Mesenchymal stem cells are capable of homing to the bone marrow of non-human primates following systemic infusion

Concise review: mesenchymal stem cells: their phenotype, differentiation capacity, immunological features, and potential for homing

MSCs are nonhematopoietic stromal cells that are capable of differentiating into, and contribute to the regeneration of, mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon, and adipose. MSCs are rare in bone marrow, representing approximately 1 in 10,000 nucleated cells. Although not immortal, they have the ability to expand manyfold in culture while retaining their growth and multilineage potential. MSCs are identified by the expression of many molecules including CD105 (SH2) and CD73 (SH3/4) and are negative for the hematopoietic markers CD34, CD45, and CD14. The properties of MSCs make these cells potentially ideal candidates for tissue engineering. It has been shown that MSCs, when transplanted systemically, are able to migrate to sites of injury in animals, suggesting that MSCs possess migratory capacity. However, the mechanisms underlying the migration of these cells remain unclear. Chemokine receptors and their ligands and adhesion molecules play an important role in tissue-specific homing of leukocytes and have also been implicated in trafficking of hematopoietic precursors into and through tissue. Several studies have reported the functional expression of various chemokine receptors and adhesion molecules on human MSCs. Harnessing the migratory potential of MSCs by modulating their chemokine-chemokine receptor interactions may be a powerful way to increase their ability to correct inherited disorders of mesenchymal tissues or facilitate tissue repair in vivo. The current review describes what is known about MSCs and their capacity to home to tissues together with the associated molecular mechanisms involving chemokine receptors and adhesion molecules.

Multipotent mesenchymal stromal cells and immune tolerance

Multipotent mesenchymal stromal cells or mesenchymal stem cells (MSC) are isolated mainly from bone marrow and adipose tissue but are identified in other tissues such as synovium, periosteum or placenta. They are characterised by their property to adhere to plastic, their phenotype and their ability to differentiate into three lineages (chondrocytes, osteoblasts and adipocytes). More recently, these cells were shown to escape immune recognition and inhibit immune responses. MSC may modulate the function of the major immune cell populations, including antigen-presenting cells, T cells, B cells and natural killer cells. The aim of this review is to focus on the molecular mechanisms, still poorly understood, which are responsible of the immunosuppressive effects mediated by the MSC. Finally, the data obtained from in vivo experimentation in various animal models as well as potential therapeutic applications will be presented.

Therapeutic applications of mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are multipotent cells that can be derived from many different organs and tissues. They have been demonstrated to play a role in tissue repair and regeneration in both preclinical and clinical studies. They also have remarkable immunosuppressive properties. We describe their application in settings that include the cardiovascular, central nervous, gastrointestinal, renal, orthopaedic and haematopoietic systems. Manufacturing of MSC for clinical trials is also discussed. Since tissue matching between MSC donor and recipient does not appear to be required, MSC may be the first cell type able to be used as an "off-the-shelf" therapeutic product.

Expression of Thy 1.2 surface antigen increases significantly during the murine mesenchymal stem cells cultivation period

This study sought to investigate the absence or expression of some surface antigens on murine mesenchymal stem cells (mMSCs) during the cultivation period of primary culture to passage 3 (equivalent to about 15 or 16 population doubling number). For this purpose, bone marrow cells from 6-8-week-old mice (either NMRI or Balb/c) were cultivated in 75-cm(2) culture flask for three successive passages, in each of which the culture was examined for the expression of CD135, CD44, CD31, Thy1.2, CD11b, CD45, CD34, Vcam1, Sca-1, and c-Kit antigens, using flow cytometry. Passage-3 cells from each strain can easily be differentiated into bone and fat, which was indicative of their mesenchymal nature. Our results demonstrated that for each given antigen, the percentages of the cells expressing that antigen had been changed by subcultures. The statistical analysis showed that nearly all differences between the passages were statistically significant. In this term, the expressional changes of Thy 1.2 seemed to be very significant in such a way that the expression increased to about half of the whole population in passage 3. In conclusion, it seems that this antigen could be considered as an enriching antigen for mMSCs population from bone marrow adherent cell culture.

Intravenous delivery of autologous mesenchymal stem cells limits infarct size and improves left ventricular function in the infarcted porcine heart

Systemic delivery of bone marrow-derived mesenchymal stem cells (MSCs) is a noninvasive approach for myocardial repair. We aimed to test this strategy in a pig model of myocardial infarction. Pigs (n = 8) received autologous MSCs (1 x 10(6)/kg body weight) labeled with fluorescent dye 48 h post proximal left anterior descending artery (LAD) occlusion. Hemodyamics, infarct size, and myocardial function were assessed at baseline and after 1 month. Morphologic analysis revealed that labeled MSCs migrated in the peri-infarct region, resulting in smaller infarct size (32 +/- 7 vs. 19 +/- 7%, p = 0.01), higher fractional area shortening (23 +/- 3 vs. 34.0 +/- 7%, p = 0.001), lower left ventricular end diastolic pressure (18.7 +/- 5 vs. 10.2 +/- 4 mmHg, p = 0.02) and higher +dp/dt (4,570 +/- 540 vs. 6,742 +/- 700 mmHg/s, p = 0.03) during inotropic stimulation. Systemic intravenous delivery of MSCs to pigs limits myocardial infarct size and is an attractive approach for tissue repair.

Potential differentiation of human mesenchymal stem cell transplanted in rat corpus cavernosum toward endothelial or smooth muscle cells

One of the causes of erectile dysfunction (ED) is the damaged penile cavernous smooth muscle cells (SMCs) and sinus endothelial cells (ECs). To investigate the feasibility of applying immortalized human mesenchymal stem cells (MSCs) to penile cavernous ECs or SMCs repair in the treatment of ED, the in vivo potential differentiation of the immortalized human MSCs toward penile cavernous endothelial or smooth muscle was investigated. One clone of immortalized human bone marrow mesenchymal stem cell line B10 cells via retroviral vector encoding v-myc were transplanted into the cavernosum of the Sprague-Dawley rats and harvested 2 weeks later. The expression of CD31, von Willebrand factor (vWF), smooth muscle cell actin (SMA), calponin and desmin was determined immunohistochemically in rat penile cavernosum. Multipotency of B10 to adipogenic, osteogenic or chondrogenic differentiation was found. Expression of EC specific markers (CD31 or vWF protein) and expression of SMC specific markers (calponin, SMA or desmin protein) were demonstrated in grafted B10 cells. When human MSCs were transplanted into the penile cavernosum, they have the potential to differentiate toward ECs or SMCs. Human MSCs may be a good candidate in the treatment of penile cavernosum injury.

Towards in situ tissue repair: human mesenchymal stem cells express chemokine receptors CXCR1, CXCR2 and CCR2, and migrate upon stimulation with CXCL8 but not CCL2

The recruitment of bone marrow CD34- mesenchymal stem- and progenitor cells (MSC) and their subsequent differentiation into distinct tissues is the precondition for in situ tissue engineering. The objective of this study was to determine the entire chemokine receptor expression profile of human MSC and to investigate their chemotactic response to the selected chemokines CCL2, CXCL8 and CXCL12. Human MSC were isolated from iliac crest bone marrow aspirates and showed a homogeneous population presenting a typical MSC-related cell surface antigen profile (CD14-, CD34-, CD44+, CD45-, CD166+, SH-2+). The expression profile of all 18 chemokine receptors was determined by real-time PCR and immunohistochemistry. Both methods consistently demonstrated that MSC express CC, CXC, C and CX(3)C receptors. Gene expression and immunohistochemical analysis documented that MSC express chemokine receptors CCR2, CCR8, CXCR1, CXCR2 and CXCR3. A dose-dependent chemotactic activity of CXCR4 and CXCR1/CXCR2 ligands CXCL12 and CXCL8 (interleukin-8) was demonstrated using a 96-well chemotaxis assay. In contrast, the CCR2 ligand CCL2 (monocyte chemoattractant protein-1, MCP-1) did not recruited human MSC. In conclusion, we report that the chemokine receptor expression profile of human MSC is much broader than known before. Furthermore, for the first time, we demonstrate that human MSC migrate upon stimulation with CXCL8 but not CCL2. In combination with already known data on MSC recruitment and differentiation these are promising results towards in situ regenerative medicine approaches based on guiding of MSC to sites of degenerated tissues.

