International variation in the interpretation of renal transplant biopsies: report of the CERTPAP Project

Molecular diagnosis of T cell-mediated rejection in human kidney transplant biopsies

Histologic diagnosis of T cell-mediated rejection is flawed by subjective assessments, nonspecific lesions and arbitrary rules. This study developed a molecular test for T cell-mediated rejection. We used microarray results from 403 kidney transplant biopsies to derive a classifier assigning T cell-mediated rejection scores to all biopsies, and compared these with histologic assessments. The score correlated with histologic lesions of T cell-mediated rejection (infiltrate, tubulitis). The accuracy of the classifier for the histology diagnoses was 89%. Very high and low molecular scores corresponded with unanimity among three pathologists on the presence or absence of T cell-mediated rejection, respectively. The molecular score had low sensitivity (50%) and positive predictive value (62%) for the histology diagnoses. However, histology showed similar disagreement between pathologists--only 45-56% sensitivity of one pathologist with diagnoses of T cell-mediated rejection by another. Discrepancies between molecular scores and histology were mostly when histology was ambiguous ("borderline") or unreliable, e.g. in cases with scarring or inflammation induced by tissue injury. Vasculitis (isolated v-lesion TCMR) was particularly discrepant, with most cases exhibiting low TCMR scores. We propose new rules to integrate molecular tests and histology into a precision diagnostic system that can reduce errors, ambiguity and interpathologist disagreement.

Interobserver variability of ultrasound elastography in transplant kidneys: correlations with clinical-Doppler parameters

Real-time sonoelastography (RSE) is a relatively new imaging technique that visualizes relative difference in tissue hardness by evaluating changes in local strain in response to external stress. Our aim was to evaluate the ability of investigators to use sonoelastography to detect differences in renal cortical stiffness and assess the relationship between stiffness and clinical-Doppler parameters. In 42 adult renal transplant recipients, sonoelastography of kidney was performed to calculate the strain ratio (SR) of the central echo complex to the renal parenchyma. Resistive index (RI) and pulsatility index (PI) were also measured. Estimated glomerular filtration rate (eGFR) was calculated. Parenchymal stiffness showed significant positive correlation with RI and PI (r: 0.41 p = 0.007 and r: 0.48 p = 0.001, respectively). Parenchymal stiffness and eGFR did not have a significant correlation (p = 0.42). Interobserver agreement, expressed as intraclass correlation coeffiicient was 0.47 (95% CI: 0.05-0.70). Parenchymal stiffness (SR) showed significant positive correlation with RI and PI but sonoelastography has also wide range intra- and low interobserver agreement in renal transplants. Further studies are warranted in larger patient groups to determine the reliability of sonoelastography in renal transplants.

Renal interstitial fibrosis: mechanisms and evaluation

PURPOSE OF REVIEW

Tubulointerstitial injury in the kidney is complex, involving a number of independent and overlapping cellular and molecular pathways, with renal interstitial fibrosis and tubular atrophy (IFTA) as the final common pathway. Furthermore, there are multiple ways to assess IFTA.

RECENT FINDINGS

Cells involved include tubular epithelial cells, fibroblasts, fibrocytes, myofibroblasts, monocyte/macrophages, and mast cells with complex and still incompletely characterized cell-molecular interactions. Molecular mediators involved are numerous and involve pathways such as transforming growth factor (TGF)-β, bone morphogenic protein (BMP), platelet-derived growth factor (PDGF), and hepatocyte growth factor (HGF). Recent genomic approaches have shed insight into some of these cellular and molecular pathways. Pathologic evaluation of IFTA is central in assessing the severity of chronic disease; however, there are a variety of methods used to assess IFTA. Most assessment of IFTA relies on pathologist assessment of special stains such as trichrome, Sirius Red, and collagen III immunohistochemistry. Visual pathologist assessment can be prone to intra and interobserver variability, but some methods employ computerized morphometery, without a clear consensus as to the best method.

SUMMARY

IFTA results from on orchestration of cell types and molecular pathways. Opinions vary on the optimal qualitative and quantitative assessment of IFTA.

New computerized color image analysis for the quantification of interstitial fibrosis in renal transplantation

BACKGROUND

Chronic allograft injury, the primary cause of late allograft failure in renal transplantation, can be diagnosed early at a preclinical stage by histopathological changes such as interstitial fibrosis (IF). Currently, assessed by semiquantitative analysis in the Banff classification, IF quantification is limited by pathologist's subjective interpretation.

METHODS

We have designed algorithms dedicated to quantify IF by computerized color image analysis. This innovative and objective software automatically extracts the green areas characteristic of IF in Masson's trichrome based on color image segmentation followed by removal of nonspecific IF staining (capsula, sclerosis glomeruli and normal glomeruli, normal basement membrane) and computes an index. It also counts automatically the number of glomeruli. Sixty-seven Masson stained renal transplant biopsies at various IF stages were imaged using a digital color camera mounted on a microscope. We tested the robustness of the method against varying acquisition parameters.

