Baboon mesenchymal stem cells can be genetically modified to secrete human erythropoietin in vivo

Mesenchymal stem cells from adult bone marrow

Mesenchymal stem cells (MSCs), sometimes referred to as marrow stromal cells or multipotential stromal cells, represent a class of adult progenitor cells capable of differentiation to several mesenchymal lineages. They can be isolated from many tissues although bone marrow has been used most often. The MSCs may prove useful for repair and regeneration of a variety of mesenchymal tissues such as bone, cartilage, muscle, marrow stroma, and the cells produce useful growth factors and cytokines that may help repair additional tissues. There is also evidence for their differentiation to nonmesenchymal lineages, but that work will not be considered here. This chapter will provide the researcher with some background, and then provide details on MSC isolation, expansion and multilineage differentiation. These are the beginning steps toward formulating tissue repair strategies. The methods provided here have been used in many laboratories around the world and the reader can begin by following the methods presented here, and then test other methods if these prove unsatisfactory for your intended purpose.

Assessment of a nuclear affinity labeling method for tracking implanted mesenchymal stem cells

Therapeutic implantation of mesenchymal stem cells (MSCs) is entering the realm of clinical trials for several human diseases, and yet much remains uncertain regarding their dynamic distribution and cell fate after in vivo application. Discrepancies in the literature can be attributed in part to the use of different cell labeling/tracking methods and cell administration protocols. To identify a stem cell detection method suitable for myocardial implantation in a large animal model, we experimented on three different MSC labeling methods: adenovirus-mediated expression of enhanced green fluorescence protein (EGFP) and beta-galactosidase (LacZ), and nuclear staining with DAPI. Intramuscular and intracoronary administrations of labeled porcine MSCs identified the nuclear affinity dye to be a reliable stem cell tracking marker. Stem cell identification is facilitated by an optimized live cell labeling condition generating bright blue fluorescence sharply confined to the nucleus. DAPI-labeled MSCs retained full viability, ceased proliferation, and exhibited an increased differentiation potential. The labeled MSCs remained fully active in expressing key growth factor and cytokine genes, and notably exhibited enhanced expression of the chemokine receptor CXCR4 and its ligand SDF1, indicating their competency in response to tissue injury. Histological analysis revealed that approximately half a million MSCs or approximately 2% of the administered MSCs remained localized in the normal pig heart 2 weeks after coronary infusion. That the vast majority of these identified MSCs were interstitial indicated the ability of MSCs to migrate across the coronary endothelium. No evidence was obtained indicating MSC differentiation to cardiomyocyte.

Efficient generation of human hepatocytes by the intrahepatic delivery of clonal human mesenchymal stem cells in fetal sheep

Alternative methods to whole liver transplantation require a suitable cell that can be expanded to obtain sufficient numbers required for successful transplantation while maintaining the ability to differentiate into hepatocytes. Mesenchymal stem cells (MSCs) possess several advantageous characteristics for cell-based therapy and have been shown to be able to differentiate into hepatocytes. Thus, we investigated whether the intrahepatic delivery of human MSCs is a safe and effective method for generating human hepatocytes and whether the route of administration influences the levels of donor-derived hepatocytes and their pattern of distribution throughout the parenchyma of the recipient's liver. Human clonally derived MSCs were transplanted by an intraperitoneal (n = 6) or intrahepatic (n = 6) route into preimmune fetal sheep. The animals were analyzed 56-70 days after transplantation by immunohistochemistry, enzyme-linked immunosorbent assay, and flow cytometry. The intrahepatic injection of human MSCs was safe and resulted in more efficient generation of hepatocytes (12.5% +/- 3.5% versus 2.6% +/- 0.4%). The animals that received an intrahepatic injection exhibited a widespread distribution of hepatocytes throughout the liver parenchyma, whereas an intraperitoneal injection resulted in a preferential periportal distribution of human hepatocytes that produced higher amounts of albumin. Furthermore, hepatocytes were generated from MSCs without the need to first migrate/lodge to the bone marrow and give rise to hematopoietic cells.

CONCLUSION

Our studies provide evidence that MSCs are a valuable source of cells for liver repair and regeneration and that, by the alteration of the site of injection, the generation of hepatocytes occurs in different hepatic zones, suggesting that a combined transplantation approach may be necessary to successfully repopulate the liver with these cells.

Immune response to stem cells and strategies to induce tolerance

Although recent progress in cardiovascular tissue engineering has generated great expectations for the exploitation of stem cells to restore cardiac form and function, the prospects of a common mass-produced cell resource for clinically viable engineered tissues and organs remain problematic. The refinement of stem cell culture protocols to increase induction of the cardiomyocyte phenotype and the assembly of transplantable vascularized tissue are areas of intense current research, but the problem of immune rejection of heterologous cell type poses perhaps the most significant hurdle to overcome. This article focuses on the potential advantages and problems encountered with various stem cell sources for reconstruction of the damaged or failing myocardium or heart valves and also discusses the need for integrating advances in developmental and stem cell biology, immunology and tissue engineering to achieve the full potential of cardiac tissue engineering. The ultimate goal is to produce 'off-the-shelf' cells and tissues capable of inducing specific immune tolerance.

High-Yield Isolation, Expansion, and Differentiation of Murine Bone Marrow-Derived Mesenchymal Stem Cells Using Fibrin Microbeads (FMB)

Transplantation of adult mesenchymal stem cells (MSCs) could provide a basis for tissue regeneration. MSCs are typically isolated from bone marrow (BM) based on their preferential adherence to plastic, although with low efficiency in terms of yield and purity. Extensive expansion is needed to reach a significant number of MSCs for any application. Fibrin microbeads (FMB) were designed to attach mesenchymal cells and to provide a matrix for their expansion. The current study was aimed at isolating a high yield of purified BM-derived mouse MSCs based on their preferential adherence and proliferation on FMB in suspension cultures. MSCs could be downloaded to plastics or further expanded on FMB. The yield of MSCs obtained by the FMB isolation technique was about one order of magnitude higher than that achieved by plastic adherence, suggesting that these cells are more abundant than previously reported. FMB-isolated cells were classified as MSCs by their fibroblastic morphology, self-renewal ability, and expression profile of their surface antigens, as examined by flow cytometry and immunostaining. In cell culture, the isolated MSCs could be induced to differentiate into three different mesodermal lineages, as demonstrated by histochemical stains and by RT-PCR analyses of tissue-specific genes. MSCs were also able to differentiate into osteocytes while still cultured on FMB. Our results suggest that FMB might serve as an efficient platform for the isolation, expansion, and differentiation of mouse BM-derived MSCs to be subsequently implanted for tissue regeneration.

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.

Mesenchymal stem cells: Immunobiology and therapeutic potential in kidney disease (Review Article)

Mesenchymal stem cells (MSC) are non-haematopoietic cells that are prevalent in the adult bone marrow but can also be isolated from a variety of other postnatal tissues. MSC are non-immunogenic and are immunosuppressive, with the ability to inhibit maturation of dendritic cells and suppress the function of naïve and memory T cells, B cells and NK cells. In addition to their immunomodulatory properties, MSC are capable of differentiating into various tissues of mesenchymal and non-mesenchymal origin and migrating to sites of tissue injury and inflammation to participate in tissue repair. A number of studies in animal models of cardiac injury, stroke and ischaemic renal injury have demonstrated the clinical potential of MSC in tissue regeneration and repair. MSC are currently being evaluated in various preclinical and clinical studies in humans and offer significant potential as a novel cellular therapy for tissue regeneration and immunological conditions. The present review focuses on the unique immunomodulatory and regenerative properties of MSC and their potential role in the treatment of kidney disease.

