Mesenchymal stem cells: Mechanisms of immunomodulation and homing

Cooperation by fibroblasts and bone marrow-mesenchymal stem cells to improve pancreatic rat-to-mouse islet xenotransplantation

Experimental and clinical experiences highlight the need to review some aspects of islet transplantation, especially with regard to site of grafting and control of the immune response. The subcutaneous space could be a good alternative to liver but its sparse vasculature is its main limitation. Induction of graft tolerance by using cells with immunoregulatory properties is a promising approach to avoid graft rejection. Both Fibroblasts and Mesenchymal Stem Cells (MSCs) have shown pro-angiogenic and immunomodulatory properties. Transplantation of islets into the subcutaneous space using plasma as scaffold and supplemented with fibroblasts and/or Bone Marrow-MSCs could be a promising strategy to achieve a functional extra-hepatic islet graft, without using immunosuppressive drugs. Xenogenic rat islets, autologous fibroblasts and/or allogenic BM-MSCs, were mixed with plasma, and coagulation was induced to constitute a Plasma-based Scaffold containing Islets (PSI), which was transplanted subcutaneously both in immunodeficient and immunocompetent diabetic mice. In immunodeficient diabetic mice, PSI itself allowed hyperglycemia reversion temporarily, but the presence of pro-angiogenic cells (fibroblasts or BM-MSCs) within PSI was necessary to improve graft re-vascularization and, thus, consistently maintain normoglycemia. In immunocompetent diabetic mice, only PSI containing BM-MSCs, but not those containing fibroblasts, normalized glycemia lasting up to one week after transplantation. Interestingly, when PSI contained both fibroblasts and BM-MSCs, the normoglycemia period showed an increase of 4-times with a physiological-like response in functional tests. Histology of immunocompetent mice showed an attenuation of the immune response in those grafts with BM-MSCs, which was improved by co-transplantation with fibroblasts, since they increased BM-MSC survival. In summary, fibroblasts and BM-MSCs showed similar pro-angiogenic properties in this model of islet xenotransplantation, whereas only BM-MSCs exerted an immunomodulatory effect, which was improved by the presence of fibroblasts. These results suggest that cooperation of different cell types with islets will be required to achieve a long-term functional graft.

Do mesenchymal stem cells modulate the milieu of reconstructed bladder wall?

To evaluate the mesenchymal stem cells (MSCs) influence on cytokines and matrix metalloproteinases (MMPs) expression in rat bladder wall regeneration. MSCs cultures from the bone marrow were established. Acellular matrices from the bladder submucosa were prepared. Bladders were reconstructed using cell-seeded (n = 5) and unseeded (n = 5) grafts. MSCs were injected into the bladder wall (n = 5), bladders were incised and MSCs were injected into the circulation (n = 5) or were left intact (n = 5). Animals were killed after 3 months. Bladder histology and immunohistochemical staining of IL-2, IL-4, IL-6, IL-10, TNF-α, TGF-β1, IFN-γ, MMP-2, and MMP-9 were done. Bladders reconstructed with cell-seeded grafts mimicked native tissue, while unseeded grafts revealed shrinkage and morphological irregularities. There were no morphological changes in bladders of other groups. Different pattern of cytokine and MMP expression was observed. Increased expression of anti-inflammatory cytokines and MMPs in bladder promotes detrusor regeneration.

Bone marrow-derived mesenchymal stem cells favor the immunosuppressive T cells skewing in a Helicobacter pylori model of gastric cancer

Bone marrow-derived mesenchymal stem cells (BM-MSCs) play an important role in Helicobacter pylori-induced gastric carcinogenesis. While the mechanism is not well understood, BM-MSCs have been shown to contribute to the immunosuppressive response found in a number of diseases. Here, BM-MSCs were transplanted into the stomach of mice with a 44-week mouse-adapted H. pylori infection. At day 28 post-transplantation, BM-MSCs migrated from the subserosal to the mucosal layer of the stomach. The grafted BM-MSCs significantly stimulated systemic and local interleukin-10 (IL-10)-secreting T cell and regulatory T cell (Treg) functions. This observation was correlated with an increased percentage of CD4⁺IL-10⁺ cells and CD4⁺CD25⁺FoxP3⁺ cells in splenic mononuclear cells compared with H. pylori-infected mice not receiving BM-MSCs. Moreover, inhibitory cytokines IL-10 and transforming growth factor-β1 increased in the gastric tissue, while there was a decrease in inflammatory interferon-γ (IFN-γ). BM-MSC-transplanted mice also developed elevated IL-10/IFN-γ secreting and Treg/Th17 ratios. A coculture system in the presence or absence of BM-MSCs was also established to evaluate the immune responses in vitro. An increase in IL-10-secreting T cells and Tregs, associated with increased expression of Gata-3 and FoxP3, generation of IL-10 in the supernatant, and proliferation of gastric epithelial cells (GECs) was observed. These findings demonstrate that transplantation of BM-MSCs into a chronic H. pylori-infected mouse model results in the generation of an immunosuppressive environment. The local and systemic immunosuppression mediated by BM-MSCs likely contributed to an environment that is compatible with the development of H. pylori-induced gastric cancer.

Conditioned medium from horse amniotic membrane-derived multipotent progenitor cells: immunomodulatory activity in vitro and first clinical application in tendon and ligament injuries in vivo

We have recently demonstrated that heterologous transplantation of horse amniotic membrane-derived mesenchymal cells (AMCs) can be useful for cell therapy applications in tendon diseases, and hypothesized that these cells may promote tendon repair via paracrine-acting molecules targeting inflammatory processes. To test this hypothesis, here we examined the immunomodulatory characteristics of AMCs and of their conditioned medium (AMC-CM) in vitro, and studied the potential therapeutic effect of AMC-CM in thirteen different spontaneous horse tendon and ligament injuries in vivo. Our results demonstrate that AMCs are capable of inhibiting peripheral blood mononuclear cell (PBMC) proliferation after allogenic stimulation either when cocultured in cell-to-cell contact, or when the two cell types are physically separated by a transwell membrane, suggesting that soluble factors are implicated in this phenomenon. Our hypothesis is further supported by the demonstration that PBMC proliferation is inhibited by AMC-CM. In our in vivo studies, no significant adverse effects were observed in treated tendons, and clinical and ultrasonographical evaluation did not reveal evidence of inappropriate tissue or tumor formation. Clinical outcomes were favorable and the significantly lower rate (15.38%) of reinjuries observed compared to untreated animals, suggests that treatment with AMC-CM is very efficacious. In conclusion, this study identifies AMC-CM as a novel therapeutic biological cell-free product for treating horse tendon and ligament diseases.

The effect of platelet lysate fibrinogen on the functionality of MSCs in immunotherapy

Human platelet lysate (PL) represents an attractive alternative to fetal bovine serum (FBS) for the ex vivo expansion of human mesenchymal stromal cells (MSCs). However, there is controversy whether MSCs propagated in unfractionated PL retain their immunosuppressive properties. Since fibrinogen can be a major component of PL, we hypothesized that the fibrinogen content in PL negatively affects the suppressor function of MSCs. Pools of outdated plateletpheresis products underwent a double freeze-thaw centrifugation and filtration to produce unfractionated platelet lysates (uPL), followed by a temperature controlled clotting procedure to produce a fibrinogen depleted platelet lysate (fdPL). Fibrinogen depletion affected neither the mitogenic properties of PL or growth factor content, however fdPL was less prone to develop precipitate over time. Functionally, fibrinogen interacted directly with MSCs, dose dependently increased IL-6, IL-8 and MCP-1 protein production, and compromised the ability of MSCs to up-regulate indoleamine dioxygenase (IDO), as well as, mitigate T-cell proliferation. Similarly uPL expanded MSCs showed a reduced capability of inducing IDO and suppressing T-cell proliferation compared to FBS expanded MSCs. Replacing uPL with fdPL largely restored the immune modulating effects of MSCs. Together these data suggest that fibrinogen negatively affects the immunomodulatory functions of MSCs and fdPL can serve as non-xenogenic mitogenic supplement for expansion of clinical grade MSCs for immune modulation.

