Spontaneous transformation of adult mesenchymal stem cells from cynomolgus macaques in vitro

Innovative Strategies for Liver Transplantation: The Role of Mesenchymal Stem Cells and Their Cell-Free Derivatives

Despite being the standard treatment for end-stage liver disease, liver transplantation has limitations like donor scarcity, high surgical costs, and immune rejection risks. Mesenchymal stem cells (MSCs) and their derivatives offer potential for liver regeneration and transplantation. MSCs, known for their multipotency, low immunogenicity, and ease of obtainability, can differentiate into hepatocyte-like cells and secrete bioactive factors that promote liver repair and reduce immune rejection. However, the clinical application of MSCs is limited by risks such as aberrant differentiation and low engraftment rates. As a safer alternative, MSC-derived secretomes and extracellular vesicles (EVs) offer promising therapeutic benefits, including enhanced graft survival, immunomodulation, and reduced ischemia-reperfusion injury. Current research highlights the efficacy of MSC-derived therapies in improving liver transplant outcomes, but further studies are necessary to standardize clinical applications. This review highlights the potential of MSCs and EVs to address key challenges in liver transplantation, paving the way for innovative therapeutic strategies.

Revisiting the role of mesenchymal stromal cells in cancer initiation, metastasis and immunosuppression

Immune checkpoint blockade (ICB) necessitates a thorough understanding of intricate cellular interactions within the tumor microenvironment (TME). Mesenchymal stromal cells (MSCs) play a pivotal role in cancer generation, progression, and immunosuppressive tumor microenvironment. Within the TME, MSCs encompass both resident and circulating counterparts that dynamically communicate and actively participate in TME immunosurveillance and response to ICB. This review aims to reevaluate various facets of MSCs, including their potential self-transformation to function as cancer-initiating cells and contributions to the creation of a conducive environment for tumor proliferation and metastasis. Additionally, we explore the immune regulatory functions of tumor-associated MSCs (TA-MSCs) and MSC-derived extracellular vesicles (MSC-EVs) with analysis of potential connections between circulating and tissue-resident MSCs. A comprehensive understanding of the dynamics of MSC-immune cell communication and the heterogeneous cargo of tumor-educated versus naïve MSCs may unveil a new MSC-mediated immunosuppressive pathway that can be targeted to enhance cancer control by ICB.

Adverse events, side effects and complications in mesenchymal stromal cell-based therapies

Numerous clinical studies have shown a wide clinical potential of mesenchymal stromal cells (MSCs) application. However, recent experience has accumulated numerous reports of adverse events and side effects associated with MSCs therapy. Furthermore, the strategies and methods of MSCs therapy did not change significantly in recent decades despite the clinical impact and awareness of potential complications. An extended understanding of limitations could lead to a wider clinical implementation of safe cell therapies and avoid harmful approaches. Therefore, our objective was to summarize the possible negative effects observed during MSCs-based therapies. We were also aimed to discuss the risks caused by weaknesses in cell processing, including isolation, culturing, and storage. Cell processing and cell culture could dramatically influence cell population profile, change protein expression and cell differentiation paving the way for future negative effects. Long-term cell culture led to accumulation of chromosomal abnormalities. Overdosed antibiotics in culture media enhanced the risk of mycoplasma contamination. Clinical trials reported thromboembolism and fibrosis as the most common adverse events of MSCs therapy. Their delayed manifestation generally depends on the patient's individual phenotype and requires specific awareness during the clinical trials with obligatory inclusion in the patient' informed consents. Finally we prepared the safety checklist, recommended for clinical specialists before administration or planning of MSCs therapy.

Stem cell therapy in liver regeneration: Focus on mesenchymal stem cells and induced pluripotent stem cells

The liver has the ability to repair itself after injury; however, a variety of pathological changes in the liver can affect its ability to regenerate, and this could lead to liver failure. Mesenchymal stem cells (MSCs) are considered a good source of cells for regenerative medicine, as they regulate liver regeneration through different mechanisms, and their efficacy has been demonstrated by many animal experiments and clinical studies. Induced pluripotent stem cells, another good source of MSCs, have also made great progress in the establishment of organoids, such as liver disease models, and in drug screening. Owing to the recent developments in MSCs and induced pluripotent stem cells, combined with emerging technologies including graphene, nano-biomaterials, and gene editing, precision medicine and individualized clinical treatment may be realized in the near future.

Novel cell sources for bone regeneration

A plethora of both acute and chronic conditions, including traumatic, degenerative, malignant, or congenital disorders, commonly induce bone disorders often associated with severe persisting pain and limited mobility. Over 1 million surgical procedures involving bone excision, bone grafting, and fracture repair are performed each year in the U.S. alone, resulting in immense levels of public health challenges and corresponding financial burdens. Unfortunately, the innate self-healing capacity of bone is often inadequate for larger defects over a critical size. Moreover, as direct transplantation of committed osteoblasts is hindered by deficient cell availability, limited cell spreading, and poor survivability, an urgent need for novel cell sources for bone regeneration is concurrent. Thanks to the development in stem cell biology and cell reprogramming technology, many multipotent and pluripotent cells that manifest promising osteogenic potential are considered the regenerative remedy for bone defects. Considering these cells' investigation is still in its relative infancy, each of them offers their own particular challenges that must be conquered before the large-scale clinical application.

