Mesenchymal stem cells engineered to inhibit complement-mediated damage. PLoS One. 2013;8:e60461. [PMID: 23555976 PMCID: PMC3608620 DOI: 10.1371/journal.pone.0060461]

Human Liver MSCs Retain Their Basic Cellular Properties in Chronically Inflamed Liver Tissue

Every 25th death worldwide is associated with liver pathology. The development of novel approaches to liver diseases therapy and protocols for maintaining the vital functions of patients on the liver transplant waiting list are urgently needed. Resident mesenchymal stem cells (MSCs) play a significant role in supporting liver tissue integrity and improve the liver condition after infusion. However, it remains unclear whether MSCs isolated from chronically inflamed livers are similar in their basic cellular properties to MSCs obtained from healthy livers. We applied a large array of tests to compare resident MSCs isolated from apparently normal liver tissue and from chronically inflamed livers of patients with fibrosis, cirrhosis, and viral hepatitis. Chronic inflammatory environment did not alter the major cellular characteristics of MSCs, including the expression of MSC markers, stem cell markers, adhesion molecules, and the hallmarks of senescence, as well as cell proliferation, migration, and secretome. Only the expression of some immune checkpoints and toll-like receptors was different. Evidently, MSCs with unchanged cellular properties are present in human liver even at late stages of inflammatory diseases. These cells can be isolated and used as starting material in the development of cell therapies of liver diseases.

Precision Nanomedicine with Bio-Inspired Nanosystems: Recent Trends and Challenges in Mesenchymal Stem Cells Membrane-Coated Bioengineered Nanocarriers in Targeted Nanotherapeutics

In the recent past, the formulation and development of nanocarriers has been elaborated into the broader fields and opened various avenues in their preclinical and clinical applications. In particular, the cellular membrane-based nanoformulations have been formulated to surpass and surmount the limitations and restrictions associated with naïve or free forms of therapeutic compounds and circumvent various physicochemical and immunological barriers including but not limited to systemic barriers, microenvironmental roadblocks, and other cellular or subcellular hinderances-which are quite heterogeneous throughout the diseases and patient cohorts. These limitations in drug delivery have been overcome through mesenchymal cells membrane-based precision therapeutics, where these interventions have led to the significant enhancements in therapeutic efficacies. However, the formulation and development of nanocarriers still focuses on optimization of drug delivery paradigms with a one-size-fits-all resolutions. As mesenchymal stem cell membrane-based nanocarriers have been engineered in highly diversified fashions, these are being optimized for delivering the drug payloads in more and better personalized modes, entering the arena of precision as well as personalized nanomedicine. In this Review, we have included some of the advanced nanocarriers which have been designed and been utilized in both the non-personalized as well as precision applicability which can be employed for the improvements in precision nanotherapeutics. In the present report, authors have focused on various other aspects of the advancements in stem cells membrane-based nanoparticle conceptions which can surmount several roadblocks and barriers in drug delivery and nanomedicine. It has been suggested that well-informed designing of these nanocarriers will lead to appreciable improvements in the therapeutic efficacy in therapeutic payload delivery applications. These approaches will also enable the tailored and customized designs of MSC-based nanocarriers for personalized therapeutic applications, and finally amending the patient outcomes.

Adipose tissue-derived human mesenchymal stromal cells can better suppress complement lysis, engraft and inhibit acute graft-versus-host disease in mice

BACKGROUND

Acute graft-versus-host disease (aGvHD) is a life-threatening complication of allogeneic hematopoietic stem cell transplantation (HSCT). Transplantation of immunosuppressive human mesenchymal stromal cells (hMSCs) can protect against aGvHD post-HSCT; however, their efficacy is limited by poor engraftment and survival. Moreover, infused MSCs can be damaged by activated complement, yet strategies to minimise complement injury of hMSCs and improve their survival are limited.

METHODS

Human MSCs were derived from bone marrow (BM), adipose tissue (AT) and umbilical cord (UC). In vitro immunomodulatory potential was determined by co-culture experiments between hMSCs and immune cells implicated in aGvHD disease progression. BM-, AT- and UC-hMSCs were tested for their abilities to protect aGvHD in a mouse model of this disease. Survival and clinical symptoms were monitored, and target tissues of aGvHD were examined by histopathology and qPCR. Transplanted cell survival was evaluated by cell tracing and by qPCR. The transcriptome of BM-, AT- and UC-hMSCs was profiled by RNA-sequencing. Focused experiments were performed to compare the expression of complement inhibitors and the abilities of hMSCs to resist complement lysis.

