Donor-specific human leukocyte antigen antibodies of the immunoglobulin G3 subclass are associated with chronic rejection and graft loss after liver transplantation

RORγt inverse agonist TF-S14 inhibits Th17 cytokines and prolongs skin allograft survival in sensitized mice

Chronic antibody mediated rejection (AMR) is the major cause of solid organ graft rejection. Th17 contributes to AMR through the secretion of IL17A, IL21 and IL22. These cytokines promote neutrophilic infiltration, B cell proliferation and donor specific antibodies (DSAs) production. In the current study we investigated the role of Th17 in transplant sensitization. Additionally, we investigated the therapeutic potential of novel inverse agonists of the retinoic acid receptor-related orphan receptor gamma t (RORγt) in the treatment of skin allograft rejection in sensitized mice. Our results show that RORγt inverse agonists reduce cytokine production in human Th17 cells in vitro. In mice, we demonstrate that the RORγt inverse agonist TF-S14 reduces Th17 signature cytokines in vitro and in vivo and leads to blocking neutrophilic infiltration to skin allografts, inhibition of the B-cell differentiation, and the reduction of de novo IgG3 DSAs production. Finally, we show that TF-S14 prolongs the survival of a total mismatch grafts in sensitized mice. In conclusion, RORγt inverse agonists offer a therapeutic intervention through a novel mechanism to treat rejection in highly sensitized patients.

Complement-activating donor-specific anti-HLA antibodies in solid organ transplantation: systematic review, meta-analysis, and critical appraisal

Introduction

Several studies have investigated the impact of circulating complement-activating anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) on organ transplant outcomes. However, a critical appraisal of these studies and a demonstration of the prognostic value of complement-activating status over anti-HLA DSA mean fluorescence intensity (MFI) level are lacking.

Methods

We conducted a systematic review, meta-analysis and critical appraisal evaluating the role of complement-activating anti-HLA DSAs on allograft outcomes in different solid organ transplants. We included studies through Medline, Cochrane, Scopus, and Embase since inception of databases till May 05, 2023. We evaluated allograft loss as the primary outcome, and allograft rejection as the secondary outcome. We used the Newcastle-Ottawa Scale and funnel plots to assess risk of bias and used bias adjustment methods when appropriate. We performed multiple subgroup analyses to account for sources of heterogeneity and studied the added value of complement assays over anti-HLA DSA MFI level.

Results

In total, 52 studies were included in the final meta-analysis (11,035 patients). Complement-activating anti-HLA DSAs were associated with an increased risk of allograft loss (HR 2.77; 95% CI 2.33-3.29, p<0.001; I²=46.2%), and allograft rejection (HR 4.98; 95% CI 2.96-8.36, p<0.01; I²=70.9%). These results remained significant after adjustment for potential sources of bias and across multiple subgroup analyses. After adjusting on pan-IgG anti-HLA DSA defined by the MFI levels, complement-activating anti-HLA DSAs were significantly and independently associated with an increased risk of allograft loss.

Discussion

We demonstrated in this systematic review, meta-analysis and critical appraisal the significant deleterious impact and the independent prognostic value of circulating complement-activating anti-HLA DSAs on solid organ transplant risk of allograft loss and rejection.

Posttransplant immune-mediated cholangiopathies

PURPOSE OF REVIEW

Liver transplantation (LT) is the treatment of end-stage chronic liver diseases, mainly decompensated cirrhosis and hepatocellular carcinoma. Biliary complications can be schematically classified into macroscopic versus microscopic lesions. Immune-related cholangiopathies include rejection, graft-versus-host disease (GVHD) and recurrence of pre-LT auto-immune biliary diseases, i.e. primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). Here, we review the various types of posttransplant immune-related cholangiopathies, and discuss their clinical implications, especially diagnostic issues.

RECENT FINDINGS

Recurrence of PBC and PSC after LT is increasingly well described in large cohorts and long-term follow-up. In this setting, the preventive effect of ursodeoxycholic acid on PBC recurrence, as well as the deleterious role of tacrolimus are now well documented. In addition, the significant negative impact of recurrent PBC on survival after LT has recently been demonstrated. With respect to rejection-associated biliary injury, a growing body of evidence is emerging on the role of anti-HLA antibody-mediated rejection.

SUMMARY

Immune-mediated cholangiopathies occurring after LT can be divided in two main nosologic groups: biliary lesions due to recurrence of PBC or PSC, or in the context of rejection, either acute or chronic, T-cell- or antibody-mediated. GVHD is very rare. Final diagnosis is strongly based on clinical context (indication for LT, delay since transplantation, biological abnormalities, imaging) but also and to an even greater extent on biopsy of liver graft. Clinico-pathological discussions are recommended, hearing in mind that diseases can be intertwined.

The incidence and risk factors of chronic rejection in acutely rejected pediatric liver transplantation

Background. Chronic graft rejection (CR) represents an increasing concern in pediatric liver transplantation (LT). Risk factors of CR in this population are uncertain. In present study, we aimed to ascertain if clinical parameters could predict the occurrence of CR in LT children.

Methods. We retrospectively analyzed the results from 47 children who had experienced acute hepatic rejection in Namazee hospital, Shiraz, Iran during 2007–2017.

