Molecular microscope strategy to improve risk stratification in early antibody-mediated kidney allograft rejection

Assessment of biological organ age using molecular pathology in pre-transplant kidney biopsies

Organ shortage is a major challenge in kidney transplantation but the use of older donors, often with co-morbidities, is hampered by inconsistent outcomes. Methods of accurately stratifying marginal donor organs by clinical and histological assessment are lacking. To better understand organ variability, we profiled the transcriptomes of 271 kidneys from deceased donors at retrieval. Following correction for biopsy composition, we assessed molecular pathways that associated with delayed, and sub-optimal one-year graft function. Analysis of cortical biopsies identified an adaptive immune gene-rich module that significantly associated with increasing age and worse outcomes. Cellular deconvolution using human kidney reference single cell transcriptomes confirmed an increase in kidney-specific B and T cell signatures, as well as kidney macrophage, myofibroblast and fibroblast gene sets in this module. Surprisingly, innate immune pathway and neutrophil gene signature enrichment was associated with better outcomes. Thus, our work uncovers cellular molecular features of pathological organ ageing, identifiable at kidney retrieval, with translational potential.

An autophagy-associated diagnostic signature based on peripheral blood for antibody-mediated rejection in renal transplantation

BACKGROUND

Antibody-mediated rejection (ABMR) emerged as a major cause of graft loss in renal transplantation. Needle biopsy is the gold standard for diagnosis of ABMR in renal allografts. Thus, noninvasive diagnosis methods of ABMR with high accuracy are urgently needed to prevent unnecessary biopsies.

METHODS

We collected peripheral blood transcriptome data from two independent renal transplantation cohorts with patients with ABMR, stable well-functioning transplants (STA), and T-cell mediated rejection (TCMR). Differentially expressed genes (DEGs) were identified by comparing the ABMR group with the STA group. In addition, functional enrichment analysis and gene set enrichment analysis were performed to seek new key underlying mechanisms in ABMR. Subsequently, we utilized a Boruta algorithm and least absolute shrinkage and selection operator logistic algorithm to establish a diagnostic model which was then evaluated and validated in an independent cohort.

RESULTS

According to functional enrichment analysis, autophagy was found to be the primary upregulated biological process in ABMR. Based on algorithms, three autophagy-associated genes, ubiquitin specific peptidase 33 (USP33), Ras homolog mTORC1 binding (RHEB), and ABL proto-oncogene 2 (ABL2), were selected to establish the diagnostic model in the training cohort. This autophagy-related gene model possessed good diagnostic value in distinguishing ABMR from STA blood samples in the training cohort (AUC = 0.907) and in the validation cohort (AUC = 0.972). In addition, this model also showed good discernibility in distinguishing ABMR from TCMR in the training and validation cohorts (AUCs = 0.908 and 0.833).

CONCLUSION

We identified and validated an autophagy-associated diagnostic model with high accuracy for renal transplant patients with ABMR. Our study provided a new potential test for the non-invasive diagnosis of ABMR in clinical practice and highlighted the importance of autophagy in ABMR.

Design, cohort profile and comparison of the KTD-Innov study: a prospective multidimensional biomarker validation study in kidney allograft rejection

There is an unmet need for robust and clinically validated biomarkers of kidney allograft rejection. Here we present the KTD-Innov study (ClinicalTrials.gov, NCT03582436), an unselected deeply phenotyped cohort of kidney transplant recipients with a holistic approach to validate the clinical utility of precision diagnostic biomarkers. In 2018-2019, we prospectively enrolled consecutive adult patients who received a kidney allograft at seven French centers and followed them for a year. We performed multimodal phenotyping at follow-up visits, by collecting clinical, biological, immunological, and histological parameters, and analyzing a panel of 147 blood, urinary and kidney tissue biomarkers. The primary outcome was allograft rejection, assessed at each visit according to the international Banff 2019 classification. We evaluated the representativeness of participants by comparing them with patients from French, European, and American transplant programs transplanted during the same period. A total of 733 kidney transplant recipients (64.1% male and 35.9% female) were included during the study. The median follow-up after transplantation was 12.3 months (interquartile range, 11.9-13.1 months). The cumulative incidence of rejection was 9.7% at one year post-transplant. We developed a distributed and secured data repository in compliance with the general data protection regulation. We established a multimodal biomarker biobank of 16,736 samples, including 9331 blood, 4425 urinary and 2980 kidney tissue samples, managed and secured in a collaborative network involving 7 clinical centers, 4 analytical platforms and 2 industrial partners. Patients' characteristics, immune profiles and treatments closely resembled those of 41,238 French, European and American kidney transplant recipients. The KTD-Innov study is a unique holistic and multidimensional biomarker validation cohort of kidney transplant recipients representative of the real-world transplant population. Future findings from this cohort are likely to be robust and generalizable.

Exploring the single-cell immune landscape of kidney allograft inflammation using imaging mass cytometry

Kidney allograft inflammation, mostly attributed to rejection and infection, is an important cause of graft injury and loss. Standard histopathological assessment of allograft inflammation provides limited insights into biological processes and the immune landscape. Here, using imaging mass cytometry with a panel of 28 validated biomarkers, we explored the single-cell landscape of kidney allograft inflammation in 32 kidney transplant biopsies and 247 high-dimensional histopathology images of various phenotypes of allograft inflammation (antibody-mediated rejection, T cell-mediated rejection, BK nephropathy, and chronic pyelonephritis). Using novel analytical tools, for cell segmentation, we segmented over 900 000 cells and developed a tissue-based classifier using over 3000 manually annotated kidney microstructures (glomeruli, tubules, interstitium, and arteries). Using PhenoGraph, we identified 11 immune and 9 nonimmune clusters and found a high prevalence of memory T cell and macrophage-enriched immune populations across phenotypes. Additionally, we trained a machine learning classifier to identify spatial biomarkers that could discriminate between the different allograft inflammatory phenotypes. Further validation of imaging mass cytometry in larger cohorts and with more biomarkers will likely help interrogate kidney allograft inflammation in more depth than has been possible to date.

