The role of donor-specific HLA alloantibodies in liver transplantation

Advancing immunosuppression in liver transplantation: A narrative review

Immunosuppression is essential to ensure recipient and graft survivals after liver transplantation (LT). However, our understanding and management of the immune system remain suboptimal. Current immunosuppressive therapy cannot selectively inhibit the graft-specific immune response and entails a significant risk of serious side effects, i.e., among others, de novo cancers, infections, cardiovascular events, renal failure, metabolic syndrome, and late graft fibrosis, with progressive loss of graft function. Pharmacological research, aimed to develop alternative immunosuppressive agents in LT, is behind other solid-organ transplantation subspecialties, and, therefore, the development of new compounds and strategies should get priority in LT. The research trajectories cover mechanisms to induce T-cell exhaustion, to inhibit co-stimulation, to mitigate non-antigen-specific inflammatory response, and, lastly, to minimize the development and action of donor-specific antibodies. Moreover, while cellular modulation techniques are complex, active research is underway to foster the action of T-regulatory cells, to induce tolerogenic dendritic cells, and to promote the function of B-regulatory cells. We herein discuss current lines of research in clinical immunosuppression, particularly focusing on possible applications in the LT setting.

Including the liver in the visceral allograft: Impact on donor-specific anti-HLA antibodies and long-term outcomes

Humoral immunity emerges as a risk factor for graft failure after visceral transplantation (VTx) and development of donor-specific anti-HLA antibodies (DSAs) has been linked with poor outcomes. In most cases, a simultaneous liver transplant can be safely performed in sensitized patients with DSA and appears protective against lymphocytotoxic antibodies. We investigated the incidence of acute (AR) and chronic rejection (CR) in 32 VTx without any B cell-depleting pre-treatment (6 isolated intestinal transplants (IT) and 26 liver-containing, multivisceral transplants (MVT) and assessed the presence of donor-specific antibodies (DSA) pre- and post-transplantation. Twenty-one patients (65 %) developed AR, 15 (57 %) of the MVT and 6 (100 %) of the IT (p = 0.05). CR occurred in 4 IT (60 %, p < 0.001). At one month, de novo DSA were present in 71 % of VTx (66 % MVT vs 100 % IT, p = 0.09). At the last available follow-up, 69 % of the MVT and 50 % of the IT patients were DSA-free. De novo DSA seemed more persistent (7/19, 37 %) than pre-Tx DSA (1/6, 17 %; p = n.s.), de novo DSA were more frequently specific for HLA class II than class I, 16/19 (84 %) vs. 7/19 (37 %; p = 0.003), and HLA-DQ was their most frequent target HLA. DQ mismatches appeared to be a risk factor for developing de novo DSA. In conclusion, liver-containing visceral allografts have superior short- and long-term outcomes compared with liver-free allografts. De novo DSA develop early and frequently after VTx performed without B cell-depleting induction therapy, but the exact role of DSA in the pathogenesis of rejection remains unclear.

Combined liver-kidney transplantation in pediatric patients

Combined liver-kidney transplantation (CLKT) is a surgical procedure that involves transplanting both liver and kidney organs. There are two types of CLKT: simultaneous liver-kidney transplantation (smLKT) and sequential LKT (sqLKT). CLKT accounts for a small percentage of liver transplantations (LTs), particularly in pediatric cases. Nevertheless, the procedure has demonstrated excellent outcomes, with high survival rates and lower rejection rates. The main indications for CLKT in pediatric patients differ somewhat from that in adults, in which end-stage kidney disease after LT is the major indication. In children, congenital diseases are common reason for performing CLKT; the examples of such diseases include autosomal recessive polycystic kidney disease with congenital hepatic fibrosis which equally affects both organs, and primary hyperoxaluria type 1, a primary liver disease leading kidney failure. The decision between smLKT or sqLKT depends on the dominant organ failure, the specific pathophysiology, and available organ sources. However, there remain significant surgical and societal challenges surrounding CLKT. Innovations in pharmacology and genetic engineering have decreased the necessity for CLKT in early-diagnosed cases without portal hypertension or kidney replacement therapy. Nonetheless, these advancements are not universally accessible. Therefore, decision-making algorithms should be crafted, considering region-specific organ allocation systems and prevailing medical environments.

The effect of donor against recipient one-way HLA mismatch on liver transplantation outcomes from a multicenter registry analysis

Donor against recipient one-way Human leukocyte antigen (HLA) mismatch (D → R one-way HLA MM) seemed strongly associated with graft-versus-host disease (GVHD). The aim of this study is to investigate the relevance of D → R one-way HLA MM in outcome of liver transplantation (LT). We retrospectively analyzed 2670 patients in Korean Organ Transplantation Registry database between April 2014 and December 2020. The patients were categorized into two groups whether D → R one-way HLA MM or not and evaluated the outcomes of LT between the two groups. 18 patients were found to be D → R one-way HLA MM. The incidence of GVHD (0.3% vs. 22.2%, p < 0.001) and mortality rate (11.6% vs. 38.9%, p = 0.003) was much higher in D → R one-way HLA MM group. D → R one-way HLA MM at 3 loci was seemed to be strongly associated with the incidence of GVHD (OR 163.3, p < 0.001), and found to be the strongest risk factor for patient death (HR 12.75, p < 0.001). Patients with D → R one-way HLA MM at 3 loci showed significantly lower overall survival (p < 0.001) but there were no significant differences in rejection-free survival and death-censored graft survival. D → R one-way HLA MM at 3 loci not only affects the overall survival of LT patients but also the incidence of GVHD.

Identification of liver transplant biopsy phenotypes associated with distinct liver biological markers and allograft survival

The intricate association between histologic lesions and circulating antihuman leucocyte antigen donor-specific antibodies (DSA) in liver transplantation (LT) requires further clarification. We conducted a probabilistic, unsupervised approach in a comprehensively well-annotated LT cohort to identify clinically relevant archetypes. We evaluated 490 pairs of LT biopsies with DSA testing from 325 recipients transplanted between 2010 and 2020 across 3 French centers and an external cohort of 202 biopsies from 128 recipients. Unsupervised archetypal analysis integrated all clinico-immuno-histologic parameters of each biopsy to identify biopsy archetypes. The median time after LT was 1.17 (interquartile range, 0.38-2.38) years. We identified 7 archetypes distinguished by clinico-immuno-histologic parameters: archetype #1: severe T cell-mediated rejection (15.9%); #2: chronic rejection with ductopenia (1.8%); #3: architectural and microvascular damages (3.5%); #4: (sub)normal (55.9%); #5: mild T cell-mediated rejection (4.9%); #6: acute antibody-mediated rejection (6.5%); and #7: chronic rejection with DSA (11.4%). Cell infiltrates vary in the archetype. These archetypes were associated with distinct liver biological markers and allograft outcomes. These findings remained consistent when stratified using the patient's age or indications for LT, with good performance in the external cohort (mean highest probability assignment = 0.58, standard deviation ± 0.17). In conclusion, we have identified clinically meaningful archetypes, providing valuable insights into the intricate DSA-histology association, which may help standardize liver allograft pathology classification.

Balancing immunosuppression in pediatric liver transplantation: Playing the long game

The overarching goal in the care of pediatric liver transplant recipients is to optimize allograft and patient health. Balancing immunosuppression to maintain allograft health while avoiding medication side effects is essential for long-term survival and optimal quality of life in pediatric liver transplant recipients. Utilizing precision medicine to personalize immunosuppression, which includes minimization and withdrawal, is core to this effort. The unique anatomy and physiology of the liver make it more tolerant to immune-mediated injury and a more favorable organ for immunosuppression minimization and withdrawal. However, several challenges exist. Standard biochemical values and histologic features may not reliably predict allograft health after a reduction in immunosuppression. Additionally, biochemical values alone do not reliably identify which patients can successfully develop operational tolerance, as there may be occult allograft injury despite normal liver enzymes. Finally, the durability of tolerance after successful reduction in immunosuppression remains uncertain over time. Innovative tools show promise in circumventing these challenges, but more research is needed to determine actual clinical utility. While immunosuppression-free transplant may not be a current reality for most pediatric liver transplant recipients, strategies to safely minimize immunosuppression without compromising allograft health are within reach. Each liver allograft and recipient pair requires a different degree of immune modulation, and through a structured process of minimization and withdrawal, immunosuppression can indeed be tailored in a precise, personalized way to optimize outcomes. This review focuses on the progress that has been made to individualize immunosuppression in pediatric liver transplantation to ensure optimal allograft and recipient health.

