The Banff 2019 Kidney Meeting Report (I): Updates on and clarification of criteria for T cell- and antibody-mediated rejection

Advancing the application of the analytical renal pathology system in allograft IgA nephropathy patients

BACKGROUND

The analytical renal pathology system (ARPS) based on convolutional neural networks has been used successfully in native IgA nephropathy (IgAN) patients. Considering the similarity of pathologic features, we aim to evaluate the performance of the ARPS in allograft IgAN patients and broaden its implementation.

METHODS

Biopsy-proven allograft IgAN patients from two different centers were enrolled for internal and external validation. We implemented the ARPS to identify glomerular lesions and intrinsic glomerular cells, and then evaluated its performance. Consistency between the ARPS and pathologists was assessed using intraclass correlation coefficients. The association of digital pathological features with clinical and pathological data was measured. Kaplan-Meier survival curve and cox proportional hazards model were applied to investigate prognosis prediction.

RESULTS

A total of 56 biopsy-proven allograft IgAN patients from the internal center and 17 biopsy-proven allograft IgAN patients from the external center were enrolled in this study. The ARPS was successfully applied to identify the glomerular lesions (F1-score, 0.696-0.959) and quantify intrinsic glomerular cells (F1-score, 0.888-0.968) in allograft IgAN patients rapidly and precisely. Furthermore, the mesangial hypercellularity score was positively correlated with all mesangial metrics provided by ARPS [Spearman's correlation coefficient (r), 0.439-0.472, and all p values < 0.001]. Besides, a higher allograft survival was noticed among patients in the high-level groups of the maximum and ratio of endothelial cells, as well as the maximum and density of podocytes.

CONCLUSION

We propose that the ARPS could be implemented in future clinical practice with outstanding capability.

Kidney injury associated with fosravuconazole L-lysine ethanolate

BACKGROUND

Fosravuconazole L-lysine ethanolate (F-RVCZ) is a prodrug of ravuconazole and a triazole antifungal drug used for the treatment of onychomycosis. It has been reported in previous studies that the kidney injury caused by F-RVCZ is 1% or less.

METHODS

Serum creatinine levels were compared, and glomerular filtration rate and urine protein were estimated before and after starting the administration of F-RVCZ, as well as after the end of the administration period. The cause of kidney injury was investigated using renal pathology, and risk factors were also investigated.

RESULTS

F-RVCZ was administered to 46 patients. Ten of these patients were excluded because three were maintenance dialysis patients and seven were not measured for serum creatinine. Remaining 36 patients were included in the analyses. Kidney injury occurred in 27.8% of patients treated with F-RVCZ; this condition persisted in 10% of patients after the end of the administration period. No changes were observed in the urinalysis after the administration of F-RVCZ. A kidney biopsy was performed in one patient, but no lesions were found that could be the cause of kidney injury. Patients who developed kidney injury were significantly more likely to be receiving angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers (odds ratio 18.9, 95% confidential interval: 1.69-210, p = 0.0169).

CONCLUSION

Kidney injury is caused by F-RVCZ more frequently than previously reported, but the mechanism remains unclear.

Spatial Transcriptomic Signatures of Early Acute T Cell-mediated Rejection in Kidney Transplants

Background

Kidney transplantation significantly improves the quality of life for those with end-stage renal failure, yet allograft rejection resulting from immune cell interactions remains a persistent challenge. Although T cell-directed immunosuppressive drugs effectively contain graft rejection in most patients, a notable proportion still experiences acute T cell-mediated rejection (TCMR). Despite an emphasis on suppressing T cell-mediated immune responses, successful control over TCMR is not always achieved, suggesting the potential involvement of factors beyond T cells.

Methods

Biopsy samples from suspicious (borderline) for acute TCMR (borderline TCMR) and non-TCMR patients were obtained 9 d postsurgery, and spatial transcriptomics profiling was conducted using the GeoMx Digital Spatial Profiler platform. Regions of interest in the glomerulus and interstitium were selected on the basis of immunohistochemistry staining anti-CD3 to identify areas with T-lymphocyte infiltration. Differential gene expression analysis was performed using unpaired t tests.

Results

Unbiased clustering of transcriptional profiles across all regions of interest showed distinct transcriptional profiles between glomeruli and interstitium in non-TCMR samples, whereas borderline TCMR samples displayed no distinct transcriptional profiles between these regions. Contrary to the prevailing T cell-centric view, we observed pathways and genes associated with innate immunity-related inflammatory conditions expressed in glomerular regions of borderline TCMR biopsies. Immunofluorescence staining for CD68 confirmed the presence of macrophages in the glomeruli of the post-TCMR sample in a validation cohort, indicating macrophage involvement in the glomerular response after TCMR.

Conclusions

Activation of the innate immune response in borderline TCMR appears to impact not only the interstitium but also the glomerulus. Glomerulus-specific immune signatures suggest the role of the innate immune system in rejection. This nuanced understanding proposes the necessity for tailored therapeutic interventions targeting both innate and adaptive immune pathways to enhance transplant outcomes.

Application of spatial-omics to the classification of kidney biopsy samples in transplantation

Improvement of long-term outcomes through targeted treatment is a primary concern in kidney transplant medicine. Currently, the validation of a rejection diagnosis and subsequent treatment depends on the histological assessment of allograft biopsy samples, according to the Banff classification system. However, the lack of (early) disease-specific tissue markers hinders accurate diagnosis and thus timely intervention. This challenge mainly results from an incomplete understanding of the pathophysiological processes underlying late allograft failure. Integration of large-scale multimodal approaches for investigating allograft biopsy samples might offer new insights into this pathophysiology, which are necessary for the identification of novel therapeutic targets and the development of tailored immunotherapeutic interventions. Several omics technologies - including transcriptomic, proteomic, lipidomic and metabolomic tools (and multimodal data analysis strategies) - can be applied to allograft biopsy investigation. However, despite their successful application in research settings and their potential clinical value, several barriers limit the broad implementation of many of these tools into clinical practice. Among spatial-omics technologies, mass spectrometry imaging, which is under-represented in the transplant field, has the potential to enable multi-omics investigations that might expand the insights gained with current clinical analysis technologies.

Evaluation of non-invasive biomarkers of kidney allograft rejection in a prospective multicenter unselected cohort study (EU-TRAIN)

Non-invasive biomarkers are promising tools for improving kidney allograft rejection monitoring, but their clinical adoption requires more evidence in specifically designed studies. To address this unmet need, we designed the EU-TRAIN study, a large prospective multicentric unselected cohort funded by the European Commission. Here, we included consecutive adult patients who received a kidney allograft in nine European transplant centers between November 2018 and June 2020. We prospectively assessed gene expression levels of 19 blood messenger RNAs, four antibodies targeting non-human leukocyte antigen (HLA) endothelial antigens, together with circulating anti-HLA donor-specific antibodies (DSA). The primary outcome was allograft rejection (antibody-mediated, T cell-mediated, or mixed) in the first year post-transplantation. Overall, 412 patients were included, with 812 biopsies paired with a blood sample. CD4 gene expression was significantly associated with rejection, while circulating anti-HLA DSA had a significant association with allograft rejection and a strong association with antibody-mediated rejection. All other tested biomarkers, including AKR1C3, CD3E, CD40, CD8A, CD9, CTLA4, ENTPD1, FOXP3, GZMB, ID3, IL7R, MS4A1, MZB1, POU2AF1, POU2F1, TCL1A, TLR4, and TRIB1, as well as antibodies against angiotensin II type 1 receptor, endothelin 1 type A receptor, C3a and C5a receptors, did not show significant associations with allograft rejection. The blood messenger RNAs and non-HLA antibodies did not show an additional value beyond standard of care monitoring parameters and circulating anti-HLA DSA to predict allograft rejection in the first year post-transplantation. Thus, our results open avenues for specifically designed studies to demonstrate the clinical relevance and implementation of other candidate non-invasive biomarkers in kidney transplantation practice.

Denovo glomerulonephritis associated with IgA anti-GBM alloantibodies after kidney transplantation in Alport syndrome: A case report with diagnostic implications

Alport syndrome (AS) is a hereditary disorder caused by pathogenic variants in COL4A3, COL4A4, or COL4A5 genes expressing α3, α4, and α5 chains of basement membrane type IV collagen (COL4). The triple-helical α3α4α5(IV) protomer is a major component of the mature glomerular basement membrane (GBM) whose defective formation in AS leads to structural GBM disruption and kidney dysfunction, often resulting in kidney replacement therapy. A genetically intact renal graft exposes the immune system to a non-tolerized α3α4α5(IV) component and an alloimmune response eventually ensues. So far, only IgG alloantibodies reacting against COL4 have been reported in AS alloimmune responses. Here, we report alloimmune glomerulonephritis mediated by IgA antibodies against the non-collagenous C-terminal domain 1 of the α5(IV) chain in a patient with autosomal recessive AS following a second kidney transplantation. The patient presented a not previously described biallelic variant in the COL4A4 gene. Immunological, diagnostic, and clinical implications are discussed.

Pathophysiology of rejection in kidney transplantation

INTRODUCTION

Rejection remains a major obstacle to successful kidney transplantation. The complex pathophysiology of rejection depends on a fine-tuned interplay between the innate and adaptive immune systems.

AREAS COVERED

This review provides a comprehensive analysis of the pathophysiology of rejection of kidney grafts, performed through careful selection of most relevant papers available on the topic in the PubMed database. The two types of rejection usually observed at the kidney biopsy, i.e. cellular and humoral rejection, are described with an accurate outline of the biological processes that lead to their development.

EXPERT OPINION

The incidence of T-cell-mediated rejection is decreasing, and most cases promptly respond to appropriate immunosuppression. However, late diagnosis or incomplete response to treatment may have deleterious consequences in the long term. The main issue is represented by antibody-mediated rejection, which unsatisfactorily responds to aggressive immunosuppression, especially when diagnosed late. Prevention of acute ABMR rests on HLA-specific antibody detection prior to transplantation, adequate immunosuppression, and optimal patients' compliance. Late diagnosis and poor response to treatment inevitably lead to chronic ABMR, for which no therapies are currently available.