Results. Out of 47 children, 22 (46.8%) and 25 (53.2%) were boys and girls respectively. Ascites, gastrointestinal bleeding, and spontaneous bacterial peritonitis were observed in 20 (44.4%), 14 (31.1%), and 4 (9.1%) respectively. Posttransplant vascular and biliary complications were observed in 3 (7%) and 4 (9.3%) cases respectively. The mean time from LT to normalization of liver enzymes was 14.2 ± 7.5 days. The mean of acute rejection episodes was 1.4 ± 0.6 (median = 1 (22, 46.8%), range of 1–3). Six (12.7%) patients experienced CR. The mean time from LT to CR was 75 ± 28.4 days. A significant association was found between CR and patients’ condition (being inpatient or outpatient) before surgery (P = 0.03). No significant relationship was found between CR and post-transplant parameters except for biliary complications (P = 0.01). Both biliary complication (RR = 33.7, 95% CI: 2.2–511, P = 0.01) and inpatient status (RR = 10.9, 95% CI: 1.1–102.5, P = 0.03) significantly increased the risk of CR.

Conclusion. Being hospitalized at the time of LT, and development of biliary complications might predict risk factors for development of CR in LT children.

B cell depletion with anti-CD20 mAb exacerbates anti-donor CD4+ T cell responses in highly sensitized transplant recipients

Pretransplant desensitization with rituximab has been applied to preformed donor-specific anti-human leukocyte antigen antibody (DSA)-positive recipients for elimination of preformed DSA. We investigated the impact of pretransplant desensitization with rituximab on anti-donor T cell responses in DSA-positive transplant recipients. To monitor the patients' immune status, mixed lymphocyte reaction (MLR) assays were performed before and after desensitization with rituximab. Two weeks after rituximab administration, the stimulation index (SI) of anti-donor CD4+ T cells was significantly higher in the DSA-positive recipients than in the DSA-negative recipients. To investigate the mechanisms of anti-donor hyper responses of CD4+ T cells after B cell depletion, highly sensitized mice models were injected with anti-CD20 mAb to eliminate B cells. Consistent with clinical observations, the SI values of anti-donor CD4+ T cells were significantly increased after anti-CD20 mAb injection in the sensitized mice models. Adding B cells isolated from untreated sensitized mice to MLR significantly inhibited the enhancement of anti-donor CD4+ T cell response. The depletion of the CD5+ B cell subset, which exclusively included IL-10-positive cells, from the additive B cells abrogated such inhibitory effects. These findings demonstrate that IL-10+ CD5+ B cells suppress the excessive response of anti-donor CD4+ T cells responses in sensitized recipients.

Set Up for Failure: Pre-Existing Autoantibodies in Lung Transplant

Lung transplant patients have the lowest long-term survival rates compared to other solid organ transplants. The complications after lung transplantation such as primary graft dysfunction (PGD) and ultimately chronic lung allograft dysfunction (CLAD) are the main reasons for this limited survival. In recent years, lung-specific autoantibodies that recognize non-HLA antigens have been hypothesized to contribute to graft injury and have been correlated with PGD, CLAD, and survival. Mounting evidence suggests that autoantibodies can develop during pulmonary disease progression before lung transplant, termed pre-existing autoantibodies, and may participate in allograft injury after transplantation. In this review, we summarize what is known about pulmonary disease autoantibodies, the relationship between pre-existing autoantibodies and lung transplantation, and potential mechanisms through which pre-existing autoantibodies contribute to graft injury and rejection.

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.

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.

Angiotensin II Type-1 Receptor Antibodies Are Associated With Active Allograft Dysfunction Following Pediatric Liver Transplantation

BACKGROUND

Angiotensin II type-1 receptor (AT1R) antibodies have been associated with rejection and allograft loss in solid organ transplantation and may act synergistically with HLA donor-specific antibodies (DSA). Our aims were to assess the prevalence of AT1R antibodies and determine if they were associated with allograft dysfunction in pediatric liver transplant recipients.

METHODS

We performed a retrospective, cross-sectional study of HLA DSA and AT1R antibodies in 2 cohorts of pediatric liver transplant recipients: a stable control cohort with normal allograft function (n = 70) who consented to have serum samples collected for research purposes during a routine clinic visit and a cohort with active allograft dysfunction (n = 9) whose serum samples were collected as part of clinical care.

RESULTS

AT1R antibodies >17 U/mL were detected in 29% of stable control patients and 89% of patients with active allograft dysfunction (P = 0.001). In stable control patients, AT1R antibodies were associated with younger age at transplant (P = 0.010), younger age at time of sample collection (P < 0.001), shorter interval since transplant (P = 0.090), and presence of HLA DSA (P = 0.003). AT1R antibodies in stable control patients were not associated with rejection or allograft loss. However, AT1R antibodies combined with HLA DSA in patients with active allograft dysfunction were associated with rejection and allograft loss.

CONCLUSIONS

Our results suggest that AT1R antibodies are more common in patients with active allograft dysfunction and may be a risk factor for worse outcomes. Further research is needed to longitudinally assess the clinical impact of HLA DSA and AT1R antibodies.

