Phenotypes Of Antibody-mediated Rejection Research Articles

The relationship of microvascular inflammation with antibody-mediated rejection in kidney transplantation

Microvascular inflammation (MVI) is a key diagnostic feature of antibody-mediated rejection (AMR); however, recipients without donor-specific antibodies (DSA) defy etiologic classification using C4d staining of peritubular capillaries (C4dptc) and conventional DSA assignment. We evaluated MVI ≥ 2 (Banff g + ptc ≥ 2) using Banff 2019 AMR (independent of MVI ≥ 2 but including C4dptc) with unconventional endothelial C4d staining of glomerular capillaries (C4dglom) and - arterial endothelium and/or intima (C4dart) using tissue immunoperoxidase, shared-eplet and subthreshold DSA (median fluorescence intensity, [MFI] 100-499), and capillary ultrastructure from 3398 kidney transplant samples for evidence of AMR. MVI ≥ 2 (n = 202 biopsies) from 149 kidneys (12.4% prevalence) correlated with DSA+, C4dptc+, C4dglom+, Banff cg, i, t, ti scores, serum creatinine, proteinuria, and graft failure compared with 202 propensity score matched normal controls. The laboratory reported DSA− MVI ≥ 2 (MFI ≥500) occurred in 34.7%; however, subthreshold (28.6%), eplet-directed (51.4%), and/or misclassified anti-Human leukocyte antigen (HLA) DSA (12.9%) were identified in 67.1% by forensic reanalysis, with vascular C4d+ staining in 67.1%, and endothelial abnormalities in 57.1%, totaling 87.1%. Etiologic analysis attributed 62.9% to AMR (77.8% for MVI with negative reported DSA [DSA− MVI ≥2] with glomerulitis) and pure T cellular rejection in 37.1%. C4dptc−DSA− MVI ≥ 2 was unrecognized AMR in 48.0%. Functional outcomes and graft survival were comparable to normal controls. We concluded that DSA− MVI ≥ 2 frequently signified a mild “borderline” phenotype of AMR which was recognizable using novel serologic and pathological techniques.

#1134 Molecular rejection phenotype patterns differentiate between probable AMR, DSA-negative microvascular inflammation, and AMR

Abstract Background and Aims Biopsy-based transcripts associated with antibody-mediated rejection (AMR) hold promise as substitutes for C4d positivity, according to the latest Banff Meeting Report of 2022. However, patterns and strength of rejection phenotype scores remain inadequately studied within the new subgroups along the AMR continuum. Method We analyzed 365 kidney allograft biopsies by histology and the Molecular Microscope Diagnostic System (MMDx) at the University Hospital of Zurich from July 2021 to November 2023. Histologic findings were classified according to Banff 2022 into (1) probable AMR (n = 32), (2) donor-specific antibodies (DSA)-negative C4d-negative microvascular inflammation (MVI, n = 32), and (3) AMR (n = 60). A control group of 118 cases without MVI was used for comparison. Results 10 out of 32 cases (31%) with probable AMR, 20 of 32 cases (63%) with DSA-negative C4d-negative MVI, and 31 of 60 cases (52%) with AMR showed molecular AMR. Among cases with molecular AMR the sum of the TCMR-related (R2) and late-stage AMR-related (R6) phenotype scores was significantly higher in probable AMR and DSA-negative MVI cases compared to AMR cases (p = 0.029). In contrast, the sum of the mixed rejection (R3), early-stage AMR (R4), fully-developed AMR (R5) phenotype scores was higher in AMR compared to probable AMR (p = 0.063). Among cases without molecular AMR the all AMR phenotype score was significantly higher in AMR and DSA-negative MVI compared to probable AMR and the control group without MVI (p = 0.012, p < 0.001). Conclusion Our results identify different molecular rejection phenotype patterns between cases with probable AMR, DSA-negative MVI, and AMR. Sub-threshold findings appear relevant along the AMR continuum.