Nuclear factor of activated T cell cytoplasmic 1 (NFATc1) insertion gene polymorphism as a possible trigger in acute T cell-mediated rejection (aTCMR) after kidney transplantation

BACKGROUND

To investigate the potential regulatory role of gene insertion or deletion (in/del) polymorphism in the occurrence of acute T cell-mediated rejection (aTCMR) after kidney transplantation.

METHODS

We retrospectively analyzed the 5-year follow-up data of 133 recipients who underwent renal transplantation at the First Affiliated Hospital of Nanjing Medical University between February 1, 2010, and December 1, 2015. With target sequencing based on next-generation sequencing (NGS), tagger in/dels selection involved calculating the Hardy-Weinberg equilibrium (HWE), Minor Allele Frequency (MAF), and the linkage disequilibrium (LD) blocks. Significant in/dels associated with aTCMR were identified by intersecting the results obtained through analysis of covariance (ANCOVA) of clinical cofounders and model analysis in Rstudio using the "SNPassoc" package. Additionally, logistic models were employed to assess the associations between genotypes and the aTCMR occurrence in 5 years after surgery.

RESULTS

NFATc1 rs55741427 insertion was identified to be significantly associated with the post-surgery aTCMR(OR = 2.66, P < 0.001). We constructed a conclusive model containing the occurrence of delayed graft function (DGF) and the insertion polymorphism of rs55741427, showing a favorable predictive ability (AUC = 0.766) for aTCMR after surgery. Based on the receiver operating characteristic (ROC) curve, all cases were stratified into aTCMR high-risk and low-risk groups. Kaplan-Meier curves for two groups revealed that the aTCMR high-risk group exhibited a more unfavorable graft survival outcome (P = 0.0048).

CONCLUSION

Insertion mutation of rs55741427 was found to be statistically correlated with the post-surgery aTCMR during 5 years of follow-up. Our model identified DGF and insertion of rs55741427 as two crucial aTCMR-related hazards, and aTCMR high-risk group showed a worse graft prognosis.

Microvascular Inflammation of Kidney Allografts and Clinical Outcomes

BACKGROUND

The heterogeneous clinical presentation of graft microvascular inflammation poses a major challenge to successful kidney transplantation. The effect of microvascular inflammation on allograft outcomes is unclear.

METHODS

We conducted a cohort study that included kidney-transplant recipients from more than 30 transplantation centers in Europe and North America who had undergone allograft biopsy between 2004 and 2023. We integrated clinical and pathological data to classify biopsy specimens according to the 2022 Banff Classification of Renal Allograft Pathology, which includes two new diagnostic categories: probable antibody-mediated rejection and microvascular inflammation without evidence of an antibody-mediated response. We then assessed the association between the newly recognized microvascular inflammation phenotypes and allograft survival and disease progression.

RESULTS

A total of 16,293 kidney-transplant biopsy specimens from 6798 patients were assessed. We identified the newly recognized microvascular inflammation phenotypes in 788 specimens, of which 641 were previously categorized as specimens with no evidence of rejection. As compared with patients without rejection, the hazard ratio for graft loss was 2.1 (95% confidence interval [CI], 1.5 to 3.1) among patients with microvascular inflammation without evidence of an antibody-mediated response and 2.7 (95% CI, 2.2 to 3.3) among patients with antibody-mediated rejection. Patients with a diagnosis of probable antibody-mediated rejection had a higher risk of graft failure beyond year 5 after biopsy than those without rejection (hazard ratio, 1.7; 95% CI, 0.8 to 3.5). Patients with a diagnosis of either newly recognized microvascular inflammation phenotype had a higher risk of progression of transplant glomerulopathy during follow-up than patients without microvascular inflammation.

CONCLUSIONS

Microvascular inflammation in kidney allografts includes distinct phenotypes, with various disease progression and allograft outcomes. Our findings support the clinical use of additional rejection phenotypes to standardize diagnostics for kidney allografts. (Funded by OrganX. ClinicalTrials.gov number, NCT06496269.).

Active immunological participation and metabolic shutdown of kidney structural cells during kidney transplant rejection

Contrary to immune cells, the response of the kidney structural cells in rejection is less established. We performed single-cell RNA sequencing on 18 kidney transplant biopsies from 14 recipients. Single-cell RNA sequencing identified cells from the major compartments of the kidney, next to infiltrated immune cells. Endothelial cells from the glomerulus, peritubular capillaries and vasa recta showed upregulation of class I and II HLA genes, adhesion molecules and cytokines and chemokines, suggesting an active participation in the alloimmune process, with compartment-specific differences. Epithelial cells including proximal tubular, loop of Henle and collecting duct cells, also showed increased expression of immune genes. Strikingly, in proximal tubule cells a strong downregulation of energy metabolism upon inflammation was observed. There was a large overlap between the cell-specific expression changes upon alloimmune inflammation and those observed in two large micro-array biopsy cohorts. In conclusion, the kidney structural cells, being the main target of the alloimmune process, appear to actively contribute herein, enhancing the damaging effects of the infiltrating immune cells. In epithelial cells, a profound shutdown of metabolism was seen upon inflammation, which associated with poor kidney function. These observations highlight the critical role of the graft in triggering and sustaining rejection after transplantation.

Archetypal Analysis of Kidney Allograft Biopsies Using Next-generation Sequencing Technology

BACKGROUND

In kidney transplantation, molecular diagnostics may be a valuable approach to improve the precision of the diagnosis. Using next-generation sequencing (NGS), we aimed to identify clinically relevant archetypes.

METHODS

We conducted an Illumina bulk RNA sequencing on 770 kidney biopsies (540 kidney recipients) collected between 2006 and 2021 from 11 European centers. Differentially expressed genes were determined for 11 Banff lesions. An ElasticNet model was used for feature selection, and 4 machine learning classifiers were trained to predict the probability of presence of the lesions. NGS-based classifiers were used in an unsupervised archetypal analysis to different archetypes. The association of the archetypes with allograft survival was assessed using the iBox risk prediction score.

RESULTS

The ElasticNet feature selection reduced the number of the genes from a range of 859-10 830 to a range of 52-867 genes. NGS-based classifiers demonstrated robust performances (precision-recall area under the curves 0.708-0.980) in predicting the Banff lesions. Archetypal analysis revealed 8 distinct phenotypes, each characterized by distinct clinical, immunological, and histological features. Although the archetypes confirmed the well-defined Banff rejection phenotypes for T cell-mediated rejection and antibody-mediated rejection, equivocal histologic antibody-mediated rejection, and borderline diagnoses were reclassified into different archetypes based on their molecular signatures. The 8 NGS-based archetypes displayed distinct allograft survival profiles with incremental graft loss rates between archetypes, ranging from 90% to 56% rates 7 y after evaluation (P < 0.0001).

CONCLUSIONS

Using molecular phenotyping, 8 archetypes were identified. These NGS-based archetypes might improve disease characterization, reclassify ambiguous Banff diagnoses, and enable patient-specific risk stratification.

Immune Checkpoint Inhibitor Therapy for Kidney Transplant Recipients - A Review of Potential Complications and Management Strategies

Immune checkpoint inhibitor (ICI) therapy has enabled a paradigm shift in Oncology, with the treatment of metastatic cancer in certain tumor types becoming akin to the treatment of chronic disease. Kidney transplant recipients (KTR) are at increased risk of developing cancer compared to the general population. Historically, KTR were excluded from ICI clinical trials due to concern for allograft rejection and decreased anti-tumor efficacy. While early post-marketing data revealed an allograft rejection risk of 40%-50%, 2 recent small prospective trials have demonstrated lower rates of rejection of 0%-12%, suggesting that maintenance immunosuppression modification prior to ICI start modulates rejection risk. Moreover, objective response rates induced by ICI for the treatment of advanced or metastatic skin cancer, the most common malignancy in KTR, have been comparable to those achieved by immune intact patients. Non-invasive biomarkers may have a role in risk-stratifying patients before starting ICI, and monitoring for rejection, though allograft biopsy is required to confirm diagnosis. This clinically focused review summarizes current knowledge on complications of ICI use in KTR, including their mechanism, risk mitigation strategies, non-invasive biomarker use, approaches to treatment of rejection, and suggestions for future directions in research.

Pig-to-human kidney xenotransplants using genetically modified minipigs

This study develops an observational model to assess kidney function recovery and xenogeneic immune responses in kidney xenotransplants, focusing on gene editing and immunosuppression. Two brain-dead patients undergo single kidney xenotransplantation, with kidneys donated by minipigs genetically modified to include triple-gene knockouts (GGTA1, β4GalNT2, CMAH) and human gene transfers (hCD55 or hCD55/hTBM). Renal xenograft functions are fully restored; however, immunosuppression without CD40-CD154 pathway blockade is ineffective in preventing acute rejection by day 12. This rejection manifests as both T cell-mediated rejection and antibody-mediated rejection (AMR), confirmed by natural killer (NK) cell and macrophage infiltration in sequential xenograft biopsies. Despite donor pigs being pathogen free before transplantation, xenografts and recipient organs test positive for porcine cytomegalovirus/porcine roseolovirus (PCMV/PRV) by the end of the observation period, indicating reactivation and contributing to significant immunopathological changes. This study underscores the critical need for extended clinical observation and comprehensive evaluation using deceased human models to advance xenograft success.

Urinary Chemokines CXCL9 and CXCL10 Are Non-Invasive Biomarkers of Kidney Transplant Rejection

BACKGROUND Rejection is the main cause of kidney allograft failure, and kidney biopsy is the criterion standard method to diagnose it. However, non-invasive techniques to detect kidney transplant rejection are necessary. This study aimed to evaluate urinary chemokines CXCL9 and CXCL10 as potential biomarkers of kidney transplant rejection and to analyze chemokine association with allograft prognosis. MATERIAL AND METHODS We collected 117 urine samples from kidney transplant recipients undergoing allograft biopsy. CXCL9 and CXCL10 levels were measured by ELISA and the ratio to urine creatinine was calculated. Histology and other clinical data were collected from medical records. RESULTS The diagnostic performance of urinary CXCL9/cre in discriminating rejection from all other histological groups showed an ROC AUC value of 0.728 (95% CI 0.632-0.824, p<0.001), and a cut-off value 0.11 ng/mmol had the best sensitivity (76.9%) and specificity (73.1%). The ability of CXCL10/cre to discriminate transplant rejection from all other histological groups had ROC AUC value 0.73 (95% CI 0.63-0.84, P<0.001), the cut-off value 0.42 ng/mmol with best sensitivity (71.4%) and specificity (84.6%). CXCL9 and CXCL10 levels were also increased in patients with polyoma BK virus, recurrent AA amyloidosis, and thrombotic microangiopathy. Patients with higher CXCL9/cre (≥0.11 ng/mmol) and CXCL10/cre (≥0.42 ng/mmol) levels were at increased risk of transplant progression to ESRD (HR 3.25, 95% CI=1.27-8.36, P=0.01), irrespective of serum creatinine at the time of biopsy. CONCLUSIONS Urinary CXCL9/cre and CXCL10/cre were able to distinguished between patients with transplant rejection and those without rejection. High levels of urinary CXCL9/cre and CXCL10/cre were associated with worse allograft survival.