RESULTS

We demonstrated that the parameters do not have an impact on this quantification and that the algorithm is able to handle biopsy color variations. The intra- and interobserver reproducibility was good (P<0.003). The kappa coefficient that was performed on another set of 90 biopsies to evaluate the concordance of our method with an expert Banff quantification was 0.68, indicating a substantial agreement. Finally, the computerized IF correlated with renal function.

CONCLUSION

This study demonstrates that computerized color image analysis is a reliable and reproducible method to evaluate renal IF in routine practice and in multi-centric studies.

Magnetic resonance elastography of the kidneys: feasibility and reproducibility in young healthy adults

PURPOSE

To evaluate the feasibility and reproducibility of renal magnetic resonance elastography (MRE) in young healthy volunteers.

MATERIALS AND METHODS

Ten volunteers underwent renal MRE twice at a 4-5 week interval. The vibrations (45 and 76 Hz) were generated by a speaker positioned beneath the volunteers' back and centered on their left kidney. For each frequency, three sagittal slices were acquired (eight phase offsets per cycle, motion-encoding gradients successively positioned along the three directions of space). Shear velocity images were reconstructed using the curl operator combined with the local frequency estimation (LFE) algorithm.

RESULTS

The mean shear velocities measured in the renal parenchyma during the two examinations were not significantly different and exhibited a mean variation of 6% at 45 Hz and 76 Hz. The mean shear velocities in renal parenchyma were 2.21 ± 0.14 m/s at 45 Hz (shear modulus of 4.9 ± 0.5 kPa) and 3.07 ± 0.17 m/s at 76 Hz (9.4 ± 0.8 kPa, P < 0.01). The mean shear velocities in the renal cortex and medulla were respectively 2.19 ± 0.13 m/s and 2.32 ± 0.16 m/s at 45 Hz (P = 0.002) and 3.06 ± 0.16 m/s and 3.10 ± 0.22 m/s at 76 Hz (P = 0.13).

CONCLUSION

Renal MRE was feasible and reproducible. Two independent measurements of shear velocities in the renal parenchyma of the same subjects showed an average variability of 6%.

Identification of lesions indicating rejection in kidney transplant biopsies: tubulitis is severely under-detected by conventional microscopy

BACKGROUND

In the current international Banff classification of kidney transplant rejection, tubulitis and intimal arteritis are regarded as the key histological features of acute rejection. Grade 1 tubulitis can sometimes be seen in biopsies that do not represent acute rejection; but in the case of intimal arteritis, just one lymphocyte can justify anti-rejection treatment. Our aim was to audit reliability and accuracy of recognizing tubulitis and intimal arteritis using the approach recommended by the Banff classification and correlate any discrepancies with subsequent graft function.

METHODS

This is a retrospective review of all kidney transplant biopsies reported as negative for rejection from 1 January 2009 to 31 December 2009 to assess the presence or absence of occult tubulitis and arteritis. Lymphocytes were immunostained with CD3, using Periodic Acid Schiff as a counterstain. Sections were reviewed to detect missed intimal arteritis and tubulitis. Discrepancies between the report and the immunostain results were analysed by biopsy type and broken down by the reporting pathologist. The graft function of any patient with missed lesions was checked to test for adverse impact on the patient.

RESULTS

'Missed' tubulitis was found in 68% of biopsies, but only two such cases subsequently developed biopsy-proven acute rejection. Only one case of missed intimal arteritis was found (1%) and the subsequent clinical course suggested that this was probably early rejection. There was no significant difference between the reporting pathologists.

CONCLUSIONS

We conclude that tubulitis is missed very frequently, but the Banff classification seems to be 'calibrated' to allow for this and it does not seriously affect the identification of clinically significant acute rejection. Immunostaining is therefore not indicated in routine practice because (by Banff criteria) it would result in over-diagnosis of rejection. Intimal arteritis can indicate acute rejection even if extremely mild.

Interstitial fibrosis evolution on early sequential screening renal allograft biopsies using quantitative image analysis

Screening renal biopsies (RB) may assess early changes of interstitial fibrosis (IF) after transplantation. The aim of this study was to quantify IF by automatic color image analysis on sequential RB. We analyzed RB performed at day (D) 0, month (M) 3 and M12 from 140 renal transplant recipients with a program of color segmentation imaging. The mean IF score was 19 ± 9% at D0, 27 ± 11% at M3 and 32 ± 11% at M12 with a 8% progression during the first 3 months and 5% between M3 and M12. IF at M3 was correlated with estimated glomerular rate (eGFR) at M3, 12 and 24 (p < 0.02) and IF at M12 with eGFR at M12 and 48 (p < 0.05). Furthermore, IF evolution between D0 and M3 (ΔIFM3-D0) was correlated with eGFR at M24, 36 and 48 (p < 0.03). IF at M12 was significantly associated with male donor gender and tacrolimus dose (p = 0.03). ΔIFM3-D0 was significantly associated with male donor gender, acute rejection episodes (p = 0.04) and diabetes mellitus (p = 0.02). Thus, significant IF is already present before transplantation. IF evolution is more important during the first 3 months and has some predictive ability for change in GFR. Intervention to decrease IF should be applied early, i.e. before 3 months, after transplantation.