Treatment of donor-specific anti-HLA antibodies-mediated rejection after liver transplantation: A French nationwide retrospective study

The deleterious effect of donor-specific anti-HLA antibodies (DSA) after liver transplantation (LT) has been increasingly recognized during the past decade. Antibody-mediated rejection (AMR) represents a rare but severe complication in the presence of DSA. However, little is known concerning the treatment of AMR after LT. The nationwide French study aimed to describe LT recipients who received specific treatment of AMR. We performed a multicenter retrospective study on 44 patients who were treated with B-cell targeting agents from January 2008 to December 2020. Median patient age at the time of AMR treatment was 51.6 years (range: 17.9-68.0). AMR was classified as acute (n = 19) or chronic (n = 25). The diagnosis of AMR was made after a median time of 16.8 months (range: 0.4-274.2) after LT. The main therapeutic combination was plasma exchange/rituximab/IVIG (n = 25, 56.8%). The median follow-up after the treatment of AMR was 32 months (range: 1-115). After the treatment, 1-, 5- and 10-year patient and graft survivals were 77%, 55.9%, and 55.9%, and 69.5%, 47.0%, and 47.0%, respectively. Initial total bilirubin (Q1-Q3 vs. Q4) was significantly associated with patient survival (log-rank test, p = 0.005) and graft survival (log-rank test, p = 0.002). After a median follow-up of 21 months (range: 12-107), DSA became undetectable in 15/38 patients (39.5%) with available DSA monitoring. In conclusion, specific treatment of AMR in LT recipients has slowly emerged in France during the past decade and has probably been considered in the most severe patients; this explains the global poor outcome, even if the outcome was favorable in some cases.

Detailed Analysis of Simultaneous Renal and Liver Allografts in the Presence of DSA

Liver allografts protect renal allografts from the same donor from some, but not all, preformed donor specific alloantibodies (DSA). However, the precise mechanisms of protection and the potential for more subtle alterations/injuries within the grafts resulting from DSA interactions require further study.

Methods

We reevaluated allograft biopsies from simultaneous liver-kidney transplant recipients who had both allografts biopsied within 60 d of one another and within 30 d of DSA being positive in serum (positive: mean florescence intensity ≥5000). Routine histology, C4d staining, and specialized immunohistochemistry for Kupffer cells (KCs; CD163) and a C4d receptor immunoglobulin-like transcript-4 were carried out in 4 patients with 6 paired biopsies.

Results

Overt antibody-mediated rejection was found in 3 of 4 renal and liver allografts. One patient had biopsy-confirmed renal and liver allograft antibody-mediated rejection despite serum clearance of DSA. All biopsies showed KC hypertrophy (minimal: 1; mild: 2; moderate: 1; severe: 2) and cytoplasmic C4d KC staining was easily detected in 2 biopsies from 2 patients; minimal and negative in 2 biopsies each. Implications of which are discussed. Control 1-y protocol liver allograft biopsies from DSA- recipients showed neither KC hypertrophy nor KC C4d staining (n = 6).

Conclusions

Partial renal allograft protection by a liver allograft from the same donor may be partially mediated by phagocytosis/elimination of antibody and complement split products by KCs, as shown decades ago in controlled sensitized experimental animal experiments.

Living Donor Liver transplantation in an alloimmunised patient: Immunological challenges and Management in Indian Settings

Liver transplantation (LT) is often associated with hematological abnormalities with immune or non-immune etiologies and require timely diagnosis and interventions. We report a case of a patient suffering from non-alcoholic steato-hepatitis (NASH) related end stage liver disease (ESLD) with multiple red cell antibodies who underwent LT surgery. In postoperative phase, she developed immune hemolysis as well as acute antibody mediated rejection (AMR) which was managed with therapeutic plasma exchange and IVIG. The case highlights the need to develop an algorithm for red cell and HLA antibody screening in high-risk patients for timely detection and management.

Morphologic and immunophenotypic evaluation of liver allograft biopsies with contemporaneous serum DSA measurements

BACKGROUND

Acute antibody mediated rejection is increasingly identified in liver allografts as a unique form of alloimmune injury associated with donor specific antibodies (DSA). This manifests pathologically as microvascular injury and C4d uptake. Despite the liver allograft's relative resistance to alloimmune injury, liver allografts are not impervious to cellular and antibody-mediated rejection.

METHODS

In this blinded control study, we evaluated CD163 immunohistochemistry and applied the Banff 2016 criteria for diagnosis of acute AMR on a group of indication allograft liver biopsies from DSA positive patients and compared them to indication biopsies from DSA negative controls.

RESULTS

Most DSA positive patients were females (75%, p = .027), and underwent transplantation for HCV infection. Significant histopathological predictors of serum DSA positivity were Banff H-score (p = .01), moderate to severe cholestasis (p = .03), and CD163 score > 2 (p = .029). Other morphologic features that showed a trend with DSA positivity include Banff portal C4d-score (p = .06), bile ductular reaction (p = .07), and central perivenulitis (p = .07). The odds of DSA sMFI ≥5000 was 12.5 times higher in those with a C4d score >1 than those with a C4d score ≤ 1 (p = .04). Incidence of definite for aAMR in the DSA positive cohort was 25% (n = 5), and 0% in the DSA negative cohort. A group of 5 DSA positive cases were not classifiable by the current scheme.

CONCLUSION

Sinusoidal CD163, Banff H-score, and diffuse C4d are predictors of serum DSA, and facilitate recognition of histopathological features associated with serum DSA and tissue-antibody interaction.

Evidence for Alloimmune Sinusoidal Injury in De Novo Nodular Regenerative Hyperplasia After Liver Transplantation

Posttransplant nodular regenerative hyperplasia (NRH) mostly remains unexplained. Microvascular injury due to antibody-mediated rejection (AMR) is suspected, but lack of donor specific antibody (DSA) testing makes it difficult to prove. Centered around a 1-year period of routine DSA testing, concomitant protocol, and indicated posttransplant liver biopsies (LB), recipients with NRH (n = 18) were compared with a matched control group (n = 36). All index, previous, and subsequent LB were reviewed. Both groups were similar in terms of demographics, timing of index LB, and DSA. In the index LB, the NRH group had higher sinusoidal C4d positivity (p = 0.029) and perisinusoidal fibrosis (p = 0.034), both independently associated with NRH (p = 0.038 and 0.050, respectively). Features of "possible" chronic AMR were detected in 28.5% of the NRH group without a known cause and 0% of the control group (p = 0.009). The NRH group had more preceding indicated LB with increased incidence of rejection and biliary obstruction pattern. In the follow-up histology, overall, sinusoidal and portal C4d positivity, sinusoidal microvasculitis, and perisinusoidal fibrosis were also higher (all p < 0.050). In conclusion, we provide evidence towards the hypothesis that some cases of posttransplant NRH are related to preceding active and persistent AMR. Large multicenter studies with protocol DSA testing are required to confirm.

