Effectiveness of T cell-mediated rejection therapy: A systematic review and meta-analysis

Epithelial cell states associated with kidney and allograft injury

The kidney epithelium, with its intricate arrangement of highly specialized cell types, constitutes the functional core of the organ. Loss of kidney epithelium is linked to the loss of functional nephrons and a subsequent decline in kidney function. In kidney transplantation, epithelial injury signatures observed during post-transplantation surveillance are strong predictors of adverse kidney allograft outcomes. However, epithelial injury is currently neither monitored clinically nor addressed therapeutically after kidney transplantation. Several factors can contribute to allograft epithelial injury, including allograft rejection, drug toxicity, recurrent infections and postrenal obstruction. The injury mechanisms that underlie allograft injury overlap partially with those associated with acute kidney injury (AKI) and chronic kidney disease (CKD) in the native kidney. Studies using advanced transcriptomic analyses of single cells from kidney or urine have identified a role for kidney injury-induced epithelial cell states in exacerbating and sustaining damage in AKI and CKD. These epithelial cell states and their associated expression signatures are also observed in transplanted kidney allografts, suggesting that the identification and characterization of transcriptomic epithelial cell states in kidney allografts may have potential clinical implications for diagnosis and therapy.

CCR7 and CD48 as Predicted Targets in Acute Rejection Related to M1 Macrophage after Pediatric Kidney Transplantation

Background

Kidney transplantation (KT) is the best treatment for end-stage renal disease. Although long and short-term survival rates for the graft have improved significantly with the development of immunosuppressants, acute rejection (AR) remains a major risk factor attacking the graft and patients. The innate immune response plays an important role in rejection. Therefore, our objective is to determine the biomarkers of congenital immunity associated with AR after KT and provide support for future research.

Materials and Methods

A differential expression genes (DEGs) analysis was performed based on the dataset GSE174020 from the NCBI gene Expression Synthesis Database (GEO) and then combined with the GSE5099 M1 macrophage-related gene identified in the Molecular Signatures Database. We then identified genes in DEGs associated with M1 macrophages defined as DEM1Gs and performed gene ontology (GO) and Kyoto Encyclopedia of Genomes (KEGG) enrichment analysis. Cibersort was used to analyze the immune cell infiltration during AR. At the same time, we used the protein-protein interaction (PPI) network and Cytoscape software to determine the key genes. Dataset, GSE14328 derived from pediatric patients, GSE138043 and GSE9493 derived from adult patients, were used to verify Hub genes. Additional verification was the rat KT model, which was used to perform HE staining, immunohistochemical staining, and Western Blot. Hub genes were searched in the HPA database to confirm their expression. Finally, we construct the interaction network of transcription factor (TF)-Hub genes and miRNA-Hub genes.

Results

Compared to the normal group, 366 genes were upregulated, and 423 genes were downregulated in the AR group. Then, 106 genes related to M1 macrophages were found among these genes. GO and KEGG enrichment analysis showed that these genes are mainly involved in cytokine binding, antigen binding, NK cell-mediated cytotoxicity, activation of immune receptors and immune response, and activation of the inflammatory NF-κB signaling pathway. Two Hub genes, namely CCR7 and CD48, were identified by PPI and Cytoscape analysis. They have been verified in external validation sets, originated from both pediatric patients and adult patients, and animal experiments. In the HPA database, CCR7 and CD48 are mainly expressed in T cells, B cells, macrophages, and tissues where these immune cells are distributed. In addition to immunoinfiltration, CD4+T, CD8+T, NK cells, NKT cells, and monocytes increased significantly in the AR group, which was highly consistent with the results of Hub gene screening. Finally, we predicted that 19 TFs and 32 miRNAs might interact with the Hub gene.

Conclusions

Through a comprehensive bioinformatic analysis, our findings may provide predictive and therapeutic targets for AR after KT.

