A reproducible immunopotency assay to measure mesenchymal stromal cell-mediated T-cell suppression

Optimisation of a potency assay for the assessment of immunomodulative potential of clinical grade multipotent mesenchymal stromal cells

Clinical use of multipotent Mesenchymal Stromal Cell (MSC)-based medicinal products requires their production in compliance with Good Manufacturing Practices, thus ensuring that the final drug product meets specifications consistently from batch to batch in terms of cell viability, identity, purity and potency. Potency relates to the efficacy of the medicine in its target clinical indication, so adequate release tests need to be defined and validated as quality controls. Herein we report the design and optimisation of parameters affecting the performance of an in vitro cell-based assay for assessing immunomodulatory potential of clinical grade MSC for human use, based on their capacity to inhibit proliferation of T lymphocytes under strong polyclonal stimuli. The resulting method was demonstrated to be reproducible and relatively simple to execute. Two case studies using clinical grade MSC are presented as examples to illustrate the applicability of the methodology described in this work.

The Therapeutic Potential of Stem Cells for Bronchopulmonary Dysplasia: "It's About Time" or "Not so Fast" ?

OBJECTIVE

While the survival of extremely premature infants has improved over the past decades, the rate of complications - especially for bronchopulmonary dysplasia (BPD) - remains unacceptably high. Over the past 50 years, no safe therapy has had a substantial impact on the incidence and severity of BPD.

METHODS

This may stem from the multifactorial disease pathogenesis and the increasing lung immaturity. Mesenchymal Stromal Cells (MSCs) display pleiotropic effects and show promising results in neonatal rodents in preventing or rescuing lung injury without adverse effects. Early phase clinical trials are now underway to determine the safety and efficacy of this therapy in extremely premature infants.

RESULTS AND CONCLUSION

This review summarizes our current knowledge about MSCs, their mechanism of action and the results of preclinical studies that provide the rationale for early phase clinical trials and discuss remaining gaps in our knowledge.

Mitochondrial Oxidative Stress Reduces the Immunopotency of Mesenchymal Stromal Cells in Adults With Coronary Artery Disease

RATIONALE

Mesenchymal stromal cells (MSCs) are promising therapeutic strategies for coronary artery disease; however, donor-related variability in cell quality is a main cause of discrepancies in preclinical studies. In vitro, MSCs from individuals with coronary artery disease have reduced ability to suppress activated T-cells. The mechanisms underlying the altered immunomodulatory capacity of MSCs in the context of atherosclerosis remain elusive.

OBJECTIVE

The aim of this study was to assess the role of mitochondrial dysfunction in the impaired immunomodulatory properties of MSCs from patients with atherosclerosis.

METHODS AND RESULTS

Adipose tissue-derived MSCs were isolated from atherosclerotic (n=38) and nonatherosclerotic (n=42) donors. MSCs:CD4⁺T-cell suppression was assessed in allogeneic coculture systems. Compared with nonatherosclerotic-MSCs, atherosclerotic-MSCs displayed higher levels of both intracellular (P=0.006) and mitochondrial (P=0.03) reactive oxygen species reflecting altered mitochondrial function. The increased mitochondrial reactive oxygen species levels of atherosclerotic-MSCs promoted a phenotypic switch characterized by enhanced glycolysis and an altered cytokine secretion (interleukin-6 P<0.0001, interleukin-8/C-X-C motif chemokine ligand 8 P=0.04, and monocyte chemoattractant protein-1/chemokine ligand 2 P=0.01). Furthermore, treatment of atherosclerotic-MSCs with the reactive oxygen species scavenger N-acetyl-l-cysteine reduced the levels of interleukin-6, interleukin-8/C-X-C motif chemokine ligand 8, and monocyte chemoattractant protein-1/chemokine ligand 2 in the MSC secretome and improved MSCs immunosuppressive capacity (P=0.03).

CONCLUSIONS

An impaired mitochondrial function of atherosclerotic-MSCs underlies their altered secretome and reduced immunopotency. Interventions aimed at restoring the mitochondrial function of atherosclerotic-MSCs improve their in vitro immunosuppressive ability and may translate into enhanced therapeutic efficiency.