Risk of cellular or antibody-mediated rejection in pediatric kidney transplant recipients with BK polyomavirus replication-an international CERTAIN registry study

BACKGROUND

In kidney transplant recipients (KTR), BK polyomavirus-associated nephropathy (BKPyVAN) is a major cause of graft loss. To facilitate the clearance of BKPyV-DNAemia, reduction of immunosuppression is currently the treatment of choice but may increase the risk of graft rejection.

METHODS

This international CERTAIN study was designed to determine the risk of alloimmune response and graft dysfunction associated with immunosuppression reduction for BKPyV treatment in 195 pediatric KTR.

RESULTS

BKPyV-DNAemia was associated with a more than twofold increased risk of late T cell-mediated rejection (TCMR) (HR 2.22, p = 0.024), of de novo donor-specific HLA antibodies (dnDSA) and/or antibody-mediated rejection (ABMR) (HR 2.64, p = 0.002), and of graft function deterioration (HR 2.73, p = 0.001). Additional independent risk factors for dnDSA/ABMR development were a higher HLA mismatch (HR 2.72, p = 0.006) and re-transplantation (HR 6.40, p = 0.000). Other independent predictors of graft function deterioration were TCMR (HR 3.98, p = 0.003), higher donor age (HR 1.03, p = 0.020), and re-transplantation (HR 3.56, p = 0.013).

CONCLUSIONS

These data indicate that reduction of immunosuppression for BKPyV-DNAemia management is associated with increased alloimmune response in pediatric KTR. Therefore, regular dnDSA screening and close monitoring of graft function in case of BKPyV-DNAemia followed by subsequent reduction of immunosuppressive therapy are recommended.

Defining the Etiology of Renal Allograft Dysfunction Using Banff 2019 Classification: Correlation with Post-Transplant Duration and Creatinine Levels-A Comprehensive Analysis of 200 Renal Biopsies at a Tertiary Care Medical Center Hospital

OBJECTIVE

Chronic kidney disease is a growing global health issue, contributing significantly to morbidity and mortality. The incidence of end-stage renal disease (ESRD) is approximately 100 per million population. Renal transplantation remains the cornerstone treatment for ESRD, with a projected 20-year survival rate of 60%. We aim to define the etiology of renal allograft dysfunction using the Banff 2019 classification by analyzing 200 renal allograft biopsies in correlation with creatinine levels across post-transplant time frames.

METHODOLOGY

200 renal allograft biopsies are analyzed using the recent Banff 2019 classification with creatinine levels and post-transplant duration correlation.

RESULTS

The study included 150 (75%) male patients and 50 (25%) female patients, with the majority 78 (39%) representing the age group of 16-30 years. 36 (18%) biopsies were within 3-month post-transplant, while 92 (46%) were 2-year post-transplant. According to the Banff 2019 classification, 92 (46.0%) transplant rejection biopsies were identified, with most 54 (27%) exhibiting antibody-mediated rejection (Category 2), including 40 (20%) active acute antibody-mediated rejection (ABMR) and 14 (7.0%) chronic active ABMR. T-cell-mediated rejection (TCMR; Category 4) represented 12 (6%) biopsies, including 10 (5%) acute TCMR and 2 (1%) chronic active TCMR. Category 5, the miscellaneous group, represented 100 (50%) biopsies, out of which 32 (16%) exhibited calcineurin inhibitor (CNI) toxicity, 38 (19%) acute tubular necrosis, and 8 (4%) thrombotic microangiopathy. A notable variation in the dysfunction distribution across different post-transplant time frames indicated a temporal evolution in the underlying causes of allograft dysfunction. Specific Banff categories showed a robust association with renal dysfunction, potentially contributing to the elevation of creatinine levels and renal function deterioration.

CONCLUSION

Our study highlights the intricate pathophysiology of renal allograft dysfunction. Most biopsies were attributed to ABMR whereas one-third of biopsies exhibited mixed lesions (ABMR and TCMR or ABMR and calcineurin inhibitor toxicity (CNIT)). Additionally, this study suggests that renal allograft rejection remains a significant contributor to graft dysfunction. A complex interplay between histological findings, Banff classification, and renal function is noted. A significant difference in the distribution of dysfunction across post-transplant time frames is noted suggesting a temporal evolution in the etiology of allograft dysfunction. Certain Banff categories demonstrate a stronger association with renal dysfunction that may influence creatinine level increase and renal function deterioration. In correspondence to the recent Banff 2019 guidelines for diagnosing ABMR, we emphasize the role of C4d staining on immunofluorescence or immunohistochemistry in allograft biopsies as imperative for timely diagnosis and immunosuppressant therapy adjustment, ultimately enhancing graft survival. Further research is needed to elucidate the underlying mechanisms driving renal dysfunction in different Banff categories, ultimately informing personalized management strategies for patients with renal allograft dysfunction. In line with the Banff 2019 guidelines for diagnosing ABMR, this study highlights the critical role of C4d staining through immunofluorescence or immunohistochemistry in allograft biopsies for early diagnosis and timely adjustment of immunosuppressive therapy, ultimately improving graft survival.

Imlifidase in Highly Sensitized Kidney Transplant Recipients With a Positive Crossmatch Against a Deceased Donor

Introduction

Imlifidase is authorized for desensitization of highly sensitized adult kidney transplant candidates with a positive crossmatch (XM) against a deceased donor. Here, we report on the results for the first 9 patients transplanted in this context who had at least 3 months of follow-up.

Methods

The eligibility criteria were as follows: calculated panel reactive antibodies (cPRA) ³ 98%, ³ 3 years on the waiting list, immunodominant donor-specific antibodies (DSAs) with mean fluorescence intensity (MFI) > 6000 (and < 5000 at 1:10 dilution) and a negative post-imlifidase complement-dependent cytotoxic XM (CDCXM).

Results

All 9 patients had been on dialysis for an average of 123 ± 41 months, with cPRA at 99% (n = 2) or 100% (n = 7). At transplantation, the mean number of DSAs was 4.3 ± 1.4. The median immunodominant DSA MFI was 9153 (6430-16,980). Flow cytometry XM (FCXM) and CDCXM before imlifidase were positive in 9 and 2 patients, respectively. After 1 injection of imlifidase, all were negative. Patients received polyclonal antibodies, i.v. Igs (IVIg), rituximab, tacrolimus, and mycophenolate. Five patients had a DSA rebound within the first 14 days: 2 had concomitant clinical antibody-mediated rejection (ABMR), 2 had subclinical ABMR, and 1 had isolated positive C4d staining. No ABMR was observed in patients without rebound. Chronic Kidney Disease-Epidemiology Collaboration formula estimated glomerular filtration rate (eGFR) was 56 ± 22 ml/min per 1.73 m2 at the last follow-up (7 ± 2.8 months). No graft loss or death were observed. Four patients developed at least 1 infection.

Conclusion

These real-life data demonstrate that the use of imlifidase to desensitize highly sensitized patients can have an acceptable short-term efficacy and safety profile in selected patients.

Clinical Value of Peripheral Blood Gene Expression Profile and Donor-Derived Cellfree DNA for Identifying Persistent Rejection

Key Points

Background

Persistent rejection is an increasingly recognized barrier to long-term kidney allograft survival. A noninvasive method to help identify patients with persistent rejection in need of biopsy would be valuable.

Methods

This was a post hoc analysis of a multicenter observational study. Patients who had a biopsy-proven acute rejection, had another biopsy within 9 months (270 days), and had a biopsy-paired biomarker sample were included.

Results

A total of 64 index rejections in 58 patients with repeat biopsies were identified with a median time to repeat biopsy of 100 days. Persistent rejection was present in 61%; 69% of follow-up biopsies were performed in clinically stable patients. Peripheral blood gene expression profile (GEP) demonstrated a sensitivity of 59%, specificity of 76%, positive predictive value (PPV) of 79%, and negative predictive value of 54%. Donor-derived cellfree DNA (dd-cfDNA) demonstrated a sensitivity of 62%, specificity of 86%, PPV of 88%, and negative predictive value of 56%. For repeat biopsies within 90 days of rejection in clinically stable patients (63% of repeat biopsies), both GEP and dd-cfDNA had specificities and PPVs of 100%. GEP was more likely to be positive in T-cell–mediated rejection while dd-cfDNA was more likely to be positive in antibody-mediated rejection.

Conclusions

Both GEP and dd-cfDNA may have utility in identifying clinically stable patients with persistent rejection in need of biopsy; however, they identify different types of rejections.

Clinical Trial registration number:

NCT01531257.

Clinical Utility of Donor-Derived Cell-Free DNA in Heart Transplant Recipients With Multi-Organ Transplants

BACKGROUND

Donor-derived cell-free DNA (dd-cfDNA) has emerged as a reliable, noninvasive method for the surveillance of allograft rejection in heart transplantation (HT) patients, but its utility in multi-organ transplants (MOT) is unknown. We describe our experience using dd-cfDNA in simultaneous MOT recipients.

METHODS

A single-center retrospective review of all HT recipients between 2018 and 2022 that had at least one measurement of dd-cfDNA collected. Patients who had simultaneous MOT were identified and included in this study. Levels of dd-cfDNA were paired with endomyocardial biopsies (EMB) performed within 1 month of blood testing if available. Acute cellular rejection (ACR) was defined as ISHLT (International Society for Heart and Lung Transplantation) grade ≥ 2R. and antibody-mediated rejection (AMR) was defined as pAMR grade > 0. The within-patient variability score of the dd-cfDNA was calculated by the variance/average.

