Toll-like receptor-mediated signaling in human adipose-derived stem cells: implications for immunogenicity and immunosuppressive potential

Enhancing Gingival-Derived Mesenchymal Stem Cell Potential in Tissue Engineering and Regenerative Medicine Through Paraprobiotics

Gingival-derived mesenchymal stem cells (GMSCs) stand for a unique source of mesenchymal stem cells (MSCs) isolated from a neural crest origin with potential application in regenerative medicine. However, there are some limitations to the usage of these cells in clinical cell therapy such as reduced cell number and undesirable differentiation of the cell throughout frequent passages. Nowadays, studies have applied manipulation strategies to improve MSCs' effectiveness in clinical therapy. Among all of the materials used for this purpose, there is a growing trend for the use of biomaterials such as probiotic extracts or their conditioned media due to their lower toxicity. In the present study, we utilized extracts from Lactobacillus reuteri and Lactobacillus rhamnosus to assess their potential to enhance the function of GMSCs. We compared the effectiveness of these bacterial extracts to determine their relative efficacy. Bacterial extracts of two lactic acid bacteria were prepared using an ultrasonic homogenizing device. The impact of these bacterial extracts on GMSCs was evaluated through Alizarin Red and Oil Red O staining, cell counting by Trypan Blue staining, and real-time polymerase chain reaction. The findings of our study indicate that the administration of 50 μg/mL L. rhamnosus extract resulted in a greater enhancement of stemness marker expression, osteogenic differentiation, and proliferation of GMSCs compared with an equivalent concentration of L. reuteri extract. Neither of these bacterial extracts revealed any effect on the differentiation of the GMSCs into the adipogenic lineage. These findings suggest that L. rhamnosus extract could be more effective at promoting GMSCs' efficacy in tissue engineering and regenerative medicine.

Factors Defining Human Adipose Stem/Stromal Cell Immunomodulation in Vitro

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

The effect of TLR3 priming conditions on MSC immunosuppressive properties

BACKGROUND

Mesenchymal stromal cells (MSCs) have regenerative and immunomodulatory properties, making them suitable for cell therapy. Toll-like receptors (TLRs) in MSCs respond to viral load by secreting immunosuppressive or proinflammatory molecules. The expression of anti-inflammatory molecules in MSCs can be altered by the concentration and duration of exposure to the TLR3 ligand polyinosinic-polycytidylic acid (poly(I:C)). This study aimed to optimize the preconditioning of MSCs with poly(I:C) to increase immunosuppressive effects and to identify MSCs with activated TLR3 (prMSCs).

METHODS

Flow cytometry and histochemical staining were used to analyze MSCs for immunophenotype and differentiation potential. MSCs were exposed to poly(I:C) at 1 and 10 μg/mL for 1, 3, and 24 h, followed by determination of the expression of IDO1, WARS1, PD-L1, TSG-6, and PTGES2 and PGE2 secretion. MSCs and prMSCs were cocultured with intact (J-) and activated (J+) Jurkat T cells. The proportion of proliferating and apoptotic J+ and J- cells, IL-10 secretion, and IL-2 production after cocultivation with MSCs and prMSCs were measured. Liquid chromatography-mass spectrometry and bioinformatics analysis identified proteins linked to TLR3 activation in MSCs.

RESULTS

Poly(I:C) at 10 μg/mL during a 3-h incubation caused the highest expression of immunosuppression markers in MSCs. Activation of prMSCs caused a 18% decrease in proliferation and a one-third increase in apoptotic J+ cells compared to intact MSCs. Cocultures of prMSCs and Jurkat cells had increased IL-10 and decreased IL-2 in the conditioned medium. A proteomic study of MSCs and prMSCs identified 53 proteins with altered expression. Filtering the dataset with Gene Ontology and Reactome Pathway revealed that poly(I:C)-induced proteins activate the antiviral response. Protein‒protein interactions by String in prMSCs revealed that the antiviral response and IFN I signaling circuits were more active than in native MSCs. prMSCs expressed more cell adhesion proteins (ICAM-I and Galectin-3), PARP14, PSMB8, USP18, and GBP4, which may explain their anti-inflammatory effects on Jurkat cells.

CONCLUSIONS

TLR3 activation in MSCs is dependent on exposure time and poly(I:C) concentration. The maximum expression of immunosuppressive molecules was observed with 10 µg/mL poly(I:C) for 3-h preconditioning. This priming protocol for MSCs enhances the immunosuppressive effects of prMSCs on T cells.

The role of toll-like receptors in orchestrating osteogenic differentiation of mesenchymal stromal cells and osteoimmunology

Osteoimmunology is a concept involving molecular and cellular crosstalk between the skeletal and immune systems. Toll-like receptors (TLRs) are widely expressed both on mesenchymal stromal cells (MSCs), the hematopoietic cells, and immune cells in the osteogenic microenvironment for bone development or repair. TLRs can sense both exogenous pathogen-associated molecular patterns (PAMPs) derived from microorganisms, and damage-associated molecular patterns (DAMPs) derived from normal cells subjected to injury, inflammation, or cell apoptosis under physiological or pathological conditions. Emerging studies reported that TLR signaling plays an important role in bone remodeling by directly impacting MSC osteogenic differentiation or osteoimmunology. However, how to regulate TLR signaling is critical and remains to be elucidated to promote the osteogenic differentiation of MSCs and new bone formation for bone tissue repair. This review outlines distinct TLR variants on MSCs from various tissues, detailing the impact of TLR pathway activation or inhibition on MSC osteogenic differentiation. It also elucidates TLR pathways' interplay with osteoclasts, immune cells, and extracellular vesicles (EVs) derived from MSCs. Furthermore, we explore biomaterial-based activation to guide MSCs' osteogenic differentiation. Therefore, understanding TLRs' role in this context has significant implications for advancing bone regeneration and repair strategies.

Influence of type 2 diabetes and obesity on adipose mesenchymal stem/stromal cell immunoregulation

Type 2 diabetes (T2D), associated with obesity, represents a state of metabolic inflammation and oxidative stress leading to insulin resistance and progressive insulin deficiency. Adipose-derived stem cells (ASCs) are adult mesenchymal stem/stromal cells identified within the stromal vascular fraction of adipose tissue. These cells can regulate the immune system and possess anti-inflammatory properties. ASCs are a potential therapeutic modality for inflammatory diseases including T2D. Patient-derived (autologous) rather than allogeneic ASCs may be a relatively safer approach in clinical perspectives, to avoid occasional anti-donor immune responses. However, patient characteristics such as body mass index (BMI), inflammatory status, and disease duration and severity may limit the therapeutic utility of ASCs. The current review presents human ASC (hASC) immunoregulatory mechanisms with special emphasis on those related to T lymphocytes, hASC implications in T2D treatment, and the impact of T2D and obesity on hASC immunoregulatory potential. hASCs can modulate the proliferation, activation, and functions of diverse innate and adaptive immune cells via direct cell-to-cell contact and secretion of paracrine mediators and extracellular vesicles. Preclinical studies recommend the therapeutic potential of hASCs to improve inflammation and metabolic indices in a high-fat diet (HFD)-induced T2D disease model. Discordant data have been reported to unravel intact or detrimentally affected immunomodulatory functions of ASCs, isolated from patients with obesity and/or T2D patients, in vitro and in vivo. Numerous preconditioning strategies have been introduced to potentiate hASC immunomodulation; they are also discussed here as possible options to potentiate the immunoregulatory functions of hASCs isolated from patients with obesity and T2D.

Fat Graft Retention: Adipose Tissue, Adipose-Derived Stem Cells, and Aging

SUMMARY

Over the past 30 years, there has been a dramatic increase in the use of autologous fat grafting for soft-tissue augmentation and to improve facial skin quality. Several studies have highlighted the impact of aging on adipose tissue, leading to a decrease of adipose tissue volume and preadipocyte proliferation and increase of fibrosis. Recently, there has been a rising interest in adipose tissue components, including adipose-derived stem/stromal cells (ASCs) because of their regenerative potential, including inflammation, fibrosis, and vascularization modulation. Because of their differentiation potential and paracrine function, ASCs have been largely used for fat grafting procedures, as they are described to be a key component in fat graft survival. However, many parameters as surgical procedures or adipose tissue biology could change clinical outcomes. Variation on fat grafting methods have led to numerous inconsistent clinical outcomes. Donor-to-donor variation could also be imputed to ASCs, tissue inflammatory state, or tissue origin. In this review, the authors aim to analyze (1) the parameters involved in graft survival, and (2) the effect of aging on adipose tissue components, especially ASCs, that could lead to a decrease of skin regeneration and fat graft retention.

