Infusion of third-party mesenchymal stromal cells after kidney transplantation: a phase I-II, open-label, clinical study

The Dual-specificity Phosphatase 3 (DUSP3): A Potential Target Against Renal Ischemia/Reperfusion Injury

Renal ischemia/reperfusion (I/R) injury is a common clinical challenge faced by clinicians in kidney transplantation. I/R is the leading cause of acute kidney injury, and it occurs when blood flow to the kidney is interrupted and subsequently restored. I/R impairs renal function in both short and long terms. Renal ischemic preconditioning refers to all maneuvers intended to prevent or attenuate ischemic damage. In this context, the present review focuses on the dual-specificity phosphatase 3 (DUSP3), also known as vaccinia H1-related phosphatase, an uncommon regulator of mitogen-activated protein kinase (MAPK) phosphorylation. DUSP3 has different biological functions: (1) it acts as a tumor modulator and (2) it is involved in the regulation of immune response, thrombosis, hemostasis, angiogenesis, and genomic stability. These functions occur either through MAPK-dependent or MAPK-independent mechanisms. DUSP3 genetic deletion dampens kidney damage and inflammation caused by I/R in mice, suggesting DUSP3 as a potential target for preventing renal I/R injury. Here, we discuss the putative role of DUSP3 in ischemic preconditioning and the potential mechanisms of such an attenuated inflammatory response via improved kidney perfusion and adequate innate immune response.

Allogeneic mesenchymal stromal cell therapy in kidney transplantation: should repeated human leukocyte antigen mismatches be avoided?

Mesenchymal stromal cells (MSCs) have immunomodulatory properties and are therefore considered promising tools in kidney transplantation. Although most studies have been conducted with autologous MSCs, using allogeneic MSCs as an off-the-shelf product is more feasible in clinical settings. However, allogeneic MSCs could potentially induce an immune response, which might eventually be directed towards the kidney allograft because of shared human leukocyte antigen (HLA) epitope mismatches between the kidney and MSC donor. In this study, we performed in-depth analyses of two cohorts (n = 20) that received third-party MSC therapy after kidney transplantation. While the Neptune Study from Leiden University Medical Center specifically selected MSC to avoid repeated HLA antigen mismatches between kidney and MSC donors, the study from the University of Liège did not perform specific MSC selection. The comparative analyses of amino acid mismatches between these cohorts showed that MSC selection to avoid repeated HLA mismatches at the split antigen level was not sufficient to prevent repeated mismatches at the amino acid level. However, repeated amino acid mismatches were not associated with the occurrence of donor-specific antibodies (DSAs). Thus, the clinical relevance of repeated amino acid mismatches seems to be limited with regard to the risk of DSA formation. Since DSA formation was limited (3 of 20 patients) in this study, larger studies are required to investigate the relevance of preventing repeated HLA mismatches in allogeneic MSC therapy in kidney transplantation.

Regulatory cell therapy for kidney transplantation and autoimmune kidney diseases

Regulatory cell therapies, including regulatory T cells and mesenchymal stromal cells, have shown promise in early clinical trials for reducing immunosuppression burden in transplantation. While regulatory cell therapies may also offer potential for treating autoimmune kidney diseases, data remains sparse, limited mainly to preclinical studies. This review synthesises current literature on the application of regulatory cell therapies in these fields, highlighting the safety and efficacy shown in existing clinical trials. We discuss the need for further clinical validation, optimisation of clinical and immune monitoring protocols, and the challenges of manufacturing and quality control under Good Manufacturing Practice conditions, particularly for investigator-led trials. Additionally, we explore the potential for expanding clinical indications and the unique challenges posed in paediatric applications. Future directions include scaling up production, refining protocols to ensure consistent quality across manufacturing sites, and extending applications to other immune-mediated diseases.

Optimization strategies for mesenchymal stem cell-based analgesia therapy: a promising therapy for pain management

Pain is a very common and complex medical problem that has a serious impact on individuals' physical and mental health as well as society. Non-steroidal anti-inflammatory drugs and opioids are currently the main drugs used for pain management, but they are not effective in controlling all types of pain, and their long-term use can cause adverse effects that significantly impair patients' quality of life. Mesenchymal stem cells (MSCs) have shown great potential in pain treatment. However, limitations such as the low proliferation rate of MSCs in vitro and low survival rate in vivo restrict their analgesic efficacy and clinical translation. In recent years, researchers have explored various innovative approaches to improve the therapeutic effectiveness of MSCs in pain treatment. This article reviews the latest research progress of MSCs in pain treatment, with a focus on methods to enhance the analgesic efficacy of MSCs, including engineering strategies to optimize the in vitro culture environment of MSCs and to improve the in vivo delivery efficiency of MSCs. We also discuss the unresolved issues to be explored in future MSCs and pain research and the challenges faced by the clinical translation of MSC therapy, aiming to promote the optimization and clinical translation of MSC-based analgesia therapy.

Mesenchymal Stem Cells and Extracellular Vesicles: Therapeutic Potential in Organ Transplantation

At present, organ transplantation remains the most appropriate therapy for patients with end-stage organ failure. However, the field of organ transplantation is still facing many challenges, including the shortage of organ donors, graft function damage caused by organ metastasis, and antibody-mediated immune rejection. It is therefore urgently necessary to find new and effective treatment. Stem cell therapy has been regarded as a "regenerative medicine technology." Mesenchymal stem cells (MSCs), as the most common source of cells for stem cell therapy, play an important role in regulating innate and adaptive immune responses and have been widely used in clinical trials for the treatment of autoimmune and inflammatory diseases. Increasing evidence has shown that MSCs mainly rely on paracrine pathways to exert immunomodulatory functions. In addition, mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) are the main components of paracrine substances of MSCs. Herein, an overview of the application of the function of MSCs and MSC-EVs in organ transplantation will focus on the progress reported in recent experimental and clinical findings and explore their uses for graft preconditioning and recipient immune tolerance regulation. Additionally, the limitations on the use of MSC and MSC-EVs are also discussed, covering the isolation of exosomes and preservation techniques. Finally, the opportunities and challenges for translating MSCs and MSC-EVs into clinical practice of organ transplantation are also evaluated.

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

Bone formation by human paediatric marrow stromal cells in a functional allogeneic immune system

Allogeneic stem-cell based regenerative medicine is a promising approach for bone defect repair. The use of chondrogenically differentiated human marrow stromal cells (MSCs) has been shown to lead to bone formation by endochondral ossification in immunodeficient pre-clinical models. However, an insight into the interactions between the allogeneic immune system and the human MSC-derived bone grafts has not been fully achieved yet. The choice of a potent source of MSCs isolated from pediatric donors with consistent differentiation and high proliferation abilities, as well as low immunogenicity, could increase the chance of success for bone allografts. In this study, we employed an immunodeficient animal model humanised with allogeneic immune cells to study the immune responses towards chondrogenically differentiated human pediatric MSCs (ch-pMSCs). We show that ch-differentiated pMSCs remained non-immunogenic to allogeneic CD4 and CD8 T cells in an in vitro co-culture model. After subcutaneous implantation in mice, ch-pMSC-derived grafts were able to initiate bone mineralisation in the presence of an allogeneic immune system for 3 weeks without the onset of immune responses. Re-exposing the splenocytes of the humanised animals to pMSCs did not trigger further T cell proliferation, suggesting an absence of secondary immune responses. Moreover, ch-pMSCs generated mature bone after 8 weeks of implantation that persisted for up to 6 more weeks in the presence of an allogeneic immune system. These data collectively show that human allogeneic chondrogenically differentiated pediatric MSCs might be a safe and potent option for bone defect repair in the tissue engineering and regenerative medicine setting.

Interleukin-37 contributes to endometrial regenerative cell-mediated immunotherapeutic effect on chronic allograft vasculopathy

BACKGROUND AIMS

Chronic allograft vasculopathy (CAV) remains a predominant contributor to late allograft failure after organ transplantation. Several factors have already been shown to facilitate the progression of CAV, and there is still an urgent need for effective and specific therapeutic approaches to inhibit CAV. Human mesenchymal-like endometrial regenerative cells (ERCs) are free from the deficiencies of traditional invasive acquisition methods and possess many advantages. Nevertheless, the exact immunomodulation mechanism of ERCs remains to be elucidated.

METHODS

C57BL/6 (B6) mouse recipients receiving BALB/c mouse donor abdominal aorta transplantation were treated with ERCs, negative control (NC)-ERCs and interleukin (IL)-37-/-ERCs (ERCs with IL-37 ablation), respectively. Pathologic lesions and inflammatory cell infiltration in the grafts, splenic immune cell populations, circulating donor-specific antibody levels and cytokine profiles were analyzed on postoperative day (POD) 40. The proliferative capacities of Th1, Th17 and Treg subpopulations were assessed in vitro.