Procoagulant activity of human mesenchymal stem cells

BACKGROUND

Allogeneic mesenchymal stem cells (MSCs) show great potential for the treatment of military and civilian trauma based on their reduced immunogenicity and ability to modulate inflammation and immune function in the recipient. Although generally considered to be safe, MSCs express tissue factor (TF), a potent activator of coagulation. In the current study, we evaluated multiple MSC populations for tissue factor expression and procoagulant activity to characterize safety considerations for systemic use of MSCs in trauma patients who may have altered coagulation homeostasis.

METHODS

Multiple MSC populations derived from either human adipose tissue or bone marrow were expanded in the recommended stem cell media. Stem cell identity was confirmed using a well-characterized panel of positive and negative markers. Tissue factor expression on the cell surface was evaluated by flow cytometry with anti-CD142 antibody. Effects on blood coagulation were determined by thromboelastography and calibrated automated thrombogram assays using platelet-poor plasma or whole blood.

RESULTS

Mesenchymal stem cells express tissue factor on their surfaces and are procoagulant in the presence of blood or plasma. The adipose-derived MSCs (Ad-MSC) evaluated were more procoagulant and expressed more tissue factor than bone marrow MSCs (BM-MSCs), which showed a greater variability in TF expression. Bone marrow MSCs were identified that exhibited low procoagulant activity, whereas all Ad-MSCs examined exhibited high procoagulant activity. The percentage of cells in a given population expressing surface tissue factor correlates roughly with functional procoagulant activity. Mesenchymal stem cell tissue factor expression and procoagulant activity change over time in culture.

CONCLUSIONS

All MSC populations are not equivalent; care should be taken to select cells for clinical use that minimize potential safety problems and maximize chance of patient benefit. Adipose-derived MSCs seem more consistently procoagulant than BM-MSCs, presenting a potential safety concern for systemic administration in coagulopathic patients. Donor variation exists between different cell populations, and culture handling conditions may also determine coagulation activity. Cells must be routinely monitored during preparation to ensure that they retain the desired characteristics before patient administration.

Omental adipose tissue is a more suitable source of canine Mesenchymal stem cells

Background

Mesenchymal Stem Cells (MSCs) are a promising therapeutic tool in veterinary medicine. Currently the subcutaneous adipose tissue is the leading source of MSCs in dogs. MSCs derived from distinct fat depots have shown dissimilarities in their accessibility and therapeutic potential. The aims of our work were to determine the suitability of omental adipose tissue as a source of MSCs, according to sampling success, cell yield and paracrine properties of isolated cells, and compared to subcutaneous adipose tissue.

Results

While sampling success of omental adipose tissue was 100% (14 collections from14 donors) for subcutaneous adipose tissue it was 71% (10 collections from 14 donors). MSCs could be isolated from both sources. Cell yield was significantly higher for omental than for subcutaneous adipose tissue (38 ± 1 vs. 30 ± 1 CFU-F/g tissue, p < 0.0001). No differences were observed between sources regarding cell proliferation potential (73 ± 1 vs. 74 ± 1 CDPL) and cell senescence (at passage 10, both cultures presented enlarged cells with cytoplasmic vacuoles and cellular debris). Omental- and subcutaneous-derived MSCs expressed at the same level bFGF, PDGF, HGF, VEGF, ANG1 and IL-10. Irrespective of the source, isolated MSCs induced proliferation, migration and vascularization of target cells, and inhibited the activation of T lymphocytes.

Conclusion

Compared to subcutaneous adipose tissue, omental adipose tissue is a more suitable source of MSCs in dogs. Since it can be procured from donors with any body condition, its collection procedure is always feasible, its cell yield is high and the MSCs isolated from it have desirable differentiation and paracrine potentials.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1053-0) contains supplementary material, which is available to authorized users.

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.

Manufacturing Differences Affect Human Bone Marrow Stromal Cell Characteristics and Function: Comparison of Production Methods and Products from Multiple Centers

Human bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) are manufactured using many different methods, but little is known about the spectrum of manufacturing methods used and their effects on BMSC characteristics and function. Seven centers using, and one developing, Good Manufacturing Practices (GMP) processes were surveyed as to their production methods. Among the seven centers, all used marrow aspirates as the starting material, but no two centers used the same manufacturing methods. Two to four BMSC lots from each center were compared using global gene expression. Among the twenty-four BMSC lots from the eight centers intra-center transcriptome variability was low and similar among centers. Principal component analysis and unsupervised hierarchical clustering analysis separated all the lots from five centers into five distinct clusters. BMSCs from six of the eight centers were tested for their ability to form bone and support hematopoiesis by in vivo transplantation (defining features of BMSCs). Those from all six centers tested formed bone, but the quantity formed was highly variable and BMSCs from only three centers supported hematopoiesis. These results show that differences in manufacturing resulted in variable BMSC characteristics including their ability to form bone and support hematopoiesis.