Development of a humanized mouse model to analyze antibodies specific for human leukocyte antigen (HLA)

In organ transplantation, human leukocyte antigen (HLA)-mismatch grafts not only induce the activation of cellular mediated immune response but also the development of chronic antibody-mediated rejection due to the donor-specific anti-HLA antibody (DSA) produced by B cells and plasma cells interacting with the graft endothelium. Significant improvement in long-term survival after transplantation can be expected if antibody-mediated rejection due to the DSA can be overcome. However, the mechanism of producing or controlling the DSA remains to be elucidated. In recent decades, “humanized” mouse models have been widely used for the basic research of human immune systems, but a humanized mouse model to analyze the mechanism of DSA production has not been established yet. Thus, we aimed to create a humanized mouse using a severe immunodeficiency mouse (NSG mouse) administered with human peripheral blood mononuclear cells (PBMCs). Initially, we detected a very low level of human total-IgG and no anti-HLA antibodies (Abs) in these mice. In our next attempt, we mixed PBMCs of various HLA antigenic combinations with or without regulatory T cells and preconditioned them by culturing on feeder cells stably transfected with human CD40 ligand (h-CD40L) alone or with h-CD40L and human B cell activating factor (h-BAFF). They were subsequently co-cultured with the corresponding irradiated stimulator PBMCs, and all cells were administered into naïve NSG mice. Although all three humanized models had sufficient human total-IgG and anti-HLA antibody production, allospecific anti-HLA Ab production was prominently suppressed whereas non-specific anti-HLA Abs were sufficiently detected. Therefore, this novel humanized mouse model might be useful for analyzing the mechanism of anti-allogeneic human B cell tolerance induction.

Chronic Antibody-Mediated Liver Rejection: More than Meets the Eye

Understanding the role of donor-specific antibodies (DSAs) in liver transplantation remains an investigative priority. Acute and chronic rejection associated with DSAs have been described. However, most transplant protocols did not consider the presence of DSAs at the moment of liver transplantation (LTx) or for the follow-up. A 65-year-old man received an ABO-compatible LTx for cirrhosis. Ten years after the LTx, he presented with a progressive elevation of liver enzymes and bilirubin. The single antigen Luminex bead assay showed the presence of DSAs against several DQ2, DQ7, and DQ8 alleles. The patient received several desensitization treatments regarding the persistence of DSAs. The anatomopathological study confirms chronic rejection. Although in this case the immunohistochemical deposits of C4d were negative, the data revealed morphological criteria of chronic graft injury and DSAs’ incompatibilities explained by structural analysis. These data support an antibody-mediated rejection (AMR). It could be reasonable to establish a protocol for human leukocyte antigen (HLA) typing of every LTx donor and recipient as well as a periodic follow-up to assess the presence of DSAs. This will make it possible to carry out studies of donor–recipient incompatibility and to confirm the existence of probable cases of AMR.

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.

Long-term outcomes and clinical impact of anti-HLA donor-specific antibodies (DSA) after liver transplantation: a prospective study in a pilot cohort

INTRODUCTION

the presence of donor-specific antibodies (DSA) is thought to affect survival of the allograft and patient after liver transplantation (LT). However, their significance is not well understood.

PATIENTS AND METHODS

a prospective study was performed of 32 adult patients who underwent LT in 2011 to analyze the existence of DSA, associated risk factors and medium-term impact. Immunological determinations were performed immediately before LT and at three, six, 12 months and five years after LT.

RESULTS

eight patients (24.2 %) presented pre-formed DSA. However, titers were negative in all patients five years after LT and there were no associated events. Eight out of 24 patients (33.3 %) developed de novo DSA. After five years, only two remained positive; both were class II with high mean fluorescence intensity (MFI) values at diagnosis (over 15,000). No association was found between the development of DSA and the risk of rejection, graft loss or death. However, an increase in liver stiffness values was observed in patients with persistent DSA, and focal sinusoidal deposition of C4d and moderate liver fibrosis were reported.

CONCLUSION

the incidence of DSA is high after LT. In addition, the persistence of de novo DSA could be associated with silent liver fibrosis with a potential impact on graft outcomes.

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.

Sensitization in transplantation: Assessment of risk (STAR) 2019 Working Group Meeting Report

The purpose of the STAR 2019 Working Group was to build on findings from the initial STAR report to further clarify the expectations, limitations, perceptions, and utility of alloimmune assays that are currently in use or in development for risk assessment in the setting of organ transplantation. The goal was to determine the precision and clinical feasibility/utility of such assays in evaluating both memory and primary alloimmune risks. The process included a critical review of biologically driven, state-of-the-art, clinical diagnostics literature by experts in the field and an open public forum in a face-to-face meeting to promote broader engagement of the American Society of Transplantation and American Society of Histocompatibility and Immunogenetics membership. This report summarizes the literature review and the workshop discussions. Specifically, it highlights (1) available assays to evaluate the attributes of HLA antibodies and their utility both as clinical diagnostics and as research tools to evaluate the effector mechanisms driving rejection; (2) potential assays to assess the presence of alloimmune T and B cell memory; and (3) progress in the development of HLA molecular mismatch computational scores as a potential prognostic biomarker for primary alloimmunity and its application in research trial design.

Investigating the relationship between class I HLA-specific immunoglobulin-G subclasses, Pan-IgG single antigen bead assays and complement mediated interference in sera from renal transplant recipients

INTRODUCTION

Antibody mediated rejection is the leading cause of kidney transplant failure. Not all antibodies are harmful and some may be protective. Immunoglulin Gs, of which there are four subtypes, are detected by single antigen bead testing. The aims of this study were to characterise the IgG subclass profiles for class I HLA-specific antibodies in an uncensored post-transplant population and to determine the underlying relationship between reactivity patterns and MFI cut-offs with the pan-IgG assay.

METHODS

Patients were recruited to the study who were transplanted in our centre between 2009 and 2014. Prospectively stored post-transplant serum initially underwent a Labscreen Mixed assay and those positive for class I HLA-specific antibody underwent standard SAB testing, EDTA, 1 in 10 dilution and IgG subclass modifications using the Luminex platform. A total of 4947 bead reactions from 51 patients were analysed.

