Tolerance and latent cellular rejection in long-term liver transplant recipients

Donor-specific immune senescence as a candidate biomarker of operational tolerance following liver transplantation in adults: Results of a prospective, multicenter cohort study

Immunosuppression can be withdrawn from selected liver transplant recipients, although robust clinical predictors of tolerance remain elusive. The Immune Tolerance Network ITN056ST study (OPTIMAL; NCT02533180) assessed clinical outcomes and mechanistic correlates of phased immunosuppression withdrawal (ISW) in nonautoimmune, nonviral adult liver transplant recipients. Enrolled subjects were ≥3 years posttransplant with minimal/absent inflammation or fibrosis on a screening liver biopsy. The primary end point was operational tolerance at 52 weeks following complete ISW. Of 61 subjects who initiated ISW, 34 failed during ISW and 10 restarted immunosuppression after completing ISW due to clinically manifest acute rejection. Only 10 of 17 clinically stable subjects remaining off immunosuppression at 1 year were ultimately deemed tolerant by biopsy. There were no cases of chronic rejection or graft loss; 28.3% developed de novo donor-specific antibody during ISW, which persisted in 11.3%. The majority of subjects (78.6%), including those who experienced rejection, ended the study on same or less calcineurin inhibitor than at baseline. A minority (16.4%) of histologically and clinically stable long-term adult liver transplant recipients can successfully discontinue and remain off immunosuppression. Increased frequency of donor-specific T cell senescence, C4d deposition, and higher density of immune synapses on the screening liver biopsy emerged as potential candidate biomarkers for operational tolerance.

Next-generation pathology detection of T cell-antigen-presenting cell immune synapses in human liver allografts

BACKGROUND AND AIMS

In otherwise near-normal appearing biopsies by routine light microscopy, next-generation pathology (NGP) detected close pairings (immune pairs; iPAIRs) between lymphocytes and antigen-presenting cells (APCs) that predicted immunosuppression weaning failure in pediatric liver transplant (LTx) recipients (Immunosuppression Withdrawal for Stable Pediatric Liver Transplant Recipients [iWITH], NCT01638559). We hypothesized that NGP-detected iPAIRs enrich for true immune synapses, as determined by nuclear shape metrics, intercellular distances, and supramolecular activation complex (SMAC) formation.

APPROACH AND RESULTS

Intralobular iPAIRs (CD45 high lymphocyte-major histocompatibility complex II + APC pairs; n = 1167, training set) were identified at low resolution from multiplex immunohistochemistry-stained liver biopsy slides from several multicenter LTx immunosuppression titration clinical trials (iWITH; NCT02474199 (Donor Alloantigen Reactive Tregs (darTregs) for Calcineurin Inhibitor (CNI) Reduction (ARTEMIS); Prospective Longitudinal Study of iWITH Screen Failures Secondary to Histopathology). After excluding complex multicellular aggregates, high-resolution imaging was used to examine immune synapse formation ( n = 998). By enriching for close intranuclear lymphocyte-APC distance (mean: 0.713 μm) and lymphocyte nuclear flattening (mean ferret diameter: 2.1), SMAC formation was detected in 29% of iPAIR-engaged versus 9.5% of unpaired lymphocytes. Integration of these morphometrics enhanced NGP detection of immune synapses (ai-iSYN). Using iWITH preweaning biopsies from eligible patients ( n = 53; 18 tolerant, 35 nontolerant; testing set), ai-iSYN accurately predicted (87.3% accuracy vs. 81.4% for iPAIRs; 100% sensitivity, 75% specificity) immunosuppression weaning failure. This confirmed the presence and importance of intralobular immune synapse formation in liver allografts. Stratification of biopsy mRNA expression data by immune synapse quantity yielded the top 20 genes involved in T cell activation and immune synapse formation and stability.

CONCLUSIONS

NGP-detected immune synapses (subpathological rejection) in LTx patients prior to immunosuppression reduction suggests that NGP-detected (allo)immune activity usefulness for titration of immunosuppressive therapy in various settings.

Efficacy and Safety of Immunosuppression Withdrawal in Pediatric Liver Transplant Recipients: Moving Toward Personalized Management

BACKGROUND AND AIMS

Tolerance is transplantation's holy grail, as it denotes allograft health without immunosuppression and its toxicities. Our aim was to determine, among stable long-term pediatric liver transplant recipients, the efficacy and safety of immunosuppression withdrawal to identify operational tolerance.

APPROACH AND RESULTS

We conducted a multicenter, single-arm trial of immunosuppression withdrawal over 36-48 weeks. Liver tests were monitored biweekly (year 1), monthly (year 2), and bimonthly (years 3-4). For-cause biopsies were done at investigators' discretion but mandated when alanine aminotransferase or gamma glutamyltransferase exceeded 100 U/L. All subjects underwent final liver biopsy at trial end. The primary efficacy endpoint was operational tolerance, defined by strict biochemical and histological criteria 1 year after stopping immunosuppression. Among 88 subjects (median age 11 years; 39 boys; 57 deceased donor grafts), 33 (37.5%; 95% confidence interval [CI] 27.4%, 48.5%) were operationally tolerant, 16 were nontolerant by histology (met biochemical but failed histological criteria), and 39 were nontolerant by rejection. Rejection, predicted by subtle liver inflammation in trial entry biopsies, typically (n = 32) occurred at ≤32% of the trial-entry immunosuppression dose and was treated with corticosteroids (n = 32) and/or tacrolimus (n = 38) with resolution (liver tests within 1.5 times the baseline) for all but 1 subject. No death, graft loss, or chronic, severe, or refractory rejection occurred. Neither fibrosis stage nor the expression level of a rejection gene set increased over 4 years for either tolerant or nontolerant subjects.

CONCLUSIONS

Immunosuppression withdrawal showed that 37.5% of selected pediatric liver-transplant recipients were operationally tolerant. Allograft histology did not deteriorate for either tolerant or nontolerant subjects. The timing and reversibility of failed withdrawal justifies future trials exploring the efficacy, safety, and potential benefits of immunosuppression minimization.

