Allogeneic Mesenchymal Stem Cells Stimulate Cartilage Regeneration and Are Safe for Single-Stage Cartilage Repair in Humans upon Mixture with Recycled Autologous Chondrons

Promotion of osteochondral repair through immune microenvironment regulation and activation of endogenous chondrogenesis via the release of apoptotic vesicles from donor MSCs

Utilizing transplanted human umbilical cord mesenchymal stem cells (HUMSCs) for cartilage defects yielded advanced tissue regeneration, but the underlying mechanism remain elucidated. Early after HUMSCs delivery to the defects, we observed substantial apoptosis. The released apoptotic vesicles (apoVs) of HUMSCs promoted cartilage regeneration by alleviating the chondro-immune microenvironment. ApoVs triggered M2 polarization in macrophages while simultaneously facilitating the chondrogenic differentiation of endogenous MSCs. Mechanistically, in macrophages, miR-100-5p delivered by apoVs activated the MAPK/ERK signaling pathway to promote M2 polarization. In MSCs, let-7i-5p delivered by apoVs promoted chondrogenic differentiation by targeting the eEF2K/p38 MAPK axis. Consequently, a cell-free cartilage regeneration strategy using apoVs combined with a decellularized cartilage extracellular matrix (DCM) scaffold effectively promoted the regeneration of osteochondral defects. Overall, new mechanisms of cartilage regeneration by transplanted MSCs were unconcealed in this study. Moreover, we provided a novel experimental basis for cell-free tissue engineering-based cartilage regeneration utilizing apoVs.

Conditioned Medium of Infrapatellar Fat Stem Cells Alleviates Degradation of Chondrocyte Extracellular Matrix and Delays Development of Osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a prevalent clinical chronic degenerative condition characterized by the degeneration of articular cartilage. Currently, drug treatments for OA come with varying degrees of side effects, making the development of new therapeutic approaches for OA imperative. Mesenchymal stem cells (MSCs) are known to mitigate the progression of OA primarily through paracrine effects. The conditioned medium (CM) derived from MSCs encapsulates a variety of paracrine factors secreted by these cells.

METHODS

In this study, we investigated the effect of the CM of infrapatellar fat pad-derived MSCs (IPFSCs) on OA in vitro and in vivo, as well as and the potential underlying mechanisms. We established three experimental groups: the normal group, the OA group, and the CM intervention group. In vitro experiments, we used methods such as qPCR, Western blot, immunofluorescence, and flow cytometry to detect the impact of CM on OA chondrocytes. In vivo experiments, we evaluated the changes in the knee joints of OA rats after intra-articular injection of CM treatment.

RESULTS

The results showed that injection of CM into the knee joint inhibited OA development in a rat model induced by destabilization of the medial meniscus and anterior cruciate ligament transection. The CM increased the deposition of extracellular matrix-related components (type II collagen and Proteoglycan). The activation of PI3K/AKT/NF-κB signaling pathway was induced by IL-1β in chondrocytes, which was finally inhibited by CM-IPFSCs treatment.

CONCLUSION

In summary, IPFSCs-CM may have therapeutic potential for OA.

Novel Treatment Options for Knee Cartilage Defects in 2023

Articular cartilage lesions are a common injury that have become increasingly treatable with joint preservation procedures. Well-documented allograft and cellular treatments for these lesions are detailed elsewhere in this volume. This article discusses three new unique options for addressing these defects taking three different paths to address these complex injuries. Agili-C is an existing FDA- and EMEA-approved option using an acellular aragonite-based scaffold to treat both chondral and osteochondral lesions, with or without concurrent arthritis. Cartistem is a stem-cell-based product composed of culture-expanded allogeneic human umbilical cord blood-derived mesenchymal stem cells and hyaluronic acid hydrogel, which is in its final clinical trial stages in the United States, but already has regulatory approval in Korea. IMPACT and RECLAIM studies have shown the safety and efficacy of a new one-stage procedure utilizing autologous chondrons combined with allogeneic mesenchymal stem cells (MSCs) that can provide another effective single-stage treatment option.

Cellular Enhancement of Frozen Meniscus Allograft Combining Native Meniscus and Mesenchymal Stromal Cell Injections

OBJECTIVE

This proof-of-concept study investigated an improved cell-based injection therapy combining mesenchymal stem cells (MSCs) and meniscus cells (MCs) to support superior meniscus allograft repopulation and early revival compared to injecting MSCs alone.

DESIGN

In this controlled laboratory study, frozen meniscus allograft samples were injected vertically with a cell suspension containing different ratios of MSCs and MCs or control (lactated ringers) and cultured for 28 days. Samples were analyzed weekly for cell viability, migration, and metabolism using histological and biochemical assays. Tissue medium was analyzed for matrix metalloproteinase (MMP) expression using zymography.

RESULTS

Cellular repopulation of frozen allografts injected with different cell suspensions was validated by immunohistochemistry. Significant higher DNA content was evidenced in grafts treated with suspensions of MCs or MC:MSC (1:4 ratio). Cell metabolic activity was significantly different between all treated groups and control group after 1 week. Allografts injected with MCs showed significantly more cell proliferation than injections with MSCs. MMP2 activity was detected in medium of all grafts cellularized with MCs with or without MSCs. Scanning electron microscopy (SEM) analysis showed resolution of the needle puncture, but not in the control group. Cell labeling of MCs upon injection of mixed MC:MSC suspensions revealed a gradual increase in the cell ratio.

CONCLUSIONS

The findings of this study establish that injection of MCs with or without MSCs enhances the cellularity of meniscus allograft to support early graft revival and remodeling.

Endogenus chondrocytes immobilized by G-CSF in nanoporous gels enable repair of critical-size osteochondral defects

Injured articular cartilage is a leading cause for osteoarthritis. We recently discovered that endogenous stem/progenitor cells not only reside in the superficial zone of mouse articular cartilage, but also regenerated heterotopic bone and cartilage in vivo. However, whether critical-size osteochondral defects can be repaired by pure induced chemotatic cell homing of these endogenous stem/progenitor cells remains elusive. Here, we first found that cells in the superficial zone of articular cartilage surrounding surgically created 3 × 1 mm defects in explant culture of adult goat and rabbit knee joints migrated into defect-filled fibrin/hylaro1nate gel, and this migration was significantly more robust upon delivery of exogenous granulocyte-colony stimulating factor (G-CSF). Remarkably, G-CSF-recruited chondrogenic progenitor cells (CPCs) showed significantly stronger migration ability than donor-matched chondrocytes and osteoblasts. G-CSF-recruited CPCs robustly differentiated into chondrocytes, modestly into osteoblasts, and barely into adipocytes. In vivo, critical-size osteochondral defects were repaired by G-CSF-recruited endogenous cells postoperatively at 6 and 12 weeks in comparison to poor healing by gel-only group or defect-only group. ICRS and O'Driscoll scores of articular cartilage were significantly higher for both 6- and 12-week G-CSF samples than corresponding gel-only and defect-only groups. Thus, endogenous stem/progenitor cells may be activated by G-CSF, a Food and Drug Administration (FDA)-cleared bone-marrow stimulating factor, to repair osteochondral defects.

Therapeutic potential of stem cells in regeneration of liver in chronic liver diseases: Current perspectives and future challenges

The deposition of extracellular matrix and hyperplasia of connective tissue characterizes chronic liver disease called hepatic fibrosis. Progression of hepatic fibrosis may lead to hepatocellular carcinoma. At this stage, only liver transplantation is a viable option. However, the number of possible liver donors is less than the number of patients needing transplantation. Consequently, alternative cell therapies based on non-stem cells (e.g., fibroblasts, chondrocytes, keratinocytes, and hepatocytes) therapy may be able to postpone hepatic disease, but they are often ineffective. Thus, novel stem cell-based therapeutics might be potentially important cutting-edge approaches for treating liver diseases and reducing patient' suffering. Several signaling pathways provide targets for stem cell interventions. These include pathways such as TGF-β, STAT3/BCL-2, NADPH oxidase, Raf/MEK/ERK, Notch, and Wnt/β-catenin. Moreover, mesenchymal stem cells (MSCs) stimulate interleukin (IL)-10, which inhibits T-cells and converts M1 macrophages into M2 macrophages, producing an anti-inflammatory environment. Furthermore, it inhibits the action of CD4+ and CD8+ T cells and reduces the activity of TNF-α and interferon cytokines by enhancing IL-4 synthesis. Consequently, the immunomodulatory and anti-inflammatory capabilities of MSCs make them an attractive therapeutic approach. Importantly, MSCs can inhibit the activation of hepatic stellate cells, causing their apoptosis and subsequent promotion of hepatocyte proliferation, thereby replacing dead hepatocytes and reducing liver fibrosis. This review discusses the multidimensional therapeutic role of stem cells as cell-based therapeutics in liver fibrosis.

