Impact of the Banff 2013 classification on the diagnosis of suspicious versus conclusive late antibody-mediated rejection in allografts without acute dysfunction

Alloimmune risk assessment for antibody-mediated rejection in kidney transplantation: A practical proposal

Kidney transplantation is the treatment of choice for patients with end-stage renal disease. Although an improvement in graft survival has been observed in the last decades with the use of different immunosuppressive drugs, this is still limited in time with antibody-mediated rejection being a main cause of graft-loss. Immune monitoring and risk assessment of antibody-mediated rejection before and after kidney transplantation with useful biomarkers is key to tailoring treatments to achieve the best outcomes. Here, we provide a review of the rationale and several accessible tools for immune monitoring, from the most classic to the modern ones. Finally, we end up discussing a practical proposal for alloimmune risk assessment in kidney transplantation, including histocompatibility leukocyte antigen (HLA) and non-HLA antibodies, HLA molecular mismatch analysis and characterization of peripheral blood immune cells.

Seeking Standardized Definitions for HLA-incompatible Kidney Transplants: A Systematic Review

BACKGROUND

There is no standard definition for "HLA incompatible" transplants. For the first time, we systematically assessed how HLA incompatibility was defined in contemporary peer-reviewed publications and its prognostic implication to transplant outcomes.

METHODS

We combined 2 independent searches of MEDLINE, EMBASE, and the Cochrane Library from 2015 to 2019. Content-expert reviewers screened for original research on outcomes of HLA-incompatible transplants (defined as allele or molecular mismatch and solid-phase or cell-based assays). We ascertained the completeness of reporting on a predefined set of variables assessing HLA incompatibility, therapies, and outcomes. Given significant heterogeneity, we conducted narrative synthesis and assessed risk of bias in studies examining the association between death-censored graft failure and HLA incompatibility.

RESULTS

Of 6656 screened articles, 163 evaluated transplant outcomes by HLA incompatibility. Most articles reported on cytotoxic/flow T-cell crossmatches (n = 98). Molecular genotypes were reported for selected loci at the allele-group level. Sixteen articles reported on epitope compatibility. Pretransplant donor-specific HLA antibodies were often considered (n = 143); yet there was heterogeneity in sample handling, assay procedure, and incomplete reporting on donor-specific HLA antibodies assignment. Induction (n = 129) and maintenance immunosuppression (n = 140) were frequently mentioned but less so rejection treatment (n = 72) and desensitization (n = 70). Studies assessing death-censored graft failure risk by HLA incompatibility were vulnerable to bias in the participant, predictor, and analysis domains.

CONCLUSIONS

Optimization of transplant outcomes and personalized care depends on accurate HLA compatibility assessment. Reporting on a standard set of variables will help assess generalizability of research, allow knowledge synthesis, and facilitate international collaboration in clinical trials.

Sensitization in transplantation: Assessment of Risk 2022 Working Group Meeting Report

The Sensitization in Transplantation: Assessment of Risk workgroup is a collaborative effort of the American Society of Transplantation and the American Society of Histocompatibility and Immunogenetics that aims at providing recommendations for clinical testing, highlights gaps in current knowledge, and proposes areas for further research to enhance histocompatibility testing in support of solid organ transplantation. This report provides updates on topics discussed by the previous Sensitization in Transplantation: Assessment of Risk working groups and introduces 2 areas of exploration: non-human leukocyte antigen antibodies and utilization of human leukocyte antigen antibody testing measurement to evaluate the efficacy of antibody-removal therapies.

Phosphorylation of S6RP in peritubular capillaries of kidney grafts and circulating HLA donor-specific antibodies

