Mesenchymal stromal cells lose their immunosuppressive potential after allotransplantation

Bone formation by human paediatric marrow stromal cells in a functional allogeneic immune system

Allogeneic stem-cell based regenerative medicine is a promising approach for bone defect repair. The use of chondrogenically differentiated human marrow stromal cells (MSCs) has been shown to lead to bone formation by endochondral ossification in immunodeficient pre-clinical models. However, an insight into the interactions between the allogeneic immune system and the human MSC-derived bone grafts has not been fully achieved yet. The choice of a potent source of MSCs isolated from pediatric donors with consistent differentiation and high proliferation abilities, as well as low immunogenicity, could increase the chance of success for bone allografts. In this study, we employed an immunodeficient animal model humanised with allogeneic immune cells to study the immune responses towards chondrogenically differentiated human pediatric MSCs (ch-pMSCs). We show that ch-differentiated pMSCs remained non-immunogenic to allogeneic CD4 and CD8 T cells in an in vitro co-culture model. After subcutaneous implantation in mice, ch-pMSC-derived grafts were able to initiate bone mineralisation in the presence of an allogeneic immune system for 3 weeks without the onset of immune responses. Re-exposing the splenocytes of the humanised animals to pMSCs did not trigger further T cell proliferation, suggesting an absence of secondary immune responses. Moreover, ch-pMSCs generated mature bone after 8 weeks of implantation that persisted for up to 6 more weeks in the presence of an allogeneic immune system. These data collectively show that human allogeneic chondrogenically differentiated pediatric MSCs might be a safe and potent option for bone defect repair in the tissue engineering and regenerative medicine setting.

Enhancing the Therapeutic Potential of Mesenchymal Stromal Cell-Based Therapies with an Anti-Fibrotic Agent for the Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) affects 1 in 10 members of the general population, placing these patients at an increasingly high risk of kidney failure. Despite the significant burden of CKD on various healthcare systems, there are no effective cures that reverse or even halt its progression. In recent years, human bone-marrow-derived mesenchymal stromal cells (BM-MSCs) have been recognised as a novel therapy for CKDs, owing to their well-established immunomodulatory and tissue-reparative properties in preclinical settings, and their promising safety profile that has been demonstrated in patients with CKDs from several clinical trials. However, renal fibrosis (scarring), a hallmark of CKD, has been shown to impair the viability and functionality of BM-MSCs post-transplantation. This has suggested that BM-MSCs might require a pre-treatment or adjunct therapy that can enhance the viability and therapeutic efficacy of these stromal cells in chronic disease settings. To address this, recent studies that have combined BM-MSCs with the anti-fibrotic drug serelaxin (RLX), have demonstrated the enhanced therapeutic potential of this combination therapy in normotensive and hypertensive preclinical models of CKD. In this review, a critical appraisal of the preclinical data available on the anti-fibrotic and renoprotective actions of BM-MSCs or RLX alone and when combined, as a treatment option for normotensive vs. hypertensive CKD, is discussed.

Human Peripheral Blood Mononucleocyte Derived Myeloid Committed Progenitor Cells Mitigate H-ARS by Exosomal Paracrine Signal

Radiation-induced loss of the hematopoietic stem cell progenitor population compromises bone marrow regeneration and development of mature blood cells. Failure to rescue bone marrow functions results in fatal consequences from hematopoietic injury, systemic infections, and sepsis. So far, bone marrow transplant is the only effective option, which partially minimizes radiation-induced hematopoietic toxicities. However, a bone marrow transplant will require HLA matching, which will not be feasible in large casualty settings such as a nuclear accident or an act of terrorism. In this study we demonstrated that human peripheral blood mononuclear cell-derived myeloid committed progenitor cells can mitigate radiation-induced bone marrow toxicity and improve survival in mice. These cells can rescue the recipient's hematopoietic stem cells from radiation toxicity even when administered up to 24 h after radiation exposure and can be subjected to allogenic transplant without GVHD development. Transplanted cells deliver sEVs enriched with regenerative and immune-modulatory paracrine signals to mitigate radiation-induced hematopoietic toxicity. This provides a natural polypharmacy solution against a complex injury process. In summary, myeloid committed progenitor cells can be prepared from blood cells as an off-the-shelf alternative to invasive bone marrow harvesting and can be administered in an allogenic setting to mitigate hematopoietic acute radiation syndrome.

Dichotomic Potency of IFNγ Licensed Allogeneic Mesenchymal Stromal Cells in Animal Models of Acute Radiation Syndrome and Graft Versus Host Disease

Mesenchymal stromal cells (MSCs) are being tested as a cell therapy in clinical trials for dozens of inflammatory disorders, with varying levels of efficacy reported. Suitable and robust preclinical animal models for testing the safety and efficacy of different types of MSC products before use in clinical trials are rare. We here introduce two highly robust animal models of immune pathology: 1) acute radiation syndrome (ARS) and 2) graft versus host disease (GvHD), in conjunction with studying the immunomodulatory effect of well-characterized Interferon gamma (IFNγ) primed bone marrow derived MSCs. The animal model of ARS is based on clinical grade dosimetry precision and bioluminescence imaging. We found that allogeneic MSCs exhibit lower persistence in naïve compared to irradiated animals, and that intraperitoneal infusion of IFNγ prelicensed allogeneic MSCs protected animals from radiation induced lethality by day 30. In direct comparison, we also investigated the effect of IFNγ prelicensed allogeneic MSCs in modulating acute GvHD in an animal model of MHC major mismatched bone marrow transplantation. Infusion of IFNγ prelicensed allogeneic MSCs failed to mitigate acute GvHD. Altogether our results demonstrate that infused IFNγ prelicensed allogeneic MSCs protect against lethality from ARS, but not GvHD, thus providing important insights on the dichotomy of IFNγ prelicensed allogenic MSCs in well characterized and robust animal models of acute tissue injury.