CLINICAL RELEVANCE STATEMENT

This review aims to enlighten surgeons about known parameters that could play a role in fat graft survival. ASCs and their potential mechanism of action in regenerative medicine are more specifically described.

Evaluation of human adipose-derived mesenchymal stromal cell Toll-like receptor priming and effects on interaction with prostate cancer cells

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are a multipotent cell population of clinical interest because of their ability to migrate to injury and tumor sites, where they may participate in tissue repair and modulation of immune response. Although the processes regulating MSC function are incompletely understood, it has been shown that stimulation of Toll-like receptors (TLRs) can alter MSC activity. More specifically, it has been reported that human bone marrow-derived MSCs can be "polarized" by TLR priming into contrasting immunomodulatory functions, with opposite (supportive or suppressive) roles in tumor progression and inflammation. Adipose-derived MSCs (ASCs) represent a promising alternative MSC subpopulation for therapeutic development because of their relative ease of isolation and higher abundance compared with their bone marrow-derived counterparts; however, the polarization of ASCs remains unreported.

METHODS

In this study, we evaluated the phenotypic and functional consequences of short-term, low-level stimulation of ASCs with TLR3 and TLR4 agonists.

RESULTS

In these assays, we identified transient gene expression changes resembling the reported pro-inflammatory and anti-inflammatory MSC phenotypes. Furthermore, these priming strategies led to changes in the functional properties of ASCs, affecting their ability to migrate and modulate immune-mediated responses to prostate cancer cells in vitro.

CONCLUSIONS

TLR3 stimulation significantly decreased ASC migration, and TLR4 stimulation increased ASC immune-mediated killing potential against prostate cancer cells.

Fused Cells between Human-Adipose-Derived Mesenchymal Stem Cells and Monocytes Keep Stemness Properties and Acquire High Mobility

Human-adipose-derived mesenchymal stem cells (hADMSCs) are multipotent stem cells which have become of great interest in stem-cell therapy due to their less invasive isolation. However, they have limited migration and short lifespans. Therefore, understanding the mechanisms by which these cells could migrate is of critical importance for regenerative medicine. Methods: Looking for novel alternatives, herein, hADMSCs were isolated from adipose tissue and co-cultured with human monocytes ex vivo. Results: A new fused hybrid entity, a foam hybrid cell (FHC), which was CD90⁺CD14⁺, resulted from this co-culture and was observed to have enhanced motility, proliferation, immunomodulation properties, and maintained stemness features. Conclusions: Our study demonstrates the generation of a new hybrid cellular population that could provide migration advantages to MSCs, while at the same time maintaining stemness properties.

Human Fetal Cartilage-Derived Progenitor Cells Exhibit Anti-Inflammatory Effect on IL-1β-Mediated Osteoarthritis Phenotypes In Vitro

BACKGROUND

In this study, we have investigated whether human fetal cartilage progenitor cells (hFCPCs) have anti-inflammatory activity and can alleviate osteoarthritis (OA) phenotypes in vitro.

METHODS

hFCPCs were stimulated with various cytokines and their combinations and expression of paracrine factors was examined to find an optimal priming factor. Human chondrocytes or SW982 synoviocytes were treated with interleukin-1β (IL-1β) to produce OA phenotype, and co-cultured with polyinosinic-polycytidylic acid (poly(I-C))-primed hFCPCs to address their anti-inflammatory effect by measuring the expression of OA-related genes. The effect of poly(I-C) on the surface marker expression and differentiation of hFCPCs into 3 mesodermal lineages was also examined.

RESULTS

Among the priming factors tested, poly(I-C) (1 µg/mL) most significantly induced the expression of paracrine factors such as indoleamine 2,3-dioxygenase, histocompatibility antigen, class I, G, tumor necrosis factor- stimulated gene-6, leukemia inhibitory factor, transforming growth factor-β1 and hepatocyte growth factor from hFCPCs. In the OA model in vitro, co-treatment of poly(I-C)-primed hFCPCs significantly alleviated IL-1β-induced expression of inflammatory factors such as IL-6, monocyte chemoattractant protein-1 and IL-1β, and matrix metalloproteinases in SW982, while it increased the expression of cartilage extracellular matrix such as aggrecan and collagen type II in human chondrocytes. We also found that treatment of poly(I-C) did not cause significant changes in the surface marker profile of hFCPCs, while showed some changes in the 3 lineages differentiation.

CONCLUSION

These results suggest that poly(I-C)-primed hFCPCs have an ability to modulate inflammatory response and OA phenotypes in vitro and encourage further studies to apply them in animal models of OA in the future.

MiR-145-5p restrains chondrogenic differentiation of synovium-derived mesenchymal stem cells by suppressing TLR4

Osteoarthritis (OA) is a progressive degeneration of articular cartilage with involvement of synovial membrane, and subchondral bone. Recently, cell-based therapies, including the application of stem cells such as mesenchymal stem cells (MSCs), have been introduced for restoration of the articular cartilage. Toll-like receptors (TLRs) were reported to participate in OA progression and MSC chondrogenesis. Here, the role and molecular mechanism of toll like receptor 4 (TLR4) in chondrogenic differentiation of synovium-derived MSCs (SMSCs) were investigated. Molecular markers (CD44, CD90, CD45 and CD14) on SMSC surfaces were identified by flow cytometry. Multi-potential differentiation capacities of SMSCs for chondrogenesis, adipogenesis and osteogenesis were examined by Alcian blue, oil red O and Alizarin red staining, respectively. TLR4 and miR-145-5p levels in SMSCs were assessed using RT-qPCR. The protein expression of TGFB3, Col II, SOX9 and Aggrecan in SMSCs was tested by western blotting. Cytokine secretions were analyzed with ELISA for IL-1β and IL-6. Intracellular NAD⁺ content and NAD⁺/NADH ratio were assessed. The interaction between miR-145-5p and TLR4 was confirmed by RNA pulldown and luciferase reporter assays. In this study, SMSCs were identified to have immunophenotypic characteristics of MSCs. TLR4 knockdown inhibited chondrogenic and osteogenic differentiation of SMSCs. Mechanistically, TLR4 was targeted by miR-145-5p in SMSCs. Moreover, TLR4 elevation offset the inhibitory impact of miR-145-5p upregulation on chondrogenic differentiation of SMSCs. Overall, miR-145-5p restrains chondrogenesis of SMSCs by suppressing TLR4.

Obesity and COVID-19: Mechanistic Insights From Adipose Tissue

Obesity is associated with an increase in morbidity and mortality from coronavirus disease 2019 (COVID-19). The risk is related to the cytokine storm, a major contributor to multiorgan failure and a pathological character of COVID-19 patients with obesity. While the exact cause of the cytokine storm remains elusive, disorders in energy metabolism has provided insights into the mechanism. Emerging data suggest that adipose tissue in obesity contributes to the disorders in several ways. First, adipose tissue restricts the pulmonary function by generation of mechanical pressures to promote systemic hypoxia. Second, adipose tissue supplies a base for severe acute respiratory syndrome coronavirus 2 entry by overexpression of viral receptors [angiotensin-converting enzyme 2 and dipeptidyl peptidase 4]. Third, impaired antiviral responses of adipocytes and immune cells result in dysfunction of immunologic surveillance as well as the viral clearance systems. Fourth, chronic inflammation in obesity contributes to the cytokine storm by secreting more proinflammatory cytokines. Fifth, abnormal levels of adipokines increase the risk of a hyperimmune response to the virus in the lungs and other organs to enhance the cytokine storm. Mitochondrial dysfunction in adipocytes, immune cells, and other cell types (endothelial cells and platelets, etc) is a common cellular mechanism for the development of cytokine storm, which leads to the progression of mild COVID-19 to severe cases with multiorgan failure and high mortality. Correction of energy surplus through various approaches is recommended in the prevention and treatment of COVID-19 in the obese patients.