Primary bone marrow mesenchymal stromal cells rescue the axonal phenotype of Twitcher mice

Krabbe's disease (KD) is a demyelinating disorder caused by the deficiency of lysosomal galactocerebrosidase (GALC), affecting both the central (CNS) and the peripheral nervous system (PNS). A current therapy, hematopoietic stem cell transplantation (HSCT), is ineffective at correcting the PNS pathology. We have previously shown that systemic delivery of immortalized bone marrow-derived murine mesenchymal stromal cells (BM-MSCs) diminishes the neuropathology of transplanted Twitcher mice, a murine model of KD. In this study, to move one step closer to clinical application, the effectiveness of a systematic delivery of primary BM-MSCs to promote recovery of the Twitcher PNS was assessed. Primary BM-MSCs grafted to the Twitcher sciatic nerve led to increased GALC activity that was not correlated to decreased psychosine (the toxic GALC substrate) accumulation. Nevertheless, BM-MSC transplantation rescued the axonal phenotype of Twitcher mice in the sciatic nerve, with an increased density of both myelinated and unmyelinated axons in transplanted animals. Whereas no increase in myelination was observed, upon transplantation an increased proliferation of Schwann cell precursors occurred. Supporting these findings, in vitro, BM-MSCs promoted neurite outgrowth of Twitcher sensory neurons and proliferation of Twitcher Schwann cells. Moreover, BM-MSCs expressed nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) and promoted increased BDNF synthesis by neighboring Schwann cells. Besides their action in neurons and glia, BM-MSCs led to macrophage activation in Twitcher sciatic nerves. In summary, primary BM-MSCs diminish the neuropathology of Twitcher sciatic nerves by coordinately affecting neurons, glia, and macrophages.

Multi-therapeutic effects of human adipose-derived mesenchymal stem cells on radiation-induced intestinal injury

Radiation-induced intestinal injuries (RIII) commonly occur in patients who suffer from pelvic or abdominal cancer. However, current management of these injuries is ineffective. Recently, mesenchymal stem cells (MSCs) have been extensively used in regenerative medicine and have achieved a high level of efficacy. In the present study, we hypothesised that human adipose-derived mesenchymal stem cells (hAd-MSCs) could be used as potential tools to heal RIII. We observed that adult Sprague-Dawley rats that received whole-abdominal irradiation benefitted from hAd-MSC injection. hAd-MSCs had RIII-healing effects, including anti-inflammation, neovascularisation and maintenance of epithelium homeostasis, as indicated by elevated serum IL-10, upregulation of vascular endothelial growth factor, basic fibroblast growth factor and epidermal growth factor in irradiated intestine, mobilisation of CD31-positive haematopoietic stem cells or haematopoietic progenitor cells, and the prolonged presence of Bmi1-positive cells within crypts. Consequently, after hAd-MSC treatment, irradiated rats survived longer than non-treated animals. These results suggest that hAd-MSCs have therapeutic potential for RIII management.

Transient proteolytic modification of mesenchymal stromal cells increases lung clearance rate and targeting to injured tissue

Systemic infusion of therapeutic cells would be the most practical and least invasive method of administration in many cellular therapies. One of the main obstacles especially in intravenous delivery of cells is a massive cell retention in the lungs, which impairs homing to the target tissue and may decrease the therapeutic outcome. In this study we showed that an alternative cell detachment of mesenchymal stromal/stem cells (MSCs) with pronase instead of trypsin significantly accelerated the lung clearance of the cells and, importantly, increased their targeting to an area of injury. Cell detachment with pronase transiently altered the MSC surface protein profile without compromising cell viability, multipotent cell characteristics, or immunomodulative and angiogenic potential. The transient modification of the cell surface protein profile was sufficient to produce effective changes in cell rolling behavior in vitro and, importantly, in the in vivo biodistribution of the cells in mouse, rat, and porcine models. In conclusion, pronase detachment could be used as a method to improve the MSC lung clearance and targeting in vivo. This may have a major impact on the bioavailability of MSCs in future therapeutic regimes.

Effects and safety of allogenic mesenchymal stem cell intravenous infusion in active ankylosing spondylitis patients who failed NSAIDs: a 20-week clinical trial

Our objective was to evaluate the feasibility, safety, and efficacy of intravenous (IV) infusion of allogenic mesenchymal stem cells (MSCs) in ankylosing spondylitis (AS) patients who are refractory to or cannot tolerate the side effects of nonsteroidal anti-inflammatory drugs (NSAIDs). AS patients enrolled in this study received four IV infusions of MSCs on days 0, 7, 14, and 21. The percentage of ASAS20 responders (the primary endpoint) at the fourth week and the mean ASAS20 response duration (the secondary endpoint) were used to assess treatment response to MSC infusion and duration of the therapeutic effects. Ankylosing Spondylitis Disease Activity Score Containing C-reactive Protein (ASDAS-CRP) and other preestablished evaluation indices were also adopted to evaluate the clinical effects. Magnetic resonance imaging (MRI) was performed to detect changes of bone marrow edema in the spine. The safety of this treatment was also evaluated. Thirty-one patients were included, and the percentage of ASAS20 responders reached 77.4% at the fourth week, and the mean ASAS20 response duration was 7.1 weeks. The mean ASDAS-CRP score decreased from 3.6 ± 0.6 to 2.4 ± 0.5 at the fourth week and then increased to 3.2 ± 0.8 at the 20th week. The average total inflammation extent (TIE) detected by MRI decreased from 533,482.5 at baseline to 480,692.3 at the fourth week (p > 0.05) and 400,547.2 at the 20th week (p < 0.05). No adverse effects were noted. IV infusion of MSCs is a feasible, safe, and promising treatment for patients with AS.

Intracoronary infusion of allogeneic mesenchymal precursor cells directly after experimental acute myocardial infarction reduces infarct size, abrogates adverse remodeling, and improves cardiac function

RATIONALE

Mesenchymal precursor cells (MPCs) are a specific Stro-3+ subpopulation of mesenchymal stem cells isolated from bone marrow. MPCs exert extensive cardioprotective effects, and are considered to be immune privileged.

OBJECTIVE

This study assessed the safety, feasibility, and efficacy of intracoronary delivery of allogeneic MPCs directly after acute myocardial infarction in sheep.

METHODS AND RESULTS

Initially, intracoronary delivery conditions were optimized in 20 sheep. These conditions were applied in a randomized study of 68 sheep with an anterior acute myocardial infarction. Coronary flow was monitored during MPC infusion, and cardiac function was assessed using invasive hemodynamics and echocardiography at baseline and during 8 weeks follow-up. Coronary flow remained within thrombolysis in myocardial infarction III definitions in all sheep during MPC infusion. Global left ventricular ejection fraction as measured by pressure-volume loop analysis deteriorated in controls to 40.7±2.6% after 8 weeks. In contrast, MPC treatment improved cardiac function to 52.8±0.7%. Echocardiography revealed significant improvement of both global and regional cardiac functions. Infarct size decreased by 40% in treated sheep, whereas infarct and border zone thickness were enhanced. Left ventricular adverse remodeling was abrogated by MPC therapy, resulting in a marked reduction of left ventricular volumes. Blood vessel density increased by >50% in the infarct and border areas. Compensatory cardiomyocyte hypertrophy was reduced in border and remote segments, accompanied by reduced collagen deposition and apoptosis. No microinfarctions in remote myocardial segments or histological abnormalities in unrelated organs were found.

CONCLUSIONS

Intracoronary infusion of allogeneic MPCs is safe, feasible, and markedly effective in a large animal model of acute myocardial infarction.