Immunosuppressive capacity of mesenchymal stem cells correlates with metabolic activity and can be enhanced by valproic acid

BACKGROUND

Mesenchymal stem cells (MSCs) have entered the clinic as an Advanced Therapy Medicinal Product and are currently evaluated in a wide range of studies for tissue regeneration or in autoimmune disorders. Various efforts have been made to standardize and optimize expansion and manufacturing processes, but until now reliable potency assays for the final MSC product are lacking. Because recent findings suggest superior therapeutic efficacy of freshly administered MSCs in comparison with frozen cells, we sought to correlate the T-cell suppressive capacity of MSCs with their metabolic activity.

METHODS

Human MSCs were obtained from patients' bone fragments and were employed in coculture with peripheral blood mononuclear cells (PBMCs) in an allogeneic T-cell proliferation assay to measure immunosuppressive function. Metabolic activity of MSCs was measured in real time in terms of aerobic glycolysis quantified by the extracellular acidification rate and mitochondrial respiration quantified by the oxygen consumption rate.

RESULTS

We show that MSC-induced suppression of T-cell proliferation was highly dependent on individual healthy donors' lymphocytes. Moreover, coculture with PBMCs increased the glycolytic and respiratory activity of MSCs considerably in a PBMC donor-dependent manner. The twofold to threefold enhancement of cell metabolism was accompanied by higher T-cell suppressive capacities of MSCs. The cryoprotectant dimethyl sulfoxide decreased metabolic and immunosuppressive performances of MSCs while valproic acid (VPA) increased their glycolytic, respiratory and T-cell suppressive capacity.

CONCLUSIONS

Functional fitness of MSCs can be determined by measuring metabolic activity and can be enhanced by exposure to VPA. Pretesting the increment of metabolic activity upon interaction of donor MSCs with patient T-cells provides a rational approach for an individualized potency assay prior to MSC therapy.

Morphological features of IFN-γ-stimulated mesenchymal stromal cells predict overall immunosuppressive capacity

Human mesenchymal stromal cell (MSC) lines can vary significantly in their functional characteristics, and the effectiveness of MSC-based therapeutics may be realized by finding predictive features associated with MSC function. To identify features associated with immunosuppressive capacity in MSCs, we developed a robust in vitro assay that uses principal-component analysis to integrate multidimensional flow cytometry data into a single measurement of MSC-mediated inhibition of T-cell activation. We used this assay to correlate single-cell morphological data with overall immunosuppressive capacity in a cohort of MSC lines derived from different donors and manufacturing conditions. MSC morphology after IFN-γ stimulation significantly correlated with immunosuppressive capacity and accurately predicted the immunosuppressive capacity of MSC lines in a validation cohort. IFN-γ enhanced the immunosuppressive capacity of all MSC lines, and morphology predicted the magnitude of IFN-γ-enhanced immunosuppressive activity. Together, these data identify MSC morphology as a predictive feature of MSC immunosuppressive function.

A Proinflammatory Secretome Mediates the Impaired Immunopotency of Human Mesenchymal Stromal Cells in Elderly Patients with Atherosclerosis

Inflammation plays a pivotal role in the initiation and progression of atherosclerosis (ATH). Due to their potent immunomodulatory properties, mesenchymal stromal cells (MSCs) are evaluated as therapeutic tools in ATH and other chronic inflammatory disorders. Aging reduces MSCs immunopotency potentially limiting their therapeutic utility. The mechanisms that mediate the effect of age on MSCs immune-regulatory function remain elusive and are the focus of this study. Human adipose tissue-derived MSCs were isolated from patients undergoing coronary artery bypass graft surgery. MSCs:CD4⁺ T-cell suppression, a readout of MSCs' immunopotency, was assessed in allogeneic coculture systems. MSCs from elderly subjects were found to exhibit a diminished capacity to suppress the proliferation of activated T cells. Soluble factors and, to a lesser extent, direct cell-cell contact mechanisms mediated the MSCs:T-cell suppression. Elderly MSCs exhibited a pro-inflammatory secretome with increased levels of interleukin-6 (IL-6), IL-8/CXCL8, and monocyte chemoattractant protein-1 (MCP-1/CCL2). Neutralization of these factors enhanced the immunomodulatory function of elderly MSCs. In summary, our data reveal that in contrast to young MSCs, MSCs from elderly individuals with ATH secrete high levels of IL-6, IL-8/CXCL8 and MCP-1/CCL2 which mediate their reduced immunopotency. Consequently, strategies aimed at targeting pro-inflammatory cytokines/chemokines produced by MSCs could enhance the efficacy of autologous cell-based therapies in the elderly. Stem Cells Translational Medicine 2017;6:1132-1140.