Antibody-mediated Rejection in Kidney Transplant: An Unmastered Area

Antibody-mediated rejection (ABMR) remains a significant cause of allograft failure in patients with kidney transplantation. Despite successful strategies to treat ABMR, irreversible injury in the form of transplant glomerulopathy commonly manifests months to years later. Treatment for ABMR is not standardized, and treatment guidelines vary among different transplant centers. The outcomes for patients at risk for ABMR have not significantly changed over the years. This is largely because of an incomplete understanding of the mechanisms of injury responsible for different phenotypes of ABMR. Establishing relevant surrogate endpoints to facilitate more informative studies will likely allow for a more accurate determination of prognosis and pave the way for new and effective therapeutic approaches. This article aims to summarize the current understanding of the mechanism of injury in ABMR and highlight current diagnostic approaches and treatment strategies.

Application of the Banff Human Organ Transplant Panel to kidney transplant biopsies with features suspicious for antibody-mediated rejection

The Banff Classification for Allograft Pathology includes the use of gene expression in the diagnosis of antibody-mediated rejection (AMR) of kidney transplants, but a predictive set of genes for classifying biopsies with 'incomplete' phenotypes has not yet been studied. Here, we developed and assessed a gene score that, when applied to biopsies with features of AMR, would identify cases with a higher risk of allograft loss. To do this, RNA was extracted from a continuous retrospective cohort of 349 biopsies randomized 2:1 to include 220 biopsies in a discovery cohort and 129 biopsies in a validation cohort. The biopsies were divided into three groups: 31 that fulfilled the 2019 Banff Criteria for active AMR, 50 with histological features of AMR but not meeting the full criteria (Suspicious-AMR), and 269 with no features of active AMR (No-AMR). Gene expression analysis using the 770 gene Banff Human Organ Transplant NanoString panel was carried out with LASSO Regression performed to identify a parsimonious set of genes predictive of AMR. We identified a nine gene score that was highly predictive of active AMR (accuracy 0.92 in the validation cohort) and was strongly correlated with histological features of AMR. In biopsies suspicious for AMR, our gene score was strongly associated with risk of allograft loss and independently associated with allograft loss in multivariable analysis. Thus, we show that a gene expression signature in kidney allograft biopsy samples can help classify biopsies with incomplete AMR phenotypes into groups that correlate strongly with histological features and outcomes.

Modelling acute antibody-mediated rejection of human kidney transplants using ex-vivo warm machine perfusion.

Transplant rejection is a major cause of graft loss and morbidity. Currently, no human models of antibody-mediated rejection (AMR) exist, limiting mechanistic investigation and organ-specific targeted therapy. Here, using 12 human kidneys and ex-vivo normothermic machine perfusion, we demonstrate phenotypes of AMR after addition of antibodies against either human HLA class I or blood group antigens (A, B), thus modelling clinical AMR that can follow HLA incompatible (HLAi) or blood group incompatible (ABOi) transplantation. Discarded human kidneys with wide ranging demographics and cold ischaemia times (11-54h) were perfused with red blood cells and fresh frozen plasma (FFP) as a source of complement/coagulation factors. For the HLAi model, 600μg of W6/32 anti-class 1 HLA antibody was added to the circuit (time '0'). For the ABOi model, high titre FFP of the relevant blood group antibody was added. Renal blood flow index (RBFi, mL/min/100 g), C3 desArg, prothrombin fragments 1+2 and histology were determined. Our endpoints included haemodynamic changes, thrombosis, and biopsy proven complement deposition. Compared to control kidneys perfused without anti-donor antibodies, both models demonstrated haemodynamic collapse after antibody perfusion with only the HLAi model showing glomerular C4d deposition. We show that a clinically relevant human kidney model of AMR is feasible, and anticipate that these models, with refinements, could provide a basis to test different strategies to prevent AMR. The Rosetrees and Stonygate Trust, The Royal College of Surgeons of England Fellowship Grant, NIHR Biomedical Research Centre/KCL Early Career Grant, Kidney Research U.K.