The Application of Mesenchymal Stem Cells in the Treatment of Liver Diseases: Mechanism, Efficacy, and Safety Issues

Mesenchymal stem cell (MSC) transplantation is a novel treatment for liver diseases due to the roles of MSCs in regeneration, fibrosis inhibition and immune regulation. However, the mechanisms are still not completely understood. Despite the significant efficacy of MSC therapy in animal models and preliminary clinical trials, issues remain. The efficacy and safety of MSC-based therapy in the treatment of liver diseases remains a challenging issue that requires more investigation. This article reviews recent studies on the mechanisms of MSCs in liver diseases and the associated challenges and suggests potential future applications.

Stem cell therapy for osteonecrosis of femoral head: Opportunities and challenges

Osteonecrosis of the femoral head (ONFH) is a progressive disease with a complex etiology and unclear pathogenesis, resulting in severe hip pain and dysfunction mainly observed in young patients. Although total hip arthroplasty (THA) is the most effective treatment for patients with ONFH in the terminal stage, the results of THA in young patients or active populations are often not favorable, with some complications related to the prosthesis. With the development of biotechnology, an increasing number of studies pay attention to use of stem cells for the treatment of ONFH. Stem cells are characterized by the ability to self-renew and differentiate into multiple cell types, including differentiation into osteoblasts and endothelial cells to mediate bone repair and angiogenesis. Furthermore, stem cells can offer growth factors to promote blood supply in the necrotic regions by paracrine effects. Therefore, stem cell therapy has become one of the hip-preserving alternatives for ONFH. This review summarized the current trends in stem cell therapy for ONFH, from clinical applications to related basic research, and showed that an increasing number of studies have confirmed the effectiveness of stem cell therapy in ONFH. However, many unsolved problems and challenges in practical applications of stem cell therapy still exist, such as patient selection, standardized procedures, safety assessment, and the fate of transplanted cells in the body. Additional studies are required to find ideal cell sources, appropriate transplantation methods, and the optimal number of cells for transplantation.

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Diversities in repair processes present a challenge in the targeted treatment of ONFH.

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Osteogenesis and angiogenesis are the primary mechanisms of MSCs treatment in ONFH.

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Systematic safety assessment and cell tracing are necessary for stem cell therapy.

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Optimal numbers and methods of cell transplantation need to be further confirmed.

Mesenchymal Stem/Progenitor Cells: The Prospect of Human Clinical Translation

Mesenchymal stem/progenitor cells (MSCs) are key players in regenerative medicine, relying principally on their differentiation/regeneration potential, immunomodulatory properties, paracrine effects, and potent homing ability with minimal if any ethical concerns. Even though multiple preclinical and clinical studies have demonstrated remarkable properties for MSCs, the clinical applicability of MSC-based therapies is still questionable. Several challenges exist that critically hinder a successful clinical translation of MSC-based therapies, including but not limited to heterogeneity of their populations, variability in their quality and quantity, donor-related factors, discrepancies in protocols for isolation, in vitro expansion and premodification, and variability in methods of cell delivery, dosing, and cell homing. Alterations of MSC viability, proliferation, properties, and/or function are also affected by various drugs and chemicals. Moreover, significant safety concerns exist due to possible teratogenic/neoplastic potential and transmission of infectious diseases. Through the current review, we aim to highlight the major challenges facing MSCs' human clinical translation and shed light on the undergoing strategies to overcome them.

Success rates in isolating mesenchymal stem cells from permanent and deciduous teeth

Stem cells from human exfoliated deciduous teeth (SHED) and human dental pulp stem cells (hDPSCs) have emerged as attractive cell sources for bone regeneration. However, the specific teeth and the conditions most suitable for stem cell isolation remain unclear. Therefore, the success rate of SHED and hDPSCs isolation, the patient age and remaining root length in deciduous teeth were evaluated. Successful isolation was defined as when the cell culture was maintained up to the third passage without any contamination or other issues. Remaining tooth length was calculated using the root-to-crown ratio from patient X-rays and compared to the norm value from the literature. The overall successful isolation rate of SHED and hDPSCs was 82% and 70%. The average patient ages at extraction of the deciduous teeth and permanent teeth were 11 years and 9 months, and 22 years and 10 months respectively. In the successful SHED group, the average remaining root length of the anterior deciduous teeth was 71.4%, and that of the deciduous molars was 61.4%. Successful isolation appears to be associated with patient age, length of the remaining root, and also mechanical stress and other factors. Tooth selection criteria need to be identified to improve the success rate.

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.

Differentiation Potential and Tumorigenic Risk of Rat Bone Marrow Stem Cells Are Affected By Long-Term In Vitro Expansion

Objective:

Mesenchymal stem cells (MSCs) have the capacity for extensive expansion and adipogenic, osteogenic, chondrogenic, myogenic, and neural differentiation in vitro. The aim of our study was to determine stemness, differentiation potential, telomerase activity, and ultrastructural characteristics of long-term cultured rat bone marrow (rBM)-MSCs.

Materials and Methods:

rBM-MSCs from passages 3, 50, and 100 (P3, P50, and P100) were evaluated through immunocytochemistry, reverse transcription-polymerase chain reaction, telomerase activity assays, and electron microscopy.

