Reversal of transplantation immunity by liver grafting

Role of T cells in liver metastasis

The liver is a major metastatic site (organ) for gastrointestinal cancers (such as colorectal, gastric, and pancreatic cancers) as well as non-gastrointestinal cancers (such as lung, breast, and melanoma cancers). Due to the innate anatomical position of the liver, the apoptosis of T cells in the liver, the unique metabolic regulation of hepatocytes and other potential mechanisms, the liver tends to form an immunosuppressive microenvironment and subsequently form a pre-metastatic niche (PMN), which can promote metastasis and colonization by various tumor cells(TCs). As a result, the critical role of immunoresponse in liver based metastasis has become increasingly appreciated. T cells, a centrally important member of adaptive immune response, play a significant role in liver based metastases and clarifying the different roles of the various T cells subsets is important to guide future clinical treatment. In this review, we first introduce the predisposing factors and related mechanisms of liver metastasis (LM) before introducing the PMN and its transition to LM. Finally, we detail the role of different subsets of T cells in LM and advances in the management of LM in order to identify potential therapeutic targets for patients with LM.

Factors associated with operational tolerance after liver transplantation: a single center retrospective study

Background

Liver transplantation has adverse effects from life-long immunosuppression that limit the improvement of long-term outcomes. Achieving clinical operational tolerance is a major goal in organ transplantation.

Methods

This study analyzed liver transplantation patients at a single institution from 1998 to 2020, excluding those who died within 1-year posttransplant. Operational tolerance was defined as normal liver function even after immunosuppressive drugs were discontinued. Propensity score matching was implemented at a 1:2 ratio for the tolerant group (TG) and the nontolerant group (NTG).

Results

Out of 2,300 recipients, 99 achieved operational tolerance without rejection. No significant differences in sex or body mass index (BMI) were found between the TG and NTG. There was a significantly higher percentage of children in the TG (24.0%) than in the NTG (10.1%). The NTG had more living donor liver transplants. Among 2,054 adult recipients, no significant differences in age, sex, or BMI were found between the TG and the NTG. However, the rate of living donor liver transplantation was 40.3% (29/75) in the TG and 84.8% in the NTG (P<0.001). The propensity score-matched analysis showed higher chronic renal failure rates and a higher graft recipient weight ratio in the TG, along with shorter warm ischemic times during surgery. After immunosuppressant withdrawal, a significant increase in the ratio of CD4+CD25+ T cells to total CD4+ T cells was observed in the TG.

Conclusions

These findings suggest that larger, healthier grafts are more conducive to inducing tolerance, and regulatory T cells are crucial in achieving tolerance.

Temporal and spatial dynamics of immune cells in spontaneous liver transplant tolerance

The liver has long been deemed a tolerogenic organ. We employed high-dimensional mass cytometry and immunohistochemistry to depict the temporal and spatial dynamics of immune cells in the spleen and liver in a murine model of spontaneous liver allograft acceptance. We depicted the immune landscape of spontaneous liver tolerance throughout the rejection and acceptance stages after liver transplantation and highlighted several points of importance. Of note, the CD4+/CD8+ T cell ratio remained low, even in the tolerance phase. Furthermore, a PhenoGraph clustering analysis revealed that exhausted CD8+ T cells were the most dominant metacluster in graft-infiltrating lymphocytes (GILs), which highly expressed the costimulatory molecule CD86. The temporal and spatial dynamics of immune cells revealed by high-dimensional analyses enable a fine-grained analysis of GIL subsets, contribute to new insights for the discovery of immunological mechanisms of liver tolerance, and provide potential ways to achieve clinical operational tolerance after liver transplantation.

Issues in multi-organ transplantation of the liver with kidney or heart in polycystic liver-kidney disease or congenital heart disease: Current practices and immunological aspects

Solid organ transplantation has become an integral part of the management of patients with end-stage diseases of the kidney, liver, heart and lungs. Most procedures occur in isolation, but multi-organ transplantation of the liver with either the kidney or heart has become an option. As more patients with congenital heart disease and cardiac cirrhosis survive into adulthood, particularly after the Fontan procedure, liver transplant teams are expected to face questions regarding multi-organ (heart-liver) transplantation. Similarly, patients with polycystic kidneys and livers may be managed by multi-organ transplantation. Herein, we review the indications and outcomes of simultaneous liver-kidney transplantation for polycystic liver-kidney disease, and discuss the indications, timing and procedural aspects of combined heart-liver transplantation. We also summarise the evidence for, and potential mechanisms underlying, the immunoprotective impact of liver allografts on the simultaneously transplanted organs.

First in Poland Simultaneous Liver-Lung Transplantation With Liver-First Approach for Recipient Due to Cystic Fibrosis: A Case Report

Cystic fibrosis is an autosomal progressive disease affecting the lung, pancreas, and liver. Some patients develop end-stage respiratory and liver failure. For such patients, combined lung-liver transplantation remains the only therapeutic option. In this article we present the first simultaneous lung-liver transplantation in Poland, as well as in Central and Eastern Europe, with detailed clinical history, surgical aspects, and postoperative course.

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.

Dendritic Cell-Mediated Regulation of Liver Ischemia-Reperfusion Injury and Liver Transplant Rejection

Liver allograft recipients are more likely to develop transplantation tolerance than those that receive other types of organ graft. Experimental studies suggest that immune cells and other non-parenchymal cells in the unique liver microenvironment play critical roles in promoting liver tolerogenicity. Of these, liver interstitial dendritic cells (DCs) are heterogeneous, innate immune cells that appear to play pivotal roles in the instigation, integration and regulation of inflammatory responses after liver transplantation. Interstitial liver DCs (recruited in situ or derived from circulating precursors) have been implicated in regulation of both ischemia/reperfusion injury (IRI) and anti-donor immunity. Thus, livers transplanted from mice constitutively lacking DCs into syngeneic, wild-type recipients, display increased tissue injury, indicating a protective role of liver-resident donor DCs against transplant IRI. Also, donor DC depletion before transplant prevents mouse spontaneous liver allograft tolerance across major histocompatibility complex (MHC) barriers. On the other hand, mouse liver graft-infiltrating host DCs that acquire donor MHC antigen via “cross-dressing”, regulate anti-donor T cell reactivity in association with exhaustion of graft-infiltrating T cells and promote allograft tolerance. In an early phase clinical trial, infusion of donor-derived regulatory DCs (DCreg) before living donor liver transplantation can induce alterations in host T cell populations that may be conducive to attenuation of anti-donor immune reactivity. We discuss the role of DCs in regulation of warm and liver transplant IRI and the induction of liver allograft tolerance. We also address design of cell therapies using DCreg to reduce the immunosuppressive drug burden and promote clinical liver allograft tolerance.

