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

Role of prostaglandin E2 in allogeneic mesenchymal stem cell therapy for cardiac repair

Ischemic heart disease is among the primary causes of cardiovascular-related deaths worldwide. Conventional treatments including surgical interventions and medical therapies aid in preventing further damage to heart muscle but are unable to provide a permanent solution. In recent years, stem cell therapy has emerged as an attractive alternative to restore damaged myocardium after myocardial injury. Allogeneic (donor-derived) mesenchymal stem cells (MSCs) have shown great promise in preclinical and clinical studies, making them the most widely accepted candidates for cardiac cell therapy. MSCs promote cardiac repair by modulating host immune system and secreting various soluble factors, of which prostaglandin E2 (PGE2) is an important one. PGE2 plays a significant role in regulating cardiac remodeling following myocardial injury. In this review, we provide an overview of allogeneic MSCs as candidates for myocardial regeneration with a focus on the role of the PGE2/cyclooxygenase-2 (COX2) pathway in mediating these effects.

New bioresorbable wraps based on oxidized polyvinyl alcohol and leukocyte-fibrin-platelet membrane to support peripheral nerve neurorrhaphy: preclinical comparison versus NeuraWrap

Nerve wrapping improves neurorrhaphy outcomes in case of peripheral nerve injuries (PNIs). The aim of this preclinical study was to assess the efficacy of two novel biodegradable wraps made of a synthetic 1% oxidized polyvinyl alcohol (OxPVA) and a natural leukocyte-fibrin-platelet membrane (LFPm) versus the commercial product NeuraWrap. After rats sciatic nerve transection and neurorrhaphy, the wraps were implanted and compared for functional outcome, by sciatic function index assessment; structural characteristics, by histological/immunohistochemical analysis; ultrastructural features, by transmission electron microscopy. Moreover, a morphometric study was also performed and collagen distribution was observed by Second Harmonic Generation microscopy. After 12 weeks from implantation, all wraps assured nerve function recovery; no scar tissue/neuromas were visible at dissection. LFPm wraps were completely resorbed, while residues of OxPVA and NeuraWrap were observed. In all groups, biocompatibility was confirmed by the absence of significant inflammatory infiltrate. According to histological/immunohistochemical analysis and morphometric findings, OxPVA and LFPm wraps were both effective in preserving nerve integrity. These results assess that bioengineered OxPVA and LFPm wraps successfully guarantee favorable lesion recovery after PNI/neurorrhaphy and, in future, may be considered an interesting alternative to the commercial NeuraWrap.

Human ADSC xenograft through IL-6 secretion activates M2 macrophages responsible for the repair of damaged muscle tissue

BACKGROUND

Adipose-derived mesenchymal stromal cells (ADSCs) are multipotent stromal cells. The cells secrete a number of cytokines and growth factors and show immunoregulatory and proangiogenic properties. Their properties may be used to repair damaged tissues. The aim of our work is to explain the muscle damage repair mechanism with the utilization of the human adipose-derived mesenchymal stromal cells (hADSCs).

METHODS

For the hADSCs isolation, we used the subcutaneous adipose tissue collected during the surgery. The murine hind limb ischemia was used as a model. The unilateral femoral artery ligation was performed on 10-12-week-old male C57BL/6NCrl and NOD SCID mice. The mice received PBS^- (controls) or 1 × 10⁶ hADSCs. One, 3, 7, 14 and 21 days after the surgery, we collected the gastrocnemius muscles for the immunohistochemical analysis. The results were analyzed with relevant tests using the Statistica software.

RESULTS

The retention time of hADSCs in the limb lasted about 14 days. In the mice receiving hADSCs, the improvement in the functionality of the damaged limb occurred faster than in the control mice. More new blood vessels were formed in the limbs of the mice receiving hADSCs than in limbs of the control mice. hADSCs also increased the infiltration of the macrophages with the M2 phenotype (7-AAD^-/CD45⁺/F4/80⁺/CD206⁺) into the ischemic limbs. hADSCs introduced into the limb of mice secreted interleukin-6. This cytokine stimulates the emergence of the proangiogenic M2 macrophages, involved, among others, in the repair of a damaged tissue. Both macrophage depletion and IL-6 blockage suppressed the therapeutic effect of hADSCs. In the mice treated with hADSCs and liposomes with clodronate (macrophages depletion), the number of capillaries formed was lower than in the mice treated with hADSCs alone. Administration of hADSCs to the mice that received siltuximab (human IL-6 blocker) did not cause an influx of the M2 macrophages, and the number of capillaries formed was at the level of the control group, as in contrast to the mice that received only the hADSCs.

CONCLUSIONS

The proposed mechanism for the repair of the damaged muscle using hADSCs is based on the activity of IL-6. In our opinion, the cytokine, secreted by the hADSCs, stimulates the M2 macrophages responsible for repairing damaged muscle and forming new blood vessels.

Human Bone Marrow Mesenchymal Stromal Cells Promote Bone Regeneration in a Xenogeneic Rabbit Model: A Preclinical Study

Significant research efforts have been undertaken during the last decades to treat musculoskeletal disorders and improve patient's mobility and quality of life. The goal is the return of function as quickly and completely as possible. Cellular therapy has been increasingly employed in this setting. The design of this study was focused on cell-based alternatives. The present study aimed at investigating the bone regeneration capacity of xenogeneic human bone marrow-derived mesenchymal stromal cell (hMSC) implantation with tricalcium phosphate (TCP) granules in an immunocompetent rabbit model of critical-size bone defects at the femoral condyles. Two experimental groups, TCP and hMSC + TCP, were compared. Combination of TCP and hMSC did not affect cell viability or osteogenic differentiation. We also observed significantly higher bone regeneration in vivo in the hMSC + TCP group, which also displayed better TCP osteointegration. Also, evidence of hMSC contribution to a better TCP osteointegration was noticed. Finally, no inflammatory reaction was detected, besides the xenotransplantation of human cells into an immunocompetent recipient. In summary, hMSC combined with TCP granules is a potential combination for bone regeneration purposes that provides better preclinical results compared to TCP alone.