RESULTS

Human MSCs derived from three tissues divergently protected against aGvHD in vivo. AT-hMSCs preferentially suppressed complement in vitro and in vivo, resisted complement lysis and survived better after transplantation when compared to BM- and UC-hMSCs. AT-hMSCs also prolonged survival and improved the symptoms and pathological features of aGvHD. We found that complement-decay accelerating factor (CD55), an inhibitor of complement, is elevated in AT-hMSCs and contributed to reduced complement activation. We further report that atorvastatin and erlotinib could upregulate CD55 and suppress complement in all three types of hMSCs.

CONCLUSION

CD55, by suppressing complement, contributes to the improved protection of AT-hMSCs against aGvHD. The use of AT-hMSCs or the upregulation of CD55 by small molecules thus represents promising new strategies to promote hMSC survival to improve the efficacy of transplantation therapy. As complement injury is a barrier to all types of hMSC therapy, our findings are of broad significance to enhance the use of hMSCs for the treatment of a wide range of disorders.

Mesenchymal progenitor cells from non-inflamed versus inflamed synovium post-ACL injury present with distinct phenotypes and cartilage regeneration capacity

BACKGROUND

Osteoarthritis (OA) is a chronic debilitating disease impacting a significant percentage of the global population. While there are numerous surgical and non-invasive interventions that can postpone joint replacement, there are no current treatments which can reverse the joint damage occurring during the pathogenesis of the disease. While many groups are investigating the use of stem cell therapies in the treatment of OA, we still don't have a clear understanding of the role of these cells in the body, including heterogeneity of tissue resident adult mesenchymal progenitor cells (MPCs).

METHODS

In the current study, we examined MPCs from the synovium and individuals with or without a traumatic knee joint injury and explored the chondrogenic differentiation capacity of these MPCs in vitro and in vivo.

RESULTS

We found that there is heterogeneity of MPCs with the adult synovium and distinct sub-populations of MPCs and the abundancy of these sub-populations change with joint injury. Furthermore, only some of these sub-populations have the ability to effect cartilage repair in vivo. Using an unbiased proteomics approach, we were able to identify cell surface markers that identify this pro-chondrogenic MPC population in normal and injured joints, specifically CD82^LowCD59⁺ synovial MPCs have robust cartilage regenerative properties in vivo.

CONCLUSIONS

The results of this study clearly show that cells within the adult human joint can impact cartilage repair and that these sub-populations exist within joints that have undergone a traumatic joint injury. Therefore, these populations can be exploited for the treatment of cartilage injuries and OA in future clinical trials.

Lysis and phenotypic modulation of mesenchymal stromal cells upon blood contact triggers anti-inflammatory skewing of the peripheral innate immune repertoire

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are used to treat immune-related disorders, including graft-versus-host disease. Upon intravenous infusion, MSCs trigger the instant blood-mediated inflammatory response, resulting in activation of both complement and coagulation cascades, and are rapidly cleared from circulation. Despite no/minimal engraftment, long-term immunoregulatory properties are evident. The aim of this study was to establish the effects of blood exposure on MSC viability and immunomodulatory functions.

METHODS

Human, bone marrow derived MSCs were exposed to human plasma +/- heat inactivation or whole blood. MSC number, viability and cellular damage was assessed using the JC-1 mitochondrial depolarization assay and annexin V staining. C3c binding and expression of the inhibitory receptors CD46, CD55 and CD59 and complement receptors C3aR and C5aR were evaluated by flow cytometry. MSCs pre-exposed to plasma were cultured with peripheral blood mononuclear cells (PBMCs) and monocyte subsets characterized by flow cytometry. The PBMC and MSC secretome was assessed using enzyme-linked immunosorbent assays against tumor necrosis factor alpha, interleukin (IL)-6 and IL-10. Monocyte recruitment towards the MSC secretome was evaluated using Boyden chambers and screened for chemotactic factors including monocyte chemoattractant protein (MCP)-1. MSC effects on the peripheral immune repertoire was also evaluated in whole blood by flow cytometry.

