Poor graft outcome in recipients with de novo donor-specific anti-HLA antibodies after living related kidney transplantation

A bibliometric and knowledge-map analysis of antibody-mediated rejection in kidney transplantation

OBJECTIVES

Antibody-mediated rejection (AMR) is a large obstacle to the long-term survival of allograft kidneys. It is urgent to find novel strategies for its prevention and treatment. Bibliometric analysis is helpful in understanding the directions of one field. Hence, this study aims to analyze the state and emerging trends of AMR in kidney transplantation.

METHODS

Literature on AMR in kidney transplantation from 1999 to 2022 was collected from the Web of Science Core Collection. HistCite (version 12.03.17), CiteSpace (version 6.2.R2), Bibliometrix 4.1.0 Package from R language, and Gephi (https://gephi.org) were applied to the bibliometric analysis of the annual publications, leading countries/regions, core journals, references, keywords, and trend topics.

RESULTS

A total of 2522 articles related to AMR in kidney transplantation were included in the analysis and the annual publications increased year by year. There were 10874 authors from 118 institutions located in 70 countries/regions contributing to AMR studies, and the United States took the leading position in both articles and citation scores. Halloran PF from Canada made the most contribution to AMR in kidney transplantation. The top 3 productive journals, American Journal of Transplantation, Transplantation, and Transplantation Proceedings, were associated with transplantation. Moreover, the recent trend topics mainly focused on transplant outcomes, survival, and clinical research.

CONCLUSIONS

North American and European countries/regions played central roles in AMR of kidney transplantation. Importantly, the prognosis of AMR is the hotspot in the future. Noninvasive strategies like plasma and urine dd-cfDNA may be the most potential direction in the AMR field.

Influence of a low-dose tacrolimus protocol on the appearance of de novo donor-specific antibodies during 7 years of follow-up after renal transplantation

BACKGROUND

Tacrolimus (TAC) is a key immunosuppressant drug for kidney transplantation (KTx). However, the optimal serum trough level of TAC for good long-term outcomes remains unclear. This study aimed to investigate the relationship between the maintenance TAC trough level and the appearance of de novo donor-specific anti-human leukocyte antigen (HLA) antibodies (dnDSAs).

METHODS

A total of 584 KTx recipients were enrolled in this study, of whom 164 developed dnDSAs during the follow-up period and 420 did not.

RESULTS

We found no significant relationship between TAC trough level during the follow-up period and dnDSA incidence. Patients who developed dnDSAs had a significantly greater number of HLA-A/B/DR mismatches (3.4 ± 1.3 versus 2.8 ± 1.5; P < 0.001), were more likely to have preformed DSAs (48.2% versus 27.1%; P < 0.001) and showed poor allograft outcome.

CONCLUSIONS

There was no clear relationship between TAC trough level and dnDSA incidence for KTx recipients whose TAC trough levels were kept within the narrow range of 4-6 ng/mL during the immunosuppression maintenance period.

Post-transplant de novo non donor-specific HLA antibodies are not associated with poor graft outcome in non-sensitized pediatric recipients of kidney transplantation

While de novo donor-specific HLA antibodies (dnDSAs) have a detrimental impact on kidney graft outcome, the clinical significance of de novo non donor-specific antibodies (dnNDSAs) is more controversial. We retrospectively evaluated for Ab development and characteristics of dnNDSAs serially collected post-transplant sera and, when available, graft biopsy eluates, from 144 non-sensitized, primary pediatric kidney recipients, consecutively transplanted at a single center between 2003 and 2017, using HLA class I and class II single-antigen flow-bead assays (SAB). The results were compared with clinical-pathologic data from HLA antibody negative and HLA dnDSA-positive patients. Forty-five out of 144 patients developed dnNDSAs (31%). Among the dnNDSA-positive patients, 86% displayed one or more class I/II antibodies recognizing antigens included in the CREG/shared epitope groups that also comprise the mismatched donor HLA antigens. Despite potential pathogenicity, as suggested by their occasional presence within the graft, dnNDSAs displayed significantly lower MFI, and limited complement binding and graft homing properties, when compared with dnDSAs. In parallel, the graft survival probability was significantly lower in patients with dnDSA than in those with dnNDSA or without HLA antibodies (p < 0.005). Indeed, the dnNDSA-positive patients remaining dnDSA-negative throughout the posttransplant period did not develop clinical antibody mediated rejection and graft loss, and maintained good graft function at a median follow-up of 9 years. The biological characteristics of dnNDSAs may account for the low graft damaging capability when compared to dnDSAs.

Immunosuppression-related neurological disorders in kidney transplantation

A large number of neurological disorders can affect renal transplant recipients, potentially leading to disabling or life-threatening complications. Prevention, early diagnosis and appropriate management of these conditions are critical to avoid irreversible lesions. A pivotal role in the pathogenesis of common post-transplant neurological disorders is played by immunosuppressive therapy. The most frequently administered regimen consists of triple immunosuppression, which comprises a calcineurin inhibitor (CNI), a purine synthesis inhibitor and glucocorticoids. Some of these immunosuppressive drugs may lead to neurological signs and symptoms through direct neurotoxic effects, and all of them may be responsible for the development of tumors or opportunistic infections. In this review, after a brief summary of neurotoxic pathogenetic mechanisms encompassing recent advances in the field, we focus on the clinical presentation of more common and severe immunosuppression-related neurological complications, classifying them by characteristics of urgency and anatomic site. Our goal is to provide a general framework that addresses such clinical issues with a multidisciplinary approach, as these conditions require.