Protective and proliferative effect of Aesculus indica extract on stressed human adipose stem cells via downregulation of NF-κB pathway

Inflammatory microenvironment after transplantation affects the proliferation and causes senescence of adipose-derived mesenchymal stem cells (hADMSCs) thus compromising their clinical efficacy. Priming stem cells with herbal extracts is considered very promising to improve their viability in the inflammatory milieu. Aesculus indica (A. indica) is used to treat many inflammatory diseases in Asia for decades. Herein, we explored the protective role of A. indica extract on human adipose-derived Mesenchymal Stem Cells (hADMSCs) against Monosodium Iodoacetate (MIA) induced stress in vitro. A. indica ameliorated the injury as depicted by significantly enhanced proliferation, viability, improved cell migration and superoxide dismutase activity. Furthermore, reduced lactate dehydrogenase activity, reactive oxygen species release, senescent and apoptotic cells were detected in A. indica primed hADMSCs. Downregulation of NF-κB pathway and associated inflammatory genes, NF-κB p65/RelA and p50/NF-κB 1, Interleukin 6 (IL-6), Interleukin 1 (IL-1β), Tumor necrosis factor alpha (TNF-α) and matrix metalloproteinase 13 (MMP-13) were observed in A. indica primed hADMSCs as compared to stressed hADMSCs. Complementary to gene expression, A. indica priming reduced the release of transcription factor p65, inhibitory-κB kinase (IKK) α and β, IL-1β and TNF-α proteins expression. Our data elucidates that A. indica extract preconditioning rescued hADMSCs against oxidative stress and improved their therapeutic potential by relieving inflammation through regulation of NF-κB pathway.

Adipose-Derived Stem/Stromal Cells in Kidney Transplantation: Status Quo and Future Perspectives

Kidney transplantation (KT) is the gold standard treatment of end-stage renal disease. Despite progressive advances in organ preservation, surgical technique, intensive care, and immunosuppression, long-term allograft survival has not significantly improved. Among the many peri-operative complications that can jeopardize transplant outcomes, ischemia–reperfusion injury (IRI) deserves special consideration as it is associated with delayed graft function, acute rejection, and premature transplant loss. Over the years, several strategies have been proposed to mitigate the impact of IRI and favor tolerance, with rather disappointing results. There is mounting evidence that adipose stem/stromal cells (ASCs) possess specific characteristics that could help prevent, reduce, or reverse IRI. Immunomodulating and tolerogenic properties have also been suggested, thus leading to the development of ASC-based prophylactic and therapeutic strategies in pre-clinical and clinical models of renal IRI and allograft rejection. ASCs are copious, easy to harvest, and readily expandable in culture. Furthermore, ASCs can secrete extracellular vesicles (EV) which may act as powerful mediators of tissue repair and tolerance. In the present review, we discuss the current knowledge on the mechanisms of action and therapeutic opportunities offered by ASCs and ASC-derived EVs in the KT setting. Most relevant pre-clinical and clinical studies as well as actual limitations and future perspective are highlighted.

Dissecting the relationship between antimicrobial peptides and mesenchymal stem cells

Among the various biological properties presented by Mesenchymal Stem Cells (MSCs), their ability to control the immune response and fight pathogen infection through the production of antimicrobial peptides (AMPs) have been the subject of intense research in recent years. AMPs secreted by MSCs exhibit activity against a wide range of microorganisms, including bacteria, fungi, yeasts, and viruses. The main AMPs produced by these cells are hepcidin, cathelicidin LL-37, and β-defensin-2. In addition to acting against pathogens, those AMPs have also been shown to interact with MSCs to modulate MSC proliferation, migration, and regeneration, indicating that such peptides exert a more diverse biological effect than initially thought. In the present review, we discuss the production of AMPs by MSCs, revise the multiple functions of these peptides, including their influence over MSCs, and present an overview of clinical situations in which the antimicrobial properties of MSCs may be explored for therapy. Finally, we discuss possibilities of combining MSCs and AMPs to generate improved therapeutic strategies.

Toll-Like Receptors in Stem/Progenitor Cells

One of the bridges that control the cross-talk between the innate and adaptive immune systems is toll-like receptors (TLRs). TLRs interact with molecules shared and maintained by the source pathogens, but also with endogenous molecules derived from injured tissues (damage/danger-associated molecular patterns - DAMPs). This is likely why some kinds of stem/progenitor cells (SCs) have been found to express TLRs. The role of TLRs in regulating basal motility, proliferation, processes of differentiation, self-renewal, and immunomodulation has been demonstrated in these cells. In this book chapter, we will discuss the many different functions assumed by the TLRs in SCs, pointing out that, depending on the context and the type of ligands they perceive, they may have different effects. In addition, the role of TLR in SC's response to specific tissue damage and in reparative processes will be addressed, as well as how the discovery of molecules mediating TLR signaling's differential function may be decisive for the development of new therapeutic strategies. Given the available studies on TLRs in SCs, the significance of TLRs in sensing an injury to stem/progenitor cells and evaluating their action and reparative activity, which depends on the circumstances, will be discussed here. It could also be possible that SCs used in therapy could theoretically be exposed to TLR ligands, which could modulate their in vivo therapeutic potential. In this context, we need to better understand the mechanisms of action of TLRs on SCs and learn how to regulate these receptors and their downstream pathways in a precise way in order to modulate SC proliferation, survival, migration, and differentiation in the pathological environment. In this way, cell therapy may be strengthened and made safer in the future.

The Transcription Factor NF-κB in Stem Cells and Development

NF-κB (nuclear factor kappa B) belongs to a family of transcription factors known to regulate a broad range of processes such as immune cell function, proliferation and cancer, neuroprotection, and long-term memory. Upcoming fields of NF-κB research include its role in stem cells and developmental processes. In the present review, we discuss one role of NF-κB in development in Drosophila, Xenopus, mice, and humans in accordance with the concept of evo-devo (evolutionary developmental biology). REL domain-containing proteins of the NF-κB family are evolutionarily conserved among these species. In addition, we summarize cellular phenotypes such as defective B- and T-cell compartments related to genetic NF-κB defects detected among different species. While NF-κB proteins are present in nearly all differentiated cell types, mouse and human embryonic stem cells do not contain NF-κB proteins, potentially due to miRNA-dependent inhibition. However, the mesodermal and neuroectodermal differentiation of mouse and human embryonic stem cells is hampered upon the repression of NF-κB. We further discuss NF-κB as a crucial regulator of differentiation in adult stem cells such as neural crest-derived and mesenchymal stem cells. In particular, c-REL seems to be important for neuronal differentiation and the neuroprotection of human adult stem cells, while RELA plays a crucial role in osteogenic and mesodermal differentiation.

Clinical experience on umbilical cord mesenchymal stem cell treatment in 210 severe and critical COVID-19 cases in Turkey

Objective

Treatment for COVID-19 is still urgent need for the critically ill and severe cases. UC-MSC administration has a therapeutic benefit for severe COVID-19 patients even in the recovery period. In this paper, we aimed to present our clinical experience with UC-MSC treatment in severe and critical severe COVID-19 patients.

Methods

In this study we evaluated the clinical outcome of severe/critically severe 210 COVID-19 patients treated with UC-MSCs, 1–2 × 10⁶ per kilogram to 210 patients from 15/10/2020 until 25/04/2021.

Results

Out of 99 critically severe intubated patients we have observed good clinical progress/discharged from ICU in 52 (52.5%) patients. Where as 86 (77.5%) of 111 severe unintubated patients discharged from ICU. Intubated 47 (47.5%) patients and unintubated 25 (22.5%) patients pass away. Significantly higher survival was observed in patients who underwent UC-MSCs before intubation (OR = 1.475, 95% CI = 1.193–1.824 p < 0.001). It was observed that the SaO₂ parameter tended to improve after UC-MSC therapy compared to all groups. But SaO₂ parameter between intubated and unintubated groups was not statistically significant (p > 0.05), while in discharged cases SaO₂ parameter was statistically significant (p = 0.01). Besides, there was a statistically significant relation with intubation status, age (OR = 3.868, 95% CI = 0.574–7.152 p = 0.02) and weigh (OR = 6.768, 95% CI = 3.423–10.112 p < 0.001) thus presented an elevated risk for COVID-19. The linear regression analysis confirmed that the high weight was associated with the risk of intubation in COVID-19 (p = 0.001).