Stem cell therapy improves myocardial perfusion and cardiac synchronicity: new application for echocardiography

OBJECTIVES

Intravenous delivery of mesenchymal stem cell (MSC) is a noninvasive approach for myocardial tissue repair. We aimed to test this strategy in a pig model of myocardial infarction and to examine the usefulness of new echocardiographic applications to monitor cardioprotective effects of stem cell therapy.

METHODS

Pigs (n = 8) received autologous or allogeneic MSCs (1 x 10(6)/kg body weight) labeled with fluorescent dye 48 hours after proximal left anterior descending coronary artery occlusion. Infarct size, myocardial function, and perfusion (A x beta) were assessed by myocardial contrast echocardiography and standard histologic methods after 1 month.

RESULTS

Morphologic analysis revealed that labeled MSCs migrated in the peri-infarct region resulting in smaller infarct size by myocardial contrast echocardiography (control vs autologous and allogeneic MSC: 38 +/- 10% vs 25 +/- 5% and 28 +/- 6%, P < .01), higher fractional area shortening (23 +/- 3% vs 34.0 +/- 7% and 28 +/- 2%, P < .01), higher cardiac synchrony (167 +/- 36 vs 68 +/- 17 and 85 +/- 26 milliseconds, P < .003), and improved microvascular flow A x beta in the ischemic border zone (0.18 +/- 0.2 vs 0.56 +/- 0.3 and 0.49 +/- 0.2, P < .03).

CONCLUSIONS

Systemic delivery of autologous and allogeneic MSCs preserves myocardial viability even in large animals and is, therefore, an attractive approach for tissue repair. Myocardial contrast echocardiography is useful to evaluate microvascular perfusion, which was enhanced by MSCs.

Co-transplantation of human mesenchymal stem cells promotes human CD34+ cells engraftment in a dose-dependent fashion in NOD/SCID mice

Mesenchymal stem cells (MSCs) have recently been identified and characterized in humans. Moreover, MSC secrete cytokines that can support hematopoietic progenitor growth. In the present study, we evaluated whether the efficacy of hematopoietic stem cell transplantation is improved by their co-transplantation with MSC, and whether this is positively correlated with the dose of infused MSCs. Accordingly, irradiated NOD/SCID mice were transplanted with 1 x 10(5) human CD34+ cells in the presence or absence of culture expanded MSCs (1 x 10(6) or 5 x 10(6)). We evaluated human hematopoietic cell engraftment by flow cytometry and assessed MSC tissue distributions by fluorescence in situ hybridization. We found that CD45+ and CD34+ cell levels were significantly elevated in a dose-dependent manner in co-transplanted mice 4 weeks after transplantation. The engraftments of CD33+ and CD19+ cells also increased dose-dependently. However, the engraftment of CD3+ cells did not increase after co-transplantation with MSCs. Human Y chromosome+ cells were observed in multiple tissues and were more frequently observed in mice co-transplanted with 5 x 10(6) rather than 1 x 10(6) MSCs. These results suggest that MSCs are capable of enhancing hematopoietic cell engraftment and distribution in multiple organs in a dose-dependent fashion.

Recent advances into the understanding of mesenchymal stem cell trafficking

The use of adult stem cells to regenerate damaged tissue circumvents the moral and technical issues associated with the use of those from an embryonic source. Mesenchymal stem cells (MSC) can be isolated from a variety of tissues, most commonly from the bone marrow, and, although they represent a very small percentage of these cells, are easily expandable. Recently, the use of MSC has provided clinical benefit to patients with osteogenesis imperfecta, graft-versus-host disease and myocardial infarction. The cellular cues that enabled the MSC to be directed to the sites of tissue damage and the mechanisms by which MSC then exert their therapeutic effect are becoming clearer. This review discusses the relative therapeutic importance of the ability of MSC to differentiate into multiple cell lineages or stimulate resident or attracted cells via a paracrine mode of action. It also reviews recent findings that MSC home to damaged tissues in a similar, but somewhat distinct, manner to that of leucocytes via the utilisation of adhesion molecules, such as selectins and integrins, and chemokines and their receptors in a manner reminiscent of leucocytes trafficking from the blood stream to inflammatory sites.

The concept of mesenchymal stem cells

In this chapter we examine whether criteria usually defining adult tissue stem cells apply to mesenchymal stem cells (MSCs) that give rise to cells of the skeletal connective tissues. MSCs appear to constitute a heterogeneous population of undifferentiated and committed, lineage-primed cells, capable of: homing upon engraftment to a number of growth microenvironments, extensive proliferation, producing large numbers of differentiated progeny, and functional tissue repair after injury. In addition, MSCs are extensively distributed throughout tissues, and bone marrow MSCs provide the stromal component of the niche of hematopoietic stem cells. The capacity of apparently differentiated mesenchymal cells to shift their differentiation pathway with changing microenvironmental conditions (known as differentiation plasticity) may be due to de-differentiation and reprogramming in MSCs. Because they present several features setting them apart from other stem cells, MSCs may constitute another paradigm for stem cell systems, where self-renewal and hierarchy are no longer essential, but where plasticity is the major characteristic.

The in vitro migration capacity of human bone marrow mesenchymal stem cells: comparison of chemokine and growth factor chemotactic activities

Adult bone marrow (BM)-derived stem cells, including hematopoietic stem cells (HSCs) and MSCs, represent an important source of cells for the repair of a number of damaged tissues. In contrast to HSCs, the soluble factors able to induce MSC migration have not been extensively studied. In the present work, we compared the in vitro migration capacity of human BM-derived MSCs, preincubated or not with the inflammatory cytokines interleukin 1beta (IL1beta) and tumor necrosis factor alpha (TNFalpha), in response to 16 growth factors (GFs) and chemokines. We show that BM MSCs migrate in response to many chemotactic factors. The GFs platelet-derived growth factor-AB (PDGF-AB) and insulin-like growth factor 1 (IGF-1) are the most potent, whereas the chemokines RANTES, macrophage-derived chemokine (MDC), and stromal-derived factor-1 (SDF-1) have limited effect. Remarkably, preincubation with TNFalpha leads to increased MSC migration toward chemokines, whereas migration toward most GFs is unchanged. Consistent with these results, BM MSCs express the tyrosine kinase receptors PDGF-receptor (R) alpha, PDGF-Rbeta, and IGF-R, as well as the RANTES and MDC receptors CCR2, CCR3, and CCR4 and the SDF-1 receptor CXCR4. TNFalpha increases CCR2, CCR3, and CCR4 expression (as opposed to that of CXCR4), together with RANTES membrane binding. These data indicate that the migration capacity of BM MSCs is under the control of a large range of receptor tyrosine kinase GFs and CC and CXC chemokines. Most chemokines are more effective on TNFalpha-primed cells. Our results suggest that the mobilization of MSCs and their subsequent homing to injured tissues may depend on the systemic and local inflammatory state. Disclosure of potential conflicts of interest is found at the end of this article.