RESULTS

The study included 25 multiorgan transplant recipients: 13 heart-kidney (H-K), 8 heart-liver (H-Li), and 4 heart-lung (H-Lu). The median age was 55 years, 44% were female; the median time from HT until the first dd-cfDNA measurement was 4.5 months (IQR 2, 10.5). The median dd-cfDNA level was 0.18% (IQR 0.15%, 0.27%) for H-K, 1.15% (IQR 0.77%, 2.33%) for H-Li, and 0.69% (IQR 0.62%, 1.07%) for H-Lu patients (p < 0.001). Prevalence of positive dd-cfDNA tests (threshold of 0.20%) were 42.2%, 97.3%, and 92.3% in the H-K, H-Li, and H-Lu groups, respectively. The within-patient variability score was highest in the H-Li group (median of 0.45 [IQR 0.29, 0.94]) and lowest in the H-K group (median of 0.09 [IQR 0.06, 0.12]); p = 0.002. No evidence of cardiac ACR or AMR was found. Three patients experienced renal allograft ACR and/or AMR, two patients experienced rejection of the liver allograft, and one patient experienced an episode of AMR-mediated lung rejection. One person in the H-K group experienced an episode of cardiac allograft dysfunction that was not associated with biopsy-confirmed rejection.

CONCLUSION

Dd-cfDNA is chronically elevated in most MOT recipients. There is a high degree of within-patient variability in levels (particularly for H-Li and H-Lu recipients), which may limit the utility of this assay in monitoring MOT recipients.

Early and Late Microvascular Inflammation Have Differing Etiological Causes and Clinical Expression

BACKGROUND

Microvascular inflammation (MVI) is an important pathological feature of antibody-mediated rejection (AMR). How posttransplant time affects its clinicopathological expression is little understood.

METHODS

This retrospective, single-center study screened 3398 kidney transplant biopsies and dichotomized 202 MVI ≥ 2 (Banff glomerulitis + peritubular capillaritis ≥ 2) samples by 9-mo median incidence time for comparison.

RESULTS

The prevalence of MVI ≥ 2 was 12.4% in transplant kidneys, which failed more frequently than propensity-matched normal controls (n = 202; P < 0.001). Epidemiological risk factors for early MVI ≥ 2 were delayed graft function, prior AMR, and circulating donor-specific antibodies (DSAs+). Prior recipient sensitization occurred in 72.3%. Early MVI ≥ 2 was classified AMR in 65.3% and cellular rejection in 34.7%, and demonstrated excellent functional recovery and graft survival comparable to normal control kidneys. Late MVI ≥ 2 was predicted by younger (18 = 29 y) age, female recipient, living-donation, prior methylprednisolone, cyclosporine (versus tacrolimus, levels <5 ng/mL), absent antiproliferative therapy, and DSA+ using multivariable epidemiological modeling. Nonadherence caused 49.5%, with iatrogenic minimization responsible for 47.5%, usually for recipient infection. Late MVI ≥ 2 was because of AMR in 93.1%, and characterized by greater interstitial fibrosis, tubular atrophy, complement degradation split-product 4d (C4d) staining of peritubular capillaries+, endothelial C4d staining of glomerular capillaries+, transplant glomerulopathy and vasculopathy scores, DSA strength, and graft failure than early MVI ≥ 2 or normal transplant kidneys. Death-censored graft survival in 149 unique MVI ≥ 2 kidneys was independently determined by nonadherence, serum creatinine, proteinuria, DSA+, Banff C4d staining of peritubular capillaries+, and chronic interstitial fibrosis scores. MVI score and time lost significance using multivariable Cox regression.

CONCLUSIONS

The changing expression of MVI ≥ 2 over time is best explained by differences in underimmunosuppression and microvascular injury from AMR impacting allograft function and survival.

Molecular landscape of kidney allograft tissues data integration portal (NephroDIP): a curated database to improve integration of high-throughput kidney transplant datasets

Introduction

Kidney transplantation is the optimal treatment for end-stage kidney disease; however, premature allograft loss remains a serious issue. While many high-throughput omics studies have analyzed patient allograft biospecimens, integration of these datasets is challenging, which represents a considerable barrier to advancing our understanding of the mechanisms of allograft loss.

Methods

To facilitate integration, we have created a curated database containing all open-access high-throughput datasets from human kidney transplant studies, termed NephroDIP (Nephrology Data Integration Portal). PubMed was searched for high-throughput transcriptomic, proteomic, single nucleotide variant, metabolomic, and epigenomic studies in kidney transplantation, which yielded 9,964 studies.

Results

From these, 134 studies with available data detailing 260 comparisons and 83,262 molecules were included in NephroDIP v1.0. To illustrate the capabilities of NephroDIP, we have used the database to identify common gene, protein, and microRNA networks that are disrupted in patients with chronic antibody-mediated rejection, the most important cause of late allograft loss. We have also explored the role of an immunomodulatory protein galectin-1 (LGALS1), along with its interactors and transcriptional regulators, in kidney allograft injury. We highlight the pathways enriched among LGALS1 interactors and transcriptional regulators in kidney fibrosis and during immunosuppression.

Discussion

NephroDIP is an open access data portal that facilitates data visualization and will help provide new insights into existing kidney transplant data through integration of distinct studies and modules (https://ophid.utoronto.ca/NephroDIP).

FCGR2C Q13 and FCGR3A V176 alleles jointly associate with worse natural killer cell-mediated antibody-dependent cellular cytotoxicity and microvascular inflammation in kidney allograft antibody-mediated rejection

Natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism of humoral allograft injury. FCGR3A V176/F176 polymorphism influences ADCC activity. Additionally, NK cell FcγRIIc expression, dictated by the Q13/STP13 polymorphism, was never investigated in kidney transplantation. To assess the clinical relevance of FCGR2C Q13/STP13 polymorphism in conjunction with FCGR3A V176/F176 polymorphism, 242 kidney transplant recipients were genotyped. NK cell Fc gamma receptor (FcγR) expression and ADCC activity were assessed. RNA sequencing was performed on kidney allograft biopsies to explore the presence of infiltrating FcγR+ NK cells. The FCGR2C Q13 allele was enriched in antibody-mediated rejection patients. FcγRIIc Q13+ NK cells had higher ADCC activity than FcγRIIc Q13- NK cells. In combination with the high-affinity FCGR3A V176 allele, Q13+V176+ NK cells were the most functionally potent. Q13+ was associated with worse microvascular inflammation and a higher risk of allograft loss. Among V176- patients, previously described in the literature as lower-risk patients, Q13+V176- showed a lower graft survival than Q13-V176- patients. In antibody-mediated rejection biopsies, FCGR2C transcripts were enriched and associated with ADCC-related transcripts. Our results suggest that FCGR2C Q13 in addition to FCGR3A V176 is a significant risk allele that may enhance NK cell-mediated ADCC and contribute to allograft injury and poor survival.

Role of vesicoureteral reflux on pediatric kidney allograft function

BACKGROUND

Vesicoureteral reflux (VUR) is a common urologic complication of pediatric kidney transplant, though there is little data on the effect of VUR on histologic graft changes or graft survival.

METHODS

All pediatric patients who received a kidney transplant from 2007 to 2020 were selected for retrospective chart review. All participants underwent a voiding cystourethrogram (VCUG) at a 6-month post-transplant. Patients were then categorized into two groups based on vesicoureteral reflux grade: no/low-grade VUR (grades 0-2) and high-grade VUR (grades 3-5). Outcomes collected included graft failure rates, graft function, urinary tract infections (UTIs), proteinuria, and Banff scores at 3- and 12-month post-transplant surveillance kidney biopsies.

RESULTS

There were 74 pediatric patients who received a kidney transplant in the designated time-period, and of those 39 had no/low-grade VUR and 35 had high-grade VUR. There was no difference in graft failure among the two groups over time when stratified for age (p = 0.389, CI 0.53-5.08). Patients with high grade VUR had a higher risk of UTI development overall (RR 1.89, 95%CI 1-3.6, p = 0.041), mostly accounted for from increased development of febrile UTI (RR 1.66, 95%CI 1.1-2.6, p = 0.038).

CONCLUSIONS

Unselected pediatric kidney transplant recipients with high-grade vesicoureteral reflux on VCUG at a 6-month post-kidney transplant are more likely to have febrile UTI compared to those in the low-grade VUR group. There is no difference in graft survival among the two groups.

Initial Experience of Metabolic Imaging with Hyperpolarized [1-13C]pyruvate MRI in Kidney Transplant Patients

BACKGROUND

Kidney transplant is the treatment of choice for patients with end-stage renal disease. Early detection of allograft injury is important to delay or prevent irreversible damage.

PURPOSE

To investigate the feasibility of hyperpolarized (HP) [1-13C]pyruvate MRI for assessing kidney allograft metabolism.

STUDY TYPE

Prospective.

SUBJECTS

6 participants (mean age, 45.2 ± 12.4 years, 2 females) scheduled for kidney allograft biopsy and 5 patients (mean age, 59.6 ± 10.4 years, 2 females) with renal cell carcinoma (RCC).

FIELD STRENGTH/SEQUENCE

3 Tesla, T2-weighted fast spin echo, multi-echo gradient echo, single shot diffusion-weighted echo-planar imaging, and time-resolved HP 13C metabolite-selective imaging.

ASSESSMENT

Five of the six kidney allograft participants underwent biopsy after MRI. Estimated glomerular filtration rate (eGFR) and urine protein-to-creatine ratio (uPCR) were collected within 4 weeks of MRI. Kidney metabolism was quantified from HP [1-13C]pyruvate MRI using the lactate-to-pyruvate ratio in allograft kidneys and non-tumor bearing kidneys from RCC patients.

STATISTICAL TESTS

Descriptive statistics (mean ± standard deviation).

RESULTS

Biopsy was performed a mean of 9 days (range 5-19 days) after HP [1-13C]pyruvate MRI. Three biopsies were normal, one showed low-grade fibrosis and one showed moderate microvascular inflammation. All had stable functioning allografts with eGFR > 60 mL/min/1.73 m2 and normal uPCR. One participant who did not undergo biopsy had reduced eGFR of 49 mL/min/1.73 m2 and elevated uPCR. The mean lactate-to-pyruvate ratio was 0.373 in participants with normal findings (n = 3) and 0.552 in participants with abnormal findings (n = 2). The lactate-to-pyruvate ratio was highest (0.847) in the participant with reduced eGFR and elevated uPRC. Native non-tumor bearing kidneys had a mean lactate-to-pyruvate ratio of 0.309.

