Transplant glomerulopathy: subclinical incidence and association with alloantibody

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.

A case of transplant glomerulopathy early after kidney transplantation

Transplant glomerulopathy (TG) has commonly been described as a late manifestation of allograft injury, occurring years after renal transplantation. We describe herein a patient who developed TG early (49 days) after kidney transplantation (KTx).

CASE REPORT

  A 44-yr-old woman received a second living-related KTx from her younger brother in October 2009. Pre-transplant donor-specific anti-human leukocyte antigen antibodies (DSA) were positive for both class I and class II. During the renal transplant operation, she suffered from hyperacute antibody-mediated rejection (AMR) and intravenous immune globulin therapy was immediately performed. Once hyperacute AMR was resolved, accelerated acute AMR occurred on the first post-transplant day (PTD). The renal allograft biopsy performed on PTD 19 diagnosed acute AMR type II. The renal allograft biopsy performed on PTD 49 showed focal lesions of double contours of glomerular basement membranes in some glomeruli. Interstitial fibrosis showed a strong, diffuse staining of C4d in peritubular capillaries (PTCs). The DSA examined on PTD 39 were still positive for both class I and class II. From these histopathological findings of TG, C4d deposition in PTC and presence of circulating DSA, we diagnosed this case to have c-AMR.

CONCLUSIONS

  TG might be recognized in early after KTx.

Immunological function of the endothelial cell within the setting of organ transplantation

In organ transplantation, development of immunosuppressive treatment and improved diagnosis of allograft rejection has resulted in increased allograft survival in recent years. Nevertheless, rejection remains a major cause of graft loss and a better understanding of the characteristics of the allo-immune response is required to identify new diagnostic and therapeutic tools. The allogeneic immune response depends upon a major family of antigenic targets: the Major Histocompatibility Complex molecules (MHC) which are present on donor cells. These molecules are targets of both the humoral and cellular arms of the graft recipient's immune system: T lymphocytes which are implicated in acute cellular rejection and antibodies which are implicated in antibody-mediated rejection (AMR). Allo-recognition of allograft MHC antigens by either T cells or allo-antibodies is the primary event which can ultimately lead to graft rejection. Although immunosuppressive strategies have mainly focused on the T cell response and acute cellular rejection has therefore become relatively rare, antibody mediated rejection (AMR) remains resistant to conventional immunosuppressive treatment and results in frequent graft loss. Damage to the endothelium is a prominent histological feature of AMR underlining the involvement of endothelial cells in initiating the allo-immune response. Furthermore, endothelial cells express both HLA class I and class II molecules in the context of organ transplantation endowing them with the capacity to present antigen to the recipient T cells. The endothelium should therefore be viewed both as a stimulator of, and as a target for allo-immune responses. In this review, we will summarize current knowledge about the implication of endothelial cells in the allo-immune response in the context of organ transplantation.

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.

Interpretation of positive flow cytometric crossmatch in the era of the single-antigen bead assay

BACKGROUND

Prognosis of renal transplants with positive flow cytometric crossmatch (FCXM) remains controversial.

METHODS

We analyzed the outcome of these kidney transplant recipients by human leukocyte antigen (HLA) donor-specific antibodies (HLA-DSA) using single-antigen bead (SAB) assays in major histocompatibility complex classes I and II. We compared them with controls with a negative FCXM.

RESULTS

Forty-five patients consecutively transplanted with a positive FCXM had significantly more acute rejection episodes than the control patients (33.3% vs. 8.9%, P=0.002). Risk of acute rejection was increased with day 0 (D0) positive T-cell FCXM (odds ratio [OR]=9.04, P=0.002), D0 positive B-cell FCXM (OR=7.43, P=0.02), and D0 HLA-DSA identified by SAB assay (OR=6.5, P=0.03). The 21 patients with D0 positive FCXM and D0 HLA-DSA had more acute rejection (62%, P=0.0001) and a lower estimated glomerular filtration rate 1-year posttransplantation (P=0.0001), when compared with controls. Mainly anti-Cw and anti-DP HLA-DSA were found in patients displaying acute rejection. The remaining FCXM-positive patients displayed short-term outcomes similar to controls. The presence of HLA-DSA detected only by the SAB assay in the context of a negative FCXM crossmatch was not associated with increased risk of acute rejection.

CONCLUSION

Identification of HLA-DSA in D0 sera by the two sensitive techniques FCXM and SAB assay indicates which patients are at highest risk of subsequent acute allograft rejection and chronic allograft dysfunction.

