Serum-free spheroid suspension culture maintains mesenchymal stem cell proliferation and differentiation potential

Nanotechnology and bioengineering approaches to improve the potency of mesenchymal stem cell as an off-the-shelf versatile tumor delivery vehicle

Targeting actionable mutations in oncogene-driven cancers and the evolution of immuno-oncology are the two prominent revolutions that have influenced cancer treatment paradigms and caused the emergence of precision oncology. However, intertumoral and intratumoral heterogeneity are the main challenges in both fields of precision cancer treatment. In other words, finding a universal marker or pathway in patients suffering from a particular type of cancer is challenging. Therefore, targeting a single hallmark or pathway with a single targeted therapeutic will not be efficient for fighting against tumor heterogeneity. Mesenchymal stem cells (MSCs) possess favorable characteristics for cellular therapy, including their hypoimmune nature, inherent tumor-tropism property, straightforward isolation, and multilineage differentiation potential. MSCs can be loaded with various chemotherapeutics and oncolytic viruses. The combination of these intrinsic features with the possibility of genetic manipulation makes them a versatile tumor delivery vehicle that can be used for in vivo selective tumor delivery of various chemotherapeutic and biological therapeutics. MSCs can be used as biofactory for the local production of chemical or biological anticancer agents at the tumor site. MSC-mediated immunotherapy could facilitate the sustained release of immunotherapeutic agents specifically at the tumor site, and allow for the achievement of therapeutic concentrations without the need for repetitive systemic administration of high therapeutic doses. Despite the enthusiasm evoked by preclinical studies that used MSC in various cancer therapy approaches, the translation of MSCs into clinical applications has faced serious challenges. This manuscript, with a critical viewpoint, reviewed the preclinical and clinical studies that have evaluated MSCs as a selective tumor delivery tool in various cancer therapy approaches, including gene therapy, immunotherapy, and chemotherapy. Then, the novel nanotechnology and bioengineering approaches that can improve the potency of MSC for tumor targeting and overcoming challenges related to their low localization at the tumor sites are discussed.

Comparative Analysis of Somatic Stem Cells With Emphasis on Osteochondral Tissue Regeneration

Congenital anomalies, diseases, and injuries may result in osteochondral damage. Recently, a big hope has been given to somatic stem cells (SSCs) which are characterized as undifferentiated cells with an ability of long-term self-renewing and plasticity. They are adherent with a fibroblast-like morphology in vitro and express various surface markers (e.g. CD29, CD73, CD90, and CD105), but they are negative for CD31, CD34, CD45, and HLA-DR. SSCs secrete various bioactive molecules, which are involved in processes of regeneration. The main goal of the present study was the characterization and comparison of biological properties of SSCs obtained from adipose tissue, dental pulp, and urine concerning osteochondral regeneration. SSCs were maintained in an appropriate growth medium up to the third passage and were analyzed by light and electron microscope. The immunophenotype was analyzed by flow cytometry. The kinetics of proliferation was measured by MTT assay. Human Cytokine/Chemokine Multiplex Assay was used, and SSCs secretory profile was measured by Luminex MAGPIX® Instrument. Pellet cultures and a chondrogenic medium were used to induce chondrogenic differentiation. Osteogenic differentiation was induced by the osteogenic medium. Chondrogenic and osteogenic differentiation was analyzed by real-time PCR. SSCs had similar fibroblast-like morphology. They have similar kinetics of proliferation. SSCs shared the expression CD29, CD44, CD73, CD90, and CD105. They lack expression of CD29 and CD34. SSCs secerned similar levels of IL10 and IL18 while differing in IFN-gamma, IL6, IL8, MCP-1, and RANTES production. SSCs possess a similar capacity for chondrogenic differentiation but slightly differ in osteogenic differentiation. In conclusion, it can be emphasized that SSCs from adipose tissue, dental pulp, and urine share the majority of cellular characteristics typical for SSCs and have great potential to be used in osteochondral tissue regeneration.

Single-Cell Transcriptomics Unveils the Dedifferentiation Mechanism of Lung Adenocarcinoma Stem Cells

Lung adenocarcinoma (LUAD) is a major subtype of lung cancer, and its prognosis is still poor due to therapy resistance, metastasis, and recurrence. In recent years, increasing evidence has shown that the existence of lung cancer stem cells is responsible for the propagation, metastasis, therapy resistance, and recurrence of the tumor. During their transition to cancer stem cells, tumor cells need to inhibit cell differentiation and acquire invasive characteristics. However, our understanding of the property and role of such lung cancer stem cells is still limited. In this study, lung adenocarcinoma cancer stem cells (LCSCs) were enriched from the PC-9 cell line in a serum-free condition. PC-9 cells grew into spheres and showed higher survival rates when exposed to gefitinib: the drug used for the treatment of LUAD. Additionally, we found that the canonical stemness marker protein CD44 was significantly increased in the enriched LCSCs. Then, LCSCs were inoculated into the groin of nude mice for 1.5 months, and tumors were detected in the animals, indicating the strong stemness of the cells. After that, we performed single-cell RNA sequencing (scRNA-seq) on 7320 LCSCs and explored the changes in their transcriptomic signatures. We identified cell populations with a heterogeneous expression of cancer stem marker genes in LCSCs and subsets with different degrees of differentiation. Further analyses revealed that the activation of the FOXM1 (oncoprotein) transcription factor is a key factor in cell dedifferentiation, which enables tumor cells to acquire an epithelial-mesenchymal transition phenotype and increases the LCSC surface marker CD44. Moreover, we found that the combination of CD44, ABCG2, and ALCAM was a specific marker for LCSCs. In summary, this study identified the potential factors and molecular mechanisms underlying the stemness properties of LUAD cancer cells; it could also provide insight into developing novel and effective therapeutic approaches.

Editing a gateway for cell therapy across the blood-brain barrier

Stem cell therapy has been shown to improve stroke outcomes in animal models and is currently advancing towards clinical practice. However, uncertainty remains regarding the optimal route for cell delivery to the injured brain. Local intracerebral injections are effective in precisely delivering cells into the stroke cavity but carry the risk of damaging adjacent healthy tissue. Systemic endovascular injections, meanwhile, are minimally invasive, but most injected cells do not cross CNS barriers and become mechanically trapped in peripheral organs. Although the blood-brain barrier and the blood-CSF barrier tightly limit the entrance of cells and molecules into the brain parenchyma, immune cells can cross these barriers especially under pathological conditions, such as stroke. Deciphering the cell surface signature and the molecular mechanisms underlying this pathophysiological process holds promise for improving the targeted delivery of systemic injected cells to the injured brain. In this review, we describe experimental approaches that have already been developed in which (i) cells are either engineered to express cell surface proteins mimicking infiltrating immune cells; or (ii) cell grafts are preconditioned with hypoxia or incubated with pharmacological agents or cytokines. Modified cell grafts can be complemented with strategies to temporarily increase the permeability of the blood-brain barrier. Although these approaches could significantly enhance homing of stem cells into the injured brain, cell entrapment in off-target organs remains a non-negligible risk. Recent developments in safety-switch systems, which enable the precise elimination of transplanted cells on the administration of a drug, represent a promising strategy for selectively removing stem cells stuck in untargeted organs. In sum, the techniques described in this review hold great potential to substantially improve efficacy and safety of future cell therapies in stroke and may be relevant to other brain diseases.