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.

Control of erythropoietin gene expression and its use in medicine

Erythropoietin (EPO) gene expression is under the control of inhibitory (GATA-2, NF-kappaB) and stimulatory (hypoxia-inducible transcription factor [HIF]-2, hepatocyte nuclear factor [HNF]-4alpha [alpha]) transcription factors. EPO deficiency is the main cause of the anemia in chronic kidney disease (CKD) and a contributing factor in the anemias of inflammation and cancer. Small, orally active compounds capable of stimulating endogenous EPO production are in preclinical or clinical trials for treatment of anemia. These agents include stabilizers of the HIFs that bind to the EPO enhancer and GATA inhibitors which prevent GATA from suppressing the EPO promoter. While HIF stabilizing drugs may prove useful as inexpensive second-line choices, at present, their side effects--particularly tumorigenicity--preclude their use as first-choice therapy. As an alternative, EPO gene therapy has been explored in animal studies and in trials on CKD patients. Here, a major problem is immunogenicity of ex vivo transfected implanted cells and of the recombinant protein produced after ex vivo or in vivo EPO complementary DNA (cDNA) transfer. Recombinant human EPO (rhEPO) engineered in Chinese hamster ovary (CHO) cell cultures (epoetin alpha and epoetin beta [beta]) and its hyperglycosylated analogue darbepoetin alpha are established and safe drugs to avoid allogeneic red blood cell transfusion. Gene-activated EPO (epoetin delta [delta]) from human fibrosarcoma cells (HT-1080) has recently been launched for use in CKD. It is important to know the basics of the technologies, production processes, and structural properties of the novel anti-anemic strategies and drugs.

Human mesenchymal stem cells induce T cell anergy and downregulate T cell allo-responses via the TH2 pathway: relevance to tissue engineering human heart valves

To generate an ''off the shelf'' tissue-engineered heart valve, the cells would need to be of allogeneic origin. Here, we report the possibility of using human bone marrow-derived mesenchymal stem cells (MSCs) as a suitable allogeneic cell source for tissue-engineered heart valves. Proliferative responses of primary and primed CD4+ T cells to allogeneic MSCs were examined. A protein microarray system was used to detect soluble factors from supernatants collected from the T cell assays. MSCs are poor stimulators of primary and primed CD4+ T cell proliferation, despite provision of B7-1 trans-co-stimulation. MSCs not only directly inhibited primary and primed T cell responses to allogeneic peripheral blood mononuclear cells (PBMCs), but 24-h pre-culture of T cells with MSCs suppressed subsequent T cell proliferative responses to allogeneic PBMCs in a contact-dependent manner. Analysis of supernatants revealed a distinctly different cytokine profile after co-culture of T cells with MSCs than with PBMCs or endothelial cells. Pro-inflammatory Th1 cytokines interleukin (IL)-1alpha and beta, interferon (IFN)gamma, and tumor necrosis factor (TNF)alpha were downregulated, whereas, anti-inflammatory Th2 cytokines IL-3, IL-5, IL-10, and IL-13 and the Th2 chemokine I-309, a chemoattractant for regulatory T cells, were upregulated. Further analysis revealed that after co-culture with MSCs, the T cells exhibited a regulatory phenotype (CD4+ CD25(lo) CD69(lo) FoxP3+). MSCs downregulate T cell responses through direct contact and secretion of anti-inflammatory and tolerogenic cytokines, which may involve the recruitment of regulatory T cells. This implies that allogeneic MSCs could be a suitable cell source for tissue engineering a heart valve.

Interleukin-7–Engineered Mesenchymal Cells: In Vitro Effects on Naive T-Cell Population

T-cell homeostasis is regulated by several molecules; among these, interleukin (IL)-7 plays an essential role in the survival and homeostatic proliferation of peripheral naive T cells. In a previous study, we investigated whether human mesenchymal stromal cells (MSCs) could be engineered with the IL-7 gene to produce functional level of this cytokine. In the present study, we analyzed the impact of different quantities of IL-7 produced by MSCs on the survival and proliferation of a negative immunoselected naive (CD3(+)/CD45RA(+)) T-cell population. Co-cultivation of peripheral naive T cells with MSCs producing low (16 pg/mL) or high (1000 pg/mL) IL-7 levels or in the presence of exogenous IL-7 (0.01 ng/mL and 100 ng/mL) maintained the CD3(+)/CD45RA(+) naive T-cell phenotype. Chemokine receptor CCR7(+) expression was also maintained among this T-cell population. Naive T-cell molecular characteristics were maintained as assessed by the Vbeta spectratyping complexity score, which showed the maintenance of a broad T-cell repertoire. No Th1 or Th2 differentiation was observed, as assessed by interferon-gamma or IL-4 accumulation. In contrast, only MSCs producing high amounts of IL-7 caused increased activation (CD25 31.2% +/- 12% vs 10% +/- 3.5%; P < .05), proliferation (CD71 17.8+/-7% vs 9.3%+/-3, P < .05), apoptosis (assessed by annexin V: 18.6% +/- 5% vs 14.9% +/- 2.6%; P > .05), and the phase S cell cycle (15% vs 6.9%, P > .05). Exogenous IL-7 exhibited no significant effect. In conclusion, we demonstrated that IL-7 produced by MSCs has a dose-independent effect on naive T-cell survival while exerting a dose-dependent effect on activation/proliferation. Due to the continuous production of IL-7 by engineered cells, our system is more efficacious than exogenous IL-7.

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.

Cellular cardiomyoplasty by catheter-based infusion of stem cells in clinical settings

Myocardial infarction is the leading cause of congestive heart failure and death in the industrialized world. However, the intrinsic repair mechanism of the heart is inadequate. Current therapy is limited in preventing ventricular remodeling, but can not regenerate the lost cardiomyocytes. Recent interests have been focused on cellular cardiomyoplasty which is an outside intervention to support the reparative process in the heart through transplantation of stem/progenitor cells or cardiac cells. Cellular cardiomyoplasty with stem cells is a possible option to reverse the adverse hemodynamic and neurohormonal imbalance after myocardial infarction. Experimental studies and clinical trials suggest that cellular cardiomyoplasty may benefit tissue perfusion and contractile performance of the injured heart. Although the mechanisms are still intensively debated, cellular cardiomyoplasty with stem cells has already been introduced into the clinical settings. However, it is an important challenge how stem cells are delivered to targeted area. In early studies on animals, intramyocardial injection of stem cells after thoracotomy is the predominant transplantation route which is not suitable for most patients in clinical settings. Then the catheter-based infusion of stem cells is clinically introduced and rapidly developed in patients because of the safety, convenience and mini-invasion. We mainly review the progress in catheter-based transplantation with stem cells in order to fully understand the application of various intervention-based approaches to stem cells transplantation in clinical settings.

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.