The histology of solitary renal allografts at 1 and 5 years after transplantation

Previous studies suggest that the majority of renal allografts are affected by progressive, severe chronic histologic injury, yet studies using current protocols are lacking. The goal of this study was to examine the prevalence and progression of histologic changes using protocol allograft biopsies at 1 and 5 years after solitary kidney transplantation in patients transplanted between 1998 and 2004. Chronic histologic changes generally were mild at both 1 and 5 years and were similar in deceased and living donor kidneys. The overall prevalence of moderate or severe fibrosis was 13% (60/447) at 1 year and 17% (60/343) at 5 years. In a subgroup of 296 patients who underwent both 1- and 5-year biopsies, mild fibrosis present at 1 year progressed to more severe forms at 5 years in 23% of allografts. The prevalence of moderate or severe arteriolar hyalinosis was similar in tacrolimus and calcineurin inhibitor-free immunosuppression. These results in the recent era of transplantation demonstrate fewer, less severe and less progressive chronic histologic changes in the first 5 years after transplantation than previously reported.

Donor-directed MHC class I antibody is preferentially cleared from sensitized recipients of combined liver/kidney transplants

For patients with chronic renal and liver diseases, simultaneous liver and kidney transplantation (SLKT) is the best therapeutic option. The role of a pretransplant donor-specific antibody (DSA) in SLKT is unclear. We report the results of a retrospective review from 7/08 to 10/09 of SLKT at our institution. Monitoring of DSA was performed using single antigen bead assay. Between 7/08 and 10/09, there were six SLKT who had preformed DSA and positive XM (four class I and II DSA, one class I DSA only, one class II only). One-year patient and renal graft survival was 83%. Death-censored liver allograft survival was 100%. Acute humoral rejection (AHR) of the kidney occurred in 66% (three with both class I and II DSA and one with only class II DSA) of patients. In those with AHR, class I antibodies were rapidly cleared (p < 0.01) while class II antibodies persisted (p = 0.25). All patients who had humoral rejection of their kidney had preformed anticlass II antibodies. Liver allografts may not be fully protective of the renal allograft, especially with pre-existing MHC class II DSA. Long-term and careful follow-up will be critical to determine the impact of DSA on both allografts.

Desensitization protocols and their outcome

In the last decade, transplantation across previously incompatible barriers has increasingly become popular because of organ donor shortage, availability of better methods of detecting and characterizing anti-HLA antibodies, ease of diagnosis, better understanding of antibody-mediated rejection, and the availability of effective regimens. This review summarizes all manuscripts published since the first publication in 2000 on desensitized patients and discusses clinical outcomes including acute and chronic antibody-mediated rejection rate, the new agents available, kidney paired exchange programs, and the future directions in sensitized patients. There were 21 studies published between 2000 and 2010, involving 725 patients with donor-specific anti-HLA antibodies (DSAs) who underwent kidney transplantation with different desensitization protocols. All studies were single center and retrospective. The patient and graft survival were 95% and 86%, respectively, at a 2-year median follow-up. Despite acceptable short-term patient and graft survivals, acute rejection rate was 36% and acute antibody-mediated rejection rate was 28%, which is significantly higher than in nonsensitized patients. Recent studies with longer follow-up of those patients raised concerns about long-term success of desensitization protocols. The studies utilizing protocol biopsies in desensitized patients also reported higher subclinical and chronic antibody-mediated rejection. An association between the strength of DSAs determined by median fluorescence intensity values of Luminex single-antigen beads and risk of rejection was observed. Two new agents, bortezomib, a proteasome inhibitor, and eculizumab, an anti-complement C5 antibody, were recently introduced to desensitization protocols. An alternative intervention is kidney paired exchange, which should be considered first for sensitized patients.

Emerging role of B cells in chronic allograft dysfunction

B cells have many possible mechanisms by which they can affect allograft survival, including antigen presentation, cytokine production, immune regulation, and differentiation into alloantibody-producing plasma cells. This report reviews the last mechanism, which the authors regard as most critical for the long-term survival of allografts, namely, the promotion of chronic rejection by alloantibodies. Chronic humoral rejection characteristically arises late after transplantation and causes transplant glomerulopathy, multilamination of peritubular capillary basement membranes, and C4d deposition in PTCs and glomeruli. Circulating antidonor human leukocyte antigen class II antibodies are commonly detected and may precede the development of graft injury. Prognosis is poor, especially when recognized after graft dysfunction has developed. Improved detection and treatment are critically needed for this common cause of late graft loss.

