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

Complement in Antibody-Mediated Rejection of the Kidney Graft: From Pathophysiology to Clinical Practice

Antibody-mediated rejection (AMR) is a leading cause of kidney graft failure. Complement activation is involved in the AMR process. Our aim is to provide the current understanding of the pathophysiology related to complement-mediated injury in AMR, to present the current evidence regarding complement blockade in AMR management, and to point out emerging therapies and future directions in this area. The complement system plays an important role in the onset and progression of AMR. There is a balance between complement-dependent and -independent mechanisms in the development of rejection lesions. Classic and leptin pathways are involved in this process. C4d positivity is no longer a mandatory feature for AMR diagnosis but remains an independent predictor of negative outcomes. The current evidence regarding AMR treatment is limited. Terminal and proximal complement blockade has gained recognition in clinical practice. Eculizumab and C1 inhibitors are effective in the treatment of AMR as adjuvant therapies to the standard of care. The availability of novel complement inhibitors will lead to more effective and tailored treatment strategies.

Relevance of Human Leukocyte Antigen Class C Donor-Specific Antibodies in Kidney Transplant

Kidney transplant is well known to be the best possible therapy for patients with end-stage kidney failure; however, allograft rejection remains a major obstacle despite the advent of modern immunosuppression regimens. Despite the well-established role of donorspecific antibodies directed at anti-HLA-A, -B, -DR, and -DQ antigens, the particular role of anti-HLA-C donorspecific antibodies in allograft longevity is not yet clear. Recently, preformed anti-native HLA-C donorspecific antibodies were reported to be possibly linked to poor allograft outcome. In addition, inclusion of HLA-C in all transplant allocation regimens has been suggested. Moreover, possible relevance of HLA-C has been shown in other fields (eg, transfusion and obstetrics). Its reduced expression could explain the diminished immunogenicity of the anti-HLA-C antibodies with subsequent lowered strength and prevalence. Furthermore, the"missed self" theory has gained interest. Here, we investigated HLA-C donorspecific antibody immunogenicity, pathogenicity, cellsurface expression, antibody heterogenicity, and possible management tools.

Early and Late Microvascular Inflammation Have Differing Etiological Causes and Clinical Expression

BACKGROUND

Microvascular inflammation (MVI) is an important pathological feature of antibody-mediated rejection (AMR). How posttransplant time affects its clinicopathological expression is little understood.

METHODS

This retrospective, single-center study screened 3398 kidney transplant biopsies and dichotomized 202 MVI ≥ 2 (Banff glomerulitis + peritubular capillaritis ≥ 2) samples by 9-mo median incidence time for comparison.

RESULTS

The prevalence of MVI ≥ 2 was 12.4% in transplant kidneys, which failed more frequently than propensity-matched normal controls (n = 202; P  < 0.001). Epidemiological risk factors for early MVI ≥ 2 were delayed graft function, prior AMR, and circulating donor-specific antibodies (DSAs+). Prior recipient sensitization occurred in 72.3%. Early MVI ≥ 2 was classified AMR in 65.3% and cellular rejection in 34.7%, and demonstrated excellent functional recovery and graft survival comparable to normal control kidneys. Late MVI ≥ 2 was predicted by younger (18 = 29 y) age, female recipient, living-donation, prior methylprednisolone, cyclosporine (versus tacrolimus, levels <5 ng/mL), absent antiproliferative therapy, and DSA+ using multivariable epidemiological modeling. Nonadherence caused 49.5%, with iatrogenic minimization responsible for 47.5%, usually for recipient infection. Late MVI ≥ 2 was because of AMR in 93.1%, and characterized by greater interstitial fibrosis, tubular atrophy, complement degradation split-product 4d (C4d) staining of peritubular capillaries+, endothelial C4d staining of glomerular capillaries+, transplant glomerulopathy and vasculopathy scores, DSA strength, and graft failure than early MVI ≥ 2 or normal transplant kidneys. Death-censored graft survival in 149 unique MVI ≥ 2 kidneys was independently determined by nonadherence, serum creatinine, proteinuria, DSA+, Banff C4d staining of peritubular capillaries+, and chronic interstitial fibrosis scores. MVI score and time lost significance using multivariable Cox regression.

CONCLUSIONS

The changing expression of MVI ≥ 2 over time is best explained by differences in underimmunosuppression and microvascular injury from AMR impacting allograft function and survival.

The relationship of microvascular inflammation with antibody-mediated rejection in kidney transplantation

Microvascular inflammation (MVI) is a key diagnostic feature of antibody-mediated rejection (AMR); however, recipients without donor-specific antibodies (DSA) defy etiologic classification using C4d staining of peritubular capillaries (C4dptc) and conventional DSA assignment. We evaluated MVI ≥ 2 (Banff g + ptc ≥ 2) using Banff 2019 AMR (independent of MVI ≥ 2 but including C4dptc) with unconventional endothelial C4d staining of glomerular capillaries (C4dglom) and - arterial endothelium and/or intima (C4dart) using tissue immunoperoxidase, shared-eplet and subthreshold DSA (median fluorescence intensity, [MFI] 100-499), and capillary ultrastructure from 3398 kidney transplant samples for evidence of AMR. MVI ≥ 2 (n = 202 biopsies) from 149 kidneys (12.4% prevalence) correlated with DSA+, C4dptc+, C4dglom+, Banff cg, i, t, ti scores, serum creatinine, proteinuria, and graft failure compared with 202 propensity score matched normal controls. The laboratory reported DSA- MVI ≥ 2 (MFI ≥500) occurred in 34.7%; however, subthreshold (28.6%), eplet-directed (51.4%), and/or misclassified anti-Human leukocyte antigen (HLA) DSA (12.9%) were identified in 67.1% by forensic reanalysis, with vascular C4d+ staining in 67.1%, and endothelial abnormalities in 57.1%, totaling 87.1%. Etiologic analysis attributed 62.9% to AMR (77.8% for MVI with negative reported DSA [DSA- MVI ≥2] with glomerulitis) and pure T cellular rejection in 37.1%. C4dptc-DSA- MVI ≥ 2 was unrecognized AMR in 48.0%. Functional outcomes and graft survival were comparable to normal controls. We concluded that DSA- MVI ≥ 2 frequently signified a mild "borderline" phenotype of AMR which was recognizable using novel serologic and pathological techniques.

Chimeric HLA antibody receptor T cell therapy for humoral transplant rejection

Antibody-mediated rejection (ABMR) is a significant obstacle to achieving optimal long-term outcomes after solid organ transplantation. The presence of donor-specific antibodies (DSAs), particularly against human leucocyte antigen (HLA), increases the risk of allograft rejection and subsequent graft loss. No effective treatment for ABMR currently exists, warranting novel approaches to target the HLA-specific humoral alloimmune response. Cellular therapies may hold promise to this end. According to publicly available sources as of now, three independent laboratories have genetically engineered a chimeric HLA antibody receptor (CHAR) and transduced it into human T cells, based on the demonstrated efficacy of chimeric antigen receptor T cell therapies in malignancies. These CHAR-T cells are designed to exclusively eliminate B cells that produce donor-specific HLA antibodies, which form the cornerstone of ABMR. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA-specific B cells, sparing B cells with other specificities. Thus CHAR technology may be used as a selective desensitization protocol and to treat ABMR after solid organ transplantation.