DATA CONCLUSION

Stable allografts with normal findings at biopsy showed lactate-to-pyruvate ratios similar to native non-tumor bearing kidneys, whereas allografts with abnormal findings showed higher lactate-to-pyruvate ratios.

Initial Experience of Metabolic Imaging With Hyperpolarized [1-13C]pyruvate MRI in Kidney Transplant Patients

BACKGROUND

Kidney transplant is the treatment of choice for patients with end-stage renal disease. Early detection of allograft injury is important to delay or prevent irreversible damage.

PURPOSE

To investigate the feasibility of hyperpolarized (HP) [1-13C]pyruvate MRI for assessing kidney allograft metabolism.

STUDY TYPE

Prospective.

SUBJECTS

Six participants (mean age, 45.2 ± 12.4 years, two females) scheduled for kidney allograft biopsy and five patients (mean age, 59.6 ± 10.4 years, two females) with renal cell carcinoma (RCC).

FIELD STRENGTH/SEQUENCE

Three Tesla, T2-weighted fast spin echo, multi-echo gradient echo, single shot diffusion-weighted echo-planar imaging, and time-resolved HP 13C metabolite-selective imaging.

ASSESSMENT

Five of the six kidney allograft participants underwent biopsy after MRI. Estimated glomerular filtration rate (eGFR) and urine protein-to-creatine ratio (uPCR) were collected within 4 weeks of MRI. Kidney metabolism was quantified from HP [1-13C]pyruvate MRI using the lactate-to-pyruvate ratio in allograft kidneys and non-tumor bearing kidneys from RCC patients.

STATISTICAL TESTS

Descriptive statistics (mean ± SD).

RESULTS

Biopsy was performed a mean of 9 days (range 5-19 days) after HP [1-13C]pyruvate MRI. Three biopsies were normal, one showed low-grade fibrosis and one showed moderate microvascular inflammation. All had stable functioning allografts with eGFR >60 mL/min/1.73 m2 and normal uPCR. One participant who did not undergo biopsy had reduced eGFR of 49 mL/min/1.73 m2 and elevated uPCR. The mean lactate-to-pyruvate ratio was 0.373 in participants with normal findings (N = 3) and 0.552 in participants with abnormal findings (N = 2). The lactate-to-pyruvate ratio was highest (0.847) in the participant with reduced eGFR and elevated uPRC. Native non-tumor bearing kidneys had a mean lactate-to-pyruvate ratio of 0.309.

DATA CONCLUSION

Stable allografts with normal findings at biopsy showed lactate-to-pyruvate ratios similar to native non-tumor bearing kidneys, whereas allografts with abnormal findings showed higher lactate-to-pyruvate ratios.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Maternal and neonatal outcomes in kidney transplant recipients: a single-center observational study

OBJECTIVE

Pregnancy poses a high risk for adverse maternal and neonatal outcomes in kidney transplant recipients (KTRs), and data on long-term allograft functions compared to the healthy population are still limited. Therefore, we aimed to conduct a comparative analysis of maternal and neonatal outcomes in KTRs.

SUBJECT AND METHODS

In this retrospective single-center study, KTRs who experienced pregnancy after transplantation were evaluated in comparison with an age-matched non-transplanted control group. Maternal outcomes included obstetric complications (preeclampsia, peripartum hemorrhage, duration of maternal hospitalization) and a composite kidney outcome for KTRs defined as progression to graft failure necessitating dialysis or retransplantation or doubling of serum creatinine at the end of follow-up. Neonatal outcomes were gestational age, preterm birth, newborn mortality, admittance to the neonatal intensive care unit (NICU), Apgar scores, and birth weight.

RESULTS

In 53 KTRs, 68 pregnancies occurred. Preeclampsia (p < 0.001) and preterm birth (p = 0.003) were significantly higher in KTRs. The KTR pregnancies had lower mean birth weights (p = 0.001) and longer durations of maternal hospitalization (p = 0.001). Neonatal mortality, NICU admissions, peripartum hemorrhage rates, and Apgar scores were similar between groups. Follow-up for a median of 105 months after the index birth showed higher serum creatinine levels at postpartum visits (p < 0.001) and at the last follow-up (p = 0.001) compared to baseline. Of the KTRs 6 (11.3%) experienced composite kidney outcomes, including 5 patients with graft failure and 1 with a doubling of serum creatinine.

CONCLUSION

The KTRs exhibit comparable neonatal mortality and NICU admission rates but have higher rates of preeclampsia and preterm birth. Importantly, graft functions worsen significantly during postpartum follow-up.

The role of C4d and donor specific antibodies in face and hand transplantation-a systematic review

To date, little is known about the mechanisms of rejection in vascularized composite allotransplantation, particularly for antibody mediated rejection. Additionally, no clear guidelines exist for the diagnosis and management of antibody-mediated rejection in vascularized composite allotransplantation. A systematic review of electronic databases (Embase and PubMed) was conducted to evaluate the relationship of donor specific antibodies and C4d deposition in correlation with cellular rejection following hand and face transplantation reported by centers between 1998 and July 2023. We extracted data on serum donor specific antibodies at the time of biopsy proven rejection according to Banff classification and C4d staining of target tissues. Mann-Whitney U tests were performed to compare rejection grade between groups divided by status of C4d deposition and serum donor specific antibodies, and Fisher's Exact test was used to assess association between the two markers. This review adhered to PRISMA guidelines. A total of 26 patients (5 face, 21 hand) were identified and data on 90 acute rejection episodes with information on Banff grade, donor specific antibody status, and C4d deposition were available. Donor specific antibodies were found to be associated with higher rejection grade (p = 0.005). C4d was not found to be associated with higher rejection grade (p = 0.33). Finally, no significant association was found between concurrent status of the two markers (p = 0.23). These findings suggest that the presence of donor specifc antibodies may be associated with higher grades of acute cellular rejection following hand and face transplantation. More consistent reporting on rejection episodes is needed in order to better understand antibody-mediated rejection in vascularized composite allotransplantation.

De novo and recurrent post-transplant membranous nephropathy cases show similar rates of concurrent antibody-mediated rejection

Background

Membranous nephropathy (MN) can develop post-kidney transplant and is classified as a recurrent disease in patients with a history of MN in the native kidneys or as de novo disease in patients without such history. The mechanism of recurrent MN is thought to be like that of primary MN, but the mechanism of de novo MN is not well delineated. An association between de novo MN and antibody-mediated rejection (AMR) has been suggested.

Methods

A search of the pathology database from our medical center identified 11 cases of recurrent and 15 cases of de novo MN, in which clinical and histologic findings were compared. No significant differences were identified in the demographic characteristics, serum creatinine and proteinuria trends, or rates of allograft failure between the recurrent and de novo MN groups.

Results

Rates of concurrent AMR were high in both groups (36% and 40%, respectively) but not statistically different from each other. PLA2R immunofluorescence (IF) positivity was seen in 64% of recurrent MN cases compared to 33% of de novo MN cases, suggesting a higher incidence of PLA2R-positive de novo MN than previously reported. No significant histologic differences were identified in the initial biopsies from the two groups, except mean IgG intensity by IF was higher in the recurrent group, suggesting a higher load of immune complex deposits at diagnosis in this group.

Conclusion

The findings do not provide support for a specific association between AMR and de novo MN, but whether there is a possible link between both forms of post-transplant MN and AMR remains an unanswered question.

Detection of Subclinical Rejection in Pediatric Kidney Transplantation: Current and Future Practices

INTRODUCTION

The successes in the field of pediatric kidney transplantation over the past 60 years have been extraordinary. Year over year, there have been significant improvements in short-term graft survival. However, improvements in longer-term outcomes have been much less apparent. One important contributor has been the phenomenon of low-level rejection in the absence of clinical manifestations-so-called subclinical rejection (SCR).

METHODS

Traditionally, rejection has been diagnosed by changes in clinical parameters, including but not limited to serum creatinine and proteinuria. This review examines the shortcomings of this approach, the effects of SCR on kidney allograft outcome, the benefits and drawbacks of surveillance biopsies to identify SCR, and new urine and blood biomarkers that define the presence or absence of SCR.

RESULTS

Serum creatinine is an unreliable index of SCR. Surveillance biopsies are the method most utilized to detect SCR. However, these have significant drawbacks. New biomarkers show promise. These biomarkers include blood gene expression profiles and donor derived-cell free DNA; urine gene expression profiles; urinary cytokines, chemokines, and metabolomics; and other promising blood and urine tests.

CONCLUSION

Specific emphasis is placed on studies carried out in pediatric kidney transplant recipients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03719339.

Histopathological Features and Role of Allograft Kidney Biopsy Among Recipients With Prolonged Delayed Graft Function: A Review

Delayed graft function (DGF) is an early posttransplant complication predictive of adverse outcomes. This "acute kidney injury of transplantation" is often defined as allograft dysfunction requiring renal replacement within 7 d posttransplantation. DGF is an important area of study because it is emerging with efforts to expand the donor pool and address the supply-demand gap in kidney transplantation. DGF is often caused by severe kidney injury mechanisms because of multiple donors, recipients, and immunologic factors. The role of kidney biopsy, particularly in prolonged DGF, is an ongoing area of research and inquiry for clinicians and researchers alike to better define, manage, and predict outcomes of this early posttransplant event. This review aims to provide an in-depth, comprehensive summary of the literature to date on the histopathology of DGF and the role of kidney transplant biopsies in prolonged DGF.