Allogeneic Mesenchymal Stem Cells After In Vivo Transplantation: A Review

Autologous mesenchymal stem cells (MSCs) are ideal for tissue regeneration because of their ability to circumvent host rejection, but their procurement and processing present logistical and time-sensitive challenges. Allogeneic MSCs provide an alternative cell-based therapy capable of positively affecting all human organ systems, and can be readily available. Extensive research has been conducted in the treatment of autoimmune, degenerative, and inflammatory diseases with such stem cells, and has demonstrated predominantly safe outcomes with minimal complications. Nevertheless, continued clinical trials are necessary to ascertain optimal harvest and transplant techniques.

The Safety and Efficacy of Human Umbilical Cord-Derived Mesenchymal Stem Cells in Patients With Heart Failure and Myocardial Infarction: A Meta-Analysis of Clinical Trials

Evidence from preclinical and clinical studies suggests that human umbilical cord-derived mesenchymal stromal cells (HUC-MSCs) may be useful in treating heart failure and acute myocardial infarction (MI). However, the effects of stem cell therapy on patients with heart failure remain the subject of ongoing controversy, and the safety and effectiveness of HUC-MSCs therapy have not yet been proven. To date, there has been no systematic overview and meta-analysis of clinical studies using HUC-MSCs therapy for heart failure and MI. The purpose of this study is to assess the safety and efficacy of HUC-MSC therapy versus a placebo in patients with heart failure and MI. While preparing this systematic review and meta-analysis, we adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A computer literature search of PubMed was performed. We considered randomized controlled trials (RCTs) that reported data on the safety and efficacy of HUC-MSC transplantation in patients with heart failure and MI. Two investigators independently searched the literature, extracted data, and rated the quality of the included research. Pooled data were analyzed using the fixed-effect model or the random-effect model in Review Manager 5.3. The Cochrane risk of bias tool was used to assess the bias of included studies. The primary outcome was ejection fraction (EF), whereas the secondary outcomes were readmission and mortality rates. Three RCTs (201 patients) were included in this meta-analysis. The overall effect did not favor either of the two groups in terms of risk of readmission (risk ratio = 0.5, 95% confidence interval (CI) = 0.22-1.15, p = 0.10) as well as mortality rate (risk ratio = 0.44, 95% CI = 0.14-1.44, p = 0.18). However, there was an improvement in EF in patients who received HUC-MSCs compared to placebo after 12 months of transplantation (mean difference (MD) = 3.21, 95% CI = 2.91-3.51, p < 0.00001). At the six-month follow-up period, there was no significant improvement in EF (MD = 1.30, 95% CI = -1.94-4.54), p = 0.43), indicating that the duration of follow-up can shape the response to therapy. Our findings indicate that HUC-MSC transplantation can improve EF but has no meaningful effect on readmission or mortality rates. Existing evidence is insufficient to confirm the efficacy of HUC-MSCs for broader therapeutic applications. Therefore, additional double-blind RCTs with larger sample sizes are required.

Repair of osteochondral defects: efficacy of a tissue-engineered hybrid implant containing both human MSC and human iPSC-cartilaginous particles

Both mesenchymal stromal cells (MSC) and induced pluripotent stem cells (iPSC) offer the potential for repair of damaged connective tissues. The use of hybrid implants containing both human MSC and iPSC was investigated to assess their combined potential to yield enhanced repair of osteochondral defects. Human iPSC-CP wrapped with tissue engineered constructs (TEC) containing human MSC attained secure defect filling with good integration to adjacent tissue in a rat osteochondral injury model. The presence of living MSC in the hybrid implants was required for effective biphasic osteochondral repair. Thus, the TEC component of such hybrid implants serves several critical functions including, adhesion to the defect site via the matrix and facilitation of the repair via live MSC, as well as enhanced angiogenesis and neovascularization. Based on these encouraging studies, such hybrid implants may offer an effective future intervention for repair of complex osteochondral defects.

Single-stage autologous cartilage repair results in positive patient-reported outcomes for chondral lesions of the knee: a systematic review

AIM

This article aims to perform a systematic review of the clinical literature regarding the efficacy of single-stage autologous cartilage repair.

METHODS

A systematic review of the literature was performed using PubMed, Scopus, Web of Science, and the Cochrane Library. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed.

RESULTS

Twelve studies were identified; however, due to overlapping patient cohorts, nine studies were included for data extraction and analysis. Six studies applied minced cartilage, while three studies utilized enzymatically processed cartilage. Two authorship groups described single-stage techniques that exclusively utilized cartilage from the debrided lesion rim, while the remaining groups either utilized healthy cartilage or combined healthy cartilage with cartilage debrided from lesion rim. Among the included techniques, scaffold augments were used in four studies, and three studies implemented bone autograft augmentation. When summarizing patient reported outcome measures for the included studies, single-stage autologous cartilage repair demonstrated an average improvement ranging from 18.7 ​± ​5.3 to 30.0 ​± ​8.0 amongst the Knee Injury and Osteoarthritis Outcome Scores subsections, 24.3 ​± ​10.5 for the International Knee Documentation Committee subjective score, and 41.0 ​± ​10.0 for Visual Analogue Scale-Pain.

CONCLUSION

Single-stage autologous cartilage repair is a promising technique with positive clinical data to date. The current study highlights the overall improvement in patient reported outcomes after repair for chondral defects to the knee with average follow-up ranging from 12 to 201 months and also the heterogeneity and variability of the single-stage surgical technique. Further discussion on the standardization of practices for a cost-effective single-stage augmented autologous cartilage technique is needed. In the future, a well-designed randomized controlled trial is needed to explore the efficacy of this therapeutic modality relative to established intervention.

LEVEL OF EVIDENCE

Systematic review; Level IV.

Engineering exosomes derived from subcutaneous fat MSCs specially promote cartilage repair as miR-199a-3p delivery vehicles in Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease involving cartilage. Exosomes derived from Mesenchymal stem cells (MSCs) therapy improves articular cartilage repair, but subcutaneous fat (SC) stromal cells derived exosomes (MSCsSC-Exos), especially engineering MSCsSC-Exos for drug delivery have been rarely reported in OA therapy. This objective of this study was to clarify the underlying mechanism of MSCsSC-Exos on cartilage repair and therapy of engineering MSCsSC-Exos for drug delivery in OA. MSCsSC-Exos could ameliorate the pathological severity degree of cartilage via miR-199a-3p, a novel molecular highly enriched in MSCsSC-Exos, which could mediate the mTOR-autophagy pathway in OA rat model. Intra-articular injection of antagomiR-199a-3p dramatically attenuated the protective effect of MSCsSC-Exos-mediated on articular cartilage in vivo. Furthermore, to achieve the superior therapeutic effects of MSCsSC-Exos on injured cartilage, engineering exosomes derived from MSCsSC as the chondrocyte-targeting miR-199a-3p delivery vehicles were investigated in vitro and in vivo. The chondrocyte-binding peptide (CAP) binding MSCsSC-Exos could particularly deliver miR-199a-3p into the chondrocytes in vitro and into deep articular tissues in vivo, then exert the excellent protective effect on injured cartilage in DMM-induced OA mice. As it is feasible to obtain human subcutaneous fat from healthy donors by liposuction operation in clinic, meanwhile engineering MSCsSC-Exos to realize targeted delivery of miR-199a-3p into chondrocytes exerted excellent therapeutic effects in OA animal model in vivo. Through combining MSCsSC-Exos therapy and miRNA therapy via an engineering approach, we develop an efficient MSCsSC-Exos-based strategy for OA therapy and promote the application of targeted-MSCsSC-Exos for drug delivery in the future.

