Isolated v-lesion in kidney transplant recipients: Characteristics, association with DSA, and histological follow-up

Clinical and molecular spectrum of v-lesion

Isolated v-lesion presents diagnostic stratification and clinical challenges. We characterized allograft outcomes for this entity based on posttransplant time (early: ≤1 month vs late: >1 month) and compared its molecular phenotype with other v+ rejection forms. Using the NanoString B-HOT panel, we analyzed 92 archival formalin-fixed paraffin-embedded tissue kidney biopsies from 3 centers: isolated v-lesion (n = 23), antibody-mediated rejection (ABMR) v+ (n = 26), T cell-mediated rejection (TCMR) v+ (n = 10), mixed rejection v+ (n = 23), and normal tissue (n = 10). Six gene sets (ABMR, DSAST, ENDAT, TCMR, early/acute injury, late injury) were assessed. Early isolated v-lesions had the poorest 1-year death-censored graft survival compared with late isolated v-lesions or other rejections (P = .034). Gene set analysis showed lower TCMR-related gene expression in isolated v+ groups than TCMR and mixed rejection (P < .001). Both early- and late isolated v-lesions had lower ABMR-related gene expression than ABMR, mixed rejection, and TCMR (P ≤ .022). Late isolated v-lesions showed reduced DSAST and ENDAT gene expression versus ABMR (P ≤ .046) and decreased early/acute injury gene expression than early isolated v+, ABMR, TCMR, and mixed rejection (P ≤ .026). In conclusion, isolated v-lesions exhibit distinct gene expression patterns versus other rejection v+ forms. Early isolated v+ is associated with poorer prognosis and increased early/acute injury gene expression than late isolated v+, suggesting distinct etiologies.

Automated Urinary Chemokine Assays for Noninvasive Detection of Kidney Transplant Rejection: A Prospective Cohort Study

RATIONALE & OBJECTIVE

Prior studies have demonstrated the diagnostic potential of urinary chemokines C-X-C motif ligand 9 (CXCL9) and CXCL10 for kidney transplant rejection. However, their benefit in addition to clinical information has not been demonstrated. We evaluated the diagnostic performance for detecting acute rejection of urinary CXCL9 and CXCL10 when integrated with clinical information.

STUDY DESIGN

Single-center prospective cohort study.

SETTING & PARTICIPANTS

We analyzed 1,559 biopsy-paired urinary samples from 622 kidney transplants performed between April 2013 and July 2019 at a single transplant center in Belgium. External validation was performed in 986 biopsy-paired urinary samples.

TESTS COMPARED

We quantified urinary CXCL9 (uCXCL9) and CXCL10 (uCXCL10) using an automated immunoassay platform and normalized the values to urinary creatinine. Urinary chemokines were incorporated into a multivariable model with routine clinical markers (estimated glomerular filtration rate, donor-specific antibodies, and polyoma viremia) (integrated model). This model was then compared with the tissue diagnosis according to the Banff classification for acute rejection.

OUTCOME

Acute rejection detected on kidney biopsy using the Banff classification.

RESULTS

Chemokines integrated with routine clinical markers had high diagnostic value for detection of acute rejection (n=150) (receiver operating characteristic area under the curve 81.3% [95% CI, 77.6-85.0]). The integrated model would help avoid 59 protocol biopsies per 100 patients when the risk for rejection is predicted to be below 10%. The performance of the integrated model was similar in the external validation cohort.

LIMITATIONS

The cross-sectional nature obviates investigating the evolution over time and prediction of future rejection.

CONCLUSIONS

The use of an integrated model of urinary chemokines and clinical markers for noninvasive monitoring of rejection could enable a reduction in the number of biopsies. Urinary chemokines may be useful noninvasive biomarkers whose use should be further studied in prospective randomized trials to clarify their role in guiding clinical care and the use of biopsies to detect rejection after kidney transplantation.

PLAIN-LANGUAGE SUMMARY

Urinary chemokines CXCL9 and CXCL10 have been suggested to be good noninvasive biomarkers of kidney transplant rejection. However, defining a context of use and integration with clinical information is necessary before clinical implementation can begin. In this study, we demonstrated that urinary chemokines CXCL9 and CXCL10, together with clinical information, have substantial diagnostic accuracy for the detection of acute kidney transplant rejection. Application of urinary chemokines together with clinical information may guide biopsy practices following kidney transplantation and potentially reduce the need for kidney transplant biopsies.

The Pathological and Clinical Diversity of Acute Vascular Rejection in Kidney Transplantation

BACKGROUND

Vascular rejection (VR) is characterized by arteritis, steroid resistance, and increased graft loss but is poorly described using modern diagnostics.

METHODS

We screened 3715 consecutive biopsies and retrospectively evaluated clinical and histological phenotypes of VR (n = 100) against rejection without arteritis (v0REJ, n = 540) and normal controls (n = 1108).