RESULTS

Allografts from untreated recipients developed typical pathology features of CAV, namely endothelial thickening, on POD 40. Compared with untreated and IL-37-/-ERC-treated groups, IL-37-secreting ERCs (ERCs and NC-ERCs) significantly reduced vascular stenosis, the intimal hyperplasia and collagen deposition. IL-37-secreting ERCs significantly inhibited the proliferation of CD4+T cells, reduced the proportions of Th1 and Th17 cells, but increased the proportion of Tregs in vitro. Furthermore, in vitro results also showed that IL-37-secreting ERCs significantly inhibited Th1 and Th17 cell responses, abolished B-cell activation, diminished donor-specific antibody production and increased Treg proportions. Notably, IL-37-secreting ERCs remarkably downregulated the levels of pro-inflammatory cytokines (interferon-γ, tumor necrosis factor-α, IL-1β, IL-6 and IL-17A) and increased IL-10 levels in transplant recipients.

CONCLUSIONS

The knockdown of IL-37 dramatically abrogates the therapeutic ability of ERCs for CAV. Thus, this study highlights that IL-37 is indispensable for ERC-mediated immunomodulation for CAV and improves the long-term allograft acceptance.

Human mesenchymal stem cells derived from adipose tissue showed a more robust effect than those from the umbilical cord in promoting corneal graft survival by suppressing lymphangiogenesis

BACKGROUND

Mesenchymal stem cells (MSCs) have shown promising potential in allograft survival. However, few reports have focused on comparing the immunosuppressive capacity of MSCs from different sources and administered via different routes in inhibiting transplant rejection. Moreover, virtually nothing is known about the role of MSCs in the regulation of graft neovascularization and lymphangiogenesis. In this study, we compared the efficacy of human adipose MSCs (hAD-MSCs) and human umbilical cord MSCs (hUC-MSCs) in vitro and in corneal transplantation models to explore the underlying molecular mechanisms and provide a powerful strategy for future clinical applications.

METHODS

hAD-MSCs and hUC-MSCs were generated, and their self-renewal and multi-differentiation abilities were evaluated. The inhibitory effect of human MSCs (hMSCs) was examined by T-cell proliferation assays with or without transwell in vitro. Two MSCs from different sources were separately adoptively transferred in mice corneal transplantation (5 × 105 or 1 × 106/mouse) via topical subconjunctival or intravenous (IV) routes. Allograft survival was evaluated every other day, and angiogenesis and lymphomagenesis were quantitatively analyzed by immunofluorescence staining. The RNA expression profiles of hMSCs were revealed by RNA sequencing (RNA-seq) and verified by quantitative real-time PCR (qRT‒PCR), western blotting or ELISA. The function of the differentially expressed gene FAS was verified by a T-cell apoptosis assay.

RESULTS

hAD-MSCs induced stronger immunosuppression in vitro than hUC-MSCs. The inhibitory effect of hUC-MSCs but not hAD-MSCs was mediated by cell-cell contact-dependent mechanisms. Systemic administration of a lower dose of hAD-MSCs showed better performance in prolonging corneal allograft survival than hUC-MSCs, while subconjunctival administration of hMSCs was safer and further prolonged corneal allograft survival. Both types of hMSCs could inhibit corneal neovascularization, while hAD-MSCs showed greater superiority in suppressing graft lymphangiogenesis. RNA-seq analysis and confirmation experiments revealed the superior performance of hAD-MSCs in allografts based on the lower expression of vascular endothelial growth factor C (VEGF-C) and higher expression of FAS.

CONCLUSIONS

The remarkable inhibitory effects on angiogenesis/lymphangiogenesis and immunological transplantation effects support the development of hAD-MSCs as a cell therapy against corneal transplant rejection. Topical administration of hMSCs was a safer and more effective route for application than systemic administration.

Recent advances in pre-conditioned mesenchymal stem/stromal cell (MSCs) therapy in organ failure; a comprehensive review of preclinical studies

Mesenchymal stem/stromal cells (MSCs)-based therapy brings the reassuring capability to regenerative medicine through their self-renewal and multilineage potency. Also, they secret a diversity of mediators, which are complicated in moderation of deregulated immune responses, and yielding angiogenesis in vivo. Nonetheless, MSCs may lose biological performance after procurement and prolonged expansion in vitro. Also, following transplantation and migration to target tissue, they encounter a harsh milieu accompanied by death signals because of the lack of proper tensegrity structure between the cells and matrix. Accordingly, pre-conditioning of MSCs is strongly suggested to upgrade their performances in vivo, leading to more favored transplantation efficacy in regenerative medicine. Indeed, MSCs ex vivo pre-conditioning by hypoxia, inflammatory stimulus, or other factors/conditions may stimulate their survival, proliferation, migration, exosome secretion, and pro-angiogenic and anti-inflammatory characteristics in vivo. In this review, we deliver an overview of the pre-conditioning methods that are considered a strategy for improving the therapeutic efficacy of MSCs in organ failures, in particular, renal, heart, lung, and liver.

Regulatory B Cells Contribute to the Clinical Response After Bone Marrow-Derived Mesenchymal Stromal Cell Infusion in Patients With Systemic Sclerosis

Mesenchymal stromal cells (MSCs) have recently emerged as an interesting therapeutic approach for patients with progressive systemic sclerosis (SSc), a rare and life-threatening orphan autoimmune disease. Whereas MSC immunomodulatory potential is considered as a central mechanism for their clinical benefit, very few data are available on the impact of MSCs on immune cell subsets in vivo. In the current extended study of a phase I/II clinical trial exploring the injection of a single dose of allogeneic bone marrow-MSCs (alloBM-MSCs) in patients with severe SSc (NCT02213705), we performed a longitudinal in-depth characterization of circulating immune cells in 19 MSC-treated patients, including 14 responders and 5 non-responders. By a combination of flow cytometry and transcriptomic analyses, we highlighted an increase in circulating CD24hiCD27posCD38lo/neg memory B cells, the main IL-10-producing regulatory B cell (Breg) subset, and an upregulation of IL10 expression in ex-vivo purified B cells, specifically in responder patients, early after the alloBM-MSC infusion. In addition, a deeper alteration of the B-cell compartment before alloBM-MSC treatment, including a higher expression of profibrotic cytokines IL6 and TGFβ by sorted B cells was associated with a non-responder clinical status. Finally, BM-MSCs were able to directly upregulate IL-10 production in activated B cells in vitro. These data suggest that cytokine-producing B cells, in particular Breg, are pivotal effectors of BM-MSC therapeutic activity in SSc. Their quantification as activity biomarkers in MSC potency assays and patient selection criteria may be considered to reach optimal clinical benefit when designing MSC-based clinical trials.

Bone marrow mesenchymal stem cells repress renal transplant immune rejection by facilitating the APRIL phosphorylation to induce regulation B cell production

Bone marrow mesenchymal stem cells (BMSCs) exert pivotal roles in suppressing immune rejection in organ transplantation. However, the function of BMSCs on immune rejection in renal transplantation remains unclear. This study aimed to evaluate the effect and underlying mechanism of BMSCs on immune rejection in renal transplantation. Following the establishment of the renal allograft mouse model, the isolated primary BMSCs were injected intravenously into the recipient mice. Enzyme-linked immunosorbent assay, flow cytometry, hematoxylin-eosin staining, and Western blot assays were conducted to investigate BMSCs' function in vivo and in vitro. Mechanistically, the underlying mechanism of BMSCs on immune rejection in renal transplantation was investigated in in vivo and in vitro models. Functionally, BMSCs alleviated the immune rejection in renal transplantation mice and facilitated B cell activation and the production of IL-10⁺ regulatory B cells (Bregs). Furthermore, the results of mechanism studies revealed that BMSCs induced the production of IL-10⁺ Bregs by facilitating a proliferation-inducing ligand (APRIL) phosphorylation to enhance immunosuppression and repressed renal transplant rejection by promoting APRIL phosphorylation to induce IL-10⁺ Bregs. BMSCs prevent renal transplant rejection by facilitating APRIL phosphorylation to induce IL-10⁺ Bregs.