Characteristics and Clinical Significance of De Novo Donor-Specific Anti-HLA Antibodies after Kidney Transplantation

BACKGROUND

The association of de novo donor-specific anti-human leukocyte antigens (HLA) antibodies (DSA) and development of antibody-mediated rejection (AMR) in kidney transplant recipients (KTRs) is still undetermined.

METHODS

We prospectively screened de novo DSA in 167 KTRs during 32 months after kidney transplantation (KT). Timing of DSA detection was at 3, 6, and 12 months post-transplant and annually thereafter and when clinically indicated. DSA levels were determined by Luminex assays and expressed as mean fluorescence intensity (MFI). We evaluated the incidence, characteristics of DSA, and association between DSA and tacrolimus trough levels or AMR.

RESULTS

De novo DSA developed in 16 KTRs (9.6%) and acute AMR occurred more commonly in KTRs with de novo DSA compared to KTRs without de novo DSA (18.8% vs. 0%, P < 0.001). All de novo DSA were against class II antigens. The mean number of DSA was 1.8 ± 1.2 and the average MFI of DSA was 7,399 ± 5,470. Tacrolimus trough level during the first 0-2 months after KT was an independent predictor of DSA development (hazard ratio, 0.70; 95% confidence interval, 0.50-0.99; P = 0.043). No differences were found in the number of DSA, average MFI of DSA, and tacrolimus levels during the first year between de novo DSA-positive KTRs with AMR and those without AMR.

CONCLUSION

The results of our study suggest that monitoring of DSA and maintaining proper tacrolimus levels are essential to prevent AMR during the initial period after KT.

Detection and clinical impact of human leukocyte antigen antibodies in lung transplantation: A systematic review and meta-analysis

There is significant variability in lung transplant centers' approach to HLA antibodies, creating heterogeneity regarding their clinical significance. Some institutions use beads coated with multiple HLA to screen candidate sera and then use single antigen bead (SAB) to determine antibody identity if the pre-screen is positive. Other centers do not pre-screen, using SAB alone, which may detect low-level antibodies of unknown significance. The primary objective of this study was to review the current literature to identify sources of heterogeneity in the identification of pre- and post-lung transplant HLA antibodies, particularly regarding antibody-detection methods. A random effects model meta-analysis was used to evaluate the relationship between pre-transplant HLA antibodies and the development of de novo donor-specific antibodies (dnDSA) and dnDSA and chronic lung allograft dysfunction (CLAD). Each outcome was stratified by the method of antibody detection (pre-screen followed by SAB vs SAB alone). We identified 13 cohort studies with a total of 3039 patients. The use of pre-screening followed by SAB testing and the use of induction immunosuppression were associated with lower prevalence of dnDSA. Patients with pre-transplant HLA antibodies were more likely to develop dnDSA (hazard ratio [HR] = 1.49, 95% confidence interval [CI]: 1.19-1.86, P < .001). dnDSA was associated with CLAD (HR = 2.02, 95% CI = 1.37-2.97, P < .001). When considering studies using SAB alone, however, pre-transplant antibody status was no longer associated with dnDSA and dnDSA was no longer associated with CLAD. Based on the current literature, SAB-alone testing may detect less clinically relevant antibodies than pre-screening followed by SAB.

Detection of T and B cells specific complement-fixing alloantibodies using flow cytometry: A diagnostic approach for a resource limited laboratory

BACKGROUND AND OBJECTIVES

Various methods have been reported for the detection of antibodies in recipient sera, which can be human leukocyte antigens (HLAs) or non-HLA specific, complement- or noncomplement fixing, as well as donor T (HLA-Class-I) and/or B cell (HLA-Class-I and II) specific. These alloantibodies play a pivotal role in antibody-mediated renal transplantation rejection. Deposition of C4d in peritubular capillaries of a kidney biopsy is a marker of antibody-mediated rejection. The C4d flow-panel reactive antibodies (PRAs) are a screening method for HLA-specific and complement fixing antibodies. However, the method is limited by the lack of donor specificity.

DESIGN AND SETTINGS

Here, we present a new and simple flow cytometric method referred to as C4d-flow cytometry crossmatch (C4d-FCXM) for the detection of donor-specific (T and/or B cell) and C4d-fixing alloantibodies.

RESULTS

The method was applied in a series of clinical cases and judged to be useful. The method may limit unwanted deferral of the donor due to positivity in C4d Flow-PRA and/or FCXM and may be helpful in prediction of antibody mediated rejections. Furthermore, this method can provide information pretransplant in contrast to kidney biopsy and C4d evaluation done posttransplant.

CONCLUSIONS

We postulate that this method incorporates most of the features of all the available modalities (i.e., National Institute of Health-complement dependent lymphocytotoxicity, FCXM, cytotoxic FCXM and C4d-flowPRA) yet cost-effective and best suited for resource-limited laboratory/ies which is a common scenario in developing countries.

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.

