The significance of donor-specific HLA antibodies in rejection and ductopenia development in ABO compatible liver transplantation

The fate of anti-HLA antibodies following liver transplantation

Introduction

Liver transplant recipients may have pre-formed anti-HLA antibodies directed to mismatched HLA of the liver donor (donor specific antibodies, DSA) or not directed to the liver donor (non-donor specific, non-DSA). We observed the fate of these antibodies (DSA and non-DSA) at 12 months after transplant.

Methods

Patients transplanted between 4/2015 and 12/2018 (N = 216) who had anti-HLA antibody measurements at both transplant and 12 months posttransplant (N = 124) and with DSAs at transplant (N = 31) were considered informative for a paired analysis of the natural history of DSA and non-DSA following liver transplantation.

Results

Class I DSAs and non-DSAs decreased between transplant and 12 months; however, Class I DSAs essentially disappeared by 12 months while Class I non-DSAs did not. Anti-HLA Class II DSAs performed differently. While there was a significant drop in values between transplant and 12 months, these antibodies mostly persisted at a low level.

Discussion

Our study demonstrated a significant difference in the kinetics of DSA compared to non-DSA following liver transplantation, most profoundly for anti-HLA Class I antibodies. Class I DSAs were mostly absent at 12 months while Class II DSAs persisted, although at lower levels. The mechanisms of reduction in anti-HLA antibodies following liver transplantation are not completely understood and were not pursued as a part of this study. This detailed analysis of Class I and Class II DSAs and non-DSAs represents and important study to explore the change in antibodies at one year from liver transplantation.

Liver graft injury caused by de novo donor-specific HLA antibodies in pediatric liver transplant recipients with low, moderate, and high immunologic risk

BACKGROUND

This study investigated the association between different risk levels of de novo donor-specific anti-human leukocyte antigen antibodies (dnDSAs) and liver graft injury after liver transplantation in pediatric patients.

METHODS

This retrospective cohort study enrolled 130 patients after liver transplantation. Subjects were divided into the following 4 groups according to the mean fluorescence intensity (MFI) of dnDSAs: high risk group(MFI ≥10,000), medium risk group(4000 ≤ MFI <10,000), low risk group(500 ≤ MFI <4000), and negative group(<500). Liver function indices were examined along with liver puncture biopsy，and the relationship between dnDSA risk level and liver injury after transplantation was assessed.

RESULTS

Pediatric liver transplant recipients showed significant differences in liver function (ALT, AST, GGT and Bilirubin) according to dnDSA risk level (P < 0.05), and no differences in cumulative incidences of rejection (P = 0.413) and liver fibrosis (P = 0.978) were observed among the number of dnDSAs group. There were differences in the cumulative incidences of antibody-mediated rejection (AMR) (P = 0.001) and T cell-mediated rejection （TCMR） (P = 0.003) across risk groups. The cumulative incidences of TCMR and liver fibrosis (P = 0.0001) were higher in the low-risk group than in the other 3 groups. There were no differences in graft survival rate (P = 0.846) across risk groups.

CONCLUSION

DnDSAs in pediatric liver transplant recipients are associated with liver transplant rejection and fibrosis. The level of dnDSAs in low risk group should not be disregarded. Routine detection of dnDSAs has clinical utility for noninvasive risk stratification in this population.

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.

Liver Transplantation in Recipients With a Positive Crossmatch: A Retrospective Single-Center Match-Pair Analysis

A positive crossmatch (XM+) is considered a contraindication to solid abdominal organ transplantation except liver transplantation (LT). Conflicting reports exist regarding the effects of XM+ on post-transplant outcomes. The goal of this retrospective single-center analysis is to evaluate the influence of XM+ on relevant outcome parameters such as survival, graft rejection, biliary and arterial complications. Forty-nine adult patients undergoing LT with a XM+ between 2002 and 2017 were included. XM+ LT recipients were matched 1:2 with crossmatch negative (XM-) LT recipients based on the balance of risk (BAR) score. Patient and graft survival were compared using Kaplan-Meier survival analysis and the log-rank test. Comparative analysis of clinical outcomes in XM+ and XM- groups were conducted. Patient and graft survival were similar in XM+ and XM- patients. Rejection episodes did not differ either. Recipients with a strong XM+ were more likely to develop a PCR+ CMV infection. A XM+ was not associated with a higher incidence of biliary or arterial complications. Donor age, cold ischemia time, PCR+ CMV infection and a rejection episode were associated with the occurrence of ischemic type biliary lesions. A XM+ has no effects on patient and graft survival or other relevant outcome parameters following LT.