Polyurethane and polyurethane/hydroxyapatite scaffold in a three-dimensional culture system

Designing a new scaffold with an optimal ability of osteogenesis differentiation is a significant step bone tissue engineering along with the growing demands for bone craft in recent decades. Herein, we used Polyurethane (PU), a novel biocompatible and flexible polymer, and Hydroxyapatite (HA), the major component of human hard tissues matrix for developing new scaffolds and analyzing the in vitro osteogenic differentiation potential of human adipose-derived mesenchymal stem cells (Ad-MSCs) in basal and induction media. Gene expression analysis was performed to evaluate the expression level of four osteogenic differentiation genes. MTT assays were also done to assess the attachment and proliferation of the cells after 7 and 21 days of seeding to scaffolds. The expression level of RUNX2 was increased in seeded cells on PU/HA scaffolds compared with the PU. Cellular adhesion and proliferation of the Ad-MSCs were higher in PU/HA than PU scaffolds according to the histology analysis. The PU and PU/HA scaffolds supported the attachment, proliferation, and differentiation of Ad-MSCs, and they are suitable candidates for producing constructs in bone regeneration. However, further in-vitro and in-vivo studies on these scaffolds are needed to introduce an appropriate candidate for clinical bone regeneration.

Dynamic Culture of Mesenchymal Stromal/Stem Cell Spheroids and Secretion of Paracrine Factors

In recent years, conditioned medium (CM) obtained from the culture of mesenchymal stromal/stem cells (MSCs) has been shown to effectively promote tissue repair and modulate the immune response in vitro and in different animal models, with potential for application in regenerative medicine. Using CM offers multiple advantages over the implantation of MSCs themselves: 1) simpler storage, transport, and preservation requirements, 2) avoidance of the inherent risks of cell transplantation, and 3) potential application as a ready-to-go biologic product. For these reasons, a large amount of MSCs research has focused on the characterization of the obtained CM, including soluble trophic factors and vesicles, preconditioning strategies for enhancing paracrine secretion, such as hypoxia, a three-dimensional (3D) environment, and biochemical stimuli, and potential clinical applications. In vitro preconditioning strategies can increase the viability, proliferation, and paracrine properties of MSCs and therefore improve the therapeutic potential of the cells and their derived products. Specifically, dynamic cultivation conditions, such as fluid flow and 3D aggregate culture, substantially impact cellular behaviour. Increased levels of growth factors and cytokines were observed in 3D cultures of MSC grown on orbital or rotatory shaking platforms, in stirred systems, such as spinner flasks or stirred tank reactors, and in microgravity bioreactors. However, only a few studies have established dynamic culture conditions and protocols for 3D aggregate cultivation of MSCs as a scalable and reproducible strategy for CM production. This review summarizes significant advances into the upstream processing, mainly the dynamic generation and cultivation of MSC aggregates, for de CM manufacture and focuses on the standardization of the soluble factor production.

Current Status of Mesenchymal Stem/Stromal Cells for Treatment of Neurological Diseases

Neurological disorders include a wide spectrum of clinical conditions affecting the central and peripheral nervous systems. For these conditions, which affect hundreds of millions of people worldwide, generally limited or no treatments are available, and cell-based therapies have been intensively investigated in preclinical and clinical studies. Among the available cell types, mesenchymal stem/stromal cells (MSCs) have been widely studied but as yet no cell-based treatment exists for neurological disease. We review current knowledge of the therapeutic potential of MSC-based therapies for neurological diseases, as well as possible mechanisms of action that may be explored to hasten the development of new and effective treatments. We also discuss the challenges for culture conditions, quality control, and the development of potency tests, aiming to generate more efficient cell therapy products for neurological disorders.

Perspectives on scaling production of adipose tissue for food applications

With rising global demand for food proteins and significant environmental impact associated with conventional animal agriculture, it is important to develop sustainable alternatives to supplement existing meat production. Since fat is an important contributor to meat flavor, recapitulating this component in meat alternatives such as plant based and cell cultured meats is important. Here, we discuss the topic of cell cultured or tissue engineered fat, growing adipocytes in vitro that could imbue meat alternatives with the complex flavor and aromas of animal meat. We outline potential paths for the large scale production of in vitro cultured fat, including adipogenic precursors during cell proliferation, methods to adipogenically differentiate cells at scale, as well as strategies for converting differentiated adipocytes into 3D cultured fat tissues. We showcase the maturation of knowledge and technology behind cell sourcing and scaled proliferation, while also highlighting that adipogenic differentiation and 3D adipose tissue formation at scale need further research. We also provide some potential solutions for achieving adipose cell differentiation and tissue formation at scale based on contemporary research and the state of the field.

Large-scale cultured meat production: Trends, challenges and promising biomanufacturing technologies

Food systems of the future will need to face an increasingly clear reality - that a protein-rich diet is essential for good health, but traditional meat products will not suffice to ensure safety, sustainability, and equity of food supply chains at a global scale. This paper provides an in-depth analysis of bioprocess technologies needed for cell-based meat production and challenges in reaching commercial scale. Specifically, it reviews state-of-the-art bioprocess technologies, current limitations, and opportunities for research across four domains: cell line development, cell culture media, scaffolding, and bioreactors. This also includes exploring innovations to make cultured meat a viable protein alternative across numerous key performance indicators and for specific applications where traditional livestock is not an option (e.g., local production, space exploration). The paper explores tradeoffs between production scale, product quality, production cost, and footprint over different time horizons. Finally, a discussion explores various factors that may impact the ability to successfully scale and market cultured meat products: social acceptance, environmental tradeoffs, regulatory guidance, and public health benefits. While the exact nature of the transition from traditional livestock to alternative protein products is uncertain, it has already started and will likely continue to build momentum in the next decade.

Culture Substrates for Improved Manufacture of Mesenchymal Stromal Cell Therapies

Recent developments in mesenchymal stromal cell (MSC) therapies have increased the demand for tools to improve their manufacture, including the selection of optimal culture substrate materials. While many clinical manufacturers use planar tissue culture plastic (TCP) surfaces for MSC production, others have begun exploring the use of alternative culture substrates that present a variety of spatial, mechanical, and biochemical cues that influence cell expansion and resulting cell quality. In this review, the effects of culture and material properties distinct from traditional planar TCP surfaces on MSC proliferation, surface marker expression, and commonly used indications for therapeutic potency are examined. The different properties summarized include the use of alternative culture formats such as cellular aggregates or 3D scaffolds, as well as the effects of culture substrate stiffness and presentation of specific adhesive ligands and topographical cues. Specific substrate properties can be related to greater cell expansion and improvement in specific therapeutic functionalities, demonstrating the utility of culture materials in further improving the clinical-scale manufacture of highly secretory MSC products.