Re-Evaluating the Transplant Glomerulopathy Lesion-Beyond Donor-Specific Antibodies

There have been significant advances in short-term outcomes in renal transplantation. However, longer-term graft survival has improved only minimally. After the first post-transplant year, it has been estimated that chronic allograft damage is responsible for 5% of graft loss per year. Transplant glomerulopathy (TG), a unique morphologic lesion, is reported to accompany progressive chronic allograft dysfunction in many cases. While not constituting a specific etiologic diagnosis, TG is primarily considered as a histologic manifestation of ongoing allo-immune damage from donor-specific anti-HLA alloantibodies (DSA). In this review article, we re-evaluate the existing literature on TG, with particular emphasis on the role of non-HLA-antibodies and complement-mediated injury, cell-mediated immune mechanisms, and early podocyte stress in the pathogenesis of Transplant Glomerulopathy.

Assessing the role of phosphorylated S6 ribosomal protein in the pathological diagnosis of pulmonary antibody-mediated rejection

BACKGROUND

Pulmonary antibody-mediated rejection is still a challenging diagnosis as C4d immunostaining has poor sensitivity. Previous studies have indicated that the phosphorylated S6 ribosomal protein, a component of the mammalian target of rapamycin (mTOR) pathway, is correlated with de novo donor-specific antibodies in lung transplantation. The objective of this study was to evaluate the phosphorylation of S6 ribosomal protein as a surrogate for antibody-mediated rejection diagnosis in lung transplant patients.

METHODS

This multicentre retrospective study analyzed transbronchial biopsies from 216 lung transplanted patients, 114 with antibody-mediated rejection and 102 without (19 with acute cellular rejection, 17 with ischemia/reperfusion injury, 18 with infection, and 48 without post-transplant complications). Immunohistochemistry was used to quantify phosphorylated S6 ribosomal protein expression in macrophages, endothelium, epithelium, and inter-pathologist agreement was assessed.

RESULTS

Median phosphorylated S6 ribosomal protein expression values were higher in antibody-mediated rejection cases than in controls for all cell components, with the highest sensitivity in macrophages (0.9) and the highest specificity in endothelial expression (0.8). The difference was mainly significant in macrophages compared to other post-lung transplantation complications. Inter-pathologist agreement was moderate for macrophages and endothelium, with higher agreement when phosphorylated S6 ribosomal protein expression was dichotomized into positive/negative. The inclusion of phosphorylated S6 ribosomal protein in the diagnostic algorithm could have increased antibody-mediated rejection certainty levels by 25%.

CONCLUSIONS

The study supports the role of the mTOR pathway in antibody-mediated rejection-related graft injury and suggests that tissue phosphorylation of S6 ribosomal protein could be a useful surrogate for a more accurate pathological diagnosis of lung antibody-mediated rejection.

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

Imlifidase for Kidney Transplantation of Highly Sensitized Patients With a Positive Crossmatch: The French Consensus Guidelines

Imlifidase recently received early access authorization for highly sensitized adult kidney transplant candidates with a positive crossmatch against an ABO-compatible deceased donor. These French consensus guidelines have been generated by an expert working group, in order to homogenize patient selection, associated treatments and follow-up. This initiative is part of an international effort to analyze properly the benefits and tolerance of this new costly treatment in real-life. Eligible patients must meet the following screening criteria: cPRA ≥ 98%, ≤ 65-year of age, ≥ 3 years on the waiting list, and a low risk of biopsy-related complications. The final decision to use Imlifidase will be based on the two following criteria. First, the results of a virtual crossmatch on recent serum, which shall show a MFI for the immunodominant donor-specific antibodies (DSA) > 6,000 but the value of which does not exceed 5,000 after 1:10 dilution. Second, the post-Imlifidase complement-dependent cytotoxicity crossmatch must be negative. Patients treated with Imlifidase will receive an immunosuppressive regimen based on steroids, rATG, high dose IVIg, rituximab, tacrolimus and mycophenolic acid. Frequent post-transplant testing for DSA and systematic surveillance kidney biopsies are highly recommended to monitor post-transplant DSA rebound and subclinical rejection.

Microvascular inflammation in the absence of human leukocyte antigen-donor-specific antibody and C4d: An orphan category in Banff classification with cytotoxic T and natural killer cell infiltration

Isolated microvascular inflammation (iMVI) without HLA donor-specific antibodies or C4d deposition in peritubular capillaries remains an enigmatic phenotype that cannot be categorized as antibody-mediated rejection (ABMR) in recent Banff classifications. We included 221 kidney transplant recipients with biopsies with ABMR (n = 73), iMVI (n = 32), and normal (n = 116) diagnoses. We compared peripheral blood leukocyte distribution by flow cytometry and inflammatory infiltrates in kidney transplant biopsies among groups. Flow cytometry showed fewer lymphocytes and total, CD4+, and CD8+ peripheral T cells in iMVI compared with ABMR and normal cases. ABMR and iMVI had fewer total natural Killer (NK) cells but more NKG2A+ NK cells. Immunohistochemistry indicated that ABMR and iMVI had greater CD3+ and CD68+ glomerular infiltration than normal biopsies, whereas CD8+ and TIA1+ cells showed only increased iMVI, suggesting they are cytotoxic T cells. Peritubular capillaries displayed more CD3+, CD56+, TIA1+, and CD68+ cells in both ABMR and iMVI. In contrast, iMVI had less plasma cell infiltration in peritubular capillaries and interstitial aggregates than ABMR. iMVI displayed decreased circulating T and NK cells mirrored by T cell and NK cell infiltration in the renal allograft, similar to ABMR. However, the lesser plasma cell infiltration in iMVI may suggest an antibody-independent underlying stimulus.

Association of Circulating Anti-HLA Donor-Specific Antibodies and Their Characteristics, including C1q-Binding Capacity, in Kidney Transplant Recipients with Long-Term Renal Graft Outcomes

Post-transplant antihuman leukocyte antigen donor-specific antibodies (anti-HLA DSAs) monitoring in kidney transplant recipients remains unclear and is currently under investigation. The pathogenicity of anti-HLA DSAs is determined by antibody classes, specificity, mean fluorescent intensity (MFI), C1q-binding capacity, and IgG subclasses. The aim of this study was to investigate the association of circulating DSAs and their characteristics with renal allograft long-term outcomes. The study included 108 consecutive patients from our transplant center who underwent kidney allograft biopsy between November 2018 and November 2020, 3 to 24 months after kidney transplantation. At the time of biopsy, patients' sera were collected for analysis of anti-HLA DSAs. Patients were followed for a median time of 39.0 months (Q1-Q3, 29.8-45.0). Detection of anti-HLA DSAs at the time of biopsy (HR = 5.133, 95% CI 2.150-12.253, p = 0.0002) and their C1q-binding capacity (HR = 14.639, 95% CI 5.320-40.283, p ≤ 0.0001) were independent predictors of the composite of sustained 30% reduction from estimated glomerular filtration rate or death-censored graft failure. Identification of anti-HLA DSAs and their C1q-binding capacity could be useful in identifying kidney transplant recipients at risk for inferior renal allograft function and graft failure. Analysis of C1q is noninvasive, accessible, and should be considered in clinical practice in post-transplant monitoring.

Banff Human Organ Transplant Transcripts Correlate with Renal Allograft Pathology and Outcome: Importance of Capillaritis and Subpathologic Rejection

BACKGROUND

To seek insights into the pathogenesis of chronic active antibody-mediated rejection (CAMR), we performed mRNA analysis and correlated transcripts with pathologic component scores and graft outcomes.

