Advances in the understanding of transplant glomerulopathy

Focal Segmental Glomerulosclerosis Superimposed on Transplant Glomerulopathy: Implications for Graft Survival

INTRODUCTION

Transplant glomerulopathy (TG) is a morphological lesion resulting from chronic glomerular endothelium injury, and it is strongly associated with poor graft survival. TG coexisting with focal segmental glomerulosclerosis (FSGS) can be found in renal allograft biopsies, but few related studies are available.

METHODS

Consecutive kidney transplant recipients with biopsy-proven TG were studied retrospectively. Patients concomitant with FSGS were identified and compared with those without FSGS. The influence of FSGS on allograft outcomes was assessed using univariate and multivariate Cox regression models.

RESULTS

Of the 66 patients with TG, 40 (60.6%) had concomitant FSGS. TG patients with FSGS had higher proteinuria (median, 2.6 vs. 0.8 g/24 h, p < 0.001) and serum creatinine levels (median, 2.5 vs. 2.1 mg/dL, p = 0.04), lower serum albumin levels, higher chronic glomerulopathy (cg) score, larger glomerular tuft area, lower number of podocytes, and higher incidences of podocyte hyperplasia, pseudotubule formation, and diffuse foot process effacement than those without FSGS (all p < 0.05). The kidney allograft loss rate of patients with FSGS was higher than that of patients without FSGS (65.7% vs. 37.5%, p = 0.03). The presence of FSGS was independently associated with allograft loss in TG (hazard ratio (HR) = 3.42, 95% confidence interval (CI): 1.30-8.98, p = 0.01). Other independent predictors were proteinuria (HR = 1.18, 95% CI: 1.02-1.37, p = 0.02), estimated glomerular filtration rate (HR = 0.94, 95% CI: 0.91-0.97, p < 0.001), and panel reactive antibody (HR = 3.99, 95% CI: 1.14-13.99, p = 0.03). Moreover, FSGS (odds ratio (OR) = 4.39, 95% CI: 1.29-14.92, p = 0.02) and cg (OR = 5.36, 95% CI: 1.56-18.40, p = 0.01) were independent risk factors for proteinuria.

CONCLUSION

In this cohort of patients with TG, the presence of FSGS was strongly associated with more severe clinicopathological features and worse allograft survival.

Arteriovenous Fistula Nonmaturation: What's the Immune System Got to Do with It?

Background

Arteriovenous fistula (AVF) nonmaturation is a persistent problem, particularly among female and Black patients. Increasingly, the immune system has been recognized as an important contributor to vascular disease, but few studies have examined immune factors relative to AVF maturation outcomes. This study evaluated the association of serum panel reactive antibodies (PRA), a measure of immune system reactivity assessed in patients undergoing kidney transplant evaluation, with AVF nonmaturation.

Methods

We identified 132 patients at our institution who underwent surgical AVF placement between 2010-2019 and had PRA testing within 1 year of AVF creation. Multivariable logistic regression was used to determine the association of patient demographic and clinical factors, class I and class II PRA levels, and preoperative arterial and venous diameters with AVF maturation outcomes.

Results

AVF nonmaturation was more likely in females than males (44% versus 20%, P=0.003) and in Black than white patients (40% versus 13%, P=0.001). Class II PRA was higher in females than males (12%±23% versus 4%±13%, P=0.02). In the multivariable model, AVF nonmaturation was associated with class II PRA (adjusted odds ratio [aOR], 1.34 per 10% increase; 95% confidence interval [95% CI], 1.04 to 1.82, P=0.02) and Black race (aOR, 3.34; 95% CI, 1.02 to 10.89, P=0.03), but not with patient sex or preoperative arterial or venous diameters.

Conclusions

The association of elevated class II PRA with AVF nonmaturation suggests the immune system may play a role in AVF maturation outcomes, especially among female patients.

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.

Histopathological characteristics and causes of kidney graft failure in the current era of immunosuppression

BACKGROUND

The histopathological findings on the failing kidney allograft in the modern era is not well studied. In this study, we present our experience working with kidney transplant recipients with graft failure within one year of the biopsy.

AIM

To report the histopathological characteristics of failed kidney allografts in the current era of immunosuppression based on the time after transplant, cause of the end-stage renal disease and induction immunosuppressive medications.

METHODS

In a single-center observational study, we characterized the histopathological findings of allograft biopsies in kidney transplant recipients with graft failure within one year after the biopsy.

