Side-effect of life-long immunosuppressants (IS) administration is a major obstacle for the long-term survival of pediatric liver transplantation (LT) recipients. Immunotolerance is the status that recipients discontinued IS with normal liver function and intrahepatic histology. So far, only a few clinical parameters were identified related with tolerance but failed to accurately discriminate tolerant recipients in clinical practice. Here, the authors aimed to provide a comprehensive view of pre-LT and post-LT risk factors associated with the achievement of tolerance after pediatric LT and established a tolerance predictive nomogram (ITPLT) with high accuracy and specificity.

The authors enrolled 2228 pediatric recipients who received LT in Renji Hospital between October 2006 and December 2020. All participants survived over 3 years after transplantation with comprehensive and intact medical history and follow-up data. They were randomly assigned to training and validation cohorts in accordance with a ratio of 1:1. Univariate and multivariable Logistic regression were used to identify clinical factors associated with post-LT immune tolerance and establish a predictive model. The model was further validated in an independent external validation cohort from Tianjin First Central Hospital.

Among all participants, 6% recipients successfully tapered IS with intact allograft function. The most common reason for IS discontinuity was pneumonia. Univariate analysis identified 15 clinical factors associated with tolerance achievement, including age at LT, follow-up time, preoperative total bilirubin, creatinine, INR, CYP polymorphism, types of transplantation, massive postoperative ascites, episodes of acute rejection, and the severity of EBV and CMV infection. Using multivariable Logistic regression, the authors established the predictive ITPLT model for post-LT tolerance, which included seven easily accessible clinical factors (age at LT, CYP3A5 genotype, types of transplantation, post-LT massive ascites, preoperative INR, creatinine, and total bilirubin levels). Then, the authors visualized the model using nomogram. The c -statistics for predicting tolerance achievement in the training, internal validation, and external validation cohorts were 0.854, 0.787, and 0.746, respectively.

Multiple pre-LT and post-LT clinical factors affected the process of immune remodeling after pediatric LT. The predictive ITPLT model, composed of seven easily accessible clinical factors, could comprehensively reveal the effect of these clinical parameters on immune remodeling and accurately identify tolerant recipients after pediatric LT. The application of ITPLT could facilitate the individualized IS strategy in the future.

• immune remodeling
• immune tolerance
• immunosuppressants
• pediatric liver transplantation
• predictive model

• Humans
• Liver Transplantation
• Child
• Immune Tolerance/immunology
• Male
• Cohort Studies
• Female
• Child, Preschool
• Infant
• Adolescent
• Graft Rejection/immunology
• Graft Rejection/prevention & control

• allograft rejection
• immunosuppressive drugs
• immunotolerance
• liver transplant
• transplant immunology

• biomarkers
• chronic kidney disease
• hepatocellular carcinoma
• liver transplantation
• recurrent primary diseases
• rejection

• Humans
• Biomarkers
• Carcinoma, Hepatocellular/surgery
• Liver Neoplasms/surgery
• Liver Transplantation
• Organ Transplantation
• Renal Insufficiency, Chronic

• B cell receptor (BCR)
• T cell receptor (TCR)
• alloimmunity
• lymphocyte receptor sequencing
• solid organ transplant

Liver-resident CD56^brightCD16^- natural killer (NK) cells are enriched in the human liver and are phenotypically distinct from their blood counterparts. Although these cells are capable of rapid cytotoxic effector activity, their functional role remains unclear. We hypothesise that they may contribute to immune tolerance in the liver during transplantation. RNA sequencing was carried out on FACS sorted NK cell subpopulations from liver perfusates (n=5) and healthy blood controls (n=5). Liver-resident CD56^brightCD16^+/- NK cells upregulate genes associated with tissue residency. They also upregulate expression of CD160 and LY9, both of which encode immune receptors capable of activating NK cells. Co-expression of CD160 and Ly9 on liver-resident NK cells was validated using flow cytometry. Hepatic NK cell cytotoxicity against allogenic T cells was tested using an in vitro co-culture system of liver perfusate-derived NK cells and blood T cells (n=10-13). In co-culture experiments, hepatic NK cells but not blood NK cells induced significant allogenic T cell death (p=0.0306). Allogenic CD8⁺ T cells were more susceptible to hepatic NK cytotoxicity than CD4⁺ T cells (p<0.0001). Stimulation of hepatic CD56^bright NK cells with an anti-CD160 agonist mAb enhanced this cytotoxic response (p=0.0382). Our results highlight a role for donor liver NK cells in regulating allogenic CD8⁺ T cell activation, which may be important in controlling recipient CD8⁺ T cell-mediated rejection post liver-transplant.

