C4d peritubular capillary staining in chronic allograft nephropathy and transplant glomerulopathy: an uncommon finding

Glomerular C3 Deposition Is an Independent Risk Factor for Allograft Failure in Kidney Transplant Recipients With Transplant Glomerulopathy

Introduction

Transplant glomerulopathy (TG) becomes increasingly prevalent in kidney transplant recipients over time, and it is strongly associated with allograft failure. To date, our prognostic biomarkers and understanding of the processes of immunologic injury in TG are limited.

Methods

This is a retrospective cohort analysis of kidney transplant recipients with TG (double contours of the glomerular basement membrane as defined by the chronic glomerulopathy score). Glomerular deposition of the complement protein C3 was determined, and its association with allograft survival was analyzed by Cox regression analysis.

Results

Of the 111 patients with TG, 72 (65%) had allograft failure, with a median follow-up time of 3 years from biopsy diagnosis of TG. C3-positive compared to C3-negative patients did not differ with respect to cause of end-stage renal disease, induction or maintenance immunosuppression, or sensitization. A greater proportion of patients with glomerular C3 deposition developed allograft failure compared to those with no C3 deposition (78% vs. 55%, P = 0.01). C3 deposition was independently associated with allograft failure in multivariate analyses (adjusted hazard ratio [HR] = 1.38, 95% confidence interval [CI] = 1.13−1.69, P = 0.002). There was no association between C4d or C1q deposition and allograft failure. Chronicity score was also associated with allograft failure in multivariate analysis (adjusted HR 1.26, 95% CI 1.12-1.41, P = 0.0001).

Conclusion

In this cohort of patients with TG, glomerular C3 deposition was independently associated with a higher risk of allograft failure. These findings identify glomerular C3 as a novel prognostic indicator in patients with TG.

Transplant glomerulopathy

In the renal allograft, transplant glomerulopathy represents a morphologic lesion and not a specific diagnosis. The hallmark pathologic feature is glomerular basement membrane reduplication by light microscopy or electron microscopy in the absence of immune complex deposits. Transplant glomerulopathy results from chronic, recurring endothelial cell injury that can be mediated by HLA alloantibodies (donor-specific antibodies), various autoantibodies, cell-mediated immune injury, thrombotic microangiopathy, or chronic hepatitis C. Clinically, transplant glomerulopathy may be silent, detectable on protocol biopsy, or present with overt manifestations, including up to nephrotic range proteinuria, hypertension, and declining glomerular filtration rate. In either case, transplant glomerulopathy is associated with reduced graft survival. This review details the morphologic features of transplant glomerulopathy found on light microscopy, immunofluorescence microscopy, and electron microscopy. The pathophysiology of the causes and risk factors are discussed. Clinical manifestations are emphasized and potential therapeutic modalities are examined.

The clinical implications of the unique glomerular complement deposition pattern in transplant glomerulopathy

The etiology and treatment of transplant glomerulopathy (TG) is not clear. TG is associated with donor-specific antibodies but the lack of C4d deposition in the peritubular capillaries (ptc-C4d) in some cases has caused the role of complement in the pathogenesis of TG to be debated. There is however, little information on C4d deposition in the glomerulus itself. We retrieved random frozen sections from 25 cases with well-established TG by light microscopy (LM) and 25 cases without TG as controls and reviewed the LM and immunofluorescence (nine biopsies were excluded due to inadequate samples). Glomerular complement deposition was assessed in all included biopsies. Glomerular C3d and C4d deposition occurred in a distinct pattern in all TG biopsies: segmental or global double linear staining of the glomerular capillary wall in 23 (100%). This pattern was not present in any NON-TG biopsies. The distinct glomerular complement deposition patterns in all TG cases are suggestive that TG is a proximal complement-mediated process and therapies should focus on proximal complement inhibition.