The Fourth International Workshop on Clinical Transplant Tolerance

The International Workshop on Clinical Transplant Tolerance is a biennial meeting that aims to provide an update on the progress of studies of immunosuppression minimization or withdrawal in solid organ transplantation. The Fourth International Workshop on Clinical Tolerance was held in Pittsburgh, Pennsylvania, September 5-6, 2019. This report is a summary of presentations on the status of clinical trials designed to minimize or withdraw immunosuppressive drugs in kidney, liver, and lung transplantation without subsequent evidence of rejection. All protocols had in common the use of donor or recipient cell therapy combined with organ transplantation. The workshop also included presentations of mechanistic studies designed to improve understanding of the cellular and molecular basis of tolerance and to identify potential predictors/biomarkers of tolerance. Strategies to enhance the safety of hematopoietic cell transplantation and to improve patient selection/risk stratification for clinical trials were also discussed.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Enhancing the Value of Histopathological Assessment of Allograft Biopsy Monitoring

Traditional histopathological allograft biopsy evaluation provides, within hours, diagnoses, prognostic information, and mechanistic insights into disease processes. However, proponents of an array of alternative monitoring platforms, broadly classified as "invasive" or "noninvasive" depending on whether allograft tissue is needed, question the value proposition of tissue histopathology. The authors explore the pros and cons of current analytical methods relative to the value of traditional and illustrate advancements of next-generation histopathological evaluation of tissue biopsies. We describe the continuing value of traditional histopathological tissue assessment and "next-generation pathology (NGP)," broadly defined as staining/labeling techniques coupled with digital imaging and automated image analysis. Noninvasive imaging and fluid (blood and urine) analyses promote low-risk, global organ assessment, and "molecular" data output, respectively; invasive alternatives promote objective, "mechanistic" insights by creating gene lists with variably increased/decreased expression compared with steady state/baseline. Proponents of alternative approaches contrast their preferred methods with traditional histopathology and: (1) fail to cite the main value of traditional and NGP-retention of spatial and inferred temporal context available for innumerable objective analyses and (2) belie an unfamiliarity with the impact of advances in imaging and software-guided analytics on emerging histopathology practices. Illustrative NGP examples demonstrate the value of multidimensional data that preserve tissue-based spatial and temporal contexts. We outline a path forward for clinical NGP implementation where "software-assisted sign-out" will enable pathologists to conduct objective analyses that can be incorporated into their final reports and improve patient care.

Biomarkers of immune tolerance in liver transplantation

The liver exhibits intrinsic immune tolerogenic properties that contribute to a unique propensity toward spontaneous acceptance when transplanted, both in animal models and in humans. Thus, in contrast to what happens after transplantation of other solid organs, several years following liver transplantation a significant subset of patients are capable of maintaining normal allograft function with histological integrity in the absence of immunosuppressive drug treatment. Significant efforts have been put into identifying sensitive and specific biomarkers of tolerance in order to stratify liver transplant recipients according to their need for immunosuppressive medication and their likelihood of being able to completely discontinue it. These biomarkers are currently being validated in prospective clinical trials of immunosuppression withdrawal both in Europe and in the United States. These studies have the potential to transform the clinical management of liver transplant recipients by mitigating, at least in part, the burden of lifelong immunosuppression.

Tolerance in clinical liver transplantation

While advances in immunosuppressive therapy have lowered the rate of acute rejection following liver transplantation, the consequence has been an increase in morbidity and mortality related to the lifelong need for maintenance immunosuppression. These complications include an increased risk of malignancy, infection, metabolic disorders, and chronic kidney disease, as well as high health care costs associated with these therapies and the required drug monitoring. Given these issues, most clinicians attempt trial and error dose minimization with variable success rates, and there has been significant interest in full drug withdrawal in select patients through research protocols. These strategies would be more successful if immunomodulatory therapies early after transplantation could be developed and if immune activation biomarkers guiding drug tapering were available to personalize these approaches. This review will review the mechanisms of liver transplant tolerance and potential strategies to achieve immunosuppression withdrawal.

Immunosuppression in pediatric liver transplant recipients: Unique aspects

Pediatric liver transplantation has experienced improved outcomes over the last 50 years. This can be attributed in part to establishing optimal use of immunosuppressive agents to achieve a balance between minimizing the risks of allograft rejection and infection. The management of immunosuppression in children is generally more complex and can be challenging when compared with the use of these agents in adult liver transplant patients. Physiologic differences in children alter the pharmacokinetics of immunosuppressive agents, which affects absorption, distribution, metabolism, and drug excretion. Children also have a longer expected period of exposure to immunosuppression, which can impact growth, risk of infection (bacterial, viral, and fungal), carcinogenesis, and likelihood of nonadherence. This review discusses immunosuppressive options for pediatric liver transplant recipients and the unique issues that must be addressed when managing this population. Further advances in the field of tolerance and accommodation are needed to relieve the acute and cumulative burden of chronic immunosuppression in children. Liver Transplantation 23 244-256 2017 AASLD.

2016 Comprehensive Update of the Banff Working Group on Liver Allograft Pathology: Introduction of Antibody-Mediated Rejection

The Banff Working Group on Liver Allograft Pathology reviewed and discussed literature evidence regarding antibody-mediated liver allograft rejection at the 11th (Paris, France, June 5-10, 2011), 12th (Comandatuba, Brazil, August 19-23, 2013), and 13th (Vancouver, British Columbia, Canada, October 5-10, 2015) meetings of the Banff Conference on Allograft Pathology. Discussion continued online. The primary goal was to introduce guidelines and consensus criteria for the diagnosis of liver allograft antibody-mediated rejection and provide a comprehensive update of all Banff Schema recommendations. Included are new recommendations for complement component 4d tissue staining and interpretation, staging liver allograft fibrosis, and findings related to immunosuppression minimization. In an effort to create a single reference document, previous unchanged criteria are also included.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

ABO-compatible liver allograft antibody-mediated rejection: an update

PURPOSE OF REVIEW

Liver allograft antibody-mediated rejection (AMR) studies have lagged behind parallel efforts in kidney and heart because of a comparative inherent hepatic resistance to AMR. Three developments, however, have increased interest: first, solid phase antibody testing enabled more precise antibody characterization; second, increased expectations for long-term, morbidity-free survival; and third, immunosuppression minimization trials.

