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Mesenchymal stem cells; Liver transplantation; Immune tolerance; Graft rejection; Immunomodulation; Cell therapy; regulatory T cells; Hepatic immunology; Immunosuppression minimization; Liver graft survival; Immunological tolerance; MSC-derived exosomes; Transplant immunology.

Introduction

Liver transplantation has evolved into a highly successful treatment for end-stage liver disease, with excellent short-term outcomes. However, long-term graft survival remains a challenge, largely due to the lifelong requirement for immunosuppressive therapy and its associated complications, including infections, metabolic disorders, and malignancies. The liver’s intrinsic tolerogenic nature offers a unique opportunity to explore novel strategies that may reduce or even eliminate the need for lifelong immunosuppression [1-5].

Among emerging approaches, mesenchymal stem cells (MSCs) have gained attention as a potential immunomodulatory therapy capable of inducing long-term immune tolerance. Due to their ability to suppress immune responses, modulate inflammatory cascades, and promote regulatory immune cell populations, MSCs may provide a safe and effective adjunct to standard immunosuppression protocols in liver transplantation.

Description

MSCs are multipotent stromal cells derived from various tissues including bone marrow, adipose tissue, umbilical cord, and liver itself. They exhibit unique immunomodulatory properties, including the suppression of T-cell proliferation, inhibition of dendritic cell maturation, and promotion of regulatory T cells (Tregs). These effects are mediated through both cell-to-cell contact and the secretion of soluble factors such as transforming growth factor-beta (TGF-β), interleukin-10 (IL-10), and prostaglandin E2 (PGE2). In liver transplantation, MSCs are particularly appealing because the hepatic environment is already inclined toward immune tolerance, and MSCs can synergize with this natural immunological bias.

Preclinical studies in animal models have demonstrated that MSC therapy can significantly prolong liver allograft survival by reducing acute rejection and fostering an environment of immune regulation. MSCs appear to inhibit both cellular and humoral components of the immune response, targeting T cells, B cells, NK cells, and antigen-presenting cells. Furthermore, MSCs support tissue regeneration and repair, contributing to graft recovery following ischemia-reperfusion injury or other post-transplant complications. When administered intravenously or intra-portal, MSCs can home to the liver and exert localized immunosuppressive effects with minimal systemic toxicity [6-10].

Discussion

Clinical trials investigating the use of MSCs in liver transplantation are still in their early phases, but preliminary results are encouraging. Early-phase studies have reported that MSC infusions are generally safe, well-tolerated, and capable of reducing the need for standard immunosuppression without increasing the risk of rejection. In one pilot study, MSC-treated liver transplant recipients were able to achieve lower doses of calcineurin inhibitors while maintaining stable graft function. Another trial suggested that MSCs may reduce the incidence of acute rejection and promote a regulatory immune phenotype, marked by increased Treg levels and decreased effector T-cell activity.

One of the most promising features of MSCs is their ability to promote operational tolerance—defined as stable graft function in the absence of immunosuppression. Although true tolerance remains rare, MSCs could serve as a bridge to immunosuppression minimization protocols. Additionally, the growing interest in MSC-derived exosomes—nano-sized vesicles containing immunoregulatory proteins and RNAs—offers a cell-free alternative with fewer logistical and safety concerns. These exosomes replicate many of MSCs’ immunosuppressive effects and may be easier to standardize and deliver clinically.

However, significant challenges remain before MSCs can be fully integrated into clinical liver transplantation protocols. The variability in MSC sources, preparation methods, dosing regimens, and routes of administration complicates the interpretation of study results. Moreover, the optimal timing for MSC infusion—whether pre-transplant, peri-transplant, or post-transplant—remains unclear. Long-term safety concerns, including potential oncogenicity or fibrosis, must be carefully evaluated in large-scale, controlled clinical trials. Regulatory hurdles and high production costs also limit the immediate clinical application of MSC-based therapies.

Conclusion

Mesenchymal stem cells represent a promising frontier in the quest to induce immune tolerance in liver transplantation. Their potent immunomodulatory capabilities, combined with the liver’s inherent tolerogenic potential, position MSCs as ideal candidates for adjunctive cell therapy aimed at reducing immunosuppressive dependence and improving long-term graft outcomes. Early experimental and clinical data support their safety and efficacy, but broader clinical adoption will require standardization of protocols, long-term safety validation, and resolution of logistical challenges. As research progresses, MSCs may pave the way for a paradigm shift in liver transplant management—transforming it from a pharmacologically sustained state to a biologically tolerized one.

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