METHODS

We utilized the NanoString nCounter platform and the Banff Human Organ Transplant gene panel to quantify transcripts on 326 archived renal allograft biopsy samples. This system allowed correlation of transcripts with Banff pathology scores from the same tissue block and correlation with long-term outcomes.

RESULTS

The only pathology score that correlated with AMR pathways in CAMR was peritubular capillaritis (ptc). C4d, cg, g, v, i, t, or ci scores did not correlate. DSA-negative CAMR had lower AMR pathway scores than DSA-positive CAMR. Transcript analysis in non-CAMR biopsies yielded evidence of increased risk of later CAMR. Among 108 patients without histologic CAMR, 23 developed overt biopsy-documented CAMR within 5 years and as a group had higher AMR pathway scores (P=3.4 × 10-5). Random forest analysis correlated 3-year graft loss with elevated damage, innate immunity, and macrophage pathway scores in CAMR and TCMR. Graft failure in CAMR was associated with TCMR transcripts but not with AMR transcripts, and graft failure in TCMR was associated with AMR transcripts but not with TCMR transcripts.

CONCLUSIONS

Peritubular capillary inflammation and DSA are the primary drivers of AMR transcript elevation. Transcripts revealed subpathological evidence of AMR, which often preceded histologic CAMR and subpathological evidence of TCMR that predicted graft loss in CAMR.

Classic and Current Opinions in Human Organ and Tissue Transplantation

Graft tolerance is a pathophysiological condition heavily reliant on the dynamic interaction of the innate and adaptive immune systems. Genetic polymorphism determines immune responses to tissue/organ transplantation, and intricate humoral and cell-mediated mechanisms control these responses. In transplantation, the clinician's goal is to achieve a delicate equilibrium between the allogeneic immune response, undesired effects of the immunosuppressive drugs, and the existing morbidities that are potentially life-threatening. Transplant immunopathology involves sensitization, effector, and apoptosis phases which recruit and engages immunological cells like natural killer cells, lymphocytes, neutrophils, and monocytes. Similarly, these cells are involved in the transfer of normal or genetically engineered T cells. Advances in tissue transplantation would involve a profound knowledge of the molecular mechanisms that underpin the respective immunopathology involved and the design of precision medicines that are safe and effective.

Helper T Cell (CD4+) Targeted Tacrolimus Delivery Mediates Precise Suppression of Allogeneic Humoral Immunity

Antibody-mediated rejection (ABMR) is a major cause of dysfunction and loss of transplanted kidney. The current treatments for ABMR involve nonspecific inhibition and clearance of T/B cells or plasma cells. However, the prognosis of patients following current treatment is poor. T follicular helper cells (Tfh) play an important role in allograft-specific antibodies secreting plasma cell (PC) development. Tfh cells are therefore considered to be important therapeutic targets for the treatment of antibody hypersecretion disorders, such as transplant rejection and autoimmune diseases. Tacrolimus (Tac), the primary immunosuppressant, prevents rejection by reducing T cell activation. However, its administration should be closely monitored to avoid serious side effects. In this study, we investigated whether Tac delivery to helper T (CD4+) cells using functionalized mesoporous nanoparticles can block Tfh cell differentiation after alloantigen exposure. Results showed that Tac delivery ameliorated humoral rejection injury in rodent kidney graft by suppressing Tfh cell development, PC, and donor-specific antibody (DSA) generation without causing severe side effects compared with delivery through the drug administration pathway. This study provides a promising therapeutic strategy for preventing humoral rejection in solid organ transplantation. The specific and controllable drug delivery avoids multiple disorder risks and side effects observed in currently used clinical approaches.

Proposed Definitions of Antibody-Mediated Rejection for Use as a Clinical Trial Endpoint in Kidney Transplantation

Antibody-mediated rejection (AMR) is caused by antibodies that recognize donor human leukocyte antigen (HLA) or other targets. As knowledge of AMR pathophysiology has increased, a combination of factors is necessary to confirm the diagnosis and phenotype. However, frequent modifications to the AMR definition have made it difficult to compare data and evaluate associations between AMR and graft outcome. The present paper was developed following a Broad Scientific Advice request from the European Society for Organ Transplantation (ESOT) to the European Medicines Agency (EMA), which explored whether updating guidelines on clinical trial endpoints would encourage innovations in kidney transplantation research. ESOT considers that an AMR diagnosis must be based on a combination of histopathological factors and presence of donor-specific HLA antibodies in the recipient. Evidence for associations between individual features of AMR and impaired graft outcome is noted for microvascular inflammation scores ≥2 and glomerular basement membrane splitting of >10% of the entire tuft in the most severely affected glomerulus. Together, these should form the basis for AMR-related endpoints in clinical trials of kidney transplantation, although modifications and restrictions to the Banff diagnostic definition of AMR are proposed for this purpose. The EMA provided recommendations based on this Broad Scientific Advice request in December 2020; further discussion, and consensus on the restricted definition of the AMR endpoint, is required.

The Clinical and Pathological Phenotype of Antibody-Mediated Vascular Rejection Diagnosed using Arterial C4d Immunoperoxidase

Introduction

The diagnosis of antibody-mediated vascular rejection (AM-VR) should be reliable and accurate. We hypothesized that arterial C4d (C4d_art) immunoperoxidase deposition represents endothelial interaction with antibody.

Methods

From 3309 consecutive, kidney transplant biopsies from a single center, 100 vascular rejection (VR) cases were compared against rejection without arteritis (n = 540) and normal controls (n = 1108). The clinical utility of C4d_art for diagnosis and classification of AM-VR was evaluated against an independent reference test.

Results

C4d_art occurred in 20.4% of acute, 11.0% of subclinical, and 46% of VR episodes. Semiquantitative C4d_art score significantly correlated with immunodominant donor-specific antibodies (DSAs) (rho = 0.500, P < 0.001), peritubular capillary C4d (C4d_ptc), microvascular inflammation, and Banff v scores. Banff v3 arteritis suggested AM-VR. Addition of C4d_art to Banff antibody-mediated rejection (AMR) schema increased diagnostic sensitivity for AM-VR from 57.9% to 93.0%, accuracy 74.0% to 92.0%, and specificity 95.4% to 90.2% versus Banff 2019 (using C4d_ptc). Death-censored graft failure was associated with C4d_art AM-VR criteria using Cox regression (adjusted hazard ratio [HR] 4.310, 95% CI 1.322–14.052, P = 0.015). VR was then etiologically classified into AM-VR (n = 57, including 36 mixed VR) or “pure” (TCM-VR, n = 43). AM-VR occurred within all post-transplant periods, characterized by greater total, interstitial, and microvascular inflammation, arterial and peritubular C4d, DSA levels, and graft failure rates compared with TCM-VR. Mixed VR kidneys had the greatest inflammatory burden and graft loss (P < 0.001).

Conclusion

C4d_art is a suggestive biomarker of the humoral alloresponse toward muscular arteries. Inclusion of C4d_art into the Banff schema improved its diagnostic performance for detection of AM-VR and etiologic classification of arteritis.

Glomerular C4d Immunoperoxidase in Chronic Antibody-Mediated Rejection and Transplant Glomerulopathy

Introduction

The diagnosis of late antibody-mediated rejection (AMR) is compromised by frequent absence of C4d in peritubular capillaries (C4d_ptc), termed “C4d-negative” AMR. We hypothesized that glomerular capillary C4d (C4d_glom) reflected endothelial interaction with antibody and could improve immunologic classification of transplant glomerulopathy (TG).