Identifying biomarkers as diagnostic tools in kidney transplantation

There is a critical need for biomarkers for early diagnosis, treatment response, and surrogate end point and outcome prediction in organ transplantation, leading to a tailored and individualized treatment. Genomic and proteomic platforms have provided multiple promising new biomarkers during the last few years. However, there is still no routine application of any of these markers in clinical transplantation. This article will discuss the existing gap between biomarker discovery and clinical application in the kidney transplant setting. Approaches to implementing biomarker monitoring into clinical practice will also be discussed.

No association of kidney graft loss with human leukocyte antigen antibodies detected exclusively by sensitive Luminex single-antigen testing: a Collaborative Transplant Study report

BACKGROUND

It is unclear whether kidney transplant recipients with preformed donor-specific human leukocyte antigen (HLA) antibodies (DSA) detectable only in the highly sensitive Luminex single-antigen (LSA) assay are at an increased risk of graft failure.

METHODS

We studied 3148 patients who received a deceased donor kidney graft between 1996 and 2008 and were enrolled in the prospective serum project of the Collaborative Transplant Study. There were 118 patients with graft loss during the first 3 years after transplantation on whom recipient and donor DNA was available for complete HLA typing. We compared the incidence of LSA-detected DSA in these patients with graft failure and matched controls with functioning grafts. All patients were found negative in the less-sensitive complement-dependent lymphocytotoxicity and enzyme-linked immunosorbent assays.

RESULTS

When mean fluorescence intensity (MFI) of greater than or equal to 1000 was used as a cutoff for Luminex positivity, 118 patients with graft loss did not show a higher incidence of DSA against HLA-A, -B, -C, -DRB1/3/4/5, -DQA1, -DQB1, -DPA1, or -DPB1 antigens than 118 matched controls without graft loss (for all loci P not significant). The incidence of strong DSA (MFI ≥2000 or MFI ≥3000) detected only by LSA was low (for all loci between 0% and 5%) and did not identify unacceptable antigens that were relevant for graft loss within the first 3 years after transplantation.

CONCLUSION

We conclude that, given currently practiced crossmatch procedures and immunosuppressive regimens, exclusion of donor organs carrying "unacceptable" HLA based exclusively on sensitive LSA antibody testing is not justified.

Validation of the Oxford classification of IgA nephropathy

The Oxford classification of IgA nephropathy (IgAN) identified four pathological elements that were of prognostic value and additive to known clinical and laboratory variables in predicting patient outcome. These features are segmental glomerulosclerosis/adhesion, mesangial hypercellularity, endocapillary proliferation, and tubular atrophy/interstitial fibrosis. Here, we tested the Oxford results using an independent cohort of 187 adults and children with IgAN from 4 centers in North America by comparing the performance of the logistic regression model and the predictive value of each of the four lesions in both data sets. The cohorts had similar clinical and histological findings, presentations, and clinicopathological correlations. During follow-up, however, the North American cohort received more immunosuppressive and antihypertensive therapies. Identifying patients with a rapid decline in the rate of renal function using the logistic model from the original study in the validation data set was good (c-statistic 0.75), although less precise than in the original study (0.82). Individually, each pathological variable offered the same predictive value in both cohorts except mesangial hypercellularity, which was a weaker predictor. Thus, this North American cohort validated the Oxford IgAN classification and supports its utilization. Further studies are needed to determine the relationship to the impact of treatment and to define the value of the mesangial hypercellularity score.

Integrative analysis of -omics data and histologic scoring in renal disease and transplantation: renal histogenomics

The histologic scoring of renal biopsies is still the gold standard for renal disease classification. The Banff classification scheme and the chronic allograft damage index are histopathologic scoring schemes widely used in renal transplantation. The determination of genome-wide gene expression profiles in human renal biopsies has the potential to serve as independent validation data sets and also provide a more precise evaluation of the functional status behind the visible morphologic alterations. It is expected that results from high-throughput-omics experiments will lead to improved classification schemes in the near future as also discussed at recent Banff meetings. In this review we give an overview on-omics studies, focusing on the association of molecular changes on the transcript as well as on the protein level and morphologic scoring schemes in renal disease and transplantation.