The pathology of chronic allograft dysfunction

Chronic allograft dysfunction is associated with a variety of fibrosing/sclerosing changes in the allograft. Fibrosis is multifactorial, a final pathway following varying types of injury. Using a range of diagnostic criteria, the pathologist can and should define specific lesions enabling identification of pathogenic processes affecting the allograft. Although some cases remain 'interstitial fibrosis and tubular atrophy, no specific cause', specific diagnoses can be made in most cases. Drug toxicity, bacterial or viral infection, hypertension, obstruction, recurrent or de novo renal diseases, and acute and chronic cell- and/or antibody-mediated rejection can be diagnosed in this setting. Of particular concern is a combination of persistent inflammation and fibrosis, which has repeatedly been shown to be correlated with poor graft outcomes. Identification of ongoing activity, and the stage of evolution of fibrosis/sclerosis provides important diagnostic and therapeutic information for patient management. Histological, immunohistological, ultrastructural, and molecular studies may be needed to adequately assess the kidney in the setting of chronic allograft dysfunction. Protocol biopsies may provide diagnostic insights in early stages of late graft deterioration, or even before evident dysfunction develops.

C1q-fixing human leukocyte antigen antibodies are specific for predicting transplant glomerulopathy and late graft failure after kidney transplantation

BACKGROUND

Human leukocyte antigen (HLA) antibodies, especially those that fix complement, are associated with antibody-mediated rejection and graft failure. The C1q assay on single antigen beads detects a subset of HLA antibodies that can fix complement and precede C4d deposition. The aim of this study was to determine whether C1q-fixing antibodies distinguish de novo donor-specific antibodies (DSA) that are clinically relevant and harmful.

METHODS

We retrospectively studied 31 of 274 kidney transplant recipients who had pretransplant and concurrent biopsy and serum specimens, 13 with C4d-positive and 18 with C4d-negative staining. We measured IgG and C1q DSA pretransplant and at the time of biopsy using single antigen bead assays. We identified 13 recipients who developed de novo DSA by IgG or C1q and examined associations with C4d deposition, transplant glomerulopathy, and graft failure.

RESULTS

Testing for DSA by IgG is more sensitive for C4d deposition (IgG: 100%, 95% confidence interval [CI] 0.60-1; C1q: 75%, 95% CI 0.36-0.96). Testing for DSA by C1q is more specific for transplant glomerulopathy (C1q: 81%, 95% CI 0.57-0.94; IgG: 67%, 95% CI 0.43-0.85) and graft loss (C1q: 79%, 95% CI 0.54-0.93; IgG: 63%, 95% CI 0.39-0.83). Absence of de novo DSA by IgG and C1q has a high negative predictive value for the absence of C4d deposition (IgG: 100%, 95% CI 0.73-1; C1q: 88%, 95% CI 0.62-0.98), transplant glomerulopathy (IgG: 100%, 95% CI 0.73-1; C1q: 100%, 95% CI 0.77-1), and graft failure (IgG: 86%, 95% CI 0.56-0.97; C1q: 88%, 95% CI 0.62-0.98).

CONCLUSION

Monitoring patients with the C1q assay, which detects antibodies that fix complement, offers a minimally invasive means of identifying patients at risk for transplant glomerulopathy and graft loss.

Chronic viral hepatitis in kidney transplantation

Chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection in potential kidney transplant candidates-once considered absolute contraindications to kidney transplantation-no longer creates overt barriers to transplantation. Advances in the medical management of HBV and HCV infection have created opportunities for a substantial number of patients to be effectively treated with antiviral therapy before transplantation. For HBV infection, a number of new drugs enable clearance of the virus with minimal adverse effects and drug resistance. Pretransplantation antiviral therapy is advisable for patients with HCV infection, but adverse effects are common and viral eradication remains challenging. Regardless of viral clearance, pretransplant patients without bridging fibrosis (as confirmed by liver biopsy) or clinical stigmata of cirrhosis should be considered for kidney transplantation as survival is superior when compared to treatment with dialysis, and progression of liver disease is unlikely. For patients with advanced liver disease, simultaneous liver-kidney transplantation is an important consideration. These treatment advances further increase the burden of organ donor shortage; however, organs from deceased donors with chronic HBV or HCV infection could be efficiently allocated to certain individuals with a viral infection of the same type to increase the pool of available transplant organs.