Results:

A dramatic reduction in the levels of myogenic markers actin and myogenin was detected in P100. Osteogenic markers Coll1, osteonectin (Sparc), and osteocalcin as well as neural marker c-Fos and chondrogenic marker Coll2 were significantly reduced in P100 compared to P3 and P50. Osteogenic marker bone morphogenic protein-2 (BMP2) and adipogenic marker peroxisome proliferator-activated receptor gamma (Pparγ) expression was reduced in late passages. The expression of stemness factor Rex-1 was lower in P100, whereas Oct4 expression was decreased in P50 compared to P3 and P100. Increased telomerase activity was observed in long-term cultured cells, signifying tumorigenic risk. Electron microscopic evaluations revealed ultrastructural changes such as smaller number of organelles and increased amount of autophagic vacuoles in the cytoplasm in long-term cultured rBM-MSCs.

Conclusion:

This study suggests that long-term culture of rBM-MSCs leads to changes in differentiation potential and increased tumorigenic risk.

Therapeutic Applications of Extracellular Vesicles: Perspectives from Newborn Medicine

With the advancements in antenatal steroid therapies and surfactant replacement, current clinical practices in neonatal intensive care units allow the survival of infants at very low gestational age. Despite these advances, there continues to be significant morbidity associated with extreme preterm birth that includes both short-term and long-term cardiorespiratory impairment. With no effective single therapy in preventing or treating developmental lung injuries, the need for new tools to treat and reduce risk of complications associated with extreme preterm birth is urgent. Stem cell-based therapies, in particular therapies utilizing mesenchymal stem (stromal) cells (MSCs), have shown promise in a number of animal models of lung pathologies relevant to neonatology. Recent studies in this field have consolidated the concept that the therapeutic mechanism of MSC action is paracrine, and this led to wide acceptance of the concept that the delivery of the MSC secretome rather than live cells may provide an alternative therapeutic approach for many complex diseases. Here, we summarize the significance and application of cell-free based therapies in preclinical models of neonatal lung injury. We emphasize the development of extracellular vesicle (EV)-based therapeutics and focus on the challenges that remain to be addressed before their application to clinical practice.

Reporting Standards in Clinical Studies Evaluating Bone Marrow Aspirate Concentrate: A Systematic Review

PURPOSE

To perform a systematic review of clinical studies evaluating bone marrow aspirate concentrate (BMAC) in the treatment of musculoskeletal pathology to compare levels of reporting with recently published minimum standards.

METHODS

A systematic review of the clinical literature from August 2002 to August 2017 was performed. Human clinical studies published in English and involving the administration of BMAC for musculoskeletal applications were included. Studies evaluating non-concentrated preparations of bone marrow aspirate or preparations of laboratory cultured cells were excluded. Studies evaluating the treatment of dental or maxillofacial conditions were excluded. Similarly, in vitro studies, editorials, letters to the editor, and reviews were excluded. Levels of reporting were compared with previously published minimum standards agreed on through an international Delphi consensus process.

RESULTS

Of 1,580 studies identified on the initial search, 46 satisfied the criteria for inclusion. Considerable deficiencies in reporting of key variables including the details of BMAC preparation and composition were noted. Studies reported information on only 42% (range, 25%-60%) of the variables included within established minimum reporting standards. No study provided adequate information to enable the precise replication of preparation protocols and accurate characterization of the BMAC formulation delivered.

CONCLUSIONS

We found that all existing clinical studies in the literature evaluating BMAC for orthopaedic or sports medicine applications are limited by inadequate reporting of both preparation protocols and composition. Deficient reporting of the variables that may critically influence outcomes precludes interpretation, prevents other researchers from reproducing experimental conditions, and makes comparisons across studies difficult. We encourage the adoption of emerging minimum reporting standards for clinical studies evaluating the use of mesenchymal stem cells in orthopaedics.

LEVEL OF EVIDENCE

Level IV, systematic review of Level I through IV studies.

Minimum Information for Studies Evaluating Biologics in Orthopaedics (MIBO): Platelet-Rich Plasma and Mesenchymal Stem Cells

BACKGROUND

A comprehensive approach to the evaluation of biologic therapies for musculoskeletal conditions is required to guide appropriate future use. Clinical studies evaluating platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) are limited by inadequate reporting of scientific details critical to outcome. We developed minimum reporting requirements for clinical studies evaluating PRP and MSCs using Delphi consensus methods.

METHODS

The need for consensus on the minimum reporting requirements for studies evaluating biologics was identified at the American Academy of Orthopaedic Surgeons/Orthopaedic Research Society (AAOS/ORS) Biologic Treatments for Orthopaedic Injuries Symposium in 2015 and the American Orthopaedic Society for Sports Medicine (AOSSM) Biologic Treatments for Sports Injuries II Think Tank in 2015. A working group facilitated the development of 2 expert consensus statements for PRP and MSCs using Delphi techniques. Exhaustive lists of items that could be reported on by clinical studies evaluating PRP or MSCs were generated by searching the published literature and protocols. PRP and MSC expert groups, each made up of 24 invited speakers at the AAOS and AOSSM symposia, were surveyed on 3 occasions to establish consensus on the inclusion of each item within minimum reporting guidelines. In addition to rating their agreement, the experts were encouraged to propose further items or modifications. Predefined criteria were used to refine item lists after each survey. Final lists were compiled into checklist statements by the working group.