Single-step ultra-purified alginate gel implantation in patients with knee chondral defects

Aims

Implantation of ultra-purified alginate (UPAL) gel is safe and effective in animal osteochondral defect models. This study aimed to examine the applicability of UPAL gel implantation to acellular therapy in humans with cartilage injury.

Methods

A total of 12 patients (12 knees) with symptomatic, post-traumatic, full-thickness cartilage lesions (1.0 to 4.0 cm²) were included in this study. UPAL gel was implanted into chondral defects after performing bone marrow stimulation technique, and assessed for up to three years postoperatively. The primary outcomes were the feasibility and safety of the procedure. The secondary outcomes were self-assessed clinical scores, arthroscopic scores, tissue biopsies, and MRI-based estimations.

Results

No obvious adverse events related to UPAL gel implantation were observed. Self-assessed clinical scores, including pain, symptoms, activities of daily living, sports activity, and quality of life, were improved significantly at three years after surgery. Defect filling was confirmed using second-look arthroscopy at 72 weeks. Significantly improved MRI scores were observed from 12 to 144 weeks postoperatively. Histological examination of biopsy specimens obtained at 72 weeks after implantation revealed an extracellular matrix rich in glycosaminoglycan and type II collagen in the reparative tissue. Histological assessment yielded a mean overall International Cartilage Regeneration & Joint Preservation Society II score of 69.1 points (SD 10.4; 50 to 80).

Conclusion

This study provides evidence supporting the safety of acellular UPAL gel implantation in facilitating cartilage repair. Despite being a single-arm study, it demonstrated the efficacy of UPAL gel implantation, suggesting it is an easy-to-use, one-step method of cartilage tissue repair circumventing the need to harvest donor cells.

Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

Clinical Trials with Mesenchymal Stem Cell Therapies for Osteoarthritis: Challenges in the Regeneration of Articular Cartilage

Osteoarthritis (OA) is a whole-joint disease primarily characterized by the deterioration of hyaline cartilage. Current treatments include microfracture and chondrocyte implantation as early surgical strategies that can be combined with scaffolds to repair osteochondral lesions; however, intra-articular (IA) injections or implantations of mesenchymal stem cells (MSCs) are new approaches that have presented encouraging therapeutic results in animal models and humans. We critically reviewed clinical trials with MSC therapies for OA, focusing on their effectiveness, quality, and outcomes in the regeneration of articular cartilage. Several sources of autologous or allogeneic MSCs were used in the clinical trials. Minor adverse events were generally reported, indicating that IA applications of MSCs are potentially safe. The evaluation of articular cartilage regeneration in human clinical trials is challenging, particularly in the inflammatory environment of osteoarthritic joints. Our findings indicate that IA injections of MSCs are efficacious in the treatment of OA and the regeneration of cartilage, but that they may be insufficient for the full repair of articular cartilage defects. The possible interference of clinical and quality variables in the outcomes suggests that robust clinical trials are still necessary for generating reliable evidence with which to support these treatments. We suggest that the administration of just-sufficient doses of viable cells in appropriate regimens is critical to achieve effective and durable effects. In terms of future perspectives, genetic modification, complex products with extracellular vesicles derived from MSCs, cell encapsulation in hydrogels, and 3D bioprinted tissue engineering are promising approaches with which to improve MSC therapies for OA.

Failure of cartilage regeneration: emerging hypotheses and related therapeutic strategies

Osteoarthritis (OA) is a disabling condition that affects billions of people worldwide and places a considerable burden on patients and on society owing to its prevalence and economic cost. As cartilage injuries are generally associated with the progressive onset of OA, robustly effective approaches for cartilage regeneration are necessary. Despite extensive research, technical development and clinical experimentation, no current surgery-based, material-based, cell-based or drug-based treatment can reliably restore the structure and function of hyaline cartilage. This paucity of effective treatment is partly caused by a lack of fundamental understanding of why articular cartilage fails to spontaneously regenerate. Thus, research studies that investigate the mechanisms behind the cartilage regeneration processes and the failure of these processes are critical to instruct decisions about patient treatment or to support the development of next-generation therapies for cartilage repair and OA prevention. This Review provides a synoptic and structured analysis of the current hypotheses about failure in cartilage regeneration, and the accompanying therapeutic strategies to overcome these hurdles, including some current or potential approaches to OA therapy.

Mesenchymal stem/stromal cells-derived extracellular vesicles as a potentially more beneficial therapeutic strategy than MSC-based treatment in a mild metabolic osteoarthritis model

BACKGROUND

Mesenchymal stromal/stem cells (MSCs) and MSC-derived extracellular vesicles (MSC-EVs) hold promise as a disease modifying treatment in osteoarthritis (OA). Obesity, and its associated inflammation, contribute to OA development and metabolic OA represents a specific and significant group of the OA patient population. Given their immunomodulatory properties, MSC and MSC-EVs are especially interesting for this group of patients as a therapeutic option. Here, we were the first to compare the therapeutic efficacy of MSCs and MSC-EVs in a mild OA model taking these metabolic aspects into consideration.

METHODS

Male Wistar-Han rats (Crl:WI(Han) (n = 36) were fed a high fat diet for 24 weeks, with unilateral induction of OA by groove surgery after 12 weeks. Eight days after surgery rats were randomized in three treatment groups receiving MSCs, MSC-EVs or vehicle injection. Pain-associated behavior, joint degeneration, and local and systemic inflammation were measured.

RESULTS

We demonstrated that despite not having a significant therapeutic effect, MSC-EV treatment results in lower cartilage degeneration, less pain behaviour, osteophytosis and joint inflammation, than MSC treatment. Suggesting that MSC-EVs could be a more promising therapeutic strategy than MSCs in this mild metabolic OA model.

CONCLUSION

In summary, we find that MSC treatment has negative effects on the joint in metabolic mild OA. This is an essential finding for the significant group of patients with metabolic OA phenotype, and might help to understand why clinical translation of MSC treatment shows varying therapeutic efficacy thus far. Our results also suggest that MSC-EV-based treatment might be a promising option for these patients, however MSC-EV therapeutic efficacy will need improvement.

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

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

Cartilage Tissue Engineering: An Introduction

Once damaged, cartilage has limited healing capability. This has led to a huge body of research that aims to repair or regenerate this important tissue. Despite the progress made, significant hurdles still need to be overcome. This chapter highlights some of the progress made, while elaborating on areas that need further research. The concept of translation and the route to clinical translation must be kept in mind if some of the promising preclinical research is to make it to routine clinical application.

Isolation of Chondrons from Hyaline Cartilage

In native healthy hyaline cartilage, the chondrocytes are surrounded by a pericellular matrix that has a distinct composition and function compared to the hyaline cartilage extracellular matrix. The chondrocyte together with its pericellular matrix is called a chondron. The type VI collagen, which is the main component of the pericellular matrix, is resistant to enzymatic digestion by pure collagenase and dispase that do digest the extracellular matrix. Therefore, this combination of enzymes can be used to enzymatically isolate chondrons from hyaline cartilage. Chondrons have a high potential for cartilage tissue engineering. This chapter describes in detail how chondrons can be isolated from hyaline cartilage for further use.

Potency Assay Considerations for Cartilage Repair, Osteoarthritis and Use of Extracellular Vesicles

Articular cartilage covers the ends of bones in synovial joints acting as a shock absorber that helps movement of bones. Damage of the articular cartilage needs treatment as it does not repair itself and the damage can progress to osteoarthritis. In osteoarthritis all the joint tissues are involved with characteristic progressive cartilage degradation and inflammation. Autologous chondrocyte implantation is a well-proven cell-based treatment for cartilage defects, but a main downside it that it requires two surgeries. Multipotent, aka mesenchymal stromal cell (MSC)-based cartilage repair has gained attention as it can be used as a one-step treatment. It is proposed that a combination of immunomodulatory and regenerative capacities make MSC attractive for the treatment of osteoarthritis. Furthermore, since part of the paracrine effects of MSCs are attributed to extracellular vesicles (EVs), small membrane enclosed particles secreted by cells, EVs are currently being widely investigated for their potential therapeutic effects. Although MSCs have entered clinical cartilage treatments and EVs are used in in vivo efficacy studies, not much attention has been given to determine their potency and to the development of potency assays. This chapter provides considerations and suggestions for the development of potency assays for the use of MSCs and MSC-EVs for the treatment of cartilage defects and osteoarthritis.