Significance of C4d Banff scores in early protocol biopsies of kidney transplant recipients with preformed donor-specific antibodies (DSA)

The significance of C4d-Banff scores in protocol biopsies of kidney transplant recipients with preformed donor-specific antibodies (DSA) has not been determined. We reviewed 157 protocol biopsies from 80 DSA+ patients obtained at 3 months and 1 year post-transplant. The C4d Banff scores (1,2,3) were associated with significant increments of microcirculation inflammation (MI) at both 3 months and 1 year post-transplant, worse transplant glomerulopathy and higher class II DSA-MFI (p < 0.01). Minimal-C4d had injury intermediate between negative and focal, while focal and diffuse-C4d had the same degree of microvascular injury. A total of 54% of patients had variation of C4d score between 3 months and 1 year post-transplant. Cumulative (3 month + 1 year) C4d scores correlated with long-term renal function worsening (p = 0.006). However, C4d staining was not a sensitive indicator of parenchymal disease, 55% of C4d-negative biopsies having evidence of concomitant MI. Multivariate analysis demonstrated that the presence of MI and class II DSA at 3 months were associated with a fourfold increased risk of progression to chronic antibody-mediated rejection independently of C4d (p < 0.05). In conclusion, the substantial fluctuation of C4d status in the first year post-transplant reflects a dynamic humoral process. However, C4d may not be a sufficiently sensitive indicator of activity, MI and DSA being more robust predictors of bad outcome.

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.

The (re)emergence of B cells in organ transplantation

PURPOSE OF REVIEW

To outline recent advances in our understanding of the role of B cells in transplantation.

RECENT FINDINGS

While T-cell-mediated alloimmunity has been largely controlled using immunosuppression, the role of B cells in transplantation is just beginning to be understood. Recent studies have outlined some of the important clinical issues involving antibody including early acute humoral rejection and late transplant glomerulopathy. In addition, recent studies have identified bone-marrow-derived long-lived plasma cells that appear to be a major source of donor-specific alloantibody in sensitized renal transplant recipients. New agents are being tested that deplete these cells in vitro and in vivo. Memory B cells appear to be important in early acute humoral rejection, but few basic studies have been performed. Finally, recent studies involving patients undergoing tolerogenic regimens suggest that T-cell tolerance does not always convey tolerance in naive B cells.

SUMMARY

Several B cell types have clear and specific roles in transplant recipients. Although our understanding of B cells in transplantation has improved, important gaps remain.

The strength of donor-specific antibody is a more reliable predictor of antibody-mediated rejection than flow cytometry crossmatch analysis in desensitized kidney recipients

The aim of this study was to evaluate the utility of donor-specific antibodies (DSA) and flow cytometry crossmatch (FCCM) as tools for predicting antibody-mediated rejection (AMR) in desensitized kidney recipients. Sera from 44 patients with DSA at the time of transplant were reviewed. Strength of DSA was determined by single antigen Luminex bead assay and expressed as mean fluorescence intensity (MFI). T- and B-cell FCCM results were expressed as mean channel shift (MCS). AMR was diagnosed by C4d deposition on biopsy. Incidence of early AMR was 31%. Significant differences in the number of DSAs (p = 0.0002), cumulative median MFI in DSA class I (p = 0.0004), and total (class I + class II) DSA (p < 0.0001) were found in patients with and without AMR. No significant difference was seen in MCS of T and B FCCM (p = 0.095 and p = 0.307, respectively). The three-yr graft survival in desensitized patients with DSA having total MFI < 9500 was 100% compared to 76% with those having total MFI > 9500 (p = 0.022). Desensitized kidney transplant recipients having higher levels of class I and total DSA MFI are at high risk for AMR and poor graft survival. Recipient DSA MFI appears to be a more reliable predictor of AMR than MCS of FCCM.

Prolongation of renal allograft survival by anergic cells: advantages and limitations

Even in the era of pharmacological calcineurin inhibitors, a current major challenge in organ transplantation remains the development of immunosuppressive regimens that protect against rejection. One potentially effective procedure is the use of donor-specific anergic T cells generated ex vivo and adoptively transferred back into the recipient after transplantation. In our own work, we first investigated the effect of anergic cells on the prolongation of graft survival in non-human primates. In six animals, half of the recipients survived for over one yr (all animals died or were killed within eight yr). The cause of death was acute renal failure because of cellular rejection (one), uncontrolled bleeding after renal biopsy (two), hydronephrosis probably because of ureteral stenosis (one), and chronic rejection (one). The remaining animal was killed at the end of the study. No infection, malignancy, or signs of graft versus host disease (GVHD) was observed in any of these monkeys. Except for the one animal that died of acute cellular rejection, there was no evidence of tubular infiltration by mononuclear cells, glomerular damage, or parenchymal necrosis. In all animals surviving for more than one yr, a mild grade of interstitial fibrosis, an increase in mesangial matrix, or glomerulopathy was noted. In two of three monkeys, no vascular narrowing of the luminal area caused by fibrointimal thickening of arteries was noted, and arteriosclerotic change was dominant. In this chapter, we summarize the efficacy and limitations of our strategy.

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.