Position paper on liver and kidney diseases from the Italian Association for the Study of Liver (AISF), in collaboration with the Italian Society of Nephrology (SIN)

Liver and kidney are strictly connected in a reciprocal manner, in both the physiological and pathological condition. The Italian Association for the Study of Liver, in collaboration with the Italian Society of Nephrology, with this position paper aims to provide an up-to-date overview on the principal relationships between these two important organs. A panel of well-recognized international expert hepatologists and nephrologists identified five relevant topics: 1) The diagnosis of kidney damage in patients with chronic liver disease; 2) Acute kidney injury in liver cirrhosis; 3) Association between chronic liver disease and chronic kidney disease; 4) Kidney damage according to different etiology of liver disease; 5) Polycystic kidney and liver disease. The discussion process started with a review of the literature relating to each of the five major topics and clinical questions and related statements were subsequently formulated. The quality of evidence and strength of recommendations were graded according to the GRADE system. The statements presented here highlight the importance of strong collaboration between hepatologists and nephrologists for the management of critically ill patients, such as those with combined liver and kidney impairment.

Tumor restriction by type I collagen opposes tumor-promoting effects of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAF) may exert tumor-promoting and tumor-suppressive functions, but the mechanisms underlying these opposing effects remain elusive. Here, we sought to understand these potentially opposing functions by interrogating functional relationships among CAF subtypes, their mediators, desmoplasia, and tumor growth in a wide range of tumor types metastasizing to the liver, the most common organ site for metastasis. Depletion of hepatic stellate cells (HSC), which represented the main source of CAF in mice and patients in our study, or depletion of all CAF decreased tumor growth and mortality in desmoplastic colorectal and pancreatic metastasis but not in nondesmoplastic metastatic tumors. Single-cell RNA-Seq in conjunction with CellPhoneDB ligand-receptor analysis, as well as studies in immune cell-depleted and HSC-selective knockout mice, uncovered direct CAF-tumor interactions as a tumor-promoting mechanism, mediated by myofibroblastic CAF-secreted (myCAF-secreted) hyaluronan and inflammatory CAF-secreted (iCAF-secreted) HGF. These effects were opposed by myCAF-expressed type I collagen, which suppressed tumor growth by mechanically restraining tumor spread, overriding its own stiffness-induced mechanosignals. In summary, mechanical restriction by type I collagen opposes the overall tumor-promoting effects of CAF, thus providing a mechanistic explanation for their dual functions in cancer. Therapeutic targeting of tumor-promoting CAF mediators while preserving type I collagen may convert CAF from tumor promoting to tumor restricting.

The Influence of Donor and Recipient Complement C3 Polymorphisms on Liver Transplant Outcome

Despite early reports of an impact of complement C3 polymorphism on liver transplant patient and graft survival, subsequent evidence has been conflicting. Our aim was to clarify the contributions of donor and recipient C3 genotype, separately and together, on patient and graft outcomes and acute rejection incidence in liver transplant recipients. Eight donor/recipient groups were analyzed according to their genotype and presence or absence of C3 F allele (FFFS, FFSS, FSFF, FSFS, FSSS, SSFF, SSFS, and SSSS) and correlated with clinical outcomes of patient survival, graft survival, and rejection. The further impact of brain death vs. circulatory death during liver donation was also considered. Over a median 5.3 y follow-up of 506 patients with clinical information and matching donor and recipient tissue, five-year patient and graft survival (95% confidence interval) were 90(81-91)% and 77(73-85)%, respectively, and 72(69-94)% were rejection-free. Early disadvantages to patient survival were associated with donor C3 F variant, especially in brain-death donors. Recipient C3 genotype was an independent determinant of graft survival by Cox proportional hazards analysis (hazard ratio 0.26, P = 0.04), and the C3 F donor variant was again associated with worse liver graft survival, particularly in brain-death donors. C3 genotype did not independently determine rejection incidence, but a greater proportion of recipient C3 F carriers were rejection-free in the circulatory death, but not the brain-death cohort. Cox proportional hazards analysis revealed significant effects of acute rejection on patient survival (hazard ratio 0.24, P = 0.018), of retransplantation on rejection risk (hazard ratio 6.3, P = 0.009), and of donor type (circulatory-death vs. brain-death) on rejection incidence (hazard ratio 4.9, P = 0.005). We conclude that both donor and recipient complement C3 genotype may influence patient and graft outcomes after liver transplantation but that the type of liver donor is additionally influential, possibly via the inflammatory environment of the transplant.

Heart-After-Liver Transplantation Attenuates Rejection of Cardiac Allografts in Sensitized Patients

BACKGROUND

In patients undergoing heart transplantation, significant allosensitization limits access to organs, resulting in longer wait times and high waitlist mortality. Current desensitization strategies are limited in enabling successful transplantation.

OBJECTIVES

The purpose of this study was to describe the cumulative experience of combined heart-liver transplantation using a novel heart-after-liver transplant (HALT) protocol resulting in profound immunologic protection.

METHODS

Reported are the results of a clinical protocol that was instituted to transplant highly sensitized patients requiring combined heart and liver transplantation at a single institution. Patients were dual-organ listed with perceived elevated risk of rejection or markedly prolonged waitlist time due to high levels of allo-antibodies. Detailed immunological data and long-term patient and graft outcomes were obtained.

RESULTS

A total of 7 patients (age 43 ± 7 years, 86% women) with high allosensitization (median calculated panel reactive antibody = 77%) underwent HALT. All had significant, unacceptable donor specific antibodies (DSA) (>4,000 mean fluorescence antibody). Prospective pre-operative flow cytometric T-cell crossmatch was positive in all, and B-cell crossmatch was positive in 5 of 7. After HALT, retrospective crossmatch (B- and T-cell) became negative in all. DSA fell dramatically; at last follow-up, all pre-formed or de novo DSA levels were insignificant at <2,000 mean fluorescence antibody. No patients experienced >1R rejection over a median follow-up of 48 months (interquartile range: 25 to 68 months). There was 1 death due to metastatic cancer and no significant graft dysfunction.

CONCLUSIONS

A heart-after-liver transplantation protocol enables successful transplantation via near-elimination of DSA and is effective in preventing adverse immunological outcomes in highly sensitized patients listed for combined heart-liver transplantation.

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.