Autologous Mesenchymal Stem Cells for Treatment of Chronic Active Antibody-Mediated Kidney Graft Rejection: Report of the Phase I/II Clinical Trial Case Series

Mesenchymal stem cell (MSCs) therapy has already been studied in kidney transplant recipients (KTRs), and the available data showed that it is safe and well tolerated. The aim of this study was to evaluate the safety and efficacy of autologous MSCs in combination with standard therapy in KTRs with biopsy-proven chronic active antibody-mediated rejection (AMR). Patients with biopsy-proven chronic active AMR received treatment with autologous bone marrow-derived MSCs (3 × 10⁶ cells/kg iv) after completion of standard therapy and were followed for up to 12 months. The primary endpoints were safety by assessment of adverse events. Secondary endpoints included assessment of kidney graft function, immunological and histological changes related to AMR activity and chronicity assessed by conventional microscopy and molecular transcripts. A total of 3 patients were enrolled in the study before it was terminated prematurely because of adverse events. We found that AMR did not improve in any of the patients after treatment with MSCs. In addition, serious adverse events were observed in one case when autologous MSCs therapy was administered in the late phase after kidney transplantation, which requires further elucidation.

The role of mesenchymal stem cell transplantation for ischemic stroke and recent research developments

Ischemic stroke is a common cerebrovascular disease that seriously affects human health. However, most patients do not practice self-care and cannot rely on the current clinical treatment for guaranteed functional recovery. Stem cell transplantation is an emerging treatment studied in various central nervous system diseases. More importantly, animal studies show that transplantation of mesenchymal stem cells (MSCs) can alleviate neurological deficits and bring hope to patients suffering from ischemic stroke. This paper reviews the biological characteristics of MSCs and discusses the mechanism and progression of MSC transplantation to provide new therapeutic directions for ischemic stroke.

Bio-distribution and longevity of mesenchymal stromal cell derived membrane particles

Vesicle-based medicines hold great promise for therapy development but essential knowledge on the bio-distribution and longevity of vesicles after administration is lacking. We generated vesicles from the membranes of human mesenchymal stromal cells (MSC) and we demonstrated earlier that these so-called membrane particles (MP) mediate immunomodulatory and regenerative responses in target cells. In the present study we examined the bio-distribution and longevity of MP after intravenous administration in mice. While most vesicle tracking methods are based on imaging techniques, which require labeling of vesicles and can only detect dense accumulations of vesicles, we used proteomics analysis to detect the presence of MP-derived proteins in multiple organs and tissues. MP proteins were mainly present in plasma and leukocytes at 1 h after injection, indicating that MP - in contrast to whole MSC - do not accumulate in the lungs upon first passage but remain in circulation. After 24 h, MP proteins were still present in plasma but were most abundant in the liver. RNA sequencing of livers demonstrated that MP impact liver function and in particular induce metabolic pathways. These data provide a clear view of the bio-distribution and longevity of MP, which is likely extrapolatable to other types of vesicles, and demonstrate that MP circulate for up to 24 h and may be a tool for targeting the liver.

IL-37 overexpression promotes endometrial regenerative cell-mediated inhibition of cardiac allograft rejection

BACKGROUND

Endometrial regenerative cells (ERCs) play an important role in attenuation of acute allograft rejection, while their effects are limited. IL-37, a newly discovered immunoregulatory cytokine of the IL-1 family, can regulate both innate and adaptive immunity. Whether IL-37 overexpression can enhance the therapeutic effects of ERCs in inhibition of acute cardiac allograft rejection remains unknown and will be explored in this study.

METHODS

C57BL/6 mice recipients receiving BALB/c mouse heterotopic heart allografts were randomly divided into the phosphate-buffered saline (untreated), ERC treated, negative lentiviral control ERC (NC-ERC) treated, and IL-37 overexpressing ERC (IL-37-ERC) treated groups. Graft pathological changes were assessed by H&E staining. The intra-graft cell infiltration and splenic immune cell populations were analyzed by immunohistochemistry and flow cytometry, respectively. The stimulatory property of recipient DCs was tested by an MLR assay. Furthermore, serum cytokine profiles of recipients were measured by ELISA assay.

RESULTS

Mice treated with IL-37-ERCs achieved significantly prolonged allograft survival compared with the ERC-treated group. Compared with all the other control groups, IL-37-ERC-treated group showed mitigated inflammatory response, a significant increase in tolerogenic dendritic cells (Tol-DCs), regulatory T cells (Tregs) in the grafts and spleens, while a reduction of Th1 and Th17 cell population. Additionally, there was a significant upregulation of immunoregulatory IL-10, while a reduction of IFN-γ, IL-17A, IL-12 was detected in the sera of IL-37-ERC-treated recipients.

CONCLUSION

IL-37 overexpression can promote the therapeutic effects of ERCs to inhibit acute allograft rejection and further prolong graft survival. This study suggests that gene-modified ERCs overexpressing IL-37 may pave the way for novel therapeutic options in the field of transplantation.

Effect of the Combination of Everolimus and Mesenchymal Stromal Cells on Regulatory T Cells Levels and in a Liver Transplant Rejection Model in Rats

Introduction

Mesenchymal stromal cells (MSCs) have particular properties that are of interest in organ transplantation, including the expansion of regulatory T cells (Tregs), a key factor in transplant tolerance induction. However, the most effective immunosuppressive drug to associate with MSCs has yet to be defined. Additionally, the impact of the association of everolimus with MSCs on Treg expansion, and on the induction of liver graft tolerance, has never been studied. The aim of this study was to evaluate the effects of MSCs in combination, or not, with everolimus on Treg expansion and in a model of rejection after liver transplantation (LT) in the rat.

Methods

Firstly, 24 Lewis rats were assigned to 4 groups (n=6 in each group) receiving intravenous MSCs or saline injection at day (D)9 with/without subcutaneous everolimus from D0 to D14. Analysis of circulating Tregs was performed at D0, D14 and D28. In a second set of experiment, 30 Lewis rats were randomized in 3 groups 48hours after LT with a Dark Agouti rat liver: everolimus (subcutaneous for 14 days), MSCs (intravenous injection at post-operative day 2 and 9), or both everolimus and MSCs. Rejection of the liver graft was assessed by liver tests, histology and survival.

Results

Individually, MSC infusion and everolimus promoted Treg expansion in rats, and everolimus had no negative impact on Treg expansion in combination with MSCs. However, in the LT model, injections of MSCs two and nine days following LT were not effective at preventing acute rejection, and the combination of MSCs with everolimus failed to show any synergistic effect when compared to everolimus alone.

Conclusion

Everolimus may be used in association with MSCs. However, in our model of LT in the rat, post-transplant MSC injections did not prevent acute rejection, and the association of MSCs with everolimus did not show any synergistic effect.

How to Make Sense out of 75,000 Mesenchymal Stromal Cell Publications?

Mesenchymal stromal cells have been the subject of an expanding number of studies over the past decades. Today, over 75,000 publications are available that shine light on the biological properties and therapeutic effects of these versatile cells in numerous pre-clinical models and early-phase clinical trials. The massive number of papers makes it hard for researchers to comprehend the whole field, and furthermore, they give the impression that mesenchymal stromal cells are wonder cells that are curative for any condition. It is becoming increasingly difficult to dissect how and for what conditions mesenchymal stromal cells exhibit true and reproducible therapeutic effects. This article tries to address the question how to make sense of 75,000, and still counting, publications on mesenchymal stromal cells.

Infusion of Allogeneic Mesenchymal Stromal Cells After Liver Transplantation: A 5-Year Follow-Up

Various properties of mesenchymal stromal cells (MSCs) might be particularly of interest after liver transplantation (LT). In this article, we report the long-term results of a prospective, controlled, and first-in-human phase 1 study evaluating the safety of a single MSC infusion after LT. A total of 10 LT recipients treated with standard immunosuppression received 1.5 to 3 × 10⁶ /kg third-party unrelated MSCs on postoperative day 3 and were prospectively compared with a control group of 10 LT recipients. Primary endpoints were set to prospectively detect potentially delayed adverse effects of MSC infusion, particularly the occurrence of infections and cancers. Secondary endpoints of liver graft and patient survival, graft rejection and function, occurrence of bile duct complications, and development of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA) against liver or MSC donors were studied. The median follow-up was 85 months. There was no difference in overall rates of infection or cancer at 5 years of follow-up between the 2 groups. There was also no difference in secondary endpoints. The prevalence of de novo liver DSAs related to HLA mismatches was twice as high in the MSC group compared with the control group. All of the de novo class II HLA antibodies against MSCs were linked to a shared HLA mismatch between the liver and MSCs. This study confirms the safety of a single MSC infusion after LT. The potential benefits of MSC injections in the context of organ transplantation have yet to be demonstrated by larger prospective studies. The development of anti-HLA antibodies against an MSC donor should be further evaluated, especially in cases of shared HLA mismatches between graft and MSC donors, despite the fact that no deleterious effect has been detected.