Donor-specific antibody levels and three generations of crossmatches to predict antibody-mediated rejection in kidney transplantation

BACKGROUND

This study evaluated the prognostic impact of pretransplant donor-specific anti-human leukocyte antigen antibodies (DSA) detected by single-antigen beads and compared the three generations of crossmatch (XM) tests in kidney transplantation.

METHODS

Thirty-seven T-cell complement-dependent cytotoxicity crossmatch (CXM) negative living donor kidney recipients with a retrospectively positive antihuman leukocyte antigen antibody screening assay were included. A single-antigen bead test, a flow cytometry XM, and a Luminex XM (LXM) were retrospectively performed, and the results were correlated with the occurrence of antibody-mediated rejections (AMRs) and graft function.

RESULTS

We found that (1) pretransplant DSA against class I (DSA-I), but not against class II, are predictive for AMR, resulting in a sensitivity of 75% and a specificity of 90% at a level of 900 mean fluorescence intensity (MFI); (2) with increasing strength of DSA-I, the sensitivity for AMR is decreasing to 50% and the specificity is increasing to 100% at 5200 MFI; (3) the LXM for class I, but not for class II, provides a higher accuracy than the flow cytometry XM and the B-cell CXM. The specificity of all XMs is increased greatly in combination with DSA-I values more than or equal to 900 MFI.

CONCLUSIONS

In sensitized recipients, the best prediction of AMR and consecutively reduced graft function is delivered by DSA-I alone at high strength or by DSA-I at low strength in combination with the LXM or CXM.

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.

Preexisting donor-specific HLA antibodies predict outcome in kidney transplantation

The clinical importance of preexisting HLA antibodies at the time of transplantation, identified by contemporary techniques, is not well understood. We conducted an observational study analyzing the association between preexisting donor-specific HLA antibodies (HLA-DSA) and incidence of acute antibody-mediated rejection (AMR) and survival of patients and grafts among 402 consecutive deceased-donor kidney transplant recipients. We detected HLA-DSA using Luminex single-antigen assays on the peak reactive and current sera. All patients had a negative lymphocytotoxic cross-match test on the day of transplantation. We found that 8-year graft survival was significantly worse (61%) among patients with preexisting HLA-DSA compared with both sensitized patients without HLA-DSA (93%) and nonsensitized patients (84%). Peak HLA-DSA Luminex mean fluorescence intensity (MFI) predicted AMR better than current HLA-DSA MFI (P = 0.028). As MFI of the highest ranked HLA-DSA detected on peak serum increased, graft survival decreased and the relative risk for AMR increased: Patients with MFI >6000 had >100-fold higher risk for AMR than patients with MFI <465 (relative risk 113; 95% confidence interval 31 to 414). The presence of HLA-DSA did not associate with patient survival. In conclusion, the risk for both AMR and graft loss directly correlates with peak HLA-DSA strength. Quantification of HLA antibodies allows stratification of immunologic risk, which should help guide selection of acceptable grafts for sensitized patients.

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.

Significance and implications of capillaritis during acute rejection of kidney allografts

BACKGROUND.: Anti-human leukocyte antigen antibodies (a-HLA) cause graft injury identified by C4d in peritubular capillaries. We investigated whether a-HLA relate to episodes of C4d negative acute rejection (AR). METHODS.: We analyzed 878 kidney recipients transplanted from January 2000 to December 2006. Pretransplant, 36% of these crossmatch negative recipients had a-HLA measured by solid phase assays. RESULTS.: AR occurred in 154 patients (18%) and 11 of them (9.4%) were C4d+. Forty-six percent of ARs were diagnosed by protocol biopsy. The risk of C4d-AR was increased in patients with a-HLA class I with donor specificity (DSA-I) (hazard ratio=1.519; confidence interval, 1.02-2.26; P=0.039). DSA-II were not associated with an increased risk of C4d-AR. The relationship between DSA-I and C4d-AR was independent of recipient age, BK nephropathy, and HLA mismatches. Compared with DSA-, in DSA+ recipients C4d-AR were most often histologically "borderline." DSA+ was associated with capillaritis in the biopsy (glomerulitis, 6.1% vs. 32%, P=0.003; peritubular capillaritis: 13% vs. 40%, P=0.0009). Compared with no AR, C4d-AR with capillaritis was associated with reduced graft survival (hazard ratio=4.164; confidence interval, 1.763-9.832; P=0.001), independent of other variables. This association was observed even in the cases of borderline AR. CONCLUSIONS.: DSA-I increases the risk of C4d-AR. The presence of DSA-I or II is associated with capillaritis during AR. Capillaritis is associated with reduced graft survival.