Alleviation of osteoarthritis by intra-articular transplantation of circulating mesenchymal stem cells

This study aimed to evaluate the efficacy of intra-articular delivery of peripheral blood derived mesenchymal stromal cells (PB-MSCs) on the progression of trauma-induced osteoarthritis (OA) in mice. Adult male C57BL/6J mice subjected to destabilization of the medial meniscus surgeries (DMM) were randomly divided into four groups: sham surgery group; vehicle control group (treated with saline), PBMSC-treated group, or adipose tissue derived MSCs (AD-MSC)-treated group (n = 4 per group). PB-MSCs and AD-MSCs were harvested and cultured following previously established protocols, and pre-labeled with BrdU for 48 h before transplantation. PB-MSCs or AD-MSCs (5 × 105 cells/mouse; passage 3-5) were intra-articular injected into the right knee joints thrice post-surgery. The mice were euthanized at 8 weeks post-surgery and knee joint samples were collected for micro-CT and histological examinations. PB-MSCs administration significantly reduced subchondral bone volume comparing to the vehicle control group. Safranin O staining showed that PB-MSCs treatment ameliorated degeneration of articular cartilage, which was comparable to AD-MSCs treatment. The expression of catabolic marker MMP13 was significantly reduced in articular cartilage of the PB-MSCs treated group comparing to that of the vehicle control group. Co-expression of BrdU and Sox9 indicated that injected PB-MSCs differentiated in chondrocytes in situ, along with reduced levels of IL-6 within peripheral sera of PB-MSCs- and AD-MSCs-treated mice. Therefore, administration of PB-MSCs or AD-MSCs attenuated trauma-induced OA progression through inhibiting cartilage degradation and inflammation. PB-MSCs are ideal cell source for treating cartilage-associated diseases.

Mitochondrial Transport from Mesenchymal Stromal Cells to Chondrocytes Increases DNA Content and Proteoglycan Deposition In Vitro in 3D Cultures

OBJECTIVE

Allogeneic mesenchymal stromal cells (MSCs) are used in the 1-stage treatment of articular cartilage defects. The aim of this study is to investigate whether transport of mitochondria exists between chondrocytes and MSCs and to investigate whether the transfer of mitochondria to chondrocytes contributes to the mechanism of action of MSCs.

DESIGN

Chondrocytes and MSCs were stained with MitoTracker, and CellTrace was used to distinguish between cell types. The uptake of fluorescent mitochondria was measured in cocultures using flow cytometry. Transport was visualized using fluorescence microscopy. Microvesicles were isolated and the presence of mitochondria was assessed. Mitochondria were isolated from MSCs and transferred to chondrocytes using MitoCeption. Pellets of chondrocytes, chondrocytes with transferred MSC mitochondria, and cocultures were cultured for 28 days. DNA content and proteoglycan content were measured. Mitochondrial DNA of cultured pellets and of repair cartilage tissue was quantified.

RESULTS

Mitochondrial transfer occurred bidirectionally within the first 4 hours until 16 hours of coculture. Transport took place via tunneling nanotubes, direct cell-cell contact, and extracellular vesicles. After 28 days of pellet culture, DNA content and proteoglycan deposition were higher in chondrocyte pellets to which MSC mitochondria were transferred than the control groups. No donor mitochondrial DNA was traceable in the biopsies, whereas an increase in MSC mitochondrial DNA was seen in the pellets.

CONCLUSIONS

These results suggest that mitochondrial transport plays a role in the chondroinductive effect of MSCs on chondrocytes in vitro. However, in vivo no transferred mitochondria could be traced back after 1 year.

Within or Without You? A Perspective Comparing In Situ and Ex Situ Tissue Engineering Strategies for Articular Cartilage Repair

Human articular cartilage has a poor ability to self-repair, meaning small injuries often lead to osteoarthritis, a painful and debilitating condition which is a major contributor to the global burden of disease. Existing clinical strategies generally do not regenerate hyaline type cartilage, motivating research toward tissue engineering solutions. Prospective cartilage tissue engineering therapies can be placed into two broad categories: i) Ex situ strategies, where cartilage tissue constructs are engineered in the lab prior to implantation and ii) in situ strategies, where cells and/or a bioscaffold are delivered to the defect site to stimulate chondral repair directly. While commonalities exist between these two approaches, the core point of distinction-whether chondrogenesis primarily occurs "within" or "without" (outside) the body-can dictate many aspects of the treatment. This difference influences decisions around cell selection, the biomaterials formulation and the surgical implantation procedure, the processes of tissue integration and maturation, as well as, the prospects for regulatory clearance and clinical translation. Here, ex situ and in situ cartilage engineering strategies are compared: Highlighting their respective challenges, opportunities, and prospects on their translational pathways toward long term human cartilage repair.

Single-Surgery Co-Implantation of Autologous Primary Articular Chondrocytes with Bone Marrow Cells in the Treatment of Articular Cartilage Lesions: Observations from the Operating Room on Tissue Input and Cell Output

OBJECTIVE

Single-surgery variants of autologous chondrocyte implantation to repair cartilage are emerging, but practical data on such procedures are scarce. We set out to describe a 1-stage autologous chondrocyte co-implantation procedure and include quantitative characteristics of the biopsy tissues collected and of the cells obtained from those tissues in the operating room.

DESIGN

Data concerning patient age, articular cartilage lesion size and location, as well as measurements of cartilage biopsy mass, bone marrow aspirate volume, and the cell yields harvested from those biopsies were intraoperatively collected for 141 patients.

RESULTS

The mean patient age was 35.7 ± 9.8 years, and the mean total lesion size was 4.0 ± 3.1 cm². Cartilage biopsy mass ranged from 0.19 to 2.0 gram and provided a mean yield of 1.23 × 10⁶ chondrocytes/gram. Bone marrow aspirate volume ranged from 7.2 to 62 milliliters and provided a mean yield of 7.18 × 10⁶ mononuclear cells/mL. The cell yields did not correlate with patient age, which ranged from 12 to 57 years. The mean primary chondrocyte supply was 272 thousand per cm² of lesion, ranging from 10.4 thousand to 1.07 million per cm². The total cell supply was kept at 9 million cells per cm² of lesion by adding mononuclear cells to the chondrocytes. The mean tissue processing time was 100 ± 19 minutes, which was frequently used to perform concurrent interventions.

CONCLUSION

Single-surgery co-implantation of clinically relevant numbers of autologous primary articular chondrocytes and bone marrow cells is feasible for a wide range of ages and lesion sizes.

PRISMA-Compliant Meta-Analysis of Randomized Controlled Trials on Osteoarthritis of Knee Managed with Allogeneic vs Autologous MSCs: Efficacy and Safety Analysis

Study Design

Meta-analysis.

Objectives

Our objective is to review the randomized controlled trials (RCTs) that have been conducted previously on the topic of osteoarthritis of the knee to assess and compare the efficacy and safety of autologous and allogeneic sources of mesenchymal stromal cells (MSCs) in the treatment of osteoarthritis.

Materials and methods

We searched the electronic databases PubMed, Embase, Web of Science, and the Cochrane Library until August 2021 for randomised controlled trials (RCTs) analysing the efficacy and safety of autologous and allogeneic sources of MSCs in the management of knee osteoarthritis. These searches were conducted independently and in duplicate. The outcomes that were taken into consideration for analysis were the visual analogue score (VAS) for pain, the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), the Lysholm score, and adverse events. The OpenMeta [Analyst] software was utilised to carry out the analysis in the R platform.

Results

In total, 21 studies with a total of 936 patients were considered for this analysis. Because none of the studies made a direct comparison of the autologous and allogeneic sources of MSCs, we pooled the results of all of the included studies of both sources and made a comparative analysis of how the two types of MSCs fared in their respective applications. Although both allogeneic and autologous sources of MSCs demonstrated significantly better VAS improvement after 6 months (p = 0.006, p = 0.001), this trend was not maintained after 1 year for the allogeneic source (p = 0.171, p = 0.027). When compared to their respective controls based on WOMAC scores after 1 year, autologous sources (p = 0.016) of MSCs performed better than allogeneic sources (p = 0.186).A similar response was noted between the sources at 2 years in their Lysholm scores (p = 0.682, p = 0.017), respectively. Moreover, allogeneic sources (p = 0.039) of MSCs produced significant adverse events than autologous sources (p = 0.556) compared to their controls.

