Increased Mesenchymal Stem Cell Functionalization in Three-Dimensional Manufacturing Settings for Enhanced Therapeutic Applications

Reliable Harvest of Injectable Human Mesenchymal Stem Cell Sheets by Modulating Cell-Substrate Adhesion Strength

Cell sheet engineering has emerged as a promising scaffold-free strategy in cell-based therapeutics, preserving essential cell-cell and cell-extracellular matrix (ECM) interactions. To enable minimally invasive delivery, a key challenge relies on making the cell sheets compatible with injection-based administration without subjecting sensitive cells to physical or thermal stresses. This study addresses a reliable method for controlling cell sheet dimensions by combining differential cell adhesion-guided micropatterning along with an isothermal detachment method. The surface composition of a copolymer, poly(ethylene glycol dimethacrylate-co-hydroxyethyl methacrylate) is delicately controlled via initiated chemical vapor deposition to ensure intact cell adhesion and rapid cell detachment under isothermal condition. The optimized surface further allows hydrophobic microcontact printing for creating micron-sized sheets. Human mesenchymal stem cell sheets harvested with this method show preserved ECM without compromising cell viability after both detachment and injection. Moreover, the injected cell sheets substantially enhance the angiogenic potential of human umbilical vein endothelial cells, demonstrating the sustained therapeutic activity of the cell sheet after injection. It is believed that this approach has great potential to broaden the scope of cell sheet engineering, serving as a robust platform for regenerative medicine.

Derivation of Mesenchymal Stem Cells through Sequential Presentation of Growth Factors via Gelatin Microparticles in Pluripotent Stem Cell Spheroids

The use of mesenchymal stem cells (MSCs) in regenerative medicine has gained considerable attention in recent years with the development of clinically relevant MSCs from induced pluripotent stem cells (iPSCs) and embryonic stem cells. Through sequential presentations of appropriate growth factors (GFs), iPSCs can be differentiated into mesodermal cells and then into MSCs. Furthermore, the formation of 3-dimensional cell spheroids, known as embryoid bodies, can be used to mimic in vivo conditions. However, the compact nature of embryoid bodies restricts the efficient and uniform delivery of GFs, leading to the formation of necrotic zones and hindered differentiation. To address this, we developed 2 types of gelatin microparticles (GelMPs) with distinct degradation rates for sequential delivery of GFs to enhance differentiation while preventing necrotic zones. In 2-dimensional culture, bone morphogenetic protein-4 (BMP4) and fibroblast growth factor 2 (FGF2) were identified as key proteins inducing iPSC differentiation into mesodermal cells and MSCs. The sequential presentation of these GFs was optimized for a 3-dimensional culture system by engineering fast-degrading GelMPs conjugated with BMP4 and slow-degrading GelMPs conjugated with FGF2. Our approach facilitated efficient iPSC differentiation into induced mesenchymal stem cells (iMSCs), as demonstrated by enhanced expression of mesodermal markers during the early stages of differentiation and MSC-specific markers at later stages. The resulting iMSCs exhibited characteristic surface markers (e.g., CD73, CD90, CD105, and CD44) and trilineage differentiation capability and were genetically stable. Compared to adult-derived MSCs, iMSCs showed superior proliferative capacity and reduced senescence, making them advantageous for cell therapy and regenerative medicine. This innovative approach of generating iMSCs has vast potential for therapeutic applications.

The bone microenvironment: new insights into the role of stem cells and cell communication in bone regeneration

Mesenchymal stem cells (MSCs) play a crucial role in bone formation and remodeling. Intrinsic genetic factors and extrinsic environmental cues regulate their differentiation into osteoblasts. Within the bone microenvironment, a complex network of biochemical and biomechanical signals orchestrates bone homeostasis and regeneration. In addition, the crosstalk among MSCs, immune cells, and neighboring cells-mediated by extracellular vesicles and non-coding RNAs (such as circular RNAs and micro RNAs) -profoundly influences osteogenic differentiation and bone remodeling. Recent studies have explored specific signaling pathways that contribute to effective bone regeneration, highlighting the potential of manipulating the bone microenvironment to enhance MSC functionality. The integration of advanced biomaterials, gene editing techniques, and controlled delivery systems is paving the way for more targeted and efficient regenerative therapies. Furthermore, artificial intelligence could improve bone tissue engineering, optimize biomaterial design, and enable personalized treatment strategies. This review explores the latest advancements in bone regeneration, emphasizing the intricate interplay among stem cells, immune cells, and signaling molecules. By providing a comprehensive overview of these mechanisms and their clinical implications, we aim to shed light on future research directions in this rapidly evolving field.

Implantation of MSC spheroid-derived 3D decellularized ECM enriched with the MSC secretome ameliorates traumatic brain injury and promotes brain repair

Traumatic brain injury (TBI) presents substantial clinical challenges, as existing treatments are unable to reverse damage or effectively promote brain tissue regeneration. Although implantable biomaterials have been proposed to support tissue repair by mitigating the adverse microenvironment in injured brains, many fail to replicate the complex composition and architecture of the native extracellular matrix (ECM), resulting in only limited therapeutic outcomes. This study introduces an innovative approach by developing a mesenchymal stem cell (MSC) spheroid-derived three-dimensional (3D) decellularized ECM (dECM) that is enriched with the MSC-derived matrisome and secretome, offering a promising solution for TBI treatment and brain tissue regeneration. Proteomic and cytokine array analyses revealed that 3D dECM retained a diverse array of MSC spheroid-derived matrisome proteins and secretome components, which are crucial for replicating the complexity of native ECM and the therapeutic capabilities of MSCs. These molecules were found to underlie the observed effects of 3D dECM on immunomodulation, proneuritogenesis, and proangiogenesis in our in vitro functional assays. Implantation of 3D dECM into TBI model mice effectively mitigated postinjury tissue damage and promoted brain repair, as evidenced by a reduced brain lesion volume, decreased cell apoptosis, alleviated neuroinflammation, reduced glial scar formation, and increased of neuroblast recruitment to the lesion site. These outcomes culminated in improved motor function recovery in animals, highlighting the multifaceted therapeutic potential of 3D dECM for TBI. In summary, our study elucidates the transformative potential of MSC spheroid-derived bioactive 3D dECM as an implantable biomaterial for effectively mitigating post-TBI neurological damage, paving the way for its broader therapeutic application.

Microbead Encapsulation Strategy for Efficient Production of Extracellular Vesicles Derived From Human Mesenchymal Stem Cells

Human mesenchymal stem cell-derived extracellular vesicles (hMSC-EVs) have shown great potential in tissue repair and regeneration. However, their scalable production and functional quality are still limited by current expansion technologies. In this study, we propose a production technology for hMSC-EVs based on three-dimensional (3D) microbead culture, which enhances the secretory behaviour of hMSC. Fixed number of MSCs were encapsulated in Matrigel at appropriate densities and printed into 3D microbeads by the custom automated microfluidic bead-jet printing technique. Compared with 2D culture group, EVs derived from 3D hMSC microbead had smaller size and increased yield by 20-fold, and the actin depolymerisation of the cell may be an important mechanism for enhancing EV secretion. Further analysis confirmed that the EVs derived from 3D hMSC microbead exhibited enhanced angiogenic and proliferative capabilities, which promoted the viability and tube-forming capacity of human umbilical vein endothelial cells (HUVEC). In conclusion, this automated microfluidic microbead encapsulation technology increased the yield and therapeutic effect of hMSC-EVs and provides a platform for scalable EV production of regenerative therapies.

Engineering Extracellular Vesicles Derived from 3D Cultivation of BMSCs Enriched with HGF Ameliorate Sepsis-Induced Lung Epithelial Barrier Damage

Sepsis is a critical condition with high mortality, often leading to acute lung injury (ALI) due to uncontrolled inflammatory responses and alveolar epithelial damage. Extracellular vesicles (EVs), particularly mesenchymal stem cell-derived EVs, have shown therapeutic potential in sepsis-related organ dysfunction by transferring RNAs and proteins. However, their clinical use is limited by low efficacy and yield. To address this, 3D-cultured MSCs (3D-MSCs) are generated using MicroTissues 3D Petri Dish. These 3D-MSCs demonstrate improved protection and proliferation of MLE-12 cells in vitro. Mechanistic studies are conducted to explore the enhanced protective effects of 3D-MSCs derived EVs (3D-EVs) in a septic-ALI model. Proteomic and molecular analyses of 3D-EVs revealed that they are enriched in hepatocyte growth factor (HGF). HGF helps maintain the barrier function of damaged alveolar epithelium through the PI3K-AKT signaling pathway. Overall, 3D-EVs effectively ameliorate sepsis-induced ALI and enhance prognosis by enriching and delivering HGF, suggesting that their application represents a promising treatment strategy for septic ALI.