Morphometric and visual evaluation of fibrosis in renal biopsies

Interstitial fibrosis is an outcome measure of increasing importance in clinical trials of both renal transplantation and native disease, but data on the comparative advantages of fibrosis measurement methods are limited. We compared four morphometric techniques and contrasted these with two visual fibrosis-scoring methods on trichrome-stained slides. Two morphometric methods included whole-slide digital images: collagen III immunohistochemistry and a new technique using trichrome and periodic acid-Schiff subtraction morphometry; the other two methods included Sirius Red with and without polarization on multiple digital fields. We evaluated 10 serial sections from 15 renal biopsies with a range of fibrosis extent and diagnoses on duplicate sections with each method on separate days. Three pathologists performed visual scoring on whole-slide images. Visual and morphometric techniques had good to excellent interassay reproducibility (R(2) = 0.62 to 0.96) and interobserver reproducibility (R(2) = 0.75 to 0.99, all P < 0.001). Morphometry showed less variation between observers than visual assessment (mean of 1% to 5% versus 11% to 13%). Collagen III, Sirius Red unpolarized, and visual scores had the strongest correlations (R(2) = 0.78 to 0.89), the greatest dynamic range, and the best correlation with estimated GFR (R(2) = 0.38 to 0.50, P < 0.01 to 0.001). Considering efficiency, reproducibility, and functional correlation, two current techniques stand out as potentially the best for clinical trials: collagen III morphometry and visual assessment of trichrome-stained slides.

Borderline rejection after renal transplantation--to treat or not to treat

According to the Banff classification of renal allograft pathology, the category borderline changes defines changes insufficient for a diagnosis of acute rejection. The relationship between borderline changes and acute renal allograft rejection still remains unclear. The appropriate clinical management for patients showing such changes is controversial. One possible interpretation of the high incidence of subacute tubulitis is that these changes in the absence of graft dysfunction are of no consequence and that treatment with intensified immunosuppression is unnecessary and perhaps harmful. Another view, consistent with the high incidence of CAN in late protocol biopsy studies, is that immunosuppression has become so powerful, that rejection may not even be manifested by a rising serum creatinine. Borderline changes should be used as part of an algorithm, but not as the only criterion, for therapeutic decision making. Based on the weak evidence of existing studies, in our patients with clinical borderline rejection, we have to weigh the individual immunological risk against the potential side effects of increased immunosuppression. Even in the knowledge that a majority of patients with borderline infiltrates will not progress into rejection, in many transplant centers, borderline rejection is treated with additional steroids or augmentation of maintenance immunosuppression.

Noninvasive diagnosis of acute rejection of renal allografts

PURPOSE OF REVIEW

Acute rejection is an immune process that begins with the recognition of the allograft as nonself and ends in graft destruction. Histological features of the allograft biopsy are currently used for the differential diagnosis of allograft dysfunction. In view of the safety and the opportunity for repetitive sampling, development of noninvasive biomarkers of allograft status is an important objective in transplantation. Herein, we review some of the progress towards the development of noninvasive biomarkers of human allograft status.

RECENT FINDINGS

Urinary cell and peripheral blood cell mRNA profiles have been associated with acute rejection of human renal allografts. Emerging data support the idea that development of noninvasive biomarkers predictive of antibody-mediated rejection is feasible. The demonstration that intragraft microRNA expression predicts renal allograft status suggests that noninvasively ascertained microRNA profiles may be of value.

SUMMARY

We are pleased with the progress to date, and anticipate clinical trials investigating the hypotheses that noninvasively ascertained mRNA profiles will minimize the need for invasive biopsy procedures, predict the development of acute rejection and chronic allograft nephropathy, facilitate preemptive therapy capable of preserving graft function, and facilitate personalization of immunosuppressive therapy for the allograft recipient.

Interstitial fibrosis quantification in renal transplant recipients randomized to continue cyclosporine or convert to sirolimus

Conversion from cyclosporine (CsA) to sirolimus at week 12 after kidney transplantation is associated with a significant improvement in renal function. The aim of this analysis was to investigate the effect of this conversion on interstitial fibrosis (IF), a hallmark of chronic allograft injury, in patients taking part in the CONCEPT trial. This multicenter, prospective, trial included 193 renal recipients randomized at week 12 to switch from CsA to sirolimus or to continue CsA, with mycophenolate mofetil. Routine biopsy with automated, quantified assessment of IF by a program of color segmentation was performed at 1 year in 121 patients. At 1 year, renal function was significantly improved in the conversion group as assessed by estimated GFR (MDRD) and measured GFR. Biopsy results, however, showed no between-group difference in percentage of IF. Calculated GFR at 1 year was significantly associated with the percentage of IF (p = 0.004, R(2)= 0.07). By multivariate analysis diabetic patients had more fibrosis than non-diabetic patients. In conclusion, although kidney transplant patients converted from CsA to sirolimus showed significant improvement in renal function, we found no difference of IF on 1-year biopsies.