Mesenchymal Stem Cells Expressing Vasoactive Intestinal Peptide Ameliorate Symptoms in a Model of Chronic Multiple Sclerosis

Multiple sclerosis (MS) is a severe debilitating disorder characterized by progressive demyelination and axonal damage of the central nervous system (CNS). Current therapies for MS inhibit the immune response and demonstrate reasonable benefits if applied during the early phase of relapsing–remitting MS (RRMS) while there are no treatments for patients that progress neither to the chronic phase nor for the primary progressive form of the disease. In this manuscript, we have studied the therapeutic efficacy of a cell and gene therapy strategy for the treatment of a mouse model of chronic MS [myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE)]. We used allogenic mesenchymal stem cells (MSCs) as a therapeutic tool and also as vehicle to deliver fully processed 3.3-kDa vasoactive intestinal peptide (VIP) to the peripheral immune organs and to the inflamed CNS. Intraperitoneal administrations of MSCs expressing VIP stopped progression and reduced symptoms when administered at peak of disease. The improvement in clinical score correlated with diminished peripheral T-cell responses against MOG as well as lower inflammation, lower demyelination, and higher neuronal integrity in the CNS. Interestingly, neither lentiviral vectors expressing VIP nor unmodified MSCs were therapeutic when administer at the peak of disease. The increased therapeutic effect of MSCs expressing VIP over unmodified MSCs requires the immunoregulatory and neuroprotective roles of both VIP and MSCs and the ability of the MSCs to migrate to peripheral lymph organs and the inflamed CNS.

Mesenchymal stem cells from a hypoxic culture improve and engraft Achilles tendon repair

BACKGROUND

Bone marrow-derived mesenchymal stem cells (MSCs) from humans cultured under hypoxic conditions increase bone healing capacity.

HYPOTHESIS

Rat MSCs cultured under hypoxic conditions increase the tendon healing potential after transplantation into injured Achilles tendons.

STUDY DESIGN

Controlled laboratory study.

METHODS

Biomechanical testing, histological analysis, and bromodeoxyuridine (BrdU) labeling/collagen immunohistochemistry were performed to demonstrate that augmentation of an Achilles tendon rupture site with hypoxic MSCs increases healing capacity compared with normoxic MSCs and controls. Fifty Sprague-Dawley rats were used for the experiments, with 2 rats as the source of bone marrow MSCs. The cut Achilles tendons in the rats were equally divided into 3 groups: hypoxic MSC, normoxic MSC, and nontreated (vehicle control). The uncut tendons served as normal uncut controls. Outcome measures included mechanical testing in 24 rats, histological analysis, and BrdU labeling/collagen immunohistochemistry in another 24 rats.

RESULTS

The ultimate failure load in the hypoxic MSC group was significantly greater than that in the nontreated or normoxic MSC group at 2 weeks after incision (2.1 N/mm(2) vs 1.1 N/mm(2) or 1.9 N/mm(2), respectively) and at 4 weeks after incision (5.5 N/mm(2) vs 1.7 N/mm(2) or 2.7 N/mm(2), respectively). The ultimate failure load in the hypoxic MSC group at 4 weeks after incision (5.5 N/mm(2)) was close to but still significantly less than that of the uncut tendon (7.2 N/mm(2)). Histological analysis as determined by the semiquantitative Bonar histopathological grading scale revealed that the hypoxic MSC group underwent a significant improvement in Achilles tendon healing both at 2 and 4 weeks when compared with the nontreated or normoxic MSC group via statistical analysis. Immunohistochemistry further demonstrated that the hypoxic and normoxic MSC groups had stronger immunostaining for type I and type III collagen than did the nontreated group both at 2 and 4 weeks after incision. Moreover, BrdU labeling of MSCs before injection further determined the incorporation and retention of transplanted cells at the rupture site.

CONCLUSION

Transplantation of hypoxic MSCs may be a better and more readily available treatment than normoxic MSCs for Achilles tendon ruptures.

CLINICAL RELEVANCE

The present study provides evidence that transplantation of hypoxic MSCs may be a promising therapy for the treatment of Achilles tendon ruptures.

Notch-RBP-J signaling is required by bone marrow stromal cells for the treatment of acute graft versus host disease

Recent evidence has shown that bone marrow stromal cells (BMSCs) may exhibit immuno-suppression activities through soluble mediators and direct cell-cell contact, but how these processes are modulated has been poorly understood. In this study, we show that the Notch signaling pathway participates in the modulation of BMSCs to elicit their immuno-suppressive roles. In a murine lethal acute graft versus host disease (aGvHD) model, BMSCs deficient for RBP-J, the critical transcription factor mediating signaling from all four mammalian Notch receptors, failed to delay the development of the disease. RBP-J deficient BMSCs were not able to inhibit the proliferation and activation of allogenic T-cells. Moreover, RBP-J deficient BMSCs could not down-regulate the expression of MHC II and co-stimulation molecules CD80 and CD86 on dendritic cells (DCs). The antigen presentation capacity of DCs co-cultured with RBP-J deficient BMSCs was not impaired in contrast to wild type BMSCs. Furthermore, we showed that the productions of IL-6 and PGE2, two critical molecules mediating the immuno-suppressive activities of BMSCs, were reduced significantly in RBP-J deficient BMSCs. Both of the two molecules were importantly involved in the regulation of BMSCs by Notch signaling. In conclusion, our data suggests that the immuno-suppressive effects of BMSCs in aGvHD are dependent on Notch-RBP-J signaling, which regulates the productions of IL-6 and PGE2.

Investigating the efficacy of amnion-derived compared with bone marrow-derived mesenchymal stromal cells in equine tendon and ligament injuries

BACKGROUND AIMS

This is the first study to compare the treatment of horse tendon and ligament injuries with the use of mesenchymal stromal cells (MSCs) obtained from two different sources: amniotic membrane (AMSCs) and bone marrow (BM-MSCs). The objective was to prove the ability of AMSCs to exert beneficial effects in vivo.

METHODS

Five million allogeneic frozen-thawed AMSCs or autologous fresh BM-MSCs were injected intralesionally in horses belonging to group A (51 horses) and group B (44 horses). The interval lesion/implantation was of 6-15 days for the AMSCs and 16-35 days for the BM-MSCs. Healing was assessed clinically and ultrasonographically. Follow-up was monitored for 2 further years from return to full work.

RESULTS

No significant adverse effects after MSCs treatment were seen in any of the horses studied, independent of the type of stromal cell implanted. All animals belonging to group A resumed their activities between 4-5 months after treatment, whereas animals of group B resumed their activities after 4-12 months. The rate of re-injury in horses treated with AMSCs is lower (4.00%) compared with the average observed when horses were treated with BM-MSCs (23.08%).

CONCLUSIONS

The possibility to inject allogeneic AMSCs in real time, before any ultrasonographic change occurs within the injured tendon and ligament, together with the higher plasticity and proliferative capacity of these cells compared with BM-MSCs, represents the main features of interest for this novel approach for the treatment of equine tendon diseases. An obvious active proliferative healing in the area injected with AMSCs makes these cells more effective than BM-MSCs.

Mesenchymal stem cells tune the development of monocyte-derived dendritic cells toward a myeloid-derived suppressive phenotype through growth-regulated oncogene chemokines

Mesenchymal stem/stromal cells (MSCs) are promising potential candidates for the treatment of immunological diseases because of their immunosuppressive functions. However, the molecular mechanisms that mediate MSCs' immunosuppressive activity remain elusive. In this article, we report for the first time, to our knowledge, that secreted growth-regulated oncogene (GRO) chemokines, specifically GRO-γ, in human MSC-conditioned media have an effect on the differentiation and the function of human monocyte-derived dendritic cells. The monocyte-derived dendritic cells were driven toward a myeloid-derived suppressor cell (MDSC)-like phenotype by the GRO chemokines. GRO-γ-treated MDSCs had a tolerogenic phenotype that was characterized by an increase in the secretion of IL-10 and IL-4, and a reduction in the production of IL-12 and IFN-γ. We have also shown that the mRNA expression levels of the arginase-1 and inducible NO synthase genes, which characterize MDSCs, were upregulated by GRO-γ-primed mouse bone marrow cells. In addition, the ability of GRO-γ-treated bone marrow-derived dendritic cells to stimulate the OVA-specific CD8(+) T (OT-1) cell proliferation and the cytokine production of IFN-γ and TNF-α were significantly decreased in vivo. Our findings allow a greater understanding of how MDSCs can be generated and offer new perspectives to exploit the potential of MDSCs for alternative approaches to treat chronic inflammation and autoimmunity, as well as for the prevention of transplant rejection.

