Donor-specific antibodies accelerate arteriosclerosis after kidney transplantation

A review of landmark studies on maintenance immunosuppressive regimens in kidney transplantation

Immunosuppressive medications play a pivotal role in kidney transplantation, and the calcineurin inhibitors (CNIs), including cyclosporine A (CsA) and tacrolimus (TAC), are considered as the backbone of maintenance immunosuppressive regimens. Since the introduction of CNIs in kidney transplantation, the incidence of acute rejection has decreased, and allograft survival has improved significantly. However, CNI nephrotoxicity has been a major concern, believed to heavily impact long-term allograft survival and function. To address this concern, several CNI-sparing regimens were developed and studied in randomized, controlled, clinical trials, aiming to reduce CNI exposure and preserve long-term allograft function. However, more recent information has revealed that CNI nephrotoxicity is not the primary cause of late allograft failure, and its histopathology is neither specific nor pathognomonic. In this review, we discuss the historical development of maintenance immunosuppressive regimens in kidney transplantation, covering the early era of transplantation, the CNI-sparing era, and the current era where the alloimmune response, rather than CNI nephrotoxicity, appears to be the major contributor to late allograft failure. Our goal is to provide a chronological overview of the development of maintenance immunosuppressive regimens and summarize the most recent information for clinicians caring for kidney transplant recipients (KTRs).

The Banff 2022 Kidney Meeting Report: Re-Appraisal of Microvascular Inflammation and the Role of Biopsy-Based Transcript Diagnostics

The XVI-th Banff Meeting for Allograft Pathology was held in Banff, Alberta, Canada, from 19th-23rd September 2022, as a joint meeting with the Canadian Society of Transplantation. To mark the 30th anniversary of the first Banff Classification, pre-meeting discussions were held on the past, present, and future of the Banff Classification. This report is a summary of the meeting highlights that were most important in terms of their effect on the Classification, including discussions around microvascular inflammation and biopsy-based transcript analysis for diagnosis. In a post-meeting survey, agreement was reached on the delineation of the following phenotypes: (1) "Probable antibody-mediated rejection (AMR)", which represents DSA-positive cases with some histological features of AMR but below current thresholds for a definitive AMR diagnosis; and (2) "Microvascular inflammation (MVI), DSA-negative and C4d-negative", a phenotype of unclear cause requiring further study, which represents cases with MVI not explained by DSA. Although biopsy-based transcript diagnostics are considered promising and remain an integral part of the Banff Classification (limited to diagnosis of AMR), further work needs to be done to agree on the exact classifiers, thresholds, and clinical context of use.

Clinicopathological Analyses of Chronic Renal Allograft Arteriopathy after Kidney Transplantation

INTRODUCTION

Herein, we discuss clinicopathological analyses of cases of chronic renal allograft arteriopathy (CRA) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of CRA.

METHODS

CRA was diagnosed in 34 renal allograft biopsy specimens (BSs) obtained from 27 renal transplant patients who were followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and December 2020.

RESULTS

CRA was diagnosed at a median of 33.4 months post-transplantation. Of the 27 patients, 16 had a history of rejection. Among the 34 BSs showing evidence of CRA, CRA was mild (cv1 in Banff's classification) in 22, moderate (cv2) in 7, and severe (cv3) in 5 patients. We then classified the 34 BSs showing evidence of CRA based on their overall histopathological features as follows: cv alone seen in 11 (32%) BSs, cv + antibody-mediated rejection (AMR) in 12 (35%), and cv + T-cell-mediated rejection (TCMR) in 8 (24%). Loss of the renal allograft occurred during the observation period in 3 patients (11%). Of the remaining patients with functioning grafts, deterioration of renal allograft function after biopsies occurred in 7 cases (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CRA in 30-40% of cases, TCMR in 20-30% of cases, isolated v lesions in 15% of cases, and cv lesions alone in 30%. The intimal arteritis was a prognostic factor in CRA.

A Banff-based histologic chronicity index is associated with graft loss in patients with a kidney transplant and antibody-mediated rejection

Antibody-mediated rejection (AMR) is the major cause of graft loss in kidney transplant recipients. The Banff classification defines two classes of AMR, active and chronic active but over time this classification has become increasingly complex. To simplify the approach to AMR, we developed activity and chronicity indices based on kidney transplant biopsy findings and examined their association with graft survival in 147 patients with active or chronic active AMR, all of whom had donor-specific antibodies and were treated for AMR. The activity index was determined as the sum of Banff glomerulitis (g), peritubular capillaritis (ptc), arteritis (v) and C4d scores, with a maximum score of 12. The chronicity index was the sum of interstitial fibrosis (ci), tubular atrophy (ct), chronic vasculopathy (cv), and chronic glomerulopathy (cg) scores, the latter doubled, with a maximum score of 15. While the activity index was generally not associated with graft loss, the chronicity index was significantly associated with graft loss with an optimal threshold value of 4 or greater for predicting graft loss. The association of the chronicity index of 4 or greater with graft loss was independent of other parameters associated with graft loss, including the estimated glomerular filtration rate at the time of biopsy, chronic active (versus active) AMR, AMR with de novo (versus persistent/rebound) donor-specific antibodies, Banff (g+ptc) scores, concurrent T cell-mediated rejection and donor-specific antibody reduction post-biopsy. The association of the chronicity index of 4 or greater with graft loss was confirmed in an independent cohort of 61 patients from Necker Hospital, Paris. Thus, our findings suggest that the chronicity index may be valuable as a simplified approach to decision-making in patients with AMR.

The Clinical Impact of Anti-HLA Donor Specific Antibody Detection Through First Year Screening on Stable Kidney Transplant Recipients

Anti-HLA Donor Specific Antibody (DSA) detection post kidney transplant has been associated with adverse outcomes, though the impact of early DSA screening on stable patients remain unclear. We analyzed impact of DSA detection through screening in 1st year stable patients (n = 736) on subsequent estimated glomerular filtration rate (eGFR), death censored graft survival (DCGS), and graft failure (graft loss including return to dialysis or re-transplant, patient death, or eGFR < 20 ml/min at last follow up). Patients were grouped using 1st year screening into DSA+ (Class I, II; n = 131) or DSA- (n = 605). DSA+ group were more DR mismatched (p = 0.02), more sensitized (cPRA ≥90%, p = 0.002), less Caucasian (p = 0.04), and had less pre-emptive (p = 0.04) and more deceased donor transplants (p = 0.03). DSA+ patients had similar eGFR (54.8 vs. 53.8 ml/min/1.73 m², p = 0.56), DCGS (91% vs. 94%, p = 0.30), and graft failure free survival (76% vs. 82%, p = 0.11). DSA timing and type did not impact survival. Among those with a protocol biopsy (n = 515), DSA detected on 1st year screening was a predictor for graft failure on multivariate analysis (1.91, 95% CI 1.03-3.55, p = 0.04). Overall, early DSA detection in stable patients was an independent risk factor for graft failure, though only among those who underwent a protocol biopsy.

