In Vivo Survival and Osteogenic Differentiation of Allogeneic Rat Bone Marrow Mesenchymal Stem Cells (MSCs)

The potent paracrine effect of umbilical cord mesenchymal stem cells mediates mitochondrial quality control to restore chemotherapy-induced damage in ovarian granulosa cells

The basic principle of chemotherapy is to attack cells with fast growth, and cancer cells are targeted by anticancer drugs because they have a faster growth rate than normal cells. High doses of anticancer drugs may cause an irreversible decline in reproductive capacity, and novel approaches for fertility preservation and/or restoration after anticancer treatment are urgently needed. Here, we provide important insights into the recovery of human reproductive cells damaged by chemotherapy. We performed a detailed screening of the cytokines of various human mesenchymal stem cells (hMSCs) to select superior MSCs. Also, we analyzed the Ovarian granulosa cell (OGC)-)-specific functions for restoring function, apoptosis, and mitochondrial functions to confirm the recovery mechanism in damaged OGCs. As a result, we demonstrated that conditioned media (CM) of Umbilical cord mesenchymal stem cells (UC-MSCs) could restore the functions of damaged OGCs primarily through antiapoptotic and antioxidant effects. Furthermore, CM changed the phenotype of damaged OGCs to an energetic status by restoring mitochondrial function and enhanced the mitochondrial metabolic activity decreased by chemotherapy. Finally, we demonstrated that the restoration of mitochondrial function in damaged OGCs was mediated through mitochondrial autophagy (mitophagy). Our findings offer new insights into the potential of stem cell-based therapy for fertility preservation and/or restoration in female cancer patients.

Combining Bone Collagen Matrix with hUC-MSCs for Application to Alveolar Process Cleft in a Rabbit Model

BACKGROUND

Most materials used clinically for filling severe bone defects either cannot induce bone re-generation or exhibit low bone conversion, therefore, their therapeutic effects are limited. Human umbilical cord mesenchymal stem cells (hUC-MSCs) exhibit good osteoinduction. However, the mechanism by which combining a heterogeneous bone collagen matrix with hUC-MSCs to repair the bone defects of alveolar process clefts remains unclear.

METHODS

A rabbit alveolar process cleft model was established by removing the bone tissue from the left maxillary bone. Forty-eight young Japanese white rabbits (JWRs) were divided into normal, control, material and MSCs groups. An equal volume of a bone collagen matrix alone or combined with hUC-MSCs was implanted in the defect. X-ray, micro-focus computerized tomography (micro-CT), blood analysis, histochemical staining and TUNEL were used to detect the newly formed bone in the defect area at 3 and 6 months after the surgery.

RESULTS

The bone formation rate obtained from the skull tissue in MSCs group was significantly higher than that in control group at 3 months (P < 0.01) and 6 months (P < 0.05) after the surgery. The apoptosis rate in the MSCs group was significantly higher at 3 months after the surgery (P < 0.05) and lower at 6 months after the surgery (P < 0.01) than those in the normal group.

CONCLUSIONS

Combining bone collagen matrix with hUC-MSCs promoted the new bone regeneration in the rabbit alveolar process cleft model through promoting osteoblasts formations and chondrocyte growth, and inducing type I collagen formation and BMP-2 generation.

Rapid and robust derivation of mesenchymal stem cells from human pluripotent stem cells via temporal induction of neuralized ectoderm

Background

Mesenchymal stem cells (MSCs) are emerging as the mainstay of regenerative medicine because of their ability to differentiate into multiple cell lineages. The infinite proliferative potential of human pluripotent stem cells (PSCs) grants an unlimited supply of MSCs. Despite their great potential in therapeutic applications, several drawbacks have hindered its clinical translation, including limited number of replication, compromised potential and altered function in late passages. The aim of this study is to establish an efficient method for the production of MSCs from pluripotent stem cells for potential clinical application in rare human disease Hutchinson-Gilford progeria syndrome.

Results

We established a robust method allowing rapid derivation of MSCs from both human iPSCs and ESCs via a temporal induction of neural ectoderm in chemically defined media. The iPSC- and ESC-derived MSCs satisfy the standard criteria of surface markers. They exhibited a high tri-lineage differentiation potential with over 90% transcriptional similarity to the primary MSCs derived from bone marrow. To evaluate the potential application of this method in disease modeling, MSCs were generated from iPSCs derived from a patient with Hutchinson-Gilford progeria syndrome (HGPS-MSCs) and from mutation-rectified HGPS-iPSCs (cHGPS-MSCs). HGPS-MSCs manifested accelerated senescence whereas mutation rectification rescued cellular senescence in HGPS-MSCs.

Conclusions

The robust method of MSC derivation from ESCs and iPSCs provides an efficient approach to rapidly generate sufficient MSCs for in vitro disease modeling and clinical applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00753-2.

Engineering of human mesenchymal stem cells resistant to multiple natural killer subtypes

Mesenchymal stem cells (MSCs) as a therapeutic promise are often quickly cleared by innate immune cells of the host including natural killer (NK) cells. Efforts have been made to generate immune-escaping human embryonic stem cells (hESCs) where T cell immunity is evaded by defecting β-2-microglobulin (B2M), a common unit for human leukocyte antigen (HLA) class I, and NK cells are inhibited via ectopic expression of HLA-E or -G. However, NK subtypes vary among recipients and even at different pathologic statuses. It is necessary to dissect and optimize the efficacy of the immune-escaping cells against NK subtypes. Here, we first generated B2M knockout hESCs and differentiated them to MSCs (EMSCs) and found that NK resistance occurred with B2M^-/- EMSCs expressing HLA-E and -G only when they were transduced via an inducible lentiviral system in a dose-dependent manner but not when they were inserted into a safe harbor. HLA-E and -G expressed at high levels together in transduced EMSCs inhibited three major NK subtypes, including NKG2A⁺/LILRB1⁺, NKG2A⁺/LILRB1^-, and NKG2A^-/LILRB1⁺, which was further potentiated by IFN-γ priming. Thus, this study engineers MSCs with resistance to multiple NK subtypes and underscores that dosage matters when a transgene is used to confer a novel effect to host cells, especially for therapeutic cells to evade immune rejection.

Allogeneic Bone-Marrow Mesenchymal Stem Cell with Moldable Cryogel for Craniofacial Bone Regeneration

Allogeneic bone-marrow mesenchymal stem cells (BMSCs) can promote bone regeneration and substitute for autologous BMSCs if autologous sources are unavailable, but the efficacy of bone regeneration by allogeneic BMSCs is still inconsistent. A Lewis rat cranium defect model was used to investigate the efficacy of bone regeneration between autologous and allogeneic BMSCs in gelatin-nanohydroxyapatite cryogel scaffolds. BMSCs from Wistar rats served as the allogeneic cell lineage. The full-thickness cranium defects were treated by either blank control, cryogel only, allogeneic BMSC-seeded cryogel, or autologous BMSC-seeded cryogel (n = 5). Bone regeneration was monitored by micro-computed tomography and examined histologically at week 12. In addition, we assessed the immune responses in vitro by mixed lymphocyte reaction (MLR) assay and CD₄⁺ immunochemistry staining ex vivo. The MLR showed that allogeneic BSMCs elicited a weak immune response on day 14 that progressively attenuated by day 28. In vivo, the bone regeneration in allogeneic BMSCs was inferior at week 4, but progressively matched the autologous BMSCs by week 12. Our results suggest that allogeneic BMSCs can serve as an alternative source for bone regeneration.

Differentiation and proliferation potencies of human bone tissue-derived mesenchymal stromal cells (hBT-MSCs) after long-term cryopreservation －Comparison among cells stored for 1, 5, 10, 15, and 20 years

INTRODUCTION

We investigated bone differentiation and proliferation potencies of human bone tissue-derived mesenchymal stromal cells (hBT-MSCs) after long-term cryopreservation. We determined the presence of any morphological and characteristic changes due to freezing to identify issues that need to be solved for future clinical applications.