Scoring total inflammation is superior to the current Banff inflammation score in predicting outcome and the degree of molecular disturbance in renal allografts

Emerging molecular analysis can be used as an objective and independent assessment of histopathological scoring systems. We compared the existing Banff i-score to the total inflammation (total i-) score for assessing the molecular phenotype in 129 renal allograft biopsies for cause. The total i-score showed stronger correlations with microarray-based gene sets representing major biological processes during allograft rejection. Receiver operating characteristic curves showed that total-i was superior (areas under the curves 0.85 vs. 0.73 for Banff i-score, p = 0.012) at assessing an abnormal cytotoxic T-cell burden, because it identified molecular disturbances in biopsies with advanced scarring. The total-i score was also a better predictor of graft survival than the Banff i-score and essentially all current diagnostic Banff categories. The exception was antibody-mediated rejection which is able to predict graft loss with greater specificity (96%) but at low sensitivity (38%) due to the fact that it only applies to cases with this diagnosis. The total i-score is able to achieve moderate sensitivities (60-80%) with losses in specificity (60-80%) across the whole population. Thus, the total i-score is superior to the current Banff i-score and most diagnostic Banff categories in predicting outcome and assessing the molecular phenotype of renal allografts.

Diagnosing rejection in renal transplants: a comparison of molecular- and histopathology-based approaches

The transcriptome has considerable potential for improving biopsy diagnoses. However, to realize this potential the relationship between the molecular phenotype of disease and histopathology must be established. We assessed 186 consecutive clinically indicated kidney transplant biopsies using microarrays, and built a classifier to distinguish rejection from nonrejection using predictive analysis of microarrays (PAM). Most genes selected by PAM were interferon-gamma-inducible or cytotoxic T-cell associated, for example, CXCL9, CXCL11, GBP1 and INDO. We then compared the PAM diagnoses to those from histopathology, which are based on the Banff diagnostic criteria. Disagreement occurred in approximately 20% of diagnoses, principally because of idiosyncratic limitations in the histopathology scoring system. The problematic diagnosis of 'borderline rejection' was resolved by PAM into two distinct classes, rejection and nonrejection. The diagnostic discrepancies between Banff and PAM in these cases were largely due to the Banff system's requirement for a tubulitis threshold in defining rejection. By examining the discrepancies between gene expression and histopathology, we provide external validation of the main features of the histopathology diagnostic criteria (the Banff consensus system), recommend improvements and outline a pathway for introducing molecular measurements.

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

[Screening biopsies in kidney transplantation: from subclinical acute rejection to chronic allograft lesions]

Kidney biopsies for screening purposes have the advantage of revealing the early appearance of lesions having a poor prognosis before kidney function is altered. Early screening of subclinical rejections allows preventive treatment of kidney transplantation in patients taking cyclosporine or azathioprine, thus improving their renal function and reducing the incidence of chronic histological lesions. However, this benefit has yet to be demonstrated in patients taking tacrolimus or mycophenolic acid. As for interstitial fibrosis lesions and tubular atrophy, biopsies can screen subclinical immunological lesions or those related to nephrotoxicity of anticalcineurins, which have a negative prognostic value in terms of graft survival. In addition, detection of these lesions could be a very useful criterion of efficacy in clinical studies. Moreover, they could help decide on modifying immunosuppressor treatment and evaluate the therapeutic strategies in patients at risk for humoral rejection. Finally, given the cost of biopsies and the inconvenience for the patient, the question of the timing and the number of screening biopsies is crucial. However, interventional studies evaluating notably immunosuppressor treatment modifications based on histological data are necessary to justify the daily use of screening biopsies.

Chronic allograft nephropathy: what have we learned from protocol biopsies?

Chronic allograft nephropathy, characterized by interstitial fibrosis and tubular atrophy, is still a major cause of graft loss after kidney transplantation. The complex pathophysiology of chronic allograft nephropathy is still poorly understood, and could be clarified by a more systematic performance of implantation and protocol biopsies of the renal allograft. This review highlights the contribution of implantation and protocol biopsies to our current knowledge of the complex interaction of multiple processes, ultimately leading to the development of interstitial fibrosis and tubular atrophy in the transplanted kidney. In addition, the safety and the limitations of protocol biopsies are discussed, as well as potential future directions for clinical practice and clinical research.

Peritubular capillaritis in renal allografts: prevalence, scoring system, reproducibility and clinicopathological correlates

While glomerulitis is graded according to the Banff classification, no criteria for scoring peritubular capillaritis (PTC) have been established. We retrospectively applied PTC-scoring criteria to 688 renal allograft (46 preimplantation, 461 protocol, 181 indication) biopsies. A total of 26.3% of all analyzed biopsies had peritubular capillaritis (implant 0%, protocol 17.6%, indication 45.5%; p < 0.0001). The most common capillaritis pattern was of moderate severity (5-10 luminal cells), focal in extent (10-50% of PTC), with a minority of neutrophils. A total of 24% of C4d- compared with 75% of C4d+ biopsies showed capillaritis (p < 0.0001). More than 80% of biopsies with glomerulitis had peritubular capillaritis. A total of 50.4% of biopsies with borderline or T-cell mediated rejection (TCMR) and 14.1% of biopsies without TCMR or antibody-mediated rejection (ABMR) showed capillaritis (p < 0.0001). The inter-observer reproducibility of the PTC-scoring features was fair to moderate. Diffuse capillaritis detected in early protocol biopsies had significant negative prognostic impact in terms of glomerular filtration rate 2 years posttransplantation. Indication biopsies show a significantly higher prevalence of capillaritis than protocol biopsies (45.5% vs. 17.6%; p < 0.0001). Capillaritis is more frequent and pronounced in ABMR, but can be observed in TCMR cases. Thus, scoring of peritubular capillaritis is feasible and can provide prognostic and diagnostic information in renal allograft biopsies.