Conclusion

Our analysis of literature showed that autologous sources of MSCs stand superior to allogeneic sources of MSC with regard to their consistent efficacy for pain, functional outcomes, and safety. However, we strongly recommend that further studies be conducted that are of a high enough quality to validate our findings and reach a consensus on the best source of MSCs for use in cellular therapy treatments for knee osteoarthritis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43465-022-00751-z.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Modification of mesenchymal stem cells for cartilage-targeted therapy

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the destruction of the articular cartilage, sclerosis of the subchondral bone, and joint dysfunction. Its pathogenesis is attributed to direct damage and mechanical destruction of joint tissues. Mesenchymal stem cells (MSCs), suggested as a potential strategy for the treatment of OA, have shown therapeutic effects on OA. However, the specific fate of MSCs after intraarticular injection, including cell attachment, proliferation, differentiation, and death, is still unclear, and there is no guarantee that stem cells can be retained in the cartilage tissue to enact repair. Direct homing of MSCs is an important determinant of the efficacy of MSC-based cartilage repair. Recent studies have revealed that the unique homing capacity of MSCs and targeted modification can improve their ability to promote tissue regeneration. Here, we comprehensively review the homing effect of stem cells in joints and highlight progress toward the targeted modification of MSCs. In the future, developments of this targeting system that accelerate tissue regeneration will benefit targeted tissue repair.

Prognostic factors for the management of chondral defects of the knee and ankle joint: a systematic review

Purpose

Different surgical techniques to manage cartilage defects are available, including microfracture (MFx), autologous chondrocyte implantation (ACI), osteoarticular auto- or allograft transplantation (OAT), autologous matrix-induced chondrogenesis (AMIC). This study investigated the patient-related prognostic factors on the clinical outcomes of surgically treated knee and ankle cartilage defects.

Methods

This study followed the PRISMA statement. In May 2022, the following databases were accessed: PubMed, Google Scholar, Embase, and Scopus. All the studies investigating the outcomes of surgical management for knee and/or talus chondral defects were accessed. Only studies performing mesenchymal stem cells transplantation, OAT, MFx, ACI, and AMIC were considered. A multiple linear model regression analysis through the Pearson Product–Moment Correlation Coefficient was used.

Results

Data from 184 articles (8905 procedures) were retrieved. Female sex showed a positive moderate association with visual analogue scale at last follow-up (P = 0.02). Patient age had a negative association with the American Orthopaedic Foot and Ankle Score (P = 0.04) and Lysholm Knee Scoring Scale (P = 0.03). BMI was strongly associated with graft hypertrophy (P = 0.01). Greater values of VAS at baseline negatively correlate with lower values of Tegner Activity Scale at last follow-up (P < 0.0001).

Conclusion

The clinical outcomes were mostly related to the patients’ performance status prior surgery. A greater BMI was associated with greater rate of hypertrophy. Female sex and older age evidenced fair influence, while symptom duration prior to the surgical intervention and cartilage defect size evidenced no association with the surgical outcome. Lesion size and symptom duration did not evidence any association with the surgical outcome.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Therapeutic Use and in Bioengineering Applications

Extracellular vesicles (EVs) are small lipid bilayer-delimited particles that are naturally released from cells into body fluids, and therefore can travel and convey regulatory functions in the distal parts of the body. EVs can transmit paracrine signaling by carrying over cytokines, chemokines, growth factors, interleukins (ILs), transcription factors, and nucleic acids such as DNA, mRNAs, microRNAs, piRNAs, lncRNAs, sn/snoRNAs, mtRNAs and circRNAs; these EVs travel to predecided destinations to perform their functions. While mesenchymal stem cells (MSCs) have been shown to improve healing and facilitate treatments of various diseases, the allogenic use of these cells is often accompanied by serious adverse effects after transplantation. MSC-produced EVs are less immunogenic and can serve as an alternative to cellular therapies by transmitting signaling or delivering biomaterials to diseased areas of the body. This review article is focused on understanding the properties of EVs derived from different types of MSCs and MSC-EV-based therapeutic options. The potential of modern technologies such as 3D bioprinting to advance EV-based therapies is also discussed.

Mesenchymal stem cells augmentation for surgical procedures in patients with symptomatic chondral defects of the knee: a systematic review

Background

The efficacy and safety profile of mesenchymal stem cells (MSCs) augmentation in chondral procedures are controversial. This systematic review updated the current evidence on MSCs augmentation for chondral procedures in patients with symptomatic chondral defects of the knee.

Methods

This study followed the PRISMA guidelines. The literature search was updated in August 2022. Two independent authors accessed PubMed, Google scholar, Embase, and Scopus. No additional filters or time constrains were used for the search. A cross reference of the bibliographies was also performed. All the clinical studies investigating surgical procedures for chondral defects of the knee augmented with MSCs were accessed. Defects of both tibiofemoral and patellofemoral joints were included. The following patient reported outcomes measures (PROMs) were retrieved at baseline and last follow-up: Visual Analogic Scale (VAS), Tegner Activity Scale, Lysholm Knee Scoring System, International Knee Documentation Committee (IKDC). Return to daily activities and data on hypertrophy, failure, revision surgery were also collected. Failures were defined as the recurrence of symptoms attributable to the index procedure. Revisions were defined as any reoperation at the site of the index procedure.

Results

A total of 15 clinical studies (411 procedures) were included. Patients returned to their prior sport activity at 2.8 ± 0.4 months. All the PROMs improved at last follow-up: Tegner (P = 0.0002), Lysholm (P < 0.0001), the IKDC (P < 0.0001), VAS (P < 0.0001). At a mean of 30.1 ± 13.9 months, 3.1% (2 of 65 patients) reported graft hypertrophy, 3.2% (2 of 63) were considered failures. No surgical revision procedures were reported. Given the lack of available quantitative data for inclusion, a formal comparison of surgical procedures was not conducted.

Conclusion

MSCs augmentation in selected chondral procedures could be effective, with a low rate of complications. Further investigations are required to overcome the current limitations to allow the clinical translation of MSCs in regenerative medicine.

Improved biological performance of human cartilage-derived progenitors in platelet lysate xenofree media in comparison to fetal bovine serum media

Primary articular cartilage-derived cells are among the preferred contenders for cell-based therapy approaches for cartilage repair. Limited access to primary human cartilage tissue necessitates the process of in vitro cell expansion to obtain sufficient cells for therapeutic purposes. Therapeutic outcomes of such cell-based approaches become highly dependent on the quality of the in vitro culture-expanded cells. The objective of this study was to determine the differential biological effects of human platelet lysate (hPL) xeno-free defined media vs FBS containing traditional media on primary human cartilage-derived cells. Our goal in pursuing this work was to identify a preferred xenofree media alternative, that can be used as a platform for expansion of cells intended for clinical applications. Primary cartilage-derived cells obtained from five patients were simultaneously cultured in two expansion media's: (1) traditional (DMEM+10%FBS+1%P/S) and (2) defined xenofree (Nutristem® complete media+0.5%hPL). Connective tissue progenitors (CTPs) were assayed by standard colony forming unit assay, morphology, proliferation in early and late passages, expression of MSC associated cell-surface markers (CD73, CD90 and CD105) and trilineage differentiation (adipogenesis, osteogenesis and chondrogenesis) were considered for comparison of biological performance. Early biological performance of primary cartilage-derived cells was significantly improved in Nutristem® expansion media in comparison to traditional expansion media with respect to (1) Colony forming efficiency tended to be higher (p = 0.058) and (2) CTPs formed larger colonies with respect to total cells per colony and colony area (p < 0.01). In the culture expanded cell population, Nutristem® expansion media was superior to traditional expansion media with respect to: (1) overall proliferation rate through passages 1-4 (p = 0.027), (2) total cells harvested at end of passage 4 (p = 0.028) and (3) total positive stain area of CD73 (p = 0.006), CD90 (p = 0.001) and CD105 (p = 0.049). Nutristem®-hPL expanded cells when differentiated in respective xenofree serum-free defined MSCgo™ differentiated media's, also showed significant improvement in adipogenic, osteogenic and chondrogenic marker expression. Overall, we convincingly demonstrated that a low concentration of hPL in combination with defined xenofree media is an effective and economic growth supplement to culture expand primary cartilage-derived cells. It can be manufactured under cGMP conditions to improve clinical-grade cell products' quality for therapeutic applications.