Strategies for Deliberate Induction of Immune Tolerance in Liver Transplantation: From Preclinical Models to Clinical Application

The liver exhibits intrinsic immune regulatory properties that maintain tolerance to endogenous and exogenous antigens, and provide protection against pathogens. Such an immune privilege contributes to susceptibility to spontaneous acceptance despite major histocompatibility complex mismatch when transplanted in animal models. Furthermore, the presence of a liver allograft can suppress the rejection of other solid tissue/organ grafts from the same donor. Despite this immune privilege of the livers, to control the undesired alloimmune responses in humans, most liver transplant recipients require long-term treatment with immune-suppressive drugs that predispose to cardiometabolic side effects and renal insufficiency. Understanding the mechanism of liver transplant tolerance and crosstalk between a variety of hepatic immune cells, such as dendritic cells, Kupffer cells, liver sinusoidas endothelial cells, hepatic stellate cells and so on, and alloreactive T cells would lead to the development of strategies for deliberate induction of more specific immune tolerance in a clinical setting. In this review article, we focus on results derived from basic studies that have attempted to elucidate the immune modulatory mechanisms of liver constituent cells and clinical trials that induced immune tolerance after liver transplantation by utilizing the immune-privilege potential of the liver.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

Organ Fabrication Using Pigs as An in Vivo Bioreactor

We present the most recent research results on the creation of pigs that can accept human cells. Pigs in which grafted human cells can flourish are essential for studies of the production of human organs in the pig and for verification of the efficacy of cells and tissues of human origin for use in regenerative therapy. First, against the background of a worldwide shortage of donor organs, the need for future medical technology to produce human organs for transplantation is discussed. We then describe proof-of-concept studies in small animals used to produce human organs. An overview of the history of studies examining the induction of immune tolerance by techniques involving fertilized animal eggs and the injection of human cells into fetuses or neonatal animals is also presented. Finally, current and future prospects for producing pigs that can accept human cells and tissues for experimental purposes are discussed.

Two phase kinetics of the inflammatory response from hepatocyte-peripheral blood mononuclear cell interactions

Active liver diseases are characterized by an infiltration of inflammatory immune cells, which interact locally with hepatocytes. Co-cultures between non- and -activated human peripheral blood mononuclear cells (PBMCs) and human hepatoma HepaRG cells were used to determine the role of these cell interactions in the inflammatory response. At the early stage, PBMC-HepaRG cell interactions increased mRNA expression and/or secretion of IL-6, IL-8, CCL-20 and MCP-1, in part through direct cell contact and the induction was higher in PHA-activated conditions. The pro-inflammatory cytokines IL-17 and/or TNFα contributed to the increase of IL-6 and IL-8 secretion. HepaRG cells modulated T cell polarization by increasing Th1 cell transcription factor expression and by reducing CD3⁺ CD4⁺ IL-17⁺ cell frequency when PBMCs were activated with PHA. At a later stage, the presence of HepaRG cells inhibited PHA-induced HLA-DR expression on PBMCs, and PBMC proliferation. In contrast, the presence of skin fibroblasts had no effect of PBMC proliferation induced by PHA. After a first pro-inflammatory phase, PBMC-HepaRG cell interactions may down-regulate the immune response. The PBMC-hepatocyte interactions can thus participate first to the initiation of hepatitis and later to the maintenance of immune tolerance in liver, possibly contributing to chronicity.

Direct recognition of hepatocyte-expressed MHC class I alloantigens is required for tolerance induction

Adeno-associated viral vector-mediated (AAV-mediated) expression of allogeneic major histocompatibility complex class I (MHC class I) in recipient liver induces donor-specific tolerance in mouse skin transplant models in which a class I allele (H-2Kb or H-2Kd) is mismatched between donor and recipient. Tolerance can be induced in mice primed by prior rejection of a donor-strain skin graft, as well as in naive recipients. Allogeneic MHC class I may be recognized by recipient T cells as an intact molecule (direct recognition) or may be processed and presented as an allogeneic peptide in the context of self-MHC (indirect recognition). The relative contributions of direct and indirect allorecognition to tolerance induction in this setting are unknown. Using hepatocyte-specific AAV vectors encoding WT allogeneic MHC class I molecules, or class I molecules containing a point mutation (D227K) that impedes direct recognition of intact allogeneic MHC class I by CD8+ T cells without hampering the presentation of processed peptides derived from allogeneic MHC class I, we show here that tolerance induction depends upon recognition of intact MHC class I. Indirect recognition alone yielded a modest prolongation of subsequent skin graft survival, attributable to the generation of CD4+ Tregs, but it was not sufficient to induce tolerance.

Increase in short-term risk of rejection in heart transplant patients receiving granulocyte colony-stimulating factor

BACKGROUND

Neutropenia is a significant adverse event after heart transplantation (HT) and increases infection risk. Granulocyte colony-stimulating factor (G-CSF) is commonly used in patients with neutropenia. In this work, we assessed the adverse effects of G-CSF treatment in the setting of a university hospital.

METHODS

Data on HT patients from January 2008 to July 2016 were reviewed. Patients who received G-CSF were identified and compared with patients without a history of therapy. Baseline characteristics, rejection episodes, and outcomes were collected. Data were analyzed by incidence rates, time to rejection and survival were analyzed using Kaplan-Meier curves, and odds ratios were generated using logistic regression analysis.

RESULTS

Two hundred twenty-two HT patients were studied and 40 (18%) received G-CSF for a total of 85 total neutropenic events (0.79 event/patient year). There were no differences in baseline characteristics between the groups. In the 3 months after G-CSF, the incidence rate of rejection was 0.067 event/month. In all other time periods considered free of G-CSF effect, the incidence rate was 0.011 event/month. This rate was similar to the overall incidence rate in the non-GCSF group, which was 0.010 event/month. There was a significant difference between the incidence rates in the G-CSF group at 0 to 3 months after G-CSF administration and the non-GCSF group (p = 0.04), but not for the other time periods (p = 0.5). Freedom from rejection in the 3 months after G-CSF administration was 87.5% compared with 97.5% in the non-GCSF group (p = 0.006).

CONCLUSIONS

G-CSF administration was found to be associated with significant short-term risk of rejection. This suggests the need for increased surveillance during this time period.

Donor-specific hypo-responsiveness occurs in simultaneous liver-kidney transplant recipients after the first year

Kidney allografts of patients who undergo simultaneous liver-kidney transplantation incur less immune-mediated injury, and retain better function compared to other kidney allografts. To characterize the host alloimmune responses in 28 of these patients, we measured the donor-specific alloresponsiveness and phenotypes of peripheral blood cells after the first year. These values were then compared to those of 61 similarly immunosuppressed recipients of a solitary kidney or 31 recipients of liver allografts. Four multicolor, non-overlapping flow cytometry protocols were used to assess the immunophenotypes. Mixed cell cultures with donor or third party cells were used to measure cell proliferation and interferon gamma production. Despite a significant overlap, simultaneous liver-kidney transplant recipients had a lower overall frequency of circulating CD8⁺, activated CD4⁺ and effector memory T cells, compared to solitary kidney transplant recipients. Simultaneous liver-kidney transplant recipient T cells had a significantly lower proliferative response to the donor cells compared to solitary kidney recipients (11.9 vs. 42.9%), although their response to third party cells was unaltered. The frequency of interferon gamma producing alloreactive T cells in simultaneous liver-kidney transplant recipients was significantly lower than that of solitary kidney transplant recipients. Flow cytometric analysis of the mixed cultures demonstrated that both alloreactive CD4⁺ and CD8⁺ compartments of the simultaneous liver-kidney transplant recipient circulating blood cells were smaller. Thus, the phenotypic and functional characteristics of the circulating blood cells of the simultaneous liver-kidney transplant recipients resembled those of solitary liver transplant recipients, and appear to be associated with donor-specific hypo-alloresponsiveness.