Methods

We evaluated C4d using immunoperoxidase in 3524 consecutive, kidney transplant biopsies from a single center.

Results

C4d_glom was detected in 16.5% and C4d_ptc in 9.9% of biopsies. C4d_glom occurred in 60.3% of TG (n = 174) and was absent in normal glomeruli. Epidemiologic risk factors for C4d_glom were younger, female, living-donor recipients with early AMR, prior treated rejection, and late presentation using multivariable analysis. Semiquantitative C4d_glom score correlated with donor specific antibody (DSA) level, C4d_ptc, microvascular inflammation (MVI), Banff cg scores, renal dysfunction, and proteinuria. Principal component analysis colocalized C4d_glom with histologic AMR. Multivariable analysis of TG found DSA, C4d_ptc, and post-transplant time associated with C4d_glom. Addition of C4d_glom into Banff chronic AMR schema improved its diagnostic sensitivity for TG (verified by electron microscopy [EM]) from 22.2% to 82.4% and accuracy from 59.6% to 93.9%, compared with Banff 2019 using only C4d_ptc. Tissue C4d_glom and chronic AMR diagnosis incorporating C4d_glom were associated with death-censored allograft failure in TG (P < 0.001), independent of the severity of glomerulopathy and chronic interstitial fibrosis.

Conclusion

C4d_glom is a promising diagnostic biomarker of endothelial interaction with antibody which substantially improved test performance of the Banff schema to correctly classify TG by pathophysiology and prognosticate graft loss. We recommend routine C4d immunoperoxidase to minimize underdiagnosis of late AMR in TG.

Allorecognition and the spectrum of kidney transplant rejection

Detection of mismatched human leukocyte antigens by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection or antibody-mediated rejection. This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several observations have recently emerged that question this dichotomization between T-cell mediated rejection and antibody-mediated rejection, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-human leukocyte antigen antibodies, the immunogenicity of donor-recipient non-human leukocyte antigen mismatches, and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies, and better outcome after kidney transplantation.

Face transplantation: A longitudinal histological study focusing on chronic active and mucosal rejection in a series with long-term follow-up

The 2007 Banff working classification of skin-containing Tissue Allograft Pathology addressed only acute T cell-mediated rejection in skin. We report the longitudinal long-term histological follow-up of six face transplant recipients, focusing on chronic and mucosal rejection. We identified three patterns suggestive of chronic rejection (lichen planus-like, vitiligo-like and scleroderma-like). Four patients presented lichen planus-like and vitiligo-like chronic rejection at 52 ± 17 months posttransplant with severe concomitant acute T cell-mediated rejection. After lichen planus-like rejection, two patients developed scleroderma-like alterations. Graft vasculopathy with C4d deposits and de novo DSA led to subsequent graft loss in one patient. Chronic active rejection was frequent and similar patterns were noted in mucosae. Concordance between 124 paired skin and mucosal biopsies acute rejection grades was low (κ = 0.2, p = .005) but most grade 0/I mucosal rejections were associated with grade 0/I skin rejections. We defined discordant (grade≥II mucosal rejection and grade 0/I skin rejection) (n = 55 [70%]) and concordant (grade≥II rejection in both biopsies) groups. Mucosal biopsies of the discordant group displayed lower intra-epithelial GranzymeB/FoxP3 ratios suggesting a less aggressive phenotype (p = .08). The grading system for acute rejection in mucosa may require phenotyping. Whether discordant infiltrates reflect a latent allo-immune reaction leading to chronic rejection remains an open question.

Revisiting the changes in the Banff classification for antibody-mediated rejection after kidney transplantation

The Banff classification for antibody-mediated rejection (ABMR) has undergone important changes, mainly by inclusion of C4d-negative ABMR in Banff'13 and elimination of suspicious ABMR (sABMR) with the use of C4d as surrogate for HLA-DSA in Banff'17. We aimed to evaluate the numerical and prognostic repercussions of these changes in a single-center cohort study of 949 single kidney transplantations, comprising 3662 biopsies that were classified according to the different versions of the Banff classification. Overall, the number of ABMR and sABMR cases increased from Banff'01 to Banff'13. In Banff'17, 248 of 292 sABMR biopsies were reclassified to No ABMR, and 44 of 292 to ABMR. However, reclassified sABMR biopsies had worse and better outcome than No ABMR and ABMR, which was mainly driven by the presence of microvascular inflammation and absence of HLA-DSA, respectively. Consequently, the discriminative performance for allograft failure was lowest in Banff'17, and highest in Banff'13. Our data suggest that the clinical and histological heterogeneity of ABMR is inadequately represented in a binary classification system. This study provides a framework to evaluate the updates of the Banff classification and assess the impact of proposed changes on the number of cases and risk stratification. Two alternative classifications introducing an intermediate category are explored.

Challenges of Diagnosing Antibody-Mediated Rejection: The Role of Invasive and Non-Invasive Biomarkers

Kidney transplantation is the best treatment modality for end-stage kidney disease, leading to improvement in a patient’s quality and quantity of life. With significant improvements in short-term outcomes, prolonging long-term allograft and patient survival remain ongoing challenges. The ability to monitor allograft function, immune tolerance and predict rejection accurately would enable personalization and better prognostication during post-transplant care. Though kidney biopsy remains the backbone of transplant diagnostics, emerging biomarkers can help detecting kidney allograft injury early enough to prevent permanent damage and detect injury before it is clinically apparent. In this review, we summarize the recent biomarkers that have shown promise in the prediction of acute rejection with a focus on antibody-mediated rejection in kidney transplantation.

Stratifying the humoral risk of candidates to a solid organ transplantation: a proposal of the ENGAGE working group

Detection of circulating antibodies directed against human leukocyte antigen (HLA) molecules, which corresponds to the current definition of 'sensitized patient', has been shown to have a severe impact on both access to transplantation and, if the anti-HLA antibodies are specific to the selected donor, survival of the graft. However, not all donor-specific antibodies (DSA) are equally harmful to the graft and progress in the understanding of humoral memory has led to the conclusion that absence of DSA at transplantation does not rule out the possibility that the patient has a preformed cellular humoral memory against the graft (thereby defining a category of DSA-negative sensitized recipients). Technological progress has led to the generation of new assays that offer unprecedented precision in exploring the different layers (serological and cellular) of alloimmune humoral memory. Based on this recent knowledge, the EuropeaN Guidelines for the mAnagement of Graft rEcipients (ENGAGE) working group to propose an updated definition of sensitization in candidates for solid organ transplantation - one that moves away from the current binary division towards a definition based on homogenous strata with similar humoral risk.

Therapies for Chronic Allograft Rejection

Remarkable advances have been made in the pathophysiology, diagnosis, and treatment of antibody-mediated rejection (ABMR) over the past decades, leading to improved graft outcomes. However, long-term failure is still high and effective treatment for chronic ABMR, an important cause of graft failure, has not yet been identified. Chronic ABMR has a relatively different phenotype from active ABMR and is a slowly progressive disease in which graft injury is mainly caused by de novo donor specific antibodies (DSA). Since most trials of current immunosuppressive therapies for rejection have focused on active ABMR, treatment strategies based on those data might be less effective in chronic ABMR. A better understanding of chronic ABMR may serve as a bridge in establishing treatment strategies to improve graft outcomes. In this in-depth review, we focus on the pathophysiology and characteristics of chronic ABMR along with the newly revised Banff criteria in 2017. In addition, in terms of chronic ABMR, we identify the reasons for the resistance of current immunosuppressive therapies and look at ongoing research that could play a role in setting better treatment strategies in the future. Finally, we review non-invasive biomarkers as tools to monitor for rejection.

