Identifying Subphenotypes of Antibody-Mediated Rejection in Kidney Transplants

Early Versus Late Acute AMR in Kidney Transplant Recipients-A Comparison of Treatment Approaches and Outcomes From the ANZDATA Registry

BACKGROUND

Antibody-mediated rejection (AMR) is a major cause of kidney allograft failure and demonstrates different properties depending on whether it occurs early (<6 mo) or late (>6 mo) posttransplantation. We aimed to compare graft survival and treatment approaches for early and late AMR in Australia and New Zealand.

METHODS

Transplant characteristics were obtained for patients with an AMR episode reported to the Australia and New Zealand Dialysis and Transplant Registry from January 2003 to December 2019. The primary outcome of time to graft loss from AMR diagnosis, with death considered a competing risk, was compared between early and late AMR using flexible parametric survival models. Secondary outcomes included treatments used, response to treatment, and time from AMR diagnosis to death.

RESULTS

After adjustment for other explanatory factors, late AMR was associated with twice the risk of graft loss relative to early AMR. The risk was nonproportional over time, with early AMR having an increased early risk. Late AMR was also associated with an increased risk of death. Early AMR was treated more aggressively than late with more frequent use of plasma exchange and monoclonal/polyclonal antibodies. There was substantial variation in treatments used by transplant centers. Early AMR was reported to be more responsive to treatment than late.

CONCLUSIONS

Late AMR is associated with an increased risk of graft loss and death compared with early AMR. The marked heterogeneity in the treatment of AMR highlights the need for effective, new therapeutic options for these conditions.

Natural Antibodies Are Associated With Rejection and Long-term Renal Allograft Loss in a Multicenter International Cohort

BACKGROUND

Potentially harmful nonhuman leukocyte antigen antibodies have been identified in renal transplantation, including natural immunoglobulin G antibodies (Nabs) reactive to varied antigenic structures, including apoptotic cells.

METHODS

In this retrospective, multicenter study, we assessed Nabs by reactivity to apoptotic cells in sera collected from 980 kidney transplant recipients across 4 centers to determine their association with graft outcomes.

RESULTS

Elevated pretransplant Nabs were associated with graft loss (hazard ratio [HR] 2.71; 95% confidence interval [CI], 1.15-6.39; P   =  0.0232), the composite endpoint of graft loss or severe graft dysfunction (HR 2.40; 95% CI, 1.13-5.10; P  = 0.0232), and T cell-mediated rejection (odds ratio [OR] 1.77; 95% CI, 1.07-3.02; P  = 0.0310). High pretransplant Nabs together with donor-specific antibodies (DSAs) were associated with increased risk of composite outcomes (HR 6.31; 95% CI, 1.81-22.0; P  = 0.0039). In patients with high pretransplant Nabs, the subsequent development of posttransplant Nabs was associated with both T cell-mediated rejection (OR 3.64; 95% CI, 1.61-8.36; P  = 0.0021) and mixed rejection (OR 3.10; 95% CI, 1.02-9.75; P  = 0.0473). Finally, elevated pre- and posttransplant Nabs combined with DSAs were associated with increased risk of composite outcomes (HR 3.97; 95% CI, 1.51-10.43; P  = 0.0052) and T cell-mediated rejection (OR 7.28; 95% CI, 2.16-25.96; P  = 0.0016).

CONCLUSIONS

The presence of pre- and posttransplant Nabs, together with DSAs, was associated with increased risk of poor graft outcomes and rejection after renal transplantation.

A Banff-based histologic chronicity index is associated with graft loss in patients with a kidney transplant and antibody-mediated rejection

Antibody-mediated rejection (AMR) is the major cause of graft loss in kidney transplant recipients. The Banff classification defines two classes of AMR, active and chronic active but over time this classification has become increasingly complex. To simplify the approach to AMR, we developed activity and chronicity indices based on kidney transplant biopsy findings and examined their association with graft survival in 147 patients with active or chronic active AMR, all of whom had donor-specific antibodies and were treated for AMR. The activity index was determined as the sum of Banff glomerulitis (g), peritubular capillaritis (ptc), arteritis (v) and C4d scores, with a maximum score of 12. The chronicity index was the sum of interstitial fibrosis (ci), tubular atrophy (ct), chronic vasculopathy (cv), and chronic glomerulopathy (cg) scores, the latter doubled, with a maximum score of 15. While the activity index was generally not associated with graft loss, the chronicity index was significantly associated with graft loss with an optimal threshold value of 4 or greater for predicting graft loss. The association of the chronicity index of 4 or greater with graft loss was independent of other parameters associated with graft loss, including the estimated glomerular filtration rate at the time of biopsy, chronic active (versus active) AMR, AMR with de novo (versus persistent/rebound) donor-specific antibodies, Banff (g+ptc) scores, concurrent T cell-mediated rejection and donor-specific antibody reduction post-biopsy. The association of the chronicity index of 4 or greater with graft loss was confirmed in an independent cohort of 61 patients from Necker Hospital, Paris. Thus, our findings suggest that the chronicity index may be valuable as a simplified approach to decision-making in patients with AMR.

Proposed Definitions of Antibody-Mediated Rejection for Use as a Clinical Trial Endpoint in Kidney Transplantation

Antibody-mediated rejection (AMR) is caused by antibodies that recognize donor human leukocyte antigen (HLA) or other targets. As knowledge of AMR pathophysiology has increased, a combination of factors is necessary to confirm the diagnosis and phenotype. However, frequent modifications to the AMR definition have made it difficult to compare data and evaluate associations between AMR and graft outcome. The present paper was developed following a Broad Scientific Advice request from the European Society for Organ Transplantation (ESOT) to the European Medicines Agency (EMA), which explored whether updating guidelines on clinical trial endpoints would encourage innovations in kidney transplantation research. ESOT considers that an AMR diagnosis must be based on a combination of histopathological factors and presence of donor-specific HLA antibodies in the recipient. Evidence for associations between individual features of AMR and impaired graft outcome is noted for microvascular inflammation scores ≥2 and glomerular basement membrane splitting of >10% of the entire tuft in the most severely affected glomerulus. Together, these should form the basis for AMR-related endpoints in clinical trials of kidney transplantation, although modifications and restrictions to the Banff diagnostic definition of AMR are proposed for this purpose. The EMA provided recommendations based on this Broad Scientific Advice request in December 2020; further discussion, and consensus on the restricted definition of the AMR endpoint, is required.

Antigen and Cell-Based Assays for the Detection of Non-HLA Antibodies

To date, human leukocyte antigens (HLA) have been the major focus in the approach to acute and chronic antibody-mediated rejection (AMBR) in solid-organ transplantation. However, evidence from the clinic and published studies has shown that non-HLA antibodies, particularly anti-endothelial cell antibodies (AECAs), are found either in the context of AMBR or synergistically in the presence of donor-specific anti-HLA antibodies (DSA). Numerous studies have explored the influence of AECAs on clinical outcomes, yet the determination of the exact clinical relevance of non-HLA antibodies in organ transplantation is not fully established. This is due to highly heterogeneous study designs including differences in testing methods and outcome measures. Efforts to develop reliable and sensitive diagnostic non-HLA antibody tests are continuously made. This is essential considering the technical difficulties of non-HLA antibody assays and the large variation in reported incidences of antibodies. In addition, it is important to take donor specificity into account in order to draw clinically relevant conclusions from non-HLA antibody assays. Here, we provide an overview of non-HLA solid-phase and cell-based crossmatch assays for use in solid-organ transplantation that are currently available, either in a research setting or commercially.

Risk Factors of Rejection in Renal Transplant Recipients: A Narrative Review

Multiple factors influence graft rejection after kidney transplantation. Pre-operative factors affecting graft function and survival include donor and recipient characteristics such as age, gender, race, and immunologic compatibility. In addition, several peri- and post-operative parameters affect graft function and rejection, such as cold and warm ischemia times, and post-operative immunosuppressive treatment. Exposure to non-self-human leucocyte antigens (HLAs) prior to transplantation up-regulates the recipient’s immune system. A higher rate of acute rejection is observed in transplant recipients with a history of pregnancies or significant exposure to blood products because these patients have higher panel reactive antibody (PRA) levels. Identifying these risk factors will help physicians to reduce the risk of allograft rejection, thereby promoting graft survival. In the current review, we summarize the existing literature on donor- and recipient-related risk factors of graft rejection and graft loss following kidney transplantation.