Soluble major histocompatibility complex molecules in immune regulation: highlighting class II antigens

The involvement of major histocompatibility complex (MHC) antigens in the development and regulation of immune response has been well defined over the years, starting from maturation, antigenic peptide loading, migration to the cell membrane for recognition by the T-cell receptor and recycling for immune response cessation. During this intracellular trafficking, MHC antigens find a way to be excreted by the cells, because they can be found as soluble MHC class I (sMHC-I) and class II (sMHC-II) molecules in all body fluids. Although secretion mechanisms have not been sufficiently studied, sMHC molecules have been shown to display important immunoregulatory properties. Their levels in the serum have been shown to be altered in a variety of diseases, including viral infections, inflammation, autoimmunities and cancer, etc. while they seem to be involved in a number of physiological reactions, including maintenance of tolerance, reproduction, as well as mate choice vis-à-vis species evolution. The present review aims to present the thus far existing literature on sMHC molecules and point out the importance of these molecules in the maintenance of immune homeostasis.

Environmental peer pressure: CD4+ T cell help in tolerance and transplantation

The liver participates in a multitude of metabolic functions that are critical for sustaining human life. Despite constant encounters with antigenic-rich intestinal blood, oxidative stress, and metabolic intermediates, there is no appreciable immune response. Interestingly, patients undergoing orthotopic liver transplantation benefit from a high rate of graft acceptance in comparison to other solid organ transplant recipients. In fact, cotransplantation of a donor liver in tandem with a rejection-prone graft increases the likelihood of graft acceptance. A variety of players may account for this phenomenon including the interaction of intrahepatic antigen-presenting cells with CD4⁺ T cells and the preferential induction of forkhead box P3 (Foxp3) expression on CD4⁺ T cells following injurious stimuli. Ineffective insult management can cause chronic liver disease, which manifests systemically as the following: antibody-mediated disorders, ineffective antiviral and antibacterial immunity, and gastrointestinal disorders. These sequelae sharing the requirement of CD4⁺ T cell help to coordinate aberrant immune responses. In this review, we will focus on CD4⁺ T cell help due to the shared requirements in hepatic tolerance and coordination of extrahepatic immune responses. Overall, intrahepatic deviations from steady state can have deleterious systemic immune outcomes and highlight the liver's remarkable capacity to maintain a balance between tolerance and inflammatory response while simultaneously being inundated with a panoply of antigenic stimuli. Liver Transplantation 24 89-97 2018 AASLD.

Intrasplenic Liver Parenchymal Cells in Conjunction with Low-Dose Rapamycin and Cyclosporine Induce a Unique and Specific Prolongation of Rat Cardiac and Small Bowel Allograft Survival

These experiments investigated the immunosuppressive properties of liver tissue. Brown Norway (BN; RT1n) rat heart allografts survived in untreated control Wistar Furth (WFu; RTlu) rat recipients for 6.2 ± 1.5 days, while allografts in animals that received rapamycin (RAPA) 0.0075 mg/kg/day and cyclosporine (CsA) 0.375 mg/kg/day delivered for 14 days by continuous intravenous infusion (civi) using osmotic pumps in conjunction with intrasplenic (i.s.) saline survived to 18.4 ± 1.3 days. i.s. addition of 3 M-KCl extracted BN hepatic antigen or unpurified BN hepatocytes (liver parenchymal cells—5 × 107/kg), which exhibited a 4.8% class II antigen expression, and which alone failed to prolong allograft survival (MST = 6.0 ± 1.4 days), increased heart allograft survival to 25.3 ± 2.3 and 27.2 ± 1.9 days, respectively (p < 0.01). Hepatocyte purification using Dynabeads and Percoll reduced class II expression to 0.9% and increased allograft survival to 32.8 ± 1.6 days (p < 0.01). In contrast, the effect of 5 × 108/kg BN erythrocytes, exhibiting only 0.1% class II expression, was much less (23.8 ± 1.9 days). Administration i.s. of BN splenocytes or nonparenchymal liver cells, demonstrated by flow cytometry to exhibit a 47.3 or 55.1% expression of class II antigen, respectively, failed to induce any significant increase in allograft survival (18.4 ± 4.6 and 19.4 ± 0.5 days, respectively). Survival of BN rat small bowel allografts was increased in Lewis (LEW; RTl1) rat recipients treated with RAPA, CsA, and unfractionated BN hepatocytes from 10.2 ± 1.9 to 21.2 ± 1.5 days. Pretreatment with i.s. BN hepatocytes, 14 days prior to harvesting, reduced WFu lymphocyte responses to allogeneic stimulation with BN or ACI spleen cells by 75 and 70%, respectively. Addition of 1 × 105 unpurified donor-specific BN or third-party Buffalo (BUF; RTlb) hepatocytes, but not supernatant, to the responder wells of MLCs resulted in a 61 and 40% suppression, respectively, of the WFu lymphocyte response induced by BN allogeneic stimulation. These findings suggest that while class I MHC expression has a significant role to play in exerting the immunosuppressive effects of hepatocytes, other influences more specific to liver may also prevail.

Translational microsurgery. A new platform for transplantation research

PURPOSE

Clinical microsurgery has been introduced in many fields, while experimental microsurgery has the cross-disciplinary features of the sciences and techniques for growth of medicine, pharmacology, veterinary, engineering etc. Training protocol, proposing a new name as Translational Microsurgery, was introduced.

METHODS

Reconstructive skills of hepatic artery in pediatric living donor liver transplantation were summarized. Ex vivo training protocol using artificial blood vessel for surgeons was proposed.

RESULTS

Clinical microsurgery requires anastomosis with delicate arteries and limited field of view. Our training protocol revealed that the relation between the score and speed was seen, while not all the surgeons with enough experience got high score. This training led to muster clinical skills and to apply excellent experimental works.

CONCLUSIONS

Our microsurgical training protocol has been planned from the points of clinical setting. Training for vascular anastomosis led to rodent transplantation models. These models were used for immunology and immunosuppressant research. Microsurgical techniques led to master catheter technique and to inject various drugs or gene vectors.