Enhanced Cardioprotection by Human Endometrium Mesenchymal Stem Cells Driven by Exosomal MicroRNA-21

Our group recently reported positive therapeutic benefit of human endometrium-derived mesenchymal stem cells (EnMSCs) delivered to infarcted rat myocardium, an effect that correlated with enhanced secretion of protective cytokines and growth factors compared with parallel cultures of human bone marrow MSCs (BMMSCs). To define more precisely the molecular mechanisms of EnMSC therapy, in the present study, we assessed in parallel the paracrine and therapeutic properties of MSCs derived from endometrium, bone marrow, and adipose tissues in a rat model of myocardial infarction (MI). EnMSCs, BMMSCs, and adipose-derived MSCs (AdMSCs) were characterized by fluorescence-activated cell sorting (FACS). Paracrine and cytoprotective actions were assessed in vitro by coculture with neonatal cardiomyocytes and human umbilical vein endothelial cells. A rat MI model was used to compare cell therapy by intramyocardial injection of BMMSCs, AdMSCs, and EnMSCs. We found that EnMSCs conferred superior cardioprotection relative to BMMSCs or AdMSCs and supported enhanced microvessel density. Inhibitor studies indicated that the enhanced paracrine actions of EnMSCs were mediated by secreted exosomes. Analyses of exosomal microRNAs (miRs) by miR array and quantitative polymerase chain reaction revealed that miR-21 expression was selectively enhanced in exosomes derived from EnMSCs. Selective antagonism of miR-21 by anti-miR treatment abolished the antiapoptotic and angiogenic effects of EnMSCs with parallel effects on phosphatase and tensin homolog (PTEN), a miR-21 target and downstream Akt. The results of the present study confirm the superior cardioprotection by EnMSCs relative to BMMSCs or AdMSCs and implicates miR-21 as a potential mediator of EnMSC therapy by enhancing cell survival through the PTEN/Akt pathway. The endometrium might be a preferential source of MSCs for cardiovascular cell therapy. Stem Cells Translational Medicine 2017;6:209-222.

Can the outcomes of mesenchymal stem cell-based therapy for myocardial infarction be improved? Providing weapons and armour to cells

Use of mesenchymal stem cell (MSC) transplantation after myocardial infarction (MI) has been found to have infarct-limiting effects in numerous experimental and clinical studies. However, recent meta-analyses of randomized clinical trials on MSC-based MI therapy have highlighted the need for improving its efficacy. There are two principal approaches for increasing therapeutic effect of MSCs: (i) preventing massive MSC death in ischaemic tissue and (ii) increasing production of cardioreparative growth factors and cytokines with transplanted MSCs. In this review, we aim to integrate our current understanding of genetic approaches that are used for modification of MSCs to enable their improved survival, engraftment, integration, proliferation and differentiation in the ischaemic heart. Genetic modification of MSCs resulting in increased secretion of paracrine factors has also been discussed. In addition, data on MSC preconditioning with physical, chemical and pharmacological factors prior to transplantation are summarized. MSC seeding on three-dimensional polymeric scaffolds facilitates formation of both intercellular connections and contacts between cells and the extracellular matrix, thereby enhancing cell viability and function. Use of genetic and non-genetic approaches to modify MSC function holds great promise for regenerative therapy of myocardial ischaemic injury.

Human Cardiac Mesenchymal Stromal Cells with CD105+CD34- Phenotype Enhance the Function of Post-Infarction Heart in Mice

Aims

The aim of the present study was to isolate mesenchymal stromal cells (MSC) with CD105⁺CD34^- phenotype from human hearts, and to investigate their therapeutic potential in a mouse model of hindlimb ischemia and myocardial infarction (MI). The study aimed also to investigate the feasibility of xenogeneic MSCs implantation.

Methods and Results

MSC isolated from human hearts were multipotent cells. Separation of MSC with CD105⁺CD34^- phenotype limited the heterogeneity of the originally isolated cell population. MSC secreted a number of anti-inflammatory and proangiogenic cytokines (mainly IL-6, IL-8, and GRO). Human MSC were transplanted into C57Bl/6NCrl mice. Using the mouse model of hindlimb ischemia it was shown that human MSC treated mice demonstrated a higher capillary density 14 days after injury. It was also presented that MSC administrated into the ischemic muscle facilitated fast wound healing (functional recovery by ischemic limb). MSC transplanted into an infarcted myocardium reduced the post-infarction scar, fibrosis, and increased the number of blood vessels both in the border area, and within the post-infarction scar. The improvement of left ventricular ejection fraction was also observed.

Conclusion

In two murine models (hindlimb ischemia and MI) we did not observe the xenotransplant rejection. Indeed, we have shown that human cardiac mesenchymal stromal cells with CD105⁺CD34^- phenotype exhibit therapeutic potential. It seems that M2 macrophages are essential for healing and repair of the post-infarcted heart.

Immunotolerant Properties of Mesenchymal Stem Cells: Updated Review

Stem cell transplantation is a potential therapeutic option to regenerate damaged myocardium and restore function after infarct. Current research is focused on the use of allogeneic mesenchymal stem cells (MSCs) due to their unique immunomodulatory characteristics and ability to be harvested from young and healthy donors. Both animal and human studies support the immunoprivileged state of MSCs and even demonstrate improvements in cardiac function after transplantation. This research continues to be a topic of interest, as advances will ultimately enable the clinical use of these universal cells for therapy after a myocardial infarction. Updated in vitro, in vivo, and clinical trial studies are discussed in detail in the following review.

Retrograde coronary vein infusion of cardiac explant-derived c-Kit+ cells improves function in ischemic heart failure

BACKGROUND

Progenitor cells isolated from cardiac explant-derived cells improve cardiac function after myocardial infarction (MI). To fully realize the therapeutic potential of these cells, it is essential to develop a safe and efficient delivery method. Therefore, the objective of this study was to determine the efficacy of our newly developed approach to retrograde coronary vein (RCV) infusion of cardiac c-Kit(+) cells in a small-animal model of congestive heart failure (CHF).

METHODS

Sprague-Dawley rats underwent experimental MI. After 21 days, cardiac explant-derived c-Kit(+) cells were delivered to both sham and CHF animals using RCV delivery. Vehicle-treated (serum-free medium) sham and CHF animals were used as controls. Cardiac function and heart tissues were evaluated 21 days post-transplantation.

RESULTS

RCV-delivered cells were retained in infarcted hearts for at least 21 days after transplantation. At 21 days post-RCV infusion, the majority of transplanted c-Kit(+)/GFP(+) cells were localized in the left ventricle. Compared with vehicle-treated CHF animals, RCV-treated rats showed a significant improvement in cardiac function. Furthermore, RCV-treated rats exhibited an increase in capillary density, a decrease in total heart collagen, and a reduction in both infarct size and cardiomyocyte hypertrophy when compared with vehicle-treated CHF rats.