Differential Treatment Effects for Renal Transplant Recipients With DSA-Positive or DSA-Negative Antibody-Mediated Rejection

Background

Antibody-mediated rejection (ABMR) is the main cause of renal allograft loss. The most common treatment strategy is based on plasmapheresis plus the subsequent administration of intravenous immunoglobulin (IVIG). Unfortunately, no approved long-term therapy is available for ABMR. The current study was designed to analyze the effect of various ABMR treatment approaches on allograft survival and to compare treatment effects in the presence or absence of donor-specific antibodies (DSAs).

Methods

This single-center study retrospectively analyzed 102 renal allograft recipients who had biopsy-proven ABMR after transplant. DSA was detectable in 61 of the 102 patients. Initial standard treatment of ABMR consisted of plasmapheresis (PS) or immunoadsorption (IA), followed by a single course of IVIG. In case of nonresponse or recurrence, additional immunosuppressive medications, such as rituximab, bortezomib, thymoglobulin, or eculizumab, were administered. In a second step, persistent ABMR was treated with increased maintenance immunosuppression, long-term therapy with IVIG (more than 1 year), or both.

Results

Overall graft survival among transplant patients with ABMR was <50% after 3 years of follow-up. Compared to the use of PS/IA and IVIG alone, the use of additional immunosuppressive medications had no beneficial effect on allograft survival (p = 0.83). Remarkably, allografts survival rates were comparable between patients treated with the combination of PS/IA and IVIG and those treated with a single administration of IVIG (p = 0.18). Renal transplant patients with ABMR but without DSAs benefited more from increased maintenance immunosuppression than did DSA-positive patients with ABMR (p = 0.01). Recipients with DSA-positive ABMR exhibited significantly better allograft survival after long-term application of IVIG for more than 1 year than did recipients with DSA-negative ABMR (p = 0.02).

Conclusions

The results of our single-center cohort study involving kidney transplant recipients with ABMR suggest that long-term application of IVIG is more favorable for DSA-positive recipients, whereas intensification of maintenance immunosuppression is more effective for recipients with DSA-negative ABMR.

The Biology and Molecular Basis of Organ Transplant Rejection

Allograft rejection is defined as tissue injury in a transplanted allogeneic organ produced by the effector mechanisms of the adaptive alloimmune response. Effector T lymphocytes and IgG alloantibodies cause two different types of rejection that can occur either individually or simultaneously: T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR). In TCMR, cognate effector T cells infiltrate the graft and orchestrate an interstitial inflammatory response in the kidney interstitium in which effector T cells engage antigen-presenting myeloid cells, activating the T cells, antigen-presenting cells, and macrophages. The result is intense expression of IFNG and IFNG-induced molecules, expression of effector T cell molecules and macrophage molecules and checkpoints, and deterioration of parenchymal function. The diagnostic lesions of TCMR follow, i.e. interstitial inflammation, parenchymal deterioration, and intimal arteritis. In ABMR, HLA IgG alloantibodies produced by plasma cells bind to the donor antigens on graft microcirculation, leading to complement activation, margination, and activation of NK cells and neutrophils and monocytes, and endothelial injury, sometimes with intimal arteritis. TCMR becomes infrequent after 5-10 years post-transplant, probably reflecting adaptive mechanisms such as checkpoints, but ABMR can present even decades post-transplant. Some rejection is triggered by inadequate immunosuppression and non-adherence, challenging the clinician to target effective immunosuppression even decades post-transplant.

Management of mixed acute rejection driven by a de novo donor-specific complement-binding anti-DQB1*03:01 antibody and intraepithelial CD8 T-cells in a kidney recipient: a case report

Mixed acute rejection is a clinicopathological entity that is difficult to accurately diagnose, and so may be under-reported. Allografts are lost more often than in either humoral or cellular rejection. The diagnosis requires both histological and immunological studies on renal biopsy and blood specimens from the transplant recipient to provide the required rescue therapy to abolish the allogeneic response against the graft. We present a clinical case report of an active mixed acute rejection driven by a de novo donor-specific complement-binding anti-DQB1*03:01 antibody and intraepithelial CD8 T-cells in a patient with a kidney transplant. The patient was diagnosed, treated, and followed up as per the local institution's procedure with a full recovery of graft function. Our case emphasises the challenge of a mixed acute rejection and supports the need to improve the post-transplant outcome of recipients and their grafts.

Many heart transplant biopsies currently diagnosed as no rejection have mild molecular antibody-mediated rejection-related changes

BACKGROUND

The Molecular Microscope (MMDx) system classifies heart transplant endomyocardial biopsies as No-rejection (NR), Early-injury, T cell-mediated (TCMR), antibody-mediated (ABMR), mixed, and possible rejection (possible TCMR, possible ABMR). Rejection-like gene expression patterns in NR biopsies have not been described. We extended the MMDx methodology, using a larger data set, to define a new "Minor" category characterized by low-level inflammation in non-rejecting biopsies.

METHODS

Using MMDx criteria from a previous study, molecular rejection was assessed in 1,320 biopsies (645 patients) using microarray expression of rejection-associated transcripts (RATs). Of these biopsies, 819 were NR. A new archetypal analysis model in the 1,320 data set split the NRs into NR-Normal (N = 462) and NR-Minor (N = 359).

RESULTS

Compared to NR-Normal, NR-Minor were more often histologic TCMR1R, with a higher prevalence of donor-specific antibody (DSA). DSA positivity increased in a gradient: NR-Normal 24%; NR-Minor 34%; possible ABMR 42%; ABMR 66%. The top 20 transcripts distinguishing NR-Minor from NR-Normal were all ABMR-related and/or IFNG-inducible, and also exhibited a gradient of increasing expression from NR-Normal through ABMR. In random forest analysis, TCMR and Early-injury were associated with reduced LVEF and increased graft loss, but NR-Minor and ABMR scores were not. Surprisingly, hearts with MMDx ABMR showed comparatively little graft loss.

CONCLUSIONS

Many heart transplants currently diagnosed as NR by histologic or molecular assessment have minor increases in ABMR-related and IFNG-inducible transcripts, associated with DSA positivity and mild histologic inflammation. These results suggest that low-level ABMR-related molecular stress may be operating in many more hearts than previously estimated. (ClinicalTrials.gov #NCT02670408).

The Problem of Subclinical Antibody-mediated Rejection in Kidney Transplantation

Defined as histologic evidence of rejection on a protocol biopsy in the absence of kidney dysfunction, subclinical rejection has garnered attention since the 1990s. The major focus of much of this research, however, has been subclinical T cell-mediated rejection (TCMR). Herein, we review the literature on subclinical antibody-mediated rejection (AMR), which may occur with either preexisting donor-specific antibodies (DSA) or upon the development of de novo DSA (dnDSA). In both situations, subsequent kidney function and graft survival are compromised. Thus, we recommend protocol biopsy routinely within the first year with preexisting DSA and at the initial detection of dnDSA. In those with positive biopsies, baseline immunosuppression should be maximized, any associated TCMR treated, and adherence stressed, but it remains uncertain if antibody-reduction treatment should be initiated. Less invasive testing of blood for donor DNA or gene profiling may have a role in follow-up of those with negative initial biopsies. If a protocol biopsy is positive in the absence of detectable HLA-DSA, it also remains to be determined whether non-HLA-DSA should be screened for either in particular or on a genome-wide basis and how these patients should be treated. Randomized controlled trials are clearly needed.

Impact of Belatacept Conversion on Renal Function, Histology, and Gene Expression in Kidney Transplant Patients With Chronic Active Antibody-mediated Rejection

BACKGROUND

Here, we present our initial experience with a prospective protocol of belatacept conversion in patients with chronic active antibody-mediated rejection (caAMR) and a high degree of chronicity at the time of diagnosis.

METHODS

We converted 19 patients (mean age, 45 ± 12 y) with biopsy-proven caAMR from tacrolimus to belatacept at a median of 44 months post-kidney transplant.