Intravenously Infused Stem Cells for Cancer Treatment

Despite the recent influx of immunotherapies and small molecule drugs to treat tumors, cancer remains a leading cause of death in the United States, in large part due to the difficulties of treating metastatic cancer. Stem cells, which are inherently tumoritropic, provide a useful drug delivery vehicle to target both primary and metastatic tumors. Intravenous infusions of stem cells carrying or secreting therapeutic payloads show significant promise in the treatment of cancer. Stem cells may be engineered to secrete cytotoxic products, loaded with oncolytic viruses or nanoparticles containing small molecule drugs, or conjugated with immunotherapies. Herein we describe these preclinical and clinical studies, discuss the distribution and migration of stem cells following intravenous infusion, and examine both the limitations of and the methods to improve the migration and therapeutic efficacy of tumoritropic, therapeutic stem cells.

Kinship of conditionally immortalized cells derived from fetal bone to human bone-derived mesenchymal stroma cells

The human fetal osteoblast cell line (hFOB 1.19) has been proposed as an accessible experimental model for study of osteoblast biology relating to drug development and biomaterial engineering. For their multilineage differentiation potential, hFOB has been compared to human mesenchymal progenitor cells and used to investigate bone-metabolism in vitro. Hereby, we studied whether and to what extent the conditionally immortalized cell line hFOB 1.19 can serve as a surrogate model for bone-marrow derived mesenchymal stromal cells (bmMSC). hFOB indeed exhibit specific characteristics reminiscent of bmMSC, as colony formation, migration capacity and the propensity to grow as multicellular aggregates. After prolonged culture, in contrast to the expected effect of immortalization, hFOB acquired a delayed growth rate. In close resemblance to bmMSC at increasing passages, also hFOB showed morphological abnormalities, enlargement and finally reduced proliferation rates together with enhanced expression of the cell cycle inhibitors p21 and p16. hFOB not only have the ability to undergo multilineage differentiation but portray several important aspects of human bone marrow mesenchymal stromal cells. Superior to primary MSC and osteoblasts, hFOB enabled the generation of continuous cell lines. These provide an advanced basis for investigating age-related dysfunctions of MSCs in an in vitro 3D-stem cell microenvironment.

Suspension culture in a T-flask with acoustic flow induced by ultrasonic irradiation

Suspension culture is an essential large-scale cell culture technique for biopharmaceutical development and regenerative medicine. To transition from monolayer culture on the culture surface of a flask to suspension culture in a bioreactor, a pre-specified cell number must first be reached. During this period of preparation for suspension culture, static suspension culture in a flask is generally performed because the medium volume is not large enough to use a paddle to circulate the medium. However, drawbacks to this static method include cell sedimentation, leading to high cell density near the bottom and resulting in oxygen and nutrient deficiencies. Here, we propose a suspension culture method with acoustic streaming induced by ultrasonic waves in a T-flask to create a more homogeneous distribution of oxygen, nutrients, and waste products during the preparation period preceding large-scale suspension culture in a bioreactor. To demonstrate the performance of the ultrasonic method, Chinese hamster ovary cells were cultured for 72 h. Results showed that, on average, the cell proliferation was improved by 40% compared with the static method. Thus, the culture time required to achieve a 1000-fold increase could be reduced by 32 h (a 14% reduction) compared with the static method. Furthermore, the ultrasonic irradiation did not compromise the metabolic activity of the cells cultured using the ultrasonic method. These results demonstrate the effectiveness of the ultrasonic method for accelerating the transition to large-scale suspension culture.

Peripheral Nerve-Derived Stem Cell Spheroids Induce Functional Recovery and Repair after Spinal Cord Injury in Rodents

Stem cell therapy is one of the most promising candidate treatments for spinal cord injury. Research has shown optimistic results for this therapy, but clinical limitations remain, including poor viability, engraftment, and differentiation. Here, we isolated novel peripheral nerve-derived stem cells (PNSCs) from adult peripheral nerves with similar characteristics to neural-crest stem cells. These PNSCs expressed neural-crest specific markers and showed multilineage differentiation potential into Schwann cells, neuroglia, neurons, and mesodermal cells. In addition, PNSCs showed therapeutic potential by releasing the neurotrophic factors, including glial cell-line-derived neurotrophic factor, insulin-like growth factor, nerve growth factor, and neurotrophin-3. PNSC abilities were also enhanced by their development into spheroids which secreted neurotrophic factors several times more than non-spheroid PNSCs and expressed several types of extra cellular matrix. These features suggest that the potential for these PNSC spheroids can overcome their limitations. In an animal spinal cord injury (SCI) model, these PNSC spheroids induced functional recovery and neuronal regeneration. These PNSC spheroids also reduced the neuropathic pain which accompanies SCI after remyelination. These PNSC spheroids may represent a new therapeutic approach for patients suffering from SCI.

Functional Properties of Human-Derived Mesenchymal Stem Cell Spheroids: A Meta-Analysis and Systematic Review

Mesenchymal stem cells (MSC) are adult multi-potent cells that can be isolated from many types of tissues including adipose tissue, bone marrow, and umbilical cord. They show great potential for cell therapy-based treatments, which is why they are being used in numerous clinical trials for a wide range of diseases. However, the success of placebo-controlled clinical trials has been limited, so new ways of improving the therapeutic effects of MSC are being developed, such as their assembly in a 3D conformation. In this meta-analysis, we review aggregate formation, in vitro functional properties and in vivo therapeutic potential displayed by adipose tissue, bone marrow, and umbilical cord-derived MSC, assembled as spheroids. The databases PubMed and SciELO were used to find eligible articles, using free-words and MeSH terms related to the subject, finding 28 published articles meeting all inclusion and exclusion criteria. Of the articles selected 15 corresponded to studies using MSC derived from bone marrow, 10 from adipose tissue and 3 from umbilical cord blood or tissue. The MSC spheroids properties analyzed that displayed enhancement in comparison with monolayer 2D culture, are stemness, angiogenesis, differentiation potential, cytokine secretion, paracrine and immunomodulatory effects. Overall studies reveal that the application of MSC spheroids in vivo enhanced therapeutic effects. For instance, research exhibited reduced inflammation, faster wound healing, and closure, functional recovery and tissue repair due to immunomodulatory effects, better MSC engraftment in damaged tissue, higher MSC survival and less apoptosis at the injury. Still, further research and clinical studies with controlled and consistent results are needed to see the real therapeutic efficacy of MSC spheroids.

Hypoxia Onset in Mesenchymal Stem Cell Spheroids: Monitoring With Hypoxia Reporter Cells

The therapeutic and differentiation potential of human mesenchymal stems cells (hMSCs) makes these cells a promising candidate for cellular therapies and tissue engineering. On the path of a successful medical application of hMSC, the cultivation of cells in a three-dimensional (3D) environment was a landmark for the transition from simple two-dimensional (2D) testing platforms to complex systems that mimic physiological in vivo conditions and can improve hMSC curative potential as well as survival after implantation. A 3D arrangement of cells can be mediated by scaffold materials where cells get entrapped in pores, or by the fabrication of spheroids, scaffold-free self-organized cell aggregates that express their own extracellular matrix. Independently from the cultivation method, cells expanded in 3D experience an inhomogeneous microenvironment. Many gradients in nutrient supply, oxygen supply, and waste disposal from one hand mimic in vivo microenvironment, but also put every cell in the 3D construct in a different context. Since oxygen concentration in spheroids is compromised in a size-dependent manner, it is crucial to have a closer insight on the thresholds of hypoxic response in such systems. In this work, we want to improve our understanding of oxygen availability and consequensing hypoxia onset in hMSC spheroids. Therefore, we utilized human adipose tissue-derived MSCs (hAD-MSCs) modified with a genetical sensor construct to reveal (I) the influence of spheroid production methods and (II) hMSCs cell number per spheroid to detect the onset of hypoxia in aggregates. We could demonstrate that not only higher cell numbers of MSCs, but also spheroid formation method plays a critical role in onset of hypoxia.

