Bone regeneration: stem cell therapies and clinical studies in orthopaedics and traumatology

Core decompression is superior to nonoperative management for humeral head osteonecrosis: a systematic review

BACKGROUND

Much of the literature on osteonecrosis has traditionally focused on the hip, which remains the most common site for this disease. The shoulder and the knee are the second most frequently affected sites (both approximately 10% of the incidence). There are a variety of techniques for managing this disease, and it is important to optimize this for our patients. This review aimed to compare the results of core decompression (CD) vs. nonoperative modalities for the treatment of osteonecrosis of the humeral head, including (1) success rate defined as lack of progression to further procedures (shoulder arthroplasty) and no need for further intervention; (2) clinical results (patient-reported pain and functional scores); and (3) radiological outcomes.

METHODS

We queried PubMed and found 15 reports that fit the inclusion criteria for studies concerning the use of CD as well as studies discussing nonoperative treatment for stage I-III osteonecrotic lesions of the shoulder. A total of 9 studies encompassed 291 shoulders that underwent CD analyzed at a mean follow-up of 8.1 years (range, 67 months-12 years), and 6 studies examined 359 shoulders that underwent nonoperative management at a mean follow-up of 8.1 years (range, 35 months-10 years). Outcomes of CD and nonoperative management included success rate, number of shoulders requiring shoulder arthroplasty, and evaluation of several normalized patient-reported outcomes. We also assessed radiographic progression (pre- to postcollapse or further collapse progression).

RESULTS

The mean success rate of CD for avoiding further procedures was 76.6% (226 of 291 shoulders) in stage I through stage III. Stage III shoulders avoided shoulder arthroplasty in 63% (27 of 43 shoulders). Nonoperative management resulted in a success rate of 13%, P < .001. In the CD studies, 7 of 9 showed improvements in clinical outcome measurements compared with 1 of 6 of the nonoperative studies. Radiographically, there was less progression in the CD group (39 of 191 shoulders [24.2%]) vs. the nonoperative group (39 of 74 shoulders [52.3%]) (P < .001).

CONCLUSIONS

Given the high success rate and positive clinical outcomes reported, CD is an effective method for management, especially when compared with nonoperative treatment methods for stage I-III osteonecrosis of the humeral head. The authors believe that it should be used as treatment to avoid arthroplasty in patients who have osteonecrosis of the humeral head.

The Ethical Implications of Tissue Engineering for Regenerative Purposes: A Systematic Review

Tissue Engineering (TE) is a branch of Regenerative Medicine (RM) that combines stem cells and biomaterial scaffolds to create living tissue constructs to restore patients' organs after injury or disease. Over the last decade, emerging technologies such as 3D bioprinting, biofabrication, supramolecular materials, induced pluripotent stem cells, and organoids have entered the field. While this rapidly evolving field is expected to have great therapeutic potential, its development from bench to bedside presents several ethical and societal challenges. To make sure TE will reach its ultimate goal of improving patient welfare, these challenges should be mapped out and evaluated. Therefore, we performed a systematic review of the ethical implications of the development and application of TE for regenerative purposes, as mentioned in the academic literature. A search query in PubMed, Embase, Scopus, and PhilPapers yielded 2451 unique articles. After systematic screening, 237 relevant ethical and biomedical articles published between 2008 and 2021 were included in our review. We identified a broad range of ethical implications that could be categorized under 10 themes. Seven themes trace the development from bench to bedside: (1) animal experimentation, (2) handling human tissue, (3) informed consent, (4) therapeutic potential, (5) risk and safety, (6) clinical translation, and (7) societal impact. Three themes represent ethical safeguards relevant to all developmental phases: (8) scientific integrity, (9) regulation, and (10) patient and public involvement. This review reveals that since 2008 a significant body of literature has emerged on how to design clinical trials for TE in a responsible manner. However, several topics remain in need of more attention. These include the acceptability of alternative translational pathways outside clinical trials, soft impacts on society and questions of ownership over engineered tissues. Overall, this overview of the ethical and societal implications of the field will help promote responsible development of new interventions in TE and RM. It can also serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. Impact statement To our knowledge, this is the first time that the ethical implications of Tissue Engineering (TE) have been reviewed systematically. By gathering existing scholarly work and identifying knowledge gaps, this review facilitates further research into the ethical and societal implications of TE and Regenerative Medicine (RM) and other emerging biomedical technologies. Moreover, it will serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. As such, our review may promote successful and responsible development of new strategies in TE and RM.

Optimal concentration of mesenchymal stem cells for fracture healing in a rat model with long bone fracture

BACKGROUND

There is still no consensus on which concentration of mesenchymal stem cells (MSCs) to use for promoting fracture healing in a rat model of long bone fracture.

AIM

To assess the optimal concentration of MSCs for promoting fracture healing in a rat model.

METHODS

Wistar rats were divided into four groups according to MSC concentrations: Normal saline (C), 2.5 × 10⁶ (L), 5.0 × 10⁶ (M), and 10.0 × 10⁶ (H) groups. The MSCs were injected directly into the fracture site. The rats were sacrificed at 2 and 6 wk post-fracture. New bone formation [bone volume (BV) and percentage BV (PBV)] was evaluated using micro-computed tomography (CT). Histological analysis was performed to evaluate fracture healing score. The protein expression of factors related to MSC migration [stromal cell-derived factor 1 (SDF-1), transforming growth factor-beta 1 (TGF-β1)] and angiogenesis [vascular endothelial growth factor (VEGF)] was evaluated using western blot analysis. The expression of cytokines associated with osteogenesis [bone morphogenetic protein-2 (BMP-2), TGF-β1 and VEGF] was evaluated using real-time polymerase chain reaction.

RESULTS

Micro-CT showed that BV and PBV was significantly increased in groups M and H compared to that in group C at 6 wk post-fracture (P = 0.040, P = 0.009; P = 0.004, P = 0.001, respectively). Significantly more cartilaginous tissue and immature bone were formed in groups M and H than in group C at 2 and 6 wk post-fracture (P = 0.018, P = 0.010; P = 0.032, P = 0.050, respectively). At 2 wk post-fracture, SDF-1, TGF-β1 and VEGF expression were significantly higher in groups M and H than in group L (P = 0.031, P = 0.014; P < 0.001, P < 0.001; P = 0.025, P < 0.001, respectively). BMP-2 and VEGF expression were significantly higher in groups M and H than in group C at 6 wk post-fracture (P = 0.037, P = 0.038; P = 0.021, P = 0.010). Compared to group L, TGF-β1 expression was significantly higher in groups H (P = 0.016). There were no significant differences in expression levels of chemokines related to MSC migration, angiogenesis and cytokines associated with osteogenesis between M and H groups at 2 and 6 wk post-fracture.

CONCLUSION

The administration of at least 5.0 × 10⁶ MSCs was optimal to promote fracture healing in a rat model of long bone fractures.

Volume and location of bone regeneration after autologous expanded mesenchymal stromal cells in hip osteonecrosis : a pilot study

AIMS

Successful cell therapy in hip osteonecrosis (ON) may help to avoid ON progression or total hip arthroplasty (THA), but the achieved bone regeneration is unclear. The aim of this study was to evaluate amount and location of bone regeneration obtained after surgical injection of expanded autologous mesenchymal stromal cells from the bone marrow (BM-hMSCs).

METHODS

A total of 20 patients with small and medium-size symptomatic stage II femoral head ON treated with 140 million BM-hMSCs through percutaneous forage in the EudraCT 2012-002010-39 clinical trial were retrospectively evaluated through preoperative and postoperative (three and 12 months) MRI. Then, 3D reconstruction of the original lesion and the observed postoperative residual damage after bone regeneration were analyzed and compared per group based on treatment efficacy.

RESULTS

The mean preoperative lesion volume was 18.7% (SD 10.2%) of the femoral head. This reduced to 11.6% (SD 7.5%) after three months (p = 0.015) and 3.7% (SD 3%) after one year (p < 0.001). Bone regeneration in healed cases represented a mean 81.2% (SD 13.8%) of the initial lesion volume at one year. Non-healed cases (n = 1 stage progression; n = 3 THAs) still showed bone regeneration but this did not effectively decrease the ON volume. A lesion size under mean 10% (SD 6%) of the femoral head at three months predicted no ON stage progression at one year. Regeneration in the lateral femoral head (C2 under Japanese Investigation Committee (JCI) classification) and in the central and posterior regions of the head was predominant in cases without ON progression.

CONCLUSION

Bone regeneration was observed in osteonecrotic femoral heads three months after expanded autologous BM-hMSC injection, and the volume and location of regeneration indicated the success of the therapy.Cite this article: Bone Joint Res 2022;11(12):881-889.

