Mesenchymal stem cells of cord blood origin are effective at preventing but not treating graft-versus-host disease

Repeated Infusions of Bone-Marrow-Derived Mesenchymal Stem Cells over 8 Weeks for Steroid-Refractory Chronic Graft-versus-Host Disease: A Prospective, Phase I/II Clinical Study

Chronic graft-versus-host disease (cGVHD) is a long-term complication of allogeneic hematopoietic stem cell transplantation associated with poor quality of life and increased morbidity and mortality. Currently, there are several approved treatments for patients who do not respond to steroids, such as ruxolitinib. Nevertheless, a significant proportion of patients fail second-line treatment, indicating the need for novel approaches. Mesenchymal stem cells (MSCs) have been considered a potential treatment approach for steroid-refractory cGVHD. To evaluate the safety and efficacy of repeated infusions of MSCs, we administered intravenous MSCs every two weeks to ten patients with severe steroid-refractory cGVHD in a prospective phase I clinical trial. Each patient received a total of four doses, with each dose containing 1 × 106 cells/kg body weight from the same donor and same passage. Patients were assessed for their response to treatment using the 2014 National Institutes of Health (NIH) response criteria during each visit. Ten patients with diverse organ involvement were enrolled, collectively undergoing 40 infusions as planned. Remarkably, the MSC infusions were well tolerated without severe adverse events. Eight weeks after the initial MSC infusion, all ten patients showed partial responses characterized by the amelioration of clinical symptoms and enhancement of their quality of life. The overall response rate was 60%, with a complete response rate of 20% and a partial response (PR) rate of 40% at the last follow-up. Overall survival was 80%, with a median follow-up of 381 days. Two patients died due to relapse of their primary disease. Immunological analyses revealed a reduction in inflammatory markers, including Suppression of Tumorigenicity 2 (ST2), C-X-C motif chemokine ligand (CXCL)10, and Secreted phosphoprotein 1(SPP1), following the MSC treatment. Repeated MSC infusions proved to be both feasible and safe, and they may be an effective salvage therapy in patients with steroid-refractory cGVHD. Further large-scale clinical studies with long-term follow-up are needed in the future to determine the role of MSCs in cGVHD.

Stromal bone marrow fibroblasts and mesenchymal stem cells support acute myeloid leukaemia cells and promote therapy resistance

The bone marrow (BM) is the primary site of adult haematopoiesis, where stromal elements (e.g. fibroblasts and mesenchymal stem cells [MSCs]) work in concert to support blood cell development. However, the establishment of an abnormal clone can lead to a blood malignancy, such as acute myeloid leukaemia (AML). Despite our increased understanding of the pathophysiology of the disease, patient survival remains suboptimal, mainly driven by the development of therapy resistance. In this review, we highlight the importance of bone marrow fibroblasts and MSCs in health and acute myeloid leukaemia and their impact on patient prognosis. We discuss how stromal elements reduce the killing effects of therapies via a combination of contact-dependent (e.g. integrins) and contact-independent (i.e. secreted factors) mechanisms, accompanied by the establishment of an immunosuppressive microenvironment. Importantly, we underline the challenges of therapeutically targeting the bone marrow stroma to improve acute myeloid leukaemia patient outcomes, due to the inherent heterogeneity of stromal cell populations. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Current perspectives on mesenchymal stromal cell therapy for graft versus host disease

Graft versus host disease (GvHD) is the clinical condition in which bone marrow-derived mesenchymal stromal cells (MSCs) have been most frequently studied. In this review, we summarize the experience from clinical trials that have paved the way to translation. While MSC-based therapy has shown an exceptional safety profile, identifying potency assays and disease biomarkers that reliably predict the capacity of a specific MSC batch to alleviate GvHD has been difficult. As GvHD diagnosis and staging are based solely on clinical criteria, individual patients recruited in the same clinical trial may have vastly different underlying biology, obscuring trial outcomes and making it difficult to determine the benefit of MSCs in subgroups of patients. An accumulating body of evidence indicates the importance of considering not only the cell product but also patient-specific biomarkers and/or immune characteristics in determining MSC responsiveness. A mode of action where intravascular MSC destruction is followed by monocyte-efferocytosis-mediated skewing of the immune repertoire in a permissive inflammatory environment would both explain why cell engraftment is irrelevant for MSC efficacy and stress the importance of biologic differences between responding and nonresponding patients. We recommend a combined analysis of clinical outcomes and both biomarkers of disease activity and MSC potency assays to identify patients with GvHD who are likely to benefit from MSC therapy.

Assessment of therapeutic role of mesenchymal stromal cells in mouse models of graft-versus-host disease using cryo-imaging

Insights regarding the biodistribution and homing of mesenchymal stromal cells (MSCs), as well as their interaction with alloreactive T-cells are critical for understanding how MSCs can regulate graft-versus-host disease (GVHD) following allogeneic (allo) bone marrow transplantation (BMT). We developed novel assays based on 3D, microscopic, cryo-imaging of whole-mouse-sized volumes to assess the therapeutic potential of human MSCs using an established mouse GVHD model. Following infusion, we quantitatively tracked fluorescently labeled, donor-derived, T-cells and third party MSCs in BMT recipients using multispectral cryo-imaging. Specific MSC homing sites were identified in the marginal zones in the spleen and the lymph nodes, where we believe MSC immunomodulation takes place. The number of MSCs found in spleen of the allo BMT recipients was about 200% more than that observed in the syngeneic group. To more carefully define the effects MSCs had on T cell activation and expansion, we developed novel T-cell proliferation assays including secondary lymphoid organ (SLO) enlargement and Carboxyfluoescein succinimidyl ester (CFSE) dilution. As anticipated, significant SLO volume enlargement and CFSE dilution was observed in allo but not syn BMT recipients due to rapid proliferation and expansion of labeled T-cells. MSC treatment markedly attenuated CFSE dilution and volume enlargement of SLO. These assays confirm evidence of potent, in vivo, immunomodulatory properties of MSC following allo BMT. Our innovative platform includes novel methods for tracking cells of interest as well as assessing therapeutic function of MSCs during GVHD induction. Our results support the use of MSCs treatment or prevention of GVHD and illuminate the wider adoption of MSCs as a standard medicinal cell therapy.

Mesenchymal stem cell-mediated transfer of mitochondria: mechanisms and functional impact

There is a steadily growing interest in the use of mitochondria as therapeutic agents. The use of mitochondria derived from mesenchymal stem/stromal cells (MSCs) for therapeutic purposes represents an innovative approach to treat many diseases (immune deregulation, inflammation-related disorders, wound healing, ischemic events, and aging) with an increasing amount of promising evidence, ranging from preclinical to clinical research. Furthermore, the eventual reversal, induced by the intercellular mitochondrial transfer, of the metabolic and pro-inflammatory profile, opens new avenues to the understanding of diseases' etiology, their relation to both systemic and local risk factors, and also leads to new therapeutic tools for the control of inflammatory and degenerative diseases. To this end, we illustrate in this review, the triggers and mechanisms behind the transfer of mitochondria employed by MSCs and the underlying benefits as well as the possible adverse effects of MSCs mitochondrial exchange. We relay the rationale and opportunities for the use of these organelles in the clinic as cell-based product.