Mesenchymal Stem Cells in Preclinical Infertility Cytotherapy: A Retrospective Review

Infertility is a global reproductive disorder which is caused by a variety of complex diseases. Infertility affects the individual, family, and community through physical, psychological, social and economic consequences. The results from recent preclinical studies regarding stem cell-based therapies are promising. Stem cell-based therapies cast a new hope for infertility treatment as a replacement or regeneration strategy. The main features and application prospects of mesenchymal stem cells in the future of infertility should be understood by clinicians. Mesenchymal stem cells (MSCs) are multipotent stem cells with abundant source, active proliferation, and multidirectional differentiation potential. MSCs play a role through cell homing, secretion of active factors, and participation in immune regulation. Another advantage is that, compared with embryonic stem cells, there are fewer ethical factors involved in the application of MSCs. However, a number of questions remain to be answered prior to safe and effective clinical application. In this review, we summarized the recent status of MSCs in the application of the diseases related to or may cause to infertility and suggest a possible direction for future cytotherapy to infertility.

Multipotent Mesenchymal Stromal Cells in Rheumatoid Arthritis and Systemic Lupus Erythematosus; From a Leading Role in Pathogenesis to Potential Therapeutic Saviors?

The pathogenesis of the autoimmune rheumatological diseases including rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is complex with the involvement of several immune cell populations spanning both innate and adaptive immunity including different T-lymphocyte subsets and monocyte/macrophage lineage cells. Despite therapeutic advances in RA and SLE, some patients have persistent and stubbornly refractory disease. Herein, we discuss stromal cells' dual role, including multipotent mesenchymal stromal cells (MSCs) also used to be known as mesenchymal stem cells as potential protagonists in RA and SLE pathology and as potential therapeutic vehicles. Joint MSCs from different niches may exhibit prominent pro-inflammatory effects in experimental RA models directly contributing to cartilage damage. These stromal cells may also be key regulators of the immune system in SLE. Despite these pro-inflammatory roles, MSCs may be immunomodulatory and have potential therapeutic value to modulate immune responses favorably in these autoimmune conditions. In this review, the complex role and interactions between MSCs and the haematopoietically derived immune cells in RA and SLE are discussed. The harnessing of MSC immunomodulatory effects by contact-dependent and independent mechanisms, including MSC secretome and extracellular vesicles, is discussed in relation to RA and SLE considering the stromal immune microenvironment in the diseased joints. Data from translational studies employing MSC infusion therapy against inflammation in other settings are contextualized relative to the rheumatological setting. Although safety and proof of concept studies exist in RA and SLE supporting experimental and laboratory data, robust phase 3 clinical trial data in therapy-resistant RA and SLE is still lacking.

Advances in the treatment of graft-versus-host disease with immunomodulatory cells

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been widely used to treat hematological malignancies and genetic diseases. Graft-versus-host disease (GVHD) induced by donor immune system is the most common complication, contributing to severe morbidity and mortality after allo-HSCT. Currently, in terms of the prevention and treatment of GVHD, the major first-line therapeutic drugs are corticosteroids. However, most patients with systemic corticosteroid treatment are prone to steroid-refractory and poor prognosis. The use of several immune cells including Tregs, Bregs and mesenchymal stromal cells (MSCs) as an alternative on prevention or therapy of GVHD has been demonstrated to be beneficial. However, there are still many defects to a certain degree. Based on immune cells, it is promising to develop new and better approaches to improve GVHD. In this article, we will review the current advance of immune cells (Tregs, Bregs, MSCs) with negative regulation in the treatment of GVHD and present emerging strategies for the prevention and treatment of GVHD by other immune regulatory cells and chimeric antigen receptor (CAR) Tregs. In addition, these new therapeutic options need to be further evaluated in well-designed prospective multicenter trials to determine the optimal treatment for GVHD patients and improve their prognosis.

Overview of current adipose-derived stem cell (ADSCs) processing involved in therapeutic advancements: flow chart and regulation updates before and after COVID-19

Adipose-derived stem cells (ADSCs) have raised big interest in therapeutic applications in regenerative medicine and appear to fulfill the criteria for a successful cell therapy. Their low immunogenicity and their ability to self-renew, to differentiate into different tissue-specific progenitors, to migrate into damaged sites, and to act through autocrine and paracrine pathways have been altogether testified as the main mechanisms whereby cell repair and regeneration occur. The absence of standardization protocols in cell management within laboratories or facilities added to the new technologies improved at patient's bedside and the discrepancies in cell outcomes and engraftment increase the limitations on their widespread use by balancing their real benefit versus the patient safety and security. Also, comparisons across pooled patients are particularly difficult in the fact that multiple medical devices are used and there is absence of harmonized assessment assays despite meeting regulations agencies and efficient GMP protocols. Moreover, the emergence of the COVID-19 breakdown added to the complexity of implementing standardization. Cell- and tissue-based therapies are completely dependent on the biological manifestations and parameters associated to and induced by this virus where the scope is still unknown. The initial flow chart identified for stem cell therapies should be reformulated and updated to overcome patient infection and avoid significant variability, thus enabling more patient safety and therapeutic efficiency. The aim of this work is to highlight the major guidelines and differences in ADSC processing meeting the current good manufacturing practices (cGMP) and the cellular therapy-related policies. Specific insights on standardization of ADSCs proceeding at different check points are also presented as a setup for the cord blood and bone marrow.

A keratin-based microparticle for cell delivery

Keratin-based biomaterials represent an attractive opportunity in the fields of wound healing and tissue regeneration, not only for their chemical and physical properties, but also for their ability to act as a delivery system for a variety of payloads. Importantly, keratins are the only natural biomaterial that is not targeted by specific tissue turnover-related enzymes, giving it potential stability advantages and greater control over degradation after implantation. However, in-situ polymerization chemistry in some keratin systems are not compatible with cells, and incorporation within constructs such as hydrogels may lead to hypoxia and cell death. To address these challenges, we envisioned a pre-formed keratin microparticle on which cells could be seeded, while other payloads (e.g. drugs, growth factors or other biologic compounds) could be contained within, although studies investigating the potential partitioning between phases during emulsion polymerization would need to be conducted. This study employs well-established water-in-oil emulsion procedures as well as a suspension culture method to load keratin-based microparticles with bone marrow-derived mesenchymal stem cells. Fabricated microparticles were characterized for size, porosity and surface structure and further analyzed to investigate their ability to form gels upon hydration. The suspension culture technique was validated based on the ability for loaded cells to maintain their viability and express actin and vinculin proteins, which are key indicators of cell attachment and growth. Maintenance of expression of markers associated with cell plasticity was also investigated. As a comparative model, a collagen-coated microparticle (Sigma) of similar size was used. Results showed that an oxidized form of keratin ("keratose" or "KOS") formed unique microparticle structures of various size that appeared to contain a fibrous sub-structure. Cell adhesion and viability was greater on keratin microparticles compared to collagen-coated microparticles, while marker expression was retained on both.

