The challenge of defining mesenchymal stromal cell potency assays and their potential use as release criteria

Wharton's jelly mesenchymal stem cells: Future regenerative medicine for clinical applications in mitigation of radiation injury

Wharton's jelly mesenchymal stem cells (WJ-MSCs) are gaining significant attention in regenerative medicine for their potential to treat degenerative diseases and mitigate radiation injuries. WJ-MSCs are more naïve and have a better safety profile, making them suitable for both autologous and allogeneic transplantations. This review highlights the regenerative potential of WJ-MSCs and their clinical applications in mitigating various types of radiation injuries. In this review, we will also describe why WJ-MSCs will become one of the most probable stem cells for future regenerative medicine along with a balanced view on their strengths and weaknesses. Finally, the most updated literature related to both preclinical and clinical usage of WJ-MSCs for their potential application in the regeneration of tissues and organs will also be compiled.

Evaluation of the Precision of Kinetic Stem Cell (KSC) Counting for Specific Quantification of Human Mesenchymal Stem Cells in Heterogeneous Tissue Cell Preparations

Kinetic stem cell (KSC) counting is a recently introduced first technology for quantifying tissue stem cells in vertebrate organ and tissue cell preparations. Previously, effective quantification of the fraction or dosage of tissue stem cells had been largely lacking in stem cell science and medicine. A general method for the quantification of tissue stem cells will accelerate progress in both of these disciplines as well as related industries like drug development. Triplicate samples of human oral alveolar bone cell preparations, which contain mesenchymal stem cells (MSCs), were used to estimate the precision of KSC counting analyses conducted at three independent sites. A high degree of intra-site precision was found, with coefficients of variation for determinations of MSC-specific fractions of 8.9% (p < 0.003), 13% (p < 0.006), and 25% (p < 0.02). The estimates of inter-site precision, 11% (p < 0.0001) and 26% (p < 0.0001), also indicated a high level of precision. Results are also presented to show the ability of KSC counting to define cell subtype-specific kinetics factors responsible for changes in the stem cell fraction during cell culture. The presented findings support the continued development of KSC counting as a new tool for advancing stem cell science and medicine.

Quantification of the Culture Stability of Stem Cell Fractions from Oral-Derived, Human Mesenchymal Stem Cell Preparations: A Significant Step toward the Clinical Translation of Cell Therapies

A continuing limitation and major challenge in the development and utilization of predictable stem cell therapies (SCTs) is the determination of the optimal dosages of stem cells. Herein, we report the quantification of stem cell fractions (SCF) of human mesenchymal stem cell (MSC) preparations derived from oral tissues. A novel computational methodology, kinetic stem cell (KSC) counting, was used to quantify the SCF and specific cell culture kinetics of stem cells in oral alveolar bone-derived MSC (aBMSCs) from eight patients. These analyses established, for the first time, that the SCF within these heterogeneous, mixed-cell populations differs significantly among donors, ranging from 7% to 77% (ANOVA p < 0.0001). Both the initial SCF of aBMSC preparations and changes in the level of the SCF with serial culture over time showed a high degree of inter-donor variation. Hence, it was revealed that the stability of the SCF of human aBMSC preparations during serial cell culture shows inter-donor variation, with some patient preparations exhibiting sufficient stability to support the long-term net expansion of stem cells. These findings provide important insights for the clinical-scale expansion and biomanufacturing of MSCs, which can facilitate establishing more effective and predictable outcomes in clinical trials and treatments employing SCT.

Advanced Technologies for Potency Assay Measurement

Crucial for their application, cell products need to be well-characterized in the cell manufacturing facilities and conform to regulatory approval criteria before infusion into the patients. Mesenchymal Stromal Cells (MSCs) are the leading cell therapy candidate in clinical trials worldwide. Early phase clinical trials have demonstrated that MSCs display an excellent safety profile and are well tolerated. However, MSCs have also exhibited contradictory efficacy in later-phase clinical trials with reasons for this discrepancy including poorly understood mechanism of MSC therapeutic action. With likelihood that a number of attributes are involved in MSC derived clinical benefit, an assay that measures a single quality of may not adequately reflect potency, thus a combination of bioassays and analytical methods, collectively called "assay matrix" are favoured for defining the potency of MSC more adequately. This chapter highlights advanced technologies and targets that can achieve quantitative measurement for a range of MSC attributes, including immunological, genomic, secretome, phosphorylation, morphological, biomaterial, angiogenic and metabolic assays.

Conglomeration of T- and B-Cell Matrix Responses Determines the Potency of Human Bone Marrow Mesenchymal Stromal Cells

Cell manufacturing facilities need to define the potency of mesenchymal stromal cells (MSCs) as cellular therapeutics in advanced clinical trials or marketing approval. Since MSCs' mechanism of action in humans is not well defined, more than a single functional property of MSCs needs to be captured as a surrogate measure of potency utilizing assay matrix technologies. However, the current limitation is the sole investigation of MSC-mediated T-cell suppression as a surrogate measure of potency. We investigated the effect of MSCs on B-cell matrix responses to be incorporated into the assay matrix potency analytical system. Our results demonstrate that MSCs inhibit B-cell differentiation and block pan-antibody secretion upon activation of B cells in the PBMCs. In contrast, MSCs are inferior in blocking B-cell matrix responses when purified B cells are used. Mechanistic analysis has demonstrated that MSC-mediated inhibition of B-cell matrix responses is non-contact dependent and Tryptophan metabolic pathway plays a major role, akin to the mechanism of MSC-mediated T-cell suppression. MSCs also inhibit both T-cell and B-cell responses when both of these lymphoid populations are concurrently activated in the PBMCs. Secretome analysis of MSC and T/B cell-activated PBMC cocultures identified direct and inverse correlative matrix signatures between humoral antibody isotypes and secretory molecules. The current analysis of the combined and concomitant investigation of T-cell and B-cell matrix responses fulfills the potency assay matrix strategy by incorporating MSCs' interaction with more than a single inflammatory immune responder.

Practical Considerations for Translating Mesenchymal Stromal Cell-Derived Extracellular Vesicles from Bench to Bed

Extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) have shown potential for the treatment of tendon and ligament injuries. This approach can eliminate the need to transplant live cells to the human body, thereby reducing issues related to the maintenance of cell viability and stability and potential erroneous differentiation of transplanted cells to bone or tumor. Despite these advantages, there are practical issues that need to be considered for successful clinical application of MSC-EV-based products in the treatment of tendon and ligament injuries. This review aims to discuss the general and tissue-specific considerations for manufacturing MSC-EVs for clinical translation. Specifically, we will discuss Good Manufacturing Practice (GMP)-compliant manufacturing and quality control (parent cell source, culture conditions, concentration method, quantity, identity, purity and impurities, sterility, potency, reproducibility, storage and formulation), as well as safety and efficacy issues. Special considerations for applying MSC-EVs, such as their compatibility with arthroscopy for the treatment of tendon and ligament injuries, are also highlighted.