Wharton's jelly-derived stromal cells and their cell therapy applications in allogeneic haematopoietic stem cell transplantation

For decades, mesenchymal stromal cells (MSCs) have been of great interest in the fields of regenerative medicine, tissue engineering and immunomodulation. Their tremendous potential makes it desirable to cryopreserve and bank MSCs to increase their accessibility and availability. Postnatally derived MSCs seem to be of particular interest because they are harvested after delivery without ethical controversy, they have the capacity to expand at a higher rate than adult‐derived MSCs, in which expansion decreases with ageing, and they have demonstrated immunological and haematological supportive properties similar to those of adult‐derived MSCs. In this review, we focus on MSCs obtained from Wharton's jelly (the mucous connective tissue of the umbilical cord between the amniotic epithelium and the umbilical vessels). Wharton's jelly MSCs (WJ‐MSCs) are a good candidate for cellular therapy in haematology, with accumulating data supporting their potential to sustain haematopoietic stem cell engraftment and to modulate alloreactivity such as Graft Versus Host Disease (GVHD). We first present an overview of their in‐vitro properties and the results of preclinical murine models confirming the suitability of WJ‐MSCs for cellular therapy in haematology. Next, we focus on clinical trials and discuss tolerance, efficacy and infusion protocols reported in haematology for GVHD and engraftment.

Mesenchymal stromal cells: Putative microenvironmental modulators become cell therapy

An exceptional safety profile has been shown in a large number of cell therapy clinical trials that use mesenchymal stromal cells (MSCs). However, reliable potency assays are still lacking to predict MSC immunosuppressive efficacy in the clinical setting. Nevertheless, MSCs are approved in Japan and Europe for the treatment of graft-versus-host and Crohn's fistular diseases, but not in the United States for any clinical indication. We discuss potential mechanisms of action for the therapeutic effects of MSC transplantation, experimental models that dissect tissue modulating function of MSCs, and approaches for identifying MSC effects in vivo by integrating biomarkers of disease and MSC activity.

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 stromal cells in hematopoietic cell transplantation

Mesenchymal stromal cells (MSCs) are widely recognized to possess potent immunomodulatory activity, as well as to stimulate repair and regeneration of diseased or damaged tissue. These fundamental properties suggest important applications in hematopoietic cell transplantation. Although the mechanisms of therapeutic activity in vivo are yet to be fully elucidated, MSCs seem to suppress lymphocytes by paracrine mechanisms, including secreted mediators and metabolic modulators. Most recently, host macrophage engulfment of apoptotic MSCs has emerged as an important contributor to the immune suppressive microenvironment. Although bone marrow-derived MSCs are the most commonly studied, the tissue source of MSCs may be a critical determinant of immunomodulatory function. The key application of MSC therapy in hematopoietic cell transplantation is to prevent or treat graft-versus-host disease (GVHD). The pathogenesis of GVHD reveals multiple potential targets. Moreover, the recently proposed concept of tissue tolerance suggests a new possible mechanism of MSC therapy for GVHD. Beyond GVHD, MSCs may facilitate hematopoietic stem cell engraftment, which could gain greater importance with increasing use of haploidentical transplantation. Despite many challenges and much doubt, commercial MSC products for pediatric steroid-refractory GVHD have been licensed in Japan, conditionally licensed in Canada and New Zealand, and have been recommended for approval by an FDA Advisory Committee in the United States. Here, we review key historical data in the context of the most salient recent findings to present the current state of MSCs as adjunct cell therapy in hematopoietic cell transplantation.

Role of ex vivo Expanded Mesenchymal Stromal Cells in Determining Hematopoietic Stem Cell Transplantation Outcome

Overall, the human organism requires the production of ∼1 trillion new blood cells per day. Such goal is achieved via hematopoiesis occurring within the bone marrow (BM) under the tight regulation of hematopoietic stem and progenitor cell (HSPC) homeostasis made by the BM microenvironment. The BM niche is defined by the close interactions of HSPCs and non-hematopoietic cells of different origin, which control the maintenance of HSPCs and orchestrate hematopoiesis in response to the body’s requirements. The activity of the BM niche is regulated by specific signaling pathways in physiological conditions and in case of stress, including the one induced by the HSPC transplantation (HSCT) procedures. HSCT is the curative option for several hematological and non-hematological diseases, despite being associated with early and late complications, mainly due to a low level of HSPC engraftment, impaired hematopoietic recovery, immune-mediated graft rejection, and graft-versus-host disease (GvHD) in case of allogenic transplant. Mesenchymal stromal cells (MSCs) are key elements of the BM niche, regulating HSPC homeostasis by direct contact and secreting several paracrine factors. In this review, we will explore the several mechanisms through which MSCs impact on the supportive activity of the BM niche and regulate HSPC homeostasis. We will further discuss how the growing understanding of such mechanisms have impacted, under a clinical point of view, on the transplantation field. In more recent years, these results have instructed the design of clinical trials to ameliorate the outcome of HSCT, especially in the allogenic setting, and when low doses of HSPCs were available for transplantation.

Polycystin-1 Enhances Stemmness Potential of Umbilical Cord Blood-Derived Mesenchymal Stem Cells

Polycystic Kidney Disease (PKD) is a disorder that affects the kidneys and other organs, and its major forms are encoded by polycystin-1 (PC1) and polycystin-2 (PC2), as PKD1 and PKD2. It is located sandwiched inside and outside cell membranes and interacts with other cells. This protein is most active in kidney cells before birth, and PC1 and PC2 work together to help regulate cell proliferation, cell migration, and interactions with other cells. The molecular relationship and the function between PKD1 and cancer is well known, such as increased or decreased cell proliferation and promoting or suppressing cell migration depending on the cancer cell type specifically. However, its function in stem cells has not been revealed. Therefore, in this study, we investigated the biological function of PC1 and umbilical cord blood-derived mesenchymal stem cell (UCB-MSC). Furthermore, we assessed how it affects cell migration, proliferation, and the viability of cells when expressed in the PKD1 gene. In addition, we confirmed in an ex vivo artificial tooth model generated by the three-dimension printing technique that the ability to differentiate into osteocytes improved according to the expression level of the stemness markers when PKD1 was expressed. This study is the first report to examine the biological function of PKD1 in UCB-MSC. This gene may be capable of enhancing differentiation ability and maintaining long-term stemness for the therapeutic use of stem cells.