SUBJECTS AND METHODS

A total of 15 samples of hBT-MSCs that had been cryopreserved for different lengths of time, ranging from one year to 20 years (n = 3 each), were thawed and recultivated after being collected from excess iliac cancellous bone specimens of patients who underwent secondary alveolar bone grafting for cleft lip and palate in our department. We determined viability by observing calcein/EthD-stained cells under a confocal microscope, and the cell proliferation experiment was performed for one week using the Water Soluble Tetrazolium salts (WST) assay method. A confocal microscope was also used to identify any excessively accumulated senescence-associated growth factor SA-βgal. Differentiation potency was assessed in the following three groups: bone differentiation, adipocyte differentiation, and nondifferentiation induction. We examined bone/adipocyte differentiation potencies using Alizarin Red staining, Ca quantitation, and Oil Red staining after continuously culturing cells for four weeks.

RESULTS

Viability test results indicated that the proportion of viable cells decreased as the number of years of cryopreservation increased. The cell proliferation experiment showed that cells cryopreserved for a shorter duration multiplied exponentially. In the aging test, cells cryopreserved for ≥5 years showed similar positive reactions independent of the number of years of cryopreservation. In the cell proliferation test, there was no statistically significant difference between the years of cryopreserving. We compared bone differentiation and adipocyte differentiation ability with the non-induction group, and the induction group was confirmed to have a statistical advantage. However, there was no significant difference in the induction group pertaining to different ages.

CONCLUSIONS

Samples cryopreserved for 20 years remained competent in bone and adipocyte differentiation. However, their differentiation direction tended to skew to either bone or adipocyte differentiation. Our results suggest that freezing does not accelerate aging, and samples cryopreserved for a long time are useful in future clinical applications.

Assessment of the Bone Healing Process Mediated by Periosteum-Derived Mesenchymal Stem Cells' Secretome and a Xenogenic Bioceramic-An In Vivo Study in the Rabbit Critical Size Calvarial Defect Model

The mesenchymal stem cell (MSC) secretome has been considered an innovative therapeutic biological approach, able to modulate cellular crosstalk and functionality for enhanced tissue repair and regeneration. This study aims to evaluate the functionality of the secretome isolated from periosteum-derived MSCs, from either basal or osteogenic-induced conditions, in the healing of a critical size calvarial bone defect in the rabbit model. A bioceramic xenograft was used as the vehicle for secretome delivery, and the biological response to the established biocomposite system was assessed by clinical, histological, histomorphometric, and microtomographic analysis. A comparative analysis revealed that the osteogenic-induced secretome presented an increased diversity of proteins, with emphasis on those related to osteogenesis. Microtomographic and histological morphometric analysis revealed that bioceramic xenografts implanted with secretomes enhanced the new bone formation process, with the osteogenic-induced secretome inducing the highest bone tissue formation. The application of the MSC secretome, particularly from osteogenic-induced populations, may be regarded as an effective therapeutic approach to enhance bone tissue healing and regeneration.

Impact of 3D cell culture on bone regeneration potential of mesenchymal stromal cells

As populations age across the world, osteoporosis and osteoporosis-related fractures are becoming the most prevalent degenerative bone diseases. More than 75 million patients suffer from osteoporosis in the USA, the EU and Japan. Furthermore, it is anticipated that the number of patients affected by osteoporosis will increase by a third by 2050. Although conventional therapies including bisphosphonates, calcitonin and oestrogen-like drugs can be used to treat degenerative diseases of the bone, they are often associated with serious side effects including the development of oesophageal cancer, ocular inflammation, severe musculoskeletal pain and osteonecrosis of the jaw.The use of autologous mesenchymal stromal cells/mesenchymal stem cells (MSCs) is a possible alternative therapeutic approach to tackle osteoporosis while overcoming the limitations of traditional treatment options. However, osteoporosis can cause a decrease in the numbers of MSCs, induce their senescence and lower their osteogenic differentiation potential.Three-dimensional (3D) cell culture is an emerging technology that allows a more physiological expansion and differentiation of stem cells compared to cultivation on conventional flat systems.This review will discuss current understanding of the effects of different 3D cell culture systems on proliferation, viability and osteogenic differentiation, as well as on the immunomodulatory and anti-inflammatory potential of MSCs.

Bone regeneration with autologous adipose-derived mesenchymal stem cells: A reliable experimental model in rats

The adult mesenchymal stem cell (MSC) has been proposed to be the definitive tool in regenerative medicine due to its multi-differentiation potential and expansion capacity ex vivo. The use of MSCs on bone regeneration has been assessed in several studies, obtaining promising results. However, the endless combinations that can be tested and the heterogeneity in the experimental conditions become a drawback when comparing results between authors. Moreover, it is very hard to find autologous studies using adipose-derived MSCs (AD-MSC) in rodents, which is the most used preclinical animal model.

In this article an experimental model for basic bone tissue engineering research is described and justified, on which adult AD-MSCs are safely isolated from the rat dorsal interscapular fat pad, allowing ex vivo expansion and autogenous orthotopic reimplantation in a bilateral mandibular bone defect made in the same animal.

This reliable and reproducible model provides a simple way to perform basic experimentation studies in a small animal model using autologous MSC for bone regeneration or cell therapy techniques prior to improve the research on large animal models.•

Predictable and safe harvest of adipose-derived MSC. No need of animal sacrifice.

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Allows for autologous studies with the most frequently used animal model: the rat. No need of allogeneic or human MSC use and, therefore, immunological concerns are avoided.

•

Bilateral mandibular critical size defect to allow direct control/experimental comparison.

Injectable Hydrogels as Three-Dimensional Network Reservoirs for Osteoporosis Treatment

Despite tremendous progresses made in the field of tissue engineering over the past several decades, it remains a significant challenge for the treatment of osteoporosis (OP) due to the lack of appropriate carriers to improve the bioavailability of therapeutic agents and the unavailability of artificial bone matrix with desired properties for the replacement of damaged bone regions. Encouragingly, the development of injectable hydrogels for the treatment of OP has attracted increasing attention in recent years because they can serve either as a reservoir for various therapeutic species or as a perfect filler for bone injuries with irregular shapes. However, the relationship between the complicated pathological mechanism of OP and the properties of diverse polymeric materials lacks elucidation, which clearly hampers the clinical application of injectable hydrogels for the efficient treatment of OP. To clarify this relationship, this article summarized both localized and systematic treatment of OP using an injectable hydrogel-based strategy. Specifically, the pathogenesis of OP and the limitations of current treatment approaches were first analyzed. We further focused on the use of hydrogels loaded with various therapeutic substances following a classification standard of the encapsulated cargoes for OP treatment with an emphasis on the application and precautions of each category. A concluding remark on existing challenges and future directions of this rapidly developing research area was finally made. Impact statement Effective osteoporosis (OP) treatment remains a significant challenge due substantially to the unavailability of appropriate drug carriers and artificial matrices with desired properties to promote bone repair and replace damaged regions. For this purpose, this review focused on the development of diverse injectable hydrogel systems for the delivery of various therapeutic agents, including drugs, stem cells, and nucleic acids, for effective increase in bone mass and favorable osteogenesis. The summarized important guidelines are believed to promote clinical development and translation of hydrogels for the efficient treatment of OP and OP-related bone damages toward improved life quality of millions of patients.