Quantification of interstitial fibrosis by image analysis on routine renal biopsy in patients receiving cyclosporine

BACKGROUND

Renal interstitial fibrosis (IF) is the main histopathological feature of chronic allograft injury. IF is currently assessed by semiquantitative analysis, but automatic color image analysis may be more reliable and reproducible. We performed a retrospective analysis to calculate IF on routine renal biopsies performed at 1 year posttransplant.

METHODS

Data were obtained from MO2ART, a prospective multicenter trial in which cyclosporine A dose was adjusted based on C2 level. One-year routine biopsies were assessed from 26 patients from two centers. For each biopsy, a section was analyzed by a program of color segmentation imaging, which automatically extracts green color areas characteristic of IF. Results were expressed as percentage of IF and grade (grade 1: <25%, grade 2: 25-50%, and grade 3: >50%).

RESULTS

Mean IF score was 0.35+/-0.04. Quantitative IF grade 1 was observed in 9 biopsies (34.6%), grade 2 in 12 (46.1%), and grade 3 in 5 (19.2%). Diabetes and cytomegalovirus infection were significantly associated with a higher percentage of IF. There was no correlation between the group of randomization and IF. We found a statistical significant correlation between Banff 05 chronic lesions classification and the IF index (P<0.02). Repeated analysis of variance demonstrated an association between high grade of automated IF and a worsening of creatinine clearance (Modification of Diet in Renal Disease) between 1 and 3 years.

CONCLUSIONS

Automatic quantification of IF on routine renal biopsies at one year posttransplant is predictive of long-term allograft function and may assist early diagnosis of the interstitial lesions of chronic allograft injury.

Microarray analysis of rejection in human kidney transplants using pathogenesis-based transcript sets

Microarrays offer potential for objective diagnosis and insights into pathogenesis of allograft rejection. We used mouse transplants to annotate pathogenesis-based transcript sets (PBTs) that reflect major biologic events in allograft rejection-cytotoxic T-cell infiltration, interferon-gamma effects and parenchymal deterioration. We examined the relationship between PBT expression, histopathologic lesions and clinical diagnoses in 143 consecutive human kidney transplant biopsies for cause. PBTs correlated strongly with one another, indicating that transcriptome disturbances in renal transplants have a stereotyped internal structure. This disturbance was continuous, not dichotomous, across rejection and nonrejection. PBTs correlated with histopathologic lesions and were the highest in biopsies with clinically apparent rejection episodes. Surprisingly, antibody-mediated rejection had changes similar to T-cell mediated rejection. Biopsies lacking PBT disturbances did not have rejection. PBTs suggested that some current Banff histopathology criteria are unreliable, particularly at the cut-off between borderline and rejection. Results were validated in 51 additional biopsies. Thus many transcriptome changes previously described in rejection are features of a large-scale disturbance characteristic of rejection but occurring at lower levels in many forms of injury. PBTs represent a quantitative measure of the inflammatory disturbances in organ transplants, and a new window on the mechanisms of these changes.

SWOT analysis of Banff: strengths, weaknesses, opportunities and threats of the international Banff consensus process and classification system for renal allograft pathology

The Banff process defined the diagnostic histologic lesions for renal allograft rejection and created a standardized classification system where none had existed. By correcting this deficit the process had universal impact on clinical practice and clinical and basic research. All trials of new drugs since the early 1990s benefited, because the Banff classification of lesions permitted the end point of biopsy-proven rejection. The Banff process has strengths, weaknesses, opportunities and threats (SWOT). The strength is its self-organizing group structure to create consensus. Consensus does not mean correctness: defining consensus is essential if a widely held view is to be proved wrong. The weaknesses of the Banff process are the absence of an independent external standard to test the classification; and its almost exclusive reliance on histopathology, which has inherent limitations in intra- and interobserver reproducibility, particularly at the interface between borderline and rejection, is exactly where clinicians demand precision. The opportunity lies in the new technology such as transcriptomics, which can form an external standard and can be incorporated into a new classification combining the elegance of histopathology and the objectivity of transcriptomics. The threat is the degree to which the renal transplant community will participate in and support this process.

To Biopsy or Not to Biopsy? Should We Screen the Histology of Stable Renal Grafts?

Chronic allograft dysfunction is currently the main cause of late allograft failure. Recent encouraging evidence suggests that it may be possible to delay the development of graft damages if adequate management is initiated early in the course of the disease. These observations have renewed interest in the performance of protocol biopsies as routine follow-up procedure for the screening of renal transplants. In the present review, we summarize the available data from the literature to determine the pros and cons of protocol renal allograft biopsies. On the basis of this evidence, we discuss the ethical concerns raised by this procedure.

