Differences in chronic intragraft inflammation between positive crossmatch and ABO-incompatible kidney transplantation

Characteristics of Early Antibody Mediated Rejection in Antibody Incompatible Living Donor Kidney Transplantation

Antibody incompatible transplantation (AIT) may be an only option for highly sensitized patients. Severe form of early antibody mediated rejection (AMR) adversely affects graft survival after AIT. The aim of this study was to identify individuals at risk of AMR. We analyzed 213 living donor AITs performed at our center. Among 120 ABOi, 58 HLAi and 35 DSA + FCXM-negative cases, the rates of early AMR were 6%, 31%, and 9%, respectively (p < 0.001). On multivariate analysis for graft loss, early AMR had a HR of 3.28 (p < 0.001). The HLAi group had worse death-censored graft survival (p = 0.003). In the HLAi group, Patients with aggressive variant AMR (AAMR) had greater percentage of C3d complement fixing DSA, higher baseline class I and total DSA MFI levels and B-cell FCXM RMF. C1q and C3d complement fixing DSA and strong positivity of baseline B- or T-cell FXCM as predictors of AAMR had 100% sensitivity. Early AMR is of significant clinical concern in AIT as it results in poor graft survival and is not well described in literature. An aggressive variant is characterized by massive rise in DSA levels at rejection. Baseline DSA, C1q, and C3d and baseline FCXM values can be used to risk-stratify candidates for AIT.

Prediction of very early subclinical rejection with machine learning in kidney transplantation

Protocol biopsy is a reliable method for assessing allografts status after kidney transplantation (KT). However, due to the risk of complications, it is necessary to establish indications and selectively perform protocol biopsies by classifying the high-risk group for early subclinical rejection (SCR). Therefore, the purpose of this study is to analyze the incidence and risk factors of early SCR (within 2 weeks) and develop a prediction model using machine learning. Patients who underwent KT at Samsung Medical Center from January 2005 to December 2020 were investigated. The incidence of SCR was investigated and risk factors were analyzed. For the development of prediction model, machine learning methods (random forest, elastic net, extreme gradient boosting [XGB]) and logistic regression were used and the performance between the models was evaluated. The cohorts of 987 patients were reviewed and analyzed. The incidence of SCR was 14.6%. Borderline cellular rejection (BCR) was the most common type of rejection, accounting for 61.8% of cases. In the analysis of risk factors, recipient age (OR 0.98, p = 0.03), donor BMI (OR 1.07, p = 0.02), ABO incompatibility (OR 0.15, p < 0.001), HLA II mismatch (two [OR 6.44, p < 0.001]), and ATG induction (OR 0.41, p < 0.001) were associated with SCR in the multivariate analysis. The logistic regression prediction model (average AUC = 0.717) and the elastic net model (average AUC = 0.712) demonstrated good performance. HLA II mismatch and induction type were consistently identified as important variables in all models. The odds ratio analysis of the logistic prediction model revealed that HLA II mismatch (OR 6.77) was a risk factor for SCR, while ATG induction (OR 0.37) was a favorable factor. Early SCR was associated with HLA II mismatches and induction agent and prediction model using machine learning demonstrates the potential to predict SCR.

Progression of histological lesions after ABO incompatible kidney transplantation

Recent large meta-analyses suggested a poorer long-term patients’ and grafts’ outcomes after ABO incompatible (ABOi) living-donor kidney transplantation (LDKT) compared to ABO compatible LDKT. However, little is known about the long-term histological pattern after ABOi LDKT. We compared the histological features observed on protocol biopsies from 03/11 to 11/19 in 94 ABOi LDKT (including 14 with preformed Donor Specific Antibodies, pDSAs), 27 LDKT ABO compatible (ABOc) with pDSAs, and 21 ABOc without pDSAs) during the first five years post transplantation. During the first 5 years post-transplantation, a progression of chronic lesions (patients with a ci >0 raised from 11% to 65%, p<0.0001, patients with a ct >0 raised from 29% to 78%, p<0.0001) was observed in ABOi LDKT without pDSAs. Histological patterns of evolution were comparable to those observed in ABOc kidney transplant patients. Microvascular inflammation was lower in ABOi LDKT without pDSAs compared to those with pDSAs (ABOi or ABOc). At last follow-up, 28 months, IQR (15-48) post-transplantation, 29 patients (36%) had a severe graft dysfunction (defined by a CKD-epi eGFR < 30 mL/min/1.73m²). The donor age was a predictive factor for the development of severe kidney allograft dysfunction at last follow-up (HR= 1.05, 95% CI [1.05-1.10], p= 0.03).