Exosomes Secreted by Young Mesenchymal Stem Cells Promote New Bone Formation During Distraction Osteogenesis in Older Rats

Distraction osteogenesis (DO) is a clinically effective procedure to regenerate large bone defects. However, the treatment duration is undesirably lengthy, especially in elderly patients. Exosomes derived from mesenchymal stem cells (MSC-Exos) could exert the beneficial effects while avoiding the possible complications of stem cell transplantation. This study aimed to evaluate the effects of MSC-Exos on bone regeneration during DO in older rats. Exosomes were isolated from the supernatants of young bone marrow mesenchymal stem cells (BMSCs) through ultra-centrifugation, and characterized using transmission electron microscopy, western blot, and tunable resistive pulse sensing analysis. The effects of MSC-Exos on the proliferation and differentiation of older BMSCs were evaluated using CCK-8 assay, ALP and ARS staining, and qRT-PCR. Unilateral tibial DO model was established on older Sprague-Dawley rats and MSC-Exos or phosphate buffer saline was locally injected into the distraction gaps after distraction weekly. Bone regeneration were evaluated using X-ray, Micro-CT, mechanical test, and histological staining. The MSC-Exos were round or cup-shaped vesicles ranging from 60 to 130 nm in diameter and expressed markers including CD9, CD63, and TSG101. The in vitro results indicated that MSC-Exos could enhance the proliferation and osteogenic differentiation of older BMSCs. Bone regeneration was markedly accelerated in rats treated with MSC-Exos according to the results of X-ray, micro-CT, and histological analysis. The distracted tibias from the MSC-Exos group also demonstrated better mechanical properties. These results suggest that MSC-Exos promote DO-mediated bone regeneration in older rats through enhancing the proliferation and osteogenic capacity of BMSCs.

All-Trans Retinoic Acid Promotes Osteogenic Differentiation and Bone Consolidation in a Rat Distraction Osteogenesis Model

Distraction osteogenesis (DO) is used to treat specific disorders associated with growth abnormalities and/or loss of bone stock secondary to trauma or disease. However, a high rate of complications and discomfort hamper its further application in clinical practice. Here, we investigated the effects of all-trans retinoic acid (ATRA) on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBMSCs) and bone consolidation in a rat DO model. Different doses of ATRA were used to treat rBMSCs. Cell viability and osteogenic differentiation were assessed using CCK-8 and alkaline phosphatase staining, respectively. The mRNA expression of osteogenic differentiation-genes (including ALP, Runx2, OCN, OPN, OSX, and BMP2) and angiogenic genes (including VEGF, HIF-1, FLK-2, ANG-2, and ANG-4) were determined by quantitative real-time PCR analysis. Further, we locally injected ATRA or PBS into the gap in the rat DO model every 3 days until termination. X-rays, micro-computed tomography (Micro-CT), mechanical testing, and immunohistochemistry stains were used to evaluate the quality of the regenerates. ATRA promoted osteogenic differentiation of rBMSCs. Moreover, ATRA elevated the mRNA expression levels of osteogenic differentiation-genes and angiogenic genes. In the rat model, new bone properties of bone volume/total tissue volume and mechanical strength were significantly higher in the ATRA-treatment group. Micro-CT examination showed more mineralized bone after the ATRA-treatment, and immunohistochemistry demonstrated more new bone formation after ATRA-treatment than that in the PBS group. In conclusion, as a readily available and very cost effective bio-source, ATRA may be a novel therapeutic method to enhance bone consolidation in the clinical setting.

The biological behavior optimization of human periodontal ligament stem cells via preconditioning by the combined application of fibroblast growth factor-2 and A83-01 in in vitro culture expansion

BACKGROUND

As the optimal source of seed cells in periodontal tissue engineering, periodontal ligament stem cells (PDLSCs) have always been researched to improve cell expansion due to their limited resource and spontaneous differentiation in vitro cultivation. Fibroblast growth factor-2 (FGF-2) has been proven to stimulate bone marrow mesenchymal stem cells (BMMSCs) proliferation and maintain their pluripotency when being added to the culture medium. As a small molecule inhibitor of transforming growth factor-beta receptors (TGF-βRs), A83-01 can also promote cell proliferation. Therefore, the aim of this study was to verify whether the combined application of FGF-2 and A83-01 could augment cell quantity and quality during in vitro culture.

METHODS

PDLSCs were preconditioned with A83-01, FGF-2, or their combination. A cell counting kit-8 (CCK8) assay, cell apoptosis assay, ALP activity assay, Alizarin Red S staining assay, RT-PCR assay, Western blot assay and ELISA were used to determine the sustained effects of different preconditioning strategies on the proliferation, apoptosis, stemness, osteogenic differentiation and paracrine action of PDLSCs.

RESULTS

The combined application of FGF-2 and A83-01 significantly augmented cell expansion, reduced cell apoptosis, magnified stemness expression, promoted later osteogenic differentiation and mineralization and increased paracrine action of PDLSCs compared with the control. Moreover, the combination presented significant advantages in enhancing proliferation, stemness expression and paracrine action over FGF-2 alone.

CONCLUSIONS

The combined application of A83-01 and FGF-2 may be an improved strategy for PDLSCs biological behavior optimization in culture expansion and advantageous for reinforcing proliferation, stemness expression and cytokine secretion over FGF-2 alone.

Treatment of Full-Thickness Rotator Cuff Tendon Tear Using Umbilical Cord Blood-Derived Mesenchymal Stem Cells and Polydeoxyribonucleotides in a Rabbit Model

Objective

The aim of this study was to investigate regenerative effects of ultrasound- (US-) guided injection with human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) and/or polydeoxyribonucleotide (PDRN) injection in a chronic traumatic full-thickness rotator cuff tendon tear (FTRCTT) in a rabbit model.

Methods

Rabbits (n = 32) were allocated into 4 groups. After a 5 mm sized FTRCTT just proximal to the insertion site on the subscapularis tendon was created by excision, the wound was immediately covered by a silicone tube to prevent natural healing. After 6 weeks, 4 injectants (0.2 mL normal saline, G1-SAL; 0.2 mL PDRN, G2-PDRN; 0.2 mL UCB-MSCs, G3-MSC; and 0.2 mL UCB-MSCs with 0.2 ml PDRN, G4-MSC + PDRN) were injected into the FTRCTT under US guidance. We evaluated gross morphologic changes on all rabbits after sacrifice. Masson's trichrome, anti-type 1 collagen antibody, bromodeoxyuridine, proliferating cell nuclear antigen, vascular endothelial growth factor, and platelet endothelial cell adhesion molecule stain were performed to evaluate histological changes. Motion analysis was also performed.

Results

The gross morphologic mean tendon tear size in G3-MSC and G4-MSC + PDRN was significantly smaller than that in G1-SAL and G2-PDRN (p < 0.05). However, there were no significant differences in the tendon tear size between G3-MSC and G4-MSC + PDRN. In G4-MSC + PDRN, newly regenerated collagen type 1 fibers, proliferating cell activity, angiogenesis, walking distance, fast walking time, and mean walking speed were greater than those in the other three groups on histological examination and motion analysis.

Conclusions

Coinjection of UCB-MSCs and PDRN was more effective than UCB-MSC injection alone in histological and motion analysis in a rabbit model of chronic traumatic FTRCTT. However, there was no significant difference in gross morphologic change of tendon tear between UCB-MSCs with/without PDRN injection. The results of this study regarding the combination of UCB-MSCs and PDRN are worth additional investigations.

Stem Cell Considerations for the Clinician

"Although there is ample evidence that beneficial results can be obtained from the use of mesenchymal stem cells, several questions regarding their use remain to be answered. For many of these questions, preclinical models will be helpful, but the task of evaluating and implementing these findings for orthopaedic patients falls onto the shoulders of clinical researchers. Evaluation of these questions is a daunting, but such a challenge fits the concept of personalized medicine in today's medicine."