Donor-Specific Antibody Monitoring: Where Is the Beef?

This review paper discusses the impact of de novo donor-specific antibodies (DSA) to donor HLA antigens in kidney transplantation and summarizes the benefits and challenges that exist with DSA monitoring. Post-transplant DSA is associated with worse allograft outcomes and its detection may precede or coincide with clinical, biochemical, and histologic allograft dysfunction. There are no absolute features of DSA testing results that perfectly discriminate between states of disease and health. In a state of antibody-associated graft dysfunction, removal or reduction in DSA may only provide clinical benefit for some. Furthermore, various factors influence test results, and detection of HLA antibodies must be interpreted within the appropriate clinical and laboratory context. The utility of DSA monitoring is further affected by the limited effectiveness of treatment for antibody-mediated rejection. Although DSA monitoring is potentially beneficial in some circumstances, the optimal screening and treatment strategies are still to be defined.

Porcine antigen-specific IFN-γ ELISpot as a potentially valuable tool for monitoring cellular immune responses in pig-to-non-human primate islet xenotransplantation

BACKGROUND

Recent progress in xenotransplantation of porcine islets to non-human primates (NHPs) gives hope for human clinical trials in the near future. Thus, implementation of an appropriate monitoring method to detect the development of detrimental porcine antigen-specific cellular immune responses is necessary. The enzyme-linked immunospot (ELISpot) assay has been widely used to monitor antigen-specific alloreactive T-cell responses in humans; however, the utility of porcine islet-specific ELISpot assay has not yet been thoroughly evaluated for pig-to-NHPs intraportal islet xenotransplantation.

METHODS

The optimal ELISpot assay conditions, including the number of responder and stimulator cells and the provision of costimulation, were determined. Then, ELISpot assays were conducted on serial stocks of peripheral blood mononuclear cell (PBMC) samples previously isolated from NHP recipients transplanted with porcine islets. Either splenocytes from donor pigs or pancreatic islets from third-party pigs were used for antigen stimulation. At the same time, the ratio of CD4(+) /CD8(+) T cells and the percentage of CD4(+) FoxP3(+) T cells in the peripheral blood were evaluated. Finally, liver biopsy samples were evaluated to assess the immunopathology of the grafts.

RESULTS

The optimal conditions for the ELISpot assay were defined as 2.5 × 10(5) responder cells incubated with 5.0 × 10(5) stimulator cells in 96-well, flat-bottom plates without further costimulation. Using donor splenocytes as stimulators, a serial interferon-gamma (IFN-γ) ELISpot assay with PBMCs from the monkeys with prolonged porcine islet grafts (>180 days) demonstrated that the number of donor antigen-specific IFN-γ-producing cells significantly increased upon overt graft rejection. However, use of third-party porcine islets as stimulators did not reflect graft rejection, suggesting that the use of donor-specific PBMCs, and not tissue (porcine islet)-specific cells, as stimulators could better serve the purpose of this assay in adult porcine islet transplantation. IFN-γ spot number was neither influenced by the peripheral blood CD4(+) /CD8(+) T-cell ratio nor the percentage of CD4(+) FoxP3(+) T cells. Finally, in cases of overt graft rejection, the number of IFN-γ spots and the graft-infiltrating T cells in biopsied liver samples increased simultaneously.

CONCLUSION

Use of PBMCs in a porcine antigen-specific IFN-γ ELISpot assay is a reliable method for monitoring T-cell-mediated rejection in pig-to-NHP islet xenotransplantation.

Association of Kidney Graft Loss With De Novo Produced Donor-Specific and Non-Donor-Specific HLA Antibodies Detected by Single Antigen Testing

BACKGROUND

The association of donor-specific HLA antibodies (DSA) with kidney graft failure has been addressed previously; however, the majority of studies were based on small numbers of patients with graft failure.

METHODS

We investigated 83 patients with failed kidney transplants for a possible association of de novo development and persistence or loss of pre-existing DSA with graft failure. Single Antigen Bead assay-detected DSA and non-DSA antibodies were compared between patients with graft loss and matched controls with functioning grafts.

RESULTS

The incidence of weak de novo DSA or non-DSA at a mean fluorescence intensity of 500 or higher was higher in the graft loss than in the nonrejector group (76% vs 40%, P < 0.001). Because of the low number of patients developing de novo DSA, the DSA results did not reach statistical significance (only 22% of patients with graft loss developed de novo DSA). However, at all cutoffs, there was a significantly higher rate of graft loss in patients with de novo non-DSA. The incidence of strong pretransplant DSA that persist after transplantation was higher in the graft loss group (10% vs 1%, P = 0.034). When C1q-binding ability in sera of rejectors and nonrejectors with posttransplant de novo or persistent DSA was compared, none of the nonrejectors demonstrated C1q positivity, whereas 43% of patients with graft loss showed C1q-positive antibodies, although not necessarily donor-specific (P < 0.001).

