS AND METHODS

To examine stem cell mobilization by s-kit, we prepared PB mononuclear cells from s-kit- or granulocyte colony-stimulating factor (G-CSF)-treated mice and assayed their colony-forming abilities and their long-term reconstituting abilities by transplantation into lethally irradiated Ly-5.2 congenic mice.

RESULTS

We confirmed the published findings that human recombinant s-kit can block SCF-stimulated hematopoietic colony growing. We then found that s-kit could mobilize colony-forming cells from bone marrow to PB, and we found long-term reconstitution cells in the PB from s-kit-treated mice. The majority of s-kit-mobilized stem cells were in the CD34(+) cell population. We also tested the additive effect between G-CSF and s-kit. The mean percentages of donor cells in the mice transplanted with Lin(-) cells from the G-CSF-treated mice and the G-CSF/s-kit-treated mice were 44.6% and 64.8%, respectively (p=0.028).

CONCLUSIONS

These findings demonstrate that stem cells with long-term engraftment capabilities can be mobilized by s-kit, and that s-kit combined with G-CSF treatment leads to significant enhancement of engraftment efficiency, suggesting mobilization via disruption between c-kit and SCF as the mechanism.

Current mechanistic scenarios in hematopoietic stem/progenitor cell mobilization

Uncovering the molecular mechanisms governing the exit of stem/progenitor cells from bone marrow to peripheral blood at steady state or after their enforced migration has been an ongoing challenge. Recently, however, several new avenues or paradigms in mobilization have emerged from ever-expanding work in humans subjected to granulocyte colony-stimulating factor (G-CSF) mobilization, as well as from studies in normal and gene-deficient mouse models. Although these developments represent notable advances that met with considerable excitement, they have been quenched by surprising vacillations in subsequent research. This perspective highlights recent developments in mobilization along with their controversies. A full understanding of the directional cues that control the migratory behavior and the fate of stem/progenitor cells once they migrate out of bone marrow will await further experimentation, aiming to bridge our current gaps in knowledge.