The Challenge in Using Mesenchymal Stromal Cells for Recellularization of Decellularized Cartilage

Some decellularized musculoskeletal extracellular matrices (ECM)s derived from tissues such as bone, tendon and fibrocartilaginous meniscus have already been clinical use for tissue reconstruction. Repair of articular cartilage with its unique zonal ECM architecture and composition is still an unsolved problem, and the question is whether allogenic or xenogeneic decellularized cartilage ECM could serve as a biomimetic scaffold for this purpose.Hence, this survey outlines the present state of preparing decellularized cartilage ECM-derived scaffolds or composites for reconstruction of different cartilage types and of reseeding it particularly with mesenchymal stromal cells (MSCs).The preparation of natural decellularized cartilage ECM scaffolds hampers from the high density of the cartilage ECM and lacking interconnectivity of the rather small natural pores within it: the chondrocytes lacunae. Nevertheless, the reseeding of decellularized ECM scaffolds before implantation provided superior results compared with simply implanting cell-free constructs in several other tissues, but cartilage recellularization remains still challenging. Induced by cartilage ECM-derived scaffolds MSCs underwent chondrogenesis.Major problems to be addressed for the application of cell-free cartilage were discussed such as to maintain ECM structure, natural chemistry, biomechanics and to achieve a homogenous and stable cell recolonization, promote chondrogenic and prevent terminal differentiation (hypertrophy) and induce the deposition of a novel functional ECM. Some promising approaches were proposed including further processing of the decellularized ECM before recellularization of the ECM with MSCs, co-culturing of MSCs with chondrocytes and establishing bioreactor culture e.g. with mechanostimulation, flow perfusion pressure and lowered oxygen tension. Graphical Abstract Synopsis of tissue engineering approaches based on cartilage-derived ECM.

Increased stem cells delivered using a silk gel/scaffold complex for enhanced bone regeneration

The low in vivo survival rate of scaffold-seeded cells is still a challenge in stem cell-based bone regeneration. This study seeks to use a silk hydrogel to deliver more stem cells into a bone defect area and prolong the viability of these cells after implantation. Rat bone marrow stem cells were mingled with silk hydrogels at the concentrations of 1.0 × 10⁵/mL, 1.0 × 10⁶/mL and 1.0 × 10⁷/mL before gelation, added dropwise to a silk scaffold and applied to a rat calvarial defect. A cell tracing experiment was included to observe the preservation of cell viability and function. The results show that the hydrogel with 1.0 × 10⁷/mL stem cells exhibited the best osteogenic effect both in vitro and in vivo. The cell-tracing experiment shows that cells in the 1.0 × 10⁷ group still survive and actively participate in new bone formation 8 weeks after implantation. The strategy of pre-mingling stem cells with the hydrogel had the effect of delivering more stem cells for bone engineering while preserving the viability and functions of these cells in vivo.

Human fetal mesenchymal stem cell secretome enhances bone consolidation in distraction osteogenesis

BACKGROUND

Distraction osteogenesis (DO) is one of the most dramatic reconstructive techniques for inducing bone regeneration, but it involves an undesirably long period for bone consolidation. Developing innovative approaches to enhance bone consolidation is a burning need. Human fetal mesenchymal stem cells (hFMSCs) have been shown to express more primitive developmental genes than those of human adult mesenchymal stem cells (hAMSCs), which is a preferable source for cell therapy and tissue regeneration. In the present study, we investigated the immunogenicity of using the human mesenchymal stem cell (MSC) secretome on rat cells, the effects of secretome on osteogenic differentiation of rat bone marrow-derived MSCs (rBMSCs), and the potential application of hFMSC secretome in promoting bone consolidation in a rat DO model.

METHODS

Secretome was collected from MSC culture and was used to treat rBMSCs. Following secretome treatment, cell proliferation, alkaline phosphatase staining, Alizarin Red S staining, and mRNA expression of osteogenic differentiation-related genes (including ALP, Runx2, OCN, OPN, and Osx) in the rBMSCs were checked, as well as mixed rat peripheral blood lymphocyte reaction. hFMSC secretome was injected locally into the regenerates from the end of lengthening every 3 days in the rat DO model, until termination. The regenerates were subject to weekly x-rays, micro-computed tomography (μCT) and mechanical testing examination. The bone quality was assessed by histology and immunohistochemistry examinations.

RESULTS

Compared to the secretome from rBMSCs and hAMSCs, hFMSC secretome had the best osteogenic induction ability and low immunogenicity. hFMSC secretome with different doses showed no effect on cell viability. hFMSC secretome at the dose of 100 μg/μl could significantly increase the expression of alkaline phosphatase and all the osteogenic marker genes, as well as the amount of calcium deposits in the rBMSCs. Finally, the local application of hFMSC secretome in distraction regenerates in a rat DO model significantly improved bone consolidation according to the results of μCT, mechanical test, and histological and immunohistochemistry analysis.

CONCLUSIONS

The current study demonstrated that hFMSC secretome promotes osteogenesis of rBMSCs and bone consolidation during DO. hFMSC secretome may be a new therapeutic strategy to enhance bone consolidation in patients undergoing DO treatment.

Evaluation of Anterior Vertebral Interbody Fusion Using Osteogenic Mesenchymal Stem Cells Transplanted in Collagen Sponge

STUDY DESIGN

The study used a rabbit model to achieve anterior vertebral interbody fusion using osteogenic mesenchymal stem cells (OMSCs) transplanted in collagen sponge.

OBJECTIVE

We investigated the effectiveness of graft material for anterior vertebral interbody fusion using a rabbit model by examining the OMSCs transplanted in collagen sponge.

SUMMARY OF BACKGROUND DATA

Anterior vertebral interbody fusion is commonly performed. Although autogenous bone graft remains the gold-standard fusion material, it requires a separate surgical procedure and is associated with significant short-term and long-term morbidity. Recently, mesenchymal stem cells from bone marrow have been studied in various fields, including posterolateral spinal fusion. Thus, we hypothesized that cultured OMSCs transplanted in porous collagen sponge could be used successfully even in anterior vertebral interbody fusion.

METHODS

Forty mature male White Zealand rabbits (weight, 3.5-4.5 kg) were randomly allocated to receive one of the following graft materials: porous collagen sponge plus cultured OMSCs (group I); porous collagen sponge alone (group II); autogenous bone graft (group III); and nothing (group IV). All animals underwent anterior vertebral interbody fusion at the L4/L5 level. The lumbar spine was harvested en bloc, and the new bone formation and spinal fusion was evaluated using radiographic analysis, microcomputed tomography, manual palpation test, and histologic examination at 8 and 12 weeks after surgery.

RESULTS

New bone formation and bony fusion was evident as early as 8 weeks in groups I and III. And there was no statistically significant difference between 8 and 12 weeks. At both time points, by microcomputed tomography and histologic analysis, new bone formation was observed in both groups I and III, fibrous tissue was observed and there was no new bone in both groups II and IV; by manual palpation test, bony fusion was observed in 40% (4/10) of rabbits in group I, 70% (7/10) of rabbits in group III, and 0% (0/10) of rabbits in both groups II and IV.

CONCLUSIONS

These findings suggest that mesenchymal stem cells that have been cultured with osteogenic differentiation medium and loaded with collagen sponge could induce bone formation and anterior vertebral interbody fusion. And the rabbit model we developed will be useful in evaluating the effects of graft materials for anterior vertebral interbody fusion. Further study is needed to determine the most appropriate carrier for OMSCs and the feasibility in the clinical setting.

Transplantation of human-induced pluripotent stem cells carried by self-assembling peptide nanofiber hydrogel improves bone regeneration in rat calvarial bone defects

Objectives/Aims

The requisite conditions for successful bone tissue engineering are efficient stem cell differentiation into osteogenic cells and a suitable scaffold. In this study, we investigated in vivo bone regeneration from transplanted induced pluripotent stem cells (iPSCs).

Materials and Methods

Two critical-sized calvarial bone defects were created in 36 rats. The surgical sites were randomly assigned to one of three treatments to test the healing effectiveness of the scaffold alone, scaffold with iPSCs or a salt solution as a control. The effectiveness of the treatments was evaluated after 2 or 4 weeks using radiographic and histological analyses of bone regeneration in the six groups.

Results

Micro-computed tomography (CT) analysis of the bone defects found minimal bone regeneration with the salt solution and nanofiber scaffold and increased bone regeneration in defects repaired with iPSCs delivered in the nanofiber scaffold.

Conclusion

Transplanted iPSCs encapsulated in a nanofiber scaffold can regenerate bone in critical-sized defects.