Assessment and management of transplant renal artery stenosis. A literature review

BACKGROUND

transplant renal artery stenosis (TRAS) following kidney transplantation is a possible cause of graft failure. This review aimed to summarize the evidence about physiopathology, diagnosis and early and late effectiveness of the endovascular treatment (EVT), including angioplasty and stenting procedures.

METHODS

a literature research was performed using Pubmed, Scopus and the Cochrane Library databases (January 2000 to September 2020) according to PRISMA guidelines. Studies were included if they describe EVT, percutaneous transluminal angioplasty or stent placement of TRAS, published in English and with a minimum of ten patients.

RESULTS

56 studies were included. TRAS incidence ranges from 1% up to 12% in transplanted kidneys. The TRAS risk factors were: elderly donor and recipient, cytomegalovirus match status, Class II Donor Specific Antibodies (DSA), expanded donor criteria, delayed graft functioning and other anatomical and technical factors. The highest frequency of TRAS presentation is after 3-6 months after kidney transplantation. The most frequent localization of stenosis was para-anastomotic (ranging from 25% to 78%). In 9 studies, all patients were treated by percutaneous transluminal angioplasty (PTA), in 16 studies all patients received percutaneous transluminal stenting (PTS) and in 21 series patients received either PTA or PTS. The Twelve months patency rates after EVT ranged from 72% to 94%. The overall complication rate was 9%, with pseudoaneurysms and hematomas as most frequent complications.

CONCLUSION

TRAS can be successfully and safely treated through an endovascular approach. Stent delivery seems to guarantee a higher patency rate compared to simple angioplasty, however further studies are needed to confirm these results.

Thirty Years of Tacrolimus in Clinical Practice

Tacrolimus was discovered in 1984 and entered clinical use shortly thereafter, contributing to successful solid organ transplantation across the globe. In this review, we cover development of tacrolimus, its evolving clinical utility, and issues affecting its current usage. Since earliest use of this class of immunosuppressant, concerns for calcineurin-inhibitor toxicity have led to efforts to minimize or eliminate these agents in clinical regimens but with limited success. Current understanding of the role of tacrolimus focuses more on its efficacy in preventing graft rejection and graft loss. As we enter the fourth decade of tacrolimus use, newer studies utilizing novel combinations (as with the mammalian target of rapamycin inhibitor, everolimus, and T-cell costimulation blockade with belatacept) offer potential for enhanced benefits.

Kidney Transplant Graftectomy by Severe Mixed-Type Rejection with Acute and Chronic Active Vascular Lesions at Entire Levels of the Renal Vasculature

Vascular lesions related to allograft rejection have a big impact on graft survival. As such, investigation of these lesions is important to understand the pathophysiology of rejection and its management. We report a case of kidney transplant graftectomy by severe mixed-type rejection with acute and chronic active vascular lesions caused by non-adherence to immunosuppressive treatment. The patient presented is a 29-year-old male who received a kidney transplantation in July 2011 (ABO compatible) from his father. He then did not come to the hospital for 3 months prior to his admission and also made his own decision to stop his medication regimen. On October 2013, the patient came to the hospital with dyspnea, nausea, and vomiting and had significant renal dysfunction (serum Cr 30.4 mg/dL, BUN 191 mg/dL). A kidney graft biopsy showed cortical necrosis with severe interstitial hemorrhage and thrombotic microangiopathy (TMA). Despite steroid pulse therapy, kidney graft function did not recover, and the patient underwent a subsequent graft resection. The resected kidney graft displayed various vascular lesions from the renal artery to the interlobular arteries and arterioles including endarteritis, TMA, fibrinoid necrosis, and transplant arteriopathy. This case shows the detailed pathological findings of the vascular lesions in the entire artery tree of kidney allograft, and the pathophysiology is discussed.

Clinicopathologic Analyses of Chronic Vascular Rejection After Kidney Transplantation

AIM

We discuss the clinicopathologic analyses of cases of biopsy specimens (BS) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of chronic vascular rejection (CVR).

PATIENTS

CVR was diagnosed in 30 renal allograft BS obtained from 23 renal transplant patients being followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and August 2017.

RESULTS

CVR was diagnosed at a median of 33.1 months post-transplantation. Among the 23 patients, 14 had a history of rejection. Among the 30 BS showing evidence of CVR, the CVR was mild (cv1 on Banff's classification) in 19, moderate (cv2) in 6, and severe (cv3) in 5. We then classified the 30 BS showing evidence of CVR by their overall histopathologic features as follows: cv alone was seen in 9 (30%), cv + antibody-mediated rejection (AMR) in 11 (37%), and cv + T-cell-mediated rejection (TCMR) in 8 (27%). Loss of the renal allograft occurred during the observation period in 2 patients (9%). Of the remaining patients with functioning grafts, deterioration of the renal allograft function after the biopsies occurred in 6 (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CVR in 30% to 40% of cases, TCMR in 20% to 30% of cases, isolated v lesions in 10% of cases, and cv lesions alone in 30%. The prognosis of the graft exhibiting CVR was not too poor even under the present immunosuppressive protocol.

Identification and Characterization of Trajectories of Cardiac Allograft Vasculopathy After Heart Transplantation: A Population-Based Study

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a major contributor of heart transplant recipient mortality. Little is known about the prototypes of CAV trajectories at the population level. We aimed to identify the different evolutionary profiles of CAV and to determine the respective contribution of immune and nonimmune factors in CAV development.

METHODS

Heart transplant recipients were from 4 academic centers (Pitié-Salpêtrière and Georges Pompidou Hospital, Paris, Katholieke Universiteit Leuven, and Cedars-Sinai, Los Angeles; 2004-2016). Patients underwent prospective, protocol-based monitoring consisting of repeated coronary angiographies together with systematic assessments of clinical, histological, and immunologic parameters. The main outcome was a prediction for CAV trajectory. We identified CAV trajectories by using unsupervised latent class mixed models. We then identified the independent predictive variables of the CAV trajectories and their association with mortality.

RESULTS

A total of 1301 patients were included (815 and 486 in the European and US cohorts, respectively). The median follow-up after transplantation was 6.6 (interquartile range, 4-9.1) years with 4710 coronary angiographies analyzed. We identified 4 distinct profiles of CAV trajectories over 10 years. The 4 trajectories were characterized by (1) patients without CAV at 1 year and nonprogression over time (56.3%), (2) patients without CAV at 1 year and late-onset slow CAV progression (7.6%), (3) patients with mild CAV at 1 year and mild progression over time (23.1%), and (4) patients with mild CAV at 1 year and accelerated progression (13.0%). This model showed good discrimination (0.92). Among candidate predictors assessed, 6 early independent predictors of these trajectories were identified: donor age (P<0.001), donor male sex (P<0.001), donor tobacco consumption (P=0.001), recipient dyslipidemia (P=0.009), class II anti-human leukocyte antigen donor-specific antibodies (P=0.004), and acute cellular rejection ≥2R (P=0.028). The 4 CAV trajectories manifested consistently in the US independent cohort with similar discrimination (0.97) and in different clinical scenarios, and showed gradients for overall-cause mortality (P<0.001).

