Real Time Central Assessment of Kidney Transplant Indication Biopsies by Microarrays: The INTERCOMEX Study.

The authors conducted a prospective trial to assess the feasibility of real time central molecular assessment of kidney transplant biopsy samples from 10 North American or European centers. Biopsy samples taken 1 day to 34 years posttransplantation were stabilized in RNAlater, sent via courier overnight at ambient temperature to the central laboratory, and processed (29 h workflow) using microarrays to assess T cell- and antibody-mediated rejection (TCMR and ABMR, respectively). Of 538 biopsy samples submitted, 519 (96%) were sufficient for microarray analysis (average length, 3 mm). Automated reports were generated without knowledge of histology and HLA antibody, with diagnoses assigned based on Molecular Microscope Diagnostic System (MMDx) classifier algorithms and signed out by one observer. Agreement between MMDx and histology (balanced accuracy) was 77% for TCMR, 77% for ABMR, and 76% for no rejection. A classification tree derived to provide automated sign-outs predicted the observer sign-outs with >90% accuracy. In 451 biopsy samples where feedback was obtained, clinicians indicated that MMDx more frequently agreed with clinical judgment (87%) than did histology (80%) (p = 0.0042). In 81% of feedback forms, clinicians reported that MMDx increased confidence in management compared with conventional assessment alone. The authors conclude that real time central molecular assessment is feasible and offers a useful new dimension in biopsy interpretation. ClinicalTrials.gov NCT#01299168.

Hyalinosis Lesions in Renal Transplant Biopsies: Time-Dependent Complexity of Interpretation.

Because calcineurin inhibitor (CNI) immunosuppressive drugs induce arteriolar hyalinosis (ah) in kidney transplants, ah lesions can potentially provide information about drug exposure. We studied the relationship of ah lesions to findings and outcomes in 562 indication biopsies taken 3 days to 35 years after transplant. Prevalence of ah lesions increased with time of biopsy after transplant (TxBx). The ah scores correlated with arterial intimal thickening and atrophy-fibrosis but, unlike atrophy-fibrosis, did not increase until after 500 days because of a background of ah1 lesions in early biopsies reflecting donor aging. Correlation of ah scores with other features varied with TxBx-in early biopsies, donor age and related changes, and in very late biopsies, chronic antibody-mediated rejection and glomerulonephritis and associated lesions. After correction for TxBx, ah0 in intermediate time periods was associated with increased risk of T cell-mediated rejection and graft loss, probably because of underimmunosuppression and nonadherence. Thus, ah lesions in indication biopsies have multiple associations: donor age (early, usually ah1), chronic glomerular diseases (late, often ah2/3), and adequate exposure to CNIs at intermediate times. This threefold TxBx-dependent complexity must be considered when interpreting indication biopsies: ah lesions often indicate adequate CNI exposure, not toxicity, and unexpected ah0 should increase vigilance for nonadherence and underimmunosuppression.

Determination of unacceptable HLA antigen mismatches in kidney transplant recipients: recommendations of the German Society for Immunogenetics.

One of the major tasks of histocompatibility and immunogenetics laboratories is the pretransplant determination of unacceptable antigen mismatches (UAM) in kidney transplant recipients. In this procedure, human leucocyte antigen (HLA) specificities are defined against which the patient has circulating alloantibodies that are expected to harm the transplanted organ. Using the information on UAM and the potential donor's complete HLA typing, prediction of the crossmatch result, the so called 'virtual crossmatch', is possible. Currently, the laboratories are using different algorithms for the determination of UAM, and depending on the algorithm, more or fewer organ offers are excluded for patients with a similar antibody profile. In order to bring homogeneity into the allocation of organs to immunized patients in Germany, the German Society for Immunogenetics established, on the basis of current knowledge, recommendations for the determination of UAM. The UAM recommendations, which are thought to serve as a common tool for responsible physicians at different transplant centers, contain technical issues that need to be considered and are individualized for sensitized patients with a high or intermediate risk of antibody-mediated rejection. The present review contains these recommendations and puts them into perspective to current international practice.

Microarray diagnosis of antibody-mediated rejection in kidney transplant biopsies: an international prospective study (INTERCOM).