A Brief Overview of Global Trends in MSC-Based Cell Therapy

Human mesenchymal stem cells (MSCs), also known as mesenchymal stromal cells or medicinal signaling cells, are important adult stem cells for regenerative medicine, largely due to their regenerative characteristics such as self-renewal, secretion of trophic factors, and the capability of inducing mesenchymal cell lineages. MSCs also possess homing and trophic properties modulating immune system, influencing microenvironment around damaged tissues and enhancing tissue repair, thus offering a broad perspective in cell-based therapies. Therefore, it is not surprising that MSCs have been the broadly used adult stem cells in clinical trials. To gain better insights into the current applications of MSCs in clinical applications, we perform a comprehensive review of reported data of MSCs clinical trials conducted globally. We summarize the biological effects and mechanisms of action of MSCs, elucidating recent clinical trials phases and findings, highlighting therapeutic effects of MSCs in several representative diseases, including neurological, musculoskeletal diseases and most recent Coronavirus infectious disease. Finally, we also highlight the challenges faced by many clinical trials and propose potential solutions to streamline the use of MSCs in routine clinical applications and regenerative medicine.

Biomarkers of immune tolerance in kidney transplantation: an overview

Kidney failure, one of the most prevalent diseases in the world and with increasing incidence, is associated with substantial morbidity and mortality. Currently available modes of kidney replacement therapy include dialysis and kidney transplantation. Though kidney transplantation is the preferred and ideal mode of kidney replacement therapy, this modality, however, is not without its risks. Kidney transplant recipients are constantly at risk of complications associated with immunosuppression, namely, opportunistic infections (e.g., Epstein-Barr virus and cytomegalovirus infections), post-transplant lymphoproliferative disorder^, and complications associated with immunosuppressants (e.g., calcineurin inhibitor- and corticosteroid-associated new onset diabetes after transplantation and calcineurin inhibitor-associated nephrotoxicity). Transplantation tolerance, an acquired state in which immunocompetent recipients have developed donor-specific unresponsiveness, may be the Holy Grail in enabling optimal allograft survival and obviating the risks associated with immunosuppression in kidney transplant recipients. This review aims to discuss the biomarkers available to predict, identify, and define the transplant immune tolerant state and various tolerance induction strategies. Regrettably, pediatric patients have not been included in any tolerance studies and this should be the focus of future studies.

Mesenchymal Stromal Cells Mediate Clinically Unpromising but Favourable Immune Responses in Kidney Transplant Patients

Background

Allograft rejection postkidney transplantation (KTx) is a major clinical challenge despite increased access to a healthcare system and improvement in immunosuppressive (IS) drugs. In recent years, mesenchymal stromal cells (MSCs) have aroused considerable interest in field of transplantation due to their immunomodulatory and regenerative properties. This study was aimed at investigating safety, feasibility, and immunological effects of autologous MSCs (auto-MSCs) and allogeneic MSCs (allo-MSCs) as a complement to IS drug therapy in KTx patients.

Methods

10 patients undergoing KTx with a living-related donor were analysed along with 5 patients in the control group. Patients were given auto-MSCs or allo-MSCs at two time points, i.e., one day before transplant (D-0) and 30 days after transplant (D-30) at the rate of 1.0-1.5 × 10⁶ MSCs per kg body weight in addition to immunosuppressants. Patients were followed up for 2 years, and 29 immunologically relevant lymphocyte subsets and 8 cytokines and important biomarkers were analysed at all time points.

Results

Patients displayed no signs of discomfort or dose-related toxicities in response to MSC infusion. Flow cytometric analysis revealed an increase in B regulatory lymphocyte populations and nonconventional T regulatory cells and a decrease in T effector lymphocyte proportions in auto-MSC-infused patients. No such favourable immune responses were observed in all MSC-infused patients.

Conclusion

This study provides evidence that auto-MSCs are safe and well tolerated. This is the first ever report to compare autologous and allogeneic MSC infusion in KTx patients. Importantly, our data demonstrated that MSC-induced immune responses in patients did not completely correlate with clinical outcomes. Our findings add to the current perspective of using MSCs in KTx and explore possibilities through which donor/recipient chimerism can be achieved to induce immune tolerance in KTx patients.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Electromagnetic field exposure as a plausible approach to enhance the proliferation and differentiation of mesenchymal stem cells in clinically relevant scenarios

Mesenchymal stem/stromal cell (MSC)‍-based therapy has been regarded as one of the most revolutionary breakthroughs in the history of modern medicine owing to its myriad of immunoregulatory and regenerative properties. With the rapid progress in the fields of osteo- and musculoskeletal therapies, the demand for MSC-based treatment modalities is becoming increasingly prominent. In this endeavor, researchers around the world have devised new and innovative techniques to support the proliferation of MSCs while minimizing the loss of hallmark features of stem cells. One such example is electromagnetic field (EMF) exposure, which is an alternative approach with promising potential. In this review, we present a critical discourse on the efficiency, practicability, and limitations of some of the relevant methods, with insurmountable evidence backing the implementation of EMF as a feasible strategy for the clinically relevant expansion of MSCs.

Ex-vivo Kidney Machine Perfusion: Therapeutic Potential

Kidney transplantation remains the gold standard treatment for patients suffering from end-stage kidney disease. To meet the constantly growing organ demands grafts donated after circulatory death (DCD) or retrieved from extended criteria donors (ECD) are increasingly utilized. Not surprisingly, usage of those organs is challenging due to their susceptibility to ischemia-reperfusion injury, high immunogenicity, and demanding immune regulation after implantation. Lately, a lot of effort has been put into improvement of kidney preservation strategies. After demonstrating a definite advantage over static cold storage in reduction of delayed graft function rates in randomized-controlled clinical trials, hypothermic machine perfusion has already found its place in clinical practice of kidney transplantation. Nevertheless, an active investigation of perfusion variables, such as temperature (normothermic or subnormothermic), oxygen supply and perfusate composition, is already bringing evidence that ex-vivo machine perfusion has a potential not only to maintain kidney viability, but also serve as a platform for organ conditioning, targeted treatment and even improve its quality. Many different therapies, including pharmacological agents, gene therapy, mesenchymal stromal cells, or nanoparticles (NPs), have been successfully delivered directly to the kidney during ex-vivo machine perfusion in experimental models, making a big step toward achievement of two main goals in transplant surgery: minimization of graft ischemia-reperfusion injury and reduction of immunogenicity (or even reaching tolerance). In this comprehensive review current state of evidence regarding ex-vivo kidney machine perfusion and its capacity in kidney graft treatment is presented. Moreover, challenges in application of these novel techniques in clinical practice are discussed.

Bone Marrow Mononuclear Cells Restore Normal Mitochondrial Ca2+ Handling and Ca2+-Induced Depolarization of the Internal Mitochondrial Membrane by Inhibiting the Permeability Transition Pore After Ischemia/Reperfusion

Acute kidney injury due to ischemia followed by reperfusion (IR) is a severe clinical condition with high death rates. IR affects the proximal tubule segments due to their predominantly oxidative metabolism and profoundly altered mitochondrial functions. We previously described the impact of IR on oxygen consumption, the generation of membrane potential (ΔΨ), and formation of reactive oxygen species, together with inflammatory and structural alterations. We also demonstrated the benefits of bone marrow mononuclear cells (BMMC) administration in these alterations. The objective of the present study has been to investigate the effect of IR and the influence of BMMC on the mechanisms of Ca²⁺ handling in mitochondria of the proximal tubule cells. IR inhibited the rapid accumulation of Ca²⁺ (Ca²⁺ green fluorescence assays) and induced the opening of the cyclosporine A-sensitive permeability transition pore (PTP), alterations prevented by BMMC. IR accelerated Ca²⁺-induced decrease of ΔΨ (Safranin O fluorescence assays), as evidenced by decreased requirement for Ca²⁺ load and t_1/2 for complete depolarization. Addition of BMMC and ADP recovered the normal depolarization profile, suggesting that stabilization of the adenine nucleotide translocase (ANT) in a conformation that inhibits PTP opening offers a partial defense mechanism against IR injury. Moreover, as ANT forms a complex with the voltage-dependent anion channel (VDAC) in the outer mitochondrial membrane, it is possible that this complex is also a target for IR injury—thus favoring Ca²⁺ release, as well as the supramolecular structure that BMMC protects. These beneficial effects are accompanied by a stimulus of the citric acid cycle—which feed the mitochondrial complexes with the electrons removed from different substrates—as the result of accentuated stimulus of citrate synthase activity by BMMC.