Renal transplantation in patients with hepatitis C virus antibody. A long national experience

Background. Renal transplantation is the best therapy for patients with hepatitis C virus (HCV) infection with end-stage renal disease. Patient and graft survival are lower in the long term compared with HCV-negative patients. The current study evaluated the results of renal transplantation in Spain in a long period (1990–2002), focusing on graft failure.

Methods. Data on the Spanish Chronic Allograft Nephropathy Study Group including 4304 renal transplant recipients, 587 of them with HCV antibody, were used to estimate graft and patient survival at 4 years with multivariate Cox models.

Results. Among recipients alive with graft function 1 year post-transplant, the 4-year graft survival was 92.8% in the whole group; this was significantly better in HCV-negative vs HCV-positive patients (94.4% vs 89.5%, P < 0.005). Notably, HCV patients showed more acute rejection, a higher degree of proteinuria accompanied by a diminution of renal function, more graft biopsies and lesions of de novo glomerulonephritis and transplant glomerulopathy. Serum creatinine and proteinuria at 1 year, acute rejection, HCV positivity and systolic blood pressure were independent risk factors for graft loss. Patient survival was 96.3% in the whole group, showing a significant difference between HCV-negative vs HCV-positive patients (96.6% vs 94.5%, P < 0.05). Serum creatinine and diastolic blood pressure at 1 year, HCV positivity and recipient age were independent risk factors for patient death.

Conclusions. Renal transplantation is an effective therapy for HCV-positive patients with good survival but inferior than results obtained in HCV-negative patients in the short term. Notably, HCV-associated renal damage appears early with proteinuria, elevated serum creatinine showing chronic allograft nephropathy, transplant glomerulopathy and, less frequently, HCV-associated de novo glomerulonephritis. We suggest that HCV infection should be recognized as a true risk factor for graft failure, and preventive measures could include pre-transplant therapy with interferon.

ABO antibody titer and risk of antibody-mediated rejection in ABO-incompatible renal transplantation

Therapeutic plasma exchange (TPE) preconditioning with immunosuppressive therapy reduces ABO antibody titers, permitting engraftment of ABO-incompatible (ABO-I) kidney transplants. The posttransplant predictive role of ABO antibody titers for antibody-mediated rejection (AMR) is unknown. This retrospective study evaluated 46 individuals who received TPE to permit ABO-I kidney transplantation. ABO antibody titers were performed using donor-type indicator red cells. Seven individuals (15.2%) experienced clinical or subclinical AMR. There was no significant difference between recipient blood group, number of pretransplant TPE and baseline titer between those with and without AMR. At 1-2 weeks posttransplant the median titer was 64 (range 4 - 512) among individuals with AMR and 16 (range 2 - 256) among individuals without AMR. Total agglutination reactivity score was significantly higher among individuals with AMR (p = 0.046). The risk of AMR was significantly higher among individuals with an elevated posttransplant titer of >or=64 (p = 0.006). The sensitivity of an elevated posttransplant titer was 57.1% with a specificity of 79.5%. The positive predictive value was 33.3% and the negative predictive value was 91.2%. Most individuals with AMR have an elevated titer, however, the positive predictive value of a high titer for AMR is poor.

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.

Baseline donor-specific antibody levels and outcomes in positive crossmatch kidney transplantation

Renal transplant candidates with donor-specific alloantibody (DSA) have increased risk of antibody-mediated allograft injury. The goal of this study was to correlate the risk of antibody-mediated rejection (AMR), transplant glomerulopathy (TG) and graft survival with the baseline DSA level (prior to initiation of pretransplant conditioning). These analyses include 119 positive crossmatch (+XM) compared to 70 negative crossmatch (-XM) transplants performed between April 2000 and July 2007. Using a combination of cell-based crossmatch tests, DSA level was stratified into very high +XM, high +XM, low +XM and -XM groups. In +XM transplants, increasing DSA level was associated with increased risk for AMR (HR = 1.76 [1.51, 2.07], p = 0.0001) but not TG (p = 0.18). We found an increased risk for both early and late allograft loss associated with very high DSA (HR = 7.71 [2.95, 20.1], p = 0.0001). Although lower DSA recipients commonly developed AMR and TG, allograft survival was similar to that of -XM patients (p = 0.31). We conclude that the baseline DSA level correlates with risk of early and late alloantibody-mediated allograft injury. With current protocols, very high baseline DSA patients have high rates of AMR and poor long-term allograft survival highlighting the need for improved therapy for these candidates.

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.