Association of non-HLA antibodies against endothelial targets and donor-specific HLA antibodies with antibody-mediated rejection and graft function in pediatric kidney transplant recipients

BackgroundNon-HLA antibodies against endothelial targets have been implicated in the pathogenesis of antibody-mediated rejection (ABMR), but data in pediatric patients are scarce.MethodsWe retrospectively analyzed a carefully phenotyped single-center (University Children’s Hospital Heidelberg, Germany) cohort of 62 pediatric kidney transplant recipients (mean age at transplantation, 8.6 ± 5.0 years) at increased risk of graft function deterioration. Patients had received their transplant between January 1, 1999, and January 31, 2010. We examined at time of late index biopsies (more than 1-year post-transplant, occurring after January 2004) the association of antibodies against the angiotensin II type 1 receptor (AT1R), the endothelin type A receptor (ETAR), the MHC class I chain-like gene A (MICA), and vimentin in conjunction with overall and complement-binding donor-specific HLA antibodies (HLA-DSA) with graft histology and function.ResultsWe observed a high prevalence (62.9%) of non-HLA antibody positivity. Seventy-two percent of HLA-DSA positive patients showed additional positivity for at least one non-HLA antibody. Antibodies against AT1R, ETAR, and MICA were associated with the histological phenotype of ABMR. The cumulative load of HLA-DSA and non-HLA antibodies in circulation was related to the degree of microinflammation in peritubular capillaries. Non-HLA antibody positivity was an independent non-invasive risk factor for graft function deterioration (adjusted hazard ratio 6.38, 95% CI, 2.11–19.3).ConclusionsOur data indicate that the combined detection of antibodies to HLA and non-HLA targets may allow a more comprehensive assessment of the patients’ immune responses against the kidney allograft and facilitates immunological risk stratification.

P1701ANTIBODY MEDIATED REJECTION: CLINICAL PHENOTYPE MATTERS

Abstract Background and Aims Protocol biopsies following kidney transplantation (KT) allow the histological diagnosis of antibody-mediated rejection (ABMR) with stable renal function (RF). Controversy arises when considering isolated proteinuria as a clinical biomarker. Currently, there is no effective treatment for ABMR and transplant units may decide on treatment independently of the clinical expression. Method KT recipients (1987-2017) with post-KT biopsies (2008-2018) showing ABMR graft lesions (category 2-Banff’2015) >1year post-KT were included. Cases were grouped into phenotypes of ABMR according to the clinical picture at biopsy : 1) acute RF impairment (↑creatinine >15% three weeks before biopsy) with/without proteinuria and with/without DSA detection. 2) sub-acute RF impairment (↑creatinine >15% six months before biopsy) with/without proteinuria and with/without DSA detection, 3) performed for DSA detection with stable RF and no proteinuria or 4) protocol biopsy, with stable RF, no proteinuria or DSA detection. We considered an additional category: 5) isolated proteinuria (↑>500 mg or x2 six months before biopsy). Categories 1), 2) and 5) were considered clinical ABMR. Categories 3) and 4) were considered subclinical ABMR. We aimed to evaluate graft outcomes in the different ABMR phenotypes. Results In a cohort of 105 KT recipients with histologic lesions of ABMR, biopsies corresponded to phenotypes 1) in 35 (33%), 2) 10 (9,5%), 3) 21 (20,3%), 4) 14 (13,4%) and y 5) in 25 23,8%). No differences between clinical and subclinical ABMR were found in baseline characteristics except for donors ‘age, who were older within the clinical group (51.8±18.8 vs. 43.88 ±16.1; p=0.04). At time of biopsy, subclinical had better RF than clinical ABMR (creatinine 1.3±0.4 mg/dl vs. 2.2±1.1 mg/dl; p=0.02) and less proteinuria (161 mg/g [IQR 93-269] vs 939 mg/g [IQR 412-2000]; p=0.001) Graft survival was worse in those patients with acute and sub-acute RF impairment, followed by those with isolated proteinuria (Figure 1). In comparison to subclinical ABMR, those with RF impairment and isolated proteinuria had an increased risk of graft lost; HR 9.4 (95% IC 2.2-40.7, p=0.002) and 4.8 (95% IC 1.01-23.2, P=0.05) respectively. DSA detection in these groups did not impact graft survival. Specific treatment was not different among groups, except for steroid pulses, which were more frequently applied in cases of ABMR with clinical manifestation. Conclusion The clinical phenotypes of ABMR influence long-term graft survival independently from treatment. Understanding graft evolution according to clinical phenotype at the time of histologic diagnosis should guide the therapeutic strategy, to balance risk-benefit ratio.