Cardiovascular Effects of Autologous Bone Marrow-Derived Mesenchymal Stromal Cell Therapy With Early Tacrolimus Withdrawal in Renal Transplant Recipients: An Analysis of the Randomized TRITON Study

Background After renal transplantation, there is a need of immunosuppressive regimens that effectively prevent allograft rejection while minimizing cardiovascular complications. This substudy of the TRITON trial evaluated the cardiovascular effects of autologous bone marrow-derived mesenchymal stromal cells (MSCs) in renal transplant recipients. Methods and Results Renal transplant recipients were randomized to MSC therapy, infused at weeks 6 and 7 after transplantation, with withdrawal at week 8 of tacrolimus or standard tacrolimus dose. Fifty-four patients (MSC group=27; control group=27) underwent transthoracic echocardiography at weeks 4 and 24 after transplantation and were included in this substudy. Changes in clinical and echocardiographic variables were compared. The MSC group showed a benefit in blood pressure control, assessed by a significant interaction between changes in diastolic blood pressure and the treatment group (P=0.005), and a higher proportion of patients achieving the predefined blood pressure target of <140/90 mm Hg compared with the control group (59.3% versus 29.6%, P=0.03). A significant reduction in left ventricular mass index was observed in the MSC group, whereas there were no changes in the control group (P=0.002). The proportion of patients with left ventricular hypertrophy decreased at 24 weeks in the MSC group (33.3% versus 70.4%, P=0.006), whereas no changes were noted in the control group (63.0% versus 48.1%, P=0.29). Additionally, MSC therapy prevented progressive left ventricular diastolic dysfunction, as demonstrated by changes in mitral deceleration time and tricuspid regurgitant jet velocity. Conclusions MSC strategy is associated with improved blood pressure control, regression of left ventricular hypertrophy, and prevention of progressive diastolic dysfunction at 24 weeks after transplantation. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03398681.

Administration of adipose stromal vascular fraction attenuates acute rejection in donation after circulatory death rat renal transplantation

OBJECTIVE

Stem cell therapy represents a new approach to induce immune tolerance in solid organ transplantation. However, the time-consuming process of stem cell expending limits the range of stem cell treatment. Uncultured adipose stromal vascular fraction is considered an attractive cell source for cell-based therapy. This study aimed to evaluate the effect of stromal vascular fraction on the immune system in donation after circulatory death rat renal transplantation.

METHODS

Stromal vascular fraction cells and splenocytes were co-cultured to evaluate the effect of stromal vascular fraction on splenocyte proliferation and viability. Sprague-Dawley rats were used as donors. and Wistar rats as recipients to establish a donation after a circulatory death rat renal transplantation model. Warm ischemia time was 5 min. Stromal vascular fraction was administered in the rat model following the intra-arterial route. The spleens and grafts of recipients were harvested on days 1, 3 and 7 post-transplantation for assessing acute rejection, infiltration of inflammatory cells, indoleamine 2, 3-dioxygenase expression and T-cell frequency in the spleen.

RESULTS

Stromal vascular fraction could inhibit proliferation and induce apoptosis of splenocytes in vitro (P < 0.05). The administration of stromal vascular fraction could significantly reduce acute rejection and infiltration of CD8⁺ T cells and mononuclear macrophages in grafts, and increase indoleamine 2, 3-dioxygenase expression (P < 0.05). The frequency of CD8⁺ T cells decreased, and the frequency of CD25⁺ Foxp3⁺ regulatory T cells increased in the spleen of the acute rejection + stromal vascular fraction group on day 7 post-transplantation (P < 0.05).

CONCLUSION

Administration of the adipose stromal vascular fraction could attenuate acute rejection in donation after circulatory death renal transplantation by increasing the ratio of regulatory T cells and enhancing indoleamine 2, 3-dioxygenase expression.

Myeloid and Mesenchymal Stem Cell Therapies for Solid Organ Transplant Tolerance

Transplantation is now performed globally as a routine procedure. However, the increased demand for donor organs and consequent expansion of donor criteria has created an imperative to maximize the quality of these gains. The goal is to balance preservation of allograft function against patient quality-of-life, despite exposure to long-term immunosuppression. Elimination of immunosuppressive therapy to avoid drug toxicity, with concurrent acceptance of the allograft-so-called operational tolerance-has proven elusive. The lack of recent advances in immunomodulatory drug development, together with advances in immunotherapy in oncology, has prompted interest in cell-based therapies to control the alloimmune response. Extensive experimental work in animals has characterized regulatory immune cell populations that can induce and maintain tolerance, demonstrating that their adoptive transfer can promote donor-specific tolerance. An extension of this large body of work has resulted in protocols for manufacture, as well as early-phase safety and feasibility trials for many regulatory cell types. Despite the excitement generated by early clinical trials in autoimmune diseases and organ transplantation, there is as yet no clinically validated, approved regulatory cell therapy for transplantation. In this review, we summarize recent advances in this field, with a focus on myeloid and mesenchymal cell therapies, including current understanding of the mechanisms of action of regulatory immune cells, and clinical trials in organ transplantation using these cells as therapeutics.

HO-1/BMMSC perfusion using a normothermic machine perfusion system reduces the acute rejection of DCD liver transplantation by regulating NKT cell co-inhibitory receptors in rats

Background

Liver transplantation (LT) is required in many end-stage liver diseases. Donation after cardiac death (DCD) livers are often used, and treatment of acute rejection (ACR) requires the use of immunosuppressive drugs that are associated with complications. Bone marrow mesenchymal stem cells (BMMSCs) are used in treatment following LT; however, they have limitations, including low colonization in the liver. An optimized BMMSC application method is required to suppress ACR.

Methods

BMMSCs were isolated and modified with the heme oxygenase 1 (HO-1) gene. HO-1/BMMSCs were perfused into donor liver in vitro using a normothermic machine perfusion (NMP) system, followed by LT into rats. The severity of ACR was evaluated based on liver histopathology. Gene chip technology was used to detect differential gene expression, and flow cytometry to analyze changes in natural killer (NK) T cells.

Results

NMP induced BMMSCs to colonize the donor liver during in vitro preservation. The survival of HO-1/BMMSCs in liver grafts was significantly longer than that of unmodified BMMSCs. When the donor liver contained HO-1/BMMSCs, the local immunosuppressive effect was improved and prolonged, ACR was controlled, and survival time was significantly prolonged. The application of HO-1/BMMSCs reduced the number of NKT cells in liver grafts, increased the expression of NKT cell co-inhibitory receptors, and reduced NKT cell expression of interferon-γ.

Conclusions

NK cell and CD8⁺ T cell activation was inhibited by application of HO-1/BMMSCs, which reduced ACR of transplanted liver. This approach could be developed to enhance the success rate of LT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02647-5.

Ultrasound-Guided Transplantation of Mesenchymal Stem Cells Improves Adriamycin Nephropathy in Rats Through the RIPK3/MLKL and TLR-4/NF-κB Signaling

Bone marrow stromal cell (BMSC) treatment has been shown to be beneficial for Adriamycin nephropathy (ADR). However, the low transplantation rate is still the key factor that affects this strategy. This study is the first to investigate the efficacy and potential mechanism of ultrasound-guided transrenal arterial transfer of BMSCs for the treatment of ADR in rats. The ADR rat model was established by two injections of doxorubicin. In addition, the rats were randomly divided into four groups (10 rats per group): the normal group (no treatment), the medium control group (treated with medium), the Adriamycin group (treated with phosphate buffer), and the BMSC group (treated with BMSCs). After 4 weeks, the levels of serum creatinine (SCr), blood urea nitrogen (BUN), and urine albumin (ALb) were measured. In addition, pathological changes in kidney tissue were evaluated by pathological sectioning and electron microscopy. Western blotting was used to determine the levels of proteins in rat kidneys. Ultrasound-guided renal artery transplantation of BMSCs reduced the levels of SCr, BUN, and ALb and improved the pathological structure of rat kidneys compared with those in the Adriamycin group. This treatment inhibited renal cell necrosis by reducing the expression of receptor-interacting Serine/threonine Kinase 3 (RIPK3) and Mixed lineage kinase domain-like pseudokinase (MLKL) and inhibited renal inflammation and fibrosis by reducing the expression of Toll-Like receptor 4 (TLR4) and nuclear factor κB (NF-κB). Our study shows that ultrasound-guided transrenal artery transplantation of BMSCs can improve adriamycin-induced renal injury in rats by regulating the RIPK3/MLKL and TLR-4/NF-κB pathways and inhibiting renal necrosis, inflammation, and fibrosis.

