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BACKGROUND AIMS. Intravenously applied mesenchymal stromal cells (MSC) are under investigation for numerous clinical indications. However, their capacity to activate shear stress-dependent adhesion to endothelial ligands is incompletely characterized. METHODS. Parallel-plate flow chambers were used to induce firm adhesion of MSC to integrin ligand vascular cell adhesion molecule (VCAM)-1. Human MSC were stimulated by chemokine (C-C motif) ligand (CCL15)/macrophage inflammatory protein (MIP-5), CCL19/MIP-3ß chemokine (C-X-C motif) ligand (CXCL8)/interleukin (IL)-8, CXCL12/ stromal derived factor (SDF-1) or CXCL13/B lymphocyte chemoattractant (BLC). RESULTS. Two MSC isolates responded to three chemokines (either to CCL15, CCL19 and CXCL13, or to CCL19, CXCL12 and CXCL13), two isolates responded to two chemokines (to CCL15 and CCL19, or to CCL19 and CXCL13), and one isolate responded to CCL19 only. In contrast, all tested MSC isolates responded to selectins (P-selectin and E-selectin) or integrin ligand VCAM-1, as visualized by a velocity reduction under flow. CONCLUSIONS. Inter-individual variability of chemokine-induced integrin activation should be considered when evaluating human MSC as cellular therapies.

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BACKGROUND AIMS: Mesenchymal stromal cells (MSC) are the focus of research in regenerative medicine aiming at the regulatory approval of these cells for specific indications. To cope with the regulatory requirements for somatic cell therapy, novel approaches that do not interfere with the natural behavior of the cells are necessary. In this context in vivo magnetic resonance imaging (MRI) of labeled MSC could be an appropriate tool. Cell labeling for MRI with a variety of different iron oxide preparations is frequently published. However, most publications lack a comprehensive assessment of the non-interference of the contrast agent with the functionality of the labeled MSC, which is a prerequisite for the validity of cell-tracking via MRI. METHODS: We studied the effects of iron oxide-poly(l-lactide) nanoparticles in MSC with flow cytometry, transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), Prussian blue staining, CyQuant® proliferation testing, colony-forming unit-fibroblast (CFU-F) assays, flow chamber adhesion testing, immunologic tests and differentiation tests. Furthermore iron-labeled MSC were studied by MRI in agarose phantoms and Wistar rats. RESULTS: It could be demonstrated that MSC show rapid uptake of nanoparticles and long-lasting intracellular persistence in the endosomal compartment. Labeling of the MSC with these particles has no influence on viability, differentiation, clonogenicity, proliferation, adhesion, phenotype and immunosuppressive properties. They show excellent MRI properties in agarose phantoms and after subcutaneous implantation in rats over several weeks. CONCLUSIONS: These particles qualify for studying MSC homing and trafficking via MRI.

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Mesenchymal stromal cells (MSCs) have come into focus for an increasing number of cellular therapies. Since most clinical protocols use intravenous application of MSCs, it has become important to understand their trafficking in the bloodstream. Moreover, since relatively little is known where the transplanted MSCs might locate, a better understanding of involved homing mechanisms will likely shed light on how MSCs exert their therapeutic effects. This review focuses on the current knowledge of homing pathways of transplanted MSCs. We describe regulatory signalling molecules and receptors involved. An outlook is given on significance of these findings for the future use of MSCs as a cellular therapeutic.

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Leukocyte adhesion deficiency-III (LAD-III) also called leukocyte adhesion deficiency-1/variant (LAD1v) is a rare congenital disease caused by defective integrin activation of leukocytes and platelets. Patients with LAD-III present with non-purulent infections and increased bleeding symptoms. We report on a novel integrin-dependent platelet dysfunction in two brothers with LAD-III syndrome caused by a homozygous mutation 1717C>T in the FERMT3 gene leading to a premature stop codon R573X in the focal adhesion protein kindlin-3. Stimulation of patients platelets with all used agonists resulted in a severely decreased binding of soluble fibrinogen indicating a defect in inside-out activation of the integrin alpha(IIb) beta(3) (GPIIb/IIIa). Patients platelets did not respond to the alpha(2)beta(1)-integrin agonist aggretin-A at all. Our data on granula secretion indicate for the first time that the thrombin receptor PAR-4 but not PAR-1 may be important in integrin-triggered granule secretion in response to thrombin. In contrast, collagen mediated platelet granule secretion was not affected in LAD-III-patients. Thus, integrin-signalling may be not essential in collagen-induced granule secretion. The patients' peripheral blood mononuclear cells showed a severe loss of adhesion capacity to VCAM-1 and to endothelial cells compared to cells from healthy donors. Rap-1 activation after PMA stimulation could be observed in controls but not in patients cells. After haematogenesis stem cell transplantation (HSCT) the brothers showed no symptoms of bleeding or immunodeficiency and the integrin-dependent platelet and leukocyte functions normalised.