Results of gal-knockout porcine thymokidney xenografts

Clinical transplantation for the treatment of end-stage organ disease is limited by a shortage of donor organs. Successful xenotransplantation could immediately overcome this limitation. The development of homozygous alpha1,3-galactosyltransferase knockout (GalT-KO) pigs removed hyperacute rejection as the major immunologic hurdle to xenotransplantation. Nevertheless, GalT-KO organs stimulate robust immunologic responses that are not prevented by immunosuppressive drugs. Murine studies show that recipient thymopoiesis in thymic xenografts induces xenotolerance. We transplanted life-supporting composite thymokidneys (composite thymus and kidneys) prepared in GalT-KO miniature swine to baboons in an attempt to induce tolerance in a preclinical xenotransplant model. Here, we report the results of seven xenogenic thymokidney transplants using a steroid-free immunosuppressive regimen that eliminated whole-body irradiation in all but one recipient. The regimen resulted in average recipient survival of over 50 days. This was associated with donor-specific unresponsiveness in vitro and early baboon thymopoiesis in the porcine thymus tissue of these grafts, suggesting the development of T-cell tolerance. The kidney grafts had no signs of cellular infiltration or deposition of IgG, and no grafts were lost due to rejection. These results show that xenogeneic thymus transplantation can support early primate thymopoiesis, which in turn may induce T-cell tolerance to solid organ xenografts.

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.

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.

Endothelial gene expression in kidney transplants with alloantibody indicates antibody-mediated damage despite lack of C4d staining

Anti-HLA alloantibody is a risk factor for graft loss, but does not indicate which kidneys are experiencing antibody-mediated rejection (ABMR). C4d staining in biopsies is specific for ABMR but insensitive. We hypothesized that altered expression of endothelial genes due to alloantibody acting on the microcirculation would be sensitive indicator of ABMR. We identified 119 endothelial-associated transcripts (ENDATs) from literature, and studied their expression by microarrays in 173 renal allograft biopsies for cause. Mean ENDAT expression was increased in all rejection but was higher in ABMR than in T-cell-mediated rejection and correlated with histopathologic lesions of ABMR, and alloantibody. Many individual ENDATs were increased in ABMR and predicted graft loss. Kidneys with high ENDATs and antibody showed increased lesions of ABMR and worse prognosis in comparison to controls. Only 40% of kidneys with high ENDAT expression and chronic ABMR or graft loss were diagnosed by C4d positivity. High ENDAT expression with antibody predicts graft loss with higher sensitivity (77% vs. 31%) and slightly lower specificity (71% vs. 94%) than C4d. The results were validated in independent set of 82 kidneys. High renal endothelial transcript expression in patients with alloantibody is indicator of active antibody-mediated allograft damage and poor graft outcome.

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.

Subclinical rejection in stable positive crossmatch kidney transplant patients: incidence and correlations

We reviewed 116 surveillance biopsies obtained approximately 1, 3, 6 and 12 months posttransplantation from 50 +XM live donor kidney transplant recipients to determine the frequency of subclinical cell-mediated rejection (CMR) and antibody-mediated rejection (AMR). Subclinical CMR was present in 39.7% of the biopsies at 1 month and >20% at all other time points. The presence of diffuse C4d on biopsies obtained at each time interval ranged from 20 to 30%. In every case, where histological and immunohistological findings were diagnostic for AMR, donor-specific antibody was found in the blood, challenging the long-held belief that low-level antibody could evade detection due to absorption on the graft. Among clinical factors, only recipient age was associated with subclinical CMR. Clinical factors associated with subclinical AMR were recipient age, positive cytotoxic crossmatch prior to desensitization and two mismatches of HLA DR 51, 52 and 53 alleles. Surveillance biopsies during the first year post-transplantation for these high-risk patients uncover clinically occult processes and phenotypes, which without intervention diminish allograft survival and function.

Rituximab and intravenous immunoglobulin treatment of chronic antibody-mediated kidney allograft rejection

Kidney transplant rejections are classified into T-cell-mediated and antibody-mediated rejections (AMR). C4d staining on allograft biopsies and solid-phase assays to measure donor-specific alloantibodies have helped to precisely define the latter. Although for acute AMRs, therapy mainly relies on plasmapheresis or immunoadsorption, no studies for treatment of chronic AMR are available. Here, we report on four kidney allograft recipients suffering from chronic AMR 1 to 27 years posttransplant, who were treated with a combination of rituximab and intravenous immunoglobulin (IVIG). Rituximab/IVIG improved kidney allograft function in all four patients, whereas donor-specific antibodies were reduced in 2 of 4 patients. However, in one patient an acute rejection episode occurred 12 months after this treatment, and another patient had severe, possibly rituximab-associated lung toxicity. Thus, rituximab/IVIG may be a useful strategy for the treatment of chronic AMR, but further randomized multicenter studies are necessary to establish its efficacy and safety profile.