Mechanically Derived Tissue Stromal Vascular Fraction Acts Anti-inflammatory on TNF Alpha-Stimulated Chondrocytes In Vitro

Enzymatically isolated stromal vascular fraction (SVF) has already shown to be effective as a treatment for osteoarthritis (OA). Yet, the use of enzymes for clinical purpose is highly regulated in many countries. Mechanical preparation of SVF results in a tissue-like SVF (tSVF) containing intact cell−cell connections including extracellular matrix (ECM) and is therefore less regulated. The purpose of this study was to investigate the immunomodulatory and pro-regenerative effect of tSVF on TNFα-stimulated chondrocytes in vitro. tSVF was mechanically derived using the Fractionation of Adipose Tissue (FAT) procedure. Characterization of tSVF was performed, e.g., cellular composition based on CD marker expression, colony forming unit and differentiation capacity after enzymatic dissociation (from heron referred to as tSVF-derived cells). Different co-cultures of tSVF-derived cells and TNFα-stimulated chondrocytes were analysed based on the production of sulphated glycosaminoglycans and the anti-inflammatory response of chondrocytes. Characterization of tSVF-derived cells mainly contained ASCs, endothelial cells, leukocytes and supra-adventitial cells. tSVF-derived cells were able to form colonies and differentiate into multiple cell lineages. Co-cultures with chondrocytes resulted in a shift of the ratio between tSVF cells: chondrocytes, in favor of chondrocytes alone (p < 0.05), and IL-1β and COX2 gene expression was upregulated in TNFα-treated chondrocytes. After treatment with (a conditioned medium of) tSVF-derived cells, IL-1β and COX2 gene expression was significantly reduced (p < 0.01). These results suggest mechanically derived tSVF stimulates chondrocyte proliferation while preserving the function of chondrocytes. Moreover, tSVF suppresses TNFα-stimulated chondrocyte inflammation in vitro. This pro-regenerative and anti-inflammatory effect shows the potential of tSVF as a treatment for osteoarthritis.

In Vitro and Ectopic In Vivo Studies toward the Utilization of Rapidly Isolated Human Nasal Chondrocytes for Single-Stage Arthroscopic Cartilage Regeneration Therapy

Nasal chondrocytes (NCs) have a higher and more reproducible chondrogenic capacity than articular chondrocytes, and the engineered cartilage tissue they generate in vitro has been demonstrated to be safe in clinical applications. Here, we aimed at determining the feasibility for a single-stage application of NCs for cartilage regeneration under minimally invasive settings. In particular, we assessed whether NCs isolated using a short collagenase digestion protocol retain their potential to proliferate and chondro-differentiate within an injectable, swiftly cross-linked and matrix-metalloproteinase (MMP)-degradable polyethylene glycol (PEG) gel enriched with human platelet lysate (hPL). NC-hPL-PEG gels were additionally tested for their capacity to generate cartilage tissue in vivo and to integrate into cartilage/bone compartments of human osteochondral plugs upon ectopic subcutaneous implantation into nude mice. NCs isolated with a rapid protocol and embedded in PEG gels with hPL at low cell density were capable of efficiently proliferating and of generating tissue rich in glycosaminoglycans and collagen II. NC-hPL-PEG gels developed into hyaline-like cartilage tissues upon ectopic in vivo implantation and integrated with surrounding native cartilage and bone tissues. The delivery of NCs in PEG gels containing hPL is a feasible strategy for cartilage repair and now requires further validation in orthotopic in vivo models.

Cell therapies for chondral defects of the talus: a systematic review

Background

This systematic review investigated the efficacy and safety of surgical procedures augmented with cell therapies for chondral defects of the talus.

Methods

The present systematic review was conducted according to the 2020 PRISMA guidelines. PubMed, Google scholar, Embase, and Scopus databases were accessed in March 2022. All the clinical trials investigating surgical procedures for talar chondral defects augmented with cell therapies were accessed. The outcomes of interest were to investigate whether surgical procedures augmented with cell therapies promoted improvement in patients reported outcomes measures (PROMs) with a tolerable rate of complications.

Results

Data from 477 procedures were retrieved. At a mean follow-up of 34.8 ± 9.7 months, the Visual Analogic Scale (VAS) improved of 4.4/10 (P = 0.002) and the American Orthopaedic Foot and Ankle Score (AOFAS) of 31.1/100 (P = 0.0001) points. No improvement was found in Tegner score (P = 0.4). Few articles reported data on complications. At last follow-up, the rate of reoperation and failure were 0.06% and 0.03%, respectively. No graft delamination or hypertrophy was observed.

Conclusion

The current evidence suggests that cell therapies may be effective and safe to enhance surgical procedures for chondral defects of the talus. These results should be considered within the limitations of the present study. The current literature should be enriched with randomized controlled clinical trials with larger population size and longer follow-up.

The 50 most-cited clinical articles in cartilage surgery research: a bibliometric analysis

PURPOSE

Articular cartilage lesions remain a challenge for orthopedic surgeons. The identification of the most important articles can help identifying the most influential techniques of the past, the current prevalent focus, and emerging strategies. The aim of this study was to identify milestones and trends in cartilage research.

METHODS

This study is a bibliometric analysis based on published articles. All citation count data included in the "Scopus database" were used to identify eligible studies up to December 2020. The 50 most-cited articles on cartilage surgery were ranked based on the citation count and analyzed regarding citation density and quality (Coleman score and RoB 2.0 tool). A further search was performed to identify the most promising clinical studies among the latest publications on cartilage surgery.

RESULTS

Different kinds of cartilage treatments were investigated in the 50 most-cited clinical articles. Regenerative techniques with chondrocytes were the most reported with a total of 23 articles, followed by microfracture technique in 17 articles and mosaicplasty or osteochondral autograft transplantation (OAT) in 11. Forty-five articles focused on the knee. A higher citation density was found in the most recent articles (p = 0.004). The study of the most promising landmarks of the most recent articles showed new cell-free or tissue engineering-based procedures and an overall increasing quality of the published studies.

CONCLUSION

This bibliometric analysis documented an increasing interest in cartilage surgery, with efforts toward high-quality studies. Over the years, the focus switched from reconstructive toward regenerative techniques, with emerging options including cell-free and tissue-engineering strategies to restore the cartilage surface.

LEVEL OF EVIDENCE

IV.

Extracellular Vesicles from Hypoxic Pretreated Urine-Derived Stem Cells Enhance the Proliferation and Migration of Chondrocytes by Delivering miR-26a-5p

OBJECTIVE

Stem-cell therapy is a promising treatment for cartilage defects. The newly identified urine-derived stem cells (USCs), which have multipotency and sufficient proliferative ability, are promising candidates for several tissue engineering therapies. In this study, we investigated the role of USC extracellular vehicles (EVs) in promoting the proliferation and migration of chondrocytes.

DESIGN

USCs were characterized by measuring induced multipotent differentiation and flow cytometry analysis of surface marker expression. The EVs were isolated from USCs under normoxic conditions (nor-EVs) and hypoxic conditions (hypo-EVs). Transmission electron microscopy and western blot analysis characterized the EVs. The chondrocytes were cultured in the USC-EVs. CCK-8 assay and EdU staining detected the proliferation of chondrocytes, and transwell assay detected their migration. miR-26a-5p expression in EVs was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The target relationship of miR-26a-5p and phosphatase and tensin homolog (PTEN) was predicted and confirmed. The roles of EVs-miR-26a-5p and PTEN on the proliferation and migration of chondrocytes were also investigated.

RESULTS

Hypo-EVs showed a superior effect in promoting the proliferation and migration of chondrocytes than nor-EVs. Mechanistically, USC-EVs delivered miR-26a-5p into chondrocytes to overexpress miR-26a-5p. PTEN was identified as an miR-26a-5p target in chondrocytes. The effects of EVs-miR-26a-5p on promoting the proliferation and migration of chondrocytes were mediated by its regulation of PTEN.

CONCLUSION

Our study suggested that hypoxic USC-EVs may represent a promising strategy for osteoarthritis by promoting the proliferation and migration of chondrocytes via miR-26a-5p transfer.

