Transplant glomerulopathy as a cause of late graft loss

Histologic and Molecular Patterns in Responders and Non-responders With Chronic-Active Antibody-Mediated Rejection in Kidney Transplants

Introduction

There is no proven therapy for chronic-active antibody-mediated rejection (caABMR), the major cause of late kidney allograft failure. Histological and molecular patterns associated with possible therapy responsiveness are not known.

Methods

Based on rigorous selection criteria this single center, retrospective study identified 16 out of 1027 consecutive kidney transplant biopsies taken between 2008 and 2016 with pure, unquestionable caABMR, without other pathologic features. The change in estimated GFR pre- and post-biopsy/treatment were utilized to differentiate subjects into responders and non-responders. Gene sets reflecting active immune processes of caABMR were defined a priori, including endothelial, inflammatory, cellular, interferon gamma (IFNg) and calcineurin inhibitor (CNI) related-genes based on the literature. Transcript measurements were performed in RNA extracted from stored, formalin-fixed, paraffin-embedded (FFPE) samples using NanoString™ technology. Histology and gene expression patterns of responders and non-responders were compared.

Results

A reductionist approach applying very tight criteria to identify caABMR and treatment response excluded the vast majority of clinical ABMR cases. Only 16 out of 139 cases with a written diagnosis of chronic rejection fulfilled the caABMR criteria. Histological associations with therapy response included a lower peritubular capillaritis score (p = 0.028) along with less glomerulitis. In contrast, no single gene discriminated responders from non-responders. Activated genes associated with NK cells and endothelial cells suggested lack of treatment response.

Conclusion

In caABMR active microvascular injury, in particular peritubular capillaritis, differentiates treatment responders from non-responders. Transcriptome changes in NK cell and endothelial cell associated genes may further help to identify treatment response. Future prospective studies will be needed which include more subjects, who receive standardized treatment protocols to identify biomarkers for treatment response.

Clinical Trial Registration

[ClinicalTrials.gov], identifier [NCT03430414].

Chronic transplant glomerulopathy: New insights into pathogenesis

There have been recent significant advances in short-term outcomes in renal transplantation, however, long-term allograft survival remains a challenge. With reported incidences as high of 74.5% of chronic graft loss in patients with biopsies showing transplant glomerulopathy (TG), this syndrome represents an important factor for chronic allograft complications. In this review we show an overview of the novel mechanistic insights into pathogenesis of TG, as well as a brief description of the pathology, diagnosis and newer prognostic indices within TG diagnosis. These data raise intriguing roles for cell-mediated immunity and podocyte stress in TG as well as reinforce previous associations of TG with ABMR. We also delve into management strategies for TG and report the paucity of existing clinical trial data for this prevalent condition in renal transplants.

Association between transplant glomerulopathy and graft outcomes following kidney transplantation: A meta-analysis

Transplant glomerulopathy (TG), a morphological lesion associated with confluent mechanisms of endothelial injury of renal allografts, may provide a viable predictor of graft failure. This systematic literature review and meta-analysis were performed according to the PRISMA statement to examine evidence describing the association between TG and graft loss or failure and time to these events. The literature review was conducted using the Scopus, EBSCO, and Cochrane Library search engines. Hazard ratios, median survival times, and 95% confidence intervals (CIs) were estimated to evaluate graft survival in the total population and prespecified subgroups. Meta-regression analysis assessed heterogeneity. Twenty-one publications comprising 6,783 patients were eligible for data extraction and inclusion in the meta-analysis. Studies were highly heterogeneous (I² = 67.3%). The combined hazard ratio of graft loss or failure from random-effects meta-analysis was 3.11 (95% CI 2.44–3.96) in patients with TG compared with those without. Median graft survival in patients with TG was 3.25 (95% CI 0.94–11.21) years—15 years shorter than in those without TG (18.82 [95% CI 10.03–35.32] years). The effect of time from transplantation to biopsy on graft outcomes did not reach statistical significance (p = 0.116). TG was associated with a threefold increase in the risk of graft loss or failure and a 15-year loss in graft survival, indicating viability as a surrogate measure for both clinical practice and studies designed to prevent or reverse antibody-mediated rejection.

Archetype Analysis Identifies Distinct Profiles in Renal Transplant Recipients with Transplant Glomerulopathy Associated with Allograft Survival

BACKGROUND

Transplant glomerulopathy, a common glomerular lesion observed after kidney transplant that is associated with poor prognosis, is not a specific entity but rather the end stage of overlapping disease pathways. Its heterogeneity has not been precisely characterized to date.

METHODS

Our study included consecutive kidney transplant recipients from three centers in France and one in Canada who presented with a diagnosis of transplant glomerulopathy (Banff cg score ≥1 by light microscopy), on the basis of biopsies performed from January of 2004 through December of 2014. We used an unsupervised archetype analysis of comprehensive pathology findings and clinical, immunologic, and outcome data to identify distinct groups of patients.

RESULTS

Among the 8207 post-transplant allograft biopsies performed during the inclusion period, we identified 552 biopsy samples (from 385 patients) with transplant glomerulopathy (incidence of 6.7%). The median time from transplant to transplant glomerulopathy diagnosis was 33.18 months. Kidney allograft survival rates at 3, 5, 7, and 10 years after diagnosis were 69.4%, 57.1%, 43.3%, and 25.5%, respectively. An unsupervised learning method integrating clinical, functional, immunologic, and histologic parameters revealed five transplant glomerulopathy archetypes characterized by distinct functional, immunologic, and histologic features and associated causes and distinct allograft survival profiles. These archetypes showed significant differences in allograft outcomes, with allograft survival rates 5 years after diagnosis ranging from 88% to 22%. Based on those results, we built an online application, which can be used in clinical practice on the basis of real patients.

CONCLUSIONS

A probabilistic data-driven archetype analysis approach applied in a large, well defined multicenter cohort refines the diagnostic and prognostic features associated with cases of transplant glomerulopathy. Reducing heterogeneity among such cases can improve disease characterization, enable patient-specific risk stratification, and open new avenues for archetype-based treatment strategies and clinical trials optimization.

