Tolerance Induction Strategies Research Articles

The self-reactive FVIII T cell repertoire in healthy individuals relies on a short set of epitopes and public clonotypes.

Non-mutated FVIII-specific CD4 T cell epitopes have been recently found to contribute to the development of inhibitors in patients with hemophilia A (HA), while auto-reactive CD4 T cells specific to FVIII circulate in the blood of healthy individuals at a frequency close to the foreign protein ovalbumin. Thus, although FVIII is a self-protein, the central tolerance raised against FVIII appears to be low. In this study, we conducted a comprehensive analysis of the FVIII CD4 T cell repertoire in 29 healthy donors. Sequencing of the CDR3β TCR region from isolated FVIII-specific CD4 T cells revealed a limited usage and pairing of TRBV and TRBJ genes as well as a mostly hydrophobic composition of the CDR3β region according to their auto-reactivity. The FVIII repertoire is dominated by a few clonotypes, with only 13 clonotypes accounting for half of the FVIII response. Through a large-scale epitope mapping of the full-length FVIII sequence, we identified 18 immunodominant epitopes located in the A1, A3, C1, and C2 domains and covering half of the T cell response. These epitopes exhibited a broad specificity for HLA-DR or DP molecules or both. T cell priming with this reduced set of peptides revealed that highly expanded clonotypes specific to these epitopes were responsible individually for up to 32% of the total FVIII repertoire. These FVIII T cell epitopes and clonotypes were shared among HLA-unrelated donors tested and previously reported HA patients. Our study highlights the role of the auto-reactive T cell response against FVIII in HA and its similarity to the response observed in healthy individuals. Thus, it provides valuable insights for the development of new tolerance induction and deimmunization strategies.

Suppressed IgG4 class switching in dupilumab- and TNF inhibitor-treated patients after mRNA vaccination.

The noninflammatory immunoglobulin G4 (IgG4) is linked to tolerance and is unique to humans. Although poorly understood, prolonged antigenic stimulation and IL-4-signaling along the T helper 2-axis may be instrumental in IgG4 class switching. Recently, repeated SARS-CoV-2 mRNA vaccination has been linked to IgG4 skewing. Although widely used immunosuppressive drugs have been shown to only moderately affect humoral responses to SARS-CoV-2 mRNA vaccination, the effect on IgG4 switching has not been investigated. Here we study the impact of such immunosuppressive drugs, including the IL-4 receptor-blocking antibody dupilumab, on IgG4 skewing upon repeated SARS-CoV-2 mRNA vaccination. Receptor-binding domain (RBD) specific antibody responses were longitudinally measured in 600 individuals, including patients with immune-mediated inflammatory diseases treated with a TNF inhibitor (TNFi) and/or methotrexate (MTX), dupilumab, and healthy/untreated controls, after repeated mRNA vaccination. We observed a substantial increase in the proportion of RBD-specific IgG4 antibodies (median 21%) in healthy/untreated controls after third vaccination. This IgG4 skewing was profoundly reduced in dupilumab-treated patients (<1%). Unexpectedly, an equally strong suppression of IgG4 skewing was observed in TNFi-treated patients (<1%), whereas MTX caused a modest reduction (7%). RBD-specific total IgG levels were hardly affected by these immunosuppressive drugs. Minimal skewing was observed, when primary vaccination was adenoviral vector-based. Our results imply a critical role for IL-4/IL-13 as well as TNF invivo IgG4 class switching. These novel findings advance our understanding of IgG4 class switch dynamics, and may benefit humoral tolerance induction strategies, treatment of IgG4 pathologies and mRNA vaccine optimization.