Specific adeno-associated virus serotypes facilitate efficient gene transfer into human and non-human primate mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) show great promise for ex vivo gene and cell-mediated therapies. The immunophenotype and in vitro differentiation capacity of primary baboon MSCs was demonstrated to be near-identical to that observed in human MSCs. To optimize gene transfer efficiency, we compared the efficiency of serotypes 1, 2, 3, 4, 5, 6, and 8 of adeno-associated virus (AAV) vectors for their ability to mediate transduction of human and baboon MSCs. AAV serotype 2 vectors were the most efficient in transducing MSCs from humans and baboons. As a reference, human Ad293 cells were transduced with these seven AAV serotypes, and were found to have the highest transduction levels followed by baboon MSCs, and then human MSCs. The order of increasing transduction efficiency for the serotypes tested was similar for human and baboon MSCs, but was different for human Ad293 cells. The transduction efficiency of MSCs isolated from different individuals was comparable within the same species. We also demonstrated that baboon MSCs transduced with AAV serotype 2 vectors retain their potential to differentiate into adipocytes in vitro, and can incorporate into injured muscle tissue of NODSCID mice in vivo. We detected beta-galactosidase reporter gene expression in host muscle tissue for up to 9 weeks in this study, indicating engraftment of transduced baboon MSCs and sustained transgene expression in vivo.

Administration of donor-derived mesenchymal stem cells can prolong the survival of rat cardiac allograft

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent adult elements that have recently been shown to have profound immunomodulatory effects both in vitro and in vivo. Herein we have examined the impact of intravenous infusion of donor MSCs on the survival of transplanted hearts in a rat allograft model.

METHODS

Recipient Fisher344 rats were transplanted with hearts from inbred Wistar rats. Wistar rat MSCs were infused via the tail vein at designated intervals. In vitro mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays were performed to assess whether MSCs downregulated T-cell responses in vivo. Real-time polymerase chain reaction (PCR) was used to analyze the Th1/Th2 balance in MSC-treated and control groups.

RESULTS

The MSCs cultured in vitro exhibited multipotential for differentiation. Survival of the allografts was markedly prolonged by administration of MSCs compared with the controls, namely mean survivals of 12.4 vs 6.4 days, respectively. Real-time PCR showed a shift in the Th1/Th2 balance toward Th2. By MLR and CML assays, untreated control rats showed greater alloreactivity than did MSC-treated rats.

CONCLUSION

Our results indicated that MSCs suppressed allogeneic T-cell responses both in vitro and in vivo. Intravenous administration of MSCs prolonged the survival of transplanted hearts, possibly by induction of allograft tolerance through changing the Th1/Th2 balance.

In vivo distribution of human adipose-derived mesenchymal stem cells in novel xenotransplantation models

The potential for human adipose-derived mesenchymal stem cells (AMSC) to traffic into various tissue compartments was examined using three murine xenotransplantation models: nonobese diabetic/severe combined immunodeficient (NOD/SCID), nude/NOD/SCID, and NOD/SCID/MPSVII mice. Enhanced green fluorescent protein was introduced into purified AMSC via retroviral vectors to assist in identification of cells after transplantation. Transduced cells were administered to sublethally irradiated immune-deficient mice through i.v., intraperitoneal, or subcutaneous injection. Up to 75 days after transplantation, tissues were harvested and DNA polymerase chain reaction (PCR) was performed for specific vector sequences as well as for human Alu repeat sequences. Duplex quantitative PCR using human beta-globin and murine rapsyn primers assessed the contribution of human cells to each tissue. The use of the novel NOD/SCID/MPSVII mouse as a recipient allowed rapid identification of human cells in the murine tissues, using an enzyme reaction that was independent of surface protein expression or transduction with an exogenous transgene. For up to 75 days after transplantation, donor-derived cells were observed in multiple tissues, consistently across the various administration routes and independent of transduction parameters. Tissue localization studies showed that the primary MSC did not proliferate extensively at the sites of lodgement. We conclude that human AMSC represent a population of stem cells with a ubiquitous pattern of tissue distribution after administration. AMSC are easily obtained and highly amenable to current transduction protocols for retroviral transduction, making them an excellent avenue for cell-based therapies that involve a wide range of end tissue targets.

Immunomodulatory properties of mesenchymal stem cells: a review based on an interdisciplinary meeting held at the Kennedy Institute of Rheumatology Division, London, UK, 31 October 2005

Multipotent mesenchymal stromal cells isolated from bone marrow and other sites are currently being studied to determine their potential role in the pathogenesis and/or management of autoimmune diseases. In vitro studies have shown that they exhibit a dose-dependent antiproliferative effect on T and B lymphocytes, dendritic cells, natural killer cells and various B cell tumour lines--an effect that is both cell contact and soluble factor dependent. Animal models of autoimmune disease treated with multipotent mesenchymal stromal cells have mostly exhibited a positive clinical response, as have a limited number of patients suffering from acute graft versus host disease. This review summarizes the findings of a 1-day meeting devoted to the subject with the aim of coordinating efforts.

Mesenchymal stem cells for cardiac regenerative therapy

Until recently, the concept of treating the injured or failing heart by generating new functional myocardium was considered physiologically impossible. Major scientific strides in the past few years have challenged the concept that the heart is a post-mitotic organ, leading to the hypothesis that cardiac regeneration could be therapeutically achieved. Bone marrow-derived adult stem cells were among the first cell populations that were used to test this hypothesis. Animal studies and early clinical experience support the concept that therapeutically delivered mesenchymal stem cells (MSCs) safely improve heart function after an acute myocardial infarction (MI). MSCs produce a variety of cardio-protective signalling molecules, and have the ability to differentiate into both myocyte and vascular lineages. Additionally, MSCs are attractive as a cellular vehicle for gene delivery, cell transplantation or for tissue engineering because they offer several practical advantages. They can be obtained in relatively large numbers through standard clinical procedures, and they are easily expanded in culture. The multi-lineage potential of MSC, in combination with their immunoprivileged status, make MSCs a promising source for cell therapy in cardiac diseases. Here we provide an overview of biological characteristics of MSCs, experimental animal studies and early clinical trials with MSCs. In addition, we discuss the routes of cell delivery, cell tracking experiments and current knowledge of the mechanistic underpinnings of their action.

Co-culture of umbilical cord blood CD34+ cells with human mesenchymal stem cells

Insufficient numbers of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) sometimes limit allogenic transplantation of umbilical cord blood (UCB). Ex vivo expansion may overcome this limitation. Mesenchymal stem cells (MSCs), as non-hematopoietic, well-characterized skeletal and connective-tissue progenitor cells within the bone marrow stroma, have been investigated as support cells for the culture of HSCs/HPCs. MSCs are attractive for the rich environmental signals that they provide and for immunological compatibility in transplantation. Thus far, HSC/MSC co-cultures have mainly been performed in 2-dimensional (2D) configuration. We postulate that a 3-dimensional (3D) culture environment that resembles the natural in vivo hematopoietic compartment might be more conducive for regulating HSC expansion. In this study, we compared the co-culture of HSCs and MSCs in 2D and 3D configurations. The results demonstrated the benefit of MSC inclusion in HSC expansion ex vivo. Direct contact between MSCs and HSCs in 3D cultures led to statistically significantly higher expansion of cord blood CD34+ cells than in 2D cultures (891- versus 545-fold increase in total cells, 96- versus 48-fold increase of CD34+ cells, and 230- versus 150-fold increase in colony-forming cell assay [CFC]). Engraftment assays in non-obese diabetic/severe combined immunodeficiency mice also indicated a high success rate of hematopoiesis reconstruction with these expanded cells.