RESULTS

Plasma induced rapid lysis of 57% of MSCs, which reduced to 1% lysis with heat inactivation plasma. Of those cells that were not lysed, C3c could be seen bound to the surface of the cells, with a significant swelling of the MSCs and induction of cell death. The MSC secretome reduced monocyte recruitment, in part due to a reduction in MCP-1, and downregulated PBMC tumor necrosis factor alpha secretion while increasing IL-6 levels in the co-culture supernatant. A significant decrease in CD14⁺ monocytes was evident after MSC addition to whole blood alongside a significant increase in IL-6 levels, with those remaining monocytes demonstrating an increase in classical and decrease in non-classical subsets. This was accompanied by a significant increase in both mononuclear and polymorphonuclear myeloid-derived suppressor cells.

CONCLUSIONS

This study demonstrates that a significant number of MSCs are rapidly lysed upon contact with blood, with those surviving demonstrating a shift in their phenotype, including a reduction in the secretion of monocyte recruitment factors and an enhanced ability to skew the phenotype of monocytes. Shifts in the innate immune repertoire, towards an immunosuppressive profile, were also evident within whole blood after MSC addition. These findings suggest that exposure to blood components can promote peripheral immunomodulation via multiple mechanisms that persists within the system long after the infused MSCs have been cleared.

Full spectrum flow cytometry reveals mesenchymal heterogeneity in first trimester placentae and phenotypic convergence in culture, providing insight into the origins of placental mesenchymal stromal cells

Single-cell technologies (RNA-sequencing, flow cytometry) are critical tools to reveal how cell heterogeneity impacts developmental pathways. The placenta is a fetal exchange organ, containing a heterogeneous mix of mesenchymal cells (fibroblasts, myofibroblasts, perivascular, and progenitor cells). Placental mesenchymal stromal cells (pMSC) are also routinely isolated, for therapeutic and research purposes. However, our understanding of the diverse phenotypes of placental mesenchymal lineages, and their relationships remain unclear. We designed a 23-colour flow cytometry panel to assess mesenchymal heterogeneity in first-trimester human placentae. Four distinct mesenchymal subsets were identified; CD73⁺CD90⁺ mesenchymal cells, CD146⁺CD271⁺ perivascular cells, podoplanin⁺CD36⁺ stromal cells, and CD26⁺CD90⁺ myofibroblasts. CD73⁺CD90⁺ and podoplanin + CD36+ cells expressed markers consistent with cultured pMSCs, and were explored further. Despite their distinct ex-vivo phenotype, in culture CD73⁺CD90⁺ cells and podoplanin⁺CD36⁺ cells underwent phenotypic convergence, losing CD271 or CD36 expression respectively, and homogenously exhibiting a basic MSC phenotype (CD73⁺CD90⁺CD31^-CD144^-CD45^-). However, some markers (CD26, CD146) were not impacted, or differentially impacted by culture in different populations. Comparisons of cultured phenotypes to pMSCs further suggested cultured pMSCs originate from podoplanin⁺CD36⁺ cells. This highlights the importance of detailed cell phenotyping to optimise therapeutic capacity, and ensure use of relevant cells in functional assays.

Tafazzin deficiency in mouse mesenchymal stem cells promote reprogramming of activated B lymphocytes toward immunosuppressive phenotypes

Barth Syndrome (BTHS) is a rare X-linked genetic disorder caused by mutation in the TAFAZZIN gene. Tafazzin (Taz) deficiency in BTHS patients results in an increased risk of infections. Mesenchymal stem cells (MSCs) are well known for their immune-inhibitory function. We examined how Taz-deficiency in murine MSCs impact their ability to modulate the function of lipopolysaccharide (LPS)-activated wild type (WT) B lymphocytes. MSCs from tafazzin knockdown (TazKD) mice exhibited a reduction in mitochondrial cardiolipin compared to wild type (WT) MSCs. However, mitochondrial bioenergetics and membrane potential were unaltered. In contrast, TazKD MSCs exhibited increased reactive oxygen species generation and increased glycolysis. The increased glycolysis was associated with an elevated proliferation, phosphatidylinositol-3-kinase expression and expression of the immunosuppressive markers indoleamine-2,3-dioxygenase, cytotoxic T-lymphocyte-associated protein 4, interleukin-10, and cluster of differentiation 59 compared to controls. Inhibition of glycolysis with 2-deoxyglucose attenuated the TazKD-mediated increased expression of cytotoxic T-lymphocyte-associated protein 4 and interleukin-10. When co-cultured with LPS-activated WT B cells, TazKD MSCs inhibited B cell proliferation and growth rate and reduced B cell secretion of immunoglobulin M compared to controls. In addition, co-culture of LPS-activated WT B cells with TazKD MSCs promoted B cell differentiation toward interleukin-10 secreting plasma cells and B regulatory cells compared to controls. The results indicate that Taz deficiency in MSCs promote reprogramming of activated B lymphocytes toward immunosuppressive phenotypes.