Liver Transplantation from a Human Leukocyte Antigen-Matched Sibling Donor: Effectiveness of Direct-Acting Antiviral Therapy against Hepatitis C Virus Infection

Through living-donor liver transplantation (LDLT) from a human leukocyte antigen (HLA)-matched sibling donor, it may be possible to stop the use of immunosuppressants. It is possible that acute antibody-mediated rejection and chronic active antibody-mediated rejection through the positivity of donor-specific anti-HLA antibodies and/or T cell-mediated rejection may affect the prognosis of liver transplantation. The etiologies of liver diseases of the recipient may also affect the post-transplantation course. Herein, we report on the successful re-treatment with direct-acting antiviral (DAA) therapy against hepatitis C virus (HCV) infection in a patient who underwent a LDLT from HLA-matched sibling donor. After liver transplantation for HCV-related liver diseases, it is easy for HCV to re-infect the graft liver under a lack of immunosuppressants. DAA therapy against HCV re-infection immediately after transplantation should be commenced, and it is important to eradicate HCV for better prognosis of the recipients in LDLT for HCV-related liver diseases.

Immunology of simultaneous liver and kidney transplants with identification and prevention of rejection

Simultaneous liver and kidney (SLK) transplantation is considered the best treatment modality among selected patients with both chronic kidney disease (CKD) and end-stage liver disease (ESLD). Since the first SLK transplant in 1983, the number of SLK transplants has increased worldwide, and particularly in the United States since the implementation of the MELD system in 2002. SLK transplants are considered a relatively low immunological risk procedure evidenced by multiple studies displaying the immunomodulatory properties of the liver on the immune system of SLK recipients. SLK recipients demonstrate lower rates of both cellular and antibody-mediated rejection on the kidney allograft when compared to kidney transplant-alone recipients. Therefore, SLK transplants in the setting of preformed donor-specific HLA antibodies (DSA) are a common practice, at many centers. Acceptance and transplantation of SLKs are based solely on ABO compatibility without much consideration of crossmatch results or DSA levels. However, some studies suggest an increased risk for rejection for SLK recipients transplanted across high levels of pre-formed HLA DSA. Despite this, there is no consensus regarding acceptable levels of pre-formed DSA, the role of pre-transplant desensitization, splenectomy, or immunosuppressive management in this unique population. Also, the impact of post-transplant DSA monitoring on long-term outcomes is not well-studied in SLK recipients. In this article, we review recent and relevant past articles in this field with a focus on the immunological risk factors among SLK recipients, and strategies to mitigate the negative outcomes among them.

The New Challenge in Pediatric Liver Transplantation: Chronic Antibody-Mediated Rejection

Antibody-mediated rejection (AMR) of liver allograft transplantation was considered as anecdotal for many decades. However recently, AMR has gained clinical awareness as a potential cause of chronic liver injury, leading to liver allograft fibrosis and eventual graft failure. (1) Methods: Literature on chronic AMR (cAMR) in pediatric post-liver transplant patients was reviewed for epidemiologic data, physiopathology, diagnosis, and treatment approaches. (2) Results: Accurate incidence of cAMR in pediatric liver transplantation remains unknown. Diagnostic criteria of cAMR were suggested by the Banff Working Group in 2016 and are based on standardized histopathological findings, C4d staining pattern, associated with the presence of donor-specific antibodies (DSA). Physio-pathological mechanisms are not clear for the technically difficult-to-obtain animal models reproducing cAMR. Treatment protocols are not established, being limited to case reports and case series, based on experience in ABO incompatible transplantation and kidney transplantation. Immunosuppression compliance with adequate dose adjustment may prevent cAMR. Conversion of Cyclosporine to Tacrolimus may improve pathological findings if treated in early phase. The association of steroids, Mycophenolate Mofetil (MMF) and mTOR inhibitors have shown some synergistic effects. Second-line treatments such as intravenous immunoglobulin (IVIG) and plasma exchange may decrease antibody titers based on ABO incompatible transplant protocols. The use of anti-CD20 (Rituximab) and proteasome inhibitors (Bortezomib) is controversial due to the lack of qualified studies. Therefore, multicenter randomized trials are needed to establish the best therapeutic strategy. In refractory cases, re-transplantation is the only treatment for allograft failure. (3) Conclusions: This literature review collects recent clinical, histopathological, and therapeutical advances of cAMR in liver allograft transplantation of pediatric patients. There are many physio-pathological aspects of cAMR to be clarified. Further efforts with multicenter prospective protocols to manage patients with cAMR are needed to improve its outcome.

Acute Antibody-Mediated Rejection in Liver Transplantation: Impact and Applicability of the Banff Working Group on Liver Allograft Pathology 2016 Criteria