Umbilical cord derived mesenchymal stromal cells in microcarrier based industrial scale culture sustain the immune regulatory functions

Mesenchymal stromal cells (MSCs) have been isolated from numerous sources and are potentially therapeutic against various diseases. Umbilical cord-derived MSCs (UC-MSCs) are considered superior to other tissue-derived MSCs since they have a higher proliferation rate and can be procured using less invasive surgical procedures. However, it has been recently reported that 2D culture systems, using conventional cell culture flasks, limit the mass production of MSCs for cell therapy. Therefore, the development of alternative technologies, including microcarrier-based cell culture in bioreactors, is required for the large-scale production and industrialization of MSC therapy. In this study, we aimed to optimize the culture conditions for UC-MSCs by using a good manufacturing practice (GMP)-compatible serum-free medium, developed in-house, and a small-scale (30 mL) bioreactor, which was later scaled up to 500 mL. UC-MSCs cultured in microcarrier-based bioreactors (MC-UC-MSCs) showed characteristics equivalent to those cultured statically in conventional cell culture flasks (ST-UC-MSCs), fulfilling the minimum International Society for Cellular Therapy criteria for MSCs. Additionally, we report, for the first time, the equivalent therapeutic effect of MC-UC-MSCs and ST-UC-MSCs in immunodeficient mice (graft-versus-host disease model). Lastly, we developed a semi-automated cell dispensing system, without bag-to-bag variation in the filled volume or cell concentration. In summary, our results show that the combination of our GMP-compatible serum-free and microcarrier-based culture systems is suitable for the mass production of MSCs at an industrial scale. Further improvements in this microcarrier-based cell culture system can contribute to lowering the cost of therapy and satisfying several unmet medical needs.

Application of mesenchymal stem cell therapy for aging frailty: from mechanisms to therapeutics

Aging frailty is a complex geriatric syndrome that becomes more prevalent with advancing age. It constitutes a major health problem due to frequent adverse outcomes. Frailty is characterized by disruption of physiological homeostasis and progressive decline of health status. Multiple factors contribute to development of frailty with advancing age, including genome instability, DNA damage, epigenetic alternations, stem cell exhaustion, among others. These interrelated factors comprehensively result in loss of tissue homeostasis and diminished reserve capacity in frailty. Therefore, the aged organism gradually represents symptoms of frailty with decline in physiological functions of organs. Notably, the brain, cardiovascular system, skeletal muscle, and endocrine system are intrinsically interrelated to frailty. The patients with frailty may display the diminished reserves capacity of organ systems. Due to the complex pathophysiology, no specific treatments have been approved for prevention of this syndrome. At such, effective strategies for intervening in pathogenic process to improve health status of frail patients are highly needed. Recent progress in cell-based therapy has greatly contributed to the amelioration of degenerative diseases related to age. Mesenchymal stem cells (MSCs) can exert regenerative effects and possess anti-inflammatory properties. Transplantation of MSCs represents as a promising therapeutic strategy to address the pathophysiologic problems of frail syndrome. Currently, MSC therapy have undergone the phase I and II trials in human subjects that have endorsed the safety and efficacy of MSCs for aging frailty. However, despite these positive results, caution is still needed with regard to potential to form tumors, and further large-scale studies are warranted to confirm the therapeutic efficacy of MSC therapy.

The effect of bone marrow-derived mesenchymal stem cell co-transplantation with hematopoietic stem cells on liver fibrosis alleviation and survival in patients with class III β-thalassemia major

Background

Hepatic fibrosis is a common complication in transfusion-dependent thalassemia patients. Data on the co-transplantation of mesenchymal stem cells (MSCs) with hematopoietic stem cells (HSCs) in beta-thalassemia major patients are scarce. Therefore, we aimed to evaluate the effect of co-transplantation of bone marrow-derived MSC with HSCs on the liver fibrosis alleviation and transplant outcomes in class III beta-thalassemia major.

Methods

Between April 1998 and January 2017, a total of 224 consecutive patients with class III beta-thalassemia major underwent allogeneic HSCT in the Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran. To assess liver fibrotic changes after transplantation, 47 patients participated in the MSC plus HSC group and 30 patients in the HSC only group at the end of the follow-up period. All patients underwent laboratory tests, especially serum ferritin and liver function testing, hepatic T2* MRI, liver biopsy, and FibroScan before and 2 years after transplantation. Kaplan-Meier curves were derived to determine survival and were compared using the log-rank test. Repeated-measure, mixed-effect linear regression models were used to examine the changes in liver fibrosis over time.

Results

The 10-year OS rate was 71.84% in the mesenchymal group and 61.89% in the non-mesenchymal group (P value = 0.294), while the 10-year TFS rate was 63.64% in the mesenchymal group and 52.78% in the non-mesenchymal group (P value = 0.285). No significant difference was observed in the 10-year NRM, rejection rate, ANC engraftment, platelet engraftment, acute GvHD, and chronic GvHD between the two groups. In addition, the results of repeated-measure, mixed-effect linear regression models showed that none of the variables determining hepatic fibrosis had a significant difference between patients receiving MSCs and patients who did not receive MSCs.

Conclusions

Based on the results of this study, a single infusion of MSCs at the time of HSCT to patients with class III beta-thalassemia major could not significantly improve the liver fibrosis alleviation and transplantation outcomes, including OS, TFS, TRM, rejection rate, ANC engraftment, platelet engraftment, acute GvHD, and chronic GvHD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02242-8.

Shattering barriers toward clinically meaningful MSC therapies

More than 1050 clinical trials are registered at FDA.gov that explore multipotent mesenchymal stromal cells (MSCs) for nearly every clinical application imaginable, including neurodegenerative and cardiac disorders, perianal fistulas, graft-versus-host disease, COVID-19, and cancer. Several companies have or are in the process of commercializing MSC-based therapies. However, most of the clinical-stage MSC therapies have been unable to meet primary efficacy end points. The innate therapeutic functions of MSCs administered to humans are not as robust as demonstrated in preclinical studies, and in general, the translation of cell-based therapy is impaired by a myriad of steps that introduce heterogeneity. In this review, we discuss the major clinical challenges with MSC therapies, the details of these challenges, and the potential bioengineering approaches that leverage the unique biology of MSCs to overcome the challenges and achieve more potent and versatile therapies.