• CD56 Antigen/metabolism
• CD8-Positive T-Lymphocytes
• Humans
• Killer Cells, Natural
• Liver
• Liver Transplantation
• Living Donors

• Health Research Board

• liver transplantation
• molecular diagnostics
• network systems biology
• pediatric samples
• rejection
• systems immunology

Spontaneous operational tolerance to the allograft develops in a proportion of liver transplant (LTx) recipients weaned off immunosuppressive drugs (IS). Several previous studies have investigated whether peripheral blood gene expression profiles could identify operational tolerance in LTx recipients. However, the reported gene expression profiles differed greatly amongst studies, which could be caused by inadequate matching of clinical parameters of study groups. Therefore, the purpose of this study was to validate differentially expressed immune system related genes described in previous studies that identified tolerant LTx recipients after IS weaning. Blood was collected of tolerant LTx recipients (TOL), a control group of LTx recipients with regular IS regimen (CTRL), a group of LTx recipients with minimal IS regimen (MIN) and healthy controls (HC), and groups were matched on age, sex, primary disease, time after LTx, and cytomegalovirus serostatus after LTx. Quantitative Polymerase Chain Reaction was used to determine expression of twenty selected genes and transcript variants in PBMCs. Several genes were differentially expressed between TOL and CTRL groups, but none of the selected genes were differentially expressed between HC and TOL. Principal component analysis revealed an IS drug dosage effect on the expression profile of these genes. These data suggest that use of IS profoundly affects gene expression in peripheral blood, and that these genes are not associated with operational tolerance. In addition, expression levels of SLAMF7 and NKG7 were affected by prior cytomegalovirus infection in LTx recipients. In conclusion, we found confounding effects of IS regimen and prior cytomegalovirus infection, on peripheral blood expression of several selected genes that were described as tolerance-associated genes by previous studies.

• cytomegalovirus infection
• immunosuppressive drugs
• liver transplantation
• operational tolerance
• peripheral blood gene expression

There is limited evidence on the safety of immunotherapy use after liver transplantation and its efficacy in treating post-liver transplant hepatocellular carcinoma (HCC) recurrence.

To assess the safety of immunotherapy after liver transplant and its efficacy in treating post-liver transplant HCC recurrence.

A literature review was performed to identify patients with prior liver transplantation and subsequent immunotherapy. We reviewed the rejection rate and risk factors of rejection. In patients treated for HCC, the oncological outcomes were evaluated including objective response rate, progression-free survival (PFS), and overall survival (OS).

We identified 25 patients from 16 publications and 3 patients from our institutional database (total n = 28). The rejection rate was 32% (n = 9). Early mortality occurred in 21% (n = 6) and was mostly related to acute rejection (18%, n = 5). Patients who developed acute rejection were given immunotherapy earlier after transplantation (median 2.9 years vs 5.3 years, P = 0.02) and their graft biopsies might be more frequently programmed death ligand-1-positive (100% vs 33%, P = 0.053). Their PFS (1.0 ± 0.1 mo vs 3.5 ± 1.1 mo, P = 0.02) and OS (1.0 ± 0.1 mo vs 19.2 ± 5.5 mo, P = 0.001) compared inferiorly to patients without rejection. Among the 19 patients treated for HCC, the rejection rate was 32% (n = 6) and the overall objective response rate was 11%. The median PFS and OS were 2.5 ± 1.0 mo and 7.3 ± 2.7 mo after immunotherapy.

Rejection risk is the major obstacle to immunotherapy use in liver transplant recipients. Further studies on the potential risk factors of rejection are warranted.

• Liver transplant
• Hepatocellular carcinoma
• Recurrence
• Immunotherapy
• Rejection
• Survival

• PRISMA
• ischemia – reperfusion
• mass spectrometry
• rejection
• tolerance

Survival after solid organ transplantation (SOT) is limited by chronic rejection as well as the need for lifelong immunosuppression and its associated toxicities. Several preclinical and clinical studies have tested methods designed to induce transplantation tolerance without lifelong immune suppression. The limited success of these strategies has led to the development of clinical protocols that combine SOT with other approaches, such as allogeneic hematopoietic stem cell transplantation (HSCT). HSCT prior to SOT facilitates engraftment of donor cells that can drive immune tolerance. Recent innovations in graft manipulation strategies and post-HSCT immune therapy provide further advances in promoting tolerance and improving clinical outcomes. In this review, we discuss conventional and unconventional immunological mechanisms underlying the development of immune tolerance in SOT recipients and how they can inform clinical advances. Specifically, we review the most recent mechanistic studies elucidating which immune regulatory cells dampen cytotoxic immune reactivity while fostering a tolerogenic environment. We further discuss how this understanding of regulatory cells can shape graft engineering and other therapeutic strategies to improve long-term outcomes for patients receiving HSCT and SOT.