Recommended Treatment for Antibody-mediated Rejection After Kidney Transplantation: The 2019 Expert Consensus From the Transplantion Society Working Group

With the development of modern solid-phase assays to detect anti-HLA antibodies and a more precise histological classification, the diagnosis of antibody-mediated rejection (AMR) has become more common and is a major cause of kidney graft loss. Currently, there are no approved therapies and treatment guidelines are based on low-level evidence. The number of prospective randomized trials for the treatment of AMR is small, and the lack of an accepted common standard for care has been an impediment to the development of new therapies. To help alleviate this, The Transplantation Society convened a meeting of international experts to develop a consensus as to what is appropriate treatment for active and chronic active AMR. The aim was to reach a consensus for standard of care treatment against which new therapies could be evaluated. At the meeting, the underlying biology of AMR, the criteria for diagnosis, the clinical phenotypes, and outcomes were discussed. The evidence for different treatments was reviewed, and a consensus for what is acceptable standard of care for the treatment of active and chronic active AMR was presented. While it was agreed that the aims of treatment are to preserve renal function, reduce histological injury, and reduce the titer of donor-specific antibody, there was no conclusive evidence to support any specific therapy. As a result, the treatment recommendations are largely based on expert opinion. It is acknowledged that properly conducted and powered clinical trials of biologically plausible agents are urgently needed to improve patient outcomes.

Microvascular inflammation is a risk factor in kidney transplant recipients with very late conversion from calcineurin inhibitor-based regimens to belatacept

Background

In de novo kidney transplant recipients (KTR) treatment with belatacept has been established as a comparable option as maintenance immunosuppression, preferably as a strategy to convert from calcineurin inhibitor (CNI)- to belatacept-based immunosuppression. Switch to belatacept demonstrated improved renal function in patients with CNI-induced nephrotoxicity, but risk of transplant rejection and the development of donor-specific antibodies (DSA) are still a matter of debate. Only few data are available in patients at increased immunological risk and late after transplantation.

Methods

We analyzed 30 long-term KTR (including 2 combined pancreas-KTR) converted from CNI to belatacept > 60 months after transplantation with moderate to severe graft dysfunction (GFR ≤ 45 mL/min). Biopsies were classified according to the Banff 2015 criteria. Group differences were assessed in a univariate analysis using Mann Whitney U or Chi square test, respectively. Multivariate analysis of risk factors for treatment failure was performed using a binary logistic regression model including significant predictors from univariate analysis. Fifty-six KTR matched for donor and recipient characteristics were used as a control cohort remaining under CNI-treatment.

Results

Patient survival in belatacept cohort at 12/24 months was 96.7%/90%, overall graft survival was 76.7 and 60.0%, while graft survival censored for death was 79.3%/66.7%. In patients with functioning grafts, median GFR improved from 22.5 mL/min to 24.5 mL/min at 24 months. Positivity for DSA at conversion was 46.7%. From univariate analysis of risk factors for graft loss, GFR < 25 mL/min (p = 0.042) and Banff microvascular inflammation (MVI) sum score ≥ 2 (p = 0.023) at conversion were significant at 24 months. In the analysis of risk factors for treatment failure, a MVI sum score ≥ 2 was significant univariately (p = 0.023) and in a bivariate (p = 0.037) logistic regression at 12 months. DSA-positivity was neither associated with graft loss nor treatment failure. The control cohort had comparable graft survival outcomes at 24 months, albeit without increase of mean GFR in patients with functioning grafts (ΔGFR of − 3.6 ± 8.5 mL/min).

Conclusion

Rescue therapy with conversion to belatacept is feasible in patients with worsening renal function, even many years after transplantation. The benefit in patients with MVI and severe GFR impairment remains to be investigated.

Automated detection algorithm for C4d immunostaining showed comparable diagnostic performance to pathologists in renal allograft biopsy

A deep learning-based image analysis could improve diagnostic accuracy and efficiency in pathology work. Recently, we proposed a deep learning-based detection algorithm for C4d immunostaining in renal allografts. The objective of this study is to assess the diagnostic performance of the algorithm by comparing pathologists' diagnoses and analyzing the associations of the algorithm with clinical data. C4d immunostaining slides of renal allografts were obtained from two different institutions (100 slides from the Asan Medical Center and 86 slides from the Seoul National University Hospital) and scanned using two different slide scanners. Three pathologists and the algorithm independently evaluated each slide according to the Banff 2017 criteria. Subsequently, they jointly reviewed the results for consensus scoring. The result of the algorithm was compared with that of each pathologist and the consensus diagnosis. Clinicopathological associations of the results of the algorithm with allograft survival, histologic evidence of microvascular inflammation, and serologic results for donor-specific antibodies were also analyzed. As a result, the reproducibility between the pathologists was fair to moderate (kappa 0.36-0.54), which is comparable to that between the algorithm and each pathologist (kappa 0.34-0.51). The C4d scores predicted by the algorithm achieved substantial concordance with the consensus diagnosis (kappa = 0.61), and they were significantly associated with remarkable microvascular inflammation (P = 0.001), higher detection rate of donor-specific antibody (P = 0.003), and shorter graft survival (P < 0.001). In conclusion, the deep learning-based C4d detection algorithm showed a diagnostic performance similar to that of the pathologists.

Transcriptional Changes in Kidney Allografts with Histology of Antibody-Mediated Rejection without Anti-HLA Donor-Specific Antibodies

BACKGROUND

Circulating donor-specific anti-HLA antibodies (HLA-DSAs) are often absent in serum of kidney allograft recipients whose biopsy specimens demonstrate histology of antibody-mediated rejection (ABMR). It is unclear whether cases involving ABMR histology without detectable HLA-DSAs represent a distinct clinical and molecular phenotype.

METHODS

In this multicenter cohort study, we integrated allograft microarray analysis with extensive clinical and histologic phenotyping from 224 kidney transplant recipients between 2011 and 2017. We used the term ABMR histology for biopsy specimens that fulfill the first two Banff 2017 criteria for ABMR, irrespective of HLA-DSA status.

RESULTS

Of 224 biopsy specimens, 56 had ABMR histology; 26 of these (46.4%) lacked detectable serum HLA-DSAs. Biopsy specimens with ABMR histology showed overexpression of transcripts mostly related to IFNγ-induced pathways and activation of natural killer cells and endothelial cells. HLA-DSA-positive and HLA-DSA-negative biopsy specimens with ABMR histology displayed similar upregulation of pathways and enrichment of infiltrating leukocytes. Transcriptional heterogeneity observed in biopsy specimens with ABMR histology was not associated with HLA-DSA status but was caused by concomitant T cell-mediated rejection. Compared with cases lacking ABMR histology, those with ABMR histology and HLA-DSA had higher allograft failure risk (hazard ratio [HR], 7.24; 95% confidence interval [95% CI], 3.04 to 17.20) than cases without HLA-DSA (HR, 2.33; 95% CI, 0.85 to 6.33), despite the absence of transcriptional differences.

CONCLUSIONS

ABMR histology corresponds to a robust intragraft transcriptional signature, irrespective of HLA-DSA status. Outcome after ABMR histology is not solely determined by the histomolecular presentation but is predicted by the underlying etiologic factor. It is important to consider this heterogeneity in further research and in treatment decisions for patients with ABMR histology.

