The heterogeneity of human mesenchymal stem cell preparations--evidence from simultaneous analysis of proteomes and transcriptomes

Single-cell sequencing advances in research on mesenchymal stem/stromal cells

Mesenchymal stem/stromal cells (MSCs), originating from the mesoderm, represent a multifunctional stem cell population capable of differentiating into diverse cell types and exhibiting a wide range of biological functions. Despite more than half a century of research, MSCs continue to be among the most extensively studied cell types in clinical research projects globally. However, their significant heterogeneity and phenotypic instability have significantly hindered their exploration and application. Single-cell sequencing technology emerges as a powerful tool to address these challenges, offering precise dissection of complex cellular samples. It uncovers the genetic structure and gene expression status of individual contained cells on a massive scale and reveals the heterogeneity among these cells. It links the molecular characteristics of MSCs with their clinical applications, contributing to the advancement of regenerative medicine. With the development and cost reduction of single-cell analysis techniques, sequencing technology is now widely applied in fundamental research and clinical trials. This study aimed to review the application of single-cell sequencing in MSC research and assess its prospects.

Organ-on-a-Chip: Ubi sumus? Fundamentals and Design Aspects

This review outlines the evolutionary journey from traditional two-dimensional (2D) cell culture to the revolutionary field of organ-on-a-chip technology. Organ-on-a-chip technology integrates microfluidic systems to mimic the complex physiological environments of human organs, surpassing the limitations of conventional 2D cultures. This evolution has opened new possibilities for understanding cell-cell interactions, cellular responses, drug screening, and disease modeling. However, the design and manufacture of microchips significantly influence their functionality, reliability, and applicability to different biomedical applications. Therefore, it is important to carefully consider design parameters, including the number of channels (single, double, or multi-channels), the channel shape, and the biological context. Simultaneously, the selection of appropriate materials compatible with the cells and fabrication methods optimize the chips' capabilities for specific applications, mitigating some disadvantages associated with these systems. Furthermore, the success of organ-on-a-chip platforms greatly depends on the careful selection and utilization of cell resources. Advances in stem cell technology and tissue engineering have contributed to the availability of diverse cell sources, facilitating the development of more accurate and reliable organ-on-a-chip models. In conclusion, a holistic perspective of in vitro cellular modeling is provided, highlighting the integration of microfluidic technology and meticulous chip design, which play a pivotal role in replicating organ-specific microenvironments. At the same time, the sensible use of cell resources ensures the fidelity and applicability of these innovative platforms in several biomedical applications.

Reversible Host-Guest Crosslinks in Supramolecular Hydrogels for On-Demand Mechanical Stimulation of Human Mesenchymal Stem Cells

Stem cells are regulated not only by biochemical signals but also by biophysical properties of extracellular matrix (ECM). The ECM is constantly monitored and remodeled because the fate of stem cells can be misdirected when the mechanical interaction between cells and ECM is imbalanced. A well-defined ECM model for bone marrow-derived human mesenchymal stem cells (hMSCs) based on supramolecular hydrogels containing reversible host-guest crosslinks is fabricated. The stiffness (Young's modulus E) of the hydrogels can be switched reversibly by altering the concentration of non-cytotoxic, free guest molecules dissolved in the culture medium. Fine-adjustment of substrate stiffness enables the authors to determine the critical stiffness level E* at which hMSCs turn the mechano-sensory machinery on or off. Next, the substrate stiffness across E* is switched and the dynamic adaptation characteristics such as morphology, traction force, and YAP/TAZ signaling of hMSCs are monitored. These data demonstrate the instantaneous switching of traction force, which is followed by YAP/TAZ signaling and morphological adaptation. Periodical switching of the substrate stiffness across E* proves that frequent applications of mechanical stimuli drastically suppress hMSC proliferation. Mechanical stimulation across E* level using dynamic hydrogels is a promising strategy for the on-demand control of hMSC transcription and proliferation.

Isolation, in vitro expansion and characterization of ovine fetal adnexa-derived mesenchymal stem cells reveals a source dependent trilineage differentiation and growth kinetics

This study was designed to isolate, cultivate, characterize and evaluate the growth kinetics of mesenchymal stem cells (MSCs) derived from fetal adnexa of sheep. The gravid uteri of ewes were collected from a local abattoir. The MSCs isolated from different fetal regions (Wharton's Jelly [oWJ], cord blood [oCB], amniotic fluid [oAF] and amniotic Sac [oAS]) were expanded in vitro and characterized for surface and pluripotency markers. The growth kinetics of MSCs was compared at 3rd and 5th passages. Similarly, the colony-forming efficiency (CFE) assay was performed at 3rd passage. The fetal adnexa-derived ovine MSCs showed the expression of CD73, CD90 and CD105. Similarly, the MSCs also expressed pluripotency markers, OCT4 and SOX2. Besides, cells also differentiated into osteogenic, chondrogenic and adipogenic lineages. The MSCs in culture showed a typical growth curve with initial lag phase, an exponential phase, a plateau phase and a decline phase. The growth rate was highest in oAF-MSCs at P5. The population doubling time (PDT) was highest in oAS-MSCs (87.28 ± 3.24 h), whereas the colony number was highest in oAF-MSCs (53.67 ± 4.06). The study reveals that oAF-MSCs were superior which outperformed other MSCs indicating that oAF-derived MSCs could be utilized for regenerative medicine.

The role of embryonic stem cells, transcription and growth factors in mammals: A review

Mammals represent a relevant species in worldwide cultures with significant commercial value. These animals are considered an attractive large animal model for biomedical and biotechnology research. The development of large animal experimental models may open alternative strategies for investigating stem cells (SCs) physiology and potential application in the veterinary field. The embryonic stem cells (ESCs) are known to possess natural pluripotency that confers the ability to differentiate into various tissues in vivo and in vitro. These notable characteristics can be useful for research and innovative applications, including biomedicine, agriculture and industry. Transcription factors play a crucial role in preserving stem cell self-renewal, whereas growth factors are involved in both growth and differentiation. However, to date, many questions concerning pluripotency, cellular differentiation regulator genes, and other molecules such as growth factors and their interactions in many mammalian species remain unresolved. The purpose of this review is to provide an overall review regarding the study of ESCs in mammals and briefly discuss the role of transcription and growth factors.

HOX genes in stem cells: Maintaining cellular identity and regulation of differentiation

Stem cells display a unique cell type within the body that has the capacity to self-renew and differentiate into specialized cell types. Compared to pluripotent stem cells, adult stem cells (ASC) such as mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) exhibit restricted differentiation capabilities that are limited to cell types typically found in the tissue of origin, which implicates that there must be a certain code or priming determined by the tissue of origin. HOX genes, a subset of homeobox genes encoding transcription factors that are generally repressed in undifferentiated pluripotent stem cells, emerged here as master regulators of cell identity and cell fate during embryogenesis, and in maintaining this positional identity throughout life as well as specifying various regional properties of respective tissues. Concurrently, intricate molecular circuits regulated by diverse stem cell-typical signaling pathways, balance stem cell maintenance, proliferation and differentiation. However, it still needs to be unraveled how stem cell-related signaling pathways establish and regulate ASC-specific HOX expression pattern with different temporal-spatial topography, known as the HOX code. This comprehensive review therefore summarizes the current knowledge of specific ASC-related HOX expression patterns and how these were integrated into stem cell-related signaling pathways. Understanding the mechanism of HOX gene regulation in stem cells may provide new ways to manipulate stem cell fate and function leading to improved and new approaches in the field of regenerative medicine.