CONCLUSIONS

Our study showed that the RCV infusion approach is an efficient technique for targeted cell delivery to the infarcted myocardium. Cardiac c-Kit(+) cells, delivered using RCV infusion ameliorated progression of heart failure, improved cardiac function and retarded myocardial remodeling in heart failure rats.

Comparative study of three types of polymer materials co-cultured with bone marrow mesenchymal stem cells for use as a myocardial patch in cardiomyocyte regeneration

The purpose of this study was to investigate the most suitable polymer material for supporting stem cell growth as a myocardial patch. After cell isolation and expansion of mouse bone marrow mesenchymal stem cells (BMSC), the cells were induced to differentiate into cardiomyocytes with 5-azacytidine to determine their differentiation potential. BMSCs were also seeded onto three types of polymer material film, including polyurethane (PU), 3-hydroxybutyrate-co-4-hydroxybutyrate [P(3HB-co-4HB)], and polypropylene carbonate (PPC). The results revealed that cell numbers were more abundant on both the PU and P(3HB-co-4HB) material surfaces. Conversely, the surface of PPC was smooth with only cell lysate debris observed. The average cell counts were as follows: 143.78 ± 38.38 (PU group), 159.50 ± 33.07 [P(3HB-co-4HB) group], and 1.40 ± 0.70 (PPC group). There was no statistically significant difference in cell numbers between the PU and P(3HB-co-4HB) groups. A statistically significant difference was identified between the PPC group and both the PU (P1) and P(3HB-co-4HB) groups (P2). Polymer biomaterial patches composed of PU and P(3HB-co-4HB) permit good stem cell growth. P(3HB-co-4HB) has the potential for development as a clinical alternative to current treatment methods for the regeneration of cardiomyocytes in patients with myocardial infarction.

Immune responses after mesenchymal stem cell implantation

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous cells have been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stromal cells (MSCs) have been reported to be uniquely immune tolerant, both in in vitro as well as in vivo transplant models. In this chapter, we summarize the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells."

Mesenchymal stromal cells as universal donor cells

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous cells have been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stromal cells (MSCs) have been reported to be uniquely immune tolerant, both in in vitro as well as in vivo transplant models. In this editorial, we briefly summarize the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "Universal Donor Cells."

Allogeneic and xenogeneic transplantation of adipose-derived stem cells in immunocompetent recipients without immunosuppressants

Mesenchymal stem cells (MSCs) are well known for their immunomodulatory capabilities. In particular, their immunosuppressive property is believed to permit their allogeneic or even xenogeneic transplantation into immunocompetent recipients without the use of immunosuppressants. Adipose-derived stem cell (ADSC), owing to its ease of isolation from an abundant tissue source, is a promising MSC for the treatment of a wide range of diseases. ADSC has been shown to lack major histocompatibility complex-II expression, and its immunosuppressive effects mediated by prostaglandin E2. Both preclinical and clinical studies have shown that allogeneic transplantation of ADSCs was able to control graft-versus-host disease. In regard to xenotransplantation a total of 27 preclinical studies have been published, with 20 of them performed with the investigators' intent. All 27 studies used ADSCs isolated from humans, possibly due to the wide availability of lipoaspirates. On the other hand, the recipients were mouse in 13 studies, rat in 11, rabbit in 2, and dog in 1. The targeted diseases varied greatly but all showed significant improvements after ADSC xenotransplantation. For clinical application in human medicine, ADSC xenotransplantation offers no obvious advantage over autotransplantation. But in veterinary medicine, xenotransplantation with porcine ADSC is a practical alternative to the costly and inconvenient autotransplantation.

Concise review: immunomodulatory properties of mesenchymal stem cells in cellular transplantation: update, controversies, and unknowns

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage, for which the use of autologous donor cells has been preferred to avoid immune rejection. Recently, however, rodent as well as human mesenchymal stem cells have been reported to be uniquely immune-tolerant, in both in vitro and in vivo transplant models. In this review, we explore in detail the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells" with fascinating clinical implications.

Adipogenic differentiation alters the immunoregulatory property of mesenchymal stem cells through BAFF secretion

Although it has been widely demonstrated that mesenchymal stem cells (MSCs) exert potent immunosuppressive effect, there is little information as to whether adipogenic-differentiated MSCs (adi-MSCs) share the same property. Here, adi-MSCs enhanced alloantigen or mitogen-stimulated lymphocyte proliferation, whereas undifferentiated MSCs (ud-MSCs) inhibited the proliferation. Transwell experiment showed that the stimulatory effect of adi-MSCs was cell-cell contact-independent, and required soluble factors. Furthermore, the supernatant of cultured adi-MSCs could effectively costimulate T and B-lymphocyte proliferation and activation in the presence of anti-CD3 and anti-mu chain treatment, respectively. Production of cytokines interferon-gamma and tumor necrosis factor-alpha by T cells, and Ig secretion by B cells also were increased by the supernatant of cultured adi-MSCs. Mechanism conducted showed that the mRNA and protein expression of costimulatory molecule B-cell activating factor (BAFF) was upregulated, and soluble BAFF was secreted in MSCs after adipogenic differentiation. By blocking the BAFF molecule with specific monoclonal antibody in the culture, T and B-lymphocyte proliferation and activation was stimulated by adi-MSCs or the supernatants were greatly reduced. In conclusion, adipogenic differentiation may alter the immunoregulatory property of MSCs, leading to stimulation of lymphocytes response. The BAFF molecule secreted by the adi-MSCs was responsible for this event.

Intracoronary mesenchymal stem cells promote postischemic myocardial functional recovery, decrease inflammation, and reduce apoptosis via a signal transducer and activator of transcription 3 mechanism

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) regulates myocardial apoptosis, cellular proliferation, and the immune response after ischemia/reperfusion (I/R). STAT3 is also necessary for the production of vascular endothelial growth factor (VEGF) by mesenchymal stem cells (MSCs), which are known to reduce myocardial injury after I/R. However, it remains unknown whether STAT3 is an important mediator of MSC-based cardioprotection. We hypothesized that knockout of stem cell STAT3 would reduce MSC-derived myocardial functional recovery and increase myocardial inflammatory and apoptotic signaling.