Tafazzin deficiency in mouse mesenchymal stem cells potentiates their immunosuppression and impairs activated B lymphocyte immune function

Barth Syndrome (BTHS) is a rare X-linked genetic disorder caused by mutation in the TAFAZZIN gene which encodes the cardiolipin (CL) transacylase tafazzin (Taz). Taz deficiency in BTHS patients results in reduced CL in their tissues and a neutropenia which contributes to the risk of infections. However, the impact of Taz deficiency in other cells of the immune system is poorly understood. Mesenchymal stem cells (MSCs) are well known for their immune inhibitory function. We examined whether Taz-deficiency in murine MSCs impacted their ability to modulate lipopolysaccharide (LPS)-activated wild type (WT) murine B lymphocytes. MSCs from tafazzin knockdown (TazKD) mice exhibited a 50% reduction in CL compared to wild type (WT) MSCs. However, mitochondrial oxygen consumption rate and membrane potential were unaltered. In contrast, TazKD MSCs exhibited increased glycolysis compared to WT MSCs and this was associated with elevated proliferation, phosphatidylinositol-3-kinase expression and expression of the immunosuppressive markers indoleamine-2,3-dioxygenase, cytotoxic T-lymphocyte-associated protein 4, interleukin-10, and cluster of differentiation 59. When co-cultured with LPS-activated WT B cells, TazKD MSCs inhibited B cell proliferation and growth rate and reduced B cell secretion of IgM to a greater extent than B cells co-cultured with WT MSCs. In addition, co-culture of LPS-activated WT B cells with TazKD MSCs induced B cell differentiation toward potent immunosuppressive phenotypes including interleukin-10 secreting plasma cells and B regulatory cells compared to activated B cells co-cultured with WT MSCs. These results indicate that Taz deficiency in MSCs enhances MSCs-mediated immunosuppression of activated B lymphocytes.

Toward a Consensus View of Mammalian Adipocyte Stem and Progenitor Cell Heterogeneity

White adipose tissue (WAT) is a cellularly heterogeneous endocrine organ that not only serves as an energy reservoir, but also actively participates in metabolic homeostasis. Among the main constituents of adipose tissue are adipocytes, which arise from adipose stem and progenitor cells (ASPCs). While it is well known that these ASPCs reside in the stromal vascular fraction (SVF) of adipose tissue, their molecular heterogeneity and functional diversity is still poorly understood. Driven by the resolving power of single-cell transcriptomics, several recent studies provided new insights into the cellular complexity of ASPCs among different mammalian fat depots. In this review, we present current knowledge on ASPCs, their population structure, hierarchy, fat depot-specific nature, function, and regulatory mechanisms, and discuss not only the similarities, but also the differences between mouse and human ASPC biology.

Shattering barriers toward clinically meaningful MSC therapies

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

Mesenchymal Stromal 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.

Dissecting Allo-Sensitization After Local Administration of Human Allogeneic Adipose Mesenchymal Stem Cells in Perianal Fistulas of Crohn's Disease Patients

Adipose mesenchymal stem cells (ASC) are considered minimally immunogenic. This is due to the low expression of human leukocyte antigens I (HLA-I), lack of HLA-II expression and low expression of co-stimulatory molecules such as CD40 and CD80. The low rate of observed immunological rejection as well as the immunomodulatory qualities, position ASC as a promising cell-based therapy for the treatment of a variety of inflammatory indications. Yet, few studies have addressed relevant aspects of immunogenicity such as ASC donor-to-patient HLA histocompatibility or assessment of immune response triggered by ASC administration, particularly in the cases of presensitization. The present study aims to assess allo-immune responses in a cohort of Crohn's disease patients administered with allogeneic ASC (darvadstrocel formerly Cx601) for the treatment of complex perianal fistulas. We identified donor-specific antibodies (DSA) generation in a proportion of patients and observed that patients showing preexisting immunity were prone to generating DSA after allogeneic therapy. Noteworthy, naïve patients generating DSA at week 12 (W12) showed a significant reduction in DSA titer at week 52 (W52), whereas DSA titer was reduced in pre-sensitized patients only with no specificities against the donor administered. Remarkably, we did not observe any correlation of DSA generation with ASC therapeutic efficacy. In vitro complement-dependent cytotoxicity (CDC) studies have revealed limited cytotoxic levels based upon HLA-I expression and binding capacity even in pro-inflammatory conditions. We sought to identify CDC coping mechanisms contributing to the limited cytotoxic killing observed in ASC in vitro. We found that ASC express membrane-bound complement regulatory proteins (mCRPs) CD55, CD46, and CD59 at basal levels, with CD46 more actively expressed in pro-inflammatory conditions. We demonstrated that CD46 is a main driver of CDC signaling; its depletion significantly enhances sensitivity of ASC to CDC. In summary, despite relatively high clearance, DSA generation may represent a major challenge for allogeneic cell therapy management. Sensitization may be a significant concern when evaluating re-treatment or multi-donor trials. It is still unknown whether DSA generation could potentially be the consequence of donor-to-patient interaction and, therefore, subsequently link to efficacy or biological activity. Lastly, we propose that CDC modulators such as CD46 could be used to ultimately link CDC specificity with allogeneic cell therapy efficacy.