CONCLUSIONS

Our data show that the posttransplant presence of persisting or de novo HLA antibodies, especially if C1q binding, is associated with graft loss, even if the antibodies are not specific for mismatched donor HLA.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

Influence of preoperative anti-HLA antibodies on short- and long-term graft survival in recipients with or without rituximab treatment

We investigated the relationship between preoperative anti-HLA antibodies (donor-specific antibody, DSA) and the graft survival rate in recipients who had or had not received rituximab (Rit) treatment. The subjects were categorized into four groups as follows: DSA+Rit-, n = 39; DSA-Rit-, n = 121; DSA+Rit+, n = 74; and DSA-Rit+, n = 47. We examined the influence of preoperative DSA on the incidence of graft rejection and the survival rate of recipients who had or who had not received rituximab before transplantation. The 6-month acute rejection rates based on graft biopsies were 39%, 19%, 15%, and 0% for the DSA+Rit-, DSA-Rit-, DSA+Rit+, and DSA-Rit+ groups. The rates of chronic antibody-mediated rejection after more than 6 months were 50%, 22%, 18%, and 0%. The 5-year graft survival rate was significantly lower in the DSA+Rit- group (84%) than in the other groups (95% for DSA-Rit-, 98% for DSA+Rit+, and 91% for DSA-Rit+). The rate of the appearance of de novo anti-HLA antibodies was higher in the groups that did not receive rituximab treatment. The rate of graft loss associated with chronic antibody-mediated rejection was also higher in the DSA+Rit- group than in the other groups (P = 0.01). The presence of DSA and the administration of rituximab had strong impacts on not only short-term graft rejection, but also long-term graft rejection and its association with the graft survival time.

Posttransplant allosensitization in low immunological risk kidney and kidney-pancreas graft recipients

Introduction. Posttransplantation allosensitization prevalence and effect on kidney grafts outcomes remain unsettled. Methods. Between 2007 and 2012, 408 patients received a primary kidney graft (with 68 patients also receiving a pancreas graft) after a negative cytotoxic crossmatch. All patients had a pretransplant negative anti-HLA screening and 0% panel reactive antibodies. We analyzed retrospectively the results of anti-HLA antibodies screening by Luminex assay, performed between 6 and 24 months after transplant, and searched for the risk factors for antibody positivity and its impact on kidney graft outcomes. Results. Anti-HLA antibodies prevalence at 6 months was 17.4%. Previous steroid-insensitive acute rejection was the only risk factor for both anti-HLA classes detected antibodies. Antithymocyte globulin induction was also a risk factor for anti-HLA-I antibodies. Antibody positivity status was associated with reduced graft function at 12 months and graft survival at 5 years (91.5% versus 96.4%, P = 0.03). In multivariable Cox analysis, delayed graft function (HR = 6.1, P < 0.01), HLA mismatches >3 (HR = 10.2, P = 0.03), and antibody positivity for anti-HLA class II (HR = 5.1, P = 0.04) or class I/II (HR = 13.8, P < 0.01) were independent predictors of graft loss. Conclusions. Allosensitization against HLA class II ± I after transplant was associated with adverse kidney graft outcomes. A screening protocol seems advisable within the first year in low immunological risk patients.

Impact of de novo donor-specific HLA antibodies detected by Luminex solid-phase assay after transplantation in a group of 88 consecutive living-donor renal transplantations

De novo donor-specific HLA antibodies (DSA) after renal transplantation are known to be correlated with poor graft outcome and the development of acute and chronic rejection. Currently, data for the influence of de novo DSA in patient cohorts including only living-donor renal transplantations (LDRT) are limited. A consecutive cohort of 88 LDRT was tested for the occurrence of de novo DSA by utilizing the highly sensitive Luminex solid-phase assay for antibody detection. Data were analyzed for risk factors for de novo DSA development and correlated with acute rejection (AR) and graft function. Patients with de novo DSA [31 (35%)] showed a trend for inferior graft function [mean creatinine change (mg/dL/year) after the first year: 0.15 DSA (+) vs. 0.02 DSA (-) (P = 0.10)] and a higher rate of AR episodes, especially in case of de novo DSA of both class I and II [6 (55%), (P = 0.05)]. Antibody-mediated rejection (AMR) appeared in five patients and was significantly correlated with de novo DSA (P = 0.05). Monitoring for de novo DSA after LDRT may help to identify patients at risk of declining renal function. Especially patients with simultaneous presence of de novo DSA class I and class II are at a high risk to suffer AR episodes.

De novo donor-specific HLA antibodies decrease patient and graft survival in liver transplant recipients

The role of de novo donor-specific HLA antibodies (DSA) in liver transplantation remains unknown as most of the previous studies have only focused on preformed HLA antibodies. To understand the significance of de novo DSA, we designed a retrospective cohort study of 749 adult liver transplant recipients with pre- and posttransplant serum samples that were analyzed for DSA. We found that 8.1% of patients developed de novo DSA 1 year after transplant; almost all de novo DSAs were against HLA class II antigens, and the majority were against DQ antigens. In multivariable modeling, the use of cyclosporine (as opposed to tacrolimus) and low calcineurin inhibitor levels increased the risk of de novo DSA formation, while a calculated MELD score >15 at transplant and recipient age >60 years old reduced the risk. Multivariable analysis also demonstrated that patients with de novo DSA at 1-year had significantly lower patient and graft survival. In conclusion, we demonstrate that de novo DSA development after liver transplantation is an independent risk factor for patient death and graft loss.

