Basic Transplantation Immunology

Graft Dysfunction and Management in Liver Transplantation

Graft dysfunction of the liver allograft manifests across a spectrum in both timing posttransplantation and clinical presentation. This can range from mild transient abnormalities of liver tests to acute liver failure potentially leading to graft failure. The causes of graft dysfunction can be divided into those resulting in early and late graft dysfunction. Although nonspecific, liver biochemistry abnormalities are still the mainstay investigation used in monitoring for dysfunction. This article provides a summary of the main causes and management strategies for liver graft dysfunction in the early through late posttransplant stages.

Development of transplant immunosuppressive agents - considerations in the use of animal models

INTRODUCTION

The development of all immunosuppressant agents to date has involved the experimental use of large and small animal models. Over the last half-century, immunosuppressive drugs have extended the lives of transplant patients worldwide. However, the use of animal models in the development of these drugs is not perfect, and this has brought to light a number of issues including idiosyncratic reactions that are found in animal models but not in humans. The 2006 highly publicized case of the 'elephant man' TGN 1412 drug trial highlights the importance of being cogent of the limitations of animal models. Areas covered: This review covers the utility and limitations of the use of animal models for the development of immunosuppressant agents. This includes both large and small animal models, particularly rodent models in the transplant setting. Expert opinion: The use of animal models represents a critical stage in the development of immunosuppressive drugs. Limitations include physiological differences to humans; this is especially true of immunologically naïve lab rodents with small memory cell populations. Toxic drug levels may differ widely between species. Animal models are also costly and raise ethical concerns. However, there is currently no way to recreate the complex environment of the human immune system purely in vitro.

Update on Immunosuppressive Drugs Used in Solid-Organ Transplantation and Their Nutrition Implications

The success of solid organ transplantation rests heavily on the major advances in immunosuppressive therapy. The early years of organ transplantation were plagued with high failure rates and frequent episodes of acute rejection. With the introduction of improved immunosuppressive agents, successful organ transplantation has become the norm. The emphasis of immunosuppressive therapy has shifted from preventing rejection to balancing acceptable rates of rejection with moderation in adverse effects of the immunosuppressive agents. Among the many possible adverse effects of immunosuppressive therapy is the potential for these agents to affect the nutrition status of the transplant recipient. Given the fact that many patients undergoing transplantation are catabolic and nutritionally vulnerable, it is particularly important for those involved in the care of these patients to be familiar with the nutrition implications of immunosuppressive drugs. In this article, we review the different classes of immunosuppressive medications used in transplantation and emphasize their interactions with the nutrition status of the transplant recipient.

The utility of animal models in developing immunosuppressive agents

The immune system comprises an integrated network of cellular interactions. Some responses are predictable, while others are more stochastic. While in vitro the outcome of stimulating a single type of cell may be stereotyped and reproducible, in vivo this is often not the case. This phenomenon often merits the use of animal models in predicting the impact of immunosuppressant drugs. A heavy burden of responsibility lies on the shoulders of the investigator when using animal models to study immunosuppressive agents. The principles of the three R׳s: refine (less suffering,), reduce (lower animal numbers) and replace (alternative in vitro assays) must be applied, as described elsewhere in this issue. Well designed animal model experiments have allowed us to develop all the immunosuppressive agents currently available for treating autoimmune disease and transplant recipients. In this review, we examine the common animal models used in developing immunosuppressive agents, focusing on drugs used in transplant surgery. Autoimmune diseases, such as multiple sclerosis, are covered elsewhere in this issue. We look at the utility and limitations of small and large animal models in measuring potency and toxicity of immunosuppressive therapies.

Immunology of vascularized composite allotransplantation: a primer for hand surgeons

Vascularized composite allotransplantation is a recent innovation in the fields of transplantation surgery, plastic and reconstructive surgery, and orthopedic surgery. The success of hand and face transplantation has been based on extensive experience in solid organ transplantation. Advances in understanding the immunology of transplantation have had a major role in achieving excellent results in this new field. The purpose of this article is to introduce the basics of human immunology (innate and adaptive systems) and the immunological basis of human transplantation (the importance of human leukocyte antigen, direct and indirect pathways of antigen recognition, the 3 signals for T-cell activation, and mechanisms and types of allograft rejection) and focus on the mode of action of immunosuppressive drugs that have evolved as the mechanisms and pathways for rejection have been defined through research. This includes recent studies involving the use of costimulatory blockade, regulatory T cells, and tolerance induction that have resulted from research in understanding the mechanisms of immune recognition and function.