Deferoxamine preconditioning potentiates mesenchymal stem cell homing in vitro and in streptozotocin-diabetic rats

OBJECTIVE

Today, cell therapy is considered a promising alternative in treatment of several diseases such as type 1 diabetes. Loss of transplanted stem cell and more importantly scarcity in the number of cells reaching to target tissue is a major obstacle in cell therapy. There is evidences showing that deferoxamine (DFO), an iron chelator, increases the mobilization and homing of progenitor cells through increasing the stability of hypoxia-inducible factor 1α (HIF-1α) protein. In this study, the effect of DFO on some factors involved in homing of bone marrow-derived mesenchymal stem cell was investigated, and the other objectives of this research were to determine whether DFO is able to increase migration and subsequent homing of mesenchymal stem cell (MSCs) both in vitro and in vivo in streptozotocin-diabetic rats.

RESEARCH DESIGN AND METHODS

MSCs were treated by DFO in minimal essential medium α (αMEM) for 24 h. The expression and localization of HIF-1α were evaluated by western blotting and immunocytochemistry. The expression of C-X-C chemokine receptor type 4 (CXCR-4) and chemokine receptor 2 (CCR2) were assessed by western blotting and RT-PCR. The activity of matrix metalloproteinases (MMP) -2 and -9 were measured by gelatin zymography. Finally, in vitro migration of MSCs toward different concentrations of stromal cell-derived factor and monocyte chemotactic protein-1 were also evaluated. To demonstrate the homing of MSCs in vivo, DFO-treated chloromethyl-benzamidodialkylcarbocyanine-labeled MSCs were injected into the tail vein of rats, and the number of stained MSCs reaching to the pancreas were determined after 24 h.

RESULTS

In DFO-treated MSCs, expression of HIF-1α (p < 0.001), CXCR4 (p < 0.001), CCR2 (p < 0.001), and the activity of MMP-2 (p < 0.01) and MMP-9 (p < 0.05) were significantly increased compared to control groups. Elevation of HIF-1α, upregulation of CXCR4/CCR2 and higher activity of MMP-2/MMP-9 in DFO-treated MSCs were reversed by 2-methoxyestradiol (2-ME; 5 μmol), a HIF-1α inhibitor. The in vitro migrations as well as in vivo homing of DFO-treated MSCs were also significantly higher than control groups (p < 0.05).

CONCLUSIONS

Preconditioning of MSCs by DFO prior to transplantation could increase homing of MSCs through affecting some chemokine receptors as well as proteases involved and eventually improving the efficacy of cell therapy.

Characteristics of equine mesenchymal stem cells derived from amnion and bone marrow: in vitro proliferative and multilineage potential assessment

REASONS FOR PERFORMING STUDY

This is the first study comparing stemness features of equine mesenchymal progenitor cells derived from amniotic membrane and bone marrow.

OBJECTIVES

To investigate an alternative and noninvasive stromal cell source for equine tissue engineering.

STUDY DESIGN

In vitro experimental study of the characteristics of equine mesenchymal progenitor cells derived from amnion and bone marrow.

METHODS

Cells isolated from amniotic membrane and bone marrow were analysed for proliferation (growth curve, doubling time, colony forming unit). Immunocytochemical detection of pluripotency markers and gene expression of stromal cell markers were also performed and these cells were studied for multilineage plasticity.

RESULTS

Amniotic stromal cells (AMSCs) and bone marrow mesenchymal cells (BM-MSCs) both exhibited mature stromal cell-specific gene expression and immunocytochemical properties, but showed substantial differences in their proliferative and differentiation potential. The mean doubling time for AMSCs was significantly lower (P<0.05) than that observed for BM-MSCs (1.17 ± 0.15 vs. 3.27 ± 0.19 days, respectively). Compared to AMSCs, BM-MSCs also demonstrated a significantly (P<0.05) lower clonogenic capability (one fibroblast-like colony forming unit from a mean of 590.15 cells seeded for BM-MSCs vs. 242.73 cells seeded for AMSCs). BM-MSCs did not differentiate into glial cells, and the osteogenic differentiation process was longer than for AMSCs.

CONCLUSIONS AND POTENTIAL RELEVANCE

The amniotic membrane could be a valuable source of MSCs to be used both for allogenic and/or autologous therapies. The noninvasive nature and low cost of collection, the rapid proliferation along with a greater differentiation potential and the 'off the shelf' preparation potential could make AMCs useful for cell therapy.

Evidences of early senescence in multiple myeloma bone marrow mesenchymal stromal cells

Background

In multiple myeloma, bone marrow mesenchymal stromal cells support myeloma cell growth. Previous studies have suggested that direct and indirect interactions between malignant cells and bone marrow mesenchymal stromal cells result in constitutive abnormalities in the bone marrow mesenchymal stromal cells.

Design and Methods

The aims of this study were to investigate the constitutive abnormalities in myeloma bone marrow mesenchymal stromal cells and to evaluate the impact of new treatments.

Results

We demonstrated that myeloma bone marrow mesenchymal stromal cells have an increased expression of senescence-associated β-galactosidase, increased cell size, reduced proliferation capacity and characteristic expression of senescence-associated secretory profile members. We also observed a reduction in osteoblastogenic capacity and immunomodulatory activity and an increase in hematopoietic support capacity. Finally, we determined that current treatments were able to partially reduce some abnormalities in secreted factors, proliferation and osteoblastogenesis.

Conclusions

We showed that myeloma bone marrow mesenchymal stromal cells have an early senescent profile with profound alterations in their characteristics. This senescent state most likely participates in disease progression and relapse by altering the tumor microenvironment.

Characteristics of mouse adipose tissue-derived stem cells and therapeutic comparisons between syngeneic and allogeneic adipose tissue-derived stem cell transplantation in experimental autoimmune thyroiditis

Previously, we found that the intravenous administration of human adipose tissue-derived mesenchymal stem cells was a promising therapeutic option for autoimmune thyroiditis even when the cells were transplanted into a xenogeneic model without an immunosuppressant. Therefore, we explored the comparison between the therapeutic effects of syngeneic and allogeneic adipose tissue-derived stem cells on an experimental autoimmune thyroiditis mouse model. Experimental autoimmune thyroiditis was induced in C57BL/6 mice by immunization with porcine thyroglobulin. Adipose tissue-derived stem cells derived from C57BL/6 mice (syngeneic) or BALB/c mice (allogeneic) or saline as a vehicle control were administered intravenously four times weekly. Blood and tissue samples were collected 1 week after the last transplantation. Adipose tissue-derived stem cells from mice were able to differentiate into multiple lineages in vitro; however, mouse adipose tissue-derived stem cells did not have immunophenotypes identical to those from humans. Syngeneic and allogeneic administrations of adipose tissue-derived stem cells reduced thyroglobulin autoantibodies and the inflammatory immune response, protected against lymphocyte infiltration into the thyroid, and restored the Th1/Th2 balance without any adverse effects. However, different humoral immune responses were observed for infused cells from different stem cell sources. The strongest humoral immune response was induced by xenogeneic transplantation, followed by allogeneic and syngeneic administration, in that order. The stem cells were mostly found in the spleen, not the thyroid. This migration might be because the stem cells primarily function in systemic immune modulation, due to being given prior to disease induction. In this study, we confirmed that there were equal effects of adipose tissue-derived stem cells in treating autoimmune thyroiditis between syngeneic and allogeneic transplantations.