European Survey on Clinical Practice of Detecting and Treating T-Cell Mediated Kidney Transplant Rejection

The KDIGO guideline for acute rejection treatment recommends use of corticosteroids and suggests using lymphocyte-depleting agents as second line treatment. Aim of the study was to determine the current practices of detection and treatment of TCMR of kidney allografts amongst European kidney transplant centres. An invitation was sent through ESOT/EKITA newsletters and through social media to transplant professionals in Europe for taking part in the survey. A total of 129 transplant professionals responded to the survey. There was equal representation of small and large sized transplant centres. The majority of centres treat borderline changes (BL) and TCMR (Grade IA-B, IIA-B) in indication biopsies and protocol biopsies with corticosteroids as first line treatment. Thymoglobulin is used mainly as second line treatment for TCMR Grade IA-B (80%) and TCMR IIA-B (85%). Treatment success is most often evaluated within one month of therapy. There were no differences observed between the large and small centres for the management of TCMR. This survey highlights the common practices and diversity in clinics for the management of TCMR in Europe. Testing new therapies for TCMR should be in comparison to the current standard of care in Europe. Better consensus on treatment success is crucial for robust study designs.

Emerging phenotypes in kidney transplant rejection

PURPOSE OF REVIEW

This review focuses on more recently emerging rejection phenotypes in the context of time post transplantation and the resulting differential diagnostic challenges. It also discusses how novel ancillary diagnostic tools can potentially increase the accuracy of biopsy-based rejection diagnosis.

RECENT FINDINGS

With advances in reducing immunological risk at transplantation and improved immunosuppression treatment renal allograft survival improved. However, allograft rejection remains a major challenge and represent a frequent course for allograft failure. With prolonged allograft survival, novel phenotypes of rejection are emerging, which can show complex overlap and transition between cellular and antibody-mediated rejection mechanisms as well as mixtures of acute/active and chronic diseases. With the emerging complexity in rejection phenotypes, it is crucial to achieve diagnostic accuracy in the individual patient.

SUMMARY

The prospective validation and adoption of novel molecular and computational diagnostic tools into well defined and appropriate clinical context of uses will improve our ability to accurately diagnose, stage, and grade allograft rejection.

Urine CXCL10 as a biomarker in kidney transplantation

PURPOSE OF REVIEW

Urine CXCL10 is a promising biomarker for posttransplant renal allograft monitoring but is currently not widely used for clinical management.

RECENT FINDINGS

Large retrospective studies and data from a prospective randomized trial as well as a prospective cohort study demonstrate that low urine CXCL10 levels are associated with a low risk of rejection and can exclude BK polyomavirus replication with high certainty. Urine CXCL10 can either be used as part of a multiparameter based risk assessment tool, or as an individual biomarker taking relevant confounders into account. A novel Luminex-based CXCL10 assay has been validated in a multicenter study, and proved to be robust, reproducible, and accurate.

SUMMARY

Urine CXCL10 is a well characterized inflammation biomarker, which can be used to guide performance of surveillance biopsies. Wide implementation into clinical practice depends on the availability of inexpensive, thoroughly validated assays with approval from regulatory authorities.

Economic and humanistic burden in kidney transplant rejection: a literature review

INTRODUCTION

Antibody-mediated rejection (ABMR) is a major cause of late kidney allograft failure, but its economic and humanistic impacts have not been well-characterized in the literature.

AREAS COVERED

We reviewed available literature on economic burden (costs and healthcare resource use) and humanistic burden (health-related quality of life impacts [HRQOL] and utility estimates) in patients diagnosed with kidney transplant rejection; ABMR-specific studies were of particular interest. In total, 21 publications reporting economic and humanistic burden were included in the review; 9 of these reported ABMR-specific outcomes. The reviewed studies consistently showed a greater burden associated with ABMR-related transplant rejection than with non-ABMR transplant rejection.