Advances and Challenges in Sepsis Management: Modern Tools and Future Directions

Sepsis, a critical condition marked by systemic inflammation, profoundly impacts both innate and adaptive immunity, often resulting in lymphopenia. This immune alteration can spare regulatory T cells (Tregs) but significantly affects other lymphocyte subsets, leading to diminished effector functions, altered cytokine profiles, and metabolic changes. The complexity of sepsis stems not only from its pathophysiology but also from the heterogeneity of patient responses, posing significant challenges in developing universally effective therapies. This review emphasizes the importance of phenotyping in sepsis to enhance patient-specific diagnostic and therapeutic strategies. Phenotyping immune cells, which categorizes patients based on clinical and immunological characteristics, is pivotal for tailoring treatment approaches. Flow cytometry emerges as a crucial tool in this endeavor, offering rapid, low cost and detailed analysis of immune cell populations and their functional states. Indeed, this technology facilitates the understanding of immune dysfunctions in sepsis and contributes to the identification of novel biomarkers. Our review underscores the potential of integrating flow cytometry with omics data, machine learning and clinical observations to refine sepsis management, highlighting the shift towards personalized medicine in critical care. This approach could lead to more precise interventions, improving outcomes in this heterogeneously affected patient population.

Evolution of human kidney allograft pathology diagnostics through 30 years of the Banff classification process

The second half of the previous century witnessed a tremendous rise in the number of clinical kidney transplants worldwide. This activity was, however, accompanied by many issues and challenges. An accurate diagnosis and appropriate management of causes of graft dysfunction were and still are, a big challenge. Kidney allograft biopsy played a vital role in addressing the above challenge. However, its interpretation was not standardized for many years until, in 1991, the Banff process was started to fill this void. Thereafter, regular Banff meetings took place every 2 years for the past 30 years. Marked changes have taken place in the interpretation of kidney allograft biopsies, diagnosis, and classification of rejection and other non-rejection pathologies from the original Banff 93 classification. This review attempts to summarize those changes for increasing the awareness and understanding of kidney allograft pathology through the eyes of the Banff process. It will interest the transplant surgeons, physicians, pathologists, and allied professionals associated with the care of kidney transplant patients.

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

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

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

Clinical recommendations for posttransplant assessment of anti-HLA (Human Leukocyte Antigen) donor-specific antibodies: A Sensitization in Transplantation: Assessment of Risk consensus document

Although anti-HLA (Human Leukocyte Antigen) donor-specific antibodies (DSAs) are commonly measured in clinical practice and their relationship with transplant outcome is well established, clinical recommendations for anti-HLA antibody assessment are sparse. Supported by a careful and critical review of the current literature performed by the Sensitization in Transplantation: Assessment of Risk 2022 working group, this consensus report provides clinical practice recommendations in kidney, heart, lung, and liver transplantation based on expert assessment of quality and strength of evidence. The recommendations address 3 major clinical problems in transplantation and include guidance regarding posttransplant DSA assessment and application to diagnostics, prognostics, and therapeutics: (1) the clinical implications of positive posttransplant DSA detection according to DSA status (ie, preformed or de novo), (2) the relevance of posttransplant DSA assessment for precision diagnosis of antibody-mediated rejection and for treatment management, and (3) the relevance of posttransplant DSA for allograft prognosis and risk stratification. This consensus report also highlights gaps in current knowledge and provides directions for clinical investigations and trials in the future that will further refine the clinical utility of posttransplant DSA assessment, leading to improved transplant management and patient care.

Unraveling complexity of antibody-mediated rejections, the mandatory way towards an accurate diagnosis and a personalized treatment

Antibody-mediated rejection (ABMR) remains one of the most challenging issues after organ transplantation and particularly after kidney transplantation. Despite many progresses during the last decade, ABMR is still the main cause of kidney graft loss and this all over the post- transplant period. In this review, we describe the recent knowledge about molecular and cellular mechanisms involved in ABMR. We focused our report on the role of the complement pathway in the process of ABMR and we give some insights into the role of inflammatory cells, NK lymphocytes and the role of endothelial cells. We further describe the potential role of non-HLA antibodies, of which the importance has been increasingly emphasized in recent years. Overall, this report could be of interest for all physicians who are working in the field of organ transplantation or who are working in the field of immunology. It gives essential information to understand new diagnosis advances and further therapeutic approaches. Antibody-mediated rejection (ABMR) is the leading cause of graft failure ([1,2]). In contrast to T-cell mediated rejection usually sensitive to steroids, active ABMR remains a therapeutic challenge. ABMR diagnosis relies on the presence of renal injuries and donor-specific antibodies (DSA) (HLA and non HLA antibodies) with sometimes the evidence of interaction between DSA and graft endothelium. Regularly revised during expert conferences, ABMR definition is currently categorized as active or chronic active. [3] The emergence of validated molecular assays targeting a better phenotyping of ABMR and the recent advances regarding the detrimental effect of DSA directed against minor antigens open the way to a better assessment of the heterogeneity of ABMR. In this review, we will address new aspects of ABMR regarding its mechanisms, diagnosis and treatments.

Banff Human Organ Transplant Transcripts Correlate with Renal Allograft Pathology and Outcome: Importance of Capillaritis and Subpathologic Rejection

BACKGROUND

To seek insights into the pathogenesis of chronic active antibody-mediated rejection (CAMR), we performed mRNA analysis and correlated transcripts with pathologic component scores and graft outcomes.

METHODS

We utilized the NanoString nCounter platform and the Banff Human Organ Transplant gene panel to quantify transcripts on 326 archived renal allograft biopsy samples. This system allowed correlation of transcripts with Banff pathology scores from the same tissue block and correlation with long-term outcomes.