Intravascular Mesenchymal Stromal/Stem Cell Therapy Product Diversification: Time for New Clinical Guidelines

Intravascular infusion is the most popular route for therapeutic multipotent mesenchymal stromal/stem cell (MSC) delivery in hundreds of clinical trials. Meta-analysis has demonstrated that bone marrow MSC infusion is safe. It is not clear if this also applies to diverse new cell products derived from other sources, such as adipose and perinatal tissues. Different MSC products display varying levels of highly procoagulant tissue factor (TF) and may adversely trigger the instant blood-mediated inflammatory reaction (IBMIR). Suitable strategies for assessing and controlling hemocompatibility and optimized cell delivery are crucial for the development of safer and more effective MSC therapies.

Challenges and Strategies for Improving the Regenerative Effects of Mesenchymal Stromal Cell-Based Therapies

Cell-based therapies have the potential to revolutionize current treatments for diseases with high prevalence and related economic and social burden. Unfortunately, clinical trials have made only modest improvements in restoring normal function to degenerating tissues. This limitation is due, at least in part, to the death of transplanted cells within a few hours after transplant due to a combination of mechanical, cellular, and host factors. In particular, mechanical stress during implantation, extracellular matrix loss upon delivery, nutrient and oxygen deprivation at the recipient site, and host inflammatory response are detrimental factors limiting long-term transplanted cell survival. The beneficial effect of cell therapy for regenerative medicine ultimately depends on the number of administered cells reaching the target tissue, their viability, and their promotion of tissue regeneration. Therefore, strategies aiming at improving viable cell engraftment are crucial for regenerative medicine. Here we review the major factors that hamper successful cell engraftment and the strategies that have been studied to enhance the beneficial effects of cell therapy. Moreover, we provide a perspective on whether mesenchymal stromal cell-derived extracellular vesicle delivery, as a cell-free regenerative approach, may circumvent current cell therapy limitations.

Mammalian MSC from selected species: Features and applications

Mesenchymal stromal/stem cells (MSC) are promising candidates for cellular therapy of different diseases in humans and in animals. Following the guidelines of the International Society for Cell Therapy, human MSC may be identified by expression of a specific panel of cell surface markers (CD105+, CD73+, CD90+, CD34-, CD14-, or CD11b-, CD79- or CD19-, HLA-DR-). In addition, multiple differentiation potential into at least the osteogenic, adipogenic, and chondrogenic lineage is a main criterion for MSC definition. Human MSC and MSC of a variety of mammals isolated from different tissues meet these criteria. In addition to the abovementioned, they express many more cell surface markers. Yet, these are not uniquely expressed by MSC. The gross phenotypic appearance like marker expression and differentiation potential is similar albeit not identical for MSC from different tissues and species. Similarly, MSC may feature different biological characteristics depending on the tissue source and the isolation and culture procedures. Their versatile biological qualities comprising immunomodulatory, anti-inflammatory, and proregenerative capacities rely largely on the migratory and secretory capabilities of MSC. They are attracted to sites of tissue lesion and secrete factors to promote self-repair of the injured tissue. This is a big perspective for clinical MSC applications in both veterinary and human medicine. Phase I/II clinical trials have been initiated to assess safety and feasibility of MSC therapies in acute and chronic disease settings. Yet, since the mode of MSC action in a specific disease environment is still unknown at large, it is mandatory to unravel the response of MSC from a given source onto a specific disease environment in suitable animal models prior to clinical applications. © 2017 International Society for Advancement of Cytometry.