Posttransplant monitoring of de novo human leukocyte antigen donor-specific antibodies in kidney transplantation

PURPOSE OF REVIEW

To summarize the evidence supporting the negative impact of de novo donor-specific antibodies (dnDSA) in renal transplantation and to describe the natural history associated with the development of dnDSA.

RECENT FINDINGS

Recent studies have increased our appreciation of the risk factors that predispose to dnDSA while illuminating how these risk factors may relate to the pathophysiology underlying its development. In addition, details regarding the natural history of dnDSA are now available in the context of the different clinical pathologic phenotypes that occur in the patients in whom it develops. Common pitfalls in defining and monitoring dnDSA, when understood, may provide some explanation for the heterogeneity in published studies.

SUMMARY

Recognizing that dnDSA is a major cause of late graft loss, and, more importantly, is detectable in many cases long before dysfunction or graft loss occurs, identifies an opportunity to intervene and change the outcome for the patient.

Maternal floor infarction/massive perivillous fibrin deposition: a manifestation of maternal antifetal rejection?

OBJECTIVE

Massive perivillous fibrin deposition (MPFD) and maternal floor infarction (MFI) are related placental lesions often associated with fetal death and fetal growth restriction. A tendency to recur in subsequent pregnancies has been reported. This study was conducted to determine whether this complication of pregnancy could reflect maternal antifetal rejection.

METHODS

Pregnancies with MPFD were identified (n = 10). Controls consisted of women with uncomplicated pregnancies who delivered at term without MPFD (n = 175). Second-trimester maternal plasma was analyzed for panel-reactive anti-HLA class I and class II antibodies. The prevalence of chronic chorioamnionitis, villitis of unknown etiology, and plasma cell deciduitis was compared between cases and controls. Immunohistochemistry was performed on available umbilical vein segments from cases with MPFD (n = 4) to determine whether there was evidence of complement activation (C4d deposition). Specific maternal HLA-antibody and fetal HLA-antigen status were also determined in paired specimens (n = 6). Plasma CXCL-10 concentrations were measured in longitudinal samples of cases (n = 28 specimens) and controls (n = 749 specimens) by ELISA. Linear mixed-effects models were used to test for differences in plasma CXCL-10 concentration.

RESULTS

(i) The prevalence of plasma cell deciduitis in the placenta was significantly higher in cases with MPFD than in those with uncomplicated term deliveries (40% versus 8.6%, P = 0.01), (ii) patients with MPFD had a significantly higher frequency of maternal anti-HLA class I positivity during the second trimester than those with uncomplicated term deliveries (80% versus 36%, P = 0.01); (iii) strongly positive C4d deposition was observed on umbilical vein endothelium in cases of MPFD, (iv) a specific maternal antibody against fetal HLA antigen class I or II was identified in all cases of MPFD; and 5) the mean maternal plasma concentration of CXCL-10 was higher in patients with evidence of MPFD than in those without evidence of MFPD (P < 0.001).

CONCLUSION

A subset of patients with MPFD has evidence of maternal antifetal rejection.

Detection of anti-HLA antibodies in maternal blood in the second trimester to identify patients at risk of antibody-mediated maternal anti-fetal rejection and spontaneous preterm delivery

PROBLEM

Maternal anti-fetal rejection is a mechanism of disease in spontaneous preterm labor. The objective of this study was to determine whether the presence of human leukocyte antigen (HLA) panel-reactive antibodies (PRA) during the second trimester increases the risk of spontaneous preterm delivery.

METHODS OF STUDY

This longitudinal case-control study included pregnant women with spontaneous preterm deliveries (n = 310) and control patients with normal term pregnancies (n = 620), matched for maternal age and gravidity. Maternal plasma samples obtained at 14-16, 16-20, 20-24, and 24-28 weeks of gestation were analyzed for HLA class I and class II PRA positivity using flow cytometry. The fetal HLA genotype and maternal HLA alloantibody epitope were determined for a subset of patients with positive HLA PRA.

RESULTS

(i) Patients with spontaneous preterm delivery were more likely to exhibit HLA class I (adjusted OR = 2.54, P < 0.0001) and class II (adjusted OR = 1.98, P = 0.002) PRA positivity than those delivering at term; (ii) HLA class I PRA positivity for patients with spontaneous preterm delivery between 28 and 34 weeks (adjusted OR = 2.88; P = 0.001) and after 34 weeks of gestation (adjusted OR = 2.53; P < 0.0001) was higher than for those delivering at term; (iii) HLA class II PRA positivity for patients with spontaneous preterm delivery after 34 weeks of gestation was higher than for those delivering at term (adjusted OR = 2.04; P = 0.002); (iv) multiparous women were at a higher risk for HLA class I PRA positivity than nulliparous women (adjusted OR = 0.097, P < 0.0001 for nulliparity); (v) nulliparous women had a higher rate of HLA class I PRA positivity with advancing gestational age (P = 0.001); and (vi) 78% of women whose fetuses were genotyped had alloantibodies specific against fetal HLA class I antigens.

CONCLUSION

Pregnant women with positive HLA class I or class II PRA during the second trimester are at an increased risk of spontaneous preterm delivery due to antibody-mediated maternal anti-fetal rejection.