RESULTS

For PRP, the working group identified 93 experimental information items from the literature. Twenty-three experts (96%) completed 3 rounds of surveys. After 3 rounds, 58 items generated consensus with >75% agreement and <5% disagreement. These items were compiled into a 23-statement checklist. For MSCs, 103 items were identified from the published literature. Twenty-three experts (96%) completed 3 rounds of surveys. After 3 rounds, the 61 items for which consensus was reached were compiled into a 25-statement checklist.

CONCLUSIONS

This study has established expert consensus on the minimum reporting requirements for clinical studies evaluating PRP and MSCs.

CLINICAL RELEVANCE

These checklists provide specifications for the minimum information that should be reported by clinical studies evaluating PRP or MSCs.

Pericytes for the treatment of orthopedic conditions

Pericytes and other perivascular stem cells are of growing interest in orthopedics and tissue engineering. Long regarded as simple regulators of angiogenesis and blood pressure, pericytes are now recognized to have MSC (mesenchymal stem cell) characteristics, including multipotentiality, self-renewal, immunoregulatory functions, and diverse roles in tissue repair. Pericytes are typified by characteristic cell surface marker expression (including αSMA, CD146, PDGFRβ, NG2, RGS5, among others). Although alone no marker is absolutely specific for pericytes, collectively these markers appear to selectively identify an MSC-like pericyte. The purification of pericytes is most well described as a CD146⁺CD34^-CD45^- cell population. Pericytes and other perivascular stem cell populations have been applied in diverse orthopedic applications, including both ectopic and orthotopic models. Application of purified cells has sped calvarial repair, induced spine fusion, and prevented fibrous non-union in rodent models. Pericytes induce these effects via both direct and indirect mechanisms. In terms of their paracrine effects, pericytes are known to produce and secrete high levels of a number of growth and differentiation factors both in vitro and after transplantation. The following review will cover existing studies to date regarding pericyte application for bone and cartilage engineering. In addition, further questions in the field will be pondered, including the phenotypic and functional overlap between pericytes and culture-derived MSC, and the concept of pericytes as efficient producers of differentiation factors to speed tissue repair.

Mesenchymal stem cells: From stem cells to sarcomas

Mesenchymal stem cells (MSCs) have garnered vast interests in clinical settings, especially in regenerative medicine due to their unique properties-they are reliably isolated and expanded from various tissue sources; they are able to differentiate into mesodermal tissues such as bones, cartilages, adipose tissues, and muscles; and they have unique immunosuppressive properties. However, there are some concerns pertaining to the role of MSCs in the human body. On one hand, they are crucial component in the regeneration and repair of the human body. On the contrary, they are shown to transform into sarcomas. Although the exact mechanisms are still unknown, many new leads have pointed to the belief that MSCs do play a role in sarcomagenesis. This review focuses on the current updates and findings of the role of MSCs in their transformation process into sarcomas.

Loss of interactions between p53 and survivin gene in mesenchymal stem cells after spontaneous transformation in vitro

Mesenchymal stem cells (MSC) from various animals undergo a spontaneous transformation in long-term culture. The transformed MSCs are highly tumorigenic and are likely to be the tumor-initiating cells of sarcoma. To explain why the transformed MSCs become tumorigenic, the present study investigated the characteristics of rat MSCs before and after spontaneous transformation. It was shown that although the transformed MSCs maintained typical surface markers of MSC, they exhibited some cancer stem cell-like characteristics such as loss of contact inhibition and multi-potency to mesenchymal lineages, and acquirement of ability of anchorage-independent growth. The expression of a key senescence regulator p16 almost disappeared, but the other one, p53 abnormally increased in the transformed MSCs. ChIP assay demonstrated that a normal negative regulation of p53 on survivin gene disappeared in the transformed cells due to a lack of p53 binding to the promoter of survivin gene. DNA sequencing revealed that the p53 gene in transformed MSCs was not a wild-type, but a 942C>T mutant with the mutation located in the sequence coding p53 protein's DNA-binding domain. These findings indicate that the transformed MSCs express high levels of a p53 mutant that loses the ability to bind survivin gene, leading to an abnormally upregulated expression of survivin, which is a key reason for the cell's unlimited proliferation.

Q&A: Mesenchymal stem cells - where do they come from and is it important?

Mesenchymal stem — or stromal — cells (MSCs) have been administered in hundreds of clinical trials for multiple indications, making them some of the most commonly used selected regenerative cells. Paradoxically, MSCs have also long remained the least characterized stem cells regarding native identity and natural function, being isolated retrospectively in long-term culture. Recent years have seen progress in our understanding of the natural history of these cells, and candidate native MSCs have been identified within fetal and adult organs. Beyond basic knowledge, deciphering the biology of innate MSCs may have important positive consequences for the therapeutic use of these cells.

Mesenchymal stem cells-based therapy as a potential treatment in neurodegenerative disorders: is the escape from senescence an answer?