Small Molecule Targeting of Oxysterol-Binding Protein (OSBP)-Related Protein 4 and OSBP Inhibits Ovarian Cancer Cell Proliferation in Monolayer and Spheroid Cell Models

The development of precision drugs for the selective treatment of ovarian cancer will require targeting proliferative factors selectively expressed in ovarian tumors or targeting unique physiological microenvironments specific for ovarian tumors. Here, we report that oxysterol-binding protein (OSBP)-related protein 4 (ORP4) is a potential druggable precision target in ovarian cancer cells. ORP4 has limited expression in normal tissues and was recently recognized to be a cancer-specific driver of cellular proliferation, including in patient-isolated leukemias. We demonstrate that ORP4 is strongly expressed in a panel of ovarian cancer cell lines. The antiproliferative natural product compound OSW-1 targets ORP4 and OSBP. Our results demonstrate that the OSW-1 compound has high antiproliferative potency in both monolayer and three-dimensional ovarian cancer spheroid models, especially compared to the standard-of-care agents cisplatin and paclitaxel. OSW-1 compound treatment induces a loss of ORP4 expression after 48 h, which is coincident with the cytotoxic effects of OSW-1. The absence of extracellular lipids markedly potentiated the cytotoxicity of OSW-1, which was reversed by addition of extracellular free cholesterol. OSBP, but not ORP4, is reported to transport cholesterol and other lipids between organelles. Our results indicate that the targeting of ORP4 is responsible for the antiproliferative activity of the OSW-1 compound, but that in the absence of exogenously supplied cholesterol, which might be similar to the in vivo ovarian cancer microenvironment, possible OSW-1 targeting of OSBP further potentiates the anticancer activity of the compound. Overall, ORP4 and potentially OSBP are revealed as potential druggable targets for the development of novel treatments for ovarian cancer.

Turning Nature's own processes into design strategies for living bone implant biomanufacturing: a decade of Developmental Engineering

A decade after the term developmental engineering (DE) was coined to indicate the use of developmental processes as blueprints for the design and development of engineered living implants, a myriad of proof-of-concept studies demonstrate the potential of this approach in small animal models. This review provides an overview of DE work, focusing on applications in bone regeneration. Enabling technologies allow to quantify the distance between in vitro processes and their developmental counterpart, as well as to design strategies to reduce that distance. By embedding Nature's robust mechanisms of action in engineered constructs, predictive large animal data and subsequent positive clinical outcomes can be gradually achieved. To this end, the development of next generation biofabrication technologies should provide the necessary scale and precision for robust living bone implant biomanufacturing.

Spheroid-Like Cultures for Expanding Angiopoietin Receptor-1 (aka. Tie2) Positive Cells from the Human Intervertebral Disc

Lower back pain is a leading cause of disability worldwide. The recovery of nucleus pulposus (NP) progenitor cells (NPPCs) from the intervertebral disc (IVD) holds high promise for future cell therapy. NPPCs are positive for the angiopoietin-1 receptor (Tie2) and possess stemness capacity. However, the limited Tie2+ NPC yield has been a challenge for their use in cell-based therapy for regenerative medicine. In this study, we attempted to expand NPPCs from the whole NP cell population by spheroid-formation assay. Flow cytometry was used to quantify the percentage of NPPCs with Tie2-antibody in human primary NP cells (NPCs). Cell proliferation was assessed using the population doublings level (PDL) measurement. Synthesis and presence of extracellular matrix (ECM) from NPC spheroids were confirmed by quantitative Polymerase Chain Reaction (qPCR), immunostaining, and microscopy. Compared with monolayer, the spheroid-formation assay enriched the percentage of Tie2+ in NPCs’ population from ~10% to ~36%. Moreover, the spheroid-formation assay also inhibited the proliferation of the Tie2- NPCs with nearly no PDL. After one additional passage (P) using the spheroid-formation assay, NPC spheroids presented a Tie2+ percentage even further by ~10% in the NPC population. Our study concludes that the use of a spheroid culture system could be successfully applied to the culture and expansion of tissue-specific progenitors.

A Shaking-Culture Method for Generating Bone Marrow Derived Mesenchymal Stromal/Stem Cell-Spheroids With Enhanced Multipotency in vitro

Mesenchymal stromal/stem cells (MSCs), which generally expand into adherent monolayers, readily lose their proliferative and multilineage potential following repeated passages. Floating culture systems can be used to generate MSC spheroids, which are expected to overcome limitations associated with conventional adherent cultures while facilitating scaffold-free cell transplantation. However, the phenotypic characteristics of spheroids after long-term culture are unknown. In addition, regenerative therapies require new culture systems to maintain their undifferentiated state. In this study, we established a novel culture method employing three-dimensional (3D) “shaking” to generate MSC spheroids using bone marrow derived MSCs. Floating 3D cultures of mouse or human MSCs formed spheroids after shaking (85–95 rpm), within 1 month. These spheroids maintained their osteogenic-, adipogenic-, and chondrogenic-differentiation capacity. The adipogenic-differentiation capacity of adherent cultured mouse and human MSCs, which is lost following several passages, was remarkedly restored by shaking-culture. Notably, human MSC spheroids exhibited a renewable “undifferentiated MSC-pool” property, wherein undifferentiated MSCs grew from spheroids seeded repeatedly on a plastic culture dish. These data suggest that the shaking-culture method maintains and restores multipotency that is lost following monolayer expansion and thereby shows potential as a promising strategy for regenerative therapies with mesenchymal tissues.

Numerical Methods for the Design and Description of In Vitro Expansion Processes of Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) are a valuable source of cells for clinical applications (e.g., treatment of acute myocardial infarction or inflammatory diseases), especially in the field of regenerative medicine. However, for autologous (patient-specific) and allogeneic (off-the-shelf) hMSC-based therapies, in vitro expansion is necessary prior to the clinical application in order to achieve the required cell numbers. Safe, reproducible, and economic in vitro expansion of hMSCs for autologous and allogeneic therapies can be problematic because the cell material is restricted and the cells are sensitive to environmental changes. It is beneficial to collect detailed information on the hydrodynamic conditions and cell growth behavior in a bioreactor system, in order to develop a so called "Digital Twin" of the cultivation system and expansion process. Numerical methods, such as Computational Fluid Dynamics (CFD) which has become widely used in the biotech industry for studying local characteristics within bioreactors or kinetic growth modelling, provide possible solutions for such tasks.In this review, we will present the current state-of-the-art for the in vitro expansion of hMSCs. Different numerical tools, including numerical fluid flow simulations and cell growth modelling approaches for hMSCs, will be presented. In addition, a case study demonstrating the applicability of CFD and kinetic growth modelling for the development of an microcarrier-based hMSC process will be shown.

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.