A systematic review of the role of C4d in the diagnosis of acute antibody-mediated rejection

In this study, we conducted a systematic review of the literature to re-evaluate the role of C4d in the diagnosis of acute antibody-mediated rejection of kidney allografts. Electronic databases were searched until September 2013. Eligible studies allowed derivation of diagnostic tables for the performance of C4d by immunofluorescence or immunohistochemistry with comparison to histopathological features of acute antibody-mediated rejection and/or donor-specific antibody (DSA) assays. Of 3492 unique abstracts, 29 studies encompassing 3485 indication and 868 surveillance biopsies were identified. Assessment of C4d by immunofluorescence and immunohistochemistry exhibited slight to moderate agreement with glomerulitis, peritubular capillaritis, solid-phase DSA assays, DSA with glomerulitis, and DSA with peritubular capillaritis. The sensitivity and specificity of C4d varied as a function of C4d and comparator test thresholds. Prognostically, the presence of C4d was associated with inferior allograft survival compared with DSA or histopathology alone. Thus, our findings support the presence of complement-dependent and -independent phenotypes of acute antibody-mediated rejection. Whether the presence of C4d in combination with histopathology or DSA should be considered for the diagnosis of acute antibody-mediated rejection warrants further study.

The specificity of acute and chronic microvascular alterations in renal allografts

The diagnosis of an antibody-mediated rejection (AMR) is made when there is evident histologic injury in the presence of detectable donor-specific alloantibodies (DSA) and diffuse peritubular capillary C4d staining (C4d-pos). In the presence of only detectable DSA or C4d-pos, the tissue injury is currently considered "presumptive" for antibody causation. In acute antibody-mediated rejection (AAMR), diagnostic morphologic features include microvascular inflammation (MVI), specifically glomerulitis and peritubular capillaritis. In the case of chronic active AMR (CAAMR), these inflammatory lesions have progressed to chronic microvascular injury, transplant glomerulopathy (TG) and peritubular capillary basement membrane multilayering (PTCBMML). Either TG or PTCBMML is sufficient morphological evidence for a diagnosis of CAAMR. Unfortunately, these lesions are not specific. MVI, TG, and PTCBMML are found in the setting of cell-mediated immunity, as well as in association with non-alloimmune mechanisms. The available treatments for AMR and CMR are different, and it is important to ascertain the dominant mechanism when approaching an individual patient. At present, no gold standard exists to establish the specific pathogenesis in the more ambiguous cases. We detail here the differential diagnosis of MVI, TG, and PTCBMML.

The importance of C4d in biopsies of kidney transplant recipients

Antibody-mediated rejection (AMR) is highly detrimental to the prolonged survival of transplanted kidneys. C4d has been regarded as a footprint of AMR tissue damage, and the introduction of C4d staining in daily clinical practice aroused an ever-increasing interest in the role of antibody-mediated mechanisms in allograft rejection. Despite the general acceptance of the usefulness of C4d in the identification of acute AMR, the data for C4d staining in chronic AMR is variable. The presence of C4d in the majority of the biopsies with features of chronic antibody-mediated rejection is reported, but this rejection without C4d staining is observed as well, suggesting that C4d is specific but not sensitive. Further studies on AMR with positive C4d staining in biopsy specimens are really important, as well as the study of novel routine markers that may participate in the pathogenesis of this process.

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.

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.

Antibody-mediated rejection in kidney transplantation: a review

Antibody mediated rejection (AMR) poses a significant and continued challenge for long term graft survival in kidney transplantation. However, in the recent years, there has emerged an increased understanding of the varied manifestations of the antibody mediated processes in kidney transplantation. In this article, we briefly discuss the various histopathological and clinical manifestations of AMRs, along with describing the techniques and methods which have made it easier to define and diagnose these rejections. We also review the emerging issues of C4d negative AMR, its significance in long term allograft survival and provide a brief summary of the current management strategies for managing AMRs in kidney transplantation.

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.

Antibodies reactive to non-HLA antigens in transplant glomerulopathy

Although T and B cell alloimmunity contribute to transplant injury, autoimmunity directed at kidney-expressed, non-HLA antigens may also participate. Because the specificity, prevalence, and importance of antibodies to non-HLA antigens in late allograft injury are poorly characterized, we used a protein microarray to compare antibody repertoires in pre- and post-transplant sera from several cohorts of patients with and without transplant glomerulopathy. Transplantation routinely induced changes in antibody repertoires, but we did not identify any de novo non-HLA antibodies common to patients with transplant glomerulopathy. The screening studies identified three reactivities present before transplantation that persisted after transplant and strongly associated with transplant glomerulopathy. ELISA confirmed that reactivity against peroxisomal-trans-2-enoyl-coA-reductase strongly associated with the development of transplant glomerulopathy in independent validation sets. In addition to providing insight into effects of transplantation on non-HLA antibody repertoires, these results suggest that pretransplant serum antibodies to peroxisomal-trans-2-enoyl-coA-reductase may predict prognosis in kidney transplantation.