Application of cell penetrating peptide in magnetic resonance imaging of bone marrow mesenchymal stem cells

Tracking the distribution and differentiation of stem cells by high-resolution imaging techniques would have significant clinical and research implications. In this study, a model cell-penetrating peptide was used to carry gadolinium particles for magnetic resonance imaging (MRI) of mesenchymal stem cells (MSCs). MSCs were isolated from rat bone marrow and identified by osteogenic differentiation in vitro. The cell-penetrating peptide labeled with fluorescein-5-isothiocyanate (FITC) and gadolinium was synthesized by a solid-phase peptide synthesis method. Fluorescein imaging analysis confirmed that this new peptide could internalize into the cytoplasm and nucleus at room temperature, 4 degrees and 37 degrees . Gadolinium were efficiently internalized into mesenchymal stem cells by the peptide in a time or concentration-dependent manner, resulting in intercellular shortening of longitudinal relaxation enhancements, which were obviously detected by 1.5 Tesla Magnetic Resonance Imaging. Cytotoxicity assay and flow cytometric analysis showed that the intercellular contrast medium incorporation did not affect cell viability at the tested concentrations. The in vitro experiment results suggested that the new constructed peptides could be a vector for tracking MSCs.

Mesenchymal stem cells display coordinated rolling and adhesion behavior on endothelial cells

To explore the initial steps by which transplanted mesenchymal stem cells (MSCs) interact with the vessel wall in the course of extravasation, we studied binding of human MSCs to endothelial cells (ECs). In a parallel plate flow chamber, MSCs bound to human umbilical vein ECs (HUVECs) similar to peripheral-blood mononuclear cells (PBMCs) or CD34(+) hematopoietic progenitors at shear stresses of up to 2 dynes/cm(2). This involved rapid extension of podia, rolling, and subsequent firm adhesion that was increased when ECs were prestimulated with TNF-alpha. MSC binding was suppressed when ECs were pretreated with function-blocking anti-P-selectin antibody, and rolling of MSCs was induced on immobilized P-selectin, indicating that P-selectin was involved in this process. Preincubation of HUVECs with anti-VCAM-1 or of MSCs with anti-VLA-4 antibodies suppressed binding of MSCs to HUVECs but did not enhance inhibition by anti-P-selectin, indicating that both P-selectin and VCAM-1 are equally required for this process. Intravital microscopy demonstrated the capacity of MSCs to roll and adhere to postcapillary venules in vivo in a mouse model in a P-selectin-dependent manner. Thus, MSCs interact in a coordinated fashion with ECs under shear flow, engaging P-selectin and VCAM-1/VLA-4.

In vitro effect of adenovirus-mediated human Gamma Interferon gene transfer into human mesenchymal stem cells for chronic myelogenous leukemia

For developing gene therapy for chronic myelogenous leukemia (CML), we evaluated the feasibility of using autologous bone marrow stromal cells (BMSCs) of one CML patient as a target cell population and studied the efficiency of recombinant adenovirus-mediated human Gamma Interferon (hIFN-gamma) gene transfer into BMSCs. BMSCs can be readily obtained, expanded, and successfully transduced with adenoviral vectors in vitro. We studied the in vitro expression of hIFN-gamma in human BMSCs following transduction with Ad/hIFN-gamma. On transduction of BMSCs at a MOI of 50, the expression and secretion of hIFN-gamma were achieved as high as 5492 +/- 660 approximately 50647 +/- 4049 ng/10(6) cells per 24 h over the course of 3 weeks. We further studied the effects of hIFN-gamma produced by transduced BMSCs on the proliferation of the human leukemia cell line K562 cells in vitro, proliferation of K562 cells was markedly inhibited in the experimental groups as compared with the other two control groups after 5 days of coculture. We also found that the percentage of K562 cells in the G(1) phase of cell cycle can be increased by treatment of hIFN-gamma produced by Ad/hIFN-gamma transduced BMSCs, but the percentage of K562 cells in the S phase of cell cycle can be decreased in the same time. Apoptosis rate of K562 cells in the experimental groups was 30.8 +/- 8.5%, as compared with the other two control groups (5.6 +/- 1.3% and 5.5 +/- 0.8%, respectively) (p < 0.01). Our results indicate that hIFN-gamma gene engineered BMSCs of CML donors could be successfully established and that local production of hIFN-gamma is sufficiently to inhibit the proliferation of K562 cells and induce apoptosis of K562 cells in vitro, suggesting an important potential use in the clinical gene therapy of CML.

Are Stem Cells Drugs?

Stem cell research and its clinical application have become political, social, and medical lightning rods, polarizing opinion among members of the lay community and among medical/scientific professionals. A potpourri of opinion, near-anecdotal observation, and scientifically sound data has sown confusion in ways rarely seen in the medical arts and sciences. A major issue is regulation, with different aspects of stem cell research falling within the purview of different government agencies and local offices. An overarching clearinghouse to review the field and recommend policy is lacking. In the following pages, I touch on the societal framework for regulation, the known and potential risks and benefits of cardiovascular stem cell therapies, whether stem cells should be regulated as drugs or in analogy to drugs, and if there is to be regulation, then by whom. In so doing, I refer to the stem cell literature only as it relates to the discussion of regulation because this is not a review of stem cell research; it is an opinion regarding regulation.

Mesenchymal stem cells enhance xenochimerism in NK-depleted hosts

BACKGROUND

Xenogeneic hematopoietic engraftment holds promise as a strategy to achieve whole organ xenograft tolerance. We tested whether xenogeneic bone marrow grafts, engineered with mesenchymal stem cells (MSCs), might provide a new nontoxic approach to enhance xenogeneic engraftment.

METHODS

ACI rat MSCs, cultured from whole bone marrow, were identified as CD29+ CD44+OX-18+, CD45-HIS36- and could differentiate into adipogenic and osteogenic tissue. Lethally irradiated B6 mice received ACI whole bone marrow either alone or in combination with ACI MSC. Xenogeneic engraftment was measured in murine peripheral blood on days 7, 50, and 100. Natural killer (NK)-cell-depleted murine recipients treated with or without MSC underwent rat skin graft transplants on the day of the bone marrow infusion.

RESULTS

In NK-depleted hosts, control animals failed to survive 60 days; 40% MSC-treated hosts survived >100 days, P < 0 .05. Rat hematopoietic engraftment exceeded 89% on days 7 and 54 and decreased to <25% by day 100. No graft-versus-host disease was observed in MSC-treated animals, P < 0.05. Skin graft survival was prolonged in the MSC-treated group, (21 +/- 1.7 days, P = 0.2).

CONCLUSIONS

Our findings present a new approach in engineering xenografts and provide an encouraging platform for additional studies.

Murine mesenchymal stem cells isolated by low density primary culture system

Murine mesenchymal stem cells (mMSC) and the difficult task of isolation and purification of them have been the subject of rather extensive investigation. The present study sought to isolate these cells from two different mouse strains, one outbred and the other inbred, primarily through a relatively simple but novel approach, the most important feature of which was the low density primary culture of bone marrow cells. For this purpose, mononuclear cells from either NMRI or BALB/c bone marrow were plated at about 500 cells per well of 24-well plates and incubated for 7 days. At this point, the fibroblastic clones that had emerged were pooled together and expanded through several subcultures. To investigate the mesenchymal nature, we differentiated the cells into the osteoblastic, chondrocytic and adipocytic lineages in different subcultures up to passage 10. According to the results, 1 week after culture initiation, several clones each comprising several fibroblastic cells appeared in each plate. The cells from different passages were capable of differentiating into corresponding skeletal tissues. In the present investigation, the best culture condition for maximum proliferation and also the expression of certain surface marker on isolated cells were examined. In this term the two murine strains showed some differences.