Human leukocyte antigen immunization in transfusion-dependent Moroccan patients with beta-thalassemia major: prevalence and risk factors

INTRODUCTION

Beta-thalassemia major patients need a regular blood transfusion to have an initial normal growth. However, these patients have an increased risk of developing alloantibodies. Our main goal was to study HLA alloimmunization in Moroccan Beta-thalassemia patients by confronting it with transfusion and demographic criteria, exploring the involvement of HLA typing profile in the development of HLA antibodies and in turn determining risk factors for their development.

METHODS

The study consisted of 53 Moroccan pediatric patients with Beta-thalassemia major. Screening for HLA alloantibodies was performed using Luminex technology Whereas HLA genotyping was done with sequence-specific primers (PCR-SSP).

RESULTS

In this study, 50.9% of patients have been identified as positive for HLA antibodies, with 59.3% having both HLA Class I and Class II antibodies. A significant increase frequency of DRB1*11 allele was revealed in non-immunized patients (34.6% vs. 0%, p = 0.001). Our results also revealed that the majority of our HLA immunized patients were women (72.4% vs. 27.6%, p = 0.001), and transfused with more than 300 units of RBC units (66.7% vs. 33.3%, p = 0.02). There were statistically significant differences when comparing these frequencies.

CONCLUSIONS

This paper revealed that the transfusion dependent Beta-thalassemia major patients are exposed to risk of developing HLA antibodies following transfusions with leukoreduced RBC units. The HLA DRB1*11 was a protective factor against HLA alloimmunization in our beta-thalassemia major patients.

Immunotolerance in liver transplantation: a primer for the clinician

The use of immunosuppressive medications for solid organ transplantation is associated with cardiovascular, metabolic, and oncologic complications. On the other hand, the development of graft rejection is associated with increased mortality and graft dysfunction. Liver transplant recipients can withdraw from immunosuppression without developing graft injury while preserving an adequate antimicrobial response - a characteristic known as immunotolerance. Immunotolerance can be spontaneously or pharmacologically achieved. Contrary to the classic dogma, clinical studies have elucidated low rates of true spontaneous immunotolerance (no serologic or histological markers of immune injury) among liver transplant recipients. However, clinical, serologic, and tissue biomarkers can aid in selecting patients in whom immunosuppression can be safely withdrawn. For those who failed an immunosuppression withdrawal trial or are at high risk of rejection, pharmacological interventions for immunotolerance induction are under development. In this review, we provide an overview of the mechanisms of immunotolerance, the clinical studies investigating predictors and biomarkers of spontaneous immunotolerance, as well as the potential pharmacological interventions for inducing it.

ABO-incompatible Pediatric Liver Transplantation With Antibody and B-cell Depletion-free Immunosuppressive Protocol in High Consanguinity Communities

The success of orthotopic liver transplantation as a life-saving treatment has led to new indications and a greater competition for organ grafts. Pediatric patients with acute liver-related crises can benefit from orthotopic liver transplantation, but organ availability in the limited time can be a major obstacle. Crossing ABO blood group barriers could increase the organs available to such patients.

METHODS

From November 2010 to June 2015, 176 children aged 0.2-to18 y were transplanted in the King Faisal Specialist Hospital and Research Center. Out of those, 19 children were transplanted across blood group barriers (ABO incompatible). The underlying diseases were biliary atresia (n = 6); progressive familial intrahepatic cholestasis type 2 (n = 4); Crigler-Najjar syndrome (n = 3); hepatoblastoma (n = 2); and urea cycle disorder, Caroli disease, cryptogenic cirrhosis, and neonatal sclerosing cholangitis (n = 1 each). Immunosuppression consisted of basiliximab, mycophenolate, tacrolimus, and steroids. Pretransplant prophylactic plasmapheresis, high-dose immunoglobulins, and rituximab were not administered.

RESULTS

The grafts were from living donors (n = 17) and deceased donors (n = 2). Living donor morbidity was nil. The recipient median age was 21 mo (5-70 mo). After a median follow-up of 44 mo, 2 recipients (10%) died because of sepsis, 1 because of uncontrolled acute myeloid leukemia. The overall rejection rate was 7%, and no grafts were lost because of antibody-mediated rejection (AMR). HLA matching was 3.8 of 6 (A, B, DR), and there were 2 patients presented with acute cellular rejection, 1 patient with AMR, and 1 patient with biliary strictures.

CONCLUSIONS

ABO incompatible liver transplantation is a feasible and life-saving option even with antibody and B-cell depletion-free protocol without increasing the risks for AMR. We speculate that this excellent result is most likely because of presence of relatively low titer ABO isoagglutinins and the high HLA match compatibility caused by habit of longstanding interfamilial marriages as typical of Saudi Arabia.

Coagulopathy and hemostasis management in patients undergoing liver transplantation: Defining a dynamic spectrum across phases of care

Patients with acute and chronic liver disease present with a wide range of disease states and severity that may require liver transplantation (LT). Physiologic alterations occur that are dynamic throughout all phases of perioperative care, creating complex management scenarios that necessitate multidisciplinary clinical care. Specifically, alterations in hemostasis in liver disease can be pronounced and evolve with disease progression over time. Recent studies and society guidance address this emerging paradigm and offer recommendations to assist with hemostatic management in patients with liver disease. However, patients undergoing LT are unique and diverse, often with unstable disease that requires specialized approaches. Our aim is to provide a focused review of hemostatic management of the LT patient, distinguish unique aspects of the three main phases of care (before LT, perioperative, and after LT), and identify knowledge gaps and critical areas of future research.

Long-term liver allograft fibrosis: A review with emphasis on idiopathic post-transplant hepatitis and chronic antibody mediated rejection

Liver transplantation (LT) is a life-saving surgical procedure and the current standard of care for most patients with end stage liver disease. With improvements in organ preservation techniques, perioperative care, and immunosuppression, there is better patient and graft survival following LT, and assessment of the liver allograft in long-term survivors is becoming increasingly important. Recurrent or de novo viral or autoimmune injury remains the most common causes of chronic hepatitis and fibrosis following liver transplantation in adults. However, no obvious cause can be identified in many adults with controlled recurrent disease and the majority of pediatric LT recipients, as they have been transplanted for non-recurrent liver diseases. Serial surveillance liver biopsies post LT have been evaluated in several adult and pediatric centers to identify long-term pathological changes. Pathological findings are frequently present in liver biopsies obtained after a year post LT. The significance of these findings is uncertain as many of these are seen in protocol liver biopsies from patients with clinically good allograft function and normal liver chemistry parameters. This narrative review summaries the factors predisposing to long-term liver allograft fibrosis, highlighting the putative role of idiopathic post-LT hepatitis and chronic antibody mediated rejection in its pathogenesis.

Prediction of Liver Transplant Rejection With a Biologically Relevant Gene Expression Signature

BACKGROUND

Noninvasive biomarkers distinguishing early immune activation before acute rejection (AR) could more objectively inform immunosuppression management in liver transplant recipients (LTRs). We previously reported a genomic profile distinguishing LTR with AR versus stable graft function. This current study includes key phenotypes with other causes of graft dysfunction and uses a novel random forest approach to augment the specificity of predicting and diagnosing AR.

METHODS

Gene expression results in LTRs with AR versus non-AR (combination of other causes of graft dysfunction and normal function) were analyzed from single and multicenter cohorts. A 70:30 approach (61 ARs; 162 non-ARs) was used for training and testing sets. Microarray data were normalized using a LT-specific vector.

RESULTS

Random forest modeling on the training set generated a 59-probe classifier distinguishing AR versus non-AR (area under the curve 0.83; accuracy 0.78, sensitivity 0.70, specificity 0.81, positive predictive value 0.54, negative predictive value [NPV] 0.89; F-score 0.61). Using a locked threshold, the classifier performed well on the testing set (accuracy 0.72, sensitivity 0.67, specificity 0.73, positive predictive value 0.48, NPV 0.86; F-score 0.56). Probability scores increased in samples preceding AR versus non-AR, when liver function tests were normal, and decreased following AR treatment (P < 0.001). Ingenuity pathway analysis of the genes revealed a high percentage related to immune responses and liver injury.