Hypoxia-Inducible Non-coding RNAs in Mesenchymal Stem Cell Fate and Regeneration

Mesenchymal stem cells (MSCs) can differentiate into multiple cell lines, which makes them an important source of cells for tissue engineering applications. They are defined by the capability to renew themselves and maintain pluripotency. This ability is modulated by the balance between complex cues from cellular microenvironment. Self-renewal and differentiation abilities are regulated by particular microenvironmental signals. Oxygen is considered to be an important part of cell microenvironment, which not only acts as a metabolic substrate but also a signal molecule. It has been proved that MSCs are hypoxic in the physiological environment. Signals from MSCs' microenvironment or niche which means the anatomical location of the MSCs, maintain the final properties of MSCs. Physiological conditions like oxygen tension are deemed to be a significant part of the mesenchymal stem cell niche, and have been proved to be involved in modulating embryonic and adult MSCs. Non-coding RNAs (ncRNAs), which play a key role in cell signal transduction, transcription and translation of genes, have been widely concerned as epigenetic regulators in a great deal of tissues. With the rapid development of bioinformatics analysis tools and high-throughput RNA sequencing technology, more and more evidences show that ncRNAs play a key role in tissue regeneration. It shows potential as a biomarker of MSC differentiation. In this paper, we reviewed the physiological correlation of hypoxia as a unique environmental parameter which is conducive to MSC expansion and maintenance, discussed the correlation of tissue engineering, and summarized the influence of hypoxia related ncRNAs on MSCs' fate and regeneration. This review will provide reference for future research of MSCs' regeneration.

Strategies to address mesenchymal stem/stromal cell heterogeneity in immunomodulatory profiles to improve cell-based therapies

Mesenchymal stromal cells (MSCs) have gained immense attention over the past two decades due to their multipotent differentiation potential and pro-regenerative and immunomodulatory cytokine secretory profiles. Their ability to modulate the host immune system and promote tolerance has prompted several allogeneic and autologous hMSC-based clinical trials for the treatment of graft-versus-host disease and several other immune-induced disorders. However, clinical success beyond safety is still controversial and highly variable, with inconclusive therapeutic benefits and little mechanistic explanation. This clinical variability has been broadly attributed to inconsistent MSC sourcing, phenotypic characterization, variable potency, and non-standard isolation protocols, leading to functional heterogeneity among administered MSCs. Homogeneous MSC populations are proposed to yield more predictable, reliable biological responses and clinically meaningful properties relevant to cell-based therapies. Limited comparisons of heterogeneous MSCs with homogenous MSCs are reported. This review addresses this gap in the literature with a critical analysis of strategies aimed at decreasing MSC heterogeneity concerning their reported immunomodulatory profiles. STATEMENT OF SIGNIFICANCE: This review collates, summarizes, and critically analyzes published strategies that seek to improve homogeneity in immunomodulatory functioning MSC populations intended as cell therapies to treat immune-based disorders, such as graft-vs-host-disease. No such review for MSC therapies, immunomodulatory profiles and cell heterogeneity analysis is published. Since MSCs represent the most clinically studied experimental cell therapy platform globally for which there remains no US domestic marketing approval, insights into MSC challenges in therapeutic product development are imperative to providing solutions for immunomodulatory variabilities.

Macrophages at the nexus of mesenchymal stromal cell potency: The emerging role of chemokine cooperativity

Pharmacological depletion of macrophages in vivo with liposomal clodronate renders mice unresponsive to adoptive transfer of mesenchymal stromal cells (MSCs) for affecting outcomes of acute inflammatory pathology. This experimental observation identifies host macrophages as necessary in mediating the salutary anti-inflammatory properties of MSCs as a cellular pharmaceutical. This theory is supported by the observation that transfusion of MSCs leads to the prompt phagocytosis of nearly half of lung entrapped MSCs by lung resident macrophages, triggering an interleukin (IL)-10 suppressive efferocytotic response. In addition, non-phagocytosed MSCs with COX2 competency shape the immune milieu by inducing tissue macrophages to express IL-10. Additional experimental evidence identifies MSC-borne IL-6, IDO and TSG-6 as directly involved in macrophage polarization. Along similar lines of functional convergence, implantation of CCL2⁺ MSCs in the extravascular space where interaction with lung resident perivascular macrophages is not operative, also leads to IL-10 polarization of CCR2⁺ macrophages within acute injured tissue far removed from MSC depot. Intriguingly, MSC-derived CCL2 on its own is not sufficient to polarize macrophages and requires heterodimerization with MSC-borne CXCL12 to trigger macrophage IL-10 polarization via CCR2, but not CXCR4. Such chemokine cooperativity opens a new venue for analysis of MSC potency especially considering the rich chemokine secretome of MSC exposed to inflammatory stimulus. As an aggregate, these data highlight a necessary MSC and host macrophage functional dyad that may inform potency attribute analysis of MSCs-including the chemokine interactome-that may be directly linked to in vivo clinical anti-inflammatory and regenerative response.

Mesenchymal Stem/Stromal Cell-Based Delivery: A Rapidly Evolving Strategy for Cancer Therapy

Mesenchymal stem/stromal cell (MSC)-based therapy has become an attractive and advanced scientific research area in the context of cancer therapy. This interest is closely linked to the MSC-marked tropism for tumors, suggesting them as a rational and effective vehicle for drug delivery for both hematological and solid malignancies. Nonetheless, the therapeutic application of the MSCs in human tumors is still controversial because of the induction of several signaling pathways largely contributing to tumor progression and metastasis. In spite of some evidence supporting that MSCs may sustain cancer pathogenesis, increasing proofs have indicated the suppressive influences of MSCs on tumor cells. During the last years, a myriad of preclinical and some clinical studies have been carried out or are ongoing to address the safety and efficacy of the MSC-based delivery of therapeutic agents in diverse types of malignancies. A large number of studies have focused on the MSC application as delivery vehicles for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), chemotherapeutic drug such as gemcitabine (GCB), paclitaxel (PTX), and doxorubicin (DOX), prodrugs such as 5-fluorocytosine (5-FC) and ganciclovir (GCV), and immune cell-activating cytokines along with oncolytic virus. In the current review, we evaluate the latest findings rendering the potential of MSCs to be employed as potent gene/drug delivery vehicle for inducing tumor regression with a special focus on the in vivo reports performed during the last two decades.

MSC Manufacturing for Academic Clinical Trials: From a Clinical-Grade to a Full GMP-Compliant Process

Following European regulation 1394/2007, mesenchymal stromal cell (MSCs) have become an advanced therapy medicinal product (ATMP) that must be produced following the good manufacturing practice (GMP) standards. We describe the upgrade of our existing clinical-grade MSC manufacturing process to obtain GMP certification. Staff organization, premises/equipment qualification and monitoring, raw materials management, starting materials, technical manufacturing processes, quality controls, and the release, thawing and infusion were substantially reorganized. Numerous studies have been carried out to validate cultures and demonstrate the short-term stability of fresh or thawed products, as well their stability during long-term storage. Detailed results of media simulation tests, validation runs and early MSC batches are presented. We also report the validation of a new variant of the process aiming to prepare fresh MSCs for the treatment of specific lesions of Crohn's disease by local injection. In conclusion, we have successfully ensured the adaptation of our clinical-grade MSC production process to the GMP requirements. The GMP manufacturing of MSC products is feasible in the academic setting for a limited number of batches with a significant cost increase, but moving to large-scale production necessary for phase III trials would require the involvement of industrial partners.