Genetically engineered mesenchymal stromal cells as a new trend for treatment of severe acute graft-versus-host disease

Mesenchymal stem cells (MSCs) are a population of non-hematopoietic and self-renewing cells characterized by the potential to differentiate into different cell subtypes. MSCs have interesting features which have attracted a lot of attention in various clinical investigations. Some basic features of MSCs are including the weak immunogenicity (absence of MHC-II and costimulatory ligands accompanied by the low expression of MHC-I) and the potential of plasticity and multi-organ homing via expressing related surface molecules. MSCs by immunomodulatory effects could also ameliorate several immune-pathological conditions like graft-versus-host diseases (GVHD). The efficacy and potency of MSCs are the main objections of MSCs therapeutic applications. It suggested that improving the MSC immunosuppressive characteristic via genetic engineering to produce therapeutic molecules consider as one of the best options for this purpose. In this review, we explain the functions, immunologic properties, and clinical applications of MSCs to discuss the beneficial application of genetically modified MSCs in GVHD.

Efficacy of treating segmental bone defects through endochondral ossification: 3D printed designs and bone metabolic activities

Three-dimensional printing (3D printing) is a promising technique for producing scaffolds for bone tissue engineering applications. Porous scaffolds can be printed directly, and the design, shape and porosity can be controlled. 3D synthetic biodegradable polymeric scaffolds intended for in situ bone regeneration must meet stringent criteria, primarily appropriate mechanical properties, good 3D design, adequate biocompatibility and the ability to enhance bone formation. In this study, healing of critical-sized (5 ​mm) femur defects of rats was enhanced by implanting two different designs of 3D printed poly(l-lactide-co-ε-caprolactone) (poly(LA-co-CL)) scaffolds seeded with rat bone marrow mesenchymal stem cells (rBMSC), which had been pre-differentiated in vitro into cartilage-forming chondrocytes. Depending on the design, the scaffolds had an interconnected porous structure of 300-500 ​μm and porosity of 50-65%. According to a computational simulation, the internal force distribution was consistent with scaffold designs and comparable between the two designs. Moreover, the defects treated with 3D-printed scaffolds seeded with chondrocyte-like cells exhibited significantly increased bone formation up to 15 weeks compared with empty defects. In all experimental animals, bone metabolic activity was monitored by positron emission tomography 1, 3, 5, 7, 11 and 14 weeks after surgery. This demonstrated a time-dependent relationship between scaffold design and metabolic activity. This confirmed that successful regeneration was highly reproducible. The in vitro and in vivo data indicated that the experimental setups had promising outcomes and could facilitate new bone formation through endochondral ossification.

Protein Expression of AEBP1, MCM4, and FABP4 Differentiate Osteogenic, Adipogenic, and Mesenchymal Stromal Stem Cells

Mesenchymal stem cells (MSCs) gain an increasing focus in the field of regenerative medicine due to their differentiation abilities into chondrocytes, adipocytes, and osteoblastic cells. However, it is apparent that the transformation processes are extremely complex and cause cellular heterogeneity. The study aimed to characterize differences between MSCs and cells after adipogenic (AD) or osteoblastic (OB) differentiation at the proteome level. Comparative proteomic profiling was performed using tandem mass spectrometry in data-independent acquisition mode. Proteins were quantified by deep neural networks in library-free mode and correlated to the Molecular Signature Database (MSigDB) hallmark gene set collections for functional annotation. We analyzed 4108 proteins across all samples, which revealed a distinct clustering between MSCs and cell differentiation states. Protein expression profiling identified activation of the Peroxisome proliferator-activated receptors (PPARs) signaling pathway after AD. In addition, two distinct protein marker panels could be defined for osteoblastic and adipocytic cell lineages. Hereby, overexpression of AEBP1 and MCM4 for OB as well as of FABP4 for AD was detected as the most promising molecular markers. Combination of deep neural network and machine-learning algorithms with data-independent mass spectrometry distinguish MSCs and cell lineages after adipogenic or osteoblastic differentiation. We identified specific proteins as the molecular basis for bone formation, which could be used for regenerative medicine in the future.

Stem cell therapy applied for digestive anastomosis: Current state and future perspectives

BACKGROUND

Digestive tract resections are usually followed by an anastomosis. Anastomotic leakage, normally due to failed healing, is the most feared complication in digestive surgery because it is associated with high morbidity and mortality. Despite technical and technological advances and focused research, its rates have remained almost unchanged the last decades. In the last two decades, stem cells (SCs) have been shown to enhance healing in animal and human studies; hence, SCs have emerged since 2008 as an alternative to improve anastomoses outcomes.

AIM

To summarise the published knowledge of SC utilisation as a preventative tool for hollow digestive viscera anastomotic or suture leaks.

METHODS

PubMed, Science Direct, Scopus and Cochrane searches were performed using the key words “anastomosis”, “colorectal/colonic anastomoses”, “anastomotic leak”, “stem cells”, “progenitor cells”, “cellular therapy” and “cell therapy” in order to identify relevant articles published in English and Spanish during the years of 2000 to 2021. Studies employing SCs, performing digestive anastomoses in hollow viscera or digestive perforation sutures and monitoring healing were finally included. Reference lists from the selected articles were reviewed to identify additional pertinent articles.

Given the great variability in the study designs, anastomotic models, interventions (SCs, doses and vehicles) and outcome measures, performing a reliable meta-analysis was considered impossible, so we present the studies, their results and limitations.

RESULTS

Eighteen preclinical studies and three review papers were identified; no clinical studies have been published and there are no registered clinical trials. Experimental studies, mainly in rat and porcine models and occasionally in very adverse conditions such as ischaemia or colitis, have been demonstrated SCs as safe and have shown some encouraging morphological, functional and even clinical results. Mesenchymal SCs are mostly employed, and delivery routes are mainly local injections and cell sheets followed by biosutures (sutures coated by SCs) or purely topical. As potential weaknesses, animal models need to be improved to make them more comparable and equivalent to clinical practice, and the SC isolation processes need to be standardised. There is notable heterogeneity in the studies, making them difficult to compare. Further investigations are needed to establish the indications, the administration system, potential adjuvants, the final efficacy and to confirm safety and exclude definitively oncological concerns.

CONCLUSION

The future role of SC therapy to induce healing processes in digestive anastomoses/sutures still needs to be determined and seems to be currently far from clinical use.

Enhanced BMP-2-Mediated Bone Repair Using an Anisotropic Silk Fibroin Scaffold Coated with Bone-like Apatite

The repair of large bone defects remains challenging and often requires graft material due to limited availability of autologous bone. In clinical settings, collagen sponges loaded with excessive amounts of bone morphogenetic protein 2 (rhBMP-2) are occasionally used for the treatment of bone non-unions, increasing the risk of adverse events. Therefore, strategies to reduce rhBMP-2 dosage are desirable. Silk scaffolds show great promise due to their favorable biocompatibility and their utility for various biofabrication methods. For this study, we generated silk scaffolds with axially aligned pores, which were subsequently treated with 10× simulated body fluid (SBF) to generate an apatitic calcium phosphate coating. Using a rat femoral critical sized defect model (CSD) we evaluated if the resulting scaffold allows the reduction of BMP-2 dosage to promote efficient bone repair by providing appropriate guidance cues. Highly porous, anisotropic silk scaffolds were produced, demonstrating good cytocompatibility in vitro and treatment with 10× SBF resulted in efficient surface coating. In vivo, the coated silk scaffolds loaded with a low dose of rhBMP-2 demonstrated significantly improved bone regeneration when compared to the unmineralized scaffold. Overall, our findings show that this simple and cost-efficient technique yields scaffolds that enhance rhBMP-2 mediated bone healing.

Identification of a clinical signature predictive of differentiation fate of human bone marrow stromal cells

BACKGROUND

Transplantation of human bone marrow stromal cells (hBMSCs) is a promising therapy for bone regeneration due to their ability to differentiate into bone forming osteoblastic cells. However, transplanted hBMSCs exhibit variable capacity for bone formation resulting in inconsistent clinical outcome. The aim of the study was to identify a set of donor- and cell-related characteristics that detect hBMSCs with optimal osteoblastic differentiation capacity.

METHODS

We collected hBMSCs from 58 patients undergoing surgery for bone fracture. Clinical profile of the donors and in vitro characteristics of cultured hBMSCs were included in uni- and multivariable analysis to determine their predictive value for osteoblastic versus adipocytic differentiation capacity assessed by quantification of mineralized matrix and mature adipocyte formation, respectively.

RESULTS

We identified a signature that explained > 50% of variation in osteoblastic differentiation outcome which included the following positive predictors: donor sex (male), absence of osteoporosis diagnosis, intake of vitamin D supplements, higher fraction of CD146+, and alkaline phosphate (ALP+) cells. With the exception of vitamin D and ALP+ cells, these variables were also negative predictors of adipocytic differentiation.