Challenges and Controversies in Human Mesenchymal Stem Cell Therapy

Stem cell therapy is being intensely investigated within the last years. Expectations are high regarding mesenchymal stem cell (MSC) treatment in translational medicine. However, many aspects concerning MSC therapy should be profoundly defined. Due to a variety of approaches that are investigated, potential effects of stem cell therapy are not transparent. On the other hand, most results of MSC administration in vivo have confirmed their safety and showed promising beneficial outcomes. However, the therapeutic effects of MSC-based treatment are still not spectacular and there is a potential risk related to MSC applications into specific cell niche that should be considered in long-term observations and follow-up outcomes. In this review, we intend to address some problems and critically discuss the complex nature of MSCs in the context of their effective and safe applications in regenerative medicine in different diseases including graft versus host disease (GvHD) and cardiac, neurological, and orthopedic disorders.

Syngeneic, in contrast to allogeneic, mesenchymal stem cells have superior therapeutic potential following spinal cord injury

We evaluated the importance of histocompatibility of transplanted MSCs in terms of therapeutic potential. Mouse syngeneic MSCs or allogeneic MSCs were transplanted following SCI in mouse. In this study we found that syngeneic, but not allogeneic, MSCs alternatively activated macrophages resulting in a down-regulation of pro-inflammation. Syngeneic MSCs also had a general suppressive effect on the immune response as compared to allogeneic MSCs. Additionally, syngeneic, but not allogeneic, MSCs significantly enhanced the recovery of hind limb function. In this study we show that the histocompatibility of transplanted MSCs is of importance for their therapeutic potential.

Effect of bone marrow mesenchymal stem cells on healing of temporomandibular joints in rats with induced rheumatoid arthritis

The healing capacity of bone marrow mesenchymal stem cells (BMMSCs) has been evaluated in various studies. This study aimed to evaluate the effect of BMMSCs on the healing of temporomandibular joints (TMJs) with induced rheumatoid arthritis. Fifty healthy male Sprague Dawley rats were divided into three groups: group I (n = 10), negative control; group II (n = 20), positive control (induction of arthritis by adjuvant followed by intravenous injection of 0.1 ml of PBS); and group III (n = 20), intervention (as for group II but injected intravenously with 1 × 10⁶  cells ml^-1 of BMMSCs suspended in PBS). Half of the rats in each group were euthanized 3 wk after the start of the experiment and the other half was euthanized after 5 wk. Group I revealed normal TMJ features. Group II showed thickening of disc, thinning of cartilage, disordered bone trabeculae, and decreased in mean % area staining positive of collagen fibers at 3 wk, while at 5 wk these effects were more aggravated. Group III showed nearly normal thickness of disc and condylar cartilage, nearly normal arrangement of bone trabeculae and regenerated collagen fibers at 3 wk, while after 5 wk the TMJ features were almost normal. Two-way anova revealed statistically significant differences between groups. Thus, treatment of induced rheumatoid arthritis with BMMSCs shows promising results that need to be further investigated in humans.

Mesenchymal stem cells provide prophylaxis against acute graft-versus-host disease following allogeneic hematopoietic stem cell transplantation: A meta-analysis of animal models

A meta-analysis of animal models was conducted to evaluate the prophylactic effects of mesenchymal stem cells (MSCs) on acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic stem cell transplantation. A total of 50 studies involving 1848 animals were included. The pooled results showed that MSCs significantly reduced aGVHD-associated mortality (risk ratio = 0.70, 95% confidence interval 0.62 to 0.79, P = 2.73×10⁻⁹) and clinical scores (standardized mean difference = −3.60, 95% confidence interval −4.43 to −2.76, P = 3.61×10⁻¹⁷). In addition, MSCs conferred robust favorable prophylactic effects on aGVHD across recipient species, MSC doses, and administration times, but not MSC sources. Our meta-analysis showed that MSCs significantly prevented mortality and alleviated the clinical manifestations of aGVHD in animal models. These data support further clinical trials aimed at evaluating the efficacy of using MSCs to prevent aGVHD.

Regulatory perspective on in vitro potency assays for human mesenchymal stromal cells used in immunotherapy

Mesenchymal stromal cells (MSCs) are multipotent cells derived from various tissues that can differentiate into several cell types. MSCs are able to modulate the response of immune cells of the innate and adaptive immune system. Because of these multimodal properties, the potential use of MSCs for immunotherapies is currently explored in various clinical indications. Due to the diversity of potential MSC medicinal products at the level of cell source, manufacturing process and indication, distinct functionality tests may be needed to ensure the quality for each of the different products. In this review, we focus on in vitro potency assays proposed for characterization and release of different MSC medicinal products. We discuss the most used functional assays, as presented in scientific advices and literature, highlighting specific advantages and limitations of the various assays. Currently, the most proposed and accepted potency assay for release is based on in vitro inhibition of T cell proliferation or other functionalities. However, for some products, assays based on other MSC or responder cell properties may be more appropriate. In all cases, the biological relevance of the proposed assay for the intended clinical activity should be substantiated with appropriate product-specific (non-)clinical data. In case practical considerations prevent the use of the ideal potency assay at release, use of a surrogate marker or test could be considered if correlation with functionality has been demonstrated. Nevertheless, as the field of MSC immunology is evolving, improvements can be expected in relevant assays and consequently in guidance related to potency testing.

Immunologic properties of differentiated and undifferentiated mesenchymal stem cells derived from umbilical cord blood

The expression of immunogenic markers after differentiation of umbilical cord blood (UCB)-derived mesenchymal stem cells (MSC) has been poorly investigated and requires extensive in vitro and in vivo testing for clinical application. The expression of human leukocyte antigen (HLA) classes on UCB-derived MSC was tested by Fluorescence-activated cell sorting analysis and immunocytochemical staining. The undifferentiated MSC were moderately positive for HLA-ABC, but almost completely negative for HLA-DR. The MSC differentiated to chondrocytes expressed neither HLA-ABC nor HLA-DR. The proliferation of MSC was not significantly affected by the allogeneic lymphocytes stimulated with concanavalin A. The responder lymphocytes showed no significant decrease in proliferation in the presence of the MSC, but the apoptosis rate of the lymphocytes was increased in the presence of MSC. Taken together, these findings indicate that UCB-derived MSC differentiated to chondrocytes expressed less HLA class I and no class II antigens. The MSC showed an immunomodulatory effect on the proliferation and apoptosis of allogeneic lymphocytes. These data suggest that the differentiated and undifferentiated allogeneic MSC derived from umbilical cord blood can be a useful candidate for allogeneic cell therapy and transplantation without a major risk of rejection.