Immunological aspects of liver cell transplantation

Within the field of regenerative medicine, the liver is of major interest for adoption of regenerative strategies due to its well-known and unique regenerative capacity. Whereas therapeutic strategies such as liver resection and orthotopic liver transplantation (OLT) can be considered standards of care for the treatment of a variety of liver diseases, the concept of liver cell transplantation (LCTx) still awaits clinical breakthrough. Success of LCTx is hampered by insufficient engraftment/long-term acceptance of cellular allografts mainly due to rejection of transplanted cells. This is in contrast to the results achieved for OLT where long-term graft survival is observed on a regular basis and, hence, the liver has been deemed an immune-privileged organ. Immune responses induced by isolated hepatocytes apparently differ considerably from those observed following transplantation of solid organs and, thus, LCTx requires refined immunological strategies to improve its clinical outcome. In addition, clinical usage of LCTx but also related basic research efforts are hindered by the limited availability of high quality liver cells, strongly emphasizing the need for alternative cell sources. This review focuses on the various immunological aspects of LCTx summarizing data available not only for hepatocyte transplantation but also for transplantation of non-parenchymal liver cells and liver stem cells.

Presentation of hepatocellular antigens

The liver is an organ in which antigen-specific T-cell responses manifest a bias toward immune tolerance. This is clearly seen in the rejection of allogeneic liver transplants, and multiple other phenomena suggest that this effect is more general. These include tolerance toward antigens introduced via the portal vein, immune failure to several hepatotropic viruses, the lack of natural liver-stage immunity to malaria parasites, and the frequent metastasis of cancers to the liver. Here we review the mechanisms by which T cells engage with hepatocellular antigens, the context in which such encounters occur, and the mechanisms that act to suppress a full T-cell response. While many mechanisms play a role, we will argue that two important processes are the constraints on the cross-presentation of hepatocellular antigens, and the induction of negative feedback inhibition driven by interferons. The constant exposure of the liver to microbial products from the intestine may drive innate immunity, rendering the local environment unfavorable for specific T-cell responses through this mechanism. Nevertheless, tolerance toward hepatocellular antigens is not monolithic and under specific circumstances allows both effective immunity and immunopathology.

Hepatic Stellate Cells Directly Inhibit B Cells via Programmed Death-Ligand 1

We demonstrated previously that mouse hepatic stellate cells (HSCs) suppress T cells via programmed death-ligand 1 (PD-L1), but it remains unknown whether they exert any effects on B cells, the other component of the adaptive immune system. In this study, we found that mouse HSCs directly inhibited B cells and that PD-L1 was also integrally involved. We found that HSCs inhibited the upregulation of activation markers on activated B cells, as well as the proliferation of activated B cells and their cytokine/Ig production in vitro, and that pharmaceutically or genetically blocking the interaction of PD-L1 with programmed cell death protein 1 impaired the ability of HSCs to inhibit B cells. To test the newly discovered B cell-inhibitory activity of HSCs in vivo, we developed a protocol of intrasplenic artery injection to directly deliver HSCs into the spleen. We found that local delivery of wild-type HSCs into the spleens of mice that had been immunized with 4-hydroxy-3-nitrophenylacetyl-Ficoll, a T cell-independent Ag, significantly suppressed Ag-specific IgM and IgG production in vivo, whereas splenic artery delivery of PD-L1-deficient HSCs failed to do so. In conclusion, in addition to inhibiting T cells, mouse HSCs concurrently inhibit B cells via PD-L1. This direct B cell-inhibitory activity of HSCs should contribute to the mechanism by which HSCs maintain the liver's immune homeostasis.

A novel anti-histone H1 monoclonal antibody, SSV monoclonal antibody, improves lung injury and survival in a mouse model of lipopolysaccharide-induced sepsis-like syndrome

Background. Histones play important roles in both host defenses and inflammation related to microbial infection. A peptide mimotope (SSV) was identified from a novel histone H1 monoclonal antibody (16G9 mAb) that was shown to inhibit the mixed lymphocyte reaction. In the present study, an anti-SSV producing hybridoma was established. We investigated the effects of SSV mAb in a mouse acute inflammation model induced by intraperitoneal injection of lipopolysaccharide (LPS). Methods. SSV mAb was generated and characterized. Mice were treated with SSV mAb or a control IgG antibody prior to LPS injection. Evaluation of survival rate and lung tissue on histological score was performed. The levels of inflammatory cytokines and histones H1, H3, and H4 in plasma and lung tissue were measured by ELISA. Results. Competitive ELISA revealed that SSV mAb binds to histone H1. SSV mAb improved lung injury and prolonged the survival of LPS-injected mice. Increased levels of histones H1, H3, and H4 and inflammatory cytokines (TNF-α, IL-1β, and IL-6) in plasma and lung tissue after LPS injection were ameliorated by SSV mAb. Conclusion. SSV mAb is shown to have anti-inflammatory activity and organ-protective effects, highlighting the importance of controlling histone H1 as well as H3 and H4 levels during inflammation.

Ambovex(®) as a novel immunological modulator drug for the treatment of hepatocellular carcinoma (HCC) in the liver: a Phase II clinical trial

Hepatocellular carcinoma (HCC) is a global public health problem, based on it being the fifth most common cancer and third leading cause of cancer-related mortality worldwide. The approved conventional treatment methods for HCC have shown life-threatening side effects with limited or negligible success, especially in multifocal HCC. As a consequence, new therapeutic approaches are being explored, including immunoregulatory molecules that may have the potential to treat or delay the progression of HCC. A novel pharmaceutical botanical drug - Ambovex(®), an immune-modulator molecule - was tested to treat or delay the progress of HCC. We conducted a 6-month randomized clinical trial with an additional 3-month washing period (no treatment) to evaluate the safety and efficacy of low-dose Ambovex oral spray in treating patients with HCC. The clinical study involved a total of 40 patients, with 33 in the treatment group and seven in the control group. The α-fetoprotein (AFP) levels were measured every month and ultrasound scans were performed at time zero and every 2 months thereafter. Computed tomography (CT) scans were performed for patients in the treatment group. Ambovex proved to be safe, as there were no significant side effects although some patients found that the drug has unpleasant taste. AFP analysis showed a significant decrease in its level (α=0.05; 95% confidence interval) in the treatment group when compared to the control group at 3 months (P=0.0031) and at 6 months (P=0.007). The ultrasound results showed improvement in the treated group, as evidenced by a significant decrease in the lesion numbers and sizes. The lesions in 38% of treated patients decreased from multiple to single with major improvements; 35% of patients exhibited a decrease from multiple lesions to multiple lesions with minor improvements, whereas 27% had stabilized lesions. CT scans in the treated group showed significant improvement, as there was complete disappearance of the lesions after 6 months of treatment with Ambovex in two patients. This clinical study showed the effective and promising results of Ambovex as an immunological modulator in treating HCC. Further exploration of Ambovex is recommended.