Comparison of Three Methods for Preparation of Autologous Cells for Use in Cell Therapy of Chronic Limb-Threatening Ischemia in People with Diabetes

Autologous cell therapy (ACT) is a new therapeutic approach for diabetic patients with no-option chronic limb-threatening ischemia (NO-CLTI). The aim of our study was to quantify cell populations of cell therapy products (CTPs) obtained by three different isolation methods and to correlate their numbers with changes in transcutaneous oxygen pressure (TcPO2). CTPs were separated either from stimulated peripheral blood (PB) (n = 11) or harvested from bone marrow (BM) processed either by Harvest SmartPReP2 (n = 50) or sedimented with succinate gelatin (n = 29). The clinical effect was evaluated by the change in TcPO2 after 1, 3 and 6 months. TcPO2 increased significantly in all three methods at each time point in comparison with baseline values (p < .01) with no significant difference among them. There was no correlation between the change in TcPO2 and the size of injected cell populations. We only observed a weak correlation between the number of injected white blood cells (WBC) and an increase in TcPO2 at 1 and 3 months. Our study showed that all three isolation methods of ACT were similarly relatively efficient in the treatment of NO-CLTI. We observed no correlation of TcPO2 increase with the number of injected monocytes, lymphocytes or CD34+. We observed a weak correlation between TcPO2 increase and the number of injected WBCs.

Steps Toward Standardized In Vitro Assessment of Immunomodulatory Equine Mesenchymal Stromal Cells Before Clinical Application

Inflammation-associated disorders are significant causes of morbidity in horses. Equine single-donor mesenchymal stromal cells (sdMSCs) hold promise as cell-therapy candidates due to their secretory nonprogenitor functions. This has been demonstrated by mononuclear cell suppression assays (MSAs) showing that sdMSCs are blood mononuclear cell (BMC) suppressive in vitro. sdMSCs derived from umbilical cord blood are of clinical interest due to their ease of procurement, multipotency, and immunomodulatory ability. Due to the inherent donor-to-donor heterogeneity of MSCs, the development of robust and easily deployable methods of potency assessment is critical for improving MSCs' predictability in treating inflammatory diseases. This study focuses on the development of robust in vitro potency assays and the assessment of potential sdMSC therapeutic end products generated from pooled sdMSCs (pMSCs). We hypothesized that, compared to MSA using only one donor, MSA using pooled BMCs (pBMCs) is a more robust sdMSC potency assay due to reduced donor BMC heterogeneity. pBMCs were generated by pooling equine BMCs isolated from peripheral blood of five donors in equal ratios. pBMCs were labeled with carboxyfluorescein succinimidyl ester (CFSE) and stored in liquid nitrogen until use. Similarly, pooling sdMSCs from multiple equine donors in equal ratios generated pMSCs. sdMSC cultures were assessed with pBMCs in MSA using Bromodeoxyuridine ELISA and CFSE. Proliferation assessment of BMCs from individual donors revealed varied responses to concanavalin A (ConA) stimulation. MSA using BMCs from single donors further demonstrated BMC donor variability. Utilizing this assay, we have also found that the immunosuppressive potencies of pMSCs are at least equal, if not more, than the calculated mean of individual cultures. MSA based on pBMCs provides a consistent and reproducible equine sdMSC potency assay. This knowledge could be used in production monitoring of cellular potency and as release criteria before clinical use.

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.

Therapeutic efficiency of bone marrow-derived mesenchymal stem cells for liver fibrosis: A systematic review of in vivo studies

Although multiple drugs are accessible for recovering liver function in patients, none are considered efficient. Liver transplantation is the mainstay therapy for end-stage liver fibrosis. However, the worldwide shortage of healthy liver donors, organ rejection, complex surgery, and high costs are prompting researchers to develop novel approaches to deal with the overwhelming liver fibrosis cases. Mesenchymal stem cell (MSC) therapy is an emerging alternative method for treating patients with liver fibrosis. However, many aspects of this therapy remain unclear, such as the efficiency compared to conventional treatment, the ideal MSC sources, and the most effective way to use it. Because bone marrow (BM) is the largest source for MSCs, this paper used a systematic review approach to study the therapeutic efficiency of MSCs against liver fibrosis and related factors. We systematically searched multiple published articles to identify studies involving liver fibrosis and BM-MSC-based therapy. Analyzing the selected studies showed that compared with conventional treatment BM-MSC therapy may be more efficient for liver fibrosis in some cases. In contrast, the cotreatment presented a more efficient way. Nevertheless, BM-MSCs are lacking as a therapy for liver fibrosis; thus, this paper also reviews factors that affect BM-MSC efficiency, such as the implementation routes and strategies employed to enhance the potential in alleviating liver fibrosis. Ultimately, our review summarizes the recent advances in the BM-MSC therapy for liver fibrosis. It is grounded in recent developments underlying the efficiency of BM-MSCs as therapy, focusing on the preclinical in vivo experiments, and comparing to other treatments or sources and the strategies used to enhance its potential while mentioning the research gaps.

Adipogenesis, Osteogenesis, and Chondrogenesis of Human Mesenchymal Stem/Stromal Cells: A Comparative Transcriptome Approach

Adipogenesis, osteogenesis and chondrogenesis of human mesenchymal stem/stromal cells (MSC) are complex and highly regulated processes. Over the years, several studies have focused on understanding the mechanisms involved in the MSC commitment to the osteogenic, adipogenic and/or chondrogenic phenotypes. High-throughput methodologies have been used to investigate the gene expression profile during differentiation. Association of data analysis of mRNAs, microRNAs, circular RNAs and long non-coding RNAs, obtained at different time points over these processes, are important to depict the complexity of differentiation. This review will discuss the results that were highlighted in transcriptome analyses of MSC undergoing adipogenic, osteogenic and chondrogenic differentiation. The focus is to shed light on key molecules, main signaling pathways and biological processes related to different time points of adipogenesis, osteogenesis and chondrogenesis.