Conclusions

According to our results and from recent studies, UC-MSC treatment is safe with high potential to be used as an added therapeutic treatment for severe COVID-19 patients. Our experience showed that UC-MSC therapy may restore oxygenation and downregulate cytokine storm in patients hospitalized with severe COVID-19. We advice wider randomised studies to discover the detailed therapeutic pathophysiology of the MSCs on COVID-19 patients.

Graphical abstract

MSCs transplantation improves the damaging effects of the cytokine storm through immunomodulation and improving tissue and organ repair. Severe patients who were unintubated were in the Phase I, while critical patients who were intubated were in the Phase II. The figure is created via biorender application, (BioRender.com).

Processing and Ex Vivo Expansion of Adipose Tissue-Derived Mesenchymal Stem/Stromal Cells for the Development of an Advanced Therapy Medicinal Product for use in Humans

Adipose tissue (AT) represents a commonly used source of mesenchymal stem/stromal cells (MSCs) whose proregenerative potential has been widely investigated in multiple clinical trials worldwide. However, the standardization of the manufacturing process of MSC-based cell therapy medicinal products in compliance with the requirements of the local authorities is obligatory and will allow us to obtain the necessary permits for product administration according to its intended use. Within the research phase (RD), we optimized the protocols used for the processing and ex vivo expansion of AT-derived MSCs (AT-MSCs) for the development of an Advanced Therapy Medicinal Product (ATMP) for use in humans. Critical process parameters (including, e.g., the concentration of enzyme used for AT digestion, cell culture conditions) were identified and examined to ensure the high quality of the final product containing AT-MSCs. We confirmed the identity of isolated AT-MSCs as MSCs and their trilineage differentiation potential according to the International Society for Cellular Therapy (ISCT) recommendations. Based on the conducted experiments, in-process quality control (QC) parameters and acceptance criteria were defined for the manufacturing of hospital exemption ATMP (HE-ATMP). Finally, we conducted a validation of the manufacturing process in a GMP facility. In the current study, we presented a process approach leading to the optimization of processing and the ex vivo expansion of AT-MSCs for the development of ATMP for use in humans.

Transcriptional Profile of Cytokines, Regulatory Mediators and TLR in Mesenchymal Stromal Cells after Inflammatory Signaling and Cell-Passaging

Adult human subcutaneous adipose tissue (AT) harbors a rich population of mesenchymal stromal cells (MSCs) that are of interest for tissue repair. For this purpose, it is of utmost importance to determine the response of AT-MSCs to proliferative and inflammatory signals within the damaged tissue. We have characterized the transcriptional profile of cytokines, regulatory mediators and Toll-like receptors (TLR) relevant to the response of MSCs. AT-MSCs constitutively present a distinct profile for each gene and differentially responded to inflammation and cell-passaging. Inflammation leads to an upregulation of IL-6, IL-8, IL-1β, TNFα and CCL5 cytokine expression. Inflammation and cell-passaging increased the expression of HGF, IDO1, PTGS1, PTGS2 and TGFβ. The expression of the TLR pattern was differentially modulated with TLR 1, 2, 3, 4, 9 and 10 being increased, whereas TLR 5 and 6 downregulated. Functional enrichment analysis demonstrated a complex interplay between cytokines, TLR and regulatory mediators central for tissue repair. This profiling highlights that following a combination of inflammatory and proliferative signals, the sensitivity and responsive capacity of AT-MSCs may be significantly modified. Understanding these transcriptional changes may help the development of novel therapeutic approaches.

Keratinocyte-Like Cells Trans-Differentiated from Human Adipose-Derived Stem Cells, Facilitate Skin Wound Healing in Mice

Background

Mesenchymal stem cells (MSCs) have been reported to promote wound healing in both animal models and human studies. Among MSCs, adipose-derived stem cells (ADSCs) can be easily harvested in large quantities.

Objective

We investigated whether skin wound healing in mice can be facilitated by keratinocyte-like cells differentiated from ADSCs (KC-ADSCs).

Methods

For the wound contraction and epithelialization model, a 20 mm×20 mm fullthickness skin wound was made on the dorsum. For the wound epithelialization model, a 6 mm×6 mm full-thickness skin wound was made on the dorsum. A nitrile rubber stent with an inner diameter of 8 mm was sutured around the wounds to minimize wound contraction. Undifferentiated ADSCs (uADSCs) or KC-ADSCs was injected around the wound base in both models. To evaluate whether the injected ADSCs could enhance wound contraction in a skin wound, the contractile activity of ADSCs was assessed by an in vitro type I collagen gel contraction assay. Alpha-smooth muscle actin (αSMA) expressions in uADSCs and KC-ADSCs were also evaluated by flow cytometry and real-time polymerase chain reaction.

Results

In a wound contraction and epithelialization model, KC-ADSCs further facilitated wound healing compared with uADSCs. In a wound epithelialization model, KC-ADSCs also further facilitated wound epithelialization compared with uADSCs. The contractile activity of KC-ADSCs was lower than that of uADSCs. The uADSCs expressed high levels of αSMA, which decreased after the differentiation into keratinocyte-like cells.

Conclusion

Our results suggest that the wound healing effect of KC-ADSCs depends primarily on re-epithelialization rather than wound contraction.

The role of inflammation in mesenchymal stromal cell therapy in osteoarthritis, perspectives for post-traumatic osteoarthritis: a review

OA is a complex and highly prevalent degenerative disease affecting the whole joint, in which factors like genetic predisposition, gender, age, obesity and traumas contribute to joint destruction. ∼50-80% of OA patients develop synovitis. OA-associated risk factors contribute to joint instability and the release of cartilage matrix fragments, activating the synovium to release pro-inflammatory factors and catabolic enzymes in turn damaging the cartilage and creating a vicious circle. Currently, no cure is available for OA. Mesenchymal stromal cells (MSCs) have been tested in OA for their chondrogenic and anti-inflammatory properties. Interestingly, MSCs are most effective when administered during synovitis. This review focusses on the interplay between joint inflammation and the immunomodulation by MSCs in OA. We discuss the potential of MSCs to break the vicious circle of inflammation and describe current perspectives and challenges for clinical application of MSCs in treatment and prevention of OA, focussing on preventing post-traumatic OA.

Clinically used JAK inhibitor blunts dsRNA-induced inflammation and calcification in aortic valve interstitial cells

Calcific aortic valve disease (CAVD) is the most prevalent valvulopathy worldwide. Growing evidence supports a role for viral and cell-derived double-stranded (ds)-RNA in cardiovascular pathophysiology. Poly(I:C), a dsRNA surrogate, has been shown to induce inflammation, type I interferon (IFN) responses, and osteogenesis through Toll-like receptor 3 in aortic valve interstitial cells (VIC). Here, we aimed to determine whether IFN signaling via Janus kinase (JAK)/Signal transducers and activators of transcription (STAT) mediates dsRNA-induced responses in primary human VIC. Western blot, ELISA, qPCR, calcification, flow cytometry, and enzymatic assays were performed to evaluate the mechanisms of dsRNA-induced inflammation and calcification. Poly(I:C) triggered a type I IFN response characterized by IFN-regulatory factors gene upregulation, IFN-β secretion, and STAT1 activation. Additionally, Poly(I:C) promoted VIC inflammation via NF-κB and subsequent adhesion molecule expression, and cytokine secretion. Pretreatment with ruxolitinib, a clinically used JAK inhibitor, abrogated these responses. Moreover, Poly(I:C) promoted a pro-osteogenic phenotype and increased VIC calcification to a higher extent in cells from males. Inhibition of JAK with ruxolitinib or a type I IFN receptor blocking antibody blunted Poly(I:C)-induced calcification. Mechanistically, Poly(I:C) promoted VIC apoptosis in calcification medium, which was inhibited by ruxolitinib. Moreover, Poly(I:C) co-operated with IFN-γ to increase VIC calcification by synergistically activating extracellular signal-regulated kinases and hypoxia-inducible factor-1α pathways. In conclusion, JAK/STAT signaling mediates dsRNA-triggered inflammation, apoptosis, and calcification and may contribute to a positive autocrine loop in human VIC in the presence of IFN-γ. Blockade of dsRNA responses with JAK inhibitors may be a promising therapeutic avenue for CAVD.