Combination of 3D tissue engineered scaffold and non-viral gene carrier enhance in vitro DNA expression of mesenchymal stem cells

The objective of this study is to enhance the expression of a plasmid DNA for mesenchymal stem cells (MSC) by combination of 3-dimensional (3D) tissue engineered scaffolds and non-viral gene carrier. As a carrier of plasmid DNA, dextran-spermine cationic polysaccharide was prepared by means of reductive-amination between oxidized dextran and the natural oligoamine, spermine. As the MSC scaffold, collagen sponges reinforced by incorporation of poly(glycolic acid) (PGA) fibers were used. A complex of the cationized dextran and plasmid DNA of BMP-2 was impregnated into the scaffolds. MCS were seeded into each scaffold and cultured by a 3D culture method. When MSC were cultured in the PGA-reinforced sponge, the level of BMP-2 expression was significantly enhanced by the cationized dextran-plasmid DNA complex impregnated into the scaffold than by the cationized dextran-plasmid DNA complex in 2-dimensional (2D) (tissue culture plate) culture method. The alkaline phosphatase activity and osteocalcin content of transfected MSC cultured in the PGA-reinforced sponge were significantly higher compared with 2D culture method. We conclude that combination of cationized dextran plasmid DNA complex and 3D tissue engineered scaffold was promising to promote the in vitro gene expression for MSC.

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.

Retrovirus-Mediated Gene Transfer of Receptor Activator of Nuclear Factor-κB-Fc Prevents Bone Loss in Ovariectomized Mice

Postmenopausal osteoporosis is characterized by increased bone resorption due to estrogen deficiency. Receptor activator of nuclear factor-kappaB-Fc (RANK-Fc), a fusion protein that specifically blocks receptor activator of nuclear factor ligand binding to RANK, has been known to be efficient and well tolerated in animal models of osteoporosis. Here we show that cell-based gene therapy with RANK-Fc effectively prevented bone loss in ovariectomized (OVX) mice. Thirty-one young adult female C57Bl/6 mice were used, and repeated intraperitoneal injection of mesenchymal stem cells (MSCs) transduced with retrovirus was performed as follows: 1) Sham-operated mice (n = 8); 2) OVX mice treated with phosphate-buffered saline (OVX-PBS; n = 8); 3) OVX mice injected with MSCs transduced with control retrovirus (OVX-green fluorescent protein [GFP]; n = 7); and 4) OVX mice injected with MSCs transduced with RANK-Fc (OVX-RANK-Fc; n = 8). Cellular expression of RANK-Fc was confirmed by Western blot analysis of cell lysates and conditioned medium and also by enzyme-linked immunosorbent assay for the mice serum. Measurement of bone mineral density (BMD) by dual-energy x-ray absorptiometry (PIXImus) revealed that the OVX-RANK-Fc group gained significantly higher BMD than either the OVX-PBS group or OVX-GFP group after 8 weeks. The expression of GFP, which is coexpressed with RANK-Fc, was detected by polymerase chain reaction analysis of DNA isolated from femur and intra-abdominal fat, whereas no GFP signal was identified in liver, brain, heart, lung, or bone marrow aspirates. These suggest that expression of RANK-Fc by genetically modified MSCs may be a feasible option for the prevention of bone loss induced by ovariectomy.

Lentiviral transduction of human postnatal skeletal (stromal, mesenchymal) stem cells: in vivo transplantation and gene silencing

Systems for gene transfer and silencing in human skeletal stem cells (hSSCs, also stromal or mesenchymal stem cells) are important for addressing critical issues in basic hSSC and skeletal biology and for developing gene therapy strategies for treatment of skeletal diseases. Whereas recent studies have shown the efficacy of lentiviral transduction for gene transfer in hSSCs in vitro, no study has yet proven that lentivector-transduced hSSCs retain their distinctive organogenic potential in vivo, as probed by in vivo transplantation assays. Therefore, in addition to analyzing the in vitro growth and differentiation properties of hSSCs transduced with advanced-generation lentivectors, we ectopically transplanted LV-eGFP-transduced hSSCs (along with an osteoconductive carrier) in the subcutaneous tissue of immunocompromised mice. eGFP-transduced cells formed heterotopic ossicles, generating osteoblasts, osteocytes, and stromal cells in vivo, which still expressed GFP at 2 months after transplantation. eGFP-expressing cells could be recovered from the ossicles 8 weeks posttransplantation and reestablished in culture as viable and proliferating cells. Further, we investigated the possibility of silencing individual genes in hSSCs using lentivectors encoding short hairpin precursors of RNA interfering sequences under the control of the Pol-III-dependent H1 promoter. Significant long-term silencing of both lamin A/C and GFP (an endogenous gene and a transgene, respectively) was obtained with lentivectors encoding shRNAs. These data provide the basis for analysis of the effect of gene knockdown during the organogenesis of bone in the in vivo transplantation system and for further studies on the silencing of alleles carrying dominant, disease-causing mutations.

Potential of mesenchymal stem cells in gene therapy approaches for inherited and acquired diseases

The intriguing biology of stem cells and their vast clinical potential is emerging rapidly for gene therapy. Bone marrow stem cells, including the pluripotent haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and possibly the multipotent adherent progenitor cells (MAPCs), are being considered as potential targets for cell and gene therapy-based approaches against a variety of different diseases. The MSCs from bone marrow are a promising target population as they are capable of differentiating along multiple lineages and, at least in vitro, have significant expansion capability. The apparently high self-renewal potential makes them strong candidates for delivering genes and restoring organ systems function. However, the high proliferative potential of MSCs, now presumed to be self-renewal, may be more apparent than real. Although expanded MSCs have great proliferation and differentiation potential in vitro, there are limitations with the biology of these cells in vivo. So far, expanded MSCs have failed to induce durable therapeutic effects expected from a true self-renewing stem cell population. The loss of in vivo self-renewal may be due to the extensive expansion of MSCs in existing in vitro expansion systems, suggesting that the original stem cell population and/or properties may no longer exist. Rather, the expanded population may indeed be heterogeneous and represents several generations of different types of mesenchymal cell progeny that have retained a limited proliferation potential and responsiveness for terminal differentiation and maturation along mesenchymal and non-mesenchymal lineages. Novel technology that allows MSCs to maintain their stem cell function in vivo is critical for distinguishing the elusive stem cell from its progenitor cell populations. The ultimate dream is to use MSCs in various forms of cellular therapies, as well as genetic tools that can be used to better understand the mechanisms leading to repair and regeneration of damaged or diseased tissues and organs.

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.

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.

Interferon-gamma-stimulated marrow stromal cells: a new type of nonhematopoietic antigen-presenting cell

Several studies have demonstrated that marrow stromal cells (MSCs) can suppress allogeneic T-cell responses. However, the effect of MSCs on syngeneic immune responses has been largely overlooked. We describe here that primary MSCs derived from C57BL/6 mice behave as conditional antigen-presenting cells (APCs) and can induce antigen-specific protective immunity. Interferon gamma (IFNgamma)-treated C57BL/6 MSCs, but not unstimulated MSCs, cocultured with ovalbumin-specific major histocompatibility (MHC) class II-restricted hybridomas in the presence of soluble ovalbumin-induced significant production of interleukin-2 (IL-2) in an antigen dose-dependent manner (P < .005). IFNgamma-treated MSCs could further activate in vitro ovalbumin-specific primary transgenic CD4+ T cells. C57BL/6 MSCs, however, were unable to induce antigen cross-presentation via the MHC class I pathway. When syngeneic mice were immunized intraperitoneally with ovalbumin-pulsed IFNgamma-treated MSCs, they developed antigen-specific cytotoxic CD8+ T cells and became fully protected (10 of 10 mice) against ovalbumin-expressing E.G7 tumors. Human MSCs were also studied for antigen-presenting functions. IFNgamma-treated DR1-positive human MSCs, but not unstimulated human MSCs, induced significant production of IL-2 when cocultured with DR1-restricted influenza-specific humanized T-cell hybridomas in the presence of purified influenza matrix protein 1. Taken together, our data strongly suggest that MSCs behave as conditional APCs in syngeneic immune responses.