Mesenchymal stem/stromal cell-based therapy: mechanism, systemic safety and biodistribution for precision clinical applications

Mesenchymal stem/stromal cells (MSCs) are a promising resource for cell-based therapy because of their high immunomodulation ability, tropism towards inflamed and injured tissues, and their easy access and isolation. Currently, there are more than 1200 registered MSC clinical trials globally. However, a lack of standardized methods to characterize cell safety, efficacy, and biodistribution dramatically hinders the progress of MSC utility in clinical practice. In this review, we summarize the current state of MSC-based cell therapy, focusing on the systemic safety and biodistribution of MSCs. MSC-associated risks of tumor initiation and promotion and the underlying mechanisms of these risks are discussed. In addition, MSC biodistribution methodology and the pharmacokinetics and pharmacodynamics of cell therapies are addressed. Better understanding of the systemic safety and biodistribution of MSCs will facilitate future clinical applications of precision medicine using stem cells.

Mesenchymal Stromal Cell-Based Therapy: A Promising Approach for Severe COVID-19

During the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), many critically ill patients died of severe pneumonia, acute respiratory distress syndrome (ARDS), or multiple organ dysfunction syndrome. To date, no specific treatments have been proven to be effective for coronavirus disease 2019 (COVID-19). In the animal models and clinical applications, mesenchymal stromal/stem cells (MSCs) have been shown safety and efficacy for the treatment of respiratory virus infection through their abilities of differentiation and immunomodulation. Besides, possessing several advantages of MSC-derived extracellular vesicles (EVs) over MSCs, EV-based therapy also holds potential therapeutic effects in respiratory virus infection. In this review, we summarized the basic characteristics and mechanisms of COVID-19 and MSCs, outlined some preclinical and clinical studies of MSCs or MSC-EVs for respiratory virus infection such as influenza virus and SARS-CoV-2, shed light on the common problems that we should overcome to translate MSC therapy into clinical application, and discussed some safe issues related to the use of MSCs.

Induction of mesenchymal stem cell‑like transformation in rat primary glial cells using hypoxia, mild hypothermia and growth factors

The transformation of rat primary glial cells into mesenchymal stem cells (MSCs) is intriguing as more seed cells can be harvested. The present study aimed to evaluate the effects of growth factors, hypoxia and mild hypothermia on the transformation of primary glial cells into MSCs. Rat primary glial cells were induced to differentiate by treatment with hypoxia, mild hypothermia and basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Immunohistochemistry and western blotting were then used to determine the expression levels of glial fibrillary acidic protein (GFAP), nestin, musashi-1, neuron specific enolase (NSE) and neuronal nuclei (NeuN), in each treatment group. bFGF and EGF increased the proportion of CD44⁺ and CD105⁺ cells, while anaerobic mild hypothermia increased the proportion of CD90⁺ cells. The combination of bFGF and EGF, and anaerobic mild hypothermia increased the proportion of CD29⁺ cells and significantly decreased the proportions of GFAP⁺ cells and NSE⁺ cells. Treatment of primary glial cells with bFGF and EGF increased the expression levels of nestin, Musashi-1, NSE and NeuN. Anaerobic mild hypothermia increased the expression levels of Musashi-1 and decreased the expression levels of NSE and NeuN in glial cells. The results of the present study demonstrated that bFGF, EGF and anaerobic mild hypothermia treatments may promote the transformation of glial cells into MSC-like cells, and that the combination of these two treatments may have the optimal effect.

Mesenchymal Stromal Cells' Therapy for Polyglutamine Disorders: Where Do We Stand and Where Should We Go?

Polyglutamine (polyQ) diseases are a group of inherited neurodegenerative disorders caused by the expansion of the cytosine-adenine-guanine (CAG) repeat. This mutation encodes extended glutamine (Q) tract in the disease protein, resulting in the alteration of its conformation/physiological role and in the formation of toxic fragments/aggregates of the protein. This group of heterogeneous disorders shares common molecular mechanisms, which opens the possibility to develop a pan therapeutic approach. Vast efforts have been made to develop strategies to alleviate disease symptoms. Nonetheless, there is still no therapy that can cure or effectively delay disease progression of any of these disorders. Mesenchymal stromal cells (MSC) are promising tools for the treatment of polyQ disorders, promoting protection, tissue regeneration, and/or modulation of the immune system in animal models. Accordingly, data collected from clinical trials have so far demonstrated that transplantation of MSC is safe and delays the progression of some polyQ disorders for some time. However, to achieve sustained phenotypic amelioration in clinics, several treatments may be necessary. Therefore, efforts to develop new strategies to improve MSC's therapeutic outcomes have been emerging. In this review article, we discuss the current treatments and strategies used to reduce polyQ symptoms and major pre-clinical and clinical achievements obtained with MSC transplantation as well as remaining flaws that need to be overcome. The requirement to cross the blood-brain-barrier (BBB), together with a short rate of cell engraftment in the lesioned area and low survival of MSC in a pathophysiological context upon transplantation may contribute to the transient therapeutic effects. We also review methods like pre-conditioning or genetic engineering of MSC that can be used to increase MSC survival in vivo, cellular-free approaches-i.e., MSC-conditioned medium (CM) or MSC-derived extracellular vesicles (EVs) as a way of possibly replacing the use of MSC and methods required to standardize the potential of MSC/MSC-derived products. These are fundamental questions that need to be addressed to obtain maximum MSC performance in polyQ diseases and therefore increase clinical benefits.

Membranes for Guided Bone Regeneration: A Road from Bench to Bedside

Bone resorption can negatively influence the osseointegration of dental implants. Barrier membranes for guided bone regeneration (GBR) are used to exclude nonosteogenic tissues from influencing the bone healing process. In addition to the existing barrier membranes available on the market, a growing variety of membranes for GBR with tailorable physicochemical properties are under preclinical evaluation. Hence, the aim of this review is to provide a comprehensive description of materials used for GBR and to report the main industrial and regulatory aspects allowing the commercialization of these medical devices (MDs). In particular, a summary of the main attributes defining a GBR membrane is reported along with a description of commercially available and under development membranes. Finally, strategies for the scaling-up of the manufacturing process and the regulatory framework of the main MD producers (USA, EU, Japan, China, and India) are presented. The description of the regulatory approval process of GBR membranes is representative of the typical path that medium- to high-risk MDs have to follow for an effective medical translation, which is of fundamental importance to increase the impact of biomedical research on public health.