RESULTS

The only pathology score that correlated with AMR pathways in CAMR was peritubular capillaritis (ptc). C4d, cg, g, v, i, t, or ci scores did not correlate. DSA-negative CAMR had lower AMR pathway scores than DSA-positive CAMR. Transcript analysis in non-CAMR biopsies yielded evidence of increased risk of later CAMR. Among 108 patients without histologic CAMR, 23 developed overt biopsy-documented CAMR within 5 years and as a group had higher AMR pathway scores (P=3.4 × 10-5). Random forest analysis correlated 3-year graft loss with elevated damage, innate immunity, and macrophage pathway scores in CAMR and TCMR. Graft failure in CAMR was associated with TCMR transcripts but not with AMR transcripts, and graft failure in TCMR was associated with AMR transcripts but not with TCMR transcripts.

CONCLUSIONS

Peritubular capillary inflammation and DSA are the primary drivers of AMR transcript elevation. Transcripts revealed subpathological evidence of AMR, which often preceded histologic CAMR and subpathological evidence of TCMR that predicted graft loss in CAMR.

Cellular Immuno-Profile in Septic Human Host: A Scoping Review

Simple Summary

Septic shock is a life-threatening disease caused by a dysregulated host response to infection, affecting millions of people every year and killing more than 25% directly despite advances in modern medicine. This pathology is characterized by apoptosis-induced depletion of immune cells and immunodepression. Many alterations in the expression of surface markers of neutrophils and monocytes have been described in septic patients. There is no specific treatment but the early identification and diagnosis of the pathology as well as timely treatment can greatly improve patient outcomes. The aim of this study was to inspect the recently published literature to inform the clinician about the most up-to-date techniques for the study of immune cell phenotypes and on the function of leukocytes of extracorporeal and non-blood purification treatments proposed for sepsis were also analyzed. The most important alteration observed in septic neutrophils is the activation of a survival program capable of resisting apoptotic death. As regards adaptive immunity, sepsis-induced apoptosis leads to lymphopenia in patients with septic shock and this process involves all types of T cells (CD4, CD8 and Natural Killer), except for regulatory T cells, favoring immunosuppression. Several promising therapies that target the host’s immune response to sepsis are currently under evaluation.

Abstract

Innate and adaptive immune system cells play a critical role in the host response to sepsis. Sepsis is a life-threatening disease characterized by apoptosis-induced depletion of immune cells and immunodepression, which contribute to morbidity and mortality. Many alterations in the expression of surface markers of neutrophils and monocytes have been described in septic patients. The aim of this study was to inspect the recently published literature to inform the clinician about the most up-to-date techniques for the study of circulating leukocytes. The impact on cell phenotypes and on the function of leukocytes of extracorporeal and non-blood purification treatments proposed for sepsis were also analyzed. We conducted a systematic review using Pubmed/Medline, Ovid/Willey, the Cochrane Library, the Cochrane Controlled Trials Register, and EMBASE, combining key terms related to immunological function in sepsis and selected the most relevant clinical trials and review articles (excluding case reports) published in the last 50 years. The most important alteration in neutrophils during sepsis is that they activate an anti-apoptotic survival program. In septic monocytes, a reduced characteristic expression of HLA-DR is observed, but their role does not seem to be significantly altered in sepsis. As regards adaptive immunity, sepsis leads to lymphopenia and immunosuppression in patients with septic shock; this process involves all types of T cells (CD4, CD8 and Natural Killer), except for regulatory T cells, which retain their function. Several promising therapies that target the host immune response are currently under evaluation. During the worldwide pandemic caused by SARS-CoV-2, it was useful to study the “cytokine storm” to find additional treatments, such as the oXiris^® filter. This therapy can decrease the concentration of inflammatory markers that affect the severity of the disease.

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.

Circulating Donor-Specific Anti-HLA Antibodies Associate With Immune Activation Independent of Kidney Transplant Histopathological Findings

Despite the critical role of cytokines in allograft rejection, the relation of peripheral blood cytokine profiles to clinical kidney transplant rejection has not been fully elucidated. We assessed 28 cytokines through multiplex assay in 293 blood samples from kidney transplant recipients at time of graft dysfunction. Unsupervised hierarchical clustering identified a subset of patients with increased pro-inflammatory cytokine levels. This patient subset was hallmarked by a high prevalence (75%) of donor-specific anti-human leukocyte antigen antibodies (HLA-DSA) and histological rejection (70%) and had worse graft survival compared to the group with low cytokine levels (HLA-DSA in 1.7% and rejection in 33.7%). Thirty percent of patients with high pro-inflammatory cytokine levels and HLA-DSA did not have histological rejection. Exploring the cellular origin of these cytokines, we found a corresponding expression in endothelial cells, monocytes, and natural killer cells in single-cell RNASeq data from kidney transplant biopsies. Finally, we confirmed secretion of these cytokines in HLA-DSA-mediated cross talk between endothelial cells, NK cells, and monocytes. In conclusion, blood pro-inflammatory cytokines are increased in kidney transplant patients with HLA-DSA, even in the absence of histology of rejection. These observations challenge the concept that histology is the gold standard for identification of ongoing allo-immune activation after transplantation.

Histologic and Molecular Patterns in Responders and Non-responders With Chronic-Active Antibody-Mediated Rejection in Kidney Transplants

Introduction

There is no proven therapy for chronic-active antibody-mediated rejection (caABMR), the major cause of late kidney allograft failure. Histological and molecular patterns associated with possible therapy responsiveness are not known.

Methods

Based on rigorous selection criteria this single center, retrospective study identified 16 out of 1027 consecutive kidney transplant biopsies taken between 2008 and 2016 with pure, unquestionable caABMR, without other pathologic features. The change in estimated GFR pre- and post-biopsy/treatment were utilized to differentiate subjects into responders and non-responders. Gene sets reflecting active immune processes of caABMR were defined a priori, including endothelial, inflammatory, cellular, interferon gamma (IFNg) and calcineurin inhibitor (CNI) related-genes based on the literature. Transcript measurements were performed in RNA extracted from stored, formalin-fixed, paraffin-embedded (FFPE) samples using NanoString™ technology. Histology and gene expression patterns of responders and non-responders were compared.