• adaptive immunity
• hematopoietic stem cell transplantation
• immune tolerance
• innate immunity
• solid organ transplantation

The liver has long been known to possess tolerogenic properties. Early experiments in liver transplantation demonstrated that in animal models, hepatic allografts could be accepted across MHC-mismatch without the use of immunosuppression, and that transplantation of livers from the same donor was capable of inducing tolerance to other solid organs that would normally otherwise be rejected. Although this phenomenon is less pronounced in human liver transplantation, lower levels of immunosuppression are nevertheless required for graft acceptance than for other solid organs, and in a minority of individuals immunosuppression can be discontinued in the longer term. The mechanisms underlying this unique hepatic property have not yet been fully delineated, however it is clear that immunological events in the early period post-liver transplant are key to generation of hepatic allograft tolerance. Both the hepatic parenchyma and the large number of donor passenger leukocytes contained within the liver allograft have been demonstrated to contribute to the generation of donor-specific tolerance in the early post-transplant phase. In particular, the unique nature of hepatic-leukocyte interactions appears to play a crucial role in the ability of the liver to silence the recipient alloimmune response. In this review, we will summarize the evidence regarding the potential mechanisms that mediate the critical early phase in the generation of hepatic allograft tolerance.

• T cells
• Transplantation
• hepatocytes
• high antigen load
• liver allograft
• passenger leucocytes
• suicidal emperipolesis
• tolerance

• biomarker
• biopsy
• classification systems: Banff classification
• clinical research/practice
• diagnostic techniques and imaging
• pathology/histopathology

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.

• immunomonitoring
• immunosuppression
• liver
• tolerance
• transplantation

• tolerance
• molecular target of rapamycin inhibitors
• tolerogenic dendritic cells
• t cell exhaustion
• genomics

• cell therapy
• immune tolerance
• immunosuppression withdrawal
• liver transplantation
• mechanisms

Current doctrine is that microvascular inflammation (MVI) triggered by a transplant -recipient antibody response against alloantigens (antibody-mediated rejection) is the main cause of graft failure. Here, we show that histological lesions are not mediated by antibodies in approximately half the participants in a cohort of 129 renal recipients with MVI on graft biopsy. Genetic analysis of these patients shows a higher prevalence of mismatches between donor HLA I and recipient inhibitory killer cell immunoglobulin-like receptors (KIRs). Human in vitro models and transplantation of β2-microglobulin-deficient hearts into wild-type mice demonstrates that the inability of graft endothelial cells to provide HLA I-mediated inhibitory signals to recipient circulating NK cells triggers their activation, which in turn promotes endothelial damage. Missing self-induced NK cell activation is mTORC1-dependent and the mTOR inhibitor rapamycin can prevent the development of this type of chronic vascular rejection.

‘Missing self’ is a mode of natural killer (NK) cell activation aimed to detect the lack of HLA-I molecules on infected or neoplastic cells. Here, the authors show that mismatch between donor HLA-I and cognate receptors on recipient NK cells mediates microvascular inflammation-associated graft rejection, a pathology that is preventable by mTOR inhibition.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide and confers a poor prognosis. Beyond standard systemic therapy with multikinase inhibitors, recent studies demonstrate the potential for robust and durable responses from immune checkpoint inhibition in subsets of HCC patients across disease etiologies. The majority of HCC arises in the context of chronic inflammation and from within a fibrotic liver, with many cases associated with hepatitis virus infections, toxins, and fatty liver disease. Many patients also have concomitant cirrhosis which is associated with both local and systemic immune deficiency. Furthermore, the liver is an immunologic organ in itself, which may enhance or suppress the immune response to cancer arising within it. Here, we explore the immunobiology of the liver from its native state to chronic inflammation, fibrosis, cirrhosis and then to cancer, and summarize how this unique microenvironment may affect the response to immunotherapy.