CONCLUSIONS

We have developed a blood-based biologically relevant biomarker that can be detected before AR-associated graft injury distinct from LTR never developing AR. Given its high NPV ("rule out AR"), the biomarker has the potential to inform precision-guided immunosuppression minimization in LTRs.

Infusion of Allogeneic Mesenchymal Stromal Cells After Liver Transplantation: A 5-Year Follow-Up

Various properties of mesenchymal stromal cells (MSCs) might be particularly of interest after liver transplantation (LT). In this article, we report the long-term results of a prospective, controlled, and first-in-human phase 1 study evaluating the safety of a single MSC infusion after LT. A total of 10 LT recipients treated with standard immunosuppression received 1.5 to 3 × 10⁶ /kg third-party unrelated MSCs on postoperative day 3 and were prospectively compared with a control group of 10 LT recipients. Primary endpoints were set to prospectively detect potentially delayed adverse effects of MSC infusion, particularly the occurrence of infections and cancers. Secondary endpoints of liver graft and patient survival, graft rejection and function, occurrence of bile duct complications, and development of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA) against liver or MSC donors were studied. The median follow-up was 85 months. There was no difference in overall rates of infection or cancer at 5 years of follow-up between the 2 groups. There was also no difference in secondary endpoints. The prevalence of de novo liver DSAs related to HLA mismatches was twice as high in the MSC group compared with the control group. All of the de novo class II HLA antibodies against MSCs were linked to a shared HLA mismatch between the liver and MSCs. This study confirms the safety of a single MSC infusion after LT. The potential benefits of MSC injections in the context of organ transplantation have yet to be demonstrated by larger prospective studies. The development of anti-HLA antibodies against an MSC donor should be further evaluated, especially in cases of shared HLA mismatches between graft and MSC donors, despite the fact that no deleterious effect has been detected.

Donor-derived cell-free DNA levels predict graft injury in liver transplant recipients

Donor-derived cell-free DNA (dd-cfDNA) has been evaluated as a rejection marker in organ transplantation. This study sought to assess the utility of dd-cfDNA to diagnose graft injury in liver transplant recipients (LTR) and as a predictive biomarker prior to different causes of graft dysfunction. Plasma from single and multicenter LTR cohorts was analyzed for dd-cfDNA. Phenotypes of treated biopsy-proven acute rejection (AR, N = 57), normal function (TX, N = 94), and acute dysfunction no rejection (ADNR; N = 68) were divided into training and test sets. In the training set, dd-cfDNA was significantly different between AR versus TX (AUC 0.95, 5.3% cutoff) and AR versus ADNR (AUC 0.71, 20.4% cutoff). Using these cutoffs in the test set, the accuracy and NPV were 87% and 100% (AR vs. TX) and 66.7% and 87.8% (AR vs. ADNR). Blood samples collected serially from LTR demonstrated incremental elevations in dd-cfDNA prior to the onset of graft dysfunction (AR > ADNR), but not in TX. Dd-cfDNA also decreased following treatment of rejection. In conclusion, the serial elevation of dd-cfDNA identifies pre-clinical graft injury in the context of normal liver function tests and is greatest in rejection. This biomarker may help detect early signs of graft injury and rejection to inform LTR management strategies.

Crossmatch, Donor-specific Antibody Testing, and Immunosuppression in Simultaneous Liver and Kidney Transplantation: A Review

Since the introduction of simultaneous liver-kidney transplantation (SLKT) in the 1960s, the potential for immunological protection from the liver allograft to a simultaneously transplanted kidney has been recognized. Due to expanded indications and changes in allocation policies, there has been increased utilization of SLKT. Despite growing experience, a lack of consensus exists regarding the extent of the immunological privilege of the liver the role for donor-specific HLA antibody (DSA) and crossmatch testing, and appropriateness of modern immunosuppression protocols in SLKT recipients. This review provides a detailed analysis of SLKT outcomes in the context of these factors, suggesting that although the liver can reduce the incidence of antibody-mediated rejection, attention should be given to liver allograft function, previous failed transplants, and other risk factors in pretransplant risk assessment. Current methods of DSA and crossmatch testing in SLKT are also discussed, and the role of specific DSA (high mean fluorescence intensity antibody, C1q+ binding) and their potential importance in posttransplant risk assessment are examined. Finally, trends in SLKT immunosuppression are discussed, including the use of nondepleting agents for induction and de-escalating use of steroids for maintenance immunosuppression. Ongoing research, including multicenter or randomized trials, will be necessary to optimize immune-related outcomes in SLKT recipients.

Antibody-mediated rejection of the liver allograft: An update and a clinico-pathological perspective

Antibody-mediated rejection after liver transplantation is an under-recognised cause of allograft injury. While definitions of acute and chronic antibody-mediated rejection have increased clinical awareness, timely identification and management of antibody-mediated rejection remain difficult because of complexities in diagnosis and histopathology, lack of treatment protocols, and unclear long-term outcomes. While recent cohort studies assessing the importance of donor-specific antibodies have aided in its diagnosis, literature on the treatment of antibody-mediated rejection in liver transplantation remain limited to case reports and small series. Further increasing the awareness and timely recognition of antibody-mediated rejection post-liver transplantation is crucial in order to stimulate future research and the development of protocols for its diagnosis and treatment. This review will summarise recent advances in the clinical diagnosis and treatment of antibody-mediated rejection in liver transplantation, as well as some of the histopathologic features (on liver biopsy tissue) of acute and chronic antibody-mediated rejection.

Cellular and Molecular Crosstalk of Graft Endothelial Cells During AMR: Effector Functions and Mechanisms

Graft endothelial cell (EC) injury is central to the pathogenesis of antibody-mediated rejection (AMR). The ability of donor-specific antibodies (DSA) to bind C1q and activate the classical complement pathway is an efficient predictor of graft rejection highlighting complement-dependent cytotoxicity as a key process operating during AMR. In the past 5 y, clinical studies further established the cellular and molecular signatures of AMR revealing the key contribution of other, IgG-dependent and -independent, effector mechanisms mediated by infiltrating NK cells and macrophages. Beyond binding to alloantigens, DSA IgG can activate NK cells and mediate antibody-dependent cell cytotoxicity through interacting with Fcγ receptors (FcγRs) such as FcγRIIIa (CD16a). FcRn, a nonconventional FcγR that allows IgG recycling, is highly expressed on ECs and may contribute to the long-term persistence of DSA in blood. Activation of NK cells and macrophages results in the production of proinflammatory cytokines such as TNF and IFNγ that induce transient and reversible changes in the EC phenotype and functions promoting coagulation, inflammation, vascular permeability, leukocyte trafficking. MHC class I mismatch between transplant donor and recipient can create a situation of "missing self" allowing NK cells to kill graft ECs. Depending on the microenvironment, cellular proximity with ECs may participate in macrophage polarization toward an M1 proinflammatory or an M2 phenotype favoring inflammation or vascular repair. Monocytes/macrophages participate in the loss of endothelial specificity in the process of endothelial-to-mesenchymal transition involved in renal and cardiac fibrosis and AMR and may differentiate into ECs enabling vessel and graft (re)-endothelialization.

Immunosuppression in liver and intestinal transplantation

Immunosuppression handling plays a key role in the early and long-term results of transplantation. The development of multiple immunosuppressive drugs led to numerous clincial trials searching to reach the ideal regimen. Due to heterogeneity of the studied patient cohorts and flaws in many, even randomized controlled, study designs, the answer still stands out. Nowadays triple-drug immunosuppression containing a calcineurin inhibitor (preferentially tacrolimus), an antimetabolite (using mycophenolate moffettil or Azathioprine) and short-term steroids with or without induction therapy (using anti-IL2 receptor blocker or anti-lymphocytic serum) is the preferred option in both liver and intestinal transplantation. This chapter aims, based on a critical review of the definitions of rejection, corticoresistant rejection and standard immunosuppression to give some reflections on how to reach an optimal immunosuppressive status and to conduct trials allowing to draw solid conclusions. Endpoints of future trials should not anymore focus on biopsy proven, acute and chronic, rejection but also on graft and patient survival. Correlation between early- and long-term biologic, immunologic and histopathologic findings will be fundamental to reach in much more patients the status of operational tolerance.

