Human CD34(+)CXCR4(-) sorted cells harbor intracellular CXCR4, which can be functionally expressed and provide NOD/SCID repopulation

Prostaglandin E2 as transduction enhancer affects competitive engraftment of human hematopoietic stem and progenitor cells

Ex vivo gene therapy (GT) is a promising treatment for inherited genetic diseases. An ideal transduction protocol should determine high gene marking in long-term self-renewing hematopoietic stem cells (HSCs), preserving their repopulation potential during in vitro manipulation. In the context of the improvement of a clinically applicable transduction protocol, we tested prostaglandin E2 (PGE2) as a transduction enhancer (TE). The addition of PGE2 shortly before transduction of human CD34+ cells determined a significant transduction increase in the in vitro cell progeny paralleled by a significant reduction of their clonogenic potential. This effect increased with the duration of PGE2 exposure and correlated with an increase of CXCR4 expression. Blockage of CXCR4 with AMD3100 (plerixafor, Mozobil) did not affect transduction efficiency but partially rescued CD34+ clonogenic impairment in vitro. Once transplanted in vivo in a competitive repopulation assay, human CD34+ cells transduced with PGE2 contributed significantly less than cells transduced with a standard protocol to the repopulation of recipient mice, indicating a relative repopulation disadvantage of the PGE2-treated CD34+ cells and a counter-selection for the PGE2-treated cell progeny in vivo. In conclusion, our data indicate the need for risk/benefit evaluations in the use of PGE2 as a TE for clinical protocols of GT.

Design, synthesis, and evaluation of pyrrolidine based CXCR4 antagonists with in vivo anti-tumor metastatic activity

The chemokine receptor CXCR4 has been proposed as a drug target based on its important functions in HIV infection, inflammation/autoimmune diseases and cancer metastasis. Herein we report the design, synthesis and evaluation of novel CXCR4 antagonists based on a pyrrolidine scaffold. The structural exploration/optimization identified numerous potent CXCR4 antagonists, represented by compound 46, which displayed potent binding affinity to CXCR4 receptor (IC₅₀ = 79 nM competitively displacing fluorescent 12G5 antibody) and inhibited CXCL12 induced cytosolic calcium flux (IC₅₀ = 0.25 nM). Moreover, in a transwell invasion assay, compound 46 significantly mitigated CXCL12/CXCR4 mediated cell migration. Compound 46 exhibited good physicochemical properties (MW 367, logD_7.4 1.12, pKa 8.2) and excellent in vitro safety profiles (e.g., hERG patch clamp IC₅₀ > 30 μM and minimal CYP isozyme inhibition). Importantly, 46 displayed much improved metabolic stability in human and rat liver microsomes. Lastly, 46 demonstrated marked efficacy in a cancer metastasis model in mice. These results strongly support 46 as a prototypical lead for the development of promising CXCR4 antagonists as clinical candidates.

Design, Synthesis, and Characterization of Novel CXCR4 Antagonists Featuring Cyclic Amines

Chemokine receptor CXCR4 and its natural ligand CXCL12 (also known as stromal cell-derived factor-1, or SDF-1) regulate a broad range of physiological functions. Dysregulation of the CXCL12/CXCR4 axis is involved in numerous pathological conditions such as HIV infection, inflammation and cancer. Herein, we report the design, synthesis, and characterization of novel CXCR4 antagonists based on cyclic amine scaffolds. Compound 24 was identified as a potent CXCR4 receptor antagonist (competitive inhibition of 12G5 binding, IC₅₀ =24 nM; functional inhibition of CXCL12-induced cytosolic calcium increase, IC₅₀ =0.1 nM). In addition, compound 24 potently inhibited cell migration in CXCR4/CXCL12-mediated chemotaxis in a matrigel invasion assay. The absolute configuration of compound 24 was elucidated by X-ray crystallography.

Design, synthesis, and evaluation of novel CXCR4 antagonists based on an aminoquinoline template

The chemokine receptor CXCR4 has been explored as a drug target due to its involvement in pathological conditions such as HIV infection and cancer metastasis. Here we report the structure-activity relationship study of novel CXCR4 antagonists based on an aminoquinoline template. This template is devoid of the chiral center in the classical tetrahydroquinoline (THQ) ring moiety and therefore can be easily synthesized. A number of potent CXCR4 antagonists were identified, exemplified by compound 3, which demonstrated excellent binding affinity with CXCR4 receptor (IC₅₀ = 57 nM) and inhibited CXCL12 induced cytosolic calcium increase (IC₅₀ = 0.24 nM). Furthermore, compound 3 potently inhibited CXLC12/CXCR4 mediated cell migration in a transwell invasion assay. The simplified synthetic approach combined with good physicochemical properties (e.g. MW 362, clogP 2.1, PSA 48, pKa 7.0 for compound 3) demonstrate the potential of this aminoquinoline template as a novel scaffold to develop CXCR4 antagonists.

Guanxin Danshen Formulation improved the effect of mesenchymal stem cells transplantation for the treatment of myocardial infarction probably via enhancing the engraftment

Although intravenous injection is the most convenient and feasible approach for mesenchymal stem cells (MSCs) delivery, the proportion of donor stem cells in the target myocardium after transplantation is small. It is believed that TCM enhances the effect of stem cell therapy by improving the hostile microenvironment and promoting the migration and survival of stem cells. Guanxin Danshen (GXDS) formulation is one of the main prescriptions for clinical treatment of ischemic heart diseases in China. The purpose of this study was to evaluate the effects of GXDS formulation administration combined with MSCs transplantation on cardiac function improvement, apoptosis, angiogenesis and survival of transplanted cells in an acute model of acute myocardial infarction (MI). After being labeled with GFP, MSCs were transplanted via intravenous injection. Meanwhile, GXDS dripping pills were given by intragastric administration for 4 weeks from 2 days before MI. Echocardiography showed moderate improvement in cardiac function after administration of GXDS formulation or intravenous transplantation of MSCs. However, GXDS formulation combined with MSCs transplantation significantly improved cardiac function after MI. The myocardial infarct size in rats treated with MSCs was similar to that in rats treated with GXDS formulation. However, GXDS formulation combined with MSCs transplantation significantly reduced infarction area. In addition, GXDS formulation combined with MSCs transplantation not only decreased cell apoptosis according to the TUNEL staining, but also enhanced angiogenesis in the peri-infarction and infarction area. Interestingly, the use of GXDS formulation increased the number of injected MSCs in the infarct area. Furthermore, GXDS formulation combined with MSCs transplantation increased SDF-1 levels in the infarcted area, but did not affect the expression of YAP. Our study provided a more feasible and accessible strategy to enhance the migration of stem cells after intravenous injection by oral administration of GXDS formulation. The combination of GXDS formulation and stem cell therapy has practical significance and application prospects in the treatment of ischemic cardiomyopathy such as MI.