Functional differences of Toll-like receptor 4 in osteogenesis, adipogenesis and chondrogenesis in human bone marrow-derived mesenchymal stem cells

Multipotent human bone marrow-derived mesenchymal stem cells (hMSCs) are promising candidates for bone and cartilage regeneration. Toll-like receptor 4 (TLR4) is expressed by hMSCs and is a receptor for both exogenous and endogenous danger signals. TLRs have been shown to possess functional differences based on the species (human or mouse) they are isolated from therefore, the effects of knockdown of TLR4 were evaluated in humans during the differentiation of MSCs into bone, fat and chondrocyte cells in vitro. We investigated the expression profile of TLR4 during the differentiation of hMSCs into three different lineages on days 7, 14 and 21 and assessed the differentiation potential of the cells in the presence of lipopolysaccharide (LPS, as an exogenous agonist) and fibronectin fragment III-1c (FnIII-1c, as an endogenous agonist). TLR4 expression increased following the induction of hMSC differentiation into all three lineages. Alkaline phosphatase activity revealed that FnIII-1c accelerated calcium deposition on day 7, whereas LPS increased calcium deposition on day 14. Chondrogenesis increased in the presence of LPS; however, FnIII-1c acted as a reducer in the late stage. TLR4 silencing led to decreased osteogenesis and increased adipogenesis. Furthermore, Wnt5a expression was inversely related to chondrogenesis during the late stage of differentiation. We suggest that understanding the functionality of TLR4 (in the presence of pathogen or stress signal) during the differentiation of hMSCs into three lineages would be useful for MSC-based treatments.

Phenotypic Features of Mesenchymal Stem Cell Subpopulations Obtained under the Influence of Various Toll-Like Receptors Ligands

The paper characterizes phenotypic features of subpopulations of human adipose tissue mesenchymal stem cells (MSC) resulting from exposure to Toll-like receptors ligands. MSC1 and MSC2 phenotypes were induced by exposure to LPS and polyinosinic-polycytidylic acid, respectively. Different exposures to Toll-like receptors ligands, short-term (3 h) and long-term (24 h), were studied. The cytokine profile of cells with the MSC2 phenotype differed depending on the duration of exposure to the inductor, while the cytokine profile of cells with the MSC1 phenotype remained stable. Morphometric features of mesenchymal stem cells with the MSC1 and MSC2 phenotypes, as well as differences in the IDO gene expression were identified. These differences can be used to distinguish between these cell types.

Stem Cells Therapy as a Possible Therapeutic Option in Treating COVID-19 Patients

An unfortunate emergence of a new virus SARS-CoV-2, causing a disease known as COVID-19, has spread all around the globe and has caused a pandemic. It primarily affects the respiratory tract and lungs in some cases causing severe organ damage and pneumonia due to overwhelming immune responses. Clinical reports show that the most commons symptoms are fever, dry cough, and shortness of breath, along with several other symptoms. It is thought that an immense cytokine dysregulation in COVID-19 patients is caused following the virus infection. Notably, if patients present with pre-existing specific comorbidities like diabetes or high blood pressure, rates of COVID-19 induced complications and deaths are escalated. Mesenchymal stem cell (MSC) therapy has been shown to alleviate pneumonia and acute respiratory syndrome (ARDS) symptoms, through their immunomodulatory activities in COVID-19 patients. Although more research studies and clinical trial results are needed to elucidate the exact mechanism by which MSCs provide relief to COVID-19 infected patients. Results from clinical trials are encouraging as patients treated with MSCs, regain lung functions and have restored levels of cytokines and trophic factors underscoring the fact that stem cell therapy can be, at least, a complementary therapy to alleviate sufferings in COVID-19 patients. This review discusses the possible therapeutic uses of MSCs for treating COVID-19. Graphical Abstract.

Promising role for mesenchymal stromal cells in coronavirus infectious disease-19 (COVID-19)-related severe acute respiratory syndrome?

Mesenchymal stromal cells (MSC) have immune regulatory and tissue regenerative properties. MSCs are being studied as a therapy option for many inflammatory and immune disorders and are approved to treat acute graft-versus-host disease (GvHD). The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic and associated coronavirus infectious disease-19 (COVID-19) has claimed many lives. Innovative therapies are needed. Preliminary data using MSCs in the setting of acute respiratory distress syndrome (ARDS) in COVID-19 are emerging. We review mechanisms of action of MSCs in inflammatory and immune conditions and discuss a potential role in persons with COVID-19.

Critical roles of TLRs on the polarization of mesenchymal stem cells for cell therapy of viral infections: a notice for COVID-19 treatment

Mesenchymal stem cells (MSCs), as one of the leading cell-based therapy, have provided a strong link between clinical investigation and basic research. MSCs have been successfully employed in treating graft versus host disease (GvHD), autoimmune disease, and several other diseases, particularly with high immune activity. Recently, MSCs have attracted attention to treating untreatable viral infections such as severe coronavirus disease 2019 (COVID-19). Given that the Toll-like receptors (TLRs) are directly able to detect internal and external hazard signals, and their stimulation has an intense effect on the ability to grow, differentiate, migrate, and maintain MSCs, it seems stimulation of these receptors can have a direct impact on the interaction of MSCs and immune cells, altering the ability to modify immune system responses. Hence, this mini-review focused on TLRs’ critical roles in the polarization of MSCs for developing MSC-based therapy in viral infections. Consequently, according to the literature review, a polarization process, mediated by TLRs concerning anti-inflammatory and proinflammatory phenotype, may be considered for MSC-therapy against viral infections.

Involvement of Mesenchymal Stem Cells in Oral Mucosal Bacterial Immunotherapy

Recent clinical observations indicate that bacterial vaccines induce cross-protection against infections produced by different microorganisms. MV130, a polyvalent bacterial sublingual preparation designed to prevent recurrent respiratory infectious diseases, reduces the infection rate in patients with recurrent respiratory tract infections. On the other hand, mesenchymal stem cells (MSCs) are key cell components that contribute to the maintenance of tissue homeostasis and exert both immunostimulatory and immunosuppressive functions. Herein, we study the effects of MV130 in human MSC functionality as a potential mechanism that contributes to its clinical benefits. We provide evidence that during MV130 sublingual immunization of mice, resident oral mucosa MSCs can take up MV130 components and their numbers remain unchanged after vaccination, in contrast to granulocytes that are recruited from extramucosal tissues. MSCs treated in vitro with MV130 show an increased viability without affecting their differentiation potential. In the short-term, MSC treatment with MV130 induces higher leukocyte recruitment and T cell expansion. In contrast, once T-cell activation is initiated, MV130 stimulation induces an up-regulated expression of immunosuppressor factors in MSCs. Accordingly, MV130-primed MSCs reduce T lymphocyte proliferation, induce the differentiation of dendritic cells with immunosuppressive features and favor M2-like macrophage polarization, thus counterbalancing the immune response. In addition, MSCs trained with MV130 undergo functional changes, enhancing their immunomodulatory response to a secondary stimulus. Finally, we show that MSCs are able to uptake, process and retain a reservoir of the TLR ligands derived from MV130 digestion which can be subsequently transferred to dendritic cells, an additional feature that also may be associated to trained immunity.