RESULTS

We identified 329 patients with graft failure that met the selection criteria between January 1, 2006 and December 31, 2016. The three most common biopsy findings were interstitial fibrosis and tubular atrophy (IFTA, 53%), acute rejection (AR, 43%) and transplant glomerulopathy (TG, 33%). Similarly, the three most common causes of graft failure based on the primary diagnosis were AR (40%), TG (17%), and IFTA (13%). Most grafts failed within two years of post-transplant (36%). Subsequently, approximately 10%-15% of grafts failed every two years: > 2-4 years (16%), > 4-6 years (13%), > 6-8 years (11%), > 8-10 years (9%) and > 10 years (16%). AR was the most common cause of graft failure in the first six years (48%), whereas TG was the most prevalent cause of graft failure after 6 years (32%) of transplant.

CONCLUSION

In the current era of immunosuppression, AR is still the most common cause of early graft failure, while TG is the most prevalent cause of late graft failure.

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.

Chronic-active antibody-mediated rejection with or without donor-specific antibodies has similar histomorphology and clinical outcome - a retrospective study

Chronic-active antibody-mediated rejection (c-aABMR) is defined as histological evidence of chronic endothelial injury (cg), also known as transplant glomerulopathy, and either microvascular inflammation (MVI) or positivity for C4d. Importantly, the presence of donor-specific antibodies (DSA) is currently still mandatory for the diagnosis of c-aABMR. This retrospective study of 41 c-aABMR patients investigates whether cases suspicious for c-aABMR (DSA negative, n = 24) differ from cases of c-aABMR (DSA positive, n = 17) with respect to renal histology, allograft function and long-term graft survival. All included patients had progressive loss of allograft function and were diagnosed by for cause biopsy and scored according to the Banff '15 criteria. In all DSApos cases, DSA were de novo and the majority was directed against HLA-II being mostly anti-HLA-DQ antibodies. There were no statistically significant differences in clinical characteristics, decline in allograft function and renal allograft survival in cases with or without DSAs. All cases showed chronic histomorphological damage and inflammation, irrespective of the presence of DSA. Renal histology and clinical outcome of patients suspicious for c-aABMR (DSAneg) do not significantly differ from patients with a diagnosis of c-aABMR (DSApos). We believe that our study adds to the ongoing debate regarding the need for DSAs to be present for the diagnosis of c-aABMR.

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.

Lymphotoxin expression in human and murine renal allografts

The kidney is the most frequently transplanted solid organ. Recruitment of inflammatory cells, ranging from diffuse to nodular accumulations with defined microarchitecture, is a hallmark of acute and chronic renal allograft injury. Lymphotoxins (LTs) mediate the communication of lymphocytes and stromal cells and play a pivotal role in chronic inflammation and formation of lymphoid tissue. The aim of this study was to assess the expression of members of the LT system in acute rejection (AR) and chronic renal allograft injury such as transplant glomerulopathy (TG) and interstitial fibrosis/tubular atrophy (IFTA). We investigated differentially regulated components in transcriptomes of human renal allograft biopsies. By microarray analysis, we found the upregulation of LTβ, LIGHT, HVEM and TNF receptors 1 and 2 in AR and IFTA in human renal allograft biopsies. In addition, there was clear evidence for the activation of the NFκB pathway, most likely a consequence of LTβ receptor stimulation. In human renal allograft biopsies with transplant glomerulopathy (TG) two distinct transcriptional patterns of LT activation were revealed. By quantitative RT-PCR robust upregulation of LTα, LTβ and LIGHT was shown in biopsies with borderline lesions and AR. Immunohistochemistry revealed expression of LTβ in tubular epithelial cells and inflammatory infiltrates in transplant biopsies with AR and IFTA. Finally, activation of LT signaling was reproduced in a murine model of renal transplantation with AR. In summary, our results indicate a potential role of the LT system in acute renal allograft rejection and chronic transplant injury. Activation of the LT system in allograft rejection in rodents indicates a species independent mechanism. The functional role of the LT system in acute renal allograft rejection and chronic injury remains to be determined.

Glomerular C4d deposits can mark structural capillary wall remodelling in thrombotic microangiopathy and transplant glomerulopathy: C4d beyond active antibody-mediated injury: a retrospective study