Chinese Severe Hemophilia a Children with High-Titer Inhibitors Obtain More Benefit from Intermediate-Dose Immune Tolerance Induction: The Interim Result of Lome Part a

Background We previously showed that low-dose immune tolerance induction (LD-ITI) strategy [incorporating immunosuppressants (IS) partially] for severe hemophilia A (SHA) patients with high-titer inhibitors (HTI) had relatively equivalent success rate with lower cost compared to those on high-dose ITI from international (I)-ITI randomized clinical trial (RCT). However, it is lack of RCT to compare the efficacy, safety, and cost of LD-ITI strategy to higher-dose ITI [intermediate-dose (MD)-ITI] strategy in China. Currently, the domestic recombinant FVIII (rFVIII) sponsored by the SinoCelltech Ltd., provides an opportunity to conduct the LOME study: a multicenter controlled randomized clinical trial of LOw- versus InterMEdiate-dose immune tolerance induction with recombinant factor VIII in China, to answer this question. Objectives Conduct the RCT to compare the efficacy, safety and cost of LD- to MD-ITI strategy using rFVIII (Omfiloctocog alfa, SCT800) for SHA children with HTI in China. Methods A perspective, multicenter RCT, enrolled SHA children ≤8year-old at enrollment, with peak historical inhibitor-titer 5 - 200 Bethesda Unit (BU)/mL, 1:1 randomized in LD- (Omfiloctocog alfa, rFVIII 50 IU/kg once-every-day) or MD- (Omfiloctocog alfa, rFVIII 100IU/kg/day) ITI group. IS was added (the initial regimen) in patients who met the criteria as follows: (i) the inhibitor titer during ITI increased to ≥200 BU/mL; (ii) the peak titer did not appear within 3 months after ITI-start; (iii) inadequate reduction (&amp;lt;20%) in titer over 6 months. Success: negative inhibitor titer twice consecutively at least 4 weeks apart and FVIII recovery ≥66% of expected within 24 months of treatment. Partial success: negative inhibitor titer twice consecutively at least 4 weeks apart, but with persistently abnormal FVIII recovery. Average consumption cost (per kg body weight) was calculated based on the median number of treatment doses consumed to achieve success. This included the cost of rFVIII and rituximab for ITI, PCC and rFVIIa for treatment of breakthrough bleeding, and IVIG for infection prevention in IS patients. The rituximab and IVIG were calculated based on the actual IS-using rate in 2 groups. Additionally, PCC and rFVIIa were calculated based on the actual using-rate in all breakthrough bleedings. Trial registration number: ChiCTR2200056603. This was the interim analysis. The first participant was enrolled on March 2022. Results Total 31 patients (16 in MD-, 15 in LD-ITI group) from 3 hemophilia centers with median followed-up 9 months since ITI-start (Table 1). A total 26 (83.9%) patients underwent peripherally inserted central catheter (PICC) (14 in MD-, 12 in LD-ITI group). A total 10 (32.3%, 2 in MD-, and 8 in LD-ITI group) patients received IS at median 2.9 months since ITI-start. Among them, 6 patients added IS because of inhibitor titer ≥200BU/mL during ITI, and the rest for delayed-occurred peak-titer or unsatisfactory decrease of titer. The MD- and LD-ITI group achieved similar success rate (75% vs. 40%). None success patients relapsed over a median follow-up period of 5.1 months since achieving success. The Kaplan-Meier curves demonstrated that patients in MD-ITI group had significantly shorter time to success (median, 2.9 months vs. 9.0 months), and partial success (2.4 months vs. 5.7 months). (Figure 1A and Figure 1B) Patients in MD-ITI group had lower mean bleeding rate (bleedings/month) (0.38 vs. 1.40) and joint bleeding rate (0.11 vs. 0.83) before achieving partial success, compared with those in LD-ITI group (Figure 1C and Figure 1D). But during the phase from achieving partial success to achieving success, the 2 groups had similar bleeding rate (0.09 vs. 0.11) and joint bleeding rate (0.07 vs. 0.16). A total 6 (23.1%) patients occurred PICC-related complications (5 in MD-, 1 in LD-ITI group) with mean follow-up period of 270 days. All complications including infection (1 person-time), thrombosis (1 person-time), rashes (3 person-time), accidental detachment (3 person-time). Similar per kg treatment cost from ITI-start to ITI success was found in 2 groups (US$ 2905.18 vs. US$ 2838.23). Conclusions Similar success rate was found in LD-ITI (rFVIII) strategy and MD-ITI (rFVIII) strategy for SHA children with HTI. On the premise of similar cost, shorter time to success, less bleedings were observed in MD-ITI strategy. PICC implantation is a safe option to conduct ITI.