Immunomodulatory Effect of Adipose-Derived Stem Cells: The Cutting Edge of Clinical Application

Adipose-derived stem cells (ASCs) represent a promising tool for soft tissue engineering as well as for clinical treatment of inflammatory and autoimmune pathologies. The well-characterized multi-differentiation potential and self-renewal properties of ASCs are coupled with their immunomodulatory ability in providing therapeutic efficacy. Yet, their impact in immune or inflammatory disorders might rely both on cell contact-dependent mechanisms and paracrine effects, resulting in the release of various soluble factors that regulate immune cells functions. Despite the widespread use of ASCs in clinical trials addressing several pathologies, the pathophysiological mechanisms at the basis of their clinical use have been not yet fully investigated. In particular, a thorough analysis of ASC immunomodulatory potential is mandatory. Here we explore such molecular mechanisms involved in ASC immunomodulatory properties, emphasizing the relevance of the milieu composition. We review the potential clinical use of ASC secretome as a mediator for immunomodulation, with a focus on in vitro and in vivo environmental conditions affecting clinical outcome. We describe some potential strategies for optimization of ASCs immunomodulatory capacity in clinical settings, which act either on adult stem cells gene expression and local microenvironment. Finally, we discuss the limitations of both allogeneic and autologous ASC use, highlighting the issues to be fixed in order to significantly improve the efficacy of ASC-based cell therapy.

Imiquimod Acts Synergistically with BMP9 through the Notch Pathway as an Osteoinductive Agent In Vitro

BACKGROUND

Autologous bone grafts used for surgical reconstruction are limited by infection or insufficient supply of host material. Experimental agents that promote differentiation of stem cells into mature bone are currently being studied for future use in the repair of bone defects. The authors hypothesized that imiquimod, a synthetic immune response modifier, increases Notch pathway gene expression and acts synergistically with bone morphogenetic protein (BMP) 9 to induce differentiation of mesenchymal stem cells toward an osteogenic phenotype.

METHODS

Alkaline phosphatase activity was used to assess the osteogenic potential of cultured mouse immortalized multipotent adipose-derived cells (iMADs) treated with 0, 4, 6, and 8 μg/ml of imiquimod with and without BMP9. Adenoviral vectors expressing human BMP9 and a dominant-negative mutant of mouse Notch1 were used to assess BMP9 and Notch blockade on osteogenic activity, respectively. Expression of Notch signaling mediators and osteogenic markers were assayed by quantitative polymerase chain reaction. Alizarin red staining was used to assess the synergism between BMP9 and imiquimod.

RESULTS

Imiquimod exposure enhanced osteogenic differentiation of iMADs by 2.8-fold (p < 0.001) and potentiated BMP9-induced osteogenic differentiation of iMADs by 1.6-fold (p < 0.001), shown by increased alkaline phosphatase activity and augmented matrix mineralization. Quantitative-real time polymerase chain reaction analysis demonstrated that imiquimod induced the expression of downstream genes (p < 0.01) of the Notch signaling pathway Hey1, Hey2, and Hes1, by increases of 9.7-, 22-, and 2.7-fold, respectively.

CONCLUSIONS

These findings identify a novel role for imiquimod to shift mesenchymal stem cells toward an osteogenic phenotype. Imiquimod may be useful clinically when scaffolds are applied to treat bone defects.

Therapeutic Mesenchymal Stromal Cells for Immunotherapy and for Gene and Drug Delivery

Mesenchymal stromal cells (MSCs) possess several fairly unique properties that, when combined, make them ideally suited for cellular-based immunotherapy and as vehicles for gene and drug delivery for a wide range of diseases and disorders. Key among these are: (1) their relative ease of isolation from a variety of tissues; (2) the ability to be expanded in culture without a loss of functionality, a property that varies to some degree with tissue source; (3) they are relatively immune-inert, perhaps obviating the need for precise donor/recipient matching; (4) they possess potent immunomodulatory functions that can be tailored by so-called licensing in vitro and in vivo; (5) the efficiency with which they can be modified with viral-based vectors; and (6) their almost uncanny ability to selectively home to damaged tissues, tumors, and metastases following systemic administration. In this review, we summarize the latest research in the immunological properties of MSCs, their use as immunomodulatory/anti-inflammatory agents, methods for licensing MSCs to customize their immunological profile, and their use as vehicles for transferring both therapeutic genes in genetic disease and drugs and genes designed to destroy tumor cells.

Broad-Spectrum Antibacterial Effects of Human Adipose-Derived Stromal Cells

Introduction

Many pathological conditions may benefit from cell therapy using mesenchymal stromal cells, particularly from adipose tissue (ASCs). Cells may be grafted in an environment with a remnant polymicrobial component. The aim is to investigate the behavior of ASCs when brought in contact with a large panel of bacteria.

Materials and Methods

Carboxyfluorescein-labelled bacterial interaction with ASCs was followed by confocal time-lapse microscopy. Costaining with LAMP-1 was also analyzed. Viability of 4 gram-negative and 4 gram-positive bacterial strains after 6 h of coculture with ASCs was assessed by agar colony counting and by flow cytometry using SYTO-62®/propidium iodide (PI) for membrane permeabilization and DiOC6 for depolarization. A murine model of periodontitis was used to assess in vivo antibacterial capacities of ASCs.

Results

A significant increase of PI-positive events for all bacterial strains and an increase of the DiOC6 signal were obtained after contact with ASCs. The number of CFU was also significantly decreased for several bacterial strains. 0.4 μm transwell systems illustrated the necessary direct contact to induce maximal bacterial membrane damages. Some bacteria were observed into phagolysosomes, confirming macrophage-like properties of ASCs. In vivo, the bacterial load was significantly lower in the ASC-grafted side compared to the control.

Conclusion

Our results highlight for the first time a broad range of antibacterial actions of ASCs, by phagocytosis, secretion of oxygenated free radicals and antibacterial molecules. These data are in line with the development of new therapeutic strategies based on ASC transplantation, appropriated in immune-dysbiotic tissue context such as periodontitis or chronic wounds.

Current Strategies to Enhance Adipose Stem Cell Function: An Update

Mesenchymal stem cells (MSCs) emerged as a promising therapeutic tool targeting a variety of inflammatory disorders due to their multiple remarkable properties, such as superior immunomodulatory function and tissue-regenerative capacity. Although bone marrow (BM) is a dominant source for adult MSCs, increasing evidence suggests that adipose tissue-derived stem cells (ASCs), which can be easily obtained at a relatively high yield, have potent therapeutic advantages comparable with BM-MSCs. Despite its outstanding benefits in pre-clinical settings, the practical efficacy of ASCs remains controversial since clinical trials with ASC application often resulted in unsatisfactory outcomes. To overcome this challenge, scientists established several strategies to generate highly functional ASCs beyond the naïve cells, including (1) pre-conditioning of ASCs with various stimulants such as inflammatory agents, (2) genetic manipulation of ASCs and (3) modification of culture conditions with three-dimensional (3D) aggregate formation and hypoxic culture. Also, exosomes and other extracellular vesicles secreted from ASCs can be applied directly to recapitulate the beneficial performance of ASCs. This review summarizes the current strategies to improve the therapeutic features of ASCs for successful clinical implementation.

Dissecting Allo-Sensitization After Local Administration of Human Allogeneic Adipose Mesenchymal Stem Cells in Perianal Fistulas of Crohn's Disease Patients

Adipose mesenchymal stem cells (ASC) are considered minimally immunogenic. This is due to the low expression of human leukocyte antigens I (HLA-I), lack of HLA-II expression and low expression of co-stimulatory molecules such as CD40 and CD80. The low rate of observed immunological rejection as well as the immunomodulatory qualities, position ASC as a promising cell-based therapy for the treatment of a variety of inflammatory indications. Yet, few studies have addressed relevant aspects of immunogenicity such as ASC donor-to-patient HLA histocompatibility or assessment of immune response triggered by ASC administration, particularly in the cases of presensitization. The present study aims to assess allo-immune responses in a cohort of Crohn's disease patients administered with allogeneic ASC (darvadstrocel formerly Cx601) for the treatment of complex perianal fistulas. We identified donor-specific antibodies (DSA) generation in a proportion of patients and observed that patients showing preexisting immunity were prone to generating DSA after allogeneic therapy. Noteworthy, naïve patients generating DSA at week 12 (W12) showed a significant reduction in DSA titer at week 52 (W52), whereas DSA titer was reduced in pre-sensitized patients only with no specificities against the donor administered. Remarkably, we did not observe any correlation of DSA generation with ASC therapeutic efficacy. In vitro complement-dependent cytotoxicity (CDC) studies have revealed limited cytotoxic levels based upon HLA-I expression and binding capacity even in pro-inflammatory conditions. We sought to identify CDC coping mechanisms contributing to the limited cytotoxic killing observed in ASC in vitro. We found that ASC express membrane-bound complement regulatory proteins (mCRPs) CD55, CD46, and CD59 at basal levels, with CD46 more actively expressed in pro-inflammatory conditions. We demonstrated that CD46 is a main driver of CDC signaling; its depletion significantly enhances sensitivity of ASC to CDC. In summary, despite relatively high clearance, DSA generation may represent a major challenge for allogeneic cell therapy management. Sensitization may be a significant concern when evaluating re-treatment or multi-donor trials. It is still unknown whether DSA generation could potentially be the consequence of donor-to-patient interaction and, therefore, subsequently link to efficacy or biological activity. Lastly, we propose that CDC modulators such as CD46 could be used to ultimately link CDC specificity with allogeneic cell therapy efficacy.