Ultrastructural morphology is distinct among primary progenitor cell isolates from normal, inflamed, and cryopreserved equine hoof tissue and CD105+K14+ progenitor cells

The equine hoof dermal-epidermal interface requires progenitor cells with distinct characteristics. This study was designed to provide accurate ultrastructural depictions of progenitor cells isolated from inflamed tissue and normal tissue before and after cryopreservation and following selection of cells expressing both keratin (K) 14 (ectodermal) and cluster of differentiation (CD) 105 (mesodermal). Passage 3 cell ultrastructure was assessed following 2D culture and after 3D culture on decellularized hoof tissue scaffolds. Outcome measures included light, transmission electron, and scanning electron microscopy, immunocytochemistry, and CD105⁺K14⁺ cell trilineage plasticity. Cells from normal tissue had typical progenitor cell characteristics. Those from inflamed tissue had organelles and morphology consistent with catabolic activities including lysosomes, irregular rough endoplasmic reticulum, and fewer vacuoles and early endosomes than those from normal tissue. Cryopreserved tissue cells appeared apoptotic with an irregular cell membrane covered by cytoplasmic protrusions closely associated with endocytic and exocytic vesicles, chromatin aggregated on the nuclear envelop, abundant, poorly organized rough endoplasmic reticulum, and plentiful lysosomes. Cells that were CD105⁺K14⁺ were distinguishable from heterogenous cells by infrequent microvilli on the cell surface, sparse endosomes and vesicles, and desmosomes between cells. Cells expressed ectodermal (K15) and mesodermal (CD105) proteins in 2D and 3D cultures. Inflamed and cryopreserved tissue isolates attached poorly to tissue scaffold while normal tissue cells attached well, but only CD105⁺K14⁺ cells produced extracellular matrix after 4 d. The CD105⁺K14⁺ cells exhibited osteoblastic, adipocytic, and neurocytic differentiation. Ultrastructural information provided by this study contributes to understanding of equine hoof progenitor cells to predict their potential contributions to tissue maintenance, healing, and damage as well post-implantation behavior.

MiR-9 Controls Chemotactic Activity of Cord Blood CD34⁺ Cells by Repressing CXCR4 Expression

Improved approaches for promoting umbilical cord blood (CB) hematopoietic stem cell (HSC) homing are clinically important to enhance engraftment of CB-HSCs. Clinical transplantation of CB-HSCs is used to treat a wide range of disorders. However, an improved understanding of HSC chemotaxis is needed for facilitation of the engraftment process. We found that ectopic overexpression of miR-9 and antisense-miR-9 respectively down- and up-regulated C-X-C chemokine receptor type 4 (CXCR4) expression in CB-CD34⁺ cells as well as in 293T and TF-1 cell lines. Since CXCR4 is a specific receptor for the stromal cell derived factor-1 (SDF-1) chemotactic factor, we investigated whether sense miR-9 and antisense miR-9 influenced CXCR4-mediated chemotactic mobility of primary CB CD34⁺ cells and TF-1 cells. Ectopic overexpression of sense miR-9 and antisense miR-9 respectively down- and up-regulated SDF-1-mediated chemotactic cell mobility. To our knowledge, this study is the first to report that miR-9 may play a role in regulating CXCR4 expression and SDF-1-mediated chemotactic activity of CB CD34⁺ cells.

Repopulating hematopoietic stem cells from steady-state blood before and after ex vivo culture are enriched in the CD34+CD133+CXCR4low fraction

The feasibility of ex vivo expansion allows us to consider the steady-state peripheral blood as an alternative source of hematopoietic stem progenitor cells for transplantation when growth factor-induced cell mobilization is contraindicated or inapplicable. Ex vivo expansion dramatically enhances the in vivo reconstituting cell population from steady-state blood. In order to investigate phenotype and the expression of homing molecules, the expression of CD34, CD133, CD90, CD45RA, CD26 and CD9 was determined on sorted CD34⁺ cells according to CXCR4 (“neg”, “low” “bright”) and CD133 expression before and after ex vivo expansion. Hematopoietic stem cell activity was determined in vivo on the basis of hematopoietic repopulation of primary and secondary recipients - NSG immuno-deficient mice. In vivo reconstituting cells in the steady-state blood CD34⁺ cell fraction before expansion belong to the CD133⁺ population and are CXCR4^low or, to a lesser extent, CXCR4^neg, while after ex vivo expansion they are contained only in the CD133⁺CXCR4^low cells. The failure of the CXCR4^bright population to engraft is probably due to the exclusive expression of CD26 by these cells. The limiting-dilution analysis showed that both repopulating cell number and individual proliferative capacity were enhanced by ex vivo expansion. Thus, steady-state peripheral blood cells exhibit a different phenotype compared to mobilized and cord blood cells, as well as to those issued from the bone marrow. These data represent the first phenotypic characterization of steady-state blood cells exhibiting short- and long-term hematopoietic reconstituting potential, which can be expanded ex vivo, a sine qua non for their subsequent use for transplantation.

Design, synthesis, and structure-activity-relationship of a novel series of CXCR4 antagonists

The important roles of the CXCL12/CXCR4 axis in numerous pathogenic pathways involving HIV infection and cancer metastasis make the CXCR4 receptor an attractive target for the development of therapeutic agents. Through scaffold hybridization of a few known CXCR4 antagonists, a series of novel aminopyrimidine derivatives was developed. Compound 3 from this new scaffold demonstrates excellent binding affinity with CXCR4 receptor (IC₅₀ = 54 nM) and inhibits CXCL12 induced cytosolic calcium increase (IC₅₀ = 2.3 nM). Furthermore, compound 3 possesses good physicochemical properties (MW 353, clogP 2.0, PSA 48, pKa 6.7) and exhibits minimal hERG and CYP isozyme (e.g. 3A4, 2D6) inhibition. Collectively, these results strongly support further optimization of this novel scaffold to develop better CXCR4 antagonists.

Migration against the direction of flow is LFA-1-dependent in human hematopoietic stem and progenitor cells

The recruitment of immune cells during inflammation is regulated by a multi-step cascade of cell rolling, activation, adhesion and transmigration through the endothelial barrier. Similarly, hematopoietic stem and progenitor cells (HSPCs) use this pathway to migrate and home to the bone marrow. After selectin-mediated braking, HSPCs migrate on adhesion ligands presented by the vascular endothelium including ICAM-1, VCAM-1 or MAdCAM-1. Here, we report that both the KG1a stem cell line and primary bone marrow CD34⁺ HSPCs can migrate against the direction of fluid flow on surfaces coated with cell adhesion molecules (CAMs), a behavior thus far only reported in T lymphocytes. We demonstrate that KG1a cells and primary HSPCs migrate upstream on surfaces presenting ICAM-1, downstream on surfaces presenting VCAM-1, and both upstream and downstream on surfaces presenting MAdCAM-1. In addition, we demonstrate that KG1a cells and HSPCs display upstream migration both on surfaces with multiple CAMs, as well as on human umbilical vein endothelial cell (HUVEC) monolayers. By blocking with monoclonal antibodies, we show that lymphocyte function-associated antigen-1 (LFA-1) is the key receptor responsible for upstream migration on the endothelium during the trafficking of HSPCs to the bone marrow.This article has an associated First Person interview with the first author of the paper.