Peritubular capillary C4d (ptc-C4d) usually marks active antibody-mediated rejection, while pseudolinear glomerular capillary C4d (GBM-C4d) is of undetermined diagnostic significance, especially when seen in isolation without concurrent ptc-C4d. We correlated GBM-C4d with structural GBM abnormalities and active antibody-mediated rejection in 319 renal transplant and 35 control native kidney biopsies. In kidney transplants, ptc-C4d was associated with GBM-C4d in 97% by immunofluorescence microscopy (IF) and 61% by immunohistochemistry (IHC; P < 0.001). Transplant glomerulopathy correlated with GBM-C4d (P < 0.001) and presented with isolated GBM-C4d lacking ptc-C4d in 69% by IF and 40% by IHC. Strong isolated GBM-C4d was found post year-1 in repeat biopsies with transplant glomerulopathy. GBM-C4d staining intensity correlated with Banff cg scores (rs = 0.45, P < 0.001). Stepwise exclusion and multivariate logistic regression corrected for active antibody-mediated rejection showed significant correlations between GBM duplication and GBM-C4d (P = 0.001). Native control biopsies with thrombotic microangiopathies demonstrated GBM-C4d in 92% (IF, P < 0.001) and 35% (IHC). In conclusion, pseudolinear GBM-C4d staining can reflect two phenomena: (i) structural GBM changes with duplication in native and transplant kidneys or (ii) active antibody-mediated rejection typically accompanied by ptc-C4d. While ptc-C4d is a dynamic 'etiologic' marker for active antibody-mediated rejection, isolated strong GBM-C4d can highlight architectural glomerular remodelling.

Morphologic patterns and treatment of transplant glomerulopathy: A retrospective analysis

Transplant glomerulopathy is mainly due to chronic antibody-mediated rejection and actually represents a major cause of long-term allograft failure. The lack of effective treatment remains a serious problem in transplantation. A retrospective and uni-center study was performed in 48 kidney allograft recipients with transplant glomerulopathy between January 2010 and December 2015. Median time for diagnosis was 7.1 (3.6-11.8) years post-transplant. Light microscopy showed severity of transplant glomerulopathy in the majority of patients (cg1=10.4%; cg2=20.8%; cg3=68.8%). Moderate microvascular inflammation was present in 56.3% (g+ptc≥2), and almost half of recipients (51.1%) were C4d positive in immunofluorescence. Female gender (P=.001), age (P=.043), renal dysfunction (P=.002), acute rejection episodes (P=.026), and anti-HLA class II antibodies (P=.004) were associated with kidney allograft failure. Treatment of transplant glomerulopathy was performed in 67.6% of patients. The histologic and laboratory features that led to a therapeutic intervention were score ptc (P=.021), C4d (P=.03), and the presence of anti-HLA antibodies (P=.029), whereas score ah (P=.005) was associated with conservative measure. The overall cumulative kidney allograft survival at 10 years was 75%. Treatment of transplant glomerulopathy was ineffective to improve long-term kidney allograft survival.

Development and validation of a prognostic index for allograft outcome in kidney recipients with transplant glomerulopathy

We studied 92 patients with transplant glomerulopathy to develop a prognostic index based on the risk factors for allograft failure within five years of diagnosis (Development cohort). During 60 months (median) follow up, 64 patients developed allograft failure. A chronic-inflammation score generated by combining Banff ci, ct and ti scores, serum creatinine and proteinuria at biopsy, were independent risk factors for allograft failure. Based on the Cox model, we developed a prognostic index and classified patients into risk groups. Compared to the low risk group (median allograft survival over 60 months from diagnosis), patients in the medium risk group had a hazard ratio of 2.83 (median survival 25 months), while those in the high risk group had a hazard ratio of 5.96 (median survival 3.7 months). We next evaluated the performance of the prognostic index in an independent external cohort of 47 patients with transplant glomerulopathy (Validation cohort). The hazard ratios were 2.18 (median survival 19 months) and 16.27 (median survival 1.6 months), respectively, for patients in the medium and high risk groups, compared to the low risk group (median survival 47 months). Our prognostic index model did well in measures of discrimination and calibration. Thus, risk stratification of transplant glomerulopathy based on our prognostic index may provide informative insight for both the patient and physician regarding prognosis and treatment.

Peritubular capillary basement membrane multilayering in early and advanced transplant glomerulopathy: quantitative parameters and diagnostic aspects

The ultrastructural quantitative aspects of peritubular capillary basement membrane multilayering (PTCBML) were examined in 57 kidney transplant biopsies with transplant glomerulopathy (TG). The measurements included three cutoffs [permissive: 1 PTC with 5 basement membrane (BM) layers, intermediate: 3 PTCs with 5 layers or 1 PTC with 7 layers, strict: 1 PTC with 7 layers and 2 PTCs with 5 layers] and the mean number of BM layers (PTC_circ). Two groups were assigned, namely patients with mild TG (Banff cg1a and cg1b) and those with moderate-to-severe TG (cg2 and cg3). Their respective clinical, serological, and morphological characteristics were then compared. The clinical data revealed that mild TG corresponded to early chronic antibody-mediated rejection (cABMR), while moderate-to-severe TG corresponded to the advanced stage of the disease. The permissive threshold displayed the lowest specificity (73 %) and the highest sensitivity (83 %) for moderate-to-severe TG, and its corresponding PTC_circ value was 3 layers. In contrast, the strict threshold-adopted by the Banff 2013 classification-displayed a specificity and sensitivity of 93 and 52 %, respectively, and the corresponding PTC_circ was 4 layers. In mild TG, 26 % of the cases met the permissive cutoff and 6 % the strict cutoff. Mild TG was associated with a lower PTC_circ (2.6 layers vs 4.5 layers in moderate-to-severe TG; p < 0.0001). Amongst the various criteria, the permissive criterion was associated most frequently with mild TG, and had prognostic relevance. Because of this, we propose its usage as a marker of early cABMR-induced PTCBML if non-alloimmune causes of PTCBML can be ruled out.