Cell-based tissue engineering augments tendon-to-bone healing in a rat supraspinatus model

Rotator cuff pathology causes substantial pain/disability and health care costs. Cell-based tissue engineering offers promise for improved outcomes in tendon to bone healing. Cells from the tendon-bone interface were used here to amplify surgical defect healing in a rat model. Cells from tendon-to-bone interface of the rotator cuff were seeded in sponges and implanted into critical rotator cuff defects: Group I, control; II, surgical defect only; III, suture-repaired defect; IV, surgical defect, repair with sponge only; V, surgical defect, repair with sponge with cells. Three, 6-, and 12-week results were assessed for histologic features. At 3 weeks, histologic indices in Group V were significantly increased versus other treatment groups. Group V (12 weeks) showed significantly improved collagen organization versus other treatment groups; there was no difference in collagen organization in Group I versus V. In summary, increased cellularity, inflammation, vascularity, and collagen organization were present at 3 weeks; increased collagen organization at 12 weeks in Group V provides evidence for improved healing with cells. Data further support the utility of tendon-bone interface cells in rotator cuff healing.

Human Mesenchymal Precursor Cells (Stro-1+) from Spinal Cord Injury Patients Improve Functional Recovery and Tissue Sparing in an Acute Spinal Cord Injury Rat Model

This study aimed to determine the potential of purified (Stro-1+) human mesenchymal precursor cells (hMPCs) to repair the injured spinal cord (SC) after transplantation into T-cell-deficient athymic RNU nude rats following acute moderate contusive spinal cord injury (SCI). hMPCs were isolated from the bone marrow (BM) stroma of SCI patients and transplanted as a suspension graft in medium [with or without immunosuppression using cyclosporin A (CsA)]. Extensive anatomical analysis shows statistically significant improvement in functional recovery, tissue sparing, and cyst reduction. We provide quantitative assessment of supraspinal projections in combination with functional outcomes. hMPC-transplanted animals consistently achieved mean BBB scores of 15 at 8 weeks postinjury. Quantitative histological staining revealed that graft-recipient animals possessed more intact spinal tissue and reduced cyst formation than controls. Fluorogold (FG) retrograde tracing revealed sparing/regeneration of supraspinal and local propriospinal axonal pathways, but no statistical differences were observed compared to controls. Immunohistochemical analysis revealed increased serotonergic (5-HT) and sensory (CGRP) axonal growth within and surrounding transplanted donor hMPCs 2 weeks posttransplantation, but no evidence of hMPC transdifferentiation was seen. Although hMPCs initially survive at 2 weeks posttransplantation, their numbers were dramatically reduced and no cells were detected at 8 weeks posttransplantation using retroviral/lentiviral GFP labeling and a human nuclear antigen (HNA) antibody. Additional immunosuppression with CsA did not improve hMPC survival or their ability to promote tissue sparing or functional recovery. We propose Stro-1+-selected hMPCs provide (i) a reproducible source for stem cell transplantation for SC therapy and (ii) a positive host microenvironment resulting in the promotion of tissue sparing/repair that subsequently improves behavioral outcomes after SCI. Our results provide a new candidate for consideration as a stem cell therapy for the repair of traumatic CNS injury.

Expression and role of Toll-like receptors on human umbilical cord mesenchymal stromal cells

BACKGROUND AIMS

Toll-like receptors (TLRs) play an important role in innate and adaptive immunity by recognizing pathogen-associated molecular patterns (PAMPs).

METHODS

In the present study, we investigated the expression and role of TLRs on human umbilical cord mesenchymal stromal cells (UC-MSCs). The proliferation, differentiation and immunoregulatory activity of UC-MSCs primed with or without TLR ligands were determined.

RESULTS

At the RNA level, the expression of TLR2, 4, 6 and 9 was relatively higher than that of other TLRs. However, TLR3 and TLR4 expression were relatively higher at the protein level. UC-MSCs expressed functional TLRs by nuclear factor-κB activation and cytokine expression assay. Poly-inosinic acid:cytidylic acid [Poly(I:C)] stimulation inhibited the proliferation of UC-MSCs, but the ligand of other TLRs had no significant effect. Poly(I:C) stimulation enhanced the adipogenic differentiation capability of UC-MSCs, but lipopolysaccharide inhibited the adipogenic differentiation. Poly(I:C) and CpG-oligonucleotide promoted the immunosuppressive potentiality of UC-MSCs, accompanied with the phosphorylation of interferon regulatory factor 3 (IRF3) and increased expression of indoleamine 2,3-dioxygenase and interferon β, whereas activation of other TLR ligands (synthetic analog fibroblast-stimulating lipopeptide-1 and lipopolysaccharide) failed to affect the immunoregulatory activity of UC-MSCs.

CONCLUSIONS

Taken together, our data demonstrated that TLR activation influenced the function of UC-MSCs, which might have important implications in future efforts to explore the clinical potentials of UC-MSCs.

Mesenchymal stem cells and their use in therapy: what has been achieved?

The considerable therapeutic potential of human multipotent mesenchymal stromal cells or mesenchymal stem cells (MSCs) has generated increasing interest in a wide variety of biomedical disciplines. Nevertheless, researchers report studies on MSCs using different methods of isolation and expansion, as well as different approaches to characterize them; therefore, it is increasingly difficult to compare and contrast study outcomes. To begin to address this issue, the Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy proposed minimal criteria to define human MSCs. First, MSCs must be plastic-adherent when maintained in standard culture conditions (α minimal essential medium plus 20% fetal bovine serum). Second, MSCs must express CD105, CD73 and CD90, and MSCs must lack expression of CD45, CD34, CD14 or CD11b, CD79α or CD19 and HLA-DR surface molecules. Third, MSCs must differentiate into osteoblasts, adipocytes and chondroblasts in vitro. MSCs are isolated from many adult tissues, in particular from bone marrow and adipose tissue. Along with their capacity to differentiate and transdifferentiate into cells of different lineages, these cells have also generated great interest for their ability to display immunomodulatory capacities. Indeed, a major breakthrough was the finding that MSCs are able to induce peripheral tolerance, suggesting that they may be used as therapeutic tools in immune-mediated disorders. Although no significant adverse events have been reported in clinical trials to date, all interventional therapies have some inherent risks. Potential risks for undesirable events, such as tumor development, that might occur while using these stem cells for therapy must be taken into account and contrasted against the potential benefits to patients.

Therapeutic potential of mesenchymal stem cell-derived microvesicles

Several studies have demonstrated that mesenchymal stem cells have the capacity to reverse acute and chronic kidney injury in different experimental models by paracrine mechanisms. This paracrine action may be accounted for, at least in part, by microvesicles (MVs) released from mesenchymal stem cells, resulting in a horizontal transfer of mRNA, microRNA and proteins. MVs, released as exosomes from the endosomal compartment, or as shedding vesicles from the cell surface, are now recognized as being an integral component of the intercellular microenvironment. By acting as vehicles for information transfer, MVs play a pivotal role in cell-to-cell communication. This exchange of information between the injured cells and stem cells has the potential to be bi-directional. Thus, MVs may either transfer transcripts from injured cells to stem cells, resulting in reprogramming of their phenotype to acquire specific features of the tissue, or conversely, transcripts could be transferred from stem cells to injured cells, restraining tissue injury and inducing cell cycle re-entry of resident cells, leading to tissue self-repair. Upon administration with a therapeutic regimen, MVs mimic the effect of mesenchymal stem cells in various experimental models by inhibiting apoptosis and stimulating cell proliferation. In this review, we discuss whether MVs released from mesenchymal stem cells have the potential to be exploited in novel therapeutic approaches in regenerative medicine to repair damaged tissues, as an alternative to stem cell-based therapy.

Anti-inflammatory role and immunomodulation of mesenchymal stem cells in systemic joint diseases: potential for treatment

INTRODUCTION

Mesenchymal stem cells (MSCs) are multipotent stromal cells characterized by their ability to differentiate into adipocytes, chondrocytes, osteocytes and a number of other lineages. Investigation into their use has increased in recent years as characterization of their immunomodulatory properties has developed, and their role in the pathophysiology of joint disease has been suggested.