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.

General regulatory effects of hypoxia on human cartilage endplate‑derived stem cells: A genome‑wide analysis of differential gene expression and alternative splicing events

Intervertebral disc (IVD) degeneration of is considered to be initiated by the degeneration of the cartilage endplate (CEP). CEP‑derived stem cells (CESCs) with the capacity for osteochondrogenic differentiation may be responsible for CEP cartilage restoration. As CEP is avascular and hypoxic, and hypoxia can greatly influence biological activities of stem cells, physiological hypoxia may serve important roles in regulating the physiological functions of CESCs. The aim of the present study was to investigate the mechanisms of hypoxia‑regulated CESCs fate by using the Human Transcriptome Array 2.0 system to identify differentially expressed genes (DEGs) and alternatively spliced genes (ASGs) in CESCs cultured under hypoxic and normoxic conditions. The high‑throughput analysis of both DEGs and ASGs were notably enriched in the immune response signal, which so far has not been investigated in IVD cells, due to their avascular nature and low immunogenicity. The present results provided a referential study direction of the mechanisms of hypoxia‑regulated CESC fate at the level of gene expression and alternative splicing, which may aid in our understanding of the processes of CEP degeneration.

A genome-wide analysis of the gene expression profiles and alternative splicing events during the hypoxia-regulated osteogenic differentiation of human cartilage endplate-derived stem cells

It has been hypothesized that intervertebral disc degeneration is initiated by degeneration of the cartilage endplate (CEP), which is characterized by cartilage ossification. CEP‑derived stem cells (CESCs), with the potential for chondro‑osteogenic differentiation, may be responsible for the balance between chondrification and ossification in the CEP. The CEP remains in an avascular and hypoxic microenvironment; the present study observed that hypoxia was able to markedly inhibit the osteogenic differentiation of CESCs. This tissue‑specific CESC differentiation in response to a hypoxic microenvironment was physiologically important for the prevention of ossification in the CEP. In order to study the hypoxia‑regulated mechanisms underlying osteogenic differentiation of CESCs, a Human Transcriptome Array 2.0 was used to detect differentially expressed genes (DEGs) and alternatively spliced genes (ASGs) during the osteogenic differentiation of CESCs under hypoxia, compared with those induced under normoxia. High‑throughput analysis of DEGs and ASGs demonstrated that genes in the complement pathway were enriched, which may be a potential mechanism underlying hypoxia inhibition of CESCs osteogenesis. The results of the present study may provide a basis for future mechanistic studies regarding gene expression levels and alternative splicing events during the hypoxia‑regulated inhibition of osteogenesis, which may be helpful in identifying targets for CEP degeneration therapy.

Effects of Different Cell-Detaching Methods on the Viability and Cell Surface Antigen Expression of Synovial Mesenchymal Stem Cells

Flow cytometric analysis of cell surface antigens is a powerful tool for the isolation and characterization of stem cells residing in adult tissues. In contrast to the collection of hematopoietic stem cells, the process of enzymatic digestion is usually necessary to prepare mesenchymal stem cells (MSCs) suspensions, which can influence the expression of cell surface markers. In this study, we examined the effects of various cell-detaching reagents and digestion times on the expression of stem cell-related surface antigens and MSC functions. Human MSCs were detached from dishes using four different reagents: trypsin, TrypLE, collagenase, and a nonenzymatic cell dissociation reagent (C5789; Sigma-Aldrich). Following dissociation reagent incubations ranging from 5 to 120 min, cell surface markers were analyzed by flow cytometry. Trypsin and TrypLE quickly dissociated the cells within 5 min, while collagenase and C5789 required 60 min to obtain maximum cell yields. C5789 significantly decreased cell viability at 120 min. Trypsin treatment significantly reduced CD44+, CD55+, CD73+, CD105+, CD140a+, CD140b+, and CD201+ cell numbers within 30 min. Collagenase treatment reduced CD140a expression by 30 min. In contrast, TrypLE treatment did not affect the expression of any cell surface antigens tested by 30 min. Despite the significant loss of surface antigen expression after 60 min of treatment with trypsin, adverse effects of enzymatic digestion on multipotency of MSCs were limited. Overall, our data indicated that TrypLE is advantageous over other cell dissociation reagents tested for the rapid preparation of viable MSC suspensions.