Deciphering carbohydrate metabolism during wheat grain development via integrated transcriptome and proteome dynamics

Grain development of Triticum aestivum is being studied extensively using individual OMICS tools. However, integrated transcriptome and proteome studies are limited mainly due to complexity of genome. Current study focused to unravel the transcriptome-proteome coordination of key mechanisms underlying carbohydrate metabolism during whole wheat grain development. Wheat grains were manually dissected to obtain grain tissues for proteomics and transcriptomics analyses. Differentially expressed proteins and transcripts at the 11 stages of grain development were compared. Computational workflow for integration of two datasets related to carbohydrate metabolism was designed. For CM proteins, output peptide sequences of proteomic analyses (via LC-MS/MS) were used as source to search corresponding transcripts. The transcript that turned out with higher number of peptides was selected as bona fide ribonucleotide sequence for respective protein synthesis. More than 90% of hits resulted in successful identification of respective transcripts. Comparative analysis of protein and transcript expression profiles resulted in overall 32% concordance between these two series of data. However, during grain development correlation of two datasets gradually increased up to ~ tenfold from 152 to 655 °Cd and then dropped down. Proteins involved in carbohydrate metabolism were divided in five categories in accordance with their functions. Enzymes involved in starch and sucrose biosynthesis showed the highest correlations between proteome-transcriptome profiles. High percentage of identification and validation of protein-transcript hits highlighted the power of omics data integration approach over existing gene functional annotation tools. We found that correlation of two datasets is highly influenced by stage of grain development. Further, gene regulatory networks would be helpful in unraveling the mechanisms underlying the complex and significant traits such as grain weight and yield.

High-efficient generation of VCAM-1+ mesenchymal stem cells with multidimensional superiorities in signatures and efficacy on aplastic anaemia mice

OBJECTIVE

Longitudinal studies have indicated VCAM-1⁺ mesenchymal stem/stromal cells (MSCs) as promising resources in regenerative medicine, yet the abundance in gene expression is far from adequate in the advantaged and "discarded" hUC-MSCs. Thus, high-efficient preparation and systematic dissection of the signatures and biofunctions of the subpopulation is the prerequisite for large-scale clinical applications.

MATERIALS AND METHODS

We primarily took advantage of a cytokine-based programming strategy for large-scale VCAM-1⁺ hUC-MSC generation (III-MSCs). Thereafter, we conducted multifaceted analyses including cytomorphology, immunophenotype, cell vitality, multilineage differentiation, whole-genome analysis, tube formation and Matrigel plug assay, lymphocyte activation and differentiation, and systemic transplantation for aplastic anaemia (AA) treatment.

RESULTS

III-MSCs with high-proportioned VCAM-1 expression were obtained by combining IL-1β, IL-4 with IFN-γ, which exhibited comparable immunophenotype with untreated hUC-MSCs (NT-MSCs) but revealed multidimensional superiorities both at the cellular and molecular levels. Simultaneously, systemic infusion of III-MSCs could significantly ameliorate clinicopathological features and finally help facilitate haematopoietic reconstruction and immunoregulation in AA mice.

CONCLUSIONS

We have established a high-efficient procedure for large-scale generation of III-MSCs with preferable signatures and efficacy upon aplastic anaemia in mice. Our findings suggested that III-MSCs were advantageous sources with multifaceted characteristics for regenerative medicine.

New Class of Crosslinker-Free Nanofiber Biomaterials from Hydra Nematocyst Proteins

Nematocysts, the stinging organelles of cnidarians, have remarkable mechanical properties. Hydra nematocyst capsules undergo volume changes of 50% during their explosive exocytosis and withstand osmotic pressures of beyond 100 bar. Recently, two novel protein components building up the nematocyst capsule wall in Hydra were identified. The cnidarian proline-rich protein 1 (CPP-1) characterized by a "rigid" polyproline motif and the elastic Cnidoin possessing a silk-like domain were shown to be part of the capsule structure via short cysteine-rich domains that spontaneously crosslink the proteins via disulfide bonds. In this study, recombinant Cnidoin and CPP-1 are expressed in E. coli and the elastic modulus of spontaneously crosslinked bulk proteins is compared with that of isolated nematocysts. For the fabrication of uniform protein nanofibers by electrospinning, the preparative conditions are systematically optimized. Both fibers remain stable even after rigorous washing and immersion into bulk water owing to the simultaneous crosslinking of cysteine-rich domains. This makes our nanofibers clearly different from other protein nanofibers that are not stable without chemical crosslinkers. Following the quantitative assessment of mechanical properties, the potential of Cnidoin and CPP-1 nanofibers is examined towards the maintenance of human mesenchymal stem cells.

Systematic comparison of hUC-MSCs at various passages reveals the variations of signatures and therapeutic effect on acute graft-versus-host disease

BACKGROUND

Mesenchymal stem cells are heterogenous populations with hematopoietic supporting and immunomodulating capacities. Enormous studies have focused on their preclinical or clinical therapeutic effects, yet the systematic study of continuous in vitro passages on signatures and functions of UC-MSCs at both the cellular and molecular levels is still lacking.

METHODS

In this study, to systematically evaluate the biological properties of MSCs at various passages, we analyzed biomarker expression, cell proliferation and apoptosis, chromosome karyotype, and tri-lineage differentiation potential. Subsequently, we took advantage of whole-exome sequencing to compare the somatic hypermutation of hUC-MSCs at P3, P6, and P15 including SNV and INDEL mutations. In addition, to explore the safety of the abovementioned hUC-MSCs, we performed metabolic pathway enrichment analysis and in vivo transplantation analysis. Furthermore, we cocultured the abovementioned hUC-MSCs with UCB-CD34⁺ HSCs to evaluate their hematopoietic supporting capacity in vitro. Finally, we transplanted the cells into acute graft-versus-host disease (aGVHD) mice to further evaluate their therapeutic effect in vivo.

RESULTS

The hUC-MSCs at P3, P6, and P15 showed similar morphology, biomarker expression, and cytokine secretion. hUC-MSCs at P15 had advantages on adipogenic differentiation and some cytokine secretion such as IL-6 and VEGF, with disadvantages on cell proliferation, apoptosis, and osteogenic and chondrogenic differentiation potential. Based on the SNP data of 334,378 exons and bioinformatic analyses, we found the somatic point mutations could be divided into 96 subsets and formed 30 kinds of signatures but did not show correlation with risk of tumorigenesis, which was confirmed by the in vivo transplantation experiments. However, hUC-MSCs at P15 showed impaired hematologic supporting effect in vitro and declined therapeutic effect on aGVHD in vivo.

CONCLUSIONS

In this study, we systematically evaluated the biological and genetic properties of hUC-MSCs at various passages. Our findings have provided new references for safety and effectiveness assessments, which will provide overwhelming evidence for the safety of hUC-MSCs after continuous in vitro passages both at the cellular and molecular levels for the first time. Taken together, our studies could help understand the controversial effects of disease treatment and benefit the clinical research of UC-MSCs.

Fate of systemically and locally administered adipose-derived mesenchymal stromal cells and their effect on wound healing

There is increasing interest in the use of adipose‐derived mesenchymal stromal cells (ASCs) for wound repair. As the fate of administered cells is still poorly defined, we aimed to establish the location, survival, and effect of ASCs when administered either systemically or locally during wound repair under physiological conditions. To determine the behavior of ASCs, a rat model with wounds on the dorsal aspect of the hind paws was used and two treatment modes were assessed: ASCs administered systemically into the tail vein or locally around the wound. ASCs were transduced to express both firefly luciferase (Fluc) and green fluorescent protein to enable tracking by bioluminescence imaging and immunohistological analysis. Systemically administered ASCs were detected in the lungs 3 hours after injection with a decrease in luminescent signal at 48 hours and signal disappearance from 72 hours. No ASCs were detected in the wound. Locally administered ASCs remained strongly detectable for 7 days at the injection site and became distributed within the wound bed as early as 24 hours post injection with a significant increase observed at 72 hours. Systemically administered ASCs were filtered out in the lungs, whereas ASCs administered locally remained and survived not only at the injection site but were also detected within the wound bed. Both treatments led to enhanced wound closure. It appears that systemically administered ASCs have the potential to enhance wound repair distally from their site of entrapment in the lungs whereas locally administered ASCs enhanced wound repair as they became redistributed within the wound bed.