Novel cell-based strategies for immunomodulation in vascularized composite allotransplantation.

Vascularized composite allotransplantation (VCA) has become a clinical reality in the past two decades. However, its routine clinical applications are limited by the risk of acute rejection, and the side effects of the lifelong immunosuppression. Therefore, there is a need for new protocols to induce tolerance and extend VCA survival. Cell- based therapies have emerged as an attractive strategy for tolerance induction in VCA. This manuscript reviews the current strategies and applications of cell-based therapies for tolerance induction in VCA. Cellular therapies, including the application of bone marrow cells (BMC), mesenchymal stem cells (MSC), adipose stem cells, regulatory T cells (Treg) cells, dendritic cells and donor recipient chimeric cells (DRCC) show promising potential as a strategy to induce tolerance in VCA. Ongoing basic science research aims to provide insights into the mechanisms of action, homing, functional specialization and standardization of these cellular therapies. Additionally, translational preclinical and clinical studies are underway, showing encouraging outcomes. Cellular therapies hold great potential and are supported by preclinical studies and clinical trials demonstrating safety and efficacy. However, further research is needed to develop novel cell-based immunosuppressive protocol for VCA.

PB1288 Immune Tolerance Induction (ITI) Strategies in Haemophilia A Patients with Inhibitors - Data from the MOTIVATE Study

PB1288 Immune Tolerance Induction (ITI) Strategies in Haemophilia A Patients with Inhibitors - Data from the MOTIVATE Study

ASA Allergy and Desensitization Protocols in the Management of CAD: A Review of Literature.

Acetylsalicylic acid (ASA) hypersensitivity still represents one of the major deals for patients with atherosclerotic cardiovascular disease (ASHD), especially for those requiring percutaneous coronary interventions in the absence of validated alternative options. Despite symptoms after ASA administration being reported in 6-20% of cases, true ASA allergy only represents a minority of the patients, pointing to the importance of challenge tests and potential strategies for tolerance induction. ASA desensitization protocols were proposed several decades ago, with accumulating the literature on their use in patients undergoing PCI either for chronic disease or acute coronary syndromes. Nevertheless, the promising results of the studies and meta-analyses have not been validated so far by the support of large-scale randomized trials or unique indications from guidelines. Therefore, ASA desensitization is still largely unapplied, leaving the management of ASA hypersensitivity to the individualized approach of cardiologists.

Creation of human hematopoietic chimeric cell (HHCC) line as a novel strategy for tolerance induction in transplantation.