Harnessing CXCR4 antagonists in stem cell mobilization, HIV infection, ischemic diseases, and oncology

CXCR4 antagonists (e.g., Plerixafor^TM ) have been successfully validated as stem cell mobilizers for peripheral blood stem cell transplantation. Applications of the CXCR4 antagonists have heralded the era of cell-based therapy and opened a potential therapeutic horizon for many unmet medical needs such as kidney injury, ischemic stroke, cancer, and myocardial infarction. In this review, we first introduce the central role of CXCR4 in diverse cellular signaling pathways and discuss its involvement in several disease progressions. We then highlight the molecular design and optimization strategies for targeting CXCR4 from a large number of case studies, concluding that polyamines are the preferred CXCR4-binding ligands compared to other structural options, presumably by mimicking the highly positively charged natural ligand CXCL12. These results could be further justified with computer-aided docking into the CXCR4 crystal structure wherein both major and minor subpockets of the binding cavity are considered functionally important. Finally, from the clinical point of view, CXCR4 antagonists could mobilize hematopoietic stem/progenitor cells with long-term repopulating capacity to the peripheral blood, promising to replace surgically obtained bone marrow cells as a preferred source for stem cell transplantation.

Interleukin-3 enhances the migration of human mesenchymal stem cells by regulating expression of CXCR4

BACKGROUND

Mesenchymal stem cells (MSCs) represent an important source for cell therapy in regenerative medicine. MSCs have shown promising results for repair of damaged tissues in various degenerative diseases in animal models and also in human clinical trials. However, little is known about the factors that could enhance the migration and tissue-specific engraftment of exogenously infused MSCs for successful regenerative cell therapy. Previously, we have reported that interleukin-3 (IL-3) prevents bone and cartilage damage in animal models of rheumatoid arthritis and osteoarthritis. Also, IL-3 promotes the differentiation of human MSCs into functional osteoblasts and increases their in-vivo bone regenerative potential in immunocompromised mice. However, the role of IL-3 in migration of MSCs is not yet known. In the present study, we investigated the role of IL-3 in migration of human MSCs under both in-vitro and in-vivo conditions.

METHODS

MSCs isolated from human bone marrow, adipose and gingival tissues were used for in-vitro cell migration, motility and wound healing assays in the presence or absence of IL-3. The effect of IL-3 preconditioning on expression of chemokine receptors and integrins was examined by flow cytometry and real-time PCR. The in-vivo migration of IL-3-preconditioned MSCs was investigated using a subcutaneous matrigel-releasing stromal cell-derived factor-1 alpha (SDF-1α) model in immunocompromised mice.

RESULTS

We observed that human MSCs isolated from all three sources express IL-3 receptor-α (IL-3Rα) both at gene and protein levels. IL-3 significantly enhances in-vitro migration, motility and wound healing abilities of MSCs. Moreover, IL-3 preconditioning upregulates expression of chemokine (C-X-C motif) receptor 4 (CXCR4) on MSCs, which leads to increased migration of cells towards SDF-1α. Furthermore, CXCR4 antagonist AMD3100 decreases the migration of IL-3-treated MSCs towards SDF-1α. Importantly, IL-3 also induces in-vivo migration of MSCs towards subcutaneously implanted matrigel-releasing-SDF-1α in immunocompromised mice.

CONCLUSIONS

The present study demonstrates for the first time that IL-3 has an important role in enhancing the migration of human MSCs through regulation of the CXCR4/SDF-1α axis. These findings suggest a potential role of IL-3 in improving the efficacy of MSCs in regenerative cell therapy.

CD34-negative hematopoietic stem cells show distinct expression profiles of homing molecules that limit engraftment in mice and sheep

We and others have reported that human hematopoietic stem cells (HSCs) are also present in the CD34-negative (CD34^-) fraction of human cord blood (CB). Here, we examined the hematopoietic engraftment potential of 13 or 18 lineage-negative (13Lin^- or 18Lin^-) CD34^+/- cells from human CB in mice and sheep. Both 13Lin^- and 18Lin^- CD34⁺ cells efficiently engrafted in mice irrespective of transplantation route, be it by tail-vein injection (TVI) or by intra-bone marrow injection (IBMI). These cells also engrafted in sheep after in utero fetal intra-hepatic injection (IHI). In contrast, neither 13Lin^- nor 18Lin^- CD34^- cells engrafted in either mice or sheep when transplanted by regular routes (i.e., TVI and fetal IHI, respectively), although both 13Lin^- and 18Lin^- CD34^- cells engrafted in mice when transplanted by IBMI and exhibited multilineage reconstitution ability. Thus, the homing ability of CD34^- HSCs is significantly more limited than that of CD34⁺ HSCs. As for 18Lin^-, CD34^- HSCs are characterized by low expression of the tetraspanin CD9, which promotes homing, and high expression of the peptidase CD26, which inhibits homing. This unique expression pattern homing-related molecules on CD34^- HSCs could thus explain in part their reduced ability to home to the BM niche.

Polymer-DNA Nanoparticle-Induced CXCR4 Overexpression Improves Stem Cell Engraftment and Tissue Regeneration in a Mouse Hindlimb Ischemia Model

Peripheral arterial disease affects nearly 202 million individuals worldwide, sometimes leading to non-healing ulcers or limb amputations in severe cases. Genetically modified stem cells offer potential advantages for therapeutically inducing angiogenesis via augmented paracrine release mechanisms and tuned dynamic responses to environmental stimuli at disease sites. Here, we report the application of nanoparticle-induced CXCR4-overexpressing stem cells in a mouse hindlimb ischemia model. We found that CXCR4 overexpression improved stem cell survival, modulated inflammation in situ, and accelerated blood reperfusion. These effects, unexpectedly, led to complete limb salvage and skeletal muscle repair, markedly outperforming the efficacy of the conventional angiogenic factor control, VEGF. Importantly, assessment of CXCR4-overexpressing stem cells in vitro revealed that CXCR4 overexpression induced changes in paracrine signaling of stem cells, promoting a therapeutically desirable pro-angiogenic and anti-inflammatory phenotype. These results suggest that nanoparticle-induced CXCR4 overexpression may promote favorable phenotypic changes and therapeutic efficacy of stem cells in response to the ischemic environment.

Targeting chemokine receptor CXCR4 for treatment of HIV-1 infection, tumor progression, and metastasis

The chemokine receptor CXCR4 is required for the entry of human immunodeficiency virus type 1 (HIV-1) into target cells and for the development and dissemination of various types of cancers, including gastrointestinal, cutaneous, head and neck, pulmonary, gynecological, genitourinary, neurological, and hematological malignancies. The T-cell (T)-tropic HIV-1 strains use CXCR4 as the entry coreceptor; consequently, multiple CXCR4 antagonistic inhibitors have been developed for the treatment of acquired immune deficiency syndrome (AIDS). However, other potential applications of CXCR4 antagonists have become apparent since its discovery in 1996. In fact, increasing evidence demonstrates that epithelial and hematopoietic tumor cells exploit the interaction between CXCR4 and its natural ligand, stromal cellderived factor (SDF)-1α, which normally regulates leukocyte migration. The CXCR4 and/or SDF-1α expression patterns in tumor cells also determine the sites of metastatic spread. In addition, the activation of CXCR4 by SDF-1α promotes invasion and proliferation of tumor cells, enhances tumor-associated neoangiogenesis, and assists in the degradation of the extracellular matrix and basement membrane. As such, the evaluation of CXCR4 and/or SDF-1α expression levels has a significant prognostic value in various types of malignancies. Several therapeutic challenges remain to be overcome before the use of CXCR4 inhibitors can be translated into clinical practice, but promising preclinical data demonstrate that CXCR4 antagonists can mobilize tumor cells from their protective microenvironments, interfere with their metastatic and tumorigenic potentials, and/or make tumor cells more susceptible to chemotherapy.