Probabilistic (Bayesian) modeling of gene expression in transplant glomerulopathy

Transplant glomerulopathy (TG) is associated with rapid decline in glomerular filtration rate and poor outcome. We used low-density arrays with a novel probabilistic analysis to characterize relationships between gene transcripts and the development of TG in allograft recipients. Retrospective review identified TG in 10.8% of 963 core biopsies from 166 patients; patients with stable function were studied for comparison. The biopsies were analyzed for expression of 87 genes related to immune function and fibrosis by using real-time PCR, and a Bayesian model was generated and validated to predict histopathology based on gene expression. A total of 57 individual genes were increased in TG compared with stable function biopsies (P < 0.05). The Bayesian analysis identified critical relationships between ICAM-1, IL-10, CCL3, CD86, VCAM-1, MMP-9, MMP-7, and LAMC2 and allograft pathology. Moreover, Bayesian models predicted TG when derived from either immune function (area under the curve [95% confidence interval] of 0.875 [0.675 to 0.999], P = 0.004) or fibrosis (area under the curve [95% confidence interval] of 0.859 [0.754 to 0.963], P < 0.001) gene networks. Critical pathways in the Bayesian models were also analyzed by using the Fisher exact test and had P values <0.005. This study demonstrates that evaluating quantitative gene expression profiles with Bayesian modeling can identify significant transcriptional associations that have the potential to support the diagnostic capability of allograft histology. This integrated approach has broad implications in the field of transplant diagnostics.

Complement independent antibody-mediated endarteritis and transplant arteriopathy in mice

Complement fixation, as evidenced by C4d in the microvasculature, is a widely accepted criterion of antibody-mediated rejection. Complement fixation has been shown to be essential in acute antibody-mediated rejection, but its role in chronic rejection has not been addressed. Previous studies showed that passive transfer of complement fixing monoclonal IgG2a anti-H-2Kk into B6.RAG1-/- KO recipients of B10.BR hearts led to progressive chronic transplant arteriopathy (CTA) over 14-28 days, accompanied by C4d deposition. The present studies were designed to test whether complement was required for these lesions. We report that a noncomplement fixing donor-specific alloantibody (DSA, monoclonal IgG1 anti-H-2Kk) injected into B6.RAG1-/- KO recipients of B10.BR hearts also promotes CTA, without C4d deposition. Furthermore, a passive transfer of DSA (monoclonal IgG2a anti-H-2Kk) initiated endarteritis followed by CTA in B6.RAG1-/- mice genetically deficient in the third component of complement (RAG1-/-C3-/-). These studies indicate that antibody to class I MHC antigens can trigger chronic arterial lesions in vivo without complement participation, in contrast to acute antibody-mediated rejection. This pathway may be relevant to C4d-negative chronic rejection sometimes observed in patients with DSA, and argues that lack of C4d deposition does not exclude antibody-mediated chronic rejection.

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.

Predominant Th1 and cytotoxic phenotype in biopsies from renal transplant recipients with transplant glomerulopathy

Transplant glomerulopathy (TGP) appears to be a pathogenic feature of chronic antibody-mediated rejection, but the pathogenesis of this histologic entity is still poorly understood. Previous studies suggest the involvement of lymphocytes but the phenotypes of these cells have never been analyzed. Here, we report the first study of mRNAs for specific markers of CD4+ T cells including Th1 (T-bet and INFgamma), Th2 (IL4 and GATA3), Treg (Foxp3) and Th17 (IL-17 and RORgammat) subsets, cytotoxic CD8 T cells (Granzyme B) and B-cell markers (CD20) in renal biopsies from renal transplant recipients suffering interstitial fibrosis and tubular atrophy (IF/TA) with or without TGP but with a similar inflammatory score and controls including transplant recipients with normal renal function. Only INFgamma, T-bet (both functionally defined markers of Th1 CD4 T cells) and granzyme B (a CD8 cytotoxic marker) were significantly more strongly expressed in patients with TGP than in patients without TGP and normal controls. These results indicate a role of an active T-mediated inflammatory and cytotoxic process in the pathogenesis of TGP.