Safety and Efficacy of Injecting Mesenchymal Stem Cells Into a Human Knee Joint To Treat Osteoarthritis: A Systematic Review

Intraarticular stem cell therapy has become increasingly used to treat knee osteoarthritis (KOA) with minimal high-quality evidence to support its use. This study aims to see how well intra-articular injections of mesenchymal stem cells (MSCs) worked and how safe they were for individuals with KOA. A total of 10 studies were extracted using PubMed, Cochrane Library, and PMC from 2017 to 2021 in the English language. An assessment of the risk of bias was applied via the Cochrane Collaborative Bias Risk Tool and Newcastle-Ottawa Quality. Changes in pain and functional outcomes in patients with KOA were measured by a Knee injury and Osteoarthritis Outcome Score (KOOS) scores, Visual Analogue Scale (VAS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at baseline, and follow-up evaluation criteria. The magnetic resonance imaging (MRI) was evaluated using the whole-organ magnetic resonance imaging score (WORMS) and cartilage volume changes. A total of six randomized controlled trials (RCTs), three prospective retrospective clinical trials, and one retrospective clinical trial included 723 patients. They were diagnosed with unilateral or bilateral KOA with Kellgren-Lawrence (KL) grade 1-4 KOA and followed up for six, 12, and 24 months. The experimental groups received multipotent MSCs, mesenchymal progenitor cells (MPCs), adipose tissue progenitor stem cells (AD-MPCs), adipose tissue mesenchymal stem cells (AD-MSCs), bone marrow mesenchymal stem cells (BM-MSCs), bone marrow aspiration (BMA), bone marrow aspiration concentration (BMAC), or micro fragmented adipose tissue (MFAT) while the controlled groups received normal saline (NS), hyaluronic acid (HA), placebo, or went through conservative management. In conclusion, significant improvements were noticed in the MSCs groups via different outcome measuring tools like KOOS, VAS, WOMAC, and MRI. Furthermore, no significant adverse events (AEs) have been observed. Therefore, intra-articular injections of MSCs are effective and safe in relieving pain and improving motor function in individuals with KOA in the short term, contrary to earlier research findings.

Does the Choice of Acellular Scaffold and Augmentation With Bone Marrow Aspirate Concentrate Affect Short-term Outcomes in Cartilage Repair? A Systematic Review and Meta-analysis

BACKGROUND

Matrix-induced chondrogenesis (MIC) is a promising treatment option for critical-size cartilage lesions of the knee; however, there exists substantial heterogeneity in the choice of acellular scaffold matrix for MIC cartilage repairs.

HYPOTHESIS

The choice of acellular matrix will not affect patient outcomes after MIC cartilage repair procedures, and the addition of concentrated bone marrow aspirate (cBMA) will improve short-term patient outcomes regardless of matrix choice.

STUDY DESIGN

Meta-analysis; Level of evidence, 4.

METHODS

Studies were stratified by matrix type: multilayered, single layered, and gel based. Continuous outcomes were analyzed with pairwise meta-analysis using the inverse variance model with random effects applied. Binary outcomes were analyzed as pooled proportions in a single-arm fashion; after which, reconstruction of relative risks (RRs) with confidence intervals was performed using the Katz logarithmic method.

RESULTS

A total of 876 patients were included: 469 received multilayered bioscaffolds; 238, gel-based scaffolds; and 169, single-layered scaffolds. The mean age of patients was 36.2 years (95% CI, 33.9 to 38.4), while the mean lesion size was 3.91 cm² (95% CI, 3.40 to 4.42). The weighted mean follow-up was 23.8 months (95% CI, 20.1 to 27.6). Multilayered bioscaffolds were most effective at improving visual analog scale scores (P = .03; weighted mean difference [WMD], -4.44 [95% CI, -4.83 to -4.06]; P < .001). There were significantly lower risks of incomplete defect filling for gel-based scaffolds when compared with multilayered scaffolds (RR, 0.78 [95% CI, 0.69 to 0.88]; P < .001) and single-layered scaffolds (RR, 0.58 [95% CI, 0.41 to 0.81]; P = .001). Augmentation with cBMA further improved clinical scores across all scaffolds, with significant improvements in Tegner score (P = .02), while decreasing incomplete defect filling rates as well. There was significantly greater improvement in visual analog scale scores (P = .01) for single-layered scaffolds with cBMA augmentation (WMD, -4.88 [95% CI, -5.38 to -4.37]; P < .001) as compared with single-layered scaffolds without cBMA augmentation (WMD, -4.08 [95% CI, -4.46 to -3.71]; P < .001). All significant improvements were below their respective minimum clinically important differences.

CONCLUSION

While cartilage repair with acellular scaffolds provides significant improvements in pain and function for patients, there is insufficient clinical evidence to suggest which scaffold material is the most superior in influencing such improvements. The enhancement of cartilage repair procedures with cBMA may provide further functional improvements and improve defect filling; however, more long-term evidence is required to evaluate the effects.

The promising role of autologous and allogeneic mesenchymal stromal cells in managing knee osteoarthritis. What is beyond Mesenchymal stromal cells?

Mesenchymal stromal cells (MSCs) express a wide range of properties anticipated to be beneficial for treating genetic, mechanical, and age-related degeneration in diseases such as osteoarthritis (OA). Although contemporary conservative management of OA is successful in many patients with mild-moderate OA, it often fails to improve symptoms in many patients who are not a candidate for any surgical management. Further, existing conservative treatment strategies do not prevent the progression of the disease and therefore fail to provide a long-term pain-free life. On the other hand, tremendous progress has been taking place in the exciting field of regenerative medicine involving MSCs (autologous and allogeneic), with promising translation taking place from basic science to the bedside. In this review, we comprehensively discuss the potential role of MSCs in treating OA, both autologous and off-the-shelf, allogeneic stem cells. Further, newer therapies are in the offing to treat OA, such as exosomes and growth factors.

Insights into the present and future of cartilage regeneration and joint repair

Knee osteoarthritis is the most common joint disease. It causes pain and suffering for affected patients and is the source of major economic costs for healthcare systems. Despite ongoing research, there is a lack of knowledge regarding disease mechanisms, biomarkers, and possible cures. Current treatments do not fulfill patients' long-term needs, and it often requires invasive surgical procedures with subsequent long periods of rehabilitation. Researchers and companies worldwide are working to find a suitable cell source to engineer or regenerate a functional and healthy articular cartilage tissue to implant in the damaged area. Potential cell sources to accomplish this goal include embryonic stem cells, mesenchymal stem cells, or induced pluripotent stem cells. The differentiation of stem cells into different tissue types is complex, and a suitable concentration range of specific growth factors is vital. The cellular microenvironment during early embryonic development provides crucial information regarding concentrations of signaling molecules and morphogen gradients as these are essential inducers for tissue development. Thus, morphogen gradients implemented in developmental protocols aimed to engineer functional cartilage tissue can potentially generate cells comparable to those within native cartilage. In this review, we have summarized the problems with current treatments, potential cell sources for cell therapy, reviewed the progress of new treatments within the regenerative cartilage field, and highlighted the importance of cell quality, characterization assays, and chemically defined protocols.

Enhanced chondrogenesis from chondrocytes co-cultured on mesenchymal stromal cells: Implication for cartilage repair

Cellular therapy based on chondrocytes implantation is the most widely used procedure for inducing cartilage regeneration. However, the dedifferentiation process that these cells suffer and their limited capacity of proliferation, when they are cultured in vitro, restrict their use in cellular therapy protocols. To investigate the capacity of mesenchymal stromal cells (MSCs) to promote chondrogenesis from chondrocytes or chondrons in 2D and 3D coculture systems. Murine chondrocytes and chondrons were cocultured with MSCs at different cell ratios (100/0, 50/50, 70/30, 0/100) in two-dimensional (2D) and three-dimensional (3D) culture systems. High proliferation of cells with chondrocyte morphology, enhanced GAG production and expression of cartilage genes (aggrecan, type II collagen, and SOX-9) were observed in chondrocytes/MSCs cocultures. In contrast, fibroblastoid cells, down-regulation of cartilage gene expression and reduction of GAG production were observed in chondrons/MSCs cocultures. Chondrocytes within cartilage lacunae and surrounded by extracellular matrix were observed in chondrocytes/MSC pellets. MSCs promote the proliferation of functional chondrocytes in 2D and 3D culture systems. Transplantation of chondrogenic construct based on MSCs and chondrocytes may constitute a potential treatment for inducing cartilage repair.