Mesenchymal Stromal Cells for Graft Versus Host Disease: Mechanism-Based Biomarkers

The immunosuppressive activity of mesenchymal stromal cells (MSCs) in graft versus host disease (GvHD) is well-documented, but their therapeutic benefit is rather unpredictable. Prospective randomized clinical trials remain the only means to address MSC clinical efficacy. However, the imperfect understanding of MSC biological mechanisms has undermined patients' stratification and the successful design of clinical studies. Furthermore, although MSC efficacy seems to be dependent on patient-associated factors, the role of patients' signature to predict and/or monitor clinical outcomes remains poorly elucidated. The analysis of GvHD patient serum has identified a set of molecules that are associated with high mortality. However, despite their importance in defining GvHD severity, their role in predicting or monitoring response to MSCs has not been confirmed. A new perspective on the use of MSCs for GvHD has been prompted by the recent findings that MSCs are actively induced to undergo apoptosis by recipient cytotoxic cells and that this process is essential to initiate MSC-induced immunosuppression. This discovery has not only reconciled the conundrum between MSC efficacy and their lack of engraftment, but also highlighted the determinant role of the patient in promoting and delivering MSC immunosuppression. In this review we will revisit the extensive use of MSCs for the treatment of GvHD and will elaborate on the need that future clinical trials must depend on mechanistic approaches that facilitate the development of robust and consistent assays to stratify patients and monitor clinical outcomes.

Pre-infusion single-dose mesenchymal stem cells promote platelet engraftment and decrease severe acute graft versus host disease without relapse in haploidentical peripheral blood stem cell transplantation

Background

Mesenchymal stem cells (MSCs) may be used to treat steroid-refractory graft versus host disease (GVHD). However, the effects of MSCs in haploidentical peripheral blood stem cell transplantation (haplo-PBSCT) have not been confirmed in randomized studies.

Methods

We conducted a randomized clinical study to investigate the effects of pre-infusion (1 × 10⁶ cells/kg) MSCs on hematopoietic recovery, Epstein–Barr and cytomegalovirus infection, GVHD, and relapse in patients undergoing haplo-PBSCT. Fifty patients with acute leukemia or myelodysplastic syndrome were randomly divided into an MSC group administered 1 × 10⁶ MSCs/kg 4 to 6 hours before infusion of peripheral stem cells and a control group without MSCs.

Results

Mean platelet engraftment time was significantly faster in the MSC compared with the control group (12.28 vs 13.29 days). The mean neutrophil engraftment time was comparable in both groups (10.76 ± 2.40 vs. 10.29 ± 1.72 days). Grade II or above acute GVHD was significantly decreased in the MSC compared with the control group (12% vs. 36%). There were no significant differences in relapse rate or overall survival between the groups.

Conclusion

These results suggest that pre-infusion single-dose MSCs promote platelet engraftment and decrease severe acute GVHD without increasing relapse rate.

Mesenchymal Stem Cells Beyond Regenerative Medicine

Mesenchymal stem cells (MSCs) are competent suitors of cellular therapy due to their therapeutic impact on tissue degeneration and immune-based pathologies. Additionally, their homing and immunomodulatory properties can be exploited in cancer malignancies to transport pharmacological entities, produce anti-neoplastic agents, or induce anti-tumor immunity. Herein, we create a portfolio for MSC properties, showcasing their distinct multiple therapeutic utilities and successes/challenges thereof in both animal studies and clinical trials. We further highlight the promising potential of MSCs not only in cancer management but also in instigating tumor-specific immunity - i.e., cancer vaccination. Finally, we reflect on the possible reasons impeding the clinical advancement of MSC-based cancer vaccines to assist in contriving novel methodologies from which a therapeutic milestone might emanate.

Mesenchymal stromal cell based therapies for the treatment of immune disorders: recent milestones and future challenges

Introduction: Mesenchymal stromal cells (MSCs) present unique immunomodulatory properties that make them promising candidates for the treatment of inflammatory and immune disorders. MSC-mediated immunomodulation is a complex combination of mechanisms, in which the secretome plays a fundamental role. The plethora of bioactive molecules MSCs produce, such as indoleamine 2,3-dioxygenase (IDO) or prostaglandin E2 (PGE2), efficiently regulates innate and adaptive immunity. As a result, MSCs have been extensively employed in preclinical studies, leading to the conduction of multiple clinical trials.Areas covered: This review summarizes the effects of some of the key biomolecules in the MSC secretome and the advances in preclinical studies exploring the treatment of disorders including graft-versus-host disease (GvHD) or inflammatory bowel disease (IBD). Further, late-stage clinical trials and the first MSC-based therapies that recently obtained regulatory approval are discussed.Expert opinion: Extensive research supports the potential of MSC-based immunomodulatory therapies. However, to establish the bases for clinical translation, the future of study lies in the standardization of protocols and in the development of strategies that boost the therapeutic properties of MSCs.

Immunoregulatory mechanisms of mesenchymal stem and stromal cells in inflammatory diseases

Mesenchymal stem cells (MSCs; also referred to as mesenchymal stromal cells) have attracted much attention for their ability to regulate inflammatory processes. Their therapeutic potential is currently being investigated in various degenerative and inflammatory disorders such as Crohn's disease, graft-versus-host disease, diabetic nephropathy and organ fibrosis. The mechanisms by which MSCs exert their therapeutic effects are multifaceted, but in general, these cells are thought to enable damaged tissues to form a balanced inflammatory and regenerative microenvironment in the presence of vigorous inflammation. Studies over the past few years have demonstrated that when exposed to an inflammatory environment, MSCs can orchestrate local and systemic innate and adaptive immune responses through the release of various mediators, including immunosuppressive molecules, growth factors, exosomes, chemokines, complement components and various metabolites. Interestingly, even nonviable MSCs can exert beneficial effects, with apoptotic MSCs showing immunosuppressive functions in vivo. Because the immunomodulatory capabilities of MSCs are not constitutive but rather are licensed by inflammatory cytokines, the net outcomes of MSC activation might vary depending on the levels and the types of inflammation within the residing tissues. Here, we review current understanding of the immunomodulatory mechanisms of MSCs and the issues related to their therapeutic applications.