HLA-DR and -DQ eplet mismatches and transplant glomerulopathy: a nested case-control study

We conducted a nested case-control study from a cohort of adult kidney transplant recipients to assess the risk of transplant glomerulopathy (TG) as a function of donor and recipient HLA-DR and -DQ incompatibility at the eplet level. Cases (n = 52) were defined as patients diagnosed with transplant glomerulopathy based on biopsies showing glomerular basement membrane duplication without immune complex deposition. Controls (n = 104) with a similar follow-up from transplantation were randomly selected from the remaining cohort. HLAMatchmaker was used to ascertain the number of DRB1/3/4/5, DQA1 and DQB1 related eplet mismatches (eplet load). Multivariable conditional logistic regression models demonstrated an increase in the odds of TG (odds ratios [OR] of 2.84 [95% confidence interval (CI): 1.03, 7.84] and 4.62 [95% CI: 1.51, 14.14]) in the presence of 27-43 and >43 HLA-DR + DQ related eplet mismatches versus <27 eplet mismatches, respectively. When the eplet load was modeled as a continuous variable, the OR for TG was 1.25 (95% CI: 1.04, 1.50) for every 10 additional HLA-DR + DQ eplet mismatches. Our study suggests that minimization of HLA-DR + DQ eplet mismatches may decrease the incidence of transplant glomerulopathy diagnosed by indication biopsies. The role of eplet immunogenicity/antigenicity as determinants of allograft outcomes requires further study.

Transplant glomerulopathy: the interaction of HLA antibodies and endothelium

Transplant glomerulopathy (TG) is a major cause of chronic graft dysfunction without effective therapy. Although the histological definition of TG is well characterized, the pathophysiological pathways leading to TG development are still poorly understood. Electron microscopy suggests an earlier appearance of TG and suggests that endothelial cell injury is the first sign of the disease. The pathogenic role of human leukocyte antigen (HLA) antibodies in endothelial cells has been described in acute vascular and humoral rejection. However the mechanisms and pathways of endothelial cell injury by HLA antibodies remain unclear. Despite the description of different causes of the morphological lesion of TG (hepatitis, thrombotic microangiopathy), the strong link between TG and chronic antibody mediated rejection suggests a major role for HLA antibodies in TG formation. In this review, we describe the effect of classes I or II HLA-antibodies in TG and especially the implication of donor specific antibodies (DSA). We update recent studies about endothelial cells and try to explain the different signals and intracellular pathways involved in the progression of TG.

Advances in the understanding of transplant glomerulopathy

Transplant glomerulopathy is a sign of chronic kidney allograft damage. It has poor survival and no effective therapies. This entity develops as a maladaptive repair/remodeling response to sustained endothelial injury and is characterized by duplication/multilamination of capillary basement membranes. This review provides up-to-date information for transplant glomerulopathy, including new insights into underlying causes and mechanisms, and highlights unmet needs in diagnostics. Transplant glomerulopathy is widely accepted as the principal manifestation of chronic antibody-mediated rejection, mostly with HLA antigen class II antibodies. However, recent data suggest that at least in some patients, there also is an association with hepatitis C virus infection, autoimmunity, and late thrombotic microangiopathy. Furthermore, intragraft molecular studies reveal nonresolving inflammation after sustained endothelial injury as a key mechanism and therapeutic target. Unfortunately, current international criteria rely heavily on light microscopy and miss patients at early stages, when they likely are treatable. Therefore, better tools, such as electron microscopy or molecular probes, are needed to detect patients when kidney injury is in an early active phase. Better understanding of causes and effector mechanisms coupled with early diagnosis can lead to the development of new therapeutics for transplant glomerulopathy and improved kidney outcomes.

Chronic histological damage in early indication biopsies is an independent risk factor for late renal allograft failure

The impact of early histological lesions of renal allografts on long-term graft survival remains unclear. We included all renal allograft recipients transplanted at a single center from 1991 to 2001 (N = 1197). All indication biopsies performed within the first year after transplantation were rescored according to the current Banff classification. Mean follow-up time was 14.8 ± 2.80 years. In multivariate Cox proportional hazards analysis, arteriolar hyalinosis and transplant glomerulopathy were independently associated with death-censored graft survival, adjusted for baseline demographic covariates. Arteriolar hyalinosis correlated with interstitial fibrosis, tubular atrophy, mesangial matrix increase, vascular intimal thickening and glomerulosclerosis. Clustering of the patients according to these chronic lesions, reflecting the global burden of chronic injury, associated better with long-term graft survival than each of the chronic lesions separately. Early chronic histological damage was an independent risk factor for late graft loss, irrespective whether a specific, progressive disease was diagnosed or not, while T cell-mediated rejection did not. We conclude that individual chronic lesions like arteriolar hyalinosis, tubular atrophy, interstitial fibrosis, glomerulosclerosis, mesangial matrix increase and vascular intimal thickening cannot be seen as individual entities. The global burden of early chronic histological damage within the first year after transplantation importantly affects the fate of the allografts.

Picking transplant glomerulopathy out of the CAN: evidence from a clinico-pathological evaluation

Background

Since the term chronic allograft nephropathy (CAN) was removed from the Banff scheme in 2005, transplant glomerulopathy (TG) has been regarded as a clinicopathological entity that is one of the major causes of graft loss. To assess the distinction between CAN and TG, we performed a comprehensive evaluation comparing TG with traditional CAN.

Methods

We compared the clinicopathological features of 43 cases of TG with 43 matched cases of non-TG CAN (non-TG group) after renal transplantation. TG was diagnosed by light microscopy based on the double contours of the glomerular basement membranes, and the Banff 97 classification system was used to score TG severity (cg0-3).

Results

Compared to the control group, we found a significantly higher incidence of positivity for human leukocyte antigen class-I and II antibodies, a higher incidence of hepatitis C virus (HCV) infection, and poorer graft survival in TG patients. Clinically, TG was associated with a higher prevalence of proteinuria, hematuria, anaemia and hypoalbuminemia. Histologically, TG strongly correlated with antibody related microcirculatory injuries, including glomerulitis, peritubular capillaritis and peritubular capillary (PTC) C4d deposition. Interestingly, the TG patients showed a significantly higher incidence of IgA deposition than the control patients. C4d-positive TG was correlated with higher TG and PTC scores, and PTC C4d deposition was correlated with a more rapid progression to graft dysfunction. TG accompanied by HCV infection was associated with heavier proteinuria, higher TG and C4d scores, and poorer graft survival.