CONCLUSIONS

Using a combination of clinical and cellular criteria, it is possible to predict differentiation outcome of hBMSCs. This signature may be helpful in selecting donor cells in clinical trials of bone regeneration.

Implantation of autologous Expanded Mesenchymal Stromal Cells in Hip Osteonecrosis through Percutaneous Forage: Evaluation of the Operative Technique

Bone forage to treat early osteonecrosis of the femoral head (ONFH) has evolved as the channel to percutaneously deliver cell therapy into the femoral head. However, its efficacy is variable and the drivers towards higher efficacy are currently unknown. The aim of this study was to evaluate the forage technique and correlate it with the efficacy to heal ONFH in a multicentric, multinational clinical trial to implant autologous mesenchymal stromal cells expanded from bone marrow (BM-hMSCs). Methods: In the context of EudraCT 2012-002010-39, patients with small and medium-sized (mean volume = 13.3%, range: 5.4 to 32.2) ONFH stage II (Ficat, ARCO, Steinberg) C1 and C2 (Japanese Investigation Committee (JIC)) were treated with percutaneous forage and implantation of 140 million BM-hMSCs in a standardized manner. Postoperative hip radiographs (AP—anteroposterior and lateral), and MRI sections (coronal and transverse) were retrospectively evaluated in 22 patients to assess the femoral head drilling orientation in both planes, and its relation to the necrotic area. Results: Treatment efficacy was similar in C1 and C2 (coronal plane) and in anterior to posterior (transverse plane) osteonecrotic lesions. The drill crossed the sclerotic rim in all cases. The forage was placed slightly valgus, at 139.3 ± 8.4 grades (range, 125.5–159.3) with higher dispersion (f = 2.6; p = 0.034) than the anatomical cervicodiaphyseal angle. Bonferroni’s correlation between both angles was 0.50 (p = 0.028). More failures were seen with a varus drill positioning, aiming at the central area of the femoral head, outside the weight-bearing area (WBA) (p = 0.049). In the transverse plane, the anterior positioning of the drill did not result in better outcomes (p = 0.477). Conclusion: The forage drilling to deliver cells should be positioned within the WBA in the coronal plane, avoiding varus positioning, and central to anterior in the transverse plane. The efficacy of delivered MSCs to regenerate bone in ONFH could be influenced by the drilling direction. Standardization of this surgical technique is desirable.

Enhancing the Surface Properties of a Bioengineered Anterior Cruciate Ligament Matrix for Use with Point-of-Care Stem Cell Therapy

We have previously developed a poly(L-lactic) acid (PLLA) bioengineered anterior cruciate ligament (ACL) matrix that has demonstrated enhanced healing when seeded with primary ACL cells prior to implantation in a rabbit model, as compared with the matrix alone. This suggests that improving cell adhesion on the matrix may beneficially affect the healing response and long-term performance of the bioengineered ACL matrix. One regenerative engineering approach involves enhancing the surface properties of the matrix to support cell adhesion and growth in combination with point-of-care stem cell therapy. Herein, we studied the cell adhesion properties of PLLA braided microfiber matrices enhanced through the physical adsorption of fibronectin and air plasma treatment. We evaluated the kinetics and binding efficiency of fibronectin onto matrices at three time points and three fibronectin concentrations. Incubating the matrix for 120 min in a solution of 25 mg mL^-1 fibronectin achieved the greatest binding efficiency to the matrix and cellular adhesion. Exposing the matrices to air plasma treatment for 5 min before fibronectin adsorption significantly enhanced the cell adhesion of rabbit bone marrow-derived mesenchymal stem cells (R-BMMSCs) 24 h post cell seeding. Finally, cellular proliferation was monitored for up to 21 d, the matrices were exposed to air plasma treatment, and fibronectin adsorption was found to result in enhanced cell number. These findings suggest that exposure to air plasma treatment and fibronectin adsorption enhances the cellular adhesion of PLLA braided microfiber matrices and may improve the clinical efficacy of the matrix in combination with point-of-care stem cell therapies.

Mitochondria transfer enhances proliferation, migration, and osteogenic differentiation of bone marrow mesenchymal stem cell and promotes bone defect healing

Background

Bone marrow-derived mesenchymal stem cell (BMSC) transplantation is considered a promising therapeutic approach for bone defect repair. However, during the transplantation procedure, the functions and viability of BMSCs may be impaired due to extended durations of in vitro culture, aging, and disease conditions of patients. Inspired by spontaneous intercellular mitochondria transfer that naturally occurs within injured tissues to rescue cellular or tissue function, we investigated whether artificial mitochondria transfer into pre-transplant BMSCs in vitro could improve cellular function and enhance their therapeutic effects on bone defect repair in situ.

Methods

Mitochondria were isolated from donor BMSCs and transferred into recipient BMSCs of the same batch and passage. Subsequently, changes in proliferative capacity and cell senescence were evaluated by live cell imaging, Cell Counting Kit-8 assay, cell cycle analysis, Ki67 staining, qPCR and Western blot analysis of c-Myc expression, and β-galactosidase staining. Migration ability was evaluated by the transwell migration assay, wound scratch healing, and cell motility tests. Alkaline phosphatase (ALP) staining, Alizarin Red staining, and combined with qPCR and Western blot analyses of Runx2 and BMP2 were performed to elucidate the effects of mitochondria transfer on the osteogenic potential of BMSCs in vitro. After that, in vivo experiments were performed by transplanting mitochondria-recipient BMSCs into a rat cranial critical-size bone defect model. Micro CT scanning and histological analysis were conducted at 4 and 8 weeks after transplantation to evaluate osteogenesis in situ. Finally, in order to establish the correlation between cellular behavioral changes and aerobic metabolism, OXPHOS (oxidative phosphorylation) and ATP production were assessed and inhibition of aerobic respiration by oligomycin was performed.

Results

Mitochondria-recipient BMSCs exhibited significantly enhanced proliferation and migration, and increased osteogenesis upon osteogenic induction. The in vivo results showed more new bone formation after transplantation of mitochondria-recipient BMSCs in situ. Increased OXPHOS activity and ATP production were observed, which upon inhibition by oligomycin attenuated the enhancement of proliferation, migration, and osteogenic differentiation induced by mitochondria transfer.

Conclusions

Mitochondria transfer is a feasible technique to enhance BMSC function in vitro and promote bone defect repair in situ through the upregulation of aerobic metabolism. The results indicated that mitochondria transfer may be a novel promising technique for optimizing stem cell therapeutic function.

Longtime Outcome After Intraosseous Application of Autologous Mesenchymal Stromal Cells in Pediatric Patients and Young Adults with Avascular Necrosis After Steroid or Chemotherapy

Avascular necrosis (AVN) is a severe complication of immunosuppressant therapy or chemotherapy. A beneficial AVN therapy with core decompression (CD) and intraosseous infusion of mesenchymal stromal cells (MSCs) has been described in adult patients, but there are only few data on MSC applications in pediatric and young adult patients (PYAP). Between 2006 and 2015, 14 AVN lesions of 10 PYAP (6 females) with a median age of 16.9 years (range 8.5-25.8 years) received CD and intraosseous application of autologous MSCs. Data of these patients were analyzed regarding efficacy, safety, and feasibility of this procedure as AVN therapy and compared with a control group of 13 AVN lesions of 11 PYAP (5 females) with a median age of 17.9 years (range 13.5-27.5 years) who received CD only. During the follow-up analysis [MSC group: median 3.1 (1.6-5.8) years after CD; CD group: median 2.0 (1.5-8.5) years after CD], relative lesion sizes (as assessed by magnetic resonance imaging) compared with the initial lesion volume, were significantly lower (P < 0.05) in the MSC group (volume reduction to a median of 18.5%) when compared with the CD group (58.0%). One lesion in the MSC group comprised a complete remission. Size progression was not observed in either group. Clinical improvement (pain, mobility) was not significantly different between the two groups. None of the patients experienced treatment-related adverse effects. CD and additional MSC application was regarded safe, effective, feasible, and superior in reducing the lesion size when compared with CD only. Prospective, randomized clinical trials are needed to further evaluate these findings.

Early efficacy evaluation of mesenchymal stromal cells (MSC) combined to biomaterials to treat long bone non-unions

BACKGROUND AND STUDY AIM

Advanced therapy medicinal products (ATMP) frequently lack of clinical data on efficacy to substantiate a future clinical use. This study aims to evaluate the efficacy to heal long bone delayed unions and non-unions, as secondary objective of the EudraCT 2011-005441-13 clinical trial, through clinical and radiological bone consolidation at 3, 6 and 12 months of follow-up, with subgroup analysis of affected bone, gender, tobacco use, and time since the original fracture.