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.

The effect of medium supplementation and serial passaging on the transcriptome of human adipose-derived stromal cells expanded in vitro

BACKGROUND

For adipose-derived stromal cells (ASCs) to be safe for use in the clinical setting, they need to be prepared using good manufacturing practices (GMPs). Fetal bovine serum (FBS), used to expand ASCs in vitro in some human clinical trials, runs the risk of xenoimmunization and zoonotic disease transmission. To ensure that GMP standards are maintained, pooled human platelet lysate (pHPL) has been used as an alternative to FBS. ASCs proliferate more rapidly in pHPL than in FBS, with no significant change in immunophenotype and differentiation capacity. However, not much is known about how pHPL affects the transcriptome of these cells.

METHODS

This study investigated the effect of pHPL and FBS on the ASC transcriptome during in vitro serial expansion from passage 0 to passage 5 (P0 to P5). RNA was isolated from ASCs at each passage and hybridized to Affymetrix HuGene 2.0 ST arrays for gene expression analysis.

RESULTS

We observed that the transcriptome of ASCs expanded in pHPL (pHPL-ASCs) and FBS (FBS-ASCs) had the greatest change in gene expression at P2. Gene ontology revealed that genes upregulated in pHPL-ASCs were enriched for cell cycle, migration, motility, and cell-cell interaction processes, while those in FBS-ASCs were enriched for immune response processes. ASC transcriptomes were most homogenous from P2 to P5 in FBS and from P3 to P5 in pHPL. FBS- and pHPL-gene-specific signatures were observed, which could be used as markers to identify cells previously grown in either FBS or pHPL for downstream clinical/research applications. The number of genes constituting the FBS-specific effect was 3 times greater than for pHPL, suggesting that pHPL may be a milder supplement for cell expansion. A set of genes were expressed in ASCs at all passages and in both media. This suggests that a unique ASC in vitro transcriptomic profile exists that is independent of the passage number or medium used.

CONCLUSIONS

GO classification revealed that pHPL-ASCs are more involved in cell cycle processes and cellular proliferation when compared to FBS-ASCs, which are involved in more specialized or differentiation processes like cardiovascular and vascular development. This makes pHPL a potential superior supplement for expanding ASCs as they retain their proliferative capacity, remain untransformed and pHPL does not affect the genes involved in differentiation in specific developmental processes.

Single cell transcriptomic analysis of human mesenchymal stem cells reveals limited heterogeneity

Mesenchymal stem cells (MSCs) are a population of multipotent cells with a superior ability to promote tissue repair by regulating regeneration and inflammation. Effective application of MSCs in disease treatment relies on the production of relatively homogeneous cell population. However, the cellular heterogeneity and the differentiation trajectories of in vitro expanded MSCs remain largely unclear. We profiled the transcriptomes of 361 single MSCs derived from two umbilical cords (UC-MSCs). These UC-MSCs were harvested at different passages and stimulated with or without inflammatory cytokines. Weighted gene correlation network analysis revealed that UC-MSCs surprisingly possess only limited heterogeneity, regardless of donors, and passages. We also found that upon pretreatment with inflammatory cytokines (IFNγ and TNFα), a classical strategy that can improve the efficiency of MSC-based therapy, MSCs exhibited uniformed changes in gene expression. Cell cycle-based principal component analysis showed that the limited heterogeneity identified in these UC-MSCs was strongly associated with their entrance into the G2/M phase. This was further proven by the observation that one featured gene, CD168, was expressed in a cell cycle-dependent manner. When CD168^high UC-MSCs were sorted and cultured in vitro, they again showed similar CD168 expression patterns. Our results demonstrated that in vitro expanded UC-MSCs are a well-organized population with limited heterogeneity dominated by cell cycle status. Thus, our studies provided information for standardization of MSCs for disease treatment.

In vitro heterogeneity of porcine adipose tissue-derived stem cells

Tissue-specific adult stem cells (ASC) are heterogeneous and characterized by a mix of progenitor cells that produce cells at various stages of differentiation, and ultimately different terminally differentiated cells. Understanding the heterogeneity of ASCs may lead to the development of improved protocols of cell isolation and optimized cell therapy clinical protocols. Using a combination of enzymatic and explant culture protocols, we obtained pADSC population, which is composed by two distinct morphologies: fibroblast-like cells (FLCs) and endothelial-like cells (ELCs). Both cell sub-types efficiently formed colonies, expressed CD90⁺/CD105⁺/CD44⁺, and differentially expressed such markers such as Nestin, Vimentin, Fibronectin, Cytokeratin, Connexin 43, CD31, CD34 and CD146 as well as the pluripotent stem cell markers Oct-4, Nanog and Sox2. Mixed populations of pADSCs did not lose their multipotentiality and the cells were able to undergo osteogenic, chondrogenic, adipogenic and myogenic differentiation. Furthermore, the mixed population spontaneously formed capillary tube structures. Our findings suggest that different subpopulations can be isolated from adipose tissue and that the ADSCs need to be better evaluated using a wide panel of different markers related to cell differentiation, which is important for stem cell therapy and regenerative medicine, particularly for advanced stem cells therapies - products that are currently under investigation or even use.

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.

Applications of mesenchymal stem cell technology in bovine species

Mesenchymal stem cells (MSCs) have received a great deal of attention over the past 20 years mainly because of the results that showed regeneration potential and plasticity that were much stronger than expected in prior decades. Recent findings in this field have contributed to progress in the establishment of cell differentiation methods, which have made stem cell therapy more clinically attractive. In addition, MSCs are easy to isolate and have anti-inflammatory and angiogenic capabilities. The use of stem cell therapy is currently supported by scientific literature in the treatment of several animal health conditions. MSC may be administered for autologous or allogenic therapy following either a fresh isolation or a thawing of a previously frozen culture. Despite the fact that MSCs have been widely used for the treatment of companion and sport animals, little is known about their clinical and biotechnological potential in the economically relevant livestock industry. This review focuses on describing the key characteristics of potential applications of MSC therapy in livestock production and explores the themes such as the concept, culture, and characterization of mesenchymal stem cells; bovine mesenchymal stem cell isolation; applications and perspectives on commercial interests and farm relevance of MSC in bovine species; and applications in translational research.

The majority of cells in so-called "mesenchymal stem cell" population are neither stem cells nor progenitors

OBJECTIVES

The first-passage adherent human bone marrow fibroblast-like cell population corresponds, in terms of phenotype and three-lineage differentiation capacity (assayed in bulk culture), to commonly termed "mesenchymal stem cells". Here we determine the proportion of high proliferative capacity multipotent cells present in this population in order to estimate the proportion of cells that can or cannot be considered as stem and progenitor cells.