STUDY DESIGN

With a Langendorff apparatus, male rat hearts were subjected to 15 minutes of equilibration and 25 minutes of ischemia, followed by 40 minutes of reperfusion. Immediately before ischemia, hearts received intracoronary infusions of vehicle, wild-type MSCs (WT MSCs) or STAT3 knockout MSCs (STAT3KO MSCs). Heart function was measured continuously. Myocardial homogenates were analyzed for production of interleukin (IL)-1, IL-6, and tumor necrosis factor-α (TNF-α). Additionally, MSC production of hepatocyte growth factor (HGF) and insulin-like growth factor-1 (IGF-1) were measured in vitro.

RESULTS

Hearts treated with WT MSCs exhibited the greatest functional recovery, and those treated with STAT3KO MSCs had equivalent recovery to vehicle. The highest proinflammatory cytokine levels were seen in vehicle-treated hearts, and the lowest in the WT MSC group. STAT3KO MSCs produced less IGF-1, but more HGF than WT MSCs. Finally, hearts treated with STAT3KO MSCs or vehicle had significantly higher caspase-3 levels than those treated with WT MSCs.

CONCLUSIONS

Intracoronary infusions of MSCs improve postischemic left ventricular function and reduce proapoptotic and proinflammatory signaling via a STAT3-dependent mechanism.

Female stem cells are superior to males in preserving myocardial function following endotoxemia

Mesenchymal stem cells (MSCs) may offer therapeutic benefit in the setting of sepsis and endotoxemia. Previous studies suggest that MSCs from female donors may possess better protective capabilities than their male counterparts. The present study examined whether female MSCs may offer a greater protective advantage in the setting of endotoxemic cardiac dysfunction compared with male MSCs. Adult male Sprague-Dawley rats were injected intraperitoneally with LPS and then treated with intraperitoneal injections of either saline, female MSCs, or male MSCs. Hearts and serum were then collected for analysis of myocardial function, myocardial protein, and myocardial and serum cytokines. Compared with male MSC or vehicle-treated animals, female MSC treatment resulted in greater preservation of myocardial function (P < 0.001). Serum and myocardial levels of all measured cytokines were comparable between rats given MSCs from male or female donors but substantially improved over rats given vehicle (P < 0.05). Reduced myocardial inflammation correlated with reduced levels of phosphorylated p38 MAPK expression in the myocardium of animals injected with MSCs of either sex (P < 0.05). The Bcl-xL/Bax ratio was increased to a greater extent following treatment with female MSCs vs. male MSCs (P < 0.05). Intraperitoneal administration of MSCs is effective in limiting myocardial inflammation and dysfunction in the rat endotoxemia model. Compared with treatment with their male counterparts, MSC treatment from female donors is associated with greater cardiac protection against acute endotoxemic injury.

Ablation of TNF-alpha receptors influences mesenchymal stem cell-mediated cardiac protection against ischemia

Mesenchymal stem cell (MSC) infusion may reduce myocardial ischemic injury. TNF-alpha is a proinflammatory cytokine produced in large quantities during myocardial ischemia that can exert beneficial or detrimental effects on MSC function by binding to a 55-kd receptor (TNFR1) or a 75-kd receptor (TNFR2) on MSCs. We investigated whether genetic modification with ablation of TNFR1 and/or TNFR2 affects MSC-mediated protection against myocardial ischemic injury. The MSCs were harvested from wild-type mice (WT-MSCs) and knockout mice with ablation of TNFR1 and/or TNFR2 (TNFR1KO, TNFR2KO, and TNFR1/R2KO MSCs). After anesthesia was initiated via inhalation of isoflurane, myocardial ischemia was induced in rats via coronary artery ligation. Hearts were then injected with vehicle or MSCs (1 x 10 cells/mL). Myocardial function was assessed 28 days postsurgery with 2-dimensional echocardiograms and isolated heart perfusion. Myocardial tissue was collected for cytokine analysis and infarct measurements. We found that MSC treatment offered significant protection against myocardial ischemia, namely by decreasing infarct size, improving heart function, and decreasing ventricular remodeling compared with vehicle. Compared with WT-MSCs, TNFR1KO MSCs conferred increased cardiac protection, although TNFR2KO and TNFR1/R2KO MSCs conferred less cardiac protection. In addition, treatment with TNFR1KO MSCs was associated with decreased levels of proinflammatory cytokines and an increased level of vascular endothelial growth factor in the myocardium, whereas treatment with TNFR2KO or TNFR1/R2KO MSCs was associated with increased levels of proinflammatory cytokines and a decreased level of vascular endothelial growth factor compared with treatment with WT-MSCs. We conclude that MSC TNFR1 and TNFR2 play important roles in MSC-mediated cardiac protection after myocardial ischemia.

Failure of xenoimplantation using porcine synovium-derived stem cell-based cartilage tissue constructs for the repair of rabbit osteochondral defects

The use of xenogeneic tissues offers many advantages with respect to availability, quality control, and timing of tissue harvest. Our previous study indicated that implantation of premature tissue constructs from allogeneic synovium-derived stem cells (SDSCs) facilitated cartilage tissue regeneration. The present study investigated the feasibility of xenoimplantation of SDSC-based premature tissue constructs for the repair of osteochondral defects. Porcine SDSCs were mixed with fibrin gel, seeded in polyglycolic acid (PGA) scaffolds, and cultured in a rotating bioreactor system supplemented for 1 month with growth factor cocktails. The engineered porcine premature tissues were implanted to repair surgically induced osteochondral defects in the medial femoral condyles of 12 rabbits. Three weeks after surgery, the xenoimplantation group exhibited a smooth, whitish surface while the untreated control remained empty. Surprisingly, 6 months after surgery, the xenoimplantation group displayed some tissue loss while the untreated control group was overgrown with fibrocartilage tissue. In the xenoimplantation group, chronic inflammation was observed in synovial tissue where porcine major histocompatibility complex (MHC) class II antigen positively stained in the engulfed foreign bodies. In addition, porcine source cells also migrated from the implantation site and may have been responsible for the observed loss of glycosaminoglycans (GAGs) underneath surrounding articular cartilage. The histological score was much worse in the xenoimplanted group than in the untreated control. Our study suggested that SDSC-based xenogeneic tissue constructs might cause delayed immune rejection. Xenotransplantation may not be an appropriate approach to repair osteochondral defects.