Cell-based and chimerism-based therapies represent a promising approach for tolerance induction in transplantation. We propose a new cell therapy of the ex vivo created human hematopoietic chimeric cells (HHCC) as an alternative approach to bone marrow (BM)-based therapies in support of solid organ and vascularized composite allotransplantation (VCA). This study aimed to characterize in vitro the phenotype, genotype, clonogenic, and tolerogenic properties of HHCC. Thirty ex vivo fusions of CD34+ cells from two unrelated human BM donors were performed. CD34+ cells were stained separately with PKH26 and PKH67 membrane dyes and fused using polyethylene glycol (PEG). Creation of human HHCC and chimeric state was confirmed by flow cytometry (FC), confocal microscopy (CM) and electron microscopy (EM). HHCC's phenotype (CD34, CD133, CD117, CD4, CD19, CD4/CD25) was assessed by FC, viability by Trypan Blue, LIVE/DEAD and apoptosis by AnnexinV/Sytox Blue and TUNEL assay, while mixed lymphocyte reaction (MLR) assay assessed HHCC's immunogenicity and tolerogenic properties. HHCC differentiation, proliferation and clonogenic potential were assessed by the colony forming unit (CFU). Polyploidy was evaluated by fluorescence in situ hybridization (FISH), whereas polymerase chain reaction-reverse sequence-specific oligonucleotide probe (PCR-rSSOP) and short tandem repeats-polymerase chain reaction (STR-PCR) assessed HHCC's genotype, and chimerism. Reverse transcription polymerase chain reaction (RT-PCR) analyzed cytokines secretion [interleukin (IL)-10, transforming growth factor-β (TGF-β) and tumor necrosis factor-α (TNF-α)] up to 14 days post-fusion. FC and CM confirmed creation of HHCC by fusion of CD34+ cells from two unrelated human donors. After fusion, maintenance of hematopoietic markers and increased expression of Treg-cells (CD4/CD25) was confirmed. Moreover, high HHCC viability (99%) and a low apoptosis rate (1.2%) were revealed HHCC presented decreased immunogenicity by MLR, and significant, 40-fold increase of IL-10 the pro-tolerogenic cytokine at 21 days after fusion (RT-PCR) P<0.0001. The number of polyploid cells was negligible (0.48%). PCR-rSSOP of HHCC after fusion confirmed presence of human leukocyte antigen (HLA) class I and class II-alleles and presence of the loci specific for both CD34+ cells BM donors by STR-PCR. We have created a new hematopoietic cell line of HHCC from two unrelated human donors, and have successfully characterized in vitro, viability, phenotype, genotype, clonogenic, and tolerogenic properties of HHCC. These unique immunomodulatory and tolerogenic properties introduce HHCC as a novel therapeutic approach for tolerance induction in VCA and solid organ transplantation.

Progress in islet xenotransplantation: Immunologic barriers, advances in gene editing, and tolerance induction strategies for xenogeneic islets in pig-to-primate transplantation.

Islet transplantation has emerged as a curative therapy for diabetes in select patients but remains rare due to shortage of suitable donor pancreases. Islet transplantation using porcine islets has long been proposed as a solution to this organ shortage. There have already been several small clinical trials using porcine islets in humans, but results have been mixed and further trials limited by calls for more rigorous pre-clinical data. Recent progress in heart and kidney xenograft transplant, including three studies of pig-to-human xenograft transplant, have recaptured popular imagination and renewed interest in clinical islet xenotransplantation. This review outlines immunologic barriers to islet transplantation, summarizes current strategies to overcome these barriers with a particular focus on approaches to induce tolerance, and describes an innovative strategy for treatment of diabetic nephropathy with composite islet-kidney transplantation.

Nanobiotechnology-Modified Cellular and Molecular Therapy as a Novel Approach for Autoimmune Diabetes Management.

Several cellular and molecular therapies such as stem cell therapy, cell replacement therapy, gene modification therapy, and tolerance induction therapy have been researched to procure a permanent cure for Type 1 Diabetes. However, due to the induction of undesirable side effects, their clinical utility is questionable. These anti-diabetic therapies can be modified with nanotechnological tools for reducing adverse effects by selectively targeting genes and/or receptors involved directly or indirectly in diabetes pathogenesis, such as the glucagon-like peptide 1 receptor, epidermal growth factor receptor, human leukocyte antigen (HLA) gene, miRNA gene and hepatocyte growth factor (HGF) gene. This paper will review the utilities of nanotechnology in stem cell therapy, cell replacement therapy, beta-cell proliferation strategies, immune tolerance induction strategies, and gene therapy for type 1 diabetes management.

Progress in Xenotransplantation: Immunologic Barriers, Advances in Gene Editing, and Successful Tolerance Induction Strategies in Pig-To-Primate Transplantation.

Organ transplantation is the most effective treatment for end stage organ failure, but there are not enough organs to meet burgeoning demand. One potential solution to this organ shortage is xenotransplantation using pig tissues. Decades of progress in xenotransplantation, accelerated by the development of rapid genome editing tools, particularly the advent of CRISPR-Cas9 gene editing technologies, have enabled remarkable advances in kidney and heart xenotransplantation in pig-to-nonhuman primates. These breakthroughs in large animal preclinical models laid the foundation for three recent pig-to-human transplants by three different groups: two kidney xenografts in brain dead recipients deemed ineligible for transplant, and one heart xenograft in the first clinical grade study of pig-to-human transplantation. However, despite tremendous progress, recent data including the first clinical case suggest that gene-modification alone will not overcome all xenogeneic immunologic barriers, and thus an active and innovative immunologic strategy is required for successful xenotransplantation. This review highlights xenogeneic immunologic barriers, advances in gene editing, and tolerance-inducing strategies in pig-to-human xenotransplantation.