Cryptic B cell response to renal transplantation

Transplantation reliably evokes allo-specific B cell and T cell responses in mice. Yet, human recipients of kidney transplants with normal function usually exhibit little or no antibody specific for the transplant donor during the early weeks and months after transplantation. Indeed, the absence of antidonor antibodies is taken to reflect effective immunosuppressive therapy and to predict a favorable outcome. Whether the absence of donor-specific antibodies reflects absence of a B cell response to the donor, tolerance to the donor or immunity masked by binding of donor-specific antibodies to the graft is not known. To distinguish between these possibilities, we devised a novel ELISPOT, using cultured donor, recipient and third-party fibroblasts as targets. We enumerated donor-specific antibody-secreting cells in the blood of nine renal allograft recipients with normal kidney function before and after transplantation. Although none of the nine subjects had detectable donor-specific antibodies before or after transplantation, all exhibited increases in the frequency of donor-specific antibody-secreting cells eight weeks after transplantation. The responses were directed against the donor HLA-class I antigens. The increase in frequency of donor-specific antibody-secreting cells after renal transplantation indicates that B cells respond specifically to the transplant donor more often than previously thought.

De novo donor-specific HLA antibodies decrease patient and graft survival in liver transplant recipients

The role of de novo donor-specific HLA antibodies (DSA) in liver transplantation remains unknown as most of the previous studies have only focused on preformed HLA antibodies. To understand the significance of de novo DSA, we designed a retrospective cohort study of 749 adult liver transplant recipients with pre- and posttransplant serum samples that were analyzed for DSA. We found that 8.1% of patients developed de novo DSA 1 year after transplant; almost all de novo DSAs were against HLA class II antigens, and the majority were against DQ antigens. In multivariable modeling, the use of cyclosporine (as opposed to tacrolimus) and low calcineurin inhibitor levels increased the risk of de novo DSA formation, while a calculated MELD score >15 at transplant and recipient age >60 years old reduced the risk. Multivariable analysis also demonstrated that patients with de novo DSA at 1-year had significantly lower patient and graft survival. In conclusion, we demonstrate that de novo DSA development after liver transplantation is an independent risk factor for patient death and graft loss.

Immunologic monitoring in kidney transplant recipients

Transplant biopsy has always been the gold standard for assessing the immune response to a kidney allograft (Chandraker A: Diagnostic techniques in the work-up of renal allograft dysfunction-an update. Curr Opin Nephrol Hypertens 8:723-728, 1999). A biopsy is not without risk and is unable to predict rejection and is only diagnostic once rejection has already occurred. However, in the past two decades, we have seen an expansion in assays that can potentially put an end to the "drug level" era, which until now has been one of the few tools available to clinicians for monitoring the immune response. A better understanding of the mechanisms of rejection and tolerance, and technological advances has led to the development of new noninvasive methods to monitor the immune response. In this article, we discuss these new methods and their potential uses in renal transplant recipients.

Rituximab prevents an anamnestic response in patients with cryptic sensitization to HLA

BACKGROUND

Some patients sensitized to HLA antigens do not have antibody present in serum specimens that are available before transplantation. However, such patients are at risk for an anamnestic response resulting from a proinflammatory response to the trauma of transplant surgery. Quantifying HLA-specific B cells provides a way to identify these patients and provide treatment to prevent an anamnestic response.

METHODS

B cells were isolated before transplantation from 59 patients, 20 of whom were treated with rituximab at the time of transplantation. Ninety-nine tests were performed to quantify HLA-specific B cells by staining with HLA tetramers. Patients were considered sensitized or nonsensitized based on the frequencies of HLA-specific B cells. Pretransplantation and posttransplantation sera were tested for the detection of antibody specific for the tetramer antigen.

RESULTS

Of the 24 cases where patients were considered sensitized to HLA antigens but did not have antibody before transplantation, no posttransplantation antibody to the tetramer antigen was detected in 10 cases when patients were treated with rituximab, but antibody was detected in 13 of 16 cases when there was no rituximab treatment (P=0.00006). The mean frequencies of B cells specific for HLA-B7 were the same in rituximab-treated patients who did not make antibody and in nontreated patients who did make antibody (6.0% vs. 5.7%; P=0.8).

CONCLUSIONS

Elimination of peripheral HLA-specific B cells in patients who are sensitized to HLA antigens but lacking detectable antibody abrogates an anamnestic response.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Peritubular capillaritis in early renal allograft dysfunction is an indicator of acute rejection

BACKGROUND

Kidneys showing acute rejection (AR) processes often are accompanied by various levels of peritubular capillaritis (Ptc), especially cases of acute humoral rejection (AHR). However, it is not known whether the presence of Ptc alone is sufficient evidence of allograft rejection. This study was performed to determine the diagnostic value of Ptc as a marker for AR among cases of early renal allograft dysfunction.

METHODS

Fifty-three AR showed C4d deposition in the peritubular capillaries (PTCs; C4d+AR group), 50 AR were without C4d deposition (C4d-AR group), 30 had Ptc alone (Ptc group), 28 had acute tubular necrosis (ATN group), and 78 were surveillance biopsies (control group).