RESULTS

A 1 in 10 dilution was used as a comparator pan-IgG assay for summed subclass and individual subclass linear regression analyses. Using a dilution to standard assay ratio we characterised all reactions for prozone potential i.e. how likely there is to be inhibition related to complement complex formation. We stratified samples into degrees of association and were able to determine suggested MFI thresholds of Log 5.35 for the dilution assay and Log 5.05 for the summed subclass assay when considering a Log MFI of 6.9 (1000) in the standard assay. Using individual subclass dominant reactions (>70%) we were able to determine linear relationships between the 1 in 10 dilution pan-IgG assay and the individual subclass assays (excluding prozone potential reactions for IgG1/3) enabling us to suggest Log MFI thresholds of 5.03, 3.58, 4.3 and 4.05 respectively for IgG1-4.

DISCUSSION

We recommend a 1 in 10 dilution as the optimum pan-IgG comparator assay for a subclass analysis. We advocate the utilisation of the summed subclass assay to determine overall relationships and potential subclass failures. Following others, we recommend serum pre-treatment of the subclass assays to mitigate prozone. We suggest cut-offs for each IgG subclass which should be used with caution given the many inhibitory influences which may include competitive inhibition for bead binding, IgM and IgA interference and under-representation of specific subclasses on the bead panel.

Effects of re-augmenting maintenance immunosuppression on post-transplant donor-specific HLA antibodies in liver transplantation

BACKGROUND

Donor-specific antibodies (DSAs) have various negative short- and long-term effects after organ transplantation. DSAs are prevalent in patients with insufficient immunosuppression; thus, even patients with stable conditions after liver transplantation should be under optimized immunosuppression. However, the effect of re-augmenting immunosuppression therapy for patients with insufficient immunosuppression remains unclear. In this study, we investigated the long-term changes and the effects of immunosuppression (IS) re-augmentation on the DSA status.

METHODS

Two DSA screenings were performed in 67 patients during long-term follow-up after liver transplantation. After the first screening, IS re-augmentation was performed in patients with consent. The effects of IS re-augmentation on the DSA status were analyzed using data of the serial DSA screenings. Negative conversion was defined as DSA positivity with MFI > 1000 converted to MFI < 1000. Improvement of DSA status was defined as either a 50% reduction of MFI or negative conversion.

RESULTS

The median interval between the first and second DSA screening was 50 months. Among 67 patients, 43 were positive for DSAs on the first screening. Among these 43 patients, 30 had minimal to no IS therapy at the time of the first screening. Among the 30 patients, IS re-augmentation was conducted in 19. A comparison between the patients with a re-augmented IS and those with a sustained minimized IS showed that the DSA levels significantly decreased in the former (63% (12/19) vs. 18% (2/11), p = 0.02).

CONCLUSIONS

The results of this study indicate that post-liver transplant IS re-augmentation had suppressive effects on the DSA status. However, the clinical significance of DSA-negative conversion and/or mean fluorescence intensity reduction needs to be further investigated through histological evaluation and/or graft survival during longer follow-up periods.

Validation and cross-reactivity pattern assessment of monoclonal antibodies used for the screening of donor-specific IgG antibody subclasses in transplant recipients

The screening for IgG subclass donor-specific antibodies (DSAs) in allograft recipients uses IgG1-4 subclass-specific monoclonal antibodies (mAbs) that should be mono-specific. The cross-reactivity discrepancies reported for IgG subclass-specific mAbs warranted a critical cross-reactivity pattern analysis of the IgG subclass-specific mAbs most commonly used to detect DSAs. We tested the reactivity of 2 anti-IgG1-, 3 anti-IgG2-, 1 anti-IgG3-, and 2 anti-IgG4-specific PE-conjugated mAbs against microbeads coated with IgG1-4 proteins separately. Each IgG subclass protein was coated at three densities on the beads (0.5, 1, and 2 μg of protein per 10⁶ beads), and the PE-conjugated mAbs were titrated from 0.04 μg/mL to 5 μg/mL. The IgG subclass reactivity of the sample was acquired on the Luminex multiplex platform. Among the IgG subclass-specific mAbs, only the anti-IgG3 (clone: HP6050) mAb was mono-specific. All other mAbs tested were binding to IgG subclass proteins other than their respective immunogen, thereby being cross-reactive. IgG subclass cross-reactivity patterns were dependent on the concentration of both IgG subclass-specific mAbs and IgG1-4 protein targets coated onto the beads. With the current IgG subclass mAbs available, 3 of the 15 possible combinations of IgG1-4 subclass protein could be identified. While the remaining 12 unique combinations cannot be distinguished clearly, 6 groups that corresponded to two different unique combinations of IgG1-4 subclass protein could be identified. The dilution of serum samples and IgG subclass-specific mAbs, other than the anti-IgG3 (clone: HP6050), must be further optimized before their implementation in IgG subclass DSA screening in allograft recipients.