Anorectal emergencies: WSES-AAST guidelines

Anorectal emergencies comprise a wide variety of diseases that share common symptoms, i.e., anorectal pain or bleeding and might require immediate management. While most of the underlying conditions do not need inpatient management, some of them could be life-threatening and need prompt recognition and treatment. It is well known that an incorrect diagnosis is frequent for anorectal diseases and that a delayed diagnosis is related to an impaired outcome. This paper aims to improve the knowledge and the awareness on this specific topic and to provide a useful tool for every physician dealing with anorectal emergencies.The present guidelines have been developed according to the GRADE methodology. To create these guidelines, a panel of experts was designed and charged by the boards of the World Society of Emergency Surgery (WSES) and American Association for the Surgery of Trauma (AAST) to perform a systematic review of the available literature and to provide evidence-based statements with immediate practical application. All the statements were presented and discussed during the WSES-AAST-WJES Consensus Conference on Anorectal Emergencies, and for each statement, a consensus among the WSES-AAST panel of experts was reached. We structured our work into seven main topics to cover the entire management of patients with anorectal emergencies and to provide an up-to-date, easy-to-use tool that can help physicians and surgeons during the decision-making process.

Epitope-Level Matching—A Review of the Novel Concept of Eplets in Transplant Histocompatibility

The development of de novo donor-specific antibodies is related to the poor matching of the human leukocyte antigen (HLA) between donor and recipient, which leads to dismal clinical outcomes and graft loss. However, new approaches that stratify the risks of long-term graft failure in solid organ transplantation have emerged, changing the paradigm of HLA compatibility. In addition, advances in software development have given rise to a new structurally based algorithm known as HLA Matchmaker, which determines compatibility at the epitope rather than the antigen level. Although this technique still has limitations, plenty of research maintains that this assessment represents a more complete and detailed definition of HLA compatibility. This review summarizes recent aspects of eplet mismatches, highlighting the most recent advances and future research directions.

Rituximab Desensitization in Liver Transplant Recipients With Preformed Donor-specific HLA Antibodies: A Japanese Nationwide Survey

Background.

The significance of preformed donor-specific anti-HLA antibodies (DSAs) in liver transplant recipients is controversial. Moreover, there has been no established desensitization protocol for DSA-positive recipients.

Methods.

A Japanese nationwide survey was performed to investigate the clinical practice among preformed DSA-positive patients with special reference to rituximab desensitization.

Results.

There was a total of 47 cases, including 2 pediatric cases, in which rituximab (287 ± 159 mg [319 (50–916)/m²]) was administered to desensitize preformed DSA. The decision for the indication of rituximab desensitization was based on a single-antigen assay in the majority of cases (83%, 39/47), and the most frequent protocol was rituximab monotherapy (n = 12) followed by quadruple treatment with rituximab tacrolimus, mycophenolate mofetil, and plasmapheresis (n = 11). The overall 1-, 3-, and 5-y graft and patient survival rates among adult patients were 85%, 83%, 83%, and 81%, 77%, 74%, respectively, while neither graft loss nor death was observed in the 2 pediatric cases. The 1-, 3-, and 12-mo cumulative incidence of antibody-mediated rejection (AMR) was 11%, 13%, and 13%, respectively. The incidence of AMR was significantly higher in the lower rituximab dose group than in the higher rituximab dose group (cutoff 300 mg/m², 4% versus 24%, P = 0.041). The rate of infusion-related adverse drug reactions (ADRs) was 4.4%, and all ADRs were mild and self-limiting. A total of 99 ADRs among 27 patients were reported, none of which were severe adverse events associated with rituximab.

Conclusions.

The rituximab induction was well tolerated among DSA-positive liver transplant recipients with a satisfactory outcome. A rituximab dose >300 mg/m² was observed to achieve less incidence of the development of AMR.

Impact of donor-specific antibodies on long-term graft survival with pediatric liver transplantation

BACKGROUND

In a previous paper, we reported a high prevalence of donor-specific antibody (DSA) in pediatric patients with chronic rejection and expressed the need for confirmation of these findings in a larger cohort.

AIM

To clarify the importance of DSAs on long-term graft survival in a larger cohort of pediatric patients.

METHODS

We performed a retrospective analysis of 123 pediatric liver transplantation (LT) recipients who participated in yearly follow-ups including Luminex testing for DSA at our center. The cohort was split into two groups according to the DSA status (DSA-positive n = 54, DSA-negative n = 69). Groups were compared with regard to liver function, biopsy findings, graft survival, need for re-LT and immunosuppressive medication.

RESULTS

DSA-positive pediatric patients showed a higher prevalence of chronic rejection (P = 0.01), fibrosis (P < 0.001) and re-transplantation (P = 0.018) than DSA-negative patients. Class II DSAs particularly influenced graft survival. Alleles DQ2, DQ7, DQ8 and DQ9 might serve as indicators for the risk of chronic rejection and/or allograft fibrosis. Mean fluorescence intensity levels and DSA number did not impact graft survival. Previous episodes of chronic rejection might lead to DSA development.

CONCLUSION

DSA prevalence significantly affected long-term liver allograft performance and liver allograft survival in our cohort of pediatric LT. Screening for class II DSAs in combination with assessment of protocol liver biopsies for chronic antibody-mediated rejection improved early identification of patients at risk of graft loss.

Current Evidence on the Clinical Relevance of Donor-specific Antibodies in Paediatric Liver Transplantation

ABSTRACT

The clinical impact of donor-specific antibodies (DSA) occurring before or after liver transplantation (LT) against donor-human leucocyte antigen (HLA) on graft outcome is still unclear. We aim to present the current consensus based on recent paediatric LT case series. Compared to kidney transplantation, the liver seems to be less susceptible to antibody-mediated graft damage, which is likely due to protective Kupffer cell activity. The incidence of DSA after liver transplantation is higher in children than in adults. DSA directed against HLA class II molecules, mainly DQ, occur more often. The presence of such anti-class II DSA (DQ/DR), especially of the complement-binding IgG3 subclass, may be associated with endothelial injury, T-cell-mediated rejection (TCMR), inflammation, and fibrosis. Regular DSA-posttransplant monitoring cannot as yet be recommended in routine practice but may be useful in selected cases.

Measuring human leukocyte antigen alloantibodies: beyond a binary decision

PURPOSE OF REVIEW

Accurate measurement of human leukocyte antigen antibodies is critical for making clinical decisions treating patients awaiting transplantation or monitoring them post transplantation. Single antigen bead assay results are given as Mean Fluorescence Intensity, falling short of providing the required quantitative measure.

RECENT FINDINGS

Titration studies were shown to circumvent the limitation of target-saturation that affect interpretation of single antigen bead assays especially in highly sensitized patients with strong antibodies. In fact, titration information can serve to measure efficacy of antibody removal during pretransplant desensitization using plasmapheresis/intravenous immunoglobulin (PP/IVIg) approaches. Moreover, recent studies indicate that knowing the donor-specific antibody titer has prognostic value that can guide PP/IVIg desensitization treatments. Newer data demonstrates an additional layer of information obtained by titration studies allowing to stratify patients with very high cPRA (>99%) based on the strength of the antibodies present, rather than the breadth. This data can thereby identify patients that are more likely to benefit from desensitization approaches on the transplant wait-list.

SUMMARY

Titration studies have a prognostic value with regards to quantifying antibody strength. Obtaining this information does not require performing the complete set of dilutions. In fact, performing two to three specific dilutions can provide relevant information while maintaining practical cost.