Constitutive and LPS-stimulated secretome of porcine Vascular Wall-Mesenchymal Stem Cells exerts effects on in vitro endothelial angiogenesis

Background

MSCs secretome is under investigation as an alternative to whole-cell-based therapies, since it is enriched of bioactive molecules: growth factors, cytokines and chemokines. Taking into account the translational value of the pig model, the leading aim of the present paper was to characterize the secretome of porcine Vascular Wall–Mesenchymal Stem Cells (pVW-MSCs) and its change in presence of LPS stimulation. Moreover, considering the importance of angiogenesis in regenerative mechanisms, we analysed the effect of pVW-MSCs secretome on in vitro angiogenesis.

Results

Our results demonstrated that conditioned medium from unstimulated pVW-MSCs contained high levels of IL-8, GM-CSF, IFN-γ and other immunomodulatory proteins: IL-6 IL-18 IL-4 IL-2 IL-10. LPS modulates pVW-MSCs gene expression and secretome composition, in particular a significant increase of IL-6 and IL-8 was observed; conversely, the amount of GM-CSF, IFN-γ, IL-2, IL-4, IL-10 and IL-18 showed a significant transient decrease with the LPS stimulation. Conditioned medium from unstimulated pVW-MSCs induced in vitro endothelial angiogenesis, which is more evident when the conditioned medium was from LPS stimulated pVW-MSCs.

Conclusions

The lines of evidence here presented shed a light on possible future application of secretome derived by pVW-MSCs on research studies in translational regenerative medicine.

Role of Toll-Like Receptors in Actuating Stem/Progenitor Cell Repair Mechanisms: Different Functions in Different Cells

Toll-like receptors (TLRs) represent one of the bridges that regulate the cross-talk between the innate and adaptive immune systems. TLRs interact with molecules shared and preserved by the pathogens of origin but also with endogenous molecules (damage/danger-associated molecular patterns (DAMPs)) that derive from injured tissues. This is probably why TLRs have been found to be expressed on several kinds of stem/progenitor cells (SCs). In these cells, the role of TLRs in the regulation of the basal motility, proliferation, differentiation processes, self-renewal, and immunomodulation has been demonstrated. In this review, we analyze the many different functions that the TLRs assume in SCs, pointing out that they can have different effects, depending on the background and on the kind of ligands that they recognize. Moreover, we discuss the TLR involvement in the response of SC to specific tissue damage and in the reparative processes, as well as how the identification of molecules mediating the differential function of TLR signaling could be decisive for the development of new therapeutic strategies. Considering the available studies on TLRs in SCs, here we address the importance of TLRs in sensing an injury by stem/progenitor cells and in determining their behavior and reparative activity, which is dependent on the conditions. Therefore, it could be conceivable that SCs employed in therapy could be potentially exposed to TLR ligands, which might modulate their therapeutic potential in vivo. In this context, to modulate SC proliferation, survival, migration, and differentiation in the pathological environment, we need to better understand the mechanisms of action of TLRs on SCs and learn how to control these receptors and their downstream pathways in a precise way. In this manner, in the future, cell therapy could be improved and made safer.

Adipose-derived stromal/stem cells from different adipose depots in obesity development

The increasing prevalence of obesity is alarming because it is a risk factor for cardiovascular and metabolic diseases (such as type 2 diabetes). The occurrence of these comorbidities in obese patients can arise from white adipose tissue (WAT) dysfunctions, which affect metabolism, insulin sensitivity and promote local and systemic inflammation. In mammals, WAT depots at different anatomical locations (subcutaneous, preperitoneal and visceral) are highly heterogeneous in their morpho-phenotypic profiles and contribute differently to homeostasis and obesity development, depending on their ability to trigger and modulate WAT inflammation. This heterogeneity is likely due to the differential behavior of cells from each depot. Numerous studies suggest that adipose-derived stem/stromal cells (ASC; referred to as adipose progenitor cells, in vivo) with depot-specific gene expression profiles and adipogenic and immunomodulatory potentials are keys for the establishment of the morpho-functional heterogeneity between WAT depots, as well as for the development of depot-specific responses to metabolic challenges. In this review, we discuss depot-specific ASC properties and how they can contribute to the pathophysiology of obesity and metabolic disorders, to provide guidance for researchers and clinicians in the development of ASC-based therapeutic approaches.

Current understanding of the immunosuppressive properties of mesenchymal stromal cells

Several studies have demonstrated the anti-inflammatory potential of mesenchymal stromal cells (MSCs) isolated from bone marrow, adipose tissue, placenta, and other sources. Nevertheless, MSCs may also induce immunosuppression when administered systemically or directly to injured environments, as shown in different preclinical disease models. MSCs express certain receptors, including toll-like receptors and the aryl-hydrocarbon receptor, that are activated by the surrounding environment, thus leading to modulation of their immunosuppressive activity. Once MSCs are activated, they can affect a wide range of immune cells (e.g., neutrophils, monocytes/macrophages, dendritic cells, natural killer cells, T and B lymphocytes), a phenomenon that has been correlated to secretion of several mediators (e.g., indolamine 2,3-dioxygenase, galectins, prostaglandin E₂, nitric oxide, and damage- and pathogen-associated molecular patterns) and stimulation of certain signaling pathways (e.g., protein kinase R, signal transducer and activator of transcription-1, nuclear factor-κB). Additionally, MSC manipulation and culture conditions, as well as the number of passages, duration of cryopreservation, and O₂ content available, can significantly affect the immunosuppressive properties of MSCs. This review sheds light on current knowledge regarding the mechanisms by which MSCs exert immunosuppressive effects both in vitro and in vivo, focusing on the receptors expressed by MSCs, the correlation between soluble factors secreted by MSCs and their immunosuppressive effects, and interactions between MSCs and immune cells.

Assessment of the Immunosuppressive Potential of INF-γ Licensed Adipose Mesenchymal Stem Cells, Their Secretome and Extracellular Vesicles

There is an active search for the ideal strategy to potentialize the effects of Mesenchymal Stem-Cells (MSCs) over the immune system. Also, part of the scientific community is seeking to elucidate the therapeutic potential of MSCs secretome and its extracellular vesicles (EVs), in order to avoid the complexity of a cellular therapy. Here, we investigate the effects of human adipose MSCs (AMSCs) licensing with INF-γ and TLR3 agonist over AMSCs proliferation, migration, as well as the immunomodulatory function. Furthermore, we evaluated how the licensing of AMSCs affected the immunomodulatory function of AMSC derived-secretome, including their EVs. INF-γ licensed-AMSCs presented an elevated expression of indoleamine 2,3-dioxygenase (IDO), accompanied by increased ICAM-1, as well as a higher immunosuppressive potential, compared to unlicensed AMSCs. Interestingly, the conditioned medium obtained from INF-γ licensed-AMSCs also revealed a slightly superior immunosuppressive potential, compared to other licensing strategies. Therefore, unlicensed and INF-γ licensed-AMSCs groups were used to isolate EVs. Interestingly, EVs isolated from both groups displayed similar capacity to inhibit T-cell proliferation. EVs isolated from both groups shared similar TGF-β and Galectin-1 mRNA content but only EVs derived from INF-γ licensed-AMSCs expressed IDO mRNA. In summary, we demonstrated that INF-γ licensing of AMSCs provides an immunosuppressive advantage both from a cell-cell contact-dependent perspective, as well as in a cell-free context. Interestingly, EVs derived from unlicensed and INF-γ licensed-AMSCs have similar ability to control activated T-cell proliferation. These results contribute towards the development of new strategies to control the immune response based on AMSCs or their derived products.