CONCLUSIONS

In a large multicenter and highly phenotyped prospective cohort of heart transplant recipients, we identified 4 CAV trajectories and their respective independent predictive variables. Our results provide the basis for a trajectory-based assessment of patients undergoing heart transplantation for early risk stratification, patient monitoring, and clinical trials. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04117152.

The relationship between pathologic lesions of active and chronic antibody-mediated rejection in renal allografts

The Banff classification of renal allograft pathology defines specific morphologic lesions that are used in the diagnosis of active (glomerulitis, peritubular capillaritis, endarteritis) and chronic (transplant glomerulopathy, peritubular capillary basement membrane multilayering, transplant arteriopathy) antibody-mediated rejection (ABMR). However, none of these individual lesions are specific for ABMR, and for this reason Banff requires 1 or more additional findings, including C4d deposition in peritubular capillaries, presence of circulating donor-specific antibodies (DSAs), and/or expression in the tissue of transcripts strongly associated with ABMR, for a definitive diagnosis of ABMR to be made. In addition, while animal studies examining serial biopsies have established the progression of morphologic lesions of active to chronic ABMR as well as intermediate forms (chronic active ABMR) exhibiting features of both, clear documentation that lesions of chronic ABMR require the earlier presence of corresponding active and intermediate lesions is less well established in human renal allografts. This review examines temporal relationships between key morphologic lesions of active and chronic ABMR in biopsies of human grafts, likely intermediate forms, and findings for and possibly against direct and potentially interruptible progression from active to chronic lesions.

Cell mediated rejection revisited: Past, current, and future directions

The Banff histopathology classification system is the gold standard for assessing the causes of kidney allograft dysfunction triggered by antibody-mediated and T-cell-mediated immune reactions, thereby providing mechanistic insight and guiding therapeutic decisions. The original Banff classification (1993) consisted of four histological categories representing cell-mediated rejection: interstitial inflammation (i), tubulitis (t), endoarteritis (v), and transplant glomerulitis (g). The revised Banff 2007 classification added total inflammation score (ti) from both scarred and unscarred areas based on evolving interpretations of interstitial infiltrates. Further reappraisal of cell-mediated interstitial inflammation led to the introduction of a new inflammation score specific for areas of interstitial fibrosis and tubular atrophy, termed i-IF/TA, in the Banff 2015 scheme, establishment of a new Banff working group on T-cell-mediated rejection (TCMR), and revised criteria of chronic active TCMR in Banff 2017 classification. These Banff scheme updates reflect the general recognition that chronic interstitial inflammation is a common denominator of poor kidney allograft outcome. However, revised theories on the pathogenic importance of interstitial infiltrates have created difficulties in interpretation of chronic tubulointerstitial inflammation, as there are currently no histological criteria to discriminate immune-mediated tissue injury from 'non-specific' injury. Evolving theories on vascular lesions, both active and chronic, have also complicated histological assessment by obscuring the distinction between antibody-mediated and T-cell-mediated tissue injury. This review provides an overview of recent ideas on interstitial inflammation and vascular lesions based on emerging concepts of T-cell-mediated rejection.

The Spectrum of Histopathological Changes in the Renal Allograft - a 12 Months Protocol Biopsy Study

INTRODUCTION

Renal transplantation became a routine and successful medical treatment for Chronic Kidney Disease in the last 30 years all over the world. Introduction of Luminex based Single Antigen Beads (SAB) and recent BANFF consensus of histopathological phenotypes of different forms of rejection enables more precise diagnosis and changes the therapeutic approach. The graft biopsies, protocol or cause, indicated, remain a golden diagnostic tool for clinical follow up of kidney transplant recipients (KTR).

AIM

The study aimed to analyse the histopathological changes in renal grafts 12 months after the surgery in KTR with satisfactory kidney function.

MATERIAL AND METHODS

A 12-month protocol biopsy study was performed in a cohort of 50 Kidney transplant recipients (42 from living and 8 from deceased donors). Usual work-up for suitable donors and recipients, standard surgical procedure, basic principles of peri and postoperative care and follow up were done in all KTR. Sequential quadruple immunosuppression including induction with Anti-thymocyte globulin (ATG) or Interleukin-2R antagonist (IL-2R), and triple drug maintenance therapy with Calcineurin Inhibitors (CNI), Mycophenolate Mofetil (MMF) and Steroids were prescribed to all pts. Different forms of Glomerulonephritis (16), Hypertension (10), End Stage Renal Disease (13), Hereditary Nephropathies (6), Diabetes (3) and Vesicoureteral Reflux (2) were the underlying diseases. All biopsies were performed under ultrasound guidance. The 16 gauge needles with automated "gun" were used to take 2 cores of tissue. The samples were stained with HE, PAS, Trichrome Masson and Silver and reviewed by the same pathologist. A revised and uploaded BANFF 2013 classification in 6 categories (Cat) was used.

RESULTS

Out of 48 biopsies, 15 (31%) were considered as normal, 4 (8%), Borderline (BL-Cat 3), 5 (10%) as Interstitial Fibrosis/Tubular Atrophy (IF/TA-Cat 5), 5 (10%) were classified as non-immunological (Cat 6), 2 as a pure antibody-mediated rejection (ABMR-Cat 2) and T-cell Mediated Rejection (TCMR-Cat 4). The remaining 17 samples were classified as a "mixed" rejection: 7 (41%) ABMR + IF/TA, 5 (29%) ABMR + BL + IF/TA, 2 (11%) BL + IF/TA, 1 (5%) ABMR + BL, 1 (5%) ABMR + TCMR and 1 (5%) TCMR + IF/TA. The mean serum creatinine at the time of the biopsy was 126.7 ± 23.4 µmol/L, while GFR-MDRD 63.4 ± 20.7 ml/min, which means that the majority of the findings were subclinical. Among the non-immunological histological findings (Cat 6), 3 cases belonged to CNI toxicity, 1 to BK nephropathy and 1 to recurrence of the primary disease.

CONCLUSION

Our 12-month protocol biopsy study revealed the presence of different forms of mixed subclinical rejection. Use of recent BANFF classification and scoring system enables more precise diagnosis and subsequently different approach to the further treatment of the KTR. More correlative long-term studies including Anti HLA antibodies and Endothelial Cell Activation- Associated Transcripts (ENDAT) are needed.

The Role of the Endothelium during Antibody-Mediated Rejection: From Victim to Accomplice

Antibody-mediated rejection (AMR) of solid organ transplants is characterized by the activation and injury of the allograft endothelium. Histological and transcriptomic studies have associated microvascular inflammation and endothelial lesions with the severity of rejection and poor graft outcomes. The allograft endothelium forms the physical barrier between the donor organ and the recipient; this position directly exposes the endothelium to alloimmune responses. However, endothelial cells are not just victims and can actively participate in the pathogenesis of rejection. In healthy tissues, the endothelium plays a major role in vascular and immune homeostasis. Organ transplantation, however, subjects the endothelium to an environment of inflammation, alloreactive lymphocytes, donor-specific antibodies, and potentially complement activation. As a result, endothelial cells become activated and have modified interactions with the cellular effectors of allograft damage: lymphocytes, natural killer, and myeloid cells. Activated endothelial cells participate in leukocyte adhesion and recruitment, lymphocyte activation and differentiation, as well as the secretion of cytokines and chemokines. Ultimately, highly activated endothelial cells promote pro-inflammatory alloresponses and become accomplices to AMR.