Association of C1q-fixing DSA with late graft failure in pediatric renal transplant recipients

BACKGROUND

We investigated the prognostic value of overall and complement-binding donor-specific HLA antibodies (DSA) in pediatric patients undergoing clinically indicated graft biopsies and their association with graft outcome and specific histological lesions.

METHODS

Sera of 62 patients at time of indication biopsy ≥1 year posttransplant were assessed for DSA and C1q-fixing DSA by single-antigen bead (SAB) technology.

RESULTS

Twenty-six patients (42 %) were DSA-positive at time of indication biopsy and nine (15 %) were C1q-positive. At 4 years postbiopsy, patients with C1q-positivity had a low graft survival (11 %) compared to DSA-positive, C1q-negative patients (82 %, p = 0.001) and to DSA-negative patients (88 %, p < 0.001). The majority (89 %) of C1q-positive patients were diagnosed with active chronic antibody-mediated rejection (ABMR). C1q DSA-positivity [adjusted hazard ratio (HR) 6.35], presence of transplant glomerulopathy (HR 9.54), and estimated glomerular filtration rate (eGFR) at the time of indication biopsy (HR 0.91) were risk factors for subsequent graft loss.

CONCLUSIONS

The presence of C1q-positive DSA in the context of an indication biopsy identifies a subgroup of pediatric renal transplant recipients with a markedly increased risk of subsequent graft loss. Because a fraction of DSA-positive patients escape rejection or graft dysfunction, the C1q assay increases the specificity of a positive DSA result regarding unfavorable transplant outcome.

Banff 2013 update: Pearls and pitfalls in transplant renal pathology

The pathological classification of rejection in renal allografts (Banff classification) has undergone substantial evolution for more than 20 years, and has been the diagnostic gold standard in clinical practice. The 2013 updated Banff classification encompasses a revised scheme of antibody-mediated rejection (ABMR) that consists of donor-specific antibody (DSA) positivity, characteristic histological manifestations for both acute and chronic ABMR, and DSA-induced endothelial cell injury which is represented by either C4d positivity, microvascular inflammation or expression of activated endothelial gene transcripts. Other modified criteria include a C4d positivity threshold, and histological definition of transplant glomerulitis and transplant glomerulopathy. Morphologically, glomerulonephritis, either recurrent or de novo, can be challenging to differentiate from ABMR-mediated transplant glomerulitis. Endothelial arteritis by itself does not warrant the diagnosis of acute T-cell mediated rejection; ABMR should also be considered based on the DSA test results. With regard to polyomavirus BK-associated nephropathy, immunohistochemical examination using anti-simian virus (SV) 40 antibody can be a promising method to assess the quantitative viral load of polyomavirus BK and graft survival. In summary, the 2013 updated Banff classification strictly defines ABMR with histopathological and serological criteria irrespective of C4d positivity. Inclusion of gene expression data relevant to ABMR highlights that the Banff criteria have entered the era of 'Seeing the Unseen' schemes, reflecting recent advances in understanding the molecular events in allograft injury.

Presentation and Outcomes of C4d-Negative Antibody-Mediated Rejection After Kidney Transplantation

The updated Banff classification allows for the diagnosis of antibody-mediated rejection (AMR) in the absence of peritubular capillary C4d staining. Our objective was to quantify allograft loss risk in patients with consistently C4d-negative AMR (n = 51) compared with C4d-positive AMR patients (n = 156) and matched control subjects without AMR. All first-year posttransplant biopsy results from January 2004 through June 2014 were reviewed and correlated with the presence of donor-specific antibody (DSA). C4d-negative AMR patients were not different from C4d-positive AMR patients on any baseline characteristics, including immunologic risk factors (panel reactive antibody, prior transplant, HLA mismatch, donor type, DSA class, and anti-HLA/ABO-incompatibility). C4d-positive AMR patients were significantly more likely to have a clinical presentation (85.3% vs. 54.9%, p < 0.001), and those patients presented substantially earlier posttransplantation (median 14 [interquartile range 8-32] days vs. 46 [interquartile range 20-191], p < 0.001) and were three times more common (7.8% vs 2.5%). One- and 2-year post-AMR-defining biopsy graft survival in C4d-negative AMR patients was 93.4% and 90.2% versus 86.8% and 82.6% in C4d-positive AMR patients, respectively (p = 0.4). C4d-negative AMR was associated with a 2.56-fold (95% confidence interval, 1.08-6.05, p = 0.033) increased risk of graft loss compared with AMR-free matched controls. No clinical characteristics were identified that reliably distinguished C4d-negative from C4d-positive AMR. However, both phenotypes are associated with increased graft loss and thus warrant consideration for intervention.