EXPERT OPINION

Evidence suggests greater economic burden and increased HRQOL impairment with ABMR-related kidney transplant rejection relative to non-ABMR, although small sample sizes and missing definitions for ABMR make meaningful comparisons between studies challenging. Because no International Classification of Diseases (ICD)-10 codes currently describe the etiologies of transplant rejection, it is difficult to characterize the burden of distinct types of transplant rejection. The paucity of high-quality data on the burden of ABMR in kidney transplant rejection demonstrates the need for more etiology-centric ICD-10 codes.

The Banff 2022 Kidney Meeting Work Plan: Data-driven refinement of the Banff Classification for renal allografts

The XVIth Banff Meeting for Allograft Pathology was held in Banff, Alberta, Canada, from September 19 to 23, 2022, as a joint meeting with the Canadian Society of Transplantation. In addition to a key focus on the impact of microvascular inflammation and biopsy-based transcript analysis on the Banff Classification, further sessions were devoted to other aspects of kidney transplant pathology, in particular T cell-mediated rejection, activity and chronicity indices, digital pathology, xenotransplantation, clinical trials, and surrogate endpoints. Although the output of these sessions has not led to any changes in the classification, the key role of Banff Working Groups in phrasing unanswered questions, and coordinating and disseminating results of investigations addressing these unanswered questions was emphasized. This paper summarizes the key Banff Meeting 2022 sessions not covered in the Banff Kidney Meeting 2022 Report paper and also provides an update on other Banff Working Group activities relevant to kidney allografts.

Circulating T cell specific extracellular vesicle profiles in cardiac allograft acute cellular rejection

There is a critical need for biomarkers of acute cellular rejection (ACR) in organ transplantation. We hypothesized that ACR leads to changes in donor-reactive T cell small extracellular vesicle (sEV) profiles in transplant recipient circulation that match the kinetics of alloreactive T cell activation. In rodent heart transplantation, circulating T cell sEV quantities (P < .0001) and their protein and mRNA cargoes showed time-specific expression of alloreactive and regulatory markers heralding early ACR in allogeneic transplant recipients but not in syngeneic transplant recipients. Next generation sequencing of their microRNA cargoes identified novel candidate biomarkers of ACR, which were validated by stem loop quantitative reverse transcription polymerase chain reaction (n = 10). Circulating T cell sEVs enriched from allogeneic transplant recipients mediated targeted cytotoxicity of donor cardiomyocytes by apoptosis assay (P < .0001). Translation of the concept and EV methodologies to clinical heart transplantation demonstrated similar upregulation of circulating T cell sEV profiles at time points of grade 2 ACR (n = 3 patients). Furthermore, T cell receptor sequencing of T cell sEV mRNA cargo demonstrated expression of T cell clones with intact complementarity determining region 3 signals. These data support the diagnostic potential of T cell sEVs as noninvasive biomarker of ACR and suggest their potential functional roles.

Follow-up biopsies identify high rates of persistent rejection in pediatric kidney transplant recipients after treatment of T cell-mediated rejection

BACKGROUND

Incomplete resolution of T cell-mediated rejection (TCMR) after treatment may not be detected with serum creatinine monitoring and is associated with donor-specific antibodies and chronic rejection. We evaluate the utility of follow-up biopsies (FUB) to identify and characterize rates of persistent TCMR after treatment in pediatric kidney transplant patients.

METHODS

Patients from two pediatric transplant centers performing standard of care FUB at 1.5-2 months after treatment for TCMR were included. FUB were evaluated for extent of rejection resolution (complete vs. incomplete) and grade. Clinical data at time of FUB and later were reported, where available.

RESULTS

Fifty-eight patients underwent FUB, at mean of 1.7 months (SD 0.7) post-index biopsy. Rejection grade on index biopsy was Banff borderline (≥i1t1 and

CONCLUSIONS

FUB were effective at detecting persistent rejection, which was common among pediatric transplant patients after standard TCMR treatment. Until more effective rejection treatments or sensitive biomarkers are available, FUB may be effectively utilized to identify patients with ongoing rejection who would benefit from further treatment.