In a reference set of 403 kidney transplant biopsies, we recently developed a microarray-based test that diagnoses antibody-mediated rejection (ABMR) by assigning an ABMR score. To validate the ABMR score and assess its potential impact on practice, we performed the present prospective INTERCOM study (clinicaltrials.gov NCT01299168) in 300 new biopsies (264 patients) from six centers: Baltimore, Barcelona, Edmonton, Hannover, Manchester and Minneapolis. We assigned ABMR scores using the classifier created in the reference set and compared it to conventional assessment as documented in the pathology reports. INTERCOM documented uncertainty in conventional assessment: In 41% of biopsies where ABMR features were noted, the recorded diagnoses did not mention ABMR. The ABMR score correlated with ABMR histologic lesions and donor-specific antibodies, but not with T cell-mediated rejection lesions. The agreement between ABMR scores and conventional assessment was identical to that in the reference set (accuracy 85%). The ABMR score was more strongly associated with failure than conventional assessment, and when the ABMR score and conventional assessment disagreed, only the ABMR score was associated with early progression to failure. INTERCOM confirms the need to reduce uncertainty in the diagnosis of ABMR, and demonstrates the potential of the ABMR score to impact practice.

Potential impact of microarray diagnosis of T cell-mediated rejection in kidney transplants: The INTERCOM study.

We previously developed a microarray-based test for T cell-mediated rejection (TCMR) in a reference set of 403 biopsies. To determine the potential impact of this test in clinical practice, we undertook INTERCOM, a prospective international study of 300 indication biopsies from 264 patients (ClinicalTrials.gov NCT01299168). Biopsies from six centers-Baltimore, Barcelona, Edmonton, Hannover, Manchester and Minneapolis-were analyzed by microarrays, assigning TCMR scores by an algorithm developed in the reference set and comparing TCMR scores to local histology assessment. The TCMR score correlated with histologic TCMR lesions-tubulitis and interstitial infiltration. The accuracy for primary histologic diagnoses (0.87) was similar to the reference set (0.89). The TCMR scores reclassified 77/300 biopsies (26%): 16 histologic TCMR were molecularly non-TCMR; 15 histologic non-TCMR were molecularly TCMR, including 6 with polyoma virus nephropathy; and all 46 "borderline" biopsies were reclassified as TCMR (8) or non-TCMR (38). Like the reference set, discrepancies were primarily in situations where histology has known limitations, for example, in biopsies with scarring and inflammation/tubulitis potentially from other diseases. Neither the TCMR score nor histologic TCMR was associated with graft loss. Thus the molecular TCMR score has potential to add new insight, particularly in situations where histology is ambiguous or potentially misleading.

The nature of biopsies with "borderline rejection" and prospects for eliminating this category.

In kidney transplantation, many inflamed biopsies with changes insufficient to be called T-cell-mediated rejection (TCMR) are labeled "borderline", leaving management uncertain. This study examined the nature of borderline biopsies as a step toward eventual elimination of this category. We compared 40 borderline, 35 TCMR and 116 nonrejection biopsies. TCMR biopsies had more inflammation than borderline but similar degrees of tubulitis and scarring. Surprisingly, recovery of function after biopsy was similar in all categories, indicating that response to treatment is unreliable for defining TCMR. We studied the molecular changes in TCMR, borderline and nonrejection using microarrays, measuring four published features: T-cell burden; a rejection classifier; a canonical TCMR classifier; and risk score. These reassigned borderline biopsies as TCMR-like 13/40 (33%) or nonrejection-like 27/40 (67%). A major reason that histology diagnosed molecularly defined TCMR as borderline was atrophy-scarring, which interfered with assessment of inflammation and tubulitis. Decision tree analysis showed that i-total >27% and tubulitis extent >3% match the molecular diagnosis of TCMR in 85% of cases. In summary, most cases designated borderline by histopathology are found to be nonrejection by molecular phenotyping. Both molecular measurements and histopathology offer opportunities for more precise assignment of these cases after clinical validation.

Understanding the causes of kidney transplant failure: the dominant role of antibody-mediated rejection and nonadherence.