Enhanced immunomodulatory effects of canine adipose tissue-derived mesenchymal stem cells in 3D culture

Introduction

Mesenchymal stem cells (MSCs) have been introduced as a treatment for dogs owing to their immunomodulatory effects. In humans, 3D-cultured MSCs have recently been applied in treating various conditions, including myocardial infarction, liver disease, and kidney disease. This study aimed to evaluate whether the immunomodulatory effects of canine adipose tissue-derived MSCs (cAT-MSCs) are enhanced when cultured in a 3D environment compared to conventional 2D culture.

Methods

cAT-MSC spheroids were generated using ultra-low-adhesion plates. The structural and hypoxic characteristics of these spheroids were assessed via confocal imaging. The expression levels of the stemness markers SOX2 and OCT4 were examined through western blotting. Additionally, the expression of inflammatory factors within the cAT-MSC spheroids was analyzed using RT-PCR and ELISA. The immunomodulatory effects were further evaluated in canine macrophages (DH82) treated with conditioned media (CM) from cAT-MSC spheroids, using RT-PCR and flow cytometry.

Results

3D culture induced hypoxic conditions within the cAT-MSC spheroids and significantly increased the expression of SOX2 and OCT4 (p < 0.05). Moreover, the expression of inflammation-associated factors, including TGF-β1, TSG-6, COX-2, PGE2, and IL-10, was upregulated in the 3D culture (p < 0.05). Treatment of DH82 cells with CM from the cAT-MSC spheroids led to a significant reduction in the expression of pro-inflammatory factors such as TNF-α, IL-1β, and IL-6 (p < 0.01). Additionally, M1 polarization was diminished in DH82 cells exposed to the CM from the cAT-MSC spheroids (p < 0.0001). And M2 polarization was increased in DH82 cells exposed to the CM from the cAT-MSC spheroids (p < 0.0001).

Conclusion

This study confirms that the immunomodulatory effects of MSCs are enhanced in 3D culture. Therefore, 3D cultured MSCs may offer a more effective therapeutic approach than conventional 2D-cultured MSCs for treating canine inflammatory diseases.

A Comprehensive Review: Advances in Mesenchymal Stem Cell Applications for Burn Wound Repair

Tissue repair following skin injury is a complex process that encompasses hemostasis, inflammation, tissue cell proliferation, and structural remodeling. Mesenchymal stem cells (MSCs) are derived from the mesodermal layer of tissues and possess multidirectional differentiation potential and self-renewal capabilities. MSCs from various sources, including the bone marrow, adipose tissue, dental pulp, umbilical cord, and amniotic membrane, have demonstrated effectiveness in promoting skin injury repair. They aid in this process by fostering the formation of new blood vessels in damaged tissues, self-renewal, or transdifferentiation into skin or sweat gland cells. Moreover, MSCs promote the proliferation and migration of skin cells, reduce wound inflammation, and restore the extracellular matrix through paracrine secretion. In this paper, we review recent findings regarding MSCs and their role in burn wound repair. Additionally, we explore the potential of combining MSCs with various biomaterials for treating burn wounds and analyze clinical cases wherein MSCs were administered to patients, offering insights into ongoing research on MSC-based therapies for skin injuries.

Efficient Fabrication of Human Corneal Stromal Cell Spheroids and Promoting Cell Stemness Based on 3D-Printed Derived PDMS Microwell Platform

Spherical culture could promote the plasticity and stemness of human corneal stromal cells (hCSCs). Here, we introduce a novel three-dimensional (3D) cell culture system based on a polydimethylsiloxane (PDMS) microwell platform composed of many V-bottom microcavities to generate human corneal stromal cell spheroids and promote cell stemness. We isolated hCSCs from SMILE-derived lenticules and maintained their physiological phenotype by culturing them in a medium supplemented with human corneal stromal extract (hCSE). Utilizing a PDMS microwell platform fabricated through 3D printing technology, we successfully generated 3D corneal stromal cell spheroids (3D-CSC) with uniform size and stable structure, exhibiting increased expression of pluripotency factors, including OCT4, NANOG, SOX2, KLF4, and PAX6. Furthermore, the iPS supernatant of E8-conditioned medium (E8-CM) significantly enhanced the stemness properties of these cells. RNA sequencing and proteomics analyses revealed that 3D-CSCs exhibited superior proliferation, differentiation, cell adhesion, migration, and neurogenesis compared to traditional monolayer cultures, underscoring the role of biophysical cues in promoting hCSCs stemness. In summary, this study presents an effective 3D cell culture platform that mimics the in vivo microenvironment, facilitating the enhancement of stemness properties and providing valuable insights into corneal tissue engineering and regenerative medicine, particularly for treating corneal opacities and diseases.

Current perspectives on the dynamic culture of mesenchymal stromal/stem cell spheroids

Mesenchymal stromal/stem cells (MSCs) are promising candidates for regenerative medicine owing to their self-renewal properties, multilineage differentiation, immunomodulatory effects, and angiogenic potential. MSC spheroids fabricated by 3D culture have recently shown enhanced therapeutic potential. MSC spheroids create a specialized niche with tight cell-cell and cell-extracellular matrix interactions, optimizing their cellular function by mimicking the in vivo environment. Methods for 3D cultivation of MSCs can be classified into 2 main forms: static suspension culture and dynamic suspension culture. Numerous studies have reported the beneficial influence of these methods on MSCs, which is displayed by increased differentiation, angiogenic, immunomodulatory, and anti-apoptotic effects, and stemness of MSC spheroids. Particularly, recent studies highlighted the benefits of dynamic suspension cultures of the MSC spheroids in terms of faster and more compact spheroid formation and the long-term maintenance of stemness properties. However, only a few studies have compared the behavior of MSC spheroids formed using static and dynamic suspension cultures, considering the significant differences between their culture conditions. This review summarizes the differences between static and dynamic suspension culture methods and discusses the biological outcomes of MSC spheroids reported in the literature. In particular, we highlight the advantages of the dynamic suspension culture of MSC spheroids and contemplate its future applications for various diseases.

Role of Perinatal Stem Cell Secretome as Potential Therapy for Muscular Dystrophies

Inflammation mechanisms play a critical role in muscle homeostasis, and in Muscular Dystrophies (MDs), the myofiber damage triggers chronic inflammation which significantly controls the disease progression. Immunomodulatory strategies able to target inflammatory pathways and mitigate the immune-mediated damage in MDs may provide new therapeutic options. Owing to its capacity of influencing the immune response and enhancing tissue repair, stem cells' secretome has been proposed as an adjunct or standalone treatment for MDs. In this review study, we discuss the challenging points related to the inflammation condition characterizing MD pathology and provide a concise summary of the literature supporting the potential of perinatal stem cells in targeting and modulating the MD inflammation.