A novel human artificial chromosome vector provides effective cell lineage-specific transgene expression in human mesenchymal stem cells

Mesenchymal stem cells (MSCs) hold promise for use in adult stem cell-mediated gene therapy. One of the major aims of stem cell-mediated gene therapy is to develop vectors that will allow appropriate levels of expression of therapeutic genes along differentiation under physiological regulation of the specialized cells. Human artificial chromosomes (HACs) are stably maintained as independent chromosomes in host cells and should be free from potential insertional mutagenesis problems of conventional transgenes. Therefore, HACs have been proposed as alternative implements to cell-mediated gene therapy. Previously, we constructed a novel HAC, termed 21 Deltapq HAC, with a loxP site in which circular DNA can be reproducibly inserted by the Cre/loxP system. We here assessed the feasibility of lineage-specific transgene expression by the 21Deltapq HAC vector using an in vitro differentiation system with an MSC cell line, hiMSCs, which has potential for osteogenic, chondrogenic, and adipogenic differentiation. An enhanced green fluorescent protein (EGFP) gene driven by a promoter for osteogenic lineage-specific osteopontin (OPN) gene was inserted onto the 21 Deltapq HAC and then transferred into hiMSC. The expression cassette was flanked by the chicken HS4 insulators to block promoter interference from adjacent drug-resistant genes. The EGFP gene was specifically expressed in the hiMSC that differentiated into osteocytes in coordination with the transcription of endogenous OPN gene but was not expressed after adipogenic differentiation induction or in noninduction culture. These results suggest that use of the HAC vector is suitable for regulated expression of transgenes in stem cell-mediated gene therapy.

Impregnation of Plasmid DNA into Three-Dimensional Scaffolds and Medium Perfusion Enhancein VitroDNA Expression of Mesenchymal Stem Cells

This article describes the development of an in vitro culture system to enhance the expression of a plasmid DNA for mesenchymal stem cells (MSCs) by a combination of plasmid DNA impregnation into three-dimensional cell scaffolds and culture methods. Gelatin was cationized by introducing spermine to the carboxyl groups for complexation with the plasmid DNA. As the MSC scaffold, poly(glycolic acid) (PGA) fiber fabrics, collagen sponges, and collagen sponges reinforced by incorporation of PGA fibers were used. A complex of cationized gelatin and plasmid DNA encoding bone morphogenetic protein 2 (BMP-2) was impregnated into the scaffolds. Plasmid DNA was released from PGA-reinforced collagen sponge for longer than from the other scaffolds. MCS were seeded into each type of scaffold and cultured by static, stirring, and perfusion methods. When MSCs were cultured in PGA-reinforced sponge, the level of BMP-2 expression was significantly enhanced by perfusion culture compared with the other culture methods, and the time of expression was prolonged. Irrespective of the culture method, the expression level was significantly higher from plasmid DNA impregnated in scaffold than by plasmid DNA in medium. The alkaline phosphatase activity and osteocalcin content of MSCs cultured in PGA-reinforced sponge by the perfusion method were significantly higher compared with those of other methods, and a significantly higher amount of plasmid DNA internalized into MSCs was observed. We conclude that a combination of plasmid DNA-impregnated PGA-reinforced sponge and the perfusion method was promising to promote in vitro gene expression for MSCs.

Role for interferon-gamma in the immunomodulatory activity of human bone marrow mesenchymal stem cells

Mesenchymal stem cells (MSCs) inhibit the proliferation of HLA-unrelated T lymphocytes to allogeneic stimulation, but the mechanisms responsible for this activity are not fully understood. We show here that MSCs suppress the proliferation of both CD4+ and CD8+ T lymphocytes, as well as of natural killer (NK) cells, whereas they do not have an effect on the proliferation of B lymphocytes. The antiproliferative effect of MSCs was not associated with any effect on the expression of cell-activation markers, induction of cell apoptosis, or mimicry/enhancement of T regulatory cell activity. The suppressive activity of MSCs was not contact-dependent and required the presence of interferon (IFN)-gamma produced by activated T cells and NK cells. Accordingly, even activated B cells became susceptible to the suppressive activity of MSCs in the presence of exogenously added IFN-gamma. The suppressive effect of IFN-gamma was related to its ability to stimulate the production by MSCs of indoleamine 2,3-dioxygenase activity, which in turn inhibited the proliferation of activated T or NK cells. These findings suggest that the beneficial effect on graft-versus-host disease induced by in vivo coinfusion with the graft of MSCs may be due to the activation of the immunomodulatory properties of MSCs by T cell- derived IFN-gamma.

Reversal of the immunosuppressive properties of mesenchymal stem cells by tumor necrosis factor alpha in collagen-induced arthritis

OBJECTIVE

Adult mesenchymal stem cells (MSCs) represent promising tools for therapeutic applications such as tissue engineering and cellular therapy. Recent data suggest that, due to their immunosuppressive nature, MSCs may be of interest to enhance allogeneic hematopoietic engraftment and prevent graft-versus-host disease. Using a murine model of rheumatoid arthritis (RA), this study investigated whether the immunosuppressive properties of MSCs could be of therapeutic value to inhibit reactive T cells in autoimmune diseases such as RA.

METHODS

In mice with collagen-induced arthritis (CIA), we injected various doses of C3 MSCs at the time of immunization or booster injection, and subsequently evaluated the clinical and immunologic parameters. The immunosuppressive properties of MSCs were determined in vitro in mixed lymphocyte reactions with or without the addition of tumor necrosis factor alpha (TNFalpha).

RESULTS

In the CIA model of arthritis, MSCs did not confer any benefit. Both the clinical and the immunologic findings suggested that MSCs were associated with accentuation of the Th1 response. Using luciferase-expressing MSCs, we were unable to detect labeled cells in the articular environment of the knee, suggesting that worsening of the symptoms was unlikely due to the homing of MSCs in the joints. Experiments in vitro showed that the addition of TNFalpha was sufficient to reverse the immunosuppressive effect of MSCs on T cell proliferation, and this observation was associated with an increase in interleukin-6 secretion.

CONCLUSION

Our data suggest that environmental parameters, in particular those related to inflammation, may influence the immunosuppressive properties of MSCs.

