Immunological effect induced by mesenchymal stem cells in a rat liver transplantation model

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.

Immunological Determinants of Liver Transplant Outcomes Uncovered by the Rat Model

For many individuals with end-stage liver disease, the only treatment option is liver transplantation. However, liver transplant rejection is observed in 24%-80% of transplant patients and lifelong drug regimens that follow the transplant procedure lead to serious side effects. Furthermore, the pool of donor livers available for transplantation is far less than the demand. Well-characterized and physiologically relevant models of liver transplantation are crucial to a deeper understanding of the cellular processes governing the outcomes of liver transplantation and serve as a platform for testing new therapeutic strategies to enhance graft acceptance. Such a model has been found in the rat transplant model, which has an advantageous size for surgical procedures, similar postoperative immunological progression, and high genome match to the human liver. From rat liver transplant studies published in the last 5 years, it is clear that the rat model serves as a strong platform to elucidate transplant immunological mechanisms. Using the model, we have begun to uncover potential players and possible therapeutic targets to restore liver tolerance and preserve host immunocompetence. Here, we present an overview of recent literature for rat liver transplant models, with an aim to highlight the value of the models and to provide future perspectives on how these models could be further characterized to enhance the overall value of rat models to the field of liver transplantation.

Regulatory effect of rat bone marrow mesenchymal stem cells on Treg/Th17 immune balance in vitro

Bone marrow mesenchymal stem cells (BM-MSCs) regulate the balance between regulatory T cells (Tregs) and T helper 17 (Th17) cells. However, the role of different factors on BM-MSCs-mediated regulation of the Treg/Th17 balance is unknown. BM-MSCs and CD4⁺ T lymphocytes were co-cultured with various treatments. The ratio of Treg/Th17 cells was calculated and the expression of different cytokines was measured. BM-MSCs were found to have a proliferative effect on Th17 cells at a basal concentration and at a 2-fold increase in the number of BM-MSCs. However, when the number of BM-MSCs used was increased 4-fold, they had an inhibitory effect on the Th17 cells. The effect of BM-MSCs on Tregs was inhibited by the addition of tacrolimus but not rapamycin. The effect of BM-MSCs on Th17 cells was inhibited by rapamycin. Additionally, the effect of BM-MSCs on Tregs were inhibited by the addition of a transforming growth factor-β (TGF-β) blocker, whereas these TGF-β-blockers had no effect on Th17 cells. Addition of an interleukin (IL)-2 blocker reduced the proportion of Th17 cells when co-cultured with a high number of MSCs compared with the low concentration group and the proportion of Treg cells was significantly decreased when cells were treated with an IL-2 blocker compared with the control group. Together, these results showed the varying effects of MSCs on the ratio of Treg/Th17, its dependence on the number of MSCs and the effects of cytokines in inducing these changes in the balance.

The immunoregulation of mesenchymal stem cells plays a critical role in improving the prognosis of liver transplantation

The liver is supplied by a dual blood supply, including the portal venous system and the hepatic arterial system; thus, the liver organ is exposed to multiple gut microbial products, metabolic products, and toxins; is sensitive to extraneous pathogens; and can develop liver failure, liver cirrhosis and hepatocellular carcinoma (HCC) after short-term or long-term injury. Although liver transplantation (LT) serves as the only effective treatment for patients with end-stage liver diseases, it is not very popular because of the complications and low survival rates. Although the liver is generally termed an immune and tolerogenic organ with adaptive systems consisting of humoral immunity and cell-mediated immunity, a high rejection rate is still the main complication in patients with LT. Growing evidence has shown that mesenchymal stromal cell (MSC) transplantation could serve as an effective immunomodulatory strategy to induce tolerance in various immune-related disorders. MSCs are reported to inhibit the immune response from innate immune cells, including macrophages, dendritic cells (DCs), natural killer cells (NK cells), and natural killer T (NKT) cells, and that from adaptive immune cells, including T cells, B cells and other liver-specific immune cells, for the generation of a tolerogenic microenvironment. In this review, we summarized the relationship between LT and immunoregulation, and we focused on how to improve the effects of MSC transplantation to improve the prognosis of LT. Only after exhaustive clarification of the potential immunoregulatory mechanisms of MSCs in vitro and in vivo can we implement MSC protocols in routine clinical practice to improve LT outcome.

Research Status of Mesenchymal Stem Cells in Liver Transplantation

Liver transplantation has been deemed the best choice for end-stage liver disease patients but immune rejection after surgery is still a serious problem. Patients have to take immunosuppressive drugs for a long time after liver transplantation, and this often leads to many side effects. Mesenchymal stem cells (MSCs) gradually became of interest to researchers because of their powerful immunomodulatory effects. In the past, a large number of in vitro and in vivo studies have demonstrated the great potential of MSCs for participation in posttransplant immunomodulation. In addition, MSCs also have properties that may potentially benefit patients undergoing liver transplantation. This article aims to provide an overview of the current understanding of the immunomodulation achieved by the application of MSCs in liver transplantation, to discuss the problems that may be encountered when using MSCs in clinical practice, and to describe some of the underlying capabilities of MSCs in liver transplantation. Cell–cell contact, soluble molecules, and exosomes have been suggested to be critical approaches to MSCs’ immunoregulation in vitro; however, the exact mechanism, especially in vivo, is still unclear. In recent years, the clinical safety of MSCs has been proven by a series of clinical trials. The obstacles to the clinical application of MSCs are decreasing, but large sample clinical trials involving MSCs are still needed to further study their clinical effects.