Conclusions

TG presents clinicopathological features that are distinct from non-TG cases and leads to poorer outcomes. PTC C4d deposition is related to a more rapid progression to graft loss, suggesting ongoing antibody reactivity. HCV-positive TG is a more severe sub-entity, that requires further investigation.

Intragraft gene expression in positive crossmatch kidney allografts: ongoing inflammation mediates chronic antibody-mediated injury

We studied intragraft gene expression profiles of positive crossmatch (+XM) kidney transplant recipients who develop transplant glomerulopathy (TG) and those who do not. Whole genome microarray analysis and quantitative rt-PCR were performed on RNA from protocol renal allograft biopsies in three groups: (1) +XM/TG+ biopsies before and after TG; (2) +XM/NoTG; and (3) negative crossmatch kidney transplants (control). Microarray comparisons showed few differentially expressed genes between paired biopsies from +XM/TG+ recipients before and after the diagnosis of TG. Comparing +XM/TG+ and control groups, significantly altered expression was seen for 2447 genes (18%) and 3200 genes (24%) at early and late time points, respectively. Canonical pathway analyses of differentially expressed genes showed inflammatory genes associated with innate and adaptive immune responses. Comparing +XM/TG+ and +XM/NoTG groups, 3718 probe sets were differentially expressed but these were over-represented in only four pathways. A classic accommodation phenotype was not identified. Using rt-PCR, the expression of inflammatory genes was significantly increased in +XM/TG+ recipients compared to the +XM/NoTG and control groups. In conclusion, pretransplant donor-specific anti-HLA antibodies results in a gene expression profile characterized by inflammation and cellular infiltration and the majority of +XM grafts are exposed to chronic injury.

Current problems of chronic active antibody-mediated rejection

The Banff 2007 classification allows chronic rejection to be differentiated based on clinicopathological characteristics evidenced by two independent immunologic mechanisms; chronic active antibody-mediated rejection and chronic active T-lymphocyte mediated rejection. However, several incompletely understood issues concerning chronic active antibody-mediated rejection remain. Chronic active antibody-mediated rejection is characterized by C4d deposition in the capillary basement membrane(PTC), the presence of circulating anti-donor antibodies(DSA), and morphologic evidence of chronic tissue injury such as glomerular double contours compatible with transplant glomerulopathy (TPG), PTC basement membrane multilayering, interstitial fibrosis/tubular atrophy, and fibrous arterial intimal thickening. PTC basement membrane multilayering correlates highly with TPG, and most of TPG have evidence of either C4d-positive staining or DSA. However, the proposed criteria do not apply to all situations of chronic active antibody-mediated rejection. C4d is not a magic marker for antibody-mediated rejection. C4d staining is not always highly sensitive for detecting antibody-mediated rejection. Multi-institutional studies should be conducted to better understand the clinicopathological context of chronic antibody-mediated rejection. These studies should include well-designed serial protocol biopsies with evaluation by electron microscopy, C4d staining performed on frozen sections, and assessment using sensitive DSA detection methods.

Overlapping pathways to transplant glomerulopathy: chronic humoral rejection, hepatitis C infection, and thrombotic microangiopathy

Transplant glomerulopathy (TG) has received much attention in recent years as a symptom of chronic humoral rejection; however, many cases lack C4d deposition and/or circulating donor-specific antibodies (DSAs). To determine the contribution of other causes, we studied 209 consecutive renal allograft indication biopsies for chronic allograft dysfunction, of which 25 met the pathological criteria of TG. Three partially overlapping etiologies accounted for 21 (84%) cases: C4d-positive (48%), hepatitis C-positive (36%), and thrombotic microangiopathy (TMA)-positive (32%) TG. The majority of patients with confirmed TMA were also hepatitis C positive, and the majority of hepatitis C-positive patients had TMA. DSAs were significantly associated with C4d-positive but not with hepatitis C-positive TG. The prevalence of hepatitis C was significantly higher in the TG group than in 29 control patients. Within the TG cohort, those who were hepatitis C-positive developed allograft failure significantly earlier than hepatitis C-negative patients. Thus, TG is not a specific diagnosis but a pattern of pathological injury involving three major overlapping pathways. It is important to distinguish these mechanisms, as they may have different prognostic and therapeutic implications.

Determinants of long-term graft outcome in transplant glomerulopathy

BACKGROUND

Transplant glomerulopathy (TG) is a renal allograft disease defined by glomerular basement membrane duplication with peritubular capillary basement membrane multilayering (PTCML), and associated with anti-human leukocyte antigen antibodies and C4d. Outcome in TG is poor but variable, and prognostic factors, particularly those affecting long-term outcome, are not well known. We investigated several potentially prognostic clinical and pathologic factors in TG and evaluated estimated glomerular filtration rate (eGFR) slopes to assess graft function and early decline.

METHODS

We examined all cases of TG from 2001 to 2005 with at least 4-year follow-up after biopsy, excluding those with a second confounding diagnosis.

RESULTS

Among 36 cases of pure TG, mean graft age at biopsy was 8.8±6 years. C4d stain was positive in 11 (33%) cases. Clinical characteristics at biopsy were not different based on C4d. C4d was associated with greater PTCML (P=0.03), peritubular capillaritis (P=0.04), and glomerulitis (P=0.03). Death-censored graft survival was significantly associated with interstitial fibrosis (P=0.001), PTCML (P=0.001), and arteriolar hyalinosis (P=0.007), and it showed a trend with proteinuria (P=0.07) and C4d positivity (P=0.08). C4d-positive cases also showed a trend toward rapid graft loss. Analysis of eGFR slopes showed a pattern of preserved, slightly negative slope from transplant until approximately 1 year before biopsy, at which point the slope became significantly more negative (P<0.001).

CONCLUSION

Interstitial fibrosis, PTCML, and arteriolar hyalinosis were significant predictors of graft survival in TG. C4d positivity was associated with a more rapid rate of function decline. eGFR slope data showed significant deterioration in graft function well before the diagnostic biopsy.