Protective action of ultrasound-guided intraparenchymal transplantation of BMSCs in adriamycin nephropathy rats through the RIPK3/MLKL and NLRP3 pathways

BACKGROUND

Bone marrow stromal cells (BMSCs) are an effective new strategy for the treatment of kidney diseases. At present, noninvasive and efficient transplantation approaches to homing BMSCs to the renal parenchyma is still a serious challenge. The aim of this study was to investigate the feasibility and potential mechanism of ultrasound-guided intraparenchymal transplantation of BMSCs for the treatment of adriamycin nephropathy (AN) in rats.

MATERIALS AND METHODS

A rat AN model was induced by 2 injections of doxorubicin. The rats were randomly divided into 4 groups (n = 10 animals in each group) : normal group (N group, no treatment), control medium group (CM group, transplant medium 1.0 mL), adriamycin nephropathy group (ADR group, phosphate buffered saline 1.0 mL), or BMSCs group (BMSCs fluid 1.0 mL). Intraparenchymal injection was completed under ultrasound guidance. After 4 weeks of treatment, blood samples were collected for serum biochemical measurements and ELISAs. The kidneys were removed for histopathological examination, electron microscopy, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), and western blot analysis.

RESULTS

No deaths occurred in any group after BMSCs transplantation through the renal parenchyma under ultrasound guidance. Compared with the N and CM groups, in the ADR group, blood serum creatinine (SCr), blood urea nitrogen (BUN) and urine albumin (ALb) were higher, glomerular and tubular dilatation was observed, the number of apoptotic cells was higher, and the protein levels of receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL) and nucleotide leukin-rich polypeptide 3 (NLRP3), key components of pathways in rat kidney, were significantly higher. Compared with those in the ADR group, the levels of SCr, BUN, ALb and serum proinflammatory cytokines in the BMSCs group were lower, the pathological structure of the kidney was improved, the number of apoptotic cells was lower, and the levels of RIPK3/MLKL and NLRP3 were significantly lower.

CONCLUSION

Ultrasound-guided intraparenchymal transplantation of BMSCs regulated the RIPK3/MLKL and NLRP3 pathways in a minimally invasive and safe manner, thereby inhibiting renal necrosis and inflammation and playing a protective role in rat AN.

Pushing the boundaries of organs before it's too late: pre-emptive regeneration

Solid organ transplantation is marked by accelerated aging and inexorable fibrosis. It is crucial to promote strategies to attenuate, or to reverse, damage before organ failure. Hence, the objective of this article is to provide insight into strategies, which aim to regenerate or rejuvenate the transplanted organs. Cell therapy with mesenchymal stromal cells is currently under investigation because of their antifibrotic properties. Their ability to promote mitochondrial biogenesis, and to transfer mitochondria to wounded cells, is another approach to boost the organ regeneration. Other teams have investigated bioengineered organs, which consists of decellularization of the damaged organ followed by recellularization. Lastly, the development of CAR-T cell-based technologies may revolutionize the field of transplantation, as recent preclinical studies showed that CAR-T cells could efficiently clear senescent cells from an organ and reverse fibrosis. Ultimately, these cutting-edge strategies may bring the holy grail of a pre-emptive regenerated organ closer to reality.

Cellular Therapies in Solid Organ Allotransplantation: Promise and Pitfalls

Donor specific transfusions have been the basis of tolerance inducing protocols since Peter Medawar showed that it was experimentally feasible in the 1950s. Though trials of cellular therapies have become increasingly common in solid organ transplantation, they have not become standard practice. Additionally, whereas some protocols have focused on cellular therapies as a method for donor antigen delivery—thought to promote tolerance in and of itself in the correct immunologic context—other approaches have alternatively focused on the intrinsic immunosuppressive properties of the certain cell types with less emphasis on their origin, including mesenchymal stem cells, regulatory T cells, and regulatory dendritic cells. Regardless of intent, all cellular therapies must contend with the potential that introducing donor antigen in a new context will lead to sensitization. In this review, we focus on the variety of cellular therapies that have been applied in human trials and non-human primate models, describe their efficacy, highlight data regarding their potential for sensitization, and discuss opportunities for cellular therapies within our current understanding of the immune landscape.

Autologous bone marrow-derived mesenchymal stem cells for interstitial fibrosis and tubular atrophy: a pilot study

Background

Mesenchymal stem cells (MSCs)-based therapy has shown promising results for renal injury. In this study, the efficacy and safety of autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) in treating nonspecific interstitial fibrosis and tubular atrophy (IFTA) were evaluated.

Methods

From March 2011 to January 2013, 11 renal transplanted patients with IFTA were recruited. At baseline, patients were given one intra-arterial infusion of BM-MSCs; 7 days and 1 month later, another two intravenous infusions of cells were followed. Serum creatinine, creatinine clearance rate, and serum cystatin-C at baseline and 7 days, 1 month, 3 months, 6 months, and 12 months after the intra-arterial infusion of BM-MSCs were used to assess renal function. At baseline and 6 months, histological examination based on hematoxylin-eosin, Masson’s trichrome and periodic acid-Schiff staining and immunohistochemistry for transforming growth factor β1 (TGF-β1) and connective tissue growth factor (CTGF) was performed. Adverse events were recorded to evaluate the safety of BM-MSCs treatment.

Results

At 12 months, the renal function of 6 patients (54.5%) was improved, 3 (27.3%) were stable and 2 (18.2%) were worsened. At 6 months, the mean IFTA scores of all participators were similar with the baseline (1.73 ± 0.41 vs.1.50 ± 0.0.77, p = 0.242); however, it was significantly decreased when only 6 patients with improved renal function were analyzed (1.67 ± 0.41 vs. 1.08 ± 0.20, p = 0.013). Besides, decreased expression of TGF-β1 and CTGF were also observed at 6 months. During 1 year follow-up period, only two minor complications including infection and allergy were observed.

Conclusion

Our results demonstrated that autologous BM-MSCs are safe and beneficial for IFTA patients. Abbreviations: MSCs: mesenchymal stem cells; BM-MSCs: marrow-derived mesenchymal stem cells; IFTA: interstitial fibrosis and tubular atrophy; CAN: chronic allograft nephropathy; CNIs: calcineurin inhibitors; Scr: serum creatinine; CCr: creatinine clearance rate; Cys-C: cystatin-C; TGF-β1: transforming growth factor β1; CTGF: connective tissue growth factor

Preconditioned Mesenchymal Stromal Cells to Improve Allotransplantation Outcome

Mesenchymal stromal cells (MSCs) are tissue-derived progenitor cells with immunomodulatory as well as multilineage differentiation capacities, and have been widely applied as cellular therapeutics in different disease systems in both preclinical models and clinical studies. Although many studies have applied MSCs in different types of allotransplantation, the efficacy varies. It has been demonstrated that preconditioning MSCs prior to in vivo administration may enhance their efficacy. In the field of organ/tissue allotransplantation, many recent studies have shown that preconditioning of MSCs with (1) pretreatment with bioactive factors or reagents such as cytokines, or (2) specific gene transfection, could prolong allotransplant survival and improve allotransplant function. Herein, we review these preconditioning strategies and discuss potential directions for further improvement.

Autologous bone marrow-derived mesenchymal stromal cell therapy with early tacrolimus withdrawal: The randomized prospective, single-center, open-label TRITON study

After renal transplantation, there is a need for immunosuppressive regimens which effectively prevent allograft rejection, while preserving renal function and minimizing side effects. From this perspective, mesenchymal stromal cell (MSC) therapy is of interest. In this randomized prospective, single-center, open-label trial, we compared MSCs infused 6 and 7 weeks after renal transplantation and early tacrolimus withdrawal with a control tacrolimus group. Primary end point was quantitative evaluation of interstitial fibrosis in protocol biopsies at 4 and 24 weeks posttransplant. Secondary end points included acute rejection, graft loss, death, renal function, adverse events, and immunological responses. Seventy patients were randomly assigned of which 57 patients were included in the final analysis (29 MSC; 28 controls). Quantitative progression of fibrosis failed to show benefit in the MSC group and GFR remained stable in both groups. One acute rejection was documented (MSC group), while subclinical rejection in week 24 protocol biopsies occurred in seven patients (four MSC; three controls). In the MSC group, regulatory T cell numbers were significantly higher compared to controls (p = .014, week 24). In conclusion, early tacrolimus withdrawal with MSC therapy was safe and feasible without increased rejection and with preserved renal function. MSC therapy is a potentially useful approach after renal transplantation.

