Chemokine-mobilized adult stem cells; defining a better hematopoietic graft

Challenges and strategies for in situ endothelialization and long-term lumen patency of vascular grafts

Vascular diseases are the most prevalent cause of ischemic necrosis of tissue and organ, which even result in dysfunction and death. Vascular regeneration or artificial vascular graft, as the conventional treatment modality, has received keen attentions. However, small-diameter (diameter < 4 mm) vascular grafts have a high risk of thrombosis and intimal hyperplasia (IH), which makes long-term lumen patency challengeable. Endothelial cells (ECs) form the inner endothelium layer, and are crucial for anti-coagulation and thrombogenesis. Thus, promoting in situ endothelialization in vascular graft remodeling takes top priority, which requires recruitment of endothelia progenitor cells (EPCs), migration, adhesion, proliferation and activation of EPCs and ECs. Chemotaxis aimed at ligands on EPC surface can be utilized for EPC homing, while nanofibrous structure, biocompatible surface and cell-capturing molecules on graft surface can be applied for cell adhesion. Moreover, cell orientation can be regulated by topography of scaffold, and cell bioactivity can be modulated by growth factors and therapeutic genes. Additionally, surface modification can also reduce thrombogenesis, and some drug release can inhibit IH. Considering the influence of macrophages on ECs and smooth muscle cells (SMCs), scaffolds loaded with drugs that can promote M2 polarization are alternative strategies. In conclusion, the advanced strategies for enhanced long-term lumen patency of vascular grafts are summarized in this review. Strategies for recruitment of EPCs, adhesion, proliferation and activation of EPCs and ECs, anti-thrombogenesis, anti-IH, and immunomodulation are discussed. Ideal vascular grafts with appropriate surface modification, loading and fabrication strategies are required in further studies.

Coordinated Regulation of Mesenchymal Stem Cell Migration by Various Chemotactic Stimuli

Endogenous bone marrow-derived mesenchymal stem cells are mobilized to peripheral blood and injured tissues in response to changes in the expression of various growth factors and cytokines in the injured tissues, including substance P (SP), transforming growth factor-beta (TGF-β), and stromal cell-derived factor-1 (SDF-1). SP, TGF-β, and SDF-1 are all known to induce the migration of bone marrow-derived mesenchymal stem cells (BM-MSCs). However, it is not yet clear how these stimuli influence or interact with each other during BM-MSC mobilization. This study used mouse bone marrow-derived mesenchymal stem cell-like ST2 cells and human BM-MSCs to evaluate whether SP, TGF-β, and SDF-1 mutually regulate their respective effects on the mobilization of BM-MSCs. SP pretreatment of ST2 and BM-MSCs impaired their response to TGF-β while the introduction of SP receptor antagonist restored the mobilization of ST2 and BM-MSCs in response to TGF-β. TGF-β pretreatment did not affect the migration of ST2 and BM-MSCs in response to SP, but downregulated their migration in response to SDF-1. SP pretreatment modulated the activation of TGF-β noncanonical pathways in ST2 cells and BM-MSCs, but not canonical pathways. These results suggest that the migration of mesenchymal stem cells is regulated by complex functional interactions between SP, TGF-β, and SDF-1. Thus, understanding the complex functional interactions of these chemotactic stimuli would contribute to ensuring the development of safe and effective combination treatments for the mobilization of BM-MSCs.

Regulation of hematopoiesis by the chemokine system

Although chemokines are best known for their role in directing cell migration, accumulating evidence indicate their involvement in many other processes. This review focus on the role of chemokines in hematopoiesis with an emphasis on myelopoiesis. Indeed, many chemokine family members are an important component of the cytokine network present in the bone marrow that controls proliferation, retention, and mobilization of hematopoietic progenitors.

Mammalian sterile 20 kinase 1 and 2 are important regulators of hematopoietic stem cells in stress condition

The mammalian Hippo signaling pathway has been implicated in the self-renewal and differentiation of stem and progenitor cells. MST1 and MST2 (MST1/2) are core serine-threonine kinases in the Hippo signaling pathway, one of which, MST1, has been extensively investigated for its role in T cell and myeloid cell function. These studies have identified MST1 as a promising therapeutic target in immunological disease. However, the roles of MST1/2 in hematopoietic stem cell (HSC) function in vivo are not fully understood. Here, we report that mice with a conditional deletion of Mst1/2 exhibit impaired hematopoietic stem and progenitor cell (HSPC) function under stress condition. Furthermore, Mst1/2 deletion markedly altered mature cell output. Therefore, MST1/2 are indispensable for maintenance as well as function of stem and progenitor cells under steady state conditions and with transplantation stress.

The Role of Lymphocytes in Radiotherapy-Induced Adverse Late Effects in the Lung

Radiation-induced pneumonitis and fibrosis are dose-limiting side effects of thoracic irradiation. Thoracic irradiation triggers acute and chronic environmental lung changes that are shaped by the damage response of resident cells, by the resulting reaction of the immune system, and by repair processes. Although considerable progress has been made during the last decade in defining involved effector cells and soluble mediators, the network of pathophysiological events and the cellular cross talk linking acute tissue damage to chronic inflammation and fibrosis still require further definition. Infiltration of cells from the innate and adaptive immune systems is a common response of normal tissues to ionizing radiation. Herein, lymphocytes represent a versatile and wide-ranged group of cells of the immune system that can react under specific conditions in various ways and participate in modulating the lung environment by adopting pro-inflammatory, anti-inflammatory, or even pro- or anti-fibrotic phenotypes. The present review provides an overview on published data about the role of lymphocytes in radiation-induced lung disease and related damage-associated pulmonary diseases with a focus on T lymphocytes and B lymphocytes. We also discuss the suspected dual role of specific lymphocyte subsets during the pneumonitic phase and fibrotic phase that is shaped by the environmental conditions as well as the interaction and the intercellular cross talk between cells from the innate and adaptive immune systems and (damaged) resident epithelial cells and stromal cells (e.g., endothelial cells, mesenchymal stem cells, and fibroblasts). Finally, we highlight potential therapeutic targets suited to counteract pathological lymphocyte responses to prevent or treat radiation-induced lung disease.

Astragalus polysaccharide promotes the release of mature granulocytes through the L-selectin signaling pathway

Background

This study aims to investigate the leukogenic effect of astragalus polysaccharide (APS), to compare its effect of increasing the numbers of mature granulocytes with that of granulocyte colony-stimulating factor (G-CSF), and to investigate the mechanism.

Methods

Rats were arbitrarily grouped into four groups (control, cyclophosphamide (CTX), CTX + APS, and CTX + G-CSF groups), and each group was then arbitrarily divided into five subgroups according to the time period since CTX infusion (0, 4, 7, 10, and 14 days). The expression of leukocyte selectin (L-selectin), its ligand, and shedding-related protease on granulocytes was analyzed. Leukocyte counts were obtained. Chemotactic capacity of polymorphonuclear leukocytes (PMNLs) was assessed.

