Mesenchymal Stem Cell Extracellular Vesicles as a New Treatment Paradigm in Solid Abdominal Organ Transplantation: A Case Series

Extracellular vesicles: a new frontier in diagnosing and treating graft-versus-host disease after allogeneic hematopoietic cell transplantation

Graft-versus-host disease (GvHD) is a prevalent complication following allogeneic hematopoietic stem cell transplantation (HSCT) and is characterized by relatively high morbidity and mortality rates. GvHD can result in extensive systemic damage in patients following allogeneic HSCT (allo-HSCT), with the skin, gastrointestinal tract, and liver frequently being the primary target organs affected. The severe manifestations of acute intestinal GvHD often indicate a poor prognosis for patients after allo-HSCT. Endoscopy and histopathological evaluation remain employed to diagnose GvHD, and auxiliary examinations exclude differential diagnoses. Currently, reliable serum biomarkers for the diagnosis and differential diagnosis of GvHD are scarce. As an essential part of standard transplant protocols, early application of immunosuppressive drugs effectively prevents GvHD. Among them, steroids represent first-line therapeutic agents, and the JAK2 inhibitor ruxolitinib represents the second-line therapeutic agent. Currently, no efficacious treatment modality exists for steroid-resistant aGvHD. Therefore, the diagnosis and treatment of GvHD still face significant medical demands. Extracellular vesicles (EVs) are nanometer to micrometer-scale biomembrane vesicles containing various bioactive components, such as proteins, nucleotides, and metabolites. Distinctive changes in serum-derived EV components occur in patients after allo-HSCT; Hence, EVs are expected to be potential biomarkers for diagnosing and treating GvHD. Furthermore, cell-free therapeutics characterized by EVs derived from mesenchymal stem cells (MSCs) have manifested remarkable therapeutic efficacy in preclinical models and preclinical trials of GvHD. Customized engineered EVs with fewer toxic and side effects for the combined treatment of GvHD hold broad prospects for clinical translation. This review article examines the potential value of translating EVs into clinical applications for the diagnosis and treatment of GvHD. It summarizes the latest advancements and prospects of engineered EVs applying GvHD.

Regulatory Immune Cell-derived Exosomes: Modes of Action and Therapeutic Potential in Transplantation

Reduced dependence on antirejection agents, improved long-term allograft survival, and induction of operational tolerance remain major unmet needs in organ transplantation due to the limitations of current immunosuppressive therapies. To address this challenge, investigators are exploring the therapeutic potential of adoptively transferred host- or donor-derived regulatory immune cells. Extracellular vesicles of endosomal origin (exosomes) secreted by these cells seem to be important contributors to their immunoregulatory properties. Twenty years ago, it was first reported that donor-derived exosomes could extend the survival of transplanted organs in rodents. Recent studies have revealed that regulatory immune cells, such as regulatory myeloid cells (dendritic cells, macrophages, or myeloid-derived suppressor cells), regulatory T cells, or mesenchymal stem/stromal cells can suppress graft rejection via exosomes that express a cargo of immunosuppressive molecules. These include cell surface molecules that interact with adaptive immune cell receptors, immunoregulatory enzymes, and micro- and long noncoding RNAs that can regulate inflammatory gene expression via posttranscriptional changes and promote tolerance through promotion of regulatory T cells. This overview analyzes the diverse molecules and mechanisms that enable regulatory immune cell-derived exosomes to modulate alloimmunity and promote experimental transplant tolerance. We also discuss the potential benefits and limitations of their application as therapeutic entities in organ transplantation.

Unlocking the promise of mesenchymal stem cells and extracorporeal photopheresis to address rejection and graft failure in intestinal transplant recipients

INTRODUCTION

In patients with irreversible intestinal failure, intestinal transplant has become a standard treatment option. Graft failure secondary to acute or chronic cellular rejection continues to be a significant challenge following transplant. Even with optimal immune suppression, some patients continue to struggle with refractory rejection. Both extracorporeal photopheresis (ECP) and extracellular vesicles derived from mesenchymal stem cells (EVs) have been used to treat refractory rejection following intestinal transplantation, although their use remains limited and consistent treatment protocols are lacking.

METHODS

Intestinal transplant recipients who received ECP only or ECP and EVs as rescue therapy for acute cellular rejection or chronic inflammation between 2016 and 2022 were included in this single-center retrospective analysis. Baseline demographics, pre- and post-treatment histopathology, endoscopic and biochemical findings, and long-term transplant outcomes were analyzed.

RESULTS

Three patients (two pediatric and one adult) with acute steroid- and biologic-refractory rejection were treated with ECP and/or EVs, as was one patient (pediatric) with chronic graft rejection and inflammation. Patients received twice weekly ECP for 4 weeks and once weekly thereafter. EVs were administered in three doses each separated by 72 h. Immunosuppression at the time of treatment initiation included high-dose tacrolimus and sirolimus. Histologic resolution of rejection was achieved in all patients over 12-16 weeks. Steroids were weaned to low-dose or withdrawn in every patient within 4 weeks of ECP/EV treatment. C-reactive protein decreased from an average of 14.75 to 1.6 mg/dL post-treatment and fecal calprotectin decreased from average 800 mg/g to 31 mg/g. Donor-induced cytotoxic T cell populations were quantified for two of the patients with acute rejection, and in both cases decreased dramatically following treatment. There were no complications associated with either treatment.

CONCLUSION

Both ECP and EVs present novel opportunities to address graft rejection and inflammation in bowel transplant recipients. More work will be needed to define the optimal therapeutic parameters for each treatment modality.

Innovative Strategies for Liver Transplantation: The Role of Mesenchymal Stem Cells and Their Cell-Free Derivatives

Despite being the standard treatment for end-stage liver disease, liver transplantation has limitations like donor scarcity, high surgical costs, and immune rejection risks. Mesenchymal stem cells (MSCs) and their derivatives offer potential for liver regeneration and transplantation. MSCs, known for their multipotency, low immunogenicity, and ease of obtainability, can differentiate into hepatocyte-like cells and secrete bioactive factors that promote liver repair and reduce immune rejection. However, the clinical application of MSCs is limited by risks such as aberrant differentiation and low engraftment rates. As a safer alternative, MSC-derived secretomes and extracellular vesicles (EVs) offer promising therapeutic benefits, including enhanced graft survival, immunomodulation, and reduced ischemia-reperfusion injury. Current research highlights the efficacy of MSC-derived therapies in improving liver transplant outcomes, but further studies are necessary to standardize clinical applications. This review highlights the potential of MSCs and EVs to address key challenges in liver transplantation, paving the way for innovative therapeutic strategies.

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.