Current Desensitization Strategies in Heart Transplantation

Heart transplant candidates sensitized to HLA antigens wait longer for transplant, are at increased risk of dying while waiting, and may not be listed at all. The increasing prevalence of HLA sensitization and limitations of current desensitization strategies underscore the urgent need for a more effective approach. In addition to pregnancy, prior transplant, and transfusions, patients with end-stage heart failure are burdened with unique factors placing them at risk for HLA sensitization. These include homograft material used for congenital heart disease repair and left ventricular assist devices (LVADs). Moreover, these risks are often stacked, forming a seemingly insurmountable barrier in some cases. While desensitization protocols are typically implemented uniformly, irrespective of the mode of sensitization, the heterogeneity in success and post-transplant outcomes argues for a more tailored approach. Achieving this will require progress in our understanding of the immunobiology underlying the innate and adaptive immune response to these varied allosensitizing exposures. Further attention to B cell activation, memory, and plasma cell differentiation is required to establish methods that durably abrogate the anti-HLA antibody response before and after transplant. The contribution of non-HLA antibodies to the net state of sensitization and the potential implications for graft longevity also remain to be comprehensively defined. The aim of this review is to first bring forth select issues unique to the sensitized heart transplant candidate. The current literature on desensitization in heart transplantation will then be summarized providing context within the immune response. Building on this, newer approaches with therapeutic potential will be discussed emphasizing the importance of not only addressing the short-term pathogenic consequences of circulating HLA antibodies, but also the need to modulate alloimmune memory.

Third-party bone marrow-derived mesenchymal stromal cell infusion before liver transplantation: A randomized controlled trial

Mesenchymal stromal cells (MSC) have emerged as a promising therapy to minimize the immunosuppressive regimen or induce tolerance in solid organ transplantation. In this randomized open-label phase Ib/IIa clinical trial, 20 liver transplant patients were randomly allocated (1:1) to receive a single pretransplant intravenous infusion of third-party bone marrow-derived MSC or standard of care alone. The primary endpoint was the safety profile of MSC administration during the 1-year follow-up. In all, 19 patients completed the study, and none of those who received MSC experienced infusion-related complications. The incidence of serious and non-serious adverse events was similar in the two groups. Circulating Treg/memory Treg and tolerant NK subset of CD56^bright NK cells increased slightly over baseline, albeit not to a statistically significant extent, in MSC-treated patients but not in the control group. Graft function and survival, as well as histologic parameters and intragraft expression of tolerance-associated transcripts in 1-year protocol biopsies were similar in the two groups. In conclusion, pretransplant MSC infusion in liver transplant recipients was safe and induced mild positive changes in immunoregulatory T and NK cells in the peripheral blood. This study opens the way for a trial on possible tolerogenic efficacy of MSC in liver transplantation. ClinicalTrials.gov identifier: NCT02260375.

Current advances of stem cell-based therapy for kidney diseases

Kidney diseases are a prevalent health problem around the world. Multidrug therapy used in the current routine treatment for kidney diseases can only delay disease progression. None of these drugs or treatments can reverse the progression to an end-stage of the disease. Therefore, it is crucial to explore novel therapeutics to improve patients’ quality of life and possibly cure, reverse, or alleviate the kidney disease. Stem cells have promising potentials as a form of regenerative medicine for kidney diseases due to their unlimited replication and their ability to differentiate into kidney cells in vitro. Mounting evidences from the administration of stem cells in an experimental kidney disease model suggested that stem cell-based therapy has therapeutic or renoprotective effects to attenuate kidney damage while improving the function and structure of both glomerular and tubular compartments. This review summarises the current stem cell-based therapeutic approaches to treat kidney diseases, including the various cell sources, animal models or in vitro studies. The challenges of progressing from proof-of-principle in the laboratory to widespread clinical application and the human clinical trial outcomes reported to date are also highlighted. The success of cell-based therapy could widen the scope of regenerative medicine in the future.

Case Report: Capillary Leak Syndrome With Kidney Transplant Failure Following Autologous Mesenchymal Stem Cell Therapy

Mesenchymal stem cells (MSCs) have attracted great interest in the field of kidney transplantation due to their immunomodulatory and reparative properties. In registered clinical trials, MSCs have been used before, at the time of, or early after transplantation and have been reported to be well-tolerated with no serious safety concerns. No results are available on the use of MSCs in the late post-transplant period. Here, we present a case report of a severe systemic complication mimicking capillary leak syndrome with ultimate kidney transplant failure after autologous transplantation of MSCs used as rescue treatment of late antibody-mediated kidney allograft rejection.

Efficacy and Safety of Bone Marrow-Derived Mesenchymal Stem Cells for Chronic Antibody-Mediated Rejection After Kidney Transplantation- A Single-Arm, Two-Dosing-Regimen, Phase I/II Study

Objective

To investigate the efficacy and safety of bone marrow-derived mesenchymal stem cells (BM-MSCs) on chronic active antibody-mediated rejection (cABMR) in the kidney allograft.

Methods

Kidney recipients with biopsy-proven cABMR were treated with allogeneic third-party BM-MSCs in this open-label, single-arm, single-center, two-dosing-regimen phase I/II clinical trial. In Regimen 1 (n=8), BM-MSCs were administered intravenously at a dose of 1.0×10⁶ cells/kg monthly for four consecutive months, while in Regimen 2 (n=15), the BM-MSCs dose was 1.0×10⁶ cells/kg weekly during four consecutive weeks. The primary endpoints were the absolute change of estimated glomerular filtration rate (eGFR) from baseline (delta eGFR) and the incidence of adverse events associated with BM-MSCs administration 24 months after the treatment. Contemporaneous cABMR patients who did not receive BM-MSCs were retrospectively analyzed as the control group (n =30).

Results

Twenty-three recipients with cABMR received BM-MSCs. The median delta eGFR of the total BM-MSCs treated patients was -4.3 ml/min per 1.73m² (interquartile range, IQR -11.2 to 1.2) 2 years after BM-MSCs treatment (P=0.0233). The median delta maximum donor-specific antibody (maxDSA) was -4310 (IQR -9187 to 1129) at 2 years (P=0.0040). The median delta eGFR of the control group was -12.7 ml/min per 1.73 m² (IQR -22.2 to -3.5) 2 years after the diagnosis, which was greater than that of the BM-MSCs treated group (P=0.0342). The incidence of hepatic enzyme elevation, BK polyomaviruses (BKV) infection, cytomegalovirus (CMV) infection was 17.4%, 17.4%, 8.7%, respectively. There was no fever, anaphylaxis, phlebitis or venous thrombosis, cardiovascular complications, or malignancy after BM-MSCs administration. Flow cytometry analysis showed a significant decreasing trend of CD27^-IgD^- double negative B cells subsets and trend towards the increase of CD3⁺CD4⁺PD-1⁺/lymphocyte population after MSCs therapy. Multiplex analysis found TNF-α, CXCL10, CCL4, CCL11 and RANTES decreased after MSCs treatment.

Conclusion

Kidney allograft recipients with cABMR are tolerable to BM-MSCs. Immunosuppressive drugs combined with intravenous BM-MSCs can delay the deterioration of allograft function, probably by decreasing DSA level and reducing DSA-induced injury. The underlying mechanism may involve immunomodulatory effect of MSCs on peripheral B and T cells subsets.

Safety and immunological proof-of-concept following treatment with tolerance-inducing cell products in patients with autoimmune diseases or receiving organ transplantation: A systematic review and meta-analysis of clinical trials

In the past years, translational approaches have led to early-stage clinical trials assessing safety and efficacy of tolerance-inducing cell-based treatments in patients. This review aims to determine if tolerance-inducing cell-based therapies, including dendritic cells, regulatory T cells and mesenchymal stem cells, are safe in adult patients who underwent organ transplantation or in those with autoimmune diseases, including multiple sclerosis, diabetes mellitus type 1, Crohn's disease and rheumatoid arthritis. Immunological and clinical outcomes were reviewed, to provide evidence for proof-of-concept and efficacy. To summarize the current knowledge, a systematic review and meta-analysis were conducted. A total of 8906 records were reviewed by 2 independent assessors and 48 records were included in the final quantitative analysis. The overall frequency of serious adverse events was low: 0.018 (95% CI: 0.006-0.051). Immunological outcomes could not be assessed quantitatively because of heterogeneity in outcome assessments and description as well as lack of individual data. Most randomized controlled studies were at a medium risk of bias due to open-label treatment without masking of assessors and/or patients to the intervention. In conclusion, tolerance-inducing cell-based therapies are safe. We advocate for harmonization of study protocols of trials investigating cell-based therapies, adverse event reporting and systematic inclusion of immunological outcome measures in clinical trials evaluating tolerance-inducingcell-basedtreatment. Registration: PROSPERO, registration number CRD42020170557.