Results

Both APS and G-CSF restored the expression of L-selectin, P-selectin glycoprotein ligand-1 (PSGL-1), CD11b/CD18, and ADAM17 to normal levels (P > 0.05 vs. control group on each time point), with APS eliciting a greater effect than G-CSF (P = 0.005 on day 7, P < 0.001 on day 10 and 14 for L-selectin; P = 0.038 on day 7, P = 0.001 on day 10, P < 0.001 on day 14 for PSGL-1; P < 0.001 on day 7, 10 and 14 for ADAM17; P < 0.001 on day 7, 10, and 14 for CD11b/CD18). The percentages of the bands and segmented bone marrow (BM) cells in myeloid neutrophils were higher in the CTX + APS group than in the CTX group on day 7 (P = 0.030) and reached normal levels on day 10 (P = 0.547) and 14 (P = 0.431) vs. control group. The ability of APS to increase numbers of PMNLs in peripheral blood after chemotherapy was significantly superior to that of G-CSF 7 days after chemotherapy (P = 0.029 on day 10, P = 0.006 on day 14). Moreover, APS more significantly improved the chemotactic ability of PMNLs among mature BM granulocytes and peripheral blood neutrophils after chemotherapy than did G-CSF (P < 0.001 on day 7, P = 0.001 on day 10 and P = 0.005 on day 14).

Conclusions

APS promoted the differentiation and chemotactic ability of BM granulocytes via the L-selectin signaling pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s13020-015-0043-z) contains supplementary material, which is available to authorized users.

Microfluidic source-sink model reveals effects of biophysically distinct CXCL12 isoforms in breast cancer chemotaxis

Chemokines critically regulate chemotaxis in normal and pathologic states, but there is limited understanding of how multicellular interactions generate gradients needed for cell migration. Previous studies of chemotaxis of CXCR4+ cells toward chemokine CXCL12 suggest the requirement of cells expressing scavenger receptor CXCR7 in a source-sink system. We leveraged an established microfluidic device to discover that chemotaxis of CXCR4 cells toward distinct isoforms of CXCL12 required CXCR7 scavenging only under conditions with higher than optimal levels of CXCL12. Chemotaxis toward CXCL12-β and -γ isoforms, which have greater binding to extracellular molecules and have been largely overlooked, was less dependent on CXCR7 than the more commonly studied CXCL12-α. Chemotaxis of CXCR4+ cells toward even low levels of CXCL12-γ and CXCL12-β still occurred during treatment with a FDA-approved inhibitor of CXCR4. We also detected CXCL12-γ only in breast cancers from patients with advanced disease. Physiological gradient formation within the device facilitated interrogation of key differences in chemotaxis among CXCL12 isoforms and suggests CXCL12-γ as a biomarker for metastatic cancer.

Neutropenia during HIV infection: adverse consequences and remedies

Neutropenia frequently occurs in patients with Human immunodeficiency virus (HIV) infection. Causes for neutropenia during HIV infection are multifactoral, including the viral toxicity to hematopoietic tissue, the use of myelotoxic agents for treatment, complication with secondary infections and malignancies, as well as the patient's association with confounding factors which impair myelopoiesis. An increased prevalence and severity of neutropenia is commonly seen in advanced stages of HIV disease. Decline of neutrophil phagocytic defense in combination with the failure of adaptive immunity renders the host highly susceptible to developing fatal secondary infections. Neutropenia and myelosuppression also restrict the use of many antimicrobial agents for treatment of infections caused by HIV and opportunistic pathogens. In recent years, HIV infection has increasingly become a chronic disease because of progress in antiretroviral therapy (ART). Prevention and treatment of severe neutropenia becomes critical for improving the survival of HIV-infected patients.

Gene and miRNA expression profiles of hematopoietic progenitor cells vary depending on their origin

Hematopoietic progenitor cells (HPCs) from granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood (G-PB), bone marrow (BM), or umbilical cord blood (CB) have differing biological properties and differing kinetics of engraftment post-transplantation, which might be explained, at least in part, by differing gene and miRNA expression patterns. To assess the differences in gene and miRNA expression, we analyzed whole genome expression profiles as well as the expression of 384 miRNAs in CD34(+) cells isolated from 18 healthy individuals (6 individuals per subtype of HPC source). We identified 43 genes and 36 miRNAs differentially expressed in the various CD34(+) cell sources. We observed that CD34(+) cells from CB and BM showed similar gene and miRNA expression profiles, whereas CD34(+) cells from G-PB had a very different expression pattern. Remarkably, 20 of the differentially expressed genes are targets of the differentially expressed miRNAs. Of note, the majority of genes differentially expressed in CD34(+) cells from G-PB are involved in cell cycle regulation, promoting the process of proliferation, survival, hematopoiesis, and cell signaling, and are targets of overexpressed and underexpressed miRNAs in CD34(+) cells from the same source. These data suggest significant differences in gene and miRNA expression among the various HPC sources used in transplantation. We hypothesize that the differentially expressed genes and miRNAs involved in cell cycle and proliferation might explain the differing kinetics of engraftment observed after transplantation of hematopoietic stem cells obtained from these different sources.

MIP-1α/CCL3-mediated maintenance of leukemia-initiating cells in the initiation process of chronic myeloid leukemia

In the initiation process of chronic myeloid leukemia (CML), a small number of transformed leukemia-initiating cells (LICs) coexist with a large number of normal hematopoietic cells, gradually increasing thereafter and eventually predominating in the hematopoietic space. However, the interaction between LICs and normal hematopoietic cells at the early phase has not been clearly delineated because of the lack of a suitable experimental model. In this study, we succeeded in causing a marked leukocytosis resembling CML from restricted foci of LICs in the normal hematopoietic system by direct transplantation of BCR-ABL gene-transduced LICs into the bone marrow (BM) cavity of nonirradiated mice. Herein, we observed that BCR-ABL(+)lineage(-)c-kit(-) immature leukemia cells produced high levels of an inflammatory chemokine, MIP-1α/CCL3, which promoted the development of CML. Conversely, ablation of the CCL3 gene in LICs dramatically inhibited the development of CML and concomitantly reduced recurrence after the cessation of a short-term tyrosine kinase inhibitor treatment. Finally, normal hematopoietic stem/progenitor cells can directly impede the maintenance of LICs in BM in the absence of CCL3 signal.