Immunodepletion and Hypoxia Preconditioning of Mouse Compact Bone Cells as a Novel Protocol to Isolate Highly Immunosuppressive Mesenchymal Stem Cells

Compact bones (CB) are major reservoirs of mouse mesenchymal stem cells (mMSC). Here, we established a protocol to isolate MSC from CB and tested their immunosuppressive potential. Collagenase type II digestion of BM-flushed CB from C57B/6 mice was performed to liberate mMSC precursors from bone surfaces to establish nondepleted mMSC. CB cells were also immunodepleted based on the expression of CD45 (leukocytes) and TER119 (erythroid cells) to eliminate hematopoietic cells. CD45^-TER119^- CB cells were subsequently used to generate depleted mMSC. CB nondepleted and depleted mMSC progenitors were cultured under hypoxic conditions to establish primary mMSC cultures. CB depleted mMSC compared to nondepleted mMSC showed greater cell numbers at subculturing and had increased functional ability to differentiate into adipocytes and osteoblasts. CB depleted mMSC had high purity and expressed key mMSC markers (>85% Sca-1, CD29, CD90) with no mature hematopoietic contaminating cells (<5% CD45, CD11b) when subcultured to passage 5 (P5). Nondepleted mMSC cultures, however, were less pure and heterogenous with <72% Sca-1⁺, CD29⁺, and CD90⁺ cells at early passages (P1 or P2), along with high percentages of contaminating CD11b⁺ (35.6%) and CD45⁺ (39.2%) cells that persisted in culture long term. Depleted and nondepleted mMSC nevertheless exhibited similar potency to suppress total (CD3⁺), CD4⁺ and CD8⁺ T cell proliferation, in a dendritic cell allostimulatory one-way mixed lymphocyte reaction. CB depleted mMSC, pretreated with proinflammatory cytokines IFN-γ, TNF-α, and IL-17A, showed superior suppression of CD8⁺ T cell, but not CD4⁺ T cell proliferation, relative to untreated-mMSC. In conclusion, CB depleted mMSC established under hypoxic conditions and treated with selective cytokines represent a novel source of potent immunosuppressive MSC. As these cells have enhanced immune modulatory function, they may represent a superior product for use in clinical allotransplantation.

The roles of immune cells in bone healing; what we know, do not know and future perspectives

Key events occurring during the bone healing include well-orchestrated and complex interactions between immune cells, multipotential stromal cells (MSCs), osteoblasts and osteoclasts. Through three overlapping phases of this physiological process, innate and adaptive immune cells, cytokines and chemokines have a significant role to play. The aim of the escalating immune response is to achieve an osseous healing in the shortest time and with the least complications facilitating the restoration of function. The uninterrupted progression of these biological events in conjunction with a favourable mechanical environment (stable fracture fixation) remains the hallmark of successful fracture healing. When failure occurs, either the biological environment or the mechanical one could have been disrupted. Not infrequently both may be compromised. Consequently, regenerative treatments involving the use of bone autograft, allograft or synthetic matrices supplemented with MSCs are increasingly used. A better understanding of the bone biology and osteoimmunology can help to improve these evolving cell-therapy based strategies. Herein, an up to date status of the role of immune cells during the different phases of bone healing is presented. Additionally, the known and yet to know events about immune cell interactions with MSCs and osteoblasts and osteoclasts and the therapeutic implications are being discussed.

Allogeneic Mesenchymal Stromal Cells Transplanted Onto the Heart Surface Achieve Therapeutic Myocardial Repair Despite Immunologic Responses in Rats

Background

Transplantation of allogeneic mesenchymal stromal cells (MSCs) is a promising treatment for heart failure. We have shown that epicardial placement of cell sheets markedly increases donor cell survival and augments therapeutic effects compared with the current methods. Although immune rejection of intramyocardially injected allogeneic MSCs have been suggested, allogeneic MSCs transplanted on the heart surface (virtual space) may undergo different courses. This study aimed to elucidate immunologic response against epicardially placed allogeneic MSCs, rejection or acceptance of these cells, and their therapeutic effects for heart failure.

Methods and Results

At 4 weeks after coronary artery ligation, Lewis rats underwent epicardial placement of MSC sheets from syngeneic Lewis or allogeneic Fischer 344 rats or sham treatment. At days 3 and 10 after treatment, similar ratios (≈50% and 30%, respectively) of grafted MSCs survived on the heart surface in both MSC sheet groups. By day 28, survival of syngeneic MSCs was substantially reduced (8.9%); survival of allogeneic MSCs was more extensively reduced (0.2%), suggesting allorejection. Correspondingly, allogeneic MSCs were found to have evoked an immunologic response, albeit low level, as characterized by accumulation of CD4⁺ T cells and upregulation of interleukin 6. Despite this alloimmune response, the allogeneic MSC sheet achieved myocardial upregulation of reparative factors, enhanced repair of the failing myocardium, and improved cardiac function to the equivalent degree observed for the syngeneic MSC sheet.

Conclusions

Allogeneic MSCs placed on the heart surface evoked an immunologic response; however, this allowed sufficient early phase donor cell survival to induce equivalent therapeutic benefits to syngeneic MSCs. Further development of this approach toward clinical application is warranted.

Accessory cells for β-cell transplantation

Despite recent advances, insulin therapy remains a treatment, not a cure, for diabetes mellitus with persistent risk of glycaemic alterations and life-threatening complications. Restoration of the endogenous β-cell mass through regeneration or transplantation offers an attractive alternative. Unfortunately, signals that drive β-cell regeneration remain enigmatic and β-cell replacement therapy still faces major hurdles that prevent its widespread application. Co-transplantation of accessory non-islet cells with islet cells has been shown to improve the outcome of experimental islet transplantation. This review will highlight current travails in β-cell therapy and focuses on the potential benefits of accessory cells for islet transplantation in diabetes.