Generation of mesenchymal stromal cells from cord blood: evaluation of in vitro quality parameters prior to clinical use

BACKGROUND

Increasing evidence suggests the safety and efficacy of mesenchymal stromal cells (MSC) as advanced therapy medicinal products because of their immunomodulatory properties and supportive role in hematopoiesis. Although bone marrow remains the most common source for obtaining off-the-shelf MSC, cord blood (CB) represents an alternative source, which can be collected noninvasively and without major ethical concerns. However, the low estimated frequency and inconsistency of successful isolation represent open challenges for the use of CB-derived MSC in clinical trials. This study explores whether CB may represent a suitable source of MSC for clinical use and analyzes several in vitro parameters useful to better define the quality of CB-derived MSC prior to clinical application.

METHODS

CB units (n = 50) selected according to quality criteria (CB volume ≥ 20 ml, time from collection ≤ 24 h) were cultured using a standardized procedure for CB-MSC generation. MSC were analyzed for their growth potential and secondary colony-forming capacity. Immunophenotype and multilineage differentiation potential of culture-expanded CB-MSC were assessed to verify MSC identity. The immunomodulatory activity at resting conditions and after inflammatory priming (IFN-γ-1b and TNF-α for 48 hours) was explored to assess the in vitro potency of CB-MSC prior to clinical application. Molecular karyotyping was used to assess the genetic stability after prolonged MSC expansion.

RESULTS

We were able to isolate MSC colonies from 44% of the processed units. Our results do not support a role of CB volume in determining the outcome of the cultures, in terms of both isolation and proliferative capacity of CB-MSC. Particularly, we have confirmed the existence of two different CB-MSC populations named short- and long-living (SL- and LL-) CBMSC, clearly diverging in their growth capacity and secondary colony-forming efficiency. Only LL-CBMSC were able to expand consistently and to survive for longer periods in vitro, while preserving genetic stability. Therefore, they may represent interesting candidates for therapeutic applications. We have also observed that LL-CBMSC were not equally immunosuppressive, particularly after inflammatory priming and despite upregulating priming-inducible markers.

CONCLUSIONS

This work supports the use of CB as a potential MSC source for clinical applications, remaining more readily available compared to conventional sources. We have provided evidence that not all LL-CBMSC are equally immunosuppressive in an inflammatory environment, suggesting the need to include the assessment of potency among the release criteria for each CB-MSC batch intended for clinical use, at least for the treatment of immune disorders as GvHD.

Cardiopulmonary and histological characterization of an acute rat lung injury model demonstrating safety of mesenchymal stromal cell infusion

BACKGROUND AIMS

In the field of cellular therapy, potential cell entrapment in the lungs following intravenous administration in a compromised or injured pulmonary system is an important concern that requires further investigation. We developed a rat model of inflammatory and fibrotic lung disease to mimic the human clinical condition of obliterative bronchiolitis (OB) and evaluate the safety of intravenous infusion of mesenchymal stromal cells (MSCs). This model was used to obtain appropriate safety information and functional characterization to support the translation of an ex vivo-generated cellular product into human clinical trials. To overcome spontaneous recovery and size limitations associated with current animal models, we used a novel multiple dose bleomycin strategy to induce lasting lung injury in rats.

METHODS

Intratracheal instillation of bleomycin was administered to rats on multiple days. MSCs were intravenously infused 7 days apart. Detailed pulmonary function tests including forced expiratory volume, total lung capacity, and invasive hemodynamic measurements were conducted to define the representative disease model and monitor cardiopulmonary hemodynamic consequences of the cell infusion. Post-euthanasia assessments included a thorough evaluation of lung morphology and histopathology.

RESULTS

The double dose bleomycin instillation regimen resulted in severe and irreversible lung injury and fibrosis. Cardiopulmonary physiological monitoring reveled that no adverse events could be attributed to the cell infusion process.