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Key Words

• biopsy
• pediatric
• rejection

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MESH Headings

• Humans
• Child
• Kidney Transplantation/adverse effects
• T-Lymphocytes
• Follow-Up Studies
• Biopsy
• Treatment Outcome
• Transplant Recipients
• Graft Rejection
• Kidney/pathology

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Grants

• R01 DK126807 NIDDK NIH HHS

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Affiliation(s)

Adina Landsberg Department of Medicine, University of Calgary, Calgary, AB, Canada
S. Sikandar Raza Department of Pediatrics, University of Alabama Heersink School of Medicine, Birmingham, AL, United States
Michael E. Seifert Department of Pediatrics, University of Alabama Heersink School of Medicine, Birmingham, AL, United States
Tom D. Blydt-Hansen BC Children’s Hospital, Division of Nephrology, Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada

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Cellular Immunobiology and Molecular Mechanisms in Alloimmunity-Pathways of Immunosuppression

Current maintenance immunosuppression commonly comprises a synergistic combination of tacrolimus as calcineurin inhibitor (CNI), mycophenolic acid, and glucocorticoids. Therapy is often individualized by steroid withdrawal or addition of belatacept or inhibitors of the mechanistic target of rapamycin. This review provides a comprehensive overview of their mode of action, focusing on the cellular immune system. The main pharmacological action of CNIs is suppression of the interleukin-2 pathway that leads to inhibition of T cell activation. Mycophenolic acid inhibits the purine pathway and subsequently diminishes T and B cell proliferation but also exerts a variety of effects on almost all immune cells, including inhibition of plasma cell activity. Glucocorticoids exert complex regulation via genomic and nongenomic mechanisms, acting mainly by downregulating proinflammatory cytokine signatures and cell signaling. Belatacept is potent in inhibiting B/T cell interaction, preventing formation of antibodies; however, it lacks the potency of CNIs in preventing T cell-mediated rejections. Mechanistic target of rapamycin inhibitors have strong antiproliferative activity on all cell types interfering with multiple metabolic pathways, partly explaining poor tolerability, whereas their superior effector T cell function might explain their benefits in the case of viral infections. Over the past decades, clinical and experimental studies provided a good overview on the underlying mechanisms of immunosuppressants. However, more data are needed to delineate the interaction between innate and adaptive immunity to better achieve tolerance and control of rejection. A better and more comprehensive understanding of the mechanistic reasons for failure of immunosuppressants, including individual risk/benefit assessments, may permit improved patient stratification.

Early conversion to belatacept-based immunosuppression regimen promotes improved long-term renal graft function in kidney transplant recipients

BACKGROUND

Belatacept has been demonstrated as an effective alternative immunosuppressant in kidney transplant recipients. This study focuses on outcomes of early and late conversion to Belatacept-based immunosuppression after kidney transplant.

MATERIALS AND METHODS

This retrospective analysis of a prospectively collected database included all adult kidney transplants patients at SUNY Upstate Medical Hospital from 1 January 2014 to 30 December 2022. Early conversion was defined as all conversions done at <6 months after kidney transplantation, and late conversion to belatacept was defined as conversion at >6 months after kidney transplantation.

RESULTS

Out of 61 patients included in this study, 33 patients (54%) were in the early conversion group, and 28 patients (46%) were in the late conversion group. The mean eGFR in the early conversion group was 26.73 ± 16.26 ml/min/1.73 m2 before conversion to belatacept, which improved to 45.3 ± 21.01 ml/min/1.73 m2 at one-year post-conversion (p = 0.0006). Furthermore, eGFR changes in the late conversion group were insignificant, with 46.30 ± 15.65 ml/min/1.73 m2 before conversion to belatacept, and 44.76 ± 22.91 ml/min/1.73 m2 after one year of follow-up (p = 0.72). All four biopsy-proven allograft rejections in the early conversion group were acute T-cell-mediated rejections (ATMR). In the late conversion group, out of three biopsy-proven rejections, one was chronic antibody-mediated rejection (CAMR), one was ATMR, and one was mixed ATMR/CAMR. All four patients with ATMR rejection received mycophenolic acid (MPA) as part of their immunosuppressive regimen, and none received tacrolimus. The one-year post-conversion allograft survival rate in early and late conversion groups was 100%. However, the one-year post-conversion patient survival rate was 90.9% in the early conversion group and 100% in the late conversion group (P = 0.11).