Development and Prospect of Intra-Articular Injection in the Treatment of Osteoarthritis: A Review

Osteoarthritis (OA) is a common degenerative disease that affects the vast majority of the elderly and may eventually embark on the road of the total knee arthroplasty (TKA), although controversy still exists in the medical community about the best therapies for osteoarthritis. Compared with physical therapy, oral analgesics and other non-operative treatments, intra-articular injection is more safe and effective. Moreover, intra-articular injection is much less invasive and has fewer adverse reactions than surgical treatment. This article reviews mechanism, benefits and adverse reactions of corticosteroids (CS), hyaluronic acid (HA), platelet-rich plasma (PRP), mesenchymal stem cell (MSCs), stromal vascular fraction (SVF) and other new therapies (for example: gene therapy). The application prospect of intra-articular injection was analyzed according to the recent progress in drug research.

Cell Therapy for Lung Disease: Current Status and Future Prospects

Purpose of Review

Mesenchymal stromal cell (MSC)–based therapies provide a platform for new therapeutic strategies in lung diseases. This review provides an overview of the current status of the field, along with some of the challenges ahead including better understanding of MSC actions in different lung diseases, personalized approaches to select patients most likely to benefit, and the growing problem of stem cell tourism.

Recent Findings

A newly evolving concept suggests that MSCs shape their immunomodulatory actions depending on the environment they encounter. Furthermore, in some models, it appears that dying or dead cells may contribute to the therapeutic efficacy by activating the host response.

Summary

Despite many pre-clinical studies demonstrating that MSCs can be used to treat lung disorders, clinical trials have failed to show improved outcome. Understanding the complex interaction between MSCs and the host microenvironment is likely to be an important area for enhancing the efficacy of MSC-based cell therapies.

Single-cell RNA-seq highlights heterogeneity in human primary Wharton's jelly mesenchymal stem/stromal cells cultured in vitro

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) are multipotent cells with a promising application potential in regenerative medicine and immunomodulation. However, MSCs cultured in vitro exhibit functional heterogeneity. The underlying molecular mechanisms that define MSC heterogeneity remain unclear.

METHODS

We investigated the gene expression profile via single-cell RNA sequencing (scRNA-seq) of human primary Wharton's jelly-derived MSCs (WJMSCs) cultured in vitro from three donors. We also isolated CD142+ and CD142- WJMSCs based on scRNA-seq data and compared their proliferation capacity and "wound healing" potential in vitro. Meanwhile, we analyzed publicly available adipose-derived MSC (ADMSCs) scRNA-seq data and performed transcriptome comparison between WJMSCs and ADMSCs at the single-cell level.

RESULTS

GO enrichment analysis of highly variable genes (HVGs) obtained from WJMSCs revealed that these genes are significantly enriched in extracellular region with binding function, involved in developmental process, signal transduction, cell proliferation, etc. Pathway analysis showed that these HVGs are associated with functional characteristics of classic MSCs, such as inflammation mediated by chemokine and cytokine signaling, integrin signaling, and angiogenesis. After regressing out the batch and cell cycle effects, these HVGs were used for dimension reduction and clustering analysis to identify candidate subpopulations. Differentially expressed gene analysis revealed the existence of several distinct subpopulations of MSCs that exhibit diverse functional characteristics related to proliferation, development, and inflammation response. In line with our data, sorted CD142+ and CD142- WJMSCs showed distinct proliferation capacity as well as "wound healing" potential. Although WJMSCs and ADMSCs were derived from different tissues and were displaying different differentiation potencies, their HVGs were largely overlapped and had similar functional enrichment.

CONCLUSION

HVGs identified in MSCs are associated with classic MSC function. Regarding therapeutic potential, these genes are associated with functional characteristics, on which the MSC clinical application were theoretically based, such as development and inflammation response. Altogether, these HVGs hold the potential to be used as candidate markers for further potency association studies.

Use of Human Umbilical Cord and Its Byproducts in Tissue Regeneration

The fresh or cryopreserved human umbilical cord (HUC) and its byproducts, such as cells and extracts, have different uses in tissue regeneration. Defining what HUC byproduct is more effective in a particular application is a challenge. Furthermore, the methods of isolation, culture and preservation, may affect cell viability and regenerative properties. In this article, we review the HUC and its byproducts' applications in research and clinical practice. We present our results of successful use of HUC as a patch to treat gastroschisis and its potential to be applied in other conditions. Our in vitro results show an increase in proliferation and migration of human fibroblasts by using an acellular HUC extract. Our goal is to promote standardization of procedures and point out that applications of HUC and its byproducts, as well as the resulting advances in regenerative medicine, will depend on rigorous quality control and on more research in this area.

The impact of cryopreservation on bone marrow-derived mesenchymal stem cells: a systematic review

Mesenchymal stem cells (MSCs) represent an invaluable asset for the field of cell therapy. Human Bone marrow-derived MSCs (hBM-MSCs) are one of the most commonly used cell types in clinical trials. They are currently being studied and tested for the treatment of a wide range of diseases and conditions. The future availability of MSCs therapies to the public will require a robust and reliable delivery process. Cryopreservation represents the gold standard in cell storage and transportation, but its effect on BM-MSCs is still not well established. A systematic review was conducted to evaluate the impact of cryopreservation on BM-MSCs and to attempt to uncover the reasons behind some of the controversial results reported in the literature. Forty-one in vitro studies were analysed, and their results organised according to the cell attributes they assess. It was concluded that cryopreservation does not affect BM-MSCs morphology, surface marker expression, differentiation or proliferation potential. However, mixed results exist regarding the effect on colony forming ability and the effects on viability, attachment and migration, genomic stability and paracrine function are undefined mainly due to the huge variabilities governing the cryopreservation process as a whole and to the lack of standardised assays.

Biological functions of mesenchymal stem cells and clinical implications

Mesenchymal stem cells (MSCs) are isolated from multiple biological tissues-adult bone marrow and adipose tissues and neonatal tissues such as umbilical cord and placenta. In vitro, MSCs show biological features of extensive proliferation ability and multipotency. Moreover, MSCs have trophic, homing/migration and immunosuppression functions that have been demonstrated both in vitro and in vivo. A number of clinical trials are using MSCs for therapeutic interventions in severe degenerative and/or inflammatory diseases, including Crohn's disease and graft-versus-host disease, alone or in combination with other drugs. MSCs are promising for therapeutic applications given the ease in obtaining them, their genetic stability, their poor immunogenicity and their curative properties for tissue repair and immunomodulation. The success of MSC therapy in degenerative and/or inflammatory diseases might depend on the robustness of the biological functions of MSCs, which should be linked to their therapeutic potency. Here, we outline the fundamental and advanced concepts of MSC biological features and underline the biological functions of MSCs in their basic and translational aspects in therapy for degenerative and/or inflammatory diseases.

Mesenchymal Stromal Cell Therapeutic Delivery: Translational Challenges to Clinical Application

For several decades, multipotent mesenchymal stromal cells (MSCs) have been extensively studied for their therapeutic potential across a wide range of diseases. In the preclinical setting, MSCs demonstrate consistent ability to promote tissue healing, down-regulate excessive inflammation and improve outcomes in animal models. Several proposed mechanisms of action have been posited and demonstrated across an array of in vitro models. However, translation into clinical practice has proven considerably more difficult. A number of prominent well-funded late-phase clinical trials have failed, thus calling out for new efforts to optimize product delivery in the clinical setting. In this review, we discuss novel topics critical to the successful translation of MSCs from pre-clinical to clinical applications. In particular, we focus on the major routes of cell delivery, aspects related to hemocompatibility, and potential safety concerns associated with MSC therapy in the different settings.