Smart Bioinks for the Printing of Human Tissue Models

3D bioprinting has tremendous potential to revolutionize the field of regenerative medicine by automating the process of tissue engineering. A significant number of new and advanced bioprinting technologies have been developed in recent years, enabling the generation of increasingly accurate models of human tissues both in the healthy and diseased state. Accordingly, this technology has generated a demand for smart bioinks that can enable the rapid and efficient generation of human bioprinted tissues that accurately recapitulate the properties of the same tissue found in vivo. Here, we define smart bioinks as those that provide controlled release of factors in response to stimuli or combine multiple materials to yield novel properties for the bioprinting of human tissues. This perspective piece reviews the existing literature and examines the potential for the incorporation of micro and nanotechnologies into bioinks to enhance their properties. It also discusses avenues for future work in this cutting-edge field.

Small Extracellular Vesicles from Human Amniotic Fluid Samples as Promising Theranostics

Since the first evidence that stem cells can provide pro-resolving effects via paracrine secretion of soluble factors, growing interest has been addressed to define the most ideal cell source for clinical translation. Leftover or clinical waste samples of human amniotic fluid obtained following prenatal screening, clinical intervention, or during scheduled caesarean section (C-section) delivery at term have been recently considered an appealing source of mesenchymal progenitors with peculiar regenerative capacity. Human amniotic fluid stem cells (hAFSC) have been demonstrated to support tissue recovery in several preclinical models of disease by exerting paracrine proliferative, anti-inflammatory and regenerative influence. Small extracellular vesicles (EVs) concentrated from the hAFSC secretome (the total soluble trophic factors secreted in the cell-conditioned medium, hAFSC-CM) recapitulate most of the beneficial cell effects. Independent studies in preclinical models of either adult disorders or severe diseases in newborns have suggested a regenerative role of hAFSC-EVs. EVs can be eventually concentrated from amniotic fluid (hAF) to offer useful prenatal information, as recently suggested. In this review, we focus on the most significant aspects of EVs obtained from either hAFSC and hAF and consider the current challenges for their clinical translation, including isolation, characterization and quantification methods.

OUP accepted manuscript

Mesenchymal progenitor cells (MPCs) have shown promise initiating articular cartilage repair, with benefits largely attributed to the trophic factors they secrete. These factors can be found in the conditioned medium (CM) collected from cell cultures, and it is believed that extracellular vesicles (EVs) within this CM are at least partially responsible for MPC therapeutic efficacy. This study aimed to examine the functionality of the EV fraction of CM compared to whole CM obtained from human adipose-derived MPCs in an in vivo murine cartilage defect model. Mice treated with whole CM or the EV fraction demonstrated an enhanced cartilage repair score and type II collagen deposition at the injury site compared to saline controls. We then developed a scalable bioprocess using stirred suspension bioreactors (SSBs) to generate clinically relevant quantities of MPC-EVs. Whereas static monolayer culture systems are simple to use and readily accessible, SSBs offer increased scalability and a more homogenous environment due to constant mixing. This study evaluated the biochemical and functional properties of MPCs and their EV fractions generated in static culture versus SSBs. Functionality was assessed using in vitro MPC chondrogenesis as an outcome measure. SSBs supported increased MPC expression of cartilage-specific genes, and EV fractions derived from both static and SSB culture systems upregulated type II collagen production by MPCs. These results suggest that SSBs are an effective platform for the generation of MPC-derived EVs with the potential to induce cartilage repair.

Scientific Developments and Clinical Applications Utilizing Chondrons and Chondrocytes with Matrix for Cartilage Repair

Injuries to articular cartilage of the knee are increasingly common. The operative management of these focal chondral lesions continues to be problematic for the treating orthopedic surgeon secondary to the limited regenerative capacity of articular cartilage. The pericellular matrix (PCM) is a specialized, thin layer of the extracellular matrix that immediately surrounds chondrocytes forming a unit together called the chondron. The advancements in our knowledge base with regard to the PCM/chondrons as well as interterritorial matrix has permeated and led to advancements in product development in conjunction with minced cartilage, marrow stimulation, osteochondral allograft, and autologous chondrocyte implantation (ACI). This review intends to summarize recent progress in chondrocytes with matrix research, with an emphasis on the role the PCM/extracellular matrix (ECM) plays for favorable chondrogenic gene expression, as a barrier/filtration unit, and in osteoarthritis. The bulk of the review describes cutting-edge and evolving clinical developments and discuss these developments in light of underlying basic science applications. Clinical applications of chondrocytes with matrix science include Reveille Cartilage Processor, Cartiform, and ACI with Spherox (which was recently recommended for the treatment of grade III or IV articular cartilage defects over 2 cm² by the National Institute of Health and Care Excellence [NICE] in the United Kingdom). The current article presents a comprehensive overview of both the basic science and clinical results of these next-generation cartilage repair techniques by focusing specifically on the scientific evolution in each category as it pertains with underlying chondrocytes with matrix theory.

Maintenance and Acceleration of Pericellular Matrix Formation within 3D Cartilage Cell Culture Models

OBJECTIVE

In native articular cartilage, chondrocytes are surrounded by a thin pericellular matrix (PCM) forming chondrons. The PCM is exclusively rich in type VI collagen. The retention of the PCM has a significant influence on the metabolic activity of the chondrocytes.

DESIGN

This study investigated the influence of 2 hydrogels (hyaluronic acid [HA] and agarose) and 2 media compositions (basal and chondrogenic) on the preservation/maintenance and acceleration of PCM formation over a 21-day time course. Different combinations of chondrocytes, chondrons, and mesenchymal stem cells (MSCs) were studied.

RESULTS

Both hydrogels preserved chondrons PCM from day 1 up to 21-day culture regardless of media composition. Type VI collagen immunostaining of the cultured chondrons appeared both dense and homogenous. The presence of MSCs did not influence this outcome. At day 1, type VI collagen was not present around chondrocytes alone or their co-culture with MSCs. In the HA hydrogel, type VI collagen was located within the PCM after 7 days in both mono- and co-cultures. In the agarose hydrogel, collagen VI was located within the PCM at 7 days (co-cultures) and 14 days (monocultures). In both hydrogel systems, chondrogenic media enhanced the production of key extracellular matrix components in both mono- and co-cultures in comparison to basal media (11.5% and 14% more in glycosaminoglycans and type II collagen for chondrocytes samples at day 21 culture samples, respectively). However, the media types did not enhance type VI collagen synthesis.

CONCLUSION

Altogether, a 3D chondrogenic hydrogel environment is the primary condition for maintenance and acceleration of PCM formation.

Autophagy Is Involved in Mesenchymal Stem Cell Death in Coculture with Chondrocytes

OBJECTIVE

Cartilage formation is stimulated in mixtures of chondrocytes and human adipose-derived mesenchymal stromal cells (MSCs) both in vitro and in vivo. During coculture, human MSCs perish. The goal of this study is to elucidate the mechanism by which adipose tissue-derived MSC cell death occurs in the presence of chondrocytes.

METHODS

Human primary chondrocytes were cocultured with human MSCs derived from 3 donors. The cells were cultured in monoculture or coculture (20% chondrocytes and 80% MSCs) in pellets (200,000 cells/pellet) for 7 days in chondrocyte proliferation media in hypoxia (2% O₂). RNA sequencing was performed to assess for differences in gene expression between monocultures or coculture. Immune fluorescence assays were performed to determine the presence of caspase-3, LC3B, and P62.

RESULTS

RNA sequencing revealed significant upregulation of >90 genes in the 3 cocultures when compared with monocultures. STRING analysis showed interconnections between >50 of these genes. Remarkably, 75% of these genes play a role in cell death pathways such as apoptosis and autophagy. Immunofluorescence shows a clear upregulation of the autophagic machinery with no substantial activation of the apoptotic pathway.

CONCLUSION

In cocultures of human MSCs with primary chondrocytes, autophagy is involved in the disappearance of MSCs. We propose that this sacrificial cell death may contribute to the trophic effects of MSCs on cartilage formation.