Protocol biopsies in renal transplantation: insights into patient management and pathogenesis

A 1-day symposium on the application of protocol biopsies in renal transplantation was held in Boston, 21 July 2006. Representatives from centers with extensive experience in the use of protocol biopsies for routine patient care and research reported results on the pathological findings and their value in patient management. The consensus was that protocol biopsies, in experienced hands, are a safe and valuable means of detecting subclinical disease that can benefit from modification of therapy. Furthermore, molecular studies reveal evidence of activity or progression not readily appreciated by histological techniques. Wider application is expected in multicenter clinical trials to predict and validate outcomes. The principal barrier to wider use of protocol biopsies is knowledge of the benefits of intervention.

Interobserver reproducibility and application of the ISN/RPS classification of lupus nephritis-a UK-wide study

We sought to assess the interobserver variation of the new International Society of Nephrology/Renal Pathology Society (ISN/RPS) classification of lupus nephritis when compared with the previous World Health Organization classification, when used by pathologists throughout the UK. We also sought differences in how the 2 classifications were applied to a single set of biopsies. Twenty unselected renal biopsies showing lupus nephritis were circulated to pathologists in the UK National Renal Pathology External Quality Assessment Scheme, before the ISN/RPS scheme was published, with a request to apply the World Health Organization classification. The same slides were recirculated approximately 1 year later with a request to apply the ISN/RPS classification. A significant improvement in interobserver reproducibility was demonstrated by the new classification (kappa 0.53 vs. 0.44, P = 0.002). The reproducibility of the assessment of disease activity and chronicity remains suboptimal (kappa = 0.33). The new classification tends to produce more diagnoses of Class IV lupus nephritis, with fewer diagnoses of Classes III and V. The improvement in interobserver reproducibility indicates that an important aim of the new classification has been achieved. Further work is needed to determine whether the increase in diagnosis of Class IV nephritis represents an improvement in biopsy interpretation or a divergence from the previous classification, as the latter could undermine attempts to relate results from the new system to treatment strategies based on clinical trials which used the old.

Nouveaux outils en transplantation rénale

Renal transplantation is the best treatment available for end stage renal disease. The determination of human genome has profoundly modified the possible approaches of renal transplant recipient by allowing tailoring of immunosuppressive drugs and immunologic diagnosis. The aim of this review article is to determine the role of these various techniques during the different step before and after transplantation. Genotyping, transcriptome analysis, proteomic as well as the specific immune response are analyzed in this article.

The significance of subclinical rejection and the value of protocol biopsies

Subclinical rejection (SCR) is diagnosed by protocol histology with a maximal prevalence occurring early after transplantation, falling to low levels by 1 year. Needle-core biopsy is safe, and the histology obtained fairly reflects subclinical immune activity. Several studies have consistently shown that SCR is associated with chronic tubulointerstitial damage, subsequent renal dysfunction and reduced graft survival. SCR is effectively treated by pulse corticosteroid therapy, although increased baseline immunosuppression may be necessary. A single randomized clinical trial of biopsy and corticosteroid therapy demonstrated significantly improved early structural and functional outcomes, and a (nonsignificant) 17% risk reduction in 4-year graft survival. Three possible approaches include: no protocol biopsies (usually accompanied by powerful immunosuppression); biopsies only in high-risk recipients (who may be difficult to reliably predict) or universal screening protocol biopsy (comprehensive but limited by cost and resource utilization). The appropriate screening methodology for a transplant unit is both a clinical and an economic decision; influenced by the SCR prevalence and potential gains of treatment, against costs and resource utilization. Further trials to quantify the cost-benefit balance in a typical, heterogeneous recipient population using modern immunosuppression are required.

Untreated rejection in 6-month protocol biopsies is not associated with fibrosis in serial biopsies or with loss of graft function

Donor age, calcineurin inhibitor nephrotoxicity, and acute rejection are the most significant predictors of chronic allograft nephropathy. Protocol biopsies, both in deceased- and living-donor renal grafts, have shown that cortical tubulointerstitial fibrosis correlates with graft survival and function. The impact of not treating subclinical acute rejection (SAR) is less clear. In this study, 126 de novo renal transplant recipients were randomly assigned to receive area-under-the-curve-controlled exposure of either a cyclosporine or a tacrolimus-based immunosuppressive regimen that included steroids, mycophenolate mofetil, and basiliximab induction. Protocol biopsies were taken before and 6 and 12 mo after transplantation. The prevalence of SAR was determined retrospectively. Fibrosis was evaluated by quantitative digital analysis of Sirius red staining in serial biopsies. Donor age correlated significantly with tubulointerstitial fibrosis in pretransplantation biopsies and inferior graft function at month 6 (rtau = -0.26; P = 0.033). Acute rejection incidence was 11.5%, and no clinical late rejection occurred. The prevalence of SAR at 6 mo was 30.8% but was not associated with differences in serial quantitative Sirius red staining at 6 or 12 mo, proteinuria, or progressive loss of GFR up to 2 yr. No differences were found in donor variables, histocompatibility, rejection history, or exposure of immunosuppressants. Controlled individualized calcineurin inhibitor exposure and subsequent tapering resulted in a low early acute rejection rate and prevented late acute rejection. Because, by design, we did not treat SAR, these results provide evidence that asymptomatic infiltrates in 6-mo surveillance biopsies may not be deleterious in the intermediate term. There is need for reliable biomarkers to prove that not all cell infiltrates are equivalent or that infiltrates may change with time.