The molecular diagnosis of rejection in liver transplant biopsies: First results of the INTERLIVER study

Molecular diagnosis of rejection is emerging in kidney, heart, and lung transplant biopsies and could offer insights for liver transplant biopsies. We measured gene expression by microarrays in 235 liver transplant biopsies from 10 centers. Unsupervised archetypal analysis based on expression of previously annotated rejection-related transcripts identified 4 groups: normal "R1_normal " (N = 129), T cell-mediated rejection (TCMR) "R2_TCMR " (N = 37), early injury "R3_injury " (N = 61), and fibrosis "R4_late " (N = 8). Groups differed in median time posttransplant, for example, R3_injury 99 days vs R4_late 3117 days. R2_TCMR biopsies expressed typical TCMR-related transcripts, for example, intense IFNG-induced effects. R3_injury displayed increased expression of parenchymal injury transcripts (eg, hypoxia-inducible factor EGLN1). R4_late biopsies showed immunoglobulin transcripts and injury-related transcripts. R2_TCMR correlated with histologic rejection although with many discrepancies, and R4_late with fibrosis. R2_TCMR , R3_injury , and R4_late correlated with liver function abnormalities. Supervised classifiers trained on histologic rejection showed less agreement with histology than unsupervised R2_TCMR scores. No confirmed cases of clinical antibody-mediated rejection (ABMR) were present in the population, and strategies that previously revealed ABMR in kidney and heart transplants failed to reveal a liver ABMR phenotype. In conclusion, molecular analysis of liver transplant biopsies detects rejection, has the potential to resolve ambiguities, and could assist with immunosuppressive management.

Distribution of de novo Donor-Specific Antibody Subclasses Quantified by Mass Spectrometry: High IgG3 Proportion Is Associated With Antibody-Mediated Rejection Occurrence and Severity

Donor-specific antibodies (DSAs) are the main risk factor for antibody-mediated rejection (ABMR) and graft loss but could have variable pathogenicity according to their IgG subclass composition. Luminex-based test might lack sensitivity for the detection of IgG subclasses and this test does not allow quantifying the relative abundance of each IgG subclass. We investigated the precise repartition of each DSA subclass and their role in ABMR occurrence and severity, using an innovative mass spectrometry-based method. Between 2014 and 2018, we enrolled 69 patients who developed de novo DSA (n = 29 without ABMR, and n = 40 with ABMR) in two transplant centers. All IgG subclasses were detected in every samples tested: 62.7% were IgG1, 26.6% were IgG2, 6.6% were IgG3, and 4.2% were IgG4. The IgG3 proportion was significantly higher in the ABMR+ compared to the ABMR– group (8.4% vs. 5.6%, p = 0.003). The proportion of IgG1, IgG2, and IgG4 of DSA was similar between the two groups. Higher IgG3 level was associated with higher C4d deposition, higher microvascular inflammation scores, and glomerular filtration rate decline >25%. IgG3 proportion was not correlated with DSA MFI. Multivariate analysis showed that proteinuria and high level of IgG3 DSA were the only two factors independently associated with ABMR. In conclusion, de novo DSA are always composed of the four IgG subclasses, but in different proportions. High IgG3 proportion is associated with ABMR occurrence and severity and with poorer outcome, independently of DSA MFI.

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.

IgG4 donor-specific HLA antibody profile is associated with subclinical rejection in stable pediatric liver recipients

The impact of donor-specific HLA antibody (DSA) following liver transplantation remains controversial. We hypothesized DSA IgG subclass characteristics, compared to total DSA IgG, might correlate with specific histopathological phenotype(s) of subclinical graft injury. We therefore studied 129 stable, arguably "clinically ideal," pediatric liver recipients at the time of a screening biopsy to enter an immunosuppression withdrawal trial. Sixty-five (50%) subjects tested positive for class II DSA. IgG subclass profile was characterized by mean fluorescence intensity (MFI) and normalized subclass composition (>5%). A prominent IgG4 DSA profile was strongly correlated with greater HLA mismatch, a histopathological phenotype characterized by the presence of interface activity (with variable degrees of fibrosis), and a transcriptional profile of attenuated T cell-mediated rejection. Specifically, compared to those without class II DSA, those with IgG4 class II DSA MFI sum >2000 exhibited an odds ratio (OR) of 20.79 (95% confidence interval [CI] 4.38-98.69) and IgG4 subclass composition >5% exhibited an OR of 8.99 (95% CI 2.70-29.9). Our data suggest that IgG4 DSA may serve as a useful biomarker to identify, among clinically and biochemically stable liver transplant recipients, a subset with histological and transcriptional features indicative of an active, suboptimally controlled alloimmune response.

The role of complement in antibody mediated transplant rejection

Antibody mediated transplant rejection (AMR) is a major cause of long-term allograft failure, and currently available treatments are of limited efficacy for treating the disease. AMR is caused by donor specific antibodies (DSA) that bind to antigens within the transplanted organ. DSA usually activate the classical pathway of complement within the allograft, and complement activation is believed to be an important cause of tissue injury in AMR. Several new clinical assays may improve our ability to identify patients at risk of AMR. Complement inhibitory drugs have also been tested in selected patients and in small series. Better understanding of the role of complement activation in the pathogenesis of AMR will likely improve our ability to diagnose the disease and to develop novel treatments.

Anti-donor immunoglobulin G subclass in liver transplantation

Immunoglobulin G (IgG) subclasses in human health and immunity have only be sporadically studied in the half century since their discovery. Different patterns of IgG subclass production are seen if the immune response is deviated towards type 1 versus type 2. The current state of our knowledge of IgG subclasses in liver transplantation is reviewed here. While several studies have been conducted in liver disease, only four relatively small studies have been undertaken in liver transplant recipients. Total IgG4 elevation in serum is related to sclerosing pancreatico-cholangiopathy that is sensitive to treatment with steroids. Conventional immunosuppressive regimes, especially with a combination of tacrolimus and sirolimus, reduce the production of all IgG subclasses after transplantation but it is not known if they deviate the immune response. Presence of anti-donor IgG3 before transplantation, or its expansion after transplantation, has been associated with rejection and liver graft loss. Anti-GSTT1 IgG4 production after transplantation is associated with de-novo immune hepatitis. Greater knowledge of anti-donor IgG subclass responses after transplantation will allow us tailor novel treatments for greater effect.