Aging is the most prominent risk factor contributing to the development of neurodegenerative disorders. In the United States, over 35 million of elderly people suffer from age-related diseases. Aging impairs the self-repair ability of neuronal cells, which undergo progressive deterioration. Once initiated, this process hampers the already limited regenerative power of the central nervous system, making the search for new therapeutic strategies particularly difficult in elderly affected patients. So far, mesenchymal stem cells have proven to be a viable option to ameliorate certain aspects of neurodegeneration, as they possess high proliferative rate and differentiate in vitro into multiple lineages. However, accumulating data have demonstrated that during long-term culture, mesenchymal stem cells undergo spontaneous transformation. Transformed mesenchymal stem cells show typical features of senescence, including the progressive shortening of telomers, which results in cell loss and, as a consequence, hampered regenerative potential. These evidences, in line with those observed in mesenchymal stem cells isolated from old donors, suggest that senescence may represent a limit to mesenchymal stem cells exploitation in therapy, prompting scholars to either find alternative sources of pluripotent cells or to arrest the age-related transformation. In the present review, we summarize findings from recent literature, and critically discuss some of the major hurdles encountered in the search of appropriate sources of mesenchymal stem cells, as well as benefits arising from their use in neurodegenerative diseases. Finally, we provide some insights that may aid in the development of strategies to arrest or, at least, delay the aging of mesenchymal stem cells to improve their therapeutic potential.

A shorter telomere is the key factor in preventing cultured human mesenchymal stem cells from senescence escape

Mesenchymal stem cells (MSCs) from various animals undergo spontaneous transformation in vitro,establishing some malignant characteristics. However,this phenomenon seems seldom appearing in human (h)MSCs. To address the question whether the hMSCs really do not undergo the spontaneous transformation and why,the present study compared MSCs from two species under the same conditions, the commercialized primary hMSCs whose in vitro life span is very uniform, and the rat (r)MSCs whose spontaneous transformation in vitro is well defined.It was demonstrated that in rMSCs, there were small numbers of re-proliferating cells appearing after a substantial senescent period. These “senescence-escaped”rMSCs were highly proliferative and did not show any sign of growth arrest during the following subcultures upto observed passage 32. Whereas after entering senescence, hMSCs no longer re-proliferated and finally died from apoptosis. Compared with rMSCs, the hMSCs possessed a much shorter telomere, and lacked both telomerase reverse transcriptase expression and telomerase activity. When proliferating from pre-senescent to senescent stages,the hMSCs had a greater loss of relative telomere length(51 % in hMSC vs. 15 % in rMSC), but both cells displayed a similar average telomere shortening per population doubling (0.50 ± 0.06 kb in rMSC vs. 0.49 ± 0.06 kbin hMSC; p > 0.05), indicating that the greater relative shortening of the hMSC telomeres was due to their original shorter length, rather than lack of telomere maintenance mechanisms. In conclusion, the hMSCs do not spontaneously initiate transformation, because they cannot escape senescence. This is particularly due to their much shorter telomere.

Genetically engineered immune privileged Sertoli cells: A new road to cell based gene therapy

Sertoli cells are immune privileged cells, important for controlling the immune response to male germ cells as well as maintaining the tolerogenic environment in the testis. Additionally, ectopic Sertoli cells have been shown to survive and protect co-grafted cells when transplanted across immunological barriers. The survival of ectopic Sertoli cells has led to the idea that they could be used in cell based gene therapy. In this review, we provide a brief overview of testis immune privilege and Sertoli cell transplantation, factors contributing to Sertoli cell immune privilege, the challenges faced by viral vector gene therapy, the use of immune privileged cells in cell based gene therapy and describe several recent studies on the use of genetically engineered Sertoli cells to provide continuous delivery of therapeutic proteins.

Guidelines for the use of cell lines in biomedical research

Cell-line misidentification and contamination with microorganisms, such as mycoplasma, together with instability, both genetic and phenotypic, are among the problems that continue to affect cell culture. Many of these problems are avoidable with the necessary foresight, and these Guidelines have been prepared to provide those new to the field and others engaged in teaching and instruction with the information necessary to increase their awareness of the problems and to enable them to deal with them effectively. The Guidelines cover areas such as development, acquisition, authentication, cryopreservation, transfer of cell lines between laboratories, microbial contamination, characterisation, instability and misidentification. Advice is also given on complying with current legal and ethical requirements when deriving cell lines from human and animal tissues, the selection and maintenance of equipment and how to deal with problems that may arise.

Guidelines for the use of cell lines in biomedical research

Cell-line misidentification and contamination with microorganisms, such as mycoplasma, together with instability, both genetic and phenotypic, are among the problems that continue to affect cell culture. Many of these problems are avoidable with the necessary foresight, and these Guidelines have been prepared to provide those new to the field and others engaged in teaching and instruction with the information necessary to increase their awareness of the problems and to enable them to deal with them effectively. The Guidelines cover areas such as development, acquisition, authentication, cryopreservation, transfer of cell lines between laboratories, microbial contamination, characterisation, instability and misidentification. Advice is also given on complying with current legal and ethical requirements when deriving cell lines from human and animal tissues, the selection and maintenance of equipment and how to deal with problems that may arise.