Results

A reductionist approach applying very tight criteria to identify caABMR and treatment response excluded the vast majority of clinical ABMR cases. Only 16 out of 139 cases with a written diagnosis of chronic rejection fulfilled the caABMR criteria. Histological associations with therapy response included a lower peritubular capillaritis score (p = 0.028) along with less glomerulitis. In contrast, no single gene discriminated responders from non-responders. Activated genes associated with NK cells and endothelial cells suggested lack of treatment response.

Conclusion

In caABMR active microvascular injury, in particular peritubular capillaritis, differentiates treatment responders from non-responders. Transcriptome changes in NK cell and endothelial cell associated genes may further help to identify treatment response. Future prospective studies will be needed which include more subjects, who receive standardized treatment protocols to identify biomarkers for treatment response.

Clinical Trial Registration

[ClinicalTrials.gov], identifier [NCT03430414].

Emerging biomarkers in kidney transplantation and challenge of clinical implementation

PURPOSE OF REVIEW

Despite improvement in short-term outcomes after kidney transplantation, long-term outcomes remain suboptimal. Conventional biomarkers are limited in their ability to reliably identify early immunologic and nonimmunologic injury. Novel biomarkers are needed for noninvasive diagnosis of subclinical injury, prediction of response to treatment, and personalization of the care of kidney transplant recipients.

RECENT FINDINGS

Recent biotechnological advances have led to the discovery of promising molecular biomarker candidates. However, translating potential biomarkers from bench to clinic is challenging, and many potential biomarkers are abandoned prior to clinical implementation. Despite these challenges, several promising urine, blood, and tissue novel molecular biomarkers have emerged and are approaching incorporation into clinical practice.

SUMMARY

This article highlights the challenges in adopting biomarker-driven posttransplant management and reviews several promising emerging novel biomarkers that are approaching clinical implementation.

Banff classification from 1991 to 2019. A significant contribution to our understanding and reporting of allograft renal biopsies

The Banff schema of classification of renal allograft biopsies, first proposed at the meeting in Banff, Canada in 1991 has evolved through subsequent meetings held once in two years and is the internationally accepted scheme of classification which is consensual, current, validated and in clinical use. This review traces the evolution of the classification and our understanding of renal transplant pathology, with emphasis on alloimmune reactions. The proceedings of the meetings and the important studies which have shaped the classification are covered.

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.

Data-Driven Kidney Transplant Phenotyping as a Histology-Independent Framework for Biomarker Discovery

BACKGROUND

In transplant medicine, clinical decision making largely relies on histology of biopsy specimens. However, histology suffers from low specificity, sensitivity, and reproducibility, leading to suboptimal stratification of patients. We developed a histology-independent immune framework of kidney graft homeostasis and rejection.

METHODS

We applied tailored RNA deconvolution for leukocyte enumeration and coregulated gene network analysis to published bulk human kidney transplant RNA transcriptomes as input for unsupervised, high-dimensional phenotype clustering. We used framework-based graft survival analysis to identify a biomarker that was subsequently characterized in independent transplant biopsy specimens.

RESULTS

We found seven immune phenotypes that confirm known rejection types and uncovered novel signatures. The molecular phenotypes allow for improved graft survival analysis compared with histology, and identify a high-risk group in nonrejecting transplants. Two fibrosis-related phenotypes with distinct immune features emerged with reduced graft survival. We identified lysyl oxidase-like 2 (LOXL2)-expressing peritubular CD68+ macrophages as a framework-derived biomarker of impaired allograft function. These cells precede graft fibrosis, as demonstrated in longitudinal biopsy specimens, and may be clinically useful as a biomarker for early fibrogenesis.

CONCLUSIONS

This study provides a comprehensive, data-driven atlas of human kidney transplant phenotypes and demonstrates its utility to identify novel clinical biomarkers.

Diagnostic application of transcripts associated with antibody-mediated rejection in kidney transplant biopsies

Background

The diagnosis of antibody-mediated rejection (AMR) is reached using the Banff Classification for Allograft Pathology, which now includes gene expression analysis. In this study, we investigate the application of ‘increased expression of thoroughly validated gene transcripts/classifiers strongly associated with AMR’ as diagnostic criteria.

Method

We used quantitative real-time polymerase chain reaction for 10 genes associated with AMR in a retrospective cohort of 297 transplant biopsies, including biopsies that met the full diagnostic criteria for AMR, even without molecular data (AMR, n = 27), biopsies that showed features of AMR, but that would only meet criteria for AMR with increased transcripts [suspicious for AMR (AMRsusp), n = 49] and biopsies that would never meet criteria for AMR (No-AMR, n = 221).

Results

A 10-gene AMR score trained by a receiver-operating characteristic to identify AMR found 16 cases with a high score among the AMRsusp cases (AMRsusp-high) that had significantly worse graft survival than those with a low score (AMRsusp-low; n = 33). In both univariate and multivariate Cox regression analysis, the AMR 10-gene score was significantly associated with an increased hazard ratio (HR) for graft loss (GL) in the AMRsusp group (HR = 1.109, P = 0.004 and HR = 1.138, P = 0.012, respectively), but not in the whole cohort. Net reclassification index and integrated discrimination improvement analyses demonstrated improved risk classification and superior discrimination, respectively, for GL when considering the gene score in addition to histological and serological data, but only in the AMRsusp group, not the whole cohort.

Conclusions

This study provides evidence that a gene score strongly associated with AMR helps identify cases at higher risk of GL in biopsies that are suspicious for AMR but do not meet full criteria.

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.

B-cell Deficiency Attenuates Transplant Glomerulopathy in a Rat Model of Chronic Active Antibody-mediated Rejection

BACKGROUND

Transplant glomerulopathy (TG) is a pathological feature of chronic active antibody-mediated rejection (cAMR) and is associated with renal allograft failure. The specific role of B cells in the pathogenesis of TG is unclear.

METHODS

We used a minor mismatched rat kidney transplant model with B cell-deficient recipients, generated by clustered regularly interspaced short palindromic repeats/Cas9 technology, to investigate the impact of B-cell depletion on the pathogenesis of TG. We hypothesized that B-cell deficiency would prevent TG in the rat kidney transplant model of cAMR. Treatment groups included syngeneic, allogeneic, sensitized allogeneic, and B cell-deficient allogeneic transplant recipients.