MSC Manufacturing for Academic Clinical Trials: From a Clinical-Grade to a Full GMP-Compliant Process

Following European regulation 1394/2007, mesenchymal stromal cell (MSCs) have become an advanced therapy medicinal product (ATMP) that must be produced following the good manufacturing practice (GMP) standards. We describe the upgrade of our existing clinical-grade MSC manufacturing process to obtain GMP certification. Staff organization, premises/equipment qualification and monitoring, raw materials management, starting materials, technical manufacturing processes, quality controls, and the release, thawing and infusion were substantially reorganized. Numerous studies have been carried out to validate cultures and demonstrate the short-term stability of fresh or thawed products, as well their stability during long-term storage. Detailed results of media simulation tests, validation runs and early MSC batches are presented. We also report the validation of a new variant of the process aiming to prepare fresh MSCs for the treatment of specific lesions of Crohn's disease by local injection. In conclusion, we have successfully ensured the adaptation of our clinical-grade MSC production process to the GMP requirements. The GMP manufacturing of MSC products is feasible in the academic setting for a limited number of batches with a significant cost increase, but moving to large-scale production necessary for phase III trials would require the involvement of industrial partners.

Ex Vivo Mesenchymal Stem Cell Therapy to Regenerate Machine Perfused Organs

Transplantation represents the treatment of choice for many end-stage diseases but is limited by the shortage of healthy donor organs. Ex situ normothermic machine perfusion (NMP) has the potential to extend the donor pool by facilitating the use of marginal quality organs such as those from donors after cardiac death (DCD) and extended criteria donors (ECD). NMP provides a platform for organ quality assessment but also offers the opportunity to treat and eventually regenerate organs during the perfusion process prior to transplantation. Due to their anti-inflammatory, immunomodulatory and regenerative capacity, mesenchymal stem cells (MSCs) are considered as an interesting tool in this model system. Only a limited number of studies have reported on the use of MSCs during ex situ machine perfusion so far with a focus on feasibility and safety aspects. At this point, no clinical benefits have been conclusively demonstrated, and studies with controlled transplantation set-ups are urgently warranted to elucidate favorable effects of MSCs in order to improve organs during ex situ machine perfusion.

Cell therapy in transplantation: A comprehensive review of the current applications of cell therapy in transplant patients with the focus on Tregs, CAR Tregs, and Mesenchymal stem cells

Organ transplantation is a practical treatment for patients with end-stage organ failure. Despite the advances in short-term graft survival, long-term graft survival remains the main challenge considering the increased mortality and morbidity associated with chronic rejection and the toxicity of immunosuppressive drugs. Since a novel therapeutic strategy to induce allograft tolerance seems urgent, focusing on developing novel and safe approaches to prolong graft survival is one of the main goals of transplant investigators. Researchers in the field of organ transplantation are interested in suppressing or optimizing the immune responses by focusing on immune cells including mesenchymal stem cells (MSCs), polyclonal regulatory Tcells (Tregs), and antigen-specific Tregs engineered with chimeric antigen receptors (CAR Tregs). We review the mechanistic pathways, phenotypic and functional characteristics of these cells, and their promising application in organ transplantation.

Mesenchymal stromal cells for corneal transplantation: Literature review and suggestions for successful clinical trials

Corneal transplantation is a routine procedure for patients with corneal blindness. Despite the streamlining of surgical techniques and deeper understanding of the cellular and molecular pathways mediating rejection, corticosteroids are still the main immunosuppressive regimen in corneal transplantation, and the 15-year survival of corneal transplants remains as low as 50%, which is poorer than that for most solid organ transplants. Recently, mesenchymal stromal cells (MSCs) with unique regenerative and immune-modulating properties have emerged as a promising cell therapy to promote transplant tolerance, minimize the use of immunosuppressants, and prevent chronic rejection. Here, we review the literature on preclinical studies of MSCs for corneal transplantation and summarize the key findings from clinical trials with MSCs in solid organ transplantation. Finally, we highlight current issues and challenges regarding MSC therapies and suggest strategies for safe and effective MSC-based therapies in clinical transplantation.

Induction therapy with mesenchymal stromal cells in kidney transplantation: a meta-analysis

Objective

The aim of this meta-analysis was to evaluate the therapeutic effects of mesenchymal stromal cells (MSCs) versus traditional regimens for induction therapy in kidney transplantation (KT), especially the safety of MSC infusion, practicability of MSCs as induction therapy agents, and posttransplant complications.

Methods

PubMed, Embase, EBSCO, Ovid, and the Cochrane Library were searched for prospective clinical trials that compared MSCs with traditional regimens for induction therapy in KT.

Results

Four trials were included, including a total of 197 patients. The pooled results revealed that MSC therapy had a lower 1-year infection rate than did the traditional therapies (RR = 0.65, 95% CI: 0.46–0.9, P = 0.01). There were no significant differences between the two protocols regarding the 1-year acute rejection (AR) rate (RR = 0.77, 95% CI: 0.41–1.45, P = 0.42), 1-year graft survival rate (RR = 0.99, 95% CI: 0.95–1.03, P = 0.74), delayed graft function (DGF) rate (RR = 0.54, 95% CI: 0.21–1.38, P = 0.2) and renal graft function at 1 month (MD = −1.56, 95% CI: − 14.2–11.08, p = 0.81), 3 months (MD = 0.15, 95% CI: − 5.63–5.93, p = 0.96), 6 months (MD = − 1.95, 95% CI: − 9.87–5.97, p = 0.63), and 12 months (MD = − 1.13, 95% CI: − 7.16–4.89, p = 0.71) postsurgery. Subgroup analysis demonstrated that the 1-year AR rate, 1-year graft survival rate, DGF rate, and renal graft function at 12 months postsurgery did not significantly differ between the low-dose calcineurin inhibitor (CNI) group and the standard-dose CNI group, indicating the potential benefits of successful CNI sparing in combination with MSC treatment. Moreover, when MSCs were applied as an alternative therapy rather than an additional therapy or allogeneic MSCs were utilized instead of autologous MSCs, all of the outcomes mentioned above were comparable.

Conclusion

Induction therapy with MSCs is safe and has similar immune response modulation effects to those of traditional regimens in the short term in KT recipients. However, regarding the long-term effects, as suggested by the 1-year infection rate and the potential of CNI sparing, MSC therapy has significant advantages. However, these advantages should be further verified in more well-designed, multicenter randomized controlled trials (RCTs) with large sample sizes and long follow-up periods.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02219-7.

Progress toward the Clinical Application of Mesenchymal Stromal Cells and Other Disease-Modulating Regenerative Therapies: Examples from the Field of Nephrology

Drawing from basic knowledge of stem-cell biology, embryonic development, wound healing, and aging, regenerative medicine seeks to develop therapeutic strategies that complement or replace conventional treatments by actively repairing diseased tissue or generating new organs and tissues. Among the various clinical-translational strategies within the field of regenerative medicine, several can be broadly described as promoting disease resolution indirectly through local or systemic interactions with a patient's cells, without permanently integrating or directly forming new primary tissue. In this review, we focus on such therapies, which we term disease-modulating regenerative therapies (DMRT), and on the extent to which they have been translated into the clinical arena in four distinct areas of nephrology: renovascular disease (RVD), sepsis-associated AKI (SA-AKI), diabetic kidney disease (DKD), and kidney transplantation (KTx). As we describe, the DMRT that has most consistently progressed to human clinical trials for these indications is mesenchymal stem/stromal cells (MSCs), which potently modulate ischemic, inflammatory, profibrotic, and immune-mediated tissue injury through diverse paracrine mechanisms. In KTx, several early-phase clinical trials have also tested the potential for ex vivo-expanded regulatory immune cell therapies to promote donor-specific tolerance and prevent or resolve allograft injury. Other promising DMRT, including adult stem/progenitor cells, stem cell-derived extracellular vesicles, and implantable hydrogels/biomaterials remain at varying preclinical stages of translation for these renal conditions. To date (2021), no DMRT has gained market approval for use in patients with RVD, SA-AKI, DKD, or KTx, and clinical trials demonstrating definitive, cost-effective patient benefits are needed. Nonetheless, exciting progress in understanding the disease-specific mechanisms of action of MSCs and other DMRT, coupled with increasing knowledge of the pathophysiologic basis for renal-tissue injury and the experience gained from pioneering early-phase clinical trials provide optimism that influential, regenerative treatments for diverse kidney diseases will emerge in the years ahead.