Molecular diagnosis of antibody-mediated rejection: Evaluating biopsy-based transcript diagnostics in the presence of donor-specific antibodies but without microvascular inflammation, a single-center descriptive analysis

Biopsy-based transcript diagnostics may identify molecular antibody-mediated rejection (AMR) when microvascular inflammation (MVI) is absent. In this single-center cohort, biopsy-based transcript diagnostics were validated in 326 kidney allograft biopsies. A total of 71 histological AMR and 35 T cell-mediated rejection (TCMR) cases were identified as molecular AMR and TCMR in 55% and 63%, respectively. Among 121 cases without MVI (glomerulitis + peritubular capillaritis = 0), 45 (37%) donor-specific antibody (DSA)-positive and 76 (63%) DSA-negative cases were analyzed. Twenty-one out of the 121 (17%) cases showed borderline changes, or TCMR, while BK nephropathy was excluded. None of the 45 DSA-positive patients showed molecular AMR. Among 76 DSA-negative patients, 2 had mixed molecular AMR/TCMR. All-AMR phenotype scores (sum of R4-R6) exhibited median values of 0.13 and 0.12 for DSA-positive and DSA-negative patients, respectively (P = .84). A total of 13% (6/45) DSA-positive and 11% (8/76) DSA-negative patients showed an all-AMR phenotype score > 0.30 (P = .77). Patients with a higher all-AMR phenotype score showed 33% more histologic TCMR (P = .005). The median all-AMR phenotype scores of glomerular basement membrane double contours = 0 and glomerular basement membrane double contours > 0 biopsies were 0.12 and 0.10, respectively (P = .35). Biopsy-based transcript diagnostics did not identify molecular AMR in cases without MVI. Follow-up biopsies and outcome data should evaluate the clinical relevance of subthreshold molecular alterations.

A universal urinary cell gene signature of acute rejection in kidney allografts

INTRODUCTION

Acute rejection (AR) undermines the life-extending benefits of kidney transplantation and is diagnosed using the invasive biopsy procedure. T cell-mediated rejection (TCMR), antibody-mediated rejection (ABMR), or concurrent TCMR + ABMR (Mixed Rejection [MR]) are the three major types of AR. Development of noninvasive biomarkers diagnostic of AR due to any of the three types is a useful addition to the diagnostic armamentarium.

METHODS

We developed customized RT-qPCR assays and measured urinary cell mRNA copy numbers in 145 biopsy-matched urine samples from 126 kidney allograft recipients. We determined whether the urinary cell three-gene signature diagnostic of TCMR (Suthanthiran et al., 2013) discriminates patients with no rejection biopsies (NR, n = 50) from those with ABMR (n = 28) or MR (n = 20) biopsies.

RESULTS

The urinary cell three-gene signature discriminated all three types of rejection biopsies from NR biopsies (P < 0.0001, One-way ANOVA). Dunnett's multiple comparisons test yielded P < 0.0001 for NR vs. TCMR; P < 0.001 for NR vs. ABMR; and P < 0.0001 for NR vs. MR. By bootstrap resampling, optimism-corrected area under the receiver operating characteristic curve (AUC) was 0.749 (bias-corrected 95% confidence interval [CI], 0.638 to 0.840) for NR vs. TCMR (P < 0.0001); 0.780 (95% CI, 0.656 to 0.878) for NR vs. ABMR (P < 0.0001); and 0.857 (95% CI, 0.727 to 0.947) for NR vs. MR (P < 0.0001). All three rejection categories were distinguished from NR biopsies with similar accuracy (all AUC comparisons P > 0.05).

CONCLUSION

The urinary cell three-gene signature score discriminates AR due to TCMR, ABMR or MR from NR biopsies in human kidney allograft recipients.

The Second International Consensus Guidelines on the Management of BK Polyomavirus in Kidney Transplantation

BK polyomavirus (BKPyV) remains a significant challenge after kidney transplantation. International experts reviewed current evidence and updated recommendations according to Grading of Recommendations, Assessment, Development, and Evaluations (GRADE). Risk factors for BKPyV-DNAemia and biopsy-proven BKPyV-nephropathy include recipient older age, male sex, donor BKPyV-viruria, BKPyV-seropositive donor/-seronegative recipient, tacrolimus, acute rejection, and higher steroid exposure. To facilitate early intervention with limited allograft damage, all kidney transplant recipients should be screened monthly for plasma BKPyV-DNAemia loads until month 9, then every 3 mo until 2 y posttransplant (3 y for children). In resource-limited settings, urine cytology screening at similar time points can exclude BKPyV-nephropathy, and testing for plasma BKPyV-DNAemia when decoy cells are detectable. For patients with BKPyV-DNAemia loads persisting >1000 copies/mL, or exceeding 10 000 copies/mL (or equivalent), or with biopsy-proven BKPyV-nephropathy, immunosuppression should be reduced according to predefined steps targeting antiproliferative drugs, calcineurin inhibitors, or both. In adults without graft dysfunction, kidney allograft biopsy is not required unless the immunological risk is high. For children with persisting BKPyV-DNAemia, allograft biopsy may be considered even without graft dysfunction. Allograft biopsies should be interpreted in the context of all clinical and laboratory findings, including plasma BKPyV-DNAemia. Immunohistochemistry is preferred for diagnosing biopsy-proven BKPyV-nephropathy. Routine screening using the proposed strategies is cost-effective, improves clinical outcomes and quality of life. Kidney retransplantation subsequent to BKPyV-nephropathy is feasible in otherwise eligible recipients if BKPyV-DNAemia is undetectable; routine graft nephrectomy is not recommended. Current studies do not support the usage of leflunomide, cidofovir, quinolones, or IVIGs. Patients considered for experimental treatments (antivirals, vaccines, neutralizing antibodies, and adoptive T cells) should be enrolled in clinical trials.

Highly Sensitized Candidates Remain at Risk for Microvascular Inflammation Even When Donor-specific Antibody Is Avoided: A Matched Cohort Study

BACKGROUND

Microvascular inflammation (MVI) is a key feature of antibody-mediated rejection (AMR) among patients with HLA donor-specific antibody (DSA), but MVI at AMR thresholds (Banff glomerulitis [g] + peritubular capillaritis [ptc] score ≥ 2) without DSA has been increasingly recognized. We aimed to determine the incidence of MVI among highly sensitized kidney transplant recipients without DSA.

METHODS

We performed a single-center, retrospective, matched cohort study comparing outcomes of kidney transplant recipients with cPRA ≥90% with preexisting DSA (n = 49), cPRA ≥90% without preexisting DSA (n = 47), and matched controls with cPRA = 0 without preexisting DSA (n = 49). Controls were matched by age, donor type, and transplant date. Indication and surveillance biopsies combined with annual de novo DSA screening were obtained.

RESULTS

Kidney transplant recipients with a cPRA ≥90% and no evidence of preexisting or de novo DSA had a higher incidence of MVI (glomerulitis + peritubular capillaritis ≥ 2) than patients with cPRA = 0 [35% (17/49) versus 12% (6/49), P  = 0.0003] over a median (interquartile range) follow-up of 5 (4-6) y posttransplant. Among this cPRA ≥90% group without DSA, MVI persisted in 54% of cases on follow-up biopsy (7/13), and 24% (4/13) of cases developed transplant glomerulopathy (Banff cg score > 0).

CONCLUSIONS

Highly sensitized transplant recipients have a high incidence of persistent and progressive MVI, even without DSA. The mechanisms underlying these histologic features needs to be elucidated, but this information is important to consider when making decisions about transplantation among highly sensitized individuals.

Approach to Kidney Allograft Dysfunction: A Brief Review

It is important for providers caring for kidney transplant recipients to be familiar with the common causes of allograft dysfunction. Early detection of allograft dysfunction leads to timely management, with the goal of preventing or delaying progression to allograft failure. Although transplant rejection is always a concern, the differential diagnoses for allograft dysfunction are broad and include perioperative complications, infections, recurrent disease, and calcineurin nephrotoxicity. In this review, we will go over early and late causes of allograft dysfunction and discuss the basic workup and principles of management for each condition.

Kidney Biopsy Findings After Lung Transplantation

Introduction

The early diagnosis of histological kidney damage after lung transplantation (LT) is of paramount importance given the negative prognostic implications of kidney disease.

Methods

Three pathologists analyzed all kidney biopsies (KBs) (N = 100) performed from 2010 to 2021 on lung transplant patients in 4 Paris transplantation centers.

Results

The main indication for biopsy was chronic renal dysfunction (72% of patients). Biopsies were performed at a median of 26.3 months after transplantation and 15 months after a decline in estimated glomerular filtration rate (eGFR) or the onset of proteinuria. Biopsies revealed a wide spectrum of chronic lesions involving the glomerular, vascular, and tubulointerstitial compartments. The 4 most frequent final diagnoses, observed in 18% to 49% of biopsies, were arteriosclerosis, acute calcineurin inhibitor (CNI) toxicity, thrombotic microangiopathy (TMA) and acute tubular necrosis (ATN). TMA was significantly associated with a combination of mTOR inhibitors (mTORi) or CNIs with biological signs present in only 50% of patients. The eGFR was poorly correlated with most lesions, particularly percent glomerulosclerosis, and with the risk of end-stage renal disease (ESRD). Thirty-four patients progressed to ESRD at an average of 20.1 months after biopsy. Three factors were independently associated with the risk of ESRD: postoperative dialysis, proteinuria >3 g/g and percent glomerulosclerosis >4%.

Conclusion

Given the great diversity of renal lesions observed in lung transplant recipients, early referral to nephrologists for KB should be considered for these patients when they present with signs of kidney disease.

Elevation of Donor-derived Cell-free DNA Before Biopsy-proven Rejection in Kidney Transplant

BACKGROUND

Standard-of-care biomarkers for renal allograft rejection are lagging indicators, signaling existing organ injury. This precludes early intervention, when immunological cascades leading to rejection are most susceptible. Donor-derived cell-free DNA (dd-cfDNA) shows promise as an early indicator of rejection, allowing earlier and possibly more effective treatment. This analysis was designed to assess this promise using real-world dd-cfDNA testing evidence.

METHODS

This retrospective analysis of the prospective, observational ProActive registry study (NCT04091984) assessed dd-cfDNA and serum creatinine levels before biopsy in 424 patients with ≥1 dd-cfDNA test (n = 1013) in the 6 mo before biopsy.

RESULTS

Of 4667 enrolled patients, 1631 patients had ≥18 mo of follow-up data, of which 424 had a biopsy and were included in this analysis. Twenty-six biopsies showed antibody-mediated rejection (ABMR), 62 showed T cell-mediated rejection, and 336 showed nonrejection; each from a unique patient. dd-cfDNA fractions were significantly elevated 5 mo before ABMR biopsies, and 2 mo before T cell-mediated rejection biopsies, compared with nonrejection biopsies. In contrast, serum creatinine did not discriminate between rejection and nonrejection in advance, or concurrent with biopsy. Among patients with nonrejection biopsies, estimated glomerular filtration rate was significantly lower in cases with ≥2 increased dd-cfDNA results (≥1%), compared with those with 0 or 1 increased dd-cfDNA result.