Inflammaging and Complement System: A Link Between Acute Kidney Injury and Chronic Graft Damage

The aberrant activation of complement system in several kidney diseases suggests that this pillar of innate immunity has a critical role in the pathophysiology of renal damage of different etiologies. A growing body of experimental evidence indicates that complement activation contributes to the pathogenesis of acute kidney injury (AKI) such as delayed graft function (DGF) in transplant patients. AKI is characterized by the rapid loss of the kidney's excretory function and is a complex syndrome currently lacking a specific medical treatment to arrest or attenuate progression in chronic kidney disease (CKD). Recent evidence suggests that independently from the initial trigger (i.e., sepsis or ischemia/reperfusions injury), an episode of AKI is strongly associated with an increased risk of subsequent CKD. The AKI-to-CKD transition may involve a wide range of mechanisms including scar-forming myofibroblasts generated from different sources, microvascular rarefaction, mitochondrial dysfunction, or cell cycle arrest by the involvement of epigenetic, gene, and protein alterations leading to common final signaling pathways [i.e., transforming growth factor beta (TGF-β), p16 ink4a , Wnt/β-catenin pathway] involved in renal aging. Research in recent years has revealed that several stressors or complications such as rejection after renal transplantation can lead to accelerated renal aging with detrimental effects with the establishment of chronic proinflammatory cellular phenotypes within the kidney. Despite a greater understanding of these mechanisms, the role of complement system in the context of the AKI-to-CKD transition and renal inflammaging is still poorly explored. The purpose of this review is to summarize recent findings describing the role of complement in AKI-to-CKD transition. We will also address how and when complement inhibitors might be used to prevent AKI and CKD progression, therefore improving graft function.

Complement-Based Therapy in the Management of Antibody-Mediated Rejection

Antibody-mediated rejection (AMR) is one of the leading causes of kidney allograft failure and is usually mediated by anti-human leukocyte antigen donor-specific antibodies (DSAs). Activation of classical pathway of the complement system is responsible for downstream effects of DSA and account for significant manifestations of AMR. Currently, the treatment of AMR is based on strategies to remove preformed antibodies or to prevent their production; however, these strategies are often unsuccessful. It is theoretically possible to inhibit complement activity to prevent the effect of DSA on kidney allograft function. Complement inhibitors such as eculizumab, a complement 5 monoclonal antibody, and complement 1 esterase inhibitors (C1 INHs) have been used in prevention and treatment of AMR with variable success. Eculizumab and C1 INH seem to reduce the incidence of early AMR and allow transplantation in highly sensitized kidney transplant recipients, but data on their long-term effect on kidney allograft function are limited. Several case reports described the successful use of eculizumab in the treatment of AMR, but there are no randomized controlled studies that showed efficacy. Treatment of AMR with C1 INH, in addition to standard of care, did not change short-term outcome but long-term studies are underway.

Evaluation and Treatment of Acute Rejection in Kidney Allografts

Advances in immunosuppressive therapy have drastically improved acute rejection rates in kidney transplant recipients over the past five decades. Nevertheless, it should remain high on any differential diagnosis of unexplained graft dysfunction because of the potential negative effect on graft longevity. Understanding the pre- and post-transplant risk factors for acute rejection can help estimate the probability of immunologic graft damage, and accurate identification of the type and severity of acute rejection will guide appropriate treatment. Tissue biopsy remains the gold standard for evaluating immunologic graft damage, and the histologic definition of acute rejection has evolved in recent years. Intravenous steroids and T cell depletion remain the standard therapy for T cell-mediated rejection and are effective in reversing most cases. Plasma exchange and intravenous Ig, with or without rituximab, are most commonly used for the treatment of antibody-mediated rejection and several newer agents have recently been investigated for severe cases. This review aims to provide the general nephrologist caring for transplant recipients with an approach to immunologic risk assessment and a summary of recent advances in the diagnosis and treatment of acute graft rejection.

Biomarkers of rejection in kidney transplantation

PURPOSE OF REVIEW

To provide an update of the literature on the use of new biomarkers of rejection in kidney transplant recipients.

RECENT FINDINGS

The kidney allograft biopsy is currently considered the gold standard for the diagnosis of rejection. However, the kidney biopsy is invasive and could be indeterminate. A significant progress has been made in discovery of new biomarkers of rejection, and some of them have been introduced recently for potential use in clinical practice including measurement of serum donor-derived cell free DNA, allo-specific CD154 + T-cytotoxic memory cells, and gene-expression 'signatures'. The literature supports that these biomarkers provide fair and reliable diagnostic accuracy and may be helpful in clinical decision-making when the kidney biopsy is contraindicated or is inconclusive.

SUMMARY

The new biomarkers provide a promising approach to detect acute rejections in a noninvasive way.

Specificity, strength, and evolution of pretransplant donor-specific HLA antibodies determine outcome after kidney transplantation

In this cohort study (N = 924), we investigated the evolution and clinical significance of pretransplant donor-specific HLA antibodies (preDSA), detected in the single-antigen beads assay but complement-dependent cytotoxicity crossmatch-negative. Donor specificity of the preDSA (N = 107) was determined by high-resolution genotyping of donor-recipient pairs. We found that in 52% of the patients with preDSA, preDSA spontaneously resolved within the first 3 months posttransplant. PreDSA that persisted posttransplant had higher pretransplant median fluorescence intensity values and more specificity against DQ. Patients with both resolved and persistent DSA had a high incidence of histological picture of antibody-mediated rejection (ABMR_h ; 54% and 59% respectively). Patients with preDSA that persisted posttransplant had worse 10-year graft survival compared to resolved DSA and preDSA-negative patients. Compared to cases without preDSA, Cox modeling revealed an increased risk of graft failure only in the patients with persistent DSA, in the presence (hazard ratio [HR] = 8.3) but also in the absence (HR = 4.3) of ABMR_h . In contrast, no increased risk of graft failure was seen in patients with resolved DSA. We conclude that persistence of preDSA posttransplant has a negative impact on graft survival, beyond ABMR_h . Even in the absence of antibody-targeting therapy, low median fluorescence intensity DSA and non-DQ preDSA often disappear early posttransplantation and are not deleterious for graft outcome.

Markers of graft microvascular endothelial injury may identify harmful donor-specific anti-HLA antibodies and predict kidney allograft loss

Graft microvasculature is a major target of donor-specific antibodies (DSA) and endothelial damage is direct evidence of antibody-mediated rejection (ABMR). Using immunohistochemistry, we analyzed the expression of three microvascular endothelial activation markers (fascin, vimentin, and hsp47), suggestive of endothelial-to-mesenchymal transition (EndMT) in 351 graft biopsies from 248 kidney recipients, with concomitant screening of circulating antihuman leukocyte antigen (HLA) DSA at the time of the biopsy. The factors associated with EndMT marker expression were DSA and the presence of microvascular inflammation (MI). EndMT expressing grafts had significantly more allograft loss compared to EndMT negative grafts (P < .0001). The expression of EndMT markers positively correlated with anti-HLA DSA class II mean fluorescence intensity (MFI) levels and especially identified DQ and DR antibodies as being more closely associated with microvascular injury. Moreover, only DSA linked to positive EndMT score affected allograft survival, regardless of DSA MFI levels or presence of C4d deposition. Thus, EndMT markers could represent a clinically relevant tool for early identification of ongoing endothelial injury, harmful DSA, and patients at high risk for allograft failure.