Antibody-mediated rejection (ABMR) caused by donor-specific HLA-antibodies (DSA) is a mediator of allograft loss after kidney transplantation (KT). DSA can activate microvascular endothelium damage through the mTOR pathway. In this study we assessed the mTOR pathway activation by DSA in KT with ABMR (ABMR + DSA+) compared to controls (ABMR−DSA−), biopsies with ABMR changes without DSA (ABMR + DSA−) and DSA without ABMR changes (ABMR−DSA+), and the potential modulation by mTOR inhibitors (mTORi). We evaluated 97 biopsies: 31 ABMR + DSA+, 33 controls ABMR-DSA−, 16 ABMR + DSA−, and 17 ABMR-DSA+ cases. Regarding immunosuppression of full ABMR + DSA+ and controls, 21 biopsies were performed under mTORi treatment (11 of them ABMR + DSA+ cases) and 43 without mTORi (20 of them ABMR + DSA+) so as to explore its effect on the mTOR pathway. Biopsies were stained for C4d, Ki67, and phosphorylated (p) S6RP, ERK, and mTOR by immunohistochemistry. Labeling was graded according to peritubular capillary staining. ABMR biopsies showed significantly higher C4d, p-S6RP, and Ki67 staining in peritubular capillaries (PTC) compared to controls, and light differences in p-ERK or p-mTOR. mTORi treatment did not modify p-S6RP, p-mTOR, and p-ERK staining. Diffuse p-S6RP in PTC in the biopsies significantly associated with circulating HLA-DSA independently of graft rejection, and with worse death-censored graft survival. These findings suggest that activation of endothelium through the mTOR pathway evidence different mechanisms of damage in ABMR + DSA+ and ABMR + DSA− despite similar histological injury.

Outcomes of paediatric kidney transplant recipients using the updated 2013/2017 Banff histopathological classification for antibody-mediated rejection

BACKGROUND

After the major changes with regard to acute and chronic ABMR in the Banff classification initiated in 2013, there has been an improvement in diagnosing antibody-mediated rejection (ABMR) in adult studies but no data have been published in the paediatric population.

METHODS

We assessed 56 paediatric kidney transplant biopsies due to kidney dysfunction in patients with donor-specific antibodies (DSA) in a retrospective single-centre study between January 2006 and March 2012. The results were compared with 2003/2007 Banff classification noting the subsequent 2017 and 2019 modifications do not change the 2013 Banff classification with regard to acute antibody-mediated rejection (apart from the addition of gene transcripts/classifiers that do not affect our analysis).

RESULTS

Following the 2013 Banff classification, there were seven cases (12.5%) diagnosed with ABMR that would have been misclassified when applying the 2003/2007 classification. Evaluating the histological features of all ABMR-related cases, we report the importance of v- (intimal arteritis) and t- (tubulitis) lesions: absence of v- and t- lesions in the biopsy is related to significantly higher kidney allograft survival (OR 7.3, 95%CI 1.1-48.8, p = 0.03 and OR 5.3, 95%CI 1.2-25.5, p = 0.04 respectively). Moreover, absence of t- lesions was associated with significantly fewer rejection episodes the year after the initial biopsy (OR 5.1, 95%CI 1.4-19.8, p = 0.01).

CONCLUSIONS

Our study supports that the updated 2013 Banff classification shows superior clinicopathological correlation in identifying ABMR in paediatric kidney transplant recipients. Our results can be extrapolated to the recently updated 2019 Banff classification.

Non-HLA Antibodies and Epitope Mismatches in Kidney Transplant Recipients With Histological Antibody-Mediated Rejection

Background

Correlation between antibody-mediated rejection (ABMR) and circulating HLA donor-specific antibodies (HLA-DSA) is strong but imperfect in kidney transplant (KT) recipients, raising the possibility of undetected HLA-DSA or non-HLA antibodies contributing to ABMR. Detailed evaluation of the degree of HLA matching together with the identification of non-HLA antibodies in KT may help to decipher the antibody involved.

Methods

We retrospectively assessed patients with transplant biopsies scored following Banff'15 classification. Pre- and post-transplant serum samples were checked for HLA and non-HLA antibodies [MICA-Ab, angiotensin-II type-1-receptor (AT1R)-Ab, endothelin-1 type-A-receptor (ETAR)-Ab and crossmatches with primary aortic endothelial cells (EC-XM)]. We also analyzed HLA epitope mismatches (HLA-EM) between donors and recipients to explore their role in ABMR histology (ABMRh) with and without HLA-DSA.