RESULTS

At a median of 29 months (interquartile range, 16-46 mo) postconversion, death-censored graft and patient survivals were 89% and 95%, respectively. When compared to a 1:2 propensity-matched control cohort from the INSERM U970 registry maintained on calcineurin inhibitor, the belatacept group had progressive improvement (P = 0.02) in estimated glomerular filtration rate from a mean of 33.9 ± 10 at baseline to 37.8 ± 13 at 6 months and 38.5 ± 12 mL/min/1.73 m2 at 12 months postconversion, as compared to a steady decline noted in the controls (36.2 [baseline] → 33.1 [6 mo] → 32.7 mL/min/1.73 m2 [12 mo] of follow-up). A paired histologic comparison of preconversion and postconversion (performed at median 9.5 mo postconversion) biopsies showed no worsening in microvascular inflammation or chronicity. The paired tissue gene expression analysis showed improved mean total rejection score (0.68 ± 0.26-0.56 ± 0.33; P = 0.02) and a trend toward improved antibody-mediated rejection score (0.64 ± 0.34-0.56 ± 0.39; P = 0.06).

CONCLUSIONS

Here, we report that in patients diagnosed with caAMR who were not subjected to intensive salvage immunosuppressive therapies, isolated belatacept conversion alone was associated with stabilization in renal function. These results are bolstered by molecular evidence of improved inflammation.

Correlation of Donor-Derived Cell-free DNA with Histology and Molecular Diagnoses of Kidney Transplant Biopsies

BACKGROUND

Circulating donor-derived cell free DNA (cfDNA), a minimally invasive diagnostic tool for kidney transplant rejection, was validated using traditional histology. The Molecular Microscope (MMDx) tissue gene expression platform may provide increased precision to traditional histology.

METHODS

In this single-center prospective study of 208 biopsies (median=5.8 months) post-transplant, we report on the calibration of cfDNA with simultaneous biopsy assessments using MMDx and histology by Area under the curve (AUC) analyses for optimal criterion, as well as for, previously published cfDNA cut-offs ≤0.21% to 'rule-out' rejection and ≥1% to 'rule-in' rejection.

RESULTS

There were significant discrepancies between histology and MMDx, with MMDx identifying more antibody-mediated rejection (65; 31%) than histology (43; 21%); the opposite was true for T-cell mediated rejection [TCMR; histology: 27 (13%) vs MMDx: 13 (6%)]. Most of the TCMR discrepancies were seen for histologic borderline/1A TCMR. AUC Curves for cfDNA and prediction of rejection were slightly better with MMDx (AUC=0.80; 95%CI: 0.74-0.86) vs. histology (AUC=0.75; 95%CI: 0.69-0.81). A cfDNA≤0.21% had similar sensitivity (~91%) to 'rule-out' rejection by histology and MMDx. Specificity was slightly higher with MMDx (92%) compared with histology (85%) to 'rule-in' rejection using cfDNA criterion≥1%. Strong positive quantitative correlations were observed between cfDNA scores and molecular acute kidney injury (AKI) for both 'rejection' and 'nonrejection' biopsies.

CONCLUSIONS

Molecular diagnostics using tissue gene expression and blood-based donor-derived cell-free DNA may add precision to some cases of traditional histology. The positive correlation of cfDNA with molecular AKI suggests a dose-dependent association with tissue injury irrespective of rejection characteristics.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

The FCGR3A 158 V/V-genotype is associated with decreased survival of renal allografts with chronic active antibody-mediated rejection

Natural killer (NK) cells express the Fc-gamma receptor CD16 (FCGR3A) and could therefore mediate renal endothelial cell damage in cases of chronic-active antibody mediated rejection (c-aABMR). The V/V-genotype of the FCGR3A 158 F/V polymorphism is associated with increased CD16 expression and cytotoxicity by NK cells. This study evaluated whether this genotype is associated with the diagnosis of c-aABMR and renal allograft loss. The distribution of the FGCR3A 158 F/V-genotypes was not different for c-aABMR cases (N = 133) compared to control kidney transplant recipients (N = 116, P = 0.65). The V-allele was associated with increased median fluorescence intensity (MFI) of CD16 by NK cells (MFI 3.5 × 10⁴ versus 1.3 × 10⁴ for V/V and F/F-genotype, P < 0.001). Increased expression of CD16 correlated with CD16-dependent degranulation of NK cells (R = 0.4; P = 0.02). Moreover, the V/V-genotype was significantly associated with a higher glomerulitis score and an independent risk factor (HR 1.98; P = 0.04) for decreased allograft survival. Death-censored graft survival in c-aABMR cases at 3 years follow-up was 33% for the FCGR3A 158 V/V-genotype versus 62% for the F/F-genotype. In conclusion, the FCGR3A V/V-genotype increases CD16-mediated NK cell cytotoxicity and is associated with a higher glomerulitis score and decreased graft survival in cases with c-aABMR.

In-silico performance, validation, and modeling of the Nanostring Banff Human Organ transplant gene panel using archival data from human kidney transplants

BACKGROUND

RNA gene expression of renal transplantation biopsies is commonly used to identify the immunological patterns of graft rejection. Mostly done with microarrays, seminal findings defined the patterns of gene sets associated with rejection and non-rejection kidney allograft diagnoses. To make gene expression more accessible, the Molecular Diagnostics Working Group of the Banff Foundation for Allograft Pathology and NanoString Technologies partnered to create the Banff Human Organ Transplant Panel (BHOT), a gene panel set of 770 genes as a surrogate for microarrays (~ 50,000 genes). The advantage of this platform is that gene expressions are quantifiable on formalin fixed and paraffin embedded archival tissue samples, making gene expression analyses more accessible. The purpose of this report is to test in silico the utility of the BHOT panel as a surrogate for microarrays on archival microarray data and test the performance of the modelled BHOT data.

METHODS

BHOT genes as a subset of genes from downloaded archival public microarray data on human renal allograft gene expression were analyzed and modelled by a variety of statistical methods.

RESULTS

Three methods of parsing genes verify that the BHOT panel readily identifies renal rejection and non-rejection diagnoses using in silico statistical analyses of seminal archival databases. Multiple modelling algorithms show a highly variable pattern of misclassifications per sample, either between differently constructed principal components or between modelling algorithms. The misclassifications are related to the gene expression heterogeneity within a given diagnosis because clustering the data into 9 groups modelled with fewer misclassifications.

CONCLUSION

This report supports using the Banff Human Organ Transplant Panel for gene expression of human renal allografts as a surrogate for microarrays on archival tissue. The data modelled satisfactorily with aggregate diagnoses although with limited per sample accuracy and, thereby, reflects and confirms the modelling complexity and the challenges of modelling gene expression as previously reported.

Urinary C-X-C Motif Chemokine 10 Is Related to Acute Graft Lesions Secondary to T Cell- and Antibody-Mediated Damage

Background

Non-invasive biomarkers of graft rejection are needed to optimize the management and outcomes of kidney transplant recipients. Urinary excretion of IFN-γ-related chemokine CXCL10 is clearly associated with clinical and subclinical T cell-mediated graft inflammation, but its relationship with antibody-mediated damage has not been fully addressed. Further, the variables influencing levels of urinary CXCL10 excretion are unknown.

Material/Methods

A total of 151 kidney graft biopsies (92 surveillance and 59 indication biopsies) and 151 matched urine samples obtained before biopsy were prospectively analyzed. T cell-mediated rejection (TCMR) and antibody-mediated rejection (AbMR) were defined according to the 2017 Banff classification criteria. Urinary CXCL10 levels were measured by ELISA and corrected by urinary creatinine.

Results

Banff scores ‘t’, ‘i’, ‘g’, and ‘ptc’ were significantly related to urinary CXCL10 levels. Multivariate analysis showed that ‘t’ (β=0.107, P=0.001) and ‘ptc’ (β=0.093, P=0.002) were significantly associated with urinary CXCL10. Donor-specific antibodies (DSAs) were related to the high excretion of urinary CXCL10 at 1 year after transplantation (odds ratio [OR] 17.817, P=0.003). Urinary CXCL10 showed good discrimination ability for AbMR (AUC-ROC 0.760, P=0.001). The third tertile of urinary CXCL10 remained significantly associated with AbMR (OR 4.577, 95% confidence interval 1.799–11.646, P=0.001) after multivariate regression analysis.