Challenges in Clinical Development of Mesenchymal Stromal/Stem Cells: Concise Review

Identified 50 years ago, mesenchymal stromal/stem cells (MSCs) immediately generated a substantial interest among the scientific community because of their differentiation plasticity and hematopoietic supportive function. Early investigations provided evidence of a relatively low engraftment rate and a transient benefit for challenging congenital and acquired diseases. The reasons for these poor therapeutic benefits forced the entire field to reconsider MSC mechanisms of action together with their ex vivo manipulation procedures. This phase resulted in advances in MSCs processing and the hypothesis that MSC‐tissue supportive functions may be prevailing their differentiation plasticity, broadening the spectrum of MSCs therapeutic potential far beyond their lineage‐restricted commitments. Consequently, an increasing number of studies have been conducted for a variety of clinical indications, revealing additional challenges and suggesting that MSCs are still lagging behind for a solid clinical translation. For this reason, our aim was to dissect the current challenges in the development of still promising cell types that, after more than half a century, still need to reach their maturity. stem cells translational medicine2019;8:1135–1148

Potency Analysis of Mesenchymal Stromal Cells Using a Phospho-STAT Matrix Loop Analytical Approach

Potency assays for mesenchymal stromal cells (MSCs) need to be defined in advanced clinical trials. Here, we have developed an assay matrix approach that captures the signal transducer and activator of transcription (STAT) phosphorylation of MSCs upon stimulation with their combined secretome that arose with the interaction of activated peripheral blood mononuclear cells (PBMCs). Secretome of heat-inactivated (HI) MSCs cocultured with and without activated PBMCs was used as an internal reference. We have compared the short-term phosphorylation status of STAT1, STAT3, STAT4, STAT5, and STAT6 on MSCs derived from human bone marrow, adipose tissue, and umbilical cord using phosflow technology. Secretome of live MSCs cocultured with activated PBMCs downregulate STAT1 and STAT3 phosphorylation on MSCs, whereas the secretome of HI-MSCs or PBMCs do not. Thus, investigation of the combined secretome of MSC and PBMC interaction on MSCs determine the potency of MSCs as the generator and sensor of the secretome. Bone marrow, adipose, and umbilical cord MSCs are comparable in modulating STAT1 and STAT3 responses. Measurements of STAT1 and STAT3 phosphorylation on MSCs as responder cells correlate and predict allogeneic T-cell suppression. Our comparative phosphomatrix approach between live and reference HI-MSCs defines the potency of MSCs as both stimulators and responders as part of a robust platform for predictive potency analysis. Stem Cells 2019;37:1119-1125.

Shaping the Future of Perinatal Cells: Lessons From the Past and Interpretations of the Present

Since their discovery and characterization, mesenchymal stromal cells (MSC) have been a topic of great interest in regenerative medicine. Over the last 10 years, detailed studies investigated the properties of MSC from perinatal tissues and have indicated that these cells may represent important tools for restoring tissue damage or promoting regeneration and repair of the tissue microenvironment. At first, perinatal tissue-derived MSC drew attention due to their potential differentiation capacities suggested by their early embryological origin. It is nowadays accepted that perinatal tissue-derived MSC are promising for a wide range of regenerative medicine applications because of their unique immune modulatory properties, rather than their differentiation ability. As a matter of fact, the activation and function of various cells of the innate and adaptive immune systems are suppressed and modulated by MSC from different perinatal tissues, such as human term placenta. However, the mechanisms by which they act on immune cells to facilitate tissue repair during pathological processes remain to be thoroughly elucidated to develop safe and efficient therapeutic approaches. In addition to immune modulatory ability, several other peculiar characteristics of placenta MSC, less explored and/or more debated, are being investigated. These include an understanding of the anti-microbial properties and the role of placental MSC in tumor progression. Moreover, a thorough investigation on preparation methods, bioactive factors, mechanisms of action of the cell secretome, and the development of potency assays to predict clinical efficacy of placenta MSC and their products, are necessary to provide a solid basis for their clinical application.

The Immunomodulatory Properties of Amniotic Cells: The Two Sides of the Coin

Among the many cell types useful in developing therapeutic treatments, human amniotic cells from placenta have been proposed as valid candidates. Both human amniotic epithelial and mesenchymal stromal cells, and the conditioned medium generated from their culture, exert multiple immunosuppressive activities. Indeed, they inhibit T and B cell proliferation, suppress inflammatory properties of monocytes, macrophages, dendritic cells, neutrophils, and natural killer cells, while promoting induction of cells with regulatory functions such as regulatory T cells and anti-inflammatory M2 macrophages. These properties have laid the foundation for their use for the treatment of inflammatory-based diseases, and encouraging results have been obtained in different preclinical disease models where exacerbated inflammation is present. Moreover, an immune-privileged status of amniotic cells has been often highlighted. However, even if long-term engraftment of amniotic cells has been reported into immunocompetent animals, only few cells survive after infusion. Furthermore, amniotic cells have been shown to be able to induce immune responses in vivo and, under specific culture conditions, they can stimulate T cell proliferation in vitro. Although immunosuppressive properties are a widely recognized characteristic of amniotic cells, immunogenic and stimulatory activities appear to be less reported, sporadic events. In order to improve therapeutic outcome, the mechanisms responsible for the suppressive versus stimulatory activity need to be carefully addressed. In this review, both the immunosuppressive and immunostimulatory activity of amniotic cells will be discussed.

Mesenchymal stem/stromal cell function in modulating cell death

Mesenchymal stem/stromal cells (MSCs) delivered as cell therapy to individuals with degenerative and/or inflammatory disorders can help improve organ features and resolve inflammation, as demonstrated in preclinical studies and to some extent in clinical studies. MSCs have trophic, homing/migration, and immunosuppression functions, with many benefits in therapeutics. MSC functions are thought to depend on the paracrine action of soluble factors and/or the expression of membrane-bound molecules, mostly belonging to the molecular class of adhesion molecules, chemokines, enzymes, growth factors, and interleukins. Cutting-edge studies underline bioactive exchanges, including that of ions, nucleic acids, proteins, and organelles transferred from MSCs to stressed cells, thereby improving the cells' survival and function. From this aspect, MSC death modulation function appears as a decisive biological function that could carry a significant part of the therapeutic effects of MSCs. Identifying the function and modes of actions of MSCs in modulating cell death may be exploited to enhance consistency and efficiency of cell therapy that is based on MSCs as medical treatment for degenerative and/or inflammatory diseases. Here, we review the essentials of MSC functions in modulating cell death in unfit cells, and its modes of actions based on current advances and outline the clinical implications.