Sensitization in Heart Transplantation: Emerging Knowledge: A Scientific Statement From the American Heart Association

Sensitization, defined as the presence of circulating antibodies, presents challenges for heart transplant recipients and physicians. When present, sensitization can limit a transplantation candidate’s access to organs, prolong wait time, and, in some cases, exclude the candidate from heart transplantation altogether. The management of sensitization is not yet standardized, and current therapies have not yielded consistent results. Although current strategies involve antibody suppression and removal with intravenous immunoglobulin, plasmapheresis, and antibody therapy, newer strategies with more specific targets are being investigated.

Characterizing the B-Cell and Humoral Response in Tertiary Lymphoid Organs in Kidney Allografts

OBJECTIVES

Tertiary lymphoid organs are formed at sites of chronic inflammation and are thought to contribute to the immune response. Here, we aimed to characterize the structure and function of tertiary lymphoid organs in a model of murine kidney allotransplant to understand their role in alloimmunity.

MATERIALS AND METHODS

We transplanted 4 C57BL/6 mouse kidneys (isograft group) and 17 DBA/2 mouse kidneys into C57BL/6 mouse recipients. Three DBA/2-to-C57BL/6 transplant mice that rejected their grafts acutely (before 10 days posttransplant) were excluded from the study. The 14 surviving DAB2 grafts were retrieved at day 45 posttransplant and evaluated histologically. The presence of antibody-secreting cells and circulating levels of donor-specific antibodies were also evaluated.

RESULTS

We found that tertiary lymphoid organs can be associated with a beneficial response in a kidney allotransplant model. Characterization of B-cell subsets within tertiary lymphoid organs in mouse kidney allografts revealed naive, plasma, and memory B cells, which were mostly grouped within or in close proximity of tertiary lymphoid organs. Staining for intracellular immunoglobulin G showed that many of the B cells within tertiary lymphoid organs were capable of producing antibodies. Although allospecific antibodies were found in the serum of recipient mice and were deposited in the transplanted kidneys, graft function was not affected in this model.

CONCLUSIONS

B cells within tertiary lymphoid organs are functional and contribute to the humoral arm of the alloresponse. However, tertiary lymphoid organs are not necessarily associated with graft rejection, suggesting that protective mechanisms are at play.

Evidence of Chronic Allograft Injury in Liver Biopsies From Long-term Pediatric Recipients of Liver Transplants

BACKGROUND & AIMS

A substantial proportion of pediatric liver transplant recipients develop subclinical chronic allograft injury. We studied whether there are distinct patterns of injury based on histopathologic features and identified associated immunologic profiles.

METHODS

We conducted a cross-sectional study of 157 stable, long-term pediatric recipients of transplanted livers (70 boys; > 6 years old at time of transplantation; mean, 8.9 ± 3.46 years after liver transplantation) who underwent liver biopsy analysis from August 13, 2012, through May 1, 2014. Participants had received livers from a living or deceased donor and had consistently normal results from liver tests. Liver biopsy specimens were scored by a central pathologist; an unsupervised hierarchical cluster analysis of histologic features was used to sort biopsy samples into 3 clusters. We conducted transcriptional and cytometric analyses of liver tissue samples and performed a systems biology analysis that incorporated clinical, serologic, histologic, and transcriptional data.

RESULTS

The mean level of alanine aminotransferase in participants was 27.6 ± 14.57 U/L, and the mean level of γ-glutamyl transferase was 17.4 ± 7.93 U/L. Cluster 1 was characterized by interface activity (n = 34), cluster 2 was characterized by periportal or perivenular fibrosis without interface activity (n = 45), and cluster 3 had neither feature (n = 78). We identified a module of genes whose expression correlated with levels of alanine aminotransferase, class II donor-specific antibody, portal inflammation, interface activity, perivenular inflammation, portal and perivenular fibrosis, and cluster assignment. The module was enriched in genes that regulate T-cell-mediated rejection (TCMR) of liver and other transplanted organs. Functional pathway analysis showed overrepresentation of TCMR gene sets for cluster 1 but not clusters 2 or 3.

CONCLUSION

In an analysis of biopsies from an apparently homogeneous group of stable, long-term pediatric liver transplant recipients with consistently normal liver test results, we found evidence of chronic graft injury (inflammation and/or fibrosis). Biopsy samples with interface activity had a gene expression pattern associated with TCMR.

Maintaining the Health of the Renal Allograft: Laboratory and Histologic Monitoring After Kidney Transplantation

Advances in posttransplant care, including new immunosuppressive medications have led to excellent short-term renal allograft survival. However, there is a small therapeutic window within which the patient and the clinician must balance the risk of rejection, with side effects such as infection, malignancy, and toxicity. Laboratory testing plays a key role in this ongoing monitoring, which includes relatively simple tests, such as serum creatinine, to complex tests, such as solid-phase assays, used to monitor for donor-specific antibody and surveillance allograft biopsies. This article reviews the role of the laboratory tests and surveillance biopsies in posttransplant monitoring.

Anti-HLA Donor-Specific IgG Subclasses and C1q-binding Evolution in Posttransplant Monitoring

Background

The identification of low-level antibodies by single-antigen bead methodology has brought advancements to risk evaluation of kidney transplant recipients. However, the use of mean fluorescence intensity (MFI) to quantify antibodies and to guide therapy is not enough. Notably, immunoglobulin G (IgG) subclass switching is hypothesized to follow a programmed sequence after an emergency signal from the germinal center. In transplantation this process is not clear yet. In the present study, we sequentially evaluate anti-HLA donor specific antibody (DSA) subclasses, their profile changes, and C1q-binding ability and the influence of those characteristics on antibody mediated rejection (AMR) occurrence and allograft function.