Fibroblast growth factor 2 enhances BMSC stemness through ITGA2-dependent PI3K/AKT pathway activation

Bone marrow-derived mesenchymal stem cells (BMSC) are promising cellular reservoirs for treating degenerative diseases, tissue injuries, and immune system disorders. However, the stemness of BMSCs tends to decrease during in vitro cultivation, thereby restricting their efficacy in clinical applications. Consequently, investigating strategies that bolster the preservation of BMSC stemness and maximize therapeutic potential is necessary. Transcriptomic and single-cell sequencing methodologies were used to perform a comprehensive examination of BMSCs with the objective of substantiating the pivotal involvement of fibroblast growth factor 2 (FGF2) and integrin alpha 2 (ITGA2) in stemness regulation. To investigate the impact of these genes on the BMSC stemness in vitro, experimental approaches involving loss and gain of function were implemented. These approaches encompassed the modulation of FGF2 and ITGA2 expression levels via small interfering RNA and overexpression plasmids. Furthermore, we examined their influence on the proliferation and differentiation capacities of BMSCs, along with the expression of stemness markers, including octamer-binding transcription factor 4, Nanog homeobox, and sex determining region Y-box 2. Transcriptomic analyzes successfully identified FGF2 and ITGA2 as pivotal genes responsible for regulating the stemness of BMSCs. Subsequent single-cell sequencing revealed that elevated FGF2 and ITGA2 expression levels within specific stem cell subpopulations are closely associated with stemness maintenance. Moreover, additional in vitro experiments have convincingly demonstrated that FGF2 effectively enhances the BMSC stemness by upregulating ITGA2 expression, a process mediated by the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. This conclusion was supported by the observed upregulation of stemness markers following the induction of FGF2 and ITGA2. Moreover, administration of the BEZ235 pathway inhibitor resulted in the repression of stemness transcription factors, suggesting the substantial involvement of the PI3K/AKT pathway in stemness preservation facilitated by FGF2 and ITGA2. This study elucidates the involvement of FGF2 in augmenting BMSC stemness by modulating ITGA2 and activating the PI3K/AKT pathway. These findings offer valuable contributions to stem cell biology and emphasize the potential of manipulating FGF2 and ITGA2 to optimize BMSCs for therapeutic purposes.

Impact of mesenchymal stem cell size and adhesion modulation on in vivo distribution: insights from quantitative PET imaging

BACKGROUND

Successful engraftment and localization of mesenchymal stem cells (MSCs) within target tissues are critical factors influencing their therapeutic efficacy for tissue repair and regeneration. However, the relative contributions of biophysical factors like cell size and adhesion capacity in regulating MSC distribution in vivo remain incompletely understood.

METHODS

Cell adhesion peptides and hanging drop method were used to modify the adhesive capacity and size of MSCs. To quantitatively track the real-time biodistribution of transplanted MSCs with defined size and adhesion profiles in living mice and rats, the non-invasive positron emission tomography (PET) imaging was applied.

RESULTS

Surface modification with integrin binding peptides like RGD, GFOGER, and HAVDI reduced MSC adhesion capacity in vitro by up to 43.5% without altering cell size, but did not significantly decrease lung entrapment in vivo. In contrast, culturing MSCs as 3D spheroids for 48 h reduced their cell diameter by 34.6% and markedly enhanced their ability to pass through the lungs and migrate to other organs like the liver after intravenous administration. This size-dependent effect on MSC distribution was more pronounced in rats compared to mice, likely due to differences in pulmonary microvessel diameters between species.

CONCLUSION

Our findings reveal that cell size is a predominant biophysical regulator of MSC localization in vivo compared to adhesion capacity, providing crucial insights to guide optimization of MSC delivery strategies for enhanced therapeutic efficacy.

The Formation of Stable Lung Tumor Spheroids during Random Positioning Involves Increased Estrogen Sensitivity

The formation of tumor spheroids on the random positioning machine (RPM) is a complex and important process, as it enables the study of metastasis ex vivo. However, this process is not yet understood in detail. In this study, we compared the RPM-induced spheroid formation of two cell types of lung carcinoma (NCI-H1703 squamous cell carcinoma cells and Calu-3 adenocarcinoma cells). While NCI-H1703 cells were mainly present as spheroids after 3 days of random positioning, Calu-3 cells remained predominantly as a cell layer. We found that two-dimensional-growing Calu-3 cells have less mucin-1, further downregulate their expression on the RPM and therefore exhibit a higher adhesiveness. In addition, we observed that Calu-3 cells can form spheroids, but they are unstable due to an imbalanced ratio of adhesion proteins (β1-integrin, E-cadherin) and anti-adhesion proteins (mucin-1) and are likely to disintegrate in the shear environment of the RPM. RPM-exposed Calu-3 cells showed a strongly upregulated expression of the estrogen receptor alpha gene ESR1. In the presence of 17β-estradiol or phenol red, more stable Calu-3 spheroids were formed, which was presumably related to an increased amount of E-cadherin in the cell aggregates. Thus, RPM-induced tumor spheroid formation depends not solely on cell-type-specific properties but also on the complex interplay between the mechanical influences of the RPM and, to some extent, the chemical composition of the medium used during the experiments.

International Society for Cell and Gene Therapy Clinical Translation Committee recommendations on mesenchymal stromal cells in graft-versus-host disease: easy manufacturing is faced with standardizing and commercialization challenges

Mesenchymal stromal cells (MSCs) have been used in multiple clinical trials for steroid-refractory moderate-severe (grade II-IV) acute graft-versus-host disease (aGVHD) across the world over the last two decades. Despite very promising results in a variety of trials, it failed to get widespread approval by regulatory agencies such as the U.S. Food and Drug Administration and the European Medicines Agency. What lessons can we learn from this for future studies on MSCs and other cell therapy products? Broad heterogeneity among published trials using MSCs in aGVHD was likely the core problem. We propose a standardized approach in regards to donor-related factors, MSCs-related characteristics, as well as clinical trial design, to limit heterogeneity in trials for aGVHD and to fulfill the requirements of regulatory agencies. This approach may be expanded beyond MSCs to other Cell and Gene therapy products and trials in other diseases.

The issue of heterogeneity of MSC-based advanced therapy medicinal products-a review

Mesenchymal stromal stem cells (MSCs) possess a remarkable potential for numerous clinical applications due to their unique properties including self-renewal, immunomodulation, paracrine actions and multilineage differentiation. However, the translation of MSC-based Advanced Therapy Medicinal Products (ATMPs) into the clinic has frequently met with inconsistent outcomes. One of the suspected reasons for this issue is the inherent and extensive variability that exists among such ATMPs, which makes the interpretation of their clinical efficacy difficult to assess, as well as to compare the results of various studies. This variability stems from numerous reasons including differences in tissue sources, donor attributes, variances in manufacturing protocols, as well as modes of administration. MSCs can be isolated from various tissues including bone marrow, umbilical cord, adipose tissue and others, each with its unique phenotypic and functional characteristics. While MSCs from different sources do share common features, they also exhibit distinct gene expression profiles and functional properites. Donor-specific factors such as age, sex, body mass index, and underlying health conditions can influence MSC phenotype, morphology, differentiation potential and function. Moreover, variations in preparation of MSC products introduces additional heterogeneity as a result of cell culture media composition, presence or absence of added growth factors, use of different serum supplements and culturing techniques. Once MSC products are formulated, storage protocols play a pivotal role in its efficacy. Factors that affect cell viability include cell concentration, delivery solution and importantly, post-thawing protocols where applicable. Ensuing, differences in administration protocols can critically affect the distribution and functionallity of administered cells. As MSC-based therapies continue to advance through numerous clinical trials, implication of strategies to reduce product heterogeneity is imperative. Central to addressing these challenges is the need for precise prediction of clinical responses, which require well-defined MSC populations and harmonized assessment of their specific functions. By addressing these issues by meaningful approaches, such as, e.g., MSC pooling, the field can overcome barriers to advance towards more consistent and effective MSC-based therapies.

Local delivery of stem cell spheroids with protein/polyphenol self-assembling armor to improve myocardial infarction treatment via immunoprotection and immunoregulation

Stem cell therapies have shown great potential for treating myocardial infarction (MI) but are limited by low cell survival and compromised functionality due to the harsh microenvironment at the disease site. Here, we presented a Mesenchymal stem cell (MSC) spheroid-based strategy for MI treatment by introducing a protein/polyphenol self-assembling armor coating on the surface of cell spheroids, which showed significantly enhanced therapeutic efficacy by actively manipulating the hostile pathological MI microenvironment and enabling versatile functionality, including protecting the donor cells from host immune clearance, remodeling the ROS microenvironment and stimulating MSC's pro-healing paracrine secretion. The underlying mechanism was elucidated, wherein the armor protected to prolong MSCs residence at MI site, and triggered paracrine stimulation of MSCs towards immunoregulation and angiogenesis through inducing hypoxia to provoke glycolysis in stem cells. Furthermore, local delivery of coated MSC spheroids in MI rat significantly alleviated local inflammation and subsequent fibrosis via mediation macrophage polarization towards pro-healing M2 phenotype and improved cardiac function. In general, this study provided critical insight into the enhanced therapeutic efficacy of stem cell spheroids coated with a multifunctional armor. It potentially opens up a new avenue for designing immunomodulatory treatment for MI via stem cell therapy empowered by functional biomaterials.