Clinical, Histological, and Molecular Markers Associated With Allograft Loss in Transplant Glomerulopathy Patients

BACKGROUND

We aimed to investigate the clinical, histopathological, and molecular factors associated with allograft loss in transplant glomerulopathy (TGP) patients.

METHODS

Of the 525 patients who underwent clinically indicated kidney biopsies, 52 (10%) had diagnosis of TGP. Gene expression profiles of 28 TGP and 11 normal transplant kidney biopsy samples were analyzed by Affymetrix HuGene 1.0 ST expression arrays.

RESULTS

Over a median follow up of 23 months (1-46 months) after the diagnosis of TGP by biopsy, 17 patients (32%) lost their allografts at a median of 16 months (1-44 months). There was no difference between the 2 groups in terms of any demographic variables, serum creatinine, panel reactive antibody levels, donor-specific antibody frequency, or mean fluorescence intensity values. Patients who lost their allograft had a significantly higher median spot protein to creatinine ratio 2.81 (1.20-6.00) compared to no graft loss patients 1.16 (0.15-2.53), (P < 0.01), and a trends toward a higher mean chronic glomerulopathy (cg) score (1.65 ± 0.93 vs 1.11 ± 0.93) (P = 0.05). There was also no difference in microvascular inflammation or any other Banff injury scores between the 2 groups. Although 117 gene transcripts were upregulated in both groups, 86 and 57 were upregulated in graft loss and functioning allograft groups, respectively. There were significantly increased levels of intragraft endothelial cell-associated transcripts, gene transcripts associated with complement cascade, interleukins and their receptors and granulysin in graft loss patients compared to patients with a functioning allograft.

CONCLUSION

Our results demonstrate differential intragraft gene expression profiles in TGP patients with allograft loss.

Relationship among C1q-fixing de novo donor specific antibodies, C4d deposition and renal outcome in transplant glomerulopathy

BACKGROUND

The C1q-binding properties of donor specific antibodies (DSA) may be related to antibody-mediated rejection and poor outcome.

METHODS

We retrospectively studied 35 kidney transplant recipients with transplant glomerulopathy (TG) and de novo DSA (dnDSA). C1q dnDSA were measured in the serum stored at renal biopsy and the association among C1q-fixing dnDSA, C4d deposition and graft loss was examined.

RESULTS

Of the 35 patients with dnDSA and TG, 15 (42.9%) had C1q-positive dnDSA and 20 (57.1%) had C1q-negative dnDSA. Ten out of 15 patients with C1q-positive dnDSA (66.6%) and 5 with C1q-negative dnDSA (25%) had C4d positive staining renal biopsies (P=0.02), being the C1q-negative dnDSA/C4d-negative TG 42.9% of the total. The C1q-positive dnDSA group has significantly higher IgG DSA Class II MFI than the C1q-negative dnDSA group (P=0.004). Patients with C4d deposits have significantly higher IgG DSA MFI for both Class I and Class II than those without C4d deposits (P=0.02). We found a trend toward higher graft loss in the C1q-positive dnDSA group (60%) versus the C1q-negative dnDSA group (40%) without a statistical significance (P=0.31).

CONCLUSION

Our study provides further characterization of TG associated with dnDSA. The major part of dnDSA-associated TG was C1q-negative and the presence of C1q-fixing dnDSA did not significantly correlate with graft outcome.

New insights regarding chronic antibody-mediated rejection and its progression to transplant glomerulopathy

PURPOSE OF THIS REVIEW

To discuss new insights regarding chronic antibody-mediated rejection (CAMR) and its progression to transplant glomerulopathy. We will describe the progression to transplant glomerulopathy from a histologic perspective and provide updates on what is known about its pathophysiology, prognosis, and potential therapy.

RECENT FINDINGS

Transplant glomerulopathy is a major contributor to long-term renal allograft loss and is most often associated with CAMR. On the basis of protocol biopsies, we have found that 3.5% of conventional transplants and 27.5% of positive crossmatch kidney transplants have transplant glomerulopathy at 1 year. The pathophysiology of the process is largely unknown, but complement activation was previously thought to be essential. However, CAMR appears to develop despite terminal complement blockade and many C4d negative cases of CAMR have been identified. Thus, complement independent mechanisms, such as direct endothelial cell activation and the infiltration of natural killer cells and monocytes, are likely key to the development of transplant glomerulopathy.