RESULTS

Biopsy sample size affected the likelihood of arterial sampling, VR diagnosis, and final Banff v scores (P < 0.001). Local v and cv scores were greatest in larger arteries (n = 258). VR comprised 15.6% of all rejection episodes, presented earlier (median 1.0 mo, interquartile range, 0.4-8 mo) with higher serum creatinine levels and inferior graft survival, versus v0REJ (P < 0.001). Early VR (≤1 mo) was common (54%) and predicted by sensitization, delayed function, and prior corticosteroid use, with associated acute dysfunction and optimal therapeutic response, independent of Banff v score. Late VR followed under-immunosuppression in 71.4% (noncompliance 38.8%, iatrogenic 32.6%), and was associated with chronic interstitial fibrosis, incomplete renal functional recovery and persistent inflammation using sequential histopathology. The etiology was "pure" antibody-mediated VR (n = 21), mixed VR (n = 36), and "pure" T cell-mediated VR (n = 43). Isolated VR (n = 34, Banff i < 1 without tubulitis) comprised 24 T cell-mediated VR and 10 antibody-mediated VR, presenting with mild renal dysfunction, minimal Banff acute scores, and better graft survival compared with inflamed VR. Interstitial inflammation influenced acute renal dysfunction and early treatment response, whereas chronic tubulointerstitial damage determined long-term graft loss.

CONCLUSIONS

VR is a heterogenous entity influenced by time-of-onset, pathophysiology, accompanying interstitial inflammation and fibrosis. Adequate histological sampling is essential for its accurate diagnostic classification and treatment.

Intimal Arteritis and Microvascular Inflammation Are Associated With Inferior Kidney Graft Outcome, Regardless of Donor-Specific Antibodies

Background: The prognostic role of intimal arteritis of kidney allografts in donor-specific antibody negative (DSA–) antibody-mediated rejection (ABMR) remains unclear.

Methods: Seventy-two out of 881 patients who had undergone kidney transplantation from 2014 to 2017 exhibited intimal arteritis in biopsies performed during the first 12 months. In 26 DSA negative cases, the intimal arteritis was accompanied by tubulointerstitial inflammation as part of T cell-mediated vascular rejection (TCMRV, N = 26); intimal arteritis along with microvascular inflammation occurred in 29 DSA negative (ABMRV/DSA–) and 19 DSA positive cases (ABMRV, DSA+, N = 17). In 60 (83%) patients with intimal arteritis, the surveillance biopsies after antirejection therapy were performed. Hundred and two patients with non-vascular ABMR with DSA (ABMR/DSA+, N = 55) and without DSA (ABMR/DSA–, N = 47) served as controls. Time to transplant glomerulopathy (TG) and graft failure were the study endpoints.

Results: Transplant glomerulopathy -free survival at 36 months was 100% in TCMRV, 85% in ABMR/DSA–, 65% in ABMRV/DSA-, 54% in ABMR/DSA+ and 31% in ABMRV/DSA+ (log rank p < 0.001). Death-censored graft survival at 36 months was 98% in ABMR/DSA-, 96% in TCMRV, 86% in ABMRV/DSA–, 79% in ABMR/DSA+, and 64% in ABMRV/DSA+ group (log rank p = 0.001). In surveillance biopsies, the resolution of rejection was found in 19 (90%) TCMRV, 14 (58%) ABMRV/DSA–, and only 4 (27%) ABMRV/DSA+ patients (p = 0.006). In the multivariable model, intimal arteritis as part of ABMR represented a significant risk for TG development (HR 2.1, 95% CI 1.2–3.8; p = 0.012) regardless of DSA status but not for graft failure at 36 months.

Conclusions: Intimal arteritis as part of ABMR represented a risk for early development of TG regardless of the presence or absence of DSA. Intimal arteritis in DSA positive ABMR represented the high-risk phenotype.

Early-Isolated V Lesion in Kidney Allograft: Acute Rejection or Ischemic Injury? A Case Report of Primary Nonfunction and Graft Loss

Intimal arteritis (v-lesion) is a negative prognostic factor for kidney allograft survival. Early isolated v-lesions do not always represent a pathologic marker of acute T cell- or antibody-mediated rejection. In particular, in the case of transplant negative for C4d and donor-specific antibodies, such a finding can suggest an ischemic-reperfusion injury. There is an intense debate in the literature concerning the origin of this histologic feature. In the present study, we analyze how this argument can have a clinical relevance. Here we report a case of a 61-year-old woman with end-stage renal disease due to autosomal dominant polycystic kidney disease. The patient underwent kidney transplant from expanded criteria donor. Organs from expanded criteria donors are more prone to ischemic-reperfusion injury. Postoperative course was characterized by primary nonfunction of the graft. A first biopsy showed early isolated v-lesion in otherwise normal renal parenchymal. Simultaneously, a computed tomography scan revealed stenosis of the main renal artery. An endovascular stent was placed. Despite improved vascularization of the graft, no clinical response was observed and the patient remained anuric. A second biopsy was performed, showing T-cell mediated rejection (Banff Classification 1A). Despite pulse steroid, the patient lost the graft.