This study was aimed to examine the clinical utility and impact of the 2016 Banff criteria for acute antibody-mediated rejection (acute AMR) in patients with liver transplantation. Among adult patients with donor-specific antibody (DSA) assays performed between 2015 and 2020, cases with proved DSA (mean fluorescent index >2000) and matched liver biopsy available were reviewed. Among 55 patients identified, 28 (51%) had class I DSA, 45 (82%) had class II DSA and 18 (33%) had both. Mild, moderate and severe microvasculitis were observed in 11 (20%), 2 (4%) and 1 (2%) case, respectively. Diffuse immunoreactivity to C4d on portal microvascular endothelia was confirmed in 5 cases (9%), which met the criteria of definite (n=2) or suspicious for acute AMR (n=3). Cases of acute AMR more commonly had class I DSA (100% vs. 46%; p=0.027) or both class I and II DSA (80% vs. 28%; p=0.018) than cases of non-acute AMR. One case of pure acute AMR with veno-occlusion was successfully treated with plasma exchange. The remaining 4 cases had features of combined acute AMR/T cell-mediated rejection (TCMR), and two progressed to ductopenic rejection within 3 weeks. In conclusion, only 9% of DSA-positive patients met the Banff criteria for acute AMR, necessitating careful morphological and immunohistochemical assessments of the allograft biopsies according to the proposed standards. Combined acute AMR/TCMR was more common than isolated acute AMR, and additional AMR in TCMR cases may be associated with rapid progression to ductopenic rejection.

Mismatch epitope load predicts de novo-DSA-free survival in pediatric liver transplantation

BACKGROUND

Our knowledge of de novo anti-HLA donor-specific antibodies (dnDSA) in liver transplantation continues to be defined. We hypothesized that differences of HLA-DR/DQ mismatches can improve precision in alloimmune risk categorization and be applied to tailor immunosuppression.

METHODS

A retrospective chart review of 244 pediatric patients consecutively transplanted at our center between 2003 and 2019 was performed to identify patients tested for dnDSA. Records were queried for: demographics, pre-transplant diagnosis, biopsy-proven T-cell-mediated rejection (TCMR), radiology proven biliary complications, tacrolimus trough levels, dnDSA characteristics, and HLA typing. The eplet mismatch analyses were performed using HLAMatchmaker^™ 3.1. All statistical analyses were conducted using R software version 3.40.

RESULTS

There were 99 dnDSA-negative patients and 73 dnDSA-positive patients (n = 70 against class II and n = 3 against class I and II). ROC analysis identified optimal cutoff of eplet mismatch load for dnDSA and defined risk groups for an alloimmune outcome. Kaplan-Meier curves and log-rank tests showed high eplet mismatch load was associated with shorter dnDSA-free survival (log-rank p = .001). Multivariable Cox regression models showed that tacrolimus coefficient of variation and tacrolimus mean levels were significantly associated with dnDSA-free survival (p < .001 and p = .036). Fisher's exact test showed that dnDSA was associated with an increased likelihood of TCMR (OR 14.94; 95% CI 3.65 - 61.19; p < .001). Patients without TCMR were more likely to have dnDSA to HLA-DQ7 and less likely to have dnDSA to HLA-DQ2 (p = .03, p = .080).

CONCLUSIONS

Mismatched epitope load predicts dnDSA-free survival in pediatric liver transplant, while dnDSA specificity may determine alloimmune outcome.

Recurrent Liver Allograft Injury in Patients With Donor-Derived Malignancy Treated With Immunosuppression Cessation and Retransplantation

OBJECTIVES

Donor-derived malignancy of the liver allograft is a rare but serious condition in the setting of necessary immunosuppression. Retransplantation after abrupt immunosuppression cessation has been performed with durable cancer-free survival.

METHODS

We present 2 cases of patients with donor-derived malignancy who were treated with complete immunosuppression cessation, which induced rapidly progressive liver allograft rejection and failure, with a need for subsequent retransplantation. We reviewed all serial liver biopsies and explants from both patients and performed C4d immunostaining.

RESULTS

Initial explants of both patients showed severe allograft rejection, with unusual features of sinusoidal obstruction syndrome and C4d positivity. Malignant tumors in the explants were necrotic, related to rejection of donor-derived cancer cells and tissue. Follow-up of both patients has shown long-term cancer-free survival but issues with recurrent allograft failure requiring a third transplant. The reasons for retransplantation in both cases were related to allograft failure from antibody-mediated rejection.

CONCLUSIONS

Clinicians should be aware of a potentially increased risk of rejection and recurrent allograft failure when strategizing treatment of donor-derived malignancy with immunosuppression cessation and retransplantation.

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.

The efficacy of rituximab treatment for antibody-mediated rejection in liver transplantation: A retrospective Japanese nationwide study

AIM

Antibody-mediated rejection (AMR) has been consistently elucidated in liver transplantation (LT); however, the treatment for AMR, including rituximab, has not been indicated as a strongly recommended therapeutic protocol.

METHODS

This study was conducted as the Japanese multicenter retrospective study to accumulate data on the use of rituximab for AMR among patients undergoing LT between August 2001 and December 2016. Thirteen patients (five children and eight adults) were enrolled.

RESULTS

The types of AMR in the pediatric cases were chronic AMR in four cases and indeterminate AMR in one case. Among the pediatric cases, rituximab treatment only showed therapeutic efficacy in two patients with chronic AMR. Among the adult patients, five patients had chronic AMR, and three had acute AMR. Although two patients with chronic AMR died due to graft failure, liver function tests revealed improvement after rituximab treatment in the other patients. Two of the three patients with acute AMR died due to graft failure; rituximab treatment showed no therapeutic efficacy in these cases. Although bacterial infections occurred within 3 months after rituximab administration in three patients, rituximab treatment could be safely administered without any direct adverse effects.