Interleukin 7-Engineered Stromal Cells: A New Approach for Hastening Naive T Cell Recruitment

In this study we determined whether human stromal cells could be engineered with a retroviral vector carrying the interleukin 7 (IL-7) gene and investigated the effects on T cells in vitro and in vivo in a murine model. Transduced mesenchymal cells strongly express CD90 (98.15%), CD105 (87.6%), and STRO-1 (86.7%). IL-7 production was 16.37 (+/-2 SD) pg/ml, which remained stable for 60 days. In vitro-immunoselected naive T cells maintained the CD45RA+ CD45RO- naive phenotype (4.2 times more than controls) after 7 days of culture with IL-7-engineered stromal cells. The apoptosis rate (4.7%) of the naive T cells cultured with transduced stromal cells overlapped with that of freshly isolated cells. Immunohistological analysis detected stromal cells in bone marrow, spleen, and thymus. Cotransplantation of IL-7-engineered stromal cells with CD34+ cells improved engraftment in terms of CD45+ cells and significantly increased the CD3+ cell count in peripheral blood, bone marrow, and spleen. These data demonstrate the following: (1) human stromal cells can be transduced, generating a normal layer; (2) transduced stromal cells in vitro maintain the naive T cell phenotype; and (3) IL-7-transduced stromal cells in vivo home to lymphoid organs and produce sufficient IL-7 in loco, supporting T cell development in a cotransplantation model. Because of their efficient cytokine production and homing, IL-7-engineered stromal cells might be an ideal vehicle to hasten immunological reconstitution in T cell-depleted hosts.

Immunobiology of Human Mesenchymal Stem Cells and Future Use in Hematopoietic Stem Cell Transplantation

Mesenchymal stem cells (MSCs) may be derived from adult bone marrow, fat, and several fetal tissues. In vitro, MSCs can be expanded and have the capacity to differentiate into several mesenchymal tissues, such as bone, cartilage, and fat. They escape the immune system in vitro, and this may make them candidates for cellular therapy in an allogeneic setting. They also have immunomodulatory effects, inhibit T-cell proliferation in mixed lymphocyte cultures, prolong skin allograft survival, and may decrease graft-versus-host disease (GVHD) when cotransplanted with hematopoietic stem cells. MSCs induce their immunosuppressive effect via a soluble factor. Some candidates have been suggested, and various mechanisms have also been suggested, although contradictory data exist; this may be due to differences in the cells and systems tested. A major problem has been that it has been difficult to identify and isolate MSCs after transplantation in vivo. However, MSCs seem to enhance hematopoietic engraftment in recipients of autologous and allogeneic grafts. Recently, they were found to reverse grade IV acute GVHD of the gut and liver. No tolerance was induced, however. Controlled studies are warranted. Thus, in allogeneic stem cell transplantation, MSCs may be used for hematopoiesis enhancement, as GVHD prophylaxis, and for the treatment of severe acute GVHD. They are also of potential use in the treatment of organ transplant rejection and in autoimmune inflammatory bowel disorders where immunomodulation and tissue repair are needed.

Study of telomere length reveals rapid aging of human marrow stromal cells following in vitro expansion

Human marrow stromal cells (MSCs) can be isolated from bone marrow and differentiate into multiple tissues in vitro and in vivo. These properties make them promising tools in cell and gene therapy. The lack of a specific MSC marker and the low frequency of MSCs in bone marrow necessitate their isolation by in vitro expansion prior to clinical use. This may severely reduce MSC proliferative capacity to the point that the residual proliferative potential is insufficient to maintain long-term tissue regeneration upon reinfusion. In this study we determined the effect of in vitro expansion on the replicative capacity of MSCs by correlating their rate of telomere loss during in vitro expansion with their behavior in vivo. We report that even protocols that involve minimal expansion induce a rapid aging of MSCs, with losses equivalent to about half their total replicative lifespan.

Human artificial chromosome (HAC) vector provides long-term therapeutic transgene expression in normal human primary fibroblasts

Human artificial chromosomes (HACs) segregating freely from host chromosomes are potentially useful to ensure both safety and duration of gene expression in therapeutic gene delivery. However, low transfer efficiency of intact HACs to the cells has hampered the studies using normal human primary cells, the major targets for ex vivo gene therapy. To elucidate the potential of HACs to be vectors for gene therapy, we studied the introduction of the HAC vector, which is reduced in size and devoid of most expressed genes, into normal primary human fibroblasts (hPFs) with microcell-mediated chromosome transfer (MMCT). We demonstrated the generation of cytogenetically normal hPFs harboring the structurally defined and extra HAC vector. This introduced HAC vector was retained stably in hPFs without translocation of the HAC on host chromosomes. We also achieved the long-term production of human erythropoietin for at least 12 weeks in them. These results revealed the ability of HACs as novel options to circumvent issues of conventional vectors for gene therapy.

Mesenchymal stem cells differentiate into an endothelial phenotype, enhance vascular density, and improve heart function in a canine chronic ischemia model

BACKGROUND

Bone marrow-derived stem cells are under investigation as a treatment for ischemic heart disease. Mesenchymal stem cells (MSCs) have been used preferentially in the acute ischemia model; data in the chronic ischemia model are lacking.

METHODS AND RESULTS

Twelve dogs underwent ameroid constrictor placement. Thirty days later, they received intramyocardial injections of either MSCs (100x10(6) MSCs/10 mL saline) (n=6) or saline only (10 mL) (controls) (n=6). All were euthanized at 60 days. Resting and stress 2D echocardiography was performed at 30 and 60 days after ameroid placement. White blood cell count (WBC), C-reactive protein (CRP), creatine kinase MB (CK-MB), and troponin I levels were measured. Histopathological and immunohistochemical analyses were performed. Mean left ventricular ejection fraction was similar in both groups at baseline but significantly higher in treated dogs at 60 days. WBC and CRP levels were similar over time in both groups. CK-MB and troponin I increased from baseline to 48 hours, eventually returning to baseline. There was a trend toward reduced fibrosis and greater vascular density in the treated group. MSCs colocalized with endothelial and smooth muscle cells but not with myocytes.

CONCLUSIONS

In a canine chronic ischemia model, MSCs differentiated into smooth muscle cells and endothelial cells, resulting in increased vascularity and improved cardiac function.

Mesenchymal stem cells and their potential as cardiac therapeutics

Mesenchymal stem cells (MSCs) represent a stem cell population present in adult tissues that can be isolated, expanded in culture, and characterized in vitro and in vivo. MSCs differentiate readily into chondrocytes, adipocytes, osteocytes, and they can support hematopoietic stem cells or embryonic stem cells in culture. Evidence suggests MSCs can also express phenotypic characteristics of endothelial, neural, smooth muscle, skeletal myoblasts, and cardiac myocyte cells. When introduced into the infarcted heart, MSCs prevent deleterious remodeling and improve recovery, although further understanding of MSC differentiation in the cardiac scar tissue is still needed. MSCs have been injected directly into the infarct, or they have been administered intravenously and seen to home to the site of injury. Examination of the interaction of allogeneic MSCs with cells of the immune system indicates little rejection by T cells. Persistence of allogeneic MSCs in vivo suggests their potential "off the shelf" therapeutic use for multiple recipients. Clinical use of cultured human MSCs (hMSCs) has begun for cancer patients, and recipients have received autologous or allogeneic MSCs. Research continues to support the desirable traits of MSCs for development of cellular therapeutics for many tissues, including the cardiovascular system. In summary, hMSCs isolated from adult bone marrow provide an excellent model for development of stem cell therapeutics, and their potential use in the cardiovascular system is currently under investigation in the laboratory and clinical settings.