Methods

A total of 30 DSA-positive patients were tested for IgG subclass content and C1q-binding in sequential serum samples.

Results

Twenty-one patients were DSA-positive before transplant; patients sensitized only by transfusion or pregnancies had IgG1 and/or IgG3, and patients sensitized by both transfusion and pregnancies or previous transplant showed a broader range of IgG subclasses. C1q binding was detected in high MFI made up of IgG1 or multiple IgG subclasses. Only 4 patients were positive for C1q posttransplantation and 3 of these showed an increase in MFI, changes in subclasses patterns, AMR, and allograft dysfunction.

Conclusions

Posttransplant evaluation of DSA subclasses and the ability to bind C1q may be informative for both AMR occurrence and allograft dysfunction. Monitoring these events may help to better define risk and interventional time points.

IGG3 anti-HLA donor-specific antibodies and graft function in pediatric kidney transplant recipients

Anti-HLA DSAs are associated with ABMR and graft loss in KT recipients, yet the influence of DSA IgG subclass on outcomes in pediatric KT recipients is not completely understood. We performed a single-center retrospective chart review of pediatric KT recipients with anti-HLA DSAs, aiming to study the association between specific DSA IgG subclasses and graft outcomes, including ABMR and significant graft dysfunction (graft loss or 50% decrease in eGFR). Thirty-six patients (mean age 15.4y) with DSAs initially detected 1 month-14.3 years post-transplantation were followed for a median of 2.8 years. Rates of IgG1, 2, 3, and 4 subclass detection were 92%, 33%, 58%, and 25%, respectively. Twenty-two patients (61%) had clinical ABMR, whereas 19% had subclinical ABMR, and 13 (36%) experienced significant graft dysfunction. Patients with IgG3+ DSAs had a higher risk of graft dysfunction compared with IgG3- patients (52% vs 13%, P = .03). In a multiple Cox proportional regression analysis, the presence of IgG3+ DSA was independently associated with significant graft dysfunction (HR 10.45, 95% CI 1.97-55.55, P = .006). In conclusion, IgG3 subclass DSAs are associated with graft dysfunction and may be useful for risk stratification and treatment decisions in DSA-positive pediatric KT recipients.

Prevalence, Risk Factors, and Impact of Donor-Specific Alloantibodies After Adult Liver Transplantation

The incidence and impact of anti-human leukocyte antigen donor-specific alloantibodies (DSAs) developing after liver transplantation (LT) remains controversial and not extensively studied. The aim of the present study was to assess the incidence of DSAs, to identify risk factors for the development of DSAs, and to understand the impact of DSAs in a large population of adult LT recipients. This single-center retrospective study included all adult patients who underwent a first LT between 2000 and 2010 in our center. The study population mainly consisted of male patients, the mean age was 52.4 years, and the main indication was alcoholic cirrhosis (54.1%). From the 297 patients included in the cross-sectional study, 14 (4.7%) had preformed DSAs, and 59 (19.9%) presented de novo DSAs (12.2% at 1 year, 13.4% at 5 years, and 19.5% at 10 years). Multivariate analysis found that female donor sex (hazard ratio [HR], 1.50; 95% confidence interval [CI], 1.12-2.01; P = 0.01) and delay between LT and DSA screening (HR, 1.10; 95% CI, 1.01-1.20; P = 0.03) were associated with occurrence of de novo DSAs. From the 190 patients included in the subgroup longitudinal analysis, exposure to tacrolimus (mean trough level during the periods 0-2 years and 0-3 years) was significantly lower for patients having DSAs at 5 years. Concerning histology, only acute rejection (P = 0.04) and portal fibrosis ≥2 (P = 0.02) were more frequent at 1 year for patients with DSAs. Patient survival and graft survival were not significantly different according to the presence or not of DSAs at 1 year. Among the 44 patients who had de novo or persistent preformed DSAs, the diagnosis of antibody-mediated rejection was made in 4 (9.1%) patients after 1, 47, 61, and 74 months following LT. In conclusion, the results of the present study suggest that DSAs are observed in a minority of LT adult patients, with limited overall impact on graft and patient outcome.

Complement-activating donor-specific anti-HLA antibodies and solid organ transplant survival: A systematic review and meta-analysis

BACKGROUND

Anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) are recognized as a major barrier to patients' access to organ transplantation and the major cause of graft failure. The capacity of circulating anti-HLA DSAs to activate complement has been suggested as a potential biomarker for optimizing graft allocation and improving the rate of successful transplantations.

METHODS AND FINDINGS

To address the clinical relevance of complement-activating anti-HLA DSAs across all solid organ transplant patients, we performed a meta-analysis of their association with transplant outcome through a systematic review, from inception to January 31, 2018. The primary outcome was allograft loss, and the secondary outcome was allograft rejection. A comprehensive search strategy was conducted through several databases (Medline, Embase, Cochrane, and Scopus). A total of 5,861 eligible citations were identified. A total of 37 studies were included in the meta-analysis. Studies reported on 7,936 patients, including kidney (n = 5,991), liver (n = 1,459), heart (n = 370), and lung recipients (n = 116). Solid organ transplant recipients with circulating complement-activating anti-HLA DSAs experienced an increased risk of allograft loss (pooled HR 3.09; 95% CI 2.55-3.74, P = 0.001; I2 = 29.3%), and allograft rejection (pooled HR 3.75; 95% CI: 2.05-6.87, P = 0.001; I2 = 69.8%) compared to patients without complement-activating anti-HLA DSAs. The association between circulating complement-activating anti-HLA DSAs and allograft failure was consistent across all subgroups and sensitivity analyses. Limitations of the study are the observational and retrospective design of almost all included studies, the higher proportion of kidney recipients compared to other solid organ transplant recipients, and the inclusion of fewer studies investigating allograft rejection.