AREAS COVERED

MSCs demonstrate immunosuppressive functionality by suppressing T- and B-cell responses following activation by cytokines such as IL-6 and IL-1α. They also can be induced to exert pro-inflammatory effects in the presence of acute inflammatory environment due to the actions of TNF-α and IFN-γ. In inflammatory joint diseases such as rheumatoid arthritis, MSCs in bone marrow migrate to joints by a TNF-α-dependent mechanism and may be in part responsible for the disease process. MSCs have also been demonstrated in increased numbers in periarticular tissues in osteoarthritis, which may reflect an attempt at joint regeneration.

EXPERT OPINION

Clinical applications for MSCs have shown promise in a number of inflammatory and autoimmune disorders. Future work is likely to further reveal the immunosuppressive characteristics of MSCs, their role in the pathophysiology of joint diseases and provide the basis for new avenues for treatment.

Mesenchymal stem cells as cellular immunotherapeutics in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment option in hematopoietic disorders, immunodeficiencies and leukemia. To date graft-versus-host disease (GvHD) represents a life-threatening complication even if associated with beneficial antileukemic reactivity. GvHD is the clinical manifestation of donor cells reacting against host tissue. Because of their ability to facilitate endogenous repair and to attenuate inflammation, MSC have evolved as a highly attractive cellular therapeutic in allo-HSCT. Here we report on the clinical experience in the use of MSC to enhance engraftment and prevent and treat acute and chronic GvHD. In early clinical trials, MSC have shown considerable benefit in the setting of manifest GvHD. These encouraging results warrant further exploration.

Long term effects of the implantation of Wharton's jelly-derived mesenchymal stem cells from the umbilical cord for newly-onset type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder resulted from T cell-mediated destruction of pancreatic β-cells, how to regenerate β-cells and prevent the autoimmune destruction of remnant and neogenetic β-cells is a tough problem. Immunomodulatory propertity of mesenchymal stem cell make it illuminated to overcome it. We assessed the long-term effects of the implantation of Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) from the umbilical cord for Newly-onset T1DM. Twenty-nine patients with newly onset T1DM were randomly divided into two groups, patients in group I were treated with WJ-MSCs and patients in group II were treated with normal saline based on insulin intensive therapy. Patients were followed-up after the operation at monthly intervals for the first 3 months and thereafter every 3 months for the next 21 months, the occurrence of any side effects and results of laboratory examinations were evaluated. There were no reported acute or chronic side effects in group I compared with group II, both the HbA1c and C peptide in group I patients were significantly better than either pretherapy values or group II patients during the follow-up period. These data suggested that the implantation of WJ-MSCs for the treatment of newly-onset T1DM is safe and effective. This therapy can restore the function of islet β cells in a longer time, although precise mechanisms are unknown, the implantation of WJ-MSCs is expected to be an effective strategy for treatment of type1 diabetes.

Decellularized tissue-engineered heart valve leaflets with recellularization potential

Tissue-engineered heart valves (TEHV) have been proposed as a promising solution for the clinical needs of pediatric patients. In vivo studies have shown TEHV leaflet contraction and regurgitation after several months of implantation. This has been attributed to contractile cells utilized to produce the extracellular matrix (ECM) during TEHV culture. Here, we utilized such cells to develop a mature ECM in a fibrin-based scaffold that generates commissural alignment in TEHV leaflets and then removed these cells using detergents. Further, we evaluated recellularization with potentially noncontractile cells. A tissue-engineered leaflet model was developed with mechanical anisotropy and tensile properties comparable to an ovine pulmonary valve leaflet. No change in tensile properties occurred after decellularization using 1% sodium dodecyl sulfate and 1% Triton detergent treatment. Cell removal was verified by DNA quantitation and western blot analysis for cellular proteins. Histological and scanning electron microscope imaging showed no significant change in the ECM organization and microstructure. We further tested the recellularization potential of decellularized leaflets by seeding human mesenchymal stem cells (hMSC) on the surface of the leaflets and evaluated them at 1 and 3 weeks in two culture conditions. One medium (M1) was chosen to maintain the MSC phenotype while a second medium (M2) was used to potentially differentiate cells to an interstitial cell phenotype. Cellular quantitation showed that the engineered leaflets were recellularized to the highest concentration with M2 followed by M1, with minimum cell invasion of decellularized native leaflets. Histology showed cellular invasion throughout the thickness of the leaflets in M2 and partial invasion in M1. hMSC stained positive for MSC markers, but also for α-smooth muscle actin in both media at 1 week, with no presence of MSC markers at 3 weeks with the exception of CD90. These results show that engineered leaflets, while having similar tensile properties and collagen content compared to native leaflets, have better recellularization potential.

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.

Mesenchymal stem cells as immunomodulators in a vascularized composite allotransplantation

Vascularized composite allotransplantations (VCAs) are not routinely performed for tissue reconstruction because of the potentially harmful adverse effects associated with lifelong administration of immunosuppressive agents. Researchers have been eagerly seeking alternative methods that circumvent the long-term use of immunosuppressants. Mesenchymal stem cells (MSCs) show promise as an immunomodulatory therapeutic agent and are currently being tested in preclinical and clinical settings as therapies for autoimmune disorders or transplant rejection. The mechanisms by which MSCs modulate the immune response are still under thorough investigation, but these most likely involve expression of local factors influencing T-cell regulation, modulation of cytokine expression (e.g., IL-10, TGF-β, TNF-α, INF-γ, etc.), and interactions with dendritic or antigen presenting cells. In this paper, we summarize the current understanding of immunomodulation achieved by MSC therapies and introduce a possible outline for future clinical applications in VCA.

Matrix metalloproteinase-9 contributes to the mobilization of bone marrow cells in the injured liver

Effective mobilization of hematopoietic stem cells (HSCs) in injured organs has not been established. Matrix metalloproteinase-9 (MMP-9) is known to release HSCs from bone marrow (BM) into the peripheral blood, but its role in the recruitment of HSCs to injured organs is unclear. In this study we tried to clarify the role of the host MMP-9 in trafficking of HSCs toward the injured liver, especially the relation of MMP-9 with the chemokine receptor 4 (CXCR4)-chemokine ligand 12 (CXCL12) axis, and to examine whether MMP-9 deficiency affects BM cell trafficking to the injured liver in mice. In vitro, we investigated the effect of MMP-9 on migration activity and CXCR4 expression on lineage-negative (Lin(-)) BM cells. In vivo, we induced acute and chronic liver injury in MMP-9 knockout (KO) and control mice by inoculation of carbon tetrachloride, followed by transplantation of Lin(-) BM cells obtained from enhanced green fluorescent protein (EGFP)-transgenic mice, and counted the BM cells mobilized in the injured liver. In a migration assay, active MMP-9, but not proMMP-9, increased the number of migrated Lin(-) BM cells, which was inhibited by tissue inhibitor of metalloproteinase-1 or a MMP inhibitor. This chemoattractant function by MMP-9 was synergistic when cotreated with CXCL12. CXCR4 expression on Lin(-) BM cells was dose- and time-dependently increased by active MMP-9. At the same time, treatment with MMP-9 enhanced CXCL12 expression, and CXCL12 reciprocally increased MMP-9 expression in BM cells. In in vivo studies, many EGFP(+) cells were seen in control recipient mice. In contrast, few EGFP(+) cells were observed in MMP-9 KO mice. BM cells tended to differentiate into desmin(+) cells. In conclusion, MMP-9 contributes to the mobilization of BM cells in the injured liver by upregulating the expression of CXCR4 on Lin(-) BM cells and attracting BM cells along its gradient of CXCL12. Therefore, host MMP-9 plays an important role in BM cell migration in the injured liver.