DISCUSSION

Although our study did not show the infusion of MSCs to result in an improvement in lung function or rescue of damaged tissue this study does confirm the safety of MSC infusion into damaged lungs.

Mesenchymal stromal cells and immunomodulation: A gathering of regulatory immune cells

Because of their well-recognized immunomodulatory properties, mesenchymal stromal cells (MSCs) represent an attractive cell population for therapeutic purposes. In particular, there is growing interest in the use of MSCs as cellular immunotherapeutics for tolerance induction in allogeneic transplantations and the treatment of autoimmune diseases. However, multiple mechanisms have been identified to mediate the immunomodulatory effects of MSCs, sometimes with several ambiguities and inconsistencies. Although published studies have mainly reported the role of soluble factors, we believe that a sizeable cellular component plays a critical role in MSC immunomodulation. We refer to these cells as regulatory immune cells, which are generated from both the innate and adaptive responses after co-culture with MSCs. In this review, we discuss the nature and role of these immune regulatory cells as well as the role of different mediators, and, in particular, regulatory immune cell induction by MSCs through interleukin-10. Once induced, immune regulatory cells accumulate and converge their regulatory pathways to create a tolerogenic environment conducive for immunomodulation. Thus, a better understanding of these regulatory immune cells, in terms of how they can be optimally manipulated and induced, would be suitable for improving MSC-based immunomodulatory therapeutic strategies.

Autologous Bone Marrow-Derived Mesenchymal Stem Cells Modulate Molecular Markers of Inflammation in Dogs with Cruciate Ligament Rupture

Mid-substance rupture of the canine cranial cruciate ligament rupture (CR) and associated stifle osteoarthritis (OA) is an important veterinary health problem. CR causes stifle joint instability and contralateral CR often develops. The dog is an important model for human anterior cruciate ligament (ACL) rupture, where rupture of graft repair or the contralateral ACL is also common. This suggests that both genetic and environmental factors may increase ligament rupture risk. We investigated use of bone marrow-derived mesenchymal stem cells (BM-MSCs) to reduce systemic and stifle joint inflammatory responses in dogs with CR. Twelve dogs with unilateral CR and contralateral stable partial CR were enrolled prospectively. BM-MSCs were collected during surgical treatment of the unstable CR stifle and culture-expanded. BM-MSCs were subsequently injected at a dose of 2x10⁶ BM-MSCs/kg intravenously and 5x10⁶ BM-MSCs by intra-articular injection of the partial CR stifle. Blood (entry, 4 and 8 weeks) and stifle synovial fluid (entry and 8 weeks) were obtained after BM-MSC injection. No adverse events after BM-MSC treatment were detected. Circulating CD8⁺ T lymphocytes were lower after BM-MSC injection. Serum C-reactive protein (CRP) was decreased at 4 weeks and serum CXCL8 was increased at 8 weeks. Synovial CRP in the complete CR stifle was decreased at 8 weeks. Synovial IFNγ was also lower in both stifles after BM-MSC injection. Synovial/serum CRP ratio at diagnosis in the partial CR stifle was significantly correlated with development of a second CR. Systemic and intra-articular injection of autologous BM-MSCs in dogs with partial CR suppresses systemic and stifle joint inflammation, including CRP concentrations. Intra-articular injection of autologous BM-MSCs had profound effects on the correlation and conditional dependencies of cytokines using causal networks. Such treatment effects could ameliorate risk of a second CR by modifying the stifle joint inflammatory response associated with cranial cruciate ligament matrix degeneration or damage.

Biodistribution and Clearance of Human Mesenchymal Stem Cells by Quantitative Three-Dimensional Cryo-Imaging After Intravenous Infusion in a Rat Lung Injury Model

To study three-dimensional (3D) cryo-imaging to measure cell biodistribution and clearance after intravenous infusion, the authors established a lung injury model in rats. Human mesenchymal stem cells (hMSCs) labeled with QTracker were infused via jugular vein. Organs were cryopreserved, followed by 3D cryo-imaging. At 60 minutes, 82 ± 9.7% of cells were detected, and at day 2, 0.06% of cells were detected. hMSCs were retained primarily in the liver, with fewer detected in lungs and spleen.