We prospectively studied kidney transplants that progressed to failure after a biopsy for clinical indications, aiming to assign a cause to every failure. We followed 315 allograft recipients who underwent indication biopsies at 6 days to 32 years posttransplant. Sixty kidneys progressed to failure in the follow-up period (median 31.4 months). Failure was rare after T-cell-mediated rejection and acute kidney injury and common after antibody-mediated rejection or glomerulonephritis. We developed rules for using biopsy diagnoses, HLA antibody and clinical data to explain each failure. Excluding four with missing information, 56 failures were attributed to four causes: rejection 36 (64%), glomerulonephritis 10 (18%), polyoma virus nephropathy 4 (7%) and intercurrent events 6 (11%). Every rejection loss had evidence of antibody-mediated rejection by the time of failure. Among rejection losses, 17 of 36 (47%) had been independently identified as nonadherent by attending clinicians. Nonadherence was more frequent in patients who progressed to failure (32%) versus those who survived (3%). Pure T-cell-mediated rejection, acute kidney injury, drug toxicity and unexplained progressive fibrosis were not causes of loss. This prospective cohort indicates that many actual failures after indication biopsies manifest phenotypic features of antibody-mediated or mixed rejection and also underscores the major role of nonadherence.

The molecular phenotype of 6-week protocol biopsies from human renal allografts: reflections of prior injury but not future course.

We assessed the molecular phenotype of 107 6-week protocol biopsies from human renal allografts, using Affymetrix microarrays. Transcript changes were summarized as nonoverlapping pathogenesis-based transcript sets (PBTs) reflecting inflammation (T cells, macrophages, IFNG effects) and the injury-repair response of the parenchyma, stroma and microcirculation-increased ('injury-up') and decreased ('injury-down') transcripts. The molecular changes were highly correlated with each other, even when all rejection and borderline cases were excluded. Inflammation and injury-down PBTs correlated with histologic inflammation and tubulitis, and the inflammation transcripts were greater in kidneys diagnosed as T cell-mediated or borderline rejection. Injury-up PBTs did not correlate with histopathology but did correlate with kidney function: thus functional disturbances are represented in transcript changes but not in histopathology. PBT changes correlated with prior delayed graft function. However, there was little difference between live donor kidneys and deceased donor kidneys that had not shown delayed graft function. Molecular changes did not predict future biopsies for clinical indications, rejection episodes, functional deterioration or allograft loss. Thus while detecting T cell-mediated inflammation, the molecular phenotype of early protocol biopsies mostly reflects the injury-repair response to implantation stresses, and has little relationship to future events and outcomes.

The molecular phenotype of heart transplant biopsies: relationship to histopathological and clinical variables.

Histopathology of endomyocardial biopsies (EMB) is the standard rejection surveillance for heart transplants. However, ISHLT consensus criteria for interpreting biopsies are arbitrarily defined. Gene expression offers an independent re-evaluation of existing diagnostic systems. We performed histologic and microarray analysis on 105 EMB from 45 heart allograft recipients. Histologic lesions, diagnosis and transcripts were compared to one another, time posttransplantation, indication for biopsy and left ventricular ejection fraction (LVEF). Histologic lesions presented in two groups: myocyte-interstitial and microcirculation lesions. Expression of transcript sets reflecting T cell and macrophage infiltration, and γ-interferon effects correlated strongly with each other and with transcripts indicating tissue/myocardium injury. This molecular phenotype correlated with Quilty (p < 0.005), microcirculation lesions (p < 0.05) and decreased LVEF (p < 0.007), but not with the histologic diagnosis of rejection. In multivariate analysis, LVEF was associated (p < 0.03) with γ-interferon inducible transcripts, time posttransplantation, ischemic injury and clinically indicated biopsies, but not the diagnosis of rejection. The results indicate that (a) the current ISHLT system for diagnosing rejection does not reflect the molecular phenotype in EMB and lacks clinical relevance; (b) the interpretation of Quilty lesions has to be revisited; (c) the assessment of molecules in heart biopsy can guide improvements of current diagnostics.

Loss of solute carriers in T cell-mediated rejection in mouse and human kidneys: an active epithelial injury-repair response.