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UNLABELLED: Background In vitro proliferative and differentiation potential of mesenchymal stromal cells generated from CD271(+) bone marrow mononuclear cells (CD271-mesenchymal stromal cells) has been demonstrated in several earlier and recent reports. In the present study we focused, in addition to proliferative and differentiation potential, on in vitro and in vivo immunosuppressive and lymphohematopoietic engraftment-promoting potential of these mesenchymal stromal cells compared to bone marrow-derived mesenchymal stromal cells generated by plastic adherence (plastic adherence-mesenchymal stromal cells). DESIGN AND METHODS: We set up a series of experimental protocols in order to determine the phenotype of CD271-mesenchymal stromal cells, and their clonogenic, proliferative, differentiation and immunosuppressive potential. The potential of CD271-mesenchymal stromal cells to improve the engraftment of CD133(+) hematopoietic stem cells at co-transplantation was evaluated in immunodeficient NOD/SCID-IL2Rgamma(null) mice. RESULTS: In vitro studies demonstrated that CD271-mesenchymal stromal cells differentiate along adipogenic, osteogenic and chondrogenic lineages (trilineage potential), produce significantly higher levels of cytokines than plastic adherence-mesenchymal stromal cells, and significantly inhibit the proliferation of allogeneic T-lymphocytes in mixed lymphocyte reaction assays. Elevated levels of prostaglandin E(2), but not nitric monoxide, mediated the majority of this immunosuppressive effect. In vivo studies showed that CD271-mesenchymal stromal cells promoted significantly greater lymphoid engraftment than did plastic adherence-mesenchymal stromal cells when co-transplanted with CD133(+) hematopoietic stem cells at a ratio of 8:1 in immunodeficient NOD/SCID-IL2Rgamma(null) mice. They induced a 10.4-fold increase in the number of T cells, a 2.5-fold increase in the number of NK cells, and a 3.6-fold increase in the number of B cells, indicating a major qualitative difference between these two mesenchymal stromal cell populations. Conclusions Our results indicate that CD271 antigen provides a versatile marker for prospective isolation and expansion of multipotent mesenchymal stromal cells with immunosuppressive and lymphohematopoietic engraftment-promoting properties. The co-transplantation of such cells together with hematopoietic stem cells in patients with hematologic malignancies may prove valuable in the prevention of impaired/delayed T-cell recovery and graft-versus-host disease.

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Intravenous (i.v.) transplantation and subsequent homing of Mesenchymal Stromal Cells (MSC) may be adversely influenced by their relatively high adhesion capacity and their tendency to aggregate, leading to clogging of capillaries especially in the lungs. We evaluated the ability of murine MSC suspended in EDTA or heparin in buffered saline solution on their spontaneous adhesion to endothelial cells in vitro, under shear stress and their in vivo tolerability after i.v. injection. We show that suspension of MSC in heparin was highly beneficial, avoiding clinical symptoms in 95% of mice, whereas application of MSC suspended in PBS/EDTA or control buffer caused severe pulmonary reactions and partly, death. In vitro studies using parallel plate flow chambers revealed increased adhesion of MSC suspended in PBS/EDTA to endothelial cells compared with MSC in PBS/heparin. These data provide a means to predict and to interfere with toxicity of i.v. transplanted MSC.