RECENT FINDINGS

Two overlapping liver allograft AMR phenotypic expressions are beginning to emerge: acute and chronic AMR. Acute AMR usually occurs within the several weeks after transplantation and characterized clinically by donor-specific antibodies (DSA) persistence, allograft dysfunction, thrombocytopenia, and hypocomplementemia. Acute AMR appears histopathologically similar to acute AMR in other organs: diffuse microvascular endothelial cell hypertrophy, C4d deposits, neutrophilic, eosinophilic, and macrophag-mediated microvasculitis/capillaritis, along with liver-specific ductular reaction, centrilobular hepatocyte swelling, and hepatocanalicular cholestasis often combined with T-cell-mediated rejection (TCMR). Chronic AMR is less well defined, but strongly linked to serum class II DSA and associated with late-onset acute TCMR, fibrosis, chronic rejection, and decreased survival. Unlike acute AMR, chronic AMR is a slowly evolving insult with a number of potential manifestations, but most commonly appears as low-grade lymphoplasmacytic portal and perivenular inflammation accompanied by unusual fibrosis patterns and variable microvascular C4d deposition; capillaritis can be more difficult to identify than in acute AMR.

SUMMARY

More precise DSA characterization, increasing expectations for long-term survival, and immunosuppression weaning precipitated a re-emergence of liver allograft AMR interest. Pathophysiological similarities exist between heart, kidney, and liver allografts, but liver-specific considerations may prove critical to our ultimate understanding of all solid organ AMR.

Tissue biopsy monitoring of operational tolerance in liver allograft recipients

PURPOSE OF REVIEW

Highly selected, long-surviving, liver allograft recipients with normal/near normal liver injury tests can be weaned from immunosuppression. Baseline biopsies document changes before weaning and can help stratify risk of rejection or dysfunction after weaning; biopsies after weaning are used to study mechanisms of operational tolerance and to monitor for subclinical events.

RECENT FINDINGS

Clinicopathological features associated with successful weaning include a lack of sensitization [negative donor-specific antibodies (DSA) and lack of tissue C4d deposits]; 'inexperienced' recipient immune system with limited potential for cross-reactivity (less immunological memory; infant recipients); noninflamed allograft in those with nonviral, nonimmunological original diseases; upregulation of liver genes associated with iron metabolism; allograft colonization with 'immunosuppressive' cells (Treg and γδ-1>γδ-2); and longer time on immunosuppression, which might signal slow clonal deletion or silencing. The differential diagnosis of histopathological findings detected before and after weaning includes emerging infections, typical and atypical cellular rejection, indolent antibody-mediated rejection, 'autoimmunity', and other causes of progressive fibrosis.

SUMMARY

Operationally tolerant liver allograft recipients can be successfully managed with very low, and sometimes no immunosuppression, but challenges exist. Newer approaches to tissue pathology and tissue, serum, and cross-platform analytics are needed to predict successful weaning and to monitor for subclinical events.

Importance of liver biopsy findings in immunosuppression management: biopsy monitoring and working criteria for patients with operational tolerance

Obstacles to morbidity-free long-term survival after liver transplantation (LT) include complications of immunosuppression (IS), recurrence of the original disease and malignancies, and unexplained chronic hepatitis and graft fibrosis. Many programs attempt to minimize chronic exposure to IS by reducing dosages and stopping steroids. A few programs have successfully weaned a highly select group of recipients from all IS without apparent adverse consequences, but long-term follow-up is limited. Patients subjected to adjustments in IS are usually followed by serial liver chemistry tests, which are relatively insensitive methods for detecting allograft damage. Protocol biopsy has largely been abandoned for hepatitis C virus-negative recipients, at least in part because of the inability to integrate routine histopathological findings into a rational clinical management algorithm. Recognizing a need to more precisely categorize and determine the clinical significance of findings in long-term biopsy samples, the Banff Working Group on Liver Allograft Pathology has reviewed the literature, pooled the experience of its members, and proposed working definitions for biopsy changes that (1) are conducive to lowering IS and are compatible with operational tolerance (OT) and (2) raise concern for closer follow-up and perhaps increased IS during or after IS weaning. The establishment of guidelines should help us to standardize analyses of the effects of various treatments and/or weaning protocols and more rigorously categorize patients who are assumed to show OT. Long-term follow-up using standardized criteria will help us to determine the consequences of lowering IS and to define and determine the incidence and robustness of OT in liver allografts.

Zinc finger protein A20 protects rats against chronic liver allograft dysfunction

AIM: To investigate the effect of zinc finger protein A20 on chronic liver allograft dysfunction in rats.

METHODS: Allogeneic liver transplantation from DA rats to Lewis rats was performed. Chronic liver allograft dysfunction was induced in the rats by administering low-dose tacrolimus at postoperative day (POD) 5. Hepatic overexpression of A20 was achieved by recombinant adenovirus (rAd.)-mediated gene transfer administered intravenously every 10 d starting from POD 10. The recipient rats were injected with physiological saline, rAdEasy-A20 (1 × 10⁹ pfu/30 g weight) or rAdEasy (1 × 10⁹ pfu/30 g weight) every 10 d through the tail vein for 3 mo starting from POD 10. Liver tissue samples were harvested on POD 30 and POD 60.

RESULTS: Liver-transplanted rats treated with only tacrolimus showed chronic allograft dysfunction with severe hepatic fibrosis. A20 overexpression ameliorated the effects on liver function, attenuated liver allograft fibrosis and prolonged the survival of the recipient rats. Treatment with A20 suppressed hepatic protein production of tumor growth factor (TGF)-β1, interleukin-1β, caspase-8, CD40, CD40L, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin. A20 treatment suppressed liver cell apoptosis and inhibited nuclear factor-κB activation of Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), and it subsequently decreased cytokine mRNA expression in KCs and LSECs and reduced the production of TGF-β1 in HSCs.

CONCLUSION: A20 might prevent chronic liver allograft dysfunction by re-establishing functional homeostasis of KCs, LSECs and HSCs.

What is the long-term outcome of the liver allograft?