CONCLUSIONS

These data indicate that dd-cfDNA is an early indicator of biopsy-proven rejection, especially ABMR, suggesting a greater role for dd-cfDNA in surveillance to identify patients at high risk of ongoing or future rejection, thus requiring closer monitoring, biopsy, or other management changes.

Validation of histopathological chronicity scores in native kidney biopsies using light microscopy and digital morphometry for predicting renal outcome

Quantitative assessment of chronicity changes in native kidney biopsies offer valuable insights in to disease prognosis, despite the strength of qualitative information. Yet, standardization and reproducibility remain challenging. The present study aims to assess and compare the prognostic utility and reproducibility of two chronicity scoring systems based on light microscopy and whole slide imaging with morphometry and also to evaluate the prognostic utility of structural measurements: cortical non-sclerotic glomerular (NSG) density and NSG area/volume. We designed a retrospective longitudinal study involving 101 adult and paediatric patients who underwent native kidney biopsies. Chronicity scoring was performed using two semi-quantitative methods: Method 1 (method proposed in PMID: 28314581) and Method 2 (method proposed in PMID: 32516862), under light microscopy as well as on whole-slide scanned images, and assessed for prognostic utility. Kidney-Failure-Risk-Equation (KFRE) was employed in combination with chronicity-scoring-methods and assessed for predictive capability. Interobserver reproducibility for the two chronicity methods was studied among three renal pathologists. Structural measurements were performed on whole-slide- scanned-images. Both the chronicity scoring methods significantly predicted decline in estimated glomerular filtration rate (eGFR) and persistent need for renal replacement therapy in follow-up. Method 1 combined with KFRE, outperformed Method 2 in predicting renal survival. Method 2 however showed higher interobserver reproducibility. Combined KFRE plus histopathological scoring methods showed better predictive accuracy. The study validates the precision of chronicity scoring using whole slide scanned images. The morphometric structural measurements showed significant correlations with follow-up eGFR, thereby providing supplementary prognostic information.

Plasma exchange-sensitive syncytial glomerulopathy in a kidney transplant patient

Microvascular inflammation (MVI), defined as the presence of glomerulitis and/or peritubular capillaritis, is the key histological lesion of anti-HLA donor-specific antibodies (DSA)-related antibody mediated rejection, but recently other possible mechanisms of MVI have emerged. However, except for peritubular capillary C4d deposition that is more frequently observed in the presence of anti-HLA-DSA, histological features are similar regardless of MVI origin. Therefore, accurately describing patterns of MVI may help differentiate etiologies and drive therapeutic choices. We describe the case of a kidney transplant recipient (primary nephropathy: autosomal dominant polycystic kidney disease) who underwent kidney biopsy for worsening renal function and new onset hypertension. Histologic findings showed severe microvascular inflammation with intense glomerulitis and presence of intracapillary multinucleated cells, positive on immunostaining for endothelial marker ETS-related gene (ERG). Focal intense peritubular capillaritis and early glomerular basement membrane reduplication, C4d negative, were observed, consistent with early chronic active ABMR. HLA-DSA were absent, but high level of anti-angiotensin II type-1 receptor (AT1R) antibodies (Ab) were detected (78 U/L, normal levels < 10 U/L). Two subsequent biopsies showed intense microvascular inflammation with diffuse peritubular capillaritis, and multinucleated, ERG-positive, endothelial cells were still seen in glomerular capillary loops. The patient was started on angiotensin receptor blockers (ARBs) and plasma exchange (PEX) sessions obtaining normalization of blood pressure and AT1R Ab and proteinuria reduction, but, after subsequent liver transplant, rituximab therapy failed to maintain remission and the patient remained PEX-dependent.

Predicting graft survival in paediatric kidney transplant recipients using machine learning

BACKGROUND

Identification of factors that affect graft survival in kidney transplantation can increase graft survival and reduce mortality. Artificial intelligence modelling enables impartial evaluation of clinician bias. This study aimed to examine factors that affect the survival of grafts in paediatric kidney transplantation through the use of machine learning.

METHODS

A retrospective review was conducted on records of paediatric patients who underwent kidney transplantation between 1994 and 2021 and had post-transplant follow-up > 12 months. The nearest neighbour method was used to impute missing fields from a total of 48 variables in the dataset. Models including Naive Bayes, logistic regression, support vector machine (SVM), multi-layer perceptron, and XGBoost were trained to predict graft survival. The study used 80% of the patients for training and the remaining 20% for testing. Modelling success was evaluated based on accuracy and F1 score metrics.

RESULTS

The study analysed 465 kidney transplant recipients. Of these, 56.7% were male. The mean age at transplantation was 12.08 ± 5.01 years. Of the kidney transplants, 73.1% (n = 339) were from living donors, 34.5% (n = 160) were pre-emptive transplants, and 2.2% (n = 10) were second-time transplants. The machine learning model identified several features associated with graft survival, including antibody-mediated rejection (+ 0.7), acute cellular rejection (+ 0.66), eGFR at 3 years (+ 0.43), eGFR at 5 years (+ 0.34), pre-transplant peritoneal dialysis (+ 0.2), and cadaveric donor (+ 0.2). The successes of the logistic regression and SVM models were similar. The F1 score was 91.9%, and accuracy was 96.5%.

CONCLUSION

Machine learning can be used to identify factors that affect graft survival in kidney transplant recipients. By expanding similar studies, risk maps can be created prior to transplantation.

Virtual crossmatching reveals upregulation of placental HLA-Class II in chronic histiocytic intervillositis

Chronic histiocytic intervillositis (CHI) is a recurrent placental lesion where maternal macrophages infiltrate the intervillous space. Its cause is unknown, though due to similarities to rejected allografts one hypothesis is that CHI represents maternal-fetal rejection. Here, virtual crossmatching was applied to healthy pregnancies and those with a history of CHI. Anti-HLA antibodies, measured by Luminex, were present in slightly more controls than CHI (8/17 (47.1%) vs 5/14 (35.7%)), but there was no significant difference in levels of sensitisation or fetal specific antibodies. Quantification of immunohistochemical staining for HLA-Class II was increased in syncytiotrophoblast of placentas with CHI (Grade 0.44 [IQR 0.1-0.7]) compared to healthy controls (0.06 [IQR 0-0.2]) and subsequent pregnancies (0.13 [IQR 0-0.3]) (P = 0.0004). HLA-Class II expression was positively related both to the severity of CHI (r = 0.67) and C4d deposition (r = 0.48). There was no difference in overall C4d and HLA-Class I immunostaining. Though increased anti-HLA antibodies were not evident in CHI, increased expression of HLA-Class II at the maternal-fetal interface suggests that they may be relevant in its pathogenesis. Further investigation of antibodies immediately after diagnosis is warranted in a larger cohort of CHI cases to better understand the role of HLA in its pathophysiology.

Exhaustion of T cells after renal transplantation

Renal transplantation is a life-saving treatment for patients with end-stage renal disease. However, the challenge of transplant rejection and the complications associated with immunosuppressants necessitates a deeper understanding of the underlying immune mechanisms. T cell exhaustion, a state characterized by impaired effector functions and sustained expression of inhibitory receptors, plays a dual role in renal transplantation. While moderate T cell exhaustion can aid in graft acceptance by regulating alloreactive T cell responses, excessive exhaustion may impair the recipient's ability to control viral infections and tumors, posing significant health risks. Moreover, drugs targeting T cell exhaustion to promote graft tolerance and using immune checkpoint inhibitors for cancer treatment in transplant recipients are areas deserving of further attention and research. This review aims to provide a comprehensive understanding of the changes in T cell exhaustion levels after renal transplantation and their implications for graft survival and patient outcomes. We discuss the molecular mechanisms underlying T cell exhaustion, the role of specific exhaustion markers, the potential impact of immunosuppressive therapies, and the pharmaceutical intervention on T cell exhaustion levels. Additionally, we demonstrate the potential to modulate T cell exhaustion favorably, enhancing graft survival. Future research should focus on the distinctions of T cell exhaustion across different immune states and subsets, as well as the interactions between exhausted T cells and other immune cells. Understanding these dynamics is crucial for optimizing transplant outcomes and ensuring long-term graft survival while maintaining immune competence.

Membranous translocation of murine double minute 2 promotes the increased renal tubular immunogenicity in ischemia-reperfusion-induced acute kidney injury

Kidneys from donors with prolonged warm and cold ischemia are prone to posttransplant T cell-mediated rejection (TCMR) due to ischemia-reperfusion injury (IRI). However, the precise mechanisms still remain obscure. Renal tubular epithelial cells (TECs) are the main target during IRI. Meanwhile, we have previously reported that murine double minute 2 (MDM2) actively participates in TEC homeostasis during IRI. In this study, we established a murine model of renal IRI and a cell model of hypoxia-reoxygenation by culturing immortalized rat renal proximal tubule cells (NRK-52E) in a hypoxic environment for different time points followed by 24 h of reoxygenation and incubating NRK-52E cells in a chemical anoxia-recovery environment. We found that during renal IRI MDM2 expression increased on the membrane of TECs and aggregated mainly on the basolateral side. This process was accompanied by a reduction of a transmembrane protein, programmed death ligand 1 (PD-L1), a coinhibitory second signal for T cells in TECs. Using mutant plasmids of MDM2 to anchor MDM2 on the cell membrane or nuclei, we found that the upregulation of membrane MDM2 could promote the ubiquitination of PD-L1 and lead to its ubiquitination-proteasome degradation. Finally, we set up a coculture system of TECs and CD4+ T cells in vitro; our results revealed that the immunogenicity of TECs was enhanced during IRI. In conclusion, our findings suggest that the increased immunogenicity of TECs during IRI may be related to ubiquitinated degradation of PD-L1 by increased MDM2 on the cell membrane, which consequently results in T-cell activation and TCMR.NEW & NOTEWORTHY Ischemic acute kidney injury (AKI) donors can effectively shorten the waiting time for kidney transplantation but increase immune rejection, especially T cell-mediated rejection (TCMR), the mechanism of which remains to be elucidated. Our study demonstrates that during ischemia-reperfusion injury (IRI), the translocation of tubular murine double minute 2 leads to basolateral programmed death ligand 1 degradation, which ultimately results in the occurrence of TCMR, which may provide a new therapeutic strategy for preventing AKI donor-associated TCMR.