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 "R1normal " (N=129), T cell-mediated rejection (TCMR) "R2TCMR " (N=37), early injury "R3injury " (N=61), and fibrosis "R4late " (N=8). Groups differed in median time posttransplant, for example, R3injury 99days vs R4late 3117days. R2TCMR biopsies expressed typical TCMR-related transcripts, for example, intense IFNG-induced effects. R3injury displayed increased expression of parenchymal injury transcripts (eg, hypoxia-inducible factor EGLN1). R4late biopsies showed immunoglobulin transcripts and injury-related transcripts. R2TCMR correlated with histologic rejection although with many discrepancies, and R4late with fibrosis. R2TCMR , R3injury , and R4late correlated with liver function abnormalities. Supervised classifiers trained on histologic rejection showed less agreement with histology than unsupervised R2TCMR 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.

Clinical Significance of Alloantibodies in Hand Transplantation: A Multicenter Study.

Donor-specific antibodies (DSAs) have a strong negative correlation with long-term survival in solid organ transplantation. Although the clinical significance of DSA and antibody-mediated rejection (AMR) in upper extremity transplantation (UET) remains to be established, a growing number of single-center reports indicate their presence and potential clinical impact. We present a multicenter study assessing the occurrence and significance of alloantibodies in UET in reference to immunological parameters and functional outcome. Our study revealed a high prevalence and early development of de novo DSA and non-DSA (43%, the majority detected within the first 3 postoperative y). HLA class II mismatch correlated with antibody development, which in turn significantly correlated with the incidence of acute cellular rejection. Cellular rejections preceded antibody development in almost all cases. A strong correlation between DSA and graft survival or function cannot be statistically established at this early stage but a correlation with a lesser outcome seems to emerge. While the phenotype and true clinical effect of AMR remain to be better defined, the high prevalence of DSA and the correlation with acute rejection highlight the need for optimizing immunosuppression, close monitoring, and the relevance of an HLA class II match in UET recipients.

Exploring Chronic Lung Transplant (LTx) Allograft Dysfunction (CLAD): The Potential Clinical Prognostic Relevance of Single Bite Transbronchial Biopsy (TBB) Microarray

Purpose TBB histologic assessment of CLAD status, particularly late post-LTx, is typically clinically unhelpful. Microarray analyses using the Molecular Microscope Diagnostic System (MMDx) in kidney & heart recipients are proving useful in providing mechanistic targets that inform therapeutic interventions, and could show similar promise in LTx. Methods LTx recipients with clinical instability- typically a falling FEV1 and symptoms- had bronchoscopic lavage with microbiologic & cytologic analyses and TBB [4-6 bites analyzed via histology, I TBB bite by MMDx microarray (Alberta Transplant Applied Genomic Center, Edmonton)]. The MMDx uses weighted equations to reflect probabilities of 4 idealized archetypes [Normal, T-cell rejection (TCMR), antibody-mediated rejection (ABMR), Injury]. One month post-TBB a clinical diagnosis was determined, & subsequent change in FEV1 was reassessed 6 months post-TBB. Clinicians were blinded to MMDx scores. Results 48 of 50 LTx who underwent TBB assessment at 1463±1296d post-LTx, (FEV1 32-118% predicted), had an assessable TBB for MMDx. Clinical diagnoses at 1 month post-TBB were CLAD n=21, infection n=17, ABMR n=5, TCMR n=4 & effusion n=1. TBB ISHLT grade was A0 n=46, A1 n=1, B0 n=11, B1 n=1; all others Ax and/or Bx. At 6 months post-TBB, using the highest of the 4 MMDx archetype scores, 1/12 (8%) Normal, 7/14 (50%) TCMR, 5/19 (26%) ABMR & 0/3 (0%) Injury recipients, had rapidly progressive CLAD. 15 patients had DSA>500, 9/15 were in ABMR group- 4 with rapidly progressive CLAD. In 31 patients without a clinical diagnosis of infection at 1 month, 11% Normal, 58% TCMR, 60% ABMR & 0% Injury group recipients went on to have rapidly progressive CLAD. Longer term follow-up (mean of 450±168d) in the TCMR arm and ABMR arm noted there were n=4 & 3 and n=2 & 1 deaths/re-LTx respectively, with 1 other re-LTx in the Normal group: all were CLAD related. Conclusion The MMDx score on single bite TBB specimens provided potentially useful mechanistic, therapeutic & prognostic detail in LTx recipients with clinical instability, whilst TBB histology was not clinically helpful in this cohort. The apparent association or confounding of infection, DSA and a predominant ABMR phenotype is notable. A prospective trial of MMDx directed therapy may be indicated.