CONCLUSIONS

Early post-transplant conversion to belatacept can improve the eGFR more meaningful when compared to late conversion. Patients who receive belatacept and MPA rather than tacrolimus may have increased rates of T-cell-mediated rejection.

Randomized Trial to Assess the Clinical Utility of Renal Allograft Monitoring by Urine CXCL10 Chemokine

SIGNIFICANCE STATEMENT

This study is the first randomized controlled trial to investigate the clinical utility of a noninvasive monitoring biomarker in renal transplantation. Although urine CXCL10 monitoring could not demonstrate a beneficial effect on 1-year outcomes, the study is a rich source for future design of trials aiming to explore the clinical utility of noninvasive biomarkers. In addition, the study supports the use of urine CXCL10 to assess the inflammatory status of the renal allograft.

BACKGROUND

Urine CXCL10 is a promising noninvasive biomarker for detection of renal allograft rejection. The aim of this study was to investigate the clinical utility of renal allograft monitoring by urine CXCL10 in a randomized trial.

METHODS

We stratified 241 patients, 120 into an intervention and 121 into a control arm. In both arms, urine CXCL10 levels were monitored at three specific time points (1, 3, and 6 months post-transplant). In the intervention arm, elevated values triggered performance of an allograft biopsy with therapeutic adaptations according to the result. In the control arm, urine CXCL10 was measured, but the results concealed. The primary outcome was a combined end point at 1-year post-transplant (death-censored graft loss, clinical rejection between month 1 and 1-year, acute rejection in 1-year surveillance biopsy, chronic active T-cell-mediated rejection in 1-year surveillance biopsy, development of de novo donor-specific HLA antibodies, or eGFR <25 ml/min).

RESULTS

The incidence of the primary outcome was not different between the intervention and the control arm (51% versus 49%; relative risk (RR), 1.04 [95% confidence interval, 0.81 to 1.34]; P = 0.80). When including 175 of 241 (73%) patients in a per-protocol analysis, the incidence of the primary outcome was also not different (55% versus 49%; RR, 1.11 [95% confidence interval, 0.84 to 1.47]; P = 0.54). The incidence of the individual end points was not different as well.

CONCLUSIONS

This study could not demonstrate a beneficial effect of urine CXCL10 monitoring on 1-year outcomes (ClinicalTrials.gov_ NCT03140514 ).

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.

Multicenter Validation of a Urine CXCL10 Assay for Noninvasive Monitoring of Renal Transplants

BACKGROUND

Urine CXCL10 (C-X-C motif chemokine ligand 10, interferon gamma-induced protein 10 [IP10]) outperforms standard-of-care monitoring for detecting subclinical and early clinical T-cell-mediated rejection (TCMR) and may advance TCMR therapy development through biomarker-enriched trials. The goal was to perform an international multicenter validation of a CXCL10 bead-based immunoassay (Luminex) for transplant surveillance and compare with an electrochemiluminescence-based (Meso Scale Discovery [MSD]) assay used in transplant trials.

METHODS

Four laboratories participated in the Luminex assay development and evaluation. Urine CXCL10 was measured by Luminex and MSD in 2 independent adult kidney transplant trial cohorts (Basel and TMCT04). In an independent test and validation set, a linear mixed-effects model to predict (log 10 -transformed) MSD CXCL10 from Luminex CXCL10 was developed to determine the conversion between assays. Net reclassification was determined after mathematical conversion.