Limited Potential or Unfavorable Manipulations? Strategies Toward Efficient Mesenchymal Stem/Stromal Cell Applications

Despite almost 50 years of research and over 20 years of preclinical and clinical studies, the question of curative potential of mesenchymal stem/stromal cells (MSCs) is still widely discussed in the scientific community. Non-reproducible treatment outcomes or even absence of treatment effects in comparison to control groups challenges the potential of these cells for routine application both in tissue engineering and in regenerative medicine. One of the reasons of such outcomes is non-standardized and often disadvantageous ex vivo manipulation of MSCs prior therapy. In most cases, clinically relevant cell numbers for MSC-based therapies can be only obtained by in vitro expansion of isolated cells. In this mini review, we will discuss point by point possible pitfalls in the production of human MSCs for cell therapies, without consideration of material-based applications. Starting with cell source, choice of donor and recipient, as well as isolation methods, we will then discuss existing expansion protocols (two-/three-dimensional cultivation, basal medium, medium supplements, static/dynamic conditions, and hypoxic/normoxic conditions) and influence of these strategies on the cell functionality after implantation. The role of potency assays will also be addressed. The final aim of this mini review is to illustrate the heterogeneity of current strategies for gaining MSCs for clinical applications with their strengths and weaknesses. Only a careful consideration and standardization of all pretreatment processes/methods for the different applications of MSCs will ensure robust and reproducible performance of these cell populations in the different experimental and clinical settings.

A comparative in vitro study of the effect of biospecific integrin recognition processes and substrate nanostructure on stem cell 3D spheroid formation

The in vitro study of the properties of the human mesenchymal stem cells as well as their manipulation in culture for clinical purposes depends on the elimination of artefacts caused by the lack of their natural environment. It is now widely accepted that mesenchymal stem cells should be studied when they are organised as 3D spheroids rather than fibroblast-like colonies. Although this can be achieved with the use of some extracellular matrix proteins or by non-adherent conditions these suffer of significant limitations. The recent development of synthetic substrates resembling the physicochemical and biochemical properties of the adult stem cell niche has prompted questions about the role played by nanotopography and receptor-mediated adhesion. In the present paper, the influence of two types of substrates bearing the same nanostructure, but exposing either a non-specific or an integrin-specific binding motif was studied. Carboxybetaine-tethered hyperbranched poly(ɛ-lysine) dendrons showed that the hyperbranched structure was fundamental to induce spheroid formation, but these were forming more slowly, were of reduced size and less stable than those growing on substrates based on the same hyperbranched structures that had been functionalised at their uppermost branching generation by a laminin amino acid sequence, i.e. YIGSR. The study shows that both nanostructure and biorecognition need to be combined to achieve a substrate for stem cell spheroid formation as that observed in vivo in the adult stem cell niche.

Morphogen Delivery by Osteoconductive Nanoparticles Instructs Stromal Cell Spheroid Phenotype

Mesenchymal stem/stromal cells (MSCs) exhibit a rapid loss in osteogenic phenotype upon removal of osteoinductive cues, as commonly occurs during transplantation. Osteogenic differentiation can be more effectively but not fully maintained by aggregating MSCs into spheroids. Therefore, the development of effective strategies that prolong the efficacy of inductive growth factors would be advantageous for advancing cell-based therapies. To address this challenge, osteoinductive bone morphogenetic protein-2 (BMP-2) was adsorbed to osteoconductive hydroxyapatite (HA) nanoparticles for incorporation into MSC spheroids. MSC induction was evaluated in osteogenic conditions and retention of the osteogenic phenotype in the absence of other osteogenic cues. HA was more uniformly incorporated into spheroids at lower concentrations, while BMP-2 dosage was dependent upon initial morphogen concentration. MSC spheroids containing BMP-2-loaded HA nanoparticles exhibited greater alkaline phosphatase (ALP) activity and more uniform spatial expression of osteocalcin compared to spheroids with uncoated HA nanoparticles. Spheroids cultured in media containing soluble BMP-2 demonstrated differentiation only at the spheroid periphery. Furthermore, the osteogenic phenotype of MSC spheroids was better retained with BMP-2-laden HA upon the removal of soluble osteogenic cues. These findings represent a promising strategy for simultaneous delivery of osteoconductive and osteoinductive signals for enhancing MSC participation in bone formation.

Serum-Free Culture of Human Mesenchymal Stem Cell Aggregates in Suspension Bioreactors for Tissue Engineering Applications

Mesenchymal stem cells (MSCs) have the capacity to differentiate towards bone, fat, and cartilage lineages. The most widely used culture and differentiation protocols for MSCs are currently limited by their use of serum-containing media and small-scale static culture vessels. Suspension bioreactors have multiple advantages over static culture vessels (e.g., scalability, control, and mechanical forces). This study sought to compare the formation and culture of 3D aggregates of human synovial fluid MSCs within suspension bioreactors and static microwell plates. It also sought to elucidate the benefits of these techniques in terms of productivity, cell number, and ability to generate aggregates containing extracellular matrix deposition. MSCs in serum-free medium were either (1) inoculated as single cells into suspension bioreactors, (2) aggregated using static microwell plates prior to being inoculated in the bioreactor environment, or (3) aggregated using microwell plates and kept in the static environment. Preformed aggregates that were size-controlled at inoculation had a greater tendency to form large, irregular super aggregates after a few days of suspension culture. The single MSCs inoculated into suspension bioreactors formed a more uniform population of smaller aggregates after a definite culture period of 8 days. Both techniques showed initial deposition of extracellular matrix within the aggregates. When the relationship between aggregate size and ECM deposition was investigated in static culture, midsized aggregates (100-300 cells/aggregate) were found to most consistently maximize sGAG and collagen productivity. Thus, this study presents a 3D tissue culture method, which avoids the clinical drawbacks of serum-containing medium that can easily be scaled for tissue culture applications.

Mesenchymal stem cells: Cell therapy and regeneration potential

Rapid advances in the isolation of multipotent progenitor cells, routinely called mesenchymal stromal/stem cells (MSCs), from various human tissues and organs have provided impetus to the field of cell therapy and regenerative medicine. The most widely studied sources of MSCs include bone marrow, adipose, muscle, peripheral blood, umbilical cord, placenta, fetal tissue, and amniotic fluid. According to the standard definition of MSCs, these clonal cells adhere to plastic, express cluster of differentiation (CD) markers such as CD73, CD90, and CD105 markers, and can differentiate into adipogenic, chondrogenic, and osteogenic lineages in vitro. However, isolated MSCs have been reported to vary in their potency and self-renewal potential. As a result, the MSCs used for clinical applications often lead to variable or even conflicting results. The lack of uniform characterization methods both in vitro and in vivo also contributes to this confusion. Therefore, the name "MSCs" itself has been increasingly questioned lately. As the use of MSCs is expanding rapidly, there is an increasing need to understand the potential sources and specific potencies of MSCs. This review discusses and compares the characteristics of MSCs and suggests that the variations in their distinctive features are dependent on the source and method of isolation as well as epigenetic changes during maintenance and growth. We also discuss the potential opportunities and challenges of MSC research with the hope to stimulate their use for therapeutic and regenerative medicine.