PATIENTS AND METHODS

Twenty-eight patients were recruited and surgically treated with autologous bone marrow derived mesenchymal stromal cells expanded under Good Manufacturing Practices, combined to bioceramics in the surgical room before implantation. Mean age was 39 ± 13 years, 57% were males, and mean Body Mass Index 27 ± 7. Thirteen (46%) were active smokers. There were 11 femoral, 4 humeral, and 13 tibial non-unions. Initial fracture occurred at a mean ± SD of 27.9 ± 31.2 months before recruitment. Efficacy results were expressed by clinical consolidation (no or mild pain if values under 30 in VAS scale), and by radiological consolidation with a REBORNE score over 11/16 points (value of or above 0.6875). Means were statistically compared and mixed models for repeated measurements estimated the mean and confidence intervals (95%) of the REBORNE Bone Healing scale. Clinical and radiological consolidation were analyzed in the subgroups with Spearman correlation tests (adjusted by Bonferroni).

RESULTS

Clinical consolidation was earlier confirmed, while radiological consolidation at 3 months was 25.0% (7/28 cases), at 6 months 67.8% (19/28 cases), and at 12 months, 92.8% (26/28 cases including the drop-out extrapolation of two failures). Bone biopsies confirmed bone formation surrounding the bioceramic granules. All locations showed similar consolidation, although this was delayed in tibial non-unions. No significant gender difference was found in 12-month consolidation (95% confidence). Higher consolidation scale values were seen in non-smoking patients at 6 (p = 0.012, t-test) and 12 months (p = 0.011, t-test). Longer time elapsed after the initial fracture did not preclude the occurrence of consolidation.

CONCLUSION

Bone consolidation was efficaciously obtained with the studied expanded hBM-MSCs combined to biomaterials, by clinical and radiological evaluation, and confirmed by bone biopsies, with lower consolidation scores in smokers.

Reconstruction of Large Skeletal Defects: Current Clinical Therapeutic Strategies and Future Directions Using 3D Printing

The healing of bone fractures is a well-orchestrated physiological process involving multiple cell types and signaling molecules interacting at the fracture site to replace and repair bone tissue without scar formation. However, when the lesion is too large, normal healing is compromised. These so-called non-union bone fractures, mostly arising due to trauma, tumor resection or disease, represent a major therapeutic challenge for orthopedic and reconstructive surgeons. In this review, we firstly present the current commonly employed surgical strategies comprising auto-, allo-, and xenograft transplantations, as well as synthetic biomaterials. Further to this, we discuss the multiple factors influencing the effectiveness of the reconstructive therapy. One essential parameter is adequate vascularization that ensures the vitality of the bone grafts thereby supporting the regeneration process, however deficient vascularization presents a frequently encountered problem in current management strategies. To address this challenge, vascularized bone grafts, including free or pedicled fibula flaps, or in situ approaches using the Masquelet induced membrane, or the patient’s body as a bioreactor, comprise feasible alternatives. Finally, we highlight future directions and novel strategies such as 3D printing and bioprinting which could overcome some of the current challenges in the field of bone defect reconstruction, with the benefit of fabricating personalized and vascularized scaffolds.

Functional expression of ZNF467 and PCBP2 supports adipogenic lineage commitment in adipose-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stromal/stem cells (BMSCs) have the potential to be employed in many different skeletal therapies. A major limitation to utilizing BMSCs as a therapeutic strategy in human disease and tissue regeneration is the low cell numbers obtained from initial isolation necessitating multiple cell passages that can lead to decreased cell quality. Adipose-derived mesenchymal stromal/stem cells (AMSCs) have been proposed as an alternative cell source for regenerative therapies; however the differentiation capacity of these cells differs from BMSCs. To understand the differences between BMSCs and AMSCs, we compared the global gene expression profiles of BMSCs and AMSCs and identified two genes, PCBP2 and ZNF467 that were differentially expressed between AMSCs and BMSCs. We demonstrate that PCBP2 and ZNF467 impact adipogenic but not osteogenic differentiation, further supporting evidence that AMSCs and BMSCs appear to be adapted to their microenvironment.

Impact of humanised isolation and culture conditions on stemness and osteogenic potential of bone marrow derived mesenchymal stromal cells

Therapeutic potential of human bone marrow stromal/stem cells (hBMSC) must be developed using well defined xenogenic-free conditions. hBMSC were isolated from healthy donors (n = 3) using different isolation and expansion methods. Donor I was isolated and expanded by either bone marrow directly seeded and cells expanded in 10% AB human serum (AB) +5 ng/ml fibroblast growth factor-2 (FGF2) [Direct(AB + FGFlow)] or Ammonium-Chloride-Potassium Lysing Buffer was used before the cells were expanded in 10% AB +5 ng/ml FGF-2 [ACK(AB + FGFlow)] or Lymphoprep density gradient medium was used before the cells were expanded in 10% AB +5 ng/ml FGF2 [Lympho(AB + FGFlow)] or bone marrow directly seeded and cells expanded in 10% pooled platelet lysate plasma (PL) + heparin (2 I/U/mL) [Direct(PL)]. Groups for donors II and III were: Direct(AB + FGFlow) or 10% AB +10 ng/ml FGF2 [Direct(AB + FGFhigh)] or Direct(PL). HBMSCs were assessed for viability, multi-potency, osteogenic, inflammatory response and replicative senescence in vitro after 1 and 3 weeks. Pre-selected culture conditions, Direct(AB + FGFhigh) or Direct(PL), were seeded on biphasic calcium phosphate granules and subcutaneously implanted in NOD/SCID mice. After 1 and 11 weeks, explants were analysed for inflammatory and osteogenic response at gene level and histologically. To identify implanted human cells, in situ hybridisation was performed. hBMSC from all conditions showed in vitro multi-lineage potency. hBMSCs expanded in PL expressed stemness markers in vitro at significantly higher levels. Generally, cells expanded in AB + FGF2 conditions expressed higher osteogenic markers after 1 week both in vitro and in vivo. After 11 weeks in vivo, Direct(AB + FGFhigh) formed mature ectopic bone, compared to immature mineralised tissues formed by Direct(PL) implants. Mouse responses showed a significant upregulation of IL-1α and IL-1β expression in Direct(PL). After 1 week, human cells were observed in both groups and after 11 weeks in Direct(AB + FGFhigh) only. To conclude, results showed a significant effect of the isolation methods and demonstrated a relatively consistent pattern of efficacy from all donors. A tendency of hBMSC expanded in PL to retain a more stem-like phenotype elucidates their delayed differentiation and different inflammatory expressions.

Biomarkers of bone healing induced by a regenerative approach based on expanded bone marrow-derived mesenchymal stromal cells

BACKGROUND

Safety and feasibility of a regenerative strategy based on the use of culture-expanded mesenchymal stromal cells (MSCs) have been investigated in phase 2 trials for the treatment of nonunion and osteonecrosis of the femoral head (ONFH). As part of the clinical study, we aimed to evaluate if bone turnover markers (BTMs) could be useful for predicting the regenerative ability of the cell therapy product.

MATERIALS AND METHODS

The bone defects of 39 patients (nonunion: n = 26; ONFH: n = 13) were treated with bone marrow-derived MSCs, expanded using a clinical-grade protocol and combined with biphasic calcium phosphate before implantation. Bone formation markers, bone-resorption markers and osteoclast regulatory proteins were measured before treatment (baseline) and after 12 and 24 weeks from surgery. At the same time-points, clinical and radiological controls were performed to evaluate the bone-healing progression.

RESULTS

We found that C-Propeptide of Type I Procollagen (CICP) and C-terminal telopeptide of type-I collagen (CTX) varied significantly, not only over time, but also according to clinical results. In patients with a good outcome, CICP increased and CTX decreased, and this trend was observed in both nonunion and ONFH. Moreover, collagen biomarkers were able to discriminate healed patients from non-responsive patients with a good diagnostic accuracy.

DISCUSSION

CICP and CTX could be valuable biomarkers for monitoring and predicting the regenerative ability of cell products used to stimulate the repair of refractory bone diseases. To be translated in a clinical setting, these results are under validation in a currently ongoing phase 3 clinical trial.

Exosomes from human umbilical cord mesenchymal stem cells enhance fracture healing through HIF-1α-mediated promotion of angiogenesis in a rat model of stabilized fracture

OBJECTIVES

Exosomes, as important players in intercellular communication due to their ability to transfer certain molecules to target cells, are believed to take similar effects in promoting bone regeneration with their derived stem cells. Studies have suggested that umbilical cord mesenchymal stem cells (uMSCs) could promote angiogenesis. This study investigated whether exosomes derived from uMSCs (uMSC-Exos) could enhance fracture healing as primary factors by promoting angiogenesis.