Intravenous transplantation of mesenchymal stem cells improves cardiac performance after acute myocardial ischemia in female rats

Mesenchymal stem cells (MSCs) are potential sources of cells for tissue repairing. However, little information is available regarding the therapeutic potency of intravenously transplanted MSCs for myocardial ischemia (MI). In the present study, MSCs were isolated from bone marrow of male rats and expanded in vitro. Three hours after ligation of left anterior descending artery, the transplanted group received an infusion of MSCs through the tail vein. At the same time, a coronary-ligated control group was injected with culture medium. Homing of MSCs to the heart was assessed by expression of the Y chromosome sry gene using fluorescent in situ hybridization (FISH). At 1 week or 8 weeks after transplantation, sry positive cells were present in cardiac tissue in the transplanted group, but not in the hearts of control group. Cardiomyocytes, smooth muscle cells, and endothelial cells that bore sry gene were identified in transplanted group at 8 weeks after transplantation. Ultrastructural observation revealed that a large number of capillary and some immature myocytes were found to survive in the ischemia region. MSCs transplantation also decreased LVEDP pressure and -dP/dt, but increased LVSP and +dP/dt. The cardiac infarct size was significantly smaller in transplanted group than in control group. Our data suggest that intravenously transplanted MSCs improve cardiac performance and promote the regeneration of blood vessels and cardiomyocytes.

Paramagnetic particles carried by cell-penetrating peptide tracking of bone marrow mesenchymal stem cells, a research in vitro

The ability to track the distribution and differentiation of stem cells by high-resolution imaging techniques would have significant clinical and research implications. In this study, a model cell-penetrating peptide was used to carry gadolinium particles for magnetic resonance imaging of the mesenchymal stem cells. The mesenchymal stem cells were isolated from rat bone marrow by Percoll and identified by osteogenic differentiation in vitro. The cell-penetrating peptides labeled with fluorescein-5-isothiocyanate and gadolinium were synthesized by a solid-phase peptide synthesis method and the relaxivity of cell-penetrating peptide-gadolinium paramagnetic conjugate on 400 MHz nuclear magnetic resonance was 5.7311 +/- 0.0122 m mol(-1) s(-1), higher than that of diethylenetriamine pentaacetic acid gadolinium (p < 0.05). Fluorescein imaging confirmed that this new peptide could internalize into the cytoplasm and nucleus. Gadolinium was efficiently internalized into mesenchymal stem cells by the peptide in a time- or concentration-dependent fashion, resulting in intercellular T1 relaxation enhancement, which was obviously detected by 1.5 T magnetic resonance imaging. Cytotoxicity assay and flow cytometric analysis showed the intercellular contrast medium incorporation did not affect cell viability and membrane potential gradient. The research in vitro suggests that the newly constructed peptides could be a vector for tracking mesenchymal stem cells.

Intravenous mesenchymal stem cell therapy early after reperfused acute myocardial infarction improves left ventricular function and alters electrophysiologic properties

Direct intramyocardial injection of mesenchymal stem cells (MSCs) improves left ventricular ejection fraction (LVEF) and may increase ventricular arrhythmia in hearts with myocardial infarction (MI). We hypothesized that intravenous MSCs given early after acute MI would engraft in injured myocardium, improve LV function, and result in pro-arrhythmic electrical remodeling. We created an apical infarction in swine by balloon occlusion/reperfusion, administered diI-labeled allogeneic bone marrow derived MSCs intravenously 30 min post-reperfusion and measured LVEF and wall thickness at baseline, 1 month, and 3 months. Epicardial effective refractory periods (ERPs) were determined before sacrifice. At 3 months, treated pigs [n=7] had significantly higher LVEF than controls [n=8] (49+/-2% vs. 44+/-3%, P=0.015) and significantly less wall thickening of non-infarcted myocardium. ERPs were significantly shorter than controls at all pacing cycle lengths (P<or=0.002), suggesting a pro-arrhythmic potential. DiI was found in the lungs, in infarct, and peri-infarct myocardium.

CONCLUSION

IV infusion of MSCs soon after acute MI in swine improves LVEF and limits wall thickening in the remote non-infarcted myocardium, consistent with a beneficial effect on post-MI ventricular remodeling. Since there is no need for immune suppression or clinical expertise, IV infusion of MSCs may expand the potential clinical application of stem cell therapy.

Mesenchymal stem cells in immunoregulation

Mesenchymal stem cells are present within the bone marrow cavity and serve as a reservoir for the continuous renewal of various mesenchymal tissues. Recent studies suggest that mesenchymal stem cells modulate immune reactions in vitro and escape from immune surveillance in vivo. We provide herein a discussion of issues including the current research progress on the in vitro interactions of mesenchymal stem cells with multiple subsets of immune cells (dendritic cells, T cells, B cells and NK cells), in vivo transplantation outcomes, the possible underlying mechanisms, future research directions as well as potential clinical implications.

Comparison of growth and differentiation of fetal and adult rhesus monkey mesenchymal stem cells

The goal of this study was to compare the growth and differentiation potential of fetal and adult rhesus monkey (Macaca mulatta) mesenchymal stem cells (rhMSCs). rhMSCs were obtained from healthy early third-trimester fetal (n = 3) and adult (n = 3) rhesus monkey bone marrow. Fetal rhMSCs were plated at 10, 50, 100, or 1,000 cells/cm(2) in medium containing 10% or 20% infant monkey serum (IMS) or fetal bovine serum (FBS). Fetal rhMSCs grown at 1,000 cells/cm(2) in 20% FBS showed faster growth rates and differentiation toward adipogenic, chondrogenic, and osteogenic lineages when compared to other culture conditions and to adult cells (p < 0.05). Fetal rhMSC showed higher population doubling times (11.3 +/- 0.5) when compared to adult cells (7.3 +/- 0.8) during the first three passages. Adult rhMSC did not grow beyond the third passage under all culture conditions, including those supplemented with insulin-like growth factor (IGF)-I, IGF-II, platelet-derived growth factor (PDGF), and fibroblast growth factor-2 (FGF-2). After the third passage, adult rhMSC cultures were observed with large syncytia and with evidence of apoptosis. Cells obtained from these cultures tested positive for simian foamy virus (SFV) by PCR, RT-PCR, and immunofluorescent assay. Adult rhMSCs cultured with 10 microM tenofovir, an antiviral agent, showed normal growth and differentiation for over 20 population doublings. These findings suggest that: (1) fetal rhMSCs possess greater self-renewal and differentiation potential when compared to adult cells; and (2) SFV can inhibit proliferation of adult rhMSCs in culture, whereas the addition of tenofovir can successfully suppress SFV replication in vitro and result in resumed growth.

Multipotential mesenchymal stem cells are mobilized into peripheral blood by hypoxia

MSCs constitute a population of multipotential cells giving rise to adipocytes, osteoblasts, chondrocytes, and vascular-smooth muscle-like hematopoietic supportive stromal cells. It remains unclear whether MSCs can be isolated from adult peripheral blood under stationary conditions and whether they can be mobilized in a way similar to hematopoietic stem cells. In this report, we show that MSCs are regularly observed in the circulating blood of rats and that the circulating MSC pool is consistently and dramatically increased (by almost 15-fold) when animals are exposed to chronic hypoxia. The immunophenotype and the adipocytic, osteoblastic, and chondrocytic differentiation potential of circulating MSCs were similar to those of bone marrow MSCs. Hypoxia-induced mobilization appears to be specific for MSCs since total circulating hematopoietic progenitor cells were not significantly increased. Our data provide an in vivo model amenable to analysis of MSC-mobilizing factors.

Mesenchymal stem cells for bone, cartilage, tendon and skeletal muscle repair

Literature data concerning the biology and differentiation potential of mesenchymal stem cells (MSCs) have become huge in less than 10 years, although some of these data still remain contradictory. MSCs seem to be a very promising tool for cell therapy because of their peculiar characteristics, which mimic partially those of embryonic stem cells, but with some advantages in terms of availability, expandability, transplantability, and ethical implications. We discuss here the potential use of MSCs in degenerative or inflammatory diseases involving bone, cartilage, tendon and muscle tissues, on the basis of the experimental evidence.