Evidence for an important role of both complement-binding and noncomplement-binding donor-specific antibodies in renal transplantation

PURPOSE OF REVIEW

The review describes the current clinical relevance of circulating anti-human leukocyte antigen (anti-HLA) antibodies in kidney transplantation and discusses recent improvements in their characterization that provide new insights into the identification and management of important clinical outcomes.

RECENT FINDINGS

Recent studies addressing the relationships between donor-specific anti-HLA antibody (HLA-DSA) properties (i.e., their strength, complement-binding capacity, and IgG subclass composition) and allograft injury and survival have highlighted their relevance in the prediction of antibody-mediated injury and allograft loss.

SUMMARY

Antibody-mediated rejection is the leading cause of kidney allograft loss. Although considerable experimental and clinical evidence suggests a causal effect of circulating HLA-DSAs in antibody-mediated rejection and allograft failure, HLA-DSAs induce a wide spectrum of injuries to the allograft that illustrate the need to delineate the characteristics of HLA-DSAs that confer pathogenesis. Current risk stratification is based on HLA-DSA characteristics, including antibody specificity, HLA class, and strength. Recently, the complement-binding capacity of HLA-DSAs has been recognized as a clinically relevant marker for predicting pathogenicity and allograft loss. Emerging data also support a role for HLA-DSA IgG subclass composition in discriminating distinct patterns of antibody-mediated injury. This progress in our understanding of HLA-DSA pathogenicity provides new tools to stratify individual immunological risks. However, specific prospective studies addressing immunological risk stratification in large and unselected populations are required to define the clinical benefit and cost-effectiveness of such a comprehensive assessment of HLA-DSAs before implementation in current clinical practice.

Chronic Antibody-Mediated Rejection in Nonhuman Primate Renal Allografts: Validation of Human Histological and Molecular Phenotypes

Molecular testing represents a promising adjunct for the diagnosis of antibody-mediated rejection (AMR). Here, we apply a novel gene expression platform in sequential formalin-fixed paraffin-embedded samples from nonhuman primate (NHP) renal transplants. We analyzed 34 previously described gene transcripts related to AMR in humans in 197 archival NHP samples, including 102 from recipients that developed chronic AMR, 80 from recipients without AMR, and 15 normal native nephrectomies. Three endothelial genes (VWF, DARC, and CAV1), derived from 10-fold cross-validation receiver operating characteristic curve analysis, demonstrated excellent discrimination between AMR and non-AMR samples (area under the curve = 0.92). This three-gene set correlated with classic features of AMR, including glomerulitis, capillaritis, glomerulopathy, C4d deposition, and DSAs (r = 0.39-0.63, p < 0.001). Principal component analysis confirmed the association between three-gene set expression and AMR and highlighted the ambiguity of v lesions and ptc lesions between AMR and T cell-mediated rejection (TCMR). Elevated three-gene set expression corresponded with the development of immunopathological evidence of rejection and often preceded it. Many recipients demonstrated mixed AMR and TCMR, suggesting that this represents the natural pattern of rejection. These data provide NHP animal model validation of recent updates to the Banff classification including the assessment of molecular markers for diagnosing AMR.

Late graft dysfunction after pediatric heart transplantation is associated with fibrosis and microvasculopathy by automated, digital whole-slide analysis

BACKGROUND

Histopathologic features of late graft dysfunction (LGD) in endomyocardial biopsies (EMBs) after pediatric heart transplantation (HT) have been incompletely described and rarely quantified. We employed automated, morphometric analysis of whole-slide EMB images to objectively quantify fibrosis and microvasculopathy after pediatric HT.

METHODS

Nine recipients with clinical LGD were matched with controls on age, listing diagnosis, crossmatch and time since HT. Fibrosis was quantified as percent tissue area with fibrosis and capillary density as capillaries per unit area, number of capillary "neighbors" within 30 μm of each myocyte and myocyte-to-nearest-capillary diffusion distance. Clinical data, including all EMB reports, were also reviewed.

RESULTS

The groups were well matched for age at HT (median 4.0 vs 3.1 years), listing diagnosis (50% congenital heart disease for each), positive crossmatch (11% each) and days post-HT (2,628 vs 2,894, p = 0.69). Despite a similar number of previous EMBs (median 23 each, p = 0.43), areas occupied by fibrosis were greater in LGD cases (44.5% vs 23.2%, p = 0.012). Capillary number/area data were not statistically different between LGD cases and controls (378/mm² vs 559/mm², p = 0.57), but LGD cases more commonly had zero capillary neighbors (35% vs 20%, p = 0.02) and greater myocyte-to-nearest-capillary distances (27.1 μm vs 18.7 μm, p = 0.005). Cumulative rejection history correlated with fibrosis (r = 0.49, p = 0.039) and myocyte-to-nearest-capillary distance (r = 0.5, p = 0.036).

CONCLUSIONS

LGD after pediatric HT is associated with previous rejection and characterized histologically by fibrosis and microvasculopathy, which are not readily appreciated by traditional semi-quantitative EMB analysis. Software-assisted EMB analysis may enable greater pathophysiologic understanding of LGD and identification of targets for future study and intervention.

Rejection of the Renal Allograft in the Absence of Demonstrable Antibody and Complement

BACKGROUND

Recent literature has stressed the prominent role of antibodies in graft loss. This study was designed to assess a growing perception that T cell-mediated rejection (TCMR) is no longer clinically relevant.

METHODS

Five hundred forty-five renal allograft recipients over a 3-year period were screened for biopsies with: (a) TCMR including borderline change (BL), (b) negative complement protein C4 degradation fragment, and (c) absence of donor-specific antibody at time of transplant, within 30 days of the biopsy, and up to 4 measurements at later time points.

RESULTS

These stringent requirements identified 28 "pure" cases of late TCMR/BL. Low-grade glomerulitis, peritubular capillaritis, or chronic transplant glomerulopathy were found in 9/28 (32%) biopsies. Serum creatinine showed complete short-term remission in 7/10 (70%) BL and 9/18 (50%) TCMR patients 1 month postbiopsy. Yet, both treated and untreated patients demonstrated further decline in graft function as assessed by serum creatinine and estimated glomerular filtration rate.

CONCLUSIONS

Late TCMR seen in 7.9% of biopsies can contribute to significant deterioration of graft function in patients in whom the dominant contribution of antibody-mediated injury has been reasonably excluded. Our data also reinforce existing literature showing that microvascular lesions do not have absolute specificity for a diagnosis of antibody-mediated rejection.