Clazakizumab in late antibody-mediated rejection: study protocol of a randomized controlled pilot trial

BackgroundLate antibody-mediated rejection (ABMR) triggered by donor-specific antibodies (DSA) is a cardinal cause of kidney allograft dysfunction and loss. Diagnostic criteria for this rejection type are well established, but effective treatment remains a major challenge. Recent randomized controlled trials (RCT) have failed to demonstrate the efficacy of widely used therapies, such as rituximab plus intravenous immunoglobulin or proteasome inhibition (bortezomib), reinforcing a great need for new therapeutic concepts. One promising target in this context may be interleukin-6 (IL-6), a pleiotropic cytokine known to play an important role in inflammation and adaptive immunity.MethodsThis investigator-driven RCT was designed to assess the safety and efficacy of clazakizumab, a genetically engineered humanized monoclonal antibody directed against IL-6. The study will include 20 DSA-positive kidney allograft recipients diagnosed with ABMR ≥ 365 days after transplantation. Participants will be recruited at two study sites in Austria and Germany (Medical University of Vienna; Charité University Medicine Berlin). First, patients will enter a three-month double-blind RCT (1,1 randomization, stratification according to ABMR phenotype and study site) and will receive either clazakizumab (subcutaneous administration of 25 mg in monthly intervals) or placebo. In a second open-label part of the trial (months 4–12), all patients will receive clazakizumab at 25 mg every month. The primary endpoint is safety and tolerability. Secondary endpoints are the pharmacokinetics and pharmacodynamics of clazakizumab, its effect on drug metabolism in the liver, DSA characteristics, morphological ABMR lesions and molecular gene expression patterns in three- and 12-month protocol biopsies, serum/urinary biomarkers of inflammation and endothelial activation/injury, Torque Teno viral load as a measure of overall immunosuppression, kidney function, urinary protein excretion, as well as transplant and patient survival.DiscussionCurrently, there is no treatment proven to be effective in halting the progression of late ABMR. Based on the hypothesis that antagonizing the effects of IL-6 improves the outcome of DSA-positive late ABMR by counteracting DSA-triggered inflammation and B cell/plasma cell-driven alloimmunity, we suggest that our trial has the potential to provide proof of concept of a novel treatment of this type of rejection.Trial registrationClinicalTrials.gov, NCT03444103. Registered on 23 February 2018 (retrospective registration).

Summary of 2017 FDA Public Workshop: Antibody-mediated Rejection in Kidney Transplantation.

Despite major advances in understanding the pathophysiology of antibody-mediated rejection (AMR); prevention, diagnosis and treatment remain unmet medical needs. It appears that early T cell-mediated rejection, de novo donor-specific antibody (dnDSA) formation and AMR result from patient or physician initiated suboptimal immunosuppression, and represent landmarks in an ongoing process rather than separate events. On April 12 and 13, 2017, the Food and Drug Administration sponsored a public workshop on AMR in kidney transplantation to discuss new advances, importance of immunosuppressive medication nonadherence in dnDSA formation, associations between AMR, cellular rejection, changes in glomerular filtration rate, and challenges of clinical trial design for the prevention and treatment of AMR. Key messages from the workshop are included in this summary. Distinction between type 1 (due to preexisting DSA) and type 2 (due to dnDSA) phenotypes of AMR needs to be considered in patient management and clinical trial design. Standardization and more widespread adoption of routine posttransplant DSA monitoring may permit timely diagnosis and understanding of the natural course of type 2 and chronic AMR. Clinical trial design, especially as related to type 2 and chronic AMR, has specific challenges, including the high prevalence of nonadherence in the population at risk, indolent nature of the process until the appearance of graft dysfunction, and the absence of accepted surrogate endpoints. Other challenges include sample size and study duration, which could be mitigated by enrichment strategies.

Antibody-mediated rejection: New approaches in prevention and management.