Neural crest stem cells from human epidermis of aged donors maintain their multipotency in vitro and in vivo

Neural crest (NC) cells are multipotent stem cells that arise from the embryonic ectoderm, delaminate from the neural tube in early vertebrate development and migrate throughout the developing embryo, where they differentiate into various cell lineages. Here we show that multipotent and functional NC cells can be derived by induction with a growth factor cocktail containing FGF2 and IGF1 from cultures of human inter-follicular keratinocytes (KC) isolated from elderly donors. Adult NC cells exhibited longer doubling times as compared to neonatal NC cells, but showed limited signs of cellular senescence despite the advanced age of the donors and exhibited significantly younger epigenetic age as compared to KC. They also maintained their multipotency, as evidenced by their ability to differentiate into all NC-specific lineages including neurons, Schwann cells, melanocytes, and smooth muscle cells (SMC). Notably, upon implantation into chick embryos, adult NC cells behaved similar to their embryonic counterparts, migrated along stereotypical pathways and contributed to multiple NC derivatives in ovo. These results suggest that KC-derived NC cells may provide an easily accessible, autologous source of stem cells that can be used for treatment of neurodegenerative diseases or as a model system for studying disease pathophysiology and drug development.

Encapsulated explant in novel low shear perfusion bioreactor improve cell isolation, expansion and colony forming unit

One of most important issue in the field of regenerative medicine is selection of appropriate cells, scaffolds and bioreactors. The present study aimed to investigate the appropriate method for the isolation of human UC-MSCs cells from explant cultured in alginate scaffold within novel perfusion bioreactor. MSCs were isolated with explant method and CD markers such CD73, CD31, CD90 and CD105 as were analyzed by flow cytometry. The culture chamber of the novel perfusion bioreactor was made from Plexiglas and housed the cell/scaffold constructs in the central part and the medium for the whole culture period. The flow behavior within the bioreactor chamber were performed for closed and open bypass systems. The shear stress profiles simulated using CFD modeling. The fluid flow distribution within the bioreactor chamber was performed in PBS solution containing a blue colorant. UC explants were resuspended in sodium alginate and were allowed to polymerize and placed in the perfusion bioreactor and cultured. MSCs were positive for mesenchymal markers such as CD73 and CD31. All 3D Perfusion bioreactor parts, except peristaltic pump was sterilizable by autoclaving. Results of CFD indicated very low wall shear stress on surface of culture chamber at flow rate 2 ml/min. The maximum wall shear stress was 1.10 × 10^-3 m/s = 0.0110 dyne/cm² (1 Pa = 10 dyne/cm²). The fluid flow distribution within the alginate gel initially exhibited oscillation. In comparison, when encapsulated explants were placed in the perfusion bioreactor, cell proliferation appeared faster (4.6 × 10¹¹ ± 9.2 × 10¹¹) than explants cultures in 2D conventional culture method (3.2 × 10¹¹ ± 1 × 10¹¹). Proliferated cell formed several colonies. Migration of chondrocytes to the periphery of the alginate bead was visible after 1 week of culture. Perfusion bioreactor with low shear stress and alginate hydrogel improve cell isolation and expansion and eliminate cell passaging and enhance colony forming unit of UC-MSCs.

Milieu for Endothelial Differentiation of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hASCs) have been shown to differentiate down many lineages including endothelial lineage. We hypothesized that hASCs would more efficiently differentiate toward the endothelial lineage when formed as three-dimensional (3D) spheroids and with the addition of vascular endothelial growth factor (VEGF). Three conditions were tested: uncoated tissue culture polystyrene (TCPS) surfaces that induced a 2D monolayer formation; elastin-like polypeptide (ELP)-collagen composite hydrogel scaffolds that induced encapsulated 3D spheroid culture; and ELP-polyethyleneimine-coated TCPS surfaces that induced 3D spheroid formation in scaffold-free condition. Cells were exposed to endothelial differentiation medium containing no additional VEGF or 20 and 50 ng/mL of VEGF for 7 days and assayed for viability and endothelial differentiation markers. While endothelial differentiation media supported endothelial differentiation of hASCs, our 3D spheroid cultures augmented this differentiation and produced more von Willebrand factor than 2D cultures. Likewise, 3D cultures were able to uptake LDL, whereas the 2D cultures were not. Higher concentrations of VEGF further enhanced differentiation. Establishing angiogenesis is a key factor in regenerative medicine. Future studies aim to elucidate how to produce physiological changes such as neoangiogenesis and sprouting of vessels which may enhance the survival of regenerated tissues.

A multiple-funnels cell culture insert for the scale-up production of uniform cell spheroids

Introduction

Formation of cell spheres is an important procedure in biomedical research. A large number of high-quality cell spheres of uniform size and shape are required for basic studies and therapeutic applications. Conventional approaches, including the hanging drop method and suspension culture, are used for cell sphere production. However, these methods are time consuming, cell spheres cannot be harvested easily, and it is difficult to control the size and geometry of cell spheres. To resolve these problems, a novel multiple-funnel cell culture insert was designed for size controlling, easy harvesting, and scale-up production of cell spheres.

Methods

The culture substrate has 680 micro-funnels with a 1-mm width top, 0.89 mm depth, and 0.5 mm square bottom. Mouse embryonic stem cells were used to test the newly developed device. The seeded embryonic stem cells settled at the downward medium surface toward the bottom opening and aggregated as embryoid bodies (EBs). For cell sphere harvest, the bottom of the culture insert was put in contact with the medium surface in another culture dish, and the medium in the device flowed down with cell spheres by hydrostatic pressure.

Results

Compact cell spheres with uniform size and shape were collected easily. The diameter of the spheres could be controlled by adjusting the seeding cell density. Spontaneous neural differentiation (nestin and Tju1) and retinoic acid-induced endodermal differentiation (Pdx-1 and insulin I) were improved in the EBs produced using the new insert compared to those in EBs produced by suspension culture.

Conclusions

This novel cell culture insert shall improve future studies of cell spheres and benefit clinical applications of cell therapy.

Single-Cell Tracking of Breast Cancer Cells Enables Prediction of Sphere Formation from Early Cell Divisions

The mammosphere assay has become widely employed to quantify stem-like cells in a population. However, the problem is there is no standard protocol employed by the field. Cell seeding densities of 1,000 to 100,000 cells/mL have been reported. These high densities lead to cellular aggregation. To address this, we have individually tracked 1,127 single MCF-7 and 696 single T47D human breast tumor cells by eye over the course of 14 days. This tracking has given us detailed information for the commonly used endpoints of 5, 7, and 14 days that is unclouded by cellular aggregation. This includes mean sphere sizes, sphere-forming efficiencies, and a well-defined minimum size for both lines. Importantly, we have correlated early cell division with eventual sphere formation. At 24 hr post seeding, we can predict the total spheres on day 14 with 98% accuracy in both lines. This approach removes cell aggregation and potentially shortens a 5- to 14-day assay to a 24 hours.