Effect of alternan versus chitosan on the biological properties of human mesenchymal stem cells

Alternan α-1,3- and α-1,6-linked glucan, promotes proliferation, migration, and differentiation of human MSCs.

Lipopolysaccharide from Escherichia coli stimulates osteogenic differentiation of human periodontal ligament stem cells through Wnt/β-catenin-induced TAZ elevation

Human periodontal ligament stem cells (PDLSCs), a type of dental tissue-derived mesenchymal stem cells (MSCs), can be clinically applied in periodontal tissue regeneration to treat periodontitis, which is initiated and sustained by bacteria. Lipopolysaccharide (LPS), the major component of the outer membrane of gram-negative bacteria, is a pertinent deleterious factor in the oral microenvironment. The aim of this study was to investigate the effect of LPS on the proliferation and osteogenic differentiation of PDLSCs, as well as the mechanisms involved. Proliferation and osteogenic differentiation of PDLSCs were detected under the stimulation of Escherichia coli-derived LPS. The data showed that E. coli-derived LPS did not affect the proliferation, viability, and cell cycle of PDLSCs. Furthermore, it promoted osteogenic differentiation with the activation of TAZ. Lentivirus-mediated depletion of TAZ (transcriptional activator with a PDZ motif) was used to determine the role of TAZ on LPS-induced enhancement of osteogenesis. PDLSCs cultured in osteogenic media with or without LPS and DKK1 (Wnt/β-catenin pathway inhibitor) were used to determine the regulatory effect of Wnt signaling. We found that TAZ depletion offset LPS-induced enhancement of osteogenesis. Moreover, treatment with DKK1 offset LPS-induced TAZ elevation and osteogenic promotion. In conclusion, E. coli-derived LPS promoted osteogenic differentiation of PDLSCs by fortifying TAZ activity. The elevation and activation of TAZ were mostly mediated by the Wnt/β-catenin pathway. PDLSC-governed alveolar bone tissue regeneration was not necessarily reduced under bacterial conditions and could be modulated by Wnt and TAZ.

TLR activation inhibits the osteogenic potential of human periodontal ligament stem cells through Akt signaling in a Myd88- or TRIF-dependent manner

BACKGROUND

This study investigated the effects of Toll-like receptors (TLRs) on human periodontal ligament stem cells (hPDLSCs) osteogenic differentiation and the associated mechanisms.

METHODS

TLR1, TLR3, TLR4, and TLR6 expression in hPDLSCs was evaluated by real-time reverse transcriptase polymerase chain reaction (RT-PCR) and flow cytometry, whereas their functional roles were assessed based on nuclear factor (NF)-κB activation and proinflammatory cytokine expression. The osteogenic effects of these TLRs were analyzed by alkaline phosphatase (ALP) staining, ALP activity, and alizarin red staining. The roles of Myd88, TRIF, and downstream molecules mitogen-activated protein kinases (MAPKs) and protein kinase B (Akt) in TLR-mediated impaired osteogenic differentiation were examined by real-time RT-PCR and western blotting using specific small interfering RNA siRNA and pharmacologic inhibitors. The involvement of Akt activation in restoring TLR1-, 4-, and 6-mediated osteogenic suppression was verified using the Akt activator SC-79.

RESULTS

TLR1, TLR3, TLR4, and TLR6 were highly expressed functionally in hPDLSCs and high doses of TLR ligands inhibited osteogenic potential. Furthermore, blocking Myd88 partly rescued the decrease in osteogenesis mediated by TLR1, TLR4, and TLR6 activation by enhancing Akt phosphorylation; likewise, TRIF suppression partially rescued lipopolysaccharide (LPS)-mediated osteogenic inhibition through ERK and Akt activation. Moreover, Akt activation restored the TLR-mediated inhibition of hPDLSC osteogenic differentiation.

CONCLUSIONS

High doses of TLR1, TLR4, and TLR6 ligands suppress hPDLSC osteogenic differentiation by inhibiting Akt activation through Myd88- or TRIF-dependent signaling pathways. Blocking these adaptors or reactivating Akt could restore the TLR-mediated decrease in hPDLSC osteogenesis, and might be an ideal strategy for periodontitis treatment.

Deferoxamine preconditioning activated hypoxia-inducible factor-1α and MyD88-dependent Toll-like receptor 4 signaling in intestinal stem cells

BACKGROUND/PURPOSE

Toll-like receptors (TLRs) are important regulators of innate immunity, and TLR4 pathway can regulate the survival, migration, and differentiation of stem cells, including intestinal stem cells (ISCs). Deferoxamine (DFO), a hypoxia-mimic compound, can activate the proliferation of ISCs. In this study, we investigated the response of TLR4 signaling to DFO-induced hypoxia in cultured ISCs in vitro.

METHODS

After DFO treatment, the crypt organoid number was counted, and the expression levels of Lgr5, Hsp70, HMGB1, HIF-1α, TLR4, MyD88, TRIF, and TRAM in ISCs were examined using QPCR and Western blotting. The chemical inhibitors of different signaling molecules were then used to determine their role in DFO-induced change in ISCs.

RESULTS

The expression levels of Lgr5, HIF-1α, TLR4, MyD88, and TRIF in ISCs increased after DFO treatment, with peak expression of these molecules 6h after DFO treatment. In addition, DFO-induced gene expression of Lgr5 and HIF-1α was partially reversed by pretreatment with the inhibitor of TLR4 or MyD88, but not TRIF inhibitor. Inhibition of HIF-1α also resulted in partial downregulation of DFO-induced elevation of Lgr5 and TLR4.

CONCLUSIONS

These results demonstrated that DFO treatment activated HIF-1α and the TLR4-MyD88 signaling pathway, which might mediate the activation of ISCs.

Mesenchymal Stem Cell Functionalization for Enhanced Therapeutic Applications

IMPACT STATEMENT

Culture expansion of MSCs has detrimental effects on various cell characteristics and attributes (e.g., phenotypic changes and senescence), which, in addition to inherent interdonor variability, negatively impact the standardization and reproducibility of their therapeutic potential. The identification of innate distinct functional MSC subpopulations, as well as the description of ex vivo protocols aimed at maintaining phenotypes and enhancing specific functions have the potential to overcome these limitations. The incorporation of those approaches into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved.

Secreted products of oral bacteria and biofilms impede mineralization of apical papilla stem cells in TLR-, species-, and culture-dependent fashion

Regenerative endodontics exploits the mineralization potential of stem cells from the apical papilla (SCAPs) in order to promote root maturation of permanent immature teeth. SCAPs may encounter post-disinfection residual bacteria either in planktonic or in biofilm growth mode. Bacterial components bind to Toll-like receptors (TLRs) and trigger pro-inflammatory responses. We hypothesized that biofilm-triggered TLR activation affects the mineralization potential of human SCAPs. SCAPs were challenged with conditioned media derived from standardized dual-species biofilms and planktonic bacterial cultures and their inflammatory status and mineralization capacity were studied. Bacterial products from both growth modes (planktonic vs. biofilm) compromised cell viability, proliferation and mineralization capacity of SCAPs, but in a species- and growth mode-dependent fashion. While TLR4 expression remained unaffected, TLR2 expression was upregulated coinciding with a pro-inflammatory activation of SCAPs. Moreover, TLR and its downstream TGF-β-associated kinase (TAK1) appeared to be blocking mineralization, as inhibition of these factors restored it. In conclusion, bacterial products promoted the pro-inflammatory status and inhibited mineralization of human SCAPs in a TLR-, species-, and culture-dependent fashion. TLR2 emerged as the pivotal mediator of these responses and further research is warranted towards the judicious manipulation of SCAPs in order to modify the untoward events of TLR-priming and signaling.