Presence of donor specific HLA class 2 antibodies (DSA class 2) is associated with development of graft fibrosis more than 10 years after liver transplantation-a retrospective single center study

Here the impact of donor specific human leukocyte antigen (HLA) class 2 antibodies (DSA cl 2) on long term outcome after liver transplantation (LT) was investigated. Altogether 156 (44 pediatric and 112 adult) LT recipients were included in the study. Graft fibrosis was assessed by liver elastography and biopsy. DSA cl 2 were determined by Luminex technology. 46% of LT recipients were positive for DSA cl 2 after a median follow-up of 15 years. In the multivariate analysis DSA cl 2 were significantly associated with immunosuppressive monotherapy (OR 5.42; 95% CI: 1.02-28.90; p = .048). Compared to DSA cl 2 negative patients, positive recipients had significantly more graft fibrosis based on the liver stiffness (mean 9.4 ± 9.0 kPa vs. 6.5 ± 6.3 kPa; p < .002) and fibrosis stages determined by liver elastography (p = .016) and the performed liver biopsies (p = .002). Also, a significantly higher incidence of chronic rejections (11% vs. 2%; p = .045) and graft losses (6% vs. 0%; p = .043) were found. In the multivariate regression analysis DSA cl 2 were significantly associated with graft fibrosis (OR 4.57; 95% CI 1.59-13.10; p = .005). So, these data suggest that development of DSA cl 2 occurs more often with immunosuppressive monotherapy and may ultimately result in chronic rejection and graft fibrosis.

Impact of human leukocyte antigen compatibility on outcomes of living donor liver transplantation: Experience from a tertiary care center

INTRODUCTION

The role of HLA compatibility in kidney, heart, and stem cell transplantation is well known, but with regard to living donor liver transplantation (LDLT), there is a different scenario. In the present study, we aim to examine the effects of donor-recipient HLA mismatches at A, B, and DR loci on various outcomes of LDLT-like graft survival, early allograft dysfunction (EAD), acute rejection, length of hospital (LOH) stay, sepsis, and cytomegalovirus (CMV) reactivation.

METHODS

This is a retrospective single center study of a cohort of adult patients who underwent first time ABO-compatible (ABOc) LDLT between January 2010 and December 2018. Transplants with incomplete records or without HLA typing data were excluded. Donor-recipient HLA-A, B, and DR mismatches were assessed in the host versus graft (HVG) direction and were correlated with various post-transplant outcomes.

RESULTS

Among 140 transplants being evaluated, approximately two third had total HLA mismatches between 2 and 3. HLA mismatches at each locus as well as cumulative HLA mismatches did not show any association with overall graft survival, EAD, acute rejection episodes, and LOH stay. However, the presence of minimum one mismatch at HLA-A and DR loci was associated with the development of CMV reactivation (P = .03) and sepsis (P = .02) post-LDLT respectively.

CONCLUSION

HLA mismatch is not associated with acute rejection, early graft dysfunction, and overall survival in LDLT. Its impact on CMV reactivation and sepsis needs further evaluation.

Immunosuppression Free Protocol for Liver Transplant from an Identical Twin Mimicking Positive Donor-Specific Antibodies: A Case Report

There are some reported cases of liver transplant between identical twins with no immunosuppressants because of their matched HLA. However, there is no mention of donor-specific antibodies (DSA). Here, we report a rare case of living donor liver transplant (LDLT) between identical twins, mimicking DSA positivity, on a low-dose immunosuppression protocol. A 57-year-old man with acute liver failure underwent LDLT using the right lobe from his identical twin. Their blood types were identical on HLA matching. However, the preoperative DSA test results were positive for class II antibodies. This was supposed to be due to the relatively large amount of blood transfusion before testing: a total of 580 units of fresh frozen plasma for plasma exchange. The presence of class II antibodies for DSA positivity was the result of the passive immunity from transfusion, and this result could not be ignored, given the risk of rejection. Therefore, we arranged low-dose postoperative immunosuppressants using tacrolimus at a quarter dose and no mycophenolate mofetil. The postoperative course was uneventful. A few months after LDLT, the patient's DSA level was negative for class II antibodies, thus confirming our preoperative hypothesis of DSA as the result of transfusion. Currently, 6 months after LDLT, he is free from immunosuppressive medication with good liver function. When administering relatively large doses of fresh frozen plasma by repeated plasma exchange before LDLT, even between identical twins, it is important to consider that the DSA test could be positive and that immunosuppressive treatment should be performed carefully.

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

BACKGROUND AND AIMS

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

APPROACH AND RESULTS

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

CONCLUSIONS

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

Implication of TIGIT+ human memory B cells in immune regulation

Regulatory B cells (Bregs) contribute to immune regulation. However, the mechanisms of action of Bregs remain elusive. Here, we report that T cell immunoreceptor with Ig and ITIM domains (TIGIT) expressed on human memory B cells especially CD19⁺CD24^hiCD27⁺CD39^hiIgD^-IgM⁺CD1c⁺ B cells is essential for effective immune regulation. Mechanistically, TIGIT on memory B cells controls immune response by directly acting on T cells and by arresting proinflammatory function of dendritic cells, resulting in the suppression of Th1, Th2, Th17, and CXCR5⁺ICOS⁺ T cell response while promoting immune regulatory function of T cells. TIGIT⁺ memory B cells are also superior to other B cells at expressing additional inhibitory molecules, including IL-10, TGFβ1, granzyme B, PD-L1, CD39/CD73, and TIM-1. Lack or decrease of TIGIT⁺ memory B cells is associated with increased donor-specific antibody and TFH response, and decreased Treg response in renal and liver allograft patients. Therefore, TIGIT⁺ human memory B cells play critical roles in immune regulation.

Strategies for Liver Transplantation Tolerance

Liver transplant (LT) recipients require life-long immunosuppression (IS) therapy to preserve allograft function. The risks of chronic IS include an increased frequency of malignancy, infection, renal impairment, and other systemic toxicities. Despite advances in IS, long-term LT outcomes have not been improved over the past three decades. Standard-of-care (SoC) therapy can, in rare cases, lead to development of operational tolerance that permits safe withdrawal of maintenance IS. However, successful IS withdrawal cannot be reliably predicted and, in current prospective studies, is attempted several years after the transplant procedure, after considerable exposure to the cumulative burden of maintenance therapy. A recent pilot clinical trial in liver tolerance induction demonstrated that peri-transplant immunomodulation, using a regulatory T-cell (Treg) approach, can reduce donor-specific alloreactivity and allow early IS withdrawal. Herein we review protocols for active tolerance induction in liver transplantation, with a focus on identifying tolerogenic cell populations, as well as barriers to tolerance. In addition, we propose the use of novel IS agents to promote immunomodulatory mechanisms favoring tolerance. With numerous IS withdrawal trials underway, improved monitoring and use of novel immunomodulatory strategies will help provide the necessary knowledge to establish an active liver tolerance induction protocol for widespread use.

Donor-specific antibody and sensitized patients in intestinal transplantation

PURPOSE OF REVIEW

It has been well established that antibody to donor HLA pretransplant and the development of anti-human leukocyte antigen (HLA) antibodies posttransplant contribute to inferior graft survival outcomes. This article serves to review the current status of the management of pretransplant sensitized intestinal transplant candidate as well as to review posttransplant care of patients that harbor antidonor HLA antibodies.