Induction of antinuclear antibodies by de novo autoimmune hepatitis regulates alloimmune responses in rat liver transplantation

Concanavalin A (Con A) is a lectin originating from the jack-bean and well known for its ability to stimulate T cells and induce autoimmune hepatitis. We previously demonstrated the induction of immunosuppressive antinuclear autoantibody in the course of Con A-induced transient autoimmune hepatitis. This study aimed to clarify the effects of Con A-induced hepatitis on liver allograft rejection and acceptance. In this study, we observed the unique phenomenon that the induction of transient de novo autoimmune hepatitis by Con A injection paradoxically overcomes the rejection without any immunosuppressive drug and exhibits significantly prolonged survival after orthotopic liver transplantation (OLT). Significantly increased titers of anti-nuclear Abs against histone H1 and high-mobility group box 1 (HMGB1) and reduced donor specific alloantibody response were observed in Con A-injected recipients. Induction of Foxp3 and IL-10 in OLT livers of Con A-injected recipients suggested the involvement of regulatory T cells in this unique phenomenon. Our present data suggest the significance of autoimmune responses against nuclear histone H1 and HMGB1 for competing allogeneic immune responses, resulting in the acceptance of liver allografts in experimental liver transplantation.

Liver transplant tolerance and its application to the clinic: can we exploit the high dose effect?

The tolerogenic properties of the liver have long been recognised, especially in regard to transplantation. Spontaneous acceptance of liver grafts occurs in a number of experimental models and also in a proportion of clinical transplant recipients. Liver graft acceptance results from donor antigen-specific tolerance, demonstrated by the extension of tolerance to other grafts of donor origin. A number of factors have been proposed to be involved in liver transplant tolerance induction, including the release of soluble major histocompatibility (MHC) molecules from the liver, its complement of immunosuppressive donor leucocytes, and the ability of hepatocytes to directly interact with and destroy antigen-specific T cells. The large tissue mass of the liver has also been suggested to act as a cytokine sink, with the potential to exhaust the immune response. In this review, we outline the growing body of evidence, from experimental models and clinical transplantation, which supports a role for large tissue mass and high antigen dose in the induction of tolerance. We also discuss a novel gene therapy approach to exploit this dose effect and induce antigen-specific tolerance robust enough to overcome a primed T cell memory response.

Nuclear antigens and auto/alloantibody responses: friend or foe in transplant immunology

In addition to cellular immune responses, humoral immune responses, mediated by natural antibodies, autoantibodies, and alloantibodies, have increasingly been recognized as causes of organ transplant rejection. In our previous studies, we have demonstrated the induction of antinuclear antibodies against histone H1 and high-mobility group box 1 (HMGB1), in both experimental and clinical liver transplant tolerance. The active induction of antinuclear antibodies is usually an undesirable phenomenon, but it is often observed after liver transplantation. However, the release of nuclear antigens and its suppression by neutralizing antibodies are proposed to be important in the initiation and regulation of immune responses. In this review article, we summarize the current understanding of nuclear antigens and corresponding antinuclear regulatory antibodies (Abregs) on infection, injury, inflammation, transplant rejection, and tolerance induction and discuss the significance of nuclear antigens as diagnostic and therapeutic targets.

Gene therapy for tolerance: high-level expression of donor major histocompatibility complex in the liver overcomes naive and memory alloresponses to skin grafts

BACKGROUND

The liver has long been recognized as having tolerogenic properties. We investigated whether recombinant adenoassociated virus (rAAV)-mediated expression of donor major histocompatibility complex in recipient livers could induce tolerance to donor-strain grafts.

METHODS

Naive B10.BR (H-2) or B10.BR recipients primed with a H-2K-expressing (K) skin graft were injected with rAAV-expressing H-2K (rAAV-K) to induce K expression on hepatocytes 7 days before challenge with a K skin graft. K-specific responses were measured by interferon (IFN)-γ ELISpot and flow cytometric assessment of directly H-2K reactive cells. Fully allogeneic grafts from C57BL/6 (H-2) donors were transplanted onto longstanding B10.BR recipients of K skin to test for linked epitope suppression.

RESULTS

rAAV-K-treated B10.BR mice accepted K skin grafts with increased median survival time (MST) more than 169 days compared to uninoculated (MST=18.5 days) and rAAV-K-treated controls (MST=19 days). rAAV-K-treated B10.BR animals primed with K skin grafts also accepted secondary K skin grafts in the long term (MST>100 days) compared to accelerated rejection in primed, uninoculated mice (MST=12 days). Treatments did not induce liver pathology, assessed by serum alanine aminotransferase levels and histology. IFN-γ ELISpot analysis of splenocytes from rAAV-K-treated mice indicated reduced responses to donor K antigen, but protection was not extended to fully allogeneic C57BL/6 skin or heart grafts, even in recipients that had accepted K skin grafts in the long term.

CONCLUSIONS

High-level expression of donor major histocompatibility complex in recipient livers promotes tolerance to skin allografts, even in animals primed to produce a memory response. This provides proof of concept for an approach using liver-targeted gene delivery for tolerance induction to donor antigen.

Immunomodulating options for liver transplant patients

Much has changed since the early years of liver transplantation. Improvements in post-transplant survival are largely due to more selective and less toxic immunosuppression regimens and advances in operative and perioperative care. This has allowed liver transplantation to become an extremely successful treatment option for patients with endstage liver disease. Beginning with cyclosporine, a cyclic endecapeptide of fungal origin and the first of the calcineurin inhibitors to find widespread use, immunosuppressive regimens have evolved to include additional calcineurin inhibitors, steroids, mTOR inhibitors, antimetabolites and antibodies, mostly targeting T-cell activation. This review will present currently available immunosuppressive agents used in the perioperative period of liver transplantation, as well as maintenance treatments, tailoring therapeutic strategies for specific populations, and advances in immune monitoring and tolerance.

Unexpected T cell regulatory activity of anti-histone H1 autoantibody: its mode of action in regulatory T cell-dependent and -independent manners

Induction of anti-nuclear antibodies against DNA or histones is a hallmark of autoimmune disorders, but their actual contribution to disease predisposition remains to be clarified. We have previously reported that autoantibodies against histone H1 work as a critical graft survival factor in a rat model of tolerogeneic liver transplantation. Here we show that an immunosuppressive anti-histone H1 monoclonal antibody (anti-H1 mAb) acts directly on T cells to inhibit their activation in response to T cell receptor (TCR) ligation. Intriguingly, the T cell activation inhibitory activity of anti-H1 mAb under suboptimal dosages required regulatory T (Treg) cells, while high dose stimulation with anti-H1 mAb triggered a Treg cell-independent, direct negative regulation of T cell activation upon TCR cross-linking. In the Treg cell-dependent mode of immunosuppressive action, anti-H1 mAb did not induce the expansion of CD4(+-)Foxp3(+) Treg cells, but rather potentiated their regulatory capacity. These results reveal a previously unappreciated T cell regulatory role of anti-H1 autoantibody, whose overproduction is generally thought to be pathogenic in the autoimmune settings.