Dimethyl Sulfoxide (DMSO) Increases Percentage of CXCR4(+) Hematopoietic Stem/Progenitor Cells, Their Responsiveness to an SDF-1 Gradient, Homing Capacities, and Survival

Cryopreservation of bone marrow (BM), mobilized peripheral blood (mPB), and cord blood (CB) hematopoietic stem/progenitor cells (HSPCs) is a routine procedure before transplantation. The most commonly used cryoprotectant for HSPCs is dimethyl sulfoxide (DMSO). The objective of this study was to evaluate the influence of DMSO on surface receptor expression and chemotactic activities of HSPCs. We found that 10 min of incubation of human mononuclear cells (MNCs) with 10% DMSO significantly increases the percentage of CXCR4(+), CD38(+), and CD34(+) cells, resulting in an increase of CD34(+), CD34(+)CXCR4(+), and CD34(+)CXCR4(+)CD38(-) subpopulations. Furthermore, DMSO significantly increased chemotactic responsiveness of MNCs and CXCR4(+) human hematopoietic Jurkat cell line to a stromal cell-derived factor-1 (SDF-1) gradient. Furthermore, we demonstrated enhanced chemotaxis of human clonogenic progenitor cells to an SDF-1 gradient, which suggests that DMSO directly enhances the chemotactic responsiveness of early human progenitors. DMSO preincubation also caused lower internalization of the CXCR4 receptor. In parallel experiments, we found that approximately 30% more of DMSO-preincubated human CD45(+) and CD45(+)CD34(+) cells homed to the mouse BM 24 h after transplantation in comparison to control cells. Finally, we demonstrated considerably higher (25 days) survival of mice transplanted with DMSO-exposed MNCs than those transplanted with the control cells. We show in this study an unexpected beneficial influence of DMSO on HSPC homing and suggest that a short priming with DMSO before transplantation could be considered a new strategy to enhance cell homing and engraftment.

Altered chemokine signalling in endothelial progenitor cells from acute ulcerative colitis patients

Ulcerative colitis (UC) is a chronic, idiopathic, inflammatory bowel disease, characterized by alternating stages of clinically active and inactive disease. UC exhibits several inflammatory characteristics, including immune activation, leukocyte infiltration, and altered vascular density. In UC, many of the upregulated inflammatory cytokines are proangiogenic and are released by diverse cell populations, such as infiltrating immune cells and endothelial cells (EC). Increasing evidences suggest that neovascularisation may involve also endothelial progenitor cells (EPCs). In this study we evaluated EPCs recruitment and homing, assessed by CXCR4 expression, in both acute and remitting phase of UC. We report an overall decrease of EPCs in UC patients (controls = 97,94 ± 37,34 cells/mL; acute = 31,10 ± 25,38 cells/mL; remitting = 30,33 ± 19,02 cells/mL; P < 0.001 for both UC groups versus controls). Moreover CXCR4⁺-EPCs, committed to home in inflammatory conditions, were found to be reduced in acute UC patients compared to both remitting patients and controls (acute = 3,13 ± 4,61 cells/mL; controls = 20,12 ± 14,0; remitting = 19,47 ± 12,83; P < 0,001). Interestingly, we found that administration of anti-inflammatory drugs in acute UC is associated with an increase in circulating EPCs, suggesting that this therapy may exert a strong influence on the progenitor cells response to inflammatory processes.

Is targeted therapy feasible in acute myelogenous leukemia?

The prognosis for patients with acute myeloid leukemia (AML) is determined to a large degree by the biology of the leukemic cell. In recent years, the identification and characterization of genetic aberrations has vastly improved our understanding of the pathogenesis of AML. In contrast, however, there has been a lack of clinically meaningful therapeutic advances. The same chemotherapeutic strategies have been applied to AML for several decades now, and while these regimens are effective in inducing remission, most patients relapse within months after initial treatment. Hence, there is an urgent need for novel therapies. We review herein a number of lines of laboratory and clinical trial data supporting the clinical value of targeted treatment approaches that will likely result in improved outcomes for patients with AML.

A differential role for CXCR4 in the regulation of normal versus malignant breast stem cell activity

C-X-C chemokine receptor type 4 (CXCR4) is known to regulate lung, pancreatic and prostate cancer stem cells. In breast cancer, CXCR4 signalling has been reported to be a mediator of metastasis, and is linked to poor prognosis. However its role in normal and malignant breast stem cell function has not been investigated. Anoikis resistant (AR) cells were collected from immortalised (MCF10A, 226L) and malignant (MCF7, T47D, SKBR3) breast cell lines and assessed for stem cell enrichment versus unsorted cells. AR cells had significantly higher mammosphere forming efficiency (MFE) than unsorted cells. The AR normal cells demonstrated increased formation of 3D structures in Matrigel compared to unsorted cells. In vivo, SKBR3 and T47D AR cells had 7- and 130-fold enrichments for tumour formationrespectively, compared with unsorted cells. AR cells contained significantly elevated CXCR4 transcript and protein levels compared to unsorted cells. Importantly, CXCR4 mRNA was higher in stem cell-enriched CD44+/CD24- patient-derived breast cancer cells compared to non-enriched cells. CXCR4 stimulation by its ligand SDF-1 reduced MFE of the normal breast cells lines but increased the MFE in T47D and patient-derived breast cancer cells. CXCR4 inhibition by AMD3100 increased stem cell activity but reduced the self-renewal capacity of the malignant breast cell line T47D. CXCR4+ FACS sorted MCF7 cells demonstrated a significantly increased MFE compared with CXCR4- cells. This significant increase in MFE was further demonstrated in CXCR4 over-expressing MCF7 cells which also had an increase in self-renewal compared to parental cells. A greater reduction in self-renewal following CXCR4 inhibition in the CXCR4 over-expressing cells compared with parental cells was also observed. Our data establish for the first time that CXCR4 signalling has contrasting effects on normal and malignant breast stem cell activity. Here, we demonstrate that CXCR4 signalling specifically regulates breast cancer stem cell activities and may therefore be important in tumour formation at the sites of metastases.

Intracellular trafficking and endocytosis of CXCR4 in fetal mesenchymal stem/stromal cells

Background

Fetal mesenchymal stem/stromal cells (MSC) represent a developmentally-advantageous cell type with translational potential.