CONCLUSIONS

The indication of rituximab therapy as an additional treatment for mild acute AMR and chronic AMR may be feasible; however, a prospective randomized control study is needed to evaluate the therapeutic efficacy of rituximab treatment for 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.

Donor-Specific Antibodies Against Donor Human Leukocyte Antigen are Associated with Graft Inflammation but Not with Fibrosis Long-Term After Liver Transplantation: An Analysis of Protocol Biopsies

Background

Donor-specific antibodies (DSA) against donor human leukocyte antigen after liver transplantation, which are associated with histological changes, have been widely studied with respect to their sustained impact on transplant function. However, their long-term impact after liver transplantation remains unclear.

Methods

We performed a cross-sectional analysis from June 2016 to July 2017 that included all patients who presented themselves for scheduled follow-up after receiving a liver transplantation between September 1989 and December 2016. In addition to a liver protocol biopsy, patients were screened for human leukocyte antigen antibodies (HLAab) and donor-specific antibodies. Subsequently, the association between human leukocyte antigen antibodies, donor-specific antibodies, histologic and clinical features, and immunosuppression was analyzed.

Results

Analysis for human leukocyte antigen antibodies and donor-specific antibodies against donor human leukocyte antigen was performed for 291 and 271 patients. A significant association between higher inflammation grades and the presence of human leukocyte antigen antibodies and donor-specific antibodies was detected, while fibrosis stages remained unaffected. These results were confirmed by multivariate logistic regression for inflammation showing a significant increase for presence of human leukocyte antigen antibodies and donor-specific antibodies (OR: 4.43; 95% CI: 1.67–12.6; p=0.0035). Furthermore, the use of everolimus in combination with tacrolimus was significantly associated with the status of negative human leukocyte antigen antibodies and donor-specific antibodies. Viral etiology for liver disease, hepatocellular carcinoma (HCC) and higher steatosis grades of the graft were significantly associated with a lower rate of human leukocyte antigen antibodies. The impact of human leukocyte antigen antibodies and donor-specific antibodies against donor human leukocyte antigen was associated with higher levels of laboratory parameters, such as transaminases and bilirubin.

Conclusion

Donor-specific antibodies against donor human leukocyte antigen are associated with histological and biochemical graft inflammation after liver transplantation, while fibrosis seems to be unaffected. Future studies should validate these findings for longer observation periods and specific subgroups.

Clinical relevance of donor-specific human leukocyte antigen antibodies after pediatric liver transplantation

Donor-specific human leukocyte antigen (HLA) antibodies (DSAs) have a significant role in graft survival after pediatric liver transplantation. To understand the significance of DSAs, a retrospective cohort study of 48 pediatric liver transplant recipients with posttransplant serum samples that were analyzed for DSAs was performed. According to their test results, the recipients were divided into a DSA-positive group and a DSA-negative group. Postoperative liver transplantation biopsies were performed in patients with abnormal liver function. The liver condition and prognosis of the recipients were recorded, and their association was analyzed. A total of 48 recipients were followed up for 2.7±0.8 years. DSA positivity was detected in 10 cases (20.8%). One case was positive for HLA class I and HLA class II antibodies, whereas 9 cases were positive for HLA class II antibodies, and the gene loci were HLA-DR and/or DQ. Antibody-mediated rejection (AMR) occurred in four of 10 patients in the DSA-positive group. Liver function was abnormal in 3 of 38 cases in the DSA-negative group. Multivariate analysis revealed that DSA positivity was an independent risk factor for liver insufficiency and long-term survival of recipients. In addition, Kaplan-Meier survival analysis demonstrated that there were significant differences in the survival of graft recipients between the DSA-positive group and the DSA-negative group (P<0.05). The positivity of DSAs after pediatric liver transplantation was closely related to the occurrence of AMR. These results suggested that DSAs should be routinely monitored post-operatively, and that DSA-positive recipients should be screened as soon as possible and given appropriate treatment.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

Immunostaining Patterns of Posttransplant Liver Biopsies Using 2 Anti-C4d Antibodies

Histopathologic diagnosis of antibody-mediated rejection in posttransplant liver biopsies is challenging. The recently proposed diagnostic criteria by the Banff Working Group on Liver Allograft Pathology require positive C4d immunohistochemical staining to establish the diagnosis. However, the reported C4d staining patterns vary widely in different studies. One potential explanation may be due to different antibody preparations used by different investigators. In this study, posttransplant liver biopsies from 69 patients histopathologically diagnosed with acute cellular rejection, chronic rejection, or recurrent hepatitis C were immunohistochemically stained using 2 polyclonal anti-C4d antibodies. On the basis of the distribution of C4d immunoreactivity, 5 different staining patterns were observed: portal vein and capillary, hepatic artery, portal stroma, central vein, and sinusoids. The frequency, extent, and intensity of positive C4d staining with the 2 antibody preparations differed significantly for portal veins/capillaries and central veins, but not for hepatic arteries and portal stroma. Positive sinusoidal staining was seen in only 1 case. There were no significant differences in the frequency, extent, and intensity of positive C4d staining among the acute cellular rejection, chronic rejection, and recurrent hepatitis C groups with the 2 anti-C4d antibodies. These data show that different anti-C4d antibodies can show different staining patterns, which may lead to different interpretation. Caution is thus needed when selecting C4d antibodies for clinical use to aid in the diagnosis of antibody-mediated rejection.