Hematopoietic progenitor cell collection after autologous transplant for multiple myeloma: low platelet count predicts for poor collection and sole use of resulting graft enhances risk of myelodysplasia

Collection of hematopoietic progenitor cells (HPC) after previous autologous hematopoietic progenitor cell transplant (aHCT) was studied in 221 patients with multiple myeloma (MM). With a total of 333 collections, the median number of CD34+ cells collected was 4.7 × 10(6) CD34+ cells/kg, and 74% of the patients collected ≥ 2.5 × 10(6) CD34+ cells/kg. Among 26 variables examined, the strongest predictor for poor collection was a platelet count <100 × 10(6)/l before mobilization (P<0.001). A subsequent aHCT was performed in 154 of the 221 patients. Sole use of HPC procured after aHCT in 86 patients was associated with delayed platelet recovery (P<0.001) and linked to development of myelodysplastic syndrome (MDS)-associated cytogenetic abnormalities (MDS-CA; P=0.027, odds ratio (OR) 10.34) and a tendency towards clinical MDS/acute myeloid leukemia (AML; P=0.091, OR 3.57). However, treatment-related mortality (P=0.766) and time to absolute neutrophil count recovery ≥0.5 × 10(9)/l (P=0.879) were similar to when a pre-aHCT graft was used. Indeed, adding HPC collected before any aHCT neutralized the risk of MDS-CA or MDS/AML. Therefore, we advise generous initial HPC collection to broaden the salvage armamentarium for patients with MM.

An emerging link in stem cell mobilization between activation of the complement cascade and the chemotactic gradient of sphingosine-1-phosphate

Under steady-state conditions, hematopoietic stem/progenitor cells (HSPCs) egress from bone marrow (BM) and enter peripheral blood (PB) where they circulate at low levels. Their number in PB, however, increases significantly in several stress situations related to infection, organ/tissue damage, or strenuous exercise. Pharmacologically mediated enforced egress of HSPCs from the BM microenvironment into PB is called "mobilization", and this phenomenon has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present the accumulated evidence that innate immunity, including the complement cascade and the granulocyte/monocyte lineage, and the PB plasma level of the bioactive lipid sphingosine-1-phosphate (S1P) together orchestrate this evolutionarily conserved mechanism that directs trafficking of HSPCs.

Innate immunity derived factors as external modulators of the CXCL12-CXCR4 axis and their role in stem cell homing and mobilization

The α-chemokine CXCL12 (stromal derived factor-1; SDF-1) and its corresponding G(αI) protein-coupled CXCR4 receptor axis play an important role in retention of hematopoietic stem progenitor cells (HSPCs) in bone marrow (BM) stem cell niches. CXCL12 has also been identified as a strong chemoattractant for HSPCs and implicated both in homing of HSPCs to BM after transplantation and in egress of these cells from BM into peripheral blood (PB). However, since CXCL12, as a peptide, is highly susceptible to degradation by proteolytic enzymes, its real biological availability in biological fluids may be somewhat limited. In this review, we will present data demonstrating that the CXCL12-CXCR4 axis is positively modulated by innate immunity-derived several external factors, ensuring that even low (near threshold) doses of CXCL12 still exert a robust chemotactic influence on HSPCs.

Enhanced homing permeability and retention of bone marrow stromal cells by noninvasive pulsed focused ultrasound

Bone marrow stromal cells (BMSCs) have shown significant promise in the treatment of disease, but their therapeutic efficacy is often limited by inefficient homing of systemically administered cells, which results in low number of cells accumulating at sites of pathology. BMSC home to areas of inflammation where local expression of integrins and chemokine gradients is present. We demonstrated that nondestructive pulsed focused ultrasound (pFUS) exposures that emphasize the mechanical effects of ultrasound-tissue interactions induced local and transient elevations of chemoattractants (i.e., cytokines, integrins, and growth factors) in the murine kidney. pFUS-induced upregulation of cytokines occurred through approximately 1 day post-treatment and returned to contralateral kidney levels by day 3. This window of significant increases in cytokine expression was accompanied by local increases of other trophic factors and integrins that have been shown to promote BMSC homing. When BMSCs were intravenously administered following pFUS treatment to a single kidney, enhanced homing, permeability, and retention of BMSC was observed in the treated kidney versus the contralateral kidney. Histological analysis revealed up to eight times more BMSC in the peritubular regions of the treated kidneys on days 1 and 3 post-treatment. Furthermore, cytokine levels in pFUS-treated kidneys following BMSC administration were found to be similar to controls, suggesting modulation of cytokine levels by BMSC. pFUS could potentially improve cell-based therapies as a noninvasive modality to target homing by establishing local chemoattractant gradients and increasing expression of integrins to enhance tropism of cells toward treated tissues.

T lymphocytes and normal tissue responses to radiation

There is compelling evidence that lymphocytes are a recurring feature in radiation damaged normal tissues, but assessing their functional significance has proven difficult. Contradictory roles have been postulated in both tissue pathogenesis and protection, although these are not necessarily mutually exclusive as the immune system can display what may seem to be opposing faces at any one time. While the exact role of T lymphocytes in irradiated normal tissue responses may still be obscure, their accumulation after tissue damage suggests they may be critical targets for radiotherapeutic intervention and worthy of further study. This is accentuated by recent findings that pathologically damaged “self,” such as occurs after exposure to ionizing radiation, can generate danger signals with the ability to activate pathways similar to those that activate adoptive immunity to pathogens. In addition, the demonstration of T cell subsets with their recognition radars tuned to “self” moieties has revolutionized our ideas on how all immune responses are controlled and regulated. New concepts of autoimmunity have resulted based on the dissociation of immune functions between different subsets of immune cells. It is becoming axiomatic that the immune system has the power to regulate radiation-induced tissue damage, from failure of regeneration to fibrosis, to acute and chronic late effects, and even to carcinogenesis. Our understanding of the interplay between T lymphocytes and radiation-damaged tissue may still be rudimentary but this is a good time to re-examine their potential roles, their radiobiological and microenvironmental influences, and the possibilities for therapeutic manipulation. This review will discuss the yin and yang of T cell responses within the context of radiation exposures, how they might drive or protect against normal tissue side effects and what we may be able do about it.

Macrophage inflammatory protein-2 (MIP-2)/CXCR2 blockade attenuates acute graft-versus-host disease while preserving graft-versus-leukemia activity

Allogenic bone marrow transplantation (BMT), an important treatment for hematological malignancies, is often complicated by graft-versus-host disease (GVHD). Suppression of GVHD is associated with the unwanted diminishment of the graft-versus-leukemia (GVL) response. The aim of this study was to maintain the benefits of GVL during GVHD suppression through isolated blockade of T-cell migration factors. To this end, we developed a murine model of B-cell leukemia, which was treated with BMT to induce GVHD. Within this model, functional blockade of MIP-2/CXCR2 was analyzed by observing proteomic, histologic and clinical variables of GVHD manifestation. Luminex assay of collected tissue identified several cytokines [granulocyte colony-stimulating factor (G-CSF), keratinocyte-derived chemokine (KC), macrophage inflammatory protein-2 (MIP-2), and interleukin-23 (IL-23)] that were upregulated during GHVD, but reduced by neutralizing the MIP-2/CXCR2 axis. In addition, donor T-cell blockade of CXCR2 combined with recipient administration of anti-MIP-2 caused a significant decrease in GVHD while preserving the GVL response. We propose that blocking the MIP-2/CXCR2 axis represents a novel strategy to separate the toxicity of GVHD from the beneficial effects of GVL after allogenic BMT.