Harnessing three-dimensional porous chitosan microsphere embedded with adipose-derived stem cells to promote nerve regeneration

BACKGROUND

Nerve guide conduits are a promising strategy for reconstructing peripheral nerve defects. Improving the survival rate of seed cells in nerve conduits is still a challenge and microcarriers are an excellent three-dimensional (3D) culture scaffold. Here, we investigate the effect of the 3D culture of microcarriers on the biological characteristics of adipose mesenchymal stem cells (ADSCs) and to evaluate the efficacy of chitosan nerve conduits filled with microcarriers loaded with ADSCs in repairing nerve defects.

METHODS

In vitro, we prepared porous chitosan microspheres by a modified emulsion cross-linking method for loading ADSCs and evaluated the growth status and function of ADSCs. In vivo, ADSCs-loaded microcarriers were injected into chitosan nerve conduits to repair a 12 mm sciatic nerve defect in rats.

RESULTS

Compared to the conventional two-dimensional (2D) culture, the prepared microcarriers were more conducive to the proliferation, migration, and secretion of trophic factors of ADSCs. In addition, gait analysis, neuro-electrophysiology, and histological evaluation of nerves and muscles showed that the ADSC microcarrier-loaded nerve conduits were more effective in improving nerve regeneration.

CONCLUSIONS

The ADSCs-loaded chitosan porous microcarrier prepared in this study has a high cell engraftment rate and good potential for peripheral nerve repair.

Murine bone-derived mesenchymal stem cells undergo molecular changes after a single passage in culture

The rarity of the mesenchymal stem cell (MSC) population poses a significant challenge for MSC research. Therefore, these cells are often expanded in vitro, prior to use. However, long-term culture has been shown to alter primary MSC properties. Additionally, early passage primary MSCs in culture are often assumed to represent the primary MSC population in situ, however, little research has been done to support this. Here, we compared the transcriptomic profiles of murine MSCs freshly isolated from the bone marrow to those that had been expanded in culture for 10 days. We identified that a single passage in culture extensively altered MSC molecular signatures associated with cell cycling, differentiation and immune response. These findings indicate the critical importance of the MSC source, highlighting the need for optimization of culture conditions to minimize the impact on MSC biology and a transition towards in vivo methodologies for the study of MSC function.

Dynamic cultivation of human mesenchymal stem/stromal cells for the production of extracellular vesicles in a 3D bioreactor system

PURPOSE

3D cell culture and hypoxia have been demonstrated to increase the therapeutic effects of mesenchymal stem/stromal cells (MSCs)-derived extracellular vesicles (EVs). In this study, a process for the production of MSC-EVs in a novel 3D bioreactor system under normoxic and hypoxic conditions was established and the resulting EVs were characterized.

METHODS

Human adipose-derived MSCs were seeded and cultured on a 3D membrane in the VITVO® bioreactor system for 7 days. Afterwards, MSC-EVs were isolated and characterized via fluorescence nanoparticle tracking analysis, flow cytometry with staining against annexin V (Anx5) as a marker for EVs exposing phosphatidylserine, as well as CD73 and CD90 as MSC surface markers.

RESULTS

Cultivation of MSC in the VITVO® bioreactor system demonstrated a higher concentration of MSC-EVs from the 3D bioreactor (9.1 × 109 ± 1.5 × 109 and 9.7 × 109 ± 3.1 × 109 particles/mL) compared to static 2D culture (4.2 × 109 ± 7.5 × 108 and 3.9 × 109 ± 3.0 × 108 particles/mL) under normoxic and hypoxic conditions, respectively. Also, the particle-to-protein ratio as a measure for the purity of EVs increased from 3.3 × 107 ± 1.1 × 107 particles/µg protein in 2D to 1.6 × 108 ± 8.3 × 106 particles/µg protein in 3D. Total MSC-EVs as well as CD73-CD90+ MSC-EVs were elevated in 2D normoxic conditions. The EV concentration and size did not differ significantly between normoxic and hypoxic conditions.

CONCLUSION

The production of MSC-EVs in a 3D bioreactor system under hypoxic conditions resulted in increased EV concentration and purity. This system could be especially useful in screening culture conditions for the production of 3D-derived MSC-EVs.

Regeneration of Rabbit Calvarial Defects with Combination of Stem Cells and Enamel Matrix Derivative: A Microcomputed Tomography and Histological Evaluation Comparing Two- and Three-Dimensional Cell Constructs

Background and Objectives: This study addresses the challenge of bone regeneration in calvarial defects, exploring the efficacy of stem cell-based therapies and enamel matrix derivative (EMD) in tissue engineering. It assesses the regenerative potential of two- and three-dimensional cell constructs combined with mesenchymal stem cells (MSCs) and EMD in rabbit calvarial defects. Materials and Methods: This research involved the use of bone-marrow-derived MSCs cultured in silicon elastomer-based concave microwells to form spheroids. White rabbits were grouped for different treatments, with Group 1 as control, Group 2 receiving only EMD, Group 3 getting EMD plus stem cells, and Group 4 being treated with EMD plus stem cell spheroids. Computed tomography (CT) and microcomputed tomography (micro-CT) imaging were used for structural assessment, while histological evaluations were conducted using hematoxylin and eosin, Masson's trichrome, and Picro-sirius red staining. Results: CT and micro-CT analyses revealed varying degrees of bone regeneration among the groups. Group 4, treated with three-dimensional MSC spheroids and EMD, showed the most significant improvement in bone regeneration. Histological analyses corroborated these findings, with Group 4 displaying enhanced bone formation and better collagen fiber organization. Conclusions: The study supported the biocompatibility and potential efficacy of three-dimensional MSC constructs combined with EMD in bone regeneration. Further investigations are needed to confirm these findings and optimize treatment protocols.

Transplantation of Stem Cell Spheroid-Laden 3-Dimensional Patches with Bioadhesives for the Treatment of Myocardial Infarction

Myocardial infarction (MI) is treated with stem cell transplantation using various biomaterials and methods, such as stem cell/spheroid injections, cell sheets, and cardiac patches. However, current treatment methods have some limitations, including low stem cell engraftment and poor therapeutic effects. Furthermore, these methods cause secondary damage to heart due to injection and suturing to immobilize them in the heart, inducing side effects. In this study, we developed stem cell spheroid-laden 3-dimensional (3D) patches (S_3DP) with biosealant to treat MI. This 3D patch has dual modules, such as open pockets to directly deliver the spheroids with their paracrine effects and closed pockets to improve the engraft rate by protecting the spheroid from harsh microenvironments. The spheroids formed within S_3DP showed increased viability and expression of angiogenic factors compared to 2-dimensional cultured cells. We also fabricated gelatin-based tissue adhesive biosealants via a thiol-ene reaction and disulfide bond formation. This biosealant showed stronger tissue adhesiveness than commercial fibrin glue. Furthermore, we successfully applied S_3DP using a biosealant in a rat MI model without suturing in vivo, thereby improving cardiac function and reducing heart fibrosis. In summary, S_3DP and biosealant have excellent potential as advanced stem cell therapies with a sutureless approach to MI treatment.

Regulation of inflammation during wound healing: the function of mesenchymal stem cells and strategies for therapeutic enhancement

A wound takes a long time to heal and involves several steps. Following tissue injury, inflammation is the primary cause of tissue regeneration and repair processes. As a result, the pathophysiological processes involving skin damage, healing, and remodeling depend critically on the control of inflammation. The fact that it is a feasible target for improving the prognosis of wound healing has lately become clear. Mesenchymal stem cells (MSCs) are an innovative and effective therapeutic option for wound healing due to their immunomodulatory and paracrine properties. By controlling the inflammatory milieu of wounds through immunomodulation, transplanted MSCs have been shown to speed up the healing process. In addition to other immunomodulatory mechanisms, including handling neutrophil activity and modifying macrophage polarization, there may be modifications to the activation of T cells, natural killer (NK) cells, and dendritic cells (DCs). Furthermore, several studies have shown that pretreating MSCs improves their ability to modulate immunity. In this review, we summarize the existing knowledge about how MSCs influence local inflammation in wounds by influencing immunity to facilitate the healing process. We also provide an overview of MSCs optimizing techniques when used to treat wounds.