MATERIAL AND METHODS

The single-cell cultures were established starting from human bone marrow-derived first-passage fibroblast-like cells and the proliferating clones were either transferred to secondary cultures to evaluate their further clonogenicity, or split into three wells to assess differentiation into each of the three different lineages.

RESULTS

The analysis of 197 single-cell cultures from three different bone marrow donors shows that only∼40% of so-called "mesenchymal stem cells" exhibit multipotency and are capable of sustained clonogenicity in secondary cultures.

CONCLUSION

Even in the first ex vivo passage under favorable conditions the majority (∼60%) of so-called "mesenchymal stem cells" are not multipotent and thus do not represent a stem cell entity.

Eminent Sources of Adult Mesenchymal Stem Cells and Their Therapeutic Imminence

In the recent times, stem cell biology has garnered the attention of the scientific fraternity and the general public alike due to the immense therapeutic potential that it holds in the field of regenerative medicine. A breakthrough in this direction came with the isolation of stem cells from human embryo and their differentiation into cell types of all three germ layers. However, the isolation of mesenchymal stem cells from adult tissues proved to be advantageous over embryonic stem cells due to the ethical and immunological naivety. Mesenchymal Stem Cells (MSCs) isolated from the bone marrow were found to differentiate into multiple cell lineages with the help of appropriate differentiation factors. Furthermore, other sources of stem cells including adipose tissue, dental pulp, and breast milk have been identified. Newer sources of stem cells have been emerging recently and their clinical applications are also being studied. In this review, we examine the eminent sources of Mesenchymal Stem Cells (MSCs), their immunophenotypes, and therapeutic imminence.

Murine Bone Marrow Mesenchymal Stromal Cells Respond Efficiently to Oxidative Stress Despite the Low Level of Heme Oxygenases 1 and 2

AIMS

Mesenchymal stromal cells (MSCs) are heterogeneous cells from adult tissues that are able to differentiate in vitro into adipocytes, osteoblasts, or chondrocytes. Such cells are widely studied in regenerative medicine. However, the success of cellular therapy depends on the cell survival. Heme oxygenase-1 (HO-1, encoded by the Hmox1 gene), an enzyme converting heme to biliverdin, carbon monoxide, and Fe²⁺, is cytoprotective and can affect stem cell performance. Therefore, our study aimed at assessing whether Hmox1 is critical for survival and functions of murine bone marrow MSCs.

RESULTS

Both MSC Hmox1^+/+ and Hmox1^-/- showed similar phenotype, differentiation capacities, and production of cytokines or growth factors. Hmox1^+/+ and Hmox1^-/- cells showed similar survival in response to 50 μmol/L hemin even in increased glucose concentration, conditions that were unfavorable for Hmox1^-/- bone marrow-derived proangiogenic cells (BDMC). Hmox1^+/+ MSCs but not fibroblasts retained low ROS levels even after prolonged incubation with 50 μmol/L hemin, although both cell types have a comparable Hmox1 expression and similarly increase its levels in response to hemin. MSCs Hmox1^-/- treated with hemin efficiently induced expression of a vast panel of antioxidant genes, especially enzymes of the glutathione pathway. Innovation and Conclusion: Hmox1 overexpression is a popular strategy to enhance viability and performance of MSCs after the transplantation. However, murine MSCs Hmox1^-/- do not differ from wild-type MSCs in phenotype and functions. MSC Hmox1^-/- show better resistance to hemin than fibroblasts and BDMCs and rapidly react to the stress by upregulation of quintessential genes in antioxidant response. Antioxid. Redox Signal. 00, 000-000.

Mesenchymal Stromal Cell Characteristics and Regenerative Potential in Cardiovascular Disease: Implications for Cellular Therapy

Administration of mesenchymal stromal cells (MSCs) is a promising strategy to treat cardiovascular disease (CVD). As progenitor cells may be negatively affected by both age and comorbidity, characterization of MSC function is important to guide decisions regarding use of allogeneic or autologous cells. Definitive answers on which factors affect MSC function can also aid in selecting which MSC donors would yield the most therapeutically efficacious MSCs. Here we provide a narrative review of MSC function in CVD based on a systematic search. A total of 41 studies examining CVD-related MSC (dys)function were identified. These data show that MSC characteristics and regenerative potential are often affected by CVD. However, studies presented conflicting results, and directed assessment of MSC parameters relevant to regenerative medicine applications was lacking in many studies. The predictive ability of in vitro assays for in vivo efficacy was rarely assessed. There was no correlation between quality of study reporting and study findings. Age mismatch was also not associated with study findings or effect size. Future research should focus on assays that assess regenerative potential in MSCs and parameters that relate to clinical success.

Mesenchymal Stromal Cells and Cutaneous Wound Healing: A Comprehensive Review of the Background, Role, and Therapeutic Potential

Cutaneous wound repair is a highly coordinated cascade of cellular responses to injury which restores the epidermal integrity and its barrier functions. Even under optimal healing conditions, normal wound repair of adult human skin is imperfect and delayed healing and scarring are frequent occurrences. Dysregulated wound healing is a major concern for global healthcare, and, given the rise in diabetic and aging populations, this medicoeconomic disease burden will continue to rise. Therapies to reliably improve nonhealing wounds and reduce scarring are currently unavailable. Mesenchymal stromal cells (MSCs) have emerged as a powerful technique to improve skin wound healing. Their differentiation potential, ease of harvest, low immunogenicity, and integral role in native wound healing physiology make MSCs an attractive therapeutic remedy. MSCs promote cell migration, angiogenesis, epithelialization, and granulation tissue formation, which result in accelerated wound closure. MSCs encourage a regenerative, rather than fibrotic, wound healing microenvironment. Recent translational research efforts using modern bioengineering approaches have made progress in creating novel techniques for stromal cell delivery into healing wounds. This paper discusses experimental applications of various stromal cells to promote wound healing and discusses the novel methods used to increase MSC delivery and efficacy.

Differentiation of Mesenchymal Stem Cells from Human Induced Pluripotent Stem Cells Results in Downregulation of c-Myc and DNA Replication Pathways with Immunomodulation Toward CD4 and CD8 Cells

Multilineage tissue-source mesenchymal stem cells (MSCs) possess strong immunomodulatory properties and are excellent therapeutic agents, but require constant isolation from donors to combat replicative senescence. The differentiation of human induced pluripotent stem cells (iPSCs) into MSCs offers a renewable source of MSCs; however, reports on their immunomodulatory capacity have been discrepant. Using MSCs differentiated from iPSCs reprogrammed using diverse cell types and protocols, and in comparison to human embryonic stem cell (ESC)-MSCs and bone marrow (BM)-MSCs, we performed transcriptome analyses and assessed for functional immunomodulatory properties. Differentiation of MSCs from iPSCs results in decreased c-Myc expression and its downstream pathway along with a concomitant downregulation in the DNA replication pathway. All four lines of iPSC-MSCs can significantly suppress in vitro activated human peripheral blood mononuclear cell (PBMC) proliferation to a similar degree as ESC-MSCs and BM-MSCs, and modulate CD4 T lymphocyte fate from a type 1 helper T cell (Th1) and IL-17A-expressing (Th17) cell fate to a regulatory T cell (Treg) phenotype. Moreover, iPSC-MSCs significantly suppress cytotoxic CD8 T proliferation, activation, and differentiation into type 1 cytotoxic T (Tc1) and IL-17-expressing CD8 T (Tc17) cells. Coculture of activated PBMCs with human iPSC-MSCs results in an overall shift of secreted cytokine profile from a pro-inflammatory environment to a more immunotolerant milieu. iPSC-MSC immunomodulation was also validated in vivo in a mouse model of induced inflammation. These findings support that iPSC-MSCs possess low oncogenicity and strong immunomodulatory properties regardless of cell-of-origin or reprogramming method and are good potential candidates for therapeutic use. Stem Cells 2018;36:903-914.