Improved endothelialization and reduced thrombosis by coating a synthetic vascular graft with fibronectin and stem cell homing factor SDF-1α

Failure of synthetic small-diameter vascular grafts is determined mainly by the lack of endothelial cells, as these cells inhibit thrombosis and intimal hyperplasia. Coating of graft material with homing factors for circulating stem cells has the potential to improve endogenous endothelialization of these grafts and to reduce graft failure. Synthetic knitted polyester grafts (6mm diameter) were coated with FN and SDF-1α before surgical interposition in the carotid artery of sheep. Similar uncoated vascular grafts were implanted in the contralateral side as internal controls. To study the early attraction of stem cells, grafts were implanted in a first series of nine sheep and explanted after 1 or 3 days. In coated grafts, four times higher fractions of CD34(+) and three to four times higher fractions of CD117(+) cells adhering to the vessel walls were found than in control grafts (P<0.05). When such coated and non-coated grafts were implanted in 12 other sheep and explanted after 3 months, all coated grafts were patent, while one control graft was occluded. EcNOS staining revealed that FN-SDF-1α coating significantly increased coverage with endothelial cells from 27 ± 4% of the graft to 48 ± 4% compared with the controls (P=0.001). This was associated with a significant reduction of intimal hyperplasia (average thickness 1.03 ± 0.09 mm in controls vs. 0.69 ± 0.04 mm in coated grafts; P=0.009) and significantly less adhesion of thrombotic material in the middle part of the graft (P=0.029). FN-SDF-1α coating of synthetic small-caliber vascular grafts stimulated the attraction of stem cells and was associated with improved endothelialization and reduced intimal hyperplasia and thrombosis.

The use of chemokine receptor agonists in stem cell mobilization

INTRODUCTION

Pharmacological mobilization has been exploited as a means to obtain hematopoietic stem progenitor cells (HSPCs) for hematopoietic reconstitution. HSPCs mobilized from bone marrow into peripheral blood (PB) are a preferred source of stem cells for transplantation, because they are easily accessible and evidence indicates that they engraft faster after transplantation than HSPCs directly harvested from bone marrow (BM) or umbilical cord blood (UCB).

AREAS COVERED

Since chemokine-chemokine receptor axes are involved in retention of HSPCs in the BM microenvironment, chemokine receptor agonists have been proposed as therapeutics to facilitate the mobilization process. These compounds include agonists of the CXCR4 receptor expressed on HSPCs (CTCE-0021 and ATI-2341) or chemokines binding to chemokine receptors expressed on granuclocytes and monocytes (e.g., CXCL2, also known as the growth-related oncogene protein-beta (Gro-β); CCL3, also known as macrophage inflammatory protein-1α (MIP-1α); or CXCL8, also known as IL-8) could be employed alone or in combination with other mobilizing agents (e.g., G-CSF or Plerixafor (AMD3100)). We discuss the current state of knowledge about chemokine receptor agonists and the rationale for their application in mobilization protocols.

EXPERT OPINION

Evidence is accumulating that CXCR4 receptor agonists could be employed alone or with other agents as mobilizing drugs. In particular they may provide an alternative for patients that are poor mobilizers.

MicroRNA126 contributes to granulocyte colony-stimulating factor-induced hematopoietic progenitor cell mobilization by reducing the expression of vascular cell adhesion molecule 1

BACKGROUND

Mobilization of hematopoietic stem/progenitor cells from the bone marrow to the peripheral blood by granulocyte colony-stimulating factor is the primary means to acquire stem cell grafts for hematopoietic cell transplantation. Since hematopoietic stem/progenitor cells represent a minority of all blood cells mobilized by granulocyte colony-stimulating factor, the underlying mechanisms need to be understood in order to develop selective drugs.

DESIGN AND METHODS

We analyzed phenotypic, biochemical and genetic changes in bone marrow cell populations from granulocyte colony-stimulating factor-mobilized and control mice, and linked such changes to effective mobilization of hematopoietic stem/progenitor cells.

RESULTS

We show that granulocyte colony-stimulating factor indirectly reduces expression of surface vascular cell adhesion molecule 1 on bone marrow hematopoietic stem/progenitor cells, stromal cells and endothelial cells by promoting the accumulation of microRNA-126 (miR126)-containing microvescicles in the bone marrow extracellular compartment. We found that hematopoietic stem/progenitor cells, stromal cells and endothelial cells readily incorporate these miR126-loaded microvescicles, and that miR126 represses vascular cell adhesion molecule 1 expression on bone marrow hematopoietic stem/progenitor cells, stromal cells and endothelial cells. In line with this, miR126-null mice displayed a reduced mobilization response to granulocyte colony-stimulating factor.

CONCLUSIONS

Our results implicate miR126 in the regulation of hematopoietic stem/progenitor cell trafficking between the bone marrow and peripheral sites, clarify the role of vascular cell adhesion molecule 1 in granulocyte colony-stimulating factor-mediated mobilization, and have important implications for improved approaches to selective mobilization of hematopoietic stem/progenitor cells.

The chemokine system in allogeneic stem-cell transplantation: a possible therapeutic target?

Further improvements in allogeneic stem-cell transplantation will probably depend on a better balance between immunosuppression to control graft-versus-host disease and immunological reconstitution sufficient to ensure engraftment, reduction of infection-related mortality and maintenance of post-transplant antileukemic immune reactivity. The chemokine network is an important part of the immune system, and, in addition, CXCL12/CXCR4 seem to be essential for granulocyte colony-stimulating factor-induced stem-cell mobilization. Partial ex vivo graft T-cell depletion based on the expression of specific chemokine receptors involved in T-cell recruitment to graft-versus-host disease target organs may also become a future therapeutic strategy; an alternative approach could be pharmacological inhibition (single-receptor inhibitors or dual-receptor inhibitors) in vivo of specific chemokine receptors involved in this T-cell recruitment. Future clinical studies should therefore be based on a better characterization of various immunocompetent cells, including their chemokine receptor profile, both in the allografts and during post-transplant reconstitution.

A novel perspective on stem cell homing and mobilization: review on bioactive lipids as potent chemoattractants and cationic peptides as underappreciated modulators of responsiveness to SDF-1 gradients

Hematopoietic stem progenitor cells (HSPCs) respond robustly to α-chemokine stromal-derived factor-1 (SDF-1) gradients, and blockage of CXCR4, a seven-transmembrane-spanning G(αI)-protein-coupled SDF-1 receptor, mobilizes HSPCs into peripheral blood. Although the SDF-1-CXCR4 axis has an unquestionably important role in the retention of HSPCs in bone marrow (BM), new evidence shows that, in addition to SDF-1, the migration of HSPCs is directed by gradients of the bioactive lipids sphingosine-1 phosphate and ceramide-1 phosphate. Furthermore, the SDF-1 gradient may be positively primed/modulated by cationic peptides (C3a anaphylatoxin and cathelicidin) and, as previously demonstrated, HSPCs respond robustly even to very low SDF-1 gradients in the presence of priming factors. In this review, we discuss the role of bioactive lipids in stem cell trafficking and the consequences of HSPC priming by cationic peptides. Together, these phenomena support a picture in which the SDF-1-CXCR4 axis modulates homing, BM retention and mobilization of HSPCs in a more complex way than previously envisioned.