Conclusions

DSA was the only variable clearly related to high urinary CXCL10 levels. Urinary CXCL10 is a good non-invasive candidate biomarker of AbMR and TCMR, supplying information independent of renal function and other variables normally used to monitor kidney transplants.

Molecular Analysis of Renal Allograft Biopsies: Where Do We Stand and Where Are We Going?

A renal core biopsy for histological evaluation is the gold standard for diagnosing renal transplant pathology. However, renal biopsy interpretation is subjective and can render insufficient precision, making it difficult to apply a targeted therapeutic regimen for the individual patient. This warrants a need for additional methods assessing disease state in the renal transplant. Significant research activity has been focused on the role of molecular analysis in the diagnosis of renal allograft rejection. The identification of specific molecular expression patterns in allograft biopsies related to different types of allograft injury could provide valuable information about the processes underlying renal transplant dysfunction and can be used for the development of molecular classifier scores, which could improve our diagnostic and prognostic ability and could guide treatment. Molecular profiling has the potential to be more precise and objective than histological evaluation and may identify injury even before it becomes visible on histology, making it possible to start treatment at the earliest time possible. Combining conventional diagnostics (histology, serology, and clinical data) and molecular evaluation will most likely offer the best diagnostic approach. We believe that the use of state-of-the-art molecular analysis will have a significant impact in diagnostics after renal transplantation. In this review, we elaborate on the molecular phenotype of both acute and chronic T cell-mediated rejection and antibody-mediated rejection and discuss the additive value of molecular profiling in the setting of diagnosing renal allograft rejection and how this will improve transplant patient care.

The immunohistochemical expression of von Willebrand factor, T-cadherin, and Caveolin-1 is increased in kidney allograft biopsies with antibody-mediated injury

BACKGROUND

There are only a few reports evaluating the applicability of endothelial-damage markers analysis by immunohistochemistry (IHC) in kidney allograft samples. This study analyzed the expression of Caveolin-1 (Cav), von Willebrand factor (Vwf), and T-cadherin (Cad) in kidney biopsies and their association with antibody-mediated injury.

METHODS

In this retrospective study, 114 cases with antibody-mediated changes (Banff, 2020) and 72 with interstitial fibrosis/tubular atrophy were selected. IHC for Cav, Vwf and Cad was performed and evaluated according to their qualitative expression in peritubular capillaries. The cases were grouped according to the presence of microvascular inflammation (MVI), donor-specific antibodies (DSA), C4d positivity and antibody-mediated rejection (AMR). A level of significance < 0.05 was adopted.

RESULTS

Vwf expression was associated with MVI (p < 0.001), DSA (p = 0.016), C4d (p < 0.001) and AMR (p < 0.001), and was higher in DSA+/C4d+ cases despite MVI (p < 0.001). The expression of Cad correlated with MVI (p = 0.015), C4d (p = 0.005) and AMR (p = < 0.001). Cad was more expressed in chronic AMR compared with acute/active cases (p = 0.001). Cav expression was associated with MVI (p = 0.029) and AMR (p = 0.016) and was also higher in chronic AMR (p = 0.049). A combined score of Vwf and Cad was higher in AMR when compared with C4d without rejection and IF/TA cases (p < 0.001).

CONCLUSION

Vwf, Cad and Cav expression shows association with antibody-mediated injury and may be helpful to support AMR diagnosis.

Impact of belatacept conversion on kidney transplant function, histology, and gene expression - a single-center study

Prior studies on belatacept conversion from calcineurin inhibitor (CNI) have been limited by an absence of postconversion surveillance biopsies that could underestimate subclinical rejection, or a case-controlled design. A total of 53 adult patients with allograft dysfunction underwent belatacept conversion (median: 6 months) post-transplant. At a median follow-up = 2.5 years, patient survival was 94% with a death-censored graft survival of 85%. Seven (13%) patients had acute rejection (including 3 subclinical) at median 6 months postconversion. Overall, eGFR improved (P = <0.001) from baseline = 31±15 to 40.2 ± 17.6 ml/min/1.73m² by 6 months postconversion, but then stayed stable. This improvement was also observed (P < 0.001) in comparison with a propensity matched control cohort on CNI, where eGFR stayed stable (mean ~ 32ml/min/1.72m² ) over 2-year follow-up. Patients converted < 6 months post-transplant were more likely to have a long-term improvement in kidney function. Paired gene expression analysis of 30 (of 53) consecutive pre- and postconversion surveillance biopsies did not reveal changes in inflammation/acute injury; although atrophy-fibrosis score worsened (mean = 0.28 to 0.44; P = 0.005). Thus, improvement in renal function with belatacept conversion occurred early and then sustained in comparison with controls where renal function remained unchanged overtime. We were unable to show molecular signals that could be related to CNI administration and regressed after withdrawal.

Lack of Histological and Molecular Signature Response to Tocilizumab in Kidney Transplants with Chronic Active Antibody Mediated Rejection: A Case Series

Background

Traditional therapies for caAbMR have unclear efficacy with significant side effects in recipients of kidney transplants (KTs). A recent single-center case series suggested tocilizumab (TCZ) could stabilize renal function and improve microvascular inflammation. Here we report our findings of the use of TCZ in patients with caAbMR.

Methods

Ten adult recipients of KTs with biopsy-proven caAbMR were treated with TCZ at 8 mg/kg per month. Patients were monitored for adverse events, and therapy was interrupted in the setting of serious infections. Six patients (60%) underwent post-treatment biopsies.

Results

Patients (mean age of 43 years) were initiated on TCZ at a median of 36 months post-KT. A majority of patients were black (70%), underwent regrafts (40%), and were sensitized (mean cPRA=41%). Patients received a median of six doses of TCZ (range=3-10). At a median follow-up of 12 months (range=8-24 months), renal function did not show improvement (mean eGFR, 42±18 ml/min per 1.73 m² to 37±24 ml/min per 1.73 m²; P=0.27). The slope of decline in eGFR remained unchanged (-0.14±0.9 to -0.33±1.1; P=0.25). There was no improvement in mean MVI (g+ptc) (4.8±1.4 to 4.2±2.0; P=0.39) scores or Molecular Microscope Diagnostic System (MMDx) AbMR scores (0.79±0.17 to 0.78±0.26; P=0.86). There was a numeric worsening of chronicity (ci+ct) scores (2.5±0.8 to 3.3±1.7; P=0.38) and MMDx atrophy fibrosis scores (0.36±0.24 to 0.58±0.15; P=0.21). Patient survival was 90%, with one patient death due to complications from a hip infection. Overall death-censored graft survival was 80%, with two graft losses in patients who had recurrent infections requiring hospitalization.

Conclusions

In this early experience, we report a lack of efficacy and toxicity with the use of TCZ for caAbMR. Prospective clinical trials are needed to clarify the role of IL-6 blockade and the possibility of increased incidence of infections in patients with caAbMR who are treated with TCZ.

An age-independent gene signature for monitoring acute rejection in kidney transplantation

Acute rejection (AR) remains a significant problem that negatively impacts long-term renal allograft survival. Numerous therapies are used to prevent AR that differ by center and recipient age. This variability confounds diagnostic methods. Methods: To develop an age-independent gene signature for AR effective across a broad array of immunosuppressive regimens, we compiled kidney transplant biopsy (n=1091) and peripheral blood (n=392) gene expression profiles from 12 independent public datasets. After removing genes differentially expressed in pediatric and adult patients, we compared gene expression profiles from biopsy and peripheral blood samples of patients with AR to those who were stable (STA), using Mann-Whitney U Tests with validation in independent testing datasets. We confirmed this signature in pediatric and adult patients (42 AR and 47 STA) from our institutional biorepository. Results: We identified a novel age-independent gene network that identified AR from both kidney and blood samples. We developed a 90-probe set signature targeting 76 genes that differentiated AR from STA and found an 8 gene subset (DIP2C, ENOSF1, FBXO21, KCTD6, PDXDC1, REXO2, HLA-E, and RAB31) that was associated with AR. Conclusion: We used publicly available datasets to create a gene signature of AR that identified AR irrespective of immunosuppression regimen or recipient age. This study highlights a novel model to screen and validate biomarkers across multiple treatment regimens.