MATERIALS AND METHODS

uMSCs were obtained to isolate uMSC-Exos by ultrafiltration, with exosomes from human embryonic kidney 293 cells (HEK293) and phosphate-buffered saline (PBS) being used as control groups. NanoSight, laser light scattering spectrometer, transmission electron microscopy and Western blotting were used to identify exosomes. Next, uMSC-Exos combined with hydrogel were transplanted into the fracture site in a rat model of femoral fracture. Bone healing processes were monitored and evaluated by radiographic methods on days 7, 14, 21 and 31 after surgery; angiogenesis of the fracture sites was assessed by radiographic and histological strategies on post-operative day 14. In vitro, the expression levels of osteogenesis- or angiogenesis-related genes after being cultured with uMSC-Exos were identified by qRT-PCR. The internalization ability of exosomes was determined using the PKH67 assay. Cell cycle analysis, EdU incorporation and immunofluorescence staining, scratch wound assay and tube formation analysis were also used to determine the altered abilities of human umbilical vein endothelial cells (HUVECs) administered with uMSC-Exos in proliferation, migration and angiogenesis. Finally, to further explore the underlying molecular mechanisms, specific RNA inhibitors or siRNAs were used, and the subsequent effects were observed.

RESULTS

uMSC-Exos had a diameter of approximately 100 nm, were spherical, meanwhile expressing CD9, CD63 and CD81. Transplantation of uMSC-Exos markedly enhanced angiogenesis and bone healing processes in a rat model of femoral fracture. In vitro, other than enhancing osteogenic differentiation, uMSC-Exos increased the expression of vascular endothelial growth factor (VEGF) and hypoxia inducible factor-1α (HIF-1α). uMSC-Exos were taken up by HUVECs and enhanced their proliferation, migration and tube formation. Finally, by using specific RNA inhibitors or siRNAs, it has been confirmed that HIF-1α played an important role in the uMSC-Exos-induced VEGF expression, pro-angiogenesis and enhanced fracture repair, which may be one of the underlying mechanisms.

CONCLUSIONS

These results revealed a novel role of exosomes in uMSC-mediated therapy and suggested that implanted uMSC-Exos may represent a crucial clinical strategy to accelerate fracture healing via the promotion of angiogenesis. HIF-1α played an important role in this process.

3D human bone marrow stromal and endothelial cell spheres promote bone healing in an osteogenic niche

The current study used an ex vivo [embryonic day (E)18] chick femur defect model to examine the bone regenerative capacity of implanted 3-dimensional (3D) skeletal–endothelial cell constructs. Human bone marrow stromal cell (HBMSC) and HUVEC spheroids were implanted within a bone defect site to determine the osteogenic potential of the skeletal–endothelial cell unit. Cells were pelleted as co- or monocell spheroids and placed within 1-mm-drill defects in the mid-diaphysis of E18 chick femurs and cultured organotypically for 10 d. Micro-computed tomography analysis revealed significantly (P = 0.0001) increased levels of bone volume (BV) and BV/tissue volume ratio in all cell-pellet groups compared with the sham defect group. The highest increase was seen in BV in femurs containing the HUVEC and HBMSC monocell constructs. Type II collagen expression was particularly pronounced within the cell spheres containing HBMSCs and HUVECs, and CD31-positive cell clusters were prominent within HUVEC-implanted defects. These studies demonstrate the importance of the 3D osteogenic-endothelial niche interaction in bone regeneration. Elucidating the component cell interactions in the osteogenic-vascular niche and the role of exogenous factors in driving these osteogenic processes will aid the development of better bone reparative strategies.—Inglis, S., Kanczler, J. M., Oreffo, R. O. C. 3D human bone marrow stromal and endothelial cell spheres promote bone healing in an osteogenic niche.

Improved in situ seeding of 3D printed scaffolds using cell-releasing hydrogels

The design of tissue engineered scaffolds based on polymerized high internal phase emulsions (polyHIPEs) has emerged as a promising bone grafting strategy. We previously reported the ability to 3D print emulsion inks to better mimic the structure and mechanical properties of native bone while precisely matching defect geometry. In the current study, redox-initiated hydrogel carriers were investigated for in situ delivery of human mesenchymal stem cells (hMSCs) utilizing the biodegradable macromer, poly(ethylene glycol)-dithiothreitol. Hydrogel carrier properties including network formation time, sol-gel fraction, and swelling ratio were modulated to achieve rapid cure without external stimuli and a target cell-release period of 5-7 days. These in situ carriers enabled improved distribution of hMSCs in 3D printed polyHIPE grafts over standard suspension seeding. Additionally, carrier-loaded polyHIPEs supported sustained cell viability and osteogenic differentiation of hMSCs post-release. In summary, these findings demonstrate the potential of this in situ curing hydrogel carrier to enhance the cell distribution and retention of hMSCs in bone grafts. Although initially focused on improving bone regeneration, the ability to encapsulate cells in a hydrogel carrier without relying on external stimuli that can be attenuated in large grafts or tissues is expected to have a wide range of applications in tissue engineering.

Enhanced cytocompatibility and osteoinductive properties of sol-gel-derived silica/zirconium dioxide coatings by metformin functionalization

The aim of this study was to evaluate the pro-osteogenic properties of sol-gel-derived silica/zirconium dioxide coatings functionalized with 1 mM of metformin. The matrices were applied on 316L stainless steel using dip-coating technique. First of all, physicochemical properties of biomaterials were evaluated. Surface morphology and topography was determined using energy-dispersive X-ray spectroscopy and atomic force microscopy. The chemical composition was evaluated using Fourier transform infrared spectroscopy. Further, wettability and surface free energy were characterized. Cytocompatibility of biomaterials was tested in vitro using model of human multipotent mesenchymal stromal cells isolated from adipose tissue. The influence of biomaterials on cells morphology and proliferation was determined. Osteogenic effect of obtained biomaterials was evaluated in terms of their influence on secretory activity of human multipotent mesenchymal stromal cells isolated from adipose tissue and matrix mineralization. Analysis was performed in relation to the control cultures i.e. maintained on pure SS316L substrate and SS316L covered with silica/zirconium dioxide. Obtained results indicate that silica/zirconium dioxide_metformin coatings ameliorated metabolic and proliferative activity of human multipotent mesenchymal stromal cells isolated from adipose tissue, as well as promoted their proper growth and adhesion. The human multipotent mesenchymal stromal cells isolated from adipose tissue cultured on biomaterials were characterized by typical fibroblast-like morphology. The addition of metformin to the silica/zirconium dioxide coatings improved functional differentiation of human multipotent mesenchymal stromal cells isolated from adipose tissue. Osteogenic cultures on silica/zirconium dioxide_metformin were characterized by formation of well-developed osteonodules rich in calcium and phosphorous. Moreover, human multipotent mesenchymal stromal cells isolated from adipose tissue cultured on silica/zirconium dioxide_metformin synthesized increased amount of alkaline phosphatase, bone morphogenetic protein 2 and osteopontin, both on messenger RNA and protein level. Obtained biomaterials modulate cellular plasticity of human multipotent mesenchymal stromal cells isolated from adipose tissue promoting their osteogenic differentiation, thus may find application in broadly defined tissue engineering.

Osteogenic Differentiation Modulates the Cytokine, Chemokine, and Growth Factor Profile of ASCs and SHED

Great efforts have been made to improve bone regeneration techniques owing to a growing variety of sources of stem cells suitable for autologous transplants. Specifically, adipose-derived stem cells (ASCs) and stems cells from human exfoliated deciduous teeth (SHED) hold great potential for bone tissue engineering and cell therapy. After a preliminary characterization of the main biomolecules ASCs and SHED released in their conditioned media, cells were kept both in normal and osteo-inducing conditions. Conventional assays were performed to prove their osteogenic potential such as quantitative real-time polymerase chain reaction (qRT-PCR) (for RUNX-2, collagen type I, osteopontin and osteonectin), alkaline phosphatase activity, osteocalcin production, and von Kossa staining. Conditioned media were tested again after the osteogenic induction and compared to maintaining condition both at base line and after 14 days of culture. The osteogenic condition inhibited the release of all the biomolecules, with the exception, concerning SHED, of growth-regulated alpha protein precursor (GROα), and, to a lesser extent, interleukin (IL)-8. In conclusion, our data support that undifferentiated ASCs and SHED may be preferable to committed ones for general cell therapy approaches, due to their higher paracrine activity. Osteoinduction significantly affects the cytokine, chemokine, and growth factor profile in a differential way, as SHED kept a more pronounced pro-angiogenic signature than ASCs.