RESULTS

The Luminex assay was precise, with an intra- and interassay coefficient of variation 8.1% and 9.3%; showed modest agreement between 4 laboratories (R 0.96 to 0.99, P < 0.001); and correlated with known CXCL10 in a single- (n = 100 urines, R 0.94 to 0.98, P < 0.001) and multicenter cohort (n = 468 urines, R 0.92, P < 0.001) but the 2 assays were not equivalent by Passing-Bablok regression. Linear mixed-effects modeling demonstrated an intercept of -0.490 and coefficient of 1.028, showing Luminex CXCL10 are slightly higher than MSD CXCL10, but the agreement is close to 1.0. After conversion of the biopsy thresholds, the decision to biopsy would be changed for only 6% (5/85) patients showing acceptable reclassification.

CONCLUSIONS

These data demonstrate this urine CXCL10 Luminex immunoassay is robust, reproducible, and accurate, indicating it can be readily translated into clinical HLA laboratories for serial posttransplant surveillance.

Transitional B cell cytokines risk stratify early borderline rejection after renal transplantation

Borderline rejection (BL) in renal transplantation is associated with decreased allograft survival, yet many patients with BL maintain stable graft function. Identifying patients with early BL at risk for shortened allograft survival would allow for timely targeted therapeutic intervention aimed at improving outcomes. 851/1187 patients transplanted between 2013-18 underwent early biopsy (0-4 mos). 217/851 (25%) had BL and were compared to 387/851 without significant inflammation (NI). Serial surveillance and for-cause biopsies and seven-year follow-up were used to evaluate histological and clinical progression. To identify high-risk patients, we examined clinical/histological parameters using regression and non-linear dimensionality reduction (tSNE) and a biomarker based on peripheral blood transitional-1 B cell (T1B) IL-10/TNFα ratio. Compared to NI, early BL was associated with increased progression to late acute rejection (AR; 5-12 mos), premature interstitial fibrosis and tubular atrophy (IFTA) and decreased seven-year graft survival. However, decreased graft survival was limited to BL patients who progressed to late AR or IFTA, and was not influenced by treatment. Although tSNE clustered patients into groups based on clinical factors, the ability of these factors to risk stratify BL patients was modest. In contrast, a low T1B IL-10/TNFα ratio at 3 months identified BL patients at high risk for progression to AR (ROC AUC 0.87) and poor 7-yr graft survival (52% vs. 92%, p=0.003), while BL patients with a high ratio had similar graft survival to patients with NI (91%, p=NS). Thus, progressive early allograft inflammation manifested as BL that progresses to late AR in the first post-transplant year represents a high-risk clinical state for poor allograft outcomes. Such high-risk status can be predicted by the T1B IL-10/TNFα ratio before irreversible scarring sets in, thus allowing timely risk stratification.

Approach to acute kidney injury following paediatric kidney transplant

PURPOSE OF REVIEW

In a child with evidence of acute kidney injury (AKI) following renal transplantation, it is important to quickly and accurately diagnose the cause to enable timely initiation of therapeutic interventions. The following article will discuss the differential diagnosis of acute graft dysfunction in paediatric kidney transplant recipients. This review will systematically guide the clinician through the common and less common causes and provide updates on current treatments.

RECENT FINDINGS

In patients with signs of graft dysfunction, rejection is an important cause to consider. Diagnosis of rejection relies on biopsy findings, an invasive and costly technique. Over the past 5 years, there has been a focus on noninvasive methods of diagnosing rejection, including serum and urinary biomarkers.

SUMMARY

This review discusses the differential diagnosis of acute graft dysfunction following transplant, with a focus on acute rejection, urinary tract infections and common viral causes, prerenal and postrenal causes, nephrotoxic medications, specifically calcineurin inhibitor toxicity, thrombotic microangiopathy and recurrence of the underlying disease. Each condition is discussed in detail, with a focus on clinical clues to the cause, incidence in the paediatric population, workup and treatment.