Ex Vivo Expanded Allogeneic Mesenchymal Stem Cells with Bone Marrow Transplantation Improved Osteogenesis in Infants with Severe Hypophosphatasia

Patients with severe hypophosphatasia (HPP) develop osteogenic impairment with extremely low alkaline phosphatase (ALP) activity, resulting in a fatal course during infancy. Mesenchymal stem cells (MSCs) differentiate into various mesenchymal lineages, including bone and cartilage. The efficacy of allogeneic hematopoietic stem cell transplantation for congenital skeletal and storage disorders is limited, and therefore we focused on MSCs for the treatment of HPP. To determine the effect of MSCs on osteogenesis, we performed multiple infusions of ex vivo expanded allogeneic MSCs for two patients with severe HPP who had undergone bone marrow transplantation (BMT) from asymptomatic relatives harboring the heterozygous mutation. There were improvements in not only bone mineralization but also muscle mass, respiratory function, and mental development, resulting in the patients being alive at the age of 3. After the infusion of MSCs, chimerism analysis of the mesenchymal cell fraction isolated from bone marrow in the patients demonstrated that donor-derived DNA sequences existed. Adverse events of BMT were tolerated, whereas those of MSC infusion did not occur. However, restoration of ALP activity was limited, and normal bony architecture could not be achieved. Our data suggest that multiple MSC infusions, following BMT, were effective and brought about clinical benefits for patients with lethal HPP. Allogeneic MSC-based therapy would be useful for patients with other congenital bone diseases and tissue disorders if the curative strategy to restore clinically normal features, including bony architecture, can be established.

A new application of cell-free bone regeneration: immobilizing stem cells from human exfoliated deciduous teeth-conditioned medium onto titanium implants using atmospheric pressure plasma treatment

Introduction

Surface modification of titanium (Ti) implants promotes bone formation and shortens the osseointegration period. The aim of this study was to promote bone regeneration and stability around implants using atmospheric pressure plasma (APP) pretreatment. This was followed by immobilization of stem cells from human exfoliated deciduous teeth-conditioned medium (SHED-CM) on the Ti implant surface.

Methods

Ti samples (implants, discs, powder) were treated with APP for 30 seconds. Subsequently, these were immobilized on the treated Ti surface, soaked and agitated in phosphate-buffered saline or SHED-CM for 24 hours at 37 °C. The surface topography of the Ti implants was observed using scanning electron microscopy with energy dispersive X-ray spectroscopy. In vivo experiments using Ti implants placed on canine femur bone were then conducted to permit histological analysis at the bone-implant boundary. For the in vitro experiments, protein assays (SDS-PAGE, Bradford assay, liquid chromatography-ion trap mass spectrometry) and canine bone marrow stromal cell (cBMSC) attachment assays were performed using Ti discs or powder.

Results

In the in vitro study, treatment of Ti implant surfaces with SHED-CM led to calcium phosphate and extracellular matrix protein immobilization. APP pretreatment increased the amount of SHED-CM immobilized on Ti powder, and contributed to increased cBMSC attachment on Ti discs. In the in vivo study, histological analysis revealed that the Ti implants treated with APP and SHED-CM stimulated new bone formation around implants.

Conclusions

Implant device APP pretreatment followed by SHED-CM immobilization may be an effective application to facilitate bone regeneration around dental implants.

Influence of Immunogenicity of Allogeneic Bone Marrow Mesenchymal Stem Cells on Bone Tissue Engineering

Allogeneic bone marrow mesenchymal stem cell (allo-BMSC)-based tissue-engineered bone (TEB) has great potential for bone defect repair. However, the immunogenicities and biological roles of allo-BMSCs are still controversial. In this study, we established an animal model of critical-sized mandibular defect in beagle dogs and compared the repairing effects of allo-BMSC-based TEB with autogenic BMSC (auto-BMSC)-based TEB without the administration of immunosuppressants. During the first 2 weeks postimplantation, a transient immune response in the allo-BMSC group was detected with an increase in proinflammation cytokines TNF-α, IFN-γ, and IL-2, a declination of anti-inflammation cytokine IL-10, and an increase in percentages of CD4(+) and CD8(+) T-cell subsets in peripheral blood. Nevertheless, there was no significant difference in bone union achievement, bone mineral density, and biomechanical properties between the two groups at 12 and 24 weeks postimplantation. Further subcutaneous implantation of allo-BMSCs/scaffold also exhibited the similar transient immune responses in the first 2 weeks postimplantation but followed by a decreased bone formation at 4 and 8 weeks postimplantation. These findings indicate that allo-BMSCs can induce a transient immunoreaction, which may temporally delay the osteogenesis of allo-BMSC/scaffold complex in early stage of in vivo implantation, whereas the long-term engineered bone formation was not affected.

Wharton's jelly derived mesenchymal stem cells: future of regenerative medicine? Recent findings and clinical significance

Around 5 million annual births in EU and 131 million worldwide give a unique opportunity to collect lifesaving Wharton's jelly derived mesenchymal stem cells (WJ-MSC). Evidences that these cells possess therapeutic properties are constantly accumulating. Collection of WJ-MSC is done at the time of delivery and it is easy and devoid of side effects associated with collection of adult stem cells from bone marrow or adipose tissue. Likewise, their rate of proliferation, immune privileged status, lack of ethical concerns, nontumorigenic properties make them ideal for both autologous and allogeneic use in regenerative medicine applications. This review provides an outline of the recent findings related to WJ-MSC therapeutic effects and possible advantage they possess over MSC from other sources. Results of first clinical trials conducted to treat immune disorders are highlighted.

Concise review: the immune status of mesenchymal stem cells and its relevance for therapeutic application

Multipotentiality and anti-inflammatory activity, the two main properties of mesenchymal stem cells (MSCs), underlie their therapeutic prospective. During the past decade, numerous studies in animal models and clinical trials explored the potential of MSCs in the treatment of diseases associated with tissue regeneration and inflammatory control. Other qualities of MSCs: ready accessibility in bone marrow and fat tissue and rapid expansion in culture make the therapeutic use of patients' own cells feasible. The prevailing belief that MSCs are nonimmunogenic encouraged the use of unrelated donor cells in immune-competent recipients. The data emerging from studies performed with immune-incompatible cells in animal models for a wide-range of human diseases show, however, conflicting results and cast doubt on the immune privileged status of MSCs. Our analysis of the preclinical literature in this review is aimed to gain a better understanding of the therapeutic potential of immune-incompatible MSCs. Emphasis was laid on applications for enhancement of tissue repair in the absence of immune-suppressive therapy.

Paracrine effect of mesenchymal stem cells derived from human adipose tissue in bone regeneration

Mesenchymal stem cell (MSC) transplantation has proved to be a promising strategy in cell therapy and regenerative medicine. Although their mechanism of action is not completely clear, it has been suggested that their therapeutic activity may be mediated by a paracrine effect. The main goal of this study was to evaluate by radiographic, morphometric and histological analysis the ability of mesenchymal stem cells derived from human adipose tissue (Ad-MSC) and their conditioned medium (CM), to repair surgical bone lesions using an in vivo model (rabbit mandibles). The results demonstrated that both, Ad-MSC and CM, induce bone regeneration in surgically created lesions in rabbit's jaws, suggesting that Ad-MSC improve the process of bone regeneration mainly by releasing paracrine factors. The evidence of the paracrine effect of MSC on bone regeneration has a major impact on regenerative medicine, and the use of their CM can address some issues and difficulties related to cell transplants. In particular, CM can be easily stored and transported, and is easier to handle by medical personnel during clinical procedures.

Changes in immunological profile of allogeneic mesenchymal stem cells after differentiation: should we be concerned?

Mesenchymal stem cells (MSCs) are an adult stromal cell population possessing potent differentiation capacity and a potential for use across major histocompatibility complex barriers. Although allogeneic MSCs have potent immunosuppressive properties, evidence also suggests that they elicit a weak allogeneic immune response. However, the effect of induced differentiation on the immunosuppressive ability and immunogenicity of allogeneic MSCs is a potential obstacle when applying MSCs in tissue replacement therapies. These concerns will be explored in this review, with particular emphasis on changes in the cell surface expression of immunogenic markers, changes in the secretion of immunosuppressive molecules and in vivo functional benefits of the cell therapy. We review the literature from a translational point of view, focusing on pre-clinical studies that have utilised and analysed the effects of allogeneic immune responses on the ability of allogeneic MSCs to regenerate damaged tissue in models of bone, heart and cartilage defects.