Comparison of Mesenchymal Stromal Cells From Different Origins for the Treatment of Graft-vs.-Host-Disease in a Humanized Mouse Model

Mesenchymal stromal cells (MSCs) have potent immunomodulatory properties that make them an attractive tool against graft- vs.-host disease (GVHD). However, despite promising results in phase I/II studies, bone marrow (BM-) derived MSCs failed to demonstrate their superiority over placebo in the sole phase III trial reported thus far. MSCs from different tissue origins display different characteristics, but their therapeutic benefits have never been directly compared in GVHD. Here, we compared the impact of BM-, umbilical cord (UC-), and adipose-tissue (AT-) derived MSCs on T-cell function in vitro and assessed their efficacy for the treatment of GVHD induced by injection of human peripheral blood mononuclear cells in NOD-scid IL-2Rγ^null HLA-A2/HHD mice. In vitro, resting BM- and AT-MSCs were more potent than UC-MSCs to inhibit lymphocyte proliferation, whereas UC- and AT-MSCs induced a higher regulatory T-cell (CD4⁺CD25⁺FoxP3⁺)/T helper 17 ratio. Interestingly, AT-MSCs and UC-MSCs activated the coagulation pathway at a higher level than BM-MSCs. In vivo, AT-MSC infusions were complicated by sudden death in 4 of 16 animals, precluding an analysis of their efficacy. Intravenous MSC infusions (UC- or BM- combined) failed to significantly increase overall survival (OS) in an analysis combining data from 80 mice (hazard ratio [HR] = 0.59, 95% confidence interval [CI] 0.32–1.08, P = 0.087). In a sensitivity analysis we also compared OS in control vs. each MSC group separately. The results for the BM-MSC vs. control comparison was HR = 0.63 (95% CI 0.30–1.34, P = 0.24) while the figures for the UC-MSC vs. control comparison was HR = 0.56 (95% CI 0.28–1.10, P = 0.09). Altogether, these results suggest that MSCs from various origins have different effects on immune cells in vitro and in vivo. However, none significantly prevented death from GVHD. Finally, our data suggest that the safety profile of AT-MSC and UC-MSC need to be closely monitored given their pro-coagulant activities in vitro.

Biomechanical Stability and Osteogenesis in a Tibial Bone Defect Treated by Autologous Ovine Cord Blood Cells-A Pilot Study

The aim of this study was to elucidate the impact of autologous umbilical cord blood cells (USSC) on bone regeneration and biomechanical stability in an ovine tibial bone defect. Ovine USSC were harvested and characterized. After 12 months, full-size 2.0 cm mid-diaphyseal bone defects were created and stabilized by an external fixateur containing a rigidity measuring device. Defects were filled with (i) autologous USSC on hydroxyapatite (HA) scaffold (test group), (ii) HA scaffold without cells (HA group), or (iii) left empty (control group). Biomechanical measures, standardized X-rays, and systemic response controls were performed regularly. After six months, bone regeneration was evaluated histomorphometrically and labeled USSC were tracked. In all groups, the torsion distance decreased over time, and radiographies showed comparable bone regeneration. The area of newly formed bone was 82.5 ± 5.5% in the control compared to 59.2 ± 13.0% in the test and 48.6 ± 2.9% in the HA group. Labeled cells could be detected in lymph nodes, liver and pancreas without any signs of tumor formation. Although biomechanical stability was reached earliest in the test group with autologous USSC on HA scaffold, the density of newly formed bone was superior in the control group without any bovine HA.

Concise Review: Exploring Immunomodulatory Features of Mesenchymal Stromal Cells in Humanized Mouse Models

With their immunosuppressive features, human mesenchymal stromal cells (MSCs), sometimes also termed as mesenchymal stem cells, hold great potential as a cell-based therapy for various immune-mediated diseases. Indeed, MSCs have already been approved as a treatment for graft versus host disease. However, contradictory data from clinical trials and lack of conclusive proof of efficacy hinder the progress toward wider clinical use of MSCs and highlight the need for more relevant disease models. Humanized mice are increasingly used as models to study immune-mediated disease, as they simulate human immunobiology more closely than conventional murine models. With further advances in their resemblance to human immunobiology, it is very likely that humanized mice will be used more commonly as models to investigate MSCs with regard to their therapeutic safety and their immunomodulatory effect and its underlying mechanisms. Recent studies that explore the immunosuppressive features of MSCs in humanized mouse models will be discussed in this review. Stem Cells 2019;37:298-305.

Efficacy and safety of mesenchymal stromal cells for the prophylaxis of chronic graft-versus-host disease after allogeneic hematopoietic stem cell transplantation: a meta-analysis of randomized controlled trials

A meta-analysis of randomized controlled trials (RCTs) was conducted to evaluate the efficacy and safety of mesenchymal stromal cells (MSCs) for the prophylaxis of chronic graft-versus-host disease (cGVHD) in patients with hematological malignancies undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Six studies involving 365 patients were included. The pooled results showed that MSCs significantly reduced the incidence of cGVHD (risk ratio [RR] 0.63, 95% confidence interval [CI] 0.46 to 0.86, P = 0.004). Favorable prophylactic effects of MSCs on cGVHD were observed with umbilical cord-derived, high-dose, and late-infusion MSCs, while bone marrow-derived, low-dose, and coinfused MSCs did not confer beneficial prophylactic effects. In addition, MSC infusion did not increase the risk of primary disease relapse and infection (RR 1.02, 95% CI 0.70 to 1.50, P = 0.913; RR 0.89, 95% CI 0.44 to 1.81, P = 0.752; respectively). Moreover, there was an apparent trend toward increased overall survival (OS) in the MSC group compared with that in the control group (RR 1.13, 95% CI 0.98 to 1.29, P = 0.084). In conclusion, this meta-analysis demonstrated that MSC infusion is an effective and safe prophylactic strategy for cGVHD in patients with hematological malignancies undergoing allo-HSCT.

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.

Mesenchymal Stromal Cells in Hematopoietic Stem Cell Transplantation

Mesenchymal stromal cells (MSCs) comprise a heterogeneous population of multipotent cells that can be isolated from various human tissues and cultured ex vivo for clinical use. Thanks to their secretion of growth factors, immunomodulatory properties and cell-to-cell interactions, MSCs play a key role in the regulation of hematopoiesis and in the modulation of immune responses against allo- and autoantigens. In light of these properties, MSCs have been employed in clinical trials in the context of hematopoietic stem cell transplantation (HSCT) to prevent/treat graft rejection and to treat steroid-resistant acute graft-versus-host disease (GvHD). The available clinical evidence derived from these studies indicates that MSC administration is safe; moreover, promising preliminary results in terms of efficacy have been reported in some clinical trials. This chapter focuses on recent advances in MSC therapy by reporting on the most important relevant studies in the field of HSCT.

Optimization of MSC therapeutic strategies for improved GVHD treatment

Mesenchymal stem cells (MSCs) have a powerful immunosuppressive capacity, and they have been used to treat numerous immune diseases, such as refractory graft-versus-host disease. Nevertheless, there are conflicting clinical data. To our knowledge, MSCs from different donors do not share the same qualities and have different immunosuppressive capacities. Infused MSCs are cleared by the recipient’s immune cells or macrophages. Therefore, the MSC therapeutic strategy might be the most important factor that determines treatment success. Repeated infusions would lead to a relatively stable MSC concentration, which would benefit a sustained therapeutic effect. In this review, we focus on the quality of MSCs and the associated therapeutic strategy, as well as other potential variables affecting their utility as a cellular pharmaceutical.

Mechanobiology of mesenchymal stem cells: Which interest for cell-based treatment?