Hence, long-term histological analysis of ABOi LDKT shows only an increase of chronic interstitial and tubular atrophy changes, without active lesions. These data confirm that ABOi LDKT programs can be securely developed.

Characterization of ABH-subtype donor-specific antibodies in ABO-A-incompatible kidney transplantation

ABO-incompatible (ABOi) transplantation requires preemptive antibody reduction; however, the relationship between antibody-mediated rejection (AMR) and ABO-antibodies, quantified by hemagglutination (HA), is inconsistent, possibly reflecting variable graft resistance to AMR or HA assay limitations. Using an ABH-glycan microarray, we quantified ABO-A antigen-subtype (A-subtype)-specific IgM and IgG in 53 ABO-O recipients of ABO-A kidneys, before and after antibody removal (therapeutic plasma exchange [TPE] or ABO-A-trisaccharide immunoadsorption [IA]) and 1-year posttransplant. IgM binding to all A-subtypes correlated highly (R²  ≥ .90) and A-subtype antibody specificities was reduced equally by IA versus TPE. IgG binding to the A-subtypes (II-IV) expressed in kidney correlated poorly (.27 ≤ R²  ≤ .69). Reduction of IgG specific to A-subtype-II was equivalent for IA and TPE, whereas IgG specific to A-subtypes-III/IV was not as greatly reduced by IA (p < .005). One-year posttransplant, IgG specific to A-II remained the most reduced antibody. Immunostaining revealed only A-II on vascular endothelium but A-subtypes II-III/IV on tubular epithelium. These results show that ABO-A-trisaccharide is sufficient for IgM binding to all A-subtypes; this is true for IgG binding to A-II, but not subtypes-III/IV, which exhibits varying degrees of specificity. We identify A-II as the major, but importantly not the sole, antigen relevant to treatment and immune modulation in adult ABO-A-incompatible kidney transplantation.

ABO-incompatible kidney transplantation in perspective of deceased donor transplantation and induction strategies: a propensity-matched analysis

Kidney transplant candidates are blood group incompatible with roughly one out of three potential living donors. We compared outcomes after ABO‐incompatible (ABOi) kidney transplantation with matched ABO‐compatible (ABOc) living and deceased donor transplantation and analyzed different induction regimens. We performed a retrospective study with propensity matching and compared patient and death‐censored graft survival after ABOi versus ABOc living donor and deceased donor kidney transplantation in a nationwide registry from 2006 till 2019. 296 ABOi were compared with 1184 center and propensity‐matched ABOc living donor and 1184 deceased donor recipients (matching: recipient age, sex, blood group, and PRA). Patient survival was better compared with deceased donor [hazard ratio (HR) for death of HR 0.69 (0.49–0.96)] and non‐significantly different from ABOc living donor recipients [HR 1.28 (0.90–1.81)]. Rate of graft failure was higher compared with ABOc living donor transplantation [HR 2.63 (1.72–4.01)]. Rejection occurred in 47% of 140 rituximab versus 22% of 50 rituximab/basiliximab, and 4% of 92 alemtuzumab‐treated recipients (P < 0.001). ABOi kidney transplantation is superior to deceased donor transplantation. Rejection rate and graft failure are higher compared with matched ABOc living donor transplantation, underscoring the need for further studies into risk stratification and induction therapy [NTR7587, www.trialregister.nl].

Histopathologic Features of Antibody Mediated Rejection: The Banff Classification and Beyond

Antibody mediated rejection (ABMR) in the kidney can show a wide range of clinical presentations and histopathologic patterns. The Banff 2019 classification currently recognizes four diagnostic categories: 1. Active ABMR, 2. Chronic active ABMR, 3. Chronic (inactive) ABMR, and 4. C4d staining without evidence of rejection. This categorization is limited in that it does not adequately represent the spectrum of antibody associated injury in allograft, it is based on biopsy findings without incorporating clinical features (e.g., time post-transplant, de novo versus preformed DSA, protocol versus indication biopsy, complement inhibitor drugs), the scoring is not adequately reproducible, and the terminology is confusing. These limitations are particularly relevant in patients undergoing desensitization or positive crossmatch kidney transplantation. In this article, I discuss Banff criteria for these ABMR categories, with a focus on patients with pre-transplant DSA, and offer a framework for considering the continuum of allograft injury associated with donor specific antibody in these patients.

