Kidney-induced cardiac allograft tolerance in miniature swine is dependent on MHC-matching of donor cardiac and renal parenchyma

Sequential transplantation of the liver-kidney-heart from different donors: a case report

Background

Multi-organ transplantation has emerged as a viable treatment strategy for patients afflicted with multiple organ failure or significant organ dysfunctions. Despite the promising therapeutic outcomes, this approach also amplifies the risk of organ rejection, infection, or neoplastic growth. We present a unique case of a patient who sequentially underwent liver, kidney, and heart transplantation, all sourced from different donors. This case brings forth intriguing possibilities about the interplay between cardiovascular diseases and complications arising post-transplantation, thereby enriching our understanding of comprehensive transplant immunomodulation and cardiovascular disease prevention.

Case summary

A 59-year-old male with chronic alcohol misuse developed liver cirrhosis in 2012 and subsequent kidney failure in 2018 due to alcoholic liver disease, type II diabetes, hyperlipidaemia, and severe hypertension. Subsequently, an incident of extensive transmural myocardial infarction (Killip III) warranted a heart transplant in 2022. Post-transplant, the patient was maintained on a standard immunosuppression regimen with regular post-operative follow-ups. No signs of rejection were noted 1-year post-final transplantation under standard immunosuppression.

Discussion

The presented case exemplifies the potential and feasibility of sequential multi-organ transplantation. The multifaceted interplay between the transplanted organs and the immunosuppressive pharmaceuticals likely exert distinct influences on transplantation immune regulation, possibly diverging from the dynamics observed in single-organ transplantation. A comprehensive exploration of the mechanisms governing immune responses in the context of multi-organ transplantation could yield valuable insights for mitigating graft dysfunction. Furthermore, the rapid progression of atherosclerosis observed after liver and kidney transplantation necessitates further scrutiny to elucidate potential correlations with the post-transplantation state.

Immunosuppressive regimens in porcine transplantation models

Pigs, or Sus scrofa domestica, are commonly used animal models in translational transplantation research due to their anatomical, physiological, and immunological similarities to humans. In solid organ transplantation studies, immunosuppressive medications may be administered to pigs to prevent rejection. We provide an overview of the immunosuppressive regimens used in allogeneic solid organ transplantation in pigs, including heart, lung, kidney, bowel and cotransplanted organs and focus on the use of tacrolimus, mycophenolate mofetil, and corticosteroids.

Transplant Tolerance, Not Only Clonal Deletion

The quest to understand how allogeneic transplanted tissue is not rejected and how tolerance is induced led to fundamental concepts in immunology. First, we review the research that led to the Clonal Deletion theory in the late 1950s that has since dominated the field of immunology and transplantation. At that time many basic mechanisms of immune response were unknown, including the role of lymphocytes and T cells in rejection. These original observations are reassessed by considering T regulatory cells that are produced by thymus of neonates to prevent autoimmunity. Second, we review "operational tolerance" induced in adult rodents and larger animals such as pigs. This can occur spontaneously especially with liver allografts, but also can develop after short courses of a variety of rejection inhibiting therapies. Over time these animals develop alloantigen specific tolerance to the graft but retain the capacity to reject third-party grafts. These animals have a "split tolerance" as peripheral lymphocytes from these animals respond to donor alloantigen in graft versus host assays and in mixed lymphocyte cultures, indicating there is no clonal deletion. Investigation of this phenomenon excludes many mechanisms, including anti-donor antibody blocking rejection as well as anti-idiotypic responses mediated by antibody or T cells. This split tolerance is transferred to a second immune-depleted host by T cells that retain the capacity to effect rejection of third-party grafts by the same host. Third, we review research on alloantigen specific inhibitory T cells that led to the first identification of the CD4+CD25+T regulatory cell. The key role of T cell derived cytokines, other than IL-2, in promoting survival and expansion of antigen specific T regulatory cells that mediate transplant tolerance is reviewed. The precise methods for inducing and diagnosing operational tolerance remain to be defined, but antigen specific T regulatory cells are key mediators.

Kidney-induced systemic tolerance of heart allografts in mice

In swine and nonhuman primates, kidney allografts can induce tolerance of heart allografts, leading to their long-term, immunosuppression-free survival. We refer to this phenomenon as kidney-induced cardiac allograft tolerance (KICAT). In this study, we have developed a murine model for KICAT to determine the underlining cellular/molecular mechanisms. Here, we show that spontaneously accepted DBA/2J kidneys in C57BL/6 recipients induce systemic tolerance that results in the long-term acceptance of DBA/2J heart allografts but not third-party cardiac allografts. The state of systemic tolerance of hearts was established 2 weeks after transplantation of the kidney, after which time, the kidney allograft is no longer required. Depletion of Foxp3⁺ T cells from these mice precipitated rejection of the heart allografts, indicating that KICAT is dependent on Treg function. Acceptance of kidney allografts and cotransplanted heart allografts did not require the thymus. In conclusion, these data show that kidney allografts induce systemic, donor-specific tolerance of cardiac allografts via Foxp3 cells, and that tolerance is independent of the thymus and continued presence of the kidney allograft. This experimental system should promote increased understanding of the tolerogenic mechanisms of the kidney.

Accepted DBA/2J kidney allografts can confer acceptance of a co-transplanted DBA/2 heart allograft, which would be rejected when transplanted in the absence of the kidney graft.