Association between transplant glomerulopathy and graft outcomes following kidney transplantation: A meta-analysis

Transplant glomerulopathy (TG), a morphological lesion associated with confluent mechanisms of endothelial injury of renal allografts, may provide a viable predictor of graft failure. This systematic literature review and meta-analysis were performed according to the PRISMA statement to examine evidence describing the association between TG and graft loss or failure and time to these events. The literature review was conducted using the Scopus, EBSCO, and Cochrane Library search engines. Hazard ratios, median survival times, and 95% confidence intervals (CIs) were estimated to evaluate graft survival in the total population and prespecified subgroups. Meta-regression analysis assessed heterogeneity. Twenty-one publications comprising 6,783 patients were eligible for data extraction and inclusion in the meta-analysis. Studies were highly heterogeneous (I² = 67.3%). The combined hazard ratio of graft loss or failure from random-effects meta-analysis was 3.11 (95% CI 2.44–3.96) in patients with TG compared with those without. Median graft survival in patients with TG was 3.25 (95% CI 0.94–11.21) years—15 years shorter than in those without TG (18.82 [95% CI 10.03–35.32] years). The effect of time from transplantation to biopsy on graft outcomes did not reach statistical significance (p = 0.116). TG was associated with a threefold increase in the risk of graft loss or failure and a 15-year loss in graft survival, indicating viability as a surrogate measure for both clinical practice and studies designed to prevent or reverse antibody-mediated rejection.

Diagnostic, Prognostic, and Therapeutic Value of Non-Coding RNA Expression Profiles in Renal Transplantation

End-stage renal disease is a public health problem responsible for millions of deaths worldwide each year. Although transplantation is the preferred treatment for patients in need of renal replacement therapy, long-term allograft survival remains challenging. Advances in high-throughput methods for large-scale molecular data generation and computational analysis are promising to overcome the current limitations posed by conventional diagnostic and disease classifications post-transplantation. Non-coding RNAs (ncRNAs) are RNA molecules that, despite lacking protein-coding potential, are essential in the regulation of epigenetic, transcriptional, and post-translational mechanisms involved in both health and disease. A large body of evidence suggests that ncRNAs can act as biomarkers of renal injury and graft loss after transplantation. Hence, the focus of this review is to discuss the existing molecular signatures of non-coding transcripts and their value to improve diagnosis, predict the risk of rejection, and guide therapeutic choices post-transplantation.

The therapeutic challenge of late antibody-mediated kidney allograft rejection

Late antibody‐mediated rejection (ABMR) is a cardinal cause of kidney allograft failure, manifesting as a continuous and, in contrast with early rejection, often clinically silent alloimmune process. While significant progress has been made towards an improved understanding of its molecular mechanisms and the definition of diagnostic criteria, there is still no approved effective treatment. In recent small randomized controlled trials, therapeutic strategies with promising results in observational studies, such as proteasome inhibitor bortezomib, anti‐C5 antibody eculizumab, or high dose intravenous immunoglobulin plus rituximab, had no significant impact in late and/or chronic ABMR. Such disappointing results reinforce a need of new innovative treatment strategies. Potential candidates may be the interference with interleukin‐6 to modulate B cell alloimmunity, or innovative compounds that specifically target antibody‐producing plasma cells, such as antibodies against CD38. Given the phenotypic heterogeneity of ABMR, the design of adequate systematic trials to assess the safety and efficiency of such therapies, however, is challenging. Several trials are currently being conducted, and new developments will hopefully provide us with effective ways to counteract the deleterious impact of antibody‐mediated graft injury. Meanwhile, the weight of evidence would suggest that, when approaching using existing treatments for established antibody‐mediated rejection, “less may be more”.

Value of monitoring circulating donor-reactive memory B cells to characterize antibody-mediated rejection after kidney transplantation

Antibody-mediated rejection (ABMR) is defined by specific histopathological lesions and evidence of circulating donor-specific antibodies (DSA). Although DSA are not always detectable, monitoring donor-reactive memory B cells (mBC) could identify patients at risk of developing ABMR. Peripheral donor-reactive mBC using a novel HLA B cell ELISpot assay, serum DSA, and numbers of different B cell subsets were assessed in 175 consecutive kidney transplants undergoing either for-cause or 6- and 24-month surveillance biopsies for their association with main histological lesions of ABMR and impact on allograft outcome. In 85 incident for-cause biopsies, high frequencies of donor-reactive mBC were detected in all 16 (100%) acute ABMR/DSA+ and most chronic ABMR, with or without DSA (24/30[80%] and 21/29[72.4%], respectively). In a longitudinal cohort of 90 nonsensitized patients, a progressively higher expansion of donor-reactive mBC than de novo DSA was observed at 6 and 24 months (8.8% vs 7.7% and 15.5% vs 11.1%, respectively) and accurately identified patients with ongoing subclinical ABMR (area under the curve = 0.917 and area under the curve = 0.809, respectively). An unsupervised hierarchical cluster analysis revealed a strong association between donor-reactive mBC with main fundamental allograft lesions associated with ABMR and conferred a significant deleterious impact on graft outcome. Monitoring donor-reactive mBC may be useful to further characterize humoral rejection after kidney transplantation.

Banff Lung Report: Current knowledge and future research perspectives for diagnosis and treatment of pulmonary antibody-mediated rejection (AMR)

The Lung session of the 2017 14th Banff Foundation for Allograft Pathology Conference, Barcelona focused on the multiple aspects of antibody-mediated rejection (AMR) in lung transplantation. Multidimensional approaches for AMR diagnosis, including classification, histological and immunohistochemical analysis, and donor- specific antibody (DSA) characterization with their current strengths and limitations were reviewed in view of recent research. The group also discussed the role of tissue gene expression analysis in the context of unmet needs in lung transplantation. The current best practice for monitoring of AMR and the therapeutic approach are summarized and highlighted in this report. The working group reached consensus of the major gaps in current knowledge and focused on the unanswered questions regarding pulmonary AMR. An important outcome of the meeting was agreement on the need for future collaborative research projects to address these gaps in the field of lung transplantation.

Long-term Immunosuppression Adherence After Kidney Transplant and Relationship to Allograft Histology

Background

Nonadherence to immunosuppression after kidney transplant is an important contributor to graft failure. Little is known about how nonadherence changes 3 years posttransplant when Medicare coverage of immunosuppression ends and how that nonadherence impacts allograft histology. The goal of this study was to compare rates of nonadherence during posttransplant years 1 to 3 to years 3 to 5 and examine the relationship between nonadherence during years 3 to 5 and 5-year allograft histology.

Methods

We retrospectively analyzed 552 conventional kidney allografts in patients transplanted at our center between January 1, 1999, and June 1, 2010, who used the Mayo Clinic Specialty Pharmacy for the first 5 years posttransplant. Nonadherence was defined as less than 80% proportion of days covered. Overall adherence to immunosuppression appeared to be higher during years 3 and 5 compared to between years 1 and 3 (89.4% vs 82.9%, respectively; P < 0.0001 [paired t test]).

Results

Overall nonadherence during posttransplant years 3 to 5 appeared to be associated with fibrosis and inflammation on 5-year allograft biopsy but not with transplant glomerulopathy (16.9% vs 5.9%, P = 0.004; 10.4% vs 8.5%, P = 0.61, respectively). After adjusting for nonadherence to calcineurin inhibitor and prednisone therapy, only nonadherence to antimetabolite therapy remained significantly associated with 5-year fibrosis and inflammation (odds ratio, 10.6; 95% confidence interval, 1.5-76.1; P = 0.02).

Conclusions

Efforts to improve long-term adherence, possibly through the use of specialty pharmacies and increased adherence to antimetabolite therapy, may improve long-term allograft histology and survival, although further studies are needed to confirm these findings.

Recent Advancements in the Assessment of Renal Transplant Dysfunction with an Emphasis on Microarray Molecular Diagnostics

Conventional assessment of renal transplant rejection and injury through use of histology, C4d staining, and HLA antibody testing, has been the standard approach to transplant management. By many measures, these methods of conventional assessment may be considered flawed, particularly with the subjective nature of histologic diagnoses. The Alberta Transplant Applied Genomics Center has developed the Molecular Microscope diagnostic system, which uses microarrays to measure gene expression. These data are analyzed using classifiers (weighted equations) that compare the tested biopsy to a proprietary reference set of biopsies to provide objective measures of the status of the renal transplant.