Painting factor H onto mesenchymal stem cells protects the cells from complement- and neutrophil-mediated damage

Mesenchymal stem cells (MSCs) are undergoing intensive testing in clinical trials as a promising new therapy for many inflammatory diseases and for regenerative medicine, but further optimization of current MSC-based therapies is required. In this study, we found that in addition to direct complement-mediated attack through the assembly of membrane attack complexes (MACs) that we and others have recently reported, of the released complement activation products, C5a, but not C3a, activates neutrophils in the blood to further damage MSCs through oxidative burst. In addition, we have developed a simple method for painting factor H, a native complement inhibitor, onto MSCs to locally inhibit complement activation on MSCs. MSCs painted with factor H are protected from both MAC- and neutrophil-mediated attack and are significantly more effective in inhibiting antigen-specific T cell responses than the mock-painted MSCs both in vitro and in vivo.

Mesenchymal Stem Cells after Polytrauma: Actor and Target

Mesenchymal stem cells (MSCs) are multipotent cells that are considered indispensable in regeneration processes after tissue trauma. MSCs are recruited to damaged areas via several chemoattractant pathways where they function as “actors” in the healing process by the secretion of manifold pro- and anti-inflammatory, antimicrobial, pro- and anticoagulatory, and trophic/angiogenic factors, but also by proliferation and differentiation into the required cells. On the other hand, MSCs represent “targets” during the pathophysiological conditions after severe trauma, when excessively generated inflammatory mediators, complement activation factors, and damage- and pathogen-associated molecular patterns challenge MSCs and alter their functionality. This in turn leads to complement opsonization, lysis, clearance by macrophages, and reduced migratory and regenerative abilities which culminate in impaired tissue repair. We summarize relevant cellular and signaling mechanisms and provide an up-to-date overview about promising future therapeutic MSC strategies in the context of severe tissue trauma.

Genetic Engineering of Mesenchymal Stem Cells to Induce Their Migration and Survival

Mesenchymal stem cells (MSCs) are very attractive for regenerative medicine due to their relatively easy derivation and broad range of differentiation capabilities, either naturally or induced through cell engineering. However, efficient methods of delivery to diseased tissues and the long-term survival of grafted cells still need improvement. Here, we review genetic engineering approaches designed to enhance the migratory capacities of MSCs, as well as extend their survival after transplantation by the modulation of prosurvival approaches, including prevention of senescence and apoptosis. We highlight some of the latest examples that explore these pivotal points, which have great relevance in cell-based therapies.

International Society for Cellular Therapy perspective on immune functional assays for mesenchymal stromal cells as potency release criterion for advanced phase clinical trials

Mesenchymal stromal cells (MSCs) as a pharmaceutical for ailments characterized by pathogenic autoimmune, alloimmune and inflammatory processes now cover the spectrum of early- to late-phase clinical trials in both industry and academic sponsored studies. There is a broad consensus that despite different tissue sourcing and varied culture expansion protocols, human MSC-like cell products likely share fundamental mechanisms of action mediating their anti-inflammatory and tissue repair functionalities. Identification of functional markers of potency and reduction to practice of standardized, easily deployable methods of measurements of such would benefit the field. This would satisfy both mechanistic research as well as development of release potency assays to meet Regulatory Authority requirements for conduct of advanced clinical studies and their eventual registration. In response to this unmet need, the International Society for Cellular Therapy (ISCT) addressed the issue at an international workshop in May 2015 as part of the 21st ISCT annual meeting in Las Vegas. The scope of the workshop was focused on discussing potency assays germane to immunomodulation by MSC-like products in clinical indications targeting immune disorders. We here provide consensus perspective arising from this forum. We propose that focused analysis of selected MSC markers robustly deployed by in vitro licensing and metricized with a matrix of assays should be responsive to requirements from Regulatory Authorities. Workshop participants identified three preferred analytic methods that could inform a matrix assay approach: quantitative RNA analysis of selected gene products; flow cytometry analysis of functionally relevant surface markers and protein-based assay of secretome. We also advocate that potency assays acceptable to the Regulatory Authorities be rendered publicly accessible in an "open-access" manner, such as through publication or database collection.

Do cryopreserved mesenchymal stromal cells display impaired immunomodulatory and therapeutic properties?