Heparan sulfate mimetics can efficiently mobilize long-term hematopoietic stem cells

BACKGROUND

Although mobilization of hematopoietic stem cells and hematopoietic progenitor cells can be achieved with a combination of granulocyte colony-stimulating factor and plerixafor (AMD3100), improving approaches for hematopoietic progenitor cell mobilization is clinically important.

DESIGN AND METHODS

Heparan sulfate proteoglycans are ubiquitous macromolecules associated with the extracellular matrix that regulates biology of hematopoietic stem cells. We studied the effects of a new family of synthetic oligosaccharides mimicking heparan sulfate on hematopoietic stem cell mobilization. These oligosaccharides were administered intravenously alone or in combination with granulocyte colony-stimulating factor and/or AMD3100 in mice. Mobilized hematopoietic cells were counted and phenotyped at different times and the ability of mobilized hematopoietic stem cells to reconstitute long-term hematopoiesis was determined by competitive transplantation into syngenic lethally irradiated mice followed by secondary transplantation.

RESULTS

Mimetics of heparan sulfate induced rapid mobilization of B-lymphocytes, T-lymphocytes, hematopoietic stem cells and hematopoietic progenitor cells. They increased the mobilization of hematopoietic stem cells and hematopoietic progenitor cells more than 3-fold when added to the granulocyte colony-stimulating factor/AMD3100 association. Hematopoietic stem cells mobilized by mimetics of heparan sulfate or by the granulocyte colony-stimulating factor/AMD3100/mimetics association were as effective as hematopoietic stem cells mobilized by the granulocyte colony-stimulating factor/AMD3100 association for primary and secondary hematopoietic reconstitution of lethally irradiated mice.

CONCLUSIONS

This new family of mobilizing agents could alone or in combination with granulocyte colony-stimulating factor and/or AMD3100 mobilize a high number of hematopoietic stem cells that were able to maintain long-term hematopoiesis. These results strengthen the role of heparan sulfates in the retention of hematopoietic stem cells in bone marrow and support the use of small glyco-drugs based on heparan sulfate in combination with granulocyte colony-stimulating factor and AMD3100 to improve high stem cell mobilization, particularly in a prospect of use in human therapeutics.

Mobilization of hematopoietic stem and leukemia cells

HSC mobilization is an essential homeostatic process during inflammation and for the maintenance of hematopoietic progenitors. It has been exploited for the therapeutic application of HSC transplantation. Recent evidence suggests that leukemic cells share surface molecules in common with stem cells and may be mobilized under similar conditions. This effect could be used for therapeutic interventions. In this review, we will provide evidence showing that leukemia cells and stem cells traffic similarly and may share a common niche. Studies are discussed comparing and contrasting the mechanism of normal stem cells and leukemic cell mobilization through the CXCR4/CXCL12 axis and other key intermediaries.

Insights into the mechanism of enhanced mobilization of hematopoietic progenitor cells and release of CXCL12 by a combination of AMD3100 and aminoglycoside-polyarginine conjugates

Mobilization of hematopoietic stem and progenitor cells (HSPCs) from the bone marrow to the peripheral blood is utilized in clinical HSPC transplantation protocols. Retention of HSPCs in the bone marrow is determined by relationships between the chemokine chemokine (C-X-C motif) ligand 12 (CXCL12) and its major receptor C-X-C chemokine receptor type 4 (CXCR4), and disruption of this retention by CXCR4 antagonists such as AMD3100 induces rapid HSPC mobilization. Here, we report that aminoglycoside-polyarginine conjugates (APACs) and N-α-acetyl-nona-D-arginine (r9) induce mobilization of white blood cells and, preferentially, immature hematopoietic progenitor cells (HPCs) in mice, similarly to AMD3100. Remarkably, administration of AMD3100 with each one of the APACs or r9 caused additional HPC mobilization. The mobilizing activity of APACs and r9 was accompanied by a significant elevation in plasma CXCL12 levels. To further understand how APACs, r9 and their combinations with AMD3100 compete with CXCL12 binding to CXCR4, as well with antibody against CXCR4 for CXCR4 binding, we have undertaken an approach combining experimental validation and docking to determine plausible binding modes for these ligands. On the basis of our biological and docking findings, and recently published NMR data, we suggest that combination of pairs of compounds such as APACs (or r9) with AMD3100 induces more efficient disruption of the CXCL12-CXCR4 interaction than AMD3100 alone, resulting in enhanced HPC mobilization.

The ins and outs of hematopoietic stem cells: studies to improve transplantation outcomes

Deciphering the mechanisms of hematopoietic stem/progenitor cell (HSPC) mobilization and homing is important for the development of strategies to enhance the efficacy of HSPC transplantation and achieve the full potential of HSPC-based cellular therapy. Investigation of these mechanisms has revealed interdependence among the various molecules, pathways and cellular components involved, and underscored the complex nature of these two processes. This review summarizes recent progress in identifying the specific factors implicated in HSPC mobilization and homing, with emphasis on our own work. Particularly, we will discuss our studies on stromal cell-derived factor-1 and its interaction with its receptor CXCR4, proteases (matrix metalloproteinases and carboxypeptidase M), complement proteins (C1q, C3a, C5a, membrane attack complex), sphingosine-1-phosphate, and pharmacologic agents such as the histone deacetylase inhibitor valproic acid and hyaluronic acid.

Chondrogenesis by chemotactic homing of synovium, bone marrow, and adipose stem cells in vitro

Cell transplantation has been well explored for cartilage regeneration. We recently showed that the entire articular surface of a synovial joint can regenerate by endogenous cell homing and without cell transplantation. However, the sources of endogenous cells that regenerate articular cartilage remain elusive. Here, we studied whether cytokines not only chemotactically recruit adipose stem cells (ASCs), mesenchymal stem cells (MSCs), and synovium stem cells (SSCs) but also induce chondrogenesis of the recruited cells. Recombinant human transforming growth factor-β3 (TGF-β3; 100 ng) and/or recombinant human stromal derived factor-1β (SDF-1β; 100 ng) was control released into an acellular collagen sponge cube with underlying ASCs, MSCs, or SSCs in monolayer culture. Although all cell types randomly migrated into the acellular collagen sponge cube, TGF-β3 and/or SDF-1β recruited significantly more cells than the cytokine-free control group. In 6 wk, TGF-β3 alone recruited substantial numbers of ASCs (558±65) and MSCs (302±52), whereas codelivery of TGF-β3 and SDF-1β was particularly chemotactic to SSCs (400±120). Proliferation of the recruited cells accounted for some, but far from all, of the observed cellularity. TGF-β3 and SDF-1β codelivery induced significantly higher aggrecan gene expression than the cytokine-free group for ASCs, MSCs, and SSCs. Type II collagen gene expression was also significantly higher for ASCs and SSCs by SDF-1 and TGF-β3 codelivery. Remarkably, the expression of aggrecan and type II collagen was detected among all cell types. Thus, homing of multiple stem/progenitor cell populations may potentially serve as an alternative or adjunctive approach to cell transplantation for cartilage regeneration.