Antibody-mediated rejection implies a poor prognosis in kidney transplantation: Results from a single center

Two major barriers to achieving long-term graft survival include patient nonadherence in taking the prescribed immunosuppression and antibody-mediated rejection(AMR). We were therefore interested in determining the prognostic impact of developing an AMR component to rejection in a prospective randomized trial of 200 kidney transplant recipients who received dual induction therapy (rATG combined with either daclizumab or alemtuzumab) and planned early corticosteroid withdrawal. With a median follow-up of 96 months post-transplant, 40/200 developed a first BPAR; 9/200 developed a second BPAR. An AMR component to rejection was observed in 70% (28/40) of cases. Percentages having C4d deposition, histopathologic evidence of acute AMR, and presence of DSAs/non-DSAs at the time of first developing the AMR component were 64.3% (18/28), 60.7% (17/28), and 53.6% (15/28), respectively. Development of an AMR component was associated with a significantly higher death-censored graft failure rate following rejection in comparison with the patient state of experiencing BPAR but without developing an AMR component (estimated hazard ratio: 4.52, P = 0.01). The observed percentage developing graft failure following development of an AMR component was 53.6% (15/28) vs only 20.0%(3/15) if it was not observed. Actuarial death-censored graft survival at 60 months following development of an AMR component was 28.3 ± 11.9%. In summary, it appears that more effective AMR prevention/treatment strategies are warranted.

Isolated v-lesion represents a benign phenotype of vascular rejection of the kidney allograft - a retrospective study

While the detrimental impact of the humoral acute vascular rejection (AVR) phenotype is recognized, the prognostic significance of isolated v-lesion (IV) remains unclear. In this retrospective single-centre study, AVR was found in 98 of 1015 patients (9.7%) who had undergone kidney transplantation in 2010-2014, with donor-specific antibodies (DSA) evaluated in all of them. The outcome of four AVR phenotypes was evaluated during median follow-up of 59 months; in 25 patients with IV, 18 with T-cell-mediated vascular rejection (TCMVR), 19 with antibody-mediated vascular rejection (AMVR) and 36 with suspected antibody-mediated rejection (sAMVR). AVR was diagnosed mainly by for-cause biopsy (81%) early after transplantation (median 19 POD) and appeared as mild-grade intimal arteritis. IV occurred in low-sensitized patients after the first transplantation (96%) in the absence of DSA. IV responded satisfactorily to treatment (88%), showed no persistence of rejection in surveillance biopsy, and had stable graft function, minimal proteinuria and excellent DCGS (96%). Contrary to that, Kaplan-Meier estimate of 3-year DCGS of AMVR was 66% (log-rank = 0.0004). Early IV represents a benign phenotype of AVR with a favourable outcome. This study prompts further research to evaluate the nature of IV before considering any change in the classification and management.

RNA expression profiling of renal allografts in a nonhuman primate identifies variation in NK and endothelial gene expression

RNA transcript expression estimates are a promising method to study the mechanisms and classification of renal allograft rejections. Here we use the Nanostring platform to profile RNA expression in renal allografts in a nonhuman primate (NHP), the Cynomolgus monkey. We analyzed protocol and indication 278 archival renal allograft samples, both protocol and indication from 76 animals with diagnoses of chronic antibody-mediated rejection (CAMR), acute cellular rejection (TCMR), and MIXED (both CAMR and TCMR), plus normals and samples with no pathological rejection using a Cynomolgus-specific probe set of 67 genes. Analysis identified RNA expression heterogeneity of endothelial and NK genes within CAMR and TCMR, including the stages of CAMR. Three factors were partitioned into additional groups. One group with the longest allograft survival time is pure CAMR without NK or CD3. Three mixed groups show variation in NK and CD3. TCMR was split into 2 groups with variation in NK genes. Additional validation of the complete gene-set correlated many of the genes with diagnoses of CAMR, MIXED, and TCMR rejections and with Banff histologic criteria defined in human subjects. These NHP data demonstrate the utility of RNA expression profiling to identify additional heterogeneity of endothelial and NK RNA gene expressions.

Tacrolimus intra-patient variability is not associated with chronic active antibody mediated rejection

Background

Chronic active antibody mediated rejection (c-aABMR) is a major cause of long-term kidney allograft loss. It is hypothesized that frequent sub-therapeutic exposure to immunosuppressive drugs, in particular tacrolimus (Tac), is a risk factor for the development of c-aABMR. The intra-patient variability (IPV) in Tac exposure may serve as a substitute biomarker for underexposure and/or non-adherence. In this study, the association between Tac IPV and the development of c-aABMR was investigated.

Methods

We retrospectively included 59 patients diagnosed with c-aABMR and compared them to 189 control patients matched for age, year of transplantation and type of kidney donor. The Tac IPV was calculated from pre-dose tacrolimus concentrations measured over a 3 year period preceding the diagnosis of c-aABMR. The mean Tac predose concentrations (C₀), Tac IPV, renal allograft function and graft survival were compared between the groups.

Results

Tac IPV was 24.4% for the cases versus 23.6% for the controls (p = 0.47). The mean Tac C₀ was comparable for the cases (5.8 ng/mL) and control patients (6.1 ng/mL, p = 0.08). Only in the c-aABMR group a significant decline in both mean Tac C₀ and allograft function over the timespan of 3 years was observed (p = 0.03 and p<0.001). Additionally, in the group of c-aABMR patients a high IPV was associated with inferior graft survival (p = 0.03).

Conclusions

A high Tac IPV per se does not predispose to the development of c-aABMR but is associated with inferior graft survival once c-aABMR is diagnosed.

Chronic-active antibody-mediated rejection with or without donor-specific antibodies has similar histomorphology and clinical outcome - a retrospective study

Chronic-active antibody-mediated rejection (c-aABMR) is defined as histological evidence of chronic endothelial injury (cg), also known as transplant glomerulopathy, and either microvascular inflammation (MVI) or positivity for C4d. Importantly, the presence of donor-specific antibodies (DSA) is currently still mandatory for the diagnosis of c-aABMR. This retrospective study of 41 c-aABMR patients investigates whether cases suspicious for c-aABMR (DSA negative, n = 24) differ from cases of c-aABMR (DSA positive, n = 17) with respect to renal histology, allograft function and long-term graft survival. All included patients had progressive loss of allograft function and were diagnosed by for cause biopsy and scored according to the Banff '15 criteria. In all DSApos cases, DSA were de novo and the majority was directed against HLA-II being mostly anti-HLA-DQ antibodies. There were no statistically significant differences in clinical characteristics, decline in allograft function and renal allograft survival in cases with or without DSAs. All cases showed chronic histomorphological damage and inflammation, irrespective of the presence of DSA. Renal histology and clinical outcome of patients suspicious for c-aABMR (DSAneg) do not significantly differ from patients with a diagnosis of c-aABMR (DSApos). We believe that our study adds to the ongoing debate regarding the need for DSAs to be present for the diagnosis of c-aABMR.

The Spectrum of Histopathological Changes in the Renal Allograft - a 12 Months Protocol Biopsy Study

INTRODUCTION

Renal transplantation became a routine and successful medical treatment for Chronic Kidney Disease in the last 30 years all over the world. Introduction of Luminex based Single Antigen Beads (SAB) and recent BANFF consensus of histopathological phenotypes of different forms of rejection enables more precise diagnosis and changes the therapeutic approach. The graft biopsies, protocol or cause, indicated, remain a golden diagnostic tool for clinical follow up of kidney transplant recipients (KTR).

AIM

The study aimed to analyse the histopathological changes in renal grafts 12 months after the surgery in KTR with satisfactory kidney function.

MATERIAL AND METHODS

A 12-month protocol biopsy study was performed in a cohort of 50 Kidney transplant recipients (42 from living and 8 from deceased donors). Usual work-up for suitable donors and recipients, standard surgical procedure, basic principles of peri and postoperative care and follow up were done in all KTR. Sequential quadruple immunosuppression including induction with Anti-thymocyte globulin (ATG) or Interleukin-2R antagonist (IL-2R), and triple drug maintenance therapy with Calcineurin Inhibitors (CNI), Mycophenolate Mofetil (MMF) and Steroids were prescribed to all pts. Different forms of Glomerulonephritis (16), Hypertension (10), End Stage Renal Disease (13), Hereditary Nephropathies (6), Diabetes (3) and Vesicoureteral Reflux (2) were the underlying diseases. All biopsies were performed under ultrasound guidance. The 16 gauge needles with automated "gun" were used to take 2 cores of tissue. The samples were stained with HE, PAS, Trichrome Masson and Silver and reviewed by the same pathologist. A revised and uploaded BANFF 2013 classification in 6 categories (Cat) was used.