With improved long-term survival following liver transplantation (LT), issues relating to the assessment of the liver allograft in long-term survivors are becoming increasingly relevant. Histological abnormalities are commonly present in late post-transplant biopsies, including protocol biopsies from patients who appear to be well with good graft function. Recurrent disease is the commonest recognised cause of abnormal graft histology, but may be modified by the effects of immunosuppression or interactions with other graft complications, resulting in complex or atypical changes. Other abnormalities seen in late post-transplant biopsies include rejection (which often has different appearances to those seen in the post-transplant period), de novo disease, "idiopathic" post-transplant hepatitis (IPTH) and nodular regenerative hyperplasia. In many cases graft dysfunction has more than one cause and liver biopsy may help to identify the predominant cause of graft damage. Problems exist with the terminology used to describe less well understood patterns of graft injury, but there is emerging evidence to suggest that late rejection, de novo autoimmune hepatitis and IPTH may all be part of an overlapping spectrum of immune-mediated injury occurring in the late post-transplant liver allograft. Careful clinico-pathological correlation is very important and the wording of the biopsy report should take into account therapeutic implications, particularly whether changes in immunosuppression may be indicated. This article will provide an overview of the main histological changes occurring in long-term survivors post-LT, focusing on areas where the assessment of late post-transplant biopsies is most relevant clinically.

Immunologic basis of graft rejection and tolerance following transplantation of liver or other solid organs

Transplantation of organs between genetically different individuals of the same species causes a T cell-mediated immune response that, if left unchecked, results in rejection and graft destruction. The potency of the alloimmune response is determined by the antigenic disparity that usually exists between donors and recipients and by intragraft expression of proinflammatory cytokines in the early period after transplantation. Studies in animal models have identified many molecules that, when targeted, inhibit T-cell activation. In addition, some of these studies have shown that certain immunologic interventions induce transplantation tolerance, a state in which the allograft is specifically accepted without the need for chronic immunosuppression. Tolerance is an important aspect of liver transplantation, because livers have a unique microenvironment that promotes tolerance rather than immunity. In contrast to the progress achieved in inducing tolerance in animal models, patients who receive transplanted organs still require nonspecific immunosuppressant drugs. The development of calcineurin inhibitors has reduced the acute rejection rate and improved short-term, but not long-term, graft survival. However, long-term use of immunosuppressive drugs leads to nephrotoxicity and metabolic disorders, as well as manifestations of overimmunosuppression such as opportunistic infections and cancers. The status of pharmacologic immunosuppression in the clinic is therefore not ideal. We review recently developed therapeutic strategies to promote tolerance to transplanted livers and other organs and diagnostic tools that might be used to identify patients most likely to accept or reject allografts.

Adding value to liver (and allograft) biopsy evaluation using a combination of multiplex quantum dot immunostaining, high-resolution whole-slide digital imaging, and automated image analysis

Various technologies including nucleic acid, protein, and metabolic array analyses of blood, liver tissue, and bile are emerging as powerful tools in the study of hepatic pathophysiology. The entire lexicon of liver disease, however, has been written using classical hematoxylin-eosin staining and light microscopic examination. The authors' goal is to develop new tools to enhance histopathologic examination of liver tissue that would enrich the information gained from liver biopsy analysis, enable quantitative analysis, and bridge the gap between various "-omics" tools and interpretation of routine liver biopsy results. This article describes the progress achieved during the past 2 years in developing multiplex quantum dot (nanoparticle) staining and combining it with high-resolution whole-slide imaging using a slide scanner equipped with filters to capture 9 distinct fluorescent signals for multiple antigens. The authors first focused on precise characterization of leukocyte subsets, but soon realized that the data generated were beyond the practical limits that could be properly evaluated, analyzed, and interpreted visually by a pathologist. Therefore, the authors collaborated with the open source FARSIGHT image analysis project (http://www.farsight-toolkit.org). FARSIGHT's goal is to develop and disseminate the next-generation toolkit of automated image analysis methods to enable quantification of molecular biomarkers on a cell-by-cell basis from multiparameter images. The resulting data can be used for histocytometric studies of the complex and dynamic tissue microenvironments that are of biomedical interest. The authors envisage that these tools will eventually be incorporated into the routine practice of surgical pathology and precipitate a revolution in the specialty.

Chronic rejection of the liver: the role of immunosuppression

Liver transplantation is now widely recognised as an effective treatment option for patients with advanced liver disease. Many units now achieve greater than 85% survival at 1 year, with the majority of patients having a high quality of life. The maintenance of a high quality of life requires careful clinical management to ensure that the continued maintenance of excellent liver graft function is not achieved at the expense of immunosuppressive drug complications or morbidity. Acute liver rejection will occur in between 30 to 45% of patients, although with modern immunosuppressive protocols, usually combining one of the calcineurin agents, either cyclosporin or tacrolimus, with both azathioprine and corticosteroids (prednisolone) ensures that relatively few grafts are lost from severe acute rejection. While the incidence and severity of acute rejection may be one factor in raising the risk of chronic rejection, it may not be the principal one in many patients. It is important to recognise that the frequency of rejection also varies with the primary underlying liver disease, with patients with hepatitis B or alcoholic liver disease having relatively low rejection rates, compared with patients with primary biliary cirrhosis (PBC) or primary sclerosing cholangitis (PSC), which range between 20 to 70%. Chronic rejection will account for some 5% of grafts lost in the first 3 to 5 years. Indeed, there is some evidence that the incidence of chronic rejection is actually declining over the past few years. While the reason for this apparent decline is uncertain, and it could relate to better immunosuppression management, or more likely to the growing recognition that chronic graft dysfunction may be due to recurrent liver disease, such as autoimmune hepatitis, PBC, PSC, or recurrent hepatitis C. The differentiation of recurrent primary liver disease from chronic rejection can prove to be very difficult in clinical practice. Thus, the clinician must carefully monitor liver and graft function, evaluate any biochemical changes, and try to reach a clear diagnosis before considering any modification of immunosuppressive schedules.

Heterogeneous inflammatory changes in liver graft recipients with normal biochemistry

BACKGROUND

Patients with established liver grafts may receive excessive immune suppression. Liver biopsies were analyzed in those with normal liver biochemistry to identify parameters that might identify such cases.