RESULTS

Analyzing the immunophenotype of infiltrating T lymphocytes and serum antibodies, discovered that 85.9% of control biopsies presented with a regulatory phenotype. Among the Ptc cohort, 93.3% of biopsies showed the cytotoxic phenotype with no significant different between C4d+AR and C4d-AR (96.2% vs 92.0%). We also observed the prevalence of panel-reactive antibody (PRA) and major-histocompatibility-complex class I chain-related gene A (MICA) antibodies to be increased among Ptc (30.0% and 43.3%, respectively), albeit not significantly different from C4d+AR (49.1% and 39.6%, respectively). The prevalences were low in other groups.

CONCLUSIONS

These results implied that Ptc in biopsy specimens from patients with early renal allograft dysfunction was an indicator of AR, especially AHR.

Evolution and clinical pathologic correlations of de novo donor-specific HLA antibody post kidney transplant

The natural history for patients with de novo donor-specific antibodies (dnDSA) and the risk factors for its development have not been well defined. Furthermore, clinical and histologic correlation with serologic data is limited. We studied 315 consecutive renal transplants without pretransplant DSA, with a mean follow-up of 6.2 ± 2.9 years. Protocol (n = 215) and for cause (n = 163) biopsies were analyzed. Solid phase assays were used to screen for dnDSA posttransplant. A total of 47 out of 315 (15%) patients developed dnDSA at a mean of 4.6 ± 3.0 years posttransplant. Independent predictors of dnDSA were HLA-DRβ1 MM > 0 (OR 5.66, p < 0.006); and nonadherence (OR 8.75, p < 0.001); with a strong trend toward clinical rejection episodes preceding dnDSA (OR 1.57 per rejection episode, p = 0.061). The median 10-year graft survival for those with dnDSA was lower than the No dnDSA group (57% vs. 96%, p < 0.0001). Pathology consistent with antibody-mediated injury can occur and progress in patients with dnDSA in the absence of graft dysfunction and furthermore, nonadherence and cellular rejection contribute to dnDSA development and progression to graft loss.

Chronic antibody-mediated rejection is reduced by targeting B-cell immunity during an introductory period

Transplantation across blood group antigen and human leukocyte antigen (HLA) barriers are immunologically high risk. Both splenectomy and rituximab injection were developed to overcome those immunological barriers. The idea behind these treatments is to control B-cell immunity before and after renal transplantation and antibody production. Between January 2001 and December 2004, recipients underwent pretransplant double-filtration plasmapheresis (DFPP) and splenectomy at the time of transplantation in the ABO-incompatible group (ABO-I-SPX; n= 45). From January 2005 to June 2009, a low dose of rituximab was given as an alternative to splenectomy (ABO-I-RIT; n = 57). As a control group, we selected 83 cases of ABO-C living-donor kidney transplantation between January 2001 and December 2007 (ABO-C). We compared the graft survival rate and chronic antibody-mediated rejection (C-AMR) rate between ABO-C and ABO-I kidney transplantation with induction treatment. C-AMR rates 2 years after the operation were 8.8, 3.5 and 28.9%, and de novo donor-specific anti-HLA antibody (DSHA) positive rates were 2.2, 1.7 and 18.1% in the ABO-I-SPX, ABO-I-RIT and ABO-C groups, respectively. The ABO-C group showed the highest rate of C-AMR and de novo DSHA. B-cell depletion protocols, such as splenectomy or rituximab administration, reduced C-AMR after kidney transplantation.

Maternal HLA panel-reactive antibodies in early gestation positively correlate with chronic chorioamnionitis: evidence in support of the chronic nature of maternal anti-fetal rejection

PROBLEM

Maternal tolerance of the fetus is essential for viviparity, yet anti-fetal rejection occurs in several pregnancy complications. Chronic chorioamnionitis is a feature of anti-fetal cellular rejection. There is a robust association between chronic chorioamnionitis and maternal seropositivity for anti-human leukocyte antigen (HLA) panel-reactive antibodies (PRA) at the time of delivery. This longitudinal study was performed to assess maternal HLA PRA status in early gestation and the temporal evolution of maternal HLA PRA in the context of chronic chorioamnionitis and, thereby, to determine whether HLA PRA during the course of pregnancy is useful for the detection of anti-fetal rejection.

METHOD OF STUDY

Maternal sera obtained before 16 weeks of gestation and at delivery were analyzed for HLA PRA in cases with (N = 100) and without (N = 150) chronic chorioamnionitis.

RESULTS

IgG (but not IgM) HLA class I and II PRA positivity at delivery was higher in cases with chronic chorioamnionitis than in those without chronic chorioamnionitis. IgG HLA class I PRA positivity before 16 weeks of gestation was higher in cases with chronic chorioamnionitis than in those without (30.3 versus 13.3%; P = 0.001). Positive conversion (negative HLA PRA before 16 weeks of gestation but positive at delivery) of IgG HLA class I and II PRA was significantly associated with chronic chorioamnionitis. Fetal HLA class I antigen-specific antibodies were confirmed in 12 of 16 mothers tested who were sensitized to HLA class I antigens before 16 weeks of gestation.

CONCLUSION

Positive maternal HLA PRA before 16 weeks of gestation and the temporal evolution of maternal HLA PRA are associated with the presence of chronic chorioamnionitis at the time of delivery. Maternal IgG HLA PRA has the potential to be a monitoring tool of anti-fetal rejection. Furthermore, the findings herein indicate that subsets of fetuses are exposed to alloimmune HLA antibodies for months, especially in cases with chronic chorioamnionitis.