Feasibility and safety of treating non-unions in tibia, femur and humerus with autologous, expanded, bone marrow-derived mesenchymal stromal cells associated with biphasic calcium phosphate biomaterials in a multicentric, non-comparative trial

BACKGROUND

ORTHO-1 is a European, multicentric, first in human clinical trial to prove safety and feasibility after surgical implantation of commercially available biphasic calcium phosphate bioceramic granules associated during surgery with autologous mesenchymal stromal cells expanded from bone marrow (BM-hMSC) under good manufacturing practices, in patients with long bone pseudarthrosis.

METHODS

Twenty-eight patients with femur, tibia or humerus diaphyseal or metaphyso-diaphyseal non-unions were recruited and surgically treated in France, Germany, Italy and Spain with 100 or 200 million BM-hMSC/mL associated with 5-10 cc of bioceramic granules. Patients were followed up during one year. The investigational advanced therapy medicinal product (ATMP) was expanded under the same protocol in all four countries, and approved by each National Competent Authority.

FINDINGS

With safety as primary end-point, no severe adverse event was reported as related to the BM-hMSC. With feasibility as secondary end-point, the participating production centres manufactured the BM-hMSC as planned. The ATMP combined to the bioceramic was surgically delivered to the non-unions, and 26/28 treated patients were found radiologically healed at one year (3 out of 4 cortices with bone bridging).

INTERPRETATION

Safety and feasibility were clinically proven for surgical implantation of expanded autologous BM-hMSC with bioceramic.

FUNDING

EU-FP7-HEALTH-2009, REBORNE Project (GA: 241876).

A Multicentric, Open-Label, Randomized, Comparative Clinical Trial of Two Different Doses of Expanded hBM-MSCs Plus Biomaterial versus Iliac Crest Autograft, for Bone Healing in Nonunions after Long Bone Fractures: Study Protocol

ORTHOUNION is a multicentre, open, comparative, three-arm, randomized clinical trial (EudraCT number 2015-000431-32) to compare the efficacy, at one and two years, of autologous human bone marrow-derived expanded mesenchymal stromal cell (hBM-MSC) treatments versus iliac crest autograft (ICA) to enhance bone healing in patients with diaphyseal and/or metaphysodiaphyseal fracture (femur, tibia, and humerus) status of atrophic or oligotrophic nonunion (more than 9 months after the acute fracture, including recalcitrant cases after failed treatments). The primary objective is to determine if the treatment with hBM-MSCs combined with biomaterial is superior to ICA in obtaining bone healing. If confirmed, a secondary objective is set to determine if the dose of 100 × 10⁶ hBM-MSCs is noninferior to that of 200 × 10⁶ hBM-MSCs. The participants (n = 108) will be randomly assigned to either the experimental low dose (n = 36), the experimental high dose (n = 36), or the comparator arm (n = 36) using a central randomization service. The trial will be conducted in 20 clinical centres in Spain, France, Germany, and Italy under the same clinical protocol. The confirmation of superiority for the proposed ATMP in nonunions may foster the future of bone regenerative medicine in this indication. On the contrary, absence of superiority may underline its limitations in clinical use.

Micro-Nanostructures of Cellulose-Collagen for Critical Sized Bone Defect Healing

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro-nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self-assemble on these microstructures to create a natural polymer-based, micro-nanostructured matrix (CAc). Poly (lactic-co-glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro-nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro-nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro-nanostructures may serve as an alternative material platform for bone regeneration.

The Poor Osteoinductive Capability of Human Acellular Bone Matrix

Demineralized bone matrix (DBM) has extensive clinical use for bone regeneration because of its osteoinductive and osteoconductive aptitude. It is suggested that the demineralization process in bone matrix preparation is influential in maintaining osteoinductivity; however, relevant investigations, especially into the osteoinductivity of acellular bone matrix, are not often performed. This study addressed the osteoinductive capability of human acellular cancellous bone matrix (ACBM) after subcutaneous implantation in a rat model. The growth and osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBM-MSCs) seeded in this material were also studied. Without the demineralization process, the ACBM we obtained had an interconnected porous network and the micropores in the surface were clearly exposed. After the ACBM was subcutaneously implanted for 4 months, new osteoid formation was noted but not typical mature bone formation. rBM-MSCs grew well in the ACBM and kept a steady morphology after continuous culture for 28 days. However, no mineralized nodule formation was detected and the expression levels of genes encoding osteogenic markers were significantly decreased. These results demonstrated that human ACBM possess the structural features of native bone and poor osteoinductivity; nonetheless this material helped to preserve the undifferentiated phenotype of rBM-MSCs. Such insights may further broaden our understanding of the application of ACBM for bone regeneration and the creation of stem cell niches.

Heterotopic bone formation in the musculus latissimus dorsi of sheep using β-tricalcium phosphate scaffolds: evaluation of different seeding techniques

Osseous reconstruction of large bone defects remains a challenge in oral and maxillofacial surgery. In addition to autogenous bone grafts, which despite potential donor-site mobility still represent the gold standard in reconstructive surgery, many studies have investigated less invasive alternatives such as in vitro cultivation techniques. This study compared different types of seeding techniques on pure β-tricalcium phosphate scaffolds in terms of bone formation and ceramic resorption in vivo. Cylindrical scaffolds loaded with autologous cancellous bone, venous blood, bone marrow aspirate concentrate or extracorporeal in vitro cultivated bone marrow stromal cells were cultured in sheep on a perforator vessel of the musculus latissimus dorsi over a 6-month period. Histological and histomorphometric analyses revealed that scaffolds loaded with cancellous bone were superior at promoting heterotopic bone formation and ceramic degradation, with autogenous bone and bone marrow aspirate concentrate inducing in vivo formation of vital bone tissue. These results confirm that autologous bone constitutes the preferred source of osteoinductive and osteogenic material that can reliably induce heterotopic bone formation in vivo.

Stem cell-derived exosomes: A promising strategy for fracture healing

OBJECTIVES

To describe the biological characteristics of exosomes and to summarize the current status of stem cell-derived exosomes on fracture healing. Meanwhile, future challenges, limitations and perspectives are also discussed.

METHODS

Search and analyze the related articles in pubmed database through the multi-combination of keywords like "stem cells","exosomes","bone regeneration" and "fracture healing".

CONCLUSION

Stem cell-derived exosome therapy for fracture healing has been enjoying popularity and is drawing increasing attention. This strategy helps to promote proliferation and migration of cells, as well as osteogenesis and angiogenesis, in the process of bone formation. Although the exact mechanisms remain elusive, exosomal miRNAs seem to play vital roles. Future studies are required to solve multiple problems before clinical application, including comprehensive and thorough understanding of exosomes, the exact roles of exosomes in regulating bone formation, and the optimal source, dose and frequency of treatment, as well as technical and safety issues. Moreover, studies based on fracture models of large animals are could offer guidance and are in demand.

Restoration of bone defects using modified heterogeneous deproteinized bone seeded with bone marrow mesenchymal stem cells

The aim of the present study was to investigate the effect of modified heterogeneous deproteinized bone combined with bone marrow mesenchymal stem cells (BMSCs) in the restoration of a validated bone defect model. BMSCs were identified by flow cytometry and multilineage differentiation assay. The structural features of the modified heterogeneous deproteinized bone scaffold and biocompatibility between BMSCs and the scaffold were confirmed by scanning electron microscope (SEM) detection. The cytotoxicity of the modified heterogeneous deproteinized bone scaffolds were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenytetrazolium bromide (MTT) assay. SEM detection proved that modified heterogeneous deproteinized bone scaffold had no negative impact on the proliferation of BMSCs. MTT assay results demonstrated that the scaffold had no apparent cytotoxicity. Biomechanical detection showed that the stiffness and ultimate loading of tibias in the scaffold + BMSCs group were significantly higher than those of the scaffold alone group (P < 0.05) and the control group (P < 0.01). Histological analyses confirmed that the greatest quantity of new bone was generated in the scaffold + BMSCs group, when compared with all other groups, at 8 weeks' post-operation. The bone mineral density (BMD) in the scaffold + BMSC group was significantly higher than that of the scaffold alone group (P < 0.05) and the control group (P < 0.01). Fluorometric analyses confirmed the presence of BMSCs at high concentration within the bone defect areas in the scaffold + BMSCs group at 4 weeks after transplantation. These findings suggest that the modified heterogeneous deproteinized bone scaffold seeded with BMSCs can effectively enhance the restoration of bone defects.