• Checkpoint blockade
• Fibrosis
• Hepatocellular carcinoma
• Immunology
• Immunotherapy
• Liver cancer

Understanding the immunological phenotype of transplant recipients is important to improve outcomes and develop new therapies. Immunophenotyping of whole peripheral blood (WPB) by flow cytometry is a rapid method to obtain large amounts of data relating to the outcomes of different transplant treatments with limited patient impact. Healthy individuals and patients with type 1 diabetes (T1D) enrolled in islet transplantation were recruited and WPB was collected. 46 fluorochrome-conjugated mouse-anti-human antibodies were used (43 of 46 antibodies were titrated). BD cytometer setup and tracking beads were used to characterize and adjust for cytometer performance. Antibody cocktails were pre-mixed <60 minutes before staining. Multicolour panels were designed based on fluorochrome brightness, antigen density, co-expression, and fluorochrome spillover into non-primary detectors in each panel on a 5 laser flow cytometer. WPB sample staining used 50–300 μl WPB for each panel and was performed within 2 hours of blood sample collection. Samples were acquired on a BD-LSRFortessa. The operating procedures, including specimen collection, antibody cocktails, staining protocol, flow-cytometer setup and data analysis, were standardized. The staining index of 43 antibodies and the spillover spreading matrix for each panel was calculated. The final concentrations for the 46 antibodies used was determined for staining of WPB samples. Absolute cell-count and 7 leukocyte profiling panels consisting of subsets and/or status of granulocytes, monocytes, dendritic, B, NK, and T cells including regulatory T cells (Tregs) and NKT were designed and established on a 5 laser BD-LSR Fortessa. 13 T1D patients, including 4 islet transplant recipients and 8 healthy controls, were evaluated. The ability to reproducibly measure immune subsets and immune-profiles of islet transplant patients up to 18 months post transplantation has been established as a tool to measure immune cell reconstitution after transplantation.

Cytomegalovirus (CMV) infection can cause significant complications after transplantation, but recent emerging data suggest that CMV may paradoxically also exert beneficial effects in two specific allogeneic transplant settings. These potential benefits have been underappreciated and are therefore highlighted in this review. First, after allogeneic hematopoietic stem cell transplantation (HSCT) for acute myeloid leukemia (AML) using T-cell and natural killer (NK) cell-replete grafts, CMV reactivation is associated with protection from leukemic relapse. This association was not observed for other hematologic malignancies. This anti-leukemic effect might be mediated by CMV-driven expansion of donor-derived memory-like NKG2C⁺ NK and Vδ2^negγδ T-cells. Donor-derived NK cells probably recognize recipient leukemic blasts by engagement of NKG2C with HLA-E and/or by the lack of donor (self) HLA molecules. Vδ2^negγδ T cells probably recognize as yet unidentified antigens on leukemic blasts via their TCR. Second, immunological imprints of CMV infection, such as expanded numbers of Vδ2^negγδ T cells and terminally differentiated TCRαβ⁺ T cells, as well as enhanced NKG2C gene expression in peripheral blood of operationally tolerant liver transplant patients, suggest that CMV infection or reactivation may be associated with liver graft acceptance. Mechanistically, poor alloreactivity of CMV-induced terminally differentiated TCRαβ⁺ T cells and CMV-induced IFN-driven adaptive immune resistance mechanisms in liver grafts may be involved. In conclusion, direct associations indicate that CMV reactivation may protect against AML relapse after allogeneic HSCT, and indirect associations suggest that CMV infection may promote allograft acceptance after liver transplantation. The causative mechanisms need further investigations, but are probably related to the profound and sustained imprint of CMV infection on the immune system.

• cytomegalovirus infections
• hematopoietic stem cell transplantation
• leukemia
• solid organ transplantation
• tolerance

• Abortion, Habitual/blood
• Abortion, Habitual/immunology
• Abortion, Habitual/pathology
• Adult
• Aged
• CD8-Positive T-Lymphocytes/immunology
• Female
• Flow Cytometry
• Glomerular Filtration Rate
• Granzymes/blood
• Humans
• Kidney/immunology
• Kidney/metabolism
• Kidney/pathology
• Kidney Transplantation/adverse effects
• Killer Cells, Natural/immunology
• Killer Cells, Natural/pathology
• Male
• Middle Aged
• Perforin/blood
• Pregnancy
• Transplant Recipients

• biomarker
• clinical research/practice
• graft survival
• kidney transplantation/nephrology

• Base Sequence
• Cohort Studies
• DNA Primers
• Humans
• Immune Tolerance/genetics
• Immunosuppressive Agents/administration & dosage
• Kidney Transplantation
• Middle Aged
• Prospective Studies
• Receptors, Antigen, B-Cell/genetics