Cell seeding density is a critical determinant for copolymer scaffolds-induced bone regeneration

Constructs intended for bone tissue engineering (TE) are influenced by the initial cell seeding density. Therefore, the objective of this study was to determine the effect of bone marrow stromal stem cells (BMSCs) density loaded onto copolymer scaffolds on bone regeneration. BMSCs were harvested from rat's bone marrow and cultured in media with or without osteogenic supplements. Cells were seeded onto poly(l‐lactide‐co‐ε‐caprolactone) [poly(LLA‐co‐CL)] scaffolds at two different densities: low density (1 × 10⁶ cells/scaffold) or high density (2 × 10⁶ cells/scaffold) using spinner modified flasks and examined after 1 and 3 weeks. Initial attachment and spread of BMSC onto the scaffolds was recorded by scanning electron microscopy. Cell proliferation was assessed by DNA quantification and cell differentiation by quantitative real‐time reverse transcriptase‐polymerized chain reaction analysis (qRT‐PCR). Five‐millimeter rat calvarial defects (24 defects in 12 rats) were implanted with scaffolds seeded with either low or high density expanded with or without osteogenic supplements. Osteogenic supplements significantly increased cell proliferation (p < 0.001). Scaffolds seeded at high cell density exhibited higher mRNA expressions of Runx2 p = 0.001, Col1 p = 0.001, BMP2 p < 0.001, BSP p < 0.001, and OC p = 0.013. More bone was formed in response to high cell seeding density (p = 0.023) and high seeding density with osteogenic medium (p = 0.038). Poly (LLA‐co‐CL) scaffolds could be appropriate candidates for bone TE. The optimal number of cells to be loaded onto scaffolds is critical for promoting Extracellular matrix synthesis and bone formation. Cell seeding density and osteogenic supplements may have a synergistic effect on the induction of new bone. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3649–3658, 2015.

New strategies for overcoming limitations of mesenchymal stem cell-based immune modulation

Mesenchymal stem cells (MSCs) have rapidly been applied in a broad field of immune-mediated disorders since the first successful clinical use of MSCs for treatment of graft-versus-host disease. Despite the lack of supporting data, expectations that MSCs could potentially treat most inflammatory conditions led to rushed application and development of commercialized products. Today, both pre-clinical and clinical studies present mixed results for MSC therapy and the discrepancy between expected and actual efficacy of MSCs in various diseases has evoked a sense of discouragement. Therefore, we believe that MSC therapy may now be at a critical milestone for re-evaluation and re-consideration. In this review, we summarize the current status of MSC-based clinical trials and focus on the discrepancy between expected and actual outcome of MSC therapy from bench to bedside. Importantly, we discuss the underlying limitations of MSCs and suggest a new guideline for MSC therapy in hopes of improving their therapeutic efficacy.

Interactions between MSCs and immune cells: implications for bone healing

It is estimated that, of the 7.9 million fractures sustained in the United States each year, 5% to 20% result in delayed or impaired healing requiring therapeutic intervention. Following fracture injury, there is an initial inflammatory response that plays a crucial role in bone healing; however, prolonged inflammation is inhibitory for fracture repair. The precise spatial and temporal impact of immune cells and their cytokines on fracture healing remains obscure. Some cytokines are reported to be proosteogenic while others inhibit bone healing. Cell-based therapy utilizing mesenchymal stromal cells (MSCs) is an attractive option for augmenting the fracture repair process. Osteoprogenitor MSCs not only differentiate into bone, but they also exert modulatory effects on immune cells via a variety of mechanisms. In this paper, we review the current literature on both in vitro and in vivo studies on the role of the immune system in fracture repair, the use of MSCs in the enhancement of fracture healing, and interactions between MSCs and immune cells. Insight into this paradigm can provide valuable clues in identifying cellular and noncellular targets that can potentially be modulated to enhance both natural bone healing and bone repair augmented by the exogenous addition of MSCs.

Interferon-gamma modification of mesenchymal stem cells: implications of autologous and allogeneic mesenchymal stem cell therapy in allotransplantation

Bone marrow-derived mesenchymal stem cells (MSC) have unique immunomodulatory and reparative properties beneficial for allotransplantation cellular therapy. The clinical administration of autologous or allogeneic MSC with immunosuppressive drugs is able to prevent and treat allograft rejection in kidney transplant recipients, thus supporting the immunomodulatory role of MSC. Interferon-gamma (IFN-γ) is known to enhance the immunosuppressive properties of MSC. IFN-γ preactivated MSC (MSC-γ) directly or indirectly modulates T cell responses by enhancing or inducing MSC inhibitory factors. These factors are known to downregulate T cell activation, enhance T cell negative signalling, alter T cells from a proinflammatory to an anti-inflammatory phenotype, interact with antigen-presenting cells and increase or induce regulatory cells. Highly immunosuppressive MSC-γ with increased migratory and reparative capacities may aid tissue repair, prolong allograft survival and induce allotransplant tolerance in experimental models. Nevertheless, there are contradictory in vivo observations related to allogeneic MSC-γ therapy. Many studies report that allogeneic MSC are immunogenic due to their inherent expression of major histocompatibility (MHC) molecules. Enhanced expression of MHC in allogeneic MSC-γ may increase their immunogenicity and this can negatively impact allograft survival. Therefore, strategies to reduce MSC-γ immunogenicity would facilitate "off-the-shelf" MSC therapy to efficiently inhibit alloimmune rejection and promote tissue repair in allotransplantation. In this review, we examine the potential benefits of MSC therapy in the context of allotransplantation. We also discuss the use of autologous and allogeneic MSC and the issues associated with their immunogenicity in vivo, with particular focus on the use of enhanced MSC-γ cellular therapy.

Clinical challenges and opportunities of mesenchymal stem cells in musculoskeletal medicine

The use of stem cells in orthopedics has been researched for many years, with robust animal data that show efficacy in cartilage healing, tendon repair, and intervertebral disk treatment. Early clinical data are also just starting to be published, and these results are encouraging. Safety data in large case series, some that lasted for many years, have also been published. The field of tissue engineering with stem cells in musculoskeletal impairments has the potential to reduce morbidity and improve clinical outcomes. The regulatory environment for this area of medicine is still developing.