RECENT FINDINGS

The intestinal transplant candidate oftentimes presents for transplant listing with high levels of anti-HLA antibodies that necessitate a careful preoperative strategy to avoid a donor-recipient pair that would result in a positive crossmatch. In the end, donor intestine offer acceptance is based on a balance between recipient clinical needs and allowable immunologic risk tolerance. The use of virtual crossmatching (VXM) enables the transplant center to effectively gauge the immunologic risk of each potential donor-recipient pair far in advance of allocating resources toward pursuing a donor organ. In those candidates with high levels of preformed donor anti-HLA antibodies, desensitization with a novel technique of donor splenic perfusion has been described as well as a single-center experience with a conventional desensitizing protocol. Posttransplant, with the use of a denovo donor-specific antibody (dnDSA) monitoring and treatment protocol, the well known deleterious effects of dnDSA can potentially be ameliorated, thus improving outcome. Efforts to establish a formal histologic criteria for antibody-mediated rejection (ABMR) in the intestinal graft continues to evolve with recent findings describing the relationship between DSA and histopathologic findings.

SUMMARY

Techniques such as the use of VXM, novel desensitization methods and protocols, monitoring and eradicating dnDSA, along with establishing new criteria for ABMR have all contributed to improving the outcomes in transplanting the immunologically challenging intestine.

Evaluation of Graft Fibrosis, Inflammation and Donor-specific Antibodies at Protocol Liver Biopsies in Pediatric Liver Transplant Patients: a Single Center Experience

BACKGROUND

The impact of graft fibrosis and inflammation on the natural history of pediatric liver transplants (LT) is still debated. Our objectives were to evaluate the evolution of posttransplant fibrosis and inflammation over time at protocol liver biopsies (PLBs), risk factors for fibrosis, presence of donor-specific antibodies (DSAs) and/or their correlation with graft and recipient factors.

METHODS

A single-center, retrospective (2000-2019) cross-sectional study on pediatric LT recipients who had at least one PLB, followed by a longitudinal evaluation in those who had at least two PLBs, was conducted. Fibrosis was assessed by the Liver Allograft Fibrosis Semiquantitative score, inflammation by the Rejection Activity Index, DSAs by Luminex®.

RESULTS

A total of 134 PLBs from 94 patients were included. Fibrosis was detected in 87% (30% mild, 45% moderate, 12% severe), 80% in the portal tracts. There was an increase in fibrosis between the 1-3 and the 4-6 year group (p=0.01), then it was stable. Inflammation was observed in 44% (30% mild, 13% moderate, 1% severe), 90% in the portal tracts. Anti-HLA II (IgG) DSAs were detected in 14/40 (35%). Portal fibrosis was associated with portal inflammation in the 1-3 year group (p=0.04). Low immunosuppression levels were correlated with sinusoidal fibrosis (p=0.04) and DSA positivity (p-value=0.006). There was no statistically significant correlation between DSA positivity and the presence of graft fibrosis or inflammation.

CONCLUSIONS

This study corroborates the concept of an early evolution of silent graft fibrosis. Suboptimal immunosuppression may play a role in the development of fibrosis and DSAs.

De Novo Donor Specific Antibody and Long-Term Outcome After Liver Transplantation: A Systematic Review and Meta-Analysis

Background

The impact of de novo anti-HLA donor-specific alloantibodies (DSA) which develop after long-term liver transplantation (LT) remains controversial and unclear. The aim of this study was to investigate the role of de novo DSAs on the outcome in LT.

Methods

We did a systematic review and meta-analysis of observational studies published until Dec 31, 2019, that reported de novo DSA outcome data (≥1 year of follow-up) after liver transplant. A literature search in the MEDLINE/PubMed, EMBASE, Cochrane Library, Scopus and Web of Science Core Collection databases was performed.

Results

Of 5,325 studies identified, 15 fulfilled our inclusion criteria. The studies which reported 2016 liver transplant recipients with de novo DSAs showed an increased complication risk, i.e. graft loss and chronic rejection (OR 3.61; 95% CI 1.94-6.71, P < 0.001; I2 58.19%), and allograft rejection alone (OR 6.43; 95% CI: 3.17-13.04; P < 0.001; I2 49.77%); they were compared to patients without de novo DSAs. The association between de novo DSAs and overall outcome failure was consistent across all subgroups and sensitivity analysis.

Conclusions

Our study suggested that de novo DSAs had a significant deleterious impact on the liver transplant risk of rejection. The routine detection of de novo DSAs may be beneficial as noninvasive biomarker-guided risk stratification.

Treatment of Anti-HLA Donor-Specific Antibodies Results in Increased Infectious Complications and Impairs Survival after Liver Transplantation

Donor-specific anti-human leukocyte antigen antibodies (DSA) are controversially discussed in the context of liver transplantation (LT). We investigated the relationship between the presence of DSA and the outcome after LT. All the LTs performed at our center between 1 January 2008 and 31 December 2015 were examined. Recipients < 18 years, living donor-, combined, high-urgency-, and re-transplantations were excluded. Out of 510 LTs, 113 DSA-positive cases were propensity score-matched with DSA-negative cases based on the components of the Balance of Risk score. One-, three-, and five-year survival after LT were 74.3% in DSA-positive vs. 84.8% (p = 0.053) in DSA-negative recipients, 71.8% vs. 71.5% (p = 0.821), and 69.3% vs. 64.9% (p = 0.818), respectively. Rejection therapy was more often applied to DSA-positive recipients (n = 77 (68.1%) vs. 37 (32.7%) in the control group, p < 0.001). At one year after LT, 9.7% of DSA-positive patients died due to sepsis compared to 1.8% in the DSA-negative group (p = 0.046). The remaining causes of death were comparable in both groups (cardiovascular 6.2% vs. 8.0%; p = 0.692; hepatic 3.5% vs. 2.7%, p = 0.788; malignancy 3.5% vs. 2.7%, p = 0.788). DSA seem to have an indirect effect on the outcome of adult LTs, impacting decision-making in post-transplant immunosuppression and rejection therapies and ultimately increasing mortality due to infectious complications.

Methods to Detect MHC-Specific IgE in Mice and Men

Humoral immunity is a major barrier limiting long-term outcome after organ transplantation. Especially, the production of antibodies directed against donor HLA/MHC antigens (i.e. donor-specific antibodies (DSA)) leading to antibody-mediated rejection (ABMR) is considered to be a major factor negatively affecting allograft survival. DSAs of the IgG isotype are routinely measured in transplant patients. However, not all patients diagnosed with IgG-DSA develop ABMR events. Therefore, research in better understanding the mechanisms of ABMR is of great importance. We recently demonstrated the production of MHC-specific IgE upon allograft rejection in mice and in transplant patients. IgE is classically connected with allergy and is known to be important for the humoral defense against helminths and worms. However, its role in autoimmune diseases and cancer has been reported recently as well. The concentration of IgE in blood is extremely low compared to other antibody isotypes. Therefore, detection of MHC-specific IgE from serum requires methods of high sensitivity. Since MHC-specific IgG-typically present at much higher serum levels-develops as well, high specificity is also required of IgE detection methods. In the murine model we developed an enzyme linked immunosorbent assay (ELISA) using MHC monomers for measurement of MHC-specific IgE, allowing us to distinguish between specificities of antibodies against different class I and class II antigens. For measurement of functional activity of MHC-specific IgE in vitro, a release assay using a rat basophil cell line (RBL-2H3) was established. For functional analysis of MHC-specific IgE in vivo, a cutaneous hypersensitivity reaction assay was adapted for this purpose using MHC monomers. Humanized RBL-2H3 cells transfected with cDNA coding for the human-high affinity IgE receptor were used for functionality measurement of donor-specific IgE in sensitized transplant patients. For detection of HLA-specific IgE, a bead assay was adapted, using beads expressing single HLA antigens. The aim of this publication is to demonstrate currently established methods for the detection and characterization of MHC-specific IgE in the murine and human setting.

Suppression of liver transplant rejection by anti-donor MHC antibodies via depletion of donor immunogenic dendritic cells

BACKGROUND

We previously found two distinct passenger dendritic cell (DC) subsets in the rat liver that played a central role in the liver transplant rejection. In addition, a tolerance-inducing protocol, donor-specific transfusion (DST), triggered systemic polytopical production of depleting alloantibodies to donor class I MHC (MHCI) antigen (DST-antibodies).