Mesenchymal stromal cell and mononuclear cell therapy in heart disease

Despite progress in percutaneous coronary intervention, bypass surgery and drug therapy, rates of mortality and morbidity after acute coronary syndrome are high due to ventricular remodeling and heart failure. Mesenchymal stromal cells (MSCs) from adult bone marrow or adipose tissue are considered potential candidates for therapeutic regenerative treatment in cardiovascular disease. Recent animal studies have demonstrated that MSCs can induce neovascularization and improve myocardial function in postinfarction myocardial ischemic hearts. This review will focus on the present preclinical and clinical knowledge about the use of mononuclear cells and MSCs for cardiac regenerative medicine, the source of MSCs for clinical use and problems to consider when conducting clinical MSC therapy.

Postinfarct intramyocardial injection of mesenchymal stem cells pretreated with TGF-alpha improves acute myocardial function

Stem cell-based therapies offer promising potential for myocardial infarction (MI), but endogenous molecules released in response to injury likely impair posttransplantation stem cell function. Stem cell-mediated cardioprotection occurs in part via paracrine effects, and transforming growth factor-alpha (TGF-alpha) has been shown to enhance paracrine function. However, it is unknown whether pretreating stem cells with TGF-alpha increases stem cell-mediated cardioprotection after acute MI. Mesenchymal stem cells (MSCs) were treated with TGF-alpha (250 ng/ml) for 24 h. Adult male Sprague-Dawley rat hearts were isolated and perfused using the Langendorff method. MI was induced by ligating the left anterior descending coronary artery. Postligation (30 min), vehicle or 1 x 10(6) MSCs with or without pretreatment were injected in the infarct border zones, and the hearts were perfused for an additional 60 min. Left ventricular function was continuously measured, and infarct size was assessed with Evans blue dye and 2,3,5-triphenyltetrazolium chloride staining. Myocardial production of interleukin (IL)-1beta and IL-6 and caspase 3 activation was also measured. Left ventricular function decreased significantly following coronary artery ligation but improved following injection of untreated MSCs and to a greater extent after injection of pretreated MSCs. In addition, the infarct area, myocardial caspase 3 activation, and IL-6 production were lowest in hearts injected with pretreated cells. Intramyocardial injection of TGF-alpha-pretreated MSCs after acute MI is associated with increased myocardial function and decreased myocardial injury. This strategy may be useful for optimizing the therapeutic efficacy of stem cells for the treatment of acute MI.

Acute homing of bone marrow-derived mononuclear cells in intramyocardial vs. intracoronary transplantation

OBJECTIVES

Cell homing optimisation after transplantation is critical in myocardial infarction (MI) cell therapy.

DESIGN

Eight pigs were randomized to receiving autologous purified (111)indium-labeled bone marrow mononuclear cells (BMMCs) (10(8) cells/2 ml) by intramyocardial (IM) (n=4) or by intracoronary (IC) (n=4) transplantation after 90 minutes occlusion of the CX-coronary artery. Dual isotope SPECT imaging was performed 2 and 24 hours postoperatively. Two animals were additionally analyzed on the sixth postoperative day. Tissue samples from the major organs were analyzed.

RESULTS

In SPECT imaging revealed that BMMCs administered using IM injection remained in the injured area. In contrast, minor proportion of IC transplanted cells remained in the myocardium, as most of the cells showed homing in the lungs. Analysis of the biopsies showed a seven-fold greater number of cells in the myocardium for the IM method and a 10-fold greater number of cells in the lungs in the IC group (p < 0.001).

CONCLUSIONS

In producing persistently high cell homing at the infarction site, the IM transplantation is superior to the IC transplantation. However, the IC administration might be more specific in targeting injured capillaries and epithelial cells within the infarcted myocardium.

Mesenchymal stromal cells for cardiovascular repair: current status and future challenges

Ischemic heart disease is the most common cause of death in most industrialized countries. Early treatment with stabilizing drugs and mechanical revascularization by percutaneous coronary intervention or coronary bypass surgery has reduced the mortality significantly. In spite of improved offers of treatments in patients with heart failure, the 1-year mortality is still approximately 20% after the diagnosis has been established. Treatment with stem cells with the potential to regenerate the damaged myocardium is a relatively new approach. Mesenchymal stromal cells are a promising source of stem cells for regenerative therapy. Clinical studies on stem cell therapy for cardiac regeneration have shown significant improvements in ventricular pump function, ventricular remodeling, myocardial perfusion, exercise potential and clinical symptoms compared with conventionally treated control groups. The results of most studies are promising, but there are still many unanswered questions. In this review, we explore present preclinical and clinical knowledge regarding the use of stem cells in cardiovascular regenerative medicine, with special focus on mesenchymal stromal cells. We take a closer look at sources of stem cells, delivery method and methods for tracking injected cells.

What's new in cardiac cell therapy? Allogeneic bone marrow stromal cells as "universal donor cells"

Cardiac cell therapies offer distinct and exciting advantages over current treatments to prevent postinfarction heart failure because they can reverse ventricular remodeling and improve function, but only if the implanted stem cells contribute biological functions and achieve prolonged engraftment within the hostile environment of the damaged heart. Unfortunately, function is diminished in autologous stem cells isolated from older patients and those with comorbidities, and so clinical trials testing the implantation of healthy, allogeneic bone marrow-derived stromal cells (MSCs) isolated from young donors are currently underway. MSCs are unique because, in addition to exerting paracrine effects that restore blood flow and recruit endogenous stem cells to the infarct, they exhibit immune-modulating properties in culture that-if retained after allogeneic implantation-imply the cells may escape immune recognition within the heart. At present, the scope of MSC immune modulation after implantation is unclear.

Transplantation of cardiac progenitor cell sheet onto infarcted heart promotes cardiogenesis and improves function

AIMS

Cell-based therapy for myocardial infarction (MI) holds great promise; however, the ideal cell type and delivery system have not been established. Obstacles in the field are the massive cell death after direct injection and the small percentage of surviving cells differentiating into cardiomyocytes. To overcome these challenges we designed a novel study to deliver cardiac progenitor cells as a cell sheet.