C1q-fixing human leukocyte antigen antibodies are specific for predicting transplant glomerulopathy and late graft failure after kidney transplantation

BACKGROUND

Human leukocyte antigen (HLA) antibodies, especially those that fix complement, are associated with antibody-mediated rejection and graft failure. The C1q assay on single antigen beads detects a subset of HLA antibodies that can fix complement and precede C4d deposition. The aim of this study was to determine whether C1q-fixing antibodies distinguish de novo donor-specific antibodies (DSA) that are clinically relevant and harmful.

METHODS

We retrospectively studied 31 of 274 kidney transplant recipients who had pretransplant and concurrent biopsy and serum specimens, 13 with C4d-positive and 18 with C4d-negative staining. We measured IgG and C1q DSA pretransplant and at the time of biopsy using single antigen bead assays. We identified 13 recipients who developed de novo DSA by IgG or C1q and examined associations with C4d deposition, transplant glomerulopathy, and graft failure.

RESULTS

Testing for DSA by IgG is more sensitive for C4d deposition (IgG: 100%, 95% confidence interval [CI] 0.60-1; C1q: 75%, 95% CI 0.36-0.96). Testing for DSA by C1q is more specific for transplant glomerulopathy (C1q: 81%, 95% CI 0.57-0.94; IgG: 67%, 95% CI 0.43-0.85) and graft loss (C1q: 79%, 95% CI 0.54-0.93; IgG: 63%, 95% CI 0.39-0.83). Absence of de novo DSA by IgG and C1q has a high negative predictive value for the absence of C4d deposition (IgG: 100%, 95% CI 0.73-1; C1q: 88%, 95% CI 0.62-0.98), transplant glomerulopathy (IgG: 100%, 95% CI 0.73-1; C1q: 100%, 95% CI 0.77-1), and graft failure (IgG: 86%, 95% CI 0.56-0.97; C1q: 88%, 95% CI 0.62-0.98).

CONCLUSION

Monitoring patients with the C1q assay, which detects antibodies that fix complement, offers a minimally invasive means of identifying patients at risk for transplant glomerulopathy and graft loss.

Induction of chronic renal allograft dysfunction in a rat model with complete and exclusive MHC incompatibility

Chronic allograft dysfunction is one of the most important reasons for late graft loss after renal transplantation. Its etiology is multifactorial and combines immunological as well as non-immunological mechanisms. It is known from large registry data that MHC mismatches are inversely correlated to long term allograft survival. Although this is a well known aspect, the mechanisms of MHC-driven graft damage and the impact of other immunological factors leading to chronic rejection are poorly understood. In patients it is impossible to study MHC mismatches without considering non-MHC differences. Further more common animal models for chronic rejection are all characterized by non-MHC as well as MHC disparities. To exclusively study MHC mediated immunoresponses we established a rat model of renal transplantation using congenic rat strains differing in their entire MHC class I and class II, but sharing the genetic background of the LEW rat. After an initial short term of immunosuppression all animals developed renal impairment with severe albuminuria. Half of the animals died of renal failure in week 7 to 14 and showed pathological characteristics of chronic allograft damage including IF/TA and severe glomerulopathy. The majority of these recipients developed circulating donor-specific MHC alloantibodies. Allografts were significantly infiltrated with T-cells, macrophages and NK-cells. We established a MHC congenic rat model to investigate immunological mechanisms of chronic renal allograft rejection exclusively induced by a complete MHC mismatch. We demonstrated humoral as well as cellular immunoresponses leading to chronic allograft loss in 50% of animals.

Clinical relevance of preformed C4d-fixing and non-C4d-fixing HLA single antigen reactivity in renal allograft recipients

Donor-specific alloantibodies (DSA), especially those fixing complement, may pose a particular immunologic risk to transplant recipients. To assess the clinical impact of C4d- or non-C4d-fixing (IgG) HLA sensitization, pretransplant sera obtained from 338 kidney allograft recipients prescreened by FlowPRA were retrospectively evaluated by Luminex single antigen (SA) testing using a novel fluorescent-labeled anti-C4d reagent for detection of antibody-triggered C4d deposition in addition to IgG binding. Recipients with [IgG]DSA (n = 39) showed a substantially higher rate of C4d positive rejection (33%) than 16 patients with [IgG] non-DSA (0%) or 283 antibody-negative patients (4%, multivariate analysis excluding retransplantation because of high co-linearity: P < 0.0001), and adversely affected 5-year death-censored graft survival (74% vs. 81% and 90%, respectively, multivariate model: P < 0.05). [C4d] DSA (n = 21) and [C4d] non-DSA (n = 25) increased rates of C4d positive rejections to a similar extent (24% and 28% vs. 4% in recipients without C4d-fixing reactivity; multivariate analysis: P <or= 0.002) with a trend towards adverse 5-year graft survival (76% and 76% vs. 90%; P <or= 0.2). In conclusion, Luminex-based characterization of HLA sensitization may be a useful strategy for risk stratification. Possibly as a result of intensified immunosuppression in presensitized recipients, identification of C4d-fixing DSA was not associated with a further increase of rejection and graft loss rates.