Cell tracking is a critical component of the safety and efficacy evaluation of therapeutic cell products. To date, cell-tracking modalities have been hampered by poor resolution, low sensitivity, and inability to track cells beyond the shortterm. Three-dimensional (3D) cryo-imaging coregisters fluorescent and bright-field microcopy images and allows for single-cell quantification within a 3D organ volume. We hypothesized that 3D cryo-imaging could be used to measure cell biodistribution and clearance after intravenous infusion in a rat lung injury model compared with normal rats. A bleomycin lung injury model was established in Sprague-Dawley rats (n = 12). Human mesenchymal stem cells (hMSCs) labeled with QTracker655 were infused via jugular vein. After 2, 4, or 8 days, a second dose of hMSCs labeled with QTracker605 was infused, and animals were euthanized after 60, 120, or 240 minutes. Lungs, liver, spleen, heart, kidney, testis, and intestine were cryopreserved, followed by 3D cryo-imaging of each organ. At 60 minutes, 82% ± 9.7% of cells were detected; detection decreased to 60% ± 17% and 66% ± 22% at 120 and 240 minutes, respectively. At day 2, 0.06% of cells were detected, and this level remained constant at days 4 and 8 postinfusion. At 60, 120, and 240 minutes, 99.7% of detected cells were found in the liver, lungs, and spleen, with cells primarily retained in the liver. This is the first study using 3D cryo-imaging to track hMSCs in a rat lung injury model. hMSCs were retained primarily in the liver, with fewer detected in lungs and spleen.

Significance

Effective bench-to-bedside clinical translation of cellular therapies requires careful understanding of cell fate through tracking. Tracking cells is important to measure cell retention so that delivery methods and cell dose can be optimized and so that biodistribution and clearance can be defined to better understand potential off-target toxicity and redosing strategies. This article demonstrates, for the first time, the use of three-dimensional cryo-imaging for single-cell quantitative tracking of intravenous infused clinical-grade mesenchymal stem cells in a clinically relevant model of lung injury. The important information learned in this study will help guide future clinical and translational stem cell therapies for lung injuries.

Effects of Oxidative Stress on Mesenchymal Stem Cell Biology

Mesenchymal stromal/stem cells (MSCs) are multipotent stem cells present in most fetal and adult tissues. Ex vivo culture-expanded MSCs are being investigated for tissue repair and immune modulation, but their full clinical potential is far from realization. Here we review the role of oxidative stress in MSC biology, as their longevity and functions are affected by oxidative stress. In general, increased reactive oxygen species (ROS) inhibit MSC proliferation, increase senescence, enhance adipogenic but reduce osteogenic differentiation, and inhibit MSC immunomodulation. Furthermore, aging, senescence, and oxidative stress reduce their ex vivo expansion, which is critical for their clinical applications. Modulation of sirtuin expression and activity may represent a method to reduce oxidative stress in MSCs. These findings have important implications in the clinical utility of MSCs for degenerative and immunological based conditions. Further study of oxidative stress in MSCs is imperative in order to enhance MSC ex vivo expansion and in vivo engraftment, function, and longevity.

Fibroblasts and Mesenchymal Stromal/Stem Cells Are Phenotypically Indistinguishable

BACKGROUND/AIMS

Human mesenchymal stromal/stem cells (MSCs), derived from many different tissues, are characterized by a fibroblast-like morphology, the expression of certain cell surface markers and their ability to differentiate into adipocytes, chondrocytes and osteoblasts. A number of studies have shown that MSCs share many characteristics with fibroblasts; however, there is no well-defined set of phenotypic characteristics that could distinguish between these 2 types of cells.

METHODS

We used 4 well-established human fibroblast strains from 3 different tissue sources and several human MSC strains from 2 different tissue sources to compare the phenotypic and immunological characteristics of these cells.

RESULTS

Fibroblast strains had a similar morphology to MSCs, expressed the same cell surface markers as MSCs and could also differentiate into adipocytes, chondrocytes and osteoblasts. Also, similar to MSCs, these fibroblasts were capable of suppressing T cell proliferation and modulating the immunophenotype of macrophages. We also show that MSCs deposit extracellular matrices of collagen type I and fibronectin, and express FSP1 in patterns similar to fibroblasts.

CONCLUSIONS

Based on currently accepted definitions for cultured human MSCs and fibroblasts, we could not find any immunophenotypic property that could make a characteristic distinction between MSCs and fibroblasts.