METHODS AND RESULTS

Cell sheets composed of rat or human cardiac progenitor cells (cardiospheres), and cardiac stromal cells were transplanted onto the infarcted myocardium after coronary artery ligation in rats. Three weeks later, transplanted cells survived, proliferated, and differentiated into cardiomyocytes (14.6 +/- 4.7%). Cell sheet transplantation suppressed cardiac wall thinning and increased capillary density (194 +/- 20 vs. 97 +/- 24 per mm(2), P < 0.05) compared with the untreated MI. Cell migration from the sheet was observed along the necrotic trails within the infarcted area. The migrated cells were located in the vicinity of stromal-derived factor (SDF-1) released from the injured myocardium, and about 20% of these cells expressed CXCR4, suggesting that the SDF-1/CXCR4 axis plays, at least, a role in cell migration. Transplantation of cell sheets resulted in a preservation of cardiac contractile function after MI, as was shown by a greater ejection fraction and lower left ventricular end diastolic pressure compared with untreated MI.

CONCLUSION

The scaffold-free cardiosphere-derived cell sheet approach seeks to efficiently deliver cells and increase cell survival. These transplanted cells effectively rescue myocardium function after infarction by promoting not only neovascularization but also inducing a significant level of cardiomyogenesis.

Cellular cardiomyoplasty: what have we learned?

Restoring blood flow, improving perfusion, reducing clinical symptoms, and augmenting ventricular function are the goals after acute myocardial infarction. Other than cardiac transplantation, no standard clinical procedure is available to restore damaged myocardium. Since we first reported cellular cardiomyoplasty in 1989, successful outcomes have been confirmed by experimental and clinical studies, but definitive long-term efficacy requires large-scale placebo-controlled double-blind randomized trials. On meta-analysis, stem cell-treated groups had significantly improved left ventricular ejection fraction, reduced infarct scar size, and decreased left ventricular end-systolic volume. Fewer myocardial infarctions, deaths, readmissions for heart failure, and repeat revascularizations were additional benefits. Encouraging clinical findings have been reported using satellite or bone marrow stem cells, but understanding of the benefit mechanisms demands additional studies. Adult mammalian ventricular myocardium lacks adequate regeneration capability, and cellular cardiomyoplasty offers a new way to overcome this; the poor retention and engraftment rate and high apoptotic rate of the implanted stem cells limit outcomes. The ideal type and number of cells, optimal timing of cell therapy, and ideal cell delivery method depend on determining the beneficial mechanisms. Cellular cardiomyoplasty has progressed rapidly in the last decade. A critical review may help us to better plan the future direction.

The immature heart: the roles of bone marrow stromal stem cells in growth and myocardial repair

Studies have shown that adult bone marrow derived stem cells (MSCs) can participate in repair of myocardial injury in adult hearts, as well as in cardiac growth during fetal development in utero. Yet, no studies have evaluated the role of MSCs with respect to normal growth or tissue repair in immature hearts after birth. The present study examines whether MSCs may participate in the myocardial growth and injury in the post-natal immature hearts. MSCs were isolated from adult Lewis rats and labeled with Lac-Z gene using retroviral vectors. These MSCs were injected systemically into groups of neonatal (NB=2days-old), immature (B=30days-old) and adult (A=>3months-old) isogeneic Lewis rats. Additionally, left coronary artery ligation was carried out in subgroups of immature (BL) and adult (AL) rats one week after MSCs injection. The hearts were harvested serially from 2-days to 6-weeks, stained with X-Gal for labeled MSCs. Cardiomyocyte phenotypic expression was evaluated by immunohistological staining for Troponin I-C and Connexin-43. Labeled MSCs were found to home into the bone marrow in all rats of different developmental stages. They could be recruited from bone marrow into the infarcted site of myocardium only in groups AL and BL. They were also capable of differentiating into cardiomyocyte phenotype after myocardial injury. In contrast to that reported in the developing fetus, MSCs did not appear to contribute to the growth of non-injured hearts after birth. However, they can be recruited from the bone marrow and regenerate damaged myocardium both in the adult and in the immature hearts.

Can mesenchymal stem cells induce tolerance to cotransplanted human embryonic stem cells?

Mesenchymal stem cells (MSCs) are reported to be immune privileged. We assessed whether their transplantation (Tx) could create a suppressive microenvironment mitigating rejection of coinjected human embryonic stem cells (hESCs). Three weeks after ligation-induced myocardial infarction, 40 immunocompetent rats received 150 microl of cardiac-specified hESCs (5 x 10(6)), MSCs (5 x 10(6)), hESC + MSC (5 x 10(6) for each), or control medium. Two months after Tx, left ventricle (LV) function was assessed by echocardiography, and hearts were processed for the detection of human cells by immunostaining and quantitative RT-PCR, patterns of rejection, fibrosis, and angiogenesis. Two months after Tx, LV ejection fraction (LVEF) was significantly higher in the ESC and ESC + MSC groups compared with controls. There were few engrafted cells, which expressed markers of endothelial, smooth muscle, and ventricular cardiac cells, particularly in the MSC group. Hearts of all groups demonstrated a similar infiltration by CD4(+) and CD3(+) cells but MSC-Tx resulted in a greater infiltration of FoxP3 compared with the control and ESC-alone groups. No teratoma was observed. Thus, cotransplantation of ESCs and MSCs provided better functional preservation compared with single-cell treatment alone. However, there was only modest evidence for an immunosuppressive effect of coinjected MSCs and their beneficial effects seemed rather mediated by trophic effects on the host tissue.

Transplanted xenogenic bone marrow stem cells survive and generate new bone formation in the posterolateral lumbar spine of non-immunosuppressed rabbits