RESULTS

B cell-deficient recipients demonstrated reduced TG lesions, decreased microvascular inflammation, reduced allograft infiltrating macrophages, and reduced interferon gamma transcripts within the allograft. Allograft transcript levels of interferon gamma, monocyte chemoattractant protein-1, and interleukin-1β correlated with numbers of intragraft macrophages. B cell-deficient recipients lacked circulating donor-specific antibodies and had an increased splenic regulatory T-cell population.

CONCLUSIONS

In this model of cAMR, B-cell depletion attenuated the development of TG with effects on T cell and innate immunity.

A 2020 Banff Antibody-mediatedInjury Working Group examination of international practices for diagnosing antibody-mediated rejection in kidney transplantation - a cohort study

The Banff antibody-mediated rejection (ABMR) classification is vulnerable to misinterpretation, but the reasons are unclear. To better understand this vulnerability, we evaluated how ABMR is diagnosed in practice. To do this, the Banff Antibody-Mediated Injury Workgroup electronically surveyed an international cohort of nephrologists/surgeons (n = 133) and renal pathologists (n = 99). Most providers (97%) responded that they use the Banff ABMR classification at least sometimes, but DSA information is often not readily available. Only 41.1% (55/133) of nephrologists/surgeons and 19.2% (19/99) of pathologists reported that they always have DSA results when the biopsy is available. Additionally, only 19.6% (26/133) of nephrologists/surgeons responded that non-HLA antibody or molecular transcripts are obtained when ABMR histologic features are present but DSA is undetected. Several respondents agreed that histologic features concerning for ABMR in the absence of DSA and/or C4d are not well accounted for in the current classification [31.3% (31/99) pathologists and 37.6% (50/133) nephrologist/surgeons]. The Banff ABMR classification appears widely accepted, but efforts to improve the accessibility of DSA information for the multidisciplinary care team are needed. Further clarity is also needed in Banff ABMR nomenclature to account for the spectrum of ABMR and for histologic features suspicious for ABMR when DSA is absent.

Therapies for Chronic Allograft Rejection

Remarkable advances have been made in the pathophysiology, diagnosis, and treatment of antibody-mediated rejection (ABMR) over the past decades, leading to improved graft outcomes. However, long-term failure is still high and effective treatment for chronic ABMR, an important cause of graft failure, has not yet been identified. Chronic ABMR has a relatively different phenotype from active ABMR and is a slowly progressive disease in which graft injury is mainly caused by de novo donor specific antibodies (DSA). Since most trials of current immunosuppressive therapies for rejection have focused on active ABMR, treatment strategies based on those data might be less effective in chronic ABMR. A better understanding of chronic ABMR may serve as a bridge in establishing treatment strategies to improve graft outcomes. In this in-depth review, we focus on the pathophysiology and characteristics of chronic ABMR along with the newly revised Banff criteria in 2017. In addition, in terms of chronic ABMR, we identify the reasons for the resistance of current immunosuppressive therapies and look at ongoing research that could play a role in setting better treatment strategies in the future. Finally, we review non-invasive biomarkers as tools to monitor for rejection.

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.

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.

Noninvasive biomarkers for prediction and diagnosis of heart transplantation rejection

For most patients with end-stage heart failure, heart transplantation is the treatment of choice. Allograft rejection is one of the major post-transplantation complications affecting graft outcome and survival. Recent advancements in science and technology offer an opportunity to integrate genomic and other omics-based biomarkers into clinical practice, facilitating noninvasive evaluation of allograft for diagnostic and prognostic purposes. Omics, including gene expression profiling (GEP) of blood immune cell components and donor-derived cell-free DNA (dd-cfDNA) are of special interest to researchers. Several studies have investigated levels of dd-cfDNA and miroRNAs in blood as potential markers for early detection of allograft rejection. One of the achievements in the field of transcriptomics is AlloMap, GEP of peripheral blood mononuclear cells (PBMC), which can identify 11 differentially expressed genes and help with detection of moderate and severe acute cellular rejection in stable heart transplant recipients. In recent years, the utilization of GEP of PBMC for identifying differentially expressed genes to diagnose acute antibody-mediated rejection and cardiac allograft vasculopathy has yielded promising results. Advancements in the field of metabolomics and proteomics as well as their potential implications have been further discussed in this paper.

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.

Recurrent antibody-mediated rejection in renal allograft: physician's dilemma

Antibody-mediated rejection is the primary cause of renal allograft failure, and the molecular mechanistic is relatively less known in comparison to cell-mediated rejection. With the advent of new immunological agents, the short-term graft survival outcomes have improved, but the long-term outcomes are still unchanged. We present a case of 47-year-old with end-stage renal disease due to presumed lupus status post deceased donor renal transplantation. The patient developed recurrent (a total of five) antibody-mediated rejections (donor-specific antibody and C4d staining negative) spanning within a year of transplant despite the standard of care therapies. The present case draws attention to the importance of non-HLA antibodies in antibody-mediated rejection and diagnostic tools we can rely on when the histology is inconclusive and the role of new immunological agents.

Advances in Detection of Kidney Transplant Injury

Early detection of graft injury after kidney transplantation is key to maintaining long-term good graft function. Graft injury could be due to a multitude of factors including ischaemia reperfusion injury, cell or antibody-mediated rejection, progressive interstitial fibrosis and tubular atrophy, infections and toxicity from the immunosuppressive drugs themselves. The current gold standard for assessing renal graft dysfunction is renal biopsy. However, biopsy is usually late when triggered by a change in serum creatinine and of limited utility in diagnosis of early injury when histological changes are equivocal. Therefore, there is a need for timely, objective and non-invasive diagnostic techniques with good early predictive value to determine graft injury and provide precision in titrating immunosuppression. We review potential novel plasma and urine biomarkers that offer sensitive new strategies for early detection and provide major insights into mechanisms of graft injury. This is a rapidly expanding field, but it is likely that a combination of biomarkers will be required to provide adequate sensitivity and specificity for detecting graft injury.

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.