Meniscus regeneration by syngeneic, minor mismatched, and major mismatched transplantation of synovial mesenchymal stem cells in a rat model

We compared the effect of syngeneic and allogeneic transplantation of synovial mesenchymal stem cells (MSCs) for meniscus regeneration in a rat model. Synovium was harvested from the knee joints of three strains of rats. The anterior half of the medial meniscus in both knees of F344 rats was removed and 5 million synovial MSCs derived from F344 (syngeneic transplantation), Lewis (minor mismatched transplantation), and ACI (major mismatched transplantation) were injected into the knee of the F344 rats. At 4 weeks, the area of the regenerated meniscus in the F344 group was significantly larger than that in the ACI group. Histological score was significantly better in the F344 and Lewis groups than in the ACI group at 8 weeks. DiI labeled cells could be observed in the knee joint in the F344 group, but were hardly detected in the ACI group at 1 week. The number of macrophages and CD8 T cells at synovium around the meniscus defect was significantly lower in the F344 group than in the ACI group at 1 week. Syngeneic and minor mismatched transplantation of synovial MSCs promoted meniscus regeneration better than major mismatched transplantation in a rat meniscectmized model.

Osteoinduction of biphasic calcium phosphate scaffolds in a nude mouse model

Bioceramics combined with isolated stem cells, or with total bone marrow, constitute the main strategies under consideration in the field of bone tissue engineering. In the present preclinical study, two biphasic calcium phosphate scaffolds currently on the market, MBCP® and MBCP+®, with different hydroxyapatite/β-tricalcium phosphate ratio, were implanted ectopically in a nude mouse model. These scaffolds were supplemented either with human mesenchymal stromal cells, or with human total bone marrow, or rat total bone marrow. Biomaterials alone were found to have potentially low, but non-zero, osteoinductive properties, while biomaterials associated with total bone marrow consistently improved osteoinduction in comparison with high concentrations of isolated human stromal cells.

Stem cell-conditioned medium accelerates distraction osteogenesis through multiple regenerative mechanisms

Distraction osteogenesis (DO) successfully induces large-scale skeletal tissue regeneration, but it involves an undesirably long treatment period. A high-speed DO mouse model (H-DO) with a distraction speed twice that of a control DO model failed to generate new bone callus in the distraction gap. Here we demonstrate that the local administration of serum-free conditioned medium from human mesenchymal stem cells (MSC-CM) accelerated callus formation in the mouse H-DO model. Secretomic analysis identified factors contained in MSC-CM that recruit murine bone marrow stromal cells (mBMSCs) and endothelial cells/endothelial progenitor cells (EC/EPCs), inhibit inflammation and apoptosis, and promote osteoblast differentiation, angiogenesis, and cell proliferation. Functional assays identified MCP-1/-3 and IL-3/-6 as essential factors in recruiting mBMSCs and EC/EPCs. IL-3/-6 also enhanced the osteogenic differentiation of mBMSCs. MSC-CM that had been depleted of MCP-1/-3 failed to recruit mBMSCs, and consequently failed to promote callus formation. Taken together, our data suggest that MSCs produce a broad repertoire of trophic factors with tissue-regenerative activities that accelerate healing in the DO process.

Osteogenically differentiated mesenchymal stem cells and ceramics for bone tissue engineering

INTRODUCTION

In the human body, cells having self-renewal and multi-differentiation capabilities reside in many tissues and are called adult stem cells. In bone marrow tissue, two types of stem cells are well known: hematopoietic stem cells and mesenchymal stem cells (MSCs). Though the number of MSCs in bone marrow tissue is very low, it can be increased by in vitro culture of the marrow, and culture-expanded MSCs are available for various tissue regeneration.

AREAS COVERED

The culture-expanded MSCs can further differentiate into osteogenic cells such as bone forming osteoblasts by culturing the MSCs in an osteogenic medium. This paper discusses osteogenically differentiated MSCs derived from the bone marrow of patients. Importantly, the differentiation can be achieved on ceramic surfaces which demonstrate mineralized bone matrix formation as well as appearance of osteogenic cells. The cell/matrix/ceramic constructs could show immediate in vivo bone formation and are available for bone reconstruction surgery.

EXPERT OPINION

Currently, MSCs are clinically available for the regeneration of various tissues due to their high proliferation/differentiation capabilities. However, the capabilities are still limited and thus technologies to improve or recover the inherent capabilities of MSCs are needed.

Chondrogenic differentiation increases antidonor immune response to allogeneic mesenchymal stem cell transplantation

Allogeneic mesenchymal stem cells (allo-MSCs) have potent regenerative and immunosuppressive potential and are being investigated as a therapy for osteoarthritis; however, little is known about the immunological changes that occur in allo-MSCs after ex vivo induced or in vivo differentiation. Three-dimensional chondrogenic differentiation was induced in an alginate matrix, which served to immobilize and potentially protect MSCs at the site of implantation. We show that allogeneic differentiated MSCs lost the ability to inhibit T-cell proliferation in vitro, in association with reduced nitric oxide and prostaglandin E2 secretion. Differentiation altered immunogenicity as evidenced by induced proliferation of allogeneic T cells and increased susceptibility to cytotoxic lysis by allo-specific T cells. Undifferentiated or differentiated allo-MSCs were implanted subcutaneously, with and without alginate encapsulation. Increased CD3(+) and CD68(+) infiltration was evident in differentiated and splenocyte encapsulated implants only. Without encapsulation, increased local memory T-cell responses were detectable in recipients of undifferentiated and differentiated MSCs; however, only differentiated MSCs induced systemic memory T-cell responses. In recipients of encapsulated allogeneic cells, only differentiated allo-MSCs induced memory T-cell responses locally and systemically. Systemic alloimmune responses to differentiated MSCs indicate immunogenicity regardless of alginate encapsulation and may require immunosuppressive therapy for therapeutic use.

Recent Patents Pertaining to Immune Modulation and Musculoskeletal Regeneration with Wharton's Jelly Cells

Umbilical cord mesenchymal stromal cells (UCMSCs) are isolated from Wharton's jelly in the umbilical cord at birth, and offer advantages over adult mesenchymal stromal cells (MSCs) such as highly efficient isolation, faster proliferation in vitro, a broader differentiation potential, and non-invasive harvesting procedure. Their expansion and differentiation potential renders them a promising cell source for tissue engineering and clinical applications. This review discusses recent updates on the differentiation strategies for musculoskeletal tissue engineering including cartilage, bone, and muscle. In addition to tissue engineering applications, UCMSCs can be utilized to support hematopoiesis and modulate immune response. We review the patents relevant to the application of MSCs including UCMSCs in hematopoiesis and immune modulation. Finally, the current hurdles in the clinical translation of UCMSCs are discussed. During clinical translation, it is critical to develop large-scale manufacturing of UCMSCs as well as the composition of expansion and differentiation media. Four clinical trials to date have examined the safety and efficacy of UCMSCs. Once public banking of UCMSCs is available to supply matched allogeneic units and once UCMSC manufacturing is standardized, we anticipate that UCMSCs will be more widely used in clinical trials.