RESULTS

Out of 48 biopsies, 15 (31%) were considered as normal, 4 (8%), Borderline (BL-Cat 3), 5 (10%) as Interstitial Fibrosis/Tubular Atrophy (IF/TA-Cat 5), 5 (10%) were classified as non-immunological (Cat 6), 2 as a pure antibody-mediated rejection (ABMR-Cat 2) and T-cell Mediated Rejection (TCMR-Cat 4). The remaining 17 samples were classified as a "mixed" rejection: 7 (41%) ABMR + IF/TA, 5 (29%) ABMR + BL + IF/TA, 2 (11%) BL + IF/TA, 1 (5%) ABMR + BL, 1 (5%) ABMR + TCMR and 1 (5%) TCMR + IF/TA. The mean serum creatinine at the time of the biopsy was 126.7 ± 23.4 µmol/L, while GFR-MDRD 63.4 ± 20.7 ml/min, which means that the majority of the findings were subclinical. Among the non-immunological histological findings (Cat 6), 3 cases belonged to CNI toxicity, 1 to BK nephropathy and 1 to recurrence of the primary disease.

CONCLUSION

Our 12-month protocol biopsy study revealed the presence of different forms of mixed subclinical rejection. Use of recent BANFF classification and scoring system enables more precise diagnosis and subsequently different approach to the further treatment of the KTR. More correlative long-term studies including Anti HLA antibodies and Endothelial Cell Activation- Associated Transcripts (ENDAT) are needed.

Clinical and histological evolution after de novo donor-specific anti-human leukocyte antigen antibodies: a single centre retrospective study

Background

Donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA) can be preformed or de novo (dn). Strategies to manage preformed DSA are well described, but data on the management and outcomes of dnDSA are lacking.

Methods

We performed a retrospective analysis of data from a single centre of the management and outcomes of 22 patients in whom a dnDSA was identified with contemporary and follow up biopsies.

Results

Evolution from baseline to follow up revealed a statistically significant loss of kidney function (estimated glomerular filtration rate: 45.9 ± 16.7 versus 37.4 ± 13.8 ml/min/1.73 m²; p = 0.005) and increase in the proportion of patients with transplant glomerulopathy (percentage with cg lesion ≥1: 27.2% vs. 45.4%; p = 0.04). Nine patients were not treated at the time of dnDSA identification, and 13 patients received various drug combinations (e.g., corticosteroids, plasmapheresis, thymoglobulins and/or rituximab). No significant pathological changes were observed for the various treatment combinations.

Conclusion

Our retrospective analysis of a small sample suggests that dnDSA should be considered a risk factor for the loss of kidney function independent of the baseline biopsy, and multidisciplinary evaluations of the transplant patient are a necessary requirement. Further confirmation in a multicentre prospective trial is required.

Review: The transcripts associated with organ allograft rejection

The molecular mechanisms operating in human organ transplant rejection are best inferred from the mRNAs expressed in biopsies because the corresponding proteins often have low expression and short half-lives, while small non-coding RNAs lack specificity. Associations should be characterized in a population that rigorously identifies T cell-mediated (TCMR) and antibody-mediated rejection (ABMR). This is best achieved in kidney transplant biopsies, but the results are generalizable to heart, lung, or liver transplants. Associations can be universal (all rejection), TCMR-selective, or ABMR-selective, with universal being strongest and ABMR-selective weakest. Top universal transcripts are IFNG-inducible (eg, CXCL11 IDO1, WARS) or shared by effector T cells (ETCs) and NK cells (eg, KLRD1, CCL4). TCMR-selective transcripts are expressed in activated ETCs (eg, CTLA4, IFNG), activated (eg, ADAMDEC1), or IFNG-induced macrophages (eg, ANKRD22). ABMR-selective transcripts are expressed in NK cells (eg, FGFBP2, GNLY) and endothelial cells (eg, ROBO4, DARC). Transcript associations are highly reproducible between biopsy sets when the same rejection definitions, case mix, algorithm, and technology are applied, but exact ranks will vary. Previously published rejection-associated transcripts resemble universal and TCMR-selective transcripts due to incomplete representation of ABMR. Rejection-associated transcripts are never completely rejection-specific because they are shared with the stereotyped response-to-injury and innate immunity.

A molecular biopsy test based on arteriolar under-hyalinosis reflects increased probability of rejection related to under-immunosuppression

Calcineurin inhibitor immunosuppressive drugs induce changes such as arteriolar hyalinosis (ah) in kidney transplants, raising the possibility that molecular changes in biopsies related to histologic ah can provide information about drug exposure. We hypothesized that molecular changes associated with less-than-expected hyalinosis might highlight a subpopulation of patients with under-immunosuppression/nonadherence at intermediate times of biopsy posttransplant (TxBx). Using gene expression data from 562 indication biopsies, we developed a molecular classifier for predicting the expected ah lesions (Mah ) at a particular TxBx. Mah -scores increased linearly with log(TxBx), but some biopsies had lower scores than expected for TxBx. The deviation of individual Mah -scores below the predicted regression line of Mah -scores vs TxBx is defined as "low hyalinosis index." Low hyalinosis indices were frequent in biopsies between 3 months and 3 years posttransplant, particularly among biopsies lacking histologic hyalinosis (ah0), and were associated with T cell-mediated rejection and a subset of recent-onset antibody-mediated rejection without glomerular double contours. In patients with medical records available for review, low hyalinosis indices were frequently associated with physician-recorded concerns about nonadherence (suspected or proven). We conclude that the Mah classifier and hyalinosis index identify indication biopsies with rejection for which the possibility of patient nonadherence should be considered.

Real Time Central Assessment of Kidney Transplant Indication Biopsies by Microarrays: The INTERCOMEX Study

The authors conducted a prospective trial to assess the feasibility of real time central molecular assessment of kidney transplant biopsy samples from 10 North American or European centers. Biopsy samples taken 1 day to 34 years posttransplantation were stabilized in RNAlater, sent via courier overnight at ambient temperature to the central laboratory, and processed (29 h workflow) using microarrays to assess T cell- and antibody-mediated rejection (TCMR and ABMR, respectively). Of 538 biopsy samples submitted, 519 (96%) were sufficient for microarray analysis (average length, 3 mm). Automated reports were generated without knowledge of histology and HLA antibody, with diagnoses assigned based on Molecular Microscope Diagnostic System (MMDx) classifier algorithms and signed out by one observer. Agreement between MMDx and histology (balanced accuracy) was 77% for TCMR, 77% for ABMR, and 76% for no rejection. A classification tree derived to provide automated sign-outs predicted the observer sign-outs with >90% accuracy. In 451 biopsy samples where feedback was obtained, clinicians indicated that MMDx more frequently agreed with clinical judgment (87%) than did histology (80%) (p = 0.0042). In 81% of feedback forms, clinicians reported that MMDx increased confidence in management compared with conventional assessment alone. The authors conclude that real time central molecular assessment is feasible and offers a useful new dimension in biopsy interpretation. ClinicalTrials.gov NCT#01299168.

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.

Longitudinal immunological characterization of the first presensitized recipient of a face transplant

Rejection affects greater than 80% of face transplants, yet no diagnostic criteria for antibody-mediated rejection (AMR) following face transplantation have been established. Given that different treatment strategies are required to address AMR and T cell-mediated rejection (TCMR), there is a critical need to delineate the features that can differentiate these two alloimmune responses. Here, we report the longitudinal immunological examination of what we believe to be the first and only highly sensitized recipient of a crossmatch-positive face transplant up to 4 years following transplantation. We conducted gene expression profiling on allograft biopsies collected during suspected AMR and TCMR episodes as well as during 5 nonrejection time points. Our data suggest that there are distinctive molecular features in AMR, characterized by overexpression of endothelial-associated genes, including ICAM1, VCAM1, and SELE. Although our findings are limited to a single patient, these findings highlight the potential importance of developing and implementing molecular markers to differentiate AMR from TCMR to guide clinical management. Furthermore, our case illustrates that molecular assessment of allograft biopsies offers the potential for new insights into the mechanisms underlying rejection. Finally, our medium-term outcomes demonstrate that face transplantation in a highly sensitized patient with a positive preoperative crossmatch is feasible and manageable.