METHODS

Patients with established grafts (>3 years from engraftment) and normal liver biochemistry (normal alanine transaminase, alkaline phosphatase, and bilirubin) were invited to undergo liver biopsy. Liver tissue was assessed by routine histopathology, a modified Ishak score, and immunohistochemistry for lymphocyte and cell-cycle markers. Circulating and intrahepatic lymphocytes were subjected to flow cytometry. Data were subjected to principal component analysis.

RESULTS

Two hundred twenty-five (40%) patients under regular review had an established graft with normal liver biochemistry; liver tissue was obtained in 55. Liver histology was normal in eight cases (14.5%). The most common abnormalities were mild nonspecific hepatitis in 25 (45.4%) and disease recurrence in 14 (25.4%). Principal component analysis identified a cluster of variables that accounted for a significant degree of variation within the dataset. These were lobular inflammation, portal inflammation, interface hepatitis, and fibrosis.

CONCLUSIONS

Inflammation persisted in established grafted livers in most patients with normal liver biochemistry. Systematic histological and lymphocyte phenotype analysis generated an index that distinguished patient groups. Those with least inflammation and the lowest alanine transaminase may have a reduced requirement for immune suppression.

Immunoregulatory profiles in liver transplant recipients on different immunosuppressive agents

We compared peripheral blood immunophenotyping in 31 adult liver transplant recipients on differing long-term immunosuppressive (IS) monotherapy with and without peri-transplantation alemtuzumab (AL) induction. All patients had been stable on monotherapy with either sirolimus (SRL) (n = 10) or without SRL (tacrolimus (TAC) (n = 10), mycophenolate mofetil (MMF) (n = 11)) for more than 6 months. Five-color flow cytometry for putative "regulatory" T and dendritic cells as well as serum assays for soluble HLA-G (sHLA-G) were performed. The SRL monotherapy group had significantly higher percentages of CD4+CD25(high+)Foxp3+ T cells (1.3 +/- 1.0) compared with the non-SRL group (0.7 +/- 0.6) (p = 0.04). The SRL effect was even higher in a subset with prior AL induction and no prior hepatitis C or rejection (1.7 +/- 0.2) compared with all other subgroups (0.7 +/- 0.6) (p = 0.02). TAC patients showed significantly higher "regulatory" DC2:DC1 ratios (10 +/- 7.6) compared with non-TAC patients (4.1 +/- 2.3) (p = 0.04). Although sHLA-G levels appeared higher in TAC patients, the differences were not statistically significant. In conclusion, IS monotherapy provides an opportunity to investigate regulatory roles of individual agents. SRL maintenance and prior AL induction in subsets of patients appeared to show a regulatory T cell immunophenotype. However, TAC patients may have other regulatory characteristics, supporting the need for larger, prospective studies to clarify differences.

Monitoring of human liver and kidney allograft tolerance: a tissue/histopathology perspective

Several factors acting together have recently enabled clinicians to seriously consider whether chronic immunosuppression is needed in all solid organ allograft recipients. This has prompted a dozen or so centers throughout the world to prospectively wean immunosuppression from conventionally treated liver allograft recipients. The goal is to lessen the impact of chronic immunosuppression and empirically identify occasional recipients who show operational tolerance, defined as gross phenotype of tolerance in the presence of an immune response and/or immune deficit that has little or no significant clinical impact. Rare operationally tolerant kidney allograft recipients have also been identified, usually by single case reports, but only a couple of prospective weaning trials in conventionally treated kidney allograft recipients have been attempted and reported. Pre- and postweaning allograft biopsy monitoring of recipients adds a critical dimension to these trials, not only for patient safety but also for determining whether events in the allografts can contribute to a mechanistic understanding of allograft acceptance. The following is based on a literature review and personal experience regarding the practical and scientific aspects of biopsy monitoring of potential or actual operationally tolerant human liver and kidney allograft recipients where the goal, intended or attained, was complete withdrawal of immunosuppression.

Protocol liver allograft biopsies

Protocol liver allograft biopsies are liver biopsies carried out at specific time points according to predetermined guidelines, rather than in response to specific indications such as change in the patient's clinical status or biochemical tests. Use of protocol liver allograft biopsy has been declining over the last decade: an informal survey of 35 transplant units showed that whereas 65% of units undertake protocol biopsies for those grafted for Hepatitis C virus infection, only 25% do so for patients grafted for other indications. In this overview, we consider the arguments against and those in favor of liver biopsies in adult liver allograft recipients. Arguments against the use of protocol liver biopsies are that they biopsies put the patient are associated with a small risk of morbidity and mortality, are expensive, do not provide useful information and do not alter clinical practice. The estimated rate of major complications is 0.6% and the estimated mortality rate 0.02%. However, the argument in favor of protocol biopsies is that even when standard liver tests are normal, there is on-going inflammation in the graft which, if immunosuppression is not altered, will lead to progressive fibrosis, cirrhosis and even graft loss. Conversely, normal liver histology may allow for reduction in the immunosuppression and so lower the risk of the complications associated with immunosuppression. Currently available diagnostic techniques are not yet sufficiently sensitive or specific to provide an accurate reflection of the state of the graft and the presence or absence of graft damage. We conclude that, while there are no clear data showing that protocol liver allograft biopsies are cost effective and lead to improved patient and graft outcome, such biopsies still have a role in the management of the liver transplant recipient.

Serial assessment of immune status by circulating CD8 effector T cell frequencies for posttransplant infectious complications

To clarify the role of CD8⁺ effector T cells for infectious complications, 92 recipients were classified according to the hierarchical clustering of preoperative CD8⁺CD45 isoforms: Group I was naive, Group II was effector memory, and Group III was effector (E) T cell-dominant. The posttransplant infection rates progressively increased from 29% in Group I to 64.3% in Group III recipients. The posttransplant immune status was compared with the pretransplant status, based on the measure (% difference) and its graphical form (scatter plot). In Groups I and II, both approaches showed a strong upward deviation from pretransplant status upon posttransplant infection, indicating an enhanced clearance of pathogens. In Group III, in contrast, both approaches showed a clear downward deviation from preoperative status, indicating deficient cytotoxicity. The % E difference and scatter plot can be used as a useful indicator of a posttransplant infectious complication.