Bone marrow stem cells (BMSCs) are pluripotent cells that have been used to facilitate bone repair because of their capability of differentiating into osteoblasts. However, it is well known that the number of BMSCs with osteogenic potential decreases in patients with old age, osteoporosis, and metabolic diseases. In such conditions, xenogenic BMSCs may provide an alternative to autologous BMSCs. In the current study, we investigated the potential of transplanted xenogenic BMSCs to survive and generate new bone formation in the posterolateral lumbar spine of non-immunosuppressed rabbits. The BMSCs were obtained from bilateral femurs of four male rats, cultured and expanded in medium with osteoinduction supplement. The BMSCs (1,000,000 cells) of male rats loaded onto 5 cc compression resistant matrix (CRM; Medtronic Sofamor Danek, USA) were implanted bilaterally onto the L4-5 intertransverse processes of 16 female rabbits (xenogenic BMSCs + CRM group). The 16 female rabbits that received 5 cc CRM alone were used as controls (CRM alone group). To exclude the possibility of migration of BMSCs from the transverse processes of the recipient rabbits, we did not decorticate the transverse processes. No rabbits received any immunosuppressive medications during the experiment. Four rabbits each in both of the experimental and control groups were killed at 1, 2, 4, and 6 months postimplantation, and the lumbar spine underwent radiological and histological analyses for evaluation of new bone formation. The polymerase chain reaction (PCR) for Sry gene (Y-chromosome-specific marker) was used to evaluate the survival of transplanted xenogenic BMSCs. The expression of Sry gene was clearly identified in the lumbar spines of all the 16 rabbits in the xenogenic BMSCs + CRM group at 1-6 months postimplantation. Serial plain radiographs showed gradual resorption of CRM; however, it was difficult to clearly identify the presence of new bone formation due to the radiopacity of the remaining CRM. Histologically, mature lamellar and woven bone with osteoblasts and osteocytes were identified in all eight rabbits in the xenogenic BMSCs + CRM group at 4 and 6 months postimplantation, but in none of the eight rabbits at 1 and 2 months postimplantation. None of CRM alone group showed new bone formation at 1-6 months postimplantation. Mild-to-moderate infiltration of inflammatory cells was identified around the CRM carriers in both the groups. No post-operative wound infection was found in either group. Our results indicate that xenogenic BMSCs loaded onto CRM survive and generate new bone formation when placed into the posterolateral lumbar spine of rabbits without immunosuppression. To determine if a solid fusion can be achieved with such techniques, further studies are needed to investigate the appropriate dose of xenogenic BMSCs, amounts of CRM, and the requisite incubation time.

Cine-MRI versus two-dimensional echocardiography to measure in vivo left ventricular function in rat heart

Two-dimensional echocardiography is the most commonly used non-invasive method for measuring in vivo cardiac function in experimental animals. In humans, measurements of cardiac function made using cine-MRI compare favourably with those made using echocardiography. However, no rigorous comparison has been made in small animals. Here, standard short-axis two-dimensional (2D) echocardiography (2D-echo) and cine-MRI measurements were made in the same rats, both control and after chronic myocardial infarction. Correlations between the two techniques were found for end diastolic area, stroke area and ejection fraction, but cine-MRI measurements of ejection fraction were 12+/-6% higher than those made using 2D-echo, because of the 1.8-fold higher temporal resolution of the MRI technique (4.6 ms vs 8.3 ms). Repeated measurements on the same group of rats over several days showed that the cine-MRI technique was more reproducible than 2D-echo, in that 2D-echo would require five times more animals to find a statistically significant difference. In summary, caution should be exercised when comparing functional results acquired using short-axis 2D-echo vs cine-MRI. The accuracy of cine-MRI allows identification of alterations in heart function that may be missed when using 2D-echo.

Myocardial regenerative therapy: immunologic basis for the potential "universal donor cells"

Stem cell transplantation is a promising approach for improving cardiac function after severe myocardial damage for which use of autologous donor cells have been preferred to avoid immune rejection. Recently however, rodent, porcine, and even human bone marrow stromal cells have been reported to be uniquely immune tolerant, both in the in vitro mixed lymphocyte co-culture studies and in the in vivo allo-transplant and xeno-transplant models. In this review, we explore the current understanding of the underlying immunologic mechanisms, which can facilitate the use of such cells as "universal donor cells" with fascinating therapeutic implications.

Transplantation of hypoxia-preconditioned mesenchymal stem cells improves infarcted heart function via enhanced survival of implanted cells and angiogenesis

OBJECTIVES

This study explored the novel strategy of hypoxic preconditioning of bone marrow mesenchymal stem cells before transplantation into the infarcted heart to promote their survival and therapeutic potential of mesenchymal stem cell transplantation after myocardial ischemia.

METHODS

Mesenchymal stem cells from green fluorescent protein transgenic mice were cultured under normoxic or hypoxic (0.5% oxygen for 24 hours) conditions. Expression of growth factors and anti-apoptotic genes were examined by immunoblot. Normoxic or hypoxic stem cells were intramyocardially injected into the peri-infarct region of rats 30 minutes after permanent myocardial infarction. Death of mesenchymal stem cells was assessed in vitro and in vivo after transplantation. Angiogenesis, infarct size, and heart function were measured 6 weeks after transplantation.

RESULTS

Hypoxic preconditioning increased expression of pro-survival and pro-angiogenic factors including hypoxia-inducible factor 1, angiopoietin-1, vascular endothelial growth factor and its receptor, Flk-1, erythropoietin, Bcl-2, and Bcl-xL. Cell death of hypoxic stem cells and caspase-3 activation in these cells were significantly lower compared with that in normoxic stem cells both in vitro and in vivo. Transplantation of hypoxic versus normoxic mesenchymal stem cells after myocardial infarction resulted in an increase in angiogenesis, as well as enhanced morphologic and functional benefits of stem cell therapy.

CONCLUSIONS

Hypoxic preconditioning enhances the capacity of mesenchymal stem cells to repair infarcted myocardium, attributable to reduced cell death and apoptosis of implanted cells, increased angiogenesis/vascularization, and paracrine effects.

Marrow stromal cells as universal donor cells for myocardial regenerative therapy: their unique immune tolerance

BACKGROUND

Recently rodent and porcine bone marrow stromal cells (MSCs) have been reported to be uniquely immune tolerant. To confirm these findings in human cells, we tested whether human MSCs are also immune tolerant, such that they can be used as universal donor cells for myocardial regenerative therapy.

METHODS

Immunocompetent female rats underwent coronary ligations (n = 90). In group I, lacZ-labeled male human MSCs were implanted into the peri-infarcted area. In groups II, III, and IV, isogeneic rat MSCs, culture medium, or human fibroblasts were injected, respectively. Echocardiography was carried out to assess cardiac function, and the specimens were examined serially for up to 8 weeks with immunohistochemistry, fluorescent in situ hybridization, and polymerase chain reaction to examine MSCs survival and differentiation.

RESULTS

Human MSCs survived within the rat myocardium for more than 8 weeks without immunosuppression. Furthermore, the implanted MSCs significantly contributed to the improvement in ventricular function and attenuated left ventricular remodeling. No cellular infiltration characteristic of immune rejection was noted in contrast to group IV.

CONCLUSIONS

Human MSCs survived within this xenogeneic environment, and contributed to the improvement in cardiac function. Our findings support the feasibility of using these cells as universal donor cells for xenogeneic or allogeneic cell therapy, as they can be prepared and stored well in advance for urgent use. Allogeneic MSCs from healthy donors may be particularly useful for severely ill or elderly patients whose own MSCs could be dysfunctional.