Stem Cell Transplantation for Lymphoma Patients with HIV Infection

The advent of Highly Active Antiretroviral Therapy (HAART) has radically changed incidence characteristics and prognosis of HIV-positive patients affected by lymphomas. At this time there is consensus in the literature that, in first line, HIV-positive patients should always be treated with curative intent preferentially following the same approach used in the HIV-negative counterpart. On the contrary, an approach of salvage therapy in HIV-positive lymphomas is still a matter of debate given that for a wide range of relapsed or resistant HIV-negative Hodgkin's disease (HD) and non-Hodgkin lymphoma (NHL) patients, autologous peripheral or allogeneic stem cell transplantation are among the established options. In the pre-HAART era, therapeutic options derived from pioneering experiences gave only anecdotal success, either when transplantation was used to cure lymphomas or to improve HIV infection itself. Concerns relating to the entity, quality, and kinetics of early and late immune reconstitutions and the possible worsening of underlying viroimmunological conditions were additional obstacles. Currently, around 100 relapsed or resistant HIV-positive lymphomas have been treated with an autologous peripheral stem cell transplantation (APSCT) in the HAART era. Published data compared favorably with any previous salvage attempt showing a percentage of complete remission ranging from 48% to 90%, and overall survival ranging from 36% to 85% at median follow-up approaching 3 years. However, experiences are still limited and have given somewhat confounding indications, especially concerning timing and patients' selection for APSCT and feasibility and outcome for allogeneic stem cell transplant. Moreover, little data exist on the kinetics of immunological reconstitution after APSCT or relevant to the outcome of HIV infection. The aim of this review is to discuss current knowledge of the role of allogeneic and autologous stem cell transplantation as a modality in the cure of HIV and hemopoietic cancer patients. Several topics dealing with practical aspects concerning the management of APSCT in HIV-positive patients, including patient selection, timing of transplant, conditioning regimen, and relapse or nonrelapse mortality, are discussed. Data relating to the effects of mobilization and transplantation on virological parameters and pre- and posttransplant immune reconstitution are reviewed. Finally, in this review, we examine several ethical and legal issues relative to banking infected or potentially infected peripheral blood stem cells and we describe our experience and strategies to protect positive and negative donors/recipients and the health of caretakers.

Increased mobilization and yield of stem cells using plerixafor in combination with granulocyte-colony stimulating factor for the treatment of non-Hodgkin's lymphoma and multiple myeloma

Multiple myeloma and non-Hodgkin’s lymphoma remain the most common indications for high-dose chemotherapy and autologous peripheral blood stem cell rescue. While a CD34+ cell dose of 1 × 10⁶/kg is considered the minimum required for engraftment, higher CD34+ doses correlate with improved outcome. Numerous studies, however, support targeting a minimum CD34+ cell dose of 2.0 × 10⁶/kg, and an “optimal” dose of 4 to 6 × 10⁶/kg for a single transplant. Unfortunately, up to 40% of patients fail to mobilize an optimal CD34+ cell dose using myeloid growth factors alone. Plerixafor is a novel reversible inhibitor of CXCR4 that significantly increases the mobilization and collection of higher numbers of hematopoietic progenitor cells. Two randomized multi-center clinical trials in patients with non-Hodgkin’s lymphoma and multiple myeloma have demonstrated that the addition of plerixafor to granulocyte-colony stimulating factor increases the mobilization and yield of CD34+ cells in fewer apheresis days, which results in durable engraftment. This review summarizes the pharmacology and evidence for the clinical efficacy of plerixafor in mobilizing hematopoietic stem and progenitor cells, and discusses potential ways to utilize plerixafor in a cost-effective manner in patients with these diseases.

CCR7 impairs hematopoiesis after hematopoietic stem cell transplantation increasing susceptibility to invasive aspergillosis

Hematopoietic stem cell transplantation (HSCT) is limited by patient susceptibility to opportunistic infections. One of the most devastating infections after HSCT is invasive aspergillosis (IA), a life-threatening disease caused by Aspergillus fumigatus. Transplantation of hematopoietic stem cells (HSCs) and myeloid progenitor cells (MPCs) has been shown to mediate protection against IA, but little is known about the factors that regulate HSC and MPC cell expansion after transplantation. Herein, we investigated the role of CCR7 in a murine model of IA after combined HSC and MPC transplantation into lethally irradiated wild-type (WT) mice. Nonirradiated CCR7−/− mice had expanded populations of HSCs in the bone marrow and spleen, compared with WT mice. Irradiated WT mice reconstituted with CCR7−/− HSCs and MPCs had increased survival, decreased fungal burden, and enhanced myeloid leukocyte numbers during IA, compared with WT controls. In addition, WT mice reconstituted with WT HSCs and MPCs and treated with anti-CCR7 exhibited accelerated myeloid cell expansion similar to that observed in CCR7−/−→WT chimeras. Thus, removal of the inhibitory effects of CCR7 through genetic alteration or ligand immunoneutralization enhanced myeloid reconstitution, thereby accelerating fungal clearance in a murine model of IA.

Adipose tissue-derived progenitor cells and cancer

Recruitment of stem cells and partially differentiated progenitor cells is a process which accompanies and facilitates the progression of cancer. One of the factors complicating the clinical course of cancer is obesity, a progressively widespread medical condition resulting from overgrowth of white adipose tissue (WAT), commonly known as white fat. The mechanisms by which obesity influences cancer risk and progression are not completely understood. Cells of WAT secret soluble molecules (adipokines) that could stimulate tumor growth, although there is no consensus on which cell populations and which adipokines are important. Recent reports suggest that WAT-derived mesenchymal stem (stromal) cells, termed adipose stem cells (ASC), may represent a cell population linking obesity and cancer. Studies in animal models demonstrate that adipokines secreted by ASC can promote tumor growth by assisting in formation of new blood vessels, a process necessary for expansion of tumor mass. Importantly, migration of ASC from WAT to tumors has been demonstrated, indicating that the tumor microenvironment in cancer may be modulated by ASC-derived trophic factors in a paracrine rather than in an endocrine manner. Here, we review possible positive and adverse implications of progenitor cell recruitment into the diseased sites with a particular emphasis on the role in cancer progression of progenitors that are expanded in obesity.