Results

One-hundred eighteen patients with normal histology (n = 19), ABMRh (n = 52) or IFTA (n = 47) were studied. ABMRh patients were HLA-DSApos (n = 38, 73%) or HLA-DSAneg (n = 14, 27%). Pre-transplant HLA-DSA and AT1R-Ab were more frequent in ABMRh compared with IFTA and normal histology cases (p = 0.006 and 0.003), without differences in other non-HLA antibodies. Only three ABMRhDSAneg cases showed non-HLA antibodies. ABMRhDSAneg and ABMRhDSApos cases showed similar biopsy changes and graft-survival. Both total class II and DRB1 HLA-EM were associated with ABMRhDSApos but not with ABMRhDSAneg. Multivariate analysis showed that pre-transplant HLA-DSA (OR: 3.69 [1.31-10.37], p = 0.013) and AT1R-Ab (OR: 5.47 [1.78-16.76], p = 0.003) were independent predictors of ABMRhDSApos.

Conclusions

In conclusion, pre-transplant AT1R-Ab is frequently found in ABMRhDSApos patients. However, AT1R-Ab, MICA-Ab, ETAR-Ab or EC-XM+ are rarely found among ABMRhDSAneg patients. Pre-transplant AT1R-Ab may act synergistically with preformed or de novo HLA-DSA to produce ABMRhDSApos but not ABMRhDSAneg. HLA epitope mismatch associates with ABMRhDSApos compared with ABMRhDSAneg, suggesting factors other than HLA are responsible for the damage.

Luminex screening first vs. direct single antigen bead assays: Different strategies for HLA antibody monitoring after kidney transplantation

MAIN PROBLEM

Luminex panel and single antigen beads (SAB) are used for screening and DSA specificity determination respectively. The cost of SAB may limit its general use, so some labs perform SAB tests only after positive screening.

METHODS

We compared both strategies: 1) SAB only if positive screening with kits from manufacturer A, and 2) direct SAB from manufacturer B, and correlate their sensitivity with histological findings.

RESULTS

We selected 118 kidney transplant recipients with a normal biopsy (n = 19), histological antibody-mediated damage (ABMR, n = 52) or interstitial fibrosis/tubular atrophy (IFTA, n = 47) following Banff 2015 and 2017 classification. Direct SAB detected DSA in 13 patients missed by screening. Strategy 1 detected DSA in 0% normal, 61.5% ABMR and 8.5% IFTA patients; percentages with strategy 2 were 5.2%, 78.8% and 14.8% (p=0.004). Strategy 2 identified DSA allowing full ABMR diagnosis in 17% cases missed by strategy 1. Thereafter, direct SAB from manufacturer A confirmed DSA in 46% DSA-positive cases with strategy 2 (55.5% ABMR cases).

CONCLUSIONS

Luminex screening failed to identify clinically relevant HLA antibodies, hampering DSA detection in patients with possible ABMR. Direct SAB testing should be the chosen strategy for post-transplantation monitoring, albeit direct SAB from the two existing manufacturers may diverge in as much as 50% of cases.

Clinical-pathological correlations in post-transplant thrombotic microangiopathy

AIMS

Post-transplant thrombotic microangiopathy (TMA) is a rare and clinically challenging finding in renal transplant biopsies. In addition to recurrent atypical haemolytic uraemic syndrome, TMA in renal transplants is associated with various conditions, such as calcineurin inhibitor (CNI) treatment, antibody-mediated rejection (ABMR), viral infections, sepsis, pregnancy, malignancies, and surgery. The therapeutic implications of this diagnosis are considerable. In order to better understand post-transplant TMA and to identify histological or clinical differences between associated causes, we conducted a multicentre retrospective study.

METHODS AND RESULTS

Clinical parameters and transplant renal biopsy findings from 81 patients with TMA were analysed. Biopsies from 38 patients were also analysed with electron microscopy. On the basis of clinical-pathological correlation, TMA was attributed to a main aetiology, whenever possible. TMA occurred at a median of 30 days post-transplantation. Systemic features of TMA were present in only 18% of cases. Twenty-two per cent of cases were attributed to CNI and 11% to ABMR. Although other potentially contributing factors were found in 56% of patients, in most cases (63%) no clearly attributable cause of TMA was identified. Histological differences between groups were minimal. The detection of ultrastructural features that are usually associated with ABMR may help to establish ABMR as the cause of TMA.