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.

Donor-specific antibodies in liver transplantation: challenges in diagnosis and determining clinical impact

PURPOSE OF REVIEW

Our understanding of the clinical impact of donor-specific antibodies in liver transplant recipients has evolved in recent years as outcomes for liver allografts have improved and advances in diagnostic testing have made recognition of antibody mediated rejection in transplant patients more sensitive.

RECENT FINDINGS

Two main types of donor-specific antibodies - preformed and de novo - have been reported in the literature to have a negative impact on graft survival, and researchers have been able to further identify subclasses of class II donor-specific antibodies as being the most clinically impactful. Furthermore, there is evidence that donor-specific antibody formation can augment cellular rejection in liver grafts and lead to worsened clinical outcomes. Recent data have shown a higher prevalence of donor-specific antibody formation than previously reported.

SUMMARY

This review explores the most recent literature regarding the clinical impact of both preformed and de-novo donor-specific antibodies and potential management guidelines for patients undergoing liver transplantation. The best practice guidelines for undergoing monitoring for donor-specific antibody formation and protocol biopsies in sensitized patients will depend on further multiinstitutional studies.

HLA class II donor specific antibodies are associated with graft cirrhosis after liver transplant independent of the mean fluorescence intensity level

Background

The importance of donor-specific antibodies (DSA) after liver transplantation (LT) for graft and patient survival is an ongoing controversy. So far it has not been elucidated when and in how far DSA are harmful for graft and patient survival. Therefore, we had the aim to investigate the association of DSA with complications after LT.

Methods

Data of 430 LT recipients were collected and statistically analyzed. Detection of HLA antibodies (Ab) was performed by Luminex assay.

Results

DSA were detected in 81 patients (18.8%). These were mainly HLA class II Ab (81.5%). HLA class II Ab show a higher MFI (median: 5.300) compared to HLA class I Ab (median: 2.300). There is no association between MFI levels and development of complications after LT. However, cirrhosis occurred significantly more often in DSA positive patients (18%) than in patients without detectable DSA (9%, P = 0.027). All DSA positive patients with cirrhosis of the graft showed HLA class II antibodies (OR: 3.028; 95% CI: 1.51–6.075; P = 0.002).

Conclusion

Occurrence of HLA class II DSA after LT is associated with graft cirrhosis and may indicate a higher risk to develop graft damage independent on MFI and requires an individualized risk management.

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.

Donor-Specific Antibodies in Liver Transplantation

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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.

Preformed donor-specific antibodies are associated with 90-day mortality in living-donor liver transplantation

AIM

The impact of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) on living donor liver transplantation (LDLT) is unclear. The aim of this study was to investigate the association between DSAs and short-term outcomes in LDLT recipients, and to clarify the clinical impact of DSAs.

METHOD

Anti-HLA antibodies were screened in preoperative serum samples taken from 40 liver transplant recipients at Ehime University (Toon, Japan) between August 2001 and July 2015. Screening was carried out using the Flow-PRA method, and DSAs were detected in anti-HLA antibody-positive recipients using the Luminex single-antigen identification test. A mean fluorescence intensity of 1000 was used as the cut-off for positivity. We retrospectively reviewed the clinical courses of patients who were DSA-positive to elucidate early clinical manifestations in LDLT recipients.

RESULTS

Fifteen (12 female and 3 male) patients (38%) had anti-HLA antibodies. Eight of the 15 anti-HLA antibody-positive patients were positive for DSAs, and all were women. The 90-day survival rate of DSA-positive patients (50%) was significantly lower than that of DSA-negative patients (84.4%) (0.0112; Wilcoxon test). On univariate analysis, the DSA-positive rate was significantly higher in the 90-day mortality group. Postoperatively, the incidence of acute cellular rejection was higher in DSA-positive than DSA-negative patients. Thrombotic microangiopathy developed only in DSA-positive patients. We found no relationship between DSA status and bile duct stricture.

CONCLUSION

Preformed DSAs could be associated with elevated 90-day mortality in LDLT recipients. Further large-scale studies are required to verify the risk associated with DSAs in LDLT.

Prevalence and Impact of Reformed and De Novo Anti-HLA Donor-Specific Antibodies in Liver Transplantation

INTRODUCTION

The prevalence and impact of pre-existing and de novo anti-HLA donor-specific antibodies (DSAs) after orthotopic liver transplantation (OLT) is still controversial. We investigated the prevalence of DSAs and their implication in the development of allograft dysfunction after OLT.