Liver biopsy interpretation for causes of late liver allograft dysfunction

Evaluation of needle biopsies and extensive clinicopathological correlation play an important role in the determination of liver allograft dysfunction occurring more than 1 year after transplantation. Interpretation of these biopsies can be quite difficult because of the high incidence of recurrent diseases that show histopathological, clinical, and serological features that overlap with each other and with rejection. Also, more than one insult can contribute to allograft injury. In an attempt to enable centers to compare and pool results, improve therapy, and better understand pathophysiological disease mechanisms, the Banff Working Group on Liver Allograft Pathology herein proposes a set of consensus criteria for the most common and problematic causes of late liver allograft dysfunction, including late-onset acute and chronic rejection, recurrent and new-onset viral and autoimmune hepatitis, biliary strictures, and recurrent primary biliary cirrhosis and primary sclerosing cholangitis. A discussion of differential diagnosis is also presented.

Inhibition of T-cell responses by hepatic stellate cells via B7-H1-mediated T-cell apoptosis in mice

In the injured liver, hepatic stellate cells (HSCs) secrete many different cytokines, recruit lymphocytes, and thus participate actively in the pathogenesis of liver disease. Little is known of the role of HSCs in immune responses. In this study, HSCs isolated from C57BL/10 (H2b) mice were found to express scant key surface molecules in the quiescent stage. Activated HSCs express major histocompatibility complex class I, costimulatory molecules, and produce a variety of cytokines. Stimulation by interferon gamma (IFN-gamma) or activated T cells enhanced expression of these molecules. Interestingly, addition of the activated (but not quiescent) HSCs suppressed thymidine uptake by T cells that were stimulated by alloantigens or by anti-CD3-mediated T-cell receptor ligation in a dose-dependent manner. High cytokine production by the T cells suggests that the inhibition was probably not a result of suppression of their activation. T-cell division was also found to be normal in a CFSE dilution assay. The HSC-induced T-cell hyporesponsiveness was associated with enhanced T-cell apoptosis. Activation of HSCs was associated with markedly enhanced expression of B7-H1. Blockade of B7-H1/PD-1 ligation significantly reduced HSC immunomodulatory activity, suggesting an important role of B7-H1. In conclusion, the bidirectional interactions between HSCs and immune cells may contribute to hepatic immune tolerance.

DEMONSTRATION THAT DONOR-SPECIFIC NONRESPONSIVENESS IN HUMAN LIVER ALLOGRAFT RECIPIENTS IS BOTH RARE AND TRANSIENT

BACKGROUND

The side effects of lifetime immunosuppression are a major cause of morbidity and mortality; however, in the absence of prospective monitoring, immunosuppression withdrawal may lead to graft loss from rejection. To detect and monitor suitable recipients for immunosuppression withdrawal, the authors used an in vitro assay of T-cell function to study 71 long-term liver allograft recipients.

METHODS

Interleukin-2 secretion by blood mononuclear cells was measured in response to recall antigens, alloantigen (donor and third-party), and phytohemagglutinin.

RESULTS

Forty-four recipients were studied at a single time point at least 1 month after transplantation. The majority reacted to all antigens (n=33), whereas four showed globally reduced or absent responses (n=4) and six had markedly reduced or absent responses to donor alloantigen in the presence of preserved responses to third-party alloantigen and recall antigens. Four of these donor-nonresponsive recipients were retested 6 to 12 months later, by which time all had redeveloped responses to donor alloantigen. Serial measurements for up to 2 years in a prospective cohort of 27 liver allograft recipients showed only two patients to be consistently donor-nonresponsive posttransplant.

CONCLUSIONS

Most patients rapidly reacquire vigorous immune responses after liver transplantation, and only a minority are hyporesponsive to donor alloantigen. Donor-specific nonresponsiveness is transient in most patients, and serial monitoring is required to define sustained periods of donor-specific nonresponsiveness. Whether such patients are suitable for immunosuppressive withdrawal is unclear.

Hepatocyte growth factor prevents chronic allograft dysfunction in liver-transplanted rats

BACKGROUND

Hepatocyte growth factor (HGF) is a growth factor with multiple biologic properties, including mitogenic, morphogenic, anti-apoptotic, and antifibrogenic activities. Long-term administration of the deletion variant of HGF (dHGF) might contribute to the prevention of chronic liver allograft dysfunction, which is attributed to immunologic and nonimmunologic reactions.

METHODS

Low-dose tacrolimus was administered to rat-liver recipients after transplantation. Effects of dHGF on transplanted livers treated with low-dose tacrolimus were investigated.

RESULTS

Rats receiving liver transplants treated with only low-dose tacrolimus administration showed chronic allograft dysfunction. Treatment with dHGF prolonged the survival time of rats that received liver allografts and suppressed fibrosis of liver allograft. Treatment with dHGF also suppressed the expression levels of interleukin (IL)-1beta, caspase-1, and transforming growth factor (TGF)-beta mRNAs in liver allografts.

CONCLUSIONS

The findings indicate that dHGF may prevent chronic liver-allograft dysfunction and thus may become a novel treatment for chronic liver-allograft dysfunction.

Immunohistochemical differences in the portal tract and acinar infiltrates between primary biliary cirrhosis and autoimmune cholangitis

BACKGROUND

Antimitochondrial antibody-negative primary biliary cirrhosis, or autoimmune cholangitis, may be indistinguishable clinically and histologically from antimitochondrial antibody-positive primary biliary cirrhosis.

AIMS

We aimed to compare the phenotypic markers of the portal and acinar infiltrates in autoimmune cholangitis and antimitochondrial antibody-positive primary biliary cirrhosis.

PATIENTS AND METHODS

Formalin-fixed, paraffin-embedded liver sections were identified from 32 patients with a clinical and histological diagnosis of primary biliary cirrhosis. Thirteen were antimitochondrial antibody-negative (autoimmune cholangitis group) and 19 were antimitochondrial antibody-positive. The groups were well matched for age, histological stage, liver biochemistry and drug treatment. Immunohistochemical staining was performed using monoclonal antibodies against CD3 (pan T cell), CD8 (cytotoxic), CD45RO (memory), CD45RA (naive), CD68 (macrophages) and against the secreted form of eosinophilic cationic protein (EG2).