METHODS

We examined the role of DST-antibodies in the trafficking of graft DC subsets and the alloresponses in a rat model. We also examined an anti-donor class II MHC (MHCII) antibody that recognizes donor DCs more selectively.

RESULTS

Preoperative transfer of DST-antibodies or DST pretreatment eliminated all passenger leukocytes, including both DC subsets and depleted the sessile DCs in the graft to ~20% of control. The CD172a+CD11b/c+ immunogenic subset was almost abolished. The intrahost direct or semi-direct allorecognition pathway was successfully blocked, leading to a significant suppression of the CD8+ T-cell response in the recipient lymphoid organs and the graft with delayed graft rejection. Anti-donor MHCII antibody had similar effects without temporary graft damage. Although DST pretreatment had a priming effect on the proliferative response of recipient regulatory T cells, DST-primed sera and the anti-donor MHCII antibody did not.

CONCLUSION

DST-antibodies and anti-donor MHCII antibodies could suppress the CD8+ T-cell-mediated liver transplant rejection by depleting donor immunogenic DCs, blocking the direct or semi-direct pathways of allorecognition. Donor MHCII-specific antibodies may be applicable as a selective suppressant of anti-donor immunity for clinical liver transplantation without the cellular damage of donor MHCII- graft cells and recipient cells.

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.

Immune and gene expression profiling during tacrolimus to everolimus conversion early after liver transplantation

Early elimination of tacrolimus in favor of everolimus can improve renal function in liver transplant recipients. However, as this approach increases the risk of acute rejection, it may benefit from predictive biomarkers guiding weaning. We enrolled 20 recipients on stable tacrolimus + everolimus to undergo tacrolimus withdrawal early post-liver transplant. Blood samples were collected at month 3 (withdrawal initiation), 4 (withdrawal completion), 4.5 and 6 (both everolimus alone). 15 patients did not reject and 5 had mild rejection responding to tacrolimus resumption. Before tacrolimus withdrawal, eventual rejecters had higher percentages of CD56⁺ NK cells and CD19⁺CD27⁺CD24⁺ memory B cells, and lower levels of T cells expressing the exhaustion marker PD-1. Over time, memory B cells, Ki-67⁺CD3⁺ (proliferating) cells and CD4⁺CD127^-CD25^HIGH FOXP3⁺ Tregs increased in rejecters. Tregs also increased in non-rejecters over time. The number of differentially expressed genes progressively increased in rejecters, particularly in mTOR, Eukaryotic Initiation Factor 2, and Neuroinflammation signaling pathways. There was no difference in anti-HLA antibodies between the groups. In summary, blood mononuclear cell and gene expression may predict successful vs. failed early tacrolimus withdrawal in liver transplant recipients. While needing validation, these preliminary findings highlight the potential for cellular and molecular biomarkers to guide decision-making during tacrolimus weaning.

De novo HLA Class II antibodies are associated with the development of chronic but not acute antibody-mediated rejection after liver transplantation - a retrospective study

Donor-specific antibodies (DSA) cause antibody-mediated rejection (AMR); however, their pathogenic role has not yet been adequately investigated after liver transplantation. The aim of our study was to analyse the clinical significance of DSA and complement-binding DSA for the prediction of AMR after liver transplantation. Our cohort included 120 liver recipients with assessed protocol biopsies one year post-transplant. All patients had defined HLA-specific and complement-binding (C1q + and C3d+) antibodies before and in regular intervals after transplantation. The incidence of DSA was evaluated in relation with clinical and histopathological data in the liver allografts. A higher occurrence of acute AMR was observed in recipients with preformed complement-binding DSA to HLA Class I antigens. Patients who developed chronic AMR had more frequently de novo-produced antibodies against HLA Class II antigens (P = 0.0002). A correlation was also found between de novo-formed C1q + and C3d+-binding antibodies to HLA Class II antigens and the development of chronic AMR (P = 0.043). Our study implies that preformed complement-binding DSA to HLA Class I antigens are related to increased risk of acute antibody-mediated rejection, while chronic AMR is more frequent in patients with de novo-produced antibodies to HLA Class II antigens after liver transplantation.

[Liver transplantation. Current aspects of pretransplantation diagnosis and rejection]

Liver transplantation is an established treatment option for patients with end-stage liver disease. The therapy management of these patients is interdisciplinary and requires pathologists to have both clinical and immunological knowledge. Continuous advances in treatment and increasing clinical experience are accompanied by the further development of pathological transplant diagnostics. This article presents and discusses the latest classification of T‑cell-mediated rejection (TCMR), antibody-mediated rejection (AMR), and aspects of pretransplant diagnostics.

Peripheral Donor-specific Antibodies Are Associated With Histology and Cellular Subtypes in Protocol Liver Biopsies of Pediatric Recipients

BACKGROUND

The cellular infiltrate in protocol liver biopsies (PB) following pediatric liver transplantation remains mostly uncharacterized, yet there is increasing concern about the role of inflammation and fibrosis in long-term liver allografts. We aimed to define cell types in PB and to analyze their relationship with donor-specific antibodies (DSA) and histological phenotype.

METHODS

PB were performed at least 1 year after transplantation. We identified 4 phenotypes: normal, fibrosis, inflammation, inflammation with fibrosis. Cell types were counted after immunostaining for CD3, CD4, CD8, CD68, CD20, MUM1, and FoxP3.

RESULTS

Forty-four patients underwent 1 PB between 2000 and 2015. Eleven percent (5/44) of PB displayed normal histology, 13.6% (6/44) fibrosis, 34.1% (15/44) inflammation, and 40.9% (18/44) inflammation and fibrosis. The main cell types in the portal tracts and lobules were CD3+ and CD68+ cells. Frequency of de novo DSA was 63% (27/44). The presence of CD8+ cells in the lobules was associated with fibrosis. Inflammation and fibrosis in PB were associated with the presence of circulating de novo DSA, number of de novo DSA, and C1q binding activity when compared to other phenotypes.

CONCLUSIONS

T cells (CD3+) and macrophages (CD68+) were the most prevalent cell-types in PB. In the presence of inflammation, portal tracts were enriched in CD3+, CD20+ but displayed fewer CD68+. This coincided with the presence and number of de novo DSA. How these cellular and humoral actors interact is unclear, but peripheral DSA may be a marker of immune cellular activity in the seemingly quiescent allograft.

Enhancing the Value of Histopathological Assessment of Allograft Biopsy Monitoring

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

Influence of Preformed Antibodies in Liver Transplantation

The significance of human leukocyte antigen (HLA) matching and preformed donor-specific antibodies (DSAs) in liver transplantation remains unclear. The aim of this study was to analyze the presence of DSAs in a large cohort of 810 liver recipients undergoing liver transplant to determine the influence on acute (AR) or chronic liver rejection (CR), graft loss and allograft survival. DSAs were identified using complement dependent cytotoxicity crossmatch (CDC-CM) and multiplexed solid-phase-based flow cytometry assay (Luminex). CDC-CM showed that a 3.2% of liver transplants were positive (+CDC-CM) with an AR frequency of 19.2% which was not different from that observed in negative patients (-CDC-CM, 22.3%). Only two patients transplanted with +CDC-CM (7.6%) developed CR and suffered re-transplant. +CDC-CM patients showed a significantly lower survival rate compared to -CDC-CM patients (23.1% vs. 59.1%, p = 0.0003), developing allograft failure within the first three months (p < 0.00001). In conclusion, we have demonstrated a relationship between the presence of preformed DSAs and the low graft liver survival, indicating the important role and the potential interest of performing this analysis before liver transplantation. Our results could help to detect patients with an increased risk of graft loss, a better choice of liver receptors as well as the establishment of individualized immunosuppressive regimens.