Glomerular damage as a predictor of renal allograft loss

Interstitial fibrosis and tubular atrophy (IF/TA) are the most common cause of renal graft failure. Chronic transplant glomerulopathy (CTG) is present in approximately 1.5-3.0% of all renal grafts. We retrospectively studied the contribution of CTG and recurrent post-transplant glomerulopathies (RGN) to graft loss. We analyzed 123 patients with chronic renal allograft dysfunction and divided them into three groups: CTG (N = 37), RGN (N = 21), and IF/TA (N = 65). Demographic data were analyzed and the variables related to graft function identified by statistical methods. CTG had a significantly lower allograft survival than IF/TA. In a multivariate analysis, protective factors for allograft outcomes were: use of angiotensin-converting enzyme inhibitor (ACEI; hazard ratio (HR) = 0.12, P = 0.001), mycophenolate mofetil (MMF; HR = 0.17, P = 0.026), hepatitis C virus (HR = 7.29, P = 0.003), delayed graft function (HR = 5.32, P = 0.016), serum creatinine > or =1.5 mg/dL at the 1st year post-transplant (HR = 0.20, P = 0.011), and proteinuria > or =0.5 g/24 h at the 1st year post-transplant (HR = 0.14, P = 0.004). The presence of glomerular damage is a risk factor for allograft loss (HR = 4.55, P = 0.015). The presence of some degree of chronic glomerular damage in addition to the diagnosis of IF/TA was the most important risk factor associated with allograft loss since it could indicate chronic active antibody-mediated rejection. ACEI and MMF were associated with better outcomes, indicating that they might improve graft survival.

Combination of peritubular c4d and transplant glomerulopathy predicts late renal allograft failure

The histologic associations and clinical implications of peritubular capillary C4d staining from long-term renal allografts are unknown. We identified 99 renal transplant patients who underwent an allograft biopsy for renal dysfunction at least 10 yr after transplantation, 25 of whom were C4d-positive and 74 of whom were C4d-negative. The average time of the index biopsy from transplantation was 14 yr in both groups. Compared with C4d-negative patients, C4d-positive patients were younger at transplantation (29 +/- 13 versus 38 +/- 12 yr; P < 0.05) and were more likely to have received an allograft from a living donor (65 versus 35%; P < 0.001). C4d-positive patients had more inflammation, were more likely to have transplant glomerulopathy, and had worse graft outcome. The combined presence of C4d positivity, transplant glomerulopathy, and serum creatinine of >2.3 mg/dl at biopsy were very strong predictors of rapid graft loss. C4d alone did not independently predict graft loss. Retrospective staining of historical samples from C4d-positive patients demonstrated C4d deposition in the majority of cases. In summary, these data show that in long-term renal allografts, peritubular capillary staining for C4d occurs in approximately 25% of biopsies, can persist for many years after transplantation, and strongly predicts graft loss when combined with transplant glomerulopathy.

Transplant glomerulopathy: ultrastructural abnormalities occur early in longitudinal analysis of protocol biopsies

Transplant glomerulopathy (TXG) presents a distinctive pattern of glomerular abnormalities. The aim of this study was to describe its sequential ultrastructural pathology. A paired cohort study of 228 protocol biopsies, from our longitudinal database (n = 1345), compared TXG (7 patients, 95 biopsies) and controls (8 patients, 133 biopsies). Ultrastructural morphometry and C4d immunoperoxidase were evaluated from implantation to 5 years after transplantation against sequential histology and functional changes. TXG was predated by early glomerular endothelial cell activation; typified by vacuolation, hypertrophy, serration and expansion of lamina rara interna from 39 +/- 23 days after transplantation. Endothelial cells were transformed into an activated phenotype, containing numerous mitochondria, Golgi and ribosomes. Transition from fenestrated to continuous endothelium, mesangial matrix expansion and podocyte fusion occurred late. Endothelial cell activation also occurred in peritubular capillaries (PTC) followed by basement membrane multi-lamination (p < 0.05-0.001). Light microscopy changes of TXG occurred at 2.3 years. PTC C4d deposition was intermittently expressed over time, correlating with endothelial abnormalities, glomerular C4d and donor-specific antibodies (DSA) (p < 0.05-0.001). In summary, endothelial and subendothelial ultrastructural abnormalities in glomerular and peritubular capillaries are sensitive, early markers of TXG, likely due to stimulation of endothelial cells into an activated phenotype by antibody-mediated sub-lytic complement deposition.

Proteinuria after kidney transplantation, relationship to allograft histology and survival

Proteinuria is associated with reduced kidney allograft survival. Herein we assessed the association between proteinuria, graft histology and survival. The cohort included 613 kidney allograft recipients who had proteinuria (measured) and surveillance biopsies at 1-year posttransplant. Proteinuria >150 mg/day was detected in 276 patients (45%) and in 182 of these, proteinuria was below 500. In >84% of patients even low levels of proteinuria were associated with albuminuria. Proteinuria was associated with the presence of graft glomerular pathology and the use of sirolimus. Eighty percent of patients with proteinuria >1500 mg/day had glomerular pathology on biopsy. However, lower levels of proteinuria were not associated with specific pathologies at 1 year. Compared to no sirolimus, sirolimus use was associated with higher prevalence of proteinuria (40% vs. 76%, p < 0.0001) and higher protein excretion (378 + 997 vs. 955 + 1986 mg/day, p < 0.0001). Proteinuria was associated with reduced graft survival (HR = 1.40, p = 0.001) independent of other risk factors including, glomerular pathology, graft function, recipient age and acute rejection. The predominant pathology in lost allografts (n = 57) was glomerular, particularly in patients with 1-year proteinuria >500. Thus, proteinuria, usually at low levels (<500 mg/day), is present in 45% of recipients at 1 year. However, and even low levels of proteinuria relate to poor graft survival. Proteinuria and glomerular pathology relate independently to survival.

Transplant glomerulopathy, late antibody-mediated rejection and the ABCD tetrad in kidney allograft biopsies for cause

To define the relative frequency of phenotypes of transplant glomerulopathy, we retrospectively reviewed the findings in 1036 biopsies for clinical indications from 1320 renal transplant patients followed in our clinics between 1997 and 2005. Transplant glomerulopathy, defined by double contours of glomerular basement membranes (D), was diagnosed in 53 biopsies (5.1%) from 41 patients (3.1%) at a median of 5.5 years post-transplant (range 3.8-381 months). In cases with D, we studied the frequency of circulating anti-HLA alloantibody (A), peritubular capillary basement membrane multilayering (B) and peritubular capillary C4d deposition (C). B was present in 48 (91%) of D biopsies. C4d staining by indirect immunofluorescence was detected in 18 of 50 D biopsies studied (36%). By Flow PRA Screening or ELISA, A was detected in 33 (70%) in 47 D cases with available sera, of which 28/33 or 85% were donor-specific. Class II (13/33) or class I and II (17/33) were more common than class I (3/33) antibodies. Thus 73% of transplant glomerulopathy has evidence of alloantibody-mediated injury (A and/or C), with ABCD and ABD being the common phenotypes in biopsies for cause. The remaining 27%, mostly BD, may be a different disease or a stage in which A and C are undetectable.