Update on immunosuppressive strategies in intestinal transplantation.

The intestine is the most immunologically complex solid organ allograft with the greatest risk of both rejection and graft-versus-host disease (GVHD). High levels of immunosuppression are required, further increasing morbidity. Due to low volume of transplants and few centers with experience, there is paucity of evidence-based, standardized, and effective therapeutic regimens. We herein review the most recent data about immunosuppression, focusing on novel and emerging therapies. Recent data are moving the field toward increasing use of basilixumab and consideration of alemtuzumab for induction and inclusion of mammalian target of rapamycin inhibitors and antimetabolites for maintenance. For rejection, we highlight novel roles for tumor necrosis factor-α inhibition, α4β7 integrin inhibition, microbiome modulation, desensitization protocols, and tolerance induction strategies. We also highlight emerging novel therapies for GVHD, especially the promising role of Janus kinase inhibition. New insights into immune pathways associated with rejection and GVHD in intestinal allografts have led to an evolution of therapies from broad-based immunosuppression to more targeted strategies that hold promise for reducing morbidity from infection, rejection, and GVHD. These should be the focus of further study to facilitate their widespread use.

Advances in Liver Transplantation: where are we in the pursuit of transplantation tolerance?

Liver transplantation is the ultimate treatment option for end-stage liver disease. Breakthroughs in surgical practice and immunosuppression have seen considerable advancements in survival after transplantation. However, the intricate management of immunosuppressive regimens, balancing desired immunological quiescence while minimizing toxicity has proven challenging. Diminishing improvements in long-term morbidity and mortality have been inextricably linked with the protracted use of these medications. As such, there is now enormous interest to devise protocols that will allow us to minimize or completely withdraw immunosuppressants after transplantation. Immunosuppression withdrawal trials have proved the reality of tolerance following liver transplantation, however, without intervention will only occur after several years at the risk of potential cumulative immunosuppression-related morbidity. Focus has now been directed at accelerating this phenomenon through tolerance-inducing strategies. In this regard, efforts have seen the use of regulatory cell immunotherapy. Here we focus particularly on regulatory T cells, discussing preclinical data that propagated several clinical trials of adoptive cell therapy in liver transplantation. Furthermore, we describe efforts to further optimize the specificity and survival of regulatory cell therapy guided by concurrent immunomonitoring studies and the development of novel technologies including chimeric antigen receptors and co-administration of low-dose IL-2.

An in vivo selection-derived d-peptide for engineering erythrocyte-binding antigens that promote immune tolerance

When displayed on erythrocytes, peptides and proteins can drive antigen-specific immune tolerance. Here, we investigated a straightforward approach based on erythrocyte binding to promote antigen-specific tolerance to both peptides and proteins. We first identified a robust erythrocyte-binding ligand. A pool of one million fully d-chiral peptides was injected into mice, blood cells were isolated, and ligands enriched on these cells were identified using nano-liquid chromatography-tandem mass spectrometry. One round of selection yielded a murine erythrocyte-binding ligand with an 80 nM apparent dissociation constant, Kd We modified an 83-kDa bacterial protein and a peptide antigen derived from ovalbumin (OVA) with the identified erythrocyte-binding ligand. An administration of the engineered bacterial protein led to decreased protein-specific antibodies in mice. Similarly, mice given the engineered OVA-derived peptide had decreased inflammatory anti-OVA CD8+ T cell responses. These findings suggest that our tolerance-induction strategy is applicable to both peptide and protein antigens and that our in vivo selection strategy can be used for de novo discovery of robust erythrocyte-binding ligands.