Current status of pediatric renal transplant pathology

Histopathology is still an indispensable tool for the diagnosis of kidney transplant dysfunction in adult and pediatric patients. This review presents consolidated knowledge, recent developments and future prospects on the biopsy procedure, the diagnostic work-up, classification schemes, the histopathology of rejection, including antibody-mediated forms, ABO-incompatible transplants, protocol biopsies, recurrent and de novo disease, post-transplant lymphoproliferative disorder, infectious complications and drug-induced toxicity. It is acknowledged that frequently the correct diagnosis can only be reached in consensus with clinical, serological, immunogenetical, bacteriological and virological findings. This review shall enhance the understanding of the pediatric nephrologist for the thought processes of nephropathologists with the aim to facilitate teamwork between these specialist groups for the benefit of the patient.

Current pathological perspectives on chronic rejection in renal allografts

Chronic rejection in renal transplantation clinically manifests as slow deterioration in allograft function and is a major contributor of late renal graft loss. Most cases of chronic rejection involve chronic antibody-mediated rejection (ABMR) triggered by the interaction of donor-specific alloantibodies with endothelial cells of the microcirculation. The evolution of the Banff classification involved a major revision of the ABMR criteria during the 2000s and led to the inclusion of detailed pathological characteristics of chronic ABMR in the 2013 Banff scheme, including microcirculation damage observed as newly formed basement membranes and arterial fibrous intimal proliferation. Inflammation of microvasculature including glomeruli and/or peritubular capillaries is also seen in substantial cases of chronic ABMR, defined as chronic active ABMR. Chronic active T cell-mediated rejection (TCMR) results from chronic T cell-mediated injury involving renal arteries but is less characterized under the current Banff classification, mainly due to the expanding histological criteria of chronic active ABMR. Characteristics shared by these two chronic rejection types can potentially cause diagnostic confusion. Hence, the diagnostic criteria or categories of chronic renal rejection require amendment of the current Banff classification. Assessment of rejection cases with molecular phenotyping advanced the mechanistic understanding of various dysfunctions in renal allograft, including ABMR and TCMR. Identification of disease-specific changes in gene expression by immunohistological studies, especially in chronic ABMR, has already been validated by several studies, warranting potential application to the pathological diagnostic process. This review provides an overview of current pathological perspectives on chronic rejection of renal allografts and future directions.

Use of Contrast-Enhanced Ultrasonography to Evaluate Chronic Allograft Nephropathy in Rats and Correlations between Time-Intensity Curve Parameters and Allograft Fibrosis

This study quantitatively analyzed changes in the hemodynamic characteristics of renal allografts at different stages in a rat chronic allograft nephropathy (CAN) model as well as the relationship between hemodynamic parameters and renal allograft fibrosis using contrast-enhanced ultrasonography (CEUS). The experimental group used a CAN rat model (n = 30), and the control group used an orthotopic syngeneic renal transplant model (n = 30). After surgery, creatinine clearance rates were regularly monitored every 2 wk. The checking times were set at 4, 12 and 24 wk after surgery, which represent early, middle and late stage of CAN, respectively. At different stages of CAN, eight rats from each group were randomly selected for CEUS examination. Time-intensity curve (TIC) parameters, including rise time, peak intensity, mean transit time, area under the curve, wash-in slope, time-to-peak and α-smooth muscle actin (α-SMA) expression; Vimentin expression; and chronic allograft damage index scores were evaluated by linear correlation analysis. Before the creatinine clearance rate showed significant abnormalities, the renal allografts in the experimental group had already presented pathologic changes associated with CAN. In the early stage after surgery, compared to the TIC curve of the control group, the experimental group showed increased rise time, mean transit time, area under the curve and time-to-peak, and decreased wash-in slope (p < 0.05). Chronic allograft damage index scores and the expression levels of α-SMA and Vimentin proteins in renal allografts were correlated with TIC parameters (p < 0.05). Compared to creatinine clearance rate, CEUS can detect CAN at earlier stages. The correlations between TIC-related parameters and the expression levels of α-SMA and Vimentin in renal allografts indicate that CEUS is a feasible way to assess the degree of renal allograft fibrosis quantitatively.

The Revised (2013) Banff Classification for Antibody-Mediated Rejection of Renal Allografts: Update, Difficulties, and Future Considerations

The Banff 2013 classification (Banff 2013) for antibody-mediated rejection (ABMR) in renal allografts represents the first major revision of the original Banff classification for ABMR that was published in 2003. The main impetus for this revision was the need to include C4d-negative ABMR, although this revised classification contains a number of additional features based on findings reported from 2007 to 2013. Since its publication, several studies have examined the validity of different aspects of Banff 2013 and compared it to earlier (2003, 2007) versions of the Banff ABMR classification. Recent evidence, albeit limited, indicates that Banff 2013 represents an improvement over the previous versions, enhancing our ability to accurately diagnose cases of acute/active and chronic active ABMR on renal allograft biopsy. Molecular studies appear to justify the threshold value of glomerulitis plus peritubular capillaritis score ≥2 required by Banff 2013 for the diagnosis of C4d-negative ABMR; however, other aspects of the classification, including its overall interobserver reproducibility, the clinical significance of the category of C4d staining without evidence of rejection, and whether surrogate markers might potentially substitute for the requirement for the presence of donor-specific antibodies, require additional investigation.

Late Failing Heart Allografts: Pathology of Cardiac Allograft Vasculopathy and Association With Antibody-Mediated Rejection

In heart transplantation, there is a lack of robust evidence of the specific causes of late allograft failure. We hypothesized that a substantial fraction of failing heart allografts may be associated with antibody-mediated injury and immune-mediated coronary arteriosclerosis. We included all patients undergoing a retransplantation for late terminal heart allograft failure in three referral centers. We performed an integrative strategy of heart allograft phenotyping by assessing the heart vascular tree including histopathology and immunohistochemistry together with circulating donor-specific antibodies. The main analysis included 40 explanted heart allografts patients and 402 endomyocardial biopsies performed before allograft loss. Overall, antibody-mediated rejection was observed in 19 (47.5%) failing heart allografts including 16 patients (40%) in whom unrecognized previous episodes of subclinical antibody-mediated rejection occurred 4.5 ± 3.5 years before allograft loss. Explanted allografts with evidence of antibody-mediated rejection demonstrated higher endothelitis and microvascular inflammation scores (0.89 ± 0.26 and 2.25 ± 0.28, respectively) compared with explanted allografts without antibody-mediated rejection (0.42 ± 0.11 and 0.36 ± 0.09, p = 0.046 and p < 0.0001, respectively). Antibody-mediated injury was observed in 62.1% of failing allografts with pure coronary arteriosclerosis and mixed (arteriosclerosis and atherosclerosis) pattern, while it was not observed in patients with pure coronary atherosclerosis (p = 0.0076). We demonstrate that antibody-mediated rejection is operating in a substantial fraction of failing heart allografts and is associated with severe coronary arteriosclerosis. Unrecognized subclinical antibody-mediated rejection episodes may be observed years before allograft failure.