T cell-mediated rejection of kidney allografts causes epithelial deterioration, manifested by tubulitis, but the mechanism remains unclear. We hypothesized that interstitial inflammation triggers a stereotyped epithelial response similar to that triggered by other types of injury such as ischemia-reperfusion. We identified solute carrier transcripts with decreased expression in mouse allografts, and compared their behavior in T cell-mediated rejection to native kidneys with ischemic acute tubular necrosis (ATN). Average loss of solute carrier expression was similar in ATN (77%) and T cell-mediated rejection (75%) with high correlation of individual transcripts. Immunostaining of SLC6A19 confirmed loss of proteins. Analysis of human kidney transplant biopsies confirmed that T cell-mediated rejection and ATN showed similar loss of solute carrier mRNAs. The loss of solute carrier expression was weakly correlated with interstitial inflammation, but kidneys with ATN showed decreased solute carriers despite minimal inflammation. Loss of renal function correlated better with decreased solute carrier expression than with histologic lesions (r = 0.396, p < 0.001). Thus the loss of epithelial transcripts in rejection is not a unique consequence of T cell-mediated rejection but an active injury-repair response of epithelium, triggered by rejection but also by other injury mechanisms.

The molecular phenotype of kidney transplants.

Microarray studies of kidney transplant biopsies provide an opportunity to define the molecular phenotype. To facilitate this process, we used experimental systems to annotate transcripts as members of pathogenesis-based transcript sets (PBTs) representing biological processes in injured or diseased tissue. Applying this annotation to microarray results revealed that changes in single molecules and PBTs reflected a large-scale coordinate disturbance, stereotyped across various diseases and injuries, without absolute specificity of individual molecules or PBTs for rejection. Nevertheless, expression of molecules and PBTs was quantitatively specific: IFNG effects for rejection; T cell and macrophage transcripts for T cell-mediated rejection; endothelial and NK transcripts for antibody-mediated rejection. Various diseases and injuries induced the same injury-repair response, undetectable by histopathology, involving epithelium, stroma and endothelium, with increased expression of developmental, cell cycle and apoptosis genes and decreased expression of differentiated epithelial features. Transcripts reflecting this injury-repair response were the best correlates of functional disturbance and risk of future graft loss. Late biopsies with atrophy-fibrosis, reflecting their cumulative burden of injury, displayed more transcripts for B cells, plasma cells and mast cells. Thus the molecular phenotype is best described in terms of three elements: specific diseases, including rejection; the injury-repair response and the cumulative burden of injury.

An integrated view of molecular changes, histopathology and outcomes in kidney transplants.

Data-driven approaches to deteriorating kidney transplants, incorporating histologic, molecular and HLA antibody findings, have created a new understanding of transplant pathology and why transplants fail. Transplant dysfunction is best understood in terms of three elements: diseases, the active injury-repair response and the cumulative burden of injury. Progression to failure is mainly attributable to antibody-mediated rejection, nonadherence and glomerular disease. Antibody-mediated rejection usually develops late due to de novo HLA antibodies, particularly anti-class II, and is often C4d negative. Pure treated T cell-mediated rejection does not predispose to graft loss because it responds well, even with endothelialitis, but it may indicate nonadherence. The cumulative burden of injury results in atrophy-fibrosis (nephron loss), arterial fibrous intimal thickening and arteriolar hyalinosis, but these are not progressive without ongoing disease/injury, and do not explain progression. Calcineurin inhibitor toxicity has been overestimated because burden-of-injury lesions invite this default diagnosis when diseases such as antibody-mediated rejection are missed. Disease/injury triggers a stereotyped active injury-repair response, including de-differentiation, cell cycling and apoptosis. The active injury-repair response is the strongest correlate of organ function and future progression to failure, but should always prompt a search for the initiating injury or disease.

NK cell transcripts and NK cells in kidney biopsies from patients with donor-specific antibodies: evidence for NK cell involvement in antibody-mediated rejection.

To explore the mechanisms of antibody-mediated rejection (ABMR) in kidney transplants, we studied the transcripts expressed in clinically indicated biopsies from patients with donor-specific antibody (DSA). Comparison of biopsies from DSA-positive versus DSA-negative patients revealed 132 differentially expressed transcripts: all were associated with class II DSA but none with class I DSA. Many transcripts were expressed in DSA-positive ABMR but were also expressed in T-cell-mediated rejection (TCMR), reflecting shared molecular features. Removal of shared transcripts created 23 DSA selective transcripts (DSASTs). Some DSASTs (6/23) showed selective high expression in NK cells, whereas others (8/23) were expressed in endothelium or in endothelium plus other cell types (7/23). Of 145 biopsies ranked by DSAST expression, the 25 with highest DSAST expression primarily consisted of ABMR (22/25, 88%), either C4d-positive or C4d-negative. By immunostaining, CD56+ and CD68+ cells in peritubular capillaries, but not CD3+ cells, were increased in ABMR compared to TCMR, compatible with a role for NK cells, as well as macrophages, as effectors in endothelial injury during ABMR. Thus, the strategy of using DSASTs in the biopsy to identify mechanism-related transcripts in biopsies from patients with clinical phenotypes indicates the selective involvement of NK cells in ABMR.