Intra-articular treatment options for knee osteoarthritis

Intra-articular drug delivery has a number of advantages over systemic administration; however, for the past 20 years, intra-articular treatment options for the management of knee osteoarthritis (OA) have been limited to analgesics, glucocorticoids, hyaluronic acid (HA) and a small number of unproven alternative therapies. Although HA and glucocorticoids can provide clinically meaningful benefits to an appreciable number of patients, emerging evidence indicates that the apparent effectiveness of these treatments is largely a result of other factors, including the placebo effect. Biologic drugs that target inflammatory processes are used to manage rheumatoid arthritis, but have not translated well into use in OA. A lack of high-level evidence and methodological limitations hinder our understanding of so-called 'stem' cell therapies and, although the off-label administration of intra-articular cell therapies (such as platelet-rich plasma and bone marrow aspirate concentrate) is common, high-quality clinical data are needed before these treatments can be recommended. A number of promising intra-articular treatments are currently in clinical development in the United States, including small-molecule and biologic therapies, devices and gene therapies. Although the prospect of new, non-surgical treatments for OA is exciting, the benefits of new treatments must be carefully weighed against their costs and potential risks.

Nomenclature Inconsistency and Selective Outcome Reporting Hinder Understanding of Stem Cell Therapy for the Knee

BACKGROUND

The prospect of treating knee cartilage injury/pathology with mesenchymal stem cells (MSCs) has garnered considerable attention in recent years, but study heterogeneity and a lack of randomized controlled trials (RCTs) preclude quantitative analysis. The purpose of this review was to provide clinicians with an overview of RCTs that addresses 2 key areas that have been largely overlooked: nomenclature inconsistency and selective outcome reporting.

METHODS

RCTs that purported to use stem cells or MSCs to treat knee cartilage were identified with use of PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses). Study variables were compiled, and methodological quality was assessed. The cell treatments and the methods used to characterize them were recorded and compared. Clinical, radiographic, and arthroscopic outcomes were extracted and evaluated qualitatively.

RESULTS

There was extensive variation among the treatments, adjuvant therapies, and outcome measures. Treatments did not coincide with terminology. Significant differences in clinical outcomes were reported infrequently, and intra-group improvements or inter-group subscore differences were consistently highlighted, particularly when inter-group comparisons were left unreported.

CONCLUSIONS

Overall, there are isolated cases in which positive efficacy results have been published, but our results suggest that the generally positive efficacy conclusions concerning stem cell therapy for knee cartilage pathology may be overstated. Nevertheless, it is important to understand that the efficacy of stem cell therapies should not be considered in aggregate. Cells that are procured or processed differently produce entirely different drugs. When evaluating the efficacy of "stem cell" therapies, clinicians must consider the methodological quality, nomenclature, and inherent distinctness of each treatment.

Clinical Application of Stem/Stromal Cells in COPD

Chronic obstructive pulmonary disease (COPD) is a progressive life-threatening disease that is significantly increasing in prevalence and is predicted to become the third leading cause of death worldwide by 2030. At present, there are no true curative treatments that can stop the progression of the disease, and new therapeutic strategies are desperately needed. Advances in cell-based therapies provide a platform for the development of new therapeutic approaches in severe lung diseases such as COPD. At present, a lot of focus is on mesenchymal stem (stromal) cell (MSC)-based therapies, mainly due to their immunomodulatory properties. Despite increasing number of preclinical studies demonstrating that systemic MSC administration can prevent or treat experimental COPD and emphysema, clinical studies have not been able to reproduce the preclinical results and to date no efficacy or significantly improved lung function or quality of life has been observed in COPD patients. Importantly, the completed appropriately conducted clinical trials uniformly demonstrate that MSC treatment in COPD patients is well tolerated and no toxicities have been observed. All clinical trials performed so far, have been phase I/II studies, underpowered for the detection of potential efficacy. There are several challenges ahead for this field such as standardized isolation and culture procedures to obtain a cell product with high quality and reproducibility, administration strategies, improvement of methods to measure outcomes, and development of potency assays. Moreover, COPD is a complex pathology with a diverse spectrum of clinical phenotypes, and therefore it is essential to develop methods to select the subpopulation of patients that is most likely to potentially respond to MSC administration. In this chapter, we will discuss the current state of the art of MSC-based cell therapy for COPD and the hurdles that need to be overcome.

Myths, reality and future of mesenchymal stem cell therapy

Mesenchymal stem cell (MSC) therapy represents an alternative approach for tissue regeneration and inflammation control. In spite of a huge amount of preclinical data that has been accumulated on the therapeutic properties of MSCs, there are many conflicting results, possibly due to differences in the properties of MSCs obtained from different sources or underestimated mechanisms of MSC in vivo behavior. This review consolidates the in vivo effects of MSC therapy, discusses the fate of MSCs after intravascular and local delivery and proposes possible trends in MSC therapy.

Potency Analysis of Mesenchymal Stromal Cells Using a Combinatorial Assay Matrix Approach

Assays that can characterize MSC immune potency need to be identified for use in advanced clinical trials. MSCs possess a number of putative regenerative and immunomodulatory properties, and an assay matrix approach may best capture involved effector pathways. We have tested two assay systems to measure the potency of MSCs derived from human subjects: MSC secretome analysis and a quantitative RNA-based array for genes specific to immunomodulatory and homing properties of MSCs. Secretome analysis identified a unique cytokine signature that is upregulated by MSCs or downregulated in responder PBMCs and correlated with T cell suppression. Use of interferon-γ as a surrogate for the action of activated PBMCs on MSCs served as an alternative for the use of human PBMCs as responder cells in a potency assay. Our approach and results define and simplify the multifunctional or matrix responses of MSCs and may serve as a platform for robust potency analysis.

Strategies to enhance paracrine potency of transplanted mesenchymal stem cells in intractable neonatal disorders

Mesenchymal stem cell (MSC) transplantation represents the next breakthrough in the treatment of currently intractable and devastating neonatal disorders with complex multifactorial etiologies, including bronchopulmonary dysplasia, hypoxic ischemic encephalopathy, and intraventricular hemorrhage. Absent engraftment and direct differentiation of transplanted MSCs, and the "hit-and-run" therapeutic effects of these MSCs suggest that their pleiotropic protection might be attributable to paracrine activity via the secretion of various biologic factors rather than to regenerative activity. The transplanted MSCs, therefore, exert their therapeutic effects not by acting as "stem cells," but rather by acting as "paracrine factors factory." The MSCs sense the microenvironment of the injury site and secrete various paracrine factors that serve several reparative functions, including antiapoptotic, anti-inflammatory, antioxidative, antifibrotic, and/or antibacterial effects in response to environmental cues to enhance regeneration of the damaged tissue. Therefore, the therapeutic efficacy of MSCs might be dependent on their paracrine potency. In this review, we focus on recent investigations that elucidate the specifically regulated paracrine mechanisms of MSCs by injury type and discuss potential strategies to enhance paracrine potency, and thus therapeutic efficacy, of transplanted MSCs, including determining the appropriate source and preconditioning strategy for MSCs and the route and timing of their administration.