IMPROVING LONG-TERM OUTCOMES IN KIDNEY TRANSPLANTATION: TOWARDS A NEW PARADIGM OF POST-TRANSPLANT CARE IN THE UNITED STATES

Since the 1950s, care for kidney transplant recipients in the United States has evolved around a model in which clinical management, quality metrics, and financial underpinnings are focused around the surgical procedure itself reflecting the concept that perioperative and short-term interventions are primary determinants of success. In the current era, short-term results are indeed excellent, but long-term success remains elusive for many. Emerging data, particularly a newfound understanding of donor-specific antibody and its consequences, now challenge the concept that late graft failure is the consequence of early events. Several major longitudinal studies, including the long-term Deterioration of Kidney Allograft Function (DeKAF) project and Clinical Trials in Organ Transplantation-09 (CTOT-09), highlight the primacy of later events in influencing long-term outcomes after kidney transplantation. Proper long-term care and monitoring of kidney recipients, with timely diagnosis and treatment of identifiable injury, offers the best prospect of improving long-term graft survival.

A significant role for anti-human leukocyte antigen antibodies and antibody-mediated rejection in the biopsy-for-cause population

The role of anti-human leukocyte antigen (HLA) antibodies and antibody-mediated rejection is well known, but our comprehension and the preventive measures we take seem to be insufficient. One of the major causes of premature renal transplant loss is recepients' immunologic hyperactivity to donors' antigens. Monitoring of humoral alloreactivity gives hope for early diagnosis and adequate therapy. The goal of our analysis was the assessment of the influence of anti-HLA antibodies on the function and survival of transplants. In our study we included 60 consecutive renal transplant recipients who had a renal transplant biopsy-for-cause performed due to insufficiency. Transplant biopsies were performed between the 7th day and 12th year (median, 2 years) after transplantation. Anti-HLA antibodies were present in 20 patients (33%). The patients were divided into 2 groups according the presence of anti-HLA antibodies. In a 12-month observation, 10/20 (50%) patients in the anti-HLA(+) group returned to dialysis in contrast with 7/40 (17.5%; P = .014) in the anti-HLA(-) group. Also, 8/10 (80%) of the anti-HLA(+) patients who lost the transplant had anti-HLA Abs class II and only 2/10 (20%) had anti-HLA Abs class I. Anti-HLA antibodies were specific to a donor (donor-specific antibodies [DSA]) in 8/10 (80%) of the patients who lost the transplant. Anti-HLA antibodies appeared de novo in 50% of patients who lost the transplant. Nonadherence was suspected in 50% of patients. Acute humoral rejection occurred in 1 patient. Also, 8/10 (90%) developed chronic active humoral rejection. Our study revealed that graft loss in the renal transplant biopsy-for-cause population with the presence of anti-HLA Abs during a 12-month observation reached 50%. Nonadherence in these patients was very high and amounted to 50%. Monitoring of renal transplant recipients and individualization of therapy considering humoral activity should prolong renal graft survival.

T-cell-mediated rejection of the kidney in the era of donor-specific antibodies: diagnostic challenges and clinical significance

PURPOSE OF REVIEW

Burgeoning literature on antibody-mediated rejection (ABMR) has led to a perception that T-cell-mediated rejection (TCMR) is no longer a significant problem. This premise needs to be carefully appraised.

RECENT FINDINGS

A review of the literature indicates that TCMR remains an independent-risk factor for graft loss. Importantly, it can occur as a sensitizing event that triggers ABMR, and adversely affects its outcome. Moreover, T cells are regularly present in lesions used to diagnose ABMR, and these lesions can also develop in the absence of donor-specific antibodies (DSA). Conversely, patients with DSA are at risk for mixed ABMR-TCMR, which is quite common in many studies, and may require a combined anti-T-cell and anti-B-cell strategy for the best outcome.

SUMMARY

T-cell-based clinical monitoring and therapy is still relevant for prophylaxis of both cellular and humoral rejection, treatment of steroid refractory TCMR, which occurs in up to 20% of patients, and optimization of clinical outcome in mixed TCMR-ABMR, which is more frequently encountered than generally appreciated, and still associated with unacceptably high rates of graft loss.

Determinants and Outcomes of Accelerated Arteriosclerosis

Rationale:

The role of circulating antibodies in addition to traditional cardiovascular risk factors in the development of accelerated arteriosclerosis and their long-term clinical consequences have not been demonstrated.

Objective:

We investigated the role of circulating antibodies in accelerated arteriosclerosis and the role of immune-associated arteriosclerosis in graft and patient survival and the occurrence of major adverse cardiovascular events.

Methods and Results:

This was an observational prospective cohort study that included 1065 kidney transplant patients (principal cohort, n=744; validation cohort, n=321) between 2004 and 2010. Participants were assessed for traditional cardiovascular risk factors and circulating anti–human leukocyte antigen (HLA) antibodies. All patients underwent allograft biopsies to assess arteriosclerotic lesions and endothelial activation, endarteritis, and complement deposition. In the principal cohort, 250 (33.6%) patients had severe arteriosclerosis (luminal narrowing >25% via fibrointimal arterial thickening). Circulating donor-specific anti-HLA antibodies were significantly associated with severe allograft arteriosclerosis (hazard ratio, 2.9; P <0.0001), independently of traditional risk factors. Patients with severe arteriosclerosis and anti-HLA antibodies (n=91, 12.2%) demonstrated allograft endothelial activation, endarteritis, and complement deposition. High levels of anti-HLA antibodies and their complement binding capacity were associated with increased severity of arteriosclerosis. Patients with antibody-associated severe arteriosclerosis had decreased allograft survival and increased mortality ( P <0.0001); they exhibited a 2.5- and 4.1-fold increased risk of major adverse cardiovascular events compared with patients who had severe arteriosclerosis without antibodies and patients with minimal arteriosclerosis, respectively ( P <0.0005). Circulating donor-specific anti-HLA antibodies were significantly associated with occurrence of major adverse cardiovascular events (hazard ratio, 2.4; P =0.0004), independently of traditional risk factors.

Conclusions:

Circulating antibodies are major determinants of severe arteriosclerosis and major adverse cardiovascular events, independent of traditional cardiovascular risk factors.

Advanced glycation end products accelerate arteriosclerosis after renal transplantation through the AGE/RAGE/ILK pathway

BACKGROUND

The effects of advanced glycation end products (AGEs) on arteriosclerosis (AS) after kidney transplantation and the molecular mechanisms involved remain unclear.

METHODS

Samples were collected from 30 healthy volunteers and 30 renal transplant recipients (RTRs) to determine the levels of AGEs and to observe both histological changes and α-smooth muscle actin (α-SMA) and osteopontin (OPN) expression. Furthermore, we analyzed α-SMA, OPN and integrin-linked kinase (ILK) in rat vascular smooth muscle cells (VSMCs) that were treated with AGEs and in ILK plasmid transfected rat VSMCs treated with AGEs. Finally, we measured the expression of ILK and the receptor for advanced glycation end (RAGE) products in rat VSMCs treated with AGEs and an anti-RAGE antibody.