Long non-coding RNA MEG3 inhibits adipogenesis and promotes osteogenesis of human adipose-derived mesenchymal stem cells via miR-140-5p

lncRNAs are an emerging class of regulators involved in multiple biological processes. MEG3, an lncRNA, acts as a tumor suppressor, has been reported to be linked with osteogenic differentiation of MSCs. However, limited knowledge is available concerning the roles of MEG3 in the multilineage differentiation of hASCs. The current study demonstrated that MEG3 was downregulated during adipogenesis and upregulated during osteogenesis of hASCs. Further functional analysis showed that knockdown of MEG3 promoted adipogenic differentiation, whereas inhibited osteogenic differentiation of hASCs. Mechanically, MEG3 may execute its role via regulating miR-140-5p. Moreover, miR-140-5p was upregulated during adipogenesis and downregulated during osteogenesis in hASCs, which was negatively correlated with MEG3. In conclusion, MEG3 participated in the balance of adipogenic and osteogenic differentiation of hASCs, and the mechanism may be through regulating miR-140-5p.

Knockdown of MicroRNA Let-7a Improves the Functionality of Bone Marrow-Derived Mesenchymal Stem Cells in Immunotherapy

Bone marrow-derived mesenchymal stem cells (MSCs) have been recently used in clinical treatment of inflammatory diseases. Practical strategies improving the immunosuppressive property of MSCs are urgently needed for MSC immunotherapy. In this study, we aimed to develop a microRNA-based strategy to improve MSC immunotherapy. Bioinformatic analysis revealed that let-7a targeted the 3' UTR of mRNA of Fas and FasL, both of which are essential for MSCs to induce T cell apoptosis. Knockdown of let-7a by specific inhibitor doubled Fas and Fas ligand (FasL) protein levels in MSCs. Because Fas attracts T cell migration and FasL induces T cell apoptosis, knockdown of let-7a significantly promoted MSC-induced T cell migration and apoptosis in vitro and in vivo. Importantly, MSCs knocked down of let-7a were more efficient to reduce the mortality, prevent the weight loss, suppress the inflammation reaction, and alleviate the tissue lesion of experimental colitis and graft-versus-host disease (GVHD) mouse models. In conclusion, knockdown of let-7a significantly improved the therapeutic effect of MSC cytotherapy on inflammatory bowel diseases and GVHD. With high safety and convenience, knockdown of let-7a is a potential strategy to improve MSC therapy for inflammatory diseases in clinic.

The Use of Adipose Tissue-Derived Progenitors in Bone Tissue Engineering - a Review

2500 years ago, Hippocrates realized that bone can heal without scaring. The natural healing potential of bone is, however, restricted to small defects. Extended bone defects caused by trauma or during tumor resections still pose a huge problem in orthopedics and cranio-maxillofacial surgery. Bone tissue engineering strategies using stem cells, growth factors, and scaffolds could overcome the problems with the treatment of extended bone defects. In this review, we give a short overview on bone tissue engineering with emphasis on the use of adipose tissue-derived stem cells and small molecules.

Concise Review: Mesenchymal Stem Cell Therapy for Pediatric Disease: Perspectives on Success and Potential Improvements

Mesenchymal stem cells (MSCs) represent a potentially revolutionary therapy for a wide variety of pediatric diseases, but the optimal cell-based therapeutics for such diversity have not yet been specified. The published clinical trials for pediatric pulmonary, cardiac, orthopedic, endocrine, neurologic, and hematologic diseases provide evidence that MSCs are indeed efficacious, but the significant heterogeneity in therapeutic approaches between studies raises new questions. The purpose of this review is to stimulate new preclinical and clinical trials to investigate these factors. First, we discuss recent clinical trials for pediatric diseases studying MSCs obtained from bone marrow, umbilical cord and umbilical cord blood, placenta, amniotic fluid, and adipose tissue. We then identify factors, some unique to pediatrics, which must be examined to optimize therapeutic efficacy, including route of administration, dose, timing of administration, the role of ex vivo differentiation, cell culture techniques, donor factors, host factors, and the immunologic implications of allogeneic therapy. Finally, we discuss some of the practicalities of bringing cell-based therapy into the clinic, including regulatory and manufacturing considerations. The aim of this review is to inform future studies seeking to maximize therapeutic efficacy for each disease and for each patient. Stem Cells Translational Medicine 2017;6:539-565.

Targeting the hypoxic response in bone tissue engineering: A balance between supply and consumption to improve bone regeneration

Bone tissue engineering is a promising therapeutic alternative for bone grafting of large skeletal defects. It generally comprises an ex vivo engineered combination of a carrier structure, stem/progenitor cells and growth factors. However, the success of these regenerative implants largely depends on how well implanted cells will adapt to the hostile and hypoxic host environment they encounter after implantation. In this review, we will discuss how hypoxia signalling may be used to improve bone regeneration in a tissue-engineered construct. First, hypoxia signalling induces angiogenesis which increases the survival of the implanted cells as well as stimulates bone formation. Second, hypoxia signalling has also angiogenesis-independent effects on mesenchymal cells in vitro, offering exciting new possibilities to improve tissue-engineered bone regeneration in vivo. In addition, studies in other fields have shown that benefits of modulating hypoxia signalling include enhanced cell survival, proliferation and differentiation, culminating in a more potent regenerative implant. Finally, the stimulation of endochondral bone formation as a physiological pathway to circumvent the harmful effects of hypoxia will be briefly touched upon. Thus, angiogenic dependent and independent processes may counteract the deleterious hypoxic effects and we will discuss several therapeutic strategies that may be combined to withstand the hypoxia upon implantation and improve bone regeneration.

Design of Injectable Materials to Improve Stem Cell Transplantation

Stem cell-based therapies are steadily gaining traction for regenerative medicine approaches to treating disease and injury throughout the body. While a significant body of work has shown success in preclinical studies, results often fail to translate in clinical settings. One potential cause is the massive transplanted cell death that occurs post injection, preventing functional integration with host tissue. Therefore, current research is focusing on developing injectable hydrogel materials to protect cells during delivery and to stimulate endogenous regeneration through interactions of transplanted cells and host tissue. This review explores the design of targeted injectable hydrogel systems for improving the therapeutic potential of stem cells across a variety of tissue engineering applications with a focus on hydrogel materials that have progressed to the stage of preclinical testing.

Utilizing Autologous Multipotent Mesenchymal Stromal Cells and β-Tricalcium Phosphate Scaffold in Human Bone Defects: A Prospective, Controlled Feasibility Trial

The purpose of this prospective controlled study was to compare healing quality following the implantation of ultraporous β-tricalcium phosphate, containing either expanded autologous mesenchymal stromal cells (trial group, 9 patients) or β-tricalcium phosphate alone (control group, 9 patients), into femoral defects during revision total hip arthroplasty. Both groups were assessed using the Harris Hip Score, radiography, and DEXA scanning at 6 weeks and 3, 6, and 12 months postoperatively. A significant difference in the bone defect healing was observed between both groups of patients (P < 0.05). In the trial group, trabecular remodeling was found in all nine patients and in the control group, in 1 patient only. Whereas, over the 12-month follow-up period, no significant difference was observed between both groups of patients in terms of the resorption of β-tricalcium phosphate, the significant differences were documented in the presence of radiolucency and bone trabeculation through the defect (P < 0.05). Using autologous mesenchymal stromal cells combined with a β-tricalcium phosphate scaffold is a feasible, safe, and effective approach for management of bone defects with compromised microenvironment. The clinical trial was registered at the EU Clinical Trials Register before patient recruitment has begun (EudraCT number 2012-005599-33).

Composite Hydrogels for Bone Regeneration

Over the past few decades, bone related disorders have constantly increased. Among all pathological conditions, osteoporosis is one of the most common and often leads to bone fractures. This is a massive burden and it affects an estimated 3 million people only in the UK. Furthermore, as the population ages, numbers are due to increase. In this context, novel biomaterials for bone fracture regeneration are constantly under development. Typically, these materials aim at favoring optimal bone integration in the scaffold, up to complete bone regeneration; this approach to regenerative medicine is also known as tissue engineering (TE). Hydrogels are among the most promising biomaterials in TE applications: they are very flexible materials that allow a number of different properties to be targeted for different applications, through appropriate chemical modifications. The present review will focus on the strategies that have been developed for formulating hydrogels with ideal properties for bone regeneration applications. In particular, aspects related to the improvement of hydrogels' mechanical competence, controlled delivery of drugs and growth factors are treated in detail. It is hoped that this review can provide an exhaustive compendium of the main aspects in hydrogel related research and, therefore, stimulate future biomaterial development and applications.

Translational research-the need of a new bioethics approach

Translational research tries to apply findings from basic science to enhance human health and well-being. Many phases of the translational research may include non-medical tasks (information technology, engineering, nanotechnology, biochemistry, animal research, economy, sociology, psychology, politics, and so on). Using common bioethics principles to these areas might sometimes be not feasible, or even impossible. However, the whole process must respect some fundamental, moral principles. The purpose of this paper is to argument the need for a different approach to the morality in translational bioethics, and to suggest some directions that might be followed when constructing such a bioethics. We will show that a new approach is needed and present a few ethical issues that are specific to the translational research.