Clinical significance of anti-HLA antibodies detected by Luminex: enhancing the interpretation of CDC-BXM and important post-transplantation monitoring tools

B-cell crossmatch (BXM) was originally introduced to increase the sensitivity to detect anti-HLA antibodies of conventional CDC crossmatch in renal transplantation. Newer techniques such as Luminex((R)) have greater sensitivity in detecting anti-HLA antibodies but have not been directly evaluated versus BXM. We discuss our experience with Luminex testing and the significance of donor-specific antibodies (DSA) defined by Luminex in three populations, as compared with the CDC crossmatch. In the general transplant population, Luminex-defined DSA were found in only one third of positive CDC-BXM and were associated with graft rejection. Luminex testing enhanced the interpretation of CDC-BXM and identified patients with clinically relevant BXM. In the highly sensitized transplant population, Luminex-defined DSA were found in two thirds of positive BXM and were a better predictor of graft rejection. Therefore, Luminex assays rather than CDC-BXM should be used to facilitate kidney allocation in highly sensitized patients. In the post-transplantation population, Luminex antibody monitoring for DSA was shown to be important, as it defined low-level de novo DSA that were associated with development of transplant glomerulopathy and a significant predictor of graft loss in those patients. Thus Luminex testing facilitated the interpretation of CDC-BXM and provided a useful predictive tool for the detection of clinically significant DSA in post-transplantation antibody monitoring.

Treatment of symptomatic transplant glomerulopathy with rituximab

Kidney transplant glomerulopathy (TG) has a poor outcome as there are no known effective therapies. Therefore, we investigated whether rituximab therapy (RTx) could halt progression of established TG. Fourteen kidney-transplant patients (nine of whom were men), with median age of 54 (range: 30-74) years, of whom seven had biologic markers for HCV infection, underwent a kidney biopsy (KB) at 118 months post-transplant because of impaired allograft function, associated with albuminuria (95-13430 mg/day), within nephrotic-range albuminuria in seven patients. KBs showed no evidence of acute cellular rejection but showed TG. Donor-specific anti-HLA antibodies were present in six cases. When diagnosis of TG was made, patients were placed on rituximab therapy (RTx) (2-4 injections of 375 mg/m2 week), and other concurrent immunosuppression treatments were not modified. By last follow up post-RTx (30 months), seven (50%) patients had lost their kidney within 6-26 months and the other seven had stable creatinine (182 vs. 161 micromol/l; NS), and albuminuria had decreased from 2660 to 500 mg/day (P = 0.03). There was prolonged B-cell lymphopenia (from 71 to 0/mm3) whereas immunoglobulin G, A, M levels remained stable, and four patients (28.5%) experienced severe infectious complications. We conclude that long-term RTx in kidney-transplant patients with TG is associated with allograft function/stabilization in 50% of cases.

Transplant glomerulopathy: clinical and pathological correlations

OBJECTIVE

Chronic transplant glomerulopathy (TG) is one of the leading causes of severe posttransplantation proteinuria and graft loss. Our current knowledge about risk factors for the development of TG, as well as factors that affect its dynamics and prognosis, is poor. We sought to describe the pathological and clinical risk factors and correlations of TG as well as parameters that influenced the survival of grafts with that pathology.

MATERIALS AND METHODS

We retrospectively reevaluated 86 kidney transplant cases with TG that have been recognized on the basis of an indication biopsy since 1997. All TG as well as all pre-TG (previous) biopsies were characterized for the presence of C4d deposits in the graft.

RESULTS

Younger recipient age and minimal immunosuppression due to drug withdrawal or suboptimal drug doses/blood levels within 3 to 6 months preceding the biopsy were associated with C4d deposition in peritubular capillaries (PTC; P = .0053 and P = .0365, respectively). Diffuse PTC-itis (P = .029, RR [95% confidence interval] = 3.349 [1.131-9.919]) and total interstitial inflammation score (P = .015, RR [95% confidence interval] = 9.662 [1.784-52.329]) were observed to show a negative impact on graft survival. C4d deposition in PTC and glomeruli, the level of pretransplantation sensitization, episodes of acute rejection, and C4d in previous (pre-TG) biopsies did not influence the survival of grafts with TG.

CONCLUSIONS

Younger recipient age and minimal immunosuppression were associated with C4d positivity in grafts with TG. The survival of kidney grafts with TG was significantly affected by the magnitude of inflammation in the interstitium and PTC, but not by C4d positivity in PTC and glomeruli.