PATIENTS AND METHODS

A total of 65 liver transplant patients were tested for anti-HLA antibodies, with single antigen bead technology, before, 1, 3, 6, and 12 months after transplantation, and thereafter annually, along with other risk factors. Sixteen out of 65 patients (24.6%) had circulating pre-existing anti-HLA antibodies, and 4 of them (25%) had DSAs. All patients positive for anti-HLA antibodies (100%) presented allograft dysfunction. Fourteen out of 65 patients (21.5%) had circulating de novo DSAs, and 12 out of 14 (85.7%) presented allograft dysfunction. The investigated risk factors for allograft dysfunction were: recipient and donor age, time on the waiting list, cold ischemia time, cytomegalovirus infection, immunosuppression regimen, de novo DSAs, Model for End-Stage Liver Disease, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transpeptidase (GGT), direct bilirubin and total bilirubin peak post-transplant, and alkaline phosphatase. The multivariate analysis showed that de novo DSAs and time on the waiting list were independent risk factors for allograft dysfunction.

CONCLUSION

Our results show that de novo DSAs are an independent risk factor for allograft dysfunction, along with time on the waiting list.

Long-term Outcomes of ABO-incompatible Pediatric Living Donor Liver Transplantation

BACKGROUND

ABO-incompatible (ABOi) living donor liver transplantation (LDLT) has been performed to compensate for donor shortage. To date, few studies have reported detailed B-cell desensitization protocols and long-term outcomes of ABOi pediatric LDLT.

METHODS

Twenty-nine pediatric ABOi LDLT recipients were retrospectively analyzed. We compared the clinical outcomes between ABOi (n = 29) and non-ABOi (n = 131) pediatric LDLT recipients. Furthermore, we evaluated the safety and efficacy of our rituximab-based regimen for ABOi pediatric LDLT (2 ≤ age < 18; n = 10).

RESULTS

There were no significant differences in the incidence of infection, vascular complications, biliary complications, and acute cellular rejection between ABOi and non-ABOi groups. The cumulative graft survival rate at 1, 3, and 5 years for non-ABOi group were 92.1%, 87.0%, and 86.1%, and those for ABOi group were 82.8%, 82.8%, and 78.2%, respectively. Rituximab-based desensitization protocol could be performed safely, and reduced CD19+ lymphocyte counts effectively. Although rituximab-treated ABOi group showed comparable clinical outcomes and graft survival rate, 2 patients developed antibody-mediated rejection.

CONCLUSIONS

ABOi LDLT is a feasible option for pediatric end-stage liver disease patients. However, it should be noted that current desensitization protocol does not completely prevent the onset of antibody-mediated rejection in several cases.

Morphological characterization of chronic antibody-mediated rejection in ABO-identical or ABO-compatible pediatric liver graft recipients

This study aims to define the morphological profile associated with the presence of donor-specific antibodies (DSAs) and/or C4d immunostaining in ABO-identical or compatible pediatric liver grafts. Ten-year protocol liver graft biopsies performed at 131.3 ± 15.3 months after transplantation in 53 pediatric liver graft recipients were reviewed. Immunostaining for C4d was systematically performed and semiquantitatively analyzed. DSAs were concurrently quantified, and results were available for 44 patients. All biopsies demonstrated fibrotic changes with a mean liver allograft fibrosis score (LAFSc) of 5.1 ± 2.2. A total of 31 (58%) biopsies exhibited C4d positivity. DSAs were detected in 20 (45%) patients, and mean maximal mean fluorescence intensity was 12,977 ± 6731. LAFSc (6.3 ± 1.3 versus 3.9 ± 2.2; P = 0.008), perivenular fibrosis (2.7 ± 0.5 versus 1.3 ± 1.0; P < 0.001), and portal inflammation (1.4 ± 0.8 versus 0.3 ± 0.5; P = 0.009) were significantly higher in the double-DSA and C4d-positive group versus the double-negative group. We defined a histological scoring system from these results, which was integrated with the 2016 Banff definition and allowed reclassifying patients for the diagnosis of chronic active antibody-mediated rejection (cAMR; 11/53 versus 13/53). Diagnoses of probable cAMR according to Banff 2016 (n = 4) were unchanged, but 2 among the 9 patients classified as possible cAMR according to the 2016 Banff definition were excluded for this diagnostic when using our histological score. In conclusion, our results confirmed that perivenular fibrosis and portal inflammation in late pediatric liver graft biopsies are features of cAMR. Our histological score could improve the accuracy of the 2016 Banff definition for the diagnosis of cAMR. Liver Transplantation 24 897-907 2018 AASLD.

A Hibernation-Like State for Transplantable Organs: Is Hydrogen Sulfide Therapy the Future of Organ Preservation?