The role of complement in antibody mediated transplant rejection

Antibody mediated transplant rejection (AMR) is a major cause of long-term allograft failure, and currently available treatments are of limited efficacy for treating the disease. AMR is caused by donor specific antibodies (DSA) that bind to antigens within the transplanted organ. DSA usually activate the classical pathway of complement within the allograft, and complement activation is believed to be an important cause of tissue injury in AMR. Several new clinical assays may improve our ability to identify patients at risk of AMR. Complement inhibitory drugs have also been tested in selected patients and in small series. Better understanding of the role of complement activation in the pathogenesis of AMR will likely improve our ability to diagnose the disease and to develop novel treatments.

Renal Transplant and Its Outcomes: Single-Center Experience From India

OBJECTIVES

Improvements in early graft survival and long-term graft function have made kidney transplant a more cost-effective alternative to dialysis. We aimed to assess renal transplant outcomes over a 9-month follow-up of recipients in a cost-limited setting (a tertiary care center in India).

MATERIALS AND METHODS

Included patients in this prospective observational study were those who underwent renal transplant from July 2016 to February 2017 (8 months) and followed for 9 months.

RESULTS

Of 122 included patients, 20 (16.4%) were women and 102 (83.6%) were men (mean age 35.61 ± 10.64 y), with 92 (75.4%) from a lower socioeconomic status. Kidneys were from first-degree relatives for 52 patients (42.6%), from spousal donors for 34 (27.9%), from deceased donors for 24 (19.7%), and from second/third degree relative donors for 12 (9.8%). All patients underwent only complementdependent cytotoxicity crossmatch due to financial constraints. Fifty patients (41%) had history of packed red blood cell transfusion. Induction was thymoglobulin in 60 patients (49.2%), basiliximab in 8 (6.6%), and no induction in 54 (44.3%). Forty patients (30.1%) underwent biopsy for graft dysfunction, and 32 (26.2%) had graft rejection: 18 (14.8%) with antibodymediated rejection, 5 (4.1%) with T-cell-mediated rejection, and 9 (7.4%) with both. Opportunistic infections were shown in 24.5% of patients, including primarily cytomegalovirus (10.7%), tuberculosis (5.7%), and aspergillosis (3.3%). Twenty-nine patients (24%) had new-onset diabetes posttransplant. At end of follow-up, 93 patients (76.2%) had normal graft function, 21 (17.2%) had chronic graft dysfunction, 3 (2.4%) had graft loss, and 5 (4.1%) died. History of blood transfusion (P = .001) predicted the occurrence of antibody-mediated rejection, and induction used showed trend toward prediction (P = .083).

CONCLUSIONS

With high rejection rates, it would be prudent to include proper immunologic testing, even in cost-limited settings, pretransplant. The high infection and death rates are also concerning.

Donor-specific Antibody Surveillance and Graft Outcomes in Pediatric Kidney Transplant Recipients

BACKGROUND

The development of de novo donor-specific antibodies (dnDSA) has been associated with rejection and graft loss in kidney transplantation, and DSA screening is now recommended in all kidney transplant recipients. However, the clinical significance of dnDSA detected by screening patients with a stable creatinine remains unclear.

METHODS

One hundred three patients younger than 18years receiving a first, kidney alone transplant between December 1, 2007, and December 31, 2013, underwent DSA screening every 3months for 2years posttransplant, with additional testing as clinically indicated. No treatment was given for DSAs in the absence of biopsy-proven rejection.

RESULTS

Twenty (19%) patients had dnDSA first detected on a screening test, and 13 (13%) patients had dnDSA first detected on a for-cause test. Mean follow-up time posttransplant was 4.4years. Screening-detected dnDSA was associated with an increased risk of rejection within 3years, microvascular inflammation, and C4d staining on a 2-year protocol biopsy. In a Cox proportional hazards regression, screening-detected dnDSA was not associated with time to 30% decline in estimated glomerular filtration rate (adjusted hazard ratio, 0.88; 95% confidence interval [CI], 0.30-2.00; P=0.598) or graft loss. dnDSA first detected on for-cause testing was associated with a 2.8 times increased risk of decline in graft function (95% CI, 1.08-7.27; P=0.034) and a 7.34 times increased risk of graft loss (95% CI, 1.37-39.23 P=0.020) compared with those who did not develop dnDSA.

CONCLUSIONS

The clinical setting in which dnDSA is first detected impacts the association between dnDSA and graft function. Further research is needed to clarify the role of dnDSA screening in pediatric kidney transplantation.

Detection of Complement-binding Donor-specific Antibodies, Not IgG-antibody Strength Nor C4d Status, at Antibody-mediated Rejection Diagnosis Is an Independent Predictor of Kidney Graft Failure

BACKGROUND

Antibody-mediated rejection (AMR) remains associated with reduced kidney graft survival and no clear prognostic marker is available.

METHODS

We investigated whether donor-specific antibodies (DSA) ability to bind C1q in comparison with AMR C4d status, both indirect signs of complement activation, improve risk stratification at time of AMR. Hence, among 467 patients in whom 1 or more graft biopsies were performed between 2008 and 2015, we included 56 with AMR according to Banff '15 criteria. Using concurrent sera, we prospectively identified DSA by single-antigen beads (IgG and C1q) assays.

RESULTS

Antibody-mediated rejection C4d (+) (n = 28) was associated with preformed DSA (P = 0.007), whereas DSA C1q (+) (n = 25) cases had stronger IgG-DSA (P < 0.001). At AMR, graft function was similar between DSA C1q groups, but in the first year after, it improved in DSA C1q (-), whereas a steady decline was observed in DSA C1q (+) cases, remaining significantly lower from 1 year until 4 years after AMR. DSA C1q (+) was significantly associated with reduced graft survival (P = 0.021), whereas AMR C4d (+) was not (P = 0.550). Importantly, a similar negative impact of DSA C1q (+) on graft survival was observed within AMR C4d (+) (P = 0.040) and (-) (P = 0.036), cases. In multivariable analysis, DSA C1q (+) (hazard ratio, 3.939, P = 0.005) and de novo DSA (hazard ratio, 4.409, P = 0.033) were independent predictors of graft failure, but stronger IgG-DSA was not. Similar results were obtained considering C1q-DSA and IgG-DSA strength as continuous variables.

CONCLUSIONS

C1q-DSA assessment at AMR can be a valuable tool in detecting patients with higher risk of graft failure.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Histological picture of antibody-mediated rejection without donor-specific anti-HLA antibodies: Clinical presentation and implications for outcome

In this cohort study (n = 935 transplantations), we investigated the phenotype and risk of graft failure in patients with histological criteria for antibody-mediated rejection (ABMR) in the absence of circulating donor-specific anti-human leukocyte antigen (HLA) antibodies (DSA), and compared this to patients with definite ABMR and HLA-DSA-positivity. The histological picture did not differ between HLA-DSA-positive (n = 85) and HLA-DSA-negative (n = 123) cases of ABMR histology, apart from increased complement split product 4d (C4d) deposition in the peritubular capillaries in HLA-DSA-positive cases. Histology of ABMR without HLA-DSA was more transient than DSA-positive ABMR, and patients with ABMR histology without HLA-DSA had graft survival superior to that of HLA-DSA-positive patients, independent of concomitant T cell-mediated rejection (38.2%) or borderline changes (17.9%). Multivariate analysis showed that the risk of graft failure was not higher in patients with histological picture of ABMR (ABMR_h ) in the absence of HLA-DSA, compared to patients without ABMR_h . Despite an association between C4d deposition and HLA-DSA-positivity, using C4d deposition as alternative for the DSA criterion in the diagnosis of ABMR, as proposed in Banff 2017, did not contribute to the prognosis of graft function and graft failure. We concluded that biopsies with ABMR_h but without detectable HLA-DSA represent a distinct, often transient phenotype with superior allograft survival.