MSCs-cells with many sides

The field of mesenchymal stromal cell (MSC) biology and clinical cellular therapy has grown exponentially over the last few decades. With discovery of multiple tissue specific sources of stromal cells, invariably being termed MSCs, and their increasing clinical application, there is a need to further delineate the true definition of a mesenchymal stromal cell and to recognise the inherit differences between cell sources; both their potential and limitations. In this review, we discuss the importance of considering every stromal cell source as an independent entity and the need to critically evaluate and appreciate the true phenotype of these cells and their safety when considering their use in novel cell therapies.

Human Platelet Lysate versus Fetal Calf Serum: These Supplements Do Not Select for Different Mesenchymal Stromal Cells

Culture medium of mesenchymal stromal cells (MSCs) is usually supplemented with either human platelet lysate (HPL) or fetal calf serum (FCS). Many studies have demonstrated that proliferation and cellular morphology are affected by these supplements – it is therefore important to determine if they favor outgrowth of different subpopulations and thereby impact on the heterogeneous composition of MSCs. We have isolated and expanded human bone marrow-derived MSCs in parallel with HPL or FCS and demonstrated that HPL significantly increases proliferation and leads to dramatic differences in cellular morphology. Remarkably, global DNA-methylation profiles did not reveal any significant differences. Even at the transcriptomic level, there were only moderate changes in pairwise comparison. Furthermore, the effects on proliferation, cytoskeletal organization, and focal adhesions were reversible by interchanging to opposite culture conditions. These results indicate that cultivation of MSCs with HPL or FCS has no systematic bias for specific cell types.

Epigenetic Classification of Human Mesenchymal Stromal Cells

Standardization of mesenchymal stromal cells (MSCs) is hampered by the lack of a precise definition for these cell preparations; for example, there are no molecular markers to discern MSCs and fibroblasts. In this study, we followed the hypothesis that specific DNA methylation (DNAm) patterns can assist classification of MSCs. We utilized 190 DNAm profiles to address the impact of tissue of origin, donor age, replicative senescence, and serum supplements on the epigenetic makeup. Based on this, we elaborated a simple epigenetic signature based on two CpG sites to classify MSCs and fibroblasts, referred to as the Epi-MSC-Score. Another two-CpG signature can distinguish between MSCs from bone marrow and adipose tissue, referred to as the Epi-Tissue-Score. These assays were validated by site-specific pyrosequencing analysis in 34 primary cell preparations. Furthermore, even individual subclones of MSCs were correctly classified by our epigenetic signatures. In summary, we propose an alternative concept to use DNAm patterns for molecular definition of cell preparations, and our epigenetic scores facilitate robust and cost-effective quality control of MSC cultures.

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

Tumorigenicity analysis of heterogeneous dental stem cells and its self-modification for chromosome instability

Heterogeneity demonstrates that stem cells are constituted by several sub-clones in various differentiation states. The heterogeneous state is maintained by cross-talk among sub-clones, thereby ensuring stem cell adaption. In this study, we investigated the roles of heterogeneity on genetic stability. Three sub-clones (DF2, DF8 and DF18) were isolated from heterogeneous dental stem cells (DSCs), and were proved to be chromosome instability (CIN) after long term expansion. Cell apoptosis were not detected in sub-clones, which exhibited strong tumorigenesis tendency, coupled with weak expression of p53 and aberrant ultra-structure. However, 3 sub-clones did not overexpress tumor related markers or induce tumorigenesis in vivo. The mixed-culture study suggested that 3-clone-mixed culturing cells (DF1) presented apparent decrease in the ratio of aneuploidy. The screening experiment further proved that 3 sub-clones functioned separately in this modification procedure but only mixed culturing all 3 sub-clones, simulated heterogeneous microenvironment, could achieve complete modification. Additionally, osteogenesis capability of 3 sub-clones was partially influenced by CIN while DSCs still kept stronger osteogenesis than sub-clones. These results suggested aberrant sub-clones isolated from heterogeneous DSCs were not tumorigenesis and could modify CIN by cross-talk among themselves, indicating that the heterogeneity played a key role in maintaining genetic stability and differentiation capability in dental stem cells.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Serum-free process development: improving the yield and consistency of human mesenchymal stromal cell production

BACKGROUND AIMS

The cost-effective production of human mesenchymal stromal cells (hMSCs) for off-the-shelf and patient specific therapies will require an increasing focus on improving product yield and driving manufacturing consistency.

METHODS

Bone marrow-derived hMSCs (BM-hMSCs) from two donors were expanded for 36 days in monolayer with medium supplemented with either fetal bovine serum (FBS) or PRIME-XV serum-free medium (SFM). Cells were assessed throughout culture for proliferation, mean cell diameter, colony-forming potential, osteogenic potential, gene expression and metabolites.

RESULTS

Expansion of BM-hMSCs in PRIME-XV SFM resulted in a significantly higher growth rate (P < 0.001) and increased consistency between donors compared with FBS-based culture. FBS-based culture showed an inter-batch production range of 0.9 and 5 days per dose compared with 0.5 and 0.6 days in SFM for each BM-hMSC donor line. The consistency between donors was also improved by the use of PRIME-XV SFM, with a production range of 0.9 days compared with 19.4 days in FBS-based culture. Mean cell diameter has also been demonstrated as a process metric for BM-hMSC growth rate and senescence through a correlation (R(2) = 0.8705) across all conditions. PRIME-XV SFM has also shown increased consistency in BM-hMSC characteristics such as per cell metabolite utilization, in vitro colony-forming potential and osteogenic potential despite the higher number of population doublings.

CONCLUSIONS

We have increased the yield and consistency of BM-hMSC expansion between donors, demonstrating a level of control over the product, which has the potential to increase the cost-effectiveness and reduce the risk in these manufacturing processes.