Factors Defining Human Adipose Stem/Stromal Cell Immunomodulation in Vitro

Human adipose tissue-derived stem/stromal cells (hASCs) are adult multipotent mesenchymal stem/stromal cells with immunomodulatory capacities. Here, we present up-to-date knowledge on the impact of different experimental and donor-related factors on hASC immunoregulatory functions in vitro. The experimental determinants include the immunological status of hASCs relative to target immune cells, contact vs. contactless interaction, and oxygen tension. Factors such as the ratio of hASCs to immune cells, the cellular context, the immune cell activation status, and coculture duration are also discussed. Conditioning of hASCs with different approaches before interaction with immune cells, hASC culture in xenogenic or xenofree culture medium, hASC culture in two-dimension vs. three-dimension with biomaterials, and the hASC passage number are among the experimental parameters that greatly may impact the hASC immunosuppressive potential in vitro, thus, they are also considered. Moreover, the influence of donor-related characteristics such as age, sex, and health status on hASC immunomodulation in vitro is reviewed. By analysis of the literature studies, most of the indicated determinants have been investigated in broad non-standardized ranges, so the results are not univocal. Clear conclusions cannot be drawn for the fine-tuned scenarios of many important factors to set a standard hASC immunopotency assay. Such variability needs to be carefully considered in further standardized research. Importantly, field experts' opinions may help to make it clearer.

Mesenchymal stem cells lose the senescent phenotype under 3D cultivation

BACKGROUND

Three-dimensional (3D) cell culture is widely used in various fields of cell biology. In comparison to conventional two-dimensional (2D) cell culture, 3D cell culture facilitates a more accurate replication of the in vivo microenvironment, which is essential for obtaining more relevant results. The application of 3D cell culture techniques in regenerative medicine, particularly in mesenchymal stem cell (MSC)-based research, has been extensively studied. Many of these studies focus on the enhanced paracrine activity of MSCs cultured in 3D environments. However, few focus on the cellular processes that occur during 3D cultivation.

METHODS

In this work, we studied the changes occurring within 3D-cultured MSCs (3D-MSCs). Specifically, we examined the expression of numerous senescent-associated markers, the actin cytoskeleton structure, the architecture of the Golgi apparatus and the localization of mTOR, one of the main positive regulators of replicative senescence. In addition, we assessed whether the selective elimination of senescent cells occurs upon 3D culturing by using cell sorting based on autofluorescence.

RESULTS

Our findings indicate that 3D-MSCs were able to lose replicative senescence markers under 3D cell culture conditions. We observed changes in actin cytoskeleton structure, Golgi apparatus architecture and revealed that 3D cultivation leads to the nuclear localization of mTOR, resulting in a decrease in its active cytoplasmic form. Additionally, our findings provide evidence that 3D cell culture promotes the phenotypic reversion of senescent cell phenotype rather than their removal from the bulk population.

CONCLUSION

These novel insights into the biology of 3D-MSCs can be applied to research in regenerative medicine to overcome replicative senescence and MSC heterogeneity as they often pose significant concerns regarding safety and effectiveness for therapeutic purposes.

Spheroid size influences cellular senescence and angiogenic potential of mesenchymal stromal cell-derived soluble factors and extracellular vesicles

Introduction: The secretome of mesenchymal stromal cells (MSCs) serves as an innovative tool employed in the regenerative medicine approach. In this particular context, three-dimensional (3D) culture systems are widely utilized to better replicate in vivo conditions and facilitate prolonged cell maintenance during culture. The use of spheroids enables the preservation of the classical phenotypical characteristics of MSCs. However, the distinct microenvironment within the spheroid may impact the secretome, thereby enhancing the angiogenic properties of adult MSCs that typically possess a reduced angiogenic potential compared to MSCs derived from perinatal tissues due to the hypoxia created in the internal region of the spheroid. Methods: In this study, large spheroids (2,600 cells, ∼300 μm diameter) and small spheroids (1,000 cells, ∼200 μm diameter) were used to examine the role of spheroid diameter in the generation of nutrients and oxygen gradients, cellular senescence, and the angiogenic potential of secreted factors and extracellular vesicles (EVs). Results: In this study, we demonstrate that large spheroids showed increased senescence and a secretome enriched in pro-angiogenic factors, as well as pro-inflammatory and anti-angiogenic cytokines, while small spheroids exhibited decreased senescence and a secretome enriched in pro-angiogenic molecules. We also demonstrated that 3D culture led to a higher secretion of EVs with classical phenotypic characteristics. Soluble factors and EVs from small spheroids exhibited higher angiogenic potential in a human umbilical vein endothelial cell (HUVEC) angiogenic assay. Discussion: These findings highlighted the necessity of choosing the appropriate culture system for obtaining soluble factors and EVs for specific therapeutic applications.

Acoustofluidic Interfaces for the Mechanobiological Secretome of MSCs

While mesenchymal stem cells (MSCs) have gained enormous attention due to their unique properties of self-renewal, colony formation, and differentiation potential, the MSC secretome has become attractive due to its roles in immunomodulation, anti-inflammatory activity, angiogenesis, and anti-apoptosis. However, the precise stimulation and efficient production of the MSC secretome for therapeutic applications are challenging problems to solve. Here, we report on Acoustofluidic Interfaces for the Mechanobiological Secretome of MSCs: AIMS. We create an acoustofluidic mechanobiological environment to form reproducible three-dimensional MSC aggregates, which produce the MSC secretome with high efficiency. We confirm the increased MSC secretome is due to improved cell-cell interactions using AIMS: the key mediator N-cadherin was up-regulated while functional blocking of N-cadherin resulted in no enhancement of the secretome. After being primed by IFN-γ, the secretome profile of the MSC aggregates contains more anti-inflammatory cytokines and can be used to inhibit the pro-inflammatory response of M1 phenotype macrophages, suppress T cell activation, and support B cell functions. As such, the MSC secretome can be modified for personalized secretome-based therapies. AIMS acts as a powerful tool for improving the MSC secretome and precisely tuning the secretory profile to develop new treatments in translational medicine.

Amniotic Fluid and Placental Membranes as Sources of Stem Cells: Progress and Challenges 2.0

The aim of the second edition of this Special Issue was to collect both review and original research articles that investigate and elucidate the possible therapeutic role of perinatal stem cells in pathological conditions, such as cardiovascular and metabolic diseases, as well as inflammatory, autoimmune, musculoskeletal, and degenerative diseases [...].

Mesenchymal Stem Cell Extracellular Vesicles from Tissue-Mimetic System Enhance Epidermal Regeneration via Formation of Migratory Cell Sheets

BACKGROUND

The secretome of adipose-derived mesenchymal stem cells (ASCs) offers a unique approach to understanding and treating wounds, including the critical process of epidermal regeneration orchestrated by keratinocytes. However, 2D culture techniques drastically alter the secretory dynamics of ASCs, which has led to ambiguity in understanding which secreted compounds (e.g., growth factors, exosomes, reactive oxygen species) may be driving epithelialization.

METHODS

A novel tissue-mimetic 3D hydrogel system was utilized to enhance the retainment of a more regenerative ASC phenotype and highlight the functional secretome differences between 2D and 3D. Subsequently, the ASC-secretome was stratified by molecular weight and the presence/absence of extracellular vesicles (EVs). The ASC-secretome fractions were then evaluated to assess for the capacity to augment specific keratinocyte activities.

RESULTS

Culture of ASCs within the tissue-mimetic system enhanced protein secretion ~ 50%, exclusively coming from the > 100 kDa fraction. The ASC-secretome ability to modulate epithelialization functions, including migration, proliferation, differentiation, and morphology, resided within the "> 100 kDa" fraction, with the 3D ASC-secretome providing the greatest improvement. 3D ASC EV secretion was enhanced two-fold and exhibited dose-dependent effects on epidermal regeneration. Notably, ASC-EVs induced morphological changes in keratinocytes reminiscent of native regeneration, including formation of stratified cell sheets. However, only 3D-EVs promoted collective cell sheet migration and an epithelial-to-mesenchymal-like transition in keratinocytes, whereas 2D-EVs contained an anti-migratory stimulus.