To enhance adult MSC migration, studies have focussed on the role of the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12), but more recent work implicates an intricate system of CXCR4 receptor dimerization, intracellular localization, multiple ligands, splice variants and nuclear accumulation. We investigated the intracellular localization of CXCR4 in fetal bone marrow-derived MSC and role of intracellular trafficking in CXCR4 surface expression and function.

Results

We found that up to 4% of human fetal MSC have detectable surface-localized CXCR4. In the majority of cells, CXCR4 is located not at the cell surface, as would be required for ‘sensing’ migratory cues, but intracellularly. CXCR4 was identified in early endosomes, recycling endosomes, and lysosomes, indicating only a small percentage of CXCR4 travelling to the plasma membrane. Notably CXCR4 was also found in and around the nucleus, as detected with an anti-CXCR4 antibody directed specifically against CXCR4 isoform 2 differing only in N-terminal sequence. After demonstrating that endocytosis of CXCR4 is largely independent of endogenously-produced SDF-1, we next applied the cytoskeletal inhibitors blebbistatin and dynasore to inhibit endocytotic recycling. These increased the number of cells expressing surface CXCR4 by 10 and 5 fold respectively, and enhanced the number of cells migrating to SDF1 in vitro (up to 2.6 fold). These molecules had a transient effect on cell morphology and adhesion, which abated after the removal of the inhibitors, and did not alter functional stem cell properties.

Conclusions

We conclude that constitutive endocytosis is implicated in the regulation of CXCR4 membrane expression, and suggest a novel pharmacological strategy to enhance migration of systemically-transplanted cells.

SDF-1 dynamically mediates megakaryocyte niche occupancy and thrombopoiesis at steady state and following radiation injury

Megakaryocyte (MK) development in the bone marrow progresses spatially from the endosteal niche, which promotes MK progenitor proliferation, to the sinusoidal vascular niche, the site of terminal maturation and thrombopoiesis. The chemokine stromal cell-derived factor-1 (SDF-1), signaling through CXCR4, is implicated in the maturational chemotaxis of MKs toward sinusoidal vessels. Here, we demonstrate that both IV administration of SDF-1 and stabilization of endogenous SDF-1 acutely increase MK-vasculature association and thrombopoiesis with no change in MK number. In the setting of radiation injury, we find dynamic fluctuations in marrow SDF-1 distribution that spatially and temporally correlate with variations in MK niche occupancy. Stabilization of altered SDF-1 gradients directly affects MK location. Importantly, these SDF-1-mediated changes have functional consequences for platelet production, as the movement of MKs away from the vasculature decreases circulating platelets, while MK association with the vasculature increases circulating platelets. Finally, we demonstrate that manipulation of SDF-1 gradients can improve radiation-induced thrombocytopenia in a manner additive with earlier TPO treatment. Taken together, our data support the concept that SDF-1 regulates the spatial distribution of MKs in the marrow and consequently circulating platelet numbers. This knowledge of the microenvironmental regulation of the MK lineage could lead to improved therapeutic strategies for thrombocytopenia.

The CXCR4 and adhesion molecule expression of CD34+ hematopoietic cells mobilized by "on-demand" addition of plerixafor to granulocyte-colony-stimulating factor

Background

Granulocyte–colony-stimulating factor (G-CSF) is routinely used for mobilization of hematopoietic stem and progenitor cells preceding autologous transplantation after high-dose chemotherapy in hematologic malignancies. However, due to high mobilization failure rates, alternative mobilization strategies are required.

Study Design and Methods

Patients who poorly mobilized CD34+ hematopoietic cells (HCs) with G-CSF additionally received the CXCR4 antagonist plerixafor. The phenotype of CD34+ HCs collected after this plerixafor-induced “rescue” mobilization, in regard to adhesion molecule and CD133, CD34, and CD38 expression in comparison to CD34+ HCs collected after traditional G-CSF administration in good mobilizers, was analyzed flow cytometrically. To confirm previous studies in our patient cohort, the efficiency of mobilization and subsequent engraftment after this “on-demand” plerixafor mobilization were analyzed.

Results

Pronounced mobilization occurred after plerixafor administration in poor mobilizers, resulting in similar CD34+ cell yields as obtained by G-CSF in good mobilizers, whereby plerixafor increased the content of primitive CD133+/CD34+/CD38– cells. The surface expression profiles of the marrow homing and retention receptors CXCR4, VLA-4, LFA-1, and CD44 on mobilized CD34+ cells and hematopoietic recovery after transplantation were similar in patients receiving G-CSF plus plerixafor or G-CSF. Unexpectedly, the expression levels of respective adhesion receptors were not related to mobilization efficiency or engraftment.

Conclusion

The results show that CD34+ HCs collected by plerixafor-induced rescue mobilization are qualitatively equivalent to CD34+ HCs collected after traditional G-CSF mobilization in good mobilizers, in regard to their adhesive phenotype and engraftment potential. Thereby, plerixafor facilitates the treatment of poor mobilizers with autologous HC transplantation after high-dose chemotherapy.

Cellular and molecular mechanisms in cancer immune escape: a comprehensive review

Immune escape is the final phase of cancer immunoediting process wherein cancer modulates our immune system to escape from being destroyed by it. Many cellular and molecular events govern the cancer's evasion of host immune response. The tumor undergoes continuous remodeling at the genetic, epigenetic and metabolic level to acquire resistance to apoptosis. At the same time, it effectively modifies all the components of the host's immunome so as to escape from its antitumor effects. Moreover, it induces accumulation of suppressive cells like Treg and myeloid derived suppressor cells and factors which also enable it to elude the immune system. Recent research in this area helps in defining the role of newer players like miRNAs and exosomes in immune escape. The immunotherapeutic approaches developed to target the escape phase appear quite promising; however, the quest for a perfect therapeutic agent that can achieve maximum cure with minimal toxicity continues.

Fusion of CCL21 non-migratory active breast epithelial and breast cancer cells give rise to CCL21 migratory active tumor hybrid cell lines

The biological phenomenon of cell fusion has been linked to tumor progression because several data provided evidence that fusion of tumor cells and normal cells gave rise to hybrid cell lines exhibiting novel properties, such as increased metastatogenic capacity and an enhanced drug resistance. Here we investigated M13HS hybrid cell lines, derived from spontaneous fusion events between M13SV1-EGFP-Neo breast epithelial cells exhibiting stem cell characteristics and HS578T-Hyg breast cancer cells, concerning CCL21/CCR7 signaling. Western Blot analysis showed that all cell lines varied in their CCR7 expression levels as well as differed in the induction and kinetics of CCR7 specific signal transduction cascades. Flow cytometry-based calcium measurements revealed that a CCL21 induced calcium influx was solely detected in M13HS hybrid cell lines. Cell migration demonstrated that only M13HS hybrid cell lines, but not parental derivatives, responded to CCL21 stimulation with an increased migratory activity. Knockdown of CCR7 expression by siRNA completely abrogated the CCL21 induced migration of hybrid cell lines indicating the necessity of CCL21/CCR7 signaling. Because the CCL21/CCR7 axis has been linked to metastatic spreading of breast cancer to lymph nodes we conclude from our data that cell fusion could be a mechanism explaining the origin of metastatic cancer (hybrid) cells.