CONCLUSIONS

Although CNI and ABMR appear to be the main contributors to post-transplant TMA, the aetiology of most cases is probably multifactorial, and TMA cannot be unequivocally attributed to a single underlying aetiology. Morphological features of TMA are not discriminating, but electron microscopy may help to identify ABMR-associated TMA.

Establishing a Core Outcome Measure for Graft Health: A Standardized Outcomes in Nephrology-Kidney Transplantation (SONG-Tx) Consensus Workshop Report

BACKGROUND

Graft loss, a critically important outcome for transplant recipients, is variably defined and measured, and incompletely reported in trials. We convened a consensus workshop on establishing a core outcome measure for graft loss for all trials in kidney transplantation.

METHODS

Twenty-five kidney transplant recipients/caregivers and 33 health professionals from 8 countries participated. Transcripts were analyzed thematically.

RESULTS

Five themes were identified. "Graft loss as a continuum" conceptualizes graft loss as a process, but requiring an endpoint defined as a discrete event. In "defining an event with precision and accuracy," loss of graft function requiring chronic dialysis (minimum, 90 days) provided an objective and practical definition; retransplant would capture preemptive transplantation; relisting was readily measured but would overestimate graft loss; and allograft nephrectomy was redundant in being preceded by dialysis. However, the thresholds for renal replacement therapy varied. Conservative management was regarded as too ambiguous and complex to use routinely. "Distinguishing death-censored graft loss" would ensure clarity and meaningfulness in interpreting results. "Consistent reporting for decision making" by specifying time points and metrics (ie time to event) was suggested. "Ease of ascertainment and data collection" of the outcome from registries could support use of registry data to efficiently extend follow-up of trial participants.

CONCLUSIONS

A practical and meaningful core outcome measure for graft loss may be defined as chronic dialysis or retransplant, and distinguished from loss due to death. Consistent reporting of graft loss using standardized metrics and time points may improve the contribution of trials to decision making in kidney transplantation.

Endothelin A Receptors Expressed in Renal Blood Vessels of Renal Transplant Patients Are Connected With Acute Tubular Necrosis or Antibody-Mediated Rejection

BACKGROUND

The role of non-HLA antibodies named antiendothelin A receptor antibodies is potentially significant but not established. The significance of the endothelin A receptor (ETAR) and its expression in renal biopsy has not been defined. We decided to evaluate the presence and relevance of ETARs in renal transplant biopsy for cause. The aim of our study was to evaluate the immunoreactivity of the ETAR and its significance in patients who had a renal transplant biopsy due to deterioration of transplant function (biopsy for cause) with detailed characterization of staining in small and intermediate arteries of renal transplant biopsies.

METHODS

Immunohistochemical expression of ETARs was analyzed in 162 renal transplant biopsies. Microscopic evaluation of ETAR expression (polyclonal antibody) was performed on paraffin sections. ETAR expression was analyzed in renal blood vessels (small and intermediate arteries) based on three-step scale.

RESULTS

We analyzed 154 patients who had renal allograft biopsy between 6 days and 24 years (median 597 days) after transplantation. Positive staining of ETAR in small and intermediate arteries was noticed in 9 patients. Among these patients, 4 had early biopsies (<3 months after transplantation), all developed acute tubular necrosis, and 1 developed additionally acute humoral rejection. Further, 4 patients had late biopsy (1-8 years after transplantation) and all developed characteristics of antibody mediated rejection. Lastly, 1 patient had no characteristic changes in the biopsy 4 months after transplantation. Graft loss 1 year after biopsy was higher in patients who were ETAR-positive but statistical significance was not achieved.

CONCLUSIONS

The expression of endothelin receptors in renal blood vessels (small and intermediate arteries) seems to be important in diagnosis of damage during acute tubular necrosis and antibody-mediated rejection.