Next Generation Immunotherapies – Emerging Strategies for Immune Modulation against Cancer, Infections, and Beyond

Next Generation Immunotherapies – Emerging Strategies for Immune Modulation against Cancer, Infections, and Beyond

Targeting Lymphoid Tissues to Promote Immune Tolerance

AbstractThe enormous research progress in autoimmune disorders makes the establishment of long‐term clinical tolerance to autoantigens an accessible goal. This strategy endows lymphoid tissues with the tolerogenic ability to induce an unresponsive state toward autoantigens. Lymphoid tissues, as the crossroads, play integral roles in initiating immune activation and immunoregulation. Enormous efforts have driven the exploration of targeting delivery of tolerogenic agents to lymphoid tissues to reverse autoimmune disorders. Herein, the development of various tolerogenic therapies for autoimmune diseases are reviewed, the mechanisms of action from various lymphoid tissues to appropriate cell types by different administration routes are highlighted, and examples of lymphoid tissue‐targeting strategies to improve tolerogenic therapy potency are discussed. First lymph nodes‐targeting strategies for tolerance induction after interstitial or intra‐lymph node (i.LN) injection are summarized, then liver and spleen‐mediated tolerance after intravenous administration are described, and finally oral tolerance‐based therapies are discussed. It is envisioned that tolerogenic therapy will emerge as a novel treatment for autoimmune diseases.

Use of Post-transplant Cyclophosphamide Treatment to Build a Tolerance Platform to Prevent Liquid and Solid Organ Allograft Rejection.

Corneal transplantation (CT) is the most frequent type of solid organ transplant (SOT) performed worldwide. Unfortunately, immunological rejection is the primary cause of graft failure for CT and therefore advances in immune regulation to induce tolerance remains an unmet medical need. Recently, our work and others in pre-clinical studies found that cyclophosphamide (Cy) administered after (“post-transplant,” PTCy) hematopoietic stem cell transplantation (HSCT), i.e., liquid transplants is effective for graft vs. host disease prophylaxis and enhances overall survival. Importantly, within the past 10 years, PTCy has been widely adopted for clinical HSCT and the results at many centers have been extremely encouraging. The present studies found that Cy can be effectively employed to prolong the survival of SOT, specifically mouse corneal allografts. The results demonstrated that the timing of PTCy administration is critical for these CT and distinct from the kinetics employed following allogeneic HSCT. PTCy was observed to interfere with neovascularization, a process critically associated with immune rejection of corneal tissue that ensues following the loss of ocular “immune privilege.” PTCy has the potential to delete or directly suppress allo-reactive T cells and treatment here was shown to diminish T cell rejection responses. These PTCy doses were observed to spare significant levels of CD4+ FoxP3+ (Tregs) which were found to be functional and could readily receive stimulating signals leading to their in vivo expansion via TNFRSF25 and CD25 agonists. In total, we posit future studies can take advantage of Cy based platforms to generate combinatorial strategies for long-term tolerance induction.

Validation of Animal Models for Facial Transplantation Research

BackgroundThe development of consistent animal experimental models is important for continued research on specific biological and immunologic aspects of vascularized composite allografts. It is also important for the translation of immune regulation and tolerance induction strategies and treatment ideas from bench to bedside. The purpose of our study is to provide an outline of the use of animal models in simulated facial transplant surgery and to investigate the feasibility of animal model use. MethodsThe animals underwent hemifacial flap transplant surgery. The flaps were placed on the external carotid artery and external jugular vein of the donor animal. Twenty-one procedures were performed in 4 different animals (6 rats, 5 rabbits, 6 dogs, 4 pigs). Two experienced plastic surgeons and 5 students performed allotransplant. ResultsAll 4 models were suitable for facial allotransplant with different anatomic characteristics. Average feasibility scores were 4.8 for pigs, 3.6 for rabbits, 3.2 for dogs, and 3.4 for rats. Evaluations concluded that pigs were the most practical and realistic models for facial allotransplant training. Other models achieved validation thresholds. ConclusionsThis study is the first comparative validation assessment of animal models used in facial allotransplant. It supports the use of pig models for surgical skills training. Pigs were the preferred simulation models, while rats, rabbits, and dogs were considered inferior models for transplant simulation.