Challenges Posed by the Banff Classification: Diagnosis and Treatment of Chronic Active T-Cell-Mediated Rejection

The three primary sites of acute T-cell-mediated rejection (TCMR) in transplanted kidneys are the tubular epithelial cells, interstitium, and the vascular endothelial cells. The pathology of acute lesions is characterized by inflammatory cell infiltration; the final diagnosis suggested by the Banff 2019 classification is guided by grading of tubulitis (the t score), interstitial inflammation (the i score), and endarteritis (the v score). Consistent major issues when using the Banff classification are the etiological classifications of interstitial fibrosis and tubular atrophy (IFTA). From 2015 to 2019, technological advances (i.e., genetic analysis in paraffin sections) increased our understanding of IFTA status in patients with smoldering acute TCMR and the roles played by inflammatory cell infiltration (the i-IFTA score) and tubulitis (the t-IFTA score) in IFTA. These two scores were introduced when establishing the diagnostic criteria for chronic active TCMR. Despite the increase in complexity and the lack of a consensus treatment for chronic active TCMR, the Banff classification may evolve as new techniques (i.e., genetic analysis in paraffin sections and deep learning of renal pathology) are introduced. The Banff conference proceeded as follows. First, lesions were defined. Next, working groups were established to better understand the lesions and to derive better classification methods. Finally, the new Banff classification was developed. This approach will continue to evolve; the Banff classification will become a very useful diagnostic standard. This paper overviews the history of TCMR diagnosis using the Banff classification, and the clinical importance, treatment, and prospects for acute and chronic active TCMR.

The Histological Spectrum and Clinical Significance of T Cell-mediated Rejection of Kidney Allografts

T cell-mediated rejection (TCMR) remains a significant cause of long-term kidney allograft loss, either indirectly through induction of donor-specific anti-HLA alloantibodies or directly through chronic active TCMR. Whether found by indication or protocol biopsy, Banff defined acute TCMR should be treated with antirejection therapy and maximized maintenance immunosuppression. Neither isolated interstitial inflammation in the absence of tubulitis nor isolated tubulitis in the absence of interstitial inflammation results in adverse outcomes, and neither requires antirejection treatment. RNA gene expression analysis of biopsy material may supplement conventional histology, especially in ambiguous cases. Lesser degrees of tubular and interstitial inflammation (Banff borderline) may portend adverse outcomes and should be treated when found on an indication biopsy. Borderline lesions on protocol biopsies may resolve spontaneously but require close follow-up if untreated. Following antirejection therapy of acute TCMR, surveillance protocol biopsies should be considered. Minimally invasive blood-borne assays (donor-derived cell-free DNA and gene expression profiling) are being increasingly studied as a means of following stable patients in lieu of biopsy. The clinical benefit and cost-effectiveness require confirmation in randomized controlled trials. Treatment of acute TCMR is not standardized but involves bolus corticosteroids with lymphocyte depleting antibodies for severe, refractory, or relapsing cases. Arteritis may be found with acute TCMR, active antibody-mediated rejection, or mixed rejections and should be treated accordingly. The optimal treatment ofchronic active TCMR is uncertain. Randomized controlled trials are necessary to optimally define therapy.

Long-term immunological outcomes of early subclinical inflammation on surveillance kidney allograft biopsies

The long-term impact of early subclinical inflammation (SCI) through surveillance biopsy has not been well studied. To do this, we recruited a prospective observational cohort that included 1000 sequential patients who received a kidney transplant from 2013-2017 at our center. A total of 586 patients who underwent a surveillance biopsy in their first year post-transplant were included after excluding those with clinical rejections, and those who were unable to undergo a surveillance biopsy. Patients were classified based on their biopsy findings: 282 with NSI (No Significant Inflammation) and 304 with SCI-T (SCI and Tubulitis) which was further subdivided into 182 with SC-BLR (Subclinical Borderline Changes) and 122 with SC-TCMR (Subclinical T Cell Mediated Rejection, Banff 2019 classification of 1A or more). We followed the clinical and immunological events including Clinical Biopsy Proven Acute Rejection [C-BPAR], long-term kidney function and death-censored graft loss over a median follow-up of five years. Episodes of C-BPAR were noted at a median of two years post-transplant. Adjusted odds of having a subsequent C-BPAR was significantly higher in the SCI-T group [SC-BLR and SC-TCMR] compared to NSI 3.8 (2.1-7.5). The adjusted hazard for death-censored graft loss was significantly higher with SCI-T compared to NSI [1.99 (1.04-3.84)]. Overall, SCI detected through surveillance biopsy within the first year post-transplant is a harbinger for subsequent immunological events and is associated with a significantly greater hazard for subsequent C-BPAR and death-censored graft loss. Thus, our study highlights the need for identifying patients with SCI through surveillance biopsy and develop strategies to prevent further alloimmune injuries.