Thanks to their immune properties, the mesenchymal stem cells (MSC) are a promising source for cell therapy. Current clinical trials show that MSC administrated to patients can treat different diseases (graft-versus-host disease (GVHD), liver cirrhosis, systemic lupus, erythematosus, rheumatoid arthritis, type I diabetes…). In this case, the most common mode of cell administration is the intravenous injection, and the hemodynamic environment of cells induced by blood circulation could interfere on their behavior during the migration and homing towards the injured site. After a brief review of the mechanobiology concept, this paper will help in understanding how the mechanical environment could interact with MSC behavior once they are injected to patient in cell-based treatment.

Humanized mouse models: Application to human diseases

Humanized mice are superior to rodents for preclinical evaluation of the efficacy and safety of drug candidates using human cells or tissues. During the past decade, humanized mouse technology has been greatly advanced by the establishment of novel platforms of genetically modified immunodeficient mice. Several human diseases can be recapitulated using humanized mice due to the improved engraftment and differentiation capacity of human cells or tissues. In this review, we discuss current advanced humanized mouse models that recapitulate human diseases including cancer, allergy, and graft-versus-host disease.

Recipient Glycemic Micro-environments Govern Therapeutic Effects of Mesenchymal Stem Cell Infusion on Osteopenia

Therapeutic effects of mesenchymal stem cell (MSC) infusion have been revealed in various human disorders, but impacts of diseased micro-environments are only beginning to be noticed. Donor diabetic hyperglycemia is reported to impair therapeutic efficacy of stem cells. However, whether recipient diabetic condition also affects MSC-mediated therapy is unknown. We and others have previously shown that MSC infusion could cure osteopenia, particularly in ovariectomized (OVX) mice. Here, we discovered impaired MSC therapeutic effects on osteopenia in recipient type 1 diabetes (T1D). Through intensive glycemic control by daily insulin treatments, therapeutic effects of MSCs on osteopenia were maintained. Interestingly, by only transiently restoration of recipient euglycemia using single insulin injection, MSC infusion could also rescue T1D-induced osteopenia. Conversely, under recipient hyperglycemia induced by glucose injection in OVX mice, MSC-mediated therapeutic effects on osteopenia were diminished. Mechanistically, recipient hyperglycemic micro-environments reduce anti-inflammatory capacity of MSCs in osteoporotic therapy through suppressing MSC interaction with T cells via the Adenosine monophosphate-activated protein kinase (AMPK) pathway. We further revealed in diabetic micro-environments, double infusion of MSCs ameliorated osteopenia by anti-inflammation, attributed to the first transplanted MSCs which normalized the recipient glucose homeostasis. Collectively, our findings uncover a previously unrecognized role of recipient glycemic conditions controlling MSC-mediated therapy, and unravel that fulfillment of potent therapeutic effects of MSCs requires tight control of recipient micro-environments.

The Role of Animal Models in the Study of Hematopoietic Stem Cell Transplantation and GvHD: A Historical Overview

Bone marrow transplantation (BMT) is the only therapeutic option for many hematological malignancies, but its applicability is limited by life-threatening complications, such as graft-versus-host disease (GvHD). The last decades have seen great advances in the understanding of BMT and its related complications; in particular GvHD. Animal models are beneficial to study complex diseases, as they allow dissecting the contribution of single components in the development of the disease. Most of the current knowledge on the therapeutic mechanisms of BMT derives from studies in animal models. Parallel to BMT, the understanding of the pathophysiology of GvHD, as well as the development of new treatment regimens, has also been supported by studies in animal models. Pre-clinical experimentation is the basis for deep understanding and successful improvements of clinical applications. In this review, we retrace the history of BMT and GvHD by describing how the studies in animal models have paved the way to the many advances in the field. We also describe how animal models contributed to the understanding of GvHD pathophysiology and how they are fundamental for the discovery of new treatments.

[Efficacy and security of matched unrelated donor hematopoietic stem cell transplant with transfusion of multipotent mesenchymal cells in pediatric severe aplastic anemia]

OBJECTIVE

To observe the efficacy of matched unrelated donor hematopoietic stem cell transplant (HSCT) with transfusion of multipotent mesenchymal cells (MSC) in pediatric severe aplastic anemia (SAA).

METHODS

19 children with SAA received matched unrelated donor HSCT with MSC, and the hematopoietic recovery and transplant-associated complications of these children were monitored.

RESULTS

All patients achieved rapid hematopoietic reconstruction after HSCT, and the median durations to neutrophil and platelet recovery were 12 (9-21) days and 14 (8-24) days respectively, but delayed rejection occurred in one case four months after HSCT. 9 cases developed grade Ⅰ acute graft-versus-host (aGVHD), and one case grade Ⅲ aGVHD and diffuse chronic graft-versus-host. Cytomegalovirus viremias were observed in 15 patients. 2 cases developed hemorrhagic cystitis, 10 children experienced infections. All the children were alive during a median following-up time of 27(8-70) months, one of them developed LPD and received rituximab and chemotherapy, delayed rejection occurred in this patient four months after HSCT, Haplo-identical HSCT from his father as the donor was performed and achieved successful engraftment.

CONCLUSION

The matched unrelated donor HSCT with MSC in pediatric SAA was safe and effective.

Interaction between Mesenchymal Stem Cells and B-Cells

Mesenchymal stem cells (MSCs) are multipotent; non-hematopoietic stem cells. Because of their immunoregulatory abilities; MSCs are widely used for different clinical applications. Compared with that of other immune cells; the investigation of how MSCs specifically regulate B-cells has been superficial and insufficient. In addition; the few experimental studies on this regulation are often contradictory. In this review; we summarize the various interactions between different types or states of MSCs and B-cells; address how different types of MSCs and B-cells affect this interaction and examine how other immune cells influence the regulation of B-cells by MSCs. Finally; we hypothesize why there are conflicting results on the interaction between MSCs and B-cells in the literature.

[Mesenchymal stromal cells in the treatment of graft-versus-host disease: where do we stand?]

Medicinal products based on mesenchymal stromal cells (MSC) are expected to have a therapeutic benefit in a variety of conditions and, accordingly, are being tested in many clinical studies. The treatment and prevention of graft-versus-host disease (GVHD) is one of the world's most widely studied MSC therapy concepts. So far, one MSC medicinal product has been approved for the treatment of GvHD. This article gives an overview of the particular features related to the production of MSC-based medicinal products, the state of non-clinical research, and the clinical development status of MSCs and the associated challenges, especially in the context of GvHD.

Enhancement of the immunoregulatory potency of mesenchymal stromal cells by treatment with immunosuppressive drugs

BACKGROUND AIMS

Multipotent mesenchymal stromal cells (MSCs) are distinguished by their ability to differentiate into a number of stromal derivatives of interest for regenerative medicine, but they also have immunoregulatory properties that are being tested in a number of clinical settings.