Banff '09 meeting report: antibody mediated graft deterioration and implementation of Banff working groups.

The 10th Banff Conference on Allograft Pathology was held in Banff, Canada from August 9 to 14, 2009. A total of 263 transplant clinicians, pathologists, surgeons, immunologists and researchers discussed several aspects of solid organ transplants with a special focus on antibody mediated graft injury. The willingness of the Banff process to adapt continuously in response to new research and improve potential weaknesses, led to the implementation of six working groups on the following areas: isolated v-lesion, fibrosis scoring, glomerular lesions, molecular pathology, polyomavirus nephropathy and quality assurance. Banff working groups will conduct multicenter trials to evaluate the clinical relevance, practical feasibility and reproducibility of potential changes to the Banff classification. There were also sessions on quality improvement in biopsy reading and utilization of virtual microscopy for maintaining competence in transplant biopsy interpretation. In addition, compelling molecular research data led to the discussion of incorporation of omics-technologies and discovery of new tissue markers with the goal of combining histopathology and molecular parameters within the Banff working classification in the near future.

Alternative macrophage activation-associated transcripts in T-cell-mediated rejection of mouse kidney allografts.

Macrophages display two activation states that are considered mutually exclusive: classical macrophage activation (CMA), inducible by IFNG, and alternative macrophage activation (AMA), inducible by IL4 and IL13. CMA is prominent in allograft rejection and AMA is associated with tissue remodeling after injury. We studied expression of AMA markers in mouse kidney allografts and in kidneys with acute tubular necrosis (ATN). In rejecting allografts, unlike interferon gamma (IFNG) effects and T-cell infiltration that developed rapidly and plateaued by day 7, AMA transcripts (Arg1, Mrc1, Mmp12 and Ear1) rose progressively as tubulitis and parenchymal deterioration developed at days 21 and 42, despite persistent IFNG effects. AMA in allografts was associated with transcripts for AMA inducers IL4, IL13 and inhibin A, but also occurred when hosts lacked IL4/IL13 receptors, suggesting a role for inhibin A. Kidneys with ATN injured by ischemia/reperfusion also had increased expression of AMA markers and inhibin A. Thus kidneys undergoing T-cell-mediated rejection progressively acquire macrophages with alternative activation phenotype despite strong local IFNG effects, independent of IL4 and IL13. Although the mechanisms and causal relationships remain to be determined, high AMA transcript levels in rejecting allografts are strongly associated with and may be a consequence of parenchymal deterioration similar to ATN.

Defining the canonical form of T-cell-mediated rejection in human kidney transplants.

Banff defines T-cell-mediated rejection (TCMR) using nonspecific lesions and arbitrary cutoffs, with no external gold standard. We reexamined features of TCMR using exclusively molecular definition independent of histopathology. The definition was derived from mouse kidney transplants with fully developed TCMR, and is based on high expression of transcripts reflecting IFNG effects and alternative macrophage activation. In 234 human kidney transplant biopsies for cause phenotyped by microarrays, we identified 26 biopsies meeting these criteria. After excluding three biopsies with unrelated diseases, all 23 biopsies had typical Banff lesions of TCMR (inflammation, tubulitis), with v lesions in 10/23. Banff histopathology diagnosed 18 as TCMR, 1 as mixed and 4 as borderline. Despite marked changes in transcriptome indicating tissue injury and dedifferentiation, all kidneys with molecularly defined TCMR, even with v lesions or late rejection, demonstrated excellent recovery of function at 6 months with no graft loss (mean follow-up 2.5 years). Thus TCMR defined exclusively by molecules manifests TCMR-related lesions and function impairment, but good recovery and survival, even with late rejection or arteritis. This combination of pathologic, clinical and molecular features constitutes the typical or canonical T-cell-mediated rejection.