Inducible Costimulator Gene-Transduced Bone Marrow-Derived Mesenchymal Stem Cells Attenuate the Severity of Acute Graft-Versus-Host Disease in Mouse Models

In murine allogeneic transplantation models, ICOS gene-transduced bone marrow-derived mesenchymal stem cells (MSCs(ICOS-EGFP)) were evaluated for their effects on GvHD severity and long-term survival. Lethally irradiated BALB/c or first filial generation of BALB/c and C57BL/6 (CB6F1) mice were transplanted with bone marrow cells and splenocytes from C57BL/6 mice to establish acute GvHD models. Recipient mice were injected with MSCs(ICOS-EGFP), MSCs, MSCs(EGFP), ICOS-Ig fusion protein, MSCs + ICOS-Ig, or PBS (control group). Long-term survival, GvHD rates and severity, CD4(+) T-cell apoptosis and proliferation, and Th1/Th2/Th17 effecter cell polarization were evaluated. In the C57BL/6 → CB6F1 HSCT model, the long-term survival in the MSC(ICOS-EGFP) group was higher than that in the GvHD group (74.29 ± 7.39% vs. 0, p < 0.01), and this survival rate was also higher than that in the MSC, ICOS-Ig, or MSC + ICOS-Ig groups (42.86 ± 8.36%, p = 0.004; 48.57 ± 8.45%, p = 0.03; or 50.43 ± 8.45% p = 0.04, respectively). The survival advantages of MSC(ICOS-EGFP)-treated group were confirmed in the C57BL/6 → BALB/c HSCT model. In both HSCT models, the low mortality in the MSC(ICOS-EGFP) group was associated with lower incidence and severity of acute GvHD. Treatment with MSCs(ICOS-EGFP) induced more CD4(+) T-cell apoptosis compared with that in the GvHD group. The effect on CD4(+) T cells was shown as early as day 2 and maintained until day 14 (p < 0.05 on days 2, 3, 7, and 14). Furthermore, we demonstrated that MSCs(ICOS-EGFP) were able to suppress Th1 and Th17 polarization and promote Th2 polarization on both protein expression and gene transcription levels. Higher serum levels of IL-4, IL-10, and lower levels of IFN-γ, IL-2, IL-12, and IL-17A were detected in the MSC(ICOS-EGFP) group. The MSCs(ICOS-EGFP) could also induce GATA-3, STAT6 expression and inhibit T-bet, STAT4, ROR-γt expression. Our results showed that injection of MSCs(ICOS-EGFP) is a promising strategy for acute GvHD prevention and treatment. It provides synergistic benefits of MSC immune modulation and ICOS-B7h pathway blockage.

Improvement of cardiac function by placenta-derived mesenchymal stem cells does not require permanent engraftment and is independent of the insulin signaling pathway

INTRODUCTION

The objective of this work was to evaluate the efficacy of placenta-derived mesenchymal stem cell (MSC) therapy in a mouse model of myocardial infarction (MI). Since MSCs can be obtained from two different regions of the human term placenta (chorionic plate or villi), cells obtained from both these regions were compared so that the best candidate for cell therapy could be selected.

METHODS

For the in vitro studies, chorionic plate MSCs (cp-MSCs) and chorionic villi MSCs (cv-MSCs) were extensively characterized for their genetic stability, clonogenic and differentiation potential, gene expression, and immunophenotype. For the in vivo studies, C57Bl/6 mice were submitted to MI and, after 21 days, received weekly intramyocardial injections of cp-MSCs for 3 weeks. Cells were also stably transduced with a viral construct expressing luciferase, under the control of the murine stem cell virus (MSCV) promoter, and were used in a bioluminescence assay. The expression of genes associated with the insulin signaling pathway was analyzed in the cardiac tissue from cp-MSCs and placebo groups.

RESULTS

Morphology, differentiation, immunophenotype, and proliferation were quite similar between these cells. However, cp-MSCs had a greater clonogenic potential and higher expression of genes related to cell cycle progression and genome stability. Therefore, we considered that the chorionic plate was preferable to the chorionic villi for the isolation of MSCs. Sixty days after MI, cell-treated mice had a significant increase in ejection fraction and a reduction in end-systolic volume. This improvement was not caused by a reduction in infarct size. In addition, tracking of cp-MSCs transduced with luciferase revealed that cells remained in the heart for 4 days after the first injection but that the survival period was reduced after the second and third injections. Quantitative reverse transcription-polymerase chain reaction revealed similar expression of genes involved in the insulin signaling pathway when comparing cell-treated and placebo groups.

CONCLUSIONS

Improvement of cardiac function by cp-MSCs did not require permanent engraftment and was not mediated by the insulin signaling pathway.

Mesenchymal stem cells, autoimmunity and rheumatoid arthritis

The vast majority of literature pertaining to mesenchymal stem cells (MSC) immunomodulation has focussed on bone marrow-derived MSC that are systemically infused to alleviate inflammatory conditions. Rheumatoid arthritis (RA) is the commonest autoimmune joint disease that has witnessed significant therapeutic advances in the past decade, but remains stubbornly difficult to treat in a subset of cases. Pre-clinical research has demonstrated that bone marrow, adipose, synovial and umbilical cord-derived MSC all suppress the functions of different immune cells thus raising the possibility of new therapies for autoimmune diseases including RA. Indeed, preliminary evidence for MSC efficacy has been reported in some cases of RA and systemic lupus erythromatosis. The potential use of bone marrow-MSC (BM-MSC) for RA therapy is emerging but the use of synovial MSC (S-MSC) to suppress the exaggerated immune response within the inflamed joints remains rudimentary. Synovial fibroblasts that are likely derived from S-MSCs, also give rise to a cell-cultured progeny termed fibroblast-like synoviocytes (FLS), which are key players in the perpetuation of joint inflammation and destruction. A better understanding of the link between these cells and their biology could be a key to developing novel MSC-based strategies for therapy. The review briefly focuses on BM-MSC and gives particular attention to joint niche synovial MSC and FLS with respect to immunoregulatory potential therapy roles.