RESULTS

In autoimmune cholangitis, both portal and acinar CD3 cell counts were significantly higher than in antimitochondrial antibody-positive primary biliary cirrhosis (median portal count 421 vs 257 cells/graticule, P< 0.03; median acinar count 18 vs 9 cells/graticule, P< 0.02). There were no differences between the groups in portal or lobular CD8, CD45RO, CD45RA, CD68 or EG2. Of the total group (antimitochondrial antibody positives and negatives), there were significantly more CD45RA cells in early (stage 1) compared with cirrhotic (stage 4) disease (median 19.3 vs 14 cells/graticule, P< 0.03). EG2 staining was found in eight of the 32 sections overall, but not in the patients with stage 1 disease (P< 0.04).

CONCLUSION

CD3 counts are higher in autoimmune cholangitis than in antimitochondrial antibody-positive primary biliary cirrhosis in both portal and acinar areas. However, there are no significant differences in memory/naïve T-cell subsets between both conditions and, in both, loss of naive T lymphocytes and secretion of eosinophilic cationic protein occur with disease progression. This implies that the effector pathways of bile duct destruction are similar in autoimmune cholangitis and primary biliary cirrhosis.

History of pediatric liver transplantation. Where are we coming from? Where do we stand?

The history of pediatric liver transplantation cannot be dissociated from one man, Thomas E. Starzl, whose pioneer efforts contributed more than anyone else to what has become a routinely successful clinical procedure. During the pre-cyclosporine era, the pediatric experience was confined nearly exclusively in Denver: first attempt in 1963, first success with survival beyond one year in 1967, cumulative experience with 84 pediatric cases in the pre-cyclosporine era (1967-1979) with a 2-year patient survival rate of 30%. The stampede for the development of other liver transplant centers came with the introduction of cyclosporine in the early eighties. Besides Pittsburgh, seven centers (Brussels, Cambridge and Hanover in Europe; Boston, Dallas, UCLA, Minneapolis in USA) had performed up to 1986 at least 20 pediatric liver transplants each with a long-term (>1 year) patient survival rate ranging between 57% and 83%. At the moment, a long-term patient survival rate in excess of 90% in elective patients -including infants - is commonly obtained in experienced centers. The shortage of size matched liver donors which was responsible for a high death rate on the cadaveric waiting list stimulated the development or technical innovations based on the segmental anatomy of the liver: reduced ('cutdown') liver graft, split graft and living liver transplantation. Challenging technical aspects in the recipient have been solved in order to reduce the incidence of surgical complications like outflow obstruction, arterial and portal thrombosis, and biliary problems. The indications of liver transplantation have been refined; regarding biliary atresia, which is the most frequent indication, a consensus has developed to propose a sequential strategy with a single attempt at hepatoportoenterostomy followed, when it fails, by liver transplantation. Some contra-indications accepted in the past are not currently valid with better understanding of the pathophysiology and/or increased clinical experience; such is the case of the hepatopulmonary syndrome. A major progress in preoperative management has been achieved through a multidisciplinary approach, particularly regarding nutrition and control of portal hypertension-related bleeding and ascites. Perioperatively, liver transplantation has derived benefit from the expertise of anesthetists managing babies with serious conditions and increased experience of the transplant surgeons regarding the knowledge of all the technical modalities, good strategy, technical skills and meticulous control of bleeding. It is well-recognized that children require more immunosuppression than adults. As in adults, the first breakthrough came with the introduction of cyclosporine which more than doubled the one-year patient survival rate. The next advance during the last decade was afforded by FK 506 - Tacrolimus which allows steroid withdrawal with the first year post-transplant in most patients. Besides its efficacy in reducing the incidence of rejection and absence of cosmetic side-effects, the steroid-sparing effect of Tacrolimus is of utmost importance to preserve the growth potential of children. The use of OKT-3 both for induction and treatment of rejection has been abandoned nearly universally because its use, cumulated with other immunosuppressants, resulted in a high incidence of lymphoproliferative disorder. In contrast, anti-IL2-receptor monoclonal antibodies, will most likely gain an increasing place in induction, with the availability of chimeric or humanized preparations. The side-effects of immunosuppression can endanger both the quality of life and the life expectancy; they are a special source of concern in pediatric recipients whose survival can be expected to be more than a few decades. Children would benefit most from the development of a marker able to identify the patients who have developed graft acceptance, allowing complete wearing of immunosuppression. Also they would benefit most from research protocols of tolerance induction. Since the vast majority of liver-transplanted children will have a reasonably normal life expectancy, the focus should be switched to their long-term rehabilitation and the assessment of their quality of life when they reach adulthood.

Differential splenic migration of dendritic cells after immunologic unresponsiveness in rat hepatic allografts induced by pretransplant donor-specific transfusion

BACKGROUND

Donor dendritic cells migrate into the recipient spleen after hepatic transplantation. We previously reported that immunologic unresponsiveness to rat hepatic allografts can be induced by prior donor-specific blood transfusion (DST). We investigated the phenotype and splenic distribution of donor dendritic cells after allografting and DST.

METHODS

Donor dendritic cells were identified with anti-rat dendritic cell (OX-62) and anti-donor class II MHC (RT1B(a)) (OX-76) antibodies. The phenotype of dendritic cells was determined with antibodies to CD45RC, CD62L, and the maturation markers CD80 (B7-1) and CD86 (B7-2). The cytokine profile of sorted CD45RC(+) OX-62(+) and CD45RC(-) OX-62(+) dendritic cells was analyzed by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Pretransplant DST significantly prolonged rat hepatic allograft survival. Immunostaining revealed OX76(+)/OX-62(+) cells in the splenic red pulp of animals receiving pretransplant DST and in the white pulp of untreated animals after transplantation. The ratio of splenic CD45RC(-) OX-62(+) cells to CD45RC(+) OX-62(+) cells was significantly higher in DST recipients than in untreated animals. CD62L, CD80, and CD86 were lower on CD45RC(-) OX-62(+) than CD45RC(+) OX-62(+) cells. RT-PCR revealed that sorted CD45RC(-) OX-62(+) cells expressed interleukin (IL)-4 and IL-10. In contrast, sorted CD45RC(+) OX-62(+) cells expressed only IL-2 and interferon gamma (IFN-gamma).