Innate immunity as orchestrator of stem cell mobilization

Hematopoietic stem and progenitor cells (HSPCs), as well as other types of stem cells, circulate under steady-state conditions at detectable levels in peripheral blood (PB), with their numbers increasing in response to stress, inflammation and tissue/organ injury. This mobilization process may be envisioned as a danger-sensing response mechanism triggered by hypoxia or mechanical or infection-induced tissue damage that recruits into PB different types of stem cells that have a role in immune surveillance and organ/tissue regeneration. Mobilization is also significantly enhanced by the administration of pharmacological agents, which has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present mounting evidence that innate immunity orchestrates this evolutionarily conserved mechanism of HSPC mobilization.

Recent advances on the use of the CXCR4 antagonist plerixafor (AMD3100, Mozobil™) and potential of other CXCR4 antagonists as stem cell mobilizers

AMD3100 was originally discovered as an anti-HIV agent effective in inhibiting the replication of HIV in vitro at nanomolar concentrations. We found it to be a potent and selective antagonist of CXCR4, the receptor for the chemokine SDF-1 (now called CXCL12). AMD3100 was then developed, and marketed, as a stem cell mobilizer, and renamed plerixafor (Mozobil™). The path to the discovery of Mozobil™ as a stem cell mobilizer was described in Biochem. Pharmacol. 77: 1655-1664 (2009). Here I review the recent advances that have consolidated the role of plerixafor in mobilizing hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) from the bone marrow into the blood circulation. Plerixafor acts synergistically with granulocyte colony-stimulating factor (G-CSF), and its usefulness has been proven particularly for the mobilization of HSCs and HPCs for autologous stem cell transplantation in patients with non-Hodgkin's lymphoma (NHL) or multiple myeloma (MM). Plerixafor also has great potential for the treatment of hematological malignancies other than NHL and MM, and non-hematological malignancies, and, eventually, several other diseases depending on the CXCL12-CXCR4 interaction. Various AMD3100 analogs have been described (i.e. AMD11070, AMD3465, KRH-3955, T-140, and 4F-benzoyl-TN14003), primarily as potential anti-HIV agents. They are all strong CXCR4 antagonists. Their role in stem cell mobilization remains to be assessed.

Hypercholesterolemia promotes bone marrow cell mobilization by perturbing the SDF-1:CXCR4 axis

Hypercholesterolemia is associated with elevated peripheral blood leukocytes and increased platelet levels, generally attributed to cholesterol-induced proinflammatory cytokines. Bone marrow (BM) cell mobilization and platelet production is achieved by disrupting the SDF-1:CXCR4 axis, namely with granulocyte colony-stimulating factor and/or CXCR4 antagonists. Here we show that high cholesterol disrupts the BM SDF-1:CXCR4 axis; promotes the mobilization of B cells, neutrophils, and progenitor cells (HPCs); and creates thrombocytosis. Hypercholesterolemia was achieved after a 30-day high-cholesterol feeding trial, resulting in elevated low-density lipoprotein (LDL) cholesterol levels and inversion of the LDL to high-density lipoprotein cholesterol ratio. Hypercholesterolemic mice displayed lymphocytosis, increased neutrophils, HPCs, and thrombocytosis with a lineage-specific decrease in the BM. Histologic analysis revealed that megakaryocyte numbers remained unaltered but, in high-cholesterol mice, they formed large clusters in contact with BM vessels. In vitro, LDL induced stromal cell–derived factor-1 (SDF-1) production, suggesting that megakaryocyte delocalization resulted from an altered SDF-1 gradient. LDL also stimulated B cells and HPC migration toward SDF-1, which was blocked by scavenger receptor class B type I (cholesterol receptor) inhibition. Accordingly, hypercholesterolemic mice had increased peripheral blood SDF-1 levels, increased platelets, CXCR4-positive B lymphocytes, neutrophils, and HPCs. High cholesterol interferes with the BM SDF-1:CXCR4 axis, resulting in lymphocytosis, thrombocytosis, and HPC mobilization.

Chemokine expression in renal ischemia/reperfusion injury is most profound during the reparative phase

Chemokines are important players in the migration of leukocytes to sites of injury and are also involved in angiogenesis, development and wound healing. In this study, we performed microarray analyses to identify chemokines that play a role during the inflammatory and repair phase after renal ischemia/reperfusion (I/R) injury and investigated the temporal relationship between chemokine expression, leukocyte accumulation and renal damage/repair. C57Bl/6 mice were subjected to unilateral ischemia for 45 min and sacrificed 3 h, 1 day and 7 days after reperfusion. From ischemic and contralateral kidney, RNA was isolated and hybridized to a microarray. Microarray results were validated with quantitative real-time reverse transcription–PCR (QRT–PCR) on RNA from an independent experiment. (Immuno)histochemical analyses were performed to determine renal damage/repair and influx of leukocytes. Twenty out of 114 genes were up-regulated at one or more reperfusion periods. All these genes were up-regulated 7 days after I/R. Up-regulated genes included CC chemokines MCP-1 and TARC, CXC chemokines KC and MIP-2α, chemokine receptors Ccr1 and Cx3cr1 and related genes like matrix metalloproteinases. Microarray data of 1 and 7 days were confirmed for 17 up-regulated genes by QRT–PCR. (Immuno)histochemical analysis showed that the inflammatory and repair phase after renal I/R injury take place after, respectively, 1 and 7 days. Interestingly, chemokine expression was highest during the repair phase. In addition, expression profiles showed a biphasic expression of all up-regulated CXC chemokines coinciding with the early inflammatory and late repair phase. In conclusion, we propose that temporal expression of chemokines is a crucial factor in the regulation of renal I/R injury and repair.

Mobilization studies in complement-deficient mice reveal that optimal AMD3100 mobilization of hematopoietic stem cells depends on complement cascade activation by AMD3100-stimulated granulocytes

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during mobilization of hematopoietic stem/progenitor cells (HSPCs) induced by granulocyte colony-stimulating factor (G-CSF) and C5 cleavage has an important function in optimal egress of HSPCs. In this work, we explored whether CC is involved in mobilization of HSPCs induced by the CXCR4 antagonist, AMD3100. To address this question, we performed mobilization studies in mice that display a defect in the activation of the proximal steps of CC (Rag(-/-), severe combined immune deficient (SCID), C2.Cfb(-/-)) as well as in mice that do not activate the distal steps of CC (C5(-/-)). We noticed that proximal CC activation-deficient mice (above C5 level), in contrast to distal step CC activation-deficient C5(-/-) ones, mobilize normally in response to AMD3100 administration. We hypothesized that this discrepancy in mobilization could be explained by AMD3100-activating C5 in Rag(-/-), SCID, and C2.Cfb(-/-) animals in a non-canonical mechanism involving activated granulocytes. To support this, granulocytes (i) first egress from BM and (ii) secrete several proteases that cleave/activate C5 in response to AMD3100. We conclude that AMD3100-directed mobilization of HSPCs, similarly to G-CSF-induced mobilization, depends on activation of CC; however, in contrast to G-CSF, AMD3100 activates the distal steps of CC directly at the C5 level. Overall, these data support that C5 cleavage fragments and distal steps of CC activation are required for optimal mobilization of HSPCs.