Therapeutic targets in the treatment of allograft fibrosis

The dramatic improvements in short-term graft survival and acute rejection rates could only have been dreamed of 20 years ago. Late graft loss following kidney transplantation is now the critical issue of this decade. Frequently, graft loss is associated with the development of tubular atrophy and interstitial fibrosis within the kidney (i.e. chronic allograft nephropathy; CAN). Major treatment strategies in this disorder are non-specific and the focus of intervention has been on limiting injurious events. Following graft injury is a fibrogenesis phase featuring both proliferative and infiltrative responses mediated by chemokines, cytokines and growth factors. In particular, TGFbeta has been strongly implicated in the pathogenesis of chronic injury and epithelial-mesenchymal transformation (EMT) may be part of this process. The cascade of events results in matrix accumulation, due to either increased production and/or reduced degradation of matrix. Recent investigations into the pathogenesis of tissue fibrosis have suggested a number of new strategies to ameliorate matrix synthesis. While the majority of therapies have focused on TGFbeta, this may not be an ideal maneuver in transplant settings and alternative targets identified in other fibrotic diseases will be discussed. Attacking graft fibrosis should be a new focus in organ transplantation.

The clinical impact of chronic transplant glomerulopathy in cyclosporine era

BACKGROUND

The clinical impact of chronic transplant glomerulopathy (CTG) on the outcome of kidney allograft receiving calcineurin inhibitors (CNIs) remains uncertain. A retrospective study of renal transplant recipients at Ospedale Maggiore of Milan was undertaken to evaluate the clinical outcome of patients with CTG.

METHODS

Among 666 biopsies taken at least 6 months after transplantation (Tx) in 498 transplant patients treated with CNIs, 28 cases (5.6%) of chronic transplant glomerulopathy (CTG) were identified and their clinical features at Tx, at follow-up and graft survival were compared with those of 56 controls transplanted in the same period and with kidney functioning 12 months after Tx. Clinical characteristics at biopsy and at 1 year after Tx were similar in the two groups.

RESULTS

After diagnosis graft function deteriorated in 22 patients (78.5%), while it remained stable in 6. Graft loss developed in 92 % of patients with proteinuria >2.5 g/day and in 33 % of those with lower proteinuria (P<0.005). In cases with more severe CTG the rate of graft loss was higher, though not significantly. Graft survival at 10 years was 48% in patients with CTG and 88% in controls (P<0.0001).

CONCLUSIONS

The incidence and clinical course of CTG do not seem to be modified by CNI-based immunosuppression. The evolution is unpredictable but the severity of glomerulopathy and proteinuria at follow-up are associated with progression to graft failure. Patients with CTG have a graft survival significantly worse than that of the general population of transplanted patients.

Chronic renal allograft dysfunction

The major causes of renal transplant loss are death from vascular, malignant or infectious disease, and loss of the allograft from chronic renal dysfunction associated with the development of graft fibrosis and glomerulosclerosis. Chronic allograft nephropathy (CAN) is the histologic description of the fibrosis, vascular and glomerular damage occurring in renal allografts. Clinical programs rely on monitoring change in serum creatinine for identification of patients at risk of CAN, but this change occurs late in the course of the disease, and underestimates the severity of pathologic change. CAN has several causes: ischemia-reperfusion injury, ineffectively or untreated clinical and subclinical rejection, and superimposed calcineurin inhibitor nephrotoxicity, exacerbating pre-existing donor disease. Once established, interstitial fibrosis and arteriolar hyalinosis lead to progressive glomerulosclerosis over the subsequent years. There have been a number of approaches to treatment aimed at reducing the impact of CAN, mostly centered around avoidance of calcineurin inhibitors through their elimination in all, or just selected, patients. These immunosuppression strategies combine corticosteroids with azathioprine or mycophenolate mofetil, and/or sirolimus and everolimus. Late identification of CAN in individual patients has meant that strategies for intervening to prevent chronic renal allograft dysfunction and subsequent graft loss tend to be "too little and far too late."

Chronic renal allograft rejection: Pathophysiologic considerations

Chronic rejection is currently the most prevalent cause of renal transplant failure. Clinically, chronic rejection presents by chronic transplant dysfunction, characterized by a slow loss of function, often in combination with proteinuria and hypertension. The histopathology is not specific in most cases but transplant glomerulopathy and multilayering of the peritubular capillaries are highly characteristic. Several risk factors have been identified such as young recipient age, black race, presensitization, histoincompatability, and acute rejection episodes, especially vascular rejection episodes and rejections that occur late after transplantation. Chronic rejection develops in grafts that undergo intermittent or persistent damage from cellular and humoral responses resulting from indirect recognition of alloantigens. Progression factors such as advanced donor age, renal dysfunction, hypertension, proteinuria, hyperlipidemia, and smoking accelerate deterioration of renal function. At the tissue level, senescence conditioned by ischemia/reperfusion (I/R) may contribute to the development of chronic allograft nephropathy (CAN). The most effective option to prevent renal failure from chronic rejection is to avoid graft injury from both immune and nonimmune mechanism together with nonnephrotoxic maintenance immunosuppression.

Antibody response against the glomerular basement membrane protein agrin in patients with transplant glomerulopathy

Chronic allograft nephropathy (CAN) of renal allografts is still the most important cause of graft loss. A subset of these patients have transplant glomerulopathy (TGP), characterized by glomerular basement membrane (GBM) duplications, but of unknown etiology. Recently, a role for the immune system in the pathogenesis of TGP has been suggested. In 11 of 16 patients with TGP and in 3 of 16 controls with CAN in the absence of TGP we demonstrate circulating antibodies reactive with GBM isolates. The presence of anti-GBM antibodies was associated with the number of rejection episodes prior to diagnosis of TGP. Sera from the TGP patients also reacted with highly purified GBM heparan sulphate proteoglycans (HSPG). Indirect immunofluorescence with patient IgG showed a GBM-like staining pattern and colocalization with the HSPGs perlecan and especially agrin. Using patient IgG, we affinity purified the antigen and identified it as agrin. Reactivity with agrin was found in 7 of 16 (44%) of patients with TGP and in 7 of 11 (64%) patients with anti-GBM reactivity. In conclusion, we have identified a humoral response against the GBM-HSPG agrin in patients with TGP, which may play a role in the pathogenesis of TGP.