Bone marrow mesenchymal stromal cells attenuate liver allograft rejection may via upregulation PD-L1 expression through downregulation of miR-17-5p

Studies have reported that bone marrow mesenchymal stem cells (BMSCs) play an important role in immune regulation after organ transplantation. Some of the BMSC-mediated regulatory mechanisms are related to PD-L1 expression. However, the regulatory mechanism of PD-L1 expression is not fully understood. In this experiment, we confirmed the regulatory role of BMSCs in the rejection of liver transplantation and explored the possible mechanism by which PD-L1 expression is regulated in BMSCs. An orthotopic liver transplantation model in rats was established based on the "double-cuff technique". Third-generation BMSCs were injected into the rejection model rats via portal vein. At the same time, sera were obtained from rats in the allograft, isograft and sham-operated groups. The sera from these groups were separately added to BMSCs complete medium to partially mimic the in vivo environment in which BMSCs are exposed. After predicting and analysing microRNAs that regulate PD-L1 expression, we examined the microRNA and PD-L1 expression in BMSCs of the three groups cultured in the conditioned media. Moreover, a luciferase reporter assay was used to confirm the interaction between PD-L1 and microRNA. The study found that the liver function and liver graft histopathology of the BMSC-treated group were better than those of the allograft group. The Kaplan-Meier survival curve analysis showed that the median survival time (MST) of the BMSC-treated group was longer than that of the allograft group. Bioinformatics prediction and analysis showed that miR-17-5p is highly likely to regulate PD-L1. Compared with the other two groups of cells, BMSCs cultured with serum from allograft models showed higher PD-L1 expression, but lower miR-17-5p expression. Pearson correlation analysis showed that miR-17-5p and PD-L1 expression was negatively correlated, and further luciferase reporter assays confirmed that miR-17-5p interacted directly with the 3´-untranslated region (UTR) of PD-L1 mRNA. The results of this study demonstrate that BMSCs can attenuate liver allograft rejection and provide us with the idea that BMSCs may further upregulate PD-L1 expression by downregulating miR-17-5p expression, thereby attenuating liver allograft rejection.

Historical Perspectives and Advances in Mesenchymal Stem Cell Research for the Treatment of Liver Diseases

Liver transplantation is the only effective therapy for patients with decompensated cirrhosis and fulminant liver failure. However, due to a shortage of donor livers and complications associated with immune suppression, there is an urgent need for new therapeutic strategies for patients with end-stage liver diseases. Given their unique function in self-renewal and differentiation potential, stem cells might be used to regenerate damaged liver tissue. Recent studies have shown that stem cell-based therapies can improve liver function in a mouse model of hepatic failure. Moreover, acellular liver scaffolds seeded with hepatocytes produced functional bioengineered livers for organ transplantation in preclinical studies. The therapeutic potential of stem cells or their differentiated progenies will depend on their capacity to differentiate into mature and functional cell types after transplantation. It will also be important to devise methods to overcome their genomic instability, immune reactivity, and tumorigenic potential. We review directions and advances in the use of mesenchymal stem cells and their derived hepatocytes for liver regeneration. We also discuss the potential applications of hepatocytes derived from human pluripotent stem cells and challenges to using these cells in treating end-stage liver disease.

Promotion of Cell-Based Therapy: Special Focus on the Cooperation of Mesenchymal Stem Cell Therapy and Gene Therapy for Clinical Trial Studies

Regenerative medicine (RM) is a promising new field of medicine that has mobilized several new tools to repair or replace lost or damaged cells or tissues by stimulating natural regenerative mechanisms nearby cell and tissue-based therapy approaches. However, mesenchymal stem cell (MSC) based therapy has been shown to be safe and effective to a certain degree in multiple clinical trial studies (CTSs) of several diseases, in most MSC CTSs the efficacy of treatment has been reported low. Therefore, researchers have focused on efficacy enhancing of MSC to improve migratory and homing, survival, stemness, differentiation and other therapeutic applicable properties by using different approaches. Gene therapy is one of the experimental technique tools that uses genes to change cells for therapeutic and investigation purposes. In this study has been focused on genetically modified MSCs for use in RM with an emphasis on CTSs. We highlight the basic concept of genetic modifications and also discuss recent clinical studies aspects. Recently reviewed studies show that MSC therapy with assistant gene therapy can be used in cancer therapy, heart diseases, Fanconi anemia and several other diseases.