Pretransplant Donor-Specific Anti-HLA Antibodies and the Risk for Rejection-Related Graft Failure of Kidney Allografts

Background

The presence of donor-specific antibodies (DSAs) against HLA before kidney transplantation has been variably associated with decreased long-term graft survival. Data on the relation of pretransplant DSA with rejection and cause of graft failure in recipients of donor kidneys are scarce.

Methods

Patients transplanted between 1995 and 2005 were included and followed until 2016. Donor-specific antibodies before transplantation were determined retrospectively. For cause, renal transplant biopsies were reviewed.

Results

Pretransplant DSAs were found in 160 cases on a total of 734 transplantations (21.8%). In 80.5% of graft failures, a diagnostic renal biopsy was performed. The presence of pretransplant DSA (DSApos) increased the risk of graft failure within the first 3 months after transplantation (5.2% vs. 9.4%) because of rejection with intragraft thrombosis (p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos, p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos, p < 0.01). One year after transplantation, DSApos recipients had an increased hazard for antibody-mediated rejection at 10 years (9% DSAneg vs. 15% DSApos.

Conclusions

Pretransplant DSAs are a risk factor for early graft loss and increase the incidence for humoral rejection and graft loss but do not affect the risk for T cell-mediated rejection.

Latest insights on ABO-incompatible living-donor renal transplantation

This review summarizes the latest insights on ABO‐incompatible living‐donor renal transplantation. Desensitization protocols and clinical outcomes were investigated, and a comparison was made with kidney‐paired donation, which is not permitted in Japan for ethical reasons. Although renal transplantation is greatly beneficial for most patients with end‐stage kidney disease, many of these patients must remain on dialysis therapy for extended periods due to the scarcity of organs from deceased donors. ABO blood type incompatibility was once believed to be a contraindication to renal transplantation due to the increased risk for antibody‐mediated rejection and early graft loss attributable to isoagglutinins. Recently, pretransplant desensitization strategies, such as removal of isoagglutinins and antibody‐producing cells, have achieved successful outcomes, although it remains unclear whether graft survival and patient morbidity are equivalent to those for ABO‐compatible renal transplantation. The present review suggested that ABO‐incompatible living‐donor renal transplantation might be a favorable radical renal replacement therapy for patients with end‐stage kidney disease.

Long-term outcomes of eculizumab-treated positive crossmatch recipients: Allograft survival, histologic findings, and natural history of the donor-specific antibodies

We aimed to determine the long-term outcomes of eculizumab-treated, positive crossmatch (+XM) kidney transplant recipients compared with +XM and age-matched negative crossmatch (-XM) controls. We performed an observational retrospective study and examined allograft survival, histologic findings, long-term B-cell flow cytometric XM (BFXM), and allograft-loss-associated factors. The mean (SD) posttransplant follow-up was 6.3 (2.5) years in the eculizumab group; 7.6 (3.5), +XM control group; 7.9 (2.5), -XM control group. The overall and death-censored allograft survival rates were similar in +XM groups (P = .73, P = .48) but reduced compared with -XM control patients (P < .001, P < .001). In the eculizumab-treated group, 57.9% (11/19) of the allografts had chronic antibody-mediated rejection, but death-censored allograft survival was 76.6%, 5 years; 75.4%, 7 years. Baseline IgG3 positivity and BFXM ≥300 were associated with allograft loss. C1q positivity was also associated with allograft loss but did not reach statistical significance. Donor-specific antibodies appeared to decrease in eculizumab-treated patients. After excluding patients with posttransplant plasmapheresis, 42.3% (9/21) had negative BFXMs; 31.8% (7/22), completely negative single-antigen beads 1 year posttransplant. Eculizumab-treated +XM patients had reduced allograft survival compared with -XM controls but similar survival to +XM controls. BFXM and complement-activating donor-specific antibodies (by IgG3 and C1q testing) may be used for risk stratification in +XM transplantation.