• R37 AI049660 NIAID NIH HHS
• UM1 AI109565 NIAID NIH HHS
• N01 AI015416 NIAID NIH HHS
• U01 AI063594 NIAID NIH HHS
• U19 AI056390 NIAID NIH HHS
• U19 AI110483 NIAID NIH HHS
• U01 AI063623 NIAID NIH HHS

• B cell
• natural killer cells
• regulatory T cells
• tolerance/suppression/anergy
• transplantation

• biomarker
• cellular assays
• immunoquiescence
• kidney transplantation
• operational tolerance

• autoimmunity
• diabetes
• transcriptomics

• mutation
• ddpcr
• ngs
• pdx
• wes
• mutation detection techniques
• qpcr

• Animals
• DNA Mutational Analysis/methods
• Heterografts/metabolism
• High-Throughput Nucleotide Sequencing/methods
• Humans
• Mice
• Neoplasm Transplantation
• Neoplasms/genetics
• Neoplasms/pathology
• Polymerase Chain Reaction/methods
• Reproducibility of Results
• Tumor Cells, Cultured

• HHSN261200800001C NCI NIH HHS
• HHSN261200800001E NCI NIH HHS
• R01 CA206027 NCI NIH HHS

• T cells
• cytometry by time of flight
• immune cells
• peripheral blood mononuclear cells
• post-transplant

• Biomarkers
• Dendritic cells
• Liver transplantation
• Operational tolerance
• Regulatory T cells

• Animals
• Biomarkers/metabolism
• Biomarkers, Tumor/immunology
• Dendritic Cells/cytology
• Homeostasis
• Humans
• Immunosuppression Therapy
• Immunosuppressive Agents/therapeutic use
• Killer Cells, Natural/cytology
• Liver Failure/immunology
• Liver Failure/surgery
• Liver Transplantation
• Macrophages/cytology
• Macrophages/immunology
• Sirolimus/therapeutic use
• T-Lymphocytes, Regulatory/cytology
• Transplantation Tolerance

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

• Liver transplantation
• Natural killer cells
• Kupffer cells
• Graft rejection
• Ischemia-reperfusion injury

• Graft Rejection/immunology
• Humans
• Immune Tolerance/immunology
• Killer Cells, Natural/immunology
• Kupffer Cells/immunology
• Liver Diseases/immunology
• Liver Transplantation
• Macrophages/immunology
• Natural Killer T-Cells/immunology
• Reperfusion Injury/immunology

• Blood collection
• Fingerstick
• Gene expression
• RNA
• Tempus
• Transcriptome

With this report we aim to make available a standard operating procedure (SOP) developed for RNA stabilization of small blood volumes collected via a finger stick. The anticipation that this procedure may be improved through peer-review and/or readers public comments is another element motivating the publication of this SOP. Procuring blood samples from human subjects can, among other uses, enable assessment of the immune status of an individual subject via the profiling of RNA abundance using technologies such as real time PCR, NanoString, microarrays or RNA-sequencing. It is often desirable to minimize blood volumes and employ methods that are the least invasive and can be practically implemented outside of clinical settings. Finger stick blood samples are increasingly used for measurement of levels of pharmacological drugs and biological analytes. It is a simple and convenient procedure amenable for instance to field use or self-collection at home using a blood sample collection kit. Such methodologies should also enable the procurement of blood samples at high frequency for health or disease monitoring applications.

• Blood collection
• Fingerstick
• Gene expression
• RNA
• Tempus
• Transcriptome

• Acute rejection
• Adaptive immunity
• Biomarker
• Kidney transplantation
• MLR
• T and B cell ELISPOT

• Bioinformatics
• Gene Expression Browser
• Immunology
• Monocyte
• Transcriptomics

Systems-scale profiling approaches have become widely used in translational research settings. The resulting accumulation of large-scale datasets in public repositories represents a critical opportunity to promote insight and foster knowledge discovery. However, resources that can serve as an interface between biomedical researchers and such vast and heterogeneous dataset collections are needed in order to fulfill this potential. Recently, we have developed an interactive data browsing and visualization web application, the Gene Expression Browser (GXB). This tool can be used to overlay deep molecular phenotyping data with rich contextual information about analytes, samples and studies along with ancillary clinical or immunological profiling data. In this note, we describe a curated compendium of 93 public datasets generated in the context of human monocyte immunological studies, representing a total of 4,516 transcriptome profiles. Datasets were uploaded to an instance of GXB along with study description and sample annotations. Study samples were arranged in different groups. Ranked gene lists were generated based on relevant group comparisons. This resource is publicly available online at http://monocyte.gxbsidra.org/dm3/landing.gsp.