Despite the success of desensitization protocols, antibody-mediated rejection (AMR) remains a significant contributor to renal allograft failure in patients with donor-specific antibodies. Plasmapheresis and high-dose intravenous immunoglobulin have proved to be effective treatments to prevent and treat AMR, but irreversible injury in the form of transplant glomerulopathy can commonly manifest months to years later. There is an unmet need to improve the outcomes for patients at risk for AMR. Updated Banff criteria now take into account the increasing understanding of the complex and heterogeneous nature of AMR phenotypes, including the timing of rejection, subclinical and chronic AMR, C4d-negative AMR, and antibody-mediated vascular rejection. Treatment for AMR is not standardized, and there is little in the way of evidence-based treatment guidelines. Refining more precisely the mechanisms of injury responsible for different AMR phenotypes and establishing relevant surrogate endpoints to facilitate more informative studies will likely allow for more accurate determination of prognosis and efficacious intervention using new therapeutic approaches. In addition to plasma exchange and intravenous immunoglobulin, a number of other add-on therapies have been tried in small studies without consistent benefit, including anti-CD20, proteasome inhibitors, complement inhibitors, anti-interleukin-6 receptor blockers, and immunoglobulin G-degrading enzyme of Streptococcus pyogenes (called IdeS).

Defining the phenotype of antibody-mediated rejection in kidney transplantation: Advances in diagnosis of antibody injury.

The diagnostic criteria for antibody-mediated rejection (ABMR) are constantly evolving in light of the evidence. Inclusion of C4d-negative ABMR has been one of the major advances in the Banff Classification in recent years. Currently Banff 2015 classification requires evidence of donor specific antibodies (DSA), interaction between DSA and the endothelium, and acute tissue injury (in the form of microvasculature injury (MVI); acute thrombotic microangiopathy; or acute tubular injury in the absence of other apparent cause). In this article we review not only the ABMR phenotypes acknowledged in the most recent Banff classification, but also the phenotypes related to novel pathogenic antibodies (non-HLA DSA, antibody isoforms and subclasses, complement-binding functionality) and molecular diagnostic tools (gene transcripts, metabolites, small proteins, cytokines, and donor-derived cell-free DNA). These novel tools are also being considered for the prognosis and monitoring of treatment response. We propose that improved classification of ABMR based on underlying pathogenic mechanisms and outcomes will be an important step in identifying patient-centered therapies to extend graft survival.

Increase in spot urine protein excretion is associated with late kidney graft rejection and predicts rejection phenotype.

A noninvasive test that foretells kidney graft rejection before loss of kidney function would be desirable. We hypothesized that an increase in estimated protein excretion rate (ePER) from spot urine samples is associated with graft rejection and predicts rejection phenotype. 151 patients who had undergone first-indication kidney biopsy due to graft dysfunction beyond 3 months after transplant were identified from a national cohort of 616 transplant recipients between 2000 and 2012 (25%). ePER were calculated from spot urine protein-to-creatinine ratios at baseline, 3 months before biopsy (ePER-3m), and at the time of biopsy (ePERbiopsy) and were correlated with histologic biopsy findings. Levels of ePER 3 months before biopsy and at the time of biopsy were greater in 32 patients with antibody-mediated rejection (ABMR) than in 77 patients with T-cell-mediated rejection (TCMR) and 42 patients with other findings (median ePER-3m 912 vs. 320 vs. 232 mg/day/1.73m2; and median ePERbiopsy 1,672 vs. 356 vs. 268 mg/day/1.73m2; p < 0.001). Receiver operator characteristics (ROC) analyses demonstrated that ePER-3m and ePERbiopsy had good diagnostic accuracy to discriminate between biopsy specimens showing ABMR vs. those showing TCMR or other histologic findings (area under the ROC curve 0.84, 95% CI 0.75-0.93 and 0.89, 95% CI 0.82-0.97, respectively; p < 0.001). An increase in ePER before kidney graft dysfunction appears to be associated with graft rejection and predicts ABMR phenotype. .

Subclinical Antibody-Mediated Rejection

Subclinical Antibody-Mediated Rejection

Eculizumab and splenectomy as salvage therapy for severe antibody-mediated rejection after HLA-incompatible kidney transplantation.