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Single-cell tracking removes confounding aggregation from the mammosphere assay

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Tracking reveals sphere-forming efficiencies much higher than commonly reported

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True clonal spheres are smaller than commonly reported

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At 24 hours, tracking can predict total day 14 spheres with 98% accuracy

Concise Review: Mesenchymal Stem Cell-Based Drug Delivery: The Good, the Bad, the Ugly, and the Promise

The development of mesenchymal stem cells (MSCs) as cell‐based drug delivery vectors for numerous clinical indications, including cancer, has significant promise. However, a considerable challenge for effective translation of these approaches is the limited tumor tropism and broad biodistribution observed using conventional MSCs, which raises concerns for toxicity to nontarget peripheral tissues (i.e., the bad). Consequently, there are a variety of synthetic engineering platforms in active development to improve tumor‐selective targeting via increased homing efficiency and/or specificity of drug activation, some of which are already being evaluated clinically (i.e., the good). Unfortunately, the lack of robust quantification and widespread adoption of standardized methodologies with high sensitivity and resolution has made accurate comparisons across studies difficult, which has significantly impeded progress (i.e., the ugly). Herein, we provide a concise review of active and passive MSC homing mechanisms and biodistribution postinfusion; in addition to in vivo cell tracking methodologies and strategies to enhance tumor targeting with a focus on MSC‐based drug delivery strategies for cancer therapy. Stem Cells Translational Medicine2018;1–13

Three-Dimensional Spheroid Culture Increases Exosome Secretion from Mesenchymal Stem Cells

BACKGROUND

Mass production of exosomes is a prerequisite for their commercial utilization. This study investigated whether three-dimensional (3D) spheroid culture of mesenchymal stem cells (MSCs) could improve the production efficiency of exosomes and if so, what was the mechanism involved.

METHODS

We adopted two models of 3D spheroid culture using the hanging-drop (3D-HD) and poly(2-hydroxyethyl methacrylate) (poly-HEMA) coating methods (3D-PH). The efficiency of exosome production from MSCs in the 3D spheroids was compared with that of monolayer culture in various conditions. We then investigated the mechanism of the 3D spheroid culture-induced increase in exosome production.

RESULTS

The 3D-HD formed a single larger spheroid, while the 3D-PH formed multiple smaller ones. However, MSCs cultured on both types of spheroids produced significantly more exosomes than those cultured in conventional monolayer culture (2D). We then investigated the cause of the increased exosome production in terms of hypoxia within the 3D spheroids, high cell density, and non-adherent cell morphology. With increasing spheroid size, the efficiency of exosome production was the largest with the least amount of cells in both 3D-HD and 3D-PH. An increase in cell density in 2D culture (2D-H) was less efficient in exosome production than the conventional, lower cell density, 2D culture. Finally, when cells were plated at normal density on the poly-HEMA coated spheroids (3D-N-PH); they formed small aggregates of less than 10 cells and still produced more exosomes than those in the 2D culture when plated at the same density. We also found that the expression of F-actin was markedly reduced in the 3D-N-PH culture.

CONCLUSION

These results suggested that 3D spheroid culture produces more exosomes than 2D culture and the non-adherent round cell morphology itself might be a causative factor. The result of the present study could provide useful information to develop an optimal process for the mass production of exosomes.

From "Bench to Bedside": Current Advancement on Large-Scale Production of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the primary cell source in cell therapy and regenerative medicine due to its extraordinary self-renewing capacity and multilineage differentiation potential. Clinical trials involving MSCs are being conducted in a range of human diseases and the number of registered cases is continuously increasing. However, a wide gap exists between the number of MSCs obtainable from the donor site and the number required for implantation to damage tissues, and also between MSC scalability and MSC phenotype stability. The clinical translation of MSCs necessitates a scalable expansion bioprocess for the biomanufacturing of therapeutically qualified cells. This review presents current achievements for expansion of MSCs. Issues involving culture condition modification, bioreactor systems, as well as microcarrier and scaffold platforms for optimal MSC systems are discussed. Most importantly, the gap between current MSC expansion and clinical application, as well as outbreak directions for the future are discussed. The present systemic review will bring new insights into future large-scale MSC expansion and clinical application.

Dynamic Cultivation of Mesenchymal Stem Cell Aggregates

Mesenchymal stem cells (MSCs) are considered as primary candidates for cell-based therapies due to their multiple effects in regenerative medicine. Pre-conditioning of MSCs under physiological conditions—such as hypoxia, three-dimensional environments, and dynamic cultivation—prior to transplantation proved to optimize their therapeutic efficiency. When cultivated as three-dimensional aggregates or spheroids, MSCs display increased angiogenic, anti-inflammatory, and immunomodulatory effects as well as improved stemness and survival rates after transplantation, and cultivation under dynamic conditions can increase their viability, proliferation, and paracrine effects, alike. Only few studies reported to date, however, have utilized dynamic conditions for three-dimensional aggregate cultivation of MSCs. Still, the integration of dynamic bioreactor systems, such as spinner flasks or stirred tank reactors might pave the way for a robust, scalable bulk expansion of MSC aggregates or MSC-derived extracellular vesicles. This review summarizes recent insights into the therapeutic potential of MSC aggregate cultivation and focuses on dynamic generation and cultivation techniques of MSC aggregates.

Efficient scalable production of therapeutic microvesicles derived from human mesenchymal stem cells

Microvesicles (MVs) released by cells are involved in a multitude of physiological events as important mediators of intercellular communication. MVs derived from mesenchymal stem cells (MSCs) contain various paracrine factors from the cells that primarily contribute to their therapeutic efficacy observed in numerous clinical trials. As nano-sized and bi-lipid layered vesicles retaining therapeutic potency equivalent to that of MSCs, MSC-derived MVs have been in focus as ideal medicinal candidates for regenerative medicine, and are preferred over MSC infusion therapy with their improved safety profiles. However, technical challenges in obtaining sufficient amounts of MVs have limited further progress in studies and clinical application. Of the multiple efforts to reinforce the therapeutic capacity of MSCs, few studies have reportedly examined the scale-up of MSC-derived MV production. In this study, we successfully amplified MV secretion from MSCs compared to the conventional culture method using a simple and efficient 3D-bioprocessing method. The MSC-derived MVs produced in our dynamic 3D-culture contained numerous therapeutic factors such as cytokines and micro-RNAs, and showed their therapeutic potency in in vitro efficacy evaluation. Our results may facilitate diverse applications of MSC-derived MVs from the bench to the bedside, which requires the large-scale production of MVs.

Advances and challenges in stem cell culture

Stem cells (SCs) hold great promise for cell therapy, tissue engineering, and regenerative medicine as well as pharmaceutical and biotechnological applications. They have the capacity to self-renew and the ability to differentiate into specialized cell types depending upon their source of isolation. However, use of SCs for clinical applications requires a high quality and quantity of cells. This necessitates large-scale expansion of SCs followed by efficient and homogeneous differentiation into functional derivatives. Traditional methods for maintenance and expansion of cells rely on two-dimensional (2-D) culturing techniques using plastic culture plates and xenogenic media. These methods provide limited expansion and cells tend to lose clonal and differentiation capacity upon long-term passaging. Recently, new approaches for the expansion of SCs have emphasized three-dimensional (3-D) cell growth to mimic the in vivo environment. This review provides a comprehensive compendium of recent advancements in culturing SCs using 2-D and 3-D techniques involving spheroids, biomaterials, and bioreactors. In addition, potential challenges to achieve billion-fold expansion of cells are discussed.