In vivo contribution of murine mesenchymal stem cells into multiple cell-types under minimal damage conditions

Murine mesenchymal stem cells are capable of differentiating in vitro into different lineages under stimulation with certain cytokines, growth factors and chemicals. However, the true capacitiy of these cells to contribute to different cell-types in vivo is still unclear, especially under minimal injury conditions. In this study, we describe a method of purifying murine mesenchymal stem cells from bone marrow and efficiently transducing them using a lentivirus vector expressing the eGFP reporter gene. Lentivirus-transduced mesenchymal stem cells retained their in vitro ability to differentiate into adipocytes, osteocytes and chondrocytes as well as into myocyte- and astrocyte-like cells. eGFP-mesenchymal stem cells were delivered systemically into minimally injured syngeneic mice. Tracking and tissue-specific differentiation were determined by PCR and immunohistochemistry, respectively. We found donor-derived hepatocytes, lung epithelial cells, myofibroblasts, myofibers and renal tubular cells in some of the recipient mice. Our data indicate that even in the absence of substantial injury, phenotypically defined murine mesenchymal stem cells could acquire tissue specific morphology and antigen expression and thus contribute to different tissue cell-types in vivo.

Human-compatible collagen matrix for prolonged and reversible systemic delivery of erythropoietin in mice from gene-modified marrow stromal cells

Bone marrow stromal cells (MSCs) can be exploited therapeutically in transgenic cell therapy approaches. Our aim was to determine if gene-modified MSCs sequestered within a clinically approved, bovine type I collagen-based viscous bulking material could serve as a retrievable implant for systemic delivery of erythropoietin (Epo). To test this hypothesis, we embedded Epo-secreting MSCs in viscous collagen (Contigen) and determined the pharmacological effect following implantation in normal mice. Primary MSCs from C57Bl/6 mice were retrovirally engineered to express murine Epo (mEpo) and 10(7) cells of a clonal population secreting 3 U of mEpo/10(6) cells/24 h were implanted subcutaneously in normal C57Bl/6 mice with and without viscous collagen. Without matrix support, Hct rose to >70% for <25 days and returned to baseline by 60 days. However, in mice implanted with viscous collagen-embedded MSCs, the Hct rose to >70% up to 203 days postimplantation (P < 0.0001). In parallel, plasma Epo concentration was significantly increased (P < 0.05) for >145 days. Moreover, surgical removal of the viscous collagen organoid 24 days after implantation led to reduction of Hct to baseline levels within 14 days. In conclusion, this investigation demonstrates that mEpo(+) MSCs embedded in a human-compatible viscous collagen matrix offers a potent, durable, and reversible approach for delivery of plasma-soluble therapeutic proteins.

Immunomodulatory effects of fetal and adult mesenchymal stem cells

Mesenchymal stem cells (MSC) derived from adult BM or fetal liver form several mesenchymal tissues after appropriate stimulation. Reports indicate that MSC have unique immunologic properties, making them ideal for cellular therapy. MSC are not immunogenic, they do not stimulate alloreactivity, and they escape lysis by cytotoxic T-cells and natural killer (NK)-cells. Thus, MSC may be transplantable between HLA-mismatched individuals without the need for host immunosuppression. Furthermore, adult MSC appear to be immunosuppressive as they reduce alloreactivity and the formation of cytotoxic lymphocytes in vitro. In vivo, adult MSC prolong the time to rejection of mis-matched skin grafts in baboons. The immunosuppressive properties of first trimester fetal MSC are less pronounced, but inducible with IFNgamma. These findings imply a potential role for MSC, not only in the repair of damaged tissues, but also in the manipulation of immune responses.

Survival of Encapsulated Human Primary Fibroblasts and Erythropoietin Expression Under Xenogeneic Conditions

Allogeneic cells are the most attractive source for cell transplantation, as the use of xenogeneic cells is hampered by safety concerns and the use of autologous cells involves practical difficulties. The immune rejection of allogeneic cells can be overcome by physical immunoprotection provided by polymer encapsulation. To study the variability of cell and donor sources, we compared different primary human cells as candidates for gene therapy-mediated delivery of human erythropoietin (hEpo). DARC-3.1 fibroblasts, MDX-01 fibroblasts, and ARPE-19 retinal pigment epithelial cells were encapsulated into polyethersulfone hollow fibers and implanted for 1 month in nude mice as well as in immunocompetent and FK506-immunosuppressed mice to test their in vivo resistance, with the assumption that xenogeneic conditions constitute a stringent model for human application. DARC-3.1 fibroblasts showed the best survival, prompting us to evaluate cell lineages from the same donor (DARC-3.2) or another donor (DARC-4.3 and DARC-4.4). With the exception of DARC-4.3, the remaining three lineages showed comparable survival in immunocompetent C3H and DBA/2J mice. DARC-3.1 fibroblasts were retrovirally engineered with hEpo cDNA, reaching a secretion level of 170 IU of hEpo per 10(6) cells per day. Encapsulated DARC-3.1-hEpo cells led to significantly increased hematocrits in the various hosts and under various transplantation conditions. The present study shows that encapsulated primary human DARC-3.1 fibroblasts are able to survive under xenogeneic conditions and, once engineered with hEpo cDNA, to increase the hematocrit of transplanted mice.

Mesenchymal stem cells: paradoxes of passaging

The field of stem cell biology continues to evolve with the ongoing characterization of multiple types of stem cells with their inherent potential for experimental and clinical application. Mesenchymal stem cells (MSC) are one of the most promising stem cell types due to their availability and the relatively simple requirements for in vitro expansion and genetic manipulation. Multiple populations described as "MSCs" have now been isolated from various tissues in humans and other species using a variety of culture techniques. Despite extensive in vitro characterization, relatively little has been demonstrated regarding their in vivo biology and therapeutic potential. Nevertheless, clinical trials utilizing MSCs are currently underway. The aim of this review is to critically analyze the field of MSC biology, particularly with respect to the current paradox between in vitro promise and in vivo efficacy. It is the authors' opinion that until this paradox is better understood, therapeutic applications will remain limited.

Marrow Stromal Cells for Interleukin-2 Delivery in Cancer Immunotherapy

Marrow stromal cells (MSCs) can be easily gene-modified and clonally expanded making them ideal candidates for transgenic cell therapy. However, recent reports suggest that MSCs possess immunosuppressive effects, which may limit their clinical applications. We investigated whether interleukin (IL)-2 gene-modified MSCs can be used to mount an effective immune response against the poorly immunogenic B16 melanoma model. We first show that primary MSCs mixed with B16 cells and injected subcutaneously in syngeneic recipients do not affect tumor growth. On the other hand, IL-2-producing MSCs mixed with B16 cells significantly delayed tumor growth in an IL-2 dose-dependent manner. Furthermore, we observed that matrix-embedded IL-2-producing MSCs injected in the vicinity of preestablished B16 tumors led to absence of tumor growth in 90% of treated mice (p < 0.001). We demonstrated that tumor-bearing mice treated with IL-2-producing MSCs developed CD8-mediated tumor-specific immunity and significantly delayed tumor growth of a B16 cell challenge (p < 0.05). In addition, treatment of cd8-/-, cd4-/- and beige mice revealed that CD8+ and natural killer (NK) cells, but not CD4+ cells, were required to achieve antitumor effect. In conclusion, MSCs can be exploited to deliver IL-2 and generate effective immune responses against melanoma in mice with normal immune systems.