Molecular Assessment of Kidney Allografts: Are We Closer to a Daily Routine?

Kidney allograft pathology assessment has been traditionally based on clinical and histological criteria. Despite improvements in Banff histological classification, the diagnostics in particular cases is problematic reflecting a complex pathogenesis of graft injuries. With the advent of molecular techniques, polymerase-chain reaction, oligo- and microarray technologies allowed to study molecular phenotypes of graft injuries, especially acute and chronic rejections. Moreover, development of the molecular microscope diagnostic system (MMDx) to assess kidney graft biopsies, represents the first clinical application of a microarray-based method in transplantation. Whether MMDx may replace conventional pathology is the subject of ongoing research, however this platform is particularly useful in complex histological findings and may help clinicians to guide the therapy.

Terminally Differentiated Effector Memory CD8+ T Cells Identify Kidney Transplant Recipients at High Risk of Graft Failure

BACKGROUND

Identifying biomarkers to predict kidney transplant failure and to define new therapeutic targets requires more comprehensive understanding of the immune response to chronic allogeneic stimulation.

METHODS

We investigated the frequency and function of CD8⁺ T cell subsets-including effector memory (EM) and terminally differentiated EM (TEMRA) CD8⁺ T cells-in blood samples from 284 kidney transplant recipients recruited 1 year post-transplant and followed for a median of 8.3 years. We also analyzed CD8⁺ T cell reactivity to donor-specific PBMCs in 24 patients who had received living-donor kidney transplants.

RESULTS

Increased frequency of circulating TEMRA CD8⁺ T cells at 1 year post-transplant associated with increased risk of graft failure during follow-up. This association remained after adjustment for a previously reported composite of eight clinical variables, the Kidney Transplant Failure Score. In contrast, increased frequency of EM CD8⁺ T cells associated with reduced risk of graft failure. A distinct TEMRA CD8⁺ T cell subpopulation was identified that was characterized by expression of FcγRIIIA (CD16) and by high levels of proinflammatory cytokine secretion and cytotoxic activity. Although donor-specific stimulation induced a similar rapid, early response in EM and TEMRA CD8⁺ T cells, CD16 engagement resulted in selective activation of TEMRA CD8⁺ T cells, which mediated antibody-dependent cytotoxicity.

CONCLUSIONS

At 1 year post-transplant, the composition of memory CD8⁺ T cell subsets in blood improved prediction of 8-year kidney transplant failure compared with a clinical-variables score alone. A subpopulation of TEMRA CD8⁺ T cells displays a novel dual mechanism of activation mediated by engagement of the T-cell receptor or of CD16. These findings suggest that TEMRA CD8⁺ T cells play a pivotal role in humoral and cellular rejection and reveal the potential value of memory CD8⁺ T cell monitoring for predicting risk of kidney transplant failure.

B cells as antigen-presenting cells in transplantation rejection and tolerance

Transplantation of fully allogeneic organs into immunocompetent recipients invariably elicits T cell and B cell responses that lead to the production of donor-specific antibodies (DSA). When immunosuppression is inadequate donor-specific T cell and B cell responses escape, leading to T cell-mediated rejection (TCMR), antibody mediated (ABMR) rejection, or mixed rejection (MR) exhibiting features of both TCMR and ABMR. Current literature suggests that ABMR is a major cause of late graft loss, and that new therapies to curtail the donor-specific humoral response are necessary. The majority of research into B cell responses elicited by allogeneic allografts in both preclinical models and clinical studies, has focused on the function of B cells as antibody-secreting cells and the pathogenic effects of DSA as mediators of ABMR. However, it has long been recognized that the DSA response to allografts is T cell-dependent, and that B cells engage in cognate interactions with T cells that provide "help" and promote B cell differentiation into antibody-secreting cells (ASCs). This review focusses the function of B cells as antigen-presenting cells (APCs) to T cells in lymphoid organs, how they may be critical APCs to T cell in the allograft, and the functional consequences of these interactions.

New Markers for Transplant Rejection

Monitoring allograft function after kidney transplant has routinely relied on the use of nonspecific markers, such as serum creatinine, glomerular filtration rate, proteinuria, and donor-specific antibodies. These traditional markers have low sensitivity and fail to detect subclinical changes. Diagnosis of renal allograft dysfunction still requires an allograft biopsy, as it remains the criterion standard for assessment of graft status. However, renal biopsy is an invasive procedure, and sampling errors may result in misdiagnosis, perhaps causing graft failure. New biomarkers have been developed to monitor allograft function, although many are not yet routinely used. Other shortcomings, such as lack of standardization and high cost, should be solved before their widespread application in the clinic. A recipient's immune status could be monitored by use of urine or blood samples. These include functional cell-based assays and the evaluation of molecular expression at the messenger RNA or protein levels. Molecular technologies, including molecular microscope diagnostic systems, have been recently developed to improve the yield of histologic evaluation of the allograft biopsy. Prospective, interventional trials are required to demonstrate whether these new biomarkers improve patient or transplant outcomes. Implementation of these technologies into standard clinical practice remains challenging until their generalizability, cost, ease of interpretation, and the identification of patients who may benefit from more than standard-of-care surveillance can be determined. These biomarkers could allow immunosuppressive therapy to be individualized for patients.

Peripheral blood transcriptome analysis and development of classification model for diagnosing antibody-mediated rejection vs accommodation in ABO-incompatible kidney transplant

The major obstacle to successful ABO blood group-incompatible kidney transplantation (ABOi KT) is antibody-mediated rejection (AMR). This study aimed to investigate transcriptional profiles through RNA sequencing and develop a minimally invasive diagnostic tool for discrimination between accommodation and early acute AMR in ABOi KT. Twenty-eight ABOi KT patients were selected: 18 with accommodation and 10 with acute AMR at the 10th day posttransplant protocol biopsy. Complete transcriptomes of their peripheral blood were analyzed by RNA sequencing. Candidate genes were selected by bioinformatics analysis, validated with quantitative polymerase chain reaction, and used to develop a classification model to diagnose accommodation. A total of 1385 genes were differentially expressed in accommodation compared with in AMR with P-adjusted < .05. Functional annotation and gene set enrichment analysis identified several immune-related and immunometabolic pathways. A 5-gene classification model including COX7A2L, CD69, CD14, CFD, and FOXJ3 was developed by logistic regression analysis. The model was further validated with an independent cohort and discriminated between accommodation and AMR with 92.7% sensitivity, 85.7% specificity, and 91.7% accuracy. Our study suggests that a classification model based on peripheral blood transcriptomics may allow minimally invasive diagnosis of acute AMR vs accommodation and subsequent patient-tailored immunosuppression in ABOi KT.