CONCLUSION

Differential splenic migration of CD45RC(-) dendritic cells is associated with immunologic unresponsiveness to rat hepatic allografts.

Clinical and subclinical acute rejection early after liver transplantation: contributing factors and relevance for the long-term course

Routine transplant aspiration cytology (TAC) after liver transplantation gives detailed information that concerns immunologic events in the graft. TAC can be helpful for diagnosis of acute rejection, but it also detects morphological signs of rejection without clinical correlate ("subclinical rejection"). The aim of this study was to systematically evaluate factors that influence the development of early clinical and subclinical rejection and to analyze the relevance of these early immunologic processes for the long-term course. The study includes the course of 340 patients after liver transplantation between 1988 and 1995 in whom TAC was performed routinely and who were followed for a minimum of 3 years. TAC findings were correlated with the following various clinical parameters: (1) Overall early clinical rejection occurred in 17.4%, subclinical rejection in 59.1%, and no immune activation was seen in 23.5% of patients. (2) Incidence of early clinical and subclinical rejection was markedly influenced by type of immunosuppression. (3) Basic disease and extent of preservation injury had only a minor influence; there was a trend towards lower early rejection associated with more severe preservation damage, increased patient age, and early retransplantation. (4) Presence of early clinical or subclinical rejection was not associated with a higher incidence of chronic dysfunction. (5) Falsely indicated antirejection treatment was associated with inferior graft survival. Subclinical rejection is very frequent early after liver transplantation, requires no treatment, and has no long-term adverse effect. Incidence of early clinical rejection is mainly determined by initial immunosuppression; its occurrence has no negative long-term effects and may even be associated with a lower risk for later immunological complications. Thus, the incidence of early acute rejection is no adequate parameter for evaluating the quality of an immunosuppressive treatment protocol.

Tolerance of rat liver allografts induced by short-term selective immunosuppression combining monoclonal antibodies directed against CD25 and CD54 with subtherapeutic cyclosporine

BACKGROUND

Our purpose was to develop and evaluate protocols for selective immunosuppression after liver transplantation using the monoclonal antibodies (mAbs) NDS-61, directed against the interleukin-2 receptor (CD25), and 1A29, directed against the intercellular adhesion molecule-1 (CD54), in combination with subtherapeutic cyclosporine (CsA).

METHODS

Orthotopic rat liver transplantation (ORLT) was performed in a DA-to-LEW strain combination. Immunosuppression was administered from day 0 to +13. Functional parameters such as survival time, body weight, and serum bilirubin levels were measured and the liver grafts were evaluated histologically.

RESULTS

A stepwise tapering of CsA from 3 to 0.25 mg/kg/day reduced the long-term survival rate. All animals died at a CsA dosage of 0.25 mg/kg/day, which was therefore defined as subtherapeutic. Monotherapy with the anti-CD25 mAb was performed at dosages of 600 and 1800 microg/kg/day. The lower mAb dosage resulted in a long-term survival rate of 12% and was defined as subtherapeutic. The combination therapy of CsA (0.25 mg/kg/day) and anti-CD25 mAb (600 microg/kg/day) produced a synergistic effect and led to a long-term survival rate of 84%. This survival rate was significantly higher than those after either CsA (P<0.005) or anti-CD25 mAb (P<0.001) monotherapy. Both dosages (10 and 30 microg/kg/day) of anti-CD54 mAb monotherapy as well as anti-CD54 mAb combined with a subtherapeutic dosage of CsA were ineffective in preventing acute allograft rejection. The addition of anti-CD54 mAb (30 microg/kg/day) to combined CsA plus anti-CD25 mAb therapy (triple therapy), however, increased the long-term survival rate to 100%. In the triple therapy group there was no rejection process in the liver allografts at any time, and donor-specific tolerance could be shown by donor-specific and third-party heterotopic heart transplantation.

CONCLUSIONS

The synergistic action of subtherapeutic CsA plus anti-CD25 mAb NDS-60 could be demonstrated, whereas anti-CD54 mAb only had a positive effect in a triple therapy group. Triple therapy prevented both acute and chronic rejection and induced donor-specific tolerance.

Pathology of the liver

Among the topics of recent investigation in liver pathology were an examination of normal portal tract structures in needle liver biopsies, computer reconstructions of the intrahepatic biliary tree, identification of oval cells (presumed progeny of hepatic stem cells) in a variety of biliary and nonbiliary diseases and tumors, the features and pathogenesis of nonalcoholic steatohepatitis, and further characterization of proliferating bile ductules. A morphometric study of portal structures in normal needle liver biopsies found that approximately one third in a given specimen may not show a portal vein and that a bile duct may not be seen in 7%. Apoptosis is a critical mechanism for the death of hepatocytes in viral hepatitis and also in endothelial injury in the cold perfusion-warm reperfusion sequence in liver transplantation. The results of two studies examining the relationship of steatosis to chronic hepatitis C virus infection in native and transplanted livers suggest that fatty change is a specific virus-mediated lesion. In the field of hepatic neoplasia, liver cell dysplasia (large cell change), long thought to be a premalignant lesion, was hypothesized to represent abnormal hepatocyte polyploidization.

Immunosuppression without immunosuppression? How to be a tolerant individual in a dangerous world

The field of transplantation has developed based on two principles: allografts are rejected because they express foreign antigens, and the immune system must be suppressed to prevent rejection. Recently, in vitro and in vivo experimental evidence has accumulated that calls both of these beliefs into question. This article reviews an alternative approach to transplantation that focuses on tissue injury as the instigator of graft rejection and employs physiological mechanisms of tolerance to avoid graft loss. Methods that allow for defense against infectious microbes while at the same time allowing for graft survival are proposed. In particular, the rationale behind the use of anti-CD154 antibody treatment is highlighted. A model is introduced that takes into consideration the experimental successes seen with anti-CD154 therapies.