Role of mesenchymal stem cells in bone regeneration and fracture repair: a review

Mesenchymal stem cells (MSCs) are non-haematopoietic stromal stem cells that have many sources, such as bone marrow, periosteum, vessel walls, adipose, muscle, tendon, peripheral circulation, umbilical cord blood, skin and dental tissues. They are capable of self-replication and of differentiating into, and contributing to the regeneration of, mesenchymal tissues, such as bone, cartilage, ligament, tendon, muscle and adipose tissue. The homing of MSCs may play an important role in the repair of bone fractures. As a composite material, the formation and growth of bone tissue is a complex process, including molecular, cell and biochemical metabolic changes. The recruitment of factors with an adequate number of MSCs and the micro-environment around the fracture are effective for fracture repair. Several studies have investigated the functional expression of various chemokine receptors, trophic factors and adhesion molecules in human MSCs. Many external factors affect MSC homing. MSCs have been used as seed cells in building tissue-engineered bone grafts. Scaffolds seeded with MSCs are most often used in tissue engineering and include biotic and abiotic materials. This knowledge provides a platform for the development of novel therapies for bone regeneration with endogenous MSCs.

MSCs: Delivery Routes and Engraftment, Cell-Targeting Strategies, and Immune Modulation

Mesenchymal stem cells (MSCs) are currently being widely investigated both in the lab and in clinical trials for multiple disease states. The differentiation, trophic, and immunomodulatory characteristics of MSCs contribute to their therapeutic effects. Another often overlooked factor related to efficacy is the degree of engraftment. When reported, engraftment is generally low and transient in nature. MSC delivery methods should be tailored to the lesion being treated, which may be local or systemic, and customized to the mechanism of action of the MSCs, which can also be local or systemic. Engraftment efficiency is enhanced by using intra-arterial delivery instead of intravenous delivery, thus avoiding the "first-pass" accumulation of MSCs in the lung. Several methodologies to target MSCs to specific organs are being developed. These cell targeting methodologies focus on the modification of cell surface molecules through chemical, genetic, and coating techniques to promote selective adherence to particular organs or tissues. Future improvements in targeting and delivery methodologies to improve engraftment are expected to improve therapeutic results, extend the duration of efficacy, and reduce the effective (MSC) therapeutic dose.

Evolution and future prospects of adipose-derived immunomodulatory cell therapeutics

Over the past two decades, tissue engineering and regenerative medicine have evolved from what many considered a theoretical science to what is now a clinical reality. Tissue engineering combines biomaterial scaffolds, growth factors and stem or progenitor cells to repair damaged tissues. Adipose tissue, an abundant and easily accessed tissue, is a potential source of stromal/stem cells for regenerative therapeutic applications. Like bone marrow-derived mesenchymal stem cells, adipose-derived stromal/stem cells display both immunomodulatory and immunosuppressive properties. The adipose cells exert these actions, in part, through their secretion of paracrine growth factors. This review highlights recent developments in the isolation, characterization and preclinical application of adipose-derived cells and the challenges facing their translation into clinical practice.

The role of small molecules in musculoskeletal regeneration

The uses of bone morphogenetic proteins and parathyroid hormone therapeutics are fraught with several fundamental problems, such as cost, protein stability, immunogenicity, contamination and supraphysiological dosage. These downsides may effectively limit their more universal use. Therefore, there is a clear need for alternative forms of biofactors to obviate the drawbacks of protein-based inductive factors for bone repair and regeneration. Our group has studied small molecules with the capacity to regulate osteoblast differentiation and mineralization because their inherent physical properties minimize limitations observed in protein growth factors. For instance, in general, small molecule inducers are usually more stable, highly soluble, nonimmunogenic, more affordable and require lower dosages. Small molecules with the ability to induce osteoblastic differentiation may represent the next generation of bone regenerative medicine. This review describes efforts to develop small molecule-based biofactors for induction, paying specific attention to their novel roles in bone regeneration.

Anti-donor immune responses elicited by allogeneic mesenchymal stem cells: what have we learned so far?

Mesenchymal stem (stromal) cells (MSCs) have potent anti-inflammatory/immunosuppressive properties which underlie much of their therapeutic potential. This fact has led to the widely accepted belief that MSCs from genetically unrelated individuals (allogeneic (allo)-MSCs) can be used therapeutically with equal efficacy to autologous MSCs and without triggering the donor-specific immune responses that are typically associated with allo-transplants. In this article, we critically review available experimental data to determine whether good in vivo evidence exists in support of the 'immune privileged' status of allo-MSCs. We also examine published studies regarding the immunogenicity of allo-MSCs following activation ('licensing') by inflammatory stimuli or following differentiation. Among the identified studies which have addressed in vivo immunogenicity of allo-MSCs, there was substantial variability as regards experimental species, disease model, route of MSC administration, cell dose and stringency of the immunological assays employed. Nonetheless, the majority of these studies has documented specific cellular (T-cell) and humoral (B-cell/antibody) immune responses against donor antigens following administration of non-manipulated, interferon-γ-activated and differentiated allo-MSCs. The consequences of such anti-donor immune responses were also variable and ranged from reduced in vivo survival of allo-MSCs with accelerated rejection of subsequent allogeneic transplants to apparent promotion of donor-specific tolerance. On the basis of these findings and on existing knowledge of allo-antigen recognition from the field of transplant immunology, we propose that the concept of the immune privileged nature of allo-MSCs should be reconsidered and that the range and clinical implications of anti-donor immune responses elicited by allo-MSCs be more precisely studied in human and animal recipients.

Structured bilaminar coculture outperforms stem cells and disc cells in a simulated degenerate disc environment

STUDY DESIGN

This study explores the use of bilaminar coculture pellets of mesenchymal stem cells (MSCs) and nucleus pulposus cells (NPCs) as a cell-based therapy for intervertebral disc regeneration. The pellets were tested under conditions that mimic the degenerative disc.

OBJECTIVE

Our goal was to optimize our cell-based therapy in vitro under conditions representative of the eventual diseased tissue.

SUMMARY OF BACKGROUND DATA

Harnessing the potential of stem cells is an important strategy for regenerative medicine. Our approach directed the behavior of stem cells by mimicking embryonic processes underlying cartilage and intervertebral disc development. Prior experiments have shown that bilaminar coculture can help differentiate MSC and substantially improve new matrix deposition.

METHODS

We have designed a novel spherical bilaminar cell pellet (BCP) where MSCs are enclosed in a shell of NPC. There were 3 groups: MSC, NPC, and BCP. The pellets were tested under 3 different culture conditions: 1) in a bioreactor that provides pressure and hypoxia (mimicking normal disc conditions): 2) with inflammatory cytokines (IL-1b and TNF-a); and 3) a bioreactor with inflammation (mimicking painful disc conditions).

RESULTS

When cultured in the bioreactor, the NPC pellets produced significantly more glycosaminoglycans (GAGs) per cell than the other groups: 70% to 80% more than the BCP and the MSC alone. When cultured in an inflammatory environment, the MSC and BCP groups produced 30% to 34% more GAGs per cell than NPC (P < 0.05). When the pellets were cultured in a bioreactor with inflammation, the BCP made 25% more GAGs per cell than the MSC and 57% more than the NPC (P < 0.05).

CONCLUSION

This study shows that BCPs outperform controls in a simulated degenerated disc environment. Adapting inductive mechanisms from development to trigger differentiation and restore diseased tissue has many advantages. As opposed to strategies that require growth factor supplements or genetic manipulations, our method is self-sustaining, targeted, and minimally invasive injection.

Enhanced functional properties of corneal epithelial cells by coculture with embryonic stem cells via the integrin β1-FAK-PI3K/Akt pathway

Adult stem cells are important cell sources in regenerative medicine, but isolating them is technically challenging. This study employed a novel strategy to generate stem-like corneal epithelial cells and promote the functional properties of these cells by coculture with embryonic stem cells. The primary corneal epithelial cells were labelled with GFP and cocultured with embryonic stem cells in a transwell or by direct cell-cell contact. The embryonic stem cells were pre-transfected with HSV-tk-puro plasmids and became sensitive to ganciclovir. After 10 days of coculture, the corneal epithelial cells were isolated by treating the cultures with ganciclovir to kill the embryonic stem cells. The expression of stem cell-associated markers (ABCG2, p63) increased whereas the differentiation mark (Keratin 3) decreased in corneal epithelial cells isolated from the cocultures as evaluated by RT-PCR and flow cytometry. Their functional properties of corneal epithelial cells, including cell adhesion, migration and proliferation, were also enhanced. These cells could regenerate a functional stratified corneal epithelial equivalent but did not form tumors. Integrin β1, phosphorylated focal adhesion kinase and Akt were significantly upregulated in corneal epithelial cells. FAK Inhibitor 14 that suppressed the expression of phosphorylated focal adhesion kinase and Akt inhibited cell adhesion, migration and proliferation. LY294002 that suppressed phosphorylated Akt but not phosphorylated focal adhesion kinase inhibited cell proliferation but had no effect on cell adhesion or migration. These findings demonstrated that the functional properties of stem-like corneal epithelial cells were enhanced by cocultured embryonic stem cells via activation of the integrin β1-FAK-PI3K/Akt signalling pathway.