SUMMARY

Transplant glomerulopathy is often the result of CAMR and leads to allograft loss. It is characterized by distinctive histologic changes, and its pathophysiology is a multifaceted process involving both innate and adaptive immunity. Despite advances in the understanding of this condition, no effective therapy exists.

siRNA technology in kidney transplantation: current status and future potential

Kidney transplantation is one of the most common transplantation operations in the world, accounting for up to 50 % of all transplantation surgeries. To curtail the damage to transplanted organs that is caused by ischemia-reperfusion injury and the recipient's immune system, small interfering RNA (siRNA) technology is being explored. Importantly, the kidney as a whole is a preferential site for non-specific systemic delivery of siRNA. To date, most attempts at siRNA-based therapy for transplantation-related conditions have remained at the in vitro stage, with only a few of them being advanced into animal models. Hydrodynamic intravenous injection of naked or carrier-bound siRNAs is currently the most common route for delivery of therapeutic constructs. To our knowledge, no systematic screens for siRNA targets most relevant for kidney transplantation have been attempted so far. A majority of researchers have arrived at one or another target of interest by analyzing current literature that dissects pathological processes taking place in transplanted organs. A majority of the genes that make up the list of 53 siRNA targets that have been tested in transplantation-related models so far belong to either apoptosis- or immune rejection-centered networks. There is an opportunity for therapeutic siRNA combinations that may be delivered within the same delivery vector or injected at the same time and, by targeting more than one pathway, or by hitting the same pathways within two different key points, will augment the effects of each other.

Histopathology of MPGN and C3 glomerulopathies

'Membranoproliferative' describes glomerular injury characterized by capillary wall thickening and mesangial expansion owing to increased matrix deposition and hypercellularity. The presence of immune deposits is indicative of membranoproliferative glomerulonephritis (MPGN). Historically, MPGN was further classified into three types according to the appearance and site of the electron-dense deposits seen by electron microscopy, but it is now recognized that many cases show only deposition of the complement component C3, owing to abnormal control of the alternative pathway of complement activation-these cases are now classified as C3 glomerulopathies. Not all cases of C3 glomerulopathy, however, show an MPGN pattern. C3 glomerulopathies include dense deposit disease, which shows dense osmiophilic deposits, and C3 glomerulonephritis, which shows isolated deposits. In many cases, the genetic mutations or autoantibodies responsible for C3 deposition have been identified. Some patients in whom complement control is abnormal will accumulate small amounts of immunoglobulin in their glomeruli and so, in everyday practice, the morphological diagnosis of 'glomerulonephritis with dominant C3' is useful for identifying patients who require investigation of the complement pathway. The recognition that many cases of MPGN are C3 glomerulopathies and that the underlying cause can often be identified in immunoglobulin-associated cases means that the diagnosis of idiopathic MPGN is now very uncommon.

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.

Better understanding of transplant glomerulopathy secondary to chronic antibody-mediated rejection

Transplant glomerulopathy (TG) is generally accepted to result from repeated episodes of endothelial activation, injury and repair, leading to pathological abnormalities of double contouring or multi-layering of the glomerular basement membrane. TG is a major sequel of chronic active antibody-mediated rejection (cABMR), from pre-existing or de novo anti-HLA antibodies. Hepatitis C infection, thrombotic microangiopathy or other factors may also contribute to TG development. TG prevalence is 5-20% in most series, reaching 55%, in some high-risk cohorts, and is associated with worse allograft outcomes. Despite its prevalence and clinical significance, few well-studied treatment options have been proposed. Similar to desensitization protocols, plasmapheresis with or without immunoabsorption, high-dose intravenous immunoglobulin, rituximab, bortezomib and eculizumab have been proposed in the treatment of TG due to cABMR individually or in various combinations. Robust clinical trials are urgently needed to address this major cause of allograft loss. This review summarizes the current knowledge of the epidemiology, etiology, pathology, and the preventive and treatment options for TG secondary to cABMR.

Electron microscopy contribution to diagnosing transplant glomerulopathy: a single-center experience

BACKGROUND

Transplant glomerulopathy (TG) may occur early after transplantation, and electron microscopy may contribute to diagnose it.

METHODS

We analyzed kidney transplant biopsies from September 2009 to September 2012 to identify the presence of histologic changes associated with TG.