Studies of the route of administration and role of conditioning with radiation on unrelated allogeneic mismatched mesenchymal stem cell engraftment in a nonhuman primate model

OBJECTIVE

The aim of this study was to examine the effects of the route of administration [intrabone marrow (IBM) vs intravenous (IV)] and the role of conditioning with irradiation in optimizing mesenchymal stem cell (MSC) transplantation.

MATERIALS AND METHODS

To determine if irradiation resulted in depletion of colony-forming unit fibroblasts (CFU-F), which might favor the engraftment of donor MSC, the number of CFU-Fs was assayed from animals receiving either hemibody irradiation (HBI) or total body irradiation (TBI).

RESULTS

TBI resulted in a marked reduction of CFU-F numbers that spontaneously resolved, whereas animals receiving HBI did not experience depletion of CFU-F. Animals receiving MSC grafts by the IV route had higher numbers of marrow CFU-F. MSC were transduced using retroviral vectors encoding the neomycin resistance gene (Neo(R)) and a second gene encoding either the human soluble tumor necrosis factor receptor (hsTNFRII) or beta-galactosidase (beta-Gal). MSCs were administered by either the IV or IBM route to animals receiving HBI. The Neo(R) transgene was detectable in hematopoietic tissues of all animals and nonhematopoietic tissues in a single animal. Evidence of transgene expression was documented by detection of beta-Gal(+) cells in BM smears and transiently elevated serum levels of hsTNFRII.

CONCLUSION

These studies indicate that 1) MSC possess the ability to engraft and persist in an unrelated mismatched allogeneic hosts; 2) 250-cGy HBI did not favor engraftment of MSC; 3) the IBM route was not more effective than the IV route in delivering MSC grafts; and 4) transplanted MSC preferentially localized to the marrow rather than nonhematopoietic tissues.

Transfer and Stable Transgene Expression of a Mammalian Artificial Chromosome into Bone Marrow-Derived Human Mesenchymal Stem Cells

Mammalian artificial chromosomes (ACEs) transferred to autologous adult stem cells (SCs) provide a novel strategy for the ex vivo gene therapy of a variety of clinical indications. Unlike retroviral vectors, ACEs are stably maintained, autonomous, and nonintegrating. In this report we assessed the delivery efficiency of ACEs and evaluated the subsequent differentiation potential of ACE-transfected bone marrow-derived human mesenchymal stem cells (hMSCs). For this, an ACE carrying multiple copies of the red fluorescent protein (RFP) reporter gene was transferred under optimized conditions into hMSCs using standard cationic transfection reagents. RFP expression was detectable in 11% of the cells 4-5 days post-transfection. The RFP-expressing hMSCs were enriched by high-speed flow cytometry and maintained their potential to differentiate along adipogenic or osteogenic lineages. Fluorescent in situ hybridization and fluorescent microscopy demonstrated that the ACEs were stably maintained as single chromosomes and expressed the RFP transgenes in both differentiated cultures. These findings demonstrate the potential utility of ACEs for human adult SC ex vivo gene therapy.

Transduction of bone-marrow-derived mesenchymal stem cells by using lentivirus vectors pseudotyped with modified RD114 envelope glycoproteins

Bone-marrow-derived mesenchymal stem cells (MSCs) have attracted considerable attention as tools for the systemic delivery of therapeutic proteins in vivo, and the ability to efficiently transfer genes of interest into such cells would create a number of therapeutic opportunities. We have designed and tested a series of human immunodeficiency virus type 1 (HIV-1)-based vectors and vectors based on the oncogenic murine stem cell virus to deliver and express transgenes in human MSCs. These vectors were pseudotyped with either the vesicular stomatitis virus G (VSV-G) glycoprotein (GP) or the feline endogenous virus RD114 envelope GP. Transduction efficiencies and transgene expression levels in MSCs were analyzed by quantitative flow cytometry and quantitative real-time PCR. While transduction efficiencies with virus particles pseudotyped with the VSV-G GP were found to be high, RD114 pseudotypes revealed transduction efficiencies that were 1 to 2 orders of magnitude below those observed with VSV-G pseudotypes. However, chimeric RD114 GPs, with the transmembrane and extracellular domains fused to the cytoplasmic domain derived from the amphotropic Moloney murine leukemia virus 4070A GP, revealed about 15-fold higher titers relative to the unmodified RD114 GP. The transduction efficiencies in human MSCs of HIV-1-based vectors pseudotyped with the chimeric RD114 GP were similar to those obtained with HIV-1 vectors pseudotyped with the VSV-G GP. Our results also indicate that RD114 pseudotypes were less toxic than VSV-G pseudotypes in human MSC progenitor assays. Taken together, these results suggest that lentivirus pseudotypes bearing alternative Env GPs provide efficient tools for ex vivo modification of human MSCs.

Comparison of multi-lineage cells from human adipose tissue and bone marrow

Our laboratory has recently characterized a population of cells from adipose tissue, termed processed lipoaspirate (PLA) cells, which have multi-lineage potential similar to bone-marrow-derived mesenchymal stem cells (MSCs). This study is the first comparison of PLA cells and MSCs isolated from the same patient. No significant differences were observed for yield of adherent stromal cells, growth kinetics, cell senescence, multi-lineage differentiation capacity, and gene transduction efficiency. Adipose tissue is an abundant and easily procured source of PLA cells, which have a potential like MSCs for use in tissue-engineering applications and as gene delivery vehicles.

HLA expression and immunologic properties of differentiated and undifferentiated mesenchymal stem cells

OBJECTIVE

Mesenchymal stem cells (MSC) do not elicit alloreactive lymphocyte responses due to immune modulations. We investigated the immunologic properties of MSC after differentiation along three lineages: bone, cartilage, and adipose.

METHODS AND RESULTS

Flow cytometry showed that undifferentiated MSC express HLA class I but not class II, although HLA class II was present intracellularly as detected by Western blot. Addition of interferon gamma (IFN-gamma) for 48 hours induced greater than 90% of cells to express HLA class II. No lymphocyte response was induced by allogeneic irradiated MSC as stimulators. Results were similar using MSC pretreated with IFN-gamma. After growth of cells in medium to induce differentiation to bone, cartilage, or adipose for 6 or 12 days, the expression of HLA class I increased but no class II was detected on the cell surface. The ability to upregulate HLA class II on the cell surface after exposure to IFN-gamma for 48 hours was clearly diminished after the cells had been cultured in differentiation medium for 6 or 12 days, with only 10% of cells expressing HLA class II. Using MSC grown in osteogenic, chondrogenic, or adipogenic medium as stimulator cells, no lymphocyte alloreactivity was seen, even if differentiated MSC had been pretreated with IFN-gamma. MSC inhibit mixed lymphocyte cultures, particularly after osteogenic differentiation. This suppression was further enhanced by IFN-gamma.

CONCLUSIONS

Undifferentiated and differentiated MSC do not elicit alloreactive lymphocyte proliferative responses and modulate immune responses. The findings support that MSC can be transplantable between HLA-incompatible individuals.