A novel application for a 3-dimensional timelapse assay that distinguishes chemotactic from chemokinetic responses of hematopoietic CD133(+) stem/progenitor cells

Efficient homing/mobilization of human hematopoietic stem/progenitor cells to/from bone marrow niches enhances their therapeutic efficacy. Additionally, homing is dependent on cell source and may be modulated by prior ex vivo cell expansion. Here, we describe a novel application of a 3-dimensional time-lapse method for assessing trafficking of individual human cord blood CD133⁺ hematopoietic stem/progenitor cells in vitro, using the key chemokine CXCL12 as a paradigm. This new methodology allows distinction between chemotactic responses (displacement of center of mass and the forward migration index of the cells), and chemokinetic responses such as total cell path traveled in any direction (accumulated distance) and cell velocity in a 3-dimensional matrix. Other key advantages of this novel assay over existing assays include the ability to assess individual cell migration over times comparable to in vivo homing and rapid mobilization assays (18–24 h) and to directly compare the strength or response of individual hematopoietic progenitor cells to different or competing stimuli and small molecule inhibitors in a single assay prior to analyses in vivo. Importantly, using this method, our results demonstrate definitively that CXCL12 regulates the chemotactic responses of human cord blood CD133⁺ cells, but not their random migration or chemokinesis.

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Development of a novel 3-dimensional timelapse chemotaxis assay application.

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Measuring individual CD133+ HSPC trafficking towards chemokines in a 3D matrix.

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Chemotactic and chemokinetic responses reflecting homin kinetics in vivo.

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Comparative analysis of inhibitors or expansion on HSPC chemotaxis and chemokinesis.

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Definitive proof that CXCL12 regulates CD133+ HSPC chemotaxis but not chemokinesis.

Incorporation of stromal cell-derived factor-1α in PCL/gelatin electrospun membranes for guided bone regeneration

The goal of this work was to evaluate the effect of membrane functionalization with a chemotactic factor on cell recruitment and bone formation in order to develop a bioactive membrane for guided bone regeneration (GBR) applications. To this end, GBR membranes were prepared by electrospinning using poly(ε-caprolactone) (PCL) blended with type B-gelatin, and functionalized with stromal cell derived factor-1α (SDF-1α) via physical adsorption. Firstly, the obtained membranes were evaluated in vitro for SDF-1α release and chemotactic effect on bone marrow stromal cells (BMSCs). Subsequently, in vivo BMSCs recruitment and bone regeneration in response to SDF-1α loaded PCL/gelatin electrospun membranes were assessed in rat cranial defects. The results showed that PCL/gelatin electrospun membranes provided a diffusion-controlled SDF-1α release profile. Furthermore, the membranes loaded with different amounts of SDF-1α (50-400 ng) significantly induced stimulated chemotactic migration of BMSCs in vitro without dose-dependent effects. Eight weeks after implantation in rat cranial defects, SDF-1α loaded membranes yielded a 6-fold increase in the amount of bone formation compared to the bare membranes, albeit that contribution of in vivo BMSCs recruitment to the bone regeneration could not be ascertained. In conclusion, the results of current study indicate the potential for using SDF-1α loaded PCL/gelatin electrospun membrane as a bioactive membrane, which is beneficial for optimizing clinical application of GBR strategies.

Molecular mechanisms underlying adhesion and migration of hematopoietic stem cells

Hematopoietic stem cell transplantation is the most powerful treatment modality for a large number of hematopoietic malignancies, including leukemia. Successful hematopoietic recovery after transplantation depends on homing of hematopoietic stem cells to the bone marrow and subsequent lodging of those cells in specific niches in the bone marrow. Migration of hematopoietic stem cells to the bone marrow is a highly regulated process that requires correct regulation of the expression and activity of various molecules including chemoattractants, selectins and integrins. This review will discuss recent studies that have extended our understanding of the molecular mechanisms underlying adhesion, migration and bone marrow homing of hematopoietic stem cells.

A novel strategy to enhance mesenchymal stem cell migration capacity and promote tissue repair in an injury specific fashion

Mesenchymal stem cells (MSCs) of bone marrow origin appear to be an attractive candidate for cell-based therapies. However, the major barrier to the effective implementation of MSC-based therapies is the lack of specific homing of exogenously infused cells and overall the inability to drive them to the diseased or damaged tissue. In order to circumvent these limitations, we developed a preconditioning strategy to optimize MSC migration efficiency and potentiate their beneficial effect at the site of injury. Initially, we screened different molecules by using an in vitro injury-migration setting, and subsequently, we evaluated the effectiveness of the different strategies in mice with acute kidney injury (AKI). Our results showed that preconditioning of MSCs with IGF-1 before infusion improved cell migration capacity and restored normal renal function after AKI. The present study demonstrates that promoting migration of MSCs could increase their therapeutic potential and indicates a new therapeutic paradigm for organ repair.

Hyaluronan expressed by the hematopoietic microenvironment is required for bone marrow hematopoiesis

The contribution of hyaluronan (HA) to the regulatory network of the hematopoietic microenvironment was studied using knock-out mice of three hyaluronan synthase genes (Has1, Has2, and Has3). The number of hematopoietic progenitors was decreased in bone marrow and increased in extramedullary sites of Prx1-Cre;Has2(flox/flox);Has1(-/-);Has3(-/-) triple knock-out (tKO) mice as compared with wild type (WT) and Has1(-/-);Has3(-/-) double knock-out (dKO) mice. In line with this observation, decreased hematopoietic activity was observed in long term bone marrow cultures (LTBMC) from tKO mice, whereas the formation of the adherent layer and generation of hematopoietic cells in WT and dKO cultures was not different. 4-Methylumbelliferone (4MU) was used to pharmacologically inhibit the production of HA in LTBMC. Treatment with 4MU inhibited HA synthesis, decreased expression of HAS2 and HAS3, and eliminated hematopoiesis in LTBMC, and this effect was alleviated by the addition of exogenous HA. Exogenous HA also augmented the cell motility in LTBMC, which correlated with the HA-stimulated production of chemokines and growth factors. Conditioned media from HA-induced LTBMC enhanced the chemotaxis of hematopoietic stem/progenitor cells (HSPC) in response to SDF-1. Exposure of endothelial cells to 4MU decreased their ability to support HSPC rolling and adhesion. In addition, migration of transplanted HSPC into the marrow of 4MU-pretreated mice was lower than in untreated mice. Collectively, the results suggest that HA depletion reduces the ability of the microenvironment to support HSPC, and confirm a role for HA as a necessary regulatory element in the structure of the hematopoietic microenvironment.

Hybrid cells derived from breast epithelial cell/breast cancer cell fusion events show a differential RAF-AKT crosstalk

BACKGROUND

The biological phenomenon of cell fusion has been linked to several characteristics of tumour progression, including an enhanced metastatogenic capacity and an enhanced drug resistance of hybrid cells. We demonstrated recently that M13SV1-EGFP-Neo breast epithelial cells exhibiting stem cell characteristics spontaneously fused with MDA-MB-435-Hyg breast cancer cells, thereby giving rise to stable M13MDA435 hybrid cells, which are characterised by a unique gene expression profile and migratory behaviour. Here we investigated the involvement of the PLC-β/γ1, PI3K/AKT and RAS-RAF-ERK signal transduction cascades in the EGF and SDF-1α induced migration of two M13MDA435 hybrid cell clones in comparison to their parental cells.