Noninvasive quantification of intrarenal allograft C4d deposition with targeted ultrasound imaging

Antibody-mediated rejection (AMR) has emerged as a major cause of renal allograft dysfunction. C4d, a specific marker for AMR diagnosis, was strongly recommended for routine surveillance; however, currently, C4d detection is dependent upon tissue biopsy, which is invasive and provides only local semi-quantitative data. Targeted ultrasound imaging has been used extensively for noninvasive and real-time molecular detection with advantages of high specificity and sensitivity. In this study, we designed C4d-targeted microbubbles (MBC4d ) using a streptavidin-biotin conjugated method and detected C4d deposition in vivo in a rat model of AMR by enhanced ultrasound imaging. This noninvasive procedure allowed successful acquisition of the first qualitative image of C4d deposition in a wide renal allograft section, which reflected real-time C4d distribution in grafts. Moreover, we introduced normal intensity difference for quantitative analysis, which exhibited a nearly linear correlation with the grade of C4d deposition according to pathologic analysis. In addition, this approach showed no influence on survival rates and pathologic features in the microbubble injection groups, thereby demonstrating its safety. These findings demonstrated a simple, noninvasive, quantitative, and safe evaluation method for C4d, with the utility of this approach potentially preventing patients from having to undergo an invasive biopsy.

Microvascular inflammation in renal allograft biopsies assessed by endothelial and leukocyte co-immunostain: a retrospective study on reproducibility and clinical/prognostic correlates

The most prominent histologic lesion in antibody-mediated rejection is microvascular inflammation (MVI); however, its recognition and scoring can be challenging and poorly reproducible between pathologists. We developed a dual immunohistochemical (IHC)-stain (anti-CD34/anti-CD45 for endothelium/leukocytes) as ancillary tool to improve on the semi-quantitative Banff scores and allow quantification of MVI. We examined the relationship between CD34-CD45 IHC-based quantitative MVI score (the inflamed peritubular capillary ratio, iptcr) and renal-graft failure or donor-specific antibodies (DSA) strength at the time of biopsy. Quantitative iptcr score was significantly associated with renal graft failure (hazard ratio 1.81, per 1 SD-unit [0.13 points] of iptcr-increase; P = 0.026) and predicted the presence and strength of DSA (ordinal odds ratio: 2.42; P = 0.005; 75 biopsies/60 kidney transplant recipients; 30 HLA- and/or ABO-incompatible). Next, we assessed inter-pathologist agreement for ptc score and ptc extent (focal/diffuse) using CD34-CD45 IHC as compared to conventional stain. Compared to conventional stain, CD34-CD45 IHC significantly increased inter-pathologist agreement on ptc score severity and extent (κ-coefficient from 0.52-0.80 and 0.46-0.68, respectively, P < 0.001). Our findings show that CD34-CD45 IHC improves reproducibility of MVI scoring and facilitates MVI quantification and introduction of a dual anti-CD34/CD45 has the potential to improve recognition of MVI ahead of DSA results.

Clinical impact of complement (C1q, C3d) binding De Novo donor-specific HLA antibody in kidney transplant recipients

Introduction

Complement binding activity of donor-specific HLA antibodies (DSA) has been suggested as a new tool to stratify immunologic risk in kidney transplantation (KT). The objective of this study was to evaluate the clinical implication of C1q/C3d binding activity of de novo DSA (dnDSA) in KT recipients.

Material and methods

A total of 161 pretransplant DSA-negative recipients were monitored for dnDSA at the time of biopsy. C1q/C3d binding activities of dnDSA were assessed using C1qScreen assay (One lambda, USA) and Lifecodes C3d detection assay (Immucor, USA), respectively. Clinical outcomes including biopsy-proven antibody mediated rejection (AMR), C4d detection and post-biopsy graft survival were investigated.

Results

De-novo DSAs were detected in fifty-four (33.5%) patients (HLA class I only, n = 19; class II only, n = 29; both class I and II, n = 6). Of them, complement binding activities were detected in 26 (48.1%) patients, including 17 C1q+ and 24 C3d+ patients. Both C1q and C3d positivity were associated with increased mean fluorescence intensity values of dnDSA. Complement binding activity of dnDSA enhanced the incidence of AMR (25.0% in C1q-C3d-, 36.4% in C1q+/C3d- or C1q-/C3d+, and 60.0% in C1q+/C3d+ patients) (P <0.001). The incidence of AMR was not different between patients with C1q+ and those with C3d+ dnDSA (64.7%, 11/17 versus 45.8%, 11/24, P = 0.238). In comparison between C1q and C3d assay according to HLA specificity, C1q+ HLA class I ± II dnDSA was the best predictor for AMR (odds ratio: 27.2). C1q+/C3d+ dnDSA was associated with more C4d deposition in allograft tissue and inferior post-biopsy graft survival. Clinical outcomes were not significantly different between C1q+ and C3d+ dnDSA-positive patients.

Conclusion

Detection of complement binding activity using both C1q and C3d assays can be a further prognostic marker for predicting AMR and allograft outcome in dnDSA+ kidney transplant patients.

Recent Advancements in the Assessment of Renal Transplant Dysfunction with an Emphasis on Microarray Molecular Diagnostics

Conventional assessment of renal transplant rejection and injury through use of histology, C4d staining, and HLA antibody testing, has been the standard approach to transplant management. By many measures, these methods of conventional assessment may be considered flawed, particularly with the subjective nature of histologic diagnoses. The Alberta Transplant Applied Genomics Center has developed the Molecular Microscope diagnostic system, which uses microarrays to measure gene expression. These data are analyzed using classifiers (weighted equations) that compare the tested biopsy to a proprietary reference set of biopsies to provide objective measures of the status of the renal transplant.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Safety and utility of surveillance biopsies in pediatric kidney transplant patients

There is currently no way to diagnose a rejection before a change in serum creatinine. This had led some to start doing SB, but little data exist on the utility and safety of SB in pediatric patients. There is also little known on practice patterns of pediatric nephrologists. A retrospective review of pediatric kidney transplant SB between January 2013 and January 2017 at a single center was performed. A survey went to the PedNeph email list. There were 47 SB; 15 at 6 months, 12 at 1 year, 13 at 2 years, and 7 at 3 years. There were 3 minor (1 gross hematuria and 2 hematomas) and no major complications. On 6-month SB, 1 had SC 1A ACR (6.7%) with no BR ACR. On the 12-month SB, there were 5 with SCBR ACR (41.7%) and 1 with SC AMR (8.3%). On the 2-year SB, there were 4 that had SCBR ACR (30.8%), and 1 with SC AMR (7.7%). On the 3-year SB, 1 had chronic transplant glomerulitis (14.3%). The survey showed that 34.3% of pediatric nephrologists perform SB. SB can be performed safely. By early identification of histological lesions, SB gives us an opportunity for individualized immunosuppressive regimens that may prevent chronic allograft dysfunction and improve long-term graft outcome.

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.