• Bioinformatics
• Gene Expression Browser
• Immunology
• Monocyte
• Transcriptomics

• AR, adrenergic receptor
• EF, ejection fraction
• EMB, endomyocardial biopsy
• GO, gene ontology
• HF, heart failure
• MYH, myosin heavy chain
• MiPP, Misclassified Penalized Posteriors
• SAM, significance analysis of microarrays
• SERCA, sarcoplasmic reticulum calcium-dependent ATPase
• TBB, transcriptomic-based biomarker
• beta-blocking agents
• biomarker
• gene expression
• heart failure
• transcriptomics

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.

• Liver cell transplantation
• Cell-based therapy
• Hepatocyte transplantation
• Transplant immunology
• Regenerative medicine

• combined transplantation
• gene expression
• human
• kidney transplantation
• liver transplantation
• microRNA
• phenotype

Induction of tolerance remains a major goal in transplantation. Indeed, despite potent immunosuppression, chronic rejection is still a real problem in transplantation. The humoral response is an important mediator of chronic rejection, and numerous strategies have been developed to target either B cells or plasma cells. However, the use of anti-CD20 therapy has highlighted the beneficial role of subpopulation of B cells, termed regulatory B cells. These cells have been characterized mainly in mice models of auto-immune diseases but emerging literature suggests their role in graft tolerance in transplantation. Regulatory B cells seem to be induced following inflammation to restrain excessive response. Different phenotypes of regulatory B cells have been described and are functional at various differentiation steps from immature to plasma cells. These cells act by multiple mechanisms such as secretion of immuno-suppressive cytokines interleukin-10 (IL-10) or IL-35, cytotoxicity, expression of inhibitory receptors or by secretion of non-inflammatory antibodies. Better characterization of the development, phenotype and mode of action of these cells seems urgent to develop novel approaches to manipulate the different B cell subsets and the response to the graft in a clinical setting.

• Regulatory B cells
• Suppression
• Immuno-suppressive cytokines interleukin-10
• Antibodies
• Tolerance

Regulatory T cells (Tregs) play an important role in immunoregulation and have been shown in animal models to promote transplantation tolerance and curb autoimmunity following their adoptive transfer. The safety and potential therapeutic efficacy of these cells has already been reported in Phase I trials of bone-marrow transplantation and type I diabetes, the success of which has motivated the broadened application of these cells in solid-organ transplantation. Despite major advances in the clinical translation of these cells, there are still key questions to be addressed to ensure that Tregs attest their reputation as ideal candidates for tolerance induction. In this review, we will discuss the unique traits of Tregs that have attracted such fame in the arena of tolerance induction. We will outline the protocols used for their ex vivo expansion and discuss the future directions of Treg cell therapy. In this regard, we will review the concept of Treg heterogeneity, the desire to isolate and expand a functionally superior Treg population and report on the effect of differing culture conditions. The relevance of Treg migratory capacity will also be discussed together with methods of in vivo visualization of the infused cells. Moreover, we will highlight key advances in the identification and expansion of antigen-specific Tregs and discuss their significance for cell therapy application. We will also summarize the clinical parameters that are of importance, alongside cell manufacture, from the choice of immunosuppression regimens to the number of injections in order to direct the success of future efficacy trials of Treg cell therapy. Years of research in the field of tolerance have seen an accumulation of knowledge and expertise in the field of Treg biology. This perpetual progression has been the driving force behind the many successes to date and has put us now within touching distance of our ultimate success, immunological tolerance.

• cellular therapy
• clinical trials
• tolerance
• transplantation
• tregs

Liver transplantation offers a unique window into transplant immunology due, in part, to the considerable proportion of recipients who develop immunological tolerance to their allograft. Biomarkers are able to identify and predict such a state of tolerance, and thereby able to establish suitable candidates for the minimization of hazardous immunosuppressive therapies, are not only of great potential clinical benefit but might also shed light on the immunological mechanisms underlying tolerance and rejection. Here, we review the emergent transcriptomic technologies serving as drivers of biomarker discovery, we appraise efforts to identify a molecular signature of liver allograft tolerance, and we consider the implications of this work on the mechanistic understanding of immunological tolerance.

• biomarkers
• gene
• liver
• tolerance
• transcriptome
• transplant
• transplantomics