Why some organ allografts are tolerated better than others: new insights for an old question

PURPOSE OF REVIEW

There is great variability in how different organ allografts respond to the same tolerance induction protocol. Well known examples of this phenomenon include the protolerogenic nature of kidney and liver allografts as opposed to the tolerance-resistance of heart and lung allografts. This suggests there are organ-specific factors which differentially drive the immune response following transplantation.

RECENT FINDINGS

The specific cells or cell products that make one organ allograft more likely to be accepted off immunosuppression than another are largely unknown. However, new insights have been made in this area recently.

SUMMARY

The current review will focus on the organ-intrinsic factors that contribute to the organ-specific differences observed in tolerance induction with a view to developing therapeutic strategies to better prevent organ rejection and promote tolerance induction of all organs.

Mechanisms of Mixed Chimerism-Based Transplant Tolerance

Immune responses to allografts represent a major barrier in organ transplantation. Immune tolerance to avoid chronic immunosuppression is a critical goal in the field, recently achieved in the clinic by combining bone marrow transplantation (BMT) with kidney transplantation following non-myeloablative conditioning. At high levels of chimerism such protocols can permit central deletional tolerance, but with a significant risk of graft-versus-host (GVH) disease (GVHD). By contrast, transient chimerism-based tolerance is devoid of GVHD risk and appears to initially depend on regulatory T cells (Tregs) followed by gradual, presumably peripheral, clonal deletion of donor-reactive T cells. Here we review recent mechanistic insights into tolerance and the development of more robust and safer protocols for tolerance induction that will be guided by innovative immune monitoring tools.

FOXP3-Positive Regulatory T Cells and Kidney Allograft Tolerance

Normal immune homeostasis is achieved by several mechanisms, and prominent among them is immunoregulation. Although several types of regulatory lymphocyte populations have been described, CD4 T cells expressing the FOXP3 transcription factor (FOXP3-positive regulatory T cells [FOXP3⁺ Tregs]) are the best understood. This population of cells is critical for maintaining self-tolerance throughout the life of the organism. FOXP3⁺ Tregs can develop within the thymus, but also under select circumstances, naive peripheral T cells can be induced to express FOXP3 and become stable Tregs as well. Abundant evidence from animal systems, as well as limited evidence in humans, implicates Tregs in transplant tolerance, although whether these Tregs recognize allo- or self-antigens is not clear. New translational approaches to promote immunosuppression minimization and/or actual tolerance are being designed to exploit these observations. These include strategies to boost the generation, maintenance, and stability of endogenous Tregs, as well as adoptive cellular therapy with exogenous Tregs.

Effects of Lung Cotransplantation on Cardiac Allograft Tolerance Across a Full Major Histocompatibility Complex Barrier in Miniature Swine

A 12-day course of high-dose tacrolimus induces tolerance of major histocompatibility complex-mismatched lung allografts in miniature swine but does not induce tolerance of heart allografts unless a kidney is cotransplanted. To determine whether lungs share with kidneys the ability to induce cardiac allograft tolerance, we investigated heart-lung cotransplantation using the same induction protocol. Hearts (n = 3), heart-kidneys (n = 3), lungs (n = 6), and hearts-lungs (n = 3) were transplanted into fully major histocompatibility complex-mismatched recipients treated with high-dose tacrolimus for 12 days. Serial biopsy samples were used to evaluate rejection, and in vitro assays were used to detect donor responsiveness. All heart-kidney recipients and five of six lung recipients demonstrated long-term graft survival for longer than 272 days, while all heart recipients rejected their allografts within 35 days. Tolerant recipients remained free of alloantibody and showed persistent donor-specific unresponsiveness by cell-mediated lympholysis/mixed-lymphocyte reaction. In contrast, heart-lung recipients demonstrated rejection of both allografts (days 47, 55, and 202) and antidonor responsiveness in vitro. In contrast to kidneys, lung cotransplantation leads to rejection of both heart and lung allografts, indicating that lungs do not have the same tolerogenic capacity as kidneys. We conclude that cells or cell products present in kidney, but not heart or lung allografts, have a unique capacity to confer unresponsiveness on cotransplanted organs, most likely by amplifying host regulatory mechanisms.

Swine model in transplant research: Review of anaesthesia and perioperative management

Pigs are one of most common animal species to be used in biomedical models due to their many anatomical visceral similarities with humans, particularly with regards to transplantation. Despite this use, in many of the researches in which pigs are selected for transplantation, the anaesthesia used is an adaptation of human anaesthesia and presents some limitations such as a reduced analgesia a limited control in perioperative period. In this review we show some of the most important conditions in the preanaesthetic management and of swine as well as we review of anaesthetic protocols for the most common types of swine model of transplantation.

Organ-specific differences in achieving tolerance

PURPOSE OF REVIEW

When it comes to tolerance induction, kidney allografts behave differently from heart allografts that behave differently from lung allografts. Here, we examine how and why different organ allografts respond differently to the same tolerance induction protocol.

RECENT FINDINGS

Allograft tolerance has been achieved in experimental and clinical kidney transplantation. Inducing tolerance in experimental recipients of heart and lung allografts has, however, proven to be more challenging. New protocols being developed in nonhuman primates based on mixed chimerism and cotransplantation of tolerogenic organs may provide mechanistic insights to help overcome these challenges.

SUMMARY

Tolerance induction protocols that are successful in patients transplanted with 'tolerance-prone' organs such as kidneys and livers will most likely not succeed in recipients of 'tolerance-resistant' organs such as hearts and lungs. Separate clinical trials using more robust tolerance protocols will be required to achieve tolerance in heart and lung recipients.