Renal transplantation 2004: where do we stand today?

In spite of considerable progress in immunosuppressive and supportive treatment, numerous problems persist which interfere with the success of renal transplantation. Before transplantation has been performed, factors impacting on outcome include the donor (living vs cadaver, age and HLA system) as well as the recipient (age, immunological reactivity, potential sensitization and duration of dialysis). These are the main factors that affect the outcome of the transplant, particularly in the long-term. After transplantation a number of events may put graft function at risk: potential recurrence of the primary renal disease in the allograft; 'de novo' renal disease triggered by infections, drugs or autoimmunity; and non-specific progression promoters, such as diabetes, hypertension, proteinuria, nephrotoxic agents and/or viral infections. The two most frequent causes of chronic allograft dysfunction are (i) chronic rejection (often triggered by preceding acute rejection, delayed graft function or poor compliance) and (ii) calcineurin-inhibitor nephrotoxicity (more likely to develop in kidneys of older donors or in marginal kidneys). The differential diagnosis between these two entities is generally difficult, but some histological clues (reduplication of glomerular basement membrane, obliterating vasculopathy and C4d deposits) as well as the demonstration of humoral antibodies are pointers suggesting rejection. Treatment of chronic graft dysfunction is difficult, whatever the cause, particularly in cases with advanced renal lesions. Therefore, early diagnosis is of paramount importance. In this regard, graft biopsy can be of great help. In spite of many problems and complications, not only short-term but also long-term results of renal transplantation are improving progressively, as documented by CTS data showing that in Europe for transplants performed between 1982 and 1984 the mean graft half-life was 7 years, while for transplants performed between 1997 and 1999 it was 20 years.

Immunologic risk factors and glomerular C4d deposits in chronic transplant glomerulopathy

BACKGROUND

Chronic transplant glomerulopathy is an uncommon cause of chronic transplant dysfunction of unknown pathogenesis. We evaluated the epidemiologic, clinical, and histologic features of chronic transplant glomerulopathy. To determine the possible contribution of humoral immune responses, we assessed glomerular deposition of C4d.

METHODS

From a cohort of 1111 kidney transplants (1983 to 2001) with at least 6 months of graft function, we identified 18 cases with chronic transplant glomerulopathy (1.6%) showing double contours of the glomerular basement membrane (GBM) on light microscopy. To assess the risk factors, this group was compared with 739 patients with stable function using multivariate Cox regression analysis. Paraffin sections of 11/18 biopsies were stained with polyclonal C4d antibodies. Sera of 13/18 patients could be tested for antidonor human leukocyte antigen (HLA) antibodies by enzyme-linked immunosorbent assay (ELISA). Patients with chronic allograft nephropathy without chronic transplant glomerulopathy or predominant cyclosporine nephrotoxicity were used as controls.

RESULTS

Chronic transplant glomerulopathy was diagnosed at a median of 8.3 (range 2.6-12.5) years posttransplantation. Panel reactive antibodies at time of transplantation, RR 1.23 (1.05-1.45) per 10% increase, and late acute rejection episodes, RR 7.6 (1.8-31.7), were independently associated with chronic transplant glomerulopathy. We found glomerular C4d deposits in 10/11 biopsies showing chronic transplant glomerulopathy and in only 2/13 controls. Peritubular capillary C4d deposits and donor-specific anti-HLA antibodies were demonstrated in 4 and 3 of the 10 patients with glomerular C4d deposits, respectively.

CONCLUSION

Presensitization and late acute rejection episodes were the risk factors identified. Glomerular C4d deposits suggest that chronic transplant glomerulopathy emerges from in situ humoral rejection. Chronic transplant glomerulopathy should be considered as a manifestation of immune-mediated injury.

The pathobiology of chronic allograft nephropathy: Immune-mediated damage and accelerated aging

Chronic allograft nephropathy includes chronic calcineurin nephrotoxicity, recurrent and de novo glomerulonephritis and a group of disorders with graft dysfunction of unknown etiology designated chronic rejection. Review of risk factors of the latter category show that the chronic rejection lesions emerge in organs that have undergone injury. Despite the relevance of nonalloantigen-dependent progression factors in the tissue injury, alloantigen-dependent factors predominate in the pathogenesis. Lately, B cell responses have received increasing interest in transplant rejection and include responses against both major histocompatibility complex (MHC) and tissue-specific antigens, mainly on the endothelium and in the glomeruli. These humoral responses are thought to be involved in the development of vascular and glomerular lesions. Furthermore, at the tissue level, markers of senescence are found in the tubular epithelium contributing to the lesions of tubular atrophy and interstitial fibrosis.

Peritubular capillary changes and C4d deposits are associated with transplant glomerulopathy but not IgA nephropathy

We examined our renal transplant population for glomerular diseases demonstrated on biopsy between January 1993 and April 2002, focusing on transplant glomerulopathy (TGP). Of 1156 patients followed in our clinics during this period, glomerular disease was diagnosed in 132 cases (11.4%). Glomerulonephritis was diagnosed in 86 transplants (7.4%), with IgA nephropathy (IgAN) being the commonest diagnosis [32 cases (2.8%)]. Thirty-one cases (2.7%) of biopsy-proven TGP were analyzed for associated factors compared with 27 cases (2.3%) of recurrent IgAN. Transplant glomerulopathy was less frequent with mycophenolate mofetil (MMF) and/or tacrolimus, whereas recurrent IgAN showed no such tendency (P= 0.02). Peritubular capillary (PTC) C4d deposition was observed in six of 24 cases (25%) with TGP but none with recurrent IgAN (P= 0.02). Peritubular capillary basement membrane (BM) multilayering was significantly greater in TGP (4.92 +/- 2.94) than in recurrent IgAN (1.86 +/- 1.04) (P < 0.001). The graft survival of TGP was worse than recurrent IgAN (P= 0.05). The association of TGP with BM multilayering and C4d deposits in PTC suggests a generalized disorder of the graft microcirculation and its BM, owing to antibody-mediated rejection in at least some cases. Transplant glomerulopathy has a serious prognosis but is less frequent in patients on newer immunosuppression, unlike recurrent IgAN.