Impact of persistent and cleared preformed HLA DSA on kidney transplant outcomes

Preformed HLA donor-specific antibodies (DSA) only detected with Luminex have been associated with increased risk of antibody-mediated rejection (ABMR) and graft failure after kidney transplantation (KT). Their evolution after KT may modify this risk. We analyzed postransplant evolution of preformed DSA identified retrospectively and their impact on outcomes of 370 KT performed 2006-2014. Antibodies were monitored prospectively at 1-3-5 years after KT and if any dysfunction. Early acute ABMR was more frequent among patients with preformed DSA class-I or I + II than isolated class-II (29.4% vs 4.5%, p = 0.02). One year post-KT, 20 of 34 patients with functioning KT had persistent DSA. Preformed DSA class-II persisted more frequently than class-I/I + II (66.7% vs 33.3%; p = 0.031). The only risk factor independently associated with persistence was pretransplant MFI. Patients with de novo DSA had the highest risk of ABMR (HR 22.2 [CI 6.1-81.2]). Although recipients with persisting preformed DSA had significantly increased ABMR risk (HR 14.7 [CI 6.5-33.0]), those with cleared preformed DSA also had a higher risk than those without DSA (HR 7.01 [CI 2.2-21.8]). Preformed DSA are a very important risk factor for ABMR and graft loss. Patients who clear preformed DSA still show an increased risk of ABMR and graft loss after KT.

Re-evaluation of glomerulitis using occlusion criteria based on the Banff 2013 revision: a retrospective study

The presence of occlusion/near-occlusion of glomerular capillaries was recently added to the existing definition of glomerulitis (g). We retrospectively re-evaluated 135 renal allograft biopsies regarding g to ensure no antibody-damaged grafts were missed. Previous and revised g scores (pg and rg, respectively) were compared for clinicopathologic correlations. The g score did not change in 100 (74.1%) biopsies. Thirty-five (25.9%) biopsies were changed to a lower score. Sensitivity and specificity of pg and rg for the presence of donor-specific antibodies (DSA) were 76% vs. 58% and 70% vs. 79%, respectively. Pg score indicated graft loss with 65% sensitivity and 63% specificity, whereas rg showed 46% sensitivity and 71% specificity. Area under the curve (AUC) values in ROC analysis for DSA and graft loss were as follows: pg, 0.773; rg, 0.693; and pg, 0.635; rg, 0.577, respectively. A comparison of the two AUC values revealed a significant difference between pg and rg only for DSA (P = 0.0076). Pg and post-transplant time of biopsy independently predicted graft loss, whereas rg did not. In conclusion, revised g scores showed lesser sensitivity but higher specificity for DSA and graft loss. Recent definition of g missed antibody-mediated rejection in few cases, and it was not an independent predictor for graft loss.

Current pathological perspectives on chronic rejection in renal allografts

Chronic rejection in renal transplantation clinically manifests as slow deterioration in allograft function and is a major contributor of late renal graft loss. Most cases of chronic rejection involve chronic antibody-mediated rejection (ABMR) triggered by the interaction of donor-specific alloantibodies with endothelial cells of the microcirculation. The evolution of the Banff classification involved a major revision of the ABMR criteria during the 2000s and led to the inclusion of detailed pathological characteristics of chronic ABMR in the 2013 Banff scheme, including microcirculation damage observed as newly formed basement membranes and arterial fibrous intimal proliferation. Inflammation of microvasculature including glomeruli and/or peritubular capillaries is also seen in substantial cases of chronic ABMR, defined as chronic active ABMR. Chronic active T cell-mediated rejection (TCMR) results from chronic T cell-mediated injury involving renal arteries but is less characterized under the current Banff classification, mainly due to the expanding histological criteria of chronic active ABMR. Characteristics shared by these two chronic rejection types can potentially cause diagnostic confusion. Hence, the diagnostic criteria or categories of chronic renal rejection require amendment of the current Banff classification. Assessment of rejection cases with molecular phenotyping advanced the mechanistic understanding of various dysfunctions in renal allograft, including ABMR and TCMR. Identification of disease-specific changes in gene expression by immunohistological studies, especially in chronic ABMR, has already been validated by several studies, warranting potential application to the pathological diagnostic process. This review provides an overview of current pathological perspectives on chronic rejection of renal allografts and future directions.