SIGNIFICANCE

Renal transplantation is the treatment of choice for end-stage renal disease, during which renal grafts from deceased donors are routinely cold stored to suppress metabolic demand and thereby limit ischemic injury. However, prolonged cold storage, followed by reperfusion, induces extensive tissue damage termed cold ischemia/reperfusion injury (IRI) and puts the graft at risk of both early and late rejection. Recent Advances: Deep hibernators constitute a natural model of coping with cold IRI as they regularly alternate between 4°C and 37°C. Recently, endogenous hydrogen sulfide (H₂S), a gas with a characteristic rotten egg smell, has been implicated in organ protection in hibernation.

CRITICAL ISSUES

In renal transplantation, H₂S also seems to confer cytoprotection by lowering metabolism, thereby creating a hibernation-like environment, and increasing preservation time while allowing cellular processes of preservation of homeostasis and tissue remodeling to take place, thus increasing renal graft survival.

FUTURE DIRECTIONS

Although the underlying cellular and molecular mechanisms of organ protection during hibernation have not been fully explored, mammalian hibernation may offer a great clinical promise to safely cold store and reperfuse donor organs. In this review, we first discuss mammalian hibernation as a natural model of cold organ preservation with reference to the kidney and highlight the involvement of H₂S during hibernation. Next, we present recent developments on the protective effects and mechanisms of exogenous and endogenous H₂S in preclinical models of transplant IRI and evaluate the potential of H₂S therapy in organ preservation as great promise for renal transplant recipients in the future. Antioxid. Redox Signal. 28, 1503-1515.

Limited impact of pre-existing donor specific HLA-antibodies (DSA) on long term allograft survival after first adult liver transplantation

The relevance of pre-existing HLA-antibodies (HLA-Ab) in liver transplantation (LTx) is controversial. While livers are allocated without HLA match or preoperative crossmatch testing, several studies point to an impact of donor specific antibodies (DSA) for acute rejection, bile duct complications or even graft loss. To investigate the role of DSA in long term liver allograft survival we analysed 177 pre transplant sera of first LTx patients with Luminex single antigen technology defining a MFI of >1500 as positive. The analyses were done retrospectively, and the DSA results had no impact on graft acceptance or patients' therapy. Three year follow up was available for all patients. 77% of our patients had any HLA-Ab pre transplantation, 55 patients were transplanted with DSA by chance. Acute rejections or ischemic type bile duct lesions (ITBL) were not higher in the DSA group, but ITBL was associated with a higher donor age. There was no difference in long term graft function or survival in patients without HLA-Ab, with non DSA or with DSA (p = 0.712). We suggest that determination of pre-existing DSA in first LTx recipients is not appropriate and we conclude that pre-existing DSA in first LTx patients are not a contraindication for liver transplantation.

Biomarkers of immune tolerance in liver transplantation

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

HLA-DQ antibodies: are they real? Are they relevant? Why so many?

PURPOSE OF REVIEW

Recent reports on donor-specific antibodies documented an overwhelming frequency of antibodies to one specific locus - human leukocyte antigen DQ (HLA-DQ). This article provides a short summary of clinical observations, a historic perspective to account for the late recognition of the role of HLA-DQ antibodies as well as potential explanations.

RECENT FINDINGS

The basic understanding of the complexity of HLA-DQ molecules (antigens and antibodies) existed already 3-4 decades ago. However, only more recent advancements in molecular techniques as well as solid phase platforms, that allow for testing antibody specificities against individual HLA targets, provided state-of-the-art tools that are also amenable to mass applications. Thus, the significance of the polymorphic nature of both polypeptide chains of the DQ molecule, DQα and DQβ, is only now re-emerging.

SUMMARY

HLA-DQ antibodies are real, relevant, and abundant. In order to achieve a clinically useful understanding of this phenomenon, HLA-DQ antigens and antibodies should be viewed at the level of the physiologic structure, as it appears on the cell surface, namely, one unit composed as DQαβ. Preliminary data demonstrated that such an approach is likely to lead to more equitable calculation of calculated panel reactive antibody, improving the accuracy of virtual crossmatch prediction, and increasing the likelihood of finding a compatible donor for the very highly sensitized patients.

Antibody-mediated rejection: what is the clinical relevance?

PURPOSE OF REVIEW

The review outlines the diagnosis, clinical implications, and treatment strategies for acute and chronic antibody-mediated rejection (AMR) after orthotopic liver transplantation (OLT).

RECENT FINDINGS

A combination of clinical work-up, histopathology, C4d staining, and donor-specific antibody (DSA) should be used to diagnose AMR. The differential diagnosis for idiopathic fibrosis now includes chronic AMR. Characterization of pathogenic DSA continues to progress. De-novo and persistent DSA, particularly of the IgG3 subtype, are associated with inferior long-term outcomes.The liver allograft may confer long-term immunologic benefits to the kidney allograft after simultaneous liver-kidney transplant.The more widespread use of rituximab has improved outcomes in ABO-incompatible OLT.Although larger long-term studies of treatment options are needed, compliance with tacrolimus-based immunosuppression and transfusion minimization are agreed upon preventive strategies.