RESULTS

Forty-eight biopsies from 65 patients, met the study criteria and were evaluated. The average evolution time of transplantation was 13.6 months. Sixty percent of patients received deceased-donor renal transplants, and biopsies were performed per protocol in most cases. Electron microscopy diagnosed the presence of changes associated with TG in 23% of patients. Light microscopy was not useful in the diagnosis of such graft pathology. The average transplantation time was significantly higher in patients with TG compared to patients without TG (20.6 mo vs 11.5 mo; P = .03). Light microscopy diagnosed mild interstitial fibrosis/tubular atrophy in 27 patients, of which 6 had early changes of TG according to the analysis by electron microscopy.

CONCLUSIONS

Electron microscopy improves accurate diagnosis of TG, in patients both with and without graft dysfunction. It also allows diagnosis of early TG and thereby identification of patients who may have lower graft survival.

A clinical and pathological variant of acute transplant glomerulopathy

Acute transplant glomerulopathy transplant glomerulopathy (TG) is a common cause of late renal allograft loss. We describe a unique case of a renal transplant recipient who developed rapid-onset nephrotic-range proteinuria and acute kidney injury secondary to C4d negative acute TG. Two courses of intravenous Rituximab resulted in significant improvement in proteinuria and allograft function. In the setting of acute nephrotic-range proteinuria postrenal allograft, both renal biopsy with electron microscopy and screening for de novo donor-specific antibody should be performed to distinguish atypical presentations of TG from other diagnoses.

Hepatitis C virus infection and kidney transplantation in 2014: what's new?

Chronic hepatitis C virus (HCV) infection remains an important health problem, which is associated with deleterious consequences in kidney transplant recipients. Besides hepatic complications, several extrahepatic complications contribute to reduced patient and allograft survival in HCV-infected kidney recipients. However, HCV infection should not be considered as a contraindication for kidney transplantation because patient survival is better with transplantation than on dialysis. Treatment of HCV infection is currently interferon-alpha (IFN-α) based, which has been associated with higher renal allograft rejection rates. Therefore, antiviral treatment before transplantation is preferable. As in the nontransplant setting, IFN-free treatment regimens, because of their greater efficacy and reduced toxicity, currently represent promising and attractive therapeutic options after kidney transplantation as well. However, clinical trials will be required to closely evaluate these regimens in kidney recipients. There is also a need for prospective controlled studies to determine the optimal immunosuppressive regimens after transplantation in HCV-infected recipients. Combined kidney and liver transplantation is required in patients with advanced liver cirrhosis. However, in patients with cleared HCV infection and early cirrhosis without portal hypertension, kidney transplantation alone may be considered. There is some agreement about the use of HCV-positive donors in HCV-infected recipients, although data regarding posttransplant survival rates are controversial.

Thrombotic microangiopathy in renal allografts: the diagnostic challenge

PURPOSE OF REVIEW

The diagnosis of thrombotic microangiopathy (TMA) is complex and often difficult. This review provides an approach to the diagnosis with emphasis on recent relevant developments.

RECENT FINDINGS

There is increasing evidence that most cases of recurrent TMA in renal allografts are secondary to mutations in genes encoding complement regulatory factors and complement components, such as factor H, factor I, membrane cofactor protein, C3, and others. Genetic work-up for these potential complement abnormalities is now available and recommended. Another important cause for recurrent TMA is the presence of autoantibodies, such as antibodies to factor H and antiphospholipid antibodies. De-novo TMA is much more common than recurrent TMA in renal allografts. De-novo TMA can be secondary to calcineurin inhibitor treatment, mammalian target of rapamycin inhibitor treatment, but frequently also to antibody-mediated rejection and less commonly to infections. Systemic signs of TMA are often absent, and the gold standard for diagnosis is the renal allograft biopsy. Unfortunately, diagnostic criteria for TMA are somewhat subjective, and the biopsy provides limited information regarding the exact underlying cause.

SUMMARY

TMA is a serious complication of renal transplantation, usually with poor outcome. However, with improving understanding of underlying pathogeneses, more effective disease-specific therapeutic interventions can be designed. Appropriate treatment depends on the correct diagnosis, which relies primarily on renal allograft biopsy. Standardization of pathologic criteria and introduction of new molecular testing methods in renal biopsy specimens hopefully will improve diagnostic accuracy.