We have recently reported that therapeutic mesenchymal stromal cells (MSCs) have low engraftment and trigger the instant blood mediated inflammatory reaction (IBMIR) after systemic delivery to patients, resulting in compromised cell function. In order to optimize the product, we compared the immunomodulatory, blood regulatory, and therapeutic properties of freeze-thawed and freshly harvested cells. We found that freeze-thawed MSCs, as opposed to cells harvested from continuous cultures, have impaired immunomodulatory and blood regulatory properties. Freeze-thawed MSCs demonstrated reduced responsiveness to proinflammatory stimuli, an impaired production of anti-inflammatory mediators, increased triggering of the IBMIR, and a strong activation of the complement cascade compared to fresh cells. This resulted in twice the efficiency in lysis of thawed MSCs after 1 hour of serum exposure. We found a 50% and 80% reduction in viable cells with freshly detached as opposed to thawed in vitro cells, indicating a small benefit for fresh cells. In evaluation of clinical response, we report a trend that fresh cells, and cells of low passage, demonstrate improved clinical outcome. Patients treated with freshly harvested cells in low passage had a 100% response rate, twice the response rate of 50% observed in a comparable group of patients treated with freeze-thawed cells at higher passage. We conclude that cryobanked MSCs have reduced immunomodulatory and blood regulatory properties directly after thawing, resulting in faster complement-mediated elimination after blood exposure. These changes seem to be paired by differences in therapeutic efficacy in treatment of immune ailments after hematopoietic stem cell transplantation.

Complement activation in the context of stem cells and tissue repair

The complement pathway is best known for its role in immune surveillance and inflammation. However, its ability of opsonizing and removing not only pathogens, but also necrotic and apoptotic cells, is a phylogenetically ancient means of initiating tissue repair. The means and mechanisms of complement-mediated tissue repair are discussed in this review. There is increasing evidence that complement activation contributes to tissue repair at several levels. These range from the chemo-attraction of stem and progenitor cells to areas of complement activation, to increased survival of various cell types in the presence of split products of complement, and to the production of trophic factors by cells activated by the anaphylatoxins C3a and C5a. This repair aspect of complement biology has not found sufficient appreciation until recently. The following will examine this aspect of complement biology with an emphasis on the anaphylatoxins C3a and C5a.

Different Procoagulant Activity of Therapeutic Mesenchymal Stromal Cells Derived from Bone Marrow and Placental Decidua

While therapeutic mesenchymal stromal/stem cells (MSCs) have usually been obtained from bone marrow, perinatal tissues have emerged as promising new sources of cells for stromal cell therapy. In this study, we present a first safety follow-up on our clinical experience with placenta-derived decidual stromal cells (DSCs), used as supportive immunomodulatory and regenerative therapy for patients with severe complications after allogeneic hematopoietic stem cell transplantation (HSCT). We found that DSCs are smaller, almost half the volume of MSCs, which may favor microvascular passage. DSCs also show different hemocompatibility, with increased triggering of the clotting cascade after exposure to human blood and plasma in vitro. After infusion of DSCs in HSCT patients, we observed a weak activation of the fibrinolytic system, but the other blood activation markers remained stable, excluding major adverse events. Expression profiling identified differential levels of key factors implicated in regulation of hemostasis, such as a lack of prostacyclin synthase and increased tissue factor expression in DSCs, suggesting that these cells have intrinsic blood-activating properties. The stronger triggering of the clotting cascade by DSCs could be antagonized by optimizing the cell graft reconstitution before infusion, for example, by use of low-dose heparin anticoagulant in the cell infusion buffer. We conclude that DSCs are smaller and have stronger hemostatic properties than MSCs, thus triggering stronger activation of the clotting system, which can be antagonized by optimizing the cell graft preparation before infusion. Our results highlight the importance of hemocompatibility safety testing for every novel cell therapy product before clinical use, when applied using systemic delivery.

Regenerative medicine: prospects for the treatment of inflammatory bowel disease

This article reviews the current understanding of the processes driving the development and progression of inflammatory bowel disease (IBD), discusses how the dynamic crosstalk between resident microorganisms, host cells and the immune system is required in order to maintain immune homeostasis, and considers innovative strategies that allow the modification or modulation of the intestinal microorganismal community as a potential approach for treating IBD. This article next rationalizes the use of cell-based regenerative medicine as treatment for IBD, discusses the obstacles hindering its success, summarizes some of the results of recent clinical trials employing these therapies, and discusses ongoing work to enhance mesenchymal stem/stromal cells, making them better suited to the task of repairing the damage within the IBD gut.