The role of B cells and alloantibody in the host response to human organ allografts

Some human organ transplants deteriorate slowly over a period of years, often developing characteristic syndromes: transplant glomerulopathy (TG) in kidneys, bronchiolitis obliterans in lungs, and coronary artery disease in hearts. In the past, we attributed late graft deterioration to "chronic rejection", a distinct but mysterious immunologic process different from conventional rejection. However, it is likely that much of chronic rejection is explained by conventional T-cell-mediated rejection (TMR), antibody-mediated rejection (AMR), and other insults. Recently, criteria have emerged to now permit us to diagnose AMR in kidney transplants, particularly C4d deposition in peritubular capillaries and circulating antibody against donor human leukocyte antigens (HLA). Some cases with AMR develop TG, although the relationship of TG to AMR is complex. Thus, a specific diagnosis of AMR in kidney can now be made, based on graft damage, C4d deposition, and donor-specific alloantibodies. Criteria for AMR in other organs must be defined. Not all late rejections are AMR; some deteriorating organs probably have smoldering TMR. The diagnosis of late ongoing AMR raises the possibility of treatment to suppress the alloantibody, but efficacy of the available treatments requires further study.

High urine sIL-6R as a predictor of late graft failure in renal transplant recipients

BACKGROUND

Chronic allograft nephropathy is an important cause of late renal transplant failure. Although numerous studies on cytokines have been carried out, the pathogenetic role of cytokines in chronic renal allograft nephropathy remains unclear.

METHODS

In a retrospective study, the authors compared posttransplant plasma and urine cytokine levels (interleukin [IL]-1alpha, IL-1beta, soluble [s] IL-1 receptor [R] antagonist [A], IL-2, sIL-2R, IL-3, IL-4, IL-6, sIL-6R, IL-10, tumor necrosis factor-alpha, transforming growth factor-beta2, and interferon-gamma) in 34 matched pairs of patients with or without late graft failure and in 50 matched pairs with either normal or increased serum creatinine levels and continued stable graft function.

RESULTS

Twelve and 6 months before late graft failure, urine levels of sIL-6R were significantly increased (P=0.003 and P=0.01, respectively). Serum creatinine levels were not associated with increased urine sIL-6R.

CONCLUSION

High urine sIL-6R appears to be predictive of late graft failure in renal transplant recipients.

Chronic rejection with or without transplant vasculopathy

BACKGROUND

Chronic allograft nephropathy (CAN) is defined and graded in the Banff '97 scheme by the severity of interstitial fibrosis and tubular atrophy. It has been denoted that chronic rejection can be diagnosed if the typical vascular lesions are seen, consisting of fibrointimal thickening. We observed several patients who developed CAN without vascular changes or signs of cyclosporine toxicity. Therefore, we assessed the risk factor profiles of CAN with and without transplant vasculopathy.

METHODS

A cohort of 654 cadaveric renal transplants performed between 1983 and 1997 that functioned for more than 6 months was studied. Fifty-four transplants had CAN defined by a significant decline in renal function together with interstitial fibrosis and tubular atrophy without signs of cyclosporine nephrotoxicity or recurrent disease. Using the Banff chronic vascular (CV) score, 23 of 54 cases (43%) had a chronic vasculopathy score of 0 or 1 whereas 31 cases (57%) had a CV score of 2 or 3. Applying multivariate logistic regression, predictor variables of the two groups were compared with 231 transplants with a stable function for at least 5 yr.

RESULTS

Graft histology was obtained at a mean of 2.4 and 2.9 yr after transplantation in the group with or without vasculopathy, respectively. Acute rejection episodes (AREs) after 3 months post-transplantation were the strongest risk factor for both forms of CAN, odds ratio (OR) 14.7 (6.0-36.0). CAN with vasculopathy was also associated with transplants performed in the 1980s, OR 4.95 (1.65-14.9) and with creatinine clearance at 6 months, OR 0.58 (0.44-0.75) per 10 mL/min increase. In contrast, young recipient age, OR 0.69 (0.47-0.99) per 10-yr increase, and the presence of panel reactive antibodies at the time of transplantation, OR 1.26 (1.08-1.47) per 10% increase, were independent risk factors for CAN without vasculopathy.

CONCLUSIONS

After exclusion of cyclosporine toxicity or recurrent disease CAN occurred without moderate or severe transplant vasculopathy in 43% of the cases. The correlation with young recipient age, sensitization and late ARE suggest an immune pathogenesis, consistent with chronic rejection.

Capillary deposition of complement split product C4d in renal allografts is associated with basement membrane injury in peritubular and glomerular capillaries: a contribution of humoral immunity to chronic allograft rejection

Endothelial deposition of the complement split product C4d is an established marker of antibody-mediated acute renal allograft rejection. A contribution of alloantibody-dependent immune reactions to chronic rejection is under discussion. In this study, the association of immunohistochemically detected endothelial C4d deposition in peritubular capillaries (PTC) with morphologic features of chronic renal allograft injury was investigated in a large study cohort. C4d deposits in PTC were detected in 73 (34%) of 213 late allograft biopsies performed in 213 patients more than 12 mo after transplantation (median, 4.9 yr) because of chronic allograft dysfunction. Endothelial C4d deposition was found to be associated with chronic transplant glomerulopathy (CG) (P < 0.0001), with basement membrane multilayering in PTC (P = 0.01), and with an accumulation of mononuclear inflammatory cells in PTC (P < 0,001). Furthermore, C4d deposits in PTC (in biopsies with normal glomerular morphology) were associated with development of CG in follow-up biopsies. Other morphologic features of chronic allograft nephropathy (with exception of tubular atrophy) were not associated with C4d deposits in PTC. Analyses of previous and follow-up biopsies revealed that C4d deposits may occur de novo and may also disappear at any time after transplantation. In conclusion, the data suggest that complement activation in renal microvasculature, indicating humoral alloreactivity, contributes to chronic rejection characterized by chronic transplant glomerulopathy and basement membrane multilayering in PTC.