METHODS

We show that brief incubations with rapamycin, everolimus, FK506 or cyclosporine A increase the immunosuppressive potency of MSCs and other cell types.

RESULTS

The treated MSCs are up to 5-fold more potent at inhibiting the induced proliferation of T lymphocytes in vitro. We show that this effect probably is due to adsorption of the drug by the MSCs during pre-treatment, with subsequent diffusion into co-cultures at concentrations sufficient to inhibit T-cell proliferation. MSCs contain measurable amounts of rapamycin after a 15-min exposure, and the potentiating effect is blocked by a neutralizing antibody to the drug. With the use of a pre-clinical model of acute graft-versus-host disease, we demonstrate that a low dose of rapamycin-treated but not untreated umbilical cord-derived MSCs significantly inhibit the onset of disease.

CONCLUSIONS

The use of treated MSCs may achieve clinical end points not reached with untreated MSCs and allow for infusion of fewer cells to reduce costs and minimize potential side effects.

Analysis of results of acute graft-versus-host disease prophylaxis with donor multipotent mesenchymal stromal cells in patients with hemoblastoses after allogeneic bone marrow transplantation

Allogeneic bone marrow transplantation (allo-BMT) is currently the only way to cure many hematoproliferative disorders. However, allo-BMT use is limited by severe complications, the foremost being graft-versus-host disease (GVHD). Due to the lack of efficiency of the existing methods of GVHD prophylaxis, new methods are being actively explored, including the use of donors' multipotent mesenchymal stromal cells (MMSC). In this work, we analyzed the results of acute GVHD (aGVHD) prophylaxis by means of MMSC injections after allo-BMT in patients with hematological malignancies. The study included 77 patients. They were randomized into two groups - those receiving standard prophylaxis of aGVHD and those who were additionally infused with MMSC derived from the bone marrow of hematopoietic stem cell donors. We found that the infusion of MMSC halves the incidence of aGVHD and increases the overall survival of patients. Four of 39 MMSC samples were ineffective for preventing aGVHD. Analysis of individual donor characteristics (gender, age, body mass index) and the MMSC properties of these donors (growth parameters, level of expression of 30 genes involved in proliferation, differentiation, and immunomodulation) revealed no significant difference between the MMSC that were effective or ineffective for preventing aGVHD. We used multiple logistic regression to establish a combination of features that characterize the most suitable MMSC samples for the prevention of aGVHD. A model predicting MMSC sample success for aGVHD prophylaxis was constructed. Significant model parameters were increased relative expression of the FGFR1 gene in combination with reduced expression levels of the PPARG and IGF1 genes. Depending on the chosen margin for probability of successful application of MMSC, this model correctly predicts the outcome of the use of MMSC in 82-94% of cases. The proposed model of prospective evaluation of the effectiveness of MMSC samples will enable prevention of the development of aGVHD in the maximal number of patients.

Human mesenchymal stromal cells attenuate graft-versus-host disease and maintain graft-versus-leukemia activity following experimental allogeneic bone marrow transplantation

We sought to define the effects and underlying mechanisms of human, marrow-derived mesenchymal stromal cells (hMSCs) on graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) activity. Irradiated B6D2F1 mice given C57BL/6 BM and splenic T cells and treated with hMSCs had reduced systemic GvHD, donor T-cell expansion, and serum TNFα and IFNγ levels. Bioluminescence imaging demonstrated that hMSCs redistributed from lungs to abdominal organs within 72 hours, and target tissues harvested from hMSC-treated allogeneic BMT (alloBMT) mice had less GvHD than untreated controls. Cryoimaging more precisely revealed that hMSCs preferentially distributed to splenic marginal zones and regulated T-cell expansion in the white pulp. Importantly, hMSCs had no effect on in vitro cytotoxic T-cell activity and preserved potent GvL effects in vivo. Mixed leukocyte cultures containing hMSCs exhibited decreased T-cell proliferation, reduced TNFα, IFNγ, and IL-10 but increased PGE2 levels. Indomethacin and E-prostanoid 2 (EP2) receptor antagonisms both reversed while EP2 agonism restored hMSC-mediated in vitro T-cell suppression, confirming the role for PGE2 . Furthermore, cyclo-oxygenase inhibition following alloBMT abrogated the protective effects of hMSCs. Together, our data show that hMSCs preserve GvL activity and attenuate GvHD and reveal that hMSC biodistribute to secondary lymphoid organs wherein they attenuate alloreactive T-cell proliferation likely through PGE2 induction.

Bottlenecks in the Efficient Use of Advanced Therapy Medicinal Products Based on Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) have been established as promising candidate sources of universal donor cells for cell therapy due to their contributions to tissue and organ homeostasis, repair, and support by self-renewal and multidifferentiation, as well as by their anti-inflammatory, antiproliferative, immunomodulatory, trophic, and proangiogenic properties. Various diseases have been treated by MSCs in animal models. Additionally, hundreds of clinical trials related to the potential benefits of MSCs are in progress. However, although all MSCs are considered suitable to exert these functions, dissimilarities have been found among MSCs derived from different tissues. The same levels of efficacy and desired outcomes have not always been achieved in the diverse studies that have been performed thus far. Moreover, autologous MSCs can be affected by the disease status of patients, compromising their use. Therefore, collecting information regarding the characteristics of MSCs obtained from different sources and the influence of the host (patient) medical conditions on MSCs is important for assuring the safety and efficacy of cell-based therapies. This review provides relevant information regarding factors to consider for the clinical application of MSCs.

Wharton's jelly mesenchymal stromal/stem cells derived under chemically defined animal product-free low oxygen conditions are rich in MSCA-1(+) subpopulation

AIM

Umbilical cord contains, within Wharton's jelly (WJ), multipotent mesenchymal stromal/stem cells (MSCs) of fetal origin that can be isolated and expanded in vitro with a minimal manipulation and very high efficiency. Our aim was to develop a highly reproducible protocol that has the unique potential to be scaled up and adapted to cGMP requirements for the use in cellular therapy.

RESULTS

We found that derivation of WJ MSCs under defined conditions in low oxygen resulted in several folds higher populations of MSCA-1(+) cells (6.0-19.2%) when compared with WJ MSCs derived in the presence of serum (0.1-2.8%) or clinical-grade bone marrow (BM) MSCs cultured under atmospheric O2 (20%). We demonstrate that WJ MSCs derived following our protocol display antiproliferative activity similar to clinical-grade BM MSCs. We also show that these WJ MSCs can be differentiated into adipo-, chondro- and osteo-genic lineages.

CONCLUSION

Easy accessibility, abundance and genetic 'naivety' make WJ MSCs logistically a more attractive source for clinical applications than BM MSCs.