An analysis of transplant glomerulopathy and thrombotic microangiopathy in kidney transplant biopsies

Glomerular diseases of the transplanted kidney are the most important cause of poor long- term outcome. The estimation of the magnitude of this problem and an elucidation of pathogenic mechanism is essential for improvement of graft survival. This study from the Indian subcontinent aims (i) to determine the incidence of transplant glomerulopathy (TG) and thrombotic microangiopathy (TMA) in a large cohort of indicated renal transplant biopsies, (ii) to evaluate the histological and ultrastructural features of TG and TMA, and (iii) to assess the relationship between the two glomerular lesions. Of a total of 1792 indication renal transplant biopsies received over 5 years (2006-2010), 266 biopsies (of 249 patients) had significant glomerular pathology and were further analyzed along with immunofluorescence, electron microscopy (EM), and C4d immunohistochemistry. TG is the most common glomerular lesion followed by TMA seen in 5.97% and 5.08% of allograft biopsies, respectively, which constitutes 40.23% and 34.2% of biopsies with significant glomerular lesions. Pathologic antibody-mediated rejection (AMR) is associated with both TG and TMA in 71% and 46.5%, respectively. A coexistent TG was found in 18.4% of biopsies with TMA. Endothelial swelling with subendothelial widening, a feature of TMA, is also seen in early TG by EM. Our findings support the concept that TG evolves from a smoldering TMA of various causes.

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.

Impact of donor-specific antibodies on the outcomes of kidney graft: Pathophysiology, clinical, therapy

Allo-antibodies, particularly when donor specific, are one of the most important factors that cause both early and late graft dysfunction. The authors review the current state of the art concerning this important issue in renal transplantation. Many antibodies have been recognized as mediators of renal injury. In particular donor-specific-Human Leukocyte Antigens antibodies appear to play a major role. New techniques, such as solid phase techniques and Luminex, have revealed these antibodies from patient sera. Other new techniques have uncovered alloantibodies and signs of complement activation in renal biopsy specimens. It has been acknowledged that the old concept of chronic renal injury caused by calcineurine inhibitors toxicity should be replaced in many cases by alloantibodies acting against the graft. In addition, the number of patients on waiting lists with preformed anti-human leukocyte antigens (HLA) antibodies is increasing, primarily from patients with a history of renal transplant failure already been sensitized. We should distinguish early and late acute antibody-mediated rejection from chronic antibody-mediated rejection. The latter often manifets late during the course of the post-transplant period and may be difficult to recognize if specific techniques are not applied. Different therapeutic strategies are used to control antibody-induced damage. These strategies may be applied prior to transplantation or, in the case of acute antibody-mediated rejection, after transplantation. Many new drugs are appearing at the horizon; however, these drugs are far from the clinic because they are in phase I-II of clinical trials. Thus the pipeline for the near future appears almost empty.

Immune responses to collagen-IV and fibronectin in renal transplant recipients with transplant glomerulopathy

Antibodies (Abs) to donor HLA (donor-specific antibodies [DSA]) have been associated with transplant glomerulopathy (TG) following kidney transplantation (KTx). Immune responses to tissue-restricted self-antigens (self-Ags) have been proposed to play a role in chronic rejection. We determined whether KTx with TG have immune responses to self-Ags, Collagen-IV (Col-IV) and fibronectin (FN). DSA were determined by solid phase assay, Abs against Col-IV and FN by enzyme-linked immunosorbent assay and CD4+ T cells secreting interferon gamma (IFN-γ), IL-17 or IL-10 by ELISPOT. Development of Abs to self-Ags following KTx increased the risk for TG with an odds ratio of 22 (p-value = 0.001). Abs to self-Ags were IgG and IgM isotypes. Pretransplant Abs to self-Ags increased the risk of TG (22% vs. 10%, p < 0.05). Abs to self-Ags were identified frequently in KTx with DSA. TG patients demonstrated increased Col-IV and FN specific CD4+ T cells secreting IFN-γ and IL-17 with reduction in IL-10. We conclude that development of Abs to self-Ags is a risk factor and having both DSA and Abs to self-Ags increases the risk for TG. The increased frequency of self-Ag-specific IFN-γ and IL-17 cells with reduction in IL-10 demonstrate tolerance breakdown to self-Ags which we propose play a role in the pathogenesis of TG.

Acute transplant glomerulopathy with monocyte rich infiltrate

Acute transplant glomerulopathy refers to alloimmune mediated endothelial injury and glomerular inflammation that typically occurs early post-kidney transplantation. We report a case of a 48-year old woman with end stage renal disease from lupus nephritis who developed an unexplained rise in serum creatinine 2 months after renal transplant. As immunosuppression, she received alemtuzumab induction followed by a tacrolimus, mycophenolate mofetil and prednisone maintenance regimen. Her biopsy revealed severe glomerular endothelial injury associated with monocyte/macrophage-rich infiltrate in addition to mild acute tubulointerstitial cellular rejection. We briefly discuss acute transplant glomerulitis, its pathology and association with chronic/overt transplant glomerulopathy, C4d negative antibody-mediated rejection and the significance of monocytes in rejection. We also postulate that alemtuzumab induction may have contributed to the unusual pattern of monocyte-rich transplant glomerulitis.

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.