Troubleshooting: Quantification of mobilization of progenitor cell subsets from bone marrow in vivo

INTRODUCTION

The molecular mechanisms that control the mobilization of specific stem cell subsets from the bone marrow are currently being intensely investigated. It is anticipated that boosting the mobilization of these stem cells via pharmacological intervention will not only produce more effective strategies for bone marrow transplant patients, but also provide novel therapeutic approaches for tissue regeneration.

METHODS

Measurement of stem cell mobilization by sampling peripheral blood is problematic because it is technically difficult to accurately determine absolute numbers of rare progenitor cells by blood sampling. Furthermore a rise in progenitors may be caused by release of stem cells from tissues other than the bone marrow (e.g. spleen and adipose), or indeed an inhibition of stem cell homing back to the bone marrow or other tissues. Finally it is not possible to distinguish whether the pharmacological agent is acting directly at the level of the bone marrow or mobilizing progenitors by a distinct indirect mechanism. To resolve these problems, we have developed a technique that allows perfusion of the vasculature of the hind limb bone marrow in situ in mice. In this system, the femoral artery and vein are cannulated in situ such that the femur and tibia bone marrow are perfused in isolation under anaesthesia. As such, pharmacological agents can be administered directly into the bone marrow vasculature. Mobilized cells are then collected via the femoral vein and colony assays performed in defined growth media to allow identification of haematopoietic, endothelial, and mesenchymal progenitor cells. We have used this system to determine the ability of a CXCR4 antagonist to mobilize these distinct types of progenitor cells from the bone marrow of mice pre-conditioned with either G-CSF or VEGF.

RESULTS AND CONCLUSION

This isolated hind limb perfusion system has allowed comparisons to be made between cytokines (G-CSF and VEGF) that act chronically, either alone or in combination with agents that act acutely on the bone marrow (CXCR4 antagonist) on their ability to directly mobilize specific populations of stem cells. Data obtained therefore gives a more accurate understanding of the efficacy of different mobilizing strategies compared to peripheral blood analysis.

The role of stromal-derived factor-1--CXCR7 axis in development and cancer

Cancer metastasis is a major clinical problem that contributes to unsuccessful therapy. Augmenting evidence indicates that metastasizing cancer cells employ several mechanisms that are involved in developmental trafficking of normal stem cells. Stromal-derived factor-1 (SDF-1) is an important alpha-chemokine that binds to the G-protein-coupled seven-transmembrane span CXCR4. The SDF-1-CXCR4 axis regulates trafficking of normal and malignant cells. SDF-1 is an important chemoattractant for a variety of cells including hematopoietic stem/progenitor cells. For many years, it was believed that CXCR4 was the only receptor for SDF-1. However, several reports recently provided evidence that SDF-1 also binds to another seven-transmembrane span receptor called CXCR7, sharing this receptor with another chemokine family member called Interferon-inducible T-cell chemoattractant (I-TAC). Thus, with CXCR7 identified as a new receptor for SDF-1, the role of the SDF-1-CXCR4 axis in regulating several biological processes becomes more complex. Based on the available literature, this review addresses the biological significance of SDF-1's interaction with CXCR7, which may act as a kind of decoy or signaling receptor depending on cell type. Augmenting evidence suggests that CXCR7 is involved in several aspects of tumorogenesis and could become an important target for new anti-metastatic and anti-cancer drugs.

The remodeling of cardiovascular bioprostheses under influence of stem cell homing signal pathways

Optimizing current heart valve replacement strategies by creating living prostheses is a necessity to alleviate complications with current bioprosthetic devices such as calcification and degeneration. Regenerative medicine, mostly in vitro tissue engineering, is the forerunner of this optimization search, yet here we show the functionality of an in vivo alternative making use of 2 homing axes for stem cells. In rats we studied the signaling pathways of stem cells on implanted bioprosthetic tissue (photooxidized bovine pericardium (POP)), by gene and protein expression analysis. We found that SDF-1alpha/CXCR4 and FN/VLA4 homing axes play a role. When we implanted vascular grafts impregnated with SDF-1alpha and/or FN as carotid artery interpositions, primitive cells were attracted from the circulation. Next, bioprosthetic heart valves, constructed from POP impregnated with SDF-1alpha and/or FN, were implanted in pulmonary position. As shown by CD90, CD34 and CD117 immunofluorescent staining they became completely recellularized after 5 months, had a normal function and biomechanical properties and specifically the combination of SDF-1alpha and FN had an optimal valve-cell phenotype.

Defective engraftment of C3aR-/- hematopoietic stem progenitor cells shows a novel role of the C3a-C3aR axis in bone marrow homing

We reported that complement (C) becomes activated and cleaved in bone marrow during preconditioning for hematopoietic transplantation and the third C component (C3) cleavage fragments, C3a and (desArg)C3a, increase responsiveness of hematopoietic stem/progenitor cells (HSPCs) to stromal-derived factor-1 (SDF-1). We also showed that this homing-promoting effect is not C3a receptor (C3aR) dependent. Herein, we report our new observation that transplantation of C3aR(-/-) HSPCs into lethally irradiated recipients results in: (1) approximately 5-7 day delay in recovery of platelets and leukocytes; (2) decrease in formation of day 12 colony-forming units-spleen; and (3) decrease in the number of donor-derived CFU-granulocyte-macrophage progenitors detectable in the bone marrow cavities at day 16 after transplantation. In agreement with the murine data, blockage of C3aR on human umbilical cord blood CD34(+) cells by C3aR antagonist SB290157 impairs their engraftment in non-obese diabetic/severe combined immunodeficient mice. However, HSPCs from C3aR(-/-) mice stimulated by C3a still better responded to SDF-1 gradient, after exposure to C3a, they secrete less matrix metalloprotease-9 and show impaired adhesion to stroma cells. We conclude that C3a, in addition to enhancing responsiveness of HSPCs to SDF-1 gradient in a C3aR independent manner, may also directly modulate HSPC homing by augmenting C3aR-mediated secretion of matrix metalloprotease-9 and cell adhesion.

Functional diversity of SDF-1 splicing variants

SDF-1 is ubiquitously expressed in vertebrate tissues in a constitutive manner. It performs an essential role in cell migration and proliferation as well as participates in tissue-specific physiological processes such as neuromodulation. It is also involved in many pathological processes including: HIV infection, metastatic malignancy, chronic inflammatory disorders and benign proliferative diseases. SDF-1 is mostly regulated at the splicing, and not transcriptional level. Different splicing variants share agonist potency to their cognate receptor, CXCR4, but are characterized by distinct properties. SDF-1alpha is the predominant isoform found in all organs, but undergoes rapid proteolysis in blood. SDF-1beta is more resistant to blood-dependent degradation, stimulates angiogenesis and is present in highly vascularized organs such as: the liver, spleen and kidneys. In contrast, SDF-1gamma is located in very active, less vascularized organs susceptible to infarction such as the heart and the brain. The understanding of the functional diversity of the different splicing variants will help in developing therapeutic strategies.