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

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

Progression of Interstitial Fibrosis and Tubular Atrophy in Low Immunological Risk Renal Transplants Monitored by Sequential Surveillance Biopsies: The Influence of TAC Exposure and Metabolism

The combination of tacrolimus (TAC) and mycophenolate is the most widely employed maintenance immunosuppression in renal transplants. Different surrogates of tacrolimus exposure or metabolism such as tacrolimus trough levels (TAC-C₀), coefficient of variation of tacrolimus (CV-TAC-C₀), time in therapeutic range (TTR), and tacrolimus concentration dose ratio (C/D) have been associated with graft outcomes. We explore in a cohort of low immunological risk renal transplants (n = 85) treated with TAC, mycophenolate mofetil (MMF), and steroids and then monitored by paired surveillance biopsies the association between histological lesions and TAC-C₀ at the time of biopsy as well as CV-TAC-C₀, TTR, and C/D during follow up. Interstitial inflammation (i-Banff score ≥ 1) in the first surveillance biopsy was associated with TAC-C₀ (odds ratio (OR): 0.69, 95% confidence interval (CI): 0.50–0.96; p = 0.027). In the second surveillance biopsy, inflammation was associated with time below the therapeutic range (OR: 1.05 and 95% CI: 1.01–1.10; p = 0.023). Interstitial inflammation in scarred areas (i-IFTA score ≥ 1) was not associated with surrogates of TAC exposure/metabolism. Progression of interstitial fibrosis/tubular atrophy (IF/TA) was observed in 35 cases (41.2%). Multivariate regression logistic analysis showed that mean C/D (OR: 0.48; 95% CI: 0.25–0.92; p = 0.026) and IF/TA in the first biopsy (OR: 0.43, 95% CI: 0.24–0.77, p = 0.005) were associated with IF/TA progression between biopsies. A low C/D ratio is associated with IF/TA progression, suggesting that TAC nephrotoxicity may contribute to fibrosis progression in well immunosuppressed patients. Our data support that TAC exposure is associated with inflammation in healthy kidney areas but not in scarred tissue.

Diagnosis of renal transplant rejection: Banff classification and beyond

Diagnosis of renal transplant rejection is dependent on interpretation of renal allograft biopsies. The Banff Classification of Allograft Pathology, which was developed as a standardized working classification system in 1991, has contributed to the standardization of definitions for histologic injuries resulting from renal allograft rejections and provided a universal grading system for assessing these injuries. It has also helped to provide insight into the underlying pathogenic mechanisms that contribute to transplant rejection. In addition to histological and immunologic parameters, molecular tools are now being used to facilitate the diagnosis of rejection. In this review, I will discuss morphologic features of renal transplant rejections as well as major revisions and pitfalls of the Banff classification system, and provide future perspectives.

Isolated Vascular Lesions (IVL) in Early Allograft Biopsies: A Case Series

This case series includes five patients diagnosed as isolated vascular lesion (IVL) on allograft biopsy in an early post-transplant period. These patients presented with graft dysfunction. The biopsies satisfied the criteria for IVL as laid down by Banff 2009. Four of these patients were treated with corticosteroids and other anti rejection measures. C4d and DSA were negative in all. The patients showed good response to treatment with stable graft function at the longest follow-up of one year. We have also reviewed the literature about IVL as a specific entity. There are differences between the molecular and clinical data of IVL. It is difficult to differentiate whether IVL is a rejection or non-rejection process. This study aims to highlight the importance of a rare entity.

Early isolated V-lesion may not truly represent rejection of the kidney allograft

Intimal arteritis is known to be a negative prognostic factor for kidney allograft survival. Isolated v-lesion (IV) is defined as intimal arteritis with minimal tubulointerstitial inflammation (TI). Although the Banff classification assesses IV as T cell-mediated rejection (TCMR), clinical, and prognostic significance of early IV (early IV, eIV) with negative C4d and donor-specific antibodies (DSA) remains unclear. To help resolve if such eIV truly represents acute rejection, a molecular study was performed. The transcriptome of eIV (n=6), T cell-mediated vascular rejection with rich TI (T cell-mediated vascular rejection, TCMRV, n=4) and non-rejection histologic findings (n=8) was compared using microarrays. A total of 310 genes were identified to be deregulated in TCMRV compared with eIV. Gene enrichment analysis categorized deregulated genes to be associated primarily with T-cells associated biological processes involved in an innate and adaptive immune and inflammatory response. Comparison of deregulated gene lists between the study groups and controls showed only a 1.7% gene overlap. Unsupervised hierarchical cluster analysis revealed clear distinction of eIV from TCMRV and showed similarity with a control group. Up-regulation of immune response genes in TCMRV was validated using RT-qPCR in a different set of eIV (n=12) and TCMRV (n=8) samples. The transcriptome of early IV (< 1 month) with negative C4d and DSA is associated with a weak immune signature compared with TCMRV and shows similarity with normal findings. Such eIV may feature non-rejection origin and reflect an injury distinct from an alloimmune response. The present study supports use of molecular methods when interpreting kidney allograft biopsy findings.

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

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