RESULTS

Analysis of the migratory behaviour by using the three-dimensional collagen matrix migration assay showed that M13SV1-EGFP-Neo cells as well as M13MDA435 hybrid cells, but not the breast cancer cell line, responded to EGF stimulation with an increased locomotory activity. By contrast, SDF-1α solely stimulated the migration of M13SV1-EGFP-Neo cells, whereas the migratory activity of the other cell lines was blocked. Analysis of signal transduction cascades revealed a putative differential RAF-AKT crosstalk in M13MDA435-1 and -3 hybrid cell clones. The PI3K inhibitor Ly294002 effectively blocked the EGF induced migration of M13MDA435-3 hybrid cells, whereas the EGF induced locomotion of M13MDA435-1 hybrid cells was markedly increased. Analysis of RAF-1 S259 phosphorylation, being a major mediator of the negative regulation of RAF-1 by AKT, showed decreased pRAF-1 S259 levels in LY294002 treated M13MDA435-1 hybrid cells. By contrast, pRAF-1 S259 levels remained unaltered in the other cell lines. Inhibition of PI3K/AKT signalling by Ly294002 relieves the AKT mediated phosphorylation of RAF-1, thereby restoring MAPK signalling.

CONCLUSIONS

Here we show that hybrid cells could evolve exhibiting a differential active RAF-AKT crosstalk. Because PI3K/AKT signalling has been chosen as a target for anti-cancer therapies our data might point to a possible severe side effect of AKT targeted cancer therapies. Inhibition of PI3K/AKT signalling in RAF-AKT crosstalk positive cancer (hybrid) cells could result in a progression of these cells. Thus, not only the receptor (activation) status, but also the activation of signal transduction molecules should be analysed thoroughly prior to therapy.

Stromal-derived factor-1 deficiency in the bone marrow of acute myeloid leukemia

Chemokine stromal-derived factor-1 (SDF-1) and its receptor CXCR4 have been shown to play an important role in the migration and homing of the transplanted hematopoietic stem cells (HSCs). Mesenchymal stem cells (MSCs) express these molecules. This study is to test the hypothesis that acute myeloid leukemia (AML) alters the expression of SDF-1/CXCR4 in human bone marrow MSCs. Expression of both CXCR4 and SDF-1 was found to be increased, but excessively retained, in the MSCs in AML. In contrast, the SDF-1 level in bone marrow plasma and supernatant of cultured MSCs from AML patients were reduced, while the SDF-1 was able to efficiently induce a dose-dependent migration of MSCs in vitro. Our results demonstrate that altered expression and distribution of SDF-1/CXCR4 in MSCs may contribute to SDF-1 deficiency in the plasma of AML patients. The migration of MSCs may be negatively affected by the SDF-1 deficiency.

Efficacy of mesenchymal stem cells in suppression of hepatocarcinorigenesis in rats: possible role of Wnt signaling

Background

The present study was conducted to evaluate the tumor suppressive effects of bone marrow derived mesenchymal stem cells (MSCs) in an experimental hepatocellular carcinoma (HCC) model in rats and to investigate the possible role of Wnt signaling in hepato-carcinogenesis.

Methods

Ninety rats were included in the study and were divided equally into: Control group, rats which received MSCs only, rats which received MSCs vehicle only, HCC group induced by diethylnitroseamine (DENA) and CCl₄, rats which received MSCs after HCC induction, rats which received MSCs before HCC induction. Histopathological examination and gene expression of Wnt signaling target genes by real time, reverse transcription-polymerase chain reaction (RT-PCR) in rat liver tissue, in addition to serum levels of ALT, AST and alpha fetoprotein were performed in all groups.

Results

Histopathological examination of liver tissue from animals which received DENA-CCl₄ only, revealed the presence of anaplastic carcinoma cells and macro-regenerative nodules type II with foci of large and small cell dysplasia. Administration of MSCs into rats after induction of experimental HCC improved the histopathological picture which showed minimal liver cell damage, reversible changes, areas of cell drop out filled with stem cells. Gene expression in rat liver tissue demonstrated that MSCs downregulated β-catenin, proliferating cell nuclear antigen (PCNA), cyclin D and survivin genes expression in liver tissues after HCC induction. Amelioration of the liver status after administration of MSCs has been inferred by the significant decrease of ALT, AST and Alpha fetoprotein serum levels. Administration of MSCs before HCC induction did not show any tumor suppressive or protective effect.

Conclusions

Administration of MSCs in chemically induced HCC has tumor suppressive effects as evidenced by down regulation of Wnt signaling target genes concerned with antiapoptosis, mitogenesis, cell proliferation and cell cycle regulation, with subsequent amelioration of liver histopathological picture and liver function.

Evolving concepts in cell therapy of liver disease and current clinical perspectives

The clinical use of cells for the treatment of liver disease is not a mere hypothesis. Indeed, it has been known for more than 30 years that, following intraportal infusion, exogenous hepatocytes isolated from a donor liver engraft into the recipient hepatic parenchyma and express metabolic activity. These experimental results encouraged pilot clinical trials using hepatocytes transplantation to treat a variety of liver diseases. More recently, the discovery of liver stem/progenitor cells further fueled the interest in the field. However, it appears that successful liver cell therapy will require better understanding of the mechanisms governing liver regeneration and of their implication in cell transplantation. This review summarizes some recent advances in the field in a bench-to-bedside perspective.

Migratory strategies of normal and malignant stem cells

The regulated migration of stem cells is critical for organogenesis during development and for tissue -homeostasis and repair during adulthood. Human bone marrow (BM) represents an accessible reservoir containing regenerative cell types from hematopoietic, endothelial, and mesenchymal-stromal lineages that together coordinate hematopoiesis and promote the repair of damaged vasculature and tissues throughout the body. Thus, a detailed understanding of lineage-specific stem cell mobilization, homing, and subsequent engraftment in areas of injury or disease is of critical importance to the rational development of novel cell-mediated regenerative therapies. Stem cell trafficking via the circulation from site of origin to peripheral tissues requires fundamental molecular pathways governing (1) niche-specific deadhesion of progenitor cells; (2) chemoattraction to guide progenitor cell homing; and (3) interstitial navigation and adhesion/retention of recruited progenitor cells. This overview chapter summarizes the diversity of migratory strategies employed by hematopoietic, endothelial, and mesenchymal-stromal progenitor cells during repair and regeneration after tissue damage. Further elucidation of stem cell homing and migration pathways will allow greater application of stem cells for targeted cell therapy and/or drug delivery for tissue repair. Strikingly similar migratory mechanisms appear to govern the in vivo migration of recently characterized cancer stem cells (CSC) in leukemias and solid tumors, indicating that conserved principles of stem cell migration and niche specificity will provide new information to target CSC in anticancer therapy.