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Infiltration of bone marrow derived cells is part of the angiogenic switch required for uncontrolled tumour growth. However, the nature of the tumour-infiltrating cells from bone marrow has not been fully elucidated. To investigate the phenotype of bone marrow derived cells within a tumour, we employed the Lewis lung carcinoma (LLC) murine tumour model. We followed bone marrow derivation of tumour-infiltrating cells through transplantation of CD45.2 bone marrow cells into pre-irradiated CD45.1 mice. We found robust CD45.2 donor type chimerism in bone marrow and blood of CD45.1 recipient tumour-bearing mice. Flow cytometric analysis of LLC tumours showed, in addition to previously described pro-angiogenic CD45(+)VEGFR2(+)'endothelial progenitor cells' (EPC), or CD45(+)Tie2(+)'Tie2-expressing monocytes' (TEM), incorporation of donor type lineage marker negative (Lin(-)) and Lin(-)Sca1(+) undifferentiated haematopoietic cell types. Immunohistochemical analysis confirmed the extravasal location of the primitive haematopoietic cells. Flow-cytometric sorting of bone marrow cells and subsequent analysis in haematopoietic colony-forming assays revealed that cells with a Lin(-)Sca1(+) phenotype, which were initially negative for VEGFR2 and Tie2, gave rise to VEGFR2(+) and/or Tie2(+) cells. Moreover, Lin(-) bone marrow cells pre-labelled with the membrane dye PKH26 (a red fluorochrome) and transplanted i.v. into tumour-bearing mice were found to extravasate and incorporate into LLC tumours within 24 hrs. Thus, primitive haematopoietic precursors which are thought to be precursors of EPC and TEMs, constitute a part of the tumour microenvironment. This makes them an attractive target cell population for tumour-directed cellular therapies.

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SUMMARY: Mesenchymal stem cells (MSCs) are primarily fibroblast-like cells. Yet, once studied under conditions of shear stress when flowing along endothelial cells in vitro or in blood vessels, as well as in classic migration assays such as chemotaxis assays, MSCs have recently been found to function similarly to leukocytes in many ways. Firstly, MSCs express several homing receptors which are typically activated during extravasation of leukocytes. Secondly, some of these receptors are definitely functional, and required for their tissue localization in certain physiological or pathological contexts. Clinical protocols have in the last few years provided the first data on whether and how human MSCs may work in patients once delivered locally e.g. by injection, or systemically via the intra-arterial or intravenous route. Still, analysis of the ability of MSCs to activate specific homing receptors has up to now received relatively little attention. Moreover, maintenance or alterations of homing receptor expression or functions during good manufacturing practice (GMP) preparation steps, and documentation of presence and function of individual pathways on MSC preparations for clinical use are often missed. Hence, we review here mechanisms predicted to be relevant for adhesion, migration, and homing competence of MSCs. We also discuss some early data on homing of MSCs, deduced from preclinical experiments and from the few clinical studies with MSCs. Finally, we introduce some assays which could be applied to monitor preservation of the homing capacity of MSCs during GMP preparation.

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Our study examined whether human bone marrow-derived MSCs are able to differentiate, in vitro, into functional epithelial-like cells. MSCs were isolated from the sternum of 8 patients with different hematological disorders. The surface phenotype of these cells was characterized.To induce epithelial differentiation, MSCs were cultured using Epidermal Growth Factor, Keratinocyte Growth Factor, Hepatocyte Growth Factor and Insulin-like growth Factor-II. Differentiated cells were further characterized both morphologically and functionally by their capacity to express markers with specificity for epithelial lineage. The expression of cytokeratin 19 was assessed by immunocytochemistry, and cytokeratin 18 was evaluated by quantitative RT-PCR (Taq-man). The data demonstrate that human MSCs isolated from human bone marrow can differentiate into epithelial-like cells and may thus serve as a cell source for tissue engineering and cell therapy of epithelial tissue.

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Dendritic cells (DCs) constitute very attractive vectors for cancer immunotherapy due to their ability to efficiently capture and present tumor antigens, which initiates tumor-directed T-cell responses. Because the initiation of cytotoxic anti-tumor immune responses requires the cross-presentation mechanism, antigen targeting to DCs represents a very important step in the chain of events that constitutes the cross-priming immune process. In the current study, we explored the ability of DCs loaded with antibody-coated melanoma and ovarian carcinoma tumor cells to cross-present tumor antigens to CD8+ T cells and elicit in vitro anti-tumor immune responses. Coating melanoma and ovarian cancer cells with monoclonal antibodies against different surface antigens (CD44, ME491, LFA-3, and CD24) expressed by the tumor cells promoted the cross-presentation of the tumor-associated antigens as MART-1, gp100, tyrosinase, and NY-ESO-1 by DCs to CD8+ T. These tumor antigen-specific CD8+ T-cell populations resulting from the DC-mediated cross-priming process were identified using specific immune tetramers and were a few fold larger than the ones generated using peptide-pulsed or apoptotic tumor cell-loaded DCs. The CD8+ T cells generated by DCs loaded with monoclonal antibody-coated tumor cells were cytotoxic against the primary melanoma and ovarian carcinoma cells. Thus, targeting monoclonal antibody-coated tumor cells to DCs is a novel method that opens new perspectives for immunotherapy strategies.

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