Isolation, expansion and characterisation of mesenchymal stem cells from human bone marrow, adipose tissue, umbilical cord blood and matrix: a comparative study

The multipotent and immunosuppressive capacities of mesenchymal stem cells (MSCs) attract several scientists worldwide towards translational research focusing on treatment of diseases including liver failure. Though MSC's have been isolated from different sources, researchers do not concur on the best source for expansion and clinical translation. In this study, we have compared the isolation, proliferation and expansion of MSCs from umbilical cord blood (UCB), Wharton's Jelly (WJ), bone marrow (BM) and adipose tissue (AT). MSCs were isolated by density gradient separation from UCB, BM and AT and by both enzymatic and explant method for WJ. The MSCs are characterized by their ability to adhere to plastic, expression of positive (CD105, CD73, CD90, CD29, CD44) and negative (CD45, CD14, CD34) markers by flow cytometry and also by their in vitro adipogenic, osteogenic and chondrogenic differentiation. This comprehensive study clearly shows that WJ is better than UCB both in terms of rapidity, yield and ease of procedure. AT and BM are autologous sources for MSC's but the specimen collection involves cumbersome and painful procedures and an invasive approach. However being autologous, they are safe and probable candidates for therapeutic future applications.

Immunogenicity of undifferentiated and differentiated allogeneic mouse mesenchymal stem cells

Mesenchymal stem cells (MSC) are multipotential cells with utility in tissue engineering and regenerative medicine. However, the immunological properties and immunogenicity of allogeneic MSC remain poorly defined. Recent studies investigating their immunogenicity remain inconclusive and this has hampered their clinical application. This study investigated the (1) immunogenicity and (2) immunomodulatory properties of bone marrow-derived MSC using an allogeneic mouse model involving Balb/c (responder) and C3H (stimulator) mice. Dermal fibroblasts (DF) were used as controls for cells of mesenchymal origin. Adaptations of the lymphocyte transformation assay (LTA) and mixed lymphocyte reaction (MLR) were used to investigate the immunogenicity and immunomodulatory properties of allogeneic undifferentiated and chondrogenic-differentiated MSC and DF. Both MSC and DF displayed a similar phenotypic profile with the exception of lower expression of CD44 and CD105 in DF. Tri-lineage differentiation of MSC and DF into adipocytes, chondrocytes and osteocytes confirmed their multipotency. In LTA, both undifferentiated and chondrogenic-differentiated allogeneic MSC stimulated lymphocyte proliferation. Allogeneic DF were non-stimulatory but chondrogenic-differentiated DF triggered responder lymphocyte proliferation. In one-way MLR, both allogeneic MSC and DF significantly suppressed Balb/c lymphocyte proliferation. The current challenges in distinguishing between MSC and fibroblasts were apparent throughout the work. These findings support the notion that although MSC possess immunosuppressive properties, they may not be immunoprivileged. Thus, clinical application of allogeneic MSC should be taken with due consideration of their potential immunogenicity.

Low immunogenicity of allogeneic human umbilical cord blood-derived mesenchymal stem cells in vitro and in vivo

Evaluation of the immunogenicity of human mesenchymal stem cells (MSCs) in an allogeneic setting during therapy has been hampered by lack of suitable models due to technical and ethical limitations. Here, we show that allogeneic human umbilical cord blood derived-MSCs (hUCB-MSCs) maintained low immunogenicity even after immune challenge in vitro. To confirm these properties in vivo, a humanized mouse model was established by injecting isolated hUCB-derived CD34+ cells intravenously into immunocompromised NOD/SCID IL2γnull (NSG) mice. After repeated intravenous injection of human peripheral blood mononuclear cells (hPBMCs) or MRC5 cells into these mice, immunological alterations including T cell proliferation and increased IFN-γ, TNF-α, and human IgG levels, were observed. In contrast, hUCB-MSC injection did not elicit these responses. While lymphocyte infiltration in the lung and small intestine and reduced survival rates were observed after hPBMC or MRC5 transplantation, no adverse events were observed following hUCB-MSC introduction. In conclusion, our data suggest that allogeneic hUCB-MSCs have low immunogenicity in vitro and in vivo, and are therefore "immunologically safe" for use in allogeneic clinical applications.

Mesenchymal stromal cells augment CD4+ and CD8+ T-cell proliferation through a CCL2 pathway

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) derived from bone marrow are immunosuppressive in vitro and in vivo. Recent evidence, however, has shown that in certain settings, MSC can also be immunostimulatory. The mechanisms involved in this process are largely unknown.

METHODS

Mouse spleen T cells were stimulated with allogeneic mixed lymphocyte reaction (MLR) or anti-CD3/CD28 beads and treated with autologous bone marrow MSC or MSC-conditioned medium. CD4+ and CD8+ T-cell proliferation was analyzed after treatment.

RESULTS

We show that MSC have both suppressive and stimulatory functions toward T cells after stimulation with anti-CD3/CD28 beads or in an MLR. This depended on the ratio of MSC to responder T cells, with low numbers of MSC increasing and higher numbers inhibiting T-cell proliferation. Immunostimulatory function was mediated, in part, by soluble factors. MSC immunosuppression of the MLR was indirect and related to inhibition of antigen-presenting cell maturation. Direct effects of MSC-conditioned medium during anti-CD3/CD28 stimulated proliferation were entirely stimulatory and required the presence of the T-cell receptor. MSC supernatant contained both CCL2 and CCL5 at high levels, but only CCL2 level correlated with the ability to augment proliferation. An anti-CCL2 antibody blocked this proliferative activity.

CONCLUSIONS

CCL2 plays an important role in the immunostimulatory function of MSC, and we further hypothesize that the immunomodulatory role of MSC is determined by a balance between inhibitory and stimulatory factors, suggesting the need for caution when these cells are investigated in clinical protocols.