ABO-Incompatible Kidney Transplant Outcomes: A Meta-Analysis

BACKGROUND AND OBJECTIVES

ABO blood group-incompatible kidney transplantation is considered a safe procedure, with noninferior outcomes in large cohort studies. Its contribution to living kidney transplantation programs is substantial and growing. Outcomes compared with center-matched ABO blood group-compatible control patients have not been ascertained.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Comprehensive searches were conducted in Embase, Medline, Cochrane, Web-of-Science, and Google Scholar. Meta-analyses Of Observational Studies in Epidemiology study guidelines for observational studies and Newcastle Ottawa bias scale were implemented to assess studies. Meta-analysis was performed using Review Manager 5.3. A subgroup analysis on antibody removal technique was performed.

RESULTS

After identifying 2728 studies addressing ABO-incompatible kidney transplantation, 26 studies were included, describing 1346 unique patients who were ABO-incompatible and 4943 ABO-compatible controls. Risk of bias was low (all studies ≥7 of 9 stars). Baseline patient characteristics revealed no significant differences in immunologic risk parameters. Statistical heterogeneity of studies was low (I2 0% for graft and patient survival). One-year uncensored graft survival of patients who were ABO-incompatible was 96% versus 98% in ABO-compatible controls (relative risk, 0.97; 95% confidence interval, 0.96 to 0.98; P<0.001). Forty-nine percent of reported causes of death in patients who were ABO-incompatible were of infectious origin, versus only 13% in patients who were ABO-compatible (P=0.02). Antibody-mediated rejection (3.86; 95% confidence interval, 2.05 to 7.29; P<0.001), severe nonviral infection (1.44; 95% confidence interval, 1.13 to 1.82; P=0.003), and bleeding (1.92; 95% confidence interval, 1.36 to 2.72; P<0.001) were also more common after ABO-incompatible transplantation.

CONCLUSIONS

ABO-incompatible kidney transplant recipients have good outcomes, albeit inferior to center-matched ABO-compatible control patients.

Evaluation of Microvascular Inflammation in ABO-Incompatible Kidney Transplantation

BACKGROUND

In ABO-incompatible kidney transplantation, the diagnostic criteria for antibody-mediated rejection remain controversial because C4d deposition is commonly observed. Thus, we investigated microvascular inflammation (MVI score ≥ 2) within 1 year as a predictor of graft outcome.

METHODS

A total of 148 recipients without preformed or de novo donor-specific anti-HLA antibody were stratified based on MVI score less than 2 (n = 117) and MVI score of 2 or greater (n = 31).

RESULTS

We found that 5-year graft survival was significantly lower (P = 0.0129) in patients with MVI (89.8%) than in patients without MVI (97.0%). Graft function, as characterized by serum estimated glomerular filtration rate, was also significantly worse for patients with MVI than it was for patients without MVI, between 3 months and 10 years after transplantation (P = 0.048). Multivariate analysis indicated that HLA class II mismatch (P = 0.0085) was an independent marker of MVI.

CONCLUSIONS

Microvascular inflammation score of 2 or greater is significantly associated with poor graft outcome after ABO-incompatible kidney transplantation. We suggest that MVI score of 2 or greater in ABOi transplantation be used as a basis to diagnose antibody-mediated rejection.

HLA Class II Antibody Activation of Endothelial Cells Promotes Th17 and Disrupts Regulatory T Lymphocyte Expansion