Incompatible live donor kidney transplantation is associated with an increased rate of antibody-mediated rejection (AMR) and subsequent transplant glomerulopathy. For patients with severe, oliguric AMR, graft loss is inevitable without timely intervention. We reviewed our experience rescuing kidney allografts with this severe AMR phenotype by using splenectomy alone (n=14), eculizumab alone (n=5), or splenectomy plus eculizumab (n=5), in addition to plasmapheresis. The study population was 267 consecutive patients with donor-specific antibody undergoing desensitization. In the first 3 weeks after transplantation (median=6 days), 24 patients developed sudden onset oliguria and rapidly rising serum creatinine with marked rebound of donor-specific antibody, and a biopsy that showed features of AMR. At a median follow-up of 533 days, 4 of 14 splenectomy-alone patients experienced graft loss (median=320 days), compared to four of five eculizumab-alone patients with graft failure (median=95 days). No patients treated with splenectomy plus eculizumab experienced graft loss. There was more chronic glomerulopathy in the splenectomy-alone and eculizumab-alone groups at 1 year, whereas splenectomy plus eculizumab patients had almost no transplant glomerulopathy. These data suggest that for patients manifesting early severe AMR, splenectomy plus eculizumab may provide an effective intervention for rescuing and preserving allograft function.

Phenotypes of antibody-mediated rejection in organ transplants

Antibody-mediated hyperacute rejection was the first rejection phenotype observed in human organ transplants. This devastating phenotype was eliminated by reliable crossmatch technologies. Since then, the focus was on T-cell-mediated rejection and de novo donor-specific antibodies were considered an epiphenomenon of cognate T-cell activation. The immune theory was that controlling the T-cell response would entail elimination of antibody-mediated rejection (ABMR). With modern immunosuppressive drugs, T-cell-mediated rejection is essentially treatable. However, this did not prevent ABMR from emerging as a significant phenotype in all types of organ transplants. It became obvious that both rejection types require distinct treatment and thus reliable diagnosis. This is the current challenge. ABMR, depending on stage, grade, time course, organ type or prior treatment, can present with a wide spectrum of phenotypes. This review summarizes the current diagnostic consensus for ABMR, describes unmet needs and challenges in diagnostics, and proposes new approaches for consideration.

Pretransplant IgG Subclasses of Donor-Specific Human Leukocyte Antigen Antibodies and Development of Antibody-Mediated Rejection

The subclass of IgG antibodies contributes to their capability to activate complement. It is currently unknown whether the pretransplant IgG subclass composition allows distinguishing harmful from presumably irrelevant donor-specific human leukocyte antigen (HLA) antibodies (HLA-DSA) detected by single-antigen flow beads (SAFB). Seventy-four patients transplanted in the presence of HLA-DSA were investigated. HLA-DSA characteristics were not different between patients experiencing antibody-mediated rejection (AMR) (n=40) and patients who did not (n=34) experience AMR. Sera were reanalyzed using SAFB with IgG subclass-specific reporter antibodies. The 74 patients had in total 141 HLA-DSA. IgG1 was the predominant subclass (78%), followed by IgG2 (49%), IgG3 (36%), and IgG4 (20%). When grouped according to the complement-activating capability, only 4 of 74 patients (5%) had exclusively weak/no complement-activating HLA-DSA (i.e., IgG2 and IgG4), 21 of 74 patients (28%) had isolated strong complement-activating HLA-DSA (i.e., IgG1 and IgG3), and 46 of 74 patients (62%) had a mixture of both. There was no difference between the strong complement-activating and the mixture group regarding incidence of AMR (57% vs. 54%; P=0.81), phenotypes of AMR (P=0.70), and death-censored allograft survival at 5 years (78% vs. 78%; P=0.74). Interestingly, patients with exclusively weak/no complement-activating HLA-DSA (n=4) had a numerically lower incidence of AMR (25%) and no allograft loss has occurred yet. In 90% of patients, pretransplant HLA-DSA are composed of isolated strong or a mixture of strong and weak/no complement-activating IgG subclasses. Because outcomes in these two groups were similar, pretransplant IgG subclass analysis is likely not providing substantial value beyond the standard IgG SAFB assay for pretransplant risk stratification.