Expansion of murine periosteal progenitor cells with fibroblast growth factor 2 reveals an intrinsic endochondral ossification program mediated by bone morphogenetic protein 2

The preservation of the bone-forming potential of skeletal progenitor cells during their ex vivo expansion remains one of the major challenges for cell-based bone regeneration strategies. We report that expansion of murine periosteal cells in the presence of FGF2, a signal present during the early stages of fracture healing, is necessary and sufficient to maintain their ability to organize in vivo into a cartilage template which gives rise to mature bone. Implantation of FGF2-primed cells in a large bone defect in mice resulted in complete healing, demonstrating the feasibility of using this approach for bone tissue engineering purposes. Mechanistically, the enhanced endochondral ossification potential of FGF2-expanded periosteal cells is predominantly driven by an increased production of BMP2 and is additionally linked to an improved preservation of skeletal progenitor cells in the cultures. This characteristic is unique for periosteal cells, as FGF2-primed bone marrow stromal cells formed significantly less bone and progressed exclusively through the intramembranous pathway, revealing essential differences between both cell pools. Taken together, our findings provide insight in the molecular regulation of fracture repair by identifying a unique interaction between periosteal cells and FGF2. These insights may promote the development of cell-based therapeutic strategies for bone regeneration which are independent of the in vivo use of growth factors, thus limiting undesired side effects.

Comparing the osteogenic potential of bone marrow and tendon-derived stromal cells to repair a critical-sized defect in the rat femur

Despite significant advancements in bone tissue-engineering applications, the clinical impact of bone marrow stromal cells (BMSCs) for the treatment of large osseous defects remains limited. Therefore, other cell sources are under investigation for their osteogenic potential to repair bone. In this study, tendon-derived stromal cells (TDSCs) were evaluated in comparison to BMSCs to support the functional repair of a 5 mm critical-sized, segmental defect in the rat femur. Analysis of the trilineage differentiation capacity of TDSCs and BMSCs cultured on collagen sponges revealed impaired osteogenic differentiation and mineral deposition of TDSCs in vitro, whereas chondrogenic and adipogenic differentiation was evident for both cell types. Radiographic assessment demonstrated that neither cell type significantly improved the healing rate of a challenging 5 mm segmental femoral defect. Transplanted TDSCs and BMSCs both led to the formation of only small amounts of bone in the defect area, and histological evaluation revealed non-mineralized, collagen-rich scar tissue to be present within the defect area. Newly formed lamellar bone was restricted to the defect margins, resulting in closure of the medullary cavity. Interestingly, in comparison to BMSCs, significantly more TDSC-derived cells were present at the osteotomy gap up to 8 weeks after transplantation and were also found to be located within newly formed lamellar bone, suggesting their capacity to directly contribute to de novo bone formation. To our knowledge, this is the first study investigating the in vivo capacity of TDSCs to regenerate a critical-sized defect in the rat femur. Copyright © 2015 John Wiley & Sons, Ltd.

Mesenchymal stem/stromal cells as a delivery platform in cell and gene therapies

Regenerative medicine relying on cell and gene therapies is one of the most promising approaches to repair tissues. Multipotent mesenchymal stem/stromal cells (MSC), a population of progenitors committing into mesoderm lineages, are progressively demonstrating therapeutic capabilities far beyond their differentiation capacities. The mechanisms by which MSC exert these actions include the release of biomolecules with anti-inflammatory, immunomodulating, anti-fibrogenic, and trophic functions. While we expect the spectra of these molecules with a therapeutic profile to progressively expand, several human pathological conditions have begun to benefit from these biomolecule-delivering properties. In addition, MSC have also been proposed to vehicle genes capable of further empowering these functions. This review deals with the therapeutic properties of MSC, focusing on their ability to secrete naturally produced or gene-induced factors that can be used in the treatment of kidney, lung, heart, liver, pancreas, nervous system, and skeletal diseases. We specifically focus on the different modalities by which MSC can exert these functions. We aim to provide an updated understanding of these paracrine mechanisms as a prerequisite to broadening the therapeutic potential and clinical impact of MSC.

MiR-26a functions oppositely in osteogenic differentiation of BMSCs and ADSCs depending on distinct activation and roles of Wnt and BMP signaling pathway

MicroRNAs (miRNAs) emerge as important regulators of stem cell lineage commitment and bone development. MiRNA-26a (miR-26a) is one of the important miRNAs regulating osteogenic differentiation of both bone marrow-derived mesenchymal stem cells (BMSCs) and adipose tissue-derived mesenchymal stem cells (ADSCs). However, miR-26a functions oppositely in osteogenic differentiation of BMSCs and ADSCs, suggesting distinct post-transcriptional regulation of tissue-specific MSC differentiation. However, the molecular basis is largely unknown. Here, we report that the function of miR-26a is largely depended on the intrinsic signaling regulation network of MSCs. Using bioinformatics and functional assay, we confirmed that miR-26a potentially targeted on GSK3β and Smad1 to regulate Wnt and BMP signaling pathway. Overall comparative analysis revealed that Wnt signaling was enhanced more potently and played a more important role than BMP signaling in osteogenic differentiation of BMSCs, whereas BMP pathway was more essential for promoting osteogenic differentiation of ADSCs. The distinct activation pattern and role of signaling pathways determined that miR-26a majorly targeted on GSK3β to activate Wnt signaling for promoting osteogenic differentiation of BMSCs, whereas it inhibited Smad1 to suppress BMP signaling for interfering with the osteogenic differentiation of ADSCs. Taken together, our study demonstrated that BMSCs and ADSCs applied different signaling pathway to facilitate their osteogenic differentiation, which determined the inverse function of miR-26a. The distinct transcriptional regulation and post-transcriptional regulation network suggested the intrinsic molecular differences between tissue-specific MSCs and the complexity in MSC research and MSC-based cell therapy.

Regenerative medicine in otorhinolaryngology

BACKGROUND

Tissue engineering using biocompatible scaffolds, with or without cells, can permit surgeons to restore structure and function following tissue resection or in cases of congenital abnormality. Tracheal regeneration has emerged as a spearhead application of these technologies, whilst regenerative therapies are now being developed to treat most other diseases within otolaryngology.

METHODS AND RESULTS

A systematic review of the literature was performed using Ovid Medline and Ovid Embase, from database inception to 15 November 2014. A total of 561 papers matched the search criteria, with 76 fulfilling inclusion criteria. Articles were predominantly pre-clinical animal studies, reflecting the current status of research in this field. Several key human research articles were identified and discussed.

CONCLUSION

The main issues facing research in regenerative surgery are translation of animal model work into human models, increasing stem cell availability so it can be used to further research, and development of better facilities to enable implementation of these advances.

Hybrid nanostructured hydroxyapatite-chitosan composite scaffold: bioinspired fabrication, mechanical properties and biological properties

The fabrication of bone scaffolds with interconnected porous structure, adequate mechanical properties, excellent biocompatibility and osteoinductivity presents a great challenge. Herein, a hybrid nanostructured hydroxyapatite-chitosan (HA-CS) composite scaffold has been fabricated according to the following steps: (i) the deposition of brushite-CS on a CS fibre porous scaffold by a dip-coating method; and (ii) the formation of a hybrid nanostructured HA-CS composite scaffold by the in situ conversion of brushite to HA using a bioinspired mineralization process. The hybrid HA-CS composite scaffold possesses three-dimensional (3D) interconnected pores with pore sizes of 30-80 μm. The HA rods with a length of ∼200 nm and width of ∼50 nm are perpendicularly oriented to the CS fibres. Interestingly, the abovementioned HA rods are composed of many smaller nanorods with a length of ∼40 nm and width of ∼10 nm oriented along the c-axis. The hybrid nanostructured HA-CS composite scaffold exhibits good mechanical properties with a compression strength of 9.41 ± 1.63 MPa and an elastic modulus of 0.17 ± 0.02 GPa, which are well-matched to those of trabecular bone. The influences of the hybrid HA-CS composite scaffold on cells have been investigated using human bone marrow stem cells (hBMSCs) as cell model and the CS fibre porous scaffold as the control sample. The hybrid HA-CS composite scaffold not only supports the adhesion and proliferation of hBMSCs, but also improves the osteoinductivity. The alkaline phosphatase activity and mineralization deposition on the hybrid HA-CS composite scaffold are higher than those on the CS fibre porous scaffold. Moreover, the hybrid HA-CS composite scaffold can promote the formation of new bone in rat calvarial defects as compared with the CS fibre porous scaffold. The excellent biocompatibility, osteoinductivity and mechanical properties suggest that the hybrid nanostructured HA-CS composite scaffold has great potential for bone tissue engineering.