A robust potency assay highlights significant donor variation of human mesenchymal stem/progenitor cell immune modulatory capacity and extended radio-resistance

The inherent immunomodulatory capacity of mesenchymal stem/progenitor cells (MSPCs) encouraged initiation of multiple clinical trials. Release criteria for therapeutic MSPCs cover identity, purity and safety but appropriate potency assessment is often missing. Reports on functional heterogeneity of MSPCs created additional uncertainty regarding donor and organ/source selection. We established a robust immunomodulation potency assay based on pooling responder leukocytes to minimize individual immune response variability. Comparing various MSPCs revealed significant potency inconsistency and generally diminished allo-immunosuppression compared to dose-dependent inhibition of mitogenesis. Gamma-irradiation to block unintended MSPC proliferation did not prohibit chondrogenesis and osteogenesis in vivo, indicating the need for alternative safety strategies.

Immunomodulatory properties and in vivo osteogenesis of human dental stem cells from fresh and cryopreserved dental follicles

In our previous study, dental follicle tissues from extracted wisdom teeth were successfully cryopreserved for use as a source of stem cells. The goals of the present study were to investigate the immunomodulatory properties of stem cells from fresh and cryopreserved dental follicles (fDFCs and cDFCs, respectively) and to analyze in vivo osteogenesis after transplantation of these DFCs into experimental animals. Third passage fDFCs and cDFCs showed similar expression levels of interferon-γ receptor (CD119) and major histocompatibility complex class I and II (MHC I and MHC II, respectively), with high levels of CD119 and MHC I and nearly no expression of MHC II. Both fresh and cryopreserved human DFCs (hDFCs) were in vivo transplanted along with a demineralized bone matrix scaffold into mandibular defects in miniature pigs and subcutaneous tissues of mice. Radiological and histological evaluations of in vivo osteogenesis in hDFC-transplanted sites revealed significantly enhanced new bone formation activities compared with those in scaffold-only implanted control sites. Interestingly, at 8 weeks post-hDFC transplantation, the newly generated bones were overgrown compared to the original size of the mandibular defects, and strong expression of osteocalcin and vascular endothelial growth factor were detected in the hDFCs-transplanted tissues of both animals. Immunohistochemical analysis of CD3, CD4, and CD8 in the ectopic bone formation sites of mice showed significantly decreased CD4 expression in DFCs-implanted tissues compared with those in control sites. These findings indicate that hDFCs possess immunomodulatory properties that involved inhibition of the adaptive immune response mediated by CD4 and MHC II, which highlights the usefulness of hDFCs in tissue engineering. In particular, long-term preserved dental follicles could serve as an excellent autologous or allogenic stem cell source for bone tissue regeneration as well as a valuable therapeutic agent for immune diseases.

Quantitative activation suppression assay to evaluate human bone marrow-derived mesenchymal stromal cell potency

BACKGROUND AIMS

With the increasing use of cell therapies involving immune modulatory cells, there is a need for a simple standardized method to evaluate and compare the suppressive potency of different cell products. We used the Karpas 299 (K299) cell line as the reference suppressor cell to develop a standardized suppression assay to quantify the immune-modulatory capacity of bone marrow-derived mesenchymal stromal cells (BM-MSCs).

METHODS

Healthy donor CD4 T cells were co-cultured with the K299 cell line or with third-party BM-MSCs. After stimulation with anti-CD3/CD28 beads, CD154 activation and proliferation of CD4 T cells were measured to calculate suppression.

RESULTS

The K299 cell line reproducibly suppressed both the activation and proliferation of healthy donor CD4 T cells in a dose-dependent manner. A rapid (16-h) assay that was based on activation-suppression was selected for development. In replicate testing, there was an inherent variability of suppression of 11% coefficient of variation between different responder T cells. Suppression by BM-MSCs on different responders correlated with suppression by K299. We therefore used K299 suppression as the reference to define suppression potency of BM-MSCs in K299 Suppression Units. We found that inter-donor variability, passage number, method of manufacture and exposure of BM-MSCs to steroids or interferon-γ all affected BM-MSC potency of suppression.

CONCLUSIONS

This method provides a platform for standardizing suppressor function to facilitate comparisons between laboratories and for use as a cell product release assay.

Age, atherosclerosis and type 2 diabetes reduce human mesenchymal stromal cell-mediated T-cell suppression

To this end human MSCs were isolated from adipose tissue and the MSC:CD4⁺ T-cell suppression was assessed in a co-culture system. In summary, this study demonstrates that advanced age, atherosclerosis and type 2 diabetes mellitus reduce the functional potency of MSCs. Optimizing the criteria for the selection of MSC donors could enhance the results of cell-based therapies.