Chronic allograft nephropathy: current concepts and future directions

The paradigm that chronic rejection causes all progressive late allograft failure has been replaced by a hypothesis of cumulative damage, where a series of time-dependent immune and nonimmune mechanisms injure the kidney and lead to chronic interstitial fibrosis and tubular atrophy, representing a final common pathway of injury and its consequent fibrotic healing response. Allograft damage is common, progressive, time-dependent, clinically important and modified by immunosuppression. Early after transplantation, tubulointerstitial damage is predominantly related to ischemia reperfusion injury, acute tubular necrosis, acute and subclinical rejection and/or calcineurin inhibitor nephrotoxicity, superimposed on preexisting donor disease. Later, cellular inflammation lessens and is replaced by microvascular and glomerular injury from calcineurin inhibitor nephrotoxicity, hypertension, immune-mediated fibrointimal vascular hyperplasia, transplant glomerulopathy and capillary injury, polyoma virus and/or recurrent glomerulonephritis. Additional mechanisms of injury include internal architectural disruption of the kidney, cortical ischemia, persistent chronic inflammation, replicative senescence, cytokine excess and fibrosis induced by epithelial-to-mesenchymal transition. Current understanding of the etiology, pathophysiology and evolution of pathological changes are detailed. An approach to histological assessment of the individual failing graft are presented and a series of postulates are defined for future studies of chronic allograft nephropathy.

Subclinical rejection associated with chronic allograft nephropathy in protocol biopsies as a risk factor for late graft loss

Chronic allograft nephropathy (CAN) in protocol biopsies is associated with graft loss while the association between subclinical rejection (SCR) and outcome has yielded contradictory results. We analyze the predictive value of SCR and/or CAN in protocol biopsies on death-censored graft survival. Since 1988, a protocol biopsy was done during the first 6 months in stable grafts with serum creatinine <300 micromol/L and proteinuria <1 g/day. Biopsies were evaluated according to Banff criteria. Borderline changes and acute rejection were grouped as SCR. CAN was defined as presence of interstitial fibrosis and tubular atrophy. Mean follow-up was 91 +/- 46 months. Sufficient tissue was obtained in 435 transplants. Biopsies were classified as normal (n = 186), SCR (n = 74), CAN (n = 110) and SCR with CAN (n = 65). Presence of SCR with CAN was associated with old donors, percentage of panel reactive antibodies and presence of acute rejection before protocol biopsy. Cox regression analysis showed that SCR with CAN (relative risk [RR]: 1.86, 95% confidence interval [CI]: 1.11-3.12; p = 0.02) and hepatitis C virus (RR: 2.27, 95% CI: 1.38-3.75; p = 0.01) were independent predictors of graft survival. In protocol biopsies, the detrimental effect of interstitial fibrosis/tubular atrophy on long-term graft survival is modulated by SCR.

Renal transplant biopsy specimen adequacy in a paediatric population

Updated guidelines on the diagnosis of acute allograft rejection including criteria for biopsy specimen adequacy were published in 1999. We sought to determine the adequacy of specimens in paediatric transplant patients and identify factors influencing adequacy. All renal transplant biopsies performed between 1998 and 2003 were classified as adequate (n =25), minimal (n =19) or inadequate (n =27) in accordance with the Banff 97 criteria, and the histological diagnoses were documented. The effect on specimen adequacy of grade of operator, method of sedation, age of child, needle gauge, number of cores and total core length was then investigated. Overall, a minimal or adequate specimen was obtained in 62% of cases. No histological diagnosis could be made in 30% of all specimens, just over half of which were inadequate. Higher rates of rejection were found in adequate (52%) than inadequate (33%) samples. The grade of operator (p =0.498), the age of the child at the time of biopsy (p =0.815) and type of sedation (p =0.188) did not affect adequacy. More than one core was obtained in 38 (54%) cases, and this was significantly associated with specimen adequacy (p <0.0005) as was longer total core length (p =0.002). Clinical features in isolation are not sufficient for the diagnosis of acute allograft rejection. Renal biopsy remains the gold standard and relies on adequate specimen collection. Our data shows that specimen adequacy according to the Banff 97 guidelines is achievable in children and that more than one core at the time of sampling significantly improves this achievement. Adequate sampling reduces the risk of an inconclusive histological diagnosis.