CONCLUSIONS

In this study, we found that circulating complement-activating anti-HLA DSAs had a significant deleterious impact on solid organ transplant survival and risk of rejection. The detection of complement-activating anti-HLA DSAs may add value at an individual patient level for noninvasive biomarker-guided risk stratification.

TRIAL REGISTRATION

National Clinical Trial protocol ID: NCT03438058.

Application and interpretation of histocompatibility data in liver transplantation

PURPOSE OF REVIEW

There has been a resurgence of interest in histocompatibility as it applies to liver transplantation. The association of persistent and de-novo donor specific antibody (DSA) and outcomes after liver transplantation continues to be investigated.

RECENT FINDINGS

Consensus continues to evolve regarding the existence of acute and chronic antibody-mediated rejection (AMR) and pathogenicity of DSA and associated pathologic findings after liver transplantation. The presence of persistent high level, complement fixing DSA or emergence of de novo, Class II DSA has been associated with rejection and worse long-term graft and patient survival. Significant adverse associations of DSA extend to patients after simultaneous liver kidney (SLK) transplant as well as in pediatric recipients of liver transplantation. A higher degree of HLA incompatibility has been recently associated with worse outcomes in living donor liver transplant.

SUMMARY

In summary, recent consensus guidelines describe and recognize the existence of acute and chronic AMR and provide a basis upon which to build further investigation. Important adverse outcomes including decreased survival, allograft failure and liver fibrosis have been linked to the presence of DSA. Routine donor and recipient HLA typing and DSA assessment will facilitate diagnosis and provide for baseline data, which may help guide future management. Future investigations may help to clarify the role of therapeutic interventions.

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.

The Road to HLA Antibody Evaluation: Do Not Rely on MFI

Technological advances in HLA laboratory testing undoubtedly improved the sensitivity and specificity of HLA antibody assessment but not without introducing a set of challenges regarding data interpretation. In particular, the introduction of solid-phase single-antigen bead (SAB) antibody assessment brought the belief that mean fluorescence intensity (MFI) was a quantifiable value. As such, MFI levels heavily influenced HLA antibody reporting, monitoring, and clinical practice. However, given that SAB testing was neither intended for nor approved to be quantifiable, is the use of MFI in current clinical and laboratory practice valid? What, if anything, does this numerical value actually reveal about the pathogenic potential of the antibody? What are the pitfalls and caveats associated with reporting MFI? Herein, we travel the road to HLA antibody assessment and explore the reliability of MFI values to make clinical decisions.

Antibody-Mediated Rejection in Kidney Transplantation Without Evidence of Anti-HLA Antibodies?

INTRODUCTION

The definition of antibody-mediated rejection (AMR) is based on serologic (presence and/or development of donor-specific anti-HLA antibodies [DSAs]) and histologic (C4d deposition and endothelial damage) criteria. However, several cases of AMR have been described without C4d deposition, and other cases of histologic AMR without DSAs, which could be driven by other non-HLA alloantibodies such as anti-MICA or anti-angiotensin II type I receptor (AT1R). Here we studied clinical and histologic humoral rejection in kidney transplant recipients without evidence of anti-HLA antibodies.

MATERIALS AND METHODS

Fifteen kidney transplant recipients with AMR defined as C4d⁺ and/or histologic g+ptc without anti-HLA antibodies in screening test were studied. Sera at the moment of biopsy and 2 months earlier were studied for anti-HLA antibodies by Luminex, in neat, diluted 1/160, and sera after treatment with dithiothreitol (DTT) and confirmed by single-antigen test. The anti-AT1R was measured by enzyme-linked immunosorbent assay.

RESULTS

A lack of anti-HLA and MICA antibodies was confirmed after anti-HLA screening test in all conditions (neat, diluted, and DTT-treated) and de novo development of AT1R antibodies was ruled out. Nevertheless, after single-antigen test, 3 patients were identified with a weak reaction against class I antigen and another 4 patients against class II antigen. Due to the lack of locus-C typing in the donors, the DSA assignment cannot be confirmed, whereas anti-HLA class II antigens were DSA.

CONCLUSIONS

A low sensitivity in the screening of anti-HLA antibody testing was observed. Our results suggest performing single-antigen test in seronegative patients with clinical humoral rejection after screening to confirm the presence of DSA.

Not All Antibodies Are Created Equal: Factors That Influence Antibody Mediated Rejection

Consistent with Dr. Paul Terasaki's "humoral theory of rejection" numerous studies have shown that HLA antibodies can cause acute and chronic antibody mediated rejection (AMR) and decreased graft survival. New evidence also supports a role for antibodies to non-HLA antigens in AMR and allograft injury. Despite the remarkable efforts by leaders in the field who pioneered single antigen bead technology for detection of donor specific antibodies, a considerable amount of work is still needed to better define the antibody attributes that are associated with AMR pathology. This review highlights what is currently known about the clinical context of pre and posttransplant antibodies, antibody characteristics that influence AMR, and the paths after donor specific antibody production (no rejection, subclinical rejection, and clinical dysfunction with AMR).