SUMMARY

AMR has evolved into an established pathology in OLT recipients. Acute AMR may lead to early graft loss whereas chronic AMR results in progressive fibrosis if unrecognized. DSAs, likely in the setting of predisposing environmental factors, appear to play a role in T cell-mediated rejection and long-term graft outcomes.

Deleterious impact of C3d-binding donor-specific anti-HLA antibodies after pediatric liver transplantation

BACKGROUND

The prevalence and clinical impact of anti-HLA donor-specific antibodies (DSA) after liver transplantation (LT) have not been extensively studied, especially in pediatric population.

METHODS

The present cross-sectional study included 100 patients who underwent a first LT in childhood. Anti HLA immunization study was performed at a single time point during routine follow-up using Luminex® single antigen tests with classical anti-IgG conjugate and anti-C3d conjugate.

RESULTS

The main indication for LT was biliary atresia (52%) and median age at LT was 4.6years. The median time between LT and DSA assessment was 7.8years (range 1-21years). DSA was identified in twenty-four patients (24%) after LT, with a prevalence of 8%, 28%, 33%, 50%, respectively 0-5years, 5-10years, 10-15years and >15years after LT. DSA were mainly class II (23/24) with a mean MFI of 9.731±5.489 and 18 (79.3%) were C3d-binding DSA. Multivariate analysis disclosed that time elapsed since LT (p<0.01) and history of fulminant hepatitis (p=0.04) were significantly associated with a higher rate of DSA. Liver function tests (at time of DSA assessment) were not different according to the presence or not of DSA (or C3d-binding DSA). Regarding histology, the DSA group had a higher rate of chronic rejection, cirrhosis and centrilobular fibrosis or cirrhosis. In addition, patients with C3d-binding DSA and high MFI (>10,000) had a significant poorer long-term graft survival (p=0.03).

CONCLUSION

In our pediatric cohort of LT, prevalence of DSA was high and increased regularly with time. Presence of C3d positive-DSA with high MFI was associated with a higher rate of graft loss.

Antibody-Mediated Rejection After Liver Transplant

Antibody-mediated rejection (AMR) in liver transplants is a field in its infancy compared with its allograft cohorts of the kidney and lung. Acute AMR is diagnosed based on specific clinical and histopathologic criteria: serum donor specific antibodies, C4d staining, histopathologic findings on liver biopsy, and exclusion of other entities. In contrast, the histologic features of chronic AMR are not as specific and it is a more challenging diagnosis to make. Treatments of acute and chronic AMR include some combination of steroids, immune-modulating agents, intravenous immunoglobulin, plasmapheresis, and proteasome inhibitors.

De Novo Donor-Specific Anti-Human Leukocyte Antigen Antibody Detection in Long-Term Adult Liver Transplantation

INTRODUCTION

Information about the consequences of de novo donor-specific anti-human leukocyte antigen (DSA) antibody development in the long term after adult liver transplantation (LT) is scarce. We conducted a cross-sectional study in LT patients with a follow-up of at least 6 years.

METHODS

A total of 28 adult LT patients were included, with a median follow-up of 77 months (range, 63 to 96) and without preformed anti- human leukocyte antigen (HLA) antibodies prior to LT. The anti-HLA identification was performed with LABScreen Single Antigen, whereas the ability to fix the complement was demonstrated with C1q test (One Lambda). In both assays, a value >3.500 mean fluorescence intensity (MFI) was considered positive. The anti-HLA antibody specificities were compared with donor HLA antigens to confirm them as DSA. Hepatic fibrosis was assessed by transient elastography.

RESULTS

In 5 patients (17.8%), de novo DSA were detected, all them against DQ locus. In all of these cases (100%) the complement fixation was confirmed by C1q binding. The grade of hepatic fibrosis in de novo DSA patients was significantly higher compared with No-DSA patients (13.2 ± 9.2 KPa vs 7.3 ± 3.7 KPa; P = .02). It is noteworthy that in both groups of patients the levels of liver function tests (LFT) at the time of the study were normal or near the normal range with no difference between patients with or without de novo DSA.

CONCLUSIONS

Our preliminary results are consistent with those previously demonstrated in pediatric LT, where de novo DSA production and humoral response could contribute to the liver fibrosis observed in the long term after LT in pediatric patients with normal or near-normal LFT.

The Role of Humoral Alloreactivity in Liver Transplantation: Lessons Learned and New Perspectives

More than ten years after the initial description of the humoral theory of transplantation by Dr. Paul I. Terasaki, the significance of humoral alloimmunity in liver transplantation has yet to be clearly defined. The liver allograft has an inherent tolerogenic capacity which confers its resistance to cell-mediated as well as antibody-mediated rejection. Nevertheless, the protection against alloimmunity is not complete, and antibody-mediated tissue injury can occur in the liver graft under specific circumstances. In this article the evidence on the clinicopathologic effects of donor-specific alloantibodies in liver transplantation will be examined and interpreted in parallel with lessons learned from renal transplantation. The unique anatomic and immunologic features of the liver will be reviewed to gain new insights into the complex interactions between humoral immune system and the liver allograft.