Drawing networks of rejection - a systems biological approach to the identification of candidate genes in heart transplantation

Technological development led to an increased interest in systems biological approaches to characterize disease mechanisms and candidate genes relevant to specific diseases. We suggested that the human peripheral blood mononuclear cells (PBMC) network can be delineated by cellular reconstruction to guide identification of candidate genes. Based on 285 microarrays (7370 genes) from 98 heart transplant patients enrolled in the Cardiac Allograft Rejection Gene Expression Observational study, we used an information-theoretic, reverse-engineering algorithm called ARACNe (algorithm for the reconstruction of accurate cellular networks) and chromatin immunoprecipitation assay to reconstruct and validate a putative gene PBMC interaction network. We focused our analysis on transcription factor (TF) genes and developed a priority score to incorporate aspects of network dynamics and information from published literature to supervise gene discovery. ARACNe generated a cellular network and predicted interactions for each TF during rejection and quiescence. Genes ranked highest by priority score included those related to apoptosis, humoural and cellular immune response such as GA binding protein transcription factor (GABP), nuclear factor of κ light polypeptide gene enhancer in B-cells (NFκB), Fas (TNFRSF6)-associated via death domain (FADD) and c-AMP response element binding protein. We used the TF CREB to validate our network. ARACNe predicted 29 putative first-neighbour genes of CREB. Eleven of these (37%) were previously reported. Out of the 18 unknown predicted interactions, 14 primers were identified and 11 could be immunoprecipitated (78.6%). Overall, 75% (n= 22) inferred CREB targets were validated, a significantly higher fraction than randomly expected (P < 0.001, Fisher’s exact test). Our results confirm the accuracy of ARACNe to reconstruct the PBMC transcriptional network and show the utility of systems biological approaches to identify possible molecular targets and biomarkers.

Success rates and immunologic responses of autogenic, allogenic, and xenogenic treatments to repair articular cartilage defects

This review examines current approaches available for articular cartilage repair, not only in terms of their regeneration potential, but also as a function of immunologic response. Autogenic repair techniques, including osteochondral plug transplantation, chondrocyte implantation, and microfracture, are the most widely accepted clinical treatment options due to the lack of immunogenic reactions, but only moderate graft success rates have been reported. Although suspended allogenic chondrocytes are shown to evoke an immune response upon implantation, allogenic osteochondral plugs and tissue-engineered grafts using allogenic chondrocytes exhibit a tolerable immunogenic response. Additionally, these repair techniques produce neotissue with success rates approaching those of currently available autogenic repair techniques, while simultaneously obviating their major hindrance of donor tissue scarcity. To date, limited research has been performed with xenogenic tissue, although several studies demonstrate the potential for its long-term success. This article focuses on the various treatment options for cartilage repair and their associated success rates and immunologic responses.

Antibody-mediated rejection: hyperacute rejection reality in liver transplantation? A case report

Hyperacute rejection is rare among ABO-compatible liver transplantations. The mechanism is donor preformed antibodies causing graft loss within a few days. Herein, we have described a case of an ABO-compatible liver transplantation that underwent hyperacute rejection, needing retransplantation for treatment. A 27-year-old man of blood group A positive who displayed fulminant hepatic failure due to hepatitis B (in agreement with the O'Grady criteria), received an ABO-compatible graft. He developed significant asthenia, fever, hypotension, oliguria, and coagulopathy. Ultrasonography revealed total thrombosis of the portal vein and absence of dilatation of bile ducts. The patient was priorized for retransplantation and underwent a good subsequent evolution. On anatomopathologic exam the explant revealed thrombosis of the intrahepatic branches of the portal vein with venous and ischemic infarcts compatible with a diagnosis of hyperacute rejection. The clinical findings of hyperacute rejection were characterized by progressive elevation of bilirubin and thrombocytopenia associated with signs of hepatic failure during the first days after transplantation. In this case, the histological exam was compatible with hyperacute rejection, excluding the diagnoses of hepatic artery thrombosis or biliary obstruction, despite the negative test for anti-HLA antibodies. The diagnosis of hyperacute rejection could be made associated with a short ischemic time and a good response after retransplantation.