Toward personalized cell therapies by using stem cells: seven relevant topics for safety and success in stem cell therapy

Stem cells, both embryonic and adult, due to the potential for application in tissue regeneration have been the target of interest to the world scientific community. In fact, stem cells can be considered revolutionary in the field of medicine, especially in the treatment of a wide range of human diseases. However, caution is needed in the clinical application of such cells and this is an issue that demands more studies. This paper will discuss some controversial issues of importance for achieving cell therapy safety and success. Particularly, the following aspects of stem cell biology will be presented: methods for stem cells culture, teratogenic or tumorigenic potential, cellular dose, proliferation, senescence, karyotyping, and immunosuppressive activity.

Ultrastructural evidence of exosome secretion by progenitor cells in adult mouse myocardium and adult human cardiospheres

The demonstration of beneficial effects of cell therapy despite the persistence of only few transplanted cells in vivo suggests secreted factors may be the active component of this treatment. This so-called paracrine hypothesis is supported by observations that culture media conditioned by progenitor cells contain growth factors that mediate proangiogenic and cytoprotective effects. Cardiac progenitor cells in semi-suspension culture form spherical clusters (cardiospheres) that deliver paracrine signals to neighboring cells. A key component of paracrine secretion is exosomes, membrane vesicles that are stored intracellularly in endosomal compartments and are secreted when these structures fuse with the cell plasma membrane. Exosomes have been identified as the active component of proangiogenic effects of bone marrow CD34⁺ stem cells in mice and the regenerative effects of embryonic mesenchymal stem cells in infarcted hearts in pigs and mice. Here, we provide electron microscopic evidence of exosome secretion by progenitor cells in mouse myocardium and human cardiospheres. Exosomes are emerging as an attractive vector of paracrine signals delivered by progenitor cells. They can be stored as an “off-the-shelf” product. As such, exosomes have the potential for circumventing many of the limitations of viable cells for therapeutic applications in regenerative medicine.

Palmitate causes endoplasmic reticulum stress and apoptosis in human mesenchymal stem cells: prevention by AMPK activator

Elevated circulating saturated fatty acids concentration is commonly associated with poorly controlled diabetes. The highly prevalent free fatty acid palmitate could induce apoptosis in various cell types, but little is known about its effects on human mesenchymal stem cells (MSCs). Here, we report that prolonged exposure to palmitate induces human bone marrow-derived MSC (hBM-MSC) and human umbilical cord-derived MSC apoptosis. We investigated the role of endoplasmic reticulum (ER) stress, which is known to promote cell apoptosis. Palmitate activated XBP1 splicing, elF2α (eukaryotic translation initiation factor 2α) phosphorylation, and CHOP, ATF4, BiP, and GRP94 transcription in hBM-MSCs. ERK1/2 and p38 MAPK phosphorylation were also induced by palmitate in hBM-MSCs. A selective p38 inhibitor inhibited palmitate activation of the ER stress, whereas the ERK1/2 inhibitors had no effect. The AMP-activated protein kinase activator aminoimidazole carboxamide ribonucleotide blocked palmitate-induced ER stress and apoptosis. These findings suggest that palmitate induces ER stress and ERK1/2 and p38 activation in hBM-MSCs, and AMP-activated protein kinase activator prevents the deleterious effects of palmitate by inhibiting ER stress and apoptosis.

Environmental Biomechanics Substantiated by Defined Pillar Micropatterns Govern Behavior of Human Mesenchymal Stem Cells

While evidence on the impact of the biomechanical environment elasticity on human mesenchymal stem cell (hMSC) behavior is growing, the aspect of micropatterning is still poorly understood. Thus, the present study aimed at investigating the influence of defined environmental micropatterning on hMSC behavior. Following characterization, hMSCs were grown on defined pillar micropatterns of 5, 7, 9, and 11 μm. With respect to cell behavior, primary hMSC adhesion was detected by indirect immunofluorescence (iIF) for paxillin, vinculin, integrin αV, and actin, while proliferation was visualized by histone H3. Morphogenesis was monitored by scanning electron microscopy and the expression of stem cell-specific biomarkers by real-time PCR. Favoritism of primary adhesion of hMSCs on pillar tops occurred at smaller pillar micropatterns, concomitant with cell flattening. While vinculin, integrin αV, and paxillin appeared initially more cytoplasmic, high pillar micropatterns favored a progressive redistribution with polarization to cell tension sites and at cell borders. Accomplishment of morphogenesis at day 3 revealed establishment of fully rotund cell somata at 5 μm, while hMSCs appeared progressively elongated at rising micropatterns. The hMSC proliferation capacity was influenced by pillar micropatterns and gene expression analysis of stem cell- and differentiation-associated biomarkers disclosed clear modulation by distinct pillar micropatterns. In response to environmental biomechanics, our results show that hMSC behavior is governed by pillar micropatterning. In turn, these findings may form the basis to prospectively direct lineage specificity of hMSCs in a customized fashion.

GMP-compliant isolation and expansion of bone marrow-derived MSCs in the closed, automated device quantum cell expansion system

The estimated frequency of MSCs in BM is about 0.001-0.01% of total nucleated cells. Most commonly, one applied therapeutic cell dose is about 1-5 million MSCs/kg body weight, necessitating a reliable, fast, and safe expansion system. The limited availability of MSCs demands for an extensive ex vivo amplification step to accumulate sufficient cell numbers. Human platelet lysate (PL) has proven to be a safe and feasible alternative to animal-derived serum as supplement for MSC cultivation. We have investigated the functionally closed automated cell culture hollow fiber bioreactor Quantum cell expansion system as an alternative novel tool to conventional tissue flasks for efficient clinical-scale MSC isolation and expansion from bone marrow using PL. Cells expanded in the Quantum system fulfilled MSC criteria as shown by flow cytometry and adipogenic, chondrogenic, and osteogenic differentiation capacity. Cell surface expression of a variety of chemokine receptors, adhesion molecules, and additional MSC markers was monitored for several passages by flow cytometry. The levels of critical media components like glucose and lactate were analyzed. PDGF-AA, PDGF-AB/BB, bFGF, TGF-β1, sICAM-1, sVCAM-1, RANTES, GRO, VEGF, sCD40L, and IL-6 were assessed using a LUMINEX platform. Originally optimized for the use of fetal calf serum (FCS) as supplement and fibronectin as coating reagent, we succeeded to obtain an average of more than 100×10(6) of MSCs from as little as 18.8-28.6 ml of BM aspirate using PL. We obtained similar yields of MSCs/µl BM in the FCS-containing and the xenogen-free expansion system. The Quantum system reliably produces a cellular therapeutic dose in a functionally closed system that requires minimal manipulation. Both isolation and expansion are possible using FCS or PL as supplement. Coating of the hollow fibers of the bioreactor is mandatory when loading MSCs. Fibronectin, PL, and human plasma may serve as coating reagents.

Hypoxia-induced secretion of TGF-β1 in mesenchymal stem cell promotes breast cancer cell progression

In solid tumors, a decreased oxygen and nutrient supply creates a hypoxic microenvironment in the central region. This hypoxic condition induces molecular responses of normal and cancer cells in the local area, including angiogenesis, metabolic changes, and metastasis. In addition, other cells including mesenchymal stem cells (MSCs) have been reported to be recruited into the hypoxic area of solid tumors. In our previous study, we found that hypoxic condition induces the secretion of growth factors and cytokines in MSCs, and here we demonstrate that elevated secretion of transforming growth factor-β1 (TGF-β1) by MSCs under hypoxia promotes the growth, motility, and invasive ability of breast cancer cells. It was found that TGF-β1 promoter activity was regulated by hypoxia, and the major hypoxia-regulated element was located between bp -1030 to -666 in front of the TGF-β1 promoter region. In ChIP assay, the results revealed that HIF-1 was bound to the hypoxia response element (HRE) of TGF-β1 promoter. Collectively, the results indicate that hypoxia microenvironment can enhance cancer cell growth through the paracrine effects of the MSCs by driving their TGF-β1 gene expression and secretion. Therefore, extra caution has to be exercised when considering hypoxia pretreatment of MSCs before cell transplantation into patients for therapeutic purposes, particularly in patients susceptible to tumor growth.