Bone Marrow Mesenchymal Stem Cells Suppress Lymphocyte Proliferation In Vitro but Fail to Prevent Graft-versus-Host Disease in Mice

Several reports have suggested that mesenchymal stem cells (MSCs) could exert a potent immunosuppressive effect in vitro, and thus may have a therapeutic potential for T cell-dependent pathologies. We aimed to establish whether MSCs could be used to control graft-vs-host disease (GVHD), a major cause of morbidity and mortality after allogeneic hemopoietic stem cell transplantation. From C57BL/6 and BALB/c mouse bone marrow cells, we purified and expanded MSCs characterized by the lack of expression of CD45 and CD11b molecules, their typical spindle-shaped morphology, together with their ability to differentiate into osteogenic, chondrogenic, and adipogenic cells. These MSCs suppressed alloantigen-induced T cell proliferation in vitro in a dose-dependent manner, independently of their MHC haplotype. However, when MSCs were added to a bone marrow transplant at a MSCs:T cells ratio that provided a strong inhibition of the allogeneic responses in vitro, they yielded no clinical benefit on the incidence or severity of GVHD. The absence of clinical effect was not due to MSC rejection because they still could be detected in grafted animals, but rather to an absence of suppressive effect on donor T cell division in vivo. Thus, in these murine models, experimental data do not support a significant immunosuppressive effect of MSCs in vivo for the treatment of GVHD.

Fuentes alternativas de hepatocitos para la terapia celular

There is an urgent need to search for alternatives to whole organ transplantation. Several methods have been proposed. Among these strategies, cell transplantation is currently one of the most promising. To achieve this aim, in addition to highly differentiated adult hepatocytes, the use of stem cells is considered a highly attractive therapeutic method for the treatment of liver disease and for temporary support of hepatic function until a liver becomes available for organ transplantation. This strategy is based on the ability of stem cells to differentiate into different cellular types according to their environment. Therefore, stem cells could be an unlimited source of hepatic cells for transplantation and gene therapy. Bone marrow is considered the most promising source of adult stem cells, partly due to the versatility of the cells obtained in repairing damaged tissues of several lineages. Several different types of stem cells have been described in bone marrow: hematopoietic, mesenchymal, side population and multipotent adult stem cells. Bone marrow cells have been hypothesized as a third recruitment source in liver regeneration in addition to hepatocytes and endogenous liver stem cells. Consequently, attempts have been made to differentiate them into hepatic lineage for their subsequent use in hepatic cell therapy. The present article reviews the progress made in this field or research.

Progenitors systemically transplanted into neonatal mice localize to areas of active bone formation in vivo: implications of cell therapy for skeletal diseases

The potential of cell or gene therapy to treat skeletal diseases was evaluated through analysis of transplanted osteoprogenitors into neonatal homozygous and heterozygous osteogenesis imperfecta mice (oim). The osteoprogenitors used for transplantation were prepared by injection of mesenchymal stem cells (MSCs) marked with the green fluorescent protein (GFP) into normal mice with the subsequent retrieval of the cells at 35 days. The retrieved cells referred to here as osteoprogenitors were expanded in culture and transplanted into the 2-day-old oim mice via the superficial temporal vein. The recipient mice were evaluated at 2 and 4 weeks after cell transplantation. Four weeks after transplantation, tissue sections made from femurs and tibias of oim mice showed that the GFP-positive (GFP(+)) cells were distributed on the surfaces of the bone spicules in the spongiosa, the area of active bone formation. In the diaphysis, the GFP(+) cells were distributed in the bone marrow, on the endosteal surfaces, and also in the cortical bone. Immunofluorescence localization for GFP confirmed that the fluorescence seen in tissue sections was due to the engrafted donor cells, not bone autofluorescence. Gene expression analysis by polymerase chain reaction of the GFP(+) cells retrieved from the bones and marrow of the recipient mice demonstrated that the cells from bone were osteoblasts, whereas those from bone marrow were progenitors. These data demonstrate that MSCs delivered systemically to developing osteogenesis imperfecta mice engraft in bones, localize to areas of active bone formation, differentiate into osteoblasts in vivo, and may contribute to bone formation in vivo.

Multiple sources of non-embryonic multipotent stem cells: processed lipoaspirates and dermis as promising alternatives to bone-marrow-derived cell therapies

A body of evidence points to the existence of stem cell stores in adult tissues, in addition to the well-known hematopoietic stem cells from bone marrow. Many reports describe the ability of these multipotent cells (developmentally non-compromised with their organs of origin) to give rise to many different cell types in response to specific stimuli. This apparent plasticity provides new perspectives in tissue engineering and suggests the usefulness of these cells in future protocols of autologous transplantation, gene therapy, and tissue reconstitution in a number of pathological processes. Lipoaspirates and dermis represent accessible sources for obtaining such cells, with minimal discomfort to the donor, and might be promising candidates for cell therapy procedures once their features are experimentally accessed. The intention of the present work has been to gather reports on the phenotypic characteristics, profile, and plastic potential of these stem cells.

Emerging role for bone marrow derived mesenchymal stem cells in myocardial regenerative therapy

Current treatments for ischemic cardiomyopathy are aimed toward minimizing the deleterious consequences of diseased myocardium. The possibility of treating heart failure by generating new myocardium and vascular tissue has been an impetus toward recent stem cell research. Mesenchymal stem cells (MSC), also referred to as marrow stromal cells, differentiate into a wide variety of lineages, including myocardial and endothelial cells. The multi-lineage potential of MSCs, their ability to elude detection by the host immune system, and their relative ease of expansion in culture make MSCs a very promising source of stem cells for transplantation. In addition, emerging experimental results with MSCs offer novel mechanistic insights into cardiac regenerative therapy in general. Here we review the characterization of MSCs, animal and human trials studying MSCs in cardiomyogenesis and vasculogenesis in postinfarct myocardium, routes of delivery, and potential mechanisms of stem cell repair.

Reconstitution of the functional human hematopoietic microenvironment derived from human mesenchymal stem cells in the murine bone marrow compartment

Hematopoiesis is maintained by specific interactions between both hematopoietic and nonhematopoietic cells. Whereas hematopoietic stem cells (HSCs) have been extensively studied both in vitro and in vivo, little is known about the in vivo characteristics of stem cells of the nonhematopoietic component, known as mesenchymal stem cells (MSCs). Here we have visualized and characterized human MSCs in vivo following intramedullary transplantation of enhanced green fluorescent protein-marked human MSCs (eGFP-MSCs) into the bone marrow (BM) of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Between 4 to 10 weeks after transplantation, eGFP-MSCs that engrafted in murine BM integrated into the hematopoietic microenvironment (HME) of the host mouse. They differentiated into pericytes, myofibroblasts, BM stromal cells, osteocytes in bone, bone-lining osteoblasts, and endothelial cells, which constituted the functional components of the BM HME. The presence of human MSCs in murine BM resulted in an increase in functionally and phenotypically primitive human hematopoietic cells. Human MSC-derived cells that reconstituted the HME appeared to contribute to the maintenance of human hematopoiesis by actively interacting with primitive human hematopoietic cells.

Antigen-presenting property of mesenchymal stem cells occurs during a narrow window at low levels of interferon-gamma

Mesenchymal stem cells (MSCs) are mostly found around the vasculature system of the adult bone marrow (BM). They function as immune suppressors, express MHC-II, are phagocytic, and support T-cell cytotoxicity. We hypothesize that these contradictory properties of MSCs are important for BM homeostasis and occur partly through antigen presentation (antigen-presenting cells [APCs]) within a narrow window. Indeed, we have verified APC functions of MSCs to recall antigens, Candida albicans and Tetanus toxoid. The target cells have been identified to be CD4(+) T cells. APC assays with IFNgamma-knockdown MSCs and with anti-IFNgamma receptor confirmed that MHC-II expression requires autocrine stimulation by IFNgamma. During APC functions, as IFNgamma levels become elevated, there was a concomitant decrease in MHC-II on MSCs. This observation was correlated with flow cytometry studies showing a gradual decrease in MHC-II expression as IFNgamma levels were increased. The reduced levels of MHC-II correlated with losses in their allogeneic potential, as indicated in mixed lymphocyte reaction. In summary, endogenous and low levels of IFNgamma are required for MHC-II expression on MSCs, and for APC functions. APC functions occur during a narrow window before IFNgamma levels are increased. The study has implications for BM protection against infection and exacerbated inflammatory responses.