Nano and Microparticle Emerging Strategies for Treatment of Autoimmune Diseases: Multiple Sclerosis and Type 1 Diabetes.

Autoimmune diseases affect 10% of the world's population, and 1 in 200 people worldwide suffer from either multiple sclerosis (MS) or type 1 diabetes (T1D). While the targeted organ systems are different, MS and T1D share similarities in terms of autoreactive immune cells playing a critical role in pathogenesis. Both diseases can be managed only symptomatically without curative remission, and treatment options are limited and non-specific. Most current therapies cause some degree of systemic immune suppression, leaving the patients susceptible to opportunistic infections and other complications. Thus, there is considerable interest in the development of immunotherapies not associated with generalized immune suppression for these diseases. This review presents current and preclinical strategies for MS and T1D treatment, emphasizing those aimed to modulate the immune response, including the most recent strategies for tolerance induction. A central focus is on the emerging approaches using nano- and microparticle platforms, their evolution as immunotherapeutic carriers, including those incorporating specific antigens to induce tolerance and reduce unwanted generalized immune suppression.

Tolerance studies in liver transplantation: are we fooling ourselves?

This article will summarize outcomes of prior immunosuppression withdrawal trials in pediatric and adult liver transplantation and provide updates on the current status of ongoing clinical tolerance studies including evolving strategies, such as identification of reliable biomarkers or immunomodulation to achieve an earlier onset and more robust level of operational tolerance. Clinical tolerance studies in liver transplantation have previously been limited by inconsistent and delayed success of immunosuppressive withdrawal, lack of substantial histological analysis from liver tissue biopsy, and the inability to translate mechanistic studies to reproducible clinical outcomes. Current clinical trials are attempting to overcome these hurdles through more comprehensive and guided immunosuppression withdrawal protocols. Novel and emerging technologies are enabling investigators to identify and validate potential biomarkers of tolerance in order to predict patient subpopulations disposed towards operational tolerance. Immune cell therapy using the adoptive transfer of various cell products have been shown to be feasible and well tolerated in early phase clinical trials and ongoing. Tolerance studies in liver transplantation are evolving and substantial progress has been made in overcoming the challenges that have prevented the widespread implementation of immunosuppression withdrawal protocols in the clinic. Identifying more sensitive and specific predictors of immunosuppression withdrawal success and tolerance induction strategies that will allow for early tolerance will advance the field tremendously towards the goal of promoting long-term allograft survival without immunosuppression.

Mechanisms of Immune Tolerance in Liver Transplantation-Crosstalk Between Alloreactive T Cells and Liver Cells With Therapeutic Prospects.

Liver transplantation (LTx) is currently the most powerful treatment for end-stage liver disease. Although liver allograft is more tolerogenic compared to other solid organs, the majority of LTx recipients still require long-term immune suppression (IS) to control the undesired alloimmune responses, which can lead to severe side effects. Thus, understanding the mechanism of liver transplant tolerance and crosstalk between immune cells, especially alloreactive T cells and liver cells, can shed light on more specific tolerance induction strategies for future clinical translation. In this review, we focus on alloreactive T cell mediated immune responses and their crosstalk with liver sinusoidal endothelial cells (LSECs), hepatocytes, hepatic stellate cells (HSCs), and cholangiocytes in transplant setting. Liver cells mainly serve as antigen presenting cells (APCs) to T cells, but with low expression of co-stimulatory molecules. Crosstalk between them largely depends on the different expression of adhesion molecules and chemokine receptors. Inflammatory cytokines secreted by immune cells further elaborate this crosstalk and regulate the fate of naïve T cells differentiation within the liver graft. On the other hand, regulatory T cells (Tregs) play an essential role in inducing and keeping immune tolerance in LTx. Tregs based adoptive cell therapy provides an excellent therapeutic option for clinical transplant tolerance induction. However, many questions regarding cell therapy still need to be solved. Here we also address the current clinical trials of adoptive Tregs therapy and other tolerance induction strategies in LTx, together with future challenges for clinical translation from bench to bedside.