Mesenchymal stem cells for the prevention and treatment of bronchopulmonary dysplasia in preterm infants

BACKGROUND

Bronchopulmonary dysplasia (BPD) remains a major complication of prematurity and currently lacks efficient treatments. Mesenchymal stem/stromal cells (MSCs) have been extensively explored as a potential therapy in several preclinical and clinical settings. Human and animal MSCs have been shown to prevent and treat lung injury in various preclinical models of lung diseases, including experimental BPD.

OBJECTIVES

To determine if MSCs, administered intravenously or endotracheally, are safe and effective in preventing or treating BPD, or both, in preterm infants.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group to search the Cochrane Central Register of Controlled Trials (CENTRAL 2016, Issue 10), MEDLINE via PubMed (1966 to 6 November 2016), Embase (1980 to 6 November 2016), and CINAHL (1982 to 6 November 2016). We also searched clinical trials databases, conference proceedings, and the reference lists of retrieved articles for randomized controlled trials (RCTs) and quasi-RCTs.

SELECTION CRITERIA

We considered RCTs and quasi-RCTs investigating prevention or treatment of BPD, or both, in preterm infants.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality according to prespecified criteria.

MAIN RESULTS

We found no RCTs or quasi-RCTs addressing the use of MSCs for prevention or treatment of BPD in premature infants. Two RCTs are currently registered and ongoing.

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine the safety and efficacy of MSCs in the treatment or prevention of BPD in premature infants. The results of the ongoing trials addressing this issue are expected in the near future.

Cryopreserved or Fresh Mesenchymal Stromal Cells: Only a Matter of Taste or Key to Unleash the Full Clinical Potential of MSC Therapy?

Mesenchymal stromal cells (MSCs) harbor great therapeutic potential for numerous diseases. From early clinical trials, success and failure analysis, bench-to-bedside and back-to-bench approaches, there has been a great gain in knowledge, still leaving a number of questions to be answered regarding optimal manufacturing and quality of MSCs for clinical application. For treatment of many acute indications, cryobanking may remain a prerequisite, but great uncertainty exists considering the therapeutic value of freshly thawed (thawed) and continuously cultured (fresh) MSCs. The field has seen an explosion of new literature lately, outlining the relevance of the topic. MSCs appear to have compromised immunomodulatory activity directly after thawing for clinical application. This may provide a possible explanation for failure of early clinical trials. It is not clear if and how quickly MSCs recover their full therapeutic activity, and if the "cryo stun effect" is relevant for clinical success. Here, we will share our latest insights into the relevance of these observations for clinical practice that will be discussed in the context of the published literature. We argue that the differences of fresh and thawed MSCs are limited but significant. A key issue in evaluating potency differences is the time point of analysis after thawing. To date, prospective double-blinded randomized clinical studies to evaluate potency of both products are lacking, although recent progress was made with preclinical assessment. We suggest refocusing therapeutic MSC development on potency and safety assays with close resemblance of the clinical reality.

Stem cells to restore insulin production and cure diabetes

BACKGROUND

The advancement of knowledge in the field of regenerative medicine is increasing the therapeutic expectations of patients and clinicians on cell therapy approaches. Within these, stem cell therapies are often evoked as a possible therapeutic option for diabetes, already ongoing or possible in the near future.

AIM

The purpose of this document is to make a point of the situation on existing knowledge and therapies with stem cells to treat patients with diabetes by focusing on some of the aspects that most frequently raise curiosity and discussion in clinical practice and in the interaction with the patient. In fact, at present there are no clinically approved treatments based on the use of stem cells for the treatment of diabetes, but several therapeutic approaches have already been evaluated or are being evaluated in clinical trials.

DATA SYNTHESIS

It is possible to identify three large potential application fields: 1) the reconstruction of the β cell mass; 2) the immunomodulation in type 1 diabetes (T1D); 3) the treatment of complications. In this study we will limit the discussion to approaches that have the potential for clinical translation, deliberately omitting aspects of basic biology and preclinical data. Also, we intentionally omit the treatment of the complications that will be the subject of a future document. Finally, an overview of the Italian situation regarding the storage of cord blood cells for the therapy of diabetes will be given.

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.

Immune dysfunctionality of replicative senescent mesenchymal stromal cells is corrected by IFNγ priming

Industrial-scale expansion of mesenchymal stromal cells (MSCs) is often used in clinical trials, and the effect of replicative senescence on MSC functionality is of mechanistic interest. Senescent MSCs exhibit cell-cycle arrest, cellular hypertrophy, and express the senescent marker β-galactosidase. Although both fit and senescent MSCs display intact lung-homing properties in vivo, senescent MSCs acquire a significant defect in inhibiting T-cell proliferation and cytokine secretion in vitro. IFNγ does not upregulate HLA-DR on senescent MSCs, whereas its silencing did not reverse fit MSCs' immunosuppressive properties. Secretome analysis of MSC and activated peripheral blood mononuclear cell coculture demonstrate that senescent MSCs are significantly defective in up (vascular endothelial growth factor [VEGF], granulocyte colony-stimulating factor [GCSF], CXCL10, CCL2) or down (IL-1ra, IFNγ, IL-2r, CCL4, tumor necrosis factor-α, IL-5) regulating cytokines/chemokines. Unlike indoleamine 2,3 dioxygenase (IDO), silencing of CXCL9, CXCL10, CXCL11, GCSF, CCL2, and exogenous addition of VEGF, fibroblast growth factor-basic do not modulate MSCs' immunosuppressive properties. Kynurenine levels were downregulated in senescent MSC cocultures compared with fit MSC counterparts, and exogenous addition of kynurenine inhibits T-cell proliferation in the presence of senescent MSCs. IFNγ prelicensing activated several immunomodulatory genes including IDO in fit and senescent MSCs at comparable levels and significantly enhanced senescent MSCs' immunosuppressive effect on T-cell proliferation. Our results define immune functional defects acquired by senescent MSCs, which are reversible by IFNγ prelicensing.

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.

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.

A relativity concept in mesenchymal stromal cell manufacturing

Mesenchymal stromal cells (MSCs) are being experimentally tested in several biological systems and clinical settings with the aim of verifying possible therapeutic effects for a variety of indications. MSCs are also known to be heterogeneous populations, with phenotypic and functional features that depend heavily on the individual donor, the harvest site, and the culture conditions. In the context of this multidimensional complexity, a recurrent question is whether it is feasible to produce MSC batches as "standard" therapeutics, possibly within scalable manufacturing systems. Here, we provide a short overview of the literature on different culture methods for MSCs, including those employing innovative technologies, and of some typically assessed functional features (e.g., growth, senescence, genomic stability, clonogenicity, etc.). We then offer our perspective of a roadmap on how to identify and refine manufacturing systems for MSCs intended for specific clinical indications. We submit that the vision of producing MSCs according to a unique standard, although commercially attractive, cannot yet be scientifically substantiated. Instead, efforts should be concentrated on standardizing methods for characterization of MSCs generated by different groups, possibly covering a vast gamut of functionalities. Such assessments, combined with hypotheses on the therapeutic mode of action and associated clinical data, should ultimately allow definition of in-process controls and measurable release criteria for MSC manufacturing. These will have to be validated as predictive of potency in suitable pre-clinical models and of therapeutic efficacy in patients.