Kidney transplantation is the most successful treatment option for patients with end-stage renal disease, and chronic antibody-mediated rejection is the principal cause of allograft loss. Predictive factors for chronic rejection include high levels of HLA alloantibodies (particularly HLA class II) and activation of graft endothelial cells (ECs). The mechanistic basis for this association is unresolved. We used an experimental model of HLA-DR antibody stimulation of microvascular ECs to examine the mechanisms underlying the association between HLA class II antibodies, EC activation and allograft damage. Activation of ECs with the F(Ab')2 fragment of HLA-DR antibody led to phosphorylation of Akt, ERK and MEK and increased IL-6 production by ECs cocultured with allogeneic peripheral blood mononuclear cells (PBMCs) in an Akt-dependent manner. We previously showed that HLA-DR-expressing ECs induce polarization of Th17 and FoxP3(bright) regulatory T cell (Treg) subsets. Preactivation of ECs with anti-HLA-DR antibody redirected EC allogenicity toward a proinflammatory response by decreasing amplification of functional Treg and by further increasing IL-6-dependent Th17 expansion. Alloimmunized patient serum containing relevant HLA-DR alloantibodies selectively bound and increased EC secretion of IL-6 in cocultures with PBMCs. These data contribute to understanding of potential mechanisms of antibody-mediated endothelial damage independent of complement activation and FcR-expressing effector cells.

Deceased donor kidney transplantation across donor-specific antibody barriers: predictors of antibody-mediated rejection

BACKGROUND

Apheresis-based desensitization allows for successful transplantation across major immunological barriers. For donor-specific antibody (DSA)- and/or crossmatch-positive transplantation, however, it has been shown that even intense immunomodulation may not completely prevent antibody-mediated rejection (ABMR).

METHODS

In this study, we evaluated transplant outcomes in 101 DSA+ deceased donor kidney transplant recipients (transplantation between 2009 and 2013; median follow-up: 24 months) who were subjected to immunoadsorption (IA)-based desensitization. Treatment included a single pre-transplant IA session, followed by anti-lymphocyte antibody and serial post-transplant IA. In 27 cases, a positive complement-dependent cytotoxicity crossmatch (CDCXM) was rendered negative immediately before transplantation. Seventy-four of the DSA+ recipients had a negative CDCXM already before IA.

RESULTS

Three-year death-censored graft survival in DSA+ patients was significantly worse than in 513 DSA- recipients transplanted during the same period (79 versus 88%, P = 0.008). Thirty-three DSA+ recipients (33%) had ABMR. While a positive baseline CDCXM showed only a trend towards higher ABMR rates (41 versus 30% in CDCXM- recipients, P = 0.2), DSA mean fluorescence intensity (MFI) in single bead assays significantly associated with rejection, showing 20 versus 71% ABMR rates at <5000 versus >15 000 peak DSA MFI. The predictive value of MFI was moderate, with the highest accuracy at a median of 13 300 MFI (after cross-validation: 0.72). Other baseline variables, including CDC assay results, human leukocyte antigen mismatch, prior transplantation or type of induction treatment, did not add independent predictive information.

CONCLUSIONS

IA-based desensitization failed to prevent ABMR in a considerable number of DSA+ recipients. Assessing DSA MFI may help stratify risk of rejection, supporting its use as a guide to organ allocation and individualized treatment.

Predicting Individual Renal Allograft Outcomes Using Risk Models with 1-Year Surveillance Biopsy and Alloantibody Data

The ability to predict outcomes for individual patients would be a significant advance for not only counseling, but also identifying those for whom interventions may be needed. The goals of this study were to validate an existing risk prediction score that incorporates easily obtainable clinical factors and determine if histologic findings at 1-year surveillance biopsy and/or serum donor-specific alloantibody status could improve predictability of graft loss by 5 years. We retrospectively studied 1465 adults who received a solitary kidney transplant between January of 1999 and December of 2008 and had sufficiently detailed 5-year follow-up data for modeling. In this cohort, the Birmingham risk model (incorporating recipient factors at 1 year, including age, sex, ethnicity, renal function, proteinuria, and prior acute rejection) predicted death-censored and overall graft survival (c statistics =0.84 and 0.78, respectively). The presence of glomerulitis or chronic interstitial fibrosis (g and ci scores by Banff, respectively) on 1-year biopsy specimens independently correlated with graft loss by 5 years. Adding these variables to the model for death-censored graft loss increased predictability (c statistic =0.90), improved calibration (ability to stratify risk from high to low), and reclassified risk of failure in 29% of patients. Adding the presence of donor-specific alloantibody at 1 year did not improve predictability or reclassification but did improve calibration marginally. We conclude that, at 1 year after kidney transplant, a risk model of graft survival that incorporates clinical factors and histologic findings at surveillance biopsy is highly predictive of individual risk and well calibrated.