Mesenchymal stromal cells and hematopoietic stem cell transplantation

Mesenchymal stromal cells (MSCs) comprise a heterogeneous population of multipotent cells that can be isolated from various human tissues and culture-expanded ex vivo for clinical use. Due to their immunoregulatory properties and their ability to secrete growth factors, MSCs play a key role in the regulation of hematopoiesis and in the modulation of immune responses against allo- and autoantigens. In light of these properties, MSCs have been employed in clinical trials in the context of hematopoietic stem cell transplantation (HSCT) to facilitate engraftment of hematopoietic stem cells (HSCs) and to prevent graft failure, as well as to treat steroid-resistant acute graft-versus-host disease (GvHD). The available clinical evidence derived from these studies indicates that MSC administration is safe. Moreover, promising preliminary results in terms of efficacy have been reported in some clinical trials, especially in the treatment of acute GvHD. In this review we critically discuss recent advances in MSC therapy by reporting on the most relevant studies in the field of HSCT.

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.

Mesenchymal stem cells in the treatment of inflammatory and autoimmune diseases in experimental animal models

Multipotent mesenchymal stromal cells [also known as mesenchymal stem cells (MSCs)] are currently being studied as a cell-based treatment for inflammatory disorders. Experimental animal models of human immune-mediated diseases have been instrumental in establishing their immunosuppressive properties. In this review, we summarize recent studies examining the effectiveness of MSCs as immunotherapy in several widely-studied animal models, including type 1 diabetes, experimental autoimmune arthritis, experimental autoimmune encephalomyelitis, inflammatory bowel disease, graft-vs-host disease, and systemic lupus erythematosus. In addition, we discuss mechanisms identified by which MSCs mediate immune suppression in specific disease models, and potential sources of functional variability of MSCs between studies.

Mesenchymal stromal cells: sensors and switchers of inflammation

In addition to their stem/progenitor properties, mesenchymal stromal cells (MSCs) possess broad immunoregulatory properties that are being investigated for potential clinical application in treating immune-based disorders. An informed view of the scope of this clinical potential will require a clear understanding of the dynamic interplay between MSCs and the innate and adaptive immune systems. In this Review, we outline current insights into the ways in which MSCs sense and control inflammation, highlighting the central role of macrophage polarization. We also draw attention to functional differences seen between vivo and in vitro contexts and between species. Finally, we discuss progress toward clinical application of MSCs, focusing on GvHD as a case study.

Human placenta-derived adherent cells induce tolerogenic immune responses

Human placenta-derived adherent cells (PDAC cells) are a culture expanded, undifferentiated mesenchymal-like population derived from full-term placental tissue, with immunomodulatory and anti-inflammatory properties. PDA-001 (cenplacel-L), an intravenous formulation of PDAC cells, is in clinical development for the treatment of autoimmune and inflammatory diseases. To elucidate the mechanisms underlying the immunoregulatory properties of PDAC cells, we investigated their effects on immune cell populations, including T cells and dendritic cells (DC) in vitro and in vivo. PDAC cells suppressed T-cell proliferation in an OT-II T-cell adoptive transfer model, reduced the severity of myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis and ameliorated inflammation in a delayed type hypersensitivity response model. In vitro, PDAC cells suppressed T-cell proliferation and inhibited Th1 and Th17 differentiation. Analysis of tissues derived from PDAC cell-treated animals revealed diminished CD86 expression on splenic DC, suggesting that they can also modulate DC populations. Furthermore, PDAC cells modulate the differentiation and maturation of mouse bone marrow-derived DC. Similarly, human DC differentiated from CD14(+) monocytes in the presence of PDAC cells acquired a tolerogenic phenotype. These tolerogenic DC failed to induce allogeneic T-cell proliferation and differentiation toward Th1, but skewed T-cell differentiation toward Th2. Inhibition of cyclo-oxygenase-2 activity resulted in a significant, but not complete, abrogation of PDAC cells' effects on DC phenotype and function, implying a role for prostaglandin E2 in PDAC-mediated immunomodulation. This study identifies modulation of DC differentiation toward immune tolerance as a key mechanism underlying the immunomodulatory activities of PDAC cells.

Bone marrow mesenchymal stromal cells to treat complications following allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a technologically complicated procedure that represents the only cure for many hematologic malignancies. However, HSCT is often complicated by life-threatening toxicities related to the chemo-radiation conditioning regimen, poor engraftment of donor HSCs, the hyperinflammatory syndrome of graft-versus-host disease (GVHD), infection risks from immunosuppression, and end-organ damage. Bone marrow stromal cells (MSCs), also known as "mesenchymal stromal cells," not only play a nurturing role in the hematopoietic microenvironment but also can differentiate into other cell types of mesenchymal origin. MSCs are poorly immunogenic, and they can modulate immunological responses through interactions with a wide range of innate and adaptive immune cells to reduce inflammation. They are easily expanded ex vivo and after infusion, home to sites of injury and inflammation to promote tissue repair. Despite promising early trial results in HSCT with significant responses that have translated into survival benefits, there have been significant barriers to successful commercialization as an off-the-shelf therapy. Current efforts with MSCs in the HSCT setting are geared toward determining the factors determining potency, understanding the precise mechanisms of action in human HSCT, knowing their kinetics and fate, optimizing dose and schedule, incorporating biomarkers as response surrogates, addressing concerns about safety, optimizing clinical trial design, and negotiating the uncharted regulatory landscape for licensable cellular therapy.

Optimization of the therapeutic efficacy of human umbilical cord blood-mesenchymal stromal cells in an NSG mouse xenograft model of graft-versus-host disease

BACKGROUND AIMS

Although in vitro studies have demonstrated the immunosuppressive capacity of mesenchymal stromal cells (MSCs), most in vivo studies on graft-versus-host disease (GVHD) have focused on prevention, and the therapeutic effect of MSCs is controversial. Moreover, optimal time intervals for infusing MSCs have not been established.

METHODS

We attempted to evaluate whether human umbilical cord blood-MSCs (hUCB-MSCs) could either prevent or treat GVHD in an NSG mouse xenograft model by injection of MSCs before or after in vivo clearance. Mice were infused with either a single dose or multiple doses of 5 × 10(5) hUCB-MSCs (3- or 7-day intervals) before or after GVHD onset.

RESULTS

Before onset, hUCB-MSCs significantly improved the survival rate only when repeatedly injected at 3-day intervals. In contrast, single or repeated injections after GVHD onset significantly increased the survival rate and effectively attenuated tissue damage and inflammation. Furthermore, the levels of prostaglandin E2 and transforming growth factor-β1 increased significantly, whereas the level of interferon-γ decreased significantly in all MSC treatment groups.

CONCLUSIONS

These data establish the optimal time intervals for preventing GVHD and show that hUCB-MSCs effectively attenuated symptoms and improved survival rate when administered after the onset of GVDH.