Rationale for Determining the Functional Potency of Mesenchymal Stem Cells in Preventing Regulated Cell Death for Therapeutic Use

Mesenchymal stem (stromal) cells (MSCs) are being investigated for treating degenerative and inflammatory disorders because of their reparative and immunomodulatory properties. Intricate mechanisms relate cell death processes with immune responses, which have implications for degenerative and inflammatory conditions. We review the therapeutic value of MSCs in terms of preventing regulated cell death (RCD). When cells identify an insult, specific intracellular pathways are elicited for execution of RCD processes, such as apoptosis, necroptosis, and pyroptosis. To some extent, exacerbated RCD can provoke an intense inflammatory response and vice versa. Emerging studies are focusing on the molecular mechanisms deployed by MSCs to ameliorate the survival, bioenergetics, and functions of unfit immune or nonimmune cells. Given these aspects, and in light of MSC actions in modulating cell death processes, we suggest the use of novel functional in vitro assays to ensure the potency of MSCs for preventing RCD. Such analyses should be associated with existing functional assays measuring the anti‐inflammatory capabilities of MSCs in vitro. MSCs selected on the basis of two in vitro functional criteria (i.e., prevention of inflammation and RCD) could possess optimal therapeutic efficacy in vivo. In addition, we underline the implications of these perspectives in clinical studies of MSC therapy, with particular focus on acute respiratory distress syndrome. Stem Cells Translational Medicine2017;6:713–719

Remestemcel-L for the treatment of graft versus host disease

INTRODUCTION

Remestemcel-L, a third-party, off-the-shelf preparation of bone-marrow derived mesenchymal stromal cells (MSCs), has been developed for experimental use in acute graft-versus-host disease (aGvHD) and other immune-mediated conditions. Several preclinical and clinical studies have indeed suggested the potential of human mesenchymal stromal cells (MSCs) as an effective treatment for steroid-refractory aGvHD. However, an unambiguous demonstration of efficacy is still lacking. Areas covered: This review critically examines the biologic rationale supporting MSCs use in aGvHD and analyzes the results of published clinical trials in this setting, with a particular focus on the potential benefits and drawbacks of Remestemcel-L. For this purpose, a systematic literature search was performed in PubMed using the following keywords: 'mesenchymal stromal cells', 'mesenchymal progenitor cells', 'multipotent stromal cells', 'mesenchymal cells', 'MSC', 'Remestemcel-L', 'Prochymal', and 'graft-versus-host disease' or 'GvHD'. Expert commentary: Remestemcel-L represents a promising alternative to second-line immunosuppressive agents for the treatment of steroid-refractory aGvHD. Despite the safety and the favorable risk/benefit profile of this cell product, which has been demonstrated in several phase I-II studies, large and prospective randomized trials are required to confirm its efficacy in aGvHD and to define the optimal schedule of administration in terms of infusion timing, cell dose and pharmacological synergism.

Cryopreserved Mesenchymal Stromal Cells Are Susceptible to T-Cell Mediated Apoptosis Which Is Partly Rescued by IFNγ Licensing

We have previously demonstrated that cryopreservation and thawing lead to altered Mesenchymal stromal cells (MSC) functionalities. Here, we further analyzed MSC's fitness post freeze-thaw. We have observed that thawed MSC can suppress T-cell proliferation when separated from them by transwell membrane and the effect is lost in a MSC:T-cell coculture system. Unlike actively growing MSCs, thawed MSCs were lysed upon coculture with activated autologous Peripheral Blood Mononuclear Cells (PBMCs) and the lysing effect was further enhanced with allogeneic PBMCs. The use of DMSO-free cryoprotectants or substitution of Human Serum Albumin (HSA) with human platelet lysate in freezing media and use of autophagy or caspase inhibitors did not prevent thaw defects. We tested the hypothesis that IFNγ prelicensing before cryobanking can enhance MSC fitness post thaw. Post thawing, IFNγ licensed MSCs inhibit T cell proliferation as well as fresh MSCs and this effect can be blocked by 1-methyl Tryptophan, an Indoleamine 2,3-dioxygenase (IDO) inhibitor. In addition, IFNγ prelicensed thawed MSCs inhibit the degranulation of cytotoxic T cells while IFNγ unlicensed thawed MSCs failed to do so. However, IFNγ prelicensed thawed MSCs do not deploy lung tropism in vivo following intravenous injection as well as fresh MSCs suggesting that IFNγ prelicensing does not fully rescue thaw-induced lung homing defect. We identified reversible and irreversible cryoinjury mechanisms that result in susceptibility to host T-cell cytolysis and affect MSC's cell survival and tissue distribution. The susceptibility of MSC to negative effects of cryopreservation and the potential to mitigate the effects with IFNγ prelicensing may inform strategies to enhance the therapeutic efficacy of MSC in clinical use. Stem Cells 2016;34:2429-2442.

Differential and transferable modulatory effects of mesenchymal stromal cell-derived extracellular vesicles on T, B and NK cell functions

Mesenchymal stromal cells (MSCs) are multipotent cells, immunomodulatory stem cells that are currently used for regenerative medicine and treatment of a number of inflammatory diseases, thanks to their ability to significantly influence tissue microenvironments through the secretion of large variety of soluble factors. Recently, several groups have reported the presence of extracellular vesicles (EVs) within MSC secretoma, showing their beneficial effect in different animal models of disease. Here, we used a standardized methodological approach to dissect the immunomodulatory effects exerted by MSC-derived EVs on unfractionated peripheral blood mononuclear cells and purified T, B and NK cells. We describe here for the first time: i. direct correlation between the degree of EV-mediated immunosuppression and EV uptake by immune effector cells, a phenomenon further amplified following MSC priming with inflammatory cytokines; ii. induction in resting MSCs of immunosuppressive properties towards T cell proliferation through EVs obtained from primed MSCs, without any direct inhibitory effect towards T cell division. Our conclusion is that the use of reproducible and validated assays is not only useful to characterize the mechanisms of action of MSC-derived EVs, but is also capable of justifying EV potential use as alternative cell-free therapy for the treatment of human inflammatory diseases.

Toward Development of iMesenchymal Stem Cells for Immunomodulatory Therapy

Mesenchymal stem cells (MSC) are under development as an immunomodulatory therapy. The anticipated immunomodulatory effects of MSC are broad, from direct inhibition of lymphocyte proliferation, induction of regulatory T and B cells, to resetting the immune system via a hit-and-run principle. There are endless flavors of MSC. Differences between MSC are originating from donors variation, differences in tissue of origin, the effects of culture conditions, and expansion time. Even standard culture conditions change the properties of MSC dramatically and generate MSC that only remotely resemble their in vivo counterparts. Adjustments in culture protocols can further emphasize properties of interest in MSC, thereby generating cells fitted for specific purposes. Culture improved immunomodulatory MSC can be designed to target particular immune disorders. In this review, we describe the observed and the desired immunomodulatory effects of MSC and propose approaches how MSC with optimal immunomodulatory properties can be developed.