Natural history of mesenchymal stem cells, from vessel walls to culture vessels

Mesenchymal stem/stromal cells (MSCs) can regenerate tissues by direct differentiation or indirectly by stimulating angiogenesis, limiting inflammation, and recruiting tissue-specific progenitor cells. MSCs emerge and multiply in long-term cultures of total cells from the bone marrow or multiple other organs. Such a derivation in vitro is simple and convenient, hence popular, but has long precluded understanding of the native identity, tissue distribution, frequency, and natural role of MSCs, which have been defined and validated exclusively in terms of surface marker expression and developmental potential in culture into bone, cartilage, and fat. Such simple, widely accepted criteria uniformly typify MSCs, even though some differences in potential exist, depending on tissue sources. Combined immunohistochemistry, flow cytometry, and cell culture have allowed tracking the artifactual cultured mesenchymal stem/stromal cells back to perivascular anatomical regions. Presently, both pericytes enveloping microvessels and adventitial cells surrounding larger arteries and veins have been described as possible MSC forerunners. While such a vascular association would explain why MSCs have been isolated from virtually all tissues tested, the origin of the MSCs grown from umbilical cord blood remains unknown. In fact, most aspects of the biology of perivascular MSCs are still obscure, from the emergence of these cells in the embryo to the molecular control of their activity in adult tissues. Such dark areas have not compromised intents to use these cells in clinical settings though, in which purified perivascular cells already exhibit decisive advantages over conventional MSCs, including purity, thorough characterization and, principally, total independence from in vitro culture. A growing body of experimental data is currently paving the way to the medical usage of autologous sorted perivascular cells for indications in which MSCs have been previously contemplated or actually used, such as bone regeneration and cardiovascular tissue repair.

Mesenchymal stem cells, cancer challenges and new directions

Therapeutic use of multipotent mesenchymal stromal stem cells (MSC) is a promising venue for a large number of degenerative diseases and cancer. Their availability from many different adult tissues, ease of expansion in culture, the ability to avoid immune rejection and their homing ability, are some of the properties of MSCs that make them a great resource for therapy. However, the challenges and risks for cell-based therapies are multifaceted. The blessing of cell culture expansion also comes with a burden. During in vitro expansion, stem cells experience a long replicative history and therefore, become subjected to damage from intracellular and extracellular influences. As previously shown cells that are manipulated to obtain an expanded replicative potential are prone to spontaneous transformation in culture. These manipulations help bypass the naturally built-in controls of the cell that govern the delicate balance between cell proliferation, senescence and carcinogenesis. Because of this, there is a risk for patients receiving stem cells that are in vitro expanded. Whether these cells are genetically engineered or harbouring xenogenic compounds, they cannot truly be considered "safe" unless the cells are closely monitored. In the present communication, we will focus on the therapeutic potential of the human mesenchymal stem cells (hMSC) with special focus on their use in cancer therapy. We will consider different mechanisms, by which stem cells can maintain telomeres and thereby the cell's ability to be expanded in vitro, and also focus on a new therapeutic venue that utilises hMSCs as delivery vehicles in innovative new cancer treatments.

Recent insights into the identity of mesenchymal stem cells

The ability of mesenchymal stem cells (MSCs) to differentiate in vitro into chondrocytes, osteocytes and myocytes holds great promise for tissue engineering. Skeletal defects are emerging as key targets for treatment using MSCs due to the high responsiveness of bone to interventions in animal models. Interest in MSCs has further expanded in recognition of their ability to release growth factors and to adjust immune responses.

Despite their increasing application in clinical trials, the origin and role of MSCs in the development, repair and regeneration of organs have remained unclear. Until recently, MSCs could only be isolated in a process that requires culture in a laboratory; these cells were being used for tissue engineering without understanding their native location and function. MSCs isolated in this indirect way have been used in clinical trials and remain the reference standard cellular substrate for musculoskeletal engineering. The therapeutic use of autologous MSCs is currently limited by the need for ex vivo expansion and by heterogeneity within MSC preparations. The recent discovery that the walls of blood vessels harbour native precursors of MSCs has led to their prospective identification and isolation. MSCs may therefore now be purified from dispensable tissues such as lipo-aspirate and returned for clinical use in sufficient quantity, negating the requirement for ex vivo expansion and a second surgical procedure.

In this annotation we provide an update on the recent developments in the understanding of the identity of MSCs within tissues and outline how this may affect their use in orthopaedic surgery in the future.

Cite this article: Bone Joint J 2014;96-B:291–8.

Cytokinesis-block micronucleus assay adapted for analyzing genomic instability of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are multipotent cells used in cell therapy research. One of the problems involving hMSCs is the possibility of genetic instability during in vitro expansion required to obtain a suitable number of cells for clinical applications. The cytokinesis-block micronucleus (CBMN) assay measures genetic instability by analyzing the presence of micronucleus (MN), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) in binucleated cells. The present study describes modifications in the CBMN assay methodology to analyze genetic instability in hMSCs isolated from the umbilical vein and in vitro expanded. The best protocol to achieve binucleated hMSCs with preserved cytoplasm was as follows: cytochalasin B concentration (4.0 μg/mL), use of hypotonic treatment (3 min), and the fixative solution (9 methanol:1 acetic acid). These adaptations were reproduced in three hMSC primary cell cultures and also in XP4PA and A549 cell lines. The frequency of hMSCs treated with mitomycin-C presenting MN was lower than that with other nuclear alterations, indicating that the hMSCs contain mechanisms to avoid a high level of chromosomal breaks. However, a high frequency of cells with NPBs was detected and spontaneous anaphase bridges under normal hMSC in vitro culture were observed. Considering that anaphase bridges are characteristic alterations in tumor cells, the CBMN assay is indicated as an important tool associated with other genetic analyses in order to ensure the safe clinical use of hMSCs in cell therapy.