RESULTS

Significant differences in the histological changes, serum AGEs, and expression of α-SMA and OPN in arterial walls were noted between healthy volunteers and RTRs. Significant OPN and ILK overexpression and reduced α-SMA expression were detected in a time-dependent manner in rat VSMCs after treatment with AGEs. Similar outcomes were observed regarding the overexpression of ILK, and these results could be prevented via RAGE inhibition.

CONCLUSIONS

AGEs may play a critical role in the formation and progression of AS after renal transplantation by inducing VSMCs-to-osteoblast trans-differentiation through the AGE/RAGE/ILK pathway.

New insights in antibody-mediated rejection

PURPOSE OF REVIEW

In the present review, we aim to describe the state of knowledge concerning antibody-mediated rejection (ABMR) spectrum and diagnosis criteria before analyzing the present and future promising leads regarding ABMR prognosis markers and treatment.

RECENT FINDINGS

Recent studies regarding complement-binding donor-specific antibodies and the molecular approach highlighted the unmet need for stratification tools for prognosis and treatment inside ABMR disease.

SUMMARY

ABMR is the leading cause of kidney allograft failure. The recent expansion of its spectrum is related to the paradigm of a continuous process, leading insidiously to a chronic form of ABMR and to the progressive acknowledgement of new entities (such as vascular ABMR, subclinical ABMR, C4d-negative ABMR). Considering the global picture of ABMR, the Banff classification gradually refined the diagnosis criteria so that it now describes a clinically relevant and coherent entity. Nevertheless, if the diagnosis mainly relies on conventional assessment, such as histological findings and circulating donor-specific antibodies, these criteria face serious limitations in terms of stratification of patients at risk of graft loss inside ABMR disease. Recently, new promising tools have emerged in order to identify long-term outcomes at the time of the diagnosis of rejection. In this regard, donor-specific antibodies' complement-fixing ability and the molecular approach contributed significantly. Currently, however, no clinically relevant surrogate marker of treatment efficiency is currently available.

Immune Sensitization and Mortality in Wait-Listed Kidney Transplant Candidates

Cardiovascular mortality is the leading cause of death in ESRD. Whereas innate and adaptive immunity have established roles in cardiovascular disease, the role of humoral immunity is unknown. We conducted a retrospective cohort study in first-time adult kidney transplant candidates (N=161,308) using data from the Scientific Registry of Transplant Recipients and the Centers for Medicare and Medicaid Services to evaluate whether anti-human leukocyte antigen antibodies, measured as panel reactive antibodies (PRAs), are related to mortality in ESRD. Relationships between time-varying PRAs and all-cause or cardiovascular mortality were assessed using Cox proportional hazards models. The analysis was repeated in subcohorts of candidates at lower risk for significant comorbidities, activated on the waiting list after 2007, or unsensitized at activation. Competing risks analyses were also conducted. Fully adjusted models showed increased hazard ratios (HRs [95% confidence intervals]) for all-cause mortality (HR, 1.02 [95% CI, 0.99 to 1.06]; HR, 1.11 [95% CI,1.07 to 1.16]; and HR,1.21 [95% CI,1.15 to 1.27]) and cardiovascular mortality (HR, 1.05 [95% CI,1.00 to 1.10]; HR,1.11 [95% CI,1.05 to 1.18]; and HR,1.21 [95% CI,1.12 to 1.31]) in PRA 1%-19%, PRA 20%-79%, and PRA 80%-100% categories compared with PRA 0%, respectively. Associations between PRA and the study outcomes were accentuated in competing risks models and in lower-risk patients and persisted in other subcohorts. Our findings suggest that PRA is an independent predictor of mortality in wait-listed kidney transplant candidates. The mechanisms by which PRA confers an incremental mortality risk in sensitized patients, and the role of transplantation in modifying this risk, warrant further study.

Recent advances in renal transplantation: antibody-mediated rejection takes center stage

Overlooked for decades, antibodies have taken center stage in renal transplantation and are now widely recognized as the first cause of allograft failure. Diagnosis of antibody-mediated rejection has considerably improved with identification of antibody-mediated lesions in graft biopsies and advances made in the detection of circulating donor-specific antibodies. Unfortunately, this progress has not yet translated into better outcomes for patients. Indeed, in the absence of a drug able to suppress antibody generation by plasma cells, available therapies can only slow down graft destruction. This review provides an overview of the current knowledge of antibody-mediated rejection and discusses future interesting research directions.

Differences in chronic intragraft inflammation between positive crossmatch and ABO-incompatible kidney transplantation

BACKGROUND

ABO-incompatible kidney transplantations (ABOiKTxs) seem to have better long-term outcomes than positive crossmatch kidney transplantations (+XMKTxs).

METHODS

This study aimed to assess the differences in chronic injury on histologic findings on 1- and 5-year surveillance biopsies and the clinical outcomes in living-donor kidney transplantations performed between May 1999 and November 2006 including 102 +XMKTxs, 73 ABOiKTxs, and 652 conventional KTxs.

RESULTS

Although 5-year patient survival was similar between groups, graft loss between 1 and 5 years was similar in ABOiKTx (2.6% per year) and conventional KTx (1.7% per yr), and both were lower than that of +XMKTx (5.8% per year). At 5 years, renal function was similar in ABOiKTx and conventional KTx, and both were higher than that of +XMKTx, which had higher rates of inflammation and chronic glomerulopathy on both 1- and 5-year biopsies. Despite having evidence of less chronic injury, ABOiKTx showed a higher rate of intragraft complement activation (C4d deposition) at 5 years compared with +XMKTx (77.8% vs. 18.9%, P<0.001).

CONCLUSION

These data suggest that +XMKTxs have high rates of chronic inflammation at 1 and 5 years after transplantation, which may explain the higher rates of graft loss and lower renal function compared with other factors such as anti-donor antibody or intragraft complement deposition.

Donor-specific antibodies in allograft recipients: etiology, impact and therapeutic approaches

PURPOSE OF REVIEW

Kidney transplantation remains the treatment of choice for patients with end-stage renal failure. However, despite significant advancements in detection of donor-specific human leukocyte antigen antibodies, improved immunosuppression and patient management, the durability of this life-saving therapy has not improved. This results in increased morbidity and mortality as well as increased cost to the healthcare system.

RECENT FINDINGS

The identification of immune-pathogenic pathways responsible for allograft failure coupled with targeted interventions will represent one of the most important future objectives of transplant immunologist and physicians. The development of sensitive donor-specific antibody (DSA) detection techniques and advancements in renal allograft pathology assessments have revealed the importance of humoral immunity in mediating allograft failure. This is especially true for complement activating DSAs (C1q+).

SUMMARY

Our current understanding suggests that reduction of immunosuppressive medications or medication nonadherence is now the major causes of DSA development and attendant pathology. Other important factors in initiation of de-novo DSA production include viral infections, human leukocyte antigen-DR/DQ mismatches and autoimmune diseases. Therapies aimed at antibody reduction, B-cell depletion and modification of the complement system will likely usher in new therapeutic approaches for prevention and treatment of DSA-mediated allograft dysfunction.