Expression of common gamma chain signalling cytokines and their receptors distinguishes rejection from tolerance in a rat organ transplant model

BACKGROUND

Signalling through the cytokine common γ chain (γc) is crucial for survival of activated T cells. In its absence, severe combined immunodeficiency ensues and transplanted tissues are not rejected.

METHODS

To determine whether differences in the availability of γc signalling cytokines correlate with rejection or acceptance, we examined expression of all γc signalling components in organs transplanted between PVG donors and DA recipients. In this combination hearts or kidneys are rejected in <10 days while livers survive >100 days. Expression of the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 and their receptors γc, IL-2Rα, IL-2Rβ/IL-15Rβ, IL-4Rα, IL-7Rα, IL-9Rα, IL-15Rα and IL-21Rα was determined by real-time PCR pre-transplant and on days 3, 5 and 7 after transplantation.

RESULTS

Most increased after transplantation, although there were significantly lower levels of IL-2, IL-2Rα, IL-4 and IL-15Rα in tolerant livers compared to rejecting hearts or kidneys. IL-9 was only expressed in normal kidneys and decreased during rejection. IL-15 was constitutively expressed and did not change after transplantation. IL-21 and IL-21R increased in all transplanted organs to a similar extent. IL-7Rα in liver was considerably increased compared with heart or kidney, consistent with its known inverse relationship to global levels of γc signalling.

CONCLUSIONS

In transplanted livers, acceptance is associated with low levels of all γc cytokines or receptors except IL-21. This is consistent with "dilution" of γc cytokines from a finite clone size of alloreactive T cells in livers, which are ten times larger than kidneys or hearts.

Immunological and regenerative aspects of hepatic mast cells in liver allograft rejection and tolerance

The precise roles of mast cells in liver allograft rejection and tolerance are still unknown. This study aimed to explore the roles of mast cells in immune regulation and liver regeneration for tolerance induction by using rat models of orthotopic liver transplantation (OLT). Stem cell factor (SCF) and its receptor c-Kit, which are critical to the migration and development of not only stem cells but also mast cells, significantly increased in the tolerogenic livers as compared with rejected livers. The significant elevation of mast cell tryptase, high-affinity IgE receptor, and histamine suggested the activation of mast cells in liver allografts at the tolerogenic phase after OLT. Immunohistochemical analysis using confocal microscope clearly showed colocalization of mast cells, Foxp3+ Tregs, γδ T cells, and recipient-derived hepatic progenitor cells with higher expression of SCF, IL-9, IL-10, TGF-β1, and IL-17 related to immunoregulation and liver regeneration in the donor grafts of a tolerogenic OLT model. Cross-talk among mast cells and other cells was evaluated by in vitro studies demonstrating that syngeneic bone marrow-derived mast cells (BMMCs) co-cultured with naïve splenocytes or primary hepatocytes significantly increased the population of splenic γδ T cells by mitogen stimulation or by mast cell degranulation, and also significantly induced the hepatocyte proliferation, respectively. Our results suggested that mast cells in the donor grafts may play important roles in the induction/maintenance of immune tolerance and liver regeneration resulting in the replacement of hepatic cells from donor to recipient.

Combined liver-kidney transplants: allosensitization and recipient outcomes

BACKGROUND

A pretransplant positive crossmatch in combined liver kidney transplants (CLK) is not considered a contraindication based on the reported immunoprotection conferred by the liver allograft. However, antibody-mediated rejection of the kidney in CLK has been reported recently. This prompted our study to investigate the impact of presensitization on CLK recipient outcomes.

METHODS

We examined kidney allograft and patient survival by indication of sensitization using Scientific Registry of Transplant Recipients data on CLK performed from 1995 to 2008. We defined sensitization as panel reactive antibody (PRA) more than 10% or a positive T-cell crossmatch (TXM).

RESULTS

Among 2484 CLK recipients with available PRA or TXM information, 30% had positive TXM or PRA more than 10%. Among those with TXM information, 12% had a positive crossmatch (n=234). In univariate analyses, patient (P=0.002) and overall kidney graft survival (P=0.015) were significantly diminished among sensitized patients. Differences in patient survival translated to estimated half-lives of 10.3 years among nonsensitized recipients versus 7.8 years among sensitized recipients, In multivariable Cox models, allosensitization was independently associated with patient death (adjusted hazard ratio=1.22, 95% CI, 1.04-1.43) and overall kidney graft loss (adjusted hazard ratio=1.16, 95% CI, 1.00-1.36).

CONCLUSIONS

These results suggest a negative impact of presensitization on patient and overall renal allograft survival in CLK. Accordingly, presensitization may need to be considered in risk stratification and clinical management of CLK.

Approaching the promise of operational tolerance in clinical transplantation

Long-term acceptance of transplanted organs without requirement for indefinite immunosuppression remains the ultimate goal of transplant clinicians and scientists. This clinical state of allograft acceptance termed "operational tolerance" has been elusive in routine practice. However, there are published reports of recipients where immunosuppression has been discontinued, by intention or patient noncompliance, in which the outcome is a nondestructive immune response and normal function. The question now arises how clinical operational tolerance might be achieved in the majority of recipients. This review provides an overview of current approaches to achieve operational tolerance, including the use of donor bone marrow and depletion of recipient T cells and the resistance of liver transplants to rejection. It also describes the key role of clinical immune monitoring and future approaches to tolerance induction including inhibition of T-cell signaling, manipulation of costimulatory pathways, and expansion of regulatory T cells. The principles of these experimental approaches may ultimately be extended to provide safe and effective control of transplant rejection and induction of clinical operational tolerance.

Operational tolerance: past lessons and future prospects

Every liver transplant (LT) center has had patients who either self-discontinue immunosuppressive (IS) therapy or are deliberately withdrawn due to a research protocol or clinical concern (ie, lymphoproliferative disorder [LPD], overwhelming infection). This is understandable because maintenance IS therapy, particularly calcineurin inhibitors (CNI), is associated with significant cost, side effects, and considerable long-term morbidity and mortality. Detrimental effects of IS therapy include increased risk of cardiovascular disease, metabolic syndrome, bone loss, opportunistic and community-acquired infections, and malignancy. In fact, LT recipients have among the highest rates of chronic kidney disease and associated mortality among all nonkidney solid organ recipients. This mortality is only ameliorated by undergoing a curative kidney transplant, usurping costs and valuable organ resources. The search for improved treatment algorithms includes trial and error CNI dose minimization, the use of alternative IS agents (antimetabolites, mammalian target of rapamycin [mTOR] inhibitors), or even complete CNI withdrawal. Yet those who are successful in achieving such operational tolerance (no immunosuppression and normal allograft function) are considered lucky. The vast majority of recipients will fail this approach, develop acute rejection or immune-mediated hepatitis, and require resumption of IS therapy. As such, withdrawal of IS following LT is not standard-of-care, leaving clinicians to currently maintain transplant patients on IS therapy for life. Nonetheless, the long-term complications of all IS therapies highlight the need for strategies to promote immunologic or operational tolerance. Clinically applicable biomarker assays signifying the potential for tolerance as well as tolerogenic IS conditioning are invariably needed if systematic, controlled rather than "hit or miss" approaches to withdrawal are considered. This review will provide an overview of the basic mechanisms of tolerance, particularly in relation to LT, data from previous IS withdrawal protocols and biomarker studies in tolerant recipients, and a discussion on the prospect of increasing the clinical feasibility and success of withdrawal.