Hepatitis C virus infection and de novo glomerular lesions in renal allografts

In the present study we examine whether hepatitis C virus (HCV) infection status influences glomerular pathologic findings in renal allografts and its effect on graft outcome. Renal allograft biopsies performed between January 1991 and June 1999 were considered. Exclusion criteria were insufficient sample, unknown HCV serological status at time of biopsy and final diagnosis of acute rejection. Light microscopy and immunofluorescence studies were performed on all biopsies. According to a predefined protocol, electron microscopy was carried out. Of 138 eligible renal allograft biopsies, 42 fulfilled at least one exclusion criterion. Of 96 biopsies selected for the study, 44 (45.8%) were from HCV-positive and 52 from HCV-negative recipients. Renal biopsy was performed 74 +/- 55 and 60 +/- 39 months after transplantation in HCV-positive and HCV-negative groups, respectively (p = 0.12). Of 44 HCV-positive biopsies, 20 (45.4%) showed membranoproliferative glomerulonephritis (MPGN) (16 type I and 4 type III). Conversely, in HCV-negative biopsies there were only three cases of MPGN (2 type I and 1 type III). De novo membranous GN (MGN) was diagnosed in 8/44 (18.2%) HCV-positive and in 4/52 (7.7%) HCV-negative cases. The prevalence of chronic transplant glomerulopathy was similar in HCV-positive and HCV-negative groups (11.4% and 11.5%, respectively). The prognosis of de novo GN (either MPGN or MGN) was worse in HCV-positive than in HCV-negative recipients (relative risk 4.89; 95% confidence interval, 1.15-20.69; p = 0.03). By multivariate analysis, HCV-positive serology infection was the only independent predictor of graft loss (relative risk 2.64; 95% confidence interval, 1.35-5.17; p = 0.005). In diagnostic renal allograft biopsies the presence of de novo immune-mediated glomerulonephritis, especially type I MPGN, is strongly associated with HCV infection and results in accelerated loss of the graft.

Antibody response against perlecan and collagen types IV and VI in chronic renal allograft rejection in the rat

Chronic rejection is the leading cause of late renal transplant failure. Various structural lesions are observed in grafts undergoing chronic rejection including glomerular basement membrane (GBM) duplications. The well-established Fisher (F344) to Lewis (LEW) rat renal transplant model for chronic rejection was used to assess the presence and role of the humoral immune response against graft antigens during chronic rejection. LEW recipients of F344 allografts develop transplant glomerulopathy and produce IgG1 antibodies directed against F344 GBM preparations that are detectable 3 weeks after transplantation. Glomerular IgG1 deposition was observed that in vitro co-localized with a rabbit anti-rat GBM antiserum in rejecting F344 grafts; elution experiments of isolated glomeruli yielded IgG1 antibodies reactive in vitro with F344 GBM, but not LEW GBM. Prevention of acute rejection by transient treatment of the recipients with cyclosporin A completely abrogated the production of anti-GBM antibodies. Using proteomic techniques we identified the antigens recognized by the LEW posttransplant sera as being the heparan sulfate proteoglycan perlecan and the alpha1 chain of collagen type VI in association with the alpha5 chain of collagen type IV. In conclusion, LEW recipients of F344 kidney grafts produce IgG1 antibodies against donor type perlecan and alpha1(VI)/alpha5(IV) collagen and develop transplant glomerulopathy. These data implicate an important role for the humoral immune response in the development of glomerulopathy during chronic rejection.

Call for revolution: a new approach to describing allograft deterioration

I propose a set of definable entities in the renal transplant course, eliminating the need for the term 'chronic rejection'. The status of a renal transplant can be defined by the presence and extent of rejection (T-cell-mediated or antibody-mediated); allograft nephropathy (parenchymal atrophy, fibrosis, and fibrous intimal thickening in arteries); transplant glomerulopathy; specific diseases; and factors which could accelerate progression. The level of function and the slope of the loss of function should be separately determined. This approach can be applied both in research and in clinical practice, and can be adapted to other organ transplants.

Early glomerular dysfunction in human renal allografts

BACKGROUND

The long-term outcome of renal allografts is characterized by a progressive deterioration of renal function and graft loss. Our aim was to determine early glomerular functional abnormalities, before they become clinically apparent.

METHODS

Glomerular hemodynamics and dextran sieving were characterized in 21 well-functioning cadaveric renal allograft recipients [normal glomerular filtration rate (GFR) and albumin excretion rate (AER), who also had a kidney biopsy with normal or minimal histological changes] and in 15 uninephrectomized kidney donors. Both groups were one to three years after transplantation or uninephrectomy.

RESULTS

The GFR and renal plasma flow (RPF) were similar in both groups (62 +/- 3 vs. 63 +/- 4, and 343 +/- 26 vs. 334 +/- 21 mL/min/1.73 m2 for GFR and RPF, in cadaveric recipients vs. donors, respectively), the AER was normal in both groups, but the mean arterial pressure was higher in renal recipients (103 +/- 3 vs. 94 +/- 3 mm Hg in uninephrectomy controls, P < 0.05). Despite similar levels of overall glomerular function in the two groups, the dextran sieving curve was uniformly elevated in the renal allograft recipients versus uninephrectomy controls (P < 0.05 for dextrans 38 to 66 A). Using a log-normal glomerular pore-size distribution model to analyze potential mechanisms, the elevation in the dextran sieving curve resulted from a shift in the distribution of glomerular filtering pores to a larger size (mean glomerular pore size 46 +/- 2 vs. 43 +/- 2 A for uninephrectomy controls, P < 0.05), resulting in a larger fraction of filtrate volume permeating very large pores. By morphometric analysis, the thickness of the glomerular basement membrane was increased in kidney allograft as compared to 2-kidney biopsy controls (614 +/- 33 vs. 427 +/- 22 nm, respectively, P < 0.05).

CONCLUSIONS

Even in "well functioning" renal allografts there is a glomerular dysfunction characterized by increased permeability to macromolecules resulting from a shift of the glomerular pores to a larger size. These changes could be mediated by ultrastructural alterations at the glomerular capillary or by alterations in intraglomerular hemodynamics. Early allograft dysfunction may contribute to the progressive renal insufficiency of renal allografts.