An in vitro model of antibody-mediated injury to glomerular endothelial cells: Upregulation of MHC class II and adhesion molecules

Chronic active antibody-mediated rejection is a major cause of allograft failure in kidney transplantation. Microvascular inflammation and transplant glomerulopathy are defining pathologic features of chronic active antibody-mediated rejection and are associated with allograft failure. However, the mechanisms of leukocyte infiltration and glomerular endothelial cell injury remain unclear. We hypothesized MHC class II ligation on glomerular endothelial cells (GEnC) would result in upregulation of adhesion molecules and production of chemoattractants. A model of endothelial cell activation in the presence of antibodies to MHC classes I and II was used to determine the expression of adhesion molecules and chemokines. Murine GEnC were activated with IFNγ, which upregulated gene expression of β2-microglobulin (MHC class I), ICAM1, VCAM1, CCL2, CCL5, and IL-6. IFNγ stimulation of GEnC increased surface expression of MHC class I, MHC class II, ICAM1, and VCAM1. Incubation with antibodies directed at MHC class I or class II did not further enhance adhesion molecule expression. Multispectral imaging flow cytometry and confocal microscopy demonstrated MHC molecules co-localized with the adhesion molecules ICAM1 and VCAM1 on the GEnC surface. GEnC secretion of chemoattractants, CCL2 and CCL5, was increased by IFNγ stimulation. CCL2 production was further enhanced by incubation with sensitized plasma. Endothelial activation induces de novo expression of MHC class II molecules and increases surface expression of MHC class I, ICAM1 and VCAM1, which are all co-localized together. Maintaining the integrity and functionality of the glomerular endothelium is necessary to ensure survival of the allograft. IFNγ stimulation of GEnC propagates an inflammatory response with production of chemokines and co-localization of MHC and adhesion molecules on the GEnC surface, contributing to endothelial cell function as antigen presenting cells and an active player in allograft injury.

WNT pathway signaling is associated with microvascular injury and predicts kidney transplant failure

Microvascular injury is associated with accelerated kidney transplant dysfunction and allograft failure. Molecular pathology can identify new mechanisms of microvascular injury while improving on the diagnostic and prognostic capabilities of traditional histology. We conducted a case-control study of archived kidney biopsy specimens stored up to 10 years with microvascular injury (n = 50) compared with biopsy specimens without histologic injury (n = 45) from patients of similar age, race, and sex. We measured WNT gene expression with a multiplex quantification platform by using digital barcoding, given the importance of WNT reactivation to the response to wounding in the kidney microvasculature and other compartments. Of 210 genes from a commercial WNT panel, 71 were associated with microvascular injury and 79 were associated with allograft failure, with considerable overlap of genes between each set. Molecular pathology identified 46 biopsy specimens with molecular evidence of microvascular injury; 18 (39%) were either C4d negative, donor-specific antibody negative, or had no microvascular injury by histology. The majority of cases with molecular evidence of microvascular injury had poor long-term outcomes. We identified novel WNT pathway genes associated with microvascular injury and allograft failure in residual clinical biopsy specimens obtained up to 10 years earlier. Further mechanistic studies may identify the WNT pathway as a new diagnostic and therapeutic target.

Markers of graft microvascular endothelial injury may identify harmful donor-specific anti-HLA antibodies and predict kidney allograft loss

Graft microvasculature is a major target of donor-specific antibodies (DSA) and endothelial damage is direct evidence of antibody-mediated rejection (ABMR). Using immunohistochemistry, we analyzed the expression of three microvascular endothelial activation markers (fascin, vimentin, and hsp47), suggestive of endothelial-to-mesenchymal transition (EndMT) in 351 graft biopsies from 248 kidney recipients, with concomitant screening of circulating antihuman leukocyte antigen (HLA) DSA at the time of the biopsy. The factors associated with EndMT marker expression were DSA and the presence of microvascular inflammation (MI). EndMT expressing grafts had significantly more allograft loss compared to EndMT negative grafts (P < .0001). The expression of EndMT markers positively correlated with anti-HLA DSA class II mean fluorescence intensity (MFI) levels and especially identified DQ and DR antibodies as being more closely associated with microvascular injury. Moreover, only DSA linked to positive EndMT score affected allograft survival, regardless of DSA MFI levels or presence of C4d deposition. Thus, EndMT markers could represent a clinically relevant tool for early identification of ongoing endothelial injury, harmful DSA, and patients at high risk for allograft failure.

Outstanding questions in transplantation: B cells, alloantibodies, and humoral rejection

Over the past three decades, improved immunosuppression has significantly reduced T cell-mediated acute rejection rates, but long-term graft survival rates have seen only marginal improvement. The cause of late graft loss has been under intense investigation, and chronic antibody-mediated rejection (AMR) has been identified as one of the leading causes, thus providing a strong rationale for basic science investigation into donor-specific B cells and antibodies in transplantation and ways to mitigate their pathogenicity. In 2018, the American Society of Transplantation launched a community-wide online discussion of Outstanding Questions in Transplantation, and the topic of B cell biology and donor-specific antibody prevention emerged as a major area of interest to the community, leading to a highly engaged dialogue, with comments from basic and translational scientists as well as physicians (http://community.myast.org/communities/community-home/digestviewer). We have summarized this discussion from a bedside to bench perspective and have organized this review into outstanding questions within the paradigm that AMR is a leading cause of graft loss in the clinic, and points of view that challenge aspects of this paradigm. We also highlight opportunities for basic and translational scientists to contribute to the resolution of these questions, mapping important future directions for the transplant research field.