Strategies to overcome the ABO barrier in kidney transplantation

Kidney transplantation across the ABO blood group barrier was long considered a contraindication for transplantation, but in an effort to increase donor pools, specific regimens for ABO-incompatible (ABOi) transplantation have been developed. These regimens are now widely used as an integral part of the available treatment options. Various desensitization protocols, commonly based on transient depletion of preformed anti-A and/or anti-B antibodies and modulation of B-cell immunity, enable excellent transplant outcomes, even in the long-term. Nevertheless, the molecular mechanisms behind transplant acceptance facilitated by a short course of anti-humoral treatment are still incompletely understood. With the evolution of efficient clinical programmes, tailoring of recipient preconditioning based on individual donor-recipient blood type combinations and the levels of pretransplant anti-A/B antibodies has become possible. In the context of low antibody titres and/or donor A2 phenotype, immunomodulation and/or apheresis might be dispensable. A concern still exists, however, that ABOi kidney transplantation is associated with an increased risk of surgical and infectious complications, partly owing to the effects of extracorporeal treatment and intensified immunosuppression. Nevertheless, a continuous improvement in desensitization strategies, with the aim of minimizing the immunosuppressive burden, might pave the way to clinical outcomes that are comparable to those achieved in ABO-compatible transplantation.

Difference in outcomes after antibody-mediated rejection between abo-incompatible and positive cross-match transplantations

Graft survival seems to be worse in positive cross-match (HLAi) than in ABO-incompatible (ABOi) transplantation. However, it is not entirely clear why these differences exist. Sixty-nine ABOi, 27 HLAi and 10 combined ABOi+HLAi patients were included in this retrospective study, to determine whether the frequency, severity and the outcome of active antibody-mediated rejection (AMR) were different. Five-year death-censored graft survival was better in ABOi than in HLAi and ABOi+HLAi patients (99%, 69% and 64%, respectively, P = 0.0002). Features of AMR were found in 38%, 95% and 100% of ABOi, HLAi and ABOi+HLAi patients that had a biopsy, respectively (P = 0.0001 and P = 0.001). After active AMR, a declining eGFR and graft loss were observed more frequently in HLAi and HLAi+ABOi than in ABOi patients. The poorer prognosis after AMR in HLAi and ABOi+HLAi transplantations was not explained by a higher severity of histological lesions or by a less aggressive treatment. In conclusion, ABOi transplantation offers better results than HLAi transplantation, partly because AMR occurs less frequently but also because outcome after AMR is distinctly better. HLAi and combined ABOi+HLAi transplantations appear to have the same outcome, suggesting there is no synergistic effect between anti-A/B and anti-HLA antibodies.

One-year protocol biopsies from ABO-incompatible renal allografts compared with a matched cohort of ABO-compatible allografts

Introduction

Early acute antibody-mediated rejection (ABMR) occurs more frequently in ABO-incompatible (ABOi) than in ABO-compatible (ABOc) kidney transplantation. This could lead to increased inflammation/scarring in the ABOi grafts. Protocol biopsy data in ABOi kidney recipients are scarce.

Methods

A single-center retrospective matched cohort study was conducted. Eighty adult living donor (LD) renal transplant recipients without HLA donor-specific antibodies (DSA) transplanted between 2009 and 2012 were included; 20 ABOi and 60 ABOc controls matched for donor age and transplantation year. Protocol biopsies at one yr were scored according to the Banff classification. Three sums of scores were constructed: tubulointerstitial inflammation (t + i = 0 vs. >0), microvascular inflammation (g + ptc = 0 vs. >0), scarring/hyalinosis (ci + ct + cv + ah ≤ 1 vs. >1. Scores and presence of subclinical rejection (SCR) at one yr were compared.

Results

Protocol biopsy findings at one yr in the ABOi vs. ABOc matched control group were not statistically different: (t + i) > 0, 30% vs. 20%; (g + ptc) > 0, 5% vs. 8%; (ci + ct + cv + ah) > 1, 85% vs. 60%, respectively. No transplant glomerulopathy occurred. SCR rate at one yr was 30% vs. 18%, subclinical ABMR 5% vs. 7% (all with de novo HLA DSA).

Conclusion

One-year protocol biopsies of ABOi and ABOc LD recipients do not differ in chronic changes, inflammation, or SCRs.