Cotransplantation of third-party mesenchymal stromal cells can alleviate single-donor predominance and increase engraftment from double cord transplantation

Although the infusion of umbilical cord blood (UCB) from multiple donors can be a strategy to overcome the cell dose limitation frequently encountered in UCB transplantation, clinical trials have revealed that cells from one donor dominate engraftment. To investigate the origin of and the factors influencing this inequality, we performed mixed transplantation of 2 UCB units with varying degrees of HLA disparities into NOD/SCID mice and determined donor origins by polymerase chain reaction-sequence-specific oligonucleotide probe (PCR-SSOP) or real-time quantitative (RQ)-PCR for human short tandem repeats (STRs). When total mononuclear cells from 2 units were transplanted as a mixture, cells from one donor predominated (ratio, 81:19), despite comparable overall engraftment when infused as single units, and no augmentation in overall engraftment was observed when compared with the single-unit controls. However, lineage depletion or cotransplantation of mesenchymal stromal cells (MSCs) expanded from third-party bone marrow resulted in more balanced coengraftment. Direct comparison of double UCB transplantation in the presence or absence of MSCs showed that the reduced deviation in the donor ratio (1.8:1 vs. 2.8:1) correlated with a higher overall level of engraftment with MSC cotransplantation. These results indicate that third-party MSCs can be used to alleviate donor deviation and to facilitate engraftment of multidonor UCB.

Telomerized human multipotent mesenchymal cells can differentiate into hematopoietic and cobblestone area-supporting cells

OBJECTIVE

To compare the hematopoietic support provided by telomerized human mesenchymal stem cells (MSCs) and telomerized MSC-derived stromal cells.

METHODS

We transfected the human telomerase catalytic subunit (hTERT) gene into primary MSCs to establish hTERT-transduced MSCs (hTERT-MSCs). Stromal induction of hTERT-MSCs was performed by replacing the culture medium with Dexter-type culture medium. Hematopoietic support was examined by coculture with cord blood CD34(+) cells.

RESULTS

The hTERT-MSCs were morphologically identical with the primary MSCs and expressed surface antigens including CD105, CD73, and CD166. hTERT-MSCs showed a similar doubling time as primary MSCs and continued to proliferate to over 80 population doublings (PD), although the primary MSCs underwent crisis in vitro at 16 PD. The osteogenic, chondrogenic, adipogenic, neurogenic, and stromal differentiation potential of hTERT-MSCs were maintained up to at least 40 PD. The degree of expansion of CD34(+) cells and total number of colony-forming units in culture (CFU-C) upon 12-day coculture with the hTERT-MSC-derived stromal cells were nearly the same as those upon 12-day coculture with hTERT-MSCs (CD34, 33.0-fold+/-2.8-fold vs 36.1-fold+/-1.7-fold of the initial cell number; CFUs, 344.4-fold+/-62.5-fold vs 239.3-fold+/-87.0-fold; CFU-mix, 368.4-fold+/-113.7-fold vs 341.3-fold+/-234.3-fold). However, on day 18 of coculture, the number of cobblestone areas (CA) observed beneath the stromal cells was 15 times higher than that beneath hTERT-MSCs (CA, 146.9+/-54.6 vs 9.4+/-8.1, p<0.01).

CONCLUSION

Stromal induction of hTERT-MSCs exclusively enhanced the support of CA formation provided by hTERT-MSCs. Our human hTERT-MSCs will be useful for elucidating the mechanism of the formation of CAs.

Immunomodulatory effects of human foetal liver-derived mesenchymal stem cells

Adult mesenchymal stem cells (MSCs) have been suggested to decrease lymphocyte proliferation in vitro. We hypothesised that foetal MSCs (fMSCs) would have an immunosuppressive effect on allograft responses in vitro. Human MSCs were isolated and cultured from first-trimester foetal livers and characterised by flow cytometry. fMSC stained positive for CD29, CD44, CD166, CD105, SH-3 and SH-4, and negative for CD14, CD34 and CD45. When plated on adipogenic, chondrogenic and osteogenic media, fMSC differentiated into the respective cell lineage. Compared to adult MSC (aMSC), the proliferative capacity of fMSC was higher. Mitogen stimulation of PBL was inhibited by fMSC. The greatest inhibition (78%) was seen when 30,000 fMSCs were added to 150,000 lymphocytes stimulated by phytohaemagglutinin. Adult and fMSCs were added to mixed lymphocyte cultures (MLC) containing peripheral blood lymphocytes or foetal liver cells. Unlike aMSC, fMSCs did not inhibit MLC. fMSC could be culture-expanded several million folds with no loss of phenotype characteristics, which makes them ideal for ex vivo expansion. fMSC inhibit lymphocyte proliferation induced by mitogens, but not alloreactivity as measured by MLC.

Correction of anemia in uremic mice by genetically modified peritoneal mesothelial cells

BACKGROUND

During peritoneal dialysis, mesothelial cells become detached from the peritoneum and accumulate in the dialysate. Our aim was to evaluate the potential of peritoneal effluent (PF)-derived human peritoneal mesothelial cells (HPMC) as target for gene therapy. We used erythropoietin (EPO) as our target gene.

METHODS

Various extracellular matrixes (ECM) were tested for optimal adhesion and growth of HPMC. The EPO gene was introduced to mouse peritoneal mesothelial cells (MPMC) and HPMC by transfection or retroviral transduction. EPO secretion from PMC was measured by enzyme-linked immunosorbent assay (ELISA) and by the TF-1 cell proliferation assay. We performed intraperitoneal or intramuscular transplantations of the genetically modified cells into regular or 5/6 nephrectomized Balb/c mice and nude mice. Finally, we measured serum EPO and hematocrit levels.

RESULTS

ECM-coated plates provided up to sixfold increase in the efficiency of PMC isolation from PF. Gelatin coated dishes (20 microg/cm2) were found optimal for isolation of PF-HPMC. RPR-120535 liposome was found to be best for PMC transduction. In vitro studies showed EPO secretion from modified HPMC over 6 months. Intraperitoneal transplantation aided with collagen matrix was the most effective. EPO, in MPMC transplanted mice, was detected up to 3 weeks (peak at 13 +/- 1 mIU/mL), and anemia of uremic mice was corrected (35.3 +/- 0.9 mIU/mL to 41.9 +/- 1.1 mIU/mL).

CONCLUSION

PF-HPMC can be considered as an appropriate target for gene therapy since these cells can be efficiently isolated, modified, and transplanted. Nevertheless, implantation techniques in the peritoneum should be directed at obtaining longer duration of transgene expression in vivo, and means should be developed for enabling regulated expression of the gene.

Engineering mesenchymal stem cells for immunotherapy

Allogeneic hematopoietic stem cell transplantation, after sublethal irradiation of recipient animals, is capable of inducing donor-specific tolerance facilitating subsequent organ transplantation. This approach could reintroduce tolerance in autoimmune diseases and it has been applied to treat autoimmune diseases with, however, a great susceptibility of recurrence. Mesenchymal stem cells (MSCs) present within the bone marrow could be critical to the immunosuppressive effect of the treatment. This tolerance induction may be useful in allogeneic transplantations, where low incidence of graft-versus-host disease was observed when the hematopoietic graft was coinjected with MSCs. In this paper, we discuss the use of MSCs in different therapeutic strategies either as immunosuppressive agents or genetically engineered to express molecules acting against the autoimmune process.