Chronic allograft nephropathy

PURPOSE OF REVIEW

Despite dramatic declines in acute rejection and early graft failure, long-term outcomes after kidney transplantation have improved little during the past 25 years. Most late allograft failure is attributed to chronic allograft nephropathy, but this is a clinicopathological description and not a diagnosis, and its pathogenesis and treatment are largely unknown.

RECENT FINDINGS

Recent studies suggest that acute rejection during the first few months, and calcineurin inhibitor toxicity thereafter, may both contribute to chronic allograft nephropathy. There is also accumulating evidence that injury from antibody-mediated rejection may play an important pathogenic role in at least some patients with chronic allograft nephropathy, particularly those with transplant glomerulopathy. Therapeutic measures, including protocols to reduce calcineurin inhibitor exposure, remain largely unproven.

SUMMARY

Understanding why so many kidney allografts fail, despite effective preventive measures for early acute rejection, is one of the most important areas of research in kidney transplantation today.

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.

Antibody-Mediated Rejection

The introduction of both complement 4d (C4d) staining in renal allograft biopsies and sensitive methods to detect anti-human leukocyte antigen antibodies, such as single antigen bead flow assays, into tissue-typing techniques have shown the importance of antibody-mediated alloimmune response in kidney transplantation. The use of these sensitive methods, combined with the increased number of transplants in highly sensitized patients with donor-specific antibodies, or patients receiving desensitization protocols, have increased the awareness and thus the incidence of acute antibody-mediated rejection. Chronic rejection also can be mediated through alloantibodies, and the term chronic antibody-mediated rejection recently was proposed. In this review article we summarize the current knowledge of the role of alloantibodies in transplantation, the diagnosis and treatment of acute and chronic antibody-mediated rejection, and their effect on graft function and outcome.

Antibody-mediated renal allograft rejection: diagnosis and pathogenesis

Alloantibodies to HLA class I or II and other antigens expressed by endothelium cause a variety of effects on renal transplants, ranging from acute to chronic rejection, and even apparent graft acceptance (accommodation). Recognition of these conditions and appropriate therapy requires demonstration of C4d in biopsies, commonly confirmed by tests for circulating alloantibody. Substantial practical experience by pathologists in the interpretation and pitfalls of C4d stains are reviewed along with considerations of the clinical significance and pathologic mechanisms of the different effects of antibody on the endothelium of the renal allograft. Clinical trials will be needed to ascertain the optimal treatment for the newly appreciated conditions chronic humoral rejection and accommodation.

Banff '05 Meeting Report: differential diagnosis of chronic allograft injury and elimination of chronic allograft nephropathy ('CAN')

The 8th Banff Conference on Allograft Pathology was held in Edmonton, Canada, 15-21 July 2005. Major outcomes included the elimination of the non-specific term "chronic allograft nephropathy" (CAN) from the Banff classification for kidney allograft pathology, and the recognition of the entity of chronic antibody-mediated rejection. Participation of B cells in allograft rejection and genomics markers of rejection were also major subjects addressed by the conference.

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.

What we CAN do about chronic allograft nephropathy: Role of immunosuppressive modulations

Given the potency of modern immunosuppressive agents, kidney transplantation across alloantingen barriers is a routine phenomenon with excellent 1-year graft survival in most centers. However, the improvement in 1-year graft survival has not been matched by improvements in long-term graft function and chronic allograft nephropathy (CAN) remains the second commonest cause of graft attrition over time. Calcineurin inhibitors, namely cyclosporine A (CyA) and tacrolimus, have been implicated as causal agents in the development of the fibrotic processes that are the hallmarks of CAN. Many studies have, therefore, concentrated on the improvement of long term graft function through the modulation of immunosuppressive therapy. It is the purpose of this review to describe and appraise the available evidence for the prevention and management of CAN through modulation of immunosuppressive agents.