The number of donor HLA-derived T cell epitopes available for indirect antigen presentation determines the risk for vascular rejection after kidney transplantation

The role of the indirect T-cell recognition pathway of allorecognition in acute T cell-mediated rejection (aTCMR) is not well defined. The amount of theoretical T-cell epitopes available for indirect allorecognition can be quantified for donor-recipient combinations by the Predicted Indirectly ReCognizable HLA Epitopes algorithm (PIRCHE-II). The PIRCHE-II score was calculated for 688 donor kidney-recipient combinations and associated with the incidence of first-time diagnosed cases of TCMR. A diagnosis of TCMR was made in 182 cases; 121 cases of tubulo-interstitial rejection cases (79 cases of borderline TCMR, 42 cases of TCMR IA-B) and 61 cases of vascular TCMR (TCMR II-III). The PIRCHE-II score for donor HLA-DR/DQ (PIRCHE-II DR/DQ) was highly associated with vascular rejection. At one year after transplantation, the cumulative percentage of recipients with a vascular rejection was 12.7%, 8.6% and 2.1% within respectively the high, medium and low tertile of the PIRCHE-II DR/DQ score (p&lt;0.001). In a multivariate regression analysis this association remained significant (p&lt;0.001 for PIRCHE-II DR/DQ tertiles). The impact of a high PIRCHE-II DR/DQ score was mitigated by older recipient age and a living donor kidney. In conclusion, indirect antigen presentation of donor HLA-peptides may significantly contribute to the risk for acute vascular rejection.

Biomarkers of alloimmune events in pediatric kidney transplantation

Alloimmune events such as the development of de novo donor-specific antibody (dnDSA), T cell-mediated rejection (TCMR), and antibody-mediated rejection (ABMR) are the primary contributors to kidney transplant failure in children. For decades, a creatinine-based estimated glomerular filtration rate (eGFR) has been the non-invasive gold standard biomarker for detecting clinically significant alloimmune events, but it suffers from low sensitivity and specificity, especially in smaller children and older allografts. Many clinically "stable" children (based on creatinine) will have alloimmune events known as "subclinical acute rejection" (based on biopsy) that merely reflect the inadequacy of creatinine-based estimates for alloimmune injury rather than a distinct phenotype from clinical rejection with allograft dysfunction. The poor biomarker performance of creatinine leads to many unnecessary surveillance and for-cause biopsies that could be avoided by integrating non-invasive biomarkers with superior sensitivity and specificity into current clinical paradigms. In this review article, we will present and appraise the current state-of-the-art in monitoring for alloimmune events in pediatric kidney transplantation. We will first discuss the current clinical standards for assessing the presence of alloimmune injury and predicting long-term outcomes. We will review principles of biomarker medicine and the application of comprehensive metrics to assess the performance of a given biomarker against the current gold standard. We will then highlight novel blood- and urine-based biomarkers (with special emphasis on pediatric biomarker studies) that have shown superior diagnostic and prognostic performance to the current clinical standards including creatinine-based eGFR. Finally, we will review some of the barriers to translating this research and implementing emerging biomarkers into common clinical practice, and present a transformative approach to using multiple biomarker platforms at different times to optimize the detection and management of critical alloimmune events in pediatric kidney transplant recipients.