Gene Transfer into Rat Mesenchymal Stem Cells: A Comparative Study of Viral and Nonviral Vectors

Mesenchymal stem cells (MSCs) have been proposed for use in combinatorial gene and cell therapy protocols for the treatment of disease and promotion of repair. The efficacy of such a therapeutic approach depends on determination of which vectors give maximal transgene expression with minimal cell death. The study was carried out on bone-marrow derived rat MSCs, and a range of vectors was tested on the same stem cell preparation. Adenovirus, adeno-associated virus (AAV; serotypes 1, 2, 4, 5, and 6), lentivirus, and nonviral vectors were compared. Lentivirus proved to be most effective with transduction efficiencies of up to 95%, concurrent with low levels of cell toxicity. Adenovirus also proved effective, but a significant increase in cell death was seen with increasing viral titer. Rat MSCs remained refractory to transduction by all AAV serotypes, in contrast to rabbit MSCs tested at the same time. Lipofection of plasmid DNA gave moderate transfection levels but was also accompanied by cell death. Electroporative gene transfer proved ineffective at the parameters tested and resulted in high cell death. High and moderate levels of cell transduction using lentivirus vectors did not affect the ability of the cells to differentiate down the adipogenic pathway.

Postnatal stem cell survival: does the niche, a rare harbor where to resist the ebb tide of differentiation, also provide lineage-specific instructions?

Postnatal stem cells regulate the homeostasis of the majority of our tissues. They continuously generate new progenitors and mature, functional cells to replace old cells, which cannot assume the tissue function anymore and are eliminated. Blood, skin, gut mucosa, muscle, cartilage, nerves, cornea, retina, liver, and many other structures are regulated by stem cells. As a result of their ability to produce large numbers of functionally mature cells, postnatal stem cells represent a promising tool for regenerative therapy. Indeed, unmanipulated stem cells or their progeny amplified in vitro are already used in some clinical applications to restore the function of injured or genetically deficient tissues. However, despite our cumulating understanding concerning postnatal stem cells, many aspects of their functionality remain unclear. For instance, in most tissues, we cannot reliably define the phenotype of the postnatal stem cells sustaining its survival. We do not know to which extent the environment surrounding the stem cell-the niche-which is a key actor insuring stem cell self-maintenance, is also implicated in the maintenance of stem cell lineage specificity. Moreover, we have to clarify whether postnatal stem cells are capable of undertaking "transdifferentiation", that is, the conversion of one cell type into another under physiological conditions. Answering these questions should help us to draw a more accurate picture of postnatal stem cell biology and should lead to the design of safe, effective therapies.

Persistence of marrow stromal cells implanted into acutely infarcted myocardium: observations in a xenotransplant model

OBJECTIVE

It has been reported that unmatched adult bone marrow stromal cells could be tolerated by immune-competent allotransplant or xenotransplant recipients under various conditions. This study examined whether xenogeneic bone marrow stromal cells implanted immediately after myocardial infarction can survive and differentiate, attenuating deterioration in left ventricular function.

METHODS

In groups I and II (n = 34), myocardial infarctions were created in immunocompetent adult Lewis rats by proximal left coronary artery ligation. In group I, 3 x 10(6)lacZ-labeled mouse bone marrow stromal cells were immediately injected into the peri-infarct area of the left ventricle, whereas in group II, only culture medium was injected. There were 10 early and 4 late deaths. At 4 weeks after injection, hearts were stained for beta-galactosidase and troponin IC. In groups IIIA and IIIB, lacZ-labeled mouse skin fibroblasts were implanted into rat myocardium (n = 10 each) with and without left coronary artery ligation, respectively, and the rats were killed serially. In group IV, animals underwent sham surgery (n = 5, no deaths). At 4 weeks, surviving rats in groups I, II, and IV (n = 10, n = 10, and n = 5, respectively) underwent blinded transthoracic echocardiography for ventricular function studies.

RESULTS

In group I, labeled mouse-derived bone marrow stromal cells were found within rat myocardium that stained positively for troponin IC 4 weeks after implantation. Functionally, mean left ventricular ejection fraction (P = .007), stroke volume (P = .03), and fractional shortening (P = .02) were all significantly higher in group I than in group II. In groups IIIA and IIIB, mouse fibroblasts induced cellular infiltration with rapid loss of donor cells. No labeled cells were found after 4 days. In group IV, there was no change in cardiac function.

CONCLUSION

Xenogeneic bone marrow stromal cells implanted into acutely ischemic myocardium induced by coronary artery ligation were immunologically tolerated, survived and differentiated, resulting in a cardiac chimera which improved left ventricular function. This unique immunologic tolerance may suggest the feasibility of using bone marrow stromal cells as universal donor cells.

The role of mesenchymal stem cells in haemopoiesis

The ontogeny of haemopoiesis during fetal life and the differentiation of blood cells in adult life depend upon a fully competent microenvironment to provide appropriate signals via production of soluble factors and cell contact interactions. The cellular constituents of the microenvironment, also defined as the haemopoietic niche, largely derive from a common progenitor of mesenchymal origin. Mesenchymal stem cells (MSC), initially identified in adult bone marrow, have also been described in fetal haemopoietic tissues where they accompany the migration of haemopoietic development. Their precise identity remains ill-defined because of the lack of specific markers. Their ability to self-renew and differentiate into tissues of mesodermal origin (osteocytes, adipocytes, chondrocytes) and their lack of expression of haemopoietic molecules are currently the main criteria for isolation. In the bone marrow the most important elements of the niche appear to be osteoblasts, whilst a less defined population of fibroblasts regulates the maturation of immature T cells in the thymus. Recently, MSC have been shown to exert a profound immunosuppressive effect on polyclonal as well as antigen-specific T cell responses by inducing a state of division arrest anergy. Thus, the multipotent capacity of MSC, their role in supporting haemopoiesis, and their immunoregulatory activity make MSC particularly attractive for therapeutic exploitation.

Characterization and gene transfer in mesenchymal stem cells derived from human umbilical-cord blood

It has been shown that the stromal-cell population found in bone marrow can be expanded and differentiated into cells with the phenotypes of bone, cartilage, muscle, neural, and fat cells. However, whether mesenchymal stem cells (MSCs) are present in human umbilical-cord blood (UCB) has been the subject of ongoing debate. In this study, we report on a population of fibroblastlike cells derived from the mononuclear fraction of human UCB with osteogenic and adipogenic potential, as well as the presence of a subset of cells that have been maintained in continuous culture for more than 6 months. These cells were found to express CD29, CD44, CD90, CD95, CD105, CD166, and MHC class, but not CD14, CD34, CD40, CD45, CD80, CD86, CD117, CD152, or MHC class II. We also compared gene expression after gene transfer using lenti- and adenoviral vectors carrying the green fluorescence protein to the MSCs derived from UCB because a reliable gene-delivery system is required to transfer target genes into MSCs, which have attracted attention as potential platforms for the systemic delivery of therapeutic genes. The lentiviral vectors can transduce these cells more efficiently than can adenoviral vectors, and we maintained transgene expression for at least 5 weeks. This is the first report showing that UCB-derived MSCs can express exogenous genes by way of a lentivirus vector. These results demonstrate that human UCB is a source of mesenchymal progenitors and may be used in cell transplantation and a wide range of gene-therapy treatments.