Long-term cultured mesenchymal stem cells frequently develop genomic mutations but do not undergo malignant transformation

Cultured human umbilical cord mesenchymal stem cells (hUC-MSCs) are being tested in several clinical trials and encouraging outcomes have been observed. To determine whether in vitro expansion influences the genomic stability of hUC-MSCs, we maintained nine hUC-MSC clones in long-term culture and comparatively analyzed them at early and late passages. All of the clones senesced in culture, exhibiting decreased telomerase activity and shortened telomeres. Two clones showed no DNA copy number variations (CNVs) at passage 30 (P30). Seven clones had ≥1 CNVs at P30 compared with P3, and one of these clones appeared trisomic chromosome 10 at the late passage. No tumor developed in immunodeficient mice injected with hUC-MSCs, regardless of whether the cells had CNVs at the late passage. mRNA-Seq analysis indicated that pathways of cell cycle control and DNA damage response were downregulated during in vitro culture in hUC-MSC clones that showed genomic instability, but the same pathways were upregulated in the clones with good genomic stability. These results demonstrated that hUC-MSCs can be cultured for many passages and attain a large number of cells, but most of the cultured hUC-MSCs develop genomic alterations. Although hUC-MSCs with genomic alterations do not undergo malignant transformation, periodic genomic monitoring and donor management focusing on genomic stability are recommended before these cells are used for clinical applications.

Detection of spontaneous tumorigenic transformation during culture expansion of human mesenchymal stromal cells

Human mesenchymal stem/stromal cells (MSCs) have been explored in a number of clinical trials as a possible method of treating various diseases. However, the effect of long-term cell expansion in vitro on physiological function and genetic stability is still poorly understood. In this study, MSC cultures derived from bone marrow and liver were evaluated for the presence of aberrant cells following long-term expansion. In 46 independent cultures, four batches of transformed MSCs (TMCs) were found, which were all beyond the culture period of five weeks. These aberrant cells were first identified based on the appearance of abnormal cytology and the acquirement of growth advantage. Despite common MSC markers being diminished or absent, TMCs remain highly susceptible to lysis by allogenic natural killer (NK) cells. When transplanted into immunodeficient mice, TMCs formed sarcoma-like tumors, whereas parental MSCs did not form tumors in mice. Using a combination of high-resolution genome-wide DNA array and short-tandem repeat profiling, we confirmed the origin of TMCs and excluded the possibility of human cell line contamination. Additional genomic duplication and deletions were observed in TMCs, which may be associated with the transformation event. Using gene and microRNA expression arrays, a number of genes were identified that were differentially expressed between TMCs and their normal parental counterparts, which may potentially serve as biomarkers to screen cultures for evidence of early transformation events. In conclusion, the spontaneous transformation of MSCs resulting in tumorigenesis is rare and occurs after relatively long-term (beyond five weeks) culture. However, as an added safety measure, cultures of MSCs can potentially be screened based on a novel gene expression signature.

Autologous transplantation of GDNF-expressing mesenchymal stem cells protects against MPTP-induced damage in cynomolgus monkeys

Glial cell-derived neurotrophic factor (GDNF) has shown beneficial effects in models of Parkinson's disease. The mild results observed in the double-blind clinical trial by intraputamenal infusion of recombinant GDNF proteins warrant a search for alternative delivery methods. In this study, we investigated the function of autologous mesenchymal stem cells (MSCs) expressing GDNF (GDNF-MSCs) for protection against MPTP-induced injury in cynomolgus monkeys. MSCs were obtained from the bone marrow of individual monkeys and gene-modified to express GDNF. Following unilateral engraftment of GDNF-MSCs into the striatum and substantia nigra, the animals were challenged with MPTP to induce a stable systemic Parkinsonian state. The motor functions were spared in the contralateral limbs of monkeys receiving GDNF-MSCs, but not in those receiving MSCs alone. In the striatum of the grafted hemisphere, dopamine levels were higher and dopamine uptake was enhanced. The results suggest that autologous MSCs may be a safe vehicle to deliver GDNF for enhancing nigro-striatum functions.

Age-associated changes in the ecological niche: implications for mesenchymal stem cell aging

Adult stem cells are critical for organ-specific regeneration and self-renewal with advancing age. The prospect of being able to reverse tissue-specific post-injury sequelae by harvesting, culturing and transplanting a patient's own stem and progenitor cells is exciting. Mesenchymal stem cells have emerged as a reliable stem cell source for this treatment modality and are currently being tested in numerous ongoing clinical trials. Unfortunately, the fervor over mesenchymal stem cells is mitigated by several lines of evidence suggesting that their efficacy is limited by natural aging. This article discusses the mechanisms and manifestations of age-associated deficiencies in mesenchymal stem cell efficacy. A consideration of recent experimental findings suggests that the ecological niche might be responsible for mesenchymal stem cell aging.