CONCLUSION

This study demonstrates how critical the culture environment is on influencing ASC-secretome regenerative capabilities. Additionally, the critical role of EVs in modulating epidermal regeneration is revealed and their translatability for future clinical therapies is discussed.

Self-assembled adipose-derived mesenchymal stem cells as an extracellular matrix component- and growth factor-enriched filler

The clinical application of mesenchymal stem cells (MSCs) is attracting attention due to their excellent safety, convenient acquisition, multipotency, and trophic activity. The clinical effectiveness of transplanted MSCs is well-known in regenerative and immunomodulatory medicine, but there is a demand for their improved viability and regenerative function after transplantation. In this study, we isolated MSCs from adipose tissue from three human donors and generated uniformly sized MSC spheroids (∼100 µm in diameter) called microblocks (MiBs) for dermal reconstitution. The viability and MSC marker expression of MSCs in MiBs were similar to those of monolayer MSCs. Compared with monolayer MSCs, MiBs produced more extracellular matrix (ECM) components, including type I collagen, fibronectin, and hyaluronic acid, and growth factors such as vascular endothelial growth factor and hepatocyte growth factor. Subcutaneously injected MiBs showed skin volume retaining capacity in mice. These results indicate that MiBs could be applied as regenerative medicine for skin conditions such as atrophic scar by having high ECM and bioactive factor expression.

Breaking the graft-versus-host-disease barrier: Mesenchymal stromal/stem cells as precision healers

Mesenchymal Stromal/Stem Cells (MSCs) are multipotent, non-hematopoietic progenitor cells with a wide range of immune modulation and regenerative potential which qualify them as a potential component of cell-based therapy for various autoimmune/chronic inflammatory ailments. Their immunomodulatory properties include the secretion of immunosuppressive cytokines, the ability to suppress T-cell activation and differentiation, and the induction of regulatory T-cells. Considering this and our interest, we here discuss the significance of MSC for the management of Graft-versus-Host-Disease (GvHD), one of the autoimmune manifestations in human. In pre-clinical models, MSCs have been shown to reduce the severity of GvHD symptoms, including skin and gut damage, which are the most common and debilitating manifestations of this disease. While initial clinical studies of MSCs in GvHD cases were promising, the results were variable in randomized studies. So, further studies are warranted to fully understand their potential benefits, safety profile, and optimal dosing regimens. Owing to these inevitable issues, here we discuss various mechanisms, and how MSCs can be employed in managing GvHD, as a cellular therapeutic approach for this disease.

Hybrid spheroids containing mesenchymal stem cells promote therapeutic angiogenesis by increasing engraftment of co-transplanted endothelial colony-forming cells in vivo

BACKGROUND

Peripheral artery disease is an ischemic vascular disease caused by the blockage of blood vessels supplying blood to the lower extremities. Mesenchymal stem cells (MSCs) and endothelial colony-forming cells (ECFCs) have been reported to alleviate peripheral artery disease by forming new blood vessels. However, the clinical application of MSCs and ECFCs has been impeded by their poor in vivo engraftment after cell transplantation. To augment in vivo engraftment of transplanted MSCs and ECFCs, we investigated the effects of hybrid cell spheroids, which mimic a tissue-like environment, on the therapeutic efficacy and survival of transplanted cells.

METHODS

The in vivo survival and angiogenic activities of the spheroids or cell suspension composed of MSCs and ECFCs were measured in a murine hindlimb ischemia model and Matrigel plug assay. In the hindlimb ischemia model, the hybrid spheroids showed enhanced therapeutic effects compared with the control groups, such as adherent cultured cells or spheroids containing either MSCs or ECFCs.

RESULTS

Spheroids from MSCs, but not from ECFCs, exhibited prolonged in vivo survival compared with adherent cultured cells, whereas hybrid spheroids composed of MSCs and ECFCs substantially increased the survival of ECFCs. Moreover, single spheroids of either MSCs or ECFCs secreted greater levels of pro-angiogenic factors than adherent cultured cells, and the hybrid spheroids of MSCs and ECFCs promoted the secretion of several pro-angiogenic factors, such as angiopoietin-2 and platelet-derived growth factor.

CONCLUSION

These results suggest that hybrid spheroids containing MSCs can serve as carriers for cell transplantation of ECFCs which have poor in vivo engraftment efficiency.

Methods and Limitations of Augmenting Mesenchymal Stem Cells for Therapeutic Applications

Significance: Given their capacity for self-renewal, multilineage differentiation, and immunomodulatory potential, mesenchymal stem cells (MSCs) represent a promising modality of clinical therapy for both regenerative medicine and immune diseases. In this study, we review the key approaches and popular methods utilized to boost potency and modify functions of MSCs for clinical purposes as well as their associated limitations. Recent Advances: Several major domains of cell modification strategies are currently employed by investigators to overcome these deficits and augment the therapeutic potential of MSCs. Priming MSCs with soluble factors or pharmacologic agents as well as manipulating oxygen availability in culture have been demonstrated to be effective biochemical methods to augment MSC potential. Distinct genetic and epigenetic methods have emerged in recent years to modify the genetic expression of target proteins and factors thereby modulating MSCs capacity for differentiation, migration, and proliferation. Physical methods utilizing three-dimensional culture methods and alternative cell delivery systems and scaffolds can be used to recapitulate the native MSC niche and augment their engraftment and viability for in vivo models. Critical Issues: Unmodified MSCs have demonstrated only modest benefits in many preclinical and clinical studies due to issues with cell engraftment, viability, heterogeneity, and immunocompatibility between donor and recipient. Furthermore, unmodified MSCs can have low inherent therapeutic potential for which intensive research over the past few decades has been dedicated to improving cell functionality and potency.

The Growing Importance of Three-Dimensional Models and Microphysiological Systems in the Assessment of Mycotoxin Toxicity

Current investigations in the field of toxicology mostly rely on 2D cell cultures and animal models. Although well-accepted, the traditional 2D cell-culture approach has evident drawbacks and is distant from the in vivo microenvironment. To overcome these limitations, increasing efforts have been made in the development of alternative models that can better recapitulate the in vivo architecture of tissues and organs. Even though the use of 3D cultures is gaining popularity, there are still open questions on their robustness and standardization. In this review, we discuss the current spheroid culture and organ-on-a-chip techniques as well as the main conceptual and technical considerations for the correct establishment of such models. For each system, the toxicological functional assays are then discussed, highlighting their major advantages, disadvantages, and limitations. Finally, a focus on the applications of 3D cell culture for mycotoxin toxicity assessments is provided. Given the known difficulties in defining the safety ranges of exposure for regulatory agency policies, we are confident that the application of alternative methods may greatly improve the overall risk assessment.

Mechano-responsive hydrogel for direct stem cell manufacturing to therapy

Bone marrow-derived mesenchymal stem cell (MSC) is one of the most actively studied cell types due to its regenerative potential and immunomodulatory properties. Conventional cell expansion methods using 2D tissue culture plates and 2.5D microcarriers in bioreactors can generate large cell numbers, but they compromise stem cell potency and lack mechanical preconditioning to prepare MSC for physiological loading expected in vivo. To overcome these challenges, in this work, we describe a 3D dynamic hydrogel using magneto-stimulation for direct MSC manufacturing to therapy. With our technology, we found that dynamic mechanical stimulation (DMS) enhanced matrix-integrin β1 interactions which induced MSCs spreading and proliferation. In addition, DMS could modulate MSC biofunctions including directing MSC differentiation into specific lineages and boosting paracrine activities (e.g., growth factor secretion) through YAP nuclear localization and FAK-ERK pathway. With our magnetic hydrogel, complex procedures from MSC manufacturing to final clinical use, can be integrated into one single platform, and we believe this 'all-in-one' technology could offer a paradigm shift to existing standards in MSC therapy.