Interleukin (IL)-10 induced by CD11b(+) cells and IL-10-activated regulatory T cells play a role in immune modulation of mesenchymal stem cells in rat islet allografts

Mesenchymal stem cells (MSCs) are suggested to be immune modulators because of their therapeutic potential in transplantation. In the present study, we evaluated the therapeutic potential of autologous MSCs for preventing graft rejection after allogeneic rat islet transplantation. We assessed the ability of MSCs to elicit an antiproliferative response in alloreactive lymphocytes and tested the immunosuppressive effect of MSCs in allogeneic islet transplantation. In islet allotransplantation, injection of autologous MSCs or a subtherapeutic dose of cyclosporine A (CsA; 5 mg/kg) alone did not prolong allograft survival. However, graft survival was attained for >100 d in 33% of autologous MSC-plus-CsA-treated recipients, indicating that graft acceptance was achieved in a subgroup of allograft recipients. Splenocytes from autologous MSC-plus-CsA-treated rats exhibited a reduced mixed lymphocyte reaction (MLR)-proliferative response to donor stimulators and increased interleukin (IL)-10 release. Interestingly, after excluding host CD11b(+) cells, splenic T cells from autologous MSC-plus-CsA-treated rats did not produce IL-10 or did not inhibit proliferative responses under the same conditions. The use of autologous MSC-plus-CsA downregulated immune responses, inducing donor-specific T-cell hyporesponsiveness by reducing the production of proinflammatory cytokines and inducing antiinflammatory cytokine production, especially that of IL-10, during the early posttransplantation period. T-regulatory cells made a contribution at a later phase. In conclusion, the combined use of autologous MSCs and low-dose CsA exerted a synergistic immunosuppressive effect in an islet allograft model, suggesting a role for autologous MSCs as an immune modulator.

Exploitation of herpesvirus immune evasion strategies to modify the immunogenicity of human mesenchymal stem cell transplants

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent cells residing in the connective tissue of many organs and holding great potential for tissue repair. In culture, human MSCs (hMSCs) are capable of extensive proliferation without showing chromosomal aberrations. Large numbers of hMSCs can thus be acquired from small samples of easily obtainable tissues like fat and bone marrow. MSCs can contribute to regeneration indirectly by secretion of cytokines or directly by differentiation into specialized cell types. The latter mechanism requires their long-term acceptance by the recipient. Although MSCs do not elicit immune responses in vitro, animal studies have revealed that allogeneic and xenogeneic MSCs are rejected.

METHODOLOGY/PRINCIPAL FINDINGS

We aim to overcome MSC immune rejection through permanent down-regulation of major histocompatibility complex (MHC) class I proteins on the surface of these MHC class II-negative cells through the use of viral immune evasion proteins. Transduction of hMSCs with a retroviral vector encoding the human cytomegalovirus US11 protein resulted in strong inhibition of MHC class I surface expression. When transplanted into immunocompetent mice, persistence of the US11-expressing and HLA-ABC-negative hMSCs at levels resembling those found in immunodeficient (i.e., NOD/SCID) mice could be attained provided that recipients' natural killer (NK) cells were depleted prior to cell transplantation.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate the potential utility of herpesviral immunoevasins to prevent rejection of xenogeneic MSCs. The observation that down-regulation of MHC class I surface expression renders hMSCs vulnerable to NK cell recognition and cytolysis implies that multiple viral immune evasion proteins are likely required to make hMSCs non-immunogenic and thereby universally transplantable.

Stem cell research in cell transplantation: sources, geopolitical influence, and transplantation

If the rapidly progressing field of stem cell research reaches its full potential, successful treatments and enhanced understanding of many diseases are the likely results. However, the full potential of stem cell science will only be reached if all possible avenues can be explored and on a worldwide scale. Until 2009, the US had a highly restrictive policy on obtaining cells from human embryos and fetal tissue, a policy that pushed research toward the use of adult-derived cells. Currently, US policy is still in flux, and retrospective analysis does show the US lagging behind the rest of the world in the proportional increase in embryonic/fetal stem cell research. The majority of US studies being on either a limited number of cell lines, or on cells derived elsewhere (or funded by other sources than Federal) rather than on freshly isolated embryonic or fetal material. Neural, mesenchymal, and the mixed stem cell mononuclear fraction are the most commonly investigated types, which can generally be classified as adult-derived stem cells, although roughly half of the neural stem cells are fetal derived. Other types, such as embryonic and fat-derived stem cells, are increasing in their prominence, suggesting that new types of stem cells are still being pursued. Sixty percent of the reported stem cell studies involved transplantation, of which over three quarters were allogeneic transplants. A high proportion of the cardiovascular systems articles were on allogeneic transplants in a number of different species, including several autologous studies. A number of pharmaceutical grade stem cell products have also recently been tested and reported on. Stem cell research shows considerable promise for the treatment of a number of disorders, some of which have entered clinical trials; over the next few years it will be interesting to see how these treatments progress in the clinic.

Enhancement of long-term proliferative capacity of rabbit corneal epithelial cells by embryonic stem cell conditioned medium

Induction of autologous stem cells for directed differentiation has become a predominant method to obtain autologous cells for tissue reconstruction. However, the low inducing efficiency and contamination with other type of cells hinder its clinical utilization. Here we report a novel phenomenon that the corneal epithelial cells maintain long-term proliferative capacity and tissue-specific cell phenotype by factors secreted from murine embryonic stem cells (ESCs). The rabbit corneal epithelial cells grew very well in culture medium with addition of 40% ESC conditioned medium (ESC-CM). These corneal epithelial cells have been serially subcultured for more than 20 passages and maintained high cell purity, cobble-stone-like morphology, enhanced colony forming efficiency, normal diploid, and capacity to regenerate a functional stratified corneal epithelial equivalent. More importantly, these cells did not form tumor, and the cells lost their proliferative capacity after withdrawal of ESC-CM. The long-term proliferative capacity of corneal epithelial cells is partly resulted from enhancement of cell survival and colony formation, and mediated by ectopic expression of telomerase. Our findings indicate that this new ESC-CM culture system can generate low-immunogenic autologous cells sufficiently for use in regenerative medicine.

Long-term human pluripotent stem cell self-renewal on synthetic polymer surfaces

Realization of the full potential of human pluripotent stem cells (hPSCs) in regenerative medicine requires the development of well-defined culture conditions for their long-term growth and directed differentiation. Current practices for maintaining hPSCs generally utilize empirically determined combinations of feeder cells and other animal-based products, which are expensive, difficult to isolate, subject to batch-to-batch variations, and unsuitable for cell-based therapies. Using a high-throughput screening approach, we identified several polymers that can support self-renewal of hPSCs. While most of these polymers provide support for only a short period of time, we identified a synthetic polymer poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-alt-MA) that supported the long-term attachment, proliferation and self-renewal of HUES1, HUES9, and iPSCs. The hPSCs cultured on PMVE-alt-MA maintained their characteristic morphology, expressed high levels of markers of pluripotency, and retained a normal karyotype. Such cost-effective, polymer-based matrices that support long-term self-renewal and proliferation of hPSCs will not only help to accelerate the translational perspectives of hPSCs, but also provide a platform to elucidate the underlying molecular mechanisms that regulate stem cell proliferation and differentiation.