A urinary Common Rejection Module (uCRM) score for non-invasive kidney transplant monitoring

A Common Rejection Module (CRM) consisting of 11 genes expressed in allograft biopsies was previously reported to serve as a biomarker for acute rejection (AR), correlate with the extent of graft injury, and predict future allograft damage. We investigated the use of this gene panel on the urine cell pellet of kidney transplant patients. Urinary cell sediments collected from patients with biopsy-confirmed acute rejection, borderline AR (bAR), BK virus nephropathy (BKVN), and stable kidney grafts with normal protocol biopsies (STA) were analyzed for expression of these 11 genes using quantitative polymerase chain reaction (qPCR). We assessed these 11 CRM genes for their abundance, autocorrelation, and individual expression levels. Expression of 10/11 genes were elevated in AR when compared to STA. Psmb9 and Cxcl10could classify AR versus STA as accurately as the 11-gene model (sensitivity = 93.6%, specificity = 97.6%). A uCRM score, based on the geometric mean of the expression levels, could distinguish AR from STA with high accuracy (AUC = 0.9886) and correlated specifically with histologic measures of tubulitis and interstitial inflammation rather than tubular atrophy, glomerulosclerosis, intimal proliferation, tubular vacuolization or acute glomerulitis. This urine gene expression-based score may enable the non-invasive and quantitative monitoring of AR.

Immunomics of Renal Allograft Acute T Cell-Mediated Rejection Biopsies of Tacrolimus- and Belatacept-Treated Patients

Supplemental digital content is available in the text.

Background

Belatacept-based therapy in kidney transplant recipient has been shown to increase long-term renal allograft and patient survival compared with calcineurin inhibitor–based therapy, however, with an increased risk of acute T cell-mediated rejection (aTCMR). An improved understanding of costimulation blockade-resistant rejections could lead to a more personalized approach to belatacept therapy. Here, immunomic profiles of aTCMR biopsies of patients treated with either tacrolimus or belatacept were compared.

Methods

Formalin-fixed paraffin-embedded renal transplant biopsies were used for immunohistochemistry and gene expression analysis using the innovative NanoString technique. To validate NanoString, transcriptomic profiles of patients with and without biopsy-proven aTCMR were compared. Biopsies from 31 patients were studied: 14 tacrolimus-treated patients with aTCMR, 11 belatacept-treated patients with aTCMR, and 6 controls without rejection.

Results

A distinct pattern was seen in biopsies with aTCMR compared to negative controls: 78 genes had a higher expression in the aTCMR group (false discovery rate P value <.05 to 1.42e–05). The most significant were T cell-associated genes (CD3, CD8, and CD4; P < 1.98e-04), γ-interferon-inducible genes (CCL5, CXCL9, CXCL11, CXCL10, TBX21; P < 1.33e-04) plus effector genes (GNLY, GZMB, ITGAX; P < 2.82e-03). Immunophenotypical analysis of the classic immune markers of the innate and adaptive immune system was comparable between patients treated with either tacrolimus or belatacept. In addition, the transcriptome of both groups was not significantly different.

Conclusions

In this small pilot study, no difference was found in immunomics of aTCMR biopsies of tacrolimus- and belatacept-treated patients. This suggests that clinically diagnosed aTCMR reflects a final common pathway of allorecognition which is unaffected by the type of immunosuppressive therapy.

Micro RNA 146a-5p expression in Kidney transplant recipients with delayed graft function

Introduction:

The development of novel non-invasive biomarkers of kidney graft dysfunction, especially in the course of the delayed graft function period would be an important step forward in the clinical practice of kidney transplantation.

Methods:

We evaluated by RT-PCR the expression of miRNA-146 to -5p ribonucleic micro-acids (miRNAs) in the peripheral blood and renal tissue obtained from kidney transplant recipients who underwent a surveillance graft biopsy during the period of delayed graft function.

Results:

In biopsy samples, the expression of miR-146a-5p was significantly increased in the group of patients with delayed graft function (DGF) (n = 33) versus stables patients (STA) (n = 13) and patients with acute rejection (AR) (n = 9) (p = 0.008). In peripheral blood samples, a non-significant increase of miR-146a-5p expression was found in the DGF group versus STA and AR groups (p = 0.083). No significant correlation was found between levels of expression in biopsy and plasma. ROC curve analysis revealed an AUC of 0.75 (95% CI: 0.62-0.88) for the renal tissue expression and 0.67 (95% CI 0.52-0.81) for the peripheral blood expression.

Conclusion:

We conclude that miR-146a-5p expression has a distinct pattern in the renal tissue and perhaps in the peripheral blood in the setting of DGF. Further refinements and strategies for studies should be developed in the field of non-invasive molecular diagnosis of kidney graft dysfunction.

Gene expression profiles for predicting antibody‑mediated kidney allograft rejection: Analysis of GEO datasets

Antibody‑mediated rejections (AMRs) are one of the most challenging complications that result in the deterioration of renal allograft function and graft loss in a large majority of cases. The purpose of the present study was to characterize a meta‑signature of differentially expressed RNAs associated with AMR in cases of kidney transplantation. Gene Expression Omnibus (GEO) dataset searches up to September 11, 2017, using Medical Subject Heading terms and keywords associated with kidney transplantation, AMR and mRNA arrays were downloaded from the GEO dataset. Using a computational analysis, a meta‑signature was determined that characterized the significant intersection of differentially expressed genes (DEGs). Gene‑set and network analyses were also performed to identify gene sets and sub‑networks associated with the AMR‑related traits. A statistically significant mRNA meta‑signature of upregulated and downregulated gene expression levels that were significantly associated with AMR was identified. C‑X‑C motif chemokine ligand 10 (CXCL10), CXCL9 and guanylate binding protein 1 were the most significantly associated with AMR. DEGs were efficiently identified and were found to be able to predict the occurrence of AMR according to a meta‑analysis approach from publicly available datasets. These methods and results can be applied for a more accurate diagnosis of AMR in transplant cases.