Assessing rejection-related disease in kidney transplant biopsies based on archetypal analysis of molecular phenotypes

Conventional histologic diagnosis of rejection in kidney transplants has limited repeatability due to its inherent requirement for subjective assessment of lesions, in a rule-based system that does not acknowledge diagnostic uncertainty. Molecular phenotyping affords opportunities for increased precision and improved disease classification to address the limitations of conventional histologic diagnostic systems and quantify levels of uncertainty. Microarray data from 1,208 kidney transplant biopsies were collected prospectively from 13 centers. Cross-validated classifier scores predicting the presence of antibody-mediated rejection (ABMR), T cell-mediated rejection (TCMR), and 5 related histologic lesions were generated using supervised machine learning methods. These scores were used as input for archetypal analysis, an unsupervised method similar to cluster analysis, to examine the distribution of molecular phenotypes related to rejection. Six archetypes were generated: no rejection, TCMR, 3 associated with ABMR (early-stage, fully developed, and late-stage), and mixed rejection (TCMR plus early-stage ABMR). Each biopsy was assigned 6 scores, one for each archetype, representing a probabilistic assessment of that biopsy based on its rejection-related molecular properties. Viewed as clusters, the archetypes were similar to existing histologic Banff categories, but there was 32% disagreement, much of it probably reflecting the "noise" in the current histologic assessment system. Graft survival was lowest for fully developed and late-stage ABMR, and it was better predicted by molecular archetype scores than histologic diagnoses. The results provide a system for precision molecular assessment of biopsies and a new standard for recalibrating conventional diagnostic systems.

Relationship Between Albuminuria During the First Year and Antibody-Mediated Rejection in Protocol Biopsies in Kidney Transplant Recipients

BACKGROUND

Antibody-mediated rejection is the main cause of deterioration of kidney transplants and frequently is detected only by means of protocol biopsies. The aim of this study was to relate the presence of albuminuria throughout the 1st year to the histologic findings detected by 1-year protocol biopsies in kidney graft recipients.

METHODS

Retrospective observational study of 86 protocol biopsies 1 year after transplantation. Albuminuria was measured at 3, 6, 9, and 12 months in urine samples and expressed as albumin/creatinine (mg/g).

RESULTS

Analysis of biopsies, reflected according to the Banff criteria, the following categories: fibrosis and tubular atrophy, 35 (40.7%); cellular rejection, 13 (15.1%); antibody-mediated rejection, 8 (9.3%); chronic glomerulopathy, 10 (11.6%); normal, 14 (16.3%); recurrence, 1 (1.2%); and other, 5 (5.8%). The proportions of patients with albuminuria for Banff scale scores (0 vs ≥1, respectively) at 6 and 12 months, respectively, after transplantation, were: for marker glomerulitis, 45.5% versus 59.3% (P = .021) and 36.4% versus 70.4% (P < .001); for marker glomerulopathy, 49.1% versus 50.0% (P = .051) and 42.1% versus 58.3% (P = .019); for marker peritubular capillaritis, 45.8% versus 60.9% (P = .047) and 39.0% versus 69.6% (P = .276); and for marker C4d, 49.2% versus 56.3% (P = .894) and 46.2% versus 56.3% (P = .774).

CONCLUSIONS

The presence of albuminuria after renal transplantation is common, especially in patients with proteinuria. Persistent albuminuria after transplantation, even at low levels, can be indicative of subclinical antibody-mediated rejection. Additional broader studies to relate the albuminuria to histologic changes observed in protocol biopsies are required.

Antibody-Mediated Rejection Due to Preexisting versus De Novo Donor-Specific Antibodies in Kidney Allograft Recipients

Antibody-mediated rejection (ABMR) can occur in patients with preexisting anti-HLA donor-specific antibodies (DSA) or in patients who develop de novo DSA. However, how these processes compare in terms of allograft injury and outcome has not been addressed. From a cohort of 771 kidney biopsy specimens from two North American and five European centers, we performed a systematic assessment of clinical and biologic parameters, histopathology, circulating DSA, and allograft gene expression for all patients with ABMR (n=205). Overall, 103 (50%) patients had preexisting DSA and 102 (50%) had de novo DSA. Compared with patients with preexisting DSA ABMR, patients with de novo DSA ABMR displayed increased proteinuria, more transplant glomerulopathy lesions, and lower glomerulitis, but similar levels of peritubular capillaritis and C4d deposition. De novo DSA ABMR was characterized by increased expression of IFNγ-inducible, natural killer cell, and T cell transcripts, but less expression of AKI transcripts compared with preexisting DSA ABMR. The preexisting DSA ABMR had superior graft survival compared with the de novo DSA ABMR (63% versus 34% at 8 years after rejection, respectively; P<0.001). After adjusting for clinical, histologic, and immunologic characteristics and treatment, we identified de novo DSA ABMR (hazard ratio [HR], 1.82 compared with preexisting DSA ABMR; 95% confidence interval [95% CI], 1.07 to 3.08; P=0.03); low eGFR (<30 ml/min per 1.73 m2) at diagnosis (HR, 3.27; 95% CI, 1.48 to 7.23; P<0.001); ≥0.30 g/g urine protein-to-creatinine ratio (HR, 2.44; 95% CI, 1.47 to 4.09; P<0.001); and presence of cg lesions (HR, 2.25; 95% CI, 1.34 to 3.79; P=0.002) as the main independent determinants of allograft loss. Our findings support the transplant of kidneys into highly sensitized patients and should encourage efforts to monitor patients for de novo DSA.

Hyalinosis Lesions in Renal Transplant Biopsies: Time-Dependent Complexity of Interpretation

Because calcineurin inhibitor (CNI) immunosuppressive drugs induce arteriolar hyalinosis (ah) in kidney transplants, ah lesions can potentially provide information about drug exposure. We studied the relationship of ah lesions to findings and outcomes in 562 indication biopsies taken 3 days to 35 years after transplant. Prevalence of ah lesions increased with time of biopsy after transplant (TxBx). The ah scores correlated with arterial intimal thickening and atrophy-fibrosis but, unlike atrophy-fibrosis, did not increase until after 500 days because of a background of ah1 lesions in early biopsies reflecting donor aging. Correlation of ah scores with other features varied with TxBx-in early biopsies, donor age and related changes, and in very late biopsies, chronic antibody-mediated rejection and glomerulonephritis and associated lesions. After correction for TxBx, ah0 in intermediate time periods was associated with increased risk of T cell-mediated rejection and graft loss, probably because of underimmunosuppression and nonadherence. Thus, ah lesions in indication biopsies have multiple associations: donor age (early, usually ah1), chronic glomerular diseases (late, often ah2/3), and adequate exposure to CNIs at intermediate times. This threefold TxBx-dependent complexity must be considered when interpreting indication biopsies: ah lesions often indicate adequate CNI exposure, not toxicity, and unexpected ah0 should increase vigilance for nonadherence and underimmunosuppression.

Antibody-mediated rejection in the cardiac allograft: diagnosis, treatment and future considerations

PURPOSE OF REVIEW

This review summarizes the latest publications dealing with antibody-mediated rejection (AMR) and defines areas of controversy and future steps that may improve the outcome for patients with this virulent form of rejection.

RECENT FINDINGS

Recent progress includes publication of standardized pathologic criteria for acute AMR by the International Society for Heart and Lung Transplantation (ISHLT) and guidelines for treatment of acute AMR by the American Heart Association, endorsed by ISHLT as well. Recently published review articles emphasize the important role of innate immune mechanisms, clarify the role of viral infection and provide insights into vascular biology and the role of innate effector populations, macrophages and dendritic cells.

SUMMARY

Strategies for future studies are discussed in the context of these new findings and similar efforts undertaken by renal and liver allograft investigators.