Hypoxic Three-Dimensional Scaffold-Free Aggregate Cultivation of Mesenchymal Stem Cells in a Stirred Tank Reactor

Extensive expansion of mesenchymal stem cells (MSCs) for cell-based therapies remains challenging since long-term cultivation and excessive passaging in two-dimensional conditions result in a loss of essential stem cell properties. Indeed, low survival rate of cells, alteration of surface marker profiles, and reduced differentiation capacity are observed after in vitro expansion and reduce therapeutic success in clinical studies. Remarkably, cultivation of MSCs in three-dimensional aggregates preserve stem cell properties. Hence, the large scale formation and cultivation of MSC aggregates is highly desirable. Besides other effects, MSCs cultivated under hypoxic conditions are known to display increased proliferation and genetic stability. Therefore, in this study we demonstrate cultivation of adipose derived human MSC aggregates in a stirred tank reactor under hypoxic conditions. Although aggregates were exposed to comparatively high average shear stress of 0.2 Pa as estimated by computational fluid dynamics, MSCs displayed a viability of 78-86% and maintained their surface marker profile and differentiation potential after cultivation. We postulate that cultivation of 3D MSC aggregates in stirred tank reactors is valuable for large-scale production of MSCs or their secreted compounds after further optimization of cultivation parameters.

Scalable microcarrier-based manufacturing of mesenchymal stem/stromal cells

Due to their unique features, mesenchymal stem/stromal cells (MSC) have been exploited in clinical settings as therapeutic candidates for the treatment of a variety of diseases. However, the success in obtaining clinically-relevant MSC numbers for cell-based therapies is dependent on efficient isolation and ex vivo expansion protocols, able to comply with good manufacturing practices (GMP). In this context, the 2-dimensional static culture systems typically used for the expansion of these cells present several limitations that may lead to reduced cell numbers and compromise cell functions. Furthermore, many studies in the literature report the expansion of MSC using fetal bovine serum (FBS)-supplemented medium, which has been critically rated by regulatory agencies. Alternative platforms for the scalable manufacturing of MSC have been developed, namely using microcarriers in bioreactors, with also a considerable number of studies now reporting the production of MSC using xenogeneic/serum-free medium formulations. In this review we provide a comprehensive overview on the scalable manufacturing of human mesenchymal stem/stromal cells, depicting the various steps involved in the process from cell isolation to ex vivo expansion, using different cell tissue sources and culture medium formulations and exploiting bioprocess engineering tools namely microcarrier technology and bioreactors.

Rapid selection of mesenchymal stem and progenitor cells in primary prostate stromal cultures

BACKGROUND

Carcinoma-associated fibroblasts (CAFs) are a dominant component of the tumor microenvironment with pro-tumorigenic properties. Despite this knowledge, their physiologic origins remain poorly understood. Mesenchymal stem cells (MSCs) can be recruited from the bone marrow to areas of tissue damage and inflammation, including prostate cancer. MSCs can generate and have many overlapping properties with CAFs in preclinical models.

METHODS

Multiparameter flow cytometry and multipotent differentiation assays used to define MSCs in primary prostate stromal cultures derived from young (<25 yrs) organ donors and prostate cancer patients compared with bone marrow-derived stromal cultures. Population doubling times, population doublings, cell size, and differentiation potential determined under multiple culture conditions, including normoxia, hypoxia, and a variety of media. TGF-β measured by ELISA.

RESULTS

MSCs and stromal progenitors are not only present in normal and malignant prostate tissue, but are quickly selected for in primary stromal cultures derived from these tissues; becoming the dominant population within just a few passages. Growth potential inversely associated with TGF-β concentrations. All conditions generated populations with an average cell diameter >15 µm. All cultures tested had the ability to undergo osteogenic and chondrogenic differentiation, but unlike bone marrow-derived MSCs, primary stromal cultures derived from normal prostate tissue lack adipogenic differentiation potential. In contrast, a subset of stromal cultures derived from prostate cancer patients retain the ability to differentiate into adipocytes; a property that is significantly suppressed under hypoxic conditions in both bone marrow- and prostate-derived MSCs.

CONCLUSIONS

Primary prostate stromal cultures are highly enriched in cells with an MSC or stromal progenitor phenotype. The use of primary cultures such as these to study CAFs raises interesting implications when considering their overlapping properties. The lack of adipogenesis in stromal cultures derived from normal prostates suggests they have a lineage-restricted progenitor phenotype. The retention of adipogenic differentiation in cultures from a subset of prostate cancer patients suggests the active recruitment of less committed progenitors or MSCs from the bone marrow as a function of disease progression. This recruitment can potentially be exploited for prognostic purposes or a cell-based platform for the systemic delivery of cytotoxic agents to sites of prostate cancer.

Long term morphological characterization of mesenchymal stromal cells 3D spheroids built with a rapid method based on entry-level equipment

Three-dimensional (3D) spheroids of mesenchymal stromal cells (MSC) have been demonstrated to improve a wide range of MSC features, such as multilineage potential, secretion of therapeutic factors, and resistance against hypoxic condition. Accordingly, they represent a promising tool in regenerative medicine for several biological and clinical applications. Many approaches have been proposed to generate MSC spheroids. They usually require specific generation systems, such as rotatory bioreactors or low-attachment plates, and each approach has its own disadvantages. Furthermore, an over-time analysis of morphological homogeneity and architectural stability of the spheroids generated is rarely provided. In this work we adapted the "pellet culture" method to obtain homogenous spheroids of MSC and maintain them in vitro for long term studies. We analysed their outer and inner structure over a 2-month period to provide morphological and architectural information regarding the spheroids generated. Quantitative and qualitative data were obtained using brightfield and confocal microscope imaging coupled to a computational analysis to estimate volume, sphericity, and jagging degree. In addition, histological evaluation was performed to more thoroughly assess the cellular composition and the internal architecture of the 3D spheroids. The results provided show that MSC spheroids generated with the proposed approach are homogeneous and stable, from both morphological and architectural points of view, for a period of at least 15 days, approximately between day 15 and day 30 after their generation. Accordingly, the approach proposed serves as a rapid, cost-effective, and efficient method to generate and maintain MSC spheroids using common entry-level laboratory equipment only.

Bioprocessing strategies for the large-scale production of human mesenchymal stem cells: a review

Human mesenchymal stem cells (hMSCs), also called mesenchymal stromal cells, have been of great interest in regenerative medicine applications because of not only their differentiation potential but also their ability to secrete bioactive factors that can modulate the immune system and promote tissue repair. This potential has initiated many early-phase clinical studies for the treatment of various diseases, disorders, and injuries by using either hMSCs themselves or their secreted products. Currently, hMSCs for clinical use are generated through conventional static adherent cultures in the presence of fetal bovine serum or human-sourced supplements. However, these methods suffer from variable culture conditions (i.e., ill-defined medium components and heterogeneous culture environment) and thus are not ideal procedures to meet the expected future demand of quality-assured hMSCs for human therapeutic use. Optimizing a bioprocess to generate hMSCs or their secreted products (or both) promises to improve the efficacy as well as safety of this stem cell therapy. In this review, current media and methods for hMSC culture are outlined and bioprocess development strategies discussed.