Frequent mechanical stress suppresses proliferation of mesenchymal stem cells from human bone marrow without loss of multipotency

Mounting evidence indicated that human mesenchymal stem cells (hMSCs) are responsive not only to biochemical but also to physical cues, such as substrate topography and stiffness. To simulate the dynamic structures of extracellular environments of the marrow in vivo, we designed a novel surrogate substrate for marrow derived hMSCs based on physically cross-linked hydrogels whose elasticity can be adopted dynamically by chemical stimuli. Under frequent mechanical stress, hMSCs grown on our hydrogel substrates maintain the expression of STRO-1 over 20 d, irrespective of the substrate elasticity. On exposure to the corresponding induction media, these cultured hMSCs can undergo adipogenesis and osteogenesis without requiring cell transfer onto other substrates. Moreover, we demonstrated that our surrogate substrate suppresses the proliferation of hMSCs by up to 90% without any loss of multiple lineage potential by changing the substrate elasticity every 2nd days. Such “dynamic in vitro niche” can be used not only for a better understanding of the role of dynamic mechanical stresses on the fate of hMSCs but also for the synchronized differentiation of adult stem cells to a specific lineage.

Massive Clonal Selection and Transiently Contributing Clones During Expansion of Mesenchymal Stem Cell Cultures Revealed by Lentiviral RGB-Barcode Technology

Mesenchymal stem (or stromal) cells (MSCs) have been used in more than 400 clinical trials for the treatment of various diseases. The clinical benefit and reproducibility of results, however, remain extremely variable. During the in vitro expansion phase, which is necessary to achieve clinically relevant cell numbers, MSCs show signs of aging accompanied by different contributions of single clones to the mass culture. Here we used multicolor lentiviral barcode labeling to follow the clonal dynamics during in vitro MSC expansion from whole umbilical cord pieces (UCPs). The clonal composition was analyzed by a combination of flow cytometry, fluorescence microscopy, and deep sequencing. Starting with highly complex cell populations, we observed a massive reduction in diversity, transiently dominating populations, and a selection of single clones over time. Importantly, the first wave of clonal constriction already occurred in the early passages during MSC expansion. Consecutive MSC cultures from the same UCP implied the existence of more primitive, MSC culture-initiating cells. Our results show that microscopically homogenous MSC mass cultures consist of many subpopulations, which undergo clonal selection and have different capabilities. Among other factors, the clonal composition of the graft might have an impact on the functional properties of MSCs in experimental and clinical settings.

SIGNIFICANCE

Mesenchymal stem cells (MSCs) can easily be obtained from various adult or embryonal tissues and are frequently used in clinical trials. For their clinical application, MSCs have to be expanded in vitro. This unavoidable step influences the features of MSCs, so that clinical benefit and experimental results are often highly variable. Despite a homogenous appearance under the microscope, MSC cultures undergo massive clonal selection over time. Multicolor fluorescence labeling and deep sequencing were used to demonstrate the dynamic clonal composition of MSC cultures, which might ultimately explain the variable clinical performance of the cells.

Evaluation of GMP-compliant culture media for in vitro expansion of human bone marrow mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) from human bone marrow serve as a resource for cell-based therapies in regenerative medicine. Clinical applications require standardized protocols according to good manufacturing practice (GMP) guidelines. Donor variability as well as the intrinsic heterogeneity of MSC populations must be taken into consideration. The composition of the culture medium is a key factor in successful MSC expansion. The aim of this study was to comparatively assess the efficiency of xeno-free human platelet lysate (HPL)-based cell expansion with two commercially available media-StemPro MSC SFM CTS (for human ex vivo tissue and cell culture processing applications) and MSCGM (non-GMP-compliant, for research only)-in an academic setting as the first optimization step toward GMP-compliant manufacturing. We report the feasibility of MSC expansion up to the yielded cell number with all three media. MSCs exhibited the typical fibroblastoid morphology, with distinct differences in cell size depending on the medium. The differentiation capacity and characteristic immunophenotype were confirmed for all MSC populations. Proliferation was highest using StemPro MSC SFM CTS, whereas HPL medium was more cost-effective and its composition could be adjusted individually according to the respective needs. In summary, we present a comprehensive evaluation of GMP-compatible culture media for MSC expansion. Both StemPro and HPL medium proved to be suitable for clinical application and allowed sufficient cell proliferation. Specific differences were observed and should be considered according to the intended use. This study provides a detailed cost analysis and tools that may be helpful for the establishment of GMP-compliant MSC expansion.

Role of Epigenetics in Stem Cell Proliferation and Differentiation: Implications for Treating Neurodegenerative Diseases

The main objectives of this review are to survey the current literature on the role of epigenetics in determining the fate of stem cells and to assess how this information can be used to enhance the treatment strategies for some neurodegenerative disorders, like Huntington’s disease, Parkinson’s disease and Alzheimer’s disease. Some of these epigenetic mechanisms include DNA methylation and histone modifications, which have a direct impact on the way that genes are expressed in stem cells and how they drive these cells into a mature lineage. Understanding how the stem cells are behaving and giving rise to mature cells can be used to inform researchers on effective ways to design stem cell-based treatments. In this review article, the way in which the basic understanding of how manipulating this process can be utilized to treat certain neurological diseases will be presented. Different genetic factors and their epigenetic changes during reprogramming of stem cells into induced pluripotent stem cells (iPSCs) have significant potential for enhancing the efficacy of cell replacement therapies.

OP9 Stromal Cells Proteins Involved in Hematoendothelial Differentiation from Human Embryonic Stem Cells

Hematopoietic cells (HCs) and endothelial cells (ECs) can be produced in vitro from human embryonic stem cells (hESCs), but the differentiation systems used are still inefficient. To overcome this obstacle, it is necessary to understand the differentiation process. One of the methods used to obtain HCs and ECs from hESCs is their co-culture with stromal cells. The soluble factors secreted by these cells and cell-cell contact have a great impact on the differentiation process. Here, we performed comparative proteomic analyses of proteins obtained from the total extract of OP9 stromal cells and secreted by these cells before and during in vitro generation of HCs and ECs (hematoendothelial) from hESCs. We identified a total of 83 secreted and 759 intracellular proteins during differentiation. Twenty-five secreted and 181 proteins from the total extract were more abundant. Some secreted proteins are involved in cell-matrix interactions and HC and/or EC development. Moreover, 13 proteins of the total extract from OP9 cells that were exclusive/or more abundant during differentiation are involved in the Nrf2/Nfe2l2 gene pathway, that is, they are described to have a key role in oxidative stress and in hematopoietic development and maturation. Our proteomic profiles provide valuable insight about the proteins involved in in vitro hematoendothelial cell generation and in the future they might be used to optimize the differentiation process and produce both cell types in vitro.

Are mesenchymal stromal cells immune cells?

Mesenchymal stromal cells (MSCs) are considered to be promising agents for the treatment of immunological disease. Although originally identified as precursor cells for mesenchymal lineages, in vitro studies have demonstrated that MSCs possess diverse immune regulatory capacities. Pre-clinical models have shown beneficial effects of MSCs in multiple immunological diseases and a number of phase 1/2 clinical trials carried out so far have reported signs of immune modulation after MSC infusion. These data indicate that MSCs play a central role in the immune response. This raises the academic question whether MSCs are immune cells or whether they are tissue precursor cells with immunoregulatory capacity. Correct understanding of the immunological properties and origin of MSCs will aid in the appropriate and safe use of the cells for clinical therapy. In this review the whole spectrum of immunological properties of MSCs is discussed with the aim of determining the position of MSCs in the immune system.