Cluster analysis of lesions in nonselected kidney transplant biopsies: microcirculation changes, tubulointerstitial inflammation and scarring.

Banff classification empirically established scoring of histologic lesions, but the relationships of lesions to each other and to underlying biologic processes remain unclear. We hypothesized that class discovery tools would reveal new relationships between individual lesions, and relate lesions to C4d staining, anti-HLA donor-specific antibody (DSA) and time posttransplant. We studied 234 nonselected renal allograft biopsies for clinical indications from 173 patients. Silhouette plotting and principal component analysis revealed three groups of lesions: microcirculation changes, including inflammation (glomerulitis, capillaritis) and deterioration (double contours, mesangial expansion); scarring/hyalinosis; and tubulointerstitial inflammation. DSA and C4d grouped with microcirculation inflammation, whereas time posttransplant grouped with scarring/hyalinosis lesions. Intimal arteritis clustered with DSA, C4d and microcirculation inflammation, but also showed correlations with tubulitis. Fibrous intimal thickening in arteries clustered with scarring/hyalinosis. Capillary basement membrane multilayering showed intermediary relationships between microcirculation deterioration and time-dependent scarring. Correlation analysis and hierarchical clustering confirmed the lesion relationships. Thus, we propose that the pathologic lesions in biopsies are not independent but are members of groups that represent distinct pathogenic forces: microcirculation changes, reflecting the stress of DSA; scarring, hyalinosis and arterial fibrosis, reflecting the cumulative burden of injury over time; and tubulointerstitial inflammation. Interpretation of lesions should reflect these associations.

Antibody-mediated microcirculation injury is the major cause of late kidney transplant failure.

We studied the phenotype of late kidney graft failure in a prospective study of unselected kidney transplant biopsies taken for clinical indications. We analyzed histopathology, HLA antibodies and death-censored graft survival in 234 consecutive biopsies from 173 patients, taken 6 days to 31 years posttransplant. Patients with late biopsies (>1 year) frequently displayed donor-specific HLA antibody (particularly class II) and microcirculation changes, including glomerulitis, glomerulopathy, capillaritis, capillary multilayering and C4d staining. Grafts biopsied early rarely failed (1/68), whereas grafts biopsied late often progressed to failure (27/105) within 3 years. T-cell-mediated rejection and its lesions were not associated with an increased risk of failure after biopsy. In multivariable analysis, graft failure correlated with microcirculation inflammation and scarring, but C4d staining was not significant. When microcirculation changes and HLA antibody were used to define antibody-mediated rejection, 17/27 (63%) of late kidney failures after biopsy were attributable to antibody-mediated rejection, but many were C4d negative and missed by current diagnostic criteria. Glomerulonephritis accounted for 6/27 late losses, whereas T-cell-mediated rejection, drug toxicity and unexplained scarring were uncommon. The major cause of late kidney transplant failure is antibody-mediated microcirculation injury, but detection of this phenotype requires new diagnostic criteria.

De novo donor-specific antibody at the time of kidney transplant biopsy associates with microvascular pathology and late graft failure.

We studied whether de novo donor-specific antibodies (DSA) in sera from patients undergoing kidney transplant biopsies associate with specific histologic lesions in the biopsy and prognosis. DSA were assessed in 145 patients at the time of biopsy between 7 days to 31 years posttransplant. DSA was detected in 54 patients (37%), of which 32 represented de novo DSA. De novo DSA was more frequent in patients having late biopsies (34%) versus early biopsies (4%), and was usually either against class II alone or class I and II but rarely against class I alone. Microcirculation inflammation (glomerulitis, capillaritis) and damage (glomuerulopathy, capillary basement membrane multilayering), and C4d staining were associated with de novo DSA. However, the degree of scarring, arterial fibrosis and tubulo-interstitial inflammation did not correlate with the presence of de novo DSA. De novo DSA correlated with reduced graft survival after the biopsy. Thus, de novo DSA at the time of a late biopsy for clinical indication is primarily against class II, and associates with microcirculation changes in the biopsy and subsequent graft failure. We propose careful assessment of de novo DSA, particularly against class II, be performed in all late kidney transplant biopsies.