Acceleration of burn wound healing by micronized amniotic membrane seeded with umbilical cord-derived mesenchymal stem cells

Umbilical cord-derived mesenchymal stem cells (UC-MSC) are promising candidates for wound healing. However, the low amplification efficiency of MSC in vitro and their low survival rates after transplantation have limited their medical application. In this study, we fabricated a micronized amniotic membrane (mAM) as a microcarrier to amplify MSC in vitro and used mAM and MSC (mAM-MSC) complexes to repair burn wounds. Results showed that MSC could live and proliferate on mAM in a 3D culture system, exhibiting higher cell activity than in 2D culture. Transcriptome sequencing of MSC showed that the expression of growth factor-related, angiogenesis-related, and wound healing-related genes was significantly upregulated in mAM-MSC compared to traditional 2D-cultured MSC, which was verified via RT-qPCR. Gene ontology (GO) analysis of differentially expressed genes (DEGs) showed significant enrichment of terms related to cell proliferation, angiogenesis, cytokine activity, and wound healing in mAM-MSC. In a burn wound model of C57BL/6J mice, topical application of mAM-MSC significantly accelerated wound healing compared to MSC injection alone and was accompanied by longer survival of MSC and greater neovascularization in the wound.

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells: Potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) have shown significant therapeutic potential, and have therefore been extensively investigated in preclinical studies of regenerative medicine. However, while MSCs have been shown to be safe as a cellular treatment, they have usually been therapeutically ineffective in human diseases. In fact, in many clinical trials it has been shown that MSCs have moderate or poor efficacy. This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs. Recently, specific priming strategies have been used to improve the therapeutic properties of MSCs. In this review, we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs. We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes. Particularly, while hypoxic priming can be used primarily for the treatment of acute diseases, inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders. The shift in approach from regeneration to inflammation implies, in MSCs, a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways. The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.

Therapeutic Perspectives for Inflammation and Senescence in Osteoarthritis Using Mesenchymal Stem Cells, Mesenchymal Stem Cell-Derived Extracellular Vesicles and Senolytic Agents

Osteoarthritis (OA) is the most common cause of disability worldwide among the elderly. Alarmingly, the incidence of OA in individuals less than 40 years of age is rising, likely due to the increase in obesity and post-traumatic osteoarthritis (PTOA). In recent years, due to a better understanding of the underlying pathophysiology of OA, several potential therapeutic approaches targeting specific molecular pathways have been identified. In particular, the role of inflammation and the immune system has been increasingly recognized as important in a variety of musculoskeletal diseases, including OA. Similarly, higher levels of host cellular senescence, characterized by cessation of cell division and the secretion of a senescence-associated secretory phenotype (SASP) within the local tissue microenvironments, have also been linked to OA and its progression. New advances in the field, including stem cell therapies and senolytics, are emerging with the goal of slowing disease progression. Mesenchymal stem/stromal cells (MSCs) are a subset of multipotent adult stem cells that have demonstrated the potential to modulate unchecked inflammation, reverse fibrosis, attenuate pain, and potentially treat patients with OA. Numerous studies have demonstrated the potential of MSC extracellular vesicles (EVs) as cell-free treatments that comply with FDA regulations. EVs, including exosomes and microvesicles, are released by numerous cell types and are increasingly recognized as playing a critical role in cell-cell communication in age-related diseases, including OA. Treatment strategies for OA are being developed that target senescent cells and the paracrine and autocrine secretions of SASP. This article highlights the encouraging potential for MSC or MSC-derived products alone or in combination with senolytics to control patient symptoms and potentially mitigate the progression of OA. We will also explore the application of genomic principles to the study of OA and the potential for the discovery of OA phenotypes that can motivate more precise patient-driven treatments.

Three-Dimensional Spheroid Culture of Human Mesenchymal Stem Cells: Offering Therapeutic Advantages and In Vitro Glimpses of the In Vivo State

As invaluable as the standard 2-dimensional (2D) monolayer in vitro cell culture system has been, there is increasing evidence that 3-dimensional (3D) non-adherent conditions are more relevant to the in vivo condition. While one of the criteria for human mesenchymal stem cells (MSCs) has been in vitro plastic adherence, such 2D culture conditions are not representative of in vivo cell-cell and cell-extracellular matrix (ECM) interactions, which may be especially important for this progenitor/stem cell of skeletal and connective tissues. The 3D spheroid, a multicellular aggregate formed under non-adherent 3D in vitro conditions, may be particularly suited as an in vitro method to better understand MSC physiological processes, since expression of ECM and other adhesion proteins are upregulated in such a cell culture system. First used in embryonic stem cell in vitro culture to recapitulate in vivo developmental processes, 3D spheroid culture has grown in popularity as an in vitro method to mimic the 3-dimensionality of the native niche for MSCs within tissues/organs. In this review, we discuss the relevance of the 3D spheroid culture for understanding MSC biology, summarize the biological outcomes reported in the literature based on such this culture condition, as well as contemplate limitations and future considerations in this rapidly evolving and exciting area.

Advanced cell-based products generated via automated and manual manufacturing platforms under the quality by design principle: Are they equivalent or different?

Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells that can be isolated from bone marrow, adipose tissue, the umbilical cord, dental pulp, etc. These cells have unique properties that give them excellent therapeutic potential, including immunoregulation, immunomodulation, and tissue regeneration functions. MSC-based products are considered advanced therapy medicinal products (ATMPs) under European regulations (1394/2007); thus, they must be manufactured under good manufacturing practices and via effective manufacturing methods. The former can be achieved via a proper laboratory design and compliance with manufacturing protocols, whereas the latter requires an approach that ensures that the quality of the products is consistent regardless of the manufacturing procedure. To meet these daunting requirements, this study proposes an exchangeable approach that combines optimized and equivalent manufacturing processes under the Quality by Design (QbD) principle, allowing investigators to convert from small laboratory-scale to large-scale manufacturing of MSC-based products for clinical applications without altering the quality and quantity of the cell-based products.

Multisized Photoannealable Microgels Regulate Cell Spreading, Aggregation, and Macrophage Phenotype through Microporous Void Space

Microgels are an emerging platform for in vitro models and guiding cell fate due to their inherent porosity and tunability. This work describes a light-based technique for rapidly annealing microgels across a range of diameters. Utilizing 8-arm poly(ethylene) glycol-vinyl sulfone, the number of arms available for crosslinking, functionalization, and annealing is stoichiometrically controlled. Small and large microgels are fabricated to explore how microgel diameter impacts void space and the role of porosity on cell spreading, cell aggregation, and macrophage polarization. Mesenchymal stromal cells spread rapidly in both formulations, yet the smaller microgels permit a higher cell density. When seeded with macrophages, the smaller microgels promote an M1 phenotype, while larger microgels promote an M2 phenotype. As another application, the inherent porosity of annealed microgels is leveraged to induce cell aggregation. Finally, the microgels are implanted to examine how different size microgels influence endogenous cell invasion and macrophage polarization. The use of ultraviolet light allows for microgels to be noninvasively injected into a desired mold or wound defect before annealing, and microgels of different properties combined to create a heterogeneous scaffold. This approach is clinically relevant given its tunability and fast annealing time.

Unsung versatility of elastin-like polypeptide inspired spheroid fabrication: A review

Lately, 3D cell culture technique has gained a lot of appreciation as a research model. Augmented with technological advancements, the area of 3D cell culture is growing rapidly with a diverse array of scaffolds being tested. This is especially the case for spheroid cultures. The culture of cells as spheroids provides opportunities for unanticipated vision into biological phenomena with its application to drug discovery, metabolic profiling, stem cell research as well as tumor, and disease biology. Spheroid fabrication techniques are broadly categorised into matrix-dependent and matrix-independent techniques. While there is a profusion of spheroid fabrication substrates with substantial biological relevance, an economical, modular, and bio-compatible substrate for high throughput production of spheroids is lacking. In this review, we posit the prospects of elastin-like polypeptides (ELPs) as a broad-spectrum spheroid fabrication platform. Elastin-like polypeptides are nature inspired, size-tunable genetically engineered polymers with wide applicability in various arena of biological considerations, has been employed for spheroid culture with profound utility. The technology offers a cheap, high-throughput, reproducible alternative for spheroid culture with exquisite adaptability. Here, we will brief the applicability of 3D cultures as compared to 2D cultures with spheroids being the focal point of the review. Common approaches to spheroid fabrication are discussed with existential limitations. Finally, the versatility of elastin-like polypeptide inspired substrates for spheroid culture has been discussed.