Modernization of Chronic Allograft Injury Research: Better Biomarkers, Better Studies, Better Outcomes

Despite dramatic improvements in acute rejection rates and short-term allograft survival, long-term allograft survival remains unchanged in the modern era, largely due to chronic allograft injury, a progressive disease that is common across all solid organ transplantation but has no proven treatment. Studies of novel diagnostic and therapeutic strategies for chronic allograft injury have been relatively sparse, in part due to the time and expense required to conduct traditional long-term clinical studies of a variably progressive disease. In this article, we review the pathophysiology of chronic allograft injury, including recent insights into key mechanisms of the disease. We discuss the barriers to progress in chronic allograft injury research and present alternative approaches to study design that could accelerate improvements in diagnosis, prevention, or treatment of the disease. We integrate these approaches with emerging biomarkers and surrogate endpoints into a model clinical study of chronic renal allograft injury, providing a framework for modern study design in solid organ transplantation.

Rational clinical trial design for antibody mediated renal allograft injury

Antibody mediated renal allograft rejection is a significant cause of acute and chronic graft loss. Recent work has revealed that AMR is a complex processes, involving B and plasma cells, donor-specific antibodies, complement, vascular endothelial cells, NK cells, Fc receptors, cytokines and chemokines. These insights have led to the development of numerous new therapies, and adaptation of others originally developed for treatment of hemetologic malignancies, autoimmune and complement mediated conditions. Here we review emerging insights into the pathophysiology of AMR as well as current and emerging therapies for both acute and chronic AMR. Finally, we discuss rational clinical trial design in light of antibody and B cell immunobiology, as well as appropriate efficacy metrics to identify robust protocols and therapeutic agents.

Chronic allograft nephropathy or interstitial fibrosis and tubular atrophy: what is in a name?

PURPOSE OF REVIEW

Chronic allograft nephropathy has fallen into disfavor as a morphologic term to describe parenchymal scarring in the renal allograft, with a recommendation that this be replaced by the more descriptive term 'interstitial fibrosis and tubular atrophy'. However, neither term addresses the underlying cause of the scarring. This review focuses on whether all interstitial fibrosis and tubular atrophy in the renal allograft has the same implications for long-term graft survival, and whether there are specific features of interstitial fibrosis and tubular atrophy that can be used to identify its underlying cause.

RECENT FINDINGS

Results from a number of studies indicate that interstitial fibrosis and tubular atrophy, when associated with interstitial inflammation, is a strong predictor of graft loss, much more so than interstitial fibrosis and tubular atrophy alone. Most notably, findings from the multicenter Long-Term Deterioration of Kidney Allograft Function study, designed to identify the causes of late allograft dysfunction, showed interstitial inflammation in the areas of interstitial fibrosis and tubular atrophy (i-IF/TA) was predictive of reduced time to graft failure, even after adjustment for serum creatinine. In addition, the presence of i-IF/TA correlates with increased acute kidney injury gene transcripts. However, neither interstitial fibrosis and tubular atrophy nor i-IF/TA is associated with any specific cause of chronic graft injury.

SUMMARY

Although (i-IF/TA), especially when widespread, is clearly associated with reduced renal allograft survival and molecular markers of active graft injury and repair, there is presently no reliable way, using either morphology alone, immunohistochemistry, or molecular techniques, to differentiate i-IF/TA (or interstitial fibrosis and tubular atrophy alone) resulting from different causes.

The significance of histological diagnosis in renal allograft biopsies in 2014

In 2014, the renal allograft biopsy still represents the best available diagnostic 'gold' standard to assess reasons for allograft dysfunction. However, it is well recognized that histological lesion observed in the biopsy is of limited diagnostic specificity and that the Banff classification as the international diagnostic standard represents mere expert consensus. Here, we review the role of the renal allograft biopsy in different clinical and diagnostic settings. To increase diagnostic accuracy and to compensate for lack of specificity, the interpretation of biopsy pathology needs to be within the clinical context, primarily defined by time post-transplantation and patient-specific risk profile. With this in mind, similar histopathological patterns will lead to different conclusions with regard to diagnosis, disease grading and staging and thus to patient-specific clinical decision-making. Consensus generation for such integrated diagnostic approach, preferably including new molecular tools, represents the next challenge to the transplant community on its way to precision medicine in transplantation.

Histopathological diagnosis of acute and chronic rejection in pediatric kidney transplantation

ABO-compatible as well as ABO-incompatible kidney transplantation are well established in the pediatric population. There are particularities in the histopathological evaluation of pediatric kidney transplant biopsies as for example the recurrence of certain diseases different from the adult population. Furthermore, the challenging transition of pediatric renal transplant recipients to adulthood is associated with an increased rate of non-adherence triggered rejection episodes. With modern immunosuppressive drugs, T-cell-mediated rejection of renal allografts is well controlled. In contrast, antibody-mediated rejection (AMR) is increasingly recognized as one of the major reasons for allograft loss. However, the 2001 diagnostic Banff criteria for antibody-mediated rejection require further refinement, as the morphological spectrum of AMR expands while effective therapeutic strategies are lacking. For example, endarteritis, which traditionally has been attributed to T-cell-mediated rejection, has recently been shown to be part of the AMR spectrum in some cases. Many findings in transplant renal biopsies are not specific for a certain disease but need consideration of differential diagnoses. To use the term "chronic allograft nephropathy" as a diagnostic entity is no longer appropriate. Therefore, the precise identification of specific diseases is paramount in the assessment of transplant renal biopsies in order to enable tailored therapeutic management.

Emerging Concepts and Controversies in Renal Pathology: C4d-Negative and Arterial Lesions as Manifestations of Antibody-Mediated Transplant Rejection

The consensus classification of antibody-mediated rejection (AMR) of renal allografts developed at the Sixth Banff Conference on Allograft Pathology, in 2001, identified three findings necessary for the diagnosis of active AMR: histologic evidence, antibodies against the graft, and capillary C4d deposition. Morphologic and molecular studies have noted evidence of microvascular injury, which, in the presence of donor-specific antibodies (DSAs) but the absence of C4d deposition, is associated with development of transplant glomerulopathy and graft loss. Recent studies suggest that intimal arteritis may in some cases be a manifestation of DSA-induced graft injury. These newly recognized lesions of AMR have now been incorporated into a revised Banff diagnostic schema.

Classification Systems in Renal Pathology: Promises and Problems

Kidney diseases are morphologically heterogeneous. Pathologic classifications of renal disease permit standardization of diagnosis and may identify clinical-pathologic subgroups with different outcomes and/or responses to treatment. To date, classifications have been proposed for lupus nephritis, allograft rejection, IgA nephropathy, focal segmental glomerulosclerosis, antineutrophil cytoplasmic antibody -related glomerulonephritis, and diabetic glomerulosclerosis. These classifications share several limitations related to lack of specificity, reproducibility, validation, and relevance to clinical practice. They offer a standardized approach to diagnosis, however, which should facilitate communication and clinical research.