Using 1/2 Descending Time in CEUS to Identify Renal Allograft Rejection

RATIONALE AND OBJECTIVES

This study investigates the potential of quantitative Contrast-Enhanced Ultrasound (CEUS) parameters to distinguish between graft dysfunction due to rejection and non-rejection in kidney transplant recipients.

METHODS

In this retrospective study, 50 kidney transplant patients who presented elevated serum creatinine or proteinuria were analyzed. They were categorized as rejection or non-rejection based on biopsy outcomes. These classifications were applied in both derivation (n = 33) and validation cohorts (n = 17). Prior to the biopsy, all patients underwent a CEUS. Quantitative parameters derived from the CEUS were further analyzed for their consistency and reliability. Additionally, the relationship between the Banff scores, a standard for diagnosing transplant rejections, and these CEUS parameters was explored.

RESULTS

Significant differences between rejection and non-rejection groups were observed in the CEUS parameters of derivation cohorts. Specifically, Peak Intensity (PI), 1/2 Descending Time (DT/2), Area Under Curve (AUC), and Mean Transit Time (MTT) stood out. Sensitivity and specificity for these parameters were 76.5% and 87.5% for PI, 76.5% and 81.2% for DT/2, 76.5% and 87.5% for AUC, and 68.8% and 94.1% for MTT, respectively. DT/2 and MTT showed superior interobserver agreement compared to PI and AUC. When extrapolating the cutoff values from the derivation cohort to the validation group, DT/2 and AUC exhibited optimal diagnostic precision with positive and negative predictive values being 91.7% vs. 100% and 100% vs. 85.7%, respectively. Additionally, DT/2 effectively differentiated between mild and moderate to severe microvascular inflammation, pivotal in diagnosing antibody-mediated renal transplant rejection.

CONCLUSION

DT/2 from CEUS parameters presents as a reliable tool to differentiate rejection from non-rejection causes in renal transplant dysfunction. Yet, large-scale, multi-center studies are essential for further validation.

Diagnostic value of selenoprotein changes in renal tissues for acute rejection of kidney transplantation as revealed by transcriptomics

BACKGROUND

There seems to be a close link between the changing levels of selenoproteins, which are important for maintaining redox homeostasis in the body, and acute rejection of kidney transplants. The aim of this study was to explore the diagnostic value of selenoprotein change characteristics in renal tissues for acute rejection of kidney transplantation.

METHODS

We first explored the potential biological functions of 25 selenoproteins in the human body by enrichment analysis and used the HPA database to clarify the expression levels of selenoproteins in kidney tissues; We then constructed a diagnostic model using "Logistic regression analysis" and "Nomogram model"; Calibration curves and ROC curves were used to evaluate the diagnostic models, and clinical decision curves (DCA) were used to assess the diagnostic value of selenoprotein changes to the clinic; Single-gene GSEA enrichment analysis to further explore the potential regulatory mechanisms of selenoproteins; The Cibersort algorithm explores the level of immune cell infiltration and uses correlation analysis to clarify the correlation between selenoproteins and immune cells; We further assessed the diagnostic value of selenoproteins in kidney transplantation ABMR and TCMR, respectively. Finally, we validated the expression level of selenoproteins in kidney tissues by constructing a rat model of acute rejection of kidney transplantation using transcriptome sequencing.

RESULTS

Our enrichment analysis revealed that selenoproteins are mainly closely associated with biological functions such as oxidative stress, inflammation, and immune regulation (P<0.05); The HPA database suggests that a total of 23 selenoproteins can be expressed in kidney tissue. We constructed a diagnostic model using these 23 selenoproteins, and both calibration curves and ROC curves proved that their change levels have good diagnostic value for acute rejection of kidney transplantation, and DCA curves proved the role of selenoproteins in clinical decision-making; Single-gene GSEA enrichment analysis revealed that selenoproteins are closely associated with immune regulation-related pathways (P<0.05); The Cibersort algorithm identified 10 immune cell infiltration levels that were significantly altered during acute rejection of kidney transplantation (P<0.05), while correlation analyses indicated that selenoproteins correlate with multiple immune cell infiltrations; In ABMR and TCMR, we again verified the diagnostic value of selenoprotein changes in acute rejection of kidney transplantation. Finally, we found significant differences in the expression levels of nine selenoproteins in a rat model of acute rejection of kidney transplantation (P<0.05).

CONCLUSION

Changes in selenoproteins in renal tissues have good diagnostic value for acute rejection of kidneyl transplantation, and selenoproteins may be able to be a potential target for alleviating acute rejection of kidney transplantation.

Cell-free DNA for the detection of kidney allograft rejection

Donor-derived cell-free DNA (dd-cfDNA) is an emerging noninvasive biomarker that has the potential to detect allograft injury. The capacity of dd-cfDNA to detect kidney allograft rejection and its added clinical value beyond standard of care patient monitoring is unclear. We enrolled 2,882 kidney allograft recipients from 14 transplantation centers in Europe and the United States in an observational population-based study. The primary analysis included 1,134 patients. Donor-derived cell-free DNA levels strongly correlated with allograft rejection, including antibody-mediated rejection (P < 0.0001), T cell-mediated rejection (P < 0.0001) and mixed rejection (P < 0.0001). In multivariable analysis, circulating dd-cfDNA was significantly associated with allograft rejection (odds ratio 2.275; 95% confidence interval (CI) 1.902-2.739; P < 0.0001) independently of standard of care patient monitoring parameters. The inclusion of dd-cfDNA to a standard of care prediction model showed improved discrimination (area under the curve 0.777 (95% CI 0.741-0.811) to 0.821 (95% CI 0.784-0.852); P = 0.0011) and calibration. These results were confirmed in the external validation cohorts (n = 1,748) including a cohort of African American patients (n = 439). Finally, dd-cfDNA showed high predictive value to detect subclinical rejection in stable patients. Our study provides insights on the potential value of assessing dd-cfDNA, in addition to standard of care monitoring, to improve the detection of allograft rejection. ClinicalTrials.gov registration: NCT05995379 .

Advancing mouse models for transplantation research

Mouse models have been instrumental in understanding mechanisms of transplant rejection and tolerance, but cross-study reproducibility and translation of experimental findings into effective clinical therapies are issues of concern. The Mouse Models in Transplantation symposium gathered scientists and physician-scientists involved in basic and clinical research in transplantation to discuss the strengths and limitations of mouse transplant models and strategies to enhance their utility. Participants recognized that increased procedure standardization, including the use of prespecified, defined endpoints, and statistical power analyses, would benefit the field. They also discussed the generation of new models that incorporate environmental and genetic variables affecting clinical outcomes as potentially important. If implemented, these strategies are expected to improve the reproducibility of mouse studies and increase their translation to clinical trials and, ideally, new Food and Drug Administration-approved drugs.

IDO+ Endothelial Cells in Glomeruli of Kidney Transplantation Patients With Glomerulitis

Background

Kidney transplantation is the preferred treatment option for patients with end-stage renal disease. However, long-term graft survival remains a challenge. The enzyme indoleamine 2,3 dioxygenase (IDO) has been reported to have immunomodulatory effects with IDO transcripts being elevated in both antibody-mediated rejection and T cell-mediated rejection.

Methods

A metal-conjugated antibody panel for the staining of kidney biopsies was developed, allowing the visualization of 41 structural and immune markers on a single tissue slide to gain in-depth insight into the composition and localization of the immune cell compartment. Staining was applied to week 4 and 24 protocol biopsies of 49 patients as well as on 15 indication biopsies of the TRITON study and 4 additional transplantation biopsies with glomerulitis.

Results

A highly distinctive and specific glomerular IDO expression was observed in biopsies from 3 of 49 patients in imaging mass cytometry. Immunohistochemistry confirmed IDO expression in glomeruli of 10 of 10 cases with glomerulitis. IDO was found to be expressed by CD31+ glomerular endothelial cells, accompanied by the presence of granzyme-B+Tbet+CD7+CD45RA+ natural killer cells and CD68+ macrophages. Furthermore, a proportion of both the immune cells and endothelial cells expressed Ki-67, indicative of cell proliferation, which was not observed in control glomeruli.

Conclusions

Our results show glomerular IDO expression in transplanted kidneys with glomerulitis, which is accompanied by increased numbers of natural killer cells and macrophages and likely reflects local immune activation.

Iguratimod ameliorates antibody-mediated rejection after renal transplant by modulating the Th17/Treg paradigm

BACKGROUND

Iguratimod (IGU) is widely used in clinical practice due to its stable anti-inflammatory effects. Our previous studies have confirmed that the proportion of Th17/Treg balance in patients taking IGU altered significantly. This study aims to explore the role of IGU in antibody-mediated rejection (ABMR) and its potential mechanisms.

METHODS

We conducted bioinformatics analysis of sequencing data from the GEO database to analyze the abundance of immune cell infiltration in transplanted kidney tissues. In vivo, IGU was intervened in a mice secondary skin transplantation model and a mice kidney transplantation ABMR model, and histological morphology of the grafts were examined by pathological staining, while relevant indicators were determined through qRT-PCR, immunohistochemistry, and enzyme-linked immunosorbent assay, observed T cell differentiation by flow cytometry, and preliminarily assessed the immunosuppressive effect of IGU. In vitro, we established Th17 and Treg cell induction and stimulation differentiation culture systems and added IGU for intervention to explore its effects on their differentiation.

RESULTS

Through bioinformatics analysis, we found that Th17 and Treg may play important roles in the occurrence and development of ABMR. In vivo, we found that IGU could effectively reduce the damage caused by ABMR to the grafts, alleviate the infiltration of inflammatory cells in the graft tissues, and reduce the deposition of C4d in the grafts. Moreover, it is also found that IGU regulated the differentiation of Th17 and Treg cells in the spleen and peripheral blood and reduced the expression of IL-17A in the grafts and serum. In addition, same changes were observed in the induction and differentiation culture system of Th17 and Treg cells in vitro after the addition of IGU.

CONCLUSION

IGU can inhibit the progression of ABMR by regulating the differentiation of Th17 and Treg cells, providing novel insights for optimizing clinical immunosuppressive treatment regimens.