The role of mesenchymal stem cells in hematopoietic stem cell transplantation: from bench to bedsides

Mesenchymal stem cells (MSCs) have been shown to be effective in the management of graft-versus-host disease (GVHD) due to their immunomodulatory effects. In addition to prevention and treatment of GVHD, many studies have demonstrated that MSCs can promote hematopoietic engraftment, accelerate lymphocyte recovery, reduce the risk of graft failure, and repair tissue damage in patients receiving hematopoietic stem cell transplantation (HSCT). Bone marrow (BM) has been considered as the traditional source of MSCs, and most of the knowledge concerning MSCs comes from BM studies. However, BM-derived MSCs have several limitations for their clinical application. Fetal-type MSCs can be isolated easier and proliferate faster in vitro as well as possessing a lower immunogenicity. Therefore, fetal-type MSCs, such as umbilical cord-derived MSCs, represent an excellent alternative source of MSCs. MSCs play multiple important roles in HSCT. Nevertheless, several issues regarding their clinical application remain to be discussed, including the safety of use in humans, the available sources and the convenience of obtaining MSCs, the quality control of in vitro-cultured MSCs and the appropriate cell passages, the optimum cell dose, and the optimum number of infusions. Furthermore, it is important to evaluate whether the rates of cancer relapse and infections increase when using MSCs for GVHD. There are still many questions regarding the clinical application of MSCs to HSCT that need to be answered, and further studies are warranted.

Cell encapsulating biomaterial regulates mesenchymal stromal/stem cell differentiation and macrophage immunophenotype

Bone marrow mesenchymal stromal/stem cell (MSC) encapsulation within a biomatrix could improve cellular delivery and extend survival and residence time over conventional intravenous administration. Although MSCs modulate monocyte/macrophage (Mø) immunophenotypic properties, little is known about how such interactions are influenced when MSCs are entrapped within a biomaterial. Furthermore, the impact of the cell-encapsulating matrix on MSC multipotency and on Møs, which infiltrate biomaterials, remains poorly understood. Here we elucidate this three-way interaction. The Mø immunophenotype and MSC differentiation were examined with regard to established and experimental collagen-based biomaterials for MSC entrapment. Tumor necrosis factor-α secretion was acutely inhibited at 4 days. MSCs cocultured with Møs demonstrated attenuated chondrocyte differentiation, whereas osteoblast differentiation was enhanced. Adipocyte differentiation was considerably enhanced for MSCs entrapped within the gelatin/polyethylene glycol-based matrix. A better understanding of the effect of cell encapsulation on differentiation potency and immunomodulation of MSCs is essential for MSC-based, biomaterial-enabled therapies.

Homeobox protein HB9 binds to the prostaglandin E receptor 2 promoter and inhibits intracellular cAMP mobilization in leukemic cells

BACKGROUND

HB9 is highly expressed in translocation t(7;12) positive infant AML.

RESULTS

HB9 binds to the PTGER2 promoter, down-regulates PTGER2 gene expression and subsequently represses cAMP synthesis in hematopoietic cells.

CONCLUSION

Expression of HLXB9 represses PTGER2 mediated signaling.

SIGNIFICANCE

First molecular report of HB9-dependent target gene regulation in hematopoietic cells. The transcription factor HB9, encoded by the homeobox gene B9 (HLXB9), is involved in the development of pancreatic beta- and motor neuronal cells. In addition, HLXB9 is recurrently rearranged in young children with acute myeloid leukemia characterized by a chromosomal translocation t(7;12)-HLXB9/TEL and concomitant high expression of the unrearranged, wild-type HLXB9 allele. However, target genes of HB9 in hematopoietic cells are not known to date. In this study, we used ChIP-on-chip analysis together with expression profiling and identified PTGER2 (prostaglandin E receptor 2) as a target gene of HB9 in a hematopoietic cell line. The functional HB9 homeodomain as well as the HB9 binding domain within the PTGER2 promoter are essential for binding of HB9 to the PTGER2 promoter region and down-regulation of PTGER2 expression. Functionally, HB9 conducted down-regulation of PTGER2 results in a reduced content of intracellular cAMP mobilization and furthermore the decreased PTGER2 gene expression is valid in bone marrow cells from translocation t(7;12) positive patients. Among the primary and secondary target genes of HB9 in the myeloid cell line HL60, 78% of significantly regulated genes are down-regulated, indicating an overall repressive function of HB9. Differentially regulated genes were preferentially confined to pathways involved in cell-adhesion and cell-cell interactions, similar to the gene expression footprint of HLXB9-expressing cells from t(7;12) positive patients.

Implantation of osteogenic differentiated donor mesenchymal stem cells causes recruitment of host cells

The interaction between host and donor cells is believed to play an important role in osteogenesis. However, it is still unclear how donor osteogenic cells behave and interact with host cells in vivo. The purpose of this study was to track the interactions between transplanted osteogenic cells and host cells during osteogenesis. In vitro migration assay was carried out to investigate the ability of osteogenic differentiated human mesenchymal stem cells (O-hMSCs) to recruit MSCs. At the in vivo level, O-hMSCs were implanted subcutaneously or into skull defects in severe combined immunodeficient (SCID) mice. New bone formation was observed by micro-CT and histological procedures. In situ hybridization (ISH) against human Alu sequences was performed to distinguish donor osteogenic cells from host cells. In vitro migration assay revealed an increased migration potential of MSCs by co-culturing with O-hMSCs. In agreement with the results of in vitro studies, ISH against human Alu sequences showed that host mouse MSCs migrated in large numbers into the transplantation site in response to O-hMSCs. Interestingly, host cells recruited by O-hMSCs were the major cell populations in newly formed bone tissues, indicating that O-hMSCs can trigger and initiate osteogenesis when transplanted in orthotopic sites. The observations from this study demonstrated that in vitro induced O-hMSCs were able to attract host MSCs in vivo and were involved in osteogenesis together with host cells, which may be of importance for bone tissue-engineering applications.

Human multipotent adult progenitor cells are nonimmunogenic and exert potent immunomodulatory effects on alloreactive T-cell responses

Multipotent adult progenitor cells (MAPCs) are bone marrow-derived nonhematopoietic stem cells with a broad differentiation potential and extensive expansion capacity. A comparative study between human mesenchymal stem cells (hMSCs) and human MAPCs (hMAPCs) has shown that hMAPCs have clearly distinct phenotypical and functional characteristics from hMSCs. In particular, hMAPCs express lower levels of MHC class I than hMSCs and cannot only differentiate into typical mesenchymal cell types but can also differentiate in vitro and in vivo into functional endothelial cells. The use of hMSCs as cellular immunomodulatory stem cell products gained much interest since their immunomodulatory capacities in vitro became evident over the last decade. Currently, the clinical grade stem cell product of hMAPCs is already used in clinical trials to prevent graft-versus-host disease (GVHD), as well as for the treatment of acute myocardial infarct, ischemic stroke, and Crohn's disease. Therefore, we studied the immune phenotype, immunogenicity, and immunosuppressive effect of hMAPCs in vitro. We demonstrated that hMAPCs are nonimmunogenic for T-cell proliferation and cytokine production. In addition, hMAPCs exert strong immunosuppressive effects on T-cell alloreactivity and on T-cell proliferation induced by mitogens and recall antigens. This immunomodulatory effect was not MHC restricted, which makes off-the-shelf use promising. The immunosuppressive effect of hMAPCs is partially mediated via soluble factors and dependent on indoleamine 2,3-dioxygenase (IDO) activity. At last, we isolated hMAPCs, the clinical grade stem cell product of hMAPCs, named MultiStem, and hMSCs from one single donor and observed that both the immunogenicity and the immunosuppressive capacities of all three stem cell products are comparable in vitro. In conclusion, hMAPCs have potent immunomodulatory properties in vitro and can serve as a valuable cell source for the clinical use of immunomodulatory cellular stem cell product.