Transplantation of mouse embryonic stem cells induces hematopoietic and tissue chimerism in rats

Embryonic stem cells (ESC) can differentiate into all cell lineages, and ESC-like cells were shown to induce hematopoietic chimerism and tolerance in allogeneic models. The aim of our study was to test the capacity of mouse ESC (mESC) to engraft in rats in a xenotransplantation setting. Forty-six rats were transplanted intravenously with 1 million mESC, without immunosuppression (group 1, n = 23) or with cyclosporine (group 2, n = 23). Three months after mESC transplantation, skin grafts were performed from allogeneic, xenogeneic identical to mESC, or xenogeneic third party donors. At day 27 post-transplant, we detected circulating mouse cells in the blood of 4/23 and 5/23 animals of group 1 and group 2, respectively. Chimerism was confirmed by PCR. We also identified long-term surviving murine cells within livers of chimeric animals. Skin grafts showed no difference in survival between allogeneic and xenogeneic donors. Transplantation of xenogeneic mouse ESC induced short-term chimerism in the blood and persistent tissue chimerism in the liver of recipient rats, but did not induce tolerance to skin grafts. Improved immunosuppressive protocols should be tested to prolong chimerism and allow tolerance.

Identification of the rat NKG2D ligands, RAE1L and RRLT, and their role in allograft rejection

NKG2D is a receptor expressed by NK cells and subsets of T lymphocytes. On NK cells, NKG2D functions as a stimulatory receptor that induces effector functions. We cloned and expressed two rat NKG2D ligands, both members of the RAE1 family, RAE1L and RRLT, and demonstrate that these ligands can induce IFN-gamma secretion and cytotoxicity by rat NK cells. To examine changes in expression of NKG2D and the NKG2D ligands RAE1L and RRLT after transplantation, we used a Dark Agouti (DA)-->Lewis rat model of liver transplantation. NKG2D expression was significantly increased in allogeneic liver grafts by day 7 post-transplant. Ligands of NKG2D, absent in normal liver, were readily detected in both syngeneic and allogeneic liver grafts by day 1 post-transplant. By day 7 post-transplant, hepatocyte RAE1L and RRLT expression was significantly and specifically increased in liver allografts. In contrast to acute rejection that develops in the DA-->Lewis model, transplantation of Lewis livers into DA recipients (Lewis-->DA) results in spontaneous tolerance. Interestingly, expression of RAE1L and RRLT is low in Lewis-->DA liver allografts, but significantly increased in DA-->Lewis liver allografts undergoing rejection. In conclusion, our results suggest that expression of NKG2D ligands may be important in allograft rejection.

Tolerance: is it achievable in pediatric solid organ transplantation?

In the clinical arena of transplantation, tolerance remains, for the most part, a concept rather than a reality. Although modern immunosuppression regimens have effectively handled acute rejection, nearly all organs except the liver commonly suffer chronic immunologic damage that impairs organ function, threatening patient and allograft survival. In addition to the imperfect control of the donor-directed immune response, there are additional costs. First, there is the burden of mortality from infection and malignancy that can be directly attributed to a crippled immune system. Second, there are insidious effects on renal function, cardiovascular profile (hypertension, hyperglycemia, and dyslipidemia), bone health, growth, psychological and neurocognitive development, and overall quality of life. It is likely that the full consequences of lifelong immunosuppression on our pediatric transplant recipients will not be fully appreciated until survival routinely extends beyond 1 or 2 decades after transplantation. Therefore, it can be argued that the holy grail of transplantation tolerance is of the utmost importance to children who undergo solid organ transplantation.

Organ transplantation has come of age

Organ transplantation started in the mid-1950s with a kidney transplant between identical twins, demonstrating the surgical technique could provide successful therapy. The immunological barrier to be overcome, however proved to be far more difficult to deal with. The introduction of immunosuppressive agents produced some success but it was not until Cyclosporin became available in the 1980s that results became sufficiently good for widespread acceptance and rapid development of organ grafting. Now with more powerful and selective agents, although there is still much room for improvement in immunosuppression, one of the main problems in organ transplantation is a result of its success, namely a shortage of organ donors. In this review, I summarise these matters.

Distinct response of liver myeloid dendritic cells to endotoxin is mediated by IL-27

BACKGROUND/AIMS

The liver lies downstream of the gut, and is constantly exposed to bacteria. Liver dendritic cells (DC) are known to possess properties of tolerance, and respond to LPS differently when compared to conventional DC, but the underlying mechanisms are not completely understood. The aim of this study was to evaluate liver DC response to LPS stimulation.

METHODS

Liver or spleen derived DC were isoloated from mice treated with plasmid-GM-CSF hydrodynamic injection. The surface molecules and TLR4 expression on DC and cytokine productions of LPS stimulated DC were determinded by FACS analysis, ELISA and qPCR. The ability of DC to elicit T cell responses and differentiation were examined by MLR/CTL assay and qPCR for molecular markers related to Th1/Th2/Treg.

RESULTS

In this study, we demonstrated that the threshold of LPS stimulation for liver DC was markedly higher than spleen DC, even though the expression of TLR4 on both DCs was comparable. In contrast to spleen DC that produced high levels of IL-12 and induced Th1 response upon LPS stimulation, LPS-liver DC preferentially produced IL-10 and IL-27, instead of IL-12. In addition, liver DC induced T cell hyporesponsiveness, associated with selective expansion of CD4(+)Foxp3(+)T regulatory cells. Addition of exogenous IL-12 only slightly enhanced liver DC-induced T cell response. Interestingly, abrogation of IL-27 ligation by using IL-27R(-/-) T cells synergistically augmented the effect of IL-12, suggesting that IL-27 produced by liver DC plays a crucial role in induction of T cell hyporesponsiveness.

CONCLUSIONS

Liver DC respond distinctly to LPS stimulation by secreting IL-27 which synergizes with silencing of bioactive IL-12 activity leading to profound T cell inhibition.