Biophysical cues to improve the immunomodulatory capacity of mesenchymal stem cells: The progress and mechanisms

Mesenchymal stem cells (MSCs) can maintain immune homeostasis and many preclinical trials with MSCs have been carried out around the world. In vitro culture of MSCs has been found to result in the decline of immunomodulatory capacity, migration and proliferation. To address these problems, simulating the extracellular environment for preconditioning of MSCs is a promising and inexpensive method. Biophysical cues in the external environment that MSCs are exposed to have been shown to affect MSC migration, residency, differentiation, secretion, etc. We review the main ways in which MSCs exert their immunomodulatory ability, and summarize recent advances in mechanical preconditioning of MSCs to enhance immunomodulatory capacity and related mechanical signal sensing and transduction mechanisms.

Mesenchymal stem cell-based therapy for non-healing wounds due to chronic limb-threatening ischemia: A review of preclinical and clinical studies

Progressive peripheral arterial disease (PAD) can result in chronic limb-threatening ischemia (CLTI) characterized by clinical complications including rest pain, gangrene and tissue loss. These complications can propagate even more precipitously in the setting of common concomitant diseases in patients with CLTI such as diabetes mellitus (DM). CLTI ulcers are cutaneous, non-healing wounds that persist due to the reduced perfusion and dysfunctional neovascularization associated with severe PAD. Existing therapies for CLTI are primarily limited to anatomic revascularization and medical management of contributing factors such as atherosclerosis and glycemic control. However, many patients fail these treatment strategies and are considered "no-option," thereby requiring extremity amputation, particularly if non-healing wounds become infected or fulminant gangrene develops. Given the high economic burden imposed on patients, decreased quality of life, and poor survival of no-option CLTI patients, regenerative therapies aimed at neovascularization to improve wound healing and limb salvage hold significant promise. Cell-based therapy, specifically utilizing mesenchymal stem/stromal cells (MSCs), is one such regenerative strategy to stimulate therapeutic angiogenesis and tissue regeneration. Although previous reviews have focused primarily on revascularization outcomes after MSC treatments of CLTI with less attention given to their effects on wound healing, here we review advances in pre-clinical and clinical studies related to specific effects of MSC-based therapeutics upon ischemic non-healing wounds associated with CLTI.

Characterization of mesenchymal stem cells in pre-B acute lymphoblastic leukemia

Components of the bone marrow microenvironment (BMM) have been shown to mediate the way in which leukemia develops, progresses and responds to treatment. Increasing evidence shows that leukemic cells hijack the BMM, altering its functioning and establishing leukemia-supportive interactions with stromal and immune cells. While previous work has highlighted functional defects in the mesenchymal stem cell (MSC) population from the BMM of acute leukemias, thorough characterization and molecular profiling of MSCs in pre-B cell acute lymphoblastic leukemia (B-ALL), the most common cancer in children, has not been conducted. Here, we investigated the cellular and transcriptome profiles of MSCs isolated from the BMM of an immunocompetent BCR-ABL1⁺ model of B-ALL. Leukemia-associated MSCs exhibited reduced self-renewal capacity in vitro and significant changes in numerous molecular signatures, including upregulation of inflammatory signaling pathways. Additionally, we found downregulation of genes involved in extracellular matrix organization and osteoblastogenesis in leukemia-associated MSCs. This study provides cellular and molecular insights into the role of MSCs during B-ALL progression.

Engineering exosomes by three-dimensional porous scaffold culture of human umbilical cord mesenchymal stem cells promote osteochondral repair

Improving the poor microenvironment in the joint cavity has potential for treating cartilage injury, and mesenchymal stem cell (MSC)-derived exosomes (MSC-Exos), which can modulate cellular behavior, are becoming a new cell-free therapy for cartilage repair. Here, we used acellular cartilage extracellular matrix (ACECM) to prepare 3D scaffolds and 2D substrates by low-temperature deposition modeling (LDM) and tape casting. We aimed to investigate whether MSC-Exos cultured on scaffolds of different dimensions could improve the poor joint cavity microenvironment caused by cartilage injury and to explore the related mechanisms. In vitro experiments showed that exosomes derived from MSCs cultured on three-dimensional (3D) scaffolds (3D-Exos) had increased efficiency. In short-term animal experiments, compared with exosomes derived from MSCs cultured in a two-dimensional (2D) environment (2D-Exos), 3D-Exos had a stronger ability to regulate the joint cavity microenvironment. Long-term animal studies confirmed the therapeutic efficacy of 3D-Exos over 2D-Exos. Thus, 3D-Exos were applied in the rat knee osteochondral defect model after adsorption in the micropores of the scaffold and combined with subsequent articular cavity injections, and they showed a stronger cartilage repair ability. These findings provide a new strategy for repairing articular cartilage damage. Furthermore, miRNA sequencing indicated that the function of 3D-Exos may be associated with high expression of miRNAs. Thus, our study provides valuable insights for the design of 3D-Exos to promote cartilage regeneration.

The Evolving Landscape of Potency Assays

There is a "goldilocks" aspect to potency assays. On the one hand, a comprehensive evaluation of the cell product with detailed quantitative measurement of the critical quality attribute/s of the desired biological activity is required. On the other hand, the potency assay benefits from simplification and lean approaches that avoid unnecessary complication and enhance robustness, to provide a reproducible and scalable product. There is a need to balance insightful knowledge of complex biological healing processes with straightforward manufacture of an advanced therapeutic medicinal product (ATMP) that can be administered in a trustworthy cost-effective manner. While earlier chapters within this book have highlighted numerous challenges facing the potency assay conundrum, this chapter offers a forward-looking perspective regarding the many recent advances concerning acellular products, cryopreservation, induced MSC, cell priming, nanotechnology, 3D culture, regulatory guidelines and evolving institutional roles, that are likely to facilitate potency assay development in the future.

Extracellular magnetic labeling of biomimetic hydrogel-induced human mesenchymal stem cell spheroids with ferumoxytol for MRI tracking

Labeling of mesenchymal stem cells (MSCs) with superparamagnetic iron oxide nanoparticles (SPIONs) has emerged as a potential method for magnetic resonance imaging (MRI) tracking of transplanted cells in tissue repair studies and clinical trials. Labeling of MSCs using clinically approved SPIONs (ferumoxytol) requires the use of transfection reagents or magnetic field, which largely limits their clinical application. To overcome this obstacle, we established a novel and highly effective method for magnetic labeling of MSC spheroids using ferumoxytol. Unlike conventional methods, ferumoxytol labeling was done in the formation of a mechanically tunable biomimetic hydrogel-induced MSC spheroids. Moreover, the labeled MSC spheroids exhibited strong MRI T2 signals and good biosafety. Strikingly, the encapsulated ferumoxytol was localized in the extracellular matrix (ECM) of the spheroids instead of the cytoplasm, minimizing the cytotoxicity of ferumoxytol and maintaining the viability and stemness properties of biomimetic hydrogel-induced MSC spheroids. This demonstrates the potential of this method for post-transplantation MRI tracking in the clinic.

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An extracellular magnetic labeling method was developed for MSC spheroids using ferumoxytol.

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Ferumoxytol encapsulated into abundant ECM proteins network of MSC spheroids ensured this method is stable and durable.

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Uniformly sized magnetic spheroids induced by mechanically tunable biomimetic hydrogels promoted MSCs stemness properties.

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Magnetically labeled MSC spheroids exhibited superior MRI imaging both in vitro and in vivo.

Therapeutic strategies of three-dimensional stem cell spheroids and organoids for tissue repair and regeneration

Three-dimensional (3D) stem cell culture systems have attracted considerable attention as a way to better mimic the complex interactions between individual cells and the extracellular matrix (ECM) that occur in vivo. Moreover, 3D cell culture systems have unique properties that help guide specific functions, growth, and processes of stem cells (e.g., embryogenesis, morphogenesis, and organogenesis). Thus, 3D stem cell culture systems that mimic in vivo environments enable basic research about various tissues and organs. In this review, we focus on the advanced therapeutic applications of stem cell-based 3D culture systems generated using different engineering techniques. Specifically, we summarize the historical advancements of 3D cell culture systems and discuss the therapeutic applications of stem cell-based spheroids and organoids, including engineering techniques for tissue repair and regeneration.