Directing stem cell trafficking via GPS

The success of stem-cell-based regenerative therapeutics critically hinges on delivering relevant stem/progenitor cells to sites of tissue injury. To achieve adequate parenchymal infiltration following intravascular administration, it is first necessary that circulating cells bind to target tissue endothelium with sufficient strength to overcome the prevailing forces of hemodynamic shear. The principal mediators of these shear-resistant binding interactions consist of a family of C-type lectins known as "selectins" that bind discrete sialofucosylated glycans on their respective ligands. One member of this family, E-selectin, is an endothelial molecule that is inducibly expressed on postcapillary venules at all sites of tissue injury, but is also constitutively expressed on the luminal surface of bone marrow and dermal microvascular endothelium. Most stem/progenitor cells express high levels of CD44, and, in particular, human hematopoietic stem cells express a specialized sialofucosylated glycoform of CD44 known as "hematopoietic cell E-/L-selectin ligand" (HCELL) that functions as a potent E-selectin ligand. This chapter describes a method called "glycosyltransferase-programmed stereosubstitution" (GPS) for custom-modifying CD44 glycans to create HCELL on the surface of living cells that natively lack HCELL. Ex vivo glycan engineering of HCELL via GPS licenses trafficking of infused cells to endothelial beds that express E-selectin, thereby enabling efficient vascular delivery of stem/progenitor cells to sites where they are needed.

CXCR4+ progenitors derived from bone mesenchymal stem cells differentiate into endothelial cells capable of vascular repair after arterial injury

Recent findings indicate that bone marrow mesenchymal stem cells (BMSCs) participate in the process of neovascularization in response to repair to injury and are involved in postinfarction myocardial repair. It is unclear what special characteristics the vascular progenitors of bone marrow origin has. CXCR4(+) stem/progenitor cells mobilized to the infarct area and improved the myocardial repair. In present study, we aimed to determine whether CXCR4(+)BMSCs contribute to the angiogenic capacity in vitro and in vivo. CXCR4(+)BMSCs were separated by using paramagnetic microbeads and cultured. RT-PCR and FACS analysis confirmed the gene expression phenotype. The uptake of acetylated low density lipoprotein (acLDL) and the tube formation evaluated the function of CXCR4(+)BMSCs. The effect of CXCR4(+)BMSCs transplantation on neovascularization was investigated in a murine model hindlimb ischemia. After induced by VEGF, CXCR4(+)BMSCs expressed the endothelial cells (ECs) phenotype. The expression of EC markers, PECAM-1, and von Willebrand factor (vWF) increased significantly at both the mRNA and protein levels. In addition, CXCR4(+)BMSCs enhanced the uptakes of Dil-acLDL and form capillary-like tubes in vitro. In vivo the local transfer of CXCR4(+)BMSCs increased neovascularization in ischemic hindlimb. These results demonstrate that CXCR4(+)BMSCs differentiate into ECs and contribute to neovascularization in the vascular lesion,, which indicate the important therapeutic implications for cardiovascular diseases and a new cell source for cell-based vascular engineering and repair in the future.

Engraftment of syngeneic bone marrow is not more efficient after intrafemoral transplantation than after traditional intravenous administration

OBJECTIVE

Hematopoietic stem cells are key elements for life-long production of mature blood cells. The success of clinical stem cell transplantation may be improved when the number of stem cells that engraft after transplantation can be increased. Here, we investigated in a syngeneic mouse model whether engraftment and reconstitution can be improved by transplantation directly into the bone marrow.

MATERIALS AND METHODS

In this study, we directly compared syngeneic transplantation of hematopoietic stem cells into the bone marrow with intravenous administration and assessed reconstitution kinetics and engraftment by bioluminescent imaging and chimerism determination.

RESULTS

Surprisingly, only about 10% of cells injected directly into the femur (intrafemoral, IF) could be retrieved within 5 minutes after injection. Only in the first 48 hours after transplantation, engraftment in IF-transplanted animals was higher compared with intravenous injection. However, at all later time points no differences could be detected using whole body bioluminescence or measuring blood cell reconstitution. Most importantly, we found that IF-transplanted cells did not outcompete cells transplanted intravenously when cotransplanted in the same recipient.

CONCLUSIONS

In conclusion, IF transplantation in a murine syngeneic setting revealed no enhanced engraftment. Previous reports on IF transplantation may have relied on escape from immune rejection in xenogeneic or allogeneic models. Therefore, we conclude that stem cells can find the proper microenvironment irrespective of the route of administration.

Mesenchymal stem cells: Mechanisms of immunomodulation and homing

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissue. A growing corpus of studies have highlighted two important aspects of MSC therapy: 1) MSCs can modulate T-cell-mediated immunological responses, and (2) systemically administered MSCs home to sites of ischemia or injury. In this review, we describe the known mechanisms of immunomodulation and homing of MSCs. First, we examine the low immunogenicity of MSCs and their antigen presentation capabilities. Next, we discuss the paracrine interactions between MSCs and innate [dendritic cells (DC)] and adaptive immune cells (T lymphocytes) with a focus on prostaglandin E(2) (PGE(2)), indoleamine 2,3-dioxygenase (IDO), and toll-like receptor (TLR) signaling pathways. We transition to outline the steps of activation, rolling/adhesion, and transmigration of MSCs into target tissues during inflammatory or ischemic conditions. These aspects of MSC grafts--immunomodulation and homing--are contextualized to understand a reported side effect of MSC therapy, cancer development.

Atorvastatin increases the number of endothelial progenitor cells after cardiac surgery: a randomized control study

Endothelial progenitor cells (EPCs) are a subtype of hematopoietic stem cells, which contribute to the repair of injured endothelium. Treatment with atorvastatin has been shown to increase EPC count in patients with coronary artery disease. Therefore, we investigated whether atorvastatin augments the number of EPCs after cardiopulmonary bypass (CPB) surgery. We conducted a randomized double-blind, placebo-controlled, 2-way crossover trial in 50 patients undergoing elective coronary surgery. Patients received either 3-week treatment with atorvastatin or placebo. EPCs were quantitated by flow cytometric phenotyping on blood samples. Levels of interleukin, IL-6 and IL-8; tumor necrosis factor alpha; SDF-1alpha; granulocyte colony-stimulating factor; and vascular endothelial growth factor were determined at recruitment, preoperatively, post-CPB, and 6, 12, and 24 hours postoperatively. The atorvastatin group showed a significantly higher amount of EPCs both pre- and postoperatively compared with the placebo, with a >4-fold increase compared with the baseline values. CPB induced an increase in all cytokines, but the levels of proinflammatory cytokines were significantly lower in the atorvastatin group (P < 0.05). Statin did not affect levels of SDF-1alpha, granulocyte colony-stimulating factor, and vascular endothelial growth factor. However, no correlation was found between plasma levels of any cytokine and number of EPCs, with the exception of SDF-1alpha. Pretreatment with atorvastatin significantly increases the amount of EPCs after CPB, by a mechanism independent of plasma levels of cytokines and cholesterol.