Comparative evaluation of in vivo osteogenic differentiation of fetal and adult mesenchymal stem cell in rat critical-sized femoral defect model

Mesenchymal stem cells (MSCs) can be obtained from various sources. MSCs from different origins appear to have different preferences for differentiation. In this study, we have compared the in vivo osteogenic potential of adult MSCs from adipose tissue (AT) and bone marrow (BM) with fetal MSCs from umbilical cord (UC) and umbilical cord blood (UCB) by using a rat critical-sized femoral defect model. We have also sought to determine whether pretreatment with an osteogenic medium promotes osteogenesis in MSCs. Study groups were divided as follows: (1) defect only, (2) scaffold only, (3) AT MSCs in scaffolds, (4) BM MSCs in scaffolds, (5) UC MSCs in scaffolds and (6) UCB MSCs in scaffolds. Groups with MSCs were further divided with respect to their pretreatment. At 12 weeks after surgery, in vivo osteogenesis was measured radiographically and by micro-computed tomography (CT). Based on quantitative assessment by micro-CT, no significant difference of the mean bone volume fraction value (BV/TV) was seen between adult MSCs (AT and BM MSCs) and fetal MSCs (UC and UCB MSCs). The mean BV/TVs were significantly higher in non-pretreated BM MSC (14.2±1.4%) and UCB MSC (14.0±1.2%) and pretreated UC MSC (14.8±2.0%) than in those with the scaffold only (11.3±1.3%; P<0.05). In addition, AT (from 10.4±1.2% to 13.1±2.2%) and UC (from 10.3±0.7% to 14.8±2.0%) MSCs from solid tissues showed a significant increase in the mean BV/TV with pretreatment (P<0.05). In contrast, BM MSC (from 14.2±1.4% to 10.9±1.2%) and UCB MSC (from 14.0±1.2% to 11.6±1.0%) from non-solid tissues showed a significant decrease with pretreatment (P<0.05).

Interferon gamma and T cells inhibit osteogenesis induced by allogeneic mesenchymal stromal cells

The mesenchymal stromal cells (MSCs) are reported to be immunoprivileged and osteogenic. We hypothesized that the use of allogeneic MSCs for bone repair was possible if they displayed an ability to induce similar osteogenesis in syngeneic as well as in allogeneic hosts. To test this hypothesis we used a cloned bone marrow derived cell, termed D1, isolated from Balb/c mice. The D1 cells were subcutaneously injected in syngeneic Balb/c, allogeneic immunocompetent B6, allogeneic T-cell deficient NCr nude, and allogeneic B6 Pfp-/- Rag2-/- mice that lack matured T and B cells as well as NK-cell cytolytic functions. D1 cells formed ectopic bones only in syngeneic or allogeneic immunocompromised hosts but not in allogeneic B6 hosts. The lack of T cells alone in allogeneic NCr mice was sufficient to promote osteogenesis in allogeneic environment. We observed a significantly higher number of T cells, B cells, macrophages and significantly higher expression of interferon gamma (IFN-γ) in B6 allogeneic implants as compared to the syngeneic implants. These factors correlated with severe inhibition of expression of alkaline phosphatase, osteocalcin, and runx2 genes in the implants from B6 mice. Our data suggest that strategies to inhibit T cells and IFN-γ functions will be useful for bone repair mediated by allogeneic MSCs.

Immunogenicity of allogeneic mesenchymal stem cells

Mesenchymal stem cells (MSCs) inhibit proliferation of allogeneic T cells and express low levels of major histocompatibility complex class I (MHCI), MHCII and vascular adhesion molecule-1 (VCAM-1). We investigated whether their immunosuppressive properties and low immunophenotype protect allogeneic rat MSCs against cytotoxic lysis in vitro and result in a reduced immune response in vivo. Rat MSCs were partially protected against alloantigen-specific cytotoxic T cells in vitro. However, after treatment with IFN-γ and IL-1β, MSCs upregulated MHCI, MHCII and VCAM-1, and cytotoxic lysis was significantly increased. In vivo, allogeneic T cells but not allogeneic MSCs induced upregulation of the activation markers CD25 and CD71 as well as downregulation of CD62L on CD4⁺ T cells from recipient rats. However, intravenous injection of allo-MSCs in rats led to the formation of alloantibodies with the capacity to facilitate complement-mediated lysis, although IgM levels were markedly decreased compared with animals that received T cells. The allo-MSC induced immune response was sufficient to lead to significantly reduced survival of subsequently injected allo-MSCs. Interestingly, no increased immunogenicity of IFN-γ stimulated allo-MSCs was observed in vivo. Both the loss of protection against cytotoxic lysis under inflammatory conditions and the induction of complement-activating antibodies will likely impact the utility of allogeneic MSCs for therapeutic applications.

Safety and efficacy of mesenchymal stromal cell therapy in autoimmune disorders

Mesenchymal stromal cells (MSCs) are being employed in clinical trials to facilitate engraftment and to treat steroid-resistant acute graft-versus-host disease after hematopoietic stem cell transplantation, as well as to repair tissue damage in inflammatory/degenerative disorders, in particular, in inflammatory bowel diseases (IBDs). When entering the clinical arena, a few potential risks of MSC therapy have to be taken into account: (i) immunogenicity of the cells, (ii) biosafety of medium components, (iii) risk of ectopic tissue formation, and (iv) potential in vitro transformation of the cells during expansion. This paper analyzes the main risks connected with the use of MSCs in cellular therapy approaches, and reports on some of the most intriguing findings on the use of MSCs in the context of regenerative medicine. Experimental studies in animal models and phase I/II clinical trials on the use of MSCs for the treatment of IBDs and other inflammatory/degenerative conditions are reviewed.

WITHDRAWN: Molecular Characteristics of Bone Marrow Mesenchymal Stem Cells: An Appealing Source for Regenerative Medicine

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.hlc.2012.04.021. The duplicate article has therefore been withdrawn.

Mesenchymal stromal cells: a new tool against graft-versus-host disease?

Mesenchymal stromal cells (MSCs) represent a heterogeneous subset of multipotent cells that can be isolated from several tissues including bone marrow and fat. MSCs exhibit immunomodulatory and anti-inflammatory properties that prompted their clinical use as prevention and/or treatment for severe graft-versus-host disease (GVHD). Although a number of phase I-II studies have suggested that MSC infusion was safe and might be effective for preventing or treating acute GVHD, definitive proof of their efficacy remains lacking thus far. Multicenter randomized studies are ongoing to more precisely assess the impact of MSC infusion on GVHD prevention/treatment, whereas further research is performed in vitro and in animal models with the aims of determining the best way to expand MSCs ex vivo as well as the most efficient dose and schedule of MSCs administration. After introducing GVHD, MSC biology, and results of MSC infusion in animal models of allogeneic hematopoietic cell transplantation, this article reviews the results of the first clinical trials investigating the use of MSC infusion as prevention or treatment of GVHD.