Human bone marrow stromal cells express a distinct set of biologically functional chemokine receptors

Stromal cells isolated from bone marrow (BMSCs), often referred to as mesenchymal stem cells, are currently under investigation for a variety of therapeutic applications. However, limited data are available regarding receptors that can influence their homing to and positioning within the bone marrow. In the present study, we found that second passage BMSCs express a unique set of chemokine receptors: three CC chemokine receptors (CCR1, CCR7, and CCR9) and three CXC chemokine receptors (CXCR4, CXCR5, and CXCR6). BMSCs cultured in serum-free medium secrete several chemokine ligands (CCL2, CCL4, CCL5, CCL20, CXCL12, CXCL8, and CX3CL1). The surface-expressed chemokine receptors were functional by several criteria. Stimulation of BMSCs with chemokine ligands triggers phosphorylation of the mitogen-activated protein kinase (e.g., extracellular signal-related kinase [ERK]-1 and ERK-2) and focal adhesion kinase signaling pathways. In addition, CXCL12 selectively activates signal transducer and activator of transcription (STAT)-5 whereas CCL5 activates STAT-1. In cell biologic assays, all of the chemokines tested stimulate chemotaxis of BMSCs, and CXCL12 induces cytoskeleton F-actin polymerization. Studies of culture-expanded BMSCs, for example, 12-16 passages, indicate loss of surface expression of all chemokine receptors and lack of chemotactic response to chemokines. The loss in chemokine receptor expression is accompanied by a decrease in expression of adhesion molecules (ICAM-1, ICAM-2, and vascular cell adhesion molecule 1) and CD157, while expression of CD90 and CD105 is maintained. The change in BMSC phenotype is associated with slowing of cell growth and increased spontaneous apoptosis. These findings suggest that several chemokine axes may operate in BMSC biology and may be important parameters in the validation of cultured BMSCs intended for cell therapy.

Mesenchymal stem cells rescue CD34+ cells from radiation-induced apoptosis and sustain hematopoietic reconstitution after coculture and cografting in lethally irradiated baboons: is autologous stem cell therapy in nuclear accident settings hype or reality?

Autologous stem cell therapy (ACT) has been proposed to prevent irradiated victims from bone marrow (BM) aplasia by grafting hematopoietic stem and progenitor cells (HSPCs) collected early after damage, provided that a functional graft of sufficient size could be produced ex vivo. To address this issue, we set up a baboon model of cell therapy in which autologous peripheral blood HSPCs collected before lethal total body irradiation were irradiated in vitro (2.5 Gy, D0 1 Gy) to mimic the cell damage, cultured in small numbers for a week in a serum-free medium in the presence of antiapoptotic cytokines and mesenchymal stem cells (MSCs) and then cografted. Our study shows that baboons cografted with expanded cells issued from 0.75 and 1 x 10(6)/kg irradiated CD34+ cells and MSCs (n=2) exhibited a stable long-term multilineage engraftment. Hematopoietic recovery became uncertain when reducing the CD34+ cell input (0.4 x 10(6)/kg CD34+ cells; n=3). However, platelet recovery was accelerated in all surviving cografted animals, when compared with baboons transplanted with unirradiated, unmanipulated CD34+ cells (0.5-1 x 10(6)/kg, n=4). Baboons grafted with MSCs alone (n=3) did not recover. In all cases, the nonhematopoietic toxicity remained huge. This baboon study suggests that ACT feasibility is limited.

Mesenchymal stem cells support expansion of in vitro irradiated CD34(+) cells in the presence of SCF, FLT3 ligand, TPO and IL3: potential application to autologous cell therapy in accidentally irradiated victims

Ex vivo expansion of residual autologous hematopoietic stem and progenitor cells collected from victims soon after accidental irradiation (autologous cell therapy) may represent an additional or alternative approach to cytokine therapy or allogeneic transplantation. Peripheral blood CD34+ cells could be a useful source of cells for this process provided that collection and ex vivo expansion of hematopoietic stem and progenitor cells could be optimized. Here we investigated whether mesenchymal stem cells could sustain culture of irradiated peripheral blood CD34+ cells. In vitro irradiated (4 Gy 60Co gamma rays) or nonirradiated mobilized peripheral blood CD34+ cells from baboons were cultured for 7 days in a serum-free medium supplemented with stem cell factor+thrombopoietin+interleukin 3+FLT3 ligand (50 ng/ml each) in the presence or absence of mesenchymal stem cells. In contrast to cultures without mesenchymal stem cells, irradiated CD34+ cells cultured with mesenchymal stem cells displayed cell amplification, i.e. CD34+ (4.9-fold), CD34++ (3.8-fold), CD34++/Thy-1+ (8.1-fold), CD41+ (12.4-fold) and MPO+ (50.6-fold), although at lower levels than in nonirradiated CD34+ cells. Fourteen times more clonogenic cells, especially BFU-E, were preserved when irradiated cells were cultured on mesenchymal stem cells. Moreover, we showed that the effect of mesenchymal stem cells is related mainly to the reduction of apoptosis and involves cell-cell contact rather than production of soluble factor(s). This experimental model suggests that mesenchymal stem cells could provide a crucial tool for autologous cell therapy applied to accidentally irradiated victims.

Allogeneic marrow stromal cells are immune rejected by MHC class I- and class II-mismatched recipient mice

It has been suggested that marrow stromal cells (MSCs) may be immunoprivileged and can engraft in allogeneic recipients with intact immune systems. We determined if the implantation of murine MSCs engineered to release erythropoietin (Epo) would be feasible in major histocompatibility complex (MHC)-mismatched allogeneic mice without immunosuppression, and we monitored hematocrit (Hct) as a reporter of MSC graft survival. MSCs from C57Bl/6 mice were engineered to release murine Epo (Epo+ MSCs) and implanted subcutaneously in either syngeneic C57Bl/6 mice or MHC-mismatched Balb/c mice. In syngeneic recipients, the Hct rapidly rose from baseline level and remained higher than .88 (88%) for more than 200 days. However, in MHC-mismatched recipient Balb/c mice, the Hct rose transiently and rapidly declined to baseline values. Repeat implantations in these same mice were associated with an acquired refractoriness in the Hct response consistent with alloimmunization to donor Epo+ MSCs. Allogeneic MSC implants had an increased proportion of host-derived lymphoid CD8+, natural killer T (NKT), and NK infiltrating cells compared with syngeneic controls, and splenocytes isolated from Balb/c mice that had received implants also displayed a significant interferon-gamma (IFNgamma) response to C57Bl/6 MSCs in vitro. These results strongly suggest that MSCs are not intrinsically immunoprivileged and cannot serve as a "universal donor" in immunocompetent MHC-mismatched recipients.

Mesenchymal stem cells obtained after bone marrow transplantation or peripheral blood stem cell transplantation originate from host tissue

Mesenchymal stem cells (MSC) obtained from human bone marrow have been described as adult stem cells with the ability of extensive self-renewal and clonal expansion, as well as the capacity to differentiate into various tissue types and to modulate the immune system. Some data indicate that leukapheresis products may also contain non-hematopoietic stem cells, as they occur in whole bone marrow transplantation (BMT). However, there is still controversy whether MSC expand in the host after transplantation like blood progenitor cells do. Therefore, we were interested in finding out if graft MSC can be detected in leukapheresis products and in bone marrow after BMT and peripheral blood stem cell transplantation (PBSCT). Every sample from total bone marrow transplants exhibited growth of MSC after in vitro culture, but not one of nine leukapheresis products did. In addition, bone marrow aspirates of 9 patients receiving BMT and of 18 patients after PBSCT were examined for origin of MSC. Almost all MSC samples exhibited a complete host profile, whereas peripheral blood cells were of donor origin. We conclude that even if trace amounts of MSC are co-transplanted during PBSCT or BMT, they do not expand significantly in the host bone marrow.