H3K9me-enhanced DNA hypermethylation of the p16INK4a gene: an epigenetic signature for spontaneous transformation of rat mesenchymal stem cells

To explore the mechanisms underlying spontaneous transformation of mesenchymal stem cells (MSCs), changes in senescence-associated molecules, particularly the epigenetic modification of the p16(INK4a) gene, including histone H3 lysine 27/9 methylation (H3K27/9me) and DNA methylation, were investigated in cultured adult rat bone marrow MSCs at different stages during the transformation process. It was shown that the MSCs underwent replicative senescence after 24 to 25 population doublings, characterized by positive staining for senescence-associated β-galactosidase, increased expression of p16(INK4a) and p21, and downregulated phosphorylation of Rb. The upregulation of p16(INK4a) was associated with decreased expression of enhancer of the zeste homolog 2 (Ezh2), and reduced levels of H3K27me and DNA methylation in the p16(INK4a) gene. At week 4 of senescence, reproliferating cells emerged among the senescent MSCs. These senescence-escaped MSCs lost their senescence-related markers (including p16(INK4a)) and became highly proliferative. In addition to H3K27me, another H3 modification pattern, H3K9me, appeared in the p16(INK4a) gene, accompanied by an enhanced DNA methylation. With continued culture, the senescence-escaped MSCs did not show any sign of growth arrest and gained the capacity for anchorage-independent growth. These immortalized (transformed) MSCs showed further enhanced DNA methylation of the p16(INK4a) gene by increased H3K9me. Ezh2 knockdown with shRNA eliminated H3K27me-mediated DNA methylation of the p16(INK4a) gene in presenescent MSCs, but had no effect on H3K9me-enhanced DNA hypermethylation in the cells after senescence escape. These findings identify an Ezh2- and H3K27me-independent, but H3K9me-enhanced, DNA hypermethylation of the p16(INK4a) gene, which might be an epigenetic signature for MSC spontaneous transformation.

Human placental decidua basalis-derived mesenchymal stem cells differentiate into dopamine neuron-like cells with no response to long-term culture in vitro

Human placental decidua basalis-derived mesenchymal stem cells (DBMSCs) have been identified as valuable sources for cell transplantation. In this study, we found that DBMSCs could be induced to form neural stem cells in the form of neurospheres. These neurospheres were further differentiated into dopamine neuron-like cells with a cocktail of cytokines. The differentiated DBMSCs were verified through the presence of a neuron-like morphology, the expression of specific dopamine neuron makers, and the production of dopamine. In addition, this differentiation capacity of DBMSCs was not affected by long-term culture, and the cells maintained a normal karyotype in vitro. The dopamine neuronal differentiation and the relative safety transplantation potential of DBMSCs may facilitate stem cell therapeutic approaches to Parkinson's disease.

Safety of mesenchymal stem cells for clinical application

Mesenchymal stem cells (MSCs) hold great promise as therapeutic agents in regenerative medicine and autoimmune diseases, based on their differentiation abilities and immunosuppressive properties. However, the therapeutic applications raise a series of questions about the safety of culture-expanded MSCs for human use. This paper summarized recent findings about safety issues of MSCs, in particular their genetic stability in long-term in vitro expansion, their cryopreservation, banking, and the role of serum in the preparation of MSCs.

Mesenchymal stem cell signaling in cancer progression

Mesenchymal (multipotent) stem/stromal cells (MSCs) may affect cancer progression through a number of secreted factors triggering activation of various cell signaling pathways. Depending on receptor status, phosphatase and tensin homolog (PTEN) status, or Wnt activation in the cancer cells, the signals may either result in increased growth and metastasis or lead to inhibition of growth with increased cell death. Thus, MSCs can play a dual role in cancer progression depending on the cellular context wherein they reside. The phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway has a central role in regulating tumor growth, and several MSC secreted factors stimulate activation of this pathway. A comprehensive understanding of the signals regulating MSC-tumor cross-talk is highly important for the development of MSCs as potential therapeutic vehicles. Thus, the presented review focuses on factors released by MSCs and on the dual role they may have on various stages of tumorigenesis.

Comment to: "Spontaneous transformation of adult mesenchymal stem cells from cynomolgus macaques in vitro" by Z. Ren et al. Exp. Cell Res. 317 (2011) 2950-2957: spontaneous transformation of mesenchymal stem cells in culture: facts or fiction?

There is at present a controversy in the literature whether MSCs are susceptible to spontaneous in vitro transformation or not. Several groups have reported spontaneous transformation of MSCs from various species. However, some of these reports were not true transformations and later proven to be due to cross-contaminating cancer cells. To date there is no solid evidence that MSCs can undergo spontaneous transformation in culture. Only two groups used DNA fingerprinting to authenticate their transformed cells, and both groups later showed cross-contamination of cancer cells in their cultures. In this commentary, we address the paper "Spontaneous transformation of adult mesenchymal stem cells from cynomolgus macaques in vitro" by Z. Ren et al. Exp. Cell Res. 317 (2011) 2950-2957. In this article the authors characterize the transformed mesenchymal cells (TMCs) and claim to have verified their origin. We question the authentication of the TMCs made by the authors and we also believe it is in the interest of the scientific community, that a highly controversial finding, such as spontaneous transformation of MSCs, should be properly verified by stringent methods, preferably DNA fingerprinting, in order to validate if an actual transformation event has occurred.

Spontaneous transformation of cynomolgus mesenchymal stem cells in vitro: further confirmation by short tandem repeat analysis

It remains a highly debatable issue whether mesenchymal stem cells (MSCs) can undergo spontaneous transformation in culture. Recently, two groups retracted their previous publications due to the finding that the claimed transformed cells are actually contaminating cancer cells, which calls for a more stringent identification of transformed cells in the field. In this study, we continued with our previous finding of spontaneous transformation of cynomolgus MSCs and provided further evidence using short tandem repeat analysis that the transformed mesenchymal stem cells were indeed derived from cynomolgus MSCs.