Stem cell technology for bone regeneration: current status and potential applications

Continued improvements in the understanding and application of mesenchymal stem cells (MSC) have revolutionized tissue engineering. This is particularly true within the field of skeletal regenerative medicine. However, much remains unknown regarding the native origins of MSC, the relative advantages of different MSC populations for bone regeneration, and even the biologic safety of such unpurified, grossly characterized cells. This review will first summarize the initial discovery of MSC, as well as the current and future applications of MSC in bone tissue engineering. Next, the relative advantages and disadvantages of MSC isolated from distinct tissue origins are debated, including the MSC from adipose, bone marrow, and dental pulp, among others. The perivascular origin of MSC is next discussed. Finally, we briefly comment on pluripotent stem cell populations and their possible application in bone tissue engineering. While continually expanding, the field of MSC-based bone tissue engineering and regeneration shows potential to become a clinical reality in the not-so-distant future.

Non-enzymatic dissociation of human mesenchymal stromal cells improves chemokine-dependent migration and maintains immunosuppressive function

BACKGROUND AIMS

Human bone marrow-derived mesenchymal stromal cells (MSC) can suppress inflammation; therefore their therapeutic potential is being explored in clinical trials. Poor engraftment of infused MSC limits their therapeutic utility; this may be caused by MSC processing before infusion, in particular the method of their detachment from culture.

METHODS

Enzymatic methods of detaching MSC (Accutase and TrypLE) were compared with non-enzymatic methods (Cell Dissociation Buffer [CDB], ethylenediamine tetra-acetic acid and scraping) for their effect on MSC viability, chemokine receptor expression, multi-potency, immunomodulation and chemokine-dependent migration.

RESULTS

TrypLE detachment preserved MSC viability and tri-lineage potential compared with non-enzymatic methods; however, this resulted in near complete loss of surface chemokine receptor expression. Of the non-enzymatic methods, CDB detachment preserved the highest viability while retaining significant tri-lineage differentiation potential. Once re-plated, CDB-detached MSC regained their original morphology and reached confluence, unlike with the use of other non-enzymatic methods. Viability was significantly reduced with the use of ethylenediamine tetra-acetic acid and further reduced with the use of cell scraping. Addition of 1% serum during CDB detachment led to higher MSC numbers entering autophagy and increased MSC recovery after re-plating. TrypLE and CDB-detached MSC suppressed CD3(+)CD4(+)CD25(-) T-cell proliferation, although TrypLE-detached MSC exhibited superior suppression at 1:20 ratio. CDB detachment retained surface chemokine receptor expression and consequently increased migration to CCL22, CXCL12 and CCL4, in contrast with TrypLE-detached MSC.

CONCLUSIONS

This study demonstrates that non-enzymatic detachment of MSC with the use of CDB minimizes the negative impact on cell viability, multipotency and immunomodulation while retaining chemokine-dependent migration, which may be of importance in MSC delivery and engraftment in sites of injury.

Phenotypic and proteomic characteristics of human dental pulp derived mesenchymal stem cells from a natal, an exfoliated deciduous, and an impacted third molar tooth

The level of heterogeneity among the isolated stem cells makes them less valuable for clinical use. The purpose of this study was to understand the level of heterogeneity among human dental pulp derived mesenchymal stem cells by using basic cell biology and proteomic approaches. The cells were isolated from a natal (NDPSCs), an exfoliated deciduous (stem cells from human exfoliated deciduous (SHED)), and an impacted third molar (DPSCs) tooth of three different donors. All three stem cells displayed similar features related to morphology, proliferation rates, expression of various cell surface markers, and differentiation potentials into adipocytes, osteocytes, and chondrocytes. Furthermore, using 2DE approach coupled with MALDI-TOF/TOF, we have generated a common 2DE profile for all three stem cells. We found that 62.3 ± 7% of the protein spots were conserved among the three mesenchymal stem cell lines. Sixty-one of these conserved spots were identified by MALDI-TOF/TOF analysis. Classification of the identified proteins based on biological function revealed that structurally important proteins and proteins that are involved in protein folding machinery are predominantly expressed by all three stem cell lines. Some of these proteins may hold importance in understanding specific properties of human dental pulp derived mesenchymal stem cells.

Adipose-derived mesenchymal stromal/stem cells: An update on their phenotype in vivo and in vitro

Adipose tissue is a rich, ubiquitous and easily accessible source for multipotent stromal/stem cells and has, therefore, several advantages compared to other sources of mesenchymal stromal/stem cells. Several studies have tried to identify the origin of the stromal/stem cell population within adipose tissue in situ. This is a complicated attempt because no marker has currently been described which unambiguously identifies native adipose-derived stromal/stem cells (ASCs). Isolated and cultured ASCs are a non-uniform preparation consisting of several subsets of stem and precursor cells. Cultured ASCs are characterized by their expression of a panel of markers (and the absence of others), whereas their in vitro phenotype is dynamic. Some markers were expressed de novo during culture, the expression of some markers is lost. For a long time, CD34 expression was solely used to characterize haematopoietic stem and progenitor cells, but now it has become evident that it is also a potential marker to identify an ASC subpopulation in situ and after a short culture time. Nevertheless, long-term cultured ASCs do not express CD34, perhaps due to the artificial environment. This review gives an update of the recently published data on the origin and phenotype of ASCs both in vivo and in vitro. In addition, the composition of ASCs (or their subpopulations) seems to vary between different laboratories and preparations. This heterogeneity of ASC preparations may result from different reasons. One of the main problems in comparing results from different laboratories is the lack of a standardized isolation and culture protocol for ASCs. Since many aspects of ASCs, such as the differential potential or the current use in clinical trials, are fully described in other recent reviews, this review further updates the more basic research issues concerning ASCs’ subpopulations, heterogeneity and culture standardization.

Standardization of Good Manufacturing Practice-compliant production of bone marrow-derived human mesenchymal stromal cells for immunotherapeutic applications

BACKGROUND AIMS

Human mesenchymal stem or stromal cells (MSCs) represent a potential resource not only for regenerative medicine but also for immunomodulatory cell therapies. The application of different MSC culture protocols has significantly hampered the comparability of experimental and clinical data from different laboratories and has posed a major obstacle for multicenter clinical trials. Manufacturing of cell products for clinical application in the European Community must be conducted in compliance with Good Manufacturing Practice and requires a manufacturing license. In Germany, the Paul-Ehrlich-Institut as the Federal Authority for Vaccines and Biomedicines is critically involved in the approval process.

METHODS

This report summarizes a consensus meeting between researchers, clinicians and regulatory experts on standard quality requirements for MSC production.

RESULTS

The strategy for quality control testing depends on the product's cell composition, the manufacturing process and the indication and target patient population. Important quality criteria in this sense are, among others, the immunophenotype of the cells, composition of the culture medium and the risk for malignant transformation, as well as aging and the immunosuppressive potential of the manufactured MSCs.

CONCLUSIONS

This position paper intends to provide relevant information to interested parties regarding these criteria to foster the development of scientifically valid and harmonized quality standards and to support approval of MSC-based investigational medicinal products.