Bone marrow–derived mononuclear cell transplantation improves myocardial recovery by enhancing cellular recruitment and differentiation at the infarction site

OBJECTIVE

Stem cell therapy in myocardial infarction is under intensive investigation; however, the mechanisms of recovery and the optimal transplantation technique remain controversial. The goal of this controlled and randomized study was to test the hypothesis that locally injected bone marrow-derived mononuclear cells can focus in on the damaged myocardium and improve cardiac function by means of active participation in remodeling.

METHODS

Myocardial infarction was introduced through occlusion of the circumflex coronary artery for 90 minutes in 14 piglets (24.0 +/- 4.9 kg) that were randomized to a cell-therapy group (n = 7) and a control group (n = 7). At reperfusion, autologous purified prelabeled or unlabeled cells (10(8) cells/2 mL) or saline were injected into the myocardium. Cardiac function was measured by using echocardiography preoperatively and postoperatively and at 3 weeks, when hearts were collected for histopathologic examination.

RESULTS

The ejection fraction recovered in the cell-therapy group (P = .02) but failed to recover in the control group, and at 3 weeks, it remained at the lower level compared with that in the cell-therapy group (P = .067). The number of living cells in the necrotic area was significantly greater in the cell-therapy group (P < .001). Labeled cells were detected in the infarcted area, and they showed signs of myocyte differentiation. Furthermore, the proportional area of muscle actin-positive cells at the granulation area was higher in the cell-therapy group (P = .035).

CONCLUSIONS

Autologous bone marrow-derived mononuclear cells at the infarcted area localize in the myocardium. The exact mechanism of recovery remains to be determined, but our findings may give new information concerning the cellular events that occur during cell therapy-enhanced recovery.

Survival of bone marrow-derived mesenchymal stem cells in a xenotransplantation model

Mesenchymal stem cells (MSCs) are immunoprivileged and the allogeneic MSCs implantation has been used to facilitate tissue repairs such as bone and cartilage defect. The present study aimed to investigate the feasibility of xenogeneic MSCs implantation. Green fluorescent protein (GFP) transgenic rat bone marrow-derived MSCs were loaded into HA/TCP Skelite blocks and implanted intramuscularly into the quadriceps of the MF1 and SCID mice. After 11 weeks, the implants were harvested and processed for further examinations. The peripheral blood mononuclear cells of each animal were also collected to measure the in vitro immune responses using mixed lymphocyte culture and cytotoxic assay. In the MF1 mice, some surviving MSCs were found in the explants after 11 weeks of implantation, but there was no sign of new bone formation as neither osteocalcin mRNA nor osteoid tissues were detected in the explants; the lymphocyte proliferation and cytotoxicity against donor MSCs were significantly increased in the animals with the xenogeneic MSCs implantation compared with the control littermates without transplantation. In the control SCID mice, osteoid tissues derived from the implanted MSCs were found in the explants; no difference of lymphocyte proliferation and cytotoxicity against the donor MSCs was detected between the SCID mice with or without MSCs implantation. The data suggested that rat MSCs survived the 11 weeks of xenotransplantation in the MF1 mice, but the increased host immune sensitization led to the impaired in vivo osteogenesis potential of MSCs.

Therapeutic Potential of Human Umbilical Cord Derived Stem Cells in a Rat Myocardial Infarction Model

BACKGROUND

Cell transplantation offers the promise in the restoration of cardiac function after myocardial infarction. We investigate the therapeutic potential of human umbilical cord derived stem (UCDS) cells in a rat myocardial infarction model.

METHODS

Two weeks after induction of myocardial infarction, the surviving rats with left ventricular ejection fraction less than 60% were randomly divided into a phosphate-buffered saline control group and a UCDS cell treated group. Cardiac function was assessed by echocardiography 2 weeks and 4 weeks after cell transplantation. Histologic study and immunofluorescence were performed to investigate differentiation of transplanted cells, capillary and arteriole density, secretion of cytokines, and cardiomyocytes apoptosis.

RESULTS

A statistically significant improvement of cardiac function was observed in the experimental group of rats compared with the control group. Four weeks after transplantation, histologic examination revealed that some of the transplanted UCDS cells survived in the infarcted myocardium and accumulated around arterioles and scattered in capillary networks. We observed some of the cells expressed cardiac troponin-T, von Willebrand factor, and smooth muscle actin, indicating regeneration of damaged myocardium by cardiomyocytic, endothelial, and smooth muscle differentiation of UCDS cells in the infarcted myocardium. The capillary and arteriole density were also markedly increased in the UCDS-cell-treated group. In addition, the apoptotic cells were decreased significantly compared with the phosphate-buffered saline controls.

CONCLUSIONS

Our findings demonstrate that transplanted UCDS cells provide benefit in cardiac function recovery after acute myocardial infarction in rats, suggesting UCDS cells represent a promising cell source for future routine cell therapy applications.

Chondrogenic differentiation alters the immunosuppressive property of bone marrow-derived mesenchymal stem cells, and the effect is partially due to the upregulated expression of B7 molecules

To investigate the immunosuppressive properties of MSCs, in the present study we examined the immunogenicity of undifferentiated and trilineage-differentiated (chondrocytes, osteoblasts, and adipocytes) rat bone marrow-derived MSCs under xenogeneic conditions. After chondrogenic differentiation, rat bone marrow-derived MSCs stimulated human dendritic cells (hDCs) derived from peripheral blood monocytes, leading to eight- and fourfold higher lymphocyte proliferation and cytotoxicity than that of undifferentiated MSCs. The chondrogenic-differentiated MSCs were chemotactic to hDCs in Dunn chamber chemotaxis system and were rosetted by hDCs in rosette assays. Flow cytometry analysis revealed that chondrogenic-differentiated MSCs had promoted hDC maturation, causing higher CD83 expression in hDCs, whereas undifferentiated MSCs and osteogenic- and adipogenic-differentiated MSCs showed an inhibitory effect on hDC maturation. The costimulatory B7 molecules were upregulated only in the chondrogenic-differentiated MSCs. After blocking B7 molecules with specific monoclonal antibodies in the chondrogenic-differentiated MSCs, CD83 expression of cocultured hDCs was greatly reduced. In conclusion, chondrogenic differentiation may increase the immunogenicity of MSCs, leading to stimulation